Flaubert Tchantchou

EGb 761 enhances adult hippocampal neurogenesis and phosphorylation of CREB in transgenic mouse model of Alzheimer’s disease

Standardized Ginkgo biloba extract EGb 761 exhibits beneficial effects to patients with Alzheimers disease (AD). It was previously demonstrated that EGb 761 inhibits amyloid beta (Aβ) oligomerization in vitro, protects neuronal cells against Aβ toxicity, and improves cognitive defects in a mouse model of AD (Tg 2576). In this study, the neurogenic potential of EGb 761 and its effect on cAMP response element binding protein (CREB) were examined in a double transgenic mouse model (TgAPP/PS1). EGb 761 significantly increases cell proliferation in the hippocampus of both young (6 months) and old (22 months) TgAPP/PS1 mice, and the total number of neuronal precursor cells in vitro in a dose‐dependent manner. Furthermore, Aβ oligomers inhibit phosphorylation of CREB and cell proliferation in the hippocampus of TgAPP/PS1 mice. Administration of EGb 761 reduces Aβ oligomers and restores CREB phosphorylation in the hippocampus of these mice. The present findings suggest that 1) enhanced neurogenesis by EGb 761 may be mediated by activation of CREB, 2) stimulation of neurogenesis by EGb 761 may contribute to its beneficial effects in AD patients and improved cognitive functions in the mouse model of AD, and 3) EGb 761 has therapeutic potential for the prevention and improved treatment of AD.—Tchantchou, F., Xu, Y., Wu, Y., Christen, Y., Luo, Y. EGb 761 enhances adult hippocampal neurogenesis and phosphorylation of CREB in transgenic mouse model of Alzheimers disease. FASEB J. 21, 2400–2408 (2007)

Stimulation of Neurogenesis and Synaptogenesis by Bilobalide and Quercetin via Common Final Pathway in Hippocampal Neurons

Loss of synapses has been correlated with dementia in Alzheimers disease (AD) as an early event during the disease progression. Hence, synaptogenesis and neurogenesis in adulthood could serve as a therapeutic target for the prevention and treatment of AD. Recently, we have demonstrated enhanced hippocampal neurogenesis by oral administration of Ginkgo biloba extract (EGb 761) to a mouse model of AD. This study aims to identify the constituents that contribute to EGb 761-induced neurogenesis. Among the constituents tested, bilobalide and quercetin significantly increased cell proliferation in the hippocampal neurons in a dose-dependent manner. Bilobalide and quercetin also enhanced phosphorylation of cyclic-AMP Response Element Binding Protein (CREB) in these cells, and elevated the levels of pCREB and, brain-derived neurotrophic factor in mice brain. Immunofluorescence staining of synaptic markers shows remarkable dendritic processes in hippocampal neurons treated with either quercetin or bilobalide. Furthermore, both constituents restored amyloid-beta oligomers (also known as ADDL)-induced synaptic loss and phosphorylation of CREB. The present findings suggest that enhanced neurogenesis and synaptogenesis by bilobalide and quercetin may share a common final signaling pathway mediated by phosphorylation of CREB. Despite a recent report showing that EGb 761 was insufficient in prevent dementia, its constituents still warrant future investigation.

Lithium Ameliorates Neurodegeneration, Suppresses Neuroinflammation, and Improves Behavioral Performance in a Mouse Model of Traumatic Brain Injury

Although traumatic brain injury (TBI) is recognized as one of the leading causes of death from trauma to the central nervous system (CNS), no known treatment effectively mitigates its effects. Lithium, a primary drug for the treatment of bipolar disorder, has been known to have neuroprotective effects in various neurodegenerative conditions such as stroke. Until this study, however, it has not been investigated as a post-insult treatment for TBI. To evaluate whether lithium could have beneficial effects following TBI, lithium at a dose of 1.5 mEq/kg was administered after injury. Assessed at 3 days and 3 weeks post-injury using hematoxylin and eosin staining, lithium treatment was found to reduce lesion volume. Lithium at doses of 2.0 and 3.0 mEq/kg also significantly reduced lesion volume at 3 days after injury, and the therapeutic window was at least 3 h post-injury. TBI-induced neuronal death, microglial activation, and cyclooxygenase-2 induction were all attenuated by lithium at 3 days after injury. In addition, lithium treatment reduced TBI-induced matrix metalloproteinase-9 expression and preserved the integrity of the blood-brain barrier. As for behavioral outcomes, lithium treatment reduced anxiety-like behavior in an open-field test, and improved short- and long-term motor coordination in rotarod and beam-walk tests. Lithium robustly increased serine phosphorylation of glycogen synthase kinase-3β (GSK-3β), suggesting that the underlying mechanisms responsible for lithiums protective effects are triggered by increasing phosphorylation of this kinase and thereby inhibiting its activity. Our results support the notion that lithium has heretofore unrecognized capacity to mitigate the neurodegenerative effects and improve functional outcomes in TBI.

S-Adenosylmethionine Mediates Glutathione Efficacy by Increasing Glutathione S-Transferase Activity: Implications for S-Adenosyl Methionine as A Neuroprotective Dietary Supplement

When maintained on a folate-deficient, iron-rich diet, transgenic mice lacking in apolipoprotein E (ApoE-/- mice) demonstrate impaired activity of glutathione S-transferase (GST), resulting in increased oxidative species within brain tissue despite abnormally high levels of glutathione. These mice also exhibit reduced levels of S-adenosyl methionine (SAM) and increased levels of its hydrolysis product S-adenosyl homocysteine, which inhibits SAM usage. Supplementation of the above diet with SAM restored GST activity and eliminated reactive oxygen species at the expense of stockpiled glutathione, suggesting that one or more SAM-dependent reactions were required to maintain GST activity. We examined herein the impact of SAM on GST activity using a cell-free assay. SAM stimulated GST activity in a dose-response manner when added to homogenates derived from the above ApoE-/- mice. SAM also increased activity of purified rat liver GST and recombinant GST. Filtering of SAM through a 4 kDa cutoff and systematic withholding of reaction components eliminated the possibility of any additional contaminating enzyme. These findings confirm that SAM can exert a direct effect on GST activity. Since Alzheimers disease is accompanied by reduced GST activity, diminished SAM and increased SAH, these findings underscore the critical role of SAM in maintenance of neuronal health.

Dietary and genetic compromise in folate availability reduces acetylcholine, cognitive performance and increases aggression: critical role of S-adenosyl methionine.

Folate deficiency has been associated with age-related neurodegeneration. One direct consequence of folate deficiency is a decline in the major methyl donor, S-adenosyl methionine (SAM). We demonstrate herein that pro-oxidant stress and dietary folate deficiency decreased levels of acetylcholine and impaired cognitive performance to various degrees in normal adult mice (9–12months of age, adult mice heterozygously lacking 5’,10’-methylene tetrahydrofolate reductase, homozygously lacking apolipoprotein E, or expressing human ApoE2, E3 or E4, and aged (2–2.5 year old) normal mice. Dietary supplementation with SAM in the absence of folate restored acetylcholine levels and cognitive performance to respective levels observed in the presence of folate. Increased aggressive behavior was observed among some but not all genotypes when maintained on the deficient diet, and was eliminated in all cases supplementation with SAM. Folate deficiency decreased levels of choline and N-methyl nicotinamine, while dietary supplementation with SAM increased methylation of nicotinamide to generate N-methyl nicotinamide and restored choline levels within brain tissue. Since N-methyl nicotinamide inhibits choline transport out of the central nervous system, and choline is utilized as an alternative methyl donor, these latter findings suggest that SAM may maintain acetylcholine levels in part by maintaining availability of choline. These findings suggest that dietary supplementation with SAM represents a useful therapeutic approach for age-related neurodegeneration which may augment pharmacological approaches to maintain acetylcholine levels, in particular during dietary or genetic compromise in folate usage.

Selective Inhibition of Alpha/Beta-Hydrolase Domain 6 Attenuates Neurodegeneration, Alleviates Blood Brain Barrier Breakdown, and Improves Functional Recovery in a Mouse Model of Traumatic Brain Injury

2-arachidonylglycerol (2-AG) is the most abundant endocannabinoid in the central nervous system and is elevated after brain injury. Because of its rapid hydrolysis, however, the compensatory and neuroprotective effect of 2-AG is short-lived. Although inhibition of monoacylglycerol lipase, a principal enzyme for 2-AG degradation, causes a robust increase of brain levels of 2-AG, it also leads to cannabinoid receptor desensitization and behavioral tolerance. Alpha/beta hydrolase domain 6 (ABHD6) is a novel 2-AG hydrolytic enzyme that accounts for a small portion of 2-AG hydrolysis, but its inhibition is believed to elevate the levels of 2-AG within the therapeutic window without causing side effect. Using a mouse model of traumatic brain injury (TBI), we found that post-insult chronic treatment with a selective ABHD6 inhibitor WWL70 improved motor coordination and working memory performance. WWL70 treatment reduced lesion volume in the cortex and neurodegeneration in the dendate gyrus. It also suppressed the expression of inducible nitric oxide synthase and cyclooxygenase-2 and enhanced the expression of arginase-1 in the ipsilateral cortex at 3 and 7 days post-TBI, suggesting microglia/macrophages shifted from M1 to M2 phenotypes after treatment. The blood-brain barrier dysfunction at 3 and 7 days post-TBI was dramatically reduced. Furthermore, the beneficial effects of WWL70 involved up-regulation and activation of cannabinoid type 1 and type 2 receptors and were attributable to the phosphorylation of the extracellular signal regulated kinase and the serine/threonine protein kinase AKT. This study indicates that the fine-tuning of 2-AG signaling by modulating ABHD6 activity can exert anti-inflammatory and neuroprotective effects in TBI.

Increased transcription and activity of glutathione synthase in response to deficiencies in folate, vitamin E, and apolipoprotein E

Oxidative stress is a major contributing factor in neurodegeneration and can arise from dietary, environmental, and genetic sources. Here we examine the separate and combined impact of deprivation of folate and vitamin E, coupled with dietary iron as a prooxidant, on normal mice and transgenic mice lacking apolipoprotein E (ApoE–/– mice). Both mouse strains exhibited increased levels of glutathione when deprived of folate and vitamin E, but a substantial further increase was observed in ApoE–/– mice. To determine the mechanism(s) underlying this increase, we quantified transcription and activity of glutathione synthase (GS). Both normal and ApoE–/– mice demonstrated increased GS activity when deprived of folate and vitamin E. However, transcription was increased only in ApoE–/– mice deprived of folate and vitamin E. These findings demonstrate that deficiency in one gene can result in compensatory up‐regulation in a second relevant gene and, furthermore, indicate that compensation for oxidative stress can occur in brain tissue at epigenetic and genetic levels depending on the nature and/or extent of oxidative stress.

The fatty acid amide hydrolase inhibitor PF-3845 promotes neuronal survival, attenuates inflammation and improves functional recovery in mice with traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death in young adults in the United States, but there is still no effective agent for treatment. N-arachidonoylethanolamine (anandamide, AEA) is a major endocannabinoid in the brain. Its increase after brain injury is believed to be protective. However, the compensatory role of AEA is transient due to its rapid hydrolysis by the fatty acid amide hydrolase (FAAH). Thus, inhibition of FAAH can boost the endogenous levels of AEA and prolong its protective effect. Using a TBI mouse model, we found that post-injury chronic treatment with PF3845, a selective and potent FAAH inhibitor, reversed TBI-induced impairments in fine motor movement, hippocampus dependent working memory and anxiety-like behavior. Treatment with PF3845 inactivated FAAH activity and enhanced the AEA levels in the brain. It reduced neurodegeneration in the dentate gyrus, and up-regulated the expression of Bcl-2 and Hsp70/72 in both cortex and hippocampus. PF3845 also suppressed the increased production of amyloid precursor protein, prevented dendritic loss and restored the levels of synaptophysin in the ipsilateral dentate gyrus. Furthermore, PF3845 suppressed the expression of inducible nitric oxide synthase and cyclooxygenase-2 and enhanced the expression of arginase-1 post-TBI, suggesting a shift of microglia/macrophages from M1 to M2 phenotype. The effects of PF3845 on TBI-induced behavioral deficits and neurodegeneration were mediated by activation of cannabinoid type 1 and 2 receptors and might be attributable to the phosphorylation of ERK1/2 and AKT. These results suggest that selective inhibition of FAAH is likely to be beneficial for TBI treatment.

N-acteyl cysteine alleviates oxidative damage to central nervous system of ApoE-deficient mice following folate and vitamin E-deficiency

Oxidative stress is an early neurodegenerative insult in Alzheimers disease (AD). Antioxidant mechanisms, including elements of the glutathione (GSH) pathway, undergo at least a transient compensatory increase that is apparently insufficient due to continued oxidative damage during disease progression. Mice deficient in apolipoprotein E, which provide a model for some aspects of AD, undergo increased oxidative damage to brain tissue and cognitive decline when maintained on a folate-free diet, despite a compensatory increase in glutathione synthase transcription and activity as well as increased levels of GSH. Dietary supplementation with N-acetyl cysteine (1 g/kg diet), a cell-permeant antioxidant and GSH precursor, alleviated oxidative damage and cognitive decline, and restored glutathione synthase and GSH levels in ApoE-deficient mice deprived of folate to those of normal mice maintained in the presence of folate. These data support the administration of antioxidant precursors to buffer oxidative damage in neurodegenerative disorders.

Apple juice concentrate prevents oxidative damage and impaired maze performance in aged mice.

Oxidative stress contributes to age-related cognitive decline. In some instances, consumption of fruits and vegetables rich in antioxidant can provide superior protection than supplementation with purified antioxidants. Our prior studies have shown that supplementation with apple juice concentrate (AJC) alleviates oxidative damage and cognitive decline in a transgenic murine model compromised in endogenous antioxidant potential when challenged with a vitamin-deficient, oxidative stress-promoting diet. Herein, we demonstrate that AJC, administered in drinking water, is neuroprotective in normal, aged mice. Normal mice aged either 9-10 months or 2-2.5 years were maintained for 1 month on a complete diet or a diet lacking folate and vitamin E and containing iron as a pro-oxidant, after which oxidative damage was assayed by thiobarbituric acid-reactive substances and cognitive decline as assayed by performance in a standard Y-maze. Mice 9-12 months of age were unaffected by the deficient diet, while older mice demonstrated statistically-increased oxidative damage and poorer performance in a Y maze test. Supplementation with AJC prevented these neurodegenerative effects. These data are consistent with normal aged individuals being susceptible to neurodegeneration following dietary compromise such as folate deficiency, and a hastened onset of neurodegeneration in those individuals harboring a genetic risk factor such as ApoE deficiency. These findings also support the efficacy of antioxidant supplementation, including consumption of antioxidant-rich foods such as apples, in preventing the decline in cognitive performance that accompanies normal aging.