The 15-lipoxygenase-modified high density lipoproteins 3 fail to inhibit the TNF-α-induced inflammatory response in human endothelial cells

Endothelial dysfunction represents one of the earliest events in vascular atherogenesis. Proinflammatory stimuli activate endothelial cells, resulting in an increased expression of adhesion molecules and chemoattractants that mediate leukocyte and monocyte adhesion, migration, and homing. High density lipoproteins (HDL) inhibit endothelial cell expression of adhesion molecules in response to proinflammatory stimuli. In the present work, we demonstrate that the modification of HDL₃ (the major and the most antiatherogenic HDL subfraction) by 15-lipoxygenase (15-LO), an enzyme overexpressed in the atherosclerotic lesions, impairs the anti-inflammatory activity of this lipoprotein. The 15-LO-modified HDL₃ failed to inhibit TNF-α-mediated mRNA and protein induction of adhesion molecules and MCP-1 in several models of human endothelial cells, and promoted inflammatory response by up-regulating the expression of such mediators of inflammation and by increasing monocyte adhesion to endothelial cells. Moreover, 15-LO-modified HDL₃ were unable to contrast the formation of reactive oxygen species in cells incubated with TNF-α, and increased the reactive oxygen species content in unstimulated cells. Activation of NF-κB and AP-1 was mainly involved in the expression of adhesion molecules and MCP-1 induced by 15-LO-HDL₃. Altogether, these results demonstrate that enzymatic modification induced by 15-LO impaired the protective role of HDL₃, generating a dysfunctional lipoprotein endowed with proinflammatory characteristics.