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

Abstract

Rationale Oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine generates a group of bioactive oxidized phospholipid products (OxPAPC) with a broad range of biological activities. Barrier-enhancing and anti-inflammatory effects of OxPAPC on pulmonary endothelial cells (EC) 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. Objective 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 pro-resolving lipid mediator, lipoxin A4 (LXA4). Methods and Results 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 EC. Administration of LXA4 reproduced anti-inflammatory effect of OxPAPC against TNFα in vitro and in the animal model of LPS-induced lung injury. The potent barrier protective and anti-inflammatory effects of OxPAPC against TNFα and LPS challenge were suppressed in human pulmonary EC with siRNA-induced knockdown of LXA4 formyl-peptide receptor-2 (FPR2/ALX) and in mFPR2−/− mice lacking the mouse homolog of human FPR2/ALX. Conclusions This is the first demonstration that inflammation- and injury-associated phospholipid oxidation triggers production of anti-inflammatory and pro-resolution molecules such as LXA4. This lipid mediator switch represents a novel mechanism of OxPAPC-assisted recovery of inflamed lung endothelium.

Oxidized Phospholipids in Healthy and Diseased Lung Endothelium

“…Indeed, these pro-resolving molecules such as lipoxins and resolvins are produced as a part of so-called "lipid program switch" at the later stages of inflammation to overcome the harmful effects of pro-inflammatory molecules generated at the early phases [101]. This phenomenon was best illustrated in one of our recent study where we found that OxPAPC stimulates the generation of lipoxin A4 (LXA4) in cultured EC as well as mice lungs that protects against TNF-α or LPS-induced vascular leak and inflammation [35]. The activation of formyl peptide receptor 2 was involved in mediating the anti-inflammatory effects of OxPAPC-generated LXA4.…”

“…More importantly, OxPAPC accelerates the recovery of thrombin-induced endothelial permeability. Comprehensive studies from our laboratory have described OxPAPC protection in several models of agonist-induced endothelial barrier dysfunction including LPS, TNF-α, Staphylococcus aureus, and mechanical forces [34][35][36]. These studies also showed that endothelial barrier protective effects of OxPLs are restricted to purified full-length oxygenated species or total OxPAPC pool containing majority of full length OxPL species at low concentrations.…”

The Good and Bad Faces of Oxidized Phospholipids: Friends or Foes of Vascular Endothelium?

“…A number of studies from our group have demonstrated the anti‐inflammatory effects of OxPAPC in various cellular as well as murine models of lung inflammation . Recently, our study showed that OxPAPC induces the production of an important anti‐inflammatory and pro‐resolving lipid mediator LXA 4 in cultured endothelial cells and in mice lungs . We found that formyl‐peptide receptor 2 (FPR2) is involved in mediating the anti‐inflammatory effects of LXA 4 formed .…”

“…Recently, our study showed that OxPAPC induces the production of an important anti‐inflammatory and pro‐resolving lipid mediator LXA 4 in cultured endothelial cells and in mice lungs . We found that formyl‐peptide receptor 2 (FPR2) is involved in mediating the anti‐inflammatory effects of LXA 4 formed . These observations suggest that identifying such beneficial lipid mediators produced by OxPAPC would be important in developing therapeutics against inflammation‐caused lung injuries.…”

“…Whether this mechanism is applicable for acute endothelial lung injury, was not studied. Additionally, a recent study has revealed a previously unknown mechanism of OxPAPC‐dependent production of an anti‐inflammatory and pro‐resolving lipid mediator lipoxin A 4 (LXA 4 ) . At a mechanistic level, small GTPases Rac and Rap1 appear to be key effector proteins mediating cytoskeletal remodeling during OxPAPC‐induced improvement of endothelial barrier function.…”