Effects of tumor necrosis factor alpha on skeletal muscle and Walker 256 carcinosarcoma protein metabolism studied in vivo

Abstract

Human tumor necrosis factor alpha (TNF) inhibits tumor growth, but its effects on tumor and skeletal muscle protein metabolism in vivo have not been adequately studied. Walker 256 carcinosarcoma growth rate was followed over an 11-day period in Sprague-Dawley rats. Tumor-bearing rats received either saline or 50 micrograms of TNF (Genentech, Inc.) s.c. on day 8 of tumor growth. This single dose of TNF reduced tumor protein growth during a 2-day posttreatment period from 27.6 +/- 4.4 to 10.5 +/- 3.7%/day (mean +/- SE; P less than 0.01). The rate of in vivo incorporation of L-[1-14C]leucine into skeletal muscle protein was significantly increased (P less than 0.05) from 5.1 +/- 0.2%/day in the saline-treated tumor-bearing rats to 7.7 +/- 1.3%/day in the TNF-treated tumor-bearing rats. The latter value was not statistically different from the 9.2 +/- 0.9%/day observed in the tumor-free control animals. TNF administration significantly increased both the total and individual acid-soluble skeletal muscle amino acid concentrations in tumor-bearing rats by an average of 86 +/- 7%, compared to values in saline-treated tumor-bearing rats. Similarly, acid-soluble skeletal muscle 3-methyl-histidine concentrations increased from 66 +/- 14 to 113 +/- 19 pmol/g protein (P less than 0.05). Tumor protein synthesis in the TNF-treated group was 50% greater than in the saline-treated group, whether expressed as %/day (72.7 +/- 9.1 versus 47.9 +/- 4.8; P less than 0.05) or was micrograms/g tumor/min (58.7 +/- 7.7 versus 40.7 +/- 4.5; P less than 0.05). In contrast, estimated tumor protein degradation rates were increased by over 200% in the TNF-treated rats, compared to the values in the saline-treated rats [62.1 +/- 10.7 versus 20.3 +/- 6.0%/day (P less than 0.01) and 50.0 +/- 8.9 versus 17.5 +/- 5.4 micrograms/g tumor/min (P less than 0.01)]. Thus, TNF appears to stimulate tumor protein degradation more than protein synthesis, explaining the overall decrease in tumor growth.