Inhibition of LDL oxidation and myeloperoxidase dependent tyrosyl radical formation by the selective estrogen receptor modulator raloxifene (LY139481 HCL)

Cellular oxidation of protein and lipoproteins is believed to contribute to the pathology associated with both acute and chronic inflammatory processes. Enzymatic, myeloperoxidase and lipoxygenase, and non- enzymatic oxidation of low density lipoprotein, LDL, has been implicated in foam cell formation and the progression of atherosclerotic changes within the arterial wall. In the present study, the in vitro protective role of the selective estrogen receptor modulator, raloxifene, in these oxidant triggered processes has been investigated. Raloxifene, as with estrogen was observed to inhibit both copper mediated LDL oxidation as well as the cellular modification of LDL by murine peritoneal macrophages. Raloxifene was, however, a more potent inhibitor of LDL oxidation than 17β-estradiol. The inhibition of macrophage LDL modification by raloxifene was not due to a non- specific effect on all effector functions as phagocytosis of opsonized yeast was comparable with control macrophage cultures. In addition to the protective effects on LDL oxidation, raloxifene also inhibited tyrosyl radical formation catalyzed by myeloperoxidase. The inhibition of myeloperoxidase activity was observed for both the isolated enzyme and in phorbol ester stimulated murine peritoneal neutrophils. In contrast, raloxifene was a weaker inhibitor of horseradish peroxidase. These results demonstrate a potential protective role for raloxifene as an anti-oxidant in in vitro assays designed to evaluate oxidant mediated radical formation and tissue damage.