Intestinal effects of filtered alkalinized water in lean and obese Zucker rats

Citation: Doblado, L.; Díaz, L.E.; Nova, E.; Marcos, A.; Monsalve, M. Intestinal Effects of Filtered Alkalinized Water in Lean and Obese Zucker Rats. Microorganisms 2024,12, 316. https://doi.org/10.3390/ microorganisms12020316 Academic Editor: Mar Larrosa Received: 5 December 2023 Revised: 22 December 2023 Accepted: 30 January 2024 Published: 2 February 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). microorganisms Article Intestinal Effects of Filtered Alkalinized Water in Lean and Obese Zucker Rats Laura Doblado 1, Ligia Esperanza Díaz 2, Esther Nova 2, Ascensión Marcos 2and María Monsalve 1,* 1 Instituto de Investigaciones Biomédicas Sols-Morreale (CSIC-UAM), Arturo Duperier 4, 28029 Madrid, Spain; [email protected] 2Institute of Science, Food Technology and Nutrition (ICTAN), Spanish National Research Council (CSIC), JoséAntonio Nováis 6, 28040 Madrid, Spain; [email protected] (L.E.D.); [email protected] (E.N.); [email protected] (A.M.) *Correspondence: [email protected] Abstract: This study evaluated the intestinal effects of alkalinized filtered water in lean and obese adult Zucker rats. For 3 months, 12-week-old rats consumed either tap water or filtered alkalinized tap water from Madrid city. Weight gain was monitored, changes in metabolism were evaluated by indirect calorimetry, and total antioxidant capacity and levels of inflammatory mediators were measured in plasma. Feces were collected, their microbial composition was analyzed and histological analysis of the small and large intestine was performed, assessing the general state of the mucosa (MUC2), the inflammatory state (F4/80) and the presence of oxidative modifications in protein 4Hydroxynonenal (4-HNE) by immunofluorescence (IF) and immunohistochemistry (IHC). The results obtained showed that the consumption of alkalinized filtered water improved the composition of the intestinal microbiome and the state of the intestinal mucosa, reducing both local and systemic inflammation and the level of oxidative stress. These changes were accompanied by a better maintenance of the oxidative status in rats. No differences were observed in antioxidant capacity nor in weight gain. The incorporation of probiotics in the diet had a significant impact on the microbiome. These effects were indicative of an improvement in general metabolic, oxidative and inflammatory status. Keywords: alkalized filtered water; probiotics; intestine; inflammation; oxidative metabolism; oxidative stress 1. Introduction Gastrointestinal (GI) diseases have an estimated prevalence of 2276.27 million [ 1 ]. Among them, functional dyspepsia and acid reflux are particularly common, with prevalence estimations reaching up to 30%, with about 10% reaching Rome IV functional dyspepsia (FD), which incurs considerable associated health impairments [ 2 ]. Current pharmacological treatments for FD aim to either neutralize acid or block its production [ 3 ]. However, emerging evidence of important side effects associated with long-term treatments have raised concerns and the boosted search for alternative approaches [ 4 ]. Among the alternative palliative interventions, drinking alkalinized water has gained considerable attention, especially in Eastern countries. The most commonly used and studied is the electrolyzed alkaline-reduced water (EARW), the consumption of which has been related to an improvement in FD symptoms [ 5 ]. The available data also suggest that the consumption of alkalinized water has anti-inflammatory effects, through still-unclear mechanisms that may be of relevance for other pathologies [ 6 ]. Of particular interest, in this context, there are other common disorders of the intestinal track such as intestinal dysbiosis. The industrial revolution fundamentally altered the intestinal microbiome ecosystem, drastically reducing its complexity and increasing its functional instability [7]. A large set of functional studies have demonstrated the key role played by nutritional patterns on the preservation of a healthy microbiome [ 8 ] and the marked association of obesity with Microorganisms 2024,12, 316. https://doi.org/10.3390/microorganisms12020316 https://www.mdpi.com/journal/microorganisms Microorganisms 2024,12, 316 2 of 16 intestinal dysbiosis [ 9 ]. Hence, this evidence has also driven the study of the effect on different water sources, on intestinal dysbiosis and metabolic homeostasis [ 10 ]. While it is generally agreed that the pH of drinking water can impact the microbiome, its nature and the effect of EARW consumption are still a matter of controversy. A two-week intervention study with EARW in healthy human volunteers concluded that water pH had no impact on the composition of the gut microbiota or glucose regulation in young male adults [ 11 ]. In contrast, in another study, mice were treated for four weeks with EARW, and the authors showed that in the fecal microbiome, the relative abundances of 20 taxa differed significantly from controls. However, the significance of these changes was not stablished [12]. Alternative alkalinization procedures, that do not involve electrolysis but make use of filter-based systems, are also in the market, but scientific studies on their presumed health effects are still at their infancy. We recently evaluated the vascular effects of filter alkalinized water consumption in rodents and found an improved vascular reactivity that was associated with reduced systemic inflammation [ 13 ], a result consistent with similar findings on EARW. Our study aimed to test the intestinal effects of alkalinized filtered water, the possible differential role in the lean healthy vs. obese, using, as a test model, Zucker rats, as well as to assess whether the intake of probiotics, a common treatment for intestinal problems, modifies its intestinal effects. Obese Zucker rats are a widely used model of genetic obesity caused by a mutation (fa) in the gene that encodes the receptor for lectin, an anorexigenic hormone. These rats, which suffer from insulin resistance, glucose intolerance, and metabolic syndrome, are the best existing rat model for studies related to obesity and diabetes [ 14 ]. Rats and mice are the most frequently used animal models for biomedical studies, with rats being physiologically, morphologically and genetically closer to humans than mice, which makes them an ideal model for biomedical and pharmacological studies. We found that filtered water reduced intestinal inflammation and oxidative stress markers, improved the gut mucosa status, and positively impacted the microbiome profile following three months of treatment. 2. Materials and Methods Rats. Male Zucker lean (lean) and obese (obese) rats were used. The animals were purchased from Charles River and housed at the Instituto de Investigaciones Biomédicas Sols-Morreale (IIBM) animal facility under controlled temperature (20–22 ◦ C) and humidity (50 ± 10%) conditions. The animals were under 12 h light/12 h dark cycles and had ad libitum access to food and water. The animal experimentation protocols were approved by the IIBM Institutional Animal Care and Use Committee, the IIBM Biosafety Committee, the Consejo Superior de Investigaciones Científicas (CSIC) Bioethics Committee and final approval was granted by the Environment Department of the Community of Madrid (Ref. PROEX 117/20). All procedures were in accordance with the Declaration of Helsinki. All animals received humane care in accordance with the criteria described in the “Guide for the Care and Use of Laboratory Animals” prepared by the National Academy of Sciences and published by the National Institutes of Health (No. 86-23 revised in 1985). The used 16week-old rats were divided into three experimental groups: one group was given tap water (not filtered, not sterilized) available at the institute to drink; the second and third groups were given the same water but previously filtered with the Alkanatur ® alkalinizing water filtration system. The water-filtering system was analyzed by an authorized laboratory (Oliver Rodés) and found to conform with AENOR Spanish Norm UNE 149101:2015 for human consumption [ 15 ]. The filtering system adds 15 mg/L of Mg 2+ , has been shown to remove Trihalomethanes (THMs) and Cl − , to provide water free of microorganisms and to not release Na + . The plastic jar has been approved for contact with food and demonstrated to be free of Bisphenol A (BPA), epoxidized soybean oil (ESBO) and phthalate esters [ 16 ]. The water was changed daily. The third group of animals was fed a diet supplemented with 3 g/kg of the probiotic Megaflora 9 EVO (Solchem ® , Barcelona, Spain). Megaflora 9 EVO contains 2 × 10 9 colony-forming units (cfu)/g of Bifidobacterium lactis W51 and Microorganisms 2024,12, 316 3 of 16 W52, Enterococcus faecium W54,Lactobacillus acidophilus W22, Lactobacillus paracasei W20, Lactobacillus plantarum W1 and W21, Lactobacillus salivarius W24 and Lactococcus lactis W19. In humans, the recommended dose is 1–2 g [ 17 ]. Each experimental group included 6 animals. Weight gain was monitored every 2 weeks. Fresh feces were collected at t= 0 , 6 weeks (6w) and three months (3mo) of treatment. The animals were treated for 3mo and then sacrificed by decapitation after intraperitoneal injection with pentobarbital sodium (100 mg/kg). Blood was collected, and plasma and peripheral blood mononuclear cells (PBMC) were separated using a Ficoll-Paque TM PLUS (Cytiva Cytiva Europe GmbH Sucursal en España, Barcelona, Spain) gradient and stored at − 80 ◦ C. The intestines were collected, washed in phosphate-buffered saline (PBS) and cut into sections. Tissue sections were snap frozen and stored at − 80 ◦ C or fixed in 10% buffered formalin, then embedded in paraffin, and 4 µ m sections were cut with a microtome, deparaffinized and hydrated prior to staining. Indirect calorimetry. The PhenoMaster indirect calorimetry system (TSE Systems GmbH, Bad Homburg vor der Höhe, Germany) was used to analyze metabolism in live, freely moving animals, automatically and continuously, over three light–dark cycles in a dedicated, controlled-environment facility at the IIBM. Rats were first acclimatized to the PhenoMaster room for three days before the experiment began. Each rat was then assigned to an individual cage with a separate gas collection and delivery system, which was controlled by TSE PhenoMaster 5.1 software. The following parameters were examined: volume (V) O 2 , VCO 2 , RER, energy expenditure (H1+), activity (XT + YT), weight of food intake and water volume consumed. Data were registered every hour over 72 h. Animals were exposed to 12 h light and 12 h dark cycles. Data were extracted and analyzed using TSE PhenoMaster 5.1 software. Data presented correspond to the mean values for O 2 consumed or CO 2 produced per hour and registered during the day (12 h) or night (12 h) periods of the second 24 h cycle (2nd day), when measurements were more stable. Microbiome. Feces samples were collected, and bacterial DNA was extracted using the QIAamp ® Fast DNA Stool Mini Kit (Quiagen, Hilden, Germany). Bacterial quantification was performed by qPCR using specific primers for each of the tested bacterial groups: Bacteroides,Blautia coccoides-Eubacterium rectale group, Clostridium cluster IV, Bifidobacterium spp., Lactobacillus spp., Enterobacteriaceae, Enterococcus spp., Faecaibacterium praustnizii and Akkermansia muciniphila directed against the genes that encode 16S rRNA. Enterobacteriaceae Eco1457 Forward 5′-CATTGACGTTACCCGCAGAAGAAGC-3′ Eco1652 Reverse 5′-CTCTACGAGACTCAAGCTTGC-3′ Blautia coccoides-Eubacterium rectale Group gCcoc Forward 5′-AAATGACGGTACCTGACTAA-3′ gCcoc Reverse 5′-CTTTGAGTTTCATTCTTGCGAA-3′ Clostridium cluster IV sg-Clept Forward 5′-GCACAAGCAGTGGAGT-3′ sg-Clept Reverse 5′-CTTCCTCCGTTTTGTCAA-3′ Enterococcus spp. Enteroc Forward 5′-CCCTTATTGTTAGTTGCCATCATT-3′ Enteroc Reverse 5′-ACTCGTTGTACTTCCCATTGT-3′ Lactobacillus spp. Lacto Forward 5′-CACCGCTACACATGGAG-3′ Lacto Reverse 5′-AGCAGTAGGGAATCTTCCA-3′ Bifidobacterium spp. Bif Forward 5′-TCGCGTC(C/T)GGTGTGAAAG-3′ Bif Reverse 5′-CCACATCCAGC(A/G)TCCAC-3′ Bacteroides fragilis Group Bfra Forward 5′-ATAGCCTTTCGAAAGRAAGAT-3′ Bfra Reverse 5′-CCAGTATCAACTGCAATTTTA-3′ Microorganisms 2024,12, 316 4 of 16 Faecalibacterium praustnizii Fprau223 Forward 5′-GATGGCCTCGCGTCCGATTAG-3′ Fprau420 Reverse 5′-CCGAAGACCTTCTTCCTCC-3′ Akkermansia muciniphila S-St-Muc-1437-a-A-20 Forward 5′- CCTTGCGGTTGGCTTCAGAT-3′ S-St-Muc-1129-a-a-20 Reverse 5′-CAGCACGTGAAGGTGGGGAC-3′ Immunohistochemistry (IHC). Tissue fixation and staining were performed using the Vectastain ABC kit and the DAB peroxidase substrate kit (both from Vector Laboratories, Burlingame, CA, USA) following the manufacturer’s instructions. Samples were incubated with anti-F4/80 primary antibody (MCA497; AbD Serotec, Oxford, UK) and then with anti-rat secondary antibody (NA935 GE Healthcare, Boston, MA, USA) linked to alkaline phosphatase (AP), exposed to the AP substrate and, once staining developed, mounted. Images were acquired with a Nikon E90i microscope equipped with a DS-Fi1 camera (Nikon, Tokyo, Japan). Immunofluorescence (IF). Fixation, staining, and analysis procedures were as previously described [ 13 ]. Primary antibodies used were anti-Mucin 2 (sc-7314; Santa Cruz Biotechnology Inc., Dallas, TX, USA) and anti-4-HNE (AB5605, Merk, Darmstadt, Germany). Immunofluorescence was detected by incubation with a fluorescent secondary antibody (FITC; Merck, Darmstadt, Germany). The samples were then counter stained with DAPI (Invitrogen Corp., Carlsbad, CA, USA), mounted, and visualized using a fluorescence microscope, Zeiss LSM 700. Image analysis. IHC and IF images were analyzed using Fiji-ImageJ 2.0.0-rc-69/1.52p software (NIH, Bethesda, MD, USA) to determine the ratio of positive area to tissue area (IHC) or total integrated fluorescence signal to tissue area (IF). Gene expression analysis. Intestinal tissue samples were homogenized in the presence of 1 mL of Trizol TM reagent (ThermoFisher Sci., Waltham, MA, USA), and total RNA was isolated following the manufacturer’s instructions. Complementary DNA (cDNA) was synthesized, from total RNA preparations, by reverse transcription of 1 µ g of RNA, using Moloney Murine Leukemia Virus (M-MLV) reverse transcriptase (RT) (Promega Biotech Ibérica SL, Alcobendas, Madrid, Spain), in a final volume of 20 µ . The mixture was incubated at 37 ◦ C for 45 min and then cooled for 2 min at 4 ◦ C. The resulting cDNA was used as a template for subsequent quantitative polymerase chain reaction (qPCR). The specific primers used are listed below. Each 10 µ L PCR reaction included 1 µ L cDNA, 5 µ L qPCRBIO SyGreen Mastermix (Cultek SL, Dutchcher Group, San Fernando de Henares, Madrid, Spain) and primers (0.3 µ M). Samples were analyzed in triplicate on a Mastercycler ® RealPlex2, Eppendorf Iberica SLU (San Sebastian de los Reyes, Madrid, Spain). 36B4 was used as loading control. 36B4 Forward 5′-GCGACCTGGAGTCCAACTA-3′ 36B4 Reverse 5′: ATCTGCTGCATCTGCTTGG-3′ IL-1B Forward 5′-GCCAACAAGTGGTATTCTCCATGAGC-3′ IL-1B Reverse 5′-TTGTCACCCCGGATGGAATG-3′ IL-10 Reverse 5′-TTGTCACCCCGGATGGAATG-3′ IL-10 Forward 5′-GCTCAGCACTGCTATGTTGC-3′ Cytokines. Circulating levels of IL-1 β , IL-4, IL-6, TNF α and IL-10 were analyzed by cellular cytometry in plasma samples using Multiplex Cytokine Assays (Pro-cartaPlex Immunoassays (ThermoFisher Scientific, Waltham, MA, USA)) at the Centro Nacional de Biotecnología (CNB, CSIC, Madrid, Spain) Flow Cytometry Unit. The lean rat samples were pooled in pairs (each analyzed sample/data point is the mixture of two plasma samples, from two rats); obese rat plasma samples were not pooled. The values obtained were corrected by the concentration of proteins in the sample determined by the Lowry method via colorimetry. Microorganisms 2024,12, 316 5 of 16 Antioxidant capacity. Antioxidant capacity was determined in plasma samples using the e-BQC electrochemical analytical system (BioQuoChem, Oviedo, Spain), which measures total (QT), fast (Q1) and slow-acting (Q2) antioxidant capacity. Statistical analysis. Microsoft Excel 16.16.27 (Microsoft, Redmond, WA, USA) was used for data processing. GraphPad Prism 9 (Dotmatics, Boston, MA, USA) was used for statistical analysis and graph preparation. Data are expressed as mean ± standard deviation (SD) or standard error of the mean (SEM), as indicated in the figure legends. The normality of the data was assessed using the Kolmogorov–Smirnov test. Statistical significance of differences between groups was assessed using two-tailed unpaired or paired t-test for comparisons between two groups; one-way and two-way ANOVA was used for the analysis of time-dependent variation and the differential response to treatments of two groups, respectively. Levene’s test was used for equality of variances. The values were considered statistically significant when p< 0.05. No values were discarded; values not included could not be obtained due to acquisition problems or technical problems with the samples or animals. 3. Results In order to test the intestinal effects of alkalinized filtered water and the differential impact in obesity, lean and obese Zucker rats were treated for 3mo with tap water or filtered water. The probiotic Megaflora 9 EVO was included in the diet of a group of rats dinking filtered water, adjusting the dose to that recommended for humans. The decision to perform a 3mo treatment (3mo) was based on our previous studies, showing significant changes in rats treated for 3mo. We also collected blood and stool samples at 6 weeks for a better follow-up of the treatment responses. 3.1. Weight Gain The rats’ weight gain was monitored every two weeks, and both absolute and relative weight gain values were determined (Figure 1). The results did not show significant differences associated with the treatments except at four weeks of treatment, when the relative weight gain (%) of the filtered water and probiotic groups was significantly greater than that of the filtered water group, but this difference was not maintained at longer treatment times. Similarly, the areas under the curve (AUC) for the absolute values did not show significant differences between treatment groups. Therefore, we concluded that the treatments did not have a relevant effect on the animals’ weight gain. Microorganisms 2024, 12, x FOR PEER REVIEW 6 of 16 Figure 1. Absolute (upper panel) and relative (lower panel) weight gain determined every 2 weeks for 3mo. In the bottom panel, weight values at t = 0 were considered 100%. The graphs show mean +/− SD. 3.2. Circulating Cytokines Next, in order to determine the general inflammatory status of the rats, the circulating levels of cytokines (IL-1β, IL-4, IL-6, TNFα and IL-10) were evaluated in blood plasma samples. Significant changes were found in the levels of IL-1β and IL-10, cytokines generally considered as markers of type M1 and M2 macrophages, respectively. After 6w of treatment, higher levels of IL-1β were observed in lean rats that consumed tap water than in rats that consumed filtered water, and lower levels of IL-10 in rats that consumed tap water than in rats that consumed filtered water (Figure 2), suggesting that drinking alkalinized water favors an immunosuppressive and anti-inflammatory profile. Figure 2. Changes in plasma levels of IL-1β and IL-10 (levels at 6w—levels at t = 0) following 6w of treatment. Tap, filter, filter + probiotic. The graph shows mean +/− SEM. * p < 0.05 (t test). 3.3. Antioxidant Capacity Then, we evaluated how the treatments affected the total antioxidant capacity in blood plasma samples. To this end, fast (Q1), slow (Q2) and total (QT) antioxidant capacities were measured using the e-BQC electrochemical reader (BioQuoChem). No significant differences were observed between the treatment groups at either 6w or 3mo (Figure Figure 1. Absolute (upper panel) and relative (lower panel) weight gain determined every 2 weeks for 3mo. In the bottom panel, weight values at t= 0 were considered 100%. The graphs show mean +/ − SD. Microorganisms 2024,12, 316 6 of 16 3.2. Circulating Cytokines Next, in order to determine the general inflammatory status of the rats, the circulating levels of cytokines (IL-1 β , IL-4, IL-6, TNF α and IL-10) were evaluated in blood plasma samples. Significant changes were found in the levels of IL-1 β and IL-10, cytokines generally considered as markers of type M1 and M2 macrophages, respectively. After 6w of treatment, higher levels of IL-1 β were observed in lean rats that consumed tap water than in rats that consumed filtered water, and lower levels of IL-10 in rats that consumed tap water than in rats that consumed filtered water (Figure 2), suggesting that drinking alkalinized water favors an immunosuppressive and anti-inflammatory profile. Microorganisms 2024, 12, x FOR PEER REVIEW 6 of 16 Figure 1. Absolute (upper panel) and relative (lower panel) weight gain determined every 2 weeks for 3mo. In the bottom panel, weight values at t = 0 were considered 100%. The graphs show mean +/− SD. 3.2. Circulating Cytokines Next, in order to determine the general inflammatory status of the rats, the circulating levels of cytokines (IL-1β, IL-4, IL-6, TNFα and IL-10) were evaluated in blood plasma samples. Significant changes were found in the levels of IL-1β and IL-10, cytokines generally considered as markers of type M1 and M2 macrophages, respectively. After 6w of treatment, higher levels of IL-1β were observed in lean rats that consumed tap water than in rats that consumed filtered water, and lower levels of IL-10 in rats that consumed tap water than in rats that consumed filtered water (Figure 2), suggesting that drinking alkalinized water favors an immunosuppressive and anti-inflammatory profile. Figure 2. Changes in plasma levels of IL-1β and IL-10 (levels at 6w—levels at t = 0) following 6w of treatment. Tap, filter, filter + probiotic. The graph shows mean +/− SEM. * p < 0.05 (t test). 3.3. Antioxidant Capacity Then, we evaluated how the treatments affected the total antioxidant capacity in blood plasma samples. To this end, fast (Q1), slow (Q2) and total (QT) antioxidant capacities were measured using the e-BQC electrochemical reader (BioQuoChem). No significant differences were observed between the treatment groups at either 6w or 3mo (Figure Figure 2. Changes in plasma levels of IL-1 β and IL-10 (levels at 6w—levels at t= 0) following 6w of treatment. Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter + probiotic. The graph shows mean +/ − SEM. * p< 0.05 (ttest). 3.3. Antioxidant Capacity Then, we evaluated how the treatments affected the total antioxidant capacity in blood plasma samples. To this end, fast (Q1), slow (Q2) and total (QT) antioxidant capacities were measured using the e-BQC electrochemical reader (BioQuoChem). No significant differences were observed between the treatment groups at either 6w or 3mo (Figure 3), suggesting that the treatments did not globally affect the antioxidant capacity of the rats. Microorganisms 2024, 12, x FOR PEER REVIEW 7 of 16 3), suggesting that the treatments did not globally affect the antioxidant capacity of the rats. Figure 3. Electrochemical analysis of the total antioxidant capacity (QT) in plasma samples from rats treated for 6w (left panel) or 3mo (right panel). Tap, filter, filter + probiotic. The graph shows the electrochemical units provided by the e-BQC reader and includes mean values +/− SD. 3.4. Indirect Calorimetry In order to analyze the impact of the treatments on systemic metabolism, an indirect calorimetry system was used to determine the rats’ O 2 consumption and CO 2 production and how they changed in response to treatments at 6w (1.5mo) and 3mo (Figure 4). The group of tap water rats showed a gradual decrease in metabolic activity, affecting both O 2 consumption and CO 2 production. These changes were significant in the night period in normal rats at 3mo and in obese rats both during the night and day periods at 3mo. The decrease in CO 2 production was also significant in the obese tap water group of rats at 6w. These reductions were not observed or did not reach statistical significance in the groups treated with filtered water, both with and without probiotics. In fact, in obese rats, the magnitude of the difference was significantly smaller in rats treated with filtered water and probiotics than in control rats, in the day and night periods, for both O 2 consumption and CO 2 production. These results suggest that treatment with filtered water, particularly in combination with probiotics, maintains a higher metabolic activity than tap water, especially in obese rats. Figure 4. Analysis of O 2 consumption (upper panels) and CO 2 production volumes (lower panels) by indirect calorimetry. The rats were evaluated before treatment, at 6w and 3mo of treatment. Tap, Filter, Filter + Probiotic. The values shown in the graphs are the difference of O 2 volume (V) consumed (upper panel) or CO 2 produced (lower panel) between the indicated time and t = 0 for each individual rat analyzed. Determinations were taken every hour for 72 h, the presented data Figure 3. Electrochemical analysis of the total antioxidant capacity (QT) in plasma samples from rats treated for 6w (left panel) or 3mo (right panel). Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter + probiotic. The graph shows the electrochemical units provided by the e-BQC reader and includes mean values +/−SD. 3.4. Indirect Calorimetry In order to analyze the impact of the treatments on systemic metabolism, an indirect calorimetry system was used to determine the rats’ O 2 consumption and CO 2 production and how they changed in response to treatments at 6w (1.5mo) and 3mo (Figure 4). The Microorganisms 2024,12, 316 7 of 16 group of tap water rats showed a gradual decrease in metabolic activity, affecting both O 2 consumption and CO 2 production. These changes were significant in the night period in normal rats at 3mo and in obese rats both during the night and day periods at 3mo. The decrease in CO 2 production was also significant in the obese tap water group of rats at 6w. These reductions were not observed or did not reach statistical significance in the groups treated with filtered water, both with and without probiotics. In fact, in obese rats, the magnitude of the difference was significantly smaller in rats treated with filtered water and probiotics than in control rats, in the day and night periods, for both O 2 consumption and CO 2 production. These results suggest that treatment with filtered water, particularly in combination with probiotics, maintains a higher metabolic activity than tap water, especially in obese rats. Microorganisms 2024, 12, x FOR PEER REVIEW 7 of 16 3), suggesting that the treatments did not globally affect the antioxidant capacity of the rats. Figure 3. Electrochemical analysis of the total antioxidant capacity (QT) in plasma samples from rats treated for 6w (left panel) or 3mo (right panel). Tap, filter, filter + probiotic. The graph shows the electrochemical units provided by the e-BQC reader and includes mean values +/− SD. 3.4. Indirect Calorimetry In order to analyze the impact of the treatments on systemic metabolism, an indirect calorimetry system was used to determine the rats’ O 2 consumption and CO 2 production and how they changed in response to treatments at 6w (1.5mo) and 3mo (Figure 4). The group of tap water rats showed a gradual decrease in metabolic activity, affecting both O 2 consumption and CO 2 production. These changes were significant in the night period in normal rats at 3mo and in obese rats both during the night and day periods at 3mo. The decrease in CO 2 production was also significant in the obese tap water group of rats at 6w. These reductions were not observed or did not reach statistical significance in the groups treated with filtered water, both with and without probiotics. In fact, in obese rats, the magnitude of the difference was significantly smaller in rats treated with filtered water and probiotics than in control rats, in the day and night periods, for both O 2 consumption and CO 2 production. These results suggest that treatment with filtered water, particularly in combination with probiotics, maintains a higher metabolic activity than tap water, especially in obese rats. Figure 4. Analysis of O 2 consumption (upper panels) and CO 2 production volumes (lower panels) by indirect calorimetry. The rats were evaluated before treatment, at 6w and 3mo of treatment. Tap, Filter, Filter + Probiotic. The values shown in the graphs are the difference of O 2 volume (V) consumed (upper panel) or CO 2 produced (lower panel) between the indicated time and t = 0 for each individual rat analyzed. Determinations were taken every hour for 72 h, the presented data Figure 4. Analysis of O 2 consumption (upper panels) and CO 2 production volumes (lower panels) by indirect calorimetry. The rats were evaluated before treatment, at 6w and 3mo of treatment. Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Filter + Probiotic. The values shown in the graphs are the difference of O 2 volume (V) consumed (upper panel) or CO 2 produced (lower panel) between the indicated time and t= 0 for each individual rat analyzed. Determinations were taken every hour for 72 h, the presented data corresponds to the mean of both 12 h day and 12 h night periods of the 2nd day, when collected values were more stable. The graph shows mean values +/−SD. * p< 0.05 (ttest). 3.5. Intestinal Mucosa 3.5.1. Mucin In order to evaluate the intestinal impact of the treatments, we studied the intestinal mucosa of the small intestine and colon through the IF labeling of intestinal tissue sections with antibodies directed against mucin (MUC2), an oligomeric protein that is a fundamental component of the intestinal mucus. The reduction in MUC2 levels is generally associated with the loss of the intestinal barrier, increasing the risk of inflammatory processes and intestinal infections [18]. In lean rats, treatment with filtered water significantly increased mucin levels in the colon. Likewise, the global comparison of all the lean rats treated with filtered water (with or without probiotic), with respect to the tap water group, showed a significant increase in mucin levels in the colon. Furthermore, in obese rats, a significant increase in mucin levels was observed in rats treated with filtered water and probiotics compared to the tap water group. The difference was also significant when rats treated with probiotics were included in the analysis (Figure 5). These results suggest that treatment with filtered water, with or without probiotics, results in a better maintenance of the intestinal mucosa than tap water. Microorganisms 2024,12, 316 8 of 16 Microorganisms 2024, 12, x FOR PEER REVIEW 8 of 16 corresponds to the mean of both 12 h day and 12 h night periods of the 2nd day, when collected values were more stable. The graph shows mean values +/− SD. * p < 0.05 (t test). 3.5. Intestinal Mucosa 3.5.1. Mucin In order to evaluate the intestinal impact of the treatments, we studied the intestinal mucosa of the small intestine and colon through the IF labeling of intestinal tissue sections with antibodies directed against mucin (MUC2), an oligomeric protein that is a fundamental component of the intestinal mucus. The reduction in MUC2 levels is generally associated with the loss of the intestinal barrier, increasing the risk of inflammatory processes and intestinal infections [18]. In lean rats, treatment with filtered water significantly increased mucin levels in the colon. Likewise, the global comparison of all the lean rats treated with filtered water (with or without probiotic), with respect to the tap water group, showed a significant increase in mucin levels in the colon. Furthermore, in obese rats, a significant increase in mucin levels was observed in rats treated with filtered water and probiotics compared to the tap water group. The difference was also significant when rats treated with probiotics were included in the analysis (Figure 5). These results suggest that treatment with filtered water, with or without probiotics, results in a better maintenance of the intestinal mucosa than tap water. Figure 5. Determination of MUC2 levels by IF analysis of tissue sections from the small intestine and colon. Tap, filter, filter + probiotic. Collected data correspond to the integrated fluorescence signal divided by the tissue area. The graphs show the x fold change relative to the mean of the lean or obese control group (tap), mean +/− SD. * p < 0.05 (t test). Each data point corresponds to the mean values per rat. Representative images of the groups taken with a 20x objective are included in the left panels. Figure 5. Determination of MUC2 levels by IF analysis of tissue sections from the small intestine and colon. Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter + probiotic. Collected data correspond to the integrated fluorescence signal divided by the tissue area. The graphs show the x fold change relative to the mean of the lean or obese control group (tap), mean +/ − SD. * p< 0.05 (ttest). Each data point corresponds to the mean values per rat. Representative images of the groups taken with a 20 × objective are included in the left panels. 3.5.2. Intestinal Inflammation •F4/80 Considering that changes in the mucosa are usually related to the inflammatory state and that the results pointed to an improvement in the inflammatory state at the systemic level, in rats treated with filtered water, we established the level of intestinal inflammation by determining the presence of macrophages by IHC staining with an F4/80 antibody. Analysis of the F4/80-positive area showed, in the small intestine of normal rats and in the colon of obese rats, a significantly lower presence of macrophages in rats treated with filtered water than in rats that consumed tap water. Rats treated with filtered water and probiotics showed a similar trend, but, in this case, the differences did not reach statistical significance (Figure 6). These data are consistent with the improvement observed in the intestinal mucosa and the reduction in inflammation at the systemic level, observed previously, supporting that rats treated with filtered water had a better intestinal status. Microorganisms 2024,12, 316 9 of 16 Microorganisms 2024, 12, x FOR PEER REVIEW 9 of 16 3.5.2. Intestinal Inflammation • F4/80 Considering that changes in the mucosa are usually related to the inflammatory state and that the results pointed to an improvement in the inflammatory state at the systemic level, in rats treated with filtered water, we established the level of intestinal inflammation by determining the presence of macrophages by IHC staining with an F4/80 antibody. Analysis of the F4/80-positive area showed, in the small intestine of normal rats and in the colon of obese rats, a significantly lower presence of macrophages in rats treated with filtered water than in rats that consumed tap water. Rats treated with filtered water and probiotics showed a similar trend, but, in this case, the differences did not reach statistical significance (Figure 6). These data are consistent with the improvement observed in the intestinal mucosa and the reduction in inflammation at the systemic level, observed previously, supporting that rats treated with filtered water had a better intestinal status. Figure 6. IHC staining of macrophages in tissue sections from the small intestine and colon using antibodies directed against F4/80. Tap, filter, filter + probiotic. Collected data correspond to the positive area divided by the tissue area. The graphs show the % relative to the mean of the control group (tap), mean +/− SD. * p < 0.05 (t-test). Each data point corresponds to the mean of the values obtained for each rat. Representative images of the groups taken with a 20x objective are included in the left panels. • Cytokine’s gene expression Subsequently, the expression levels of IL-1B and IL-10 in the intestinal tissue were analyzed. The mRNA levels of IL-1B in the small intestine of obese rats treated with filtered water and probiotics were lower than those of tap-water-treated rats. However, regarding the other groups, no significant changes were found, although obese rats treated with filtered water showed a trend towards lower levels of IL-1B and higher levels of IL10 than rats treated with tap water, both in the small and large intestine sections, an observation consistent with the data derived from plasma samples (Figure 7). Figure 6. IHC staining of macrophages in tissue sections from the small intestine and colon using antibodies directed against F4/80. Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter + probiotic. Collected data correspond to the positive area divided by the tissue area. The graphs show the % relative to the mean of the control group (tap), mean +/ − SD. * p< 0.05 (t-test). Each data point corresponds to the mean of the values obtained for each rat. Representative images of the groups taken with a 20 × objective are included in the left panels. •Cytokine’s gene expression Subsequently, the expression levels of IL-1B and IL-10 in the intestinal tissue were analyzed. The mRNA levels of IL-1B in the small intestine of obese rats treated with filtered water and probiotics were lower than those of tap-water-treated rats. However, regarding the other groups, no significant changes were found, although obese rats treated with filtered water showed a trend towards lower levels of IL-1B and higher levels of IL-10 than rats treated with tap water, both in the small and large intestine sections, an observation consistent with the data derived from plasma samples (Figure 7). Microorganisms 2024, 12, x FOR PEER REVIEW 10 of 16 Figure 7. qRT-PCR analysis of the expression levels of IL-1B and IL-10 in small intestine and colon tissue samples. Tap, filter, filter + probiotic. The graphs show the differences in ΔΔCt of the individual values per rat and the mean value of the corresponding control group (tap), mean +/− SD. For clarity’s sake, −ΔΔCt values are presented, with higher values indicating higher mRNA expression. * p < 0.05 (t test). • Oxidative stress (OS) To determine if these changes were related to the levels of oxidative stress present in the tissue, the presence of proteins modified with 4-HNE was analyzed by IF, using specific antibodies. Rats treated with filtered water had, overall, significantly less modified proteins in the small intestine than tap water rats. The same trend was observed in the colon, as well as in rats treated with filtered water and probiotics, although differences did not reach statistical significance (Figure 8). Therefore, these data support the idea that treatment with filtered water reduces oxidative stress at the intestinal level, an effect that may be related to an improvement in the inflammatory status and the preservation of the mucosa. Figure 8. Determination of 4-HNE-modified protein levels by IF analysis of tissue sections from the small intestine and colon. Tap, filter, filter + probiotic. Collected data correspond to the integrated fluorescence signal divided by the tissue area. The graphs show the % relative to the mean of the control group (tap), mean +/− SD. *** p < 0.001 (t test). Each data point corresponds to the mean Figure 7. qRT-PCR analysis of the expression levels of IL-1B and IL-10 in small intestine and colon tissue samples. Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison Tap, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter, Microorganisms 2024, 12, x FOR PEER REVIEW 13 of 16 performed a previous study that tested the effects of the consumption of filtered alkalinized water in mice and rats for 3mo and found evidence suggesting a reduction in oxidative stress and inflammation [13]. The present study, thus, aimed to evaluate the intestinal impact of filtered alkalinized water in lean and obese rats. The results obtained support the hypothesis that filtered alkalinized water, when compared to unfiltered–unsterilized tap water from Madrid city, has a positive effect on both systemic and intestinal inflammation, better preserving the intestinal mucin layer and preventing intestinal dysbiosis. These changes were linked to a better maintenance of oxidative metabolism, suggesting a better metabolic status of the rats consuming filtered water (Figure 4). Of note, the improved metabolic profile is not related to any detectable changes in weight gain (Figure 1). Taking into consideration the detected changes in the microbiome, with increased Akkermansia muciniphila and Clostidium cluster IV and decreased Enterobacteriaceae in response to treatment with filtered alkalinized water (Figure 9), it is tempting to speculate that these changes are likely the main drivers of the preservation of the intestinal mucin layer, leading, in turn, to reduced intestinal and systemic inflammation, with a general positive impact on whole body metabolism. Akkermansia muciniphila is a mucin-degrading bacterium that has also been shown to stimulate mucin production with a net positive impact on the thickness of the mucin layer, the preservation of gut barrier function and intestinal immune homeostasis [33]. Clostridium cluster IV is well known for efficiently fermenting the plant polysaccharides composing dietary fiber. Clostridium species have been reported to attenuate inflammation, and its metabolites, including butyrate, secondary bile acids and indolepropionic acid, have been shown to play a probiotic role, primarily through their effects on intestinal epithelial cells, strengthening the intestinal barrier [34]. Enterobacteriaceae are facultative anaerobes that, in normal conditions, play a key role in intestinal oxygen consumption, allowing for the proliferation of anaerobes, necessary for polysaccharide fermentation. Nutrient overload and exposure to inflammatory mediators have been proposed to reduce their oxidative capacity and drive their proliferation, thus promoting obesity-related dysbiosis [35]. Figure 9. qPCR analysis of microbial content in feces. The graphs show the analysis of bacterial groups analyzed at the indicated times. Tap, filter, filter + probiotic. The represented values in the graphs are the differences in the number of bacteria between the values obtained at the indicated time and t = 0 for each individual rat analyzed, mean values +/− SD. Statistical comparison filter + probiotic. The graphs show the differences in ∆∆ Ct of the individual values per rat and the mean value of the corresponding control group (tap), mean +/ − SD. For clarity’s sake, −∆∆ Ct values are presented, with higher values indicating higher mRNA expression. * p< 0.05 (ttest). Microorganisms 2024,12, 316 16 of 16 34. Guo, P.; Zhang, K.; Ma, X.; He, P. Clostridium Species as Probiotics: Potentials and Challenges. J. Anim. Sci. Biotechnol. 2020,11, 24. [CrossRef] [PubMed] 35. Baldelli, V.; Scaldaferri, F.; Putignani, L.; Del Chierico, F. The Role of Enterobacteriaceae in Gut Microbiota Dysbiosis in Inflammatory Bowel Diseases. Microorganisms 2021,9, 697. [CrossRef] [PubMed] Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.