Fatty Streak Formation in Fat-Fed Mice Expressing Human Copper-Zinc Superoxide Dismutase

Abstract

Abstract Studies in vitro have shown that copper-zinc superoxide dismutase (CuZn-SOD) inhibits a number of events putatively involved in atherogenesis, including cell-mediated oxidation of LDL. To investigate whether increased activity of CuZn-SOD reduces atherogenesis in vivo, we examined diet-induced fatty streak formation in CuZn-SOD transgenic mice (n=24) as compared with their nontransgenic littermates (n=28). Transgenic animals were originally created by introduction of an EcoRI-Bam HI human genomic DNA fragment containing the CuZn-SOD gene and its regulatory elements into B6SJL zygotes. For the current studies, the transgene was bred for 12 generations into the atherosclerosis-susceptible C57BL/6 background. Animals were fed atherogenic diets (15% fat, 1.25% cholesterol, 0.5% Na cholate) starting at 10 weeks of age and extending for 18 weeks. At the end of the diet period, aortic SOD activity was two-fold higher in transgenics than nontransgenics (mean±SE: 46.7±5.8 versus 20.1±2.4 units/mg of protein, P <.001). Levels of protein-bound amino acid oxidation products ( meta -, ortho -, and dityrosine) were either similar or lower in aorta and heart from transgenics as compared with nontransgenics, suggesting that amplification of CuZn-SOD activity above the normal complement had modest inhibitory effects on basal oxidative stress in these tissues. CuZn-SOD overexpression did not reduce the extent of lesion development as analyzed by quantitative lipid staining of serial sections of the proximal aorta; mean lesion areas (±SE) were 997±478 and 943±221 μ 2 in transgenics and nontransgenics, respectively. Notably, the range of values for lesion area was 2.2-fold greater in transgenics (0-8403 versus 0-3868 μ 2 in nontransgenics). Moreover, within this group, lesion area showed a significant positive correlation with SOD activity ( r =.611, P <.03). These results do not support an antiatherogenic effect of CuZn-SOD over expression, and the possibility that high tissue SOD activity may potentiate atherogenesis in fat-fed atherosclerosis-susceptible mice.