CHOLESTEROL CHLOROHYDRIN SYNTHESIS BY THE MYELOPEROXIDASE-HYDROGEN PEROXIDE-CHLORIDE SYSTEM - POTENTIAL MARKERS FOR LIPOPROTEINS OXIDATIVELY DAMAGED BY PHAGOCYTES

Myeloperoxidase, a heme protein secreted by activated phagocytes, uses hydrogen peroxide to produce potent cytotoxins. One important substra te is chloride, which is converted to hypochlorous acid (HOCl). This d iffusible oxidant plays a critical role in the destruction of invading pathogens. Under pathological conditions, HOCl may also injure normal tissue. Recent studies have shown that myeloperoxidase is a component of human atherosclerotic lesions. Because oxidized lipoproteins may p lay a central role in atherogenesis, we have explored the possibility that cholesterol is a target for damage by myeloperoxidase. Three majo r classes of sterol oxidation products were apparent when cholesterol- phosphatidylcholine multilamellar vesicles which had been exposed to a myeloperoxidase-hydrogen peroxide-chloride system were subsequently a nalyzed by normal-phase thin layer chromatography. The products were i dentified by gas chromatography-mass spectrometry as cholesterol alpha - and beta-chlorohydrins (6 beta-chlorocholestane-3 beta,5 alpha-diol and 5 alpha-chlorocholestane-3 beta,6 beta-diol), cholesterol alpha- a nd beta-epoxides (cholesterol 5 alpha,6 alpha-epoxide and cholesterol 5 beta,6 beta-epoxide), and a novel cholesterol chlorohydrin. Conversi on of cholesterol to the oxidation products required active myeloperox idase, hydrogen peroxide, and halide and could be blocked by catalase or by scavengers of HOCl. Moreover, in the absence of the enzymatic sy stem, reagent HOCl generated the same distribution of products. These results indicate that myeloperoxidase can convert cholesterol to chlor ohydrins and epoxides by a reaction involving HOCl. Other oxygenated s terols are cytotoxic and mutagenic and are potent regulators of choles terol homeostasis in cultured mammalian cells. Cholesterol chlorohydri ns might similarly mediate powerful biological effects in the artery w all. Because chlorohydrins are stable under our experimental condition s, chlorinated sterols may prove useful as markers for lipoproteins ox idatively damaged by activated phagocytes.