Human neutrophils employ the myeloperoxidase/hydrogen peroxide/chloride system to oxidatively damage apolipoprotein A-I.
The structural integrity of apolipoprotein A-I (apo A-I) is critical to the physiological function of high-density lipoprotein (HDL). Oxidized lipoproteins are thought to be of central importance in atherogenesis, and oxidation products characteristic of myeloperoxidase, a heme protein secreted by activated phagocytes, have been detected in human atherosclerotic tissue. At plasma concentrations of halide ion, hypochlorous acid is a major product of the myeloperoxidase-hydrogen peroxide-chloride system. We therefore investigated the effects of activated human neutrophils, a potent source of myeloperoxidase and hydrogen peroxide, on the protein and lipid components of HDL. Both free and HDL-associated apo A-I exposed to activated human neutrophils underwent extensive degradation as monitored by RP-HPLC and Western blotting with a polyclonal antibody to apo A-I. Replacement of the neutrophils with reagent HOCl resulted in comparable damage (at molar oxidant : HDL subclass 3 ratio = 100) as observed in the presence of activated phagocytes. Apo A-I degradation by activated neutrophils was partially inhibited by the HOCl scavenger methionine, by the heme inhibitor azide, by chloride-free conditions, by the peroxide scavenger catalase, and by a combination of superoxide dismutase (SOD)/catalase, implicating HOCl in the cell-mediated reaction. The addition of a protease inhibitor (3,4-dichloroisocoumarin) further reduced the extent of apo A-I damage. In contrast to the protein moiety, there was little evidence for oxidation of unsaturated fatty acids or cholesterol in HDL3 exposed to activated neutrophils, suggesting that HOCl was selectively damaging apo A-I. Our observations indicate that HOCl generated by myeloperoxidase represents one pathway for protein degradation in HDL3 exposed to activated phagocytes.
Bergt
C
C
Institute of Medical Biochemistry and Molecular Biology, University Graz, Austria.
Marsche
G
G
Panzenboeck
U
U
Heinecke
J W
JW
Malle
E
E
Sattler
W
W
D015153:Blotting, Western; D002374:Catalase / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D009504:Neutrophils / Q000201:enzymology / Q000378:metabolism*; D009195:Peroxidase / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism
D002712:Chlorides; D006861:Hydrogen Peroxide; D002374:Catalase; D009195:Peroxidase; D013482:Superoxide Dismutase