Inhibition of cyclooxygenase-2 aggravates secretory phospholipase A2-mediated progression of acute liver injury

Our previous study [Bhave, V. S., Donthamsetty, S., Latendresse, J. R., Muskhelishvili, L., and Mehendale, H. M. 2008-this issue. Secretory phospholipase A(2) mediates progression of acute liver injury in the absence of sufficient COX-2. Toxicol Appl Pharmacol] showed that in the absence of sufficient induction and co-presence of cyclooxygenase-2 (COX-2), secretory phospholipase A(2) (sPLA(2)) appearing in the intercellular spaces for cleanup of post-necrotic debris seems to contribute to the progression of toxicant-initiated liver injury, possibly by hydrolysis of membrane phospholipids of hepatocytes in the perinecrotic areas. To further test our hypothesis on the protective role of COX-2, male Fisher-344 rats were administered a selective COX-2 inhibitor, NS-398, and then challenged with a moderately toxic dose of CCl(4). This led to a 5-fold increase in the susceptibility of the COX-2 inhibited rats to CCl(4) hepatotoxicity and mortality. The CCl(4) bioactivating enzyme CYP2E1 protein, CYP2E1 enzyme activity, and the (14)CCl(4)-derived radiolabel covalently bound to the liver proteins were unaffected by the COX-2 inhibitor suggesting that the increased hepatotoxic sensitivity of the COX-2 inhibited rats was not due to higher bioactivation of CCl(4). Further investigation showed that this increased mortality was due to higher plasma and hepatic sPLA(2) activities, inhibited PGE(2) production, and progression of liver injury as compared to the non-intervened rats(.) In conclusion, inhibition of COX-2 mitigates the tissue protective mechanisms associated with COX-2 induction, which promotes sPLA(2)-mediated progression of liver injury in an acute liver toxicity model. Because increased sPLA(2) activity in the intercellular space is associated with increased progression of injury, and induced COX-2 is associated with hepatoprotection, ratios of hepatic COX-2 and sPLA(2) activities may turn out to be a useful tool in predicting the extent of hepatotoxicities.