Protein metabolism in rheumatoid arthritis and aging. Effects of muscle strength training and tumor necrosis factor α

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Abstract
Objective. To determine the effects of rheumatoid arthritis (RA) on whole‐body protein metabolism. Methods. We examined protein metabolism and its hormonal and cytokine mediators before and 12 weeks after progressive resistance muscle strength training in 8 healthy young (mean ± SD age 25 ± 2 years) and 8 healthy elderly (70 ± 5 years) men and women, and in 8 adults with RA (42 ± 13 years). An additional 6 healthy elderly subjects (69 ± 3 years) served as a swimming‐only control group. Results. Subjects with RA had higher rates of protein breakdown than did young or elderly healthy subjects (79.9 ± 17.2 versus 60.3 ± 5.8 and 63.7 ± 12.4 μmoles/gm total body potassium/hour, respectively, P < 0.05), while there was no effect of age per se. Patients treated with methotrexate had normal rates of protein breakdown (P < 0.01 versus RA without methotrexate; P not significant versus healthy young subjects). Increased protein catabolism in RA was no longer evident after strength training. In multiple regression analysis, levels of tumor necrosis factor α (TNFα) (r = 0.47, P = 0.01) and growth hormone (r = ‐0.51, P = 0.006) were associated with protein breakdown, and plasma glucagon levels were inversely correlated with protein synthesis (r = ‐0.45, P = 0.02). Growth hormone (r = ‐0.56, P = 0.002) and glucagon (r = 0.45, P = 0.04), levels were associated with protein oxidation. Conclusion. Adults with RA have increased whole‐body protein breakdown, which correlates with growth hormone, glucagon, and TNFα production.