Anti-Inflammatory Effects of OxPAPC Involve Endothelial Cell-Mediated Generation of LXA4

Oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) generates a group of bioactive oxidized phospholipid products with a broad range of biological activities. Barrier-enhancing and anti-inflammatory effects of OxPAPC on pulmonary endothelial cells are critical for prevention of acute lung injury caused by bacterial pathogens or excessive mechanical ventilation. Anti-inflammatory properties of OxPAPC are associated with its antagonistic effects on Toll-like receptors and suppression of RhoA GTPase signaling.

Because OxPAPC exhibits long-lasting anti-inflammatory and lung-protective effects even after single administration in vivo, we tested the hypothesis that these effects may be mediated by additional mechanisms, such as OxPAPC-dependent production of anti-inflammatory and proresolving lipid mediator, lipoxin A4 (LXA4).

Mass spectrometry and ELISA assays detected significant accumulation of LXA4 in the lungs of OxPAPC-treated mice and in conditioned medium of OxPAPC-exposed pulmonary endothelial cells. Administration of LXA4 reproduced anti-inflammatory effect of OxPAPC against tumor necrosis factor-α in vitro and in the animal model of lipopolysaccharide-induced lung injury. The potent barrier-protective and anti-inflammatory effects of OxPAPC against tumor necrosis factor-α and lipopolysaccharide challenge were suppressed in human pulmonary endothelial cells with small interfering RNA-induced knockdown of LXA4 formyl peptide receptor-2 (FPR2/ALX) and in mFPR2^-/- (mouse formyl peptide receptor 2) mice lacking the mouse homolog of human FPR2/ALX.

This is the first demonstration that inflammation- and injury-associated phospholipid oxidation triggers production of anti-inflammatory and proresolution molecules, such as LXA4. This lipid mediator switch represents a novel mechanism of OxPAPC-assisted recovery of inflamed lung endothelium.