Abstract 159: Protective Effect of Metallothionein in Ischemic Hindlimb against Oxidative Stress Induced by Benzo[ a ]pyrene

Abstract

Background: A wide range of biological responses to and toxic effects of exogenous compounds, such as polycyclic and halogenated aromatic hydrocarbons and dioxins, is mediated by the aryl hydrocarbon receptor (AHR). Given that smoking is an important risk factor for ischemic heart disease and peripheral vascular disease, we hypothesized that benzo-[ a ]pyrene (B[a]P), a prototype carcinogen of tobacco smoke, might impair angiogenesis and AHR might play an important role in the regulation of angiogenesis after exposure to B[a]P. The present study investigated this hypothesis in a surgical model of ischemia. Methods and Results: Ischemia was produced by femoral artery ligature in the AHR gene-deficient (AHR −/ − ) and wild type (WT) mice. B[a]P was administered by oral gavage in corn oil (10 ml/kg) at 125 mg/kg once per week beginning at 12 weeks of age (each group; n = 8). Laser Doppler perfusion analyses showed that the ischemic/nonischemic blood flow ratio of WT mice exposed to B[a]P was significantly reduced compared with that of control WT mice (0.67 ± 0.03 vs. 0.78 ± 0.02, P < 0.05) at 3 weeks after surgery. Furthermore, the blood flow ratio was significantly greater in AHR −/ − mice exposed to B[a]P than in WT mice exposed to B[a]P (P < 0.05). At 3 days after ligature, the abundance of cytochrome P450 1A1 mRNA, determined by quantitative RT-PCR analysis, was markedly greater in both ischemic and nonischemic hindlimbs of WT mice exposed to B[a]P than in those of AHR −/ − mice expose to B[a]P. The abundance of metallothionein I and II mRNA was significantly greater in the ischemic hindlimb than in the nonischemic hindlimb among all groups and was, moreover, significantly greater in the ischemic hindlimb of WT mice exposed to B[a]P than in that of AHR −/ − mice expose to B[a]P. Conclusions: The results show that the deletion of AHR gene reduced the adverse effects of exposure to B[a]P on angiogenesis. Our results also suggest that hypoxia in ischemia tissues activates the expression of metallothionein I and II, which may have protective effects against B[a]P-induced oxidative stress responses.