Changes in cerebral membrane lipid composition and fluidity during thioacetamide-induced hepatic encephalopathy.
Lipids are an essential structural and functional component of cellular membranes. Changes in membrane lipid composition are known to affect the activities of many membrane-associated enzymes, endocytosis, exocytosis, membrane fusion and neurotransmitter uptake, and have been implicated in the pathophysiology of many neurodegenerative disorders. In the present study, we investigated changes in the lipid composition of membranes isolated from the cerebral cortex of rats treated with thioacetamide (TAA), a hepatotoxin that induces fulminant hepatic failure (FHF) and thereon hepatic encephalopathy (HE). HE refers to acute neuropsychiatric changes accompanying FHF. The estimation of membrane phospholipids, cholesterol and fatty acid content in cerebral cortex membranes from TAA-treated rats revealed a decrease in cholesterol, phosphatidylserine, sphingomyelin, a monounsaturated fatty acid, namely oleic acid, and the polyunsaturated fatty acids gamma-linolenic acid, decosa hexanoic acid and arachidonic acid compared with controls. Assessment of membrane fluidity with pyrene, 1,6-diphenyl-1,3,5-hexatriene and 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene revealed a decrease in the annular membrane fluidity, whereas the global fluidity was unaffected. The level of the thiobarbituric acid reactive species marker for lipid peroxidation also increased in membranes from TAA-treated rats, thereby indicating the prevalence of oxidative stress. Results from the present study demonstrate gross alterations in cerebral cortical membrane lipid composition and fluidity during TAA-induced HE, and their possible implications in the pathogenesis of this condition are also discussed.