C-reactive protein modulates lipid mediators in a pro-inflammatory direction

C-reactive protein (CRP) is a risk factor for atherosclerosis. Although inflammation may confound this association, CRP itself has been hypothesized to possess both pro-atherosclerotic and pro-inflammatory properties. In this study, we aimed to elucidate the mechanism by which CRP may modulate bioactive lipid mediators. We found that the overexpression of human CRP increased plasma IL-6 and TNF-a levels in mice. Moreover, the conditioned medium of CRP-overexpressing HepG2 cells increased the release of these cytokines from RAW264.7 cells to a greater degree than recombinant CRP. Lipidomics analyses then revealed that the overexpression of CRP increased the total levels of plasma lysophosphatidic acid, lysophosphatidylethanolamine, lysophosphatidylglycerol, lysophosphatidylinositol, and sphingosine 1-phosphate in mice. It also increased the levels of pro-inflammatory arachidonic acid derivatives, including PGE2 metabolites, LTA4 metabolites, and oxylipids, and decreased the levels of anti-inflammatory eicosapentaenoic acid- and docosahexaenoic acid-derived mediators. In regard to the mechanisms, analyses of CRP-overexpressing HepG2 cells suggested that CRP may increase the hepatic production of glycero-lysophospholipids, and may also modulate eicosanoids and related mediators outside the liver. Finally, analyses of the fraction separated using anti-CRP IgG suggested that CRP can bind several lipid mediators including sphingosine 1-phosphate, PGE2, and PGF2a. CRP may modulate lysophospholipids, and eicosanoids, and related mediators in pro-atherosclerotic and pro-inflammatory directions.