Charles Ramassamy

The ginkgo biloba extract (EGb 761) protects hippocampal neurons against cell death induced by β-amyloid

Substantial evidence suggests that the accumulation of β‐amyloid (Aβ)‐derived peptides, and to a lesser extent free radicals, may contribute to the aetiology and/or progression of Alzheimers disease (AD). Ginkgo biloba extract (EGb 761) is a well‐defined plant extract containing two major groups of constituents, i.e. flavonoids and terpenoids. It is viewed as a polyvalent agent with a possible therapeutic use in the treatment of neurodegenerative diseases of multifactorial origin, e.g. AD. We have investigated here the potential effectiveness of EGb 761 against toxicity induced by (Aβ)‐derived peptides (Aβ25−35, Aβ1−40 and Aβ1−42) on hippocampal primary cultured cells, this area being severely affected in AD. A co‐treatment with EGb 761 concentration‐dependently (10–100 μg/mL) protected hippocampal neurons against toxicity induced by Aβ fragments, with a maximal and complete protection at the highest concentration tested. Similar, albeit less potent protective effects were seen with the flavonoid fraction of the extract (CP 205), while the terpenes were ineffective. Most interestingly, EGb 761 (100 μg/mL) was even able to protect (up to 8 h) hippocampal cells from a pre‐exposure to Aβ25−35 and Aβ1−40. EGb 761 was also able to both protect and rescue hippocampal cells from toxicity induced by H2O2 (50–150 μm), a major peroxide possibly involved in mediating Aβ toxicity. Moreover, EGb 761 (10–100 μg/mL), and to a lesser extent CP 205 (10–50 μg/mL), completely blocked Aβ‐induced events, e.g. reactive oxygen species accumulation and apoptosis. These results suggest that the neuroprotective effects of EGb 761 are partly associated with its antioxidant properties and highlight its possible effectiveness in neurodegenerative diseases, e.g. AD via the inhibition of Aβ‐induced toxicity and cell death.

Challenges for research on polyphenols from foods in Alzheimer's disease: bioavailability, metabolism, and cellular and molecular mechanisms.

Polyphenols are the most abundant antioxidants in diet. Indeed, fruits, vegetables, beverages (tea, wine, juices), plants, and some herbs are loaded with powerful antioxidant polyphenols. Despite their wide distribution, research on human health benefits truly began in the mid-1990s (Scalbert, A.; Johnson, I. T.; Saltmarsh, M. Am. J. Clin. Nutr. 2005, 81, S15S-217S). Phenolic compounds have been receiving increasing interest from consumers and manufacturers because numerous epidemiological studies have suggested associations between consumption of polyphenol-rich foods or beverages and the prevention of certain chronic diseases such as cancers and cardiovascular diseases (Manach, C.; Mazur, A.; Scalbert, A. Curr. Opin. Lipidol. 2005, 16, 77-84; Duthie, S. J. Mol. Nutr. Food Res. 2007, 51, 665-674). Furthermore, in the past 10 years, research on the neuroprotective effects of dietary polyphenols has developed considerably. These compounds are able to protect neuronal cells in various in vivo and in vitro models through different intracellular targets (Ramassamy, C. Eur. J. Pharmacol. 2006, 545, 51-64). However, it is not at all clear whether these compounds reach the brain in sufficient concentrations and in a biologically active form to exert beneficial effects. On the other hand, it has become clear that the mechanisms of action of these polyphenols go beyond their antioxidant activity and the attenuation of oxidative stress. Therefore, there is a need for more research on their intracellular and molecular targets as special pathways underlying distinct polyphenol-induced neuroprotection. The focus of this review is aimed at presenting the role of some polyphenols from fruits, vegetables, and beverages in neuroprotection and particularly in Alzheimers disease and the research challenges in this area.

Dehydroepiandrosterone (DHEA) protects hippocampal cells from oxidative stress-induced damage.

It has been postulated that decreases in plasma levels of dehydroepiandrosterone (DHEA) may contribute to the development of some age-related disorders. Along with neuroprotective and memory enhancing effects, DHEA has been shown to display antioxidant properties. Moreover, oxidative stress is known to cause lipid peroxidation and degenerative changes in the hippocampus, an area involved in memory processes and especially afflicted in Alzheimers disease (AD). Accordingly, we investigated the antioxidant effects of DHEA in models of oxidative stress using rat primary hippocampal cells and human hippocampal tissue from AD patients and age-matched controls. A pre-treatment of rat primary mixed hippocampal cell cultures with DHEA (10-100 microM) protected against the toxicity induced by H2O2 and sodium nitroprusside. Moreover, DHEA (10-100 microM) was also able to prevent H2O2/FeSO4-stimulated lipid oxidation in both control and AD hippocampal tissues. Taken together, these data suggest that DHEA may be useful in treating age-related central nervous system diseases based on its protective effects in the hippocampus.

Oxidative damage and protection by antioxidants in the frontal cortex of Alzheimer’s disease is related to the apolipoprotein E genotype

A great number of epidemiological studies have demonstrated that the frequency of the epsilon4 allele of the apolipoprotein E gene (APOE) is markedly higher in sporadic and in familial late onset Alzheimer disease (AD). In the frontal cortex of AD patients, oxidative damage is elevated. We address the hypothesis that the APOE genotype and reactive oxygen-mediated damage are linked in the frontal cortex of AD patients. We have related the APOE genotype to the levels of lipid oxidation (LPO) and to the antioxidant status, in frontal cortex tissues from age-matched control and AD cases with different APOE genotypes. LPO levels were significantly elevated in tissues from Alzheimers cases which are homozygous for the epsilon4 allele of APOE, compared to AD epsilon3/epsilon3 cases and controls. Activities of enzymatic antioxidants, such as catalase and glutathione peroxidase (GSH-PX), were also higher in AD cases with at least one epsilon4 allele of APOE, while superoxide dismutase (SOD) activity was unchanged. In the frontal cortex, the concentration of apoE protein was not different between controls and AD cases, and was genotype independent. The Ginkgo biloba extract (EGb 761), the neurosteroid dehydroepiandrosterone (DHEA) and human recombinant apoE3 (hapoE3rec) were able to protect control, AD epsilon3/epsilon3 and epsilon3/epsilon4 cases against hydrogen peroxide/iron-induced LPO, while hapoE4rec was completely ineffective. Moreover, EGb 761 and DHEA had no effect in homozygous epsilon4 cases. These results demonstrate that oxidative stress-induced injury and protection by antioxidants in the frontal cortex of AD cases are related to the APOE genotype.

The neurobiology of apolipoproteins and their receptors in the CNS and Alzheimer's disease

The importance of apolipoproteins in the central nervous system became increasingly clear with the association in 1993 of the epsilon4 allele of apolipoprotein E with familial and sporadic late-onset Alzheimers disease. Apolipoprotein E is a ligand for several receptors, most of which are found to some extent in the brain. This review summarizes the various apolipoproteins and lipoprotein receptors found in the brain. A growing body of evidence now implicates irregular lipoprotein metabolism in several neurodegenerative disorders. We then focus on research linking apolipoprotein E and Alzheimers disease, from clinical studies to biochemical models, which may explain some of the complex neurobiology of this disorder.

Apolipoprotein E and β-amyloid levels in the hippocampus and frontal cortex of Alzheimer's disease subjects are disease-related and apolipoprotein E genotype dependent

The epsilon4 allele of apolipoprotein E (apoE) is associated with increased risk for the development of Alzheimers disease (AD), possibly due to interactions with the beta-amyloid (Abeta) protein. The mechanism by which these two proteins are linked to AD is still unclear. To further assess their potential relationship with the disease, we have determined levels of apoE and Abeta isoforms from three brain regions of neuropathologically confirmed AD and non-AD tissue. In two brain regions affected by AD neuropathology, the hippocampus and frontal cortex, apoE levels were found to be decreased while Abeta(1-40) levels were increased. Levels of apoE were unchanged in AD cerebellum. Furthermore, levels of apoE and Abeta(1-40) were found to be apoE genotype dependent, with lowest levels of apoE and highest levels of Abeta(1-40) occurring in epsilon4 allele carriers. These results suggest that reduction in apoE levels may give rise to increased deposition of amyloid peptides in AD brain.

Neurotherapeutic applications of nanoparticles in Alzheimer's disease.

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

Role of By-Products of Lipid Oxidation in Alzheimer's Disease Brain: A Focus on Acrolein

Abundant data consistently support the idea that oxidative stress occurs and is a constant feature of Alzheimers disease (AD). Some recent evidence indicated that phenomenon is an early event and might be implicated in the pathogenesis of this disease. Lipid peroxidation leads to the formation of a number of aldehydes by-products, including malondialdehyde (MDA), 4-hydroxy-2-nonenal (HNE), and acrolein. The most abundant aldehydes are HNE and MDA while acrolein is the most reactive. Increased levels of specific HNE-histidine and glutathione-HNE Michael adducts in AD brain has been reported. Proteomic analysis demonstrated a large number of protein-bound HNE in AD brain. F2-isoprostanes (F2-IsoPs) levels and neuroprostanes were also significantly increased in mild cognitive impairment (MCI) patients and in late-stage AD. In brain from patients with AD, acrolein has been found to be elevated in hippocampus and temporal cortex where oxidative stress is high. Due to its high reactivity, acrolein is not only a marker of lipid peroxidation but also an initiator of oxidative stress by adducting cellular nucleophilic groups found on proteins, lipids, and nucleic acids. Interestingly, data indicates that lipid peroxidation occurs in the brain of MCI and also in preclinical AD patients suggesting that oxidative damage may play an early role in the pathogenesis of AD. In this review, we will summarize some mechanisms implicated in the toxicity of by-products of lipid peroxidation such as IsoPs, HNE, and acrolein and their implication in AD.

Impact of apoE deficiency on oxidative insults and antioxidant levels in the brain

Apolipoprotein E (apoE) is a lipid transport molecule, which has been linked to the pathogenesis of Alzheimers disease. Recently we have demonstrated that the oxidative insults in hippocampus from AD patients were dependent on the apoE genotype. Interestingly, apoE protein concentration in hippocampus follows a genotype-dependent gradient with the lowest level occurring in varepsilon4 allele carrier. We raised the possibility that, in the hippocampus, the apoE level affects the oxidant/antioxidant balance. Here, we have examined in the apoE-deficient mouse the oxidant/antioxidant status in hippocampus and in frontal cortex from APOE-KO and wild-type mice at 3 and 13 months. We provided evidence that, in the hippocampus, the absence of apoE has a clear impact on the oxidant/antioxidant status. Endogenous level of thiobarbituric acid-reactive substances (TBARS) was found to be markedly elevated whereas level of alpha-tocopherol was decreased in APOE-deficient mice at 3 and 13 months. Superoxide dismutase activities were also lower in APOE-deficient mice at 13 months. Taken together, these data indicate that the steady state level of apoE may influence, to a certain extent, the balance between oxidants and antioxidants in hippocampus.

Challenges associated with curcumin therapy in Alzheimer disease

Curcumin, the phytochemical agent in the spice turmeric, which gives Indian curry its yellow colour, is also a traditional Indian medicine. It has been used for millennia as a wound-healing agent and for treating a variety of ailments. The antioxidant, anti-inflammatory, antiproliferative and other properties of curcumin have only recently gained the attention of modern pharmacology. The mechanism of action of curcumin is complex and multifaceted. In part, curcumin acts by activating various cytoprotective proteins that are components of the phase II response. Over the past decade, research with curcumin has increased significantly. In vitro and in vivo studies have demonstrated that curcumin could target pathways involved in the pathophysiology of Alzheimer disease (AD), such as the β-amyloid cascade, tau phosphorylation, neuroinflammation or oxidative stress. These findings suggest that curcumin might be a promising compound for the development of AD therapy. However, its insolubility in water and poor bioavailability have limited clinical trials and its therapeutic applications. To be effective as a drug therapy, curcumin must be combined with other drugs, or new delivery strategies need to be developed.