Advances in nanomedicine for the treatment of Alzheimer's and Parkinson's diseases

1 of Alzheimer's and Parkinson's diseases Sara Hernando1,2,&, Oihane Gartziandia1,2,&, Enara Herran1,2, Jose Luis Pedraz1,2, Manoli Igartua1,2, Rosa Maria Hernandez1,2,* 1NanoBioCel Group, Laboratory of Pharmaceutics, School of Pharmacy, University of the Basque Country (UPV/EHU), Vitoria-Gasteiz, 01006, Spain; 2Biomedical Research Networking Centre in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Vitoria-Gasteiz, 01006, Spain. *Corresponding author: R.M. Hernández (rosa.hernande[email protected]s). NanoBioCel Group, Laboratory of Pharmaceutics, School of Pharmacy, University of the Basque Country (UPV/EHU), Paseo de la Universidad 7, 01006 Vitoria-Gasteiz, Spain. Tel: +34 945013095; Fax: +34 945013040 &These two authors contributed equally to the work. Advances in nanomedicine for the treatment Hernando, S., Gartziandia, O., Herran, E., Pedraz, J. L., Igartua, M., & Hernandez, R. M. (2016). Advances in Nanomedicine for the Treatment of Alzheimer’s and Parkinson’s Diseases. Nanomedicine, 11(10), 1267–1285. . This is an Accepted Manuscript of an article published by Taylor & Francis in Nanomedicine on 14 Apr 2016, available at: https:// doi.org/10.2217/nnm-2016-0019. It is deposited under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/ licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way 2 ABSTRACT Alzheimer‘s disease (AD) and Parkinson’s disease (PD) are the most common neurodegenerative diseases (NDs) worldwide. Despite all the efforts made by the scientific community, current available treatments have limited effectiveness, without halting the progression of the disease. That is why, new molecules such as growth factors (GF), antioxidants and metal chelators have been raised as new therapeutical approaches. However, these molecules have difficulties to cross the blood brain barrier (BBB) limiting its therapeutic effect. The development of nanometric drug delivery systems (DDS) may permit a targeted and sustained release of old and new treatments offering a novel strategy to treat these neurodegenerative disorders. This review summarized the main investigated DDS as promising approaches to treat AD and PD. Keywords: Alzheimer’s disease, Parkinson’s disease, nanotechnology, nanomedicine, drug delivery systems 3 INTRODUCTION Neurodegenerative diseases (NDs) are characterized by a continuous structural and functional neuronal loss, usually correlated with neuronal death. Due to this deterioration, some cognitive, motor, emotional and sensory functions of patients are affected. Between different NDs, Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the first and the second most common disorders, respectively [1]. AD is caused by an irreversible neuronal loss and vascular toxicity due to amyloid beta (Aβ) peptide extracellular deposition in senile plaques, together with neurofibrillary tangles of phosphorylated tau protein. The progressive loss of memory, deterioration of judgment decision, orientation to physical surrounding and language are the most important clinical hallmarks of this disease [2-5]. Regarding PD, it is pathologically characterized by the degeneration of midbrain dopaminergic neurons in the substantia nigra (SN), followed by the dopamine decrease in the striatum (ST). The parkinsonism is the set of clinical symptoms that characterize the disease, among which are bradykinesia, resting tremor, rigidity and postural instability [5,6]. As shown in Table 1, the approved and most commonly used treatments for AD are acetylcholinestrase inhibitors (tacrine, donepezil, rivastigmine, galantamine) and N-methyl-D-aspartate receptor antagonist (memantine). All of them are administered by the oral route, and rivastigmine can also be transdermically administered using patches. In relation to PD, current pharmacological therapies are based on dopamimetic drugs (Benserazide/Levodopa, Levodopa/Carbidopa, Levodopa/Carbidopa/Entacapona) administered by the oral route. Table 1. Current pharmacological treatments for AD and PD. ND Drug Mode of action AD Tacrine Acetylcholinestrase inhibitors Donepezil Rivastigmine Galantamine Memantine N-methyl-Daspartatereceptor antagonist PD Benserazide/Levodopa Dopamimetic Levodopa/Carbidopa Levodopa/Carbidopa/Entacapona Nevertheless, it is important to note that the treatments mentioned above are only symptomatic, with a temporary effect, and without halting the progression of the disease [3]. Thereby, the researchers are making big efforts searching new therapies to address the neurodegenerative process. NEW PROMISING MOLECULES FOR THE TREATMENT OF AD AND PD Bearing in mind that nowadays the clinical treatments for AD and PD are mainly symptomatic, the development of new therapeutic options to address the main causes of neurodegenerative diseases are urgently needed. In this sense, in the last years new promising molecules such as neurotrophic factors (NTFs), antioxidant molecules and metal chelators have been considered promising approaches to attain this purpose. 4 Accordingly, growth factors (GFs) are a group of proteins which are able to improve the growth, proliferation and differentiation of neuronal cells, having also a significant role in tissue morphogenesis, cell differentiation, angiogenesis and neurite outgrowth [7-9]. Table 2 describes the main neurotrophic factors (NTFs) used to develop new therapies towards AD and PD, in order to address directly the progression of the disease. Table 2. Different growth factors and their main functions in the central nervous system (CNS). Growth factor Main functions Ref Glial-derived neurotrophic factor (GDNF) High specificity against dopaminergic neurons. Protective and trophic effects on noradrenergic neurons of the locus coeruleus. [10,11] Brain-derived neurotrophic factor (BDNF) Important role in the normal development of the peripheral and CNS. Promotes the synaptic plasticity and survival of neurons in adult brains. [12] Nerve growth factor (NGF) Promotes the survival, differentiation and maintenance of sympathetic and sensory neurons, having neuroprotective and repair functions. [13] Ciliary neurotrophic factor (CNTF) Ability to support the survival and/or differentiation of sympathetic, sensory, or motor neurons. [14] Insulin growth factor-I (IGF-I) Helps in the survival of neurons and rescue from neurotoxicity, stimulating also the neurogenesis and synaptogenesis. [15] Vascular endothelial growth factor (VEGF) Stimulates angiogenesis and the development of endothelial cells. Enhances neuronal growth and survival, and axonal outgrowth. [16,17] Neurotrophin (NT-3) Survival and differentiation of neurons, and in neurite growth. [18] On the other hand, it is commonly known that oxidative stress plays an important role in the pathophysiology of NDs such as AD and PD. Recent research works have demonstrated that the products generated from free-radical mediated reactions are increased in NDs, being related with the hallmarks of these diseases [19-28]. Moreover, transition metals have been suggested to be responsible of neuronal damage in AD [20]. In an attempt to treat or prevent these NDs, both antioxidants and metal chelators have been raised as new treatment approaches. In the Table 3 it has been summarized the studied molecules and the outcome of their use in AD and PD. Table 3. Antioxidants and metal chelators and their therapeutic functions in CNS Molecule Main functions Ref. Resveratrol Reduction in Aβ pathway and attenuation of cognitive decline. [21] [22,23] 5 Upregulation of the antioxidant status and reduction of dopaminergic neuronal loss, improving the rotational behavior. Curcumin Increase of β-amyloid-degrading enzymes; Protection against oxidation and improvement of behavioral tests. [24] [25] Catechins Decrease in Aβ levels and plaques. [24] Metal chelators 49% decrease in Aβ deposition; inhibition of τ phosphorilation. [26,27] Coenzyme Q10 Protection of the nigrostriatal dopaminergic system; Delay of the syntomatology in PD patients. [28] Nevertheless, whatever the treatment, the clinical application of all of these new molecules is limited. Some of these drawbacks come after their in vivo administration, due to their short circulation half-life and rapid degradation rate [29]. Hence, high doses are required to obtain therapeutic levels in the brain, with the risk of suffering adverse systemic effects [30]. However, the main obstacle for most of the drugs to access the brain is the presence of the blood brain-barrier (BBB) (Figure 1), having big difficulties to cross it, due to their unsuitable lipophility, molecular weight or charge. Thus, this barrier restricts the effective delivery and diffusion of therapeutic molecules to the CNS [31], maintaining CNS homeostasis and hindering the free penetration and diffusion of foreign components from the bloodstream to the brain [32]. Figure 1. Schematic illustration of the BBB and its tight junction structure. The figure shows an irrigated blood vessel in the brain which forms the BBB. The BBB is formed by endothelial cells with tight junctions, surrounded by pericytes and astrocyte end-feet. Therefore, over the years different strategies to access the brain have been developed, and the different approaches to cross or by-pass the BBB can be divided into invasive and noninvasive techniques (Figures 2 and 3) [32]. As shown in Figure 2, the invasive techniques enclose surgical methods to administer drugs directly into the brain, and the disruption of the 6 BBB to intentionally open it, while the non-invasive techniques showed in Figure 3 include nonaggressive approaches to access into the brain, such as the intranasal administration or the encapsulation of drugs within nanotechnological carriers. Figure 2. A schematic representation of the invasive techniques used to deliver drugs to the brain. Figure 3. A schematic representation of the non-invasive techniques used to deliver drugs to the brain. All in all, great efforts are being made by scientific community in the search of adequate technologies for brain targeting, and in the last years, the nanotechnology has appeared as a promising solution to deal with this challenge [31]. NANOTECHNOLOGY SOLUTIONS FOR NEURODEGENERATIVE DISEASES Nanotechnology is an emerging field of science with promising physiochemical properties for the treatment of neurodegenerative diseases [33-35]. In this section we have focused on describing the advances made in nanomedicine for the treatments of PD and AD, concretely. 7 Table 4 summarized the drug delivery systems (DDS) mainly investigated for the administration of different drugs to treat NDs (Table 4). Table 4. Mainly used DDSs in the treatment of NDs. AD and nanotechnology. DDSs to release acetylcholinestrase inhibitors and NMDA receptor antagonist. Rivastigmine (RT) is a reversible inhibitor of both acetylcholinestrase (AchE) and butrylcholinestrase (BuChE) which has low bioavailability due to its hidrophilic nature. The Nanotechnology device Schematic illustrations Characteristics Ref. Polymeric (functionalized) nanoparticles (NP) Microspheres and nanospheres are constituted of biodegradable and biocompatible materials. Therapeutic agents are entrapped in the colloidal matrix or coated on the surface by adsorption or conjugation. Moreover, ligands can be linked on the surface enhancing cell penetration. Polymer m icrocapsules and nanocapsules can be produced with different synthetic and natural monomers/polymers and with different preparation methods, their surface can be also functionalized for specific brain targeting. [36-39] (Nano)liposomes Vesicles composed by concentric bilayers of phospolipid-based membranes. Its surface may be modified by targeting agents achieving transport across BBB. [40] Solid lipid nanoparticle (SLN) Lipid nanocarriers formed by mono-di and tri glycerides, fatty acids, steroids and waxes and stabilized by various classes of emulsifiers. [41] Nanostructured lipid carrier (NLC) Mixture of solid and liquid lipids with higher encapsulation efficiency and better release properties. [42] Gene therapy: viral and non viral vectors Specific gene or DNA compacted carriers to target cells or tissues, entering to the nucleus to be expressed. [43,44] 8 limited entry to the brain makes necessary frequent dosing worsening cholinergic side effects [41,45]. The application of DDSs to overcome these disadvantages could be suitable. For example, Joshi et al. prepared RT loaded poly lactide-co-gycolide (PLGA) and poly (nbutylcyanoacrylate) NP coated with polysorbate 80 (PBCA-80) to improve brain targeting. Moreover, these NP provide sustained release, reducing dosing frequency and minimizing side effects. The results from the Morris Water Maze (MWM) Test showed the suitability of these nanoformulations regaining memory faster than RT solution in a scopolamine-induced amnesic mouse (Figure 4) [46]. Furthermore, PBCA nanoparticles haven been developed with the aim of improving diagnostic imaging. For instance, Kulkarni et al. prepared PBCA loaded I-clioquinol (CQ, 5-chloro-7-iodo-8-hydroxyquinoline)NPs, showing more efficient brain entry and rapid clearance, which are the ideal characteristics for in vivo imaging [47]. Figure 4. Saline-treated mice: (a) Test 1: learning and intact reference memory, (b) Test 2: short-term working memory. (n = 4); scopolamine-treated mice: (c) Test 1: learning and intact reference memory, and (d) Test 2: short-term working memory. (n = 4). Abbreviations: RS, RT solution; RNP, RT loaded PLGA NPs; RNPB, RT loaded PBCA NPs; ip, intraperitoneal; scop ip, scopolamine intraperitoneal. Reproduced with permission from [46]. On the other hand, Wilson et al elaborated PBCA-80 NP for the targeted delivery of RT into the brain. They observed that the uptake of RT after intravenous administration of RT loaded PBCA-80 NP was 3.82 fold higher than the free drug [48]. Chitosan NP of RT have also been developed by Naqpal et al. in an attempt to increase this drug therapeutic efficacy and tolerance profile. The studies demonstrated the reduction of the toxicity as well as improved memory activity in RT chitosan NP treated mice compared with free RT [49]. In addition to the intravenous route, the nasal route has also been investigated to avoid first pass metabolism and distribution to non-targeted organs thus, decreasing peripheral side effects. The administration of RT chitosan NP via intranasal route has showed an increase in brain AchE concentrations, decreasing the levels at lungs or liver [45]. 9 SLN have also been studied as a new approach for intranasal delivery of RT. Despite the hidrophylic nature of RT, the SLN system enhances its diffusion across nasal membrane due to the lipidic nature of these nanosystems [41]. Regarding liposomal formulations, subcutaneous administration of RT loaded liposomes has been investigated. The pharmacodynamic study in MWM Test manifested overcoming effect of RT loaded liposomes to RT solution normalizing cognitive level [50]. Another commercialized inhibitor of AchE is donepezil. In vivo studies of donepezil loaded PLGA NP were carried out by Bhavna et al. They revealed that the brain accumulation of donepezil was higher when the drug was encapsulated in NP as it was confirmed in the gamma scintigraphic image. This donepezil loaded NP were coated with Tween 80 improving the opening of the tight junctions in BBB and inhibiting P-glycoprotein efflux system enhancing drug delivery to the brain [51]. Galantamine is also known for been a reversible, competitive, AchE inhibitor used in the treatment of AD. Nevertheless, its poor brain penetration results in lower bioavailability to the target organ. With the aim to improve these disadvantages, Misra et al. elaborated SLN loaded with galantamine. After in vivo administration, injected nanoformulations presented higher bioavailability than the free drug. In addition, the nanoformulated galantamine improved behavioral deficits presented in treated rats when compared with the control group [52]. In this case the DDSs can also be functionalized to improve brain targeting. In an attempt to obtain it, Mufamadi et al. developed pegylated nanoliposomes for targeted delivery of galantamine. They studied the cellular uptake of functionalizated galantamine loaded nanoliposomes in cell cultures, showing higher targeted delivery than non-functionalized liposomes [40]. Finally, Laserra et al. synthetized a codrug of the NMDA antagonist, memantine, and (R)-αlipoic acid (LA-MEM) with neuroprotective properties. This codrug was loaded in SLN showing lack of toxicity in both N2a neuroblastoma cells (NB) and primary whole blood (PHWB) after using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) and lactate dehydrogenase (LDH) assays [53]. DDSs to release GFs Regarding GFs, our research group developed VEGF loaded PLGA nanospheres (NS) administered by craniotomy as a novel therapeutic approach to AD. In vitro studies in cortical neuronal cultures showed their effectiveness increasing cell viability and protecting neurons from Aβ induced toxicity. Furthermore, hippocampal neurogenesis was enhanced in APP/Ps1 mouse model treated group, which was confirmed with an increase in BrdU+cells, specially in the dentate gyrus. Behavioral studies were also carried out to demonstrate the therapeutic effect of VEFG loaded NS. Mice treated with VEGF NS presented better results in T-maze test and object recognition test, with higher exploratory memory and an improvement in shortterm memory, respectively, as shown in Figure 5 [54,55]. 16 pharmacodynamic outcomes as they decreased akinesias in 6-OHDA hemiparkinsonian rats [83]. Not only akinesia but also catalepsia and oxidative stress levels have been improved in the research work developed by Shadab et al. Moreover, gamma scintigraphy imaging has demonstrated the capacity of bromocriptine loaded chitosan NP for drug targeted brain delivery [37]. Finally, apomorphine is a non-narcotic derivative of morphine which is used in the treatment of patients with advanced PD. PLGA based NP were used for the encapsulation of this drug, improving the physiochemical characteristics of the molecule and obtaining a sustained release according to in vitro studies [36]. Apomorphine loaded SLN were developed by Tsai et. al. for oral administration. This nanosystem enhanced the brain uptake of the drug in the striatum as well as its bioavailability [84]. DDSs to release GFs Jollivet et al. were the first ones to propose DDSs to release NTFs in order to treat neurodegenerative disorders. They designed PLGA MS to release GDNF directly into the brain in a partial lesioned rat model of PD. The outcomes of these studies revealed the suitability of this formulation after intrastriatal administration to stimulate the axonal regeneration of mesencephalic dopaminergic neurons, which are affected in PD. Moreover, the brain implantation of GDNF-PLGA-MS increased TH+ fibers (Figure 8) and neuronal density in the striatum and substantia nigra which was accompanied by functional improvement in the lesioned animals [85,86]. Figure 8. Photomicrographs of striatal TH-ir fibers. Five sections, which were used for optical density (OD) measurements, are shown. The two-sites lesion induced an extensive dorsolateral and caudal lesion in the non-treated rat (A). Blank MS implantation induced an increase of the fibers density (B) whereas GDNF-loaded MS induced a stronger reinnervation (C). Reproduced with permission from [85]. 17 These results are consistent with Garbayo et al. published work, which confirmed the capability of PLGA MS to release this biologically active NTF in both in vivo and in vitro studies. Moreover, GDNF treated animals showed an improvement in amphetamine-induced rotational asymmetry test and in inmunohistochemical analysis with an increase in the density of TH+ fibers at the striatal level. They could also confirm an increase in dopaminergic striatal neurons and long-term neuroprotection and neurorestoration by GDNF-MS [87,88]. With the aim of regulating the GDNF release from MP, Gujral et al. developed PLGA/collagen MS that encapsulated GDNF fused with a collagen binding protein. Only when collagenase penetrates into the MS through its porous surface, is the collagen phase degraded. Then, the GDNF should be de-link from the collagen and diffuse out of the MS. In vitro studies after PLGA formulation administration, demonstrated the differentiation of neuronal progenitor cells into mature neurons, which are promising results for the treatment of PD [89]. The co-administration of GDNF with other NTFs has also been studied in order to investigate the synergistic effects of these molecules after the administration into the brain. For example, Lampe et al. investigated the brain administration of BDNF and GDNF loaded PLGA MS within a degradable PEG-based hydrogel. This approach allowed a different release profile for both grow factors decreasing the microglial response related with sham brain surgeries [90]. In a different study, our research group demonstrated the neuroregenerative potential of PLGA MS and NP encapsulating VEGF, GDNF and their combination on severely and partially lesioned rat models. The results of these works proved the biological activities of encapsulated NTFs in both in vitro and in vivo studies. Behavioral and inmunohistochemical tests were improved in the treated 6-OHDA lesioned rats as shown in Figure 9, due to the synergistic effect of NTF, permitting a reduction of the dose by a half [91-93]. 18 Figure 9. Histological evaluation of the treatments in the SN. Notes: (A) Schematic illustration of the SN with the “external SN” delimited. This area is topologically related to the lesioned area of striatum and includes SNL, a part of the SNR, and half of the SNC. (B) Picture of whole SN and delimited “external SN”. Scale bar =1 mm. (C) Density of dopaminergic neurons in “external SN”. The results are expressed as a percentage of lesioned hemisphere compared to the non-lesioned one (control). Data are shown as the mean ± standard error of the mean (n=6–8) (#P<0.05 GDNF NS group versus sham group; ***P<0.001 VEGF NS and GDNF NS group versus sham and empty NS groups). (D) Photomicrographs of SN immunostained for tyrosine hydroxylase from a representative intact hemisphere (control) and 6-OHDA lesioned hemispheres from the different experimental groups. Scale bar =1 mm. Abbreviations: 6-OHDA, 6-hydroxydopamine; GDNF, glial cell linederived neurotrophic factor; NS, nanospheres; SN, substantia nigra; SNC, SN pars compacta; SNL, SN lateral; SNR, SN pars reticulata; SNE, SN externa; VEGF, vascular endothelial growth factor. Reproduced with permission from [92]. Although GDNF is one of the most studied NTF for the treatment of PD, other similar molecules have also been encapsulated to improve its bioavailability. NGF loaded PBCA NPs were able to reduce the basic symptoms of PD in a MPTP (1-methyl-4-phenyl-1,2,3,6tetrahydropyridine) rat mode[94]. Besides this, gelatin NLC encapsulating bFGF has been studied as a novel approach to target the brain via nasal administration. The intranasal NLCs improved rotational behavior, monoamine neurotransmitter levels and TH expression in in vitro and in vivo studies without any adverse effects on the integrity of nasal mucosa [95]. Finally, as in AD, gene therapy has also been considered as a potential approach for the treatment of PD [44]. In an attempt to obtain this main goal, adenoviral-mediated GDNF gene transfer has been studied in a rat model of PD. Kozlowski et al. results revealed the suitability of this nanosystem increasing the number of dopaminergic neurons in the substantia nigra and maintaining functional connections to the striatum [96]. In addition, Chen et al. research work reinforces these outcomes since they could demonstrate the protective effect of GDNF gene transfer after intracerebral administration. Moreover, adenoviral (Ad) GDNF treated animals showed an improvement in behavioral tests and an increase in the survival of TH+ cells [97]. Not only has been demonstrated the effectiveness of Ad vectors in mouse models, but also, studies in non-human primate models of PD have been performed. Eslamboli et al and Eberling et al. showed that Ad-GDNF enhanced DA activity in the striatum, which was associated with clinical improvements without adverse effects in MPTP and 6-OHDA primate models of PD, respectively [98,99]. Moreover, the investigation led by Kordower et al. demonstrated that the delivery of neurturin, a GDNF analogous, via Ad vectors provided structural and functional neuroprotection and neurorestoration in MPTP-treated monkeys without histological pathology [100]. However, due to the risk of viral gene therapy associated with inmunogenecity and safety, safer and effective non viral gene delivery vectors have been developed [43]. A neurotensin polyplex carrier was elaborated for delivering GDNF gene into nigral dopamine neurons of hemiparkinsonian rats with stereotaxic procedures. RT-PCR and western blot analysis confirmed that GDNF was correctly transfected in the substantia nigra reducing PD symptoms 19 [101]. In order to improve transfection efficiency of nonviral gene vectors, different modifications on their surface have been made. For instance, Chung-Fang et al. developed intravenous GDNF plasmid DNA using Trojan horse liposomes (THLs) targeted with a monoclonal antibody (MAb) to the rat transferring receptor (TfR). They observed an increase in the concentrations of GDNF in the substantia nigra, which resulted in a reduction in apomorphine-induced rotations with different doses of encapsulated GF (Figure 10) and an increase in striatal TH enzyme activity [102]. Figure 10. Apomorphine-induced rotation, measured in r.p.m., in rats with experimental PD, and treated intravenously with saline, or TfRMAb-targeted THLs carrying 2, 10 or 20 µg/rat of encapsulated pTHpro-GDNF plasmid DNA. The THLs were given on day 0, and rotation behaviour was measured at 7, 14, 21, 28, 35 and 42 days after the single intravenous injection of THLs. The rats were lesioned with intra-cerebral 6-hydroxydopamine 14 days before THL administration. Statististical differences were determined by ANOVA with Tukey's post-hoc correction; difference from saline control: #p < 0.05; *p < 0. Reproduced with permission from [102]. Furthermore, Huang et al. proposed a lactoferrin-modified vector which was demonstrated to be effective for brain gene delivery of GDNF. Neuroprotective effects of these NPs were assayed in 6-OHDA lesioned rats and in rotenone-induced chronic PD model. In vivo studies revealed its capability for improving locomotor activity, reducing dopaminergic neuronal loss and enhancing monoamine neurotransmissor levels with multiple intravenous administrations and without brain toxicity [103,104]. DDSs to release other molecules. Although there are scientific studies supporting the use of coenzyme Q10 to treat PD, the results derived from clinical trials are inconclusive. It is may be due to the low solubility, bioavailability and brain penetration of this molecule. In an attempt to overcome these all drawbacks, Sikorska et al. developed a nanomicellar formulation of coenzyme Q10 and tested its effectiveness in a mouse MPTP model. The outcomes of this investigation revealed the therapeutic effect of coenzyme Q10 via oral administration offsetting the neurotoxicity before 20 and after MPTP injection. This was confirmed by cell counts, analyses of striatal dopamine levels and improved animals’ motor skills on behavioral tests [105]. The antioxidant effect of resveratrol has also been enhanced after been loaded in liposomes. The behaviors, TH+ cells, apoptotic cells, ROS level and antioxidant capacity were determined in in vivo studies, showing resveratrol liposome more favorable effects than free resveratrol[106]. Resveratrol has also been loaded in Vitamin E nanoemulsion to improve its pharmachological activities. Pharmacokinetic studies showed a higher concentration of the drug in the brain with the nanoemulsion, which was consistent with higher antioxidant activity evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) assay [107]. CONCLUSIONS AND FUTURE OUTLOOK Current available therapies to treat AD and PD are only symptomatic without modifying the progression of these diseases. This fact, along with the difficulty of researching the pathways that cause NDs, drives the need for the development of new therapeutic alternatives to address the problem of these NDs. Given this difficult situation, in the last years, not only the standardized drugs, but also new molecules such as growth factors, metal chelators and antioxidants have been investigated in order to study their potential activity in the restoration and promotion of neuronal processes. However, the physicochemical properties of these molecules make difficult their pass across the BBB to the brain, limiting their effectiveness and clinical application in vivo. Therefore, there is a critical need to develop new DDSs to overcome these drawbacks with the aim of obtaining targeted drug delivery and a sustained release profile of the above mentioned drugs into the brain. The rapid progression of the nanomedicine in the neuroscience area, is giving rise to design different nanometric formulations that permit the encapsulation of the drugs, protecting them against the enzymatic degradation and helping to reach therapeutic drug concentrations into the CNS after their in vivo administration. The results presented in this review support the use of nanotechnology as a promising approach to control the release of old and new drugs for the treatment of AD and PD. Nevertheless, not only further studies of the properties of these nanocarriers, but also more preclinical test are needed to assess the therapeutic use and safety values of this nanocarriers for future applications in human clinical trials. 21 EXECUTIVE SUMMARY NEW PROMISING MOLECULES FOR THE TREATMENT OF AD AND PD • In the last years new molecules such as neurotrophic factors (NTFs), antioxidant molecules and metal chelators have been considered promising approaches to address the main causes of NDs. • Grow factors are a group of proteins which are able to improve the growth, proliferation and differentiation of neuronal cells. • Antioxidants have been raised as new treatment approaches to address the oxidative stress produced in AD and PD. • The main obstacle for most of these drugs to access into the brain is the presence of the BBB, therefore, different strategies have been developed to cross or by-pass this barrier. 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