Decreased Arachidonate Metabolism in Mouse Peritoneal Macrophages after Foam Cell Transformation with Oxidized Low-Density Lipoproteins

Abstract

Oxidized low density lipoproteins (LDL) are now considered to be one of the atherogenic lipoproteins in vivo and to play an important role in the pathogenesis of atherosclerosis. We previously demonstrated in mouse peritoneal macrophages that oxidized LDL stimulated prostaglandin (PG) E₂ synthesis when incorporated into the cells [Yokode, M. et al. (1988) J. Clin. Invest. 81, 720-729]. In this study, we investigated arachidonate metabolism in macrophages after foam cell transformation. The cells were incubated with 100μg/ml of oxidized LDL for 18h, then stimulated with zymosan. Lipid-enriched macrophages which had taken up oxidized LDL produced much less eicosanoids, such as PGE₂, 6-keto-PGF_1α, and leukotriene C₄ than control cells. After labeling of the cells with [¹⁴C] arachidonic acid, they were stimulated with zymosan and the phospholipase activity was determined. The activity of lipid-enriched cells was about two-thirds of that of control cells. Then we investigated the fatty acid composition of their phospholipid fraction to clarify arachidonic acid content and mobilization. Percent of arachidonic acid of lipid-enriched cells decreased and less arachidonic acid mobilization was observed after stimulation with zymosan. These data suggest that impaired arachidonate metabolism in lipid-enriched macrophages can be explained by their decreased phospholipase activity and changes in their fatty acid composition.