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.