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Toxin-Induced Activation of Rat Hepatocyte Prostaglandin Synthesis and Phospholipid Metabolism

Abstract : The effects of microcystin-LR, a trichothecene, T-2 and saxitoxin on membrane lipid mediators of inflammatory processes were evaluated in cultured rat hepatocytes. Microcystin-LR significantly stimulated the release of prostacyclin, measured as 6-keto PGF(a a) by 38% (p<0.01) and thromboxane B2 (TxB2) by 50%, (p<0.001) in a concentration-dependent manner. The trichothecene toxin, T-2 enhanced the release of prostaglandin F(2a) (PGF2a) by 24% (p <0.05) and arachidonic acid by 29% (p <0.05); while saxitoxin failed to cause the release of prostaglandins or arachidonic acid. Incorporation of arachidonic acid into the lipid pool was reduced to 47% (p <0.025) by 1 micromole microcystin-LR. Changes in phospholipid classes indicated that prostaglandin formation induced by microcystin-LR was due to the release of arachidonic acid from the phosphatidylinositol pool. No statistically significant effect of toxin was observed on other classes of phospholipids or neutral lipids. A 10% increase in phosphatidylcholine in hepatocytes treated with microcystin-LR may have resulted from conversion of phosphatidylethanolamine to phosphatidylcholine via the N- methylation pathway. These results indicate that microcystin-LR has important effects on the regulation of inflammatory mediator synthesis in hepatocytes.