Bing Gong

Brain-Targeted Proanthocyanidin Metabolites for Alzheimer's Disease Treatment

While polyphenolic compounds have many health benefits, the potential development of polyphenols for the prevention/treatment of neurological disorders is largely hindered by their complexity as well as by limited knowledge regarding their bioavailability, metabolism, and bioactivity, especially in the brain. We recently demonstrated that dietary supplementation with a specific grape-derived polyphenolic preparation (GP) significantly improves cognitive function in a mouse model of Alzheimers disease (AD). GP is comprised of the proanthocyanidin (PAC) catechin and epicatechin in monomeric (Mo), oligomeric, and polymeric forms. In this study, we report that following oral administration of the independent GP forms, only Mo is able to improve cognitive function and only Mo metabolites can selectively reach and accumulate in the brain at a concentration of ∼400 nm. Most importantly, we report for the first time that a biosynthetic epicatechin metabolite, 3′-O-methyl-epicatechin-5-O-β-glucuronide (3′-O-Me-EC-Gluc), one of the PAC metabolites identified in the brain following Mo treatment, promotes basal synaptic transmission and long-term potentiation at physiologically relevant concentrations in hippocampus slices through mechanisms associated with cAMP response element binding protein (CREB) signaling. Our studies suggest that select brain-targeted PAC metabolites benefit cognition by improving synaptic plasticity in the brain, and provide impetus to develop 3′-O-Me-EC-Gluc and other brain-targeted PAC metabolites to promote learning and memory in AD and other forms of dementia.

Nicotinamide riboside restores cognition through an upregulation of proliferator-activated receptor-γ coactivator 1α regulated β-secretase 1 degradation and mitochondrial gene expression in Alzheimer's mouse models

Nicotinamide adenine dinucleotide (NAD)(+), a coenzyme involved in redox activities in the mitochondrial electron transport chain, has been identified as a key regulator of the lifespan-extending effects, and the activation of NAD(+) expression has been linked with a decrease in beta-amyloid (Aβ) toxicity in Alzheimers disease (AD). Nicotinamide riboside (NR) is a NAD(+) precursor, it promotes peroxisome proliferator-activated receptor-γ coactivator 1 (PGC)-1α expression in the brain. Evidence has shown that PGC-1α is a crucial regulator of Aβ generation because it affects β-secretase (BACE1) degradation. In this study we tested the hypothesis that NR treatment in an AD mouse model could attenuate Aβ toxicity through the activation of PGC-1α-mediated BACE1 degradation. Using the Tg2576 AD mouse model, using in vivo behavioral analyses, biochemistry assays, small hairpin RNA (shRNA) gene silencing and electrophysiological recording, we found (1) dietary treatment of Tg2576 mice with 250 mg/kg/day of NR for 3 months significantly attenuates cognitive deterioration in Tg2576 mice and coincides with an increase in the steady-state levels of NAD(+) in the cerebral cortex; (2) application of NR to hippocampal slices (10 μM) for 4 hours abolishes the deficits in long-term potentiation recorded in the CA1 region of Tg2576 mice; (3) NR treatment promotes PGC-1α expression in the brain coinciding with enhanced degradation of BACE1 and the reduction of Aβ production in Tg2576 mice. Further in vitro studies confirmed that BACE1 protein content is decreased by NR treatment in primary neuronal cultures derived from Tg2576 embryos, in which BACE1 degradation was prevented by PGC-1α-shRNA gene silencing; and (4) NR treatment and PGC-1α overexpression enhance BACE1 ubiquitination and proteasomal degradation. Our studies suggest that dietary treatment with NR might benefit AD cognitive function and synaptic plasticity, in part by promoting PGC-1α-mediated BACE1 ubiquitination and degradation, thus preventing Aβ production in the brain.

Identification of brain-targeted bioactive dietary quercetin-3-O-glucuronide as a novel intervention for Alzheimer’s disease

Epidemiological and preclinical studies indicate that polyphenol intake from moderate consumption of red wines may lower the relative risk for developing Alzheimers disease (AD) dementia. There is limited information regarding the specific biological activities and cellular and molecular mechanisms by which wine polyphenolic components might modulate AD. We assessed accumulations of polyphenols in the rat brain following oral dosage with a Cabernet Sauvignon red wine and tested brain‐targeted polyphenols for potential beneficial AD disease‐modifying activities. We identified accumulations of select polyphenolic metabolites in the brain. We demonstrated that, in comparison to vehicle‐control treatment, one of the brain‐targeted polyphenol metabolites, quercetin‐3‐O‐glucuronide, significantly reduced the generation of β‐amyloid (Aβ) peptides by primary neuron cultures generated from the Tg2576 AD mouse model. Another brain‐targeted metabolite, malvidin‐3‐O‐glucoside, had no detectable effect on Aβ generation. Moreover, in an in vitro analysis using the photo‐induced cross‐linking of unmodified proteins (PICUP) technique, we found that quercetin‐3‐O‐glucuronide is also capable of interfering with the initial protein‐protein interaction of Aβ1–40 and Aβ1–42 that is necessary for the formation of neurotoxic oligomeric Aβ species. Lastly, we found that quercetin‐3‐O‐glucuronide treatment, compared to vehicle‐control treatment, significantly improved AD‐type deficits in hippocampal formation basal synaptic transmission and long‐term potentiation, possibly through mechanisms involving the activation of the c‐Jun N‐terminal kinases and the mitogen‐activated protein kinase signaling pathways. Brain‐targeted quercetin‐3‐O‐glucuronide may simultaneously modulate multiple independent AD disease‐modifying mechanisms and, as such, may contribute to the benefits of dietary supplementation with red wines as an effective intervention for AD.—Ho, L., Ferruzzi, M. G., Janle, E. M., Wang, J., Gong, B., Chen, T.‐Y., Lobo, J., Cooper, B., Wu, Q. L., Talcott, S. T., Percival, S. S., Simon, J. E., Pasinetti, G. M. Identification of brain‐targeted bioactive dietary quercetin‐3‐O‐glucuronide as a novel intervention for Alzheimers disease. FASEB J. 27, 769–781 (2013). www.fasebj.org

Targeting multiple pathogenic mechanisms with polyphenols for the treatment of Alzheimer's disease-experimental approach and therapeutic implications

Alzheimers disease (AD) is the most prevalent neurodegenerative disease of aging and currently has no cure. Its onset and progression are influenced by multiple factors. There is growing consensus that successful treatment will rely on simultaneously targeting multiple pathological features of AD. Polyphenol compounds have many proven health benefits. In this study, we tested the hypothesis that combining three polyphenolic preparations (grape seed extract, resveratrol, and Concord grape juice extract), with different polyphenolic compositions and partially redundant bioactivities, may simultaneously and synergistically mitigate amyloid-β (Aβ) mediated neuropathology and cognitive impairments in a mouse model of AD. We found that administration of the polyphenols in combination did not alter the profile of bioactive polyphenol metabolites in the brain. We also found that combination treatment resulted in better protection against cognitive impairments compared to individual treatments, in J20 AD mice. Electrophysiological examination showed that acute treatment with select brain penetrating polyphenol metabolites, derived from these polyphenols, improved oligomeric Aβ (oAβ)-induced long term potentiation (LTP) deficits in hippocampal slices. Moreover, we found greatly reduced total amyloid content in the brain following combination treatment. Our studies provided experimental evidence that application of polyphenols targeting multiple disease-mechanisms may yield a greater likelihood of therapeutic efficacy.

SCFFbx2-E3-ligase-mediated degradation of BACE1 attenuates Alzheimer’s disease amyloidosis and improves synaptic function

BACE1 (β‐secretase) plays a central role in the β‐amyloidogenesis of Alzheimer’s disease (AD). The ubiquitin–proteasome system, a major intracellular protein quality control system, has been implicated recently in BACE1 metabolism. We report that the SCFFbx2‐E3 ligase is involved in the binding and ubiquitination of BACE1 via its Trp 280 residue of F‐box‐associated domain. Physiologically, we found that Fbx2 was expressed in various intracellular organelles in brain neurons and that BACE1 is colocalized with Fbx2 and the amyloid precursor protein (APP), mainly at the early endosome and endoplasmic reticulum. The former are believed to be the major intracellular compartments where the APP is cleaved by BACE1 and β‐amyloid is produced. Importantly, we found that overexpression of Fbx2 in the primary cortical and hippocampal neurons derived from Tg2576 transgenic mice significantly promoted BACE1 degradation and reduced β‐amyloid production. In the search for specific endogenous modulators of Fbx2 expression, we found that PPARγ coactivator‐1α (PGC‐1α) was capable of promoting the degradation of BACE1 through a mechanism involving Fbx2 gene expression. Interestingly, we found that the expression of both Fbx2 and PGC‐1α was significantly decreased in the brains of aging Tg2576 mice. Our in vivo studies using a mouse model of AD revealed that exogenous adenoviral Fbx2 expression in the brain significantly decreased BACE1 protein levels and activity, coincidentally reducing β‐amyloid levels and rescuing synaptic deficits. Our study is the first to suggest that promoting Fbx2 in the brain may represent a novel strategy for the treatment of AD.

Epigenetic mechanisms linking diabetes and synaptic impairments

Diabetes is one of the major risk factors for dementia. However, the molecular mechanism underlying the risk of diabetes for dementia is largely unknown. Recent studies revealed that epigenetic modifications may play a role in the pathogenesis of diabetes. We hypothesized that diabetes may cause epigenetic changes in the brain that may adversely affect synaptic function. We found significant elevation in the expression of histone deacetylases (HDACs) class IIa in the brains of diabetic subjects compared with control subjects, and these changes coincide with altered expression of synaptic proteins. In a mouse model of diet-induced type 2 diabetes (T2D), we found that, similar to humans, T2D mice also showed increased expression of HDAC IIa in the brain, and these alterations were associated with increased susceptibility to oligomeric Aβ-induced synaptic impairments in the hippocampal formation and eventually led to synaptic dysfunction. Pharmacological inhibition of HDAC IIa restored synaptic plasticity. Our study demonstrates that diabetes may induce epigenetic modifications affecting neuropathological mechanisms in the brain leading to increased susceptibility to insults associated with neurodegenerative or vascular impairments. Our study provides, for the first time, an epigenetic explanation for the increased risk of diabetic patients developing dementia.

IVIG immunotherapy protects against synaptic dysfunction in Alzheimer's disease through complement anaphylatoxin C5a-mediated AMPA-CREB-C/EBP signaling pathway.

BACKGROUNDnComplement component C5-derived C5a locally generated in the brain has been shown to protect against glutamate-induced neuronal apoptosis and beta-amyloid (Aβ) toxicity, but the mechanism is not clear. In this study, we tested the hypothesis that C5a influences upstream signal transduction pathways associated with cAMP-response element-binding protein (CREB) activation, in which alterations of CREB levels are associated with cognitive deterioration in AD.nnnMETHODSnCREB signaling pathway, synaptic plasticity and cognitive function were studied in C5a receptor knockout mice (C5aR(-/-)), C5a over expressing mice (C5a/GFAP) and in Tg2576 mice, an AD mouse model.nnnRESULTSn(1) Cognitive function is severely impaired in C5aR(-/-) mice, coincident with the down-regulated CREB/CEBP pathway in brain. (2) Either the application of recombinant-human-C5a (hrC5a) or exogenous expression of C5a in the brain of a mouse model (C5a/GFAP) enhances this pathway. (3) Application of hrC5a in brain slices from Tg2576 mice significantly improves deficits in long-term potentiation (LTP), while this effect is blocked by a specific AMPA receptor antagonist. (4) Searching for a pharmacological approach to locally mediate C5a responses in the brain, we found that low-dose human intravenous immunoglobulin (IVIG) treatment improves synaptic plasticity and cognitive function through C5a-mediated induction of the CREB/CEBP pathway, while the levels of Aβ in the brain are not significantly affected.nnnCONCLUSIONnThis study for the first time provides novel evidence suggesting that C5a may beneficially influence cognitive function in AD through an up-regulation of AMPA-CREB signaling pathway. IVIG may systematically improve cognitive function in AD brain by passing Aβ toxicity.

Role of standardized grape polyphenol preparation as a novel treatment to improve synaptic plasticity through attenuation of features of metabolic syndrome in a mouse model.

SCOPEnMetabolic syndrome has become an epidemic and poses tremendous burden on the health system. People with metabolic syndrome are more likely to experience cognitive decline. As obesity and sedentary lifestyles become more common, the development of early prevention strategies is critical. In this study, we explore the potential beneficial effects of a combinatory polyphenol preparation composed of grape seed extract, Concord purple grape juice extract, and resveratrol, referred to as standardized grape polyphenol preparation (SGP), on peripheral as well as brain dysfunction induced by metabolic syndrome.nnnMETHODS AND RESULTSnWe found dietary fat content had minimal effect on absorption of metabolites of major polyphenols derived from SGP. Using a diet-induced animal model of metabolic syndrome (DIM), we found that brain functional connectivity and synaptic plasticity are compromised in the DIM mice. Treatment with SGP not only prevented peripheral metabolic abnormality but also improved brain synaptic plasticity.nnnCONCLUSIONnOur study demonstrated that SGP, comprised of multiple bioavailable and bioactive components targeting a wide range of metabolic syndrome related pathological features, provides greater global protection against peripheral and central nervous system dysfunctions and can be potentially developed as a novel prevention/treatment for improving brain connectivity and synaptic plasticity important for learning and memory.

Childhood and adolescent obesity and long‐term cognitive consequences during aging

The prevalence of childhood/adolescent obesity and insulin resistance has reached an epidemic level. Obesitys immediate clinical impacts have been extensively studied; however, current clinical evidence underscores the long‐term implications. The current study explored the impacts of brief childhood/adolescent obesity and insulin resistance on cognitive function in later life. To mimic childhood/adolescent obesity and insulin resistance, we exposed 9‐week‐old C57BL/6J mice to a high‐fat diet for 15 weeks, after which the mice exhibited diet‐induced obesity and insulin resistance. We then put these mice back on a normal low‐fat diet, after which the mice exhibited normal body weight and glucose tolerance. However, a spatial memory test in the forms of the Morris water maze (MWM) and contextual fear conditioning at 85 weeks of age showed that these mice had severe deficits in learning and long‐term memory consolidation. Mechanistic investigations identified increased expression of histone deacetylases 5, accompanied by reduced expression of brain‐derived neurotrophic factor, in the brains 61 weeks after the mice had been off the high‐fat diet. Electrophysiology studies showed that hippocampal slices isolated from these mice are more susceptible to synaptic impairments compared with slices isolated from the control mice. We demonstrated that a 15‐week occurrence of obesity and insulin resistance during childhood/adolescence induces irreversible epigenetic modifications in the brain that persist following restoration of normal metabolic homeostasis, leading to brain synaptic dysfunction during aging. Our study provides experimental evidence that limited early‐life exposure to obesity and insulin resistance may have long‐term deleterious consequences in the brain, contributing to the onset/progression of cognitive dysfunction during aging. J. Comp. Neurol. 523:757–768, 2015.

Cocoa Extracts Reduce Oligomerization of Amyloid-β: Implications for Cognitive Improvement in Alzheimer's Disease

BACKGROUNDnAlzheimers disease (AD) is the most common age-related neurodegenerative disorder, characterized by pathological aggregates of amyloid peptide-β (Aβ) and tau protein. Currently available therapies mediate AD symptoms without modifying disease progression. Polyphenol-rich diets are reported to reduce the risk for AD.nnnOBJECTIVEnIn the present study, we investigated the AD disease-modifying effects of cocoa, a rich source of flavanols, which are a class of polyphenols. We hypothesized that cocoa extracts interfere with amyloid-β oligomerization to prevent synaptic deficits.nnnMETHODSnWe tested the effects of three different cocoa extracts, viz. Natural, Dutched, and Lavado extracts, on Aβ42 and Aβ40 oligomerization, using photo-induced cross-linking of unmodified proteins technique. To assess the effects of cocoa extracts on synaptic function, we measured long term potentiation in mouse brain hippocampal slices exposed to oligomeric Aβ.nnnRESULTSnOur results indicate that cocoa extracts are effective in preventing the oligomerization of Aβ, with Lavado extract being most effective. Lavado extract, but not Dutched extract, was effective in restoring the long term potentiation response reduced by oligomeric Aβ.nnnCONCLUSIONnOur findings indicate that cocoa extracts have multiple disease-modifying properties in AD and present a promising route of therapeutic and/or preventative initiatives.