HOCI-HDL impairs endothelium-dependent dilatation

One of the potential in vivo oxidants able to modify/oxidize (lipo)proteins is hypochlorous acid (HOCI) which is generated by the myeloperoxidase-H2O2-halide system of activated phagocytes. HOCI-modified (lipo )proteins colocalize with monocytes/macrophages and endothelial cells in human lesion material. We have recently shown that modification of high density lipoprotein (HDL) by HOCI (added as reagent or generated by the myeloperoxidase-H2O2-halide system) transformed an antiatherogenic lipoprotein particle into a modified lipoprotein particle with characteristics similar to lipoproteins commonly thought to initiate foam cell formation. We further could show that HOCl-HDL is bound and internalized by scavenger receptors present on human endothelial cells. We now hypothesize that HOCI-HDL shifts the balance between endothelium-mediated vasodilation and vasoconstriction and alters the expression of molecules promoting leukocyte adhesion. We propose an impaired biosynthesis of NO and NO synthase (NOS) by HOCI-HDL. Finally we hypothesize that regulation of scavenger receptors and activation of NF-kB will represent a major cause for impaired HOCI-HDL- dependent endothelium dilatation. Specific aims for testing the central hypothesis are: 1. Understand the underlying mechanisms of impaired NO biosynthesis and modulation of expression of NOS by HOCI-HDL in endothelial cells. 2. Delineate the pathways of expression of adhesion molecules and NF-kB on endothelial cells by HOCI-HDL. 3. Identify whether HOCI-HDL modulates expression of LOX-l and hSR-BI, scavenger receptors mediating holoparticle uptake or selective lipid uptake from HOCl-HDL. 4. Investigate whether HOCl-HDL may alter [Ca2+ ]i, phospholipase A2, and eicosanoid biosynthesis in endothelial cells. We believe that the outcome of this proposal will provide new and useful information to understand biological properties of endothelial cells that are exposed to a potentially proatherogenic lipoproteins occurring in vivo.

One of the potential in vivo oxidants able to modify/oxidize (lipo)proteins is hypochlorous acid (HOCl) which is generated by the myeloperoxidase-H2 O2 -halide system of activated phagocytes. HOCl-modified (lipo)proteins colocalize with monocytes/macrophages and endothelial cells in human lesion material. We have recently shown that modification of high density lipoprotein (HDL) by HOCl (added as reagent or generated by the myeloperoxidase-H2 O2 -halide system) transformed an antiatherogenic lipoprotein particle into a modified lipoprotein particle with characteristics similar to lipoproteins commonly thought to initiate foam cell formation. We further could show that HOCl-HDL is bound and internalized by scavenger receptors present on human endothelial cells. We now hypothesize that HOCl-HDL shifts the balance between endothelium-mediated vasodilation and vasoconstriction and alters the expression of molecules promoting leukocyte adhesion. We propose an impaired biosynthesis of NO and NO synthase (NOS) by HOCl-HDL. Finally we hypothesize that regulation of scavenger receptors will represent a major cause for impaired HOCl-HDL-dependent endothelium dilatation. Here we show that HDL - modified with physiologically relevant HOCl concentrations - attenuates the expression and activity of vasculoprotective endothelial nitric oxide synthase. HOCl-HDL promotes dislocalization of endothelial nitric oxide synthase from the plasma membrane and perinuclear location of human umbilical venous endothelial cells. We could identify 2-chlorohexadecanal as the active component mediating this inhibitory activity. This chlorinated fatty aldehyde is formed during HOCl-mediated oxidative cleavage of HDL-associated plasmalogen. 2-Chlorohexadecanal, produced by the myeloperoxidase-hydrogen peroxide-chloride system of activated phagocytes may act as a mediator of vascular injury associated with ischemia-reperfusion injury, glomerulosclerosis, atherosclerosis, and cardiac death.