Multiple antioxidants in the prevention and treatment of Alzheimer disease: analysis of biologic rationale

Ginkgo biloba extract mitigates the neurotoxicity of AlCl3 in alzheimer rat's model: role of apolipoprotein E4 and clusterin genes in stimulating ROS generation and apoptosis

PURPOSE

Alzheimer's disease (AD) appears as a result of an increase in the accumulation of amyloid beta peptide (Aβ) and a decrease in neurotransmitters (acetylcholine) within the brain cells which may be due to increase in acetylcholinesterase (AchE) activity and change in expression of Apolipoprotein E4 (ApoE4) and Clusterin (Clu) genes. The aim of the present study was using natural products such as Ginkgo biloba (G. biloba) extract that has the potential to reduce Aβ formation and increase AchE inhibition with its ability to save neuronal DNA from damage.

METHODS

Sixty male aged rats were divided into six experimental groups exposed to AlCl3 to induce AD model and were treated with G. biloba extract. Collected brain tissues were used to assess the apoptosis rate, reactive oxygen species (ROS) generation, AchE inhibitory activity, expression alteration in ApoE4 and Clu genes, DNA fragmentations and gutathione peroxidase (GPx) activity.Results: The results exhibited that rats exposed to AlCl3 increased significantly rate of apoptosis, ROS formation, DNA fragmentation, up-regulation of ApoE4 and Clu genes as well as decrease of AchE inhibitory activity and GPx activity compared with those in control rats. However, treatment of AlCl3-rats with G. biloba extract improved the above neurotoxicity results induced by AlCl3 exposure.

CONCLUSIONS

It is therefore likely that G. biloba extract's protective properties against AD are due to its ability to activate the response against oxidative stress.

Biomolecular Screening of Pimpinella anisum L. for Antioxidant and Anticholinesterase Activity in Mice Brain

Hundreds of the plants have been explored and evaluated for antioxidant and anti-amnesic activities, so far. This study was designed to report the biomolecules of Pimpinella anisum L. for the said activities. The aqueous extract of dried P. anisum seeds was fractionated via column chromatography and the fractions so obtained were assessed for the inhibition of acetylcholinesterase (AChE) via in vitro analysis. The fraction which best inhibited AChE was so named as the P. anisum active fraction (P.aAF). The P.aAF was then chemically analyzed via GCMS, which indicated that oxadiazole compounds were present in it. The P.aAF was then administered to albino mice to conduct the in vivo (behavioral and biochemical) studies. The results of the behavioral studies indicated the significant (p < 0.001) increase in inflexion ratio, by the number of hole-pokings through holes and time spent in a dark area by P.aAF treated mice. Biochemical studies demonstrated that the oxadiazole present in P.aAF on one hand presented a noteworthy reduction in MDA and the AChE level and on the other hand promoted the levels of CAT, SOD and GSH in mice brain. The LD₅₀ for P.aAF was calculated as 95 mg/Kg/p.o. The findings thus supported that the antioxidant and anticholinesterase activities of P. anisum are due to its oxadiazole compounds.

Naturally Occurring Antioxidant Therapy in Alzheimer's Disease

It is estimated that the prevalence rate of Alzheimer's disease (AD) will double by the year 2040. Although currently available treatments help with symptom management, they do not prevent, delay the progression of, or cure the disease. Interestingly, a shared characteristic of AD and other neurodegenerative diseases and disorders is oxidative stress. Despite profound evidence supporting the role of oxidative stress in the pathogenesis and progression of AD, none of the currently available treatment options address oxidative stress. Recently, attention has been placed on the use of antioxidants to mitigate the effects of oxidative stress in the central nervous system. In preclinical studies utilizing cellular and animal models, natural antioxidants showed therapeutic promise when administered alone or in combination with other compounds. More recently, the concept of combination antioxidant therapy has been explored as a novel approach to preventing and treating neurodegenerative conditions that present with oxidative stress as a contributing factor. In this review, the relationship between oxidative stress and AD pathology and the neuroprotective role of natural antioxidants from natural sources are discussed. Additionally, the therapeutic potential of natural antioxidants as preventatives and/or treatment for AD is examined, with special attention paid to natural antioxidant combinations and conjugates that are currently being investigated in human clinical trials.

Neuroprotective Natural Products for Alzheimer's Disease

Alzheimer's disease (AD) is the number one neurovegetative disease, but its treatment options are relatively few and ineffective. In efforts to discover new strategies for AD therapy, natural products have aroused interest in the research community and in the pharmaceutical industry for their neuroprotective activity, targeting different pathological mechanisms associated with AD. A wide variety of natural products from different origins have been evaluated preclinically and clinically for their neuroprotective mechanisms in preventing and attenuating the multifactorial pathologies of AD. This review mainly focuses on the possible neuroprotective mechanisms from natural products that may be beneficial in AD treatment and the natural product mixtures or extracts from different sources that have demonstrated neuroprotective activity in preclinical and/or clinical studies. It is believed that natural product mixtures or extracts containing multiple bioactive compounds that can work additively or synergistically to exhibit multiple neuroprotective mechanisms might be an effective approach in AD drug discovery.

Maltol (3-Hydroxy-2-methyl-4-pyrone) Slows d-Galactose-Induced Brain Aging Process by Damping the Nrf2/HO-1-Mediated Oxidative Stress in Mice

Maltol, a maillard reaction product from ginseng (Panax ginseng C. A. Meyer), has been confirmed to inhibit oxidative stress in several animal models. Its beneficial effect on oxidative stress related brain aging is still unclear. In this study, the mouse model of d-galactose (d-Gal)-induced brain aging was employed to investigate the therapeutic effects and potential mechanisms of maltol. Maltol treatment significantly restored memory impairment in mice as determined by the Morris water maze tests. Long-term d-Gal treatment reduced expression of cholinergic regulators, i.e., the cholineacetyltransferase (ChAT) (0.456 ± 0.10 vs 0.211 ± 0.03 U/mg prot), the acetylcholinesterase (AChE) (36.4 ± 5.21 vs 66.5 ± 9.96 U/g). Maltol treatment prevented the reduction of ChAT and AChE in the hippocampus. Maltol decreased oxidative stress levels by reducing levels of reactive oxygen species (ROS) and malondialdehyde (MDA) production in the brain and by elevating antioxidative enzymes. Furthermore, maltol treatment minimized oxidative stress by increasing the phosphorylation levels of phosphatidylinositol-3-kinase (PI3K), protein kinase B (Akt), nuclear factor-erythroid 2-related factor 2 (Nrf2), and hemeoxygenase-1 (HO-1). The above results clearly indicate that supplementation of maltol diminishes d-Gal-induced behavioral dysfunction and neurological deficits via activation of the PI3K/Akt-mediated Nrf2/HO-1 signaling pathway in brain. Maltol might become a potential drug to slow the brain aging process and stimulate endogenous antioxidant defense capacity. This study provides the novel evidence that maltol may slow age-associated brain aging.

Modulation of nitrosative stress via glutathione-dependent formaldehyde dehydrogenase and S-nitrosoglutathione reductase

Glutathione-dependent formaldehyde dehydrogenase (GFD) from Taiwanofungus camphorata plays important roles in formaldehyde detoxification and antioxidation. The enzyme is bifunctional. In addition to the GFD activity, it also functions as an effective S-nitrosoglutathione reductase (GSNOR) against nitrosative stress. We investigated the modulation of HEK (human embryonic kidney) 293T cells under nitrosative stress by transfecting a codon optimized GFD cDNA from Taiwanofungus camphorata (Tc-GFD-O) to these cells. The parental and transfected HEK 293T cells were then subjected to S-nitrosoglutathione treatment to induce nitrosative stress. The results showed that in Tc-GFD-O-transfected 293T cells, the expression and activity of GFD increased. Additionally, these cells under the nitrosative stress induced by S-nitrosoglutathione showed both higher viability and less apoptosis than the parental 293T cells. This finding suggests that the Tc-GFD-O in HEK 293T cells may provide a protective function under nitrosative stress.

Target- and mechanism-based therapeutics for neurodegenerative diseases: strength in numbers

The development of new therapeutics for the treatment of neurodegenerative pathophysiologies currently stands at a crossroads. This presents an opportunity to transition future drug discovery efforts to target disease modification, an area in which much still remains unknown. In this Perspective we examine recent progress in the areas of neurodegenerative drug discovery, focusing on some of the most common targets and mechanisms: N-methyl-d-aspartic acid (NMDA) receptors, voltage gated calcium channels (VGCCs), neuronal nitric oxide synthase (nNOS), oxidative stress from reactive oxygen species, and protein aggregation. These represent the key players identified in neurodegeneration and are part of a complex, intertwined signaling cascade. The synergistic delivery of two or more compounds directed against these targets, along with the design of small molecules with multiple modes of action, should be explored in pursuit of more effective clinical treatments for neurodegenerative diseases.

Synthesis and study of 2-amino-7-bromofluorenes modified with nitroxides and their precursors as dual anti-amyloid and antioxidant active compounds

A series of 2-aminofluorenes N-alkylated with nitroxides or their precursors were synthesized. The new compounds were tested on hydroxyl radical and peroxyl radical scavenging ability and inflammatory assay on the endothelial brain cells. In agreement with ROS scavenging ability the same compound 7-bromo-N -[(1-Oxyl-2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine-4yl)methyl]-9H-fluoren-2-amine (3b) and its hydroxylamine salt (3b/OH/HCl) showed the anti-inflammatory property on the endothelial brain cells.

Effect of plant extracts on Alzheimer's disease: An insight into therapeutic avenues

Alzheimer's disease (AD) is a devastative neurodegenerative disorder which needs adequate studies on effective treatment options. The extracts of plants and their effect on the amelioration of AD symptoms have been extensively studied. This paper summarizes the mechanisms like acetylcholinesterase (AChE) inhibition, modification of monoamines, antiamyloid aggregation effect, and antioxidant activity which are actively entailed in the process of amelioration of AD symptoms. These effects are induced by extracts of a few plants of different origin like Yizhi Jiannao, Moringa oleifera (Drumstick tree), Ginkgo Biloba (Ginkgo/Maidenhair tree), Cassia obtisufolia (Sicklepod), Desmodium gangeticum (Sal Leaved Desmodium), Melissa officinalis (Lemon Balm), and Salvia officinalis (Garden sage, common sage).

Microbial and host cells acquire enhanced oxidant-scavenging abilities by binding polyphenols

The dilemma whether supplementations of dietary antioxidants might prevent the adverse consequences of oxidative stress, the inadequacy of the analytical methods employed to quantify oxidant scavenging ability (OSA) levels in whole blood and the distribution and fate of polyphenols and their metabolites in various body compartments following oral consumption are discussed. While none-metabolized polyphenols might exert their antioxidant effects mainly in the oral cavity, metabolized polyphenols might be beneficial in the gastrointestinal tract to counteract the toxicity of oxidants and also of the sequelae of inflammatory processes. Although only micromolar amounts of polyphenols and their metabolites eventually reach the blood circulation, these may nevertheless still be highly effective as scavengers of reactive oxygen and nitrogen species because of their ability to synergize with plasma low molecular-weight antioxidants and with albumin. Polyphenols can avidly bind to surfaces of microorganisms and of blood cells to markedly enhance their OSA, therefore the routine quantifications of antioxidant levels conducted in clinical settings should always use catalase-rich whole blood but not as customary, plasma alone. In addition to their antioxidant and metal chelating properties, polyphenols may also act as signaling agents capable of affecting metabolic, inflammatory, autoimmune, carcinogenic and aging processes.

Nanoparticle and iron chelators as a potential novel Alzheimer therapy

Current therapies for Alzheimer disease (AD) such as the acetylcholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of the disease, but do not arrest the disease progression or bring in meaningful remission. New approaches to the disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferrioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. Here, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may provide a safer and more effective means of reducing the metal load in neural tissue, thus attenuating the harmful effects of oxidative damage and its sequelae. Experimental procedures are presented in this chapter.

Metal chelators coupled with nanoparticles as potential therapeutic agents for Alzheimer's disease

Alzheimer's disease (AD) is a devastating neuro-degenerative disorder characterized by the progressive and irreversible loss of memory followed by complete dementia. Despite the disease's high prevalence and great economic and social burden, an explicative etiology or viable cure is not available. Great effort has been made to better understand the disease's pathogenesis, and to develop more effective therapeutic agents. However, success is greatly hampered by the presence of the blood-brain barrier that limits a large number of potential therapeutics from entering the brain. Nanoparticle-mediated drug delivery is one of the few valuable tools for overcoming this impediment and its application as a potential AD treatment shows promise. In this review, the current studies on nanoparticle delivery of chelation agents as possible therapeutics for AD are discussed because several metals are found excessive in the AD brain and may play a role in the disease development. Specifically, a novel approach involving transport of iron chelation agents into and out of the brain by nanoparticles is highlighted. This approach may provide a safer and more effective means of simultaneously reducing several toxic metals in the AD brain. It may also provide insights into the mechanisms of AD pathophysiology, and prove useful in treating other iron-associated neurodegenerative diseases such as Friedreich's ataxia, Parkinson's disease, Huntington's disease and Hallervorden-Spatz Syndrome. It is important to note that the use of nanoparticle-mediated transport to facilitate toxicant excretion from diseased sites in the body may advance nanoparticle technology, which is currently focused on targeted drug delivery for disease prevention and treatment. The application of nanoparticle-mediated drug transport in the treatment of AD is at its very early stages of development and, therefore, more studies are warranted.

Multipotent natural agents to combat Alzheimer's disease. Functional spectrum and structural features

With the accelerated aging of human society, Alzheimeros disease (AD) is becoming one of the biggest threats to human health. Since multiple pathogenetic factors are implicated in the disease, the current hitting-one-target therapeutic strategy has proved inefficient to AD. As a result, finding multipotent agents that aim at multiple targets is attracting more and more attention. Although multifunctional anti-AD agents can be created by incorporating two or more pharmacophores in one scaffold, naturally occurring multipotent agents also attracted much attention. In this review, we first describe the functions of some typical naturally originated multipotent anti-AD compounds, then summarize their structural features and reveal that phenolics with certain flexibility predominate in these agents, which are of significance to find novel multipotent drugs to combat AD and other neurodegenerative diseases as well.

Alzheimer's disease pathogenesis and therapeutic interventions

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system associated with progressive cognitive and memory loss. Molecular hallmarks of the disease are characterized by extracellular deposition of the amyloid beta peptide (Abeta) in senile plaques, the appearance of intracellular neurofibrillary tangles (NFT), cholinergic deficit, extensive neuronal loss and synaptic changes in the cerebral cortex and hippocampus and other areas of brain essential for cognitive and memory functions. Abeta deposition causes neuronal death via a number of possible mechanisms including oxidative stress, excitotoxicity, energy depletion, inflammation and apoptosis. Despite their multifactorial etiopathogenesis, genetics plays a primary role in progression of disease. To date genetic studies have revealed four genes that may be linked to autosomal dominant or familial early onset AD (FAD). These four genes include: amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2) and apolipoprotein E (ApoE). Plaques are formed mostly from the deposition of Abeta, a peptide derived from APP. The main factors responsible for Abeta formation are mutation of APP or PS1 and PS2 genes or ApoE gene. All mutations associated with APP and PS proteins can lead to an increase in the production of Abeta peptides, specifically the more amyloidogenic form, Abeta42. In addition to genetic influences on amyloid plaque and intracellular tangle formation, environmental factors (e.g., cytokines, neurotoxins, etc.) may also play important role in the development and progression of AD. A direct understanding of the molecular mechanism of protein aggregation and its effects on neuronal cell death could open new therapeutic approaches. Some of the therapeutic approaches that have progressed to the clinical arena are the use of acetylcholinesterase inhibitors, nerve growth factors, nonsteroidal inflammatory drugs, estrogen and the compounds such as antioxidants, neuronal calcium channel blockers or antiapoptotic agents. Inhibition of secretase activity and blocking the formation of beta-amyloid oligomers and fibrils which may inhibit fibrilization and fibrilization-dependent neurotoxicity are the most promising therapeutic strategy against the accumulation of beta-amyloid fibrils associated with AD. Furthermore, development of immunotherapy could be an evolving promising therapeutic approach for the treatment of AD.

Evidence of oxidative stress-induced BNIP3 expression in amyloid beta neurotoxicity

The formation of Abeta and its subsequent deposition in senile plaques are considered to be initial events that lead to a cascade of pathological changes in AD. Mediators of Abeta-induced oxidative stress are known to cause oxidative damage to macromolecules. However, the molecular mechanisms by which Abeta-induced oxidative stress leads to neuronal cell death are not fully understood. Here we show that Abeta-induced oxidative stress activates the pro-death gene BNIP3. Abeta treatment results in mitochondrial dysfunction, accumulation of reactive oxygen species, and subsequent expression of BNIP3 in rat primary cortical neurons. Pretreatment with antioxidants abolished Abeta-induced BNIP3 expression and attenuated cell death, demonstrating the role of oxidative stress in BNIP3 induction. Abeta-induced BNIP3 expression may be mediated by hypoxia-inducible factor-1 (HIF-1) because Abeta-treatment induced accumulation and nuclear translocation of HIF-1 and knock-down of HIF-1 by RNAi inhibited BNIP3 expression. Finally, knockdown of BNIP3 reduced Abeta-induced neuronal death. Together, these results suggest a potential pathological role of BNIP3 in the etiology of AD.

Same causes, same cures

Thanks to the continuing bio-medicinal efforts, similar causes underlying the pathogenesis of Alzheimer's disease (AD) and prion diseases (PDs) have been revealed, which include oxidative stress, excessive transition metal ions, and misfolded/aggregated proteins. Therefore, the therapeutic strategy for one disease may be effective for the other. More interestingly, accumulating evidence indicates that not just the strategies but also the prescriptions may be shared by AD and PD treatments. In this review, we first summarize the known dual fighters against AD and PDs (which include antioxidants, metal chelators, and protein aggregation inhibitors), and then indicate that some super-dual-fighters may hit multiple targets implicated in AD and PDs, whose structural features highlight the importance of aromatic moiety and phenolic groups. These findings not only provide important clues to accelerating the screening of anti-AD and anti-PDs drugs but also help to understand the etiology of AD and PDs.

Protective Effect of Lignophenol Derivative from Beech (Fagus crenata Blume) on Copper- and Zinc-Mediated Cell Death in PC12 Cells

Lignophenol, prepared using a phase-separation system, is a derivative of lignin, which is one of the components in the plant cell wall, and possesses high phenolic function, high stability and antioxidant properties. However, little is known about the beneficial effect of lignophenol. In this study, we investigated the protective effect of lignophenol from the beech tree (Fagus crenata Blume) on copper- and zinc-mediated apoptosis in PC12 cells by using DNA fragmentation and TUNEL assays. In DNA fragmentation assays, the DNA ladder patterns in the PC12 cells treated with 200 microM Cu and 200 microM Zn were enhanced, whereas the DNA ladder pattern was hardly observed in these cells treated with 20 mM lignophenol. In the TUNEL assay, TUNEL signals increased significantly in the untreated PC12 cells exposed to 200 microM Cu compared with the control. In contrast, the degree of apoptosis in the 20 mM lignophenol-treated cells was significantly lower than in the untreated cells, indicating that lignophenol inhibited Cu-induced apoptotic cell death in PC 12 cells. In the 200 microM Zn-exposed group, the degree of apoptosis in the 20 mM lignophenol-treated cells was also low compared with the untreated cells. In conclusion, these results suggest that lignophenol plays a role in protecting against Cu- and Zn-mediated PC12 apoptotic cell death.

La lunga attesa: towards a molecular approach to neuroimaging and therapeutics in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are Aβ amyloid plaques, neurofibrillary tangles (NFT), synaptic loss and reactive gliosis. Current diagnosis of AD is made by clinical, neuropsychologic, and neuroimaging assessments. Routine structural neuroimaging evaluation with computed tomography (CT) and magnetic resonance imaging (MRI) is based on non-specific features such as atrophy, a late feature in the progression of the disease, hence the crucial importance of developing new approaches for early and specific recognition at the prodromal stages of AD. Functional neuroimaging techniques such as functional magnetic resonance imaging (fMRI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single photon emission computed tomography (SPECT), possibly in conjuction with other related Aβ biomarkers in plasma and CSF, could prove to be valuable in the differential diagnosis of AD, as well as in assessing prognosis. With the advent of new therapeutic strategies aimed at reducing the Aβ amyloid burden in the brain, there is increasing interest in the development of MRI contrast agents and PET and SPECT radioligands that will permit the assessment of Aβ amyloid burden in vivo. - ma dov'è / la lenta processione di stagioni / che fu un'alba infinita e senza strade, / dov'è la lunga attesa e qual è il nome / del vuoto che ci invade. - Eugenio Montale.

Molecular mechanisms for Alzheimer's disease: implications for neuroimaging and therapeutics

Alzheimer's disease is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are beta-amyloid (Abeta) plaques, neurofibrillary tangles, synaptic loss and reactive gliosis. The current therapeutic effort is directed towards developing drugs that reduce Abeta burden or toxicity by inhibiting secretase cleavage, Abeta aggregation, Abeta toxicity, Abeta metal interactions or by promoting Abeta clearance. A number of clinical trials are currently in progress based on these different therapeutic strategies and they should indicate which, if any, of these approaches will be efficacious. Current diagnosis of Alzheimer's disease is made by clinical, neuropsychologic and neuroimaging assessments. Routine structural neuroimaging evaluation with computed tomography and magnetic resonance imaging is based on non-specific features such as atrophy, a late feature in the progression of the disease, hence the crucial importance of developing new approaches for early and specific recognition at the prodromal stages of Alzheimer's disease. Functional neuroimaging techniques such as functional magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography and single photon emission computed tomography, possibly in conjunction with other related Abeta biomarkers in plasma and CSF, could prove to be valuable in the differential diagnosis of Alzheimer's disease, as well as in assessing prognosis. With the advent of new therapeutic strategies there is increasing interest in the development of magnetic resonance imaging contrast agents and positron emission tomography and single photon emission computed tomography radioligands that will permit the assessment of Abeta burden in vivo.

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.

Nanoparticle and other metal chelation therapeutics in Alzheimer disease

Current therapies for Alzheimer disease (AD) such as the anticholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of disease, but do not arrest disease progression or supply meaningful remission. As such, new approaches to disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. In this review, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show a unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may prove to be a safe and effective means of reducing the metal load in neural tissue thus staving off the harmful effects of oxidative damage and its sequelae.

Caffeine induces sonic hedgehog gene expression in cultured astrocytes and neurons

Caffeine affects early in vivo murine brain development by accelerating the evagination of the primitive neuroepithelium into telencephalic vesicles. In this model, caffeine induces the expression of the regulatory subunit alpha of protein kinase A (PKA RI alpha) and of Sonic hedgehog (Shh). The understanding of the molecular mechanisms linking caffeine and neural gene expression would benefit from a reproducible in vitro model. Accordingly, the present study aimed to determine whether caffeine modulated the expression of these genes in primary neuronal and astroglial cultures derived from developing murine neocortex. Using real-time PCR, the results showed that caffeine induced robust overexpression of Shh mRNA in both cell types without significantly modifying PKA RI alpha gene expression.

An antioxidant hispidin from the mycelial cultures of Phellinus linteus

In the course of screening for reactive oxygen species scavengers from natural products, an antioxidant was isolated from the mycelial culture broth of Phellinus linteus and identified as hispidin. The hispidin content was reached its maximum level at 12 days after onset of inoculation. About 2.5 mg/mL of hispidin was produced by P. linteus in a yeast-malt medium (pH 5.8, 25 degrees C). Hispidin inhibited 22.6 and 56.8% of the super oxide anion radical, 79.4 and 95.3% of the hydroxyl radical, and 28.1 and 85.5% of the DPPH radical at 0.1 and 1.0 mM, respectively. The positive control alpha-tocopherol scavenged 25.6 and 60.3%, 74.6 and 96.3%, and 32.7 and 77.5% of each radical, respectively, at the same concentrations. However, hispidin showed no significant activity on the hydrogen peroxide radical.

A prolyl endopeptidase-inhibiting antioxidant from Phyllanthus ussurensis

A prolyl endopeptidase inhibitor was isolated from the ethyl acetate soluble fraction of Phyllanthus ussurensis. The active compound was identified as an ellagitannin, corilagin. It was shown to non-competitively inhibit prolyl endopeptidase (PEP) with the IC50 value of 1.17x10(-6) microM. The Ki value was 6.70x10(-7) M. Corilagin was less inhibitory to other serine proteases such as chymotrypsin, trypsin, and elastase, indicating that it was relatively a specific inhibitor of PEP. Corilagin also effectively inhibited reactive oxygen species such as hydroxide and superoxide anion radical, hydrogen peroxide, and DPPH. Especially, corilagin showed potent scavenging activity on the superoxide anion radical in the ESR method (IC50 = 3.79x10(-6) M) as well as xanthine oxidase system.

Targeted deletion of BMK1/ERK5 in adult mice perturbs vascular integrity and leads to endothelial failure

Big mitogen-activated protein kinase 1 (BMK1), also known as ERK5, is a member of the MAPK family. Genetic ablation of BMK1 in mice leads to embryonic lethality, precluding the exploration of pathophysiological roles of BMK1 in adult mice. We generated a BMK1 conditional mutation in mice in which disruption of the BMK1 gene is under the control of the inducible Mx1-Cre transgene. Ablation of BMK1 in adult mice led to lethality within 2-4 weeks after the induction of Cre recombinase. Physiological analysis showed that the blood vessels became abnormally leaky after deletion of the BMK1 gene. Histological analysis revealed that, after BMK1 ablation, hemorrhages occurred in multiple organs in which endothelial cells lining the blood vessels became round, irregularly aligned, and, eventually, apoptotic. In vitro removal of BMK1 protein also led to the death of endothelial cells partially due to the deregulation of transcriptional factor MEF2C, which is a direct substrate of BMK1. Additionally, endothelial-specific BMK1-KO leads to cardiovascular defects identical to that of global BMK1-KO mutants, whereas, surprisingly, mice lacking BMK1 in cardiomyocytes developed to term without any apparent defects. Taken together, the data provide direct genetic evidence that the BMK1 pathway is critical for endothelial function and for maintaining blood vessel integrity.

Loss of nicotinic receptors induced by beta-amyloid peptides in PC12 cells: possible mechanism involving lipid peroxidation

The mechanisms involved in the loss of nicotinic acetylcholine receptors (nAChRs), seen in brains of patients with Alzheimer's disease (AD) and in cultured cells treated by beta-amyloid peptides (A betas), remain elusive. We give results to show that lipid peroxidation induced directly by A beta might be involved in the deficits of nAChRs. In the study, PC12 cells were treated by addition of 5 microM of A beta(25-35) and A beta(1-40), respectively, with or without a antioxidant, vitamin E. Besides significantly decreased MTT (3-(4,5-dimethylthiazol-2-yl)-2,5,diphenyltetrazolium bromide) reduction, an increased lipid peroxidation was detected in the cells, but no protein oxidation. Significant reductions in [(3)H]epibatidine and [(125)I]alpha-bungarotoxin binding sites and in the protein levels of the alpha 3 and alpha 7 nAChR subunits were observed in the cells treated with A betas. Furthermore, A beta(25-35) decreased the level of ubiquinone-9 in PC12 cells, but did not change the amount of cholesterol, providing further evidence for lipid peroxidation. Interestingly, when PC12 cells were pretreated by antioxidant before the addition of A betas, the lipid peroxidation and the decreased ubiquinone resulted from A betas were prohibited. The decreases of nAChR binding sites and subunit proteins resulted from A betas were mostly prevented by the pretreatment with antioxidant. These findings suggest that lipid peroxidation stimulated by A betas might be a mechanism for the loss of nAChRs associated with the pathogenesis of AD.

Risk factors for Alzheimer's disease: role of multiple antioxidants, non-steroidal anti-inflammatory and cholinergic agents alone or in combination in prevention and treatment

The etiology of Alzheimer's disease (AD) is not well understood. Etiologic factors, chronic inflammatory reactions, oxidative and nitrosylative stresses and high cholesterol levels are thought to be important for initiating and promoting neurodegenerative changes commonly found in AD brains. Even in familial AD, oxidative stress plays an important role in the early onset of the disease. Mitochondrial damage and proteasome inhibition represent early events in the pathogenesis of AD, whereas increased processing of amyloid precursor protein (APP) to beta-amyloid (Abeta) fragments (Abeta(40) and Abeta(42)) and formation of senile plaques and neurofibrillary tangles (NFTs) represent late events. We propose a hypothesis that in idiopathic AD, epigenetic components of neurons such as mitochondria, proteasomes and post-translation protein modifications (processing of amyloid precursor protein to beta-amyloid and hyperphosphorylation of tau), rather than nuclear genes, are the primary targets for the action of diverse groups of neurotoxins. Based on epidemiologic, laboratory and limited clinical studies, we propose that a combination of non steroidal anti-inflammatory drugs (NSAIDs) and appropriate levels and types of multiple micronutrients, including antioxidants, may be more effective than the individual agents in the prevention, and they, in combination with a cholinergic agent, may be more effective in the treatment of AD than the individual agents alone. In addition, agents, which can prevent formation of plaques or dissolve these plaques may further enhance the efficacy of our proposed treatment strategy.

Antioxidants as treatment for neurodegenerative disorders

Oxidative stress is a ubiquitously observed hallmark of neurodegenerative disorders. Neuronal cell dysfunction and cell death due to oxidative stress may causally contribute to the pathogenesis of progressive neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, as well as acute syndromes of neurodegeneration, such as ischaemic and haemorrhagic stroke. Neuroprotective antioxidants are considered a promising approach to slowing the progression and limiting the extent of neuronal cell loss in these disorders. The clinical evidence demonstrating that antioxidant compounds can act as protective drugs in neurodegenerative disease, however, is still relatively scarce. In the following review, the available data from clinical, animal and cell biological studies regarding the role of antioxidant neuroprotection in progressive neurodegenerative disease will be summarised, focussing particularly on Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. The general complications in developing potent neuroprotective antioxidant drugs directed against these long-term degenerative conditions will also be discussed. The major challenges for drug development are the slow kinetics of disease progression, the unsolved mechanistic questions concerning the final causalities of cell death, the necessity to attain an effective permeation of the blood-brain barrier and the need to reduce the high concentrations currently required to evoke protective effects in cellular and animal model systems. Finally, an outlook as to which direction antioxidant drug development and clinical practice may be leading to in the near future will be provided.

Antioxidant neuroprotection in Alzheimer's disease as preventive and therapeutic approach

Various neurodegenerative disorders and syndromes are associated with oxidative stress. The deleterious consequences of excessive oxidations and the pathophysiological role of reactive oxygen species (ROS) have been intensively studied in Alzheimer's disease (AD). Neuronal cell dysfunction and oxidative cell death caused by the AD-associated amyloid beta protein may causally contribute to the pathogenesis of AD. Antioxidants that prevent the detrimental consequences of ROS are consequently considered to be a promising approach to neuroprotection. While there is ample experimental evidence demonstrating neuroprotective activities of antioxidants in vitro, the clinical evidence that antioxidant compounds act as protective drugs is still relatively scarce. Nevertheless, antioxidants constitute a major part of the panel of clinical and experimental drugs that are currently considered for AD prevention and therapy. Here, focus is put mainly on phenolic antioxidant structures that belong to the class of direct antioxidants. Experimental and clinical evidence for the neuroprotective potential of alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) is shortly summarized and an outlook is given on possible novel antioxidant lead structures with improved pharmacological features.

Achieving and maintaining cognitive vitality with aging

Cognitive vitality is essential to quality of life and survival in old age. With normal aging, cognitive changes such as slowed speed of processing are common, but there is substantial interindividual variability, and cognitive decline is clearly not inevitable. In this review, we focus on recent research investigating the association of various lifestyle factors and medical comorbidities with cognitive aging. Most of these factors are potentially modifiable or manageable, and some are protective. For example, animal and human studies suggest that lifelong learning, mental and physical exercise, continuing social engagement, stress reduction, and proper nutrition may be important factors in promoting cognitive vitality in aging. Manageable medical comorbidities, such as diabetes, hypertension, and hyperlipidemia, also contribute to cognitive decline in older persons. Other comorbidities such as smoking and excess alcohol intake may contribute to cognitive decline, and avoiding these activities may promote cognitive vitality in aging. Various therapeutics, including cognitive enhancers and protective agents such as antioxidants and anti-inflammatories, may eventually prove useful as adjuncts for the prevention and treatment of cognitive decline with aging. The data presented in this review should interest physicians who provide preventive care management to middle-aged and older individuals who seek to maintain cognitive vitality with aging.

Determination of cadmium and zinc in Alzheimer's brain tissue using inductively coupled plasma mass spectrometry

In this work, brain tissue was taken from Alzheimer's Disease (AD) subjects (n=11), 'normal' subjects (n=10) and from subjects with senile involutive cortical changes (SICC) (n=6). Concentrations of Cd and Zn were determined in all samples, using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The brain tissue was selected and obtained from the Netherlands Brain Bank. Samples were taken in each case, from both hemispheres of the superior frontal gyrus, the superior parietal gyrus, the medial temporal gyrus, the hippocampus and the thalamus of the same brain.Cd which is known to have no essential role in the brain was found to follow, as expected, a lognormal distribution of concentrations in 'normal' subjects (Shapiro-Wilk's test (0.98) (p<0.18)). For the Alzheimer's Disease subjects and SICC subjects, the data tends to follow a lognormal distribution, rather than a normal distribution, but is still significantly different from it (Shapiro-Wilk's test (0.97) (p<0.03); (0.93) (p<0.0067), respectively)). In the case of Zn concentrations, the data tends to follow a normal distribution for the 'normal' subject group, even though the data is significantly different from it (Shapiro-Wilk's test (0.95) (p<0.001)). Whereas in the Alzheimer's Disease and SICC subject groups, the data follows a normal distribution (Shapiro-Wilk's test (0.98) (p<0.21); (0.97) (p<0.2002), respectively)). When comparing age-matched groups, for all regions and both hemispheres, no significant differences (p>0.1) for Cd were found between 'normals' and Alzheimer's Disease subjects and Alzheimer's Disease subjects and SICC but at a low level of significance, lower concentrations of Cd were found in the SICC group compared to the 'normals'. For all regions and both hemispheres, Zn was found to be significantly decreased in the Alzheimer's Disease group, compared to the 'normal' and SICC groups. Zn concentrations were also found to be significantly decreased in the 'normals' compared to the SICC group. It is also of interest that Cd negatively correlates with the scale of tangles in both 'normals' (p<0.001) and Alzheimer's Disease subjects (p<0.01). In the SICC subjects Cd correlates negatively with the tangles but not significantly so (p>0.1).

Oxidative nerve cell death in Alzheimer's disease and stroke: antioxidants as neuroprotective compounds

Many neurodegenerative disorders and syndromes are associated with an excessive generation of reactive oxygen species (ROS) and oxidative stress. The pathways to nerve cell death induced by diverse potential neurotoxins such as peptides, excitatory amino acids, cytokines or synthetic drugs commonly share oxidative downstream processes, which can cause either an acute oxidative destruction or activate secondary events leading to apoptosis. The pathophysiological role of ROS has been intensively studied in in vitro and in vivo models of chronic neurodegenerative diseases such as Alzheimer's disease (AD) and of syndromes associated with rapid nerve cell loss as occuring in stroke. In AD, oxidative neuronal cell dysfunction and cell death caused by protofibrils and aggregates of the AD-associated amyloid beta protein (Abeta) may causally contribute to pathogenesis and progression. ROS and reactive nitrogen species also take part in the complex cascade of events and the detrimental effects occuring during ischemia and reperfusion in stroke. Direct antioxidants such as chain-breaking free radical scavengers can prevent oxidative nerve cell death. Although there is ample experimental evidence demonstrating neuroprotective activities of direct antioxidants in vitro, the clinical evidence for antioxidant compounds to act as protective drugs is relatively scarce. Here, the neuroprotective potential of antioxidant phenolic structures including alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) in vitro is summarized. In addition, the antioxidant and cytoprotective activities of lipophilic tyrosine- and tryptophan-containing structures are discussed. Finally, an outlook is given on the neuroprotective potential of aromatic amines and imines, which may comprise novel lead structures for antioxidant drug design.

Protection of human endothelial cells from oxidative stress: role of Ras-ERK1/2 signaling

BACKGROUND

Reactive oxygen species play a critical role in inducing apoptosis. The small GTPase p21 Ras and the ERK1/2 MAPK have been proposed as key regulators of the signaling cascade triggered by oxidative stress (H2O2). Harvey-Ras (Ha-Ras) and Kirsten-Ras (Ki-Ras) isoforms are so far functionally indistinguishable, because they activate the same downstream effectors, including ERK1/2. Moreover, ERK1/2 signaling has been involved in both protection and induction of apoptosis.

METHODS AND RESULTS

Human umbilical vein endothelial cells (HUVECs) were subjected to H2O2, and apoptosis was detected by fluorescence-activated cell sorting analysis, fluorescence microscopy, and caspase-3 activation. Transfection of Ha-Ras and Ki-Ras genes in HUVECs was performed to evaluate the response to H2O2. We have found that, whereas Ha-Ras decreases tolerance to oxidative stress, Ki-Ras has a potent antiapoptotic activity. Both effects are mediated by ERK1/2. Tolerance to H2O2 is encoded by a unique stretch of lysines at the COOH terminus of the Ki-Ras, lacking in Ha-Ras, and it is relatively independent of the farnesylated anchor. Inhibition of p21 Ras signaling by farnesylation inhibitors increased the resistance to apoptosis in Ha-Ras-expressing cells.

CONCLUSIONS

These findings explain the opposite effects of ERK1/2 stimulation on apoptosis found in different cell types and suggest that local activation of ERK1/2 signaling may account for the opposing response to oxidative stress by Ha-Ras or Ki-Ras-expressing cells. Modulation of cell reactivity to oxidative stress by p21 Ras points to the specific and predictive effects of Ras inhibitors in vivo as potential therapeutic drugs in disorders produced by increase of reactive oxygen species inside the cells.

The use of antioxidants in transmissible spongiform encephalopathies: a case report

BACKGROUND

Transmissible spongiform encephalopathies (TSE), which include Creutzfeldt-Jakob disease and new variant Creutzfeldt-Jakob disease, are diseases characterized by progressive deterioration in the central nervous system with neuronal degeneration, vacuolatization of the neuropil, and gliosis. Little is known about the pathogenic mechanisms of infection, and controversy exits around the inciting infective agent. It has been shown that an important factor in pathogenesis is the immune system.

CASE

The reported case points to beneficial effects when antioxidant therapies are used in transmissible spongiform encephalopathies. The case revealed an early reversal in cognitive decline and subsequent improvements in myoclonus, apnea and rigidity. Although death was the ultimate outcome, the patient succumbed to the illness over 22 months after the onset of symptoms when the early rapid decline predicted demise within a few months.

CONCLUSION

It is possible that strategies blocking the effect of proinflammatory cytokines and the resulting oxidative damage may stem the progressive damage to the neuropil that occurs in spongiform encephalopathies. Further investigation into the use of antioxidants and other types of agents quelling inflammation needs to be undertaken. If antioxidants could be combined with treatments for the inciting infective agent, a new direction could be taken in the outcome of transmissible spongiform encephalopathies including CJD and vCJD.

Role of redox status on the activation of mitogen-activated protein kinase cascades by NSAIDs

High concentrations of non steroidal antiinflammatory drugs (NSAIDs) exert preventive effects against carcinogenesis. Their molecular mechanism of action remains to be elucidated. Based on previous reports with salicylate, we have made the hypothesis that various NSAIDs can activate the mitogen-activated protein kinases (MAPK). Moreover, we tested the idea that NSAIDs act by increasing the effects of oxidative stress. We report that in human colorectal carcinoma cells NSAIDs stimulated the three families of MAPK, extracellular regulated kinases, c-Jun N-terminal kinases, p38 MAPK and that this stimulation is prevented by N-acetyl cysteine. In cultured astrocytes, a biological system less sensitive to oxidative stress, we show that a short treatment by NSAIDs strongly activated the three MAP kinases in the presence of H(2)O(2). A 25 microM H(2)O(2), unable to stimulate by itself the MAP kinases, promote an almost complete activation of MAP kinases in the presence of NSAIDs. The activation of MAP kinases by H(2)O(2) and NSAIDs was suppressed by quinone reductase inhibitors, suggesting that "redox cycling" was involved in the activation mechanisms of MAP kinases by H(2)O(2) and NSAIDs. The mobility on SDS-PAGE of the apoptosis signal-regulating kinase, which activates C-Jun N-terminal kinases and p38 MAPK cascades, was reduced by H(2)O(2) and NSAIDs, suggesting, that H(2)O(2) and NSAIDs activated apoptosis signal-regulating kinase by increasing its state of phosphorylation. In conclusion, we demonstrate that various NSAIDs can activate the three families of MAP kinases and that this activation depends on the presence of reactive oxygenated species. These results give a new insight into the mechanism of the action of NSAIDs.

Protective activity of aromatic amines and imines against oxidative nerve cell death

Oxidative stress is a widespread phenomenon in the pathology of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Neuronal cell death due to oxidative stress may causally contribute to the pathogeneses of these diseases. Therefore, neuroprotective antioxidants are considered to be a promising approach to slow down disease progression. We have investigated different aromatic amine and imine compounds for neuroprotective antioxidant functions in cell culture, and found that these compounds possess excellent cytoprotective potential in diverse paradigms of oxidative neuronal cell death, including clonal cell lines, primary cerebellar neurons, and organotypic hippocampal slice cultures. Aromatic amines and imines are effective against oxidative glutamate toxicity, glutathione depletion, and hydrogen peroxide toxicity. Their mode of action as direct antioxidants was experimentally confirmed by electron spin resonance spectroscopy, cell-free brain lipid peroxidation assays, and intracellular peroxide measurements. With half-maximal effective concentrations of 20-75 nM in different neuroprotection experiments, the aromatic imines phenothiazine, phenoxazine, and iminostilbene proved to be about two orders of magnitude more effective than common phenolic antioxidants. This remarkable efficacy could be directly correlated to calculated properties of the compounds by means of a novel, quantitative structure-activity relationship model. We conclude that bridged bisarylimines with a single free NH-bond, such as iminostilbene, are superior neuroprotective antioxidants, and may be promising lead structures for rational drug development.

Modulation of NO and cytokines in microglial cells by Cu/Zn-superoxide dismutase

The activation of microglial cells in response to neuropathological stimuli is one of the prominent features of human neurodegenerative diseases. Cytokines such as IL-1 beta and TNF-alpha and inflammation-related enzymes such as inducible nitric oxide synthase are usually induced during the activation of microglial cells. We investigated the modulation of the activation of microglial cell by transfecting a Cu/Zn-SOD cDNA into BV-2 cells. Parental and transfected BV-2 cells were then subjected to LPS stimulation. The results showed that in Cu/Zn-SOD-transfected BV-2 cells, the expression and activity of Cu/Zn-SOD increased. On the other hand, upon activation by LPS, these cells produced less NO, IL-1 beta, and TNF-alpha than the parental microglial cells. This finding suggests that superoxide may be an early signal triggering the induction of cytokines and that the transfected Cu/Zn-SOD may provide a neuroprotective function via suppression of microglial activation. In addition, this approach may provide a rationale for the development of treatments for neurodegenerative diseases.

Combination Therapies and the Theoretical Limits of Evidence-Based Medicine

BACKGROUND

Advances in molecular pharmacology and surgical, endovascular, and radiation techniques have yielded multiple effective or promising, and potentially complementary, classes of treatments for virtually every major medical disorder. Consequently, determining the optimum combination of therapies for a condition is a burgeoning challenge to clinical trialists and practicing physicians.

METHODS

General phase III trial strategies for testing combination regimens are described, and then applied to two illustrative conditions, Alzheimer disease and ischemic stroke.

RESULTS

Strategies for testing combination regimens include: head to head trials of all combinations, which lead to unwieldy trial numbers; very large multi-arm trials, which impractically delay interval information on regimen utility; and hierarchical, serial clinical trials. Systematic literature review revealed seven classes of agents already approved or in late phase III testing for preventing the development or slowing the progression of Alzheimer disease and five for ischemic stroke prevention. Possible combination regimens number 128 (2(7)) for Alzheimer disease and 32 (2(5)) for ischemic stroke. Hierarchical, serial clinical trials would permit identification of the optimum combination of these agent classes for Alzheimer disease through 127 trials, enrolling 63,500 patients, requiring 286 years; for ischemic stroke through 31 trials, enrolling 186,000 patients, requiring 155 years.

CONCLUSIONS

Marked limitations in the ability of clinical trials to interrogate varied treatment combinations to determine the most effective ensemble exist, and their scope is widely underappreciated. Steps that may attenuate, though not eliminate, the challenge of a surfeit of combination treatment regimens include preclinical testing to identify the most promising regimens, use of surrogate outcome measures in exploratory clinical trials, and use of hierarchical, serial and factorial phase III trials.

In vitro evaluation of antioxidant activity by electrophoresis and high performance liquid chromatography

Two methods for the analysis of antioxidants, based on polyacrylamide gel electrophoresis (PAGE) and gel permeation high performance liquid chromatography (HPLC) were developed. Both of them exploit the variations of the signal (band or peak) given by human serum albumin (0.2% w/v in 100 mM sodium phosphate pH 7) upon oxidation with hypochlorite (1% of a solution containing 4% active Cl), quantitatively determined by densitometric analysis or peak integration. Based on such changes, two formulas were defined which allowed the determination of the antioxidant activity of ascorbic acid (EC(50,PAGE)=4.8x10(-4) M, EC(50,HPLC)=3.6x10(-4) M), glutathione (EC(50,PAGE)=1.5x10(-4) M, EC(50,HPLC)=2.0x10(-4) M) and melatonin (EC(50,PAGE)=5.2x10(-4) M, EC(50,HPLC)=3.2x10(-4) M), chosen as reference compounds. A good correlation was found between the activities of these substances in the two assays, which are also in good agreement with literature data, indicating that the two methods are essentially equivalent. These assays could be useful for the screening of new antioxidant drugs for pathological conditions such as cataract, rheumatic diseases, atherosclerosis and Alzheimer's disease.