Effects of oxidized low density lipoproteins on arachidonic acid metabolism in smooth muscle cells

The role of oxidized plasma lipoproteins in modifying arachidonic acid (AA) metabolism was studied in smooth muscle cells (SMC). Very low density lipoproteins (VLDL), unoxidized low density lipoproteins (LDLBHT) isolated with butylated hydroxytoluene (BHT), and oxidized LDL (LDLOXID) were separated from human serum. Thiobarbituric acid reactant (TBAR) levels were adjusted by saline incubations. Prostanoids in guinea pig SMC cultures were measured either by radioimmunoassay (RIA) or the isolation by high performance liquid chromatography (HPLC) of labeled prostanoids from SMC prelabeled with 14C]AA. Cell morphology and viability were studied by staining with Giemsa, nile red, and propidium iodide. VLDL and LDLBHT had little effect on prostanoid synthesis. Low-TBAR-LDLOXID enhanced total prostanoid levels and diminished the release of labeled prostanoids. Similar effects were found with exogenous free AA (unlabeled). Low-TBAR-LDLOXID did not affect the release of endogenous phospholipid AA as free AA. Synergism occurred between LDLOXID and exogenous free AA in prostanoid synthesis. Low-TBAR-LDLOXID evidently enhanced prostanoid levels in SMC both by supplying AA and by stimulating cyclooxygenase. High-TBAR-LDLOXID blocked prostanoid synthesis and enhanced cell death but time and pulse-recovery experiments showed that these effects were unrelated. High-TBAR-LDLOXID stimulated prostanoid synthesis when BHT was added to the incubation media. High-TBAR-LDLOXID also caused massive free AA release and the formation of many nonprostanoid derivatives. High-TBAR-LDLOXID evidently diminished overall prostanoid levels in SMC by inhibiting cyclooxygenase and at the same time stimulating AA release and the formation of other AA derivatives.