ABSTRACT
BACKGROUND: Heme oxygenase-1 (HO-1) is proposed to have a variety of adaptive responses against oxidative stress. To examine the function of HO-1 against atherogenesis in vivo, we observed the effects of HO-1 inhibition on atherosclerotic lesion formation in Watanabe heritable hyperlipidemic rabbits (WHHL). Methods and Results- During 4 weeks of a 1% cholesterol diet, intravenous injections of Sn-protoporphyrin IX to inhibit HO-1 (S group, n=10) and saline as a control (C group, n=10) were given to 3-month-old WHHL rabbits. The percentages of en face atherosclerotic lesion areas in total descending aorta by Sudan IV staining (EFA) and the ratio of intima to media in microscopic atherosclerotic lesions in the ascending aortas (I/M) were calculated. Two different quantitative methods revealed significantly greater atherosclerotic lesions in the S group than the C group (EFA, P<0.001; I/M, P<0.005). HO-1 expression in atherosclerotic lesions was confirmed by Northern blot and immunohistochemical analyses. The dominant cell types expressing HO-1 were macrophages and foam cells, in which oxidized phospholipids were also accumulated. HO inhibition increased plasma and tissue lipid peroxide levels without affecting plasma lipid co osition. CONCLUSIONS: These results suggest the possibilities that HO-1 has antiatherogenic properties in vivo and that the antiatherogenic properties of HO-1 are conducted through the prevention of lipid peroxidation.
Subject(s)
Aorta/metabolism , Arteriosclerosis/prevention & control , Arteriosclerosis/physiopathology , Heme Oxygenase (Decyclizing)/metabolism , Hyperlipidemias/enzymology , Animals , Aorta/pathology , Arteriosclerosis/etiology , Arteriosclerosis/pathology , Blotting, Northern , Diet, Atherogenic , Disease Models, Animal , Enzyme Activation/drug effects , Enzyme Induction/drug effects , Enzyme Inhibitors/pharmacology , Heme Oxygenase (Decyclizing)/antagonists & inhibitors , Heme Oxygenase (Decyclizing)/genetics , Heme Oxygenase-1 , Hyperlipidemias/complications , Hyperlipidemias/genetics , Immunohistochemistry , Lipid Peroxidation/drug effects , Lipid Peroxides/metabolism , Lipoproteins/metabolism , Liver/metabolism , Male , RNA, Messenger/metabolism , RabbitsABSTRACT
Heme oxygenase-1 (HO-1) is induced by a variety of conditions associated with oxidative stress. We demonstrated that mildly oxidized LDL markedly induces HO-1 in human aortic endothelial and smooth muscle cell cocultures and that its induction results in the attenuation of monocyte chemotaxis resulting from treatment with mildly oxidized LDL in vitro. To elucidate the role of HO-1 in the development of atherosclerotic lesions in vivo, we modulated HO-1 expression in LDL-receptor knockout mice fed high-fat diets. During 6-week high-fat diet trials, intraperitoneal injections of hemin (H group) or hemin and desferrioxamine (HD group) to induce HO-1, Sn-protoporphyrin IX to inhibit HO-1 (Sn group), and saline as control (C group) were performed. Both the H and HD groups showed significantly less mean atherosclerotic lesions in the proximal aorta compared with the C group, whereas the Sn group showed larger lesion compared with the C group. Modulation of HO expression and HO activities were confirmed by Northern blot analysis and HO activity assay. Immunohistochemical studies revealed significant HO-1 expression in atherosclerotic lesions, where oxidized phospholipids also localized. Major cell types expressing HO-1 were macrophages and foam cells in the lesions. HO modulations affected plasma lipid hydroperoxide (LPO) levels and nitrite/nitrate levels. These results suggest that HO-1, induced under hyperlipidemia, functioned as an intrinsic protective factor against atherosclerotic lesion formation, possibly by inhibiting lipid peroxidation and influencing the nitric oxide pathway.
