Antioxidants and Alzheimer's disease: from bench to bedside (and back again)

Identification of Natural Compounds of the Apple as Inhibitors against Cholinesterase for the Treatment of Alzheimer's Disease: An In Silico Molecular Docking Simulation and ADMET Study

Alzheimer's disease (AD), the most common type of dementia in older people, causes neurological problems associated with memory and thinking. The key enzymes involved in Alzheimer's disease pathways are acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Because of this, there is a lot of interest in finding new AChE inhibitors. Among compounds that are not alkaloids, flavonoids have stood out as good candidates. The apple fruit, Malus domestica (Rosaceae), is second only to cranberries regarding total phenolic compound concentration. Computational tools and biological databases were used to investigate enzymes and natural compounds. Molecular docking techniques were used to analyze the interactions of natural compounds of the apple with enzymes involved in the central nervous system (CNS), acetylcholinesterase, and butyrylcholinesterase, followed by binding affinity calculations using the AutoDock tool. The molecular docking results revealed that CID: 107905 exhibited the best interactions with AChE, with a binding affinity of -12.2 kcal/mol, and CID: 163103561 showed the highest binding affinity with BuChE, i.e., -11.2 kcal/mol. Importantly, it was observed that amino acid residue Trp286 of AChE was involved in hydrogen bond formation, Van Der Walls interactions, and Pi-Sigma/Pi-Pi interactions in the studied complexes. Moreover, the results of the Molecular Dynamics Simulation (MDS) analysis indicated interaction stability. This study shows that CID: 12000657 could be used as an AChE inhibitor and CID: 135398658 as a BuChE inhibitor to treat Alzheimer's disease and other neurological disorders.

Implication of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase and Its Inhibitors in Alzheimer's Disease Murine Models

Alzheimer’s disease (AD) is one of the main human dementias around the world which is constantly increasing every year due to several factors (age, genetics, environment, etc.) and there are no prevention or treatment options to cure it. AD is characterized by memory loss associated with oxidative stress (OS) in brain cells (neurons, astrocytes, microglia, etc.). OS can be produced by amyloid beta (Aβ) protein aggregation and its interaction with metals, mitochondrial damage and alterations between antioxidants and oxidant enzymes such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. NADPH oxidase produces reactive oxygen species (ROS) and it is overexpressed in AD, producing large amounts of superoxide anions and hydrogen peroxide which damage brain cells and the vasculature. In addition, it has been reported that NADPH oxidase causes an imbalance of pH which could also influence in the amyloid beta (Aβ) production. Therefore, NADPH oxidase had been proposed as a therapeutic target in AD. However, there are no drugs for AD treatment such as an NADPH oxidase inhibitor despite great efforts made to stabilize the ROS production using antioxidant molecules. So, in this work, we will focus our attention on NADPH oxidase (NOX2 and NOX4) in AD as well as in AD models and later discuss the use of NADPH oxidase inhibitor compounds in AD.

Involvement of Lipids in Alzheimer's Disease Pathology and Potential Therapies

Lipids constitute the bulk of the dry mass of the brain and have been associated with healthy function as well as the most common pathological conditions of the brain. Demographic factors, genetics, and lifestyles are the major factors that influence lipid metabolism and are also the key components of lipid disruption in Alzheimer's disease (AD). Additionally, the most common genetic risk factor of AD, APOE ϵ4 genotype, is involved in lipid transport and metabolism. We propose that lipids are at the center of Alzheimer's disease pathology based on their involvement in the blood-brain barrier function, amyloid precursor protein (APP) processing, myelination, membrane remodeling, receptor signaling, inflammation, oxidation, and energy balance. Under healthy conditions, lipid homeostasis bestows a balanced cellular environment that enables the proper functioning of brain cells. However, under pathological conditions, dyshomeostasis of brain lipid composition can result in disturbed BBB, abnormal processing of APP, dysfunction in endocytosis/exocytosis/autophagocytosis, altered myelination, disturbed signaling, unbalanced energy metabolism, and enhanced inflammation. These lipid disturbances may contribute to abnormalities in brain function that are the hallmark of AD. The wide variance of lipid disturbances associated with brain function suggest that AD pathology may present as a complex interaction between several metabolic pathways that are augmented by risk factors such as age, genetics, and lifestyles. Herewith, we examine factors that influence brain lipid composition, review the association of lipids with all known facets of AD pathology, and offer pointers for potential therapies that target lipid pathways.

Erythrocytes as Potential Link between Diabetes and Alzheimer's Disease

Many studies support the existence of an association between type 2 diabetes (T2DM) and Alzheimer's disease (AD). In AD, in addition to brain, a number of peripheral tissues and cells are affected, including red blood cell (RBC) and because there are currently no reliable diagnostic biomarkers of AD in the blood, a gradually increasing attention has been given to the study of RBC's alterations. Recently it has been evidenced in diabetes, RBC alterations superimposable to the ones occurring in AD RBC. Furthermore, growing evidence suggests that oxidative stress plays a pivotal role in the development of RBC's alterations and vice versa. Once again this represents a further evidence of a shared pathway between AD and T2DM. The present review summarizes the two disorders, highlighting the role of RBC in the postulated common biochemical links, and suggests RBC as a possible target for clinical trials.

Medicinal Effect of Nutraceutical Fruits for the Cognition and Brain Health

The recent era is witnessing evaluation of medicinal and nutritional value of fruits and fruit juices for the management and prevention of brain diseases like headache stress, anxiety, hypertension, and Alzheimer's and Parkinson's diseases by the scientists and researchers worldwide. Fruits possess various chemicals such as antioxidants and polyphenols, which reduce and balance the effect of hormone in brain responsible for brain disease. Natural remedy is cheap, easily available, nontoxic, and easy to prepare and provides good mental health as compared to other remedies. The main objective of this review is to acknowledge medicinal benefits of fruits for the cognition and management of brain disease.

Reducing mitochondrial decay with mitochondrial nutrients to delay and treat cognitive dysfunction, Alzheimer's disease, and Parkinson's disease

Mitochondrial decay due to oxidative damage is a contributor to brain aging and age-related neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). One type of mitochondrial decay is oxidative modification of key mitochondrial enzymes. Enzyme dysfunction, that is due to poor binding of substrates and coenzymes may be ameliorated by supplementing adequate levels of substrates or coenzyme precursors. Such supplementation with mitochondrial nutrients (mt-nutrients) may be useful to prevent or delay mitochondrial decay, thus prevent or treat AD and PD. In the present review, we survey the literature to identify mt-nutrients that can (1) protect mitochondrial enzymes and/or stimulate enzyme activity by elevating levels of substrates and cofactors; (2) induce phase-2 enzymes to enhance antioxidant defenses; (3) scavenge free radicals and prevent oxidant production in mitochondria, and (4) repair mitochondrial membrane. Then, we discuss the relationships among mt-nutrient deficiency, mitochondrial decay, and cognitive dysfunction, and summarize available evidence suggesting an effect of mt-nutrient supplementation on AD and PD. It appears that greater effects might be obtained by longer-term administration of combinations of mt-nutrients. Thus, optimal doses of combinations of mt-nutrients to delay and repair mitochondrial decay could be a strategy for preventing and treating cognitive dysfunction, including AD and PD.

Repeated administration of PEP-1-Cu,Zn-superoxide dismutase and PEP-1-peroxiredoxin-2 to senescent mice induced by D-galactose improves the hippocampal functions

Oxidative stress initiates age-related reduction in hippocampal neurogenesis and the use of antioxidants has been proposed as an effective strategy to prevent or attenuate the reduction of neurogenesis in the hippocampus. In the present study, we investigated the effects of Cu,Zn-superoxide dismutase (SOD1) and/or peroxiredoxin-2 (PRX2) on cell proliferation and neuroblast differentiation in the dentate gyrus in a model of D-galactose-induced aging model. For this study, we constructed an expression vector, PEP-1, fused PEP-1 with SOD1 or PRX2, and generated PEP-1-SOD1 and PEP-1-PRX2 fusion protein. The aging model was induced by subcutaneous injection of D-galactose (100 mg/kg) to 6-week-old male mice for 10 weeks. PEP-1, PEP-1-SOD1 and/or PEP-1-PRX2 fusion protein was intraperitoneally administered to these mice at 13-week-old once a day for 3 weeks and sacrificed at 30 min after the last administrations. The administration of PEP-1-SOD1 and/or PEP-1-PRX2 significantly improved D-galactose-induced deficits on the escape latency, swimming speeds, platform crossings, spatial preference for the target quadrant in Morris water maze test. In addition, the administration of PEP-1-SOD1 and/or PEP-1-PRX2 ameliorated D-galactose-induced reductions of cell proliferation and neuroblast differentiation in the dentate gyrus and significantly reduced D-galactose-induced lipid peroxidation in the hippocampus. These effects were more prominent in the PEP-1-SOD1-treated group with PEP-1-PRX2. These results suggest that a SOD1 and/or PRX2 supplement to aged mice could improve the memory deficits, cell proliferation and neuroblast differentiation in the dentate gyrus of D-galactose induced aged mice by reducing lipid peroxidation.

Combination of Aβ clearance and neurotrophic factors as a potential treatment for Alzheimer's disease

There is no effective drug to treat Alzheimer's disease (AD), a neurodegenerative disease affecting an estimated 30 million people around the world. Strongly supported by preclinical and clinical studies, amyloid-beta (Aβ) may be a target for developing drugs against AD. Meanwhile, the fact that localized neuronal death/loss and synaptic impairment occur in AD should also be considered. Neuronal regeneration, which does not occur normally in the mammalian central nervous system, can be promoted by neurotrophic factors (NTFs). Evidence from clinical trials has shown that both Aβ clearance and NTFs are potentially effective in treating AD, thus a new approach combining Aβ clearance and administration of NTFs may be an effective therapeutic strategy.

Prevention of age-related changes in hippocampal levels of 5-methylcytidine by caloric restriction

Aberrant DNA methylation patterns have been linked to molecular and cellular alterations in the aging brain. Caloric restriction (CR) and upregulation of antioxidants have been proposed as interventions to prevent or delay age-related brain pathology. Previously, we have shown in large cohorts of aging mice, that age-related increases in DNA methyltransferase 3a (Dnmt3a) immunoreactivity in the mouse hippocampus were attenuated by CR, but not by overexpression of superoxide dismutase 1 (SOD1). Here, we investigated age-related alterations of 5-methylcytidine (5-mC), a marker of DNA methylation levels, in a hippocampal subregion-specific manner. Examination of 5-mC immunoreactivity in 12- and 24-month-old wild type (WT) mice on control diet, mice overexpressing SOD1 on control diet, wild type mice on CR, and SOD1 mice on CR, indicated an age-related increase in 5-mC immunoreactivity in the hippocampal dentate gyrus, CA3, and CA1-2 regions, which was prevented by CR but not by SOD1 overexpression. Moreover, positive correlations between 5-mC and Dnmt3a immunoreactivity were observed in the CA3 and CA1-2. These findings suggest a crucial role for DNA methylation in hippocampal aging and in the mediation of the beneficial effects of CR on aging.

Chemical nanotherapy: nitroxyl radical-containing nanoparticle protects neuroblastoma SH-SY5Y cells from Aβ-induced oxidative stress

Background: Excessive accumulation of β-amyloid (Aβ) has been proposed as a pivotal event in the pathogenesis of Alzheimer’s disease. Possible mechanisms underlying Aβ-induced neuronal cytotoxicity include excess production of reactive oxygen species (ROS) and apoptosis. We have designed novel nanoparticles, nitroxyl radical-containing nanoparticles (RNPs), which possess nitroxyl radical in the core and chemically scavenges ROS. This study aimed to determine the potential neuroprotective role of RNPs on Aβ-induced cytotoxicity in human neuroblastoma SH-SY5Y cells. Method: SH-SY5Y cells were preincubated with 0.1–1 mM RNP for 24 h and then incubated with 20 µM Aβ1–42 for 48 h. In every group, cell viability, apoptotic rate, ROS levels including superoxide anion radicals and hydroxyl radicals, ROS production including lipid peroxidation, protein oxidation and DNA oxidation were measured. Results: SH-SY5Y cells preincubated with 0.1–2 mM RNP for 24 h were protected from Aβ-induced damage. SH-SY5Y cells preincubated with more than 2 mM RNP for 24 h showed cytotoxicity. From the quantitative analyses, it was observed that RNPs reduced intracellular oxidative stress. RNP treatment significantly reduced the amount of oxidized lipids, proteins and DNA. It also reduced DNA fragmentations, which caused lower apoptosis levels. Conclusion: RNPs are promising intracellular ROS scavengers.

Caloric restriction attenuates age-related changes of DNA methyltransferase 3a in mouse hippocampus

Recent studies have suggested that DNA methylation is implicated in age-related changes in gene expression as well as in cognition. DNA methyltransferase 3a (Dnmt3a), which catalyzes DNA methylation, is essential for memory formation and underlying changes in neuronal and synaptic plasticity. Because caloric restriction (CR) and upregulation of antioxidants have been suggested as strategies to attenuate age-related alterations in the brain, we hypothesized that both a diet restricted in calories and transgenic overexpression of normal human Cu/Zn superoxide dismutase 1 (SOD) attenuate age-related changes in Dnmt3a in the aging mouse hippocampus. For this purpose, we performed qualitative and quantitative analyses of Dnmt3a-immunoreactivity (IR) for the hippocampal dentate gyrus (DG), CA3 and CA1-2 regions in 12- and 24-month-old mice from 4 groups, i.e. (1) wild-type (WT) mice on a control diet (WT-CD), (2) SOD-CD mice, (3) WT mice on CR (WT-CR), and (4) SOD-CR. Qualitative analyses revealed two types of Dnmt3a immunoreactive cells: type I cells--present throughout all hippocampal cell layers showing moderate levels of nuclear Dnmt3a-IR, and type II cells--a subpopulation of hippocampal cells showing very intense nuclear Dnmt3a-IR, and colocalization with Bromodeoxyuridine. Quantitative analyses indicated that the age-related increase in Dnmt3a-IR within the CA3 and CA1-2 in type I cells was attenuated by CR, but not by SOD overexpression. In contrast, the density of type II Dnmt3a immunoreactive cells showed an age-related reduction, without significant effects of both CR and SOD. These changes in Dnmt3a levels in the mouse hippocampus may have a significant impact on gene expression and associated cognitive functioning.

Gene-environment interaction research and transgenic mouse models of Alzheimer's disease

The etiology of the sporadic form of Alzheimer's disease (AD) remains largely unknown. Recent evidence has suggested that gene-environment interactions (GxE) may play a crucial role in its development and progression. Whereas various susceptibility loci have been identified, like the apolipoprotein E4 allele, these cannot fully explain the increasing prevalence of AD observed with aging. In addition to such genetic risk factors, various environmental factors have been proposed to alter the risk of developing AD as well as to affect the rate of cognitive decline in AD patients. Nevertheless, aside from the independent effects of genetic and environmental risk factors, their synergistic participation in increasing the risk of developing AD has been sparsely investigated, even though evidence points towards such a direction. Advances in the genetic manipulation of mice, modeling various aspects of the AD pathology, have provided an excellent tool to dissect the effects of genes, environment, and their interactions. In this paper we present several environmental factors implicated in the etiology of AD that have been tested in transgenic animal models of the disease. The focus lies on the concept of GxE and its importance in a multifactorial disease like AD. Additionally, possible mediating mechanisms and future challenges are discussed.

Prevention of dementia: focus on lifestyle

The objective of this paper is to summarize current knowledge on the possible advantages of lifestyle interventions, with particular attention to physical fitness, cognitive activity, leisure and social activity as well as nutrition. There is a large amount of published papers providing partial evidence and asserting the need for immediate, appropriate preventive lifestyle measures against dementia and AD development. Nevertheless, there are currently great difficulties in drafting effective guidelines in this field. This depends mainly upon lack of randomized controlled trials assessing benefits versus risks of particular lifestyle interventions strategies. However, due to the rapid increase of dementia burden, lifestyle factors and their amelioration should be already made part of decision making in light of their health-maintaining effects while awaiting for results of well-designed large prospective cohort studies in dementia.

Strategies for improving cognition with aging: insights from a longitudinal study of antioxidant and behavioral enrichment in canines

Studies in humans suggest that lifestyle factors can have a beneficial impact on the risk for developing cognitive decline and dementia with age. There is growing evidence that maintaining a physically and intellectually active lifestyle can positively impact cognitive ability in older individuals. Dietary factors, such as the intake of antioxidants, may also prevent age-related cognitive decline. However, studies in humans are challenging; many variables cannot be controlled, making it difficult for researchers to determine the exact types and quantities of enrichment and dietary factors necessary for positive effects on cognition. Studies in animal models of human aging allow researchers to precisely control such variables, and can be used to assess the mechanisms and molecular pathways underlying any positive effects. Here we review the results of an intervention study using a canine model of human aging. The study was unique in that it compared the effects of dietary antioxidant supplementation alone and in combination with behavioral enrichment. We found that both interventions lead to improvements in cognitive ability in aged dogs; however, combining the treatments preserved cognition to a greater extent than either treatment alone. Overall, the results suggest that antioxidant supplementation and behavioral enrichment target separate yet complementary molecular pathways to improve cognition, and support the idea that combinations of treatments to improve cognition and slow brain aging will produce greater benefits than single interventions.

Effects of age, dietary, and behavioral enrichment on brain mitochondria in a canine model of human aging

Dogs develop cognitive decline and a progressive accumulation of oxidative damage. In a previous longitudinal study, we demonstrated that aged dogs treated with either an antioxidant diet or with behavioral enrichment show cognitive improvement. The antioxidant diet included cellular antioxidants (vitamins E and C, fruits and vegetables) and mitochondrial cofactors (lipoic acid and carnitine). Behavioral enrichment consisted of physical exercise, social enrichment, and cognitive training. We hypothesized that the antioxidant treatment improved neuronal function through increased mitochondrial function. Thus, we measured reactive oxygen species (ROS) production and bioenergetics in mitochondria isolated from young, aged, and treated aged animals. Aged canine brain mitochondria show significant increases in ROS production and a reduction in NADH-linked respiration. Mitochondrial function (ROS and NADH-linked respiration) was improved selectively in aged dogs treated with an antioxidant diet. In contrast, behavioral enrichment had no effect on any mitochondrial parameters. These results suggest that an antioxidant diet improves cognition by maintaining mitochondrial homeostasis, which may be an independent molecular pathway not engaged by behavioral enrichment.

Catalytic antioxidants and neurodegeneration

Oxidative stress, resulting from mitochondrial dysfunction, excitotoxicity, or neuroinflammation, is implicated in numerous neurodegenerative conditions. Damage due to superoxide, hydroxyl radical, and peroxynitrite has been observed in diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as in acute conditions that lead to neuronal death, such as stroke and epilepsy. Antioxidant therapies to remove these toxic compounds have been of great interest in treating these disorders. Catalytic antioxidants mimic the activities of superoxide dismutase or catalase or both, detoxifying superoxide and hydrogen peroxide, and in some cases, peroxynitrite and other toxic species as well. Several compounds have demonstrated efficacy in in vitro and in animal models of neurodegeneration, leading to optimism that catalytic antioxidants may prove to be useful therapies in human disease.

An updated systematic review with meta-analysis for the clinical evidence of silymarin

BACKGROUND

The potential benefit of silymarin (special extract from the fruits of Silybum marianum) in the treatment of liver diseases remains a controversial issue.

METHODS

For this systematic review electronic databases identified 65 papers for the search terms silymarin, silibinin, silicristin or milk thistle and clinical trial. Only 19 complied with the criteria'double-' or 'single-blind'. These publications were analysed from a clinical point of view and meta-analytic calculations were performed.

RESULTS

The clinical evidence ofa therapeutic effect of silymarin in toxic liver diseases is scarce. There is no evidence of a favourable influence on the evolution of viral hepatitis, particularly hepatitis C. In alcoholic liver disease, comparing with placebo, aspartate aminotransferase was reduced in the silymarin-treated groups (p = 0.01) while alkaline phosphatase was not. In liver cirrhosis, mostly alcoholic, total mortality was 16.1% with silymarin vs. 20.5% with placebo (n.s.); liver-related mortality was 10.0% with silymarin vs. 17.3% with placebo(p = 0.01).

CONCLUSIONS

Based on the available clinical evidence it can be concluded - concerning possible risks /probable benefits - that it is reasonable to employ silymarin as a supportive element in the therapy of Amanita phalloides poisoning but also (alcoholic and grade Child 'A') liver cirrhosis. A consistent research programme, consolidating existing evidence and exploring new potential uses,would be very welcome.

Oxidative damage and cognitive dysfunction: antioxidant treatments to promote healthy brain aging

Oxidative damage in the brain may lead to cognitive impairments in aged humans. Further, in age-associated neurodegenerative disease, oxidative damage may be exacerbated and associated with additional neuropathology. Epidemiological studies in humans show both positive and negative effects of the use of antioxidant supplements on healthy cognitive aging and on the risk of developing Alzheimer disease (AD). This contrasts with consistent behavioral improvements in aged rodent models. In a higher mammalian model system that naturally accumulates human-type pathology and cognitive decline (aged dogs), an antioxidant enriched diet leads to rapid learning improvements, memory improvements after prolonged treatment and cognitive maintenance. Cognitive benefits can be further enhanced by the addition of behavioral enrichment. In the brains of aged treated dogs, oxidative damage is reduced and there is some evidence of reduced AD-like neuropathology. In combination, antioxidants may be beneficial for promoting healthy brain aging and reducing the risk of neurodegenerative disease.

Accumulation of nuclear DNA damage or neuron loss: molecular basis for a new approach to understanding selective neuronal vulnerability in neurodegenerative diseases

According to a long-standing hypothesis, aging is mainly caused by accumulation of nuclear (n) DNA damage in differentiated cells such as neurons due to insufficient nDNA repair during lifetime. In line with this hypothesis it was until recently widely accepted that neuron loss is a general consequence of normal aging, explaining some degree of decline in brain function during aging. However, with the advent of more accurate procedures for counting neurons, it is currently widely accepted that there is widespread preservation of neuron numbers in the aging brain, and the changes that do occur are relatively specific to certain brain regions and types of neurons. Whether accumulation of nDNA damage and decline in nDNA repair is a general phenomenon in the aging brain or also shows cell-type specificity is, however, not known. It has not been possible to address this issue with the biochemical and molecular-biological methods available to study nDNA damage and nDNA repair. Rather, it was the introduction of autoradiographic methods to study quantitatively the relative amounts of nDNA damage (measured as nDNA single-strand breaks) and nDNA repair (measured as unscheduled DNA synthesis) on tissue sections that made it possible to address this question in a cell-type-specific manner under physiological conditions. The results of these studies revealed a formerly unknown inverse relationship between age-related accumulation of nDNA damage and age-related impairment in nDNA repair on the one hand, and the age-related, selective, loss of neurons on the other hand. This inverse relation may not only reflect a fundamental process of aging in the central nervous system but also provide the molecular basis for a new approach to understand the selective neuronal vulnerability in neurodegenerative diseases, particularly Alzheimer's disease.

Combining an Antioxidant-Fortified Diet with Behavioral Enrichment Leads to Cognitive Improvement and Reduced Brain Pathology in Aging Canines: Strategies for Healthy Aging

The number of elderly individuals in our population is rapidly rising and age-associated neurodegenerative disease is becoming more prevalent. Thus, identifying ways by which we can promote healthy aging are becoming more critical. Lifestyle factors, such as engaging in physical, intellectual, and social activities, are protective against dementia in aged individuals. Similarly, there is some evidence to suggest that antioxidants are beneficial. Observational studies in humans have been confirmed and extended in rodent model systems. We present additional evidence that, in a canine model of aging, combining an antioxidant-enriched diet and behavioral enrichment (including social, physical, and cognitive components) can lead to substantial improvements in cognition and reduced brain pathology. These results suggest that modifying lifestyle factors can have a beneficial impact on the aging process, even in aged individuals with existing cognitive decline and brain pathology.

Micronutrients and Alzheimer's disease

The current high life expectancy is overshadowed by neurodegenerative illnesses that lead to dementia and dependence. Alzheimer's disease (AD) is the most common of these conditions, and is considered to be a proteinopathy, with amyloid-β42 as a key factor, leading via a cascade of events to neurodegeneration. Major factors involved are oxidative stress, perturbed Ca homeostasis and impaired energy metabolism. Protection against oxidative stress by micronutrients (including secondary bioactive substances) has been shown in transgenic Alzheimer model systems to delay AD. Epidemiological evidence is less conclusive, but the vast majority of the evidence supports a protective effect on cognitive functions in old age and AD. Thus, a diet rich in fruits and vegetables but also containing meat and fish is the most suitable to provide adequate micronutrients. The strong link between cardiovascular risk and AD may be explained by common pathogenetic mechanisms mediated, for example, by homocysteine and thus dependant on B-vitamins (folate and vitamins B12 and B6). However, micronutrients may also be harmful. The high affinity of amyloid for metals (Fe, Al and Zn) favours the generation of reactive oxygen species and triggers an inflammatory response. Micronutrients in a balanced diet have a long-lasting, albeit low, protective impact on brain aging, hence prevention should be life long.

The molecular basis of the prevention of Alzheimer’s disease through healthy nutrition

The Alzheimer's disease (AD) brain shows numerous pathological phenomena, including amyloid plaques, neurofibrillary tangles, elevated levels of advanced glycation endproducts and their receptor, oxidative damage and inflammation, all of which contribute to neurodegeneration. In this review, we consider these neuropathologies associated with AD and propose that inflammation and oxidative stress play major pathogenic roles throughout disease progression. It is believed that oxidative stress and inflammation not only play major roles early in the disease, but that they act in a reinforcing cycle, amplifying their damaging effects. Therefore, epidemiological studies indicate that anti-inflammatory, antioxidant and neuroprotective agents including those from medicinal plants and health promoting foods may protect against AD, possibly through scavenging of reactive oxygen species, cytokine downregulation and strengthening the neurons antioxidant defense. This concept is further supported by evidence that certain diets (such as a Mediterranean diet) have been associated with a lower incidence of AD. This review highlights specific foods and diets thought to lower the risk of developing AD and discusses the potential of healthy nutrition in disease prevention.

A review of antioxidants and Alzheimer's disease

BACKGROUND

In this article, we review a diverse body of research and draw conclusions about the usefulness, or lack there-of, of specific antioxidants in the prevention of Alzheimer's disease (AD).

METHODS

The National Library of Medicine's database was searched for the years 1996-2004 using the search terms "Alzheimer's, anti-oxidants, antioxidants."

RESULTS

Over 300 articles were identified and 187 articles were selected for inclusion based on relevance to the topic. Agents that show promise in helping prevent AD include: 1) aged garlic extract, 2) curcumin, 3) melatonin, 4) resveratrol, 5) Ginkgo biloba extract, 6) green tea, 7) vitamin C and 8) vitamin E.

CONCLUSIONS

While the clinical value of antioxidants for the prevention of AD is often ambiguous, some can be recommended based upon: 1) epidemiological evidence, 2) known benefits for prevention of other maladies, and 3) benign nature of the substance. Long-term, prospective studies are recommended.

Antioxidant treatment in Alzheimer's disease: current state

Accumulating data from experimental and human studies indicate that oxidative stress (OS) plays a major role in the pathogenesis of Alzheimer's disease (AD). The production of reactive oxygen species (ROS), which leads to OS, can occur very early, even before the appearance of symptoms and molecular events (beta-amyloid plaques and neurofibrillary tangles), leading to tissue damage via several different cellular molecular pathways. ROS can cause damage to cardinal cellular components such as lipids, proteins, and nucleic acids (e.g., RNA, DNA), causing cell death by modes of necrosis or apoptosis. The damage can become more widespread because of the weakened cellular antioxidant defense systems. Therefore, treatment with antioxidants might theoretically act to prevent propagation of tissue damage and improve both survival and neurological outcome. Indeed, several studies preformed to date examined whether dietary intake of several antioxidants, mainly vitamins, might prevent or reduce the progression of AD. Although a few of the antioxidants showed some efficacy in these trials, no answer is yet available as to whether antioxidants are truly protective against AD. Reasons for these results might include, in part, blood-brain barrier (BBB) permeability, inappropriate timing of administration, or suboptimal drug levels at the target site in the central nervous system. Thus, antioxidant cocktails or antioxidants combined with other drugs may have more successful synergistic effects. Further, well-designed intervention, as well as observational investigations based on large cohorts studied over a long period of time with several methods for assessing antioxidant exposure, including relation to BBB penetration, are needed to test this hypothesis.

S-Allylcysteine prevents amyloid-β peptide-induced oxidative stress in rat hippocampus and ameliorates learning deficits

The effects of S-allylcysteine on oxidative damage and spatial learning and memory deficits produced by an intrahippocampal injection of amyloid-beta peptide 25-35 (Abeta(25-35)) in rats were investigated. The formation of reactive oxygen species, lipid peroxidation and the activities of the antioxidant enzymes superoxide dismutase and glutathione peroxidase were all measured in hippocampus 120 min after Abeta(25-35) injection (1 microl of 100 microM solution), while learning and memory skills were evaluated 2 and 35 days after the infusion of Abeta(25-35) to rats, respectively. Abeta(25-35) increased both reactive oxygen species and lipid peroxidation, whereas pretreatment with S-allylcysteine (300 mg/kg, i.p.) 30 min before peptide injection decreased both of these markers. In addition, Abeta(25-35)-induced incorrect learning responses were prevented in most of trials by S-allylcysteine. In contrast, enzyme activities were found unchanged in all groups tested. Findings of this work: (i) support the participation of reactive oxygen species in Abeta(25-35)-induced hippocampal toxicity and learning deficits; and (ii) suggest that the protective effects of S-allylcysteine were related to its ability to scavenge reactive oxygen species.