Biosynthesis of oxidized lipid mediators via lipoprotein-associated phospholipase A₂ hydrolysis of extracellular cardiolipin induces endothelial toxicity

We (66) have previously described an NSAID-insensitive intramitochondrial biosynthetic pathway involving oxidation of the polyunsaturated mitochondrial phospholipid, cardiolipin (CL), followed by hydrolysis [by calcium-independent mitochondrial calcium-independent phospholipase A_2-γ (iPLA_2γ)] of oxidized CL (CLox), leading to the formation of lysoCL and oxygenated octadecadienoic metabolites. We now describe a model system utilizing oxidative lipidomics/mass spectrometry and bioassays on cultured bovine pulmonary artery endothelial cells (BPAECs) to assess the impact of CLox that we show, in vivo, can be released to the extracellular space and may be hydrolyzed by lipoprotein-associated PLA₂ (Lp-PLA₂). Chemically oxidized liposomes containing bovine heart CL produced multiple oxygenated species. Addition of Lp-PLA₂ hydrolyzed CLox and produced (oxygenated) monolysoCL and dilysoCL and oxidized octadecadienoic metabolites including 9-and 13-hydroxyoctadecadienoic (HODE) acids. CLox caused BPAEC necrosis that was exacerbated by Lp-PLA₂. Lower doses of nonlethal CLox increased permeability of BPAEC monolayers. This effect was exacerbated by Lp-PLA₂ and partially mimicked by authentic monolysoCL or 9-or 13-HODE. Control mice plasma contained virtually no detectable CLox; in contrast, 4 h after Pseudomonas aeruginosa (P. aeruginosa) infection, 34 ± 8 mol% (n = 6; P < 0.02) of circulating CL was oxidized. In addition, molar percentage of monolysoCL increased twofold after P. aeruginosa in a subgroup analyzed for these changes. Collectively, these studies suggest an important role for 1) oxidation of CL in proinflammatory environments and 2) possible hydrolysis of CLox in extracellular spaces producing lysoCL and oxidized octadecadienoic acid metabolites that may lead to impairment of pulmonary endothelial barrier function and necrosis.