Amelioration of age-related cognitive decline and anxiety in mice by Centella asiatica extract varies by sex, dose and mode of administration

Background: A water extract (CAW) of the Ayurvedic plant Centella asiatica administered in drinking water has been shown to improve cognitive deficits in mouse models of aging and neurodegenerative diseases. Here the effects of CAW administered in drinking water or the diet on cognition, measures of anxiety and depression-like behavior in healthy aged mice are compared. Methods: Three- and eighteen-month-old male and female C57BL6 mice were administered rodent AIN-93M diet containing CAW (0, 0.2, 0.5 or 1% w/w) to provide 0, 200 mg/kg/d, 500 mg/kg/d or 1,000 mg/kg/d CAW for a total of 5 weeks. An additional group of eighteen-month-old mice were treated with CAW (10 mg/mL) in their drinking water CAW for a total of 5 weeks to deliver the same exposure of CAW as the highest dietary dose (1,000 mg/kg/d). CAW doses delivered were calculated based on food and water consumption measured in previous experiments. In the fourth and fifth weeks, mice underwent behavioral testing of cognition, anxiety and depression (n = 12 of each sex per treatment group in each test). Results: Aged mice of both sexes showed cognitive deficits relative to young mice while only female aged mice showed increased anxiety compared to the young female mice and no differences in depression were observed between the different ages. CAW (1,000 mg/kg/d) in the drinking water improved deficits in aged mice in learning, executive function and recognition memory in both sexes and attenuated the increased measures of anxiety observed in the aged female mice. However, CAW in the diet only improved executive function in aged mice at the highest dose (1,000 mg/kg/d) in both sexes and did so less robustly than when given in the water. There were no effects of CAW on depression-like behavior in aged animals regardless of whether it was administered in the diet or the water. Conclusions: These results suggest that CAW can ameliorate age-related changes in measures of anxiety and cognition and that the mode of administration is important for the effects of CAW on resilience to these age-related changes.

Gardenin A treatment attenuates inflammatory markers, synuclein pathology and deficits in tyrosine hydroxylase expression and improves cognitive and motor function in A53T-α-syn mice

Oxidative stress and neuroinflammation are widespread in the Parkinson's disease (PD) brain and contribute to the synaptic degradation and dopaminergic cell loss that result in cognitive impairment and motor dysfunction. The polymethoxyflavone Gardenin A (GA) has been shown to activate the NRF2-regulated antioxidant pathway and inhibit the NFkB-dependent pro-inflammatory pathway in a Drosophila model of PD. Here, we evaluate the effects of GA on A53T alpha-synuclein overexpressing (A53TSyn) mice. A53TSyn mice were treated orally for 4 weeks with 0, 25, or 100 mg/kg GA. In the fourth week, mice underwent behavioral testing and tissue was harvested for immunohistochemical analysis of tyrosine hydroxylase (TH) and phosphorylated alpha synuclein (pSyn) expression, and quantification of synaptic, antioxidant and inflammatory gene expression. Results were compared to vehicle-treated C57BL6J mice. Treatment with 100 mg/kg GA improved associative memory and decreased abnormalities in mobility and gait in A53TSyn mice. GA treatment also reduced pSyn levels in both the cortex and hippocampus and attenuated the reduction in TH expression in the striatum seen in A53Tsyn mice. Additionally, GA increased cortical expression of NRF2-regulated antioxidant genes and decreased expression of NFkB-dependent pro-inflammatory genes. GA was readily detectable in the brains of treated mice and modulated the lipid profile in the deep gray brain tissue of those animals. While the beneficial effects of GA on cognitive deficits, motor dysfunction and PD pathology are promising, future studies are needed to further fully elucidate the mechanism of action of GA, optimizing dosing and confirm these effects in other PD models.

Mode of administration influences plasma levels of active Centella asiatica compounds in 5xFAD mice while markers of neuroinflammation remain unaltered

Introduction

A water extract of Centella asiatica (L.) Urban [Apiaceae] (CAW) has demonstrated cognitive-enhancing effects in mouse models of Alzheimer's disease and aging, the magnitude of which is influenced by whether CAW is delivered in the drinking water or the diet. These cognitive benefits are accompanied by improvements in oxidative stress and mitochondrial function in the brain, two pathways related to the neuroinflammatory response. The effect of CAW on neuroinflammation, however, has not been directly studied. Here, we investigated the effect of CAW on neuroinflammation in 5xFAD mice and compared plasma levels of CAW's active compounds following two modes of CAW administration.

Methods

Eight-to-nine-month-old male and female 5xFAD mice and their wild-type littermates were administered CAW in their diet or drinking water (0 or 1,000 mg/kg/day) for five weeks. Immunohistochemistry was performed for β-amyloid (Aβ), glial fibrillary acidic protein (GFAP), and Griffonia simplicifolia lectin I (GSL I) in the cortex and hippocampus. Gene expression of inflammatory mediators (IL-6, TNFα, IL-1β, TREM2, AIF1, CX3CR1, CX3CL1, CD36, C3AR1, RAGE, CCR6, CD3E) was measured in the deep grey matter.

Results

CAW decreased cortical Aβ plaque burden in female 5xFAD mice administered CAW in the drinking water but had no effect on Aβ plaques in other treatment groups. CAW did not impact elevated levels of GFAP or GSL I in 5xFAD mice, regardless of sex, brain region, or mode of CAW administration. In the deep grey matter, CAW increased C3AR1 expression in 5xFAD females administered CAW in the drinking water and decreased IL-1β expression in 5xFAD males administered CAW in the diet. CAW had no effect, however, on gene expression levels of any other inflammatory mediator in the deep grey, for either sex or mode of CAW administration. Mice administered CAW in the drinking water versus the diet had significantly higher plasma levels of CAW compounds.

Discussion

CAW had little impact on the neuroinflammatory markers selected for evaluation in the present study, suggesting that the cognitive benefits of CAW may not be mediated by an anti-inflammatory effect or that additional molecular markers are needed to fully characterize the effect of CAW on neuroinflammation.

Integrating High-Resolution Mass Spectral Data, Bioassays and Computational Models to Annotate Bioactives in Botanical Extracts: Case Study Analysis of C. asiatica Extract Associates Dicaffeoylquinic Acids with Protection against Amyloid-β Toxicity

Rapid screening of botanical extracts for the discovery of bioactive natural products was performed using a fractionation approach in conjunction with flow-injection high-resolution mass spectrometry for obtaining chemical fingerprints of each fraction, enabling the correlation of the relative abundance of molecular features (representing individual phytochemicals) with the read-outs of bioassays. We applied this strategy for discovering and identifying constituents of Centella asiatica (C. asiatica) that protect against Aβ cytotoxicity in vitro. C. asiatica has been associated with improving mental health and cognitive function, with potential use in Alzheimer's disease. Human neuroblastoma MC65 cells were exposed to subfractions of an aqueous extract of C. asiatica to evaluate the protective benefit derived from these subfractions against amyloid β-cytotoxicity. The % viability score of the cells exposed to each subfraction was used in conjunction with the intensity of the molecular features in two computational models, namely Elastic Net and selectivity ratio, to determine the relationship of the peak intensity of molecular features with % viability. Finally, the correlation of mass spectral features with MC65 protection and their abundance in different sub-fractions were visualized using GNPS molecular networking. Both computational methods unequivocally identified dicaffeoylquinic acids as providing strong protection against Aβ-toxicity in MC65 cells, in agreement with the protective effects observed for these compounds in previous preclinical model studies.

Amelioration of age-related cognitive decline and anxiety in mice by Centella asiatica extract varies by sex, dose and mode of administration

We have previously reported that a water extract (CAW) of the Ayurvedic plant Centella asiatica administered in drinking water can improve cognitive deficits in mouse models of aging and neurodegenerative diseases. Here we compared the effects of CAW administered in drinking water or the diet on cognition, measures of anxiety and depression-like behavior in healthy aged mice. Three- and eighteen-month-old male and female C57BL6 mice were administered rodent AIN-93M diet containing CAW (0, 0.2, 0.5 or 1% w/w) to provide 0, 200 mg/kg/d, 500 mg/kg/d or 1000 mg/kg/d for a total of 5 weeks. An additional group of eighteen-month-old mice were treated with CAW (10 mg/mL) in their drinking water for a total of five weeks to deliver the same exposure of CAW as the highest dietary dose (1000 mg/kg/d). CAW doses delivered were calculated based on food and water consumption measured in previous experiments. In the fourth and fifth weeks, mice underwent behavioral testing of cognition, anxiety and depression (n=12 of each sex per treatment group in each test). Aged mice of both sexes showed cognitive deficits relative to young mice while only female aged mice showed increased anxiety compared to the young female mice and no differences in depression were observed between the different ages. CAW (1000 mg/kg/d) in the drinking water improved deficits in aged mice in learning, executive function and recognition memory in both sexes and attenuated the increased measures of anxiety observed in the aged female mice. However, CAW in the diet only improved executive function in aged mice at the highest dose (1000 mg/kg/d) in both sexes and did so less robustly than when given in the water. There were no effects of CAW on depression-like behavior in aged animals regardless of whether it was administered in the diet or the water. These results suggest that CAW can ameliorate age-related changes in measures of anxiety and cognition and that the mode of administration is important for the effects of CAW on resilience to these age-related changes.

Quantification of Caffeoylquinic Acids and Triterpenes as Targeted Bioactive Compounds of Centella asiatica in Extracts and Formulations by Liquid Chromatography Mass Spectrometry

Centella asiatica (CA) is a culinary vegetable and well-known functional food that is widely used as a medicinal herb and dietary supplement. CA is rich in pentacyclic triterpenes (TTs), including asiaticoside (AS), madecassoside (MS) and the related aglycones asiatic acid (AA), madecassic acid (MA). Traditionally, TTs have been associated with the bioactivity and health promoting effect of CA. Recently, mono-caffeoylquinic acids (MonoCQAs) and di-caffeoylquinic acids (DiCQAs) have been found to contribute to the bioactivity of CA as well. This work reports an analytical strategy based on liquid chromatography coupled to multiple reaction monitoring mass spectrometry (LC-MRM-MS) for the simultaneous rapid and accurate quantification of 12 bioactive compounds in CA, namely AS, MS, AA, MA, 5-CQA, 4-CQA, 3-CQA, 1,3-DiCQA, 3,4-DiCQA, 1,5-DiCQA, 3,5-DiCQA, 4,5-DiCQA. Method selectivity, accuracy, precision, repeatability, robustness, linearity range, limit of detection (LOD), and limit of quantitation (LOQ) were validated. The validated LC-MRM-MS method has been successfully applied to quantify the 12 bioactive compounds in CA aqueous extracts and two related formulations: a standardized CA product (CAP) used in a phase I clinical trial and formulated CA rodent diets used in preclinical studies. The validated method allows us to support the standardization of CA products used for clinical trials and conduct routine LC-MRM-MS analyses of formulated preclinical diets to confirm correct levels of CA phytochemical markers.

Gardenin A improves cognitive and motor function in A53T-α-syn mice

Oxidative stress and neuroinflammation are widespread in the Parkinson's disease (PD) brain and contribute to the synaptic degradation and dopaminergic cell loss that result in cognitive impairment and motor dysfunction. The polymethoxyflavone Gardenin A (GA) has been shown to activate the NRF2-regulated antioxidant pathway and inhibit the NFkB-dependent pro-inflammatory pathway in a Drosophila model of PD. Here, we evaluate the effects of GA on A53T alpha-synuclein overexpressing (A53TSyn) mice. A53TSyn mice were treated orally for 4 weeks with 0, 25, or 100 mg/kg GA. In the fourth week, mice underwent behavioral testing and tissue was harvested for immunohistochemical analysis of tyrosine hydroxylase (TH) and phosphorylated alpha synuclein (pSyn) expression, and quantification of synaptic, antioxidant and inflammatory gene expression. Results were compared to vehicle-treated C57BL6 mice. Treatment with 100 mg/kg GA improved associative memory and decreased abnormalities in mobility and gait in A53TSyn mice. GA treatment also reduced cortical and hippocampal levels of pSyn and attenuated the reduction in TH expression in the striatum. Additionally, GA increased cortical expression of NRF2-regulated antioxidant genes and decreased expression of NFkB-dependent pro-inflammatory genes. GA was readily detectable in the brains of treated mice and modulated the lipid profile in the deep gray brain tissue of those animals. While the beneficial effects of GA on cognitive deficits, motor dysfunction and PD pathology are promising, future studies are needed to further fully elucidate the mechanism of action of GA, optimizing dosing and confirm these effects in other PD models.

Significance Statement

The polymethoxyflavone Gardenin A can improve cognitive and motor function and attenuate both increases in phosphorylated alpha synuclein and reductions in tyrosine hydroxylase expression in A53T alpha synuclein overexpressing mice. These effects may be related to activation of the NRF2-regulated antioxidant response and downregulation of NFkB-dependent inflammatory response by Gardenin A in treated animals. The study also showed excellent brain bioavailability of Gardenin A and modifications of the lipid profile, possibly through interactions between Gardenin A with the lipid bilayer, following oral administration. The study confirms neuroprotective activity of Gardenin A previously reported in toxin induced Drosophila model of Parkinson's disease.

Centella asiatica promotes antioxidant gene expression and mitochondrial oxidative respiration in experimental autoimmune encephalomyelitis

Centella asiatica (Centella) is a traditional botanical medicine that shows promise in treating dementia based on behavioral alterations seen in animal models of aging and cognitive dysfunction. In order to determine if Centella could similarly improve cognitive function and reduce disease burden in multiple sclerosis (MS), we tested its effects in the neuroinflammatory experimental autoimmune encephalomyelitis (EAE) model of MS. In two independent experiments, C57BL/6J mice were treated following induction of EAE with either a standardized water extract of Centella (CAW) or placebo for 2 weeks. At the dosing schedule and concentrations tested, CAW did not improve behavioral performance, EAE motor disability, or degrees of demyelination. However, CAW-treated mice demonstrated increases in nuclear factor (erythroid-derived 2)-like 2 and other antioxidant response element genes, and increases in mitochondrial respiratory activity. Caw also decreased spinal cord inflammation. Our findings indicate that CAW can increase antioxidant gene expression and mitochondrial respiratory activity in mice with EAE, supporting investigation of the clinical effects of CAW in people with MS.

The novel estrogen receptor modulator STX attenuates Amyloid-β neurotoxicity in the 5XFAD mouse model of Alzheimer's disease

Based on previous evidence that the non-steroidal estrogen receptor modulator STX mitigates the effects of neurotoxic Amyloid-β (Aβ) in vitro, we have evaluated its neuroprotective benefits in a mouse model of Alzheimer's disease. Cohorts of 5XFAD mice, which begin to accumulate cerebral Aβ at two months of age, were treated with orally-administered STX starting at 6 months of age for two months. After behavioral testing to evaluate cognitive function, biochemical and immunohistochemical assays were used to analyze key markers of mitochondrial function and synaptic integrity. Oral STX treatment attenuated Aβ-associated mitochondrial toxicity and synaptic toxicity in the brain, as previously documented in cultured neurons. STX also moderately improved spatial memory in 5XFAD mice. In addition, STX reduced markers for reactive astrocytosis and microgliosis surrounding amyloid plaques, and also unexpectedly reduced overall levels of cerebral Aβ in the brain. The neuroprotective effects of STX were more robust in females than in males. These results suggest that STX may have therapeutic potential in Alzheimer's Disease.

Pharmacokinetics and Pharmacodynamics of Key Components of a Standardized Centella asiatica Product in Cognitively Impaired Older Adults: A Phase 1, Double-Blind, Randomized Clinical Trial

Centella asiatica is reputed in Eastern medicine to improve cognitive function in humans. Preclinical studies have demonstrated that aqueous extracts of C. asiatica improve cognition in mouse models of aging and Alzheimer's disease (AD) through the modulation of mitochondrial biogenesis and nuclear factor-erythroid-2-related factor 2 (Nrf2)-dependent antioxidant response genes. This randomized, double-blind, crossover Phase I trial explored the oral bioavailability and pharmacokinetics of key compounds from two doses (2 g and 4 g) of a standardized C. asiatica aqueous extract product (CAP), over 10 h, in four mildly demented older adults on cholinesterase inhibitor therapy. The analysis focused on triterpenes (TTs) and caffeoylquinic acids (CQAs), which are known to contribute to C. asiatica's neurological activity. The acute safety of CAP and the effects on NRF2 gene expression in peripheral blood mononuclear cells were evaluated. Single administration of 2 g or 4 g of CAP was safe and well-tolerated. The TT aglycones, asiatic acid and madecassic acid, were identified in plasma and urine, while the parent glycosides, asiaticoside and madecassoside, although abundant in CAP, were absent in plasma and had limited renal excretion. Similarly, mono- and di-CQAs showed delayed absorption and limited presence in plasma or urine, while the putative metabolites of these compounds showed detectable plasma pharmacokinetic profiles and urinary excretion. CAP elicited a temporal change in NRF2 gene expression, mirroring the TT aglycone's pharmacokinetic curve in a paradoxical dose-dependent manner. The oral bioavailability of active compounds or their metabolites, NRF2 target engagement, and the acute safety and tolerability of CAP support the validity of using CAP in future clinical studies.

Withania somnifera and Centella asiatica Extracts Ameliorate Behavioral Deficits in an In Vivo Drosophila melanogaster Model of Oxidative Stress

Due to an increase in the aging population, age-related diseases and age-related changes, such as diminished cognition and sleep disturbances, are an increasing health threat. It has been suggested that an increase in oxidative stress underlies many of these changes. Current treatments for these diseases and changes either have low efficacy or have deleterious side effects preventing long-time use. Therefore, alternative treatments that promote healthy aging and provide resilience against these health threats are needed. The herbs Withania somnifera and Centella asiatica may be two such alternatives because both have been connected with reducing oxidative stress and could therefore ameliorate age-related impairments. To test the effects of these herbs on behavioral phenotypes induced by oxidative stress, we used the Drosophila melanogaster sniffer mutant which has high levels of oxidative stress due to reduced carbonyl reductase activity. Effects on cognition and mobility were assessed using phototaxis assays and both, W. somnifera and C. asiatica water extracts improved phototaxis in sniffer mutants. In addition, W. somnifera improved nighttime sleep in male and female sniffer flies and promoted a less fragmented sleep pattern in male sniffer flies. This suggests that W. somnifera and C. asiatica can ameliorate oxidative stress-related changes in behavior and that by doing so they might promote healthy aging in humans.

Centella asiatica Alters Metabolic Pathways Associated With Alzheimer's Disease in the 5xFAD Mouse Model of ß-Amyloid Accumulation

Centella asiatica is an herb used in Ayurvedic and traditional Chinese medicine for its beneficial effects on brain health and cognition. Our group has previously shown that a water extract of Centella asiatica (CAW) elicits cognitive-enhancing effects in animal models of aging and Alzheimer's disease, including a dose-related effect of CAW on memory in the 5xFAD mouse model of ß-amyloid accumulation. Here, we endeavor to elucidate the mechanisms underlying the effects of CAW in the brain by conducting a metabolomic analysis of cortical tissue from 5xFAD mice treated with increasing concentrations of CAW. Tissue was collected from 8-month-old male and female 5xFAD mice and their wild-type littermates treated with CAW (0, 200, 500, or 1,000 mg/kg/d) dissolved in their drinking water for 5 weeks. High-performance liquid chromatography coupled to high-resolution mass spectrometry analysis was performed and relative levels of 120 annotated metabolites were assessed in the treatment groups. Metabolomic analysis revealed sex differences in the effect of the 5xFAD genotype on metabolite levels compared to wild-type mice, and variations in the metabolomic response to CAW depending on sex, genotype, and CAW dose. In at least three of the four treated groups (5xFAD or wild-type, male or female), CAW (500 mg/kg/d) significantly altered metabolic pathways related to purine metabolism, nicotinate and nicotinamide metabolism, and glycerophospholipid metabolism. The results are in line with some of our previous findings regarding specific mechanisms of action of CAW (e.g., improving mitochondrial function, reducing oxidative stress, and increasing synaptic density). Furthermore, these findings provide new information about additional, potential mechanisms for the cognitive-enhancing effect of CAW, including upregulation of nicotinamide adenine dinucleotide in the brain and modulation of brain-derived neurotrophic factor. These metabolic pathways have been implicated in the pathophysiology of Alzheimer's disease, highlighting the therapeutic potential of CAW in this neurodegenerative disease.

The Impact of the hAPP695SW Transgene and Associated Amyloid-β Accumulation on Murine Hippocampal Biochemical Pathways

Background: Alzheimer’s disease (AD) is a neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) peptide in the brain. Objective: Gain a better insight into alterations in major biochemical pathways underlying AD. Methods: We compared metabolomic profiles of hippocampal tissue of 20-month-old female Tg2576 mice expressing the familial AD-associated hAPP695SW transgene with their 20-month-old wild type female littermates. Results: The hAPP695SW transgene causes overproduction and accumulation of Aβ in the brain. Out of 180 annotated metabolites, 54 metabolites differed (30 higher and 24 lower in Tg2576 versus wild-type hippocampal tissue) and were linked to the amino acid, nucleic acid, glycerophospholipid, ceramide, and fatty acid metabolism. Our results point to 1) heightened metabolic activity as indicated by higher levels of urea, enhanced fatty acid β-oxidation, and lower fatty acid levels; 2) enhanced redox regulation; and 3) an imbalance of neuro-excitatory and neuro-inhibitory metabolites in hippocampal tissue of aged hAPP695SW transgenic mice. Conclusion: Taken together, our results suggest that dysregulation of multiple metabolic pathways associated with a concomitant shift to an excitatory-inhibitory imbalance are contributing mechanisms of AD-related pathology in the Tg2576 mouse.

Identification of TrkB Binders from Complex Matrices Using a Magnetic Drug Screening Nanoplatform

Brain-derived neurotrophic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB) have been shown to play an important role in numerous neurological disorders, such as Alzheimer's disease. The identification of biologically active compounds interacting with TrkB serves as a drug discovery strategy to identify drug leads for neurological disorders. Here, we report effective immobilization of functional TrkB on magnetic iron oxide nanoclusters, where TrkB receptors behave as "smart baits" to bind compounds from mixtures and magnetic nanoclusters enable rapid isolation through magnetic separation. The presence of the immobilized TrkB was confirmed by specific antibody labeling. Subsequently, the activity of the TrkB on iron oxide nanoclusters was evaluated with ATP/ADP conversion experiments using a known TrkB agonist. The immobilized TrkB receptors can effectively identify binders from mixtures containing known binders, synthetic small molecule mixtures, and Gotu Kola (Centella asiatica) plant extracts. The identified compounds were analyzed by an ultrahigh-performance liquid chromatography system coupled with a quadrupole time-of-flight mass spectrometer. Importantly, some of the identified TrkB binders from Gotu Kola plant extracts matched with compounds previously linked to neuroprotective effects observed for a Gotu Kola extract approved for use in a clinical trial. Our studies suggest that the possible therapeutic effects of the Gotu Kola plant extract in dementia treatment, at least partially, might be associated with compounds interacting with TrkB. The unique feature of this approach is its ability to fast screen potential drug leads using less explored transmembrane targets. This platform works as a drug-screening funnel at early stages of the drug discovery pipeline. Therefore, our approach will not only greatly benefit drug discovery processes using transmembrane proteins as targets but also allow for evaluation and validation of cellular pathways targeted by drug leads.

Loss of NRF2 accelerates cognitive decline, exacerbates mitochondrial dysfunction, and is required for the cognitive enhancing effects of Centella asiatica during aging

The water extract of Centella asiatica (CAW) improves cognitive and mitochondrial function and activates the nuclear factor erythroid 2-related factor 2 (NRF2) regulated antioxidant response pathway in aged mice. Here we investigate whether NRF2 activation is required for the cognitive and mitochondrial effects of prolonged CAW exposure during aging. Five-month-old NRF2 knockout (NRF2KO) and wild-type mice were treated with CAW for 1, 7, or 13 months. Each cohort underwent cognitive testing and hippocampal mitochondrial analyses. Age-related cognitive decline was accelerated in NRF2KO mice and while CAW treatment improved cognitive performance in wild-type mice, it had no effect on NRF2KO animals. Hippocampal mitochondrial function also declined further with age in NRF2KO mice and greater hippocampal mitochondrial dysfunction was associated with poorer cognitive performance in both genotypes. Long-term CAW treatment did not affect mitochondrial endpoints in animals of either genotype. These data indicate that loss of NRF2 results in accelerated age-related cognitive decline and worsened mitochondrial deficits. NRF2 also appears to be required for the cognitive enhancing effects of CAW during aging.

Prolonged Treatment with Centella asiatica Improves Memory, Reduces Amyloid-β Pathology, and Activates NRF2-Regulated Antioxidant Response Pathway in 5xFAD Mice

BACKGROUND

The medicinal herb Centella asiatica has been long been used for its neuroprotective and cognitive enhancing effects. We have previously shown that two weeks of treatment with a water extract of Centella asiatica (CAW) improves cognition and activates the endogenous antioxidant response pathway without altering amyloid-β (Aβ) plaque burden.

OBJECTIVE

Here, we assess the effect of long-term treatment of CAW in the 5xFAD mouse model of Aβ accumulation.

METHODS

Four-month-old 5xFAD mice were treated with CAW in their drinking water (2 g/L) for three months at which point they underwent cognitive testing as well as analysis of Aβ plaque levels and antioxidant and synaptic gene expression. In order to confirm the involvement of the antioxidant regulatory transcription factor NRF2 on the effects of CAW on synaptic plasticity, neurons isolated from 5xFAD mice were also treated with CAW and the targeted inhibitor ML385.

RESULTS

Three months of treatment with CAW improved spatial and contextual memory as well as executive function in 5xFAD mice. This improvement was accompanied by increased antioxidant gene expression and a decrease in Aβ plaque burden relative to untreated 5xFAD animals. In isolated neurons, treatment with ML385 blocked the effects of CAW on dendritic arborization and synaptic gene expression.

CONCLUSION

These results suggest that prolonged CAW exposure could be beneficial in Alzheimer's disease and that these effects likely involve NRF2 activation. Moreover, these findings suggest that targeting NRF2 itself may be a relevant therapeutic strategy for improving synaptic plasticity and cognitive function in Alzheimer's disease.

Peripheral Blood NRF2 Expression as a Biomarker in Human Health and Disease

Nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor which plays a critical role in maintenance of cellular redox, has been identified as a therapeutic target in a number of human diseases. Several reports have demonstrated beneficial effects of NRF2 manipulation in animal models of disease, and one NRF2-activating drug, dimethyl fumarate, is already approved for the treatment of multiple sclerosis. However, drug discovery is slowed due to a dearth of biomarkers which can inform target engagement and magnitude and duration of action. Peripheral blood mononuclear cells (PBMCs) are an accessible, minimally-invasive source of biomarkers which can be readily assayed and objectively monitored as a surrogate endpoint of NRF2 activation in clinical trials. We undertook a review of the literature on PBMC NRF2 measurements in human studies to explore its role as a suitable biomarker in various contexts of health and disease. It is clear that NRF2 and its target genes can be readily assayed from PBMCs in multiple disease contexts and may track with disease progression. Further work needs to be undertaken to evaluate its stability but should be considered as an exploratory marker in clinical trials targeting NRF2 activation.

Integration of mass spectral fingerprinting analysis with precursor ion (MS1) quantification for the characterisation of botanical extracts: application to extracts of Centella asiatica (L.) Urban

INTRODUCTION

The phytochemical composition of plant material governs the bioactivity and potential health benefits as well as the outcomes and reproducibility of laboratory studies and clinical trials.

OBJECTIVE

The objective of this work was to develop an efficient method for the in-depth characterisation of plant extracts and quantification of marker compounds that can be potentially used for subsequent product integrity studies. Centella asiatica (L.) Urb., an Ayurvedic herb with potential applications in enhancing mental health and cognitive function, was used as a case study.

METHODS

A quadrupole time-of-flight analyser in conjunction with an optimised high-performance liquid chromatography (HPLC) separation was used for in-depth untargeted fingerprinting and post-acquisition precursor ion quantification to determine levels of distinct phytochemicals in various C. asiatica extracts.

RESULTS

We demonstrate the utility of this workflow for the characterisation of extracts of C. asiatica. This integrated workflow allowed the identification or tentative identification of 117 compounds, chemically interconnected based on Tanimoto chemical similarity, and the accurate quantification of 24 phytochemicals commonly found in C. asiatica extracts.

CONCLUSION

We report a phytochemical analysis method combining liquid chromatography, high resolution mass spectral data acquisition, and post-acquisition interrogation that allows chemical fingerprints of botanicals to be obtained in conjunction with accurate quantification of distinct phytochemicals. The variability in the composition of specialised metabolites across different C. asiatica accessions was substantial, demonstrating that detailed characterisation of plant extracts is a prerequisite for reproducible use in laboratory studies, clinical trials and safe consumption. The methodological approach is generally applicable to other botanical products.

Copper Modulation and Memory Impairment due to Hippocampal Tau Pathology

Background:Environmental copper has been implicated in the pathogenesis of Alzheimer’s disease based on evidence that: 1) brain copper levels increase with age, 2) copper promotes misfolding and toxicity of amyloid-β in vitro, 3) copper-modulating interventions reduce amyloid pathology in animal models. However, the effect of copper upon non-amyloid Alzheimer’s pathology is relatively under-explored.Objective:To determine if modulation of brain copper level affects brain tau pathology and/or associated cognitive impairment.Methods:We tested the hypothesis that brain copper modulates tau pathology by manipulating brain levels of copper in the PS19 transgenic mouse model of tau pathology. We treated PS19 and wild-type mice with oral zinc acetate, an established therapy for long term control of excess brain copper, and examined treatment effects upon brain copper, brain tau, NFT-like pathology, and spatial memory. We treated a second cohort of mice with exogenous dietary copper in order to evaluate whether excess environmental copper promotes brain tau pathology.Results:Copper-lowering with oral zinc attenuated spatial memory impairment in female but not male PS19 mice, without a significant effect upon tau pathology. Copper loading increased brain copper, but did not have an effect on brain tau pathology or spatial memory function.Conclusion:These findings suggest that a strategy to lower brain copper may be viable for symptomatic benefit in the setting of tau neuropathology, but unlikely to have robust effects on the underlying pathology. These findings are consistent with dietary or other exogenous copper being unlikely to promote tau pathology.

Age-Associated DNA Methylation Patterns Are Shared Between the Hippocampus and Peripheral Blood Cells

As the population ages, interest in identifying biomarkers of healthy aging and developing antiaging interventions has increased. DNA methylation has emerged as a potentially powerful molecular marker of aging. Methylation changes at specific sites in the human genome that have been identified in peripheral blood have been used as robust estimators of chronological age. Similar age-related DNA methylation signatures are also seen in various tissue types in rodents. However, whether these peripheral alterations in methylation status reflect changes that also occur in the central nervous system remains unknown. This study begins to address this issue by identifying age-related methylation patterns in the hippocampus and blood of young and old mice. Reduced-representation bisulfite sequencing (RBSS) was used to identify differentially methylated regions (DMRs) in the blood and hippocampus of 2- and 20-month-old C57/Bl6 mice. Of the thousands of DMRs identified genome-wide only five were both found in gene promoters and significantly changed in the same direction with age in both tissues. We analyzed the hippocampal expression of these five hypermethylated genes and found that three were expressed at significantly lower levels in aged mice [suppressor of fused homolog (Sufu), nitric oxide synthase 1 (Nos1) and tripartite motif containing 2 (Trim2)]. We also identified several transcription factor binding motifs common to both hippocampus and blood that were enriched in the DMRs. Overall, our findings suggest that some age-related methylation changes that occur in the brain are also evident in the blood and could have significant translational relevance.

NRF2 as a Therapeutic Target in Neurodegenerative Diseases

Increased reactive oxygen species production and oxidative stress have been implicated in the pathogenesis of numerous neurodegenerative conditions including among others Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Friedrich’s ataxia, multiple sclerosis, and stroke. The endogenous antioxidant response pathway protects cells from oxidative stress by increasing the expression of cytoprotective enzymes and is regulated by the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2). In addition to regulating the expression of antioxidant genes, NRF2 has also been shown to exert anti-inflammatory effects and modulate both mitochondrial function and biogenesis. This is because mitochondrial dysfunction and neuroinflammation are features of many neurodegenerative diseases as well NRF2 has emerged as a promising therapeutic target. Here, we review evidence for a beneficial role of NRF2 in neurodegenerative conditions and the potential of specific NRF2 activators as therapeutic agents.

Loss of NRF2 leads to impaired mitochondrial function, decreased synaptic density and exacerbated age-related cognitive deficits

Activation of the antioxidant regulatory transcription factor NRF2 (Nuclear factor erythroid-derived 2) regulates cellular bioenergetics and improves neuronal health in aging. Yet how NRF2 participates in maintaining synaptic, mitochondrial and cognitive function has not been fully elucidated. This study investigates how loss of NRF2 affects neuronal metabolism, synaptic density and cognitive performance in aged mice. Dendritic arborization as well as synaptic and mitochondrial gene expression was evaluated in hippocampal neurons isolated from mice lacking NRF2 (NRF2KO) and from wild-type (WT) C57BL6 mice. Mitochondrial function of these neurons was evaluated using the Seahorse XF platform. Additionally learning, memory and executive function were assessed in 20 month old NRF2KO and age-matched WT mice using conditioned fear response (CFR) and odor discrimination reversal learning (ODRL) tests. Hippocampal bioenergetics was profiled using mitochondria isolated from these animals and tissue was harvested for assessment of mitochondrial and synaptic genes. NRF2KO neurons had reduced dendritic complexity and diminished synaptic gene expression. This was accompanied by impaired mitochondrial function and decreased mitochondrial gene expression. Similar mitochondrial deficits were observed in the brains of aged NRF2KO mice. These animals also had significantly impaired cognitive performance and reduced synaptic gene expression as well. These data point to a role for NRF2 in maintaining mitochondrial and cognitive function during aging and suggest that the transcription factor may be a viable target for cognitive enhancing interventions. Because mitochondrial dysfunction and cognitive impairment also occur together in many neurodegenerative conditions there may be broad therapeutic potential of NRF2 activating agents.

Centella Asiatica Improves Memory and Promotes Antioxidative Signaling in 5XFAD Mice

Centella asiatica (CA) herb is a traditional medicine, long reputed to provide cognitive benefits. We have reported that CA water extract (CAW) treatment improves cognitive function of aged Alzheimer’s disease (AD) model Tg2576 and wild-type (WT) mice, and induces an NRF2-regulated antioxidant response in aged WT mice. Here, CAW was administered to AD model 5XFAD female and male mice and WT littermates (age: 7.6 +/− 0.6 months), and object recall and contextual fear memory were tested after three weeks treatment. CAW’s impact on amyloid-β plaque burden, and markers of neuronal oxidative stress and synaptic density, was assessed after five weeks treatment. CAW antioxidant activity was evaluated via nuclear transcription factor (erythroid-derived 2)-like 2 (NRF2) and NRF2-regulated antioxidant response element gene expression. Memory improvement in both genders and genotypes was associated with dose-dependent CAW treatment without affecting plaque burden, and marginally increased synaptic density markers in the hippocampus and prefrontal cortex. CAW treatment increased Nrf2 in hippocampus and other NRF2 targets (heme oxygenase-1, NAD(P)H quinone dehydrogenase 1, glutamate-cysteine ligase catalytic subunit). Reduced plaque-associated SOD1, an indicator of oxidative stress, was observed in the hippocampi and cortices of CAW-treated 5XFAD mice. We postulate that CAW treatment leads to reduced oxidative stress, contributing to improved neuronal health and cognition.

An ANGPTL4-ceramide-protein kinase Cζ axis mediates chronic glucocorticoid exposure-induced hepatic steatosis and hypertriglyceridemia in mice

Chronic or excess glucocorticoid exposure causes lipid disorders such as hypertriglyceridemia and hepatic steatosis. Angptl4 (angiopoietin-like 4), a primary target gene of the glucocorticoid receptor in hepatocytes and adipocytes, is required for hypertriglyceridemia and hepatic steatosis induced by the synthetic glucocorticoid dexamethasone. Angptl4 has also been shown to be required for dexamethasone-induced hepatic ceramide production. Here, we further examined the role of ceramide-mediated signaling in hepatic dyslipidemia caused by chronic glucocorticoid exposure. Using a stable isotope-labeling technique, we found that dexamethasone treatment induced the rate of hepatic de novo lipogenesis and triglyceride synthesis. These dexamethasone responses were compromised in Angptl4-null mice (Angptl4^-/-). Treating mice with myriocin, an inhibitor of the rate-controlling enzyme of de novo ceramide synthesis, serine palmitoyltransferase long-chain base subunit 1 (SPTLC1)/SPTLC2, decreased dexamethasone-induced plasma and liver triglyceride levels in WT but not Angptl4^-/- mice. We noted similar results in mice infected with adeno-associated virus-expressing small hairpin RNAs targeting Sptlc2. Protein phosphatase 2 phosphatase activator (PP2A) and protein kinase Cζ (PKCζ) are two known downstream effectors of ceramides. We found here that mice treated with an inhibitor of PKCζ, 2-acetyl-1,3-cyclopentanedione (ACPD), had lower levels of dexamethasone-induced triglyceride accumulation in plasma and liver. However, small hairpin RNA-mediated targeting of the catalytic PP2A subunit (Ppp2ca) had no effect on dexamethasone responses on plasma and liver triglyceride levels. Overall, our results indicate that chronic dexamethasone treatment induces an ANGPTL4-ceramide-PKCζ axis that activates hepatic de novo lipogenesis and triglyceride synthesis, resulting in lipid disorders.

Centella asiatica attenuates hippocampal mitochondrial dysfunction and improves memory and executive function in β-amyloid overexpressing mice

Centella asiatica is a medicinal plant used to enhance memory. We have previously shown that a water extract of Centella asiatica (CAW) attenuates β-amyloid (Aβ)-induced spatial memory deficits in mice and improves neuronal health. Yet the effect of CAW on other cognitive domains remains unexplored as does its in vivo mechanism of improving Aβ-related cognitive impairment. This study investigates the effects of CAW on learning, memory and executive function as well as mitochondrial function and antioxidant response in the 5xFAD model of Aβ accumulation. Seven month old 5xFAD female mice were treated with CAW (2 mg/mL) in their drinking water for two weeks prior to behavioral testing. Learning, memory and executive function were assessed using the object location memory task (OLM), conditioned fear response (CFR) and odor discrimination reversal learning (ODRL) test. Mitochondrial function was profiled using the Seahorse XF platform in hippocampal mitochondria isolated from these animals and tissue was harvested for assessment of mitochondrial, antioxidant and synaptic proteins. CAW improved performance in all behavioral tests in the 5xFAD but had no effect on WT animals. Hippocampal mitochondrial function was improved and hippocampal and cortical expression of mitochondrial genes was increased in CAW-treated 5xFAD mice. Gene expression of the transcription factor NRF2, as well as its antioxidant target enzymes, was also increased with CAW treatment in both WT and 5xFAD mice. CAW treatment also decreased Aβ-plaque burden in the hippocampus of treated 5xFAD mice but had no effect on plaques in the cortex. These data show that CAW can improve many facets of Aβ-related cognitive impairment in 5xFAD mice. Oral treatment with CAW also attenuates hippocampal mitochondrial dysfunction in these animals. Because mitochondrial dysfunction and oxidative stress accompany cognitive impairment in many pathological conditions beyond Alzheimer's disease, this suggests potentially broad therapeutic utility of CAW.

Centella asiatica increases hippocampal synaptic density and improves memory and executive function in aged mice

INTRODUCTION

Centella asiatica is a plant used for centuries to enhance memory. We have previously shown that a water extract of Centella asiatica (CAW) attenuates age-related spatial memory deficits in mice and improves neuronal health. Yet the effect of CAW on other cognitive domains remains unexplored as does its mechanism of improving age-related cognitive impairment. This study investigates the effects of CAW on a variety of cognitive tasks as well as on synaptic density and mitochondrial and antioxidant pathways.

METHODS

Twenty-month-old CB6F1 mice were treated with CAW (2 mg/ml) in their drinking water for 2 weeks prior to behavioral testing. Learning, memory, and executive function were assessed using the novel object recognition task (NORT), object location memory task (OLM), and odor discrimination reversal learning (ODRL) test. Tissue was collected for Golgi analysis of spine density as well as assessment of mitochondrial, antioxidant, and synaptic proteins.

RESULTS

CAW improved performance in all behavioral tests suggesting effects on hippocampal and cortical dependent memory as well as on prefrontal cortex mediated executive function. There was also an increase in synaptic density in the treated animals, which was accompanied by increased expression of the antioxidant response gene NRF2 as well as the mitochondrial marker porin.

CONCLUSIONS

These data show that CAW can increase synaptic density as well as antioxidant and mitochondrial proteins and improve multiple facets of age-related cognitive impairment. Because mitochondrial dysfunction and oxidative stress also accompany cognitive impairment in many pathological conditions this suggests a broad therapeutic utility of CAW.

Centella asiatica triterpenes for diabetic neuropathy: a randomized, double-blind, placebo-controlled, pilot clinical study

BACKGROUND

Diabetic neuropathy (DN), a common complication of diabetes mellitus, results from hyperglycemia, poor microcirculation and attendant nerve damage. Currently available treatments relieve symptoms, but do not modify the neurodegeneration underlying DN. Centella asiatica (CA) triterpenes improved microcirculation in earlier clinical studies, and showed neurotropic effects in preclinical models suggesting a potential disease modifying effect in DN. This 52-week, randomized, double-blind, placebo-controlled trial examined the effects of CAST, a standardized CA extract containing triterpenes, on neuropathy symptoms in Type II diabetic subjects.

PATIENTS AND METHODS

The study enrolled patients with a history of Type II diabetes, with evidence of symptomatic symmetrical DN with total symptom score (TSS) ≥4, and stable HbA1c level <8. The primary outcome measure was TSS, which assessed intensity and frequency of parasthesia, numbness, pain and burning symptoms self-reported by patients. Secondary measures were nerve conduction, neurological impairment score, and quantitative sensory testing.

RESULTS

Comparing CAST (n=21) and Placebo (n=22) groups, significant reductions from baseline for TSS (p<0.01) and paresthesia (p<0.01) were seen only in CAST treated groups. Numbness increased from baseline only in the Placebo group (p<0.05) and was significantly higher than for the CAST group (p<0.001). Burning sensation was reduced in both groups (p<0.01). Plasma triterpene levels in patients treated with CAST mirrored neurotropic concentrations in vitro.

CONCLUSIONS

CAST is a potential oral treatment for diabetic neuropathy, as it is well tolerated and effective in reducing the severity of DN symptoms in patients with Type II diabetes.

Centella asiatica - Phytochemistry and mechanisms of neuroprotection and cognitive enhancement

This review describes in detail the phytochemistry and neurological effects of the medicinal herb Centella asiatica (L.) Urban. C. asiatica is a small perennial plant that grows in moist, tropical and sub-tropical regions throughout the world. Phytochemicals identified from C. asiatica to date include isoprenoids (sesquiterpenes, plant sterols, pentacyclic triterpenoids and saponins) and phenylpropanoid derivatives (eugenol derivatives, caffeoylquinic acids, and flavonoids). Contemporary methods for fingerprinting and characterization of compounds in C. asiatica extracts include liquid chromatography and/or ion mobility spectrometry in conjunction with high-resolution mass spectrometry. Multiple studies in rodent models, and a limited number of human studies support C. asiatica's traditional reputation as a cognitive enhancer, as well as its anxiolytic and anticonvulsant effects. Neuroprotective effects of C.asiatica are seen in several in vitro models, for example against beta amyloid toxicity, and appear to be associated with increased mitochondrial activity, improved antioxidant status, and/or inhibition of the pro-inflammatory enzyme, phospholipase A2. Neurotropic effects of C. asiatica include increased dendritic arborization and synaptogenesis, and may be due to modulations of signal transduction pathways such as ERK1/2 and Akt. Many of these neurotropic and neuroprotective properties of C.asiatica have been associated with the triterpene compounds asiatic acid, asiaticoside and madecassoside. More recently, caffeoylquinic acids are emerging as a second important group of active compounds in C. asiatica, with the potential of enhancing the Nrf2-antioxidant response pathway. The absorption, distribution, metabolism and excretion of the triterpenes, caffeoylquinic acids and flavonoids found in C. asiatica have been studied in humans and animal models, and the compounds or their metabolites found in the brain. This review highlights the remarkable potential for C. asiatica extracts and derivatives to be used in the treatment of neurological conditions, and considers the further research needed to actualize this possibility.

The C-terminal fibrinogen-like domain of angiopoietin-like 4 stimulates adipose tissue lipolysis and promotes energy expenditure

Angptl4 (Angiopoietin-like 4) is a circulating protein secreted by white and brown adipose tissues and the liver. Structurally, Angptl4 contains an N-terminal coiled-coil domain (CCD) connected to a C-terminal fibrinogen-like domain (FLD) via a cleavable linker, and both full-length Angptl4 and its individual domains circulate in the bloodstream. Angptl4 inhibits extracellular lipoprotein lipase (LPL) activity and stimulates the lipolysis of triacylglycerol stored by adipocytes in the white adipose tissue (WAT). The former activity is furnished by the CCD, but the Angptl4 domain responsible for stimulating adipocyte lipolysis is unknown. We show here that the purified FLD of Angptl4 is sufficient to stimulate lipolysis in mouse primary adipocytes and that increasing circulating FLD levels in mice through adenovirus-mediated overexpression (Ad-FLD) not only induces WAT lipolysis in vivo but also reduces diet-induced obesity without affecting LPL activity. Intriguingly, reduced adiposity in Ad-FLD mice was associated with increased oxygen consumption, fat utilization, and the expression of thermogenic genes (Ucp1 and Ppargc1a) in subcutaneous WAT. Moreover, Ad-FLD mice exhibited increased glucose tolerance. Chronically enhancing WAT lipolysis could produce ectopic steatosis because of an overflow of lipids from the WAT to peripheral tissues; however, this did not occur when Ad-FLD mice were fed a high-fat diet. Rather, these mice had reductions in both circulating triacylglycerol levels and the mRNA levels of lipogenic genes in the liver and skeletal muscle. We conclude that separating the FLD from the CCD-mediated LPL-inhibitory activity of full-length Angptl4 reveals lipolytic and thermogenic properties with therapeutic relevance to obesity and diabetes.

Centella asiatica attenuates Aβ-induced neurodegenerative spine loss and dendritic simplification

The medicinal plant Centella asiatica has long been used to improve memory and cognitive function. We have previously shown that a water extract from the plant (CAW) is neuroprotective against the deleterious cognitive effects of amyloid-β (Aβ) exposure in a mouse model of Alzheimer's disease, and improves learning and memory in healthy aged mice as well. This study explores the physiological underpinnings of those effects by examining how CAW, as well as chemical compounds found within the extract, modulate synaptic health in Aβ-exposed neurons. Hippocampal neurons from amyloid precursor protein over-expressing Tg2576 mice and their wild-type (WT) littermates were used to investigate the effect of CAW and various compounds found within the extract on Aβ-induced dendritic simplification and synaptic loss. CAW enhanced arborization and spine densities in WT neurons and prevented the diminished outgrowth of dendrites and loss of spines caused by Aβ exposure in Tg2576 neurons. Triterpene compounds present in CAW were found to similarly improve arborization although they did not affect spine density. In contrast caffeoylquinic acid (CQA) compounds from CAW were able to modulate both of these endpoints, although there was specificity as to which CQAs mediated which effect. These data suggest that CAW, and several of the compounds found therein, can improve dendritic arborization and synaptic differentiation in the context of Aβ exposure which may underlie the cognitive improvement observed in response to the extract in vivo. Additionally, since CAW, and its constituent compounds, also improved these endpoints in WT neurons, these results may point to a broader therapeutic utility of the extract beyond Alzheimer's disease.

Centella asiatica modulates antioxidant and mitochondrial pathways and improves cognitive function in mice

ETHNOPHARMACOLOGICAL RELEVANCE

This study investigates the cognitive enhancing effects of the plant Centella asiatica which is widely used Ayurvedic and traditional Chinese medicine.

AIM OF THE STUDY

The goal of this study was to determine the effects of a water extract of the medicinal plant Centella asiatica (CAW) on cognitive ability as well as mitochondrial and antioxidant response pathways in vivo.

MATERIALS AND METHODS

Old and young C57BL/6 mice were treated with CAW (2mg/mL) in their drinking water. Learning and memory was assessed using Morris Water Maze (MWM) and then tissue was collected and gene expression analyzed.

RESULTS

CAW improved performance in the MWM in aged animals and had a modest effect on the performance of young animals. CAW also increased the expression of mitochondrial and antioxidant response genes in the brain and liver of both young and old animals. Expression of synaptic markers was also increased in the hippocampus and frontal cortex, but not in the cerebellum of CAW-treated animals.

CONCLUSIONS

These data indicate a cognitive enhancing effect of CAW in healthy mice. The gene expression changes caused by CAW suggest a possible effect on mitochondrial biogenesis, which in conjunction with activation of antioxidant response genes could contribute to cognitive improvement.

Centella asiatica Attenuates Amyloid-β-Induced Oxidative Stress and Mitochondrial Dysfunction

BACKGROUND

We previously showed that a water extract of the medicinal plant Centella asiatica (CAW) attenuates amyloid-β (Aβ)-induced cognitive deficits in vivo, and prevents Aβ-induced cytotoxicity in vitro. Yet the neuroprotective mechanism of CAW is unknown.

OBJECTIVE

The goal of this study was to identify biochemical pathways altered by CAW using in vitro models of Aβ toxicity.

METHODS

The effects of CAW on aberrations in antioxidant response, calcium homeostasis, and mitochondrial function induced by Aβ were evaluated in MC65 and SH-SY5Y neuroblastoma cells.

RESULTS

CAW decreased intracellular reactive oxygen species and calcium levels elevated in response to Aβ, and induced the expression of antioxidant response genes in both cell lines. In SH-SY5Y cells, CAW increased basal and maximal oxygen consumption without altering spare capacity, and attenuated Aβ-induced decreases in mitochondrial respiration. CAW also prevented Aβ-induced decreases in ATP and induced the expression of mitochondrial genes and proteins in both cell types. Caffeoylquinic acids from CAW were shown to have a similar effect on antioxidant and mitochondrial gene expression in neuroblastoma cells. Primary rat hippocampal neurons treated with CAW also showed an increase in mitochondrial and antioxidant gene expression.

CONCLUSIONS

These data suggest an effect of CAW on mitochondrial biogenesis, which in conjunction with activation of antioxidant response genes and normalizing calcium homeostasis, likely contributes to its neuroprotective action against Aβ toxicity.

STX, a Novel Membrane Estrogen Receptor Ligand, Protects Against Amyloid-β Toxicity

Because STX is a selective ligand for membrane estrogen receptors, it may be able to confer the beneficial effects of estrogen without eliciting the deleterious side effects associated with activation of the nuclear estrogen receptors. This study evaluates the neuroprotective properties of STX in the context of amyloid-β (Aβ) exposure. MC65 and SH-SY5Y neuroblastoma cell lines, as well as primary hippocampal neurons from wild type (WT) and Tg2576 mice, were used to investigate the ability of STX to attenuate cell death, mitochondrial dysfunction, dendritic simplification, and synaptic loss induced by Aβ. STX prevented Aβ-induced cell death in both neuroblastoma cell lines; it also normalized the decrease in ATP and mitochondrial gene expression caused by Aβ in these cells. Notably, STX also increased ATP content and mitochondrial gene expression in control neuroblastoma cells (in the absence of Aβ). Likewise in primary neurons, STX increased ATP levels and mitochondrial gene expression in both genotypes. In addition, STX treatment enhanced dendritic arborization and spine densities in WT neurons and prevented the diminished outgrowth of dendrites caused by Aβ exposure in Tg2576 neurons. These data suggest that STX can act as an effective neuroprotective agent in the context of Aβ toxicity, improving mitochondrial function as well as dendritic growth and synaptic differentiation. In addition, since STX also improved these endpoints in the absence of Aβ, this compound may have broader therapeutic value beyond Alzheimer's disease.

Alterations in mitochondrial number and function in Alzheimer's disease fibroblasts

Mitochondrial dysfunction is observed in brains of Alzheimer's Disease patients as well as many rodent model systems including those modeling mutations in preseinilin 1 (PSEN1). The aim of our study was to characterize mitochondrial function and number in fibroblasts from AD patients with PSEN1 mutations. We used biochemical assays, metabolic profiling and fluorescent labeling to assess mitochondrial number and function in fibroblasts from three AD patients compared to fibroblasts from three controls. The mutant AD fibroblasts had increased Aβ42 relative to controls along with reduction in ATP, basal and maximal mitochondrial respiration as well as impaired spare mitochondrial respiratory capacity. Fluorescent staining and expression of genes encoding electron transport chain enzymes showed diminished mitochondrial content in the AD fibroblasts. This study demonstrates that mitochondrial dysfunction is observable in AD fibroblasts and provides evidence that this model system could be useful as a tool to screen disease-modifying compounds.

Caffeoylquinic acids in Centella asiatica protect against amyloid-β toxicity

The accumulation of amyloid-β (Aβ) is a hallmark of Alzheimer's disease and is known to result in neurotoxicity both in vivo and in vitro. We previously demonstrated that treatment with the water extract of Centella asiatica (CAW) improves learning and memory deficits in Tg2576 mice, an animal model of Aβ accumulation. However the active compounds in CAW remain unknown. Here we used two in vitro models of Aβ toxicity to confirm this neuroprotective effect and identify several active constituents of the CAW extract. CAW reduced Aβ-induced cell death and attenuated Aβ-induced changes in tau expression and phosphorylation in both the MC65 and SH-SY5Y neuroblastoma cell lines. We confirmed and quantified the presence of several mono- and dicaffeoylquinic acids (CQAs) in CAW using chromatographic separation coupled to mass spectrometry and ultraviolet spectroscopy. Multiple dicaffeoylquinic acids showed efficacy in protecting MC65 cells against Aβ-induced cytotoxicity. Isochlorogenic acid A and 1,5-dicaffeoylquinic acid were found to be the most abundant CQAs in CAW, and the most active in protecting MC65 cells from Aβ-induced cell death. Both compounds showed neuroprotective activity in MC65 and SH-SY5Y cells at concentrations comparable to their levels in CAW. Each compound not only mitigated Aβ-induced cell death, but was able to attenuate Aβ-induced alterations in tau expression and phosphorylation in both cell lines, as seen with CAW. These data suggest that CQAs are active neuroprotective components in CAW, and therefore are important markers for future studies on CAW standardization, bioavailability, and dosing.

Angiopoietin-like 4 (Angptl4): A glucocorticoid-dependent gatekeeper of fatty acid flux during fasting

Angiopoietin-like 4 (Angptl4) is a secreted protein modulating triacylglycerol homeostasis. Its transcription is induced by glucocorticoids, which act to elevate circulating Angptl4 levels during fasting. In investigating the role of Angptl4 in glucocorticoid action, we identified that in addition to its known ability to inhibit lipoprotein lipase, Angptl4 stimulates intracellular adipocyte lipolysis. Fatty acid release by murine adipocytes following fasting or treatment with glucocorticoids or catecholamines is highly Angptl4-dependent. In fact, Angptl4 can directly stimulate cAMP-dependent PKA signaling and lipolysis when added to adipocytes. Here, we detail this novel Angptl4-dependent lipolytic regulatory mechanism and discuss its physiological and therapeutic implications.

Regulation of triglyceride metabolism by glucocorticoid receptor

Glucocorticoids are steroid hormones that play critical and complex roles in the regulation of triglyceride (TG) homeostasis. Depending on physiological states, glucocorticoids can modulate both TG synthesis and hydrolysis. More intriguingly, glucocorticoids can concurrently affect these two processes in adipocytes. The metabolic effects of glucocorticoids are conferred by intracellular glucocorticoid receptors (GR). GR is a transcription factor that, upon binding to glucocorticoids, regulates the transcriptional rate of specific genes. These GR primary target genes further initiate the physiological and pathological responses of glucocorticoids. In this article, we overview glucocorticoid-regulated genes, especially those potential GR primary target genes, involved in glucocorticoid-regulated TG metabolism. We also discuss transcriptional regulators that could act with GR to participate in these processes. This knowledge is not only important for the fundamental understanding of steroid hormone actions, but also are essential for future therapeutic interventions against metabolic diseases associated with aberrant glucocorticoid signaling, such as insulin resistance, dyslipidemia, central obesity and hepatic steatosis.

Angiopoietin-like 4 (Angptl4) protein is a physiological mediator of intracellular lipolysis in murine adipocytes

Intracellular triacylglycerol (TG) hydrolysis and fatty acid release by the white adipose tissue (WAT) during a fast is stimulated by counter-regulatory factors acting in concert, although how adipocytes integrate these lipolytic inputs is unknown. We tested the role of angiopoietin-like 4 (Angptl4), a secreted protein induced by fasting or glucocorticoid treatment, in modulating intracellular adipocyte lipolysis. Glucocorticoid receptor blockade prevented fasting-induced tissue Angptl4 expression and WAT TG hydrolysis in mice, and TG hydrolysis induced by fasts of 6 or 24 h was greatly reduced in mice lacking Angptl4 (Angptl4(-/-)). Glucocorticoid treatment mimicked the lipolytic effects of fasting, although with slower kinetics, and this too required Angptl4. Thus, fasting-induced WAT TG hydrolysis requires glucocorticoid action and Angptl4. Both fasting and glucocorticoid treatment also increased WAT cAMP levels and downstream phosphorylation of lipolytic enzymes. Angptl4 deficiency markedly reduced these effects, suggesting that Angptl4 may stimulate lipolysis by modulating cAMP-dependent signaling. In support of this, cAMP levels and TG hydrolysis were reduced in primary Angptl4(-/-) murine adipocytes treated with catecholamines, which stimulate cAMP-dependent signaling to promote lipolysis, and was restored by treatment with purified human ANGPTL4. Remarkably, human ANGPTL4 treatment alone increased cAMP levels and induced lipolysis in these cells. Pharmacologic agents revealed that Angptl4 modulation of cAMP-dependent signaling occurs upstream of adenylate cyclase and downstream of receptor activation. We show that Angptl4 is a glucocorticoid-responsive mediator of fasting-induced intracellular lipolysis and stimulates cAMP signaling in adipocytes. Such a role is relevant to diseases of aberrant lipolysis, such as insulin resistance.

Angiopoietin-like 4 (ANGPTL4, fasting-induced adipose factor) is a direct glucocorticoid receptor target and participates in glucocorticoid-regulated triglyceride metabolism

Glucocorticoids are important regulators of lipid homeostasis, and chronically elevated glucocorticoid levels induce hypertriglyceridemia, hepatic steatosis, and visceral obesity. The occupied glucocorticoid receptor (GR) is a transcription factor. However, those genes regulating lipid metabolism under GR control are not fully known. Angiopoietin-like 4 (ANGPTL4, fasting-induced adipose factor), a protein inhibitor of lipoprotein lipase, is synthesized and secreted during fasting, when circulating glucocorticoid levels are physiologically increased. We therefore tested whether the ANGPTL4 gene (Angptl4) is transcriptionally controlled by GR. We show that treatment with the synthetic glucocorticoid dexamethasone increased Angptl4 mRNA levels in primary hepatocytes and adipocytes (2-3-fold) and in the livers and white adipose tissue of mice (approximately 4-fold). We tested the mechanism of this increase in H4IIE hepatoma cells and found that dexamethasone treatment increased the transcriptional rate of Angptl4. Using bioinformatics and chromatin immunoprecipitation, we identified a GR binding site within the rat Angptl4 sequence. A reporter plasmid containing this site was markedly activated by dexamethasone, indicative of a functional glucocorticoid response element. Dexamethasone treatment also increased histone H4 acetylation and DNase I accessibility in genomic regions near this site, further supporting that it is a glucocorticoid response element. Glucocorticoids promote the flux of triglycerides from white adipose tissue to liver. We found that mice lacking ANGPTL4 (Angptl4(-/-)) had reductions in dexamethasone-induced hypertriglyceridemia and hepatic steatosis, suggesting that ANGPTL4 is required for this flux. Overall, we establish that ANGPTL4 is a direct GR target that participates in glucocorticoid-regulated triglyceride metabolism.

Endocrine-immune-paracrine interactions in prostate cells as targeted by phytomedicines

Dehydroepiandrosterone (DHEA) is used as a dietary supplement and can be metabolized to androgens and/or estrogens in the prostate. We investigated the hypothesis that DHEA metabolism may be increased in a reactive prostate stroma environment in the presence of proinflammatory cytokines such as transforming growth factor beta1 (TGFbeta1), and further, whether red clover extract, which contains a variety of compounds including isoflavones, can reverse this effect. LAPC-4 prostate cancer cells were grown in coculture with prostate stromal cells (6S) and treated with DHEA +/- TGFbeta1 or interleukin-6. Prostate-specific antigen (PSA) expression and testosterone secretion in LAPC-4/6S cocultures were compared with those in monocultured epithelial and stromal cells by real-time PCR and/or ELISA. Combined administration of TGFbeta1 + DHEA to cocultures increased PSA protein secretion two to four times, and PSA gene expression up to 50-fold. DHEA + TGFbeta1 also increased coculture production of testosterone over DHEA treatment alone. Red clover isoflavone treatment led to a dose-dependent decrease in PSA protein and gene expression and testosterone metabolism induced by TGFbeta1 + DHEA in prostate LAPC-4/6S cocultures. In this coculture model of endocrine-immune-paracrine interactions in the prostate, TGFbeta1 greatly increased stromal-mediated DHEA effects on testosterone production and epithelial cell PSA production, whereas red clover isoflavones reversed these effects.

Human prostate stromal cells stimulate increased PSA production in DHEA-treated prostate cancer epithelial cells

Dehydroepiandrosterone (DHEA) is commonly used as a dietary supplement and may affect prostate pathophysiology when metabolized to androgens and/or estrogens. Human prostate LAPC-4 cancer cells with a wild type androgen receptor (AR) were treated with DHEA, androgens dihydrotestosterone (DHT), T, or R1881), and E2 and assayed for prostate specific antigen (PSA) protein and gene expression. In LAPC-4 monocultures, DHEA and E2 induced little or no increase in PSA protein or mRNA expression compared to androgen-treated cells. When prostate cancer-associated (6S) stromal cells were added in coculture, DHEA stimulated LAPC-4 cell PSA protein secretion to levels approaching induction by DHT. Also, DHEA induced 15-fold more PSA mRNA in LAPC-4 cocultures than in monocultures. LAPC-4 proliferation was increased 2-3-fold when cocultured with 6S stromal cells regardless of hormone treatment. DHEA-treated 6S stromal cells exhibited a dose- and time-dependent increase in T secretion, demonstrating stromal cell metabolism of DHEA to T. Coculture with non-cancerous stroma did not induce LAPC-4 PSA production, suggesting a differential modulation of DHEA effect in a cancer-associated prostate stromal environment. This coculture model provides a research approach to reveal detailed endocrine, intracrine, and paracrine signaling between stromal and epithelial cells that regulate tissue homeostasis within the prostate, and the role of the tumor microenvironment in cancer progression.

Effects of neuropeptide Y on feeding microstructure: Dissociation of appetitive and consummatory actions

The effects of intracerebroventricular application of Neuropeptide Y (NPY) on licking microstructure for sucrose, saccharin, and water solutions were evaluated. In Experiment 1, NPY increased meal size for three sucrose concentrations (0.03 M, 0.3 M, and 1.0 M) by increasing licking burst number but not size and by extending meals more than four-fold in duration with a slow, sustained rate of ingestion in late phases of the meal. Results are consistent with the interpretation that NPY suppressed inhibitory postingestive feedback. Experiment 2 supported this conclusion. NPY significantly increased the number of meals initiated for water, 0.1% saccharin, and 1.0 M sucrose solutions, but meal size was only increased for 1.0 M sucrose. Therefore, NPY also increased appetitive feeding behaviors, but its consummatory effects were limited to caloric solutions. The results are discussed with regard to their potential to explain current discrepancies in the literature.

The expression profile for the tumour suppressor gene PTEN and associated polymorphic markers

PTEN, a putative tumour suppressor gene associated with prostate and other cancers, is known to be located within the chromosomal region 10q23.3. Transcription of the PTEN gives rise to multiple mRNA species. Analyses by Northern blots, using cell lines which express PTEN together with cell lines which have lost the PTEN or carry a truncated version of the gene, has allowed us to demonstrate that the pseudogene is not transcribed. In addition, 3' RACE studies confirmed that the multiple mRNA species arising from the gene probably result from the use of alternative polyadenylation sites. No evidence for tissue- or cell-specific patterns of transcription was found. Analysis by 5' RACE placed the putative site for the start of transcription around 830 bp upstream of the start codon. A map of the location of the PTEN gene with a series of overlapping YAC, BAC and PACs has been constructed and the relative position of eight microsatellite markers sited. Two known and one novel marker have been positioned within the gene, the others are in flanking regions. The more accurate location of these markers should help in future studies of the extent of gene loss. Several polymorphisms were also identified, all were within introns. Four of the common polymorphisms appear to be linked. In blood, DNA from 200 individuals, including normal, BPH and prostate cancer patients, confirmed this link. Only two samples of 200 did not carry the linked haplotype, both were patients with advanced prostate cancer. It is possible that such rearrangements within PTEN could be evidence of predisposition to prostate cancer in this small number of cases.

Mutation and expression analysis of the putative prostate tumour-suppressor gene PTEN

The chromosomal region 10q23-24 is frequently deleted in a number of tumour types, including prostate adenocarcinoma and glioma. A candidate tumour-suppressor gene at 10q23.3, designated PTENor MMAC1, with putative actin-binding and tyrosine phosphatase domains has recently been described. Mutations in PTEN have been identified in cell lines derived from gliomas, melanomas and prostate tumours and from a number of tumour specimens derived from glial, breast, endometrial and kidney tissue. Germline mutations in PTEN appear to be responsible for Cowden disease. We identified five PTEN mutations in 37 primary prostatic tumours analysed and found that 70% of tumours showed loss or alteration of at least one PTEN allele, supporting the evidence for PTEN involvement in prostate tumour progression. We raised antisera to a peptide from PTEN and showed that reactivity occurs in numerous small cytoplasmic organelles and that the protein is commonly expressed in a variety of cell types. Northern blot analysis revealed multiple RNA species; some arise as a result of alternative polyadenylation sites, but others may be due to alternative splicing.