Inhibition of the mitogen activated protein kinase, p38α, prevents proinflammatory cytokine induction by human adherent mononuclear leukocytes in response to lipid loading

Macrophage infiltration, inflammatory processes and oxidatively modified low density lipoprotein (LDL) are known contributing factors in the formation of the atherosclerotic plaque. To determine whether a direct link might exist between these factors, we examined the effect of oxidized LDL upon proinflammatory cytokine production in adherent human peripheral blood mononuclear leukocytes. Oxidized LDL, as well as a combination of cholesterol and 25-hydroxycholesterol, induced tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) mRNA as measured by quantitative real time PCR, by a maximum of two- to fourfold following a 24-h incubation. Analysis of cell culture supernatants revealed a concomitant stimulation of TNFα and IL-1β secreted protein as determined by ELISA. Treatment of human peripheral blood mononuclear leukocytes with oxidized LDL or the combination of cholesterol and 25-hydroxycholesterol caused activation of p38α as determined by the ability of immunoprecipitated p38 to phosphorylate an ATF-2 fusion protein, a surrogate substrate of p38α. VK-19911 (Pyridine, 4-[4-(4-fluorophenyl)-1-(4-piperidinyl)-1H-imidazol-5-yl]-dihydrochloride), a specific inhibitor of p38α, prevented the induction of TNFα and IL-1β by oxidized LDL in a dose-dependent manner. Activated p38α is known to be involved in the stabilization of cyclooxygenase-2 mRNA in response to stimuli such as lipopolysaccharide; however, in the setting of oxidized LDL-induced p38α activation, COX-2 mRNA levels were not affected. Taken together, the data imply a potential role for p38α activation in lipid-associated inflammatory processes.