Protein breakdown on whole-body and organ level in non-cachectic tumour-bearing mice undergoing surgery

Background & aims Since both cancer and surgery are known to alter protein turnover, we investigated how the presence of tumour affects post-operative protein breakdown. Methods Controls and tumour-bearing non-cachectic mice were studied, both with and without laparotomy (n=8 per group). One day after laparotomy, stable isotopes of phenylalanine and 3-methylhistidine were used in a steady-state protocol to assess total protein breakdown on whole-body level and in muscle, intestines, liver and kidney, in addition to whole-body myofibrillar protein breakdown and body composition. Proteasomal chymotrypsin-like activity was measured to determine activity of the ATP-dependent ubiquitin pathway. Results On whole-body level, the presence of tumour increased total protein breakdown from 47±6 to 58±4 nmol/10 g/min (p<0.05) and myofibrillar protein breakdown from 0.70±0.04 to 1.22±0.14 nmol/10 g/min (p<0.05) without affecting protein breakdown in organs, body composition or proteasomal activity. Laparotomy increased myofibrillar protein breakdown in controls (from 0.70±0.04 to 0.98±0.12 nmol/10 g/min, p<0.05) and tumour-bearing mice (from 1.22±0.14 to 1.54±0.22 nmol/10 g/min, p=0.15) to a similar extent. Conclusions Whole-body total protein breakdown, total protein breakdown across organs, body composition or proteasomal activity were not affected by laparotomy. Tumour-bearing mice had increased total and myofibrillar protein breakdown on whole-body level even before weight loss was obvious. However, this did not affect the post-operative response in protein breakdown or body composition.