Selective inhibition of cytosolic phospholipase A2 in activated human monocytes. Regulation of superoxide anion production and low density lipoprotein oxidation.

Our previous studies have shown that monocyte activation and release of O-2 are required for monocyte-mediated low density lipoprotein (LDL) lipid oxidation. We have also found that intracellular Ca2+ levels and protein kinase C activity are requisite participants in this potentially pathogenic process. In these studies, we further investigated the mechanisms involved in the oxidation of LDL lipids by activated human monocytes, particularly the potential contributions of the cytosolic phospholipase A2 (cPLA2) signaling pathway. The most well-studied cPLA2, has a molecular mass of 85 kDa and has been reported to be regulated by both Ca2+ and phosphorylation. We found that cPLA2 protein levels and cPLA2 enzymatic activity were induced upon activation of human monocytes by opsonized zymosan. Pharmacologic inhibition of cPLA2 activity by AACOCF3, which has been reported to be a specific inhibitor of cPLA2 as compared with sPLA2, caused a dose-dependent inhibition of cPLA2 enzymatic activity and LDL lipid oxidation by activated human monocytes, whereas sPLA2 activity was not affected. To corroborate these findings, we used specific antisense oligonucleotides to inhibit cPLA2. We observed that treatment with antisense oligonucleotides caused suppression of both cPLA2 protein expression and enzymatic activity as well as monocyte-mediated LDL lipid oxidation. Furthermore, antisense oligonucleotide treatment caused a substantial inhibition of O-2 production by activated human monocytes. In parallel experimental groups, cPLA2 sense oligonucleotides did not affect cPLA2 protein expression, cPLA2 enzymatic activity, O-2 production, or monocyte-mediated LDL lipid oxidation. These studies support the proposal that cPLA2 activity is required for activated monocytes to oxidize LDL lipids.