Ellagic acid ameliorates learning and memory deficits in a rat model of Alzheimer's disease: an exploration of underlying mechanisms

Ellagic acid ameliorates learning and memory impairment in APP/PS1 transgenic mice via inhibition of β-amyloid production and tau hyperphosphorylation

β-amyloid (Aβ) aggregation and tau hyperphosphorylation are considered to be the primary pathological hallmarks of Alzheimer's disease (AD). Targeted inhibition of these pathological processes may provide effective treatments for AD. Accumulating evidence has demonstrated that ellagic acid (EA) exerts neuroprotective effects in several diseases. The present study investigated the effects of EA on AD-associated learning and memory deficits on APP/PS1 double transgenic mice and the underlying mechanisms. APP/PS1 mice or wild-type C57BL/6 mice were intragastrically administered EA (50 mg/kg/day) or vehicle for 60 consecutive days. The learning and memory abilities of mice were investigated using the Morris water maze test. Hippocampal regions were examined for the presence of amyloid plaques, neuronal apoptosis and tau phosphorylation. Expression levels of APP, Aβ, RAC-αserine/threonine-protein kinase and glycogen synthase kinase (GSK)3β in the hippocampus were determined by western blot analysis and ELISA. The results demonstrated that EA treatment ameliorated spatial learning and memory impairment in APP/PS1 mice and significantly reduced neuronal apoptosis and Aβ deposition in the hippocampus (P<0.05 and P<0.01). In addition, EA significantly inhibited the hyperphosphorylation of tau and significantly decreased the activity of glycogen synthase kinase (GSK)3β (P<0.01), which is involved in tau phosphorylation. Overall, these findings indicated that the beneficial effects of EA on AD-associated cognitive impairments may be attributed to the inhibition of Aβ production and tau hyperphosphorylation, and its beneficial action may be mediated in part, by the RAC-α serine/threonine-protein kinase/GSK3β signaling pathway.

Ellagic acid prevents dementia through modulation of PI3-kinase-endothelial nitric oxide synthase signalling in streptozotocin-treated rats

Ellagic acid (EGA)-enriched dietary supplements are widely acclaimed, owing to its versatile bioactivities. Previously, we reported that chronic administration of EGA prevented the impairment of cognitive abilities in rats using the intracerebroventricular-administered streptozotocin (STZ-ICV) model of Alzheimer's disease. Impairment of phosphoinositide 3 (PI3)-kinase-regulated endothelial nitric oxide synthase (eNOS) activity by central administration of STZ in rodents instigates dementia. The aim of the present study was to delineate the role of PI3-kinase-eNOS activity in the prevention of STZ-ICV-induced memory dysfunctions by EGA. The Morris water maze and elevated plus maze tests were conducted, and brain oxidative stress markers (TBARS, GSH, SOD, CAT), nitrite, acetylcholinesterase (AChE), LDH, TNF-α and eNOS were quantified. Administration of EGA (35 mg/k, p.o.) for 4 weeks daily attenuated the STZ-ICV (3 mg/kg)-triggered increase of brain oxidative stress, nitrite and TNF-α levels; AChE and LDH activity; and decline of brain eNOS activity. The memory restoration by EGA in STZ-ICV-treated rats was conspicuously impaired by N(G)-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg, 28 days) and wortmannin (5 μg/rat; ICV) treatments. Wortmannin (PI3-kinase inhibitor) and L-NAME groups manifested elevated brain oxidative stress, TNF-α content and AChE and LDH activity and diminished nitrite content. L-NAME (arginine-based competitive eNOS inhibitor) enhanced the eNOS expression (not activity) whereas wortmannin reduced the brain eNOS levels in EGA- and STZ-ICV-treated rats. However, the L-NAME group exhibited superior cognitive abilities in comparison to the wortmannin group. It can be concluded that EGA averted the memory deficits by precluding the STZ-ICV-induced loss of PI3-kinase-eNOS signalling in the brain of rats.

Ellagic acid attenuates arsenic induced neuro-inflammation and mitochondrial dysfunction associated apoptosis

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Ellagic acid mitigates arsenic mediated genotoxicity in rat brain hippocampi.

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Ellagic acid ameliorates arsenic induced exacerbation in levels of ROS and pro-inflammatory cytokines in rat brain hippocampi.

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Ellagic acid has the propensity to modulate mRNA expression of BAX, Bcl₂ and caspase3, suggestive of its neuroprotective efficacy.

Arsenic, being a global pollutant needs a potential remedy which could fight against its associated toxicities. Ellagic acid (EA) is a known agent for its anti-inflammatory, antioxidant and antiapoptotic effects, and it is commonly found in fruits. The present study is designed to determine protective efficacy of EA against arsenic induced toxicity with special mention to inflammation and mitochondrial dysfunction in hippocampi of wistar rats. Rats were pre-treated with EA (20 and 40 mg/kg b.wt; p.o. for 11 days) along with arsenic (10 mg/kg; p.o. for 8 days). Total reactive oxygen species level and mitochondrial membrane potential were analyzed using flow cytometry. Protein and mRNA expression of apoptotic and inflammatory markers were also evaluated in rat hippocampus. Our results show that arsenic exposure increased total ROS generation and DNA fragmentation, decreased mitochondrial membrane potential alongwith an increase in expression of pro-apoptotic and inflammatory markers. suggesting that EA complementation downregulated total ROS generation dose dependently. Apoptotic markers, BAX and Bcl₂ as well as inflammatory markers, IL-1β, TNFα, INFγ got altered significantly on its administration. Moreover, it also attenuated effects on mitochondrial membrane potential. Based on our findings, EA might substantiate to be a budding therapeutic candidate against arsenic induced neurotoxicity.

Ellagic acid in suppressing in vivo and in vitro oxidative stresses

Oxidative stress is a biological condition produced by a variety of factors, causing several chronic diseases. Oxidative stress was, therefore, treated with natural antioxidants, such as ellagic acid (EA). EA has a major role in protecting against different diseases associated with oxidative stress. This review critically discussed the antioxidant role of EA in biological systems. The in vitro and in vivo studies have confirmed the protective role of EA in suppressing oxidative stress. The review also discussed the mechanism of EA in suppressing of oxidative stress, which showed that EA activates specific endogenous antioxidant enzymes and suppresses specific genes responsible for inflammation, diseases, or disturbance of biochemical systems. The amount of EA used and duration, which plays a significant role in the treatment of oxidative stress has been discussed. In conclusion, EA is a strong natural antioxidant, which possesses the suppressing power of oxidative stress in biological systems.