Inhibition by unsaturated fatty acids of type II secretory phospholipase A₂ synthesis in guinea‐pig alveolar macrophages

Abstract

The effect of arachidonic acid (C20:4) on the production of secretory type II phospholipase A 2 (sPLA 2 -II) by guinea-pig alveolar macrophages was investigated. We show that incubation of these cells with 1±30 mm of arachidonic acid inhibits the synthesis of sPLA 2 -II in a concentration-dependent manner with an IC 50 of < 7.5 mm. The inhibition by low concentrations (5 mm) of arachidonic acid was partially reduced by pretreatment of alveolar macrophages with cyclooxygenase or cytochrome P450 inhibitors (aspirin and 1-aminobenzotriazole, respectively), but not by lipoxygenase inhibitor, BW A4C. However, these inhibitors failed to interfere with the effect of high concentrations (30 mm) of arachidonic acid, suggesting that the latter may act on the expression of sPLA 2 -II, at least in part, independently of eicosanoid generation. Indeed, a similar inhibitory effect on sPLA 2 -II activity and mRNA expression was observed with other unsaturated fatty acids such as eicosapentaenoic (C20:5) and oleic (C18:1) acids, but not with the saturated fatty acid, palmitic acid (C16:0). In addition, arachidonic acid partially reduced the secretion of tumor necrosis factor a, an important intermediate in the induction of sPLA 2 -II synthesis by guinea-pig alveolar macrophages. However, addition of recombinant tumor necrosis factor a failed to reverse the inhibitory effect of arachidonic acid on sPLA 2 -II expression, suggesting that this process occurs downstream of tumor necrosis factor a secretion. We conclude that the expression of sPLA 2 -II in alveolar macrophages is down-regulated at the transcriptional level by arachidonic acid either directly or via its cyclooxygenase and cytochrome P450-derived metabolites.

85-kDa Cytosolic Phospholipase A2 Mediates Peroxisome Proliferator-activated Receptor γ Activation in Human Lung Epithelial Cells

“…D, the cPLA 2 inhibitor, AACOCF 3 , inhibits PPAR binding in a dose-dependent manner. A549 cells were incubated with Me 2 SO or preincubated (for 30 min) with AACOCF 3 (10,25, and 50 M) followed by an incubation with A23187 (10 Ϫ6 M) or media with Me 2 SO for 1 h. Cells were harvested, and nuclear protein was extracted for EMSA as described under "Experimental Procedures." From each sample, 3 g of nuclear protein were incubated with 32 P-labeled PPAR oligonucleotide probes.…”

“…For example, leukotriene B 4 , a lipoxygenase product of AA, is a natural ligand for PPAR␣ (15), and 15-deoxy-⌬ 12,14 prostaglandin J 2 , a cyclooxygenase pathway product, is a potent ligand for PPAR␥ (16,17). In addition to the known effect of prostaglandins and leukotrienes, arachidonic acid itself also activates PPARs (10). These findings suggest a potentially important role of AA metabolism in the regulation of intracellular signal events through activation of PPARs.…”