Purpose To measure plasma concentrations of extracellular superoxide dismutase (EC-SOD) in healthy mature athletes.
Methods Subjects were identified at the annual meeting of the American Alpine Club who were over age 40 and active in mountaineering. They completed a questionnaire describing their aerobic training when not on expeditions and their general health, a health status survey (SF-36), and had pulmonary function tests performed. Blood samples were drawn and assayed for plasma EC-SOD using ELISA. A control group of similar-aged healthy subjects who were not selected for activity or interests was enrolled for comparison. Neither group reported a history of cardiovascular disease.
Summary The mean age of the mountaineer group was 52.7 years and the control group 55.7 years. Pulmonary function tests showed that the mountaineer group had a mean forced vital capacity as a percentage of predicted volume of 105 ± 3% (mean ± standard error of the mean) and forced expiratory volume in 1 second as a percentage of the predicted volume of 101 ± 3%. Plasma EC-SOD concentrations were 142.8 ± 17.4 ng/mL in the control group and 22.4 ± 2.56 ng/mL in the mountaineer group (p < .001). Looking at the mountaineer group alone and dividing them into an active (3 days per week of aerobic exercise) group and an extremely active (5 or more days per week of aerobic exercise) group the EC-SOD levels were 27.2 ± 3.4 and 17.6 ± 3.4 (t = 1.99, p = .058).
Conclusions EC-SOD is the primary catalytic antioxidant in the extracellular spaces and fluids. It scavenges superoxide and protects the vulnerable macromolecules of the extracellular matrix, such as collagen and proteoglycan, from oxidant damage. The majority of EC-SOD is bound to tissue and is in equilibrium with plasma levels. EC-SOD is highly expressed in the musculoskeletal tissues and exercise training has been shown to decrease plasma EC-SOD and raise tissue binding. Low EC-SOD plasma levels have been associated with a worse prognosis in cardiovascular disease but in the context of healthy, fit mountaineers may reflect the effect of increased tissue binding and better protection of the musculoskeletal system from oxidant injury. This is the first population study that has looked at plasma EC-SOD levels in relation to a group of individuals with a history of high-performance athletics and may provide insight into mechanisms of how exercise enhances function.
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