Arachidonic Acid Cascade Driven Neurotoxicity in Hypobaric Hypoxia: An invivo Study

Abstract

BackgroundA continuous supply of oxygen to cerebral tissue is required for maintaining its homeostasis. Any interruption in delivery of oxygen leads to cerebral hypoxia related neuronal damage. . The growing bodies of evidences reveal that cerebral hypoxia induced at high altitude promotes the production of excessive ROS resulting in oxidative stress. Cerebral tissue is prone to oxidative stress damage because of high content of PUFA in their cell membrane and weak antioxidant defence system. Arachidonic acid(C20) is the most abundant form of PUFA which is present in brain. Under stress conditions arachidonic acid is metabolized by cyclooxygenase(COX‐2) and 12/15 Lipoxygenase in cerebral tissue which leads to the production of several prooxidant and anti‐inflammatory molecules. Experimental studies suggest that hypoxia induce oxidative burden which initiate the upregulation of arachodonic acid cascade enzyme 12/15LOX and COX‐2.MethodIn present study we aimed to investigate the modulatory role of 12/15 LOX and COX‐2 by using specific inhibitor of 12/15 LOX (baicalein) and COX‐2 (NS398) on neuronal damage induced by hypobaric hypoxia.ResultsAnimals subjected to hypobaric hypoxia in a specially designed decompression chamber experience cerebral hypoxia as confirmed by the elevated expression of HIF‐1a protein which is universal transcription factor that senses oxygen balance in cellular milieu. Further COX‐2 and 12/15 lipoxygenase gene and protein expression were significantly upregulated in hypoxia condition. Moreover histopathological study showed marked increase in death of neurons in hypoxia condition and inhibitor of 12/15 LOX and COX‐2 attenuated the neurotoxicity during cerebral hypoxia suggesting the contribution of arachidonic acid cascade in hypoxia condition. In addition to above biochemical studies like LDH assay, MDA assay for lipid peroxidation and nitric oxide levels revealed that oxidative stress mediated neuronal damage caused by hypoxia was attenuated significantly by 12/15 LOX and COX‐2 inhibitors confirming involvement of 12/15 LOX and COX‐2. TUNEL analysis confirmed the apoptotic form of cell death in hypoxia as dUTP labeled DNA fragments were significantly increased further 12/15LOX and COX‐2 enzyme inhibitor rescued the neuronal cells from apoptosis.ConclusionThe primary study using pharmacological inhibitors provide the strong evidence towards the contribution of arachidonic acid cascade in pathogenesis of cerebral hypoxia injury .Support or Funding InformationAuthors acknowledge Council for Scientific and Industrial Research (CSIR) India for financial assistance.