Objective: Systemic oxidative stress is associated with insulin resistance and obesity. We tested the hypothesis that systemic oxidative stress is linked to lower aerobic capacity and skeletal muscle dysfunction in metabolic syndrome (MetS).
Research design and methods: The incremental exercise testing with cycle ergometer was performed in 14 male patients with MetS and 13 age-, sex-, and activity-matched healthy subjects. Systemic lipid peroxidation was assessed by serum thiobarbituric acid reactive substances (TBARS), and systemic antioxidant defense capacity was assessed by serum total thiols and enzymatic activity of superoxide dismutase (SOD). To assess skeletal muscle energy metabolism, we measured high-energy phosphates in the calf muscle during plantar flexion exercise and intramyocellular lipid (IMCL) in the resting leg muscle, using (31)P- and (1)proton-magnetic resonance spectroscopy, respectively.
Results: Serum TBARS were elevated (12.4 ± 7.1 vs. 3.7 ± 1.1 μmol/L; P < 0.01), and serum total thiols and SOD activity were decreased (290.8 ± 51.2 vs. 398.7 ± 105.2 μmol/L, P < 0.01; and 22.2 ± 8.4 vs. 31.5 ± 8.5 units/L, P < 0.05, respectively) in patients with MetS compared with healthy subjects. Peak VO2 and anaerobic threshold normalized to body weight were significantly lower in MetS patients by 25 and 31%, respectively, and inversely correlated with serum TBARS (r = -0.49 and r = -0.50, respectively). Moreover, muscle phosphocreatine loss during exercise was 1.4-fold greater in patients with MetS (P < 0.05), and IMCL content was 2.9-fold higher in patients with MetS (P < 0.01), indicating impaired skeletal muscle energy metabolism, and these indices positively correlated with serum TBARS (r = 0.45 and r = 0.63, respectively).
Conclusions: Systemic oxidative stress was associated with lower aerobic capacity and impaired skeletal muscle energy metabolism in patients with MetS.