8-hydroxyguanosine and Body-Weight

Artificial selection in rat has yielded high-capacity runners (HCR) and low-capacity runners (LCR) that differ in intrinsic (untrained) aerobic exercise ability and metabolic disease risk. To gain insight into how oxygen metabolism may have been affected by selection, we compared mitochondrial function, oxidative DNA damage (8-dihydroxy-guanosine; 8dOHG), and antioxidant enzyme activities in soleus muscle (Sol) and gastrocnemius muscle (Gas) of adult and aged LCR vs. HCR rats. In Sol of adult HCR rats, maximal ADP-stimulated respiration was 37% greater, whereas in Gas of adult HCR rats, there was a 23% greater complex IV-driven respiratory capacity and 54% greater leak as a fraction of electron transport capacity (suggesting looser mitochondrial coupling) vs. LCR rats. H(2)O(2) emission per gram of muscle was 24-26% greater for both muscles in adult HCR rats vs. LCR, although H(2)O(2) emission in Gas was 17% lower in HCR, after normalizing for citrate synthase activity (marker of mitochondrial content). Despite greater H(2)O(2) emission, 8dOHG levels were 62-78% lower in HCR rats due to 62-96% higher superoxide dismutase activity in both muscles and 47% higher catalase activity in Sol muscle in adult HCR rats, with no evidence for higher 8 oxoguanine glycosylase (OGG1; DNA repair enzyme) protein expression. We conclude that genetic segregation for high running capacity has generated a molecular network of cellular adaptations, facilitating a superior response to oxidative stress.

Topics: Adaptation, Physiological; Adenosine Diphosphate; Animals; Antioxidants; Body Weight; Breeding; Catalase; Cell Respiration; Citrate (si)-Synthase; DNA Damage; DNA Glycosylases; Electron Transport Complex IV; Female; Guanosine; Hydrogen Peroxide; Male; Mitochondria, Muscle; Muscle, Skeletal; Oxidative Stress; Physical Endurance; Rats; Rats, Inbred Strains; Reactive Oxygen Species; Running; Superoxide Dismutase

Increased oxidative DNA damage due to increased peroxisomal generation of H2O2 is a potential mechanism in the carcinogenicity of chemical peroxisome proliferators (PP) in rodent liver. In order to determine the relationship between carcinogenicity and peroxisome-dependent DNA damage, levels of DNA base oxidation were examined by comparing 8-hydroxydeoxyguanosine (8-OHdG) in DNA from unfractionated liver of male F344 rats following dietary exposure to PP [WY-14,643, 0.1% or 0.005%; di(2-ethylhexyl)phthalate (DEHP), 1.2%; clofibric acid, 0.5%] or phenobarbital (0.05%). Exposure-related increases in 8-OHdG were not observed at 3 or 11 weeks for any of the compounds fed. At 22 weeks, 8-OHdG was similarly elevated (2-3x) by WY-14,643 (0.1% and 0.005%) and clofibric acid (0.5%). These equivalent increases in 8-OHdG in DNA from unfractionated liver did not parallel the divergent carcinogenicity of these different dietary exposures in the present or previous studies. The potential oxidation of nuclear DNA was examined by comparing levels of 8-OHdG in DNA isolated from purified liver nuclei and unfractionated liver. Elevated levels of 8-OHdG were not detected in DNA isolated from nuclear fractions of livers from rats fed clofibric acid for 22 weeks, indicating the dependence of PP-induced oxidative DNA damage on extranuclear components of samples for DNA isolation. The absence of a quantitative relationship between PP-induced carcinogenicity and oxidative DNA base damage (as 8-OHdG), and the failure to localize this oxidative damage to nuclear DNA, suggest two possible conclusions: (1) quantitation of 8-OHdG, a specific and sensitive indicator of oxidative DNA damage, does not accurately reflect the potential peroxisomal H2O2-dependent DNA damage and carcinogenicity of PP exposure in rodents; (2) other hepatic responses may be more critical features of the mechanism of PP carcinogenicity.

Topics: Animals; Body Weight; Carcinogens; Cell Nucleus; Clofibric Acid; Diethylhexyl Phthalate; DNA; Guanosine; Liver; Male; Microbodies; Organ Size; Phenobarbital; Pyrimidines; Rats; Rats, Inbred F344