Withania somnifera root extract ameliorates hypobaric hypoxia induced memory impairment in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Withania somnifera (WS) root extract has been used traditionally in ayurvedic system of medicine as a memory enhancer and anti-stress agent. AIM OF THE STUDY: To evaluate the neuroprotective and prophylactic potential of WS root extract in ameliorating hypobaric hypoxia (HH) induced memory impairment and to explore the underlying molecular mechanism. MATERIALS AND METHODS: WS root extract was administered to male Sprague Dawley rats during a period of 21 days pre-exposure and 07 days exposure to a simulated altitude of 25,000 ft. Spatial memory was assessed by Morris Water Maze. Neurodegeneration, corticosterone, acetylcholine (Ach) levels, acetylcholine esterase (AchE) activity, oxidative stress markers and nitric oxide (NO) concentration were assessed in the hippocampus. Synaptic and apoptotic markers were also investigated by immunoblotting. To study the role of NO in regulating corticosterone mediated signaling, the neuronal nitric oxide synthase (n-NOS) inhibitor, L-Nitro-arginine methyl ester (L-Name) and NO agonist sodium nitroprusside (SNP) were administered from 3rd to 7th day of hypoxic exposure. RESULTS: Administration of WS root extract prevented HH induced memory impairment and neurodegeneration along with decreased NO, corticosterone, oxidative stress and AchE activity in hippocampal region. Inhibition of NO synthesis by administration of L-Name reduced corticosterone levels in hippocampus during hypoxic exposure while co-administration of corticosterone increased neurodegeneration. Administration of sodium nitroprusside (SNP) along with WS root extract supplementation during hypoxic exposure increased corticosterone levels and increased the number of pyknotic cells. CONCLUSION: WS root extract ameliorated HH induced memory impairment and neurodegeneration in hippocampus through NO mediated modulation of corticosterone levels.

Acetyl-L-carnitine-mediated neuroprotection during hypoxia is attributed to ERK1/2-Nrf2-regulated mitochondrial biosynthesis.

Neuronal damage in hypoxia and several neurodegenerative disorders is invariably associated with oxidative damage and mitochondrial dysfunction. Administration of acetyl-L-carnitine (ALCAR) on the other hand attenuates neuronal damage, prevents apoptosis, and improves energy status in hypoxic stress through less understood mechanisms. Becasue mitochondrial biogenesis could be a possible mechanism for ALCAR-induced improvement in bioenergetics in neurons, the present study aimed at exploring signaling pathways of ALCAR-induced neuroprotection in hypoxia and possible occurrence of mitochondrial biogenesis. To create global hypoxia, adult Sprague-Dawley rats were exposed to a simulated altitude of 7,620 m at standard temperature and humidity conditions. We here demonstrate that administration of ALCAR to hypoxic rats for a period of 2 weeks effectively protected hippocampal neurons from mitochondrial dysfunction, excitotoxicity, and neurodegeneration. ALCAR administration resulted in peroxisome proliferator-activated receptor γ coactivator-1α and nuclear respiratory factor-1-induced mitochondrial biogenesis, the expression of which was regulated by an extracellular-related kinase-nuclear factor erythroid 2-related factor 2 (ERK-Nrf2)-mediated mechanism. Most notably, calcium buffering into nonfunctional mitochondria ameliorated excitotoxicity and improved bioenergetic status of the hippocampal neurons. Together, the data reveal the immense therapeutic potential of ALCAR for the treatment of ischemia, stroke, and other neurodegenerative disorders associated with hypoxic stress and excitotoxicity.

Oxidative-stress-induced alterations in Sp factors mediate transcriptional regulation of the NR1 subunit in hippocampus during hypoxia.

Ascent to high altitude is associated with tissue hypoxia resulting from the decrease in partial pressure of atmospheric oxygen. The hippocampus, in particular, is highly vulnerable to hypoxic insult, which at least in part can be attributed to the occurrence of glutamate excitotoxicity. Although this excitotoxic damage is often related to increased NMDA receptor activation and subsequent calcium-mediated free radical generation, the mechanisms involving the transcriptional regulation of NMDA receptor subunit expression by hypoxic stress remains to be explored. Our study reveals a novel mechanism for the regulation of expression of the NR1 subunit of NMDA receptors by the Sp family of transcription factors through an oxidative-stress-mediated mechanism that also involves the molecular chaperone Hsp90. The findings not only show the occurrence of lipid peroxidation and DNA damage in hippocampal cells exposed to hypoxia but also reveal a calcium-independent mechanism of selective oxidation and degradation of Sp3 by the 20S proteasome. This along with increased DNA binding activity of Sp1 leads to NR1 upregulation in the hippocampus during hypoxic stress. The study therefore provides evidence for free radical-mediated regulation of gene expression in hypoxia and the scope of the use of antioxidants in preventing excitotoxic neuronal damage during hypoxia.