HIGH-DENSITY-LIPOPROTEIN 3 PHYSICOCHEMICAL MODIFICATIONS INDUCED BY INTERACTION WITH HUMAN POLYMORPHONUCLEAR LEUKOCYTES AFFECT THEIR ABILITY TO REMOVE CHOLESTEROL FROM CELLS

1. We have recently reported that a short incubation (60 min) in vitro of high-density lipoprotein (HDL) 3 with human polymorphonuclear leuc ocytes (PMNs) leads to a proteolytic cleavage of apolipoprotein (ape) AII and to a change in the distribution of apo AI isoforms [Cogny, Pau l, Atger, Soni and Moatti (1994) Fur. J. Biochem. 222, 965-973]. Since PMNs have been observed to be present in the earliest atherosclerotic lesions for a number of days, we investigated the HDL3 physicochemica l modifications induced by in vitro interaction for a long period of t ime (24 h) with PMNs and the consequences of the changes on the abilit y of HDL3 to remove cholesterol from cells, 2. The stimulated PMN modi fication of HDL3 over 24 h resulted in a partial loss of protein with no variation in lipid molar ratio and a loss of 50% of HDL alpha-tocop herol content. The decrease in total protein was due first to a comple te degradation of apo AII, and secondly to a partial loss of apo AI. T he apo AI remaining on the particles was in part hydrolysed and the ap o AI-1 isoform was completely shifted to the apo AI-2 isoform. These a po changes were accompanied by a displacement of the native HDL3 appar ent size toward predominantly larger particles. 3. The ability of PMN- modified HDL3 to remove H-3-labelled free cholesterol from cells was m easured in two cell lines: Fu5AH rat hepatoma cells and J774 mouse mac rophages, HDL3 which had only a limited contact with PMNs (60 min) sho wed only a small non-significant reduction in the efficiency of choles terol efflux. On the other hand, compared with native HDL3, HDL3 modif ied by PMNs for 24 h had a markedly reduced ability to remove choleste rol from cells, regardless of the type of cell. 4. The results suggest that PMN-modified HDL3, if occurring in vivo, could contribute to acc eleration of the atherogenic process by decreasing the cholesterol eff lux from cells.