The effects of an extract of Ginkgo biloba, EGb 761, on cognitive behavior and longevity in the rat

New Insight into the Mechanisms of Ginkgo Biloba Extract in Vascular Aging Prevention

BACKGROUND

Aging-associated vascular dysfunction promotes cardiovascular diseases. Recently, Ginkgo biloba extract (GBE) has attracted considerable attention in the prevention of aged vasculature.

METHODS

This review discusses the pathophysiological alterations in aged vasculature and the underlying mechanisms of GBE in vascular aging suppression.

RESULTS

Both arterial stiffening and endothelial dysfunction are critical aging-related vascular phenotypes that result in the progression of cardiovascular diseases in the general population. Consistent oxidative stress and inflammatory reaction lead to vascular dysfunction. GBE ameliorates aging-related vascular dysfunction, due to its antioxidant and anti-inflammatory properties. The main effects of GBE in aged vasculature might be associated with the longevity signaling pathways. GBE also attenuates the progression of vascular aging in diabetes mellitus via regulation of glucose and lipid metabolism.

CONCLUSION

GBE plays an important role in the prevention of vascular aging process. It is a promising therapeutic approach to ameliorate aging-related vascular dysfunction and cardiovascular diseases.

Small Molecule Natural Products and Alzheimer's Disease

Alzheimer's disease (AD) is a progressive and deadly neurodegenerative disease that is characterized by memory loss, cognitive impairment and dementia. Several hypotheses have been proposed for the pathogenesis based on the pathological changes in the brain of AD patients during the last few decades. Unfortunately, there is no effective agents/therapies to prevent or control AD at present. Currently, only a few drugs, which function as acetylcholinesterase (AChE) inhibitors or N-methyl-Daspartate (NMDA) receptor antagonists, are available to alleviate symptoms. Since many small molecule natural products have shown their functions as agonists or antagonists of receptors, as well as inhibitors of enzymes and proteins in the brain during the development of central nervous system (CNS) drugs, it is likely that natural products will play an important role in anti-AD drug development. We review recent papers on using small molecule natural products as drug candidates for the treatment of AD. These natural products possess antioxidant, anti-inflammatory, anticholinesterase, anti-amyloidogenic and neuroprotective activities. Moreover, bioactive natural products intended to be used for preventing AD, reducing the symptoms of AD and the new targets for treatment of AD are summarized.

Therapeutic efficacy of the Ginkgo special extract EGb761® within the framework of the mitochondrial cascade hypothesis of Alzheimer's disease

OBJECTIVES

The mitochondrial cascade hypothesis of dementia assumes mitochondrial dysfunction as an important common pathomechanism for the whole spectrum of age-associated memory disorders from cognitive symptoms in the elderly over mild cognitive impairment to Alzheimer's dementia. Thus, a drug such as the Ginkgo special extract EGb 761^® which improves mitochondrial function should be able to ameliorate cognitive deficits over the whole aging spectrum.

METHODS

We review the most relevant publications about effects of EGb 761^® on cognition and synaptic deficits in preclinical studies as well as on cognitive deficits in man from aging to dementia.

RESULTS

EGb 761^® improves mitochondrial dysfunction and cognitive impairment over the whole spectrum of age-associated cognitive disorders in relevant animal models and in vitro experiments, and also shows clinical efficacy in improving cognition over the whole range from aging to Alzheimer's or even vascular dementia.

CONCLUSIONS

EGb 761^® shows clinical efficacy in the treatment of cognitive deficits over the whole spectrum of age-associated memory disorders. Thus, EGb 761^® can serve as an important pharmacological argument for the mitochondrial cascade hypothesis of dementia.

Ginkgo biloba extract EGb 761® in the symptomatic treatment of mild-to-moderate dementia: a profile of its use

EGb 761^® (Tanakan^®) is a standardized extract of Ginkgo biloba leaves that has demonstrated protective properties against neuronal and vascular damage. Overall, in randomized, placebo-controlled clinical trials and meta-analyses in adults with mild-to-moderate dementia, EGb 761^® displayed positive effects, with changes from baseline in outcomes related to cognition, behaviour and global change that are generally better than those shown with placebo. EGb 761^® is generally well tolerated, with no safety issues being identified during its many years of widespread use.

Ginkgo biloba: A Cognitive Enhancer?

Ginkgo biloba is an herb often used as an alternative treatment to improve cognitive functions. Like most herbal treatments, the use of ginkgo is poorly regulated by government agencies, on the basis of either its efficacy or its health risks. This article reviews the experimental evidence available regarding efficacy, neurobiological actions, and health risks. Findings obtained in studies of humans often include demonstrations of rather mild cognitive enhancement. Interpretation of these findings is complicated by somewhat inconsistent findings, by experimental designs that do not permit identification of cognitive functions susceptible to the influence of ginkgo, and by the paucity of direct comparisons with other treatments. The number of peer-reviewed reports of studies in nonhuman animals is surprisingly small. In this small set, the findings reveal mild behavioral effects that might be attributable to actions on cognitive functions. However, these experiments in rodents, like those in humans, do not involve the use of designs to assess ginkgo's effects on particular cognitive attributes, and generally do not include direct comparisons with other treatments. Interpretation of the findings is further complicated by evidence, obtained in studies of both humans and rats, showing that a single administration of the treatment enhances performance on cognitive measures.

If ginkgo has effects on cognition, there should be effects evident on biological processes as well. Neurobiological studies have largely examined the effects of chronic ginkgo administration, mirroring the most common design in behavioral studies. However, the addition of findings that single administration of ginkgo may influence behavior directs biological investigations to short-term actions of the treatment. Biological effects of ginkgo include vasodilation, protection of neurons from oxidative stress, and actions mediated by effects via neurotransmitters. Adverse reactions to ginkgo consumption have been observed but are relatively rare.

Collectively, the behavioral literature reviewed cannot be used conclusively to document or to refute the efficacy of ginkgo in improving cognitive functions. At best, the effects seem quite modest. In particular, it is questionable whether effects of ginkgo, if present, are equal to those obtained by administration of acetylcholinesterase inhibitors, hearing an arousing story, or ingesting glucose.

The effects of Ginkgo biloba extract on cognitive functions in aged female rats: the role of oxidative stress and brain-derived neurotrophic factor

The aim of this study was to investigate the effects of Ginkgo biloba extract (GBE) on cognitive functions as well as oxidative stress and brain-derived neurotrophic factor (BDNF) levels in aged female rats. Rats were divided into 4 groups according to age (young vs. aged) and treatment (GBE vs. vehicle). GBE or vehicle was given for 30 d, and a series of behavioral tests were performed. Following behavioral testing, blood samples and brain tissues were obtained for analysis of BDNF, malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), and glutathione levels, and superoxide dismutase activity. Locomotor activity and anxiety levels were lower in the aged rats. Based on Morris water maze probe trial findings, GBE supplementation increased the number of platform crossings in the aged rats. MDA and 8-OHdG levels were lower in the brain tissue, and BDNF levels were higher in plasma in the rates treated with GBE. Based on these findings, we concluded that GBE supplementation improved cognitive functions by decreasing oxidative damage and increasing the BDNF level in aged female rats.

Chronic administration of quercetin prevent spatial learning and memory deficits provoked by chronic stress in rats

There are several reports that cognitive impairment is observed in stress related disorders and chronic stress impairs learning and memory. However, very few studies have looked into the possible ways of preventing this stress-induced deficit. This research study was conducted to evaluate the effects of quercetin, a natural flavonoid, with strong antioxidant and free radical scavenger properties, on chronic stress induced learning and memory deficits and oxidative stress in hippocampus. For chronic stress, rats were restrained daily for 6h/day (from 9:00 to 15:00) for 21 days in well-ventilated plexiglass tubes without access to food and water. The animals were injected with quercetin or vehicle 60 min before restraint stress over a period of 21 days. Then, rats trained with six trials per day for 6 consecutive days in the water maze. On day 28, a probe test was done to measure memory retention. In addition, oxidative stress markers in the hippocampus were evaluated. Results of this study demonstrated that chronic stress exposure rats exhibited higher escape latency during training trials and reduced time spent in target quadrant, higher escape location latency and average proximity in probe trial test. Quercetin (50mg/kg) treatment during restraint stress (21 days) markedly decreased escape latency and increased time spent in target quadrant during Morris water maze task. In comparison to vehicle treated group, chronic-stress group had significantly higher malondialdehyde (MDA) levels, significantly higher superoxide dismutase (SOD) activity and significantly lower glutathione peroxidase (GPx) activity in the hippocampus. Quercetin treatment caused a significant decrease in the hippocampus MDA levels and improves SOD and GPx activities in stressed animals. Finally, quercetin significantly decreased plasma corticosterone levels in stressed animals. Based on results of this study, chronic stress has detrimental effects on learning and memory and quercetin treatment can prevent from oxidative stress and impairment of learning and memory induced by chronic stress.

Long-lived worms and aging

Several investigators have generated long-lived nematode worms (Caenorhabditis elegans) in the past decade by mutation of genes in the organism in order to study the genetics of aging and longevity. Dozens of longevity assurance genes (LAG) that dramatically increase the longevity of this organism have been identified. All long-lived mutants of C. elegans are also resistant to environmental stress, such as high temperature, reactive oxygen species (ROS), and ultraviolet irradiation. Double mutations of some LAGs further extended life span up to 400%, providing more insight into cellular mechanisms that put limits on the life span of organisms. With the availability of the LAG mutants and the combined DNA microarray and RNAi technology, the understanding of actual biochemical processes that determine life span is within reach: the downstream signal transduction pathway may regulate life span by up-regulating pro-longevity genes such as those that encode antioxidant enzymes and/or stress-response proteins, and down-regulating specific life-shortening genes. Furthermore, longevity could be modified through chemical manipulation. Results from these studies further support the free radical theory of aging, suggest that the molecular mechanism of aging process may be shared in all organisms, and provide insight for therapeutic intervention in age-related diseases.

Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases

Human intervention trials have provided evidence for protective effects of various (poly)phenol-rich foods against chronic disease, including cardiovascular disease, neurodegeneration, and cancer. While there are considerable data suggesting benefits of (poly)phenol intake, conclusions regarding their preventive potential remain unresolved due to several limitations in existing studies. Bioactivity investigations using cell lines have made an extensive use of both (poly)phenolic aglycones and sugar conjugates, these being the typical forms that exist in planta, at concentrations in the low-μM-to-mM range. However, after ingestion, dietary (poly)phenolics appear in the circulatory system not as the parent compounds, but as phase II metabolites, and their presence in plasma after dietary intake rarely exceeds nM concentrations. Substantial quantities of both the parent compounds and their metabolites pass to the colon where they are degraded by the action of the local microbiota, giving rise principally to small phenolic acid and aromatic catabolites that are absorbed into the circulatory system. This comprehensive review describes the different groups of compounds that have been reported to be involved in human nutrition, their fate in the body as they pass through the gastrointestinal tract and are absorbed into the circulatory system, the evidence of their impact on human chronic diseases, and the possible mechanisms of action through which (poly)phenol metabolites and catabolites may exert these protective actions. It is concluded that better performed in vivo intervention and in vitro mechanistic studies are needed to fully understand how these molecules interact with human physiological and pathological processes.

Protective effects of Ginkgo biloba extract on ligature-induced periodontitis in rats

OBJECTIVE

The aim of this study was to test the hypothesis that the systemic administration of extract of Ginkgo biloba (EGb) would prevent excessive tissue destruction in ligature-induced periodontitis in a rat model.

MATERIALS AND METHODS

Thirty-two male Wistar albino rats were used in the current study. The rats were randomly divided into four groups of eight rats each: (1) non-ligated treatment (NL) group, (2) ligature-only (LO) group, (3) ligature plus GB28 (28 mg/kg, daily for 11 days) group and (4) ligature plus GB56 (56 mg/kg, daily for 11 days) group.

RESULTS

Measurement of alveolar bone loss in the mandibular molar tooth revealed significantly lower bone loss values in the LO group compared to groups NL, GB28 and GB56 (p < 0.05).

CONCLUSION

The present results are the first data which suggests that host response in periodontitis can be modified by EGb administration. EGb minimized progression of periodontal disease.

Effect of a phytopharmaceutical medicine, Ginko biloba extract 761, in an animal model of Parkinson's disease: therapeutic perspectives

Ginkgo Biloba extract 761 (EGb 761) is a patented and well-defined mixture of active compounds extracted from Ginkgo biloba leaves. This extract contains two main groups of active compounds, flavonoids (24%) and terpenoids (6%). EGb 761 is used clinically to treat dementia and vaso-occlusive and cochleovestibular disorders. This extract has neuroprotective effects, exerted probably by means of its antioxidant function. Parkinson's disease (PD) is a neurodegenerative disorder that affects 2% of the population older than 60 y. It produces a progressive loss of dopaminergic neurons and depletion of dopamine (DA), leading to movement impairment. The production of reactive oxygen species, which act as mediators of oxidative damage, is linked to PD. This disease is routinely treated with the DA precursor, L-3,4-dihydroxyphenylalanine. However, this produces severe side effects, and its neurotoxic properties can be due to a free radical production. Thus, administration of antioxidant drugs might be used to prevent neuronal death produced by oxidative mechanisms. The use of synthetic antioxidants has decreased because of their suspected activity as carcinogenic promoters. We describe the studies related to the antioxidant effect of EGb 761 in an animal model of PD. It has been shown that EGb761 can provide a neuroprotective/neurorecovery effect against the damage to midbrain DA neurons in an animal model of PD. EGb 761 also has been found to lessen the impairment of locomotion, correlating with an increase of DA and other morphologic and biochemical parameters related to its antioxidant effect in an animal model of PD. These studies suggest it as an alternative in the future treatment of PD.

Flavonoids as modulators of memory and learning: molecular interactions resulting in behavioural effects

There is considerable interest in the potential of a group of dietary-derived phytochemicals known as flavonoids in modulating neuronal function and thereby influencing memory, learning and cognitive function. The present review begins by detailing the molecular events that underlie the acquisition and consolidation of new memories in the brain in order to provide a critical background to understanding the impact of flavonoid-rich diets or pure flavonoids on memory. Data suggests that despite limited brain bioavailability, dietary supplementation with flavonoid-rich foods, such as blueberry, green tea and Ginkgo biloba lead to significant reversals of age-related deficits on spatial memory and learning. Furthermore, animal and cellular studies suggest that the mechanisms underpinning their ability to induce improvements in memory are linked to the potential of absorbed flavonoids and their metabolites to interact with and modulate critical signalling pathways, transcription factors and gene and/or protein expression which control memory and learning processes in the hippocampus; the brain structure where spatial learning occurs. Overall, current evidence suggests that human translation of these animal investigations are warranted, as are further studies, to better understand the precise cause-and-effect relationship between flavonoid intake and cognitive outputs.

Review of the literature and suggestions for the design of rodent survival studies for the identification of compounds that increase health and life span

Much of the literature describing the search for agents that increase the life span of rodents was found to suffer from confounds. One-hundred-six studies, absent 20 contradictory melatonin studies, of compounds or combinations of compounds were reviewed. Only six studies reported both life span extension and food consumption data, thereby excluding the potential effects of caloric restriction. Six other studies reported life span extension without a change in body weight. However, weight can be an unreliable surrogate measure of caloric consumption. Twenty studies reported that food consumption or weight was unchanged, but it was unclear whether these data were anecdotal or systematic. Twenty-nine reported extended life span likely due to induced caloric restriction. Thirty-six studies reported no effect on life span, and three a decrease. The remaining studies suffer from more serious confounds. Though still widely cited, studies showing life span extension using short-lived or "enfeebled" rodents have not been shown to predict longevity effects in long-lived animals. We suggest improvements in experimental design that will enhance the reliability of the rodent life span literature. First, animals should receive measured quantities of food and its consumption monitored, preferably daily, and reported. Weights should be measured regularly and reported. Second, a genetically heterogeneous, long-lived rodent should be utilized. Third, chemically defined diets should be used. Fourth, a positive control (e.g., a calorically restricted group) is highly desirable. Fifth, drug dosages should be chosen based on surrogate endpoints or accepted cross-species scaling factors. These procedures should improve the reliability of the scientific literature and accelerate the identification of longevity and health span-enhancing agents.

Flavonoids, cognition, and dementia: actions, mechanisms, and potential therapeutic utility for Alzheimer disease

There is increasing evidence that the consumption of flavonoid-rich foods can beneficially influence normal cognitive function. In addition, a growing number of flavonoids have been shown to inhibit the development of Alzheimer disease (AD)-like pathology and to reverse deficits in cognition in rodent models, suggestive of potential therapeutic utility in dementia. The actions of flavonoid-rich foods (e.g., green tea, blueberry, and cocoa) seem to be mediated by the direct interactions of absorbed flavonoids and their metabolites with a number of cellular and molecular targets. For example, their specific interactions within the ERK and PI3-kinase/Akt signaling pathways, at the level of receptors or kinases, have been shown to increase the expression of neuroprotective and neuromodulatory proteins and increase the number of, and strength of, connections between neurons. Concurrently, their effects on the vascular system may also lead to enhancements in cognitive performance through increased brain blood flow and an ability to initiate neurogenesis in the hippocampus. Additional mechanisms have been suggested for the ability of flavonoids to delay the initiation of and/or slow the progression of AD-like pathology and related neurodegenerative disorders, including a potential to inhibit neuronal apoptosis triggered by neurotoxic species (e.g., oxidative stress and neuroinflammation) or disrupt amyloid β aggregation and effects on amyloid precursor protein processing through the inhibition of β-secretase (BACE-1) and/or activation of α-secretase (ADAM10). Together, these processes act to maintain the number and quality of synaptic connections in key brain regions and thus flavonoids have the potential to prevent the progression of neurodegenerative pathologies and to promote cognitive performance.

The neuroprotective potential of flavonoids: a multiplicity of effects

Flavonoids exert a multiplicity of neuroprotective actions within the brain, including a potential to protect neurons against injury induced by neurotoxins, an ability to suppress neuroinflammation, and the potential to promote memory, learning and cognitive function. These effects appear to be underpinned by two common processes. Firstly, they interact with critical protein and lipid kinase signalling cascades in the brain leading to an inhibition of apoptosis triggered by neurotoxic species and to a promotion of neuronal survival and synaptic plasticity. Secondly, they induce beneficial effects on the vascular system leading to changes in cerebrovascular blood flow capable of causing angiogenesis, neurogenesis and changes in neuronal morphology. Through these mechanisms, the consumption of flavonoid-rich foods throughout life holds the potential to limit neurodegeneration and to prevent or reverse age-dependent loses in cognitive performance. The intense interest in the development of drugs capable of enhancing brain function means that flavonoids may represent important precursor molecules in the quest to develop of a new generation of brain enhancing drugs.

Gingko biloba extract inhibits oxidative stress and ameliorates impaired glial fibrillary acidic protein expression, but can not improve spatial learning in offspring from hyperhomocysteinemic rat dams

We aimed to study the effects of gingko biloba extract (EGb) on oxidative stress, astrocyte maturation and cognitive disfunction in offspring of hyperhomocysteinemic rats. Hyperhomocysteinemia was induced in the pregnant rats by administration of methionine (1 gr/kg body weight) dissolved in drinking water throughout pregnancy. One group of animals has received same amount of methionine plus 100 mg/kg/day EGb during pregnancy. On the postnatal day 1, half of the pups from all groups were sacrificed to study the lipid peroxidation (LPO) in different subfractions of brain. Other half of pups were tested in Morris water maze to assess differences in learning and memory performance at the 75 days of age. Maternal hyperhomocysteinemia significantly increased LPO levels especially in mitochondrial subfraction of fetal pup brains. EGb significantly prevented this LPO inrease. Methionine administration to animals reduced glial fibrillary acidic protein (GFAP) expression in pup brains significantly. EGb administration improved GFAP expression significantly. Offspring of hyperhomocysteinemic animals had poor long term spatial memory performance on Morris water maze and EGb administration had no effect on impaired spatial memory. In conclusion, maternally induced hyperhomocysteinemia significantly increased oxidative stress, decreased expression of GFAP and impaired learning performance.

The facilitative effects of bilobalide, a unique constituent of Ginkgo biloba, on synaptic transmission and plasticity in hippocampal subfields

Bilobalide, a unique constituent of Ginkgo biloba, has been reported to potentiate population spikes in hippocampal CA1 pyramidal cells and to protect the brain against cell death. In this study, the effects of bilobalide on synaptic transmission and its plasticity in rat hippocampal subfields were electrophysiologically investigated. Bilobalide (50 μM) significantly potentiated the input-output relationship at Schaffer collateral (SC)-CA1 synapses but not at medial perforant path (MPP)-dentate gyrus (DG), lateral perforant path (LPP)-DG, or mossy fiber (MF)-CA3 synapses. Facilitative effects of bilobalide on synaptic plasticity were only observed at MPP-DG synapses, in which the induction of long-term depression was blocked in the presence of bilobalide. However, no effect on synaptic plasticity was observed at SC-CA1 synapses. These results suggest that bilobalide has differential effects on synaptic efficacy in each hippocampal subfield.

Polyphenols and human health: prevention of disease and mechanisms of action

Polyphenols are found ubiquitously in plants and their regular consumption has been associated with a reduced risk of a number of chronic diseases, including cancer, cardiovascular disease (CVD) and neurodegenerative disorders. Rather than exerting direct antioxidant effects, the mechanisms by which polyphenols express these beneficial properties appear to involve their interaction with cellular signaling pathways and related machinery that mediate cell function under both normal and pathological conditions. We illustrate that their interactions with two such pathways, the MAP kinase (ERK, JNK, p38) and PI3 kinase/Akt signaling cascades, allow them to impact upon normal and abnormal cell function, thus influencing the cellular processes involved in the initiation and progression of cancer, CVD and neurodegeneration. For example, their ability to activate ERK in neurons leads to a promotion of neuronal survival and cognitive enhancements, both of which influence the progression of Alzheimer’s disease, whilst ERK activation by polyphenols in vascular endothelial cells influences nitric oxide production, blood pressure and ultimately CVD risk. The main focus of this review is to provide an overview of the role that polyphenols play in the prevention of cancer, cardiovascular disease and neurodegeneration. We present epidemiological data, human intervention study findings, as well as animal and in vitro studies in support of these actions and in each case we consider how their actions at the cellular level may underpin their physiological effects.

Effects of Ginkgo biloba extract on promotion of neurogenesis in the hippocampal dentate gyrus in C57BL/6 mice

Ginkgo biloba leaf extract (Gb) has been known to improve blood flow and preclude the tissue from free radical damage. Effects of Gb were examined by using Ki67, a specific proliferative marker for cellular proliferation, and doublecortin (DCX), a marker for immature neurons, indicating degree of neuroblast differentiation in the hippocampal dentate gyrus (DG) of adult C57BL/6 mice. The mice were fed with Gb at 40 and 100 mg/kg once daily for 28 days. The increase of Ki67- and DCX-immunoreactive cells in the DG was increased in a dose-dependent manner. Especially, the group having 100 mg/kg Gb showed a significant increase of DCX-immunoreactive neuroblasts with well-developed tertiary dendrites. Expression of DCX protein in the Gb groups was also significantly increased upon compared with the vehicle group. The results suggested that repeated intake of Gb would enhance cell proliferation and neuroblast differentiation in the mouse DG.

Caloric restriction: from soup to nuts

Caloric restriction (CR), reduced protein, methionine, or tryptophan diets; and reduced insulin and/or IGFI intracellular signaling can extend mean and/or maximum lifespan and delay deleterious age-related physiological changes in animals. Mice and flies can shift readily between the control and CR physiological states, even at older ages. Many health benefits are induced by even brief periods of CR in flies, rodents, monkeys, and humans. In humans and nonhuman primates, CR produces most of the physiologic, hematologic, hormonal, and biochemical changes it produces in other animals. In primates, CR provides protection from type 2 diabetes, cardiovascular and cerebral vascular diseases, immunological decline, malignancy, hepatotoxicity, liver fibrosis and failure, sarcopenia, inflammation, and DNA damage. It also enhances muscle mitochondrial biogenesis, affords neuroprotection; and extends mean and maximum lifespan. CR rapidly induces antineoplastic effects in mice. Most claims of lifespan extension in rodents by drugs or nutrients are confounded by CR effects. Transcription factors and co-activators involved in the regulation of mitochondrial biogenesis and energy metabolism, including SirT1, PGC-1alpha, AMPK and TOR may be involved in the lifespan effects of CR. Paradoxically, low body weight in middle aged and elderly humans is associated with increased mortality. Thus, enhancement of human longevity may require pharmaceutical interventions.

Understanding the molecular basis of Alzheimer's disease using a Caenorhabditis elegans model system

Alzheimer's disease (AD) is the major cause of dementia in the United States. At the cellular level, the brains of AD patients are characterized by extracellular dense plaques and intracellular neurofibrillary tangles whose major components are the beta-amyloid peptide and tau, respectively. The beta-amyloid peptide is a cleavage product of the amyloid precursor protein (APP); mutations in APP have been correlated with a small number of cases of familial Alzheimer's disease. APP is the canonical member of the APP family, whose functions remain unclear. The nematode Caenorhabditis elegans, one of the premier genetic workhorses, is being used in a variety of ways to address the functions of APP and determine how the beta-amyloid peptide and tau can induce toxicity. First, the function of the C. elegans APP-related gene, apl-1, is being examined. Although different organisms may use APP and related proteins, such as APL-1, in different functional contexts, the pathways in which they function and the molecules with which they interact are usually conserved. Second, components of the gamma-secretase complex and their respective functions are being revealed through genetic analyses in C. elegans. Third, to address questions of toxicity, onset of degeneration, and protective mechanisms, different human beta-amyloid peptide and tau variants are being introduced into C. elegans and the resultant transgenic lines examined. Here, we summarize how a simple system such as C. elegans can be used as a model to understand APP function and suppression of beta-amyloid peptide and tau toxicity in higher organisms.

The extract of Ginkgo biloba EGb 761 reactivates a juvenile profile in the skeletal muscle of sarcopenic rats by transcriptional reprogramming

Background

Sarcopenia is a major public health problem in industrialized nations, placing an increasing burden on public healthcare systems because the loss of skeletal muscle mass and strength that characterizes this affection increases the dependence and the risk of injury caused by sudden falls in elderly people. Albeit exercise and caloric restriction improve sarcopenia-associated decline of the muscular performances, a more suitable and focused pharmacological treatment is still lacking.

Methodology/Principal Findings

In order to evaluate such a possible treatment, we investigated the effects of EGb 761, a Ginkgo biloba extract used in chronic age-dependent neurological disorders, on the function of the soleus muscle in aged rats. EGb 761 induced a gain in muscular mass that was associated with an improvement of the muscular performances as assessed by biochemical and electrophysiological tests. DNA microarray analysis shows that these modifications are accompanied by the transcriptional reprogramming of genes related to myogenesis through the TGFβ signaling pathway and to energy production via fatty acids and glucose oxidation. EGb 761 restored a more juvenile gene expression pattern by regenerating the aged muscle and reversing the age-related metabolic shift from lipids to glucose utilization.

Conclusions/Significance

Thus, EGb 761 may represent a novel treatment for sarcopenia both more manageable and less cumbersome than exercise and caloric restriction.

Flavonoids and cognition: the molecular mechanisms underlying their behavioural effects

Evidence suggests that a group of phytochemicals known as flavonoids are highly effective in reversing age-related declines in neuro-cognitive performance through their ability to interact with the cellular and molecular architecture of the brain responsible for memory and by reducing neuronal loss due to neurodegenerative processes. In particular, they may increase the number of, and strength of, connections between neurons, via their specific interactions with the ERK and Akt signalling pathways, leading to an increase in neurotrophins such as BDNF. Concurrently, their effects on the peripheral and cerebral vascular system may also lead to enhancements in cognitive performance through increased brain blood flow and an ability to initiate neurogenesis in the hippocampus. Finally, they have also been shown to reduce neuronal damage and losses induced by various neurotoxic species and neuroinflammation. Together, these processes act to maintain the number and quality of synaptic connections in the brain, a factor known to be essential for efficient LTP, synaptic plasticity and ultimately the efficient working of memory.

The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

Emerging evidence suggests that a group of dietary-derived phytochemicals known as flavonoids are able to induce improvements in memory, learning and cognition. Flavonoids have been shown to modulate critical neuronal signalling pathways involved in processes of memory, and therefore are likely to affect synaptic plasticity and long-term potentiation mechanisms, widely considered to provide a basis for memory. Animal dietary supplementation studies have further shown that flavonoid-rich foods are able to reverse age-related spatial memory and spatial learning impairments. A more accurate understanding of how a particular spatial memory task works and of which aspects of memory and learning can be assessed in each case, are necessary for a correct interpretation of data relating to diet-cognition experiments. Further understanding of how specific behavioural tasks relate to the functioning of hippocampal circuitry during learning processes might be also elucidative of the specific observed memory improvements. The overall goal of this review is to give an overview of how the hippocampal circuitry operates as a memory system during behavioural tasks, which we believe will provide a new insight into the underlying mechanisms of the action of flavonoids on cognition.

Regional distribution of Ginkgo biloba-induced c-Fos immunoreactivity

A growing literature supports the notion that Ginkgo biloba has cognitive enhancing and anxiolytic properties; however, its effects on neuronal populations have yet to be characterized. The present study used c-Fos immunoreactivity (Fos-IR) to characterize functional activity in selected brain regions following administration of a standardized Ginkgo biloba extract. Because Ginkgo is typically consumed orally, Exp 1 sought to identify patterns of neural activity induced by oral administration. To ensure that the alterations in functional neural activity observed in Exp 1 were not simply due to novel gustatory experience, Exp 2 characterized patterns of Fos-IR following intraperitoneal administration of Ginkgo. Rats were habituated to handling and experimental conditions. In Exp 1, rats self-administered 150 mg/kg Ginkgo or vehicle alone (strawberry jam) orally. In Exp 2, rats were injected with Ginkgo (2.5 or 25 mg/kg, i.p.) or vehicle (0.3% gum Arabic). Animals were anaesthetized and perfused transcardially. Brains were sectioned, immunostained using a c-Fos antibody, then the number of labelled cells was quantified microscopically in selected brain regions. In both experiments Ginkgo increased Fos-IR in numerous brain regions including the insular cortex and amygdala. Intraperitoneal administration induced Fos-IR in some additional regions including the nucleus accumbens and dentate gyrus. Results provide important preliminary data serving to identify several candidate neural sites involved in the cognitive enhancing and anxiolytic effects of Ginkgo biloba.

Modulation of in vivo oxidative status by exogenous corticosterone and restraint stress in rats

Physical and psychological stressors not only enhance activity of the hypothalamo-pituitary-adrenocortical axis, but also cause oxidative damage by inducing an imbalance between the in vivo pro-oxidant and antioxidant status. The involvement of adrenal steroid stress hormones in oxidative damage associated with these stressors has not been extensively investigated. Therefore, this study was designed to probe any direct role of glucocorticoids on induction of oxidative processes by comparing the effects of low, intermediate and high doses of exogenously administered corticosterone, without other applied stressors, on a wide range of key components of the antioxidant defence system. The data presented here indicate a substantial decline in antioxidant defences by actions of corticosterone, evidenced by coordinate decreases in the activities in the brain, liver and heart of free-radical scavenging enzymes superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and glutathione reductase (GR), as well as the non-enzymatic antioxidants glutathione (GSH) and serum urate. Also, lipid peroxidation and protein carbonyl contents, oxidative stress markers, were found to be significantly increased in brain, liver and heart. The compromised in vivo antioxidant status was strikingly analogous to the deleterious effects of restraint stress, indicating a direct effect of stress hormones on induction of oxidative damage during physical or psychological stress. A dose-dependent decrease of SOD and CAT, and increase in protein oxidation was observed between the high (40 mg/kg) and low (10 mg/kg) doses of corticosterone. The findings have fundamental implications for oxidative stress as a major pathological mechanism in the maladaptation to chronic stress. Thus, the study suggests that stress hormones have a causal role in impacting oxidative processes induced during the adaptive response. This may hold important implications for pharmacological interventions targeting cellular antioxidants as a promising strategy for protecting against oxidative insults in various psychiatric and non-psychiatric conditions induced by physical or psychological stress.

Chronic administration of a Ginkgo biloba leaf extract facilitates acquisition but not performance of a working memory task

RATIONALE

Ginkgo biloba leaf extracts have been shown to improve learning and memory when administered chronically prior to the learning phase. However, the influence of Ginkgo on learning without prior chronic treatment and on memory per se (i.e., post-training administration) is less clear. Thus, experiment 1 investigated the influence of Ginkgo on acquisition, and experiment 2 examined the acute and chronic effects of Ginkgo on memory in rats using a food-reinforced two-component double Y-maze task.

MATERIALS AND METHODS

In experiment 1, 17 rats were treated daily with a standardized G. biloba extract (13.75 mg/kg, i.p.) or vehicle 30 min prior to daily maze training for 14 days. In experiment 2, 12 rats received 24 training trials daily, then received Ginkgo (0, 0.25, 2.5, 13.75, or 25 mg/kg, i.p.) 30 min prior to each test session. Subsequently, the same rats received daily injections of either Ginkgo (13.75 mg/kg, i.p.) or its vehicle. Memory was tested after 10 and 20 days of drug treatment, once under the influence of the drug and once in a drug-free state.

RESULTS

In experiment 1, Ginkgo-treated rats reached the training criteria significantly faster and made fewer errors. In experiment 2, post-training Ginkgo administration did not enhance memory.

DISCUSSION

Taken together, results demonstrate that repeated daily pre-session Ginkgo injection subtly facilitates acquisition of a spatial working memory task, but neither acute nor chronic post-training exposure enhances spatial working memory. We conclude that ongoing Ginkgo administration does not offer any continued beneficial effects in an already-learned working memory task.

Preventive action of Ginkgo biloba in stress- and corticosterone-induced impairment of spatial memory in rats

In this study, we tested preventive effects of a natural medicine the extract of Ginkgo biloba (EGB 761) on post-stress cognitive dysfunction. Exposure to chronic restraint stress in rats and psychosocial stress in humans has been shown to alter cognitive functions such as learning and memory and have been linked to the pathophysiology of mood and anxiety disorders. Our findings indicate that chronic restraint stress impaired egocentric spatial memory as observed in the eight-arm radial maze but it did not alter the allocentric spatial memory in the Morris water maze. In control rats EGB 761 (100mg/kg, orally) improved spatial memory in these two tests. Also, EGB 761 normalized cognitive deficits seen in rats chronically stressed or treated with an 'equivalent' dose of exogenous corticosterone (5mg/kg, subcutaneously). We conclude that, in rats, repeated administration of EGB 761 prevents stress- and corticosterone-induced impairments of spatial memory.

Multifaceted therapeutic benefits of Ginkgo biloba L.: chemistry, efficacy, safety, and uses

The new age of nutraceuticals is now embracing the centuries old herbal extract of Ginkgo biloba (Mantissa Plantarum Altera, 1771, Ginkgoceae). The standardized preparation of the Ginkgo leaf extract (EGb 761) contained 2 main bioactive constituents, flavonoid glycosides (24%) and terpene lactones (6%), along with less than 5 ppm of the allergenic component, ginkgolic acid. The Ginkgo leaf extract has been reported to have neuroprotective, anticancer, cardioprotective, stress alleviating, and memory enhancing effects and possible effects on tinnitus, geriatric complaints, and psychiatric disorders. The therapeutic mechanisms of action of the Ginkgo leaf extract are suggested to be through its antioxidant, antiplatelet, antihypoxic, antiedemic, hemorrheologic, and microcirculatory actions, where the flavonoid and the terpenoid constituents may act in a complementary manner. Toxicity studies show that the Ginkgo leaf extract is relatively safe for consumption, although a few side effects have been reported, that is, intracerebral hemorrhage, gastrointestinal disturbances, headaches, dizziness, and allergic skin reactions. The use of Ginkgo leaf extract may be promising for treatment of certain conditions, although its long-term use still needs to be evaluated.

Ginkgo biloba extract EGb 761 and Wisconsin Ginseng delay sarcopenia in Caenorhabditis elegans

Previously we reported that the standardized Ginkgo biloba extract EGb 761 extended life span and increased stress resistance in Caenorhabditis elegans. In this study, pharmacological modulation of age-dependent muscle degeneration, or sarcopenia, was determined. Transgenic C. elegans strain (PD4251) expressing green fluorescent protein (GFP)-MYO-3, localized in body wall muscles and vulval muscle nuclei, were fed with EGb 761 or Wisconsin Ginseng, and muscle integrity was analyzed by quantification of GFP fluorescence. Both EGb 761 and Wisconsin Ginseng significantly delayed sarcopenia. Ginseng was more effective in worms of more advanced age, which is consistent with the ultrastructural changes observed by transmission electron microscopy. Furthermore, both agents ameliorated age-associated decline of locomotive behaviors including locomotion, body bend, and pharyngeal pumping. These results suggest that pharmacological extension of life span is a consequence of maintaining functional capacity of the tissue, and that C. elegans is a valid model system for testing therapeutic intervention for delaying the progress of sarcopenia.

Ginkgo biloba leave extract: biological, medicinal, and toxicological effects

Ginkgo biloba leave extract is among the most widely sold herbal dietary supplements in the United States. Its purported biological effects include: scavenging free radical; lowering oxidative stress; reducing neural damages, reducing platelets aggregation; anti-inflammation; anti-tumor activities; and anti-aging. Clinically, it has been prescribed to treat CNS disorders such as Alzheimer's disease and cognitive deficits. It exerts allergy and changes in bleeding time. While its mutagenicity or carcinogenic activity has not been reported, its components, quercetin, kaempferol and rutin have been shown to be genotoxic. There are no standards or guidelines regulating the constituent components of Ginkgo biloba leave extract nor are exposure limits imposed. Safety evaluation of Ginkgo biloba leave extract is being conducted by the U.S. National Toxicology Program.

Stress and ageing interactions: A paradox in the context of shared etiological and physiopathological processes

Gerontology has made considerable progress in the understanding of the mechanisms underlying the ageing process and age-related neurodegenerative disorders. However, ways to improve quality of life in the elderly remain to be elucidated. It is now clear that stress and the ageing process share a number of underlying mechanisms bound in a very close, if not indissociable, relationship. The ageing process is regulated by the factors underlying the ability to adjust to stress, whilst stress has an influence on the life span and the quality of ageing. In addition, the ability to cope with stress in adulthood predicts life expectancy and quality of life at senescence. The ageing process and stress also share several common mechanisms, particularly in relation to the energy factor. Stress consumes energy and ageing may be considered as a cost of the energy expended to deal with the stressors to which the body is exposed throughout its lifetime. This suggests that the ageing process is associated with and/or a consequence of a long-lasting activation of the major stress responsive systems. However, despite common features, the interaction between stress and the ageing process gives rise to some paradoxes. Stress can either diminish or exacerbate the ageing process just as the ageing process can worsen or counter the effects of stress. There has been little attempt to understand how ageing and stress might interact to promote "successful" or pathological ageing. A key factor in this respect is the individual's ability to adapt to stress. Viewed from this angle, the quality of life of aged subjects may be improved through therapy designed to improve the tolerance to stress.

Ginkgo biloba extract improves spatial memory in rats mainly but not exclusively via a histaminergic mechanism

In order to clarify the mechanism of Ginkgo biloba extract (GBE) on learning and memory, we studied the effect of GBE on spatial memory deficits induced by diphenhydramine, pyrilamine and scopolamine using the eight-arm radial maze performance of rats, in comparison with donepezil. Total error (TE), reference memory error (RME) and working memory error (WME) were used as indices of spatial memory deficits. Both GBE and donepezil caused a potent antagonistic effect on the increase in TE, RME and WME induced by diphenhydramine. GBE and donepezil also antagonized scopolamine-induced spatial memory deficits. Although the antagonistic effect of GBE on pyrilamine-induced spatial memory deficits was weak, a significant difference was observed with TE and WME. However, donepezil caused no antagonistic effect on pyrilamine-induced memory deficits. From these findings, we concluded that the effects of GBE are mainly contributable to cholinergic activity and perhaps partly due to a histaminergic mechanism.

The in vivo synaptic plasticity mechanism of EGb 761-induced enhancement of spatial learning and memory in aged rats

It has not been uniform to date that the Ginkgo biloba extracts enhance cognitive function in aged animals, and the mechanisms of action remain difficult to elucidate. In this study, the Morris water maze task and electrophysiological methods were used to study the effects of repeated daily administration of EGb 761, a standardized extract from G. biloba leaves, on hippocampal-dependent spatial learning and memory and synaptic plasticity of aged rats. The adult subjects perform the Morris water maze task better than aged rats, as a cellular mechanism, the hippocampal long-term potentiation (LTP) elicited from adult animals is robust (139.29+/-2.7%). In addition, the spatial learning and memory of aged rats that had been fed on an EGb 761-supplemented diet (60 mg kg(-1)) for 30 days were significantly better than those of control aged rats. The magnitude of LTP (116.63+/-3.6%) recorded in vivo from the hippocampus CA1 area of aged rats was significantly enhanced by EGb 761 (60 mg kg(-1)). In conclusion, the spatial learning and memory of aged rats is worse than that of young subjects, and EGb 761, acting as a 'cognitive enhancer', has benefit on synaptic plasticity and cognition in aged rats. The present data further confirmed that enhancement of synaptic plasticity of the hippocampus might ameliorate the deficit in spatial learning and memory in aged rats.

Improvement of leukocyte functions in prematurely aging mice after five weeks of diet supplementation with polyphenol-rich cereals

OBJECTIVE

We investigated the beneficial effects of diet supplementation with two types of cereals naturally rich in polyphenolic compounds on several functions of peritoneal leukocytes from prematurely aging mice (PAM).

METHODS

Two-hundred sixty healthy mice, 8 wk of age, were recruited and their behavioral responses were tested in a simple T-maze to identify PAM. Then the mice were fed a diet supplemented with 20% (wt/wt) of two different cereal fractions, named B (wheat germ) and C (buckwheat flour), rich in polyphenols (gallic acid, catechin, p-hydroxybenzoic acid, vanillic acid, p-coumaric acid, sinapic acid, ferulic acid, quercetin, and rutin), or a standard diet (controls) for 5 wk. Several parameters of innate (adherence to tissues, chemotaxis, phagocytosis, microbicidal capacity, and natural killer activity) and acquired immune (lymphoproliferation and interleukin-2 release) responses were measured.

RESULTS

The PAM control group showed worse immune functions (P < 0.001 to 0.05) compared with the non-PAM control group. The PAM group that received cereal B showed increases in phagocytosis (P < 0.01), microbicidal activity (P < 0.001 to 0.01), natural killer activity (P < 0.001) and lymphoproliferation in response to lipopolysaccharide (P < 0.01) and interleukin-2 release (P < 0.001), and the PAM group that received cereal C showed a similar pattern, with increases in macrophage chemotaxis (P < 0.01), phagocytosis (P < 0.01), microbicidal activity (P < 0.001 to 0.01), natural killer activity (P < 0.01), lymphoproliferative response to concanavalin A and lipopolysaccharide (P < 0.001), and interleukin-2 release (P < 0.001).

CONCLUSIONS

Dietary supplementation with polyphenol-rich cereals appears to have a protective effect on immune cell functions in mice with premature senescence. Thus, regular intake of these compounds could delay normal aging and improve quality of life.

Effects of Ginkgo biloba administered after spatial learning on water maze and radial arm maze performance in young adult rats

Ginkgo biloba is reported to improve learning and memory in animals. However, many studies do not directly test the effects of Ginkgo on memory because the drug is administered during the learning phase of the experiments. In this study, we examined the effect of 10 mg/kg, 20 mg/kg, or 40 mg/kg G. biloba extract on spatial memory by administering the drug in the interval between training and testing. Rats were tested for long-term reference memory retention in the radial arm maze and in the Morris water maze during daily probe trials in which the hidden platform was removed. G. biloba had no effect on reference memory in either the water maze or radial arm maze. To test short-term working spatial memory using the radial arm maze, animals were removed after receiving the reward from 4 of the 8 arms and were returned to complete the maze 2 h later. While Ginkgo had no effect on working memory, over time animals exposed to Ginkgo learned task better than control animals. Thus, Ginkgo appears to enhance neither short-term working memory nor long-term reference memory, but it may promote learning of spatial information.

Alzheimer's disease, the nematode Caenorhabditis elegans, and ginkgo biloba leaf extract

Alzheimer's disease (AD) is affecting larger and larger proportions of our population as lifespan increases. Thus, the means to prevent or reduce the rate of this disorder is a high priority for medical research. A standardized extract of Ginkgo biloba leaves EGb 761 is a popular dietary supplement taken by the general public to enhance mental focus and by the elderly to delay onset of age-related loss of cognitive function. EGb 761 has been used for treatment of certain cerebral dysfunctions and dementias associated with aging and AD. Substantial evidence indicates that EGb 761 has neuroprotective effects. But, mechanisms of action of the components of the extract are, unfortunately, poorly understood. Research in my laboratory focuses on understanding mechanisms of action of the components of the herbal extract EGb 761 in protection against Alzheimer's disease. We have demonstrated that EGb 761 inhibited amyloid beta aggregation in vitro and attenuates reactive oxidative species (ROS) in a model organism - the round worm Caenorhabditis elegans. Furthermore, EGb 761 eased its toxicity in the transgenic C. elegans. We also found that only a certain size of the amyloid beta aggregates is toxic to the worms. These findings suggest that EGb 761 has a clear therapeutic potential for prevention and/or treatment of AD. A better understanding of the mechanisms of neuroprotection by EGb 761 will be important for designing therapeutic strategies, for basic understanding of the underlying neurodegenerative processes, and for a better understanding of the effectiveness and complexity of this herbal medicine.

Extract of Ginkgo biloba leaves reverses yohimbine-induced spatial working memory deficit in rats

Extract of Ginkgo biloba is used to alleviate age-related decline in cognitive function, which may be associated with the loss of catecholamines in the prefrontal cortex. The purpose of this study was to verify whether alpha-2 adrenergic activity is involved in the facilitative effects of extract of Ginkgo biloba on prefrontal cognitive function. Male Wistar rats were trained to reach criterion in the delayed alternation task (0, 25, and 50-s delay intervals). A pilot study found that 3 or 4 mg/kg of yohimbine (intraperitoneal) reduced the choice accuracy of the delayed alternation task in a dose and delay-dependent manner, without influencing motor ability or perseverative behaviour. Acute oral pre-treatment with doses of 50, 100, or 200 mg/kg (but not 25 mg/kg) of extract of Ginkgo biloba prevented the reduction in choice accuracy induced by 4 mg/kg yohimbine. These data suggest that the prefrontal cognition-enhancing effects of extract of Ginkgo biloba are related to its actions on alpha-2-adrenoceptors.

Protective effects of Ginkgo biloba leaf extract on aluminum-induced brain dysfunction in rats

This study examined the protective effects of Ginkgo biloba extract (GbE) on the learning and memory function in aluminum-treated rats and potential mechanisms. Wistar rats were given daily aluminum chloride 500 mg/kg, i.g, for one month, followed by continuous exposure via the drinking water containing 1600 ppm aluminum chloride for up to 5 months. The ability of spatial learning and memory was tested by Morris water maze. Aluminum administration significantly increased escape latency and searching distance, indicative of brain dysfunction. GbE treatment (50-200 mg/kg, i.g) significantly protected against aluminum-induced brain dysfunction, as evidenced by decreased escape latency and searching distance compared with the Al alone group. To examine the mechanisms of the protection, the expressions of amyloid precursor protein (APP) and caspase-3 in brain regions were examined by immunohistochemistry. GbE treatment reduced the contents of APP and caspase-3 in hippocampus of aluminum-treated rats in a dose-dependent manner. At the highest dose of GbE (200 mg/kg), the immunostain for APP and caspase-3 was returned to normal levels. In summary, this study demonstrates that GbE is effective in improving the ability of spatial learning and memory of aluminum-intoxicated rats. This protection appears to be due to a decreased expression of APP and caspase-3 in rat brain, resulting in a decrease in the production of insoluble fragments of Abeta-amyloid.

Effects of ginkgo biloba extract on cation currents in rat ventricular myocytes

Ginkgo biloba extract (GBE), a valuable natural product for cerebral and cardiovascular diseases, is mainly composed of two classes of constituents: terpene lactones (e.g., ginkgolide A and B, bilobalide) and flavone glycosides (e.g., quercetin and kaempferol). Its electrophysiological action in heart is yet unclear. In the present study, using whole-cell patch clamp technique, we investigated electrophysiological effects of GBE on cation channel currents in ventricular myocytes isolated from rat hearts. We found that GBE 0.01-0.1% inhibited significantly the sodium current (I(Na)), L-type calcium current (I(Ca)) and transient outward potassium current (IK(to)) in a concentration-dependent manner. Surprisingly, its main ingredients, ginkgolide A (GB A), ginkgolide B (GB B) and bilobalide (GB BA) at 0.1 mM did not exhibit any significant effect on these cation channel currents. These results suggested that GBE is a potent non-selective cation channel modulator in cardiaomyocytes. Other constituents (rather than GB A, GB B and GB BA) might be responsible for the observed inhibitory effects of GBE on cation channels.

Effects of Ginkgo biloba extract (EGb 761) on hydroxyl radical-induced thymocyte apoptosis and on age-related thymic atrophy and peripheral immune dysfunctions in mice

In this study, the effect of EGb 761, a standard extract of Ginkgo biloba leaf, on thymocyte apoptosis and age-related thymic atrophy and on peripheral immune dysfunctions was investigated in mice. When primary culture of thymocytes was preincubated with 100 microg/ml EGb 761 before their exposure to hydroxyl radicals (*OH) generated by Fe(2+)-mediated Fenton reaction, apoptotic cell death induced by *OH was distinctly prevented as determined by DNA laddering, the TUNEL assay and flow cytometric analysis. Furthermore, oral EGb 761 administration (about 1.5 mg/day/mouse) for 60 consecutive days led to a significant thymic regrowth in 22-month-old mice as revealed by the increment of thymus weight and total numbers of thymocytes. Partial recovery of peripheral immune capacities such as mitogen responsiveness and NK cell activity were also found in the old mice after 60 days of EGb 761 supplementation. Taken together, our study indicates that in addition to its protective and rescuing abilities on neurodegenerative disorders and cardiovascular diseases, EGb 761 was also found active in the rejuvenation of degenerated thymus and accordingly the strengthening of the immune system. These beneficial effects of EGb 761 on immune system are based on its antioxidant properties as well as the cell proliferation-stimulating effect.

Ginkgo biloba promotes short-term retention of spatial memory in rats

This study examines possible interactions between exposure to Ginkgo biloba extract and enriched environments on the acquisition and retention of spatial learning following massed and spaced trials. After 4 weeks of exposure to either ginkgo or vehicle, 8-week-old rats were tested using a Morris Water Maze in either massed or spaced trials. While ginkgo did not have an effect on maze acquisition or long-term retention, it did promote short-term retention of spatial memory. Following reversal training, ginkgo promoted short-term retention for two groups but impaired retention for a third. These results suggest that ginkgo has powerful effects on short-term retention that vary with training conditions.

Expression of the small heat‐shock protein Hsp‐16‐2 inCaenorhabditis elegansis suppressed byGinkgo bilobaextract EGb 761

EGb 761, a standardized extract of Ginkgo biloba leaves, has been shown to have antioxidative properties. We have previously demonstrated that EGb 761 increases stress resistance and mean life span in the model organism Caenorhabditis elegans. In this study, the molecular mechanism of EGb 761 on alleviating effects of oxidative stress is further investigated using transgenic C. elegans expressing a jellyfish green fluorescent protein (GFP)-tagged inducible small heat-shock protein gene (hsp-16-2). The expression of hsp-16-2 induced by the pro-oxidant juglone and by heat shock was significantly suppressed by 86% and 33%, respectively, in the transgenic nematode fed with EGb 761. These effects of EGb 761 correlate with its ability to increase mean survival rate of the nematode in response to acute oxidative and thermal stresses, as well as to attenuate the basal levels of hydrogen peroxide in the organism. Thus, we interpret the suppression of hsp-16-2/GFP expression as an indication that EGb 761 decreases cellular stress resulting from exogenous treatments, therefore leading to a decreased transcriptional induction of the reporter transgene. These results support the hypothesis that EGb 761 augments the natural antistress system of C. elegans, thus increasing stress resistance and life span.

Ginkgo biloba extract: cognitive enhancer or antistress buffer

Constituents extracted from the leaves of the Ginkgo biloba tree possess beneficial properties that may buffer the aging nervous system from deterioration due to oxidative stress. In the present investigation, a standardized extract of G. biloba (EGb 761) or an equal volume of the vehicle was administered (100 mg/kg/day) to senescent (20-month) C57BL/6 male mice for up to 82 consecutive days. Animals were tested twice in the Morris water maze (MWM) after 28 and 70 days of treatment. No differences were observed in acquisition or retention of performance on the water maze. Elevated-plus maze (EPM) trials were conducted prior to and subsequent to the chronic treatment regimen. Marked baseline differences in plus-maze performance were present in the first experiment. A second experiment used a matched-pairs design to minimize preexisting differences. Results supported the hypothesis that EGb 761 may serve as an antistress buffer, attenuating the increase in anxiety typically observed in animals after cold water exposure. Tissue samples from the hippocampus and cortex were analyzed by Western blot for the transcription factor cyclic-AMP response element binding (CREB) protein. EGb 761 had no significant effect on immunoreactivity to CREB from either the hippocampus or the cerebral cortex.

Dietary flavonoids as potential neuroprotectants

There is an increasing awareness of the role of certain nutritional components, including dietary flavonoids found in fruit, vegetables and beverages, in the maintenance of health and prevention of chronic diseases. In this regard, recent studies highlight an exciting role with respect to their potential neuroprotective actions, in particular towards deficits commonly observed with aging, such as reduced performance of cognitive, memory and learning tasks. These neurological functions, and possible mechanisms involved in controlling them, can be influenced by supplementation of single dietary flavonoids, or as part of a flavonoid-rich preparation. With this, a renewed emphasis is aimed at further understanding their modes and sites of action. Moreover a common theme among many in vitro studies examining mechanisms of neuroprotection is the failure to include biologically relevant metabolites of the flavonoids known to enter the circulation, and thus most likely to be bioavailable to cells and tissues. This oversight will ultimately influence the mechanisms of action proposed to explain the neuroprotection observed in animals and human studies. As such, emerging findings suggest a variety of potential mechanisms of action of flavonoids and their bioavailable metabolites in cytoprotection against oxidative stress, which may be independent of conventional antioxidant reducing activities. Such mechanisms might involve their interaction with cell signalling cascades, their influence on gene expression and the down regulation of pathways leading to cell death.

Enhanced maze performance and reduced oxidative stress by combined extracts of zingiber officinale and ginkgo biloba in the aged rat

Here we assessed the effects of i.g. administration of Zingicomb (ZC), a mixture of zingiber officinale and ginkgo biloba extracts, on learning and memory, and on indicators of oxidative stress in aged rats. Effects of ZC (1 and 10 mg/kg) were investigated in 22-24 months old Wistar rats using the Morris water maze, in which they show deficient performance as compared to 3 months old rats in the undrugged state (days 1 and 2). Treatment was administered on days 3 and 4 of training, then over 7 days with training discontinued, and again on days 5 and 6 when training was resumed. Thereafter chronic treatment was maintained over 5 months. 1 mg/kg ZC improved escape learning in the water maze. The two capital indicators of oxidative stress in brain homogenates, the amount of oxidized proteins (assessed as carbonyl group containing proteins) and lipid peroxidation, were significantly reduced in ZC treated animals. Thus, ZC, which had previously been shown to improve inhibitory avoidance learning and to have anxiolytic properties in adult animals, might also facilitate spatial learning in aged animals, and reduces indices of oxidative stress in brain tissue after chronic treatment.