STRUCTURAL-CHANGES OF HIGH-DENSITY-LIPOPROTEIN APOLIPOPROTEINS FOLLOWING INCUBATION WITH HUMAN POLYMORPHONUCLEAR CELLS

Based on the analogy in mechanisms and events between the pathogenesis of atherosclerosis and the inflammatory reaction, we investigated the impact of human polymorphonuclear leukocyte (PMN) degranulation and o xidative process on high-density-lipoprotein (HDL) structure. HDL were incubated (37 degrees C) with PMN at a physiological ratio (370 nmol cholesterol-HDL/ml with 2x10(6) PMN/ml) for 15, 30 and 60 min with or without stimulating agent. PMN activation was assessed by measurement of superoxide anion generation and elastase production, which both rea ched peak concentration at 15 min. HDL apolipoproteins (ape) analysed by immunoblotting after SDS/PAGE and electrofocusing evidenced the fol lowing modifications: (a) a slow hydrolysis of apo AII and apo Cs; (b) a rapid hydrolysis of apo E; (c) a change in apo AI isoform distribut ion with an increase in the most acidic isoform (AI-2) at the expense of a less acidic form (AI-1); (d) a shift of the major apo AII isoform into two more basic forms. In contrast, no quantifiable lipid modific ation nor lipid oxidation, assessed by thiobarbituric-acid-reactive su bstances (TBARS) were noted. Despite a lack of variation of TBARS, a d ecrease in HDL vitamin E content by 80% was observed. Since this decre ase was prevented by addition of superoxide dismutase in the medium, w e concluded the occurence of an oxidative process affecting HDL. Exper iments with proteolytic inhibitors showed that elastase caused the pro teolytic cleavage of apolipoprotein E, AII and Cs. In contrast, apo AI modification might involve both oxidative and proteolytic processes.