Effect of acetaminophen on the myeloperoxidase-hydrogen peroxide-nitrite mediated oxidation of LDL.

Myeloperoxidase, in the presence of hydrogen peroxide and nitrite, promotes the lipid peroxidation of low density lipoprotein (LDL); the modified lipoprotein is then capable of being readily endocytosed by macrophages. Since acetaminophen has been shown to inhibit the leukocyte myeloperoxidase antimicrobial system and is, under certain experimental conditions, an antioxidant, the effect of acetaminophen on the myeloperoxidase-hydrogen peroxide-nitrite mediated oxidation of LDL was examined. The content of LDL lipid hydroperoxides after incubation with 50 nM myeloperoxidase, 100 microM nitrite and a hydrogen peroxide generating system for 6 h was reduced by approx. 80% in the presence of 25-250 microM acetaminophen. The production of thiobarbituric acid-reactive substances was also inhibited by acetaminophen to a similar extent. Acetylsalicylic acid (25-100 microM) did not inhibit LDL lipid peroxidation mediated by the myeloperoxidase enzyme system. LDL, treated with myeloperoxidase, hydrogen peroxide and nitrite for 14 h, was metabolized by macrophages to a much greater extent than native LDL. The presence of acetaminophen prevented the modification of LDL; the lipoprotein was metabolized by macrophages to the same extent as was native LDL. These results demonstrate that acetaminophen is a potent inhibitor of the myeloperoxidase-hydrogen peroxide-nitrite mediated modification of LDL.