Phenolic compounds prevent Alzheimer's pathology through different effects on the amyloid-beta aggregation pathway

Inhibition of amyloid formation

Amyloid is aggregated protein in the form of insoluble fibrils. Amyloid deposition in human tissue-amyloidosis-is associated with a number of diseases including all common dementias and type II diabetes. Considerable progress has been made to understand the mechanisms leading to amyloid formation. It is, however, not yet clear by which mechanisms amyloid and protein aggregates formed on the path to amyloid are cytotoxic. Strategies to prevent protein aggregation and amyloid formation are nevertheless, in many cases, promising and even successful. This review covers research on intervention of amyloidosis and highlights several examples of how inhibition of protein aggregation and amyloid formation has been achieved in practice. For instance, rational design can provide drugs that stabilize a native folded state of a protein, protein engineering can provide new binding proteins that sequester monomeric peptides from aggregation, small molecules and peptides can be designed to block aggregation or direct it into non-cytotoxic paths, and monoclonal antibodies have been developed for therapies towards neurodegenerative diseases based on inhibition of amyloid formation and clearance.

Apricot carotenoids possess potent anti-amyloidogenic activity in vitro

Alzheimer's disease (AD) is the most common form of dementia and is characterized by the progressive accumulation of amyloid β protein (Aβ) in areas of the brain. There has been an increased interest in screening for food-grade anti-amyloidogenic compounds in foodstuffs. The purpose of this study was to screen and identify bioactive compounds with anti-amyloidogenicity in apricot fruits using synthetic Aβ(1-42). The anti-amyloidogenicity was investigated using thioflavin T fluorescence assay, electron microscopy, and dot blotting analysis. The carotenoid fraction from apricot showed strong inhibitory effects against oligomer and fibril formation of Aβ and fibril-destabilizing effects. Among the peaks in the HPLC chromatogram, lutein showed the strongest inhibitory effect on Aβ fibril formation. The inhibitory effect was dependent on the number and portion of hydroxyl groups on both sides of carotenoids. These findings suggest that lutein in fruits may be useful as a preventive agent for amyloid-associated diseases.

The natural antioxidant rosmarinic acid spontaneously penetrates membranes to inhibit lipid peroxidation in situ

Exogenous molecules from dietary sources such as polyphenols are very efficient in preventing the alteration of lipid membranes by oxidative stress. Among the polyphenols, we have chosen to study rosmarinic acid (RA). We investigated the efficiency of RA in preventing lipid peroxidation and in interacting with lipids. We used liposomes of 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) to show that RA was an efficient antioxidant. By HPLC, we determined that the maximum amount of RA associated with the lipids was ~1 mol%. Moreover, by using Langmuir monolayers, we evidenced that cholesterol decreases the penetration of RA. The investigation of transferred lipid/RA monolayers by atomic force microscopy revealed that 1 mol% of RA in the membrane was not sufficient to alter the membrane structure at the nanoscale. By fluorescence, we observed no significant modification of membrane permeability and fluidity caused by the interaction with RA. We also deduced that RA molecules were mainly located among the polar headgroups of the lipids. Finally, we prepared DLPC/RA vesicles to evidence for the first time that up to 1 mol% of RA inserts spontaneously in the membrane, which is high enough to fully prevent lipid peroxidation without any noticeable alteration of the membrane structure due to RA insertion.

Binding of curcumin to senile plaques and cerebral amyloid angiopathy in the aged brain of various animals and to neurofibrillary tangles in Alzheimer's brain

The binding of curcumin to senile plaques (SPs) and cerebral amyloid angiopathy (CAA) was examined in the aged brain of various animal species and a human patient with Alzheimer's disease (AD), together with its binding to neurofibrillary tangles (NFTs). Brain sections were immunostained with anti-amyloid β protein 1-42 (Aβ42) and anti-amyloid β protein 1-40 (Aβ40) antibodies. These sections were also stained with alkaline Congo red, periodic acid-methenamine silver (PAM), and curcumin (0.009% curcumin solution) with or without formic acid pretreatment. The sections from the AD brain were also immunostained for anti-paired helical filament-tau (PHF-tau), and were stained with Gallyas silver for NFTs. Some SPs in the AD, monkey, dog, bear, and amyloid precursor protein transgenic mouse (APP Tg-mouse) brains contained congophilic materials, and were intensely positive for curcumin. In addition, curcumin labeled some diffuse SPs negative for Congo red in the AD, monkey, bear, and APP Tg-mouse brains. In all animals, CAA was intensely positive for both Congo red and curcumin. The specific curcumin staining activity was lost by formic acid pretreatment. In the AD brain, NFTs positive for PHF-tau and Gallyas silver were moderately stained with curcumin. These findings indicate that curcumin specifically binds to the aggregated Aβ molecules in various animals, and further to phosphorylated tau protein, probably according to its conformational nature.

Apple Procyanidins Suppress Amyloid β-Protein Aggregation

Procyanidins (PCs) are major components of the apple polyphenols (APs). We previously reported that treatment with PC extended the mean lifespan of Caenorhabditis elegans (Sunagawa et al., 2011). In order to estimate the neuroprotective effects of PC, we investigated the antiaggregative activity of PC on amyloid β-protein (Aβ) aggregation, which is a pathological hallmark of Alzheimer's disease. We herein report that PC significantly suppressed Aβ42 aggregation and dissociated Aβ42 aggregates in a dose-dependent manner, indicating that PC is a potent suppressor of Aβ aggregation. Furthermore, PC significantly inhibited Aβ42 neurotoxicity and stimulated proliferation in PC-12 cells. These results suggested that the PC and AP acted as neuroprotective factors against toxic Aβ aggregates.

Development and validation of a yeast high-throughput screen for inhibitors of Aβ₄₂ oligomerization

Recent reports point to small soluble oligomers, rather than insoluble fibrils, of amyloid β (Aβ), as the primary toxic species in Alzheimer’s disease. Previously, we developed a low-throughput assay in yeast that is capable of detecting small Aβ₄₂ oligomer formation. Specifically, Aβ₄₂ fused to the functional release factor domain of yeast translational termination factor, Sup35p, formed sodium dodecyl sulfate (SDS)-stable low-n oligomers in living yeast, which impaired release factor activity. As a result, the assay for oligomer formation uses yeast growth to indicate restored release factor activity and presumably reduced oligomer formation. We now describe our translation of this assay into a high-throughput screen (HTS) for anti-oligomeric compounds. By doing so, we also identified two presumptive anti-oligomeric compounds from a sub-library of 12,800 drug-like small molecules. Subsequent biochemical analysis confirmed their anti-oligomeric activity, suggesting that this form of HTS is an efficient, sensitive and cost-effective approach to identify new inhibitors of Aβ₄₂ oligomerization.

Observation of reduced cytotoxicity of aggregated amyloidogenic peptides with chaperone-like molecules

The pathogenesis of many neurodegenerative diseases is associated with different types of aggregates of amyloidogenic peptides, including senile plaques, fibrils, protofibrils, and oligomers. It is therefore valuable to explore diversity of approaches toward reducing the cytotoxicity of amyloidogenic peptides by modulating aggregation behaviors. Herein we report an approach toward reducing the neuronal cytotoxicity of amyloidogenic peptides by accelerating the aggregation process, which is different from prevalent methods via inhibiting the aggregation of peptides. The pyridyl derivatives behave like chaperones to dramatically change the assembling characteristics of the peptides via strong hydrogen bond formation with C-termini of amyloid β (Aβ) peptides, which is revealed by using scanning probe microscopy. The light scattering experiments demonstrated the effect of the chaperone-like molecules on accelerating the aggregation process of Aβ peptides, accompanied by the reduced neuronal cytotoxicity of amyloidogenic peptides. These results would give rise to a complementary approach for modulating biological effects of the aggregates of amyloidogenic peptides.

Mechanisms underlying the protective effects of myricetin and quercetin following oxygen-glucose deprivation-induced cell swelling and the reduction in glutamate uptake in glial cells

The protective effects of the flavonoid polyphenols, myricetin and quercetin, were investigated on key features of ischemic injury in cultures including cell swelling and the reduction in glutamate uptake. C6 glial cells were exposed to oxygen-glucose deprivation (OGD) for 5 h and cell swelling was determined 90 min after the end of OGD. OGD-induced swelling was significantly blocked by both quercetin and myricetin although higher concentrations were required for quercetin. OGD-induced free radical production, a contributing factor in cell swelling, was significantly reduced by both myricetin and quercetin. However, depolarization of the inner mitochondrial membrane potential (ΔΨ(m)), the blockade of which generally reduces swelling, was significantly diminished by myricetin, but not quercetin. This indicated that quercetin could reduce swelling despite its inability to prevent depolarization of ΔΨ(m) possibly through other signaling pathways. Increased intracellular calcium ([Ca²+](i)) is an important characteristic of ischemic injury and is implicated in swelling. Both myricetin and quercetin attenuated the increase in [Ca²+](i). Further, a reduction in [Ca²+](i), through the use of nifedipine, nimodipine, verapamil, dantrolene, or BAPTA-AM, significantly reduced OGD-induced cell swelling indicating that one possible mechanism by which such flavonoids attenuate cell swelling may be through regulating [Ca²+](i). OGD-induced decrease in glutamate uptake was attenuated by myricetin, but not quercetin. Cyclosporin A, a blocker of the mitochondrial permeability transition (mPT) pore, but not FK506 (that does not block the mPT), attenuated the decline in glutamate uptake after OGD, indicating the involvement of the mPT in glutamate uptake. Our results indicated that while blockade of ΔΨ(m) may be sufficient to reduce swelling, it may not be a necessary factor, and that flavonoids reduce cell swelling by regulating [Ca²+](i). The differential effects of myricetin and quercetin on OGD-induced reduction on glutamate uptake may be due to their differential effects on mitochondria.

Modulation of lipid peroxidation and mitochondrial function improves neuropathology in Huntington's disease mice

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. Oxidative damage has been associated with pathological neuronal loss in HD. The therapeutic modulation of oxidative stress and mitochondrial function using low molecular weight compounds may be an important strategy for delaying the onset and slowing the progression of HD. In the present study, we found a marked increase of 4-hydroxy-2-nonenal (4-HNE) adducts, a lipid peroxidation marker, in the caudate and putamen of HD brains and in the striatum of HD mice. Notably, 4-HNE immunoreactivity was colocalized with mutant huntingtin inclusions in the striatal neurons of R6/2 HD mice. Administration of nordihydroguaiaretic acid (NDGA), an antioxidant that functions by inhibiting lipid peroxidation, markedly reduced 4-HNE adduct formation in the nuclear inclusions of R6/2 striatal neurons. NDGA also protected cultured neurons against oxidative stress-induced cell death by improving ATP generation and mitochondrial morphology and function. In addition, NDGA restored mitochondrial membrane potential, mitochondrial structure, and synapse structure in the striatum of R6/2 mice and increased their lifespan. The present findings suggest that further therapeutic studies using NDGA are warranted in HD and other neurodegenerative diseases characterized by increased oxidative stress and altered mitochondrial function.

Inhibition and disaggregation of α-synuclein oligomers by natural polyphenolic compounds

Aggregation of alpha-synuclein (αS) into oligomers is critically involved in the pathogenesis of Parkinson's disease (PD). Using confocal single-molecule fluorescence spectroscopy, we have studied the effects of 14 naturally-occurring polyphenolic compounds and black tea extract on αS oligomer formation. We found that a selected group of polyphenols exhibited potent dose-dependent inhibitory activity on αS aggregation. Moreover, they were also capable of robustly disaggregating pre-formed αS oligomers. Based upon structure-activity analysis, we propose that the key molecular scaffold most effective in inhibiting and destabilizing self-assembly by αS requires: (i) aromatic elements for binding to the αS monomer/oligomer and (ii) vicinal hydroxyl groups present on a single phenyl ring. These findings may guide the design of novel therapeutic drugs in PD.

Kinetic characterization of amyloid-beta 1-42 aggregation with a multimethodological approach

Extensive evidence suggests that the self-assembly of amyloid-beta peptide (Aβ) is a nucleation-dependent process that involves the formation of several oligomeric intermediates. Despite neuronal toxicity being recently related to Aβ soluble oligomers, results from aggregation studies are often controversial, mainly because of the low reproducibility of several experimental protocols. Here a multimethodological study that included atomic force microscopy (AFM), transmission electron microscopy (TEM), fluorescence microscopy (FLM), mass spectrometry techniques (matrix-assisted laser desorption/ionization time-of-flight [MALDI-TOF] and electrospray ionization quadrupole time-of-flight [ESI-QTOF]), and direct thioflavin T (ThT) fluorescence spectroscopy were enabled to set up a reliable and highly reproducible experimental protocol for the characterization of the morphology and dimension of Aβ 1-42 (Aβ42) aggregates along the self-assembly pathway. This multimethodological approach allowed elucidating the diverse assembly species formed during the Aβ aggregation process and was applied to the detailed investigation of the mechanism of Aβ42 inhibition by myricetin. In particular, a very striking result was the molecular weight determination of the initial oligomeric nuclei by MALDI-TOF, composed of up to 10 monomers, and their morphology by AFM.

REVIEW: Curcumin and Alzheimer's disease

Curcumin has a long history of use as a traditional remedy and food in Asia. Many studies have reported that curcumin has various beneficial properties, such as antioxidant, antiinflammatory, and antitumor. Because of the reported effects of curcumin on tumors, many clinical trials have been performed to elucidate curcumin's effects on cancers. Recent reports have suggested therapeutic potential of curcumin in the pathophysiology of Alzheimer's disease (AD). In in vitro studies, curcumin has been reported to inhibit amyloid-β-protein (Aβ) aggregation, and Aβ-induced inflammation, as well as the activities of β-secretase and acetylcholinesterase. In in vivo studies, oral administration of curcumin has resulted in the inhibition of Aβ deposition, Aβ oligomerization, and tau phosphorylation in the brains of AD animal models, and improvements in behavioral impairment in animal models. These findings suggest that curcumin might be one of the most promising compounds for the development of AD therapies. At present, four clinical trials concerning the effects of curcumin on AD has been conducted. Two of them that were performed in China and USA have been reported no significant differences in changes in cognitive function between placebo and curcumin groups, and no results have been reported from two other clinical studies. Additional trials are necessary to determine the clinical usefulness of curcumin in the prevention and treatment of AD.

Curcumin activates Wnt/β-catenin signaling pathway through inhibiting the activity of GSK-3β in APPswe transfected SY5Y cells

Wnt/β-catenin signaling pathway plays an important role in the genesis and development of Alzheimer's disease. The study aims to investigate the effect of Curcumin on the expression of GSK-3β, β-catenin and CyclinD1 in vitro, which are tightly correlated with Wnt/β-catenin signaling pathway, and also to explore the mechanisms, which will provide a novel therapeutic intervention for treatment of Alzheimer's disease. Plasmid APPswe and BACE1-mychis were transiently co-transfected into SHSY5Y cells by Liposfectamin™2000. The cells were treated with Curcumin at 0, 1.25, 5.0, 20.0 μmol/L for 24 h, or with Curcumin at 5.0 μmol/L for 0, and 12, 24 and 48 h for time course assay. Cell lysates were collected for RT-PCR, Western blot assay and immunofluorescent staining were carried out for detecting the effect of Curcumin on the expression of GSK-3β, β-catenin and CyclinD1. RT-PCR and Western blot results showed that the expression of GSK-3β mRNA and protein significantly decreased in the transfected cells treated with Curcumin, and that the changes were in a dose and time-dependent manner (P<0.05); however, the protein expression of GSK-3β-Ser9 was increased (P<0.05). Meanwhile, the expressions of β-catenin and transcriptional factors CyclinD1 mRNA and protein increased and the changes were also in a dose and time-dependent manner (P<0.05). Immunofluorescent staining results not only confirmed the above changes, but also showed that β-catenin had translocated into the nucleus gradually with the increased dosage of Curcumin. Therefore, GSK-3β is a potential target for treatment of AD. Curcumin could activate the Wnt/β-catenin signaling pathway through inhibiting the expression of GSK-3β and inducing the expression of β-catenin and CyclinD1, which will provide a new theory for treatment of neurodegenerative diseases by Curcumin.

Low-n oligomers as therapeutic targets of Alzheimer's disease

The pathogenesis of Alzheimer's disease involves the progressive accumulation of amyloid β-protein (Aβ). Recent studies using synthetic Aβ peptides, a cell culture model, Aβ precursor protein transgenic mice models suggest that pre-fibrillar forms of Aβ are more deleterious than extracellular fibril forms. Recent findings obtained using synthetic Aβ peptides and human samples indicated that low-n oligomers (from dimers to octamers) may be proximate toxins for neuron and synapse. Here, we review the recent studies on the soluble oligomers, especially low-n oligomers in Alzheimer's disease.

Tissue transglutaminase-mediated glutamine deamidation of beta-amyloid peptide increases peptide solubility, whereas enzymatic cross-linking and peptide fragmentation may serve as molecular triggers for rapid peptide aggregation

Tissue transglutaminase (TGase) has been implicated in a number of cellular processes and disease states, where the enzymatic actions of TGase may serve in both, cell survival and apoptosis. To date, the precise functional properties of TGase in cell survival or cell death mechanisms still remain elusive. TGase-mediated cross-linking has been reported to account for the formation of insoluble lesions in conformational diseases. We report here that TGase induces intramolecular cross-linking of β-amyloid peptide (Aβ), resulting in structural changes of monomeric Aβ. Using high resolution mass spectrometry (MS) of cross-linked Aβ peptides, we observed a shift in mass, which is, presumably associated with the loss of NH3 due to enzymatic transamidation activity and hence intramolecular peptide cross-linking. We have observed that a large population of Aβ monomers contained an 0.984 Da increase in mass at a glutamine residue, indicating that glutamine 15 serves as an indispensable substrate in TGase-mediated deamidation to glutamate 15. We provide strong analytical evidence on TGase-mediated Aβ peptide dimerization, through covalent intermolecular cross-linking and hence the formation of Aβ1-40 dimers. Our in depth analyses indicate that TGase-induced post-translational modifications of Aβ peptide may serve as an important seed for aggregation.

Formation of the 42-mer Amyloid β Radical and the Therapeutic Role of Superoxide Dismutase in Alzheimer's Disease

Oxidative stress is closely involved in age-related diseases and ageing itself. There is evidence of the leading contribution of oxidative damage to neurodegenerative disease, in contrast to other diseases where oxidative stress plays a secondary role. The 42-mer amyloid β (Aβ42) peptide is thought to be a culprit in the pathogenesis of Alzheimer's disease (AD). Aβ42 aggregates form the oligomeric assembly and show neurotoxicity, causing synaptic dysfunction. Aβ42 also induces tissue oxidation (DNA/RNA, proteins, and lipids) through trace metals (Cu, Zn, and Fe), which can be protected by antioxidant enzymes, vitamin C, and vitamin E. Superoxide dismutase catalyzes the conversion of toxic superoxide radical to less reactive hydrogen peroxide, contributing to protection from AD. Here we review the involvement of oxidative stress in AD progression induced from an imbalance between the radical formation of Aβ42 itself together with unique turn structure at positions Glu22 and Asp23 and several defense systems.

Natural products as a source of Alzheimer's drug leads

This review focuses on recent developments in the use of natural products as therapeutics for Alzheimer's disease. The compounds span a diverse array of structural classes and are organized according to their mechanism of action, with the focus primarily on the major hypotheses. Overall, the review discusses more than 180 compounds and summarizes 400 references.

A novel ring-expanded product with enhanced tyrosinase inhibitory activity from classical Fe-catalyzed oxidation of rosmarinic acid, a potent antioxidative Lamiaceae polyphenol

The iron-ion catalyzed oxidation of the ethanol solution of rosmarinic acid, a potent antioxidant polyphenol of Lamiaceae (Labiatae) plants, afforded a highly tyrosinase-inhibitory active product. The structure of the active product in the oxidation product mixture was determined using extensive NMR spectroscopy to have a novel oxygen-containing seven-membered ring system. The formation mechanism of the unique ring structure from the catechol part of the rosmarinic acid was proposed.

Hydralazine modifies Aβ fibril formation and prevents modification by lipids in vitro

Lipid oxidative damage and amyloid β (Aβ) misfolding contribute to Alzheimer's disease (AD) pathology. Thus, the prevention of oxidative damage and Aβ misfolding are attractive targets for drug discovery. At present, no AD drugs approved by the Food and Drug Administration (FDA) prevent or halt disease progression. Hydralazine, a smooth muscle relaxant, is a potential drug candidate for AD drug therapy as it reduces Aβ production and prevents oxidative damage via its antioxidant hydrazide group. We evaluated the efficacy of hydralazine, and related hydrazides, in reducing (1) Aβ misfolding and (2) Aβ protein modification by the reactive lipid 4-hydroxy-2-nonenal (HNE) using transmission electron microscopy and Western blotting. While hydralazine did not prevent Aβ aggregation as measured using the protease protection assay, there were more oligomeric species observed by electron microscopy. Hydralazine prevented lipid modification of Aβ, and Aβ was used as a proxy for classes of proteins which either misfold or are modified by HNE. All of the other hydrazides prevented lipid modification of Aβ and also did not prevent Aβ aggregation. Surprisingly, a few of the compounds, carbazochrome and niclosamide, appeared to augment Aβ formation. Thus, hydrazides reduced lipid oxidative damage, and hydralazine additionally reduced Aβ misfolding. While hydralazine would require specific chemical modifications for use as an AD therapeutic itself (to improve blood brain barrier permeability, reduce vasoactive side effects, and optimization for amyloid inhibition), this study suggests its potential merit for further AD drug development.

Neurotherapeutic applications of nanoparticles in Alzheimer's disease

A rapid increase in incidence of neurodegenerative disorders has been observed with the aging of the population. Alzheimer's disease (AD) is the most common neurodegenerative disorder among the elderly. It is characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation and impairment of judgement clinically. Unfortunately, clinical development of drugs for the symptomatic and disease-modifying treatment of AD has resulted in both promise and disappointment. Indeed, a large number of drugs with differing targets and mechanisms of action were investigated with only a few of them being clinically available. The targeted drug delivery to the central nervous system (CNS), for the diagnosis and treatment of neurodegenerative disorders such as AD, is restricted due to the limitations posed by the blood-brain barrier (BBB) as well as due to opsonization by plasma proteins in the systemic circulation and peripheral side-effects. Over the last decade, nanoparticle-mediated drug delivery represents one promising strategy to successfully increase the CNS penetration of several therapeutic moieties. Different nanocarriers are being investigated to treat and diagnose AD by delivering at a constant rate a host of therapeutics over times extending up to days, weeks or even months. This review provides a concise incursion on the current pharmacotherapies for AD besides reviewing and discussing the literature on the different drug molecules that have been successfully encapsulated in nanoparticles (NPs). Some of them have been shown to cross the BBB and have been tested either for diagnosis or treatment of AD. Finally, the route of NPs administration and the future prospects will be discussed.

Structure-activity relationship of flavonoids derived from medicinal plants in preventing methylmercury-induced mitochondrial dysfunction

In the present study, we investigated the potential protective effects of three flavonoids (myricetin, myricitrin and rutin) derived from medicinal plants against methyl mercury (MeHg)-induced mitochondrial dysfunction in vitro. Incubation of mouse brain mitochondria with MeHg induced a significant decrease in mitochondrial function, which was correlated with decreased glutathione (GSH) levels and increased generation of reactive oxygen species (ROS) and lipid peroxidation. The co-incubation of mouse brain mitochondria with myricetin or myricitrin caused a concentration-dependent decrease of MeHg-induced mitochondrial dysfunction and oxidative stress. The flavonoid rutin was ineffective in counteracting MeHg toxicity. Among the three tested flavonoids, myricetin was the most efficient in protecting against MeHg-induced mitochondrial dysfunction. Moreover, myricetin completely blocked MeHg-induced ROS formation and lipid peroxidation and partially prevented MeHg-induced GSH depletion. The ability of myricetin to attenuate MeHg-induced mitochondrial dysfunction and oxidative stress appears to be related to its higher scavenging capability when compared to myricitrin and rutin. Overall, the results suggest that MeHg-induced mitotoxicity is associated with oxidative stress. The ability of myricetin to prevent MeHg-induced oxidative damage in brain mitochondria renders this flavonoid a promising molecule for further in vivo studies in the search for potential antidotes to counteract MeHg-induced neurotoxicity.

Future Trends in the Pharmacogenomics of Brain Disorders and Dementia: Influence of APOE and CYP2D6 Variants

About 80% of functional genes in the human genome are expressed in the brain and over 1,200 different genes have been associated with the pathogenesis of CNS disorders and dementia. Pharmacogenetic studies of psychotropic drug response have focused on determining the relationship between variations in specific candidate genes and the positive and adverse effects of drug treatment. Approximately, 18% of neuroleptics are substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of CYP3A4. 10-20% of Western populations are defective in genes of the CYP superfamily; and the pharmacogenomic response of psychotropic drugs also depends on genetic variants associated with dementia. Prospective studies with anti-dementia drugs or with multifactorial strategies have revealed that the therapeutic response to conventional drugs in Alzheimer’s disease is genotype-specific. The disease-modifying effects (cognitive performance, biomarker modification) of therapeutic intervention are APOE-dependent, with APOE-4 carriers acting as the worst responders (APOE-3/3 > APOE-3/4 > APOE-4/4). APOE-CYP2D6 interactions also influence the therapeutic outcome in patients with dementia.

Targeting NADPH oxidase and phospholipases A2 in Alzheimer's disease

Alzheimer's disease (AD) is marked by an increase in the production of extracellular beta amyloid plaques and intracellular neurofibrillary tangles associated with a decline in brain function. Increases in oxidative stress are regarded as an early sign of AD pathophysiology, although the source of reactive oxygen species (ROS) and the mechanism(s) whereby beta amyloid peptides (Abeta) impact oxidative stress have not been adequately investigated. Recent studies provide strong evidence for the involvement of NADPH oxidase and its downstream oxidative signaling pathways in the toxic effects elicited by Abeta. ROS produced by NADPH oxidase activate multiple signaling pathways leading to neuronal excitotoxicity and glial cell-mediated inflammation. This review describes recent studies demonstrating the neurotoxic effects of Abeta in conjunction with ROS produced by NADPH oxidase and the downstream pathways leading to activation of cytosolic phospholipase A(2) (PLA(2)) and secretory PLA(2). In addition, this review also describes recent studies using botanical antioxidants to protect against oxidative damage associated with AD. Investigating the metabolic and signaling pathways involving Abeta NADPH oxidase and PLA(2) can help understand the mechanisms underlying the neurodegenerative effects of oxidative stress in AD. This information should provide new therapeutic approaches for prevention of this debilitating disease.