Alpesh Kumar Sharma

Hypobaric hypoxia induces oxidative stress in rat brain

High altitude exposure results in decreased partial pressure of oxygen and an increased formation of reactive oxygen and nitrogen species (RONS), which causes oxidative damage to lipids, proteins and DNA. Exposure to high altitude appears to decrease the activity and effectiveness of antioxidant enzyme system. The antioxidant system is very less in brain tissue and is very much susceptible to hypoxic stress. The aim of the present study was to investigate the time dependent and region specific changes in cortex, hippocampus and striatum on oxidative stress markers on chronic exposure to hypobaric hypoxia. The rats were exposed to simulated high altitude equivalent to 6100 m in animal decompression chamber for 3 and 7 days. Results indicate an increase in oxidative stress as seen by increase in free radical production, nitric oxide level, lipid peroxidation and lactate dehydrogenase levels. The magnitude of increase in oxidative stress was more in 7 days exposure group as compared to 3 days exposure group. The antioxidant defence system such as reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD) and reduced/oxidized glutathione (GSH/GSSG) levels were significantly decreased in all the three regions. The observation suggests that the hippocampus is more susceptible to hypoxia than the cortex and striatum. It may be concluded that hypoxia differentially affects the antioxidant status in the cortex, hippocampus and striatum.

Acetylcholinesterase inhibitors enhance cognitive functions in rats following hypobaric hypoxia

Hypobaric hypoxia (HBH) can produce neuropsychological disorders such as insomnia, dizziness, memory deficiencies, headache and nausea. It is well known that exposure to HBH cause alterations of neurotransmitters and cognitive impairment in terms of learning and memory. But the mechanisms are poorly understood. The present study aimed to investigate the cholinergic system alterations associated with simulated HBH induced cognitive impairment. Male Sprague-Dawley rats were exposed to HBH equivalent to 6100 m for 7 days in a simulation chamber. The cognitive performance was assessed using Morris Water Maze (MWM) task. Cholinergic markers like acetylcholine (ACh) and acetylcholinesterase (AChE) were evaluated in hippocampus and cortex of rats. Neuronal damage was also studied through morphological changes. Exposure to HBH led to impairment in relearning ability and memory retrieval and it was accompanied by decrease in ACh level and increase in AChE and led to morphological damage. Administration of AChE inhibitor (AChEI), physostigmine (PHY) and galantamine (GAL) to rats during HBH exposure resulted in amelioration of the deleterious effects induced by HBH. The AChEIs were able to improve the cholinergic activity by restoring the level of ACh by blocking the AChE activity. In addition, the AChEIs also prevented neurodegeneration by reducing the AChE level in cortical and hippocampal neurons.

Preventive effect of piracetam and vinpocetine on hypoxia-reoxygenation induced injury in primary hippocampal culture.

The present study investigates the potential of Piracetam and Vinpocetine (nootropic drugs, known to possess neuroprotective properties) in preventing hypoxia-reoxygenation induced oxidative stress in primary hippocampal cell culture. The hippocampal culture was exposed to hypoxia (95% N(2), 5% CO(2)) for 3h and followed by 1h of reoxygenation (21% O(2) and 5% CO(2)) at 37 °C. The primary hippocampal cultures were supplemented with the optimum dose of Piracetam and Vinpocetine, independently, and the cultures were divided into six groups, viz. Control/Normoxia, Hypoxia, Hypoxia+Piracetam, Hypoxia+Vinpocetine, Normoxia + Piracetam and Normoxia+Vinpocetine. The cell-viability assays and biochemical oxidative stress parameters were evaluated for each of the six groups. Administration of 1mM Piracetam or 500 nM Vinpocetine significantly prevents the culture from hypoxia-reoxygenation injury when determined by Neutral Red assay, LDH release and Acetylcholine esterase activity. Results showed that Piracetam and Vinpocetine supplementation significantly prevented the fall of mitochondrial membrane potential, rise in ROS generation and reduction in antioxidant levels associated with the hypoxia-reoxygenation injury. In conclusion, the present study establishes that both Piracetam and Vinpocetine give neuroprotection against hypoxia-reoxygenation injury in primary hippocampal cell culture.

Possible role of cholinesterase inhibitors on memory consolidation following hypobaric hypoxia of rats.

ABSTRACT High altitude (HA) generates a deleterious effect known as hypobaric hypoxia (HBH). This causes severe physiological and psychological changes such as acute mountain sickness (AMS) and cognitive functions in terms of learning and memory. The present study has evaluated the effect of cholinesterase inhibitors on memory consolidation following HBH. Adult male Sprague Dawley rats (80–90 days old) with an average body weight of 250 ± 25 g were used. Rats were assessed memory consolidation by using Morris water maze (MWM) for 8 days. After assessment of memory consolidation, rats were then exposed to HBH in stimulated chamber for 7 days at 6,100 m. After exposure to HBH, the memory consolidation of rats has been assessed in MWM. The results showed that there was memory consolidation impairment in HBH-exposed rats as compared to normoxic rats in terms of time spent in quaradents, rings, and counters. The rats which have been treated with physostigmine (PHY) and galantamine (GAL) showed better time spent in quaradents, rings, and counters as compared with hypoxic rats. In conclusion, the cholinesterase inhibitors could ameliorate the impairment of memory consolidation following HBH.

Chromenone and quinolinone derivatives as potent antioxidant agents

The antioxidant activity (AOA) of three different classes of phenolic compounds viz chromen-2-ones, chromen-4-ones, and quinolin-2-ones was systematically studied using DPPH, ABTS, FRAP, and in vitro lipid peroxidation inhibition assays. The effect of incorporation of hydrophobic group on AOA was also studied. In DPPH, ABTS, and FRAP assays, the highest AOA was registered for the dihydroxy chromenones among all the phenolic derivatives. Presence of alkyl group led to reduction in AOA in the above three assays. However, in lipid peroxidation inhibition assay for selected compounds, incorporation of alkyl group led to enhancement in AOA. The AOA of few compounds was observed to be more than three times higher in comparison to standard “Trolox” in lipid peroxidation inhibitory assay.

Changes in ghrelin, CCK, GLP-1, and peroxisome proliferator-activated receptors in a hypoxia-induced anorexia rat model

INTRODUCTION A high-altitude environment causes appetite loss in unacclimatised humans, leading to weight reduction. Ghrelin, cholecystokinin (CCK), and glucagon like peptide-1 (GLP-1), are gut hormones involved in the regulation of food intake and energy metabolism. The liver is an important site of metabolic regulation, and together with the gut it plays a role in food intake regulation. This study intends to study the time-dependent changes occurring in plasma gut hormones, PPARα, PPARδ, and PGC1α, in the stomach and liver during hypoxia. MATERIAL AND METHODS Male Sprague Dawley rats were exposed to hypobaric hypoxia in a decompression chamber at 7620 m for different durations up to seven days. RESULTS Hypoxia increased circulating ghrelin from the third day onwards while CCK and GLP-1 decreased immediately. An increase in ghrelin, ghrelin receptor protein levels, and GOAT mRNA levels in the stomach was observed. Stomach cholecystokinin receptor (CCKAR), PPARα, and PPARδ decreased. Liver CCKAR decreased during the first day of hypoxia and returned to normal levels from the third day onwards. PPARα and PGC1α expression increased while PPARδ protein levels reduced in the liver on third day. CONCLUSION Hypoxia alters the expression of ghrelin and ghrelin receptor in the stomach, CCKAR in the liver, and PPAR and its cofactors, which might be possible role players in the contribution of gut and liver to anorexia at high altitude.

PRMT1 promotes hyperglycemia in a FoxO1-dependent manner, affecting glucose metabolism, during hypobaric hypoxia exposure, in rat model

PurposeHigh-altitude (HA) environment causes changes in cellular metabolism among unacclimatized humans. Previous studies have revealed that insulin-dependent activation of protein kinase B (Akt) regulates metabolic processes via discrete transcriptional effectors. Moreover, protein arginine methyltransferase (PRMT)1-dependent arginine modification of forkhead box other (FoxO)1 protein interferes with Akt-dependent phosphorylation. The present study was undertaken to test the involvement of PRMT1 on FoxO1 activation during hypobaric hypoxia (HH) exposure in rat model.MethodsSamples were obtained from normoxia control (NC) and HH-exposed (H) rats, subdivided according to the duration of HH exposure. To explore the specific role played by PRMT1 during HH exposure, samples from 1d pair-fed (PF) NC, 1d acute hypoxia-exposed (AH) placebo-treated, and 1d AH TC-E-5003-treated rats were investigated. Quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) was performed to determine expressions of glycolytic, gluconeogenic enzymes, and insulin response regulating genes. Immuno-blot and enzyme linked immunosorbent assay (ELISA) were used for insulin response regulating proteins. Nuclear translocation of FoxO1 was analyzed using deoxyribonucleic acid (DNA)-binding ELISA kit.ResultsWe observed HH-induced increase in glycolytic enzyme expressions in hepatic tissue unlike hypothalamic tissue. PRMT1 expression increased during HH exposure, causing insulin resistance and resulting increase in FoxO1 nuclear translocation, leading to hyperglycemia. Conversely, PRMT1 inhibitor treatment promoted inhibition of FoxO1 activity and increase in glucose uptake during HH exposure leading to reduction in blood-glucose and hepatic glycogen levels.ConclusionsPRMT1 might have a potential importance as a therapeutic target for the treatment of HH-induced maladies.