Structural changes of high‐density‐lipoprotein apolipoproteins following incubation with human polymorphonuclear cells

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Abstract
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 oxidative 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 2 x 10(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 reached peak concentration at 15 min. HDL apolipoproteins (apo) analysed by immunoblotting after SDS/PAGE and electrofocusing evidenced the following 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 distribution 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 modification nor lipid oxidation, assessed by thiobarbituric-acid-reactive substances (TBARS) were noted. Despite a lack of variation of TBARS, a decrease in HDL vitamin E content by 80% was observed. Since this decrease was prevented by addition of superoxide dismutase in the medium, we concluded the occurrence of an oxidative process affecting HDL. Experiments with proteolytic inhibitors showed that elastase caused the proteolytic cleavage of apolipoprotein E, AII and Cs. In contrast, apo AI modification might involve both oxidative and proteolytic processes.