High altitude and oxidative stress.

Exposure to high altitude, which is associated with decreased oxygen pressure, could result in oxidative/reductive stress, enhanced generation of reactive oxygen and nitrogen species (RONS), and related oxidative damage to lipids, proteins, and DNA. The severity of oxidative challenge is related to the degree of altitude. A wide range of RONS generating systems are activated during exposure to high altitude, including the mitochondrial electron transport chain, xanthine oxidase, and nitric oxide synthase. High altitude appears to weaken the enzymatic and non-enzymatic antioxidant systems, and increased nutritional uptake of antioxidant vitamins are beneficial to reduce the altitude-induced oxidative damage. The pattern of high altitude exposure-associated oxidative damage resembles ischemia/reperfusion injury. The adaptive process to this oxidative challenge requires a relatively long period of time. Physical exercise or an enhanced level of physical activity at high altitude, exacerbates the extent of the oxidative challenge. Therefore, special attention is necessary to curb the degree of oxidative stress.

The effects of moderate, strenuous, and overtraining on oxidative stress markers and DNA repair in rat liver.

Physical exercise above a certain load has been suggested as being a cause of oxidative stress. We have tested whether training with moderate (MT), strenuous (ST), or over (OT) load can cause alterations in the activities of antioxidant enzymes, lipid peroxidation, protein oxidation, DNA damage, or activity of 8-oxoG-DNA glycosylase (OGG1) in rat liver. The levels of corticosterone decreased in all exercising groups but the differences were not significant. Adrenocorticotrophin hormone (ACTH) levels decreased, not significantly, in MT and OT compared to C. Activity levels of antioxidant enzymes did not change significantly in the liver. The levels of reactive carbonyl derivative (RCD) content decreased in the liver of exercising animals, and the differences reached significance between control and moderately trained groups. The changes in the levels of lipid peroxidation (LIPOX) were not significant, but were lower in the exercised groups. The 8-hydroxydeoxyguanosine (8-OHdG) levels increased in the OT group, and the activity of OGG1 measured from crude cell extracts tended to increase in MT and ST. The findings of this study imply that overtraining induces oxidative damage to nuclear DNA, but not to liver lipids and proteins.