Tumor necrosis factor-alpha and soluble TNF-alpha receptor responses in young vs. middle-aged males following eccentric exercise

Background: Tumor necrosis factor-alpha (TNF-alpha) has been shown to be implicated in both muscle regeneration and muscle wasting. However, it remains unclear whether TNF-alpha is responsible for the age-related losses in muscle size and function. Also, due to the high clearance rate of TNF-a from circulation, analyzing the circulating levels of soluble TNF-alpha receptors 1 and 2 (STNFR1 and STNFR2) may provide a better indication of inflammatory events. The aim of this study was to examine changes in circulating concentrations of TNF-alpha, STNFR1, and STNFR2 following acute eccentric exercise in young (YA) and middle-aged (MA) men. Methods and materiah: Nine YA (N = 9, 21.8 +/- 2.2 y, 179.5 +/- 4.9 cm, 91.2 +/- 12.2 kg, 21.8 +/- 4.3% body fat) and ten MA (N = 10, 47.0 +/- 4.4 y, 176.8 +/- 7.6 cm; 96.0 +/- 21.5 kg, 25.4 +/- 5.3% body fat) men completed an acute muscle damaging protocol (MDP). Blood samples were obtained at baseline (BL), immediately (IP), 30-minute (30P), 60-minute (60P), 120-minute (120P), 24-hour (24H), and 48-hour (48H) post-MDP. Lower body performance was assessed via isokinetic dynamometer at BL, IP, 120P, 24H, and 48H. Results: YA displayed higher values of peak torque (p = 0.023) and mean torque (p = 0.036) at BL. No significant group differences were observed for markers of muscle damage or TNF-alpha. Plasma concentrations of TNF-alpha were unchanged following MDP. STNFRl concentrations were significantly higher in the YA group compared to MA (p = 0.036). Significant time effects were observed for STNFR1 (p< 0.001) and STNFR2 (p = 0.001). With both groups combined, serum STNFR1 was decreased at 30P (p = 0.001), while STNFR2 was decreased at 30P (p = 0.008), 60P (p = 0.003), and 120P (p = 0.002) relative to BL. Conclusions: The pro-inflammatory response to muscle damage does not appear to decline at middle age when individuals are recreationally trained. However, young men showed significantly higher serum STNFR1 concentrations than middle age men. This may suggest that natural inhibitors of TNF-alpha decline as early as middle age.