Lipid hydroperoxides inhibit nitric oxide production in RAW264.7 macrophages

The effects of oxidatively modified low density lipoprotein (oxLDL) on athe rogenesis may be partly mediated by alterations in the production of nitric oxide (NO) by vascular cells. Lipid hydroperoxides (LOOH) and lysophosphat idylcholine (lysoPC) are the major primary products of LDL oxidation. The p urpose of this study was to characterize the effects of oxLDL, LOOK and lys oPC on NO production and the expression of inducible nitric oxide synthase (iNOS) gene in lipopolysaccharide (LPS) stimulated macrophages. LDL was oxi dized using an ate-initiator 2,2'-azobis (2-amidinopropane) HCl (ABAP) and octadecadienoic acid was oxidized by Lipoxygenase to generate 13-hydroperox yl octadecadienoic acid (13-HPODE). Our study showed that oxLDL markedly de creased the production of NO, the levels of iNOS protein and iNOS mRNA in L PS stimulated macrophages. The inhibition potential of oxLDL on NO producti on and iNOS gene expression depended on the levels of LOOK formed in oxLDL and was not due to oxLDL cytotoxicity. Furthermore, 13-HPODE markedly reduc ed NO production and iNOS protein levels, whereas lysoPC showed only slight reduction. The effects of 13-HPODE and lysoPC did not require an acetylate d LDL carrier. Our results suggest that 13-HPODE is a much more potent inhi bitor of NO production and iNOS gene expression than lysoPC in LPS stimulat ed RAW264.7 macrophages. (C) 1999 Elsevier Science Inc.