Metabolic and morphological alterations induced by proteolysis-inducing factor from Walker tumour-bearing rats in C2C12 myotubes

In this work, we used cytotoxicity and enzymatic assays and morphological analysis to examine the effects of a proteolysis-inducing factor (PIF)-like molecule purified from ascitic fluid of Walker tumour-bearing rats (WF), which has been suggested to be responsible for muscle atrophy, on cultured C2C12 muscle cells.WF decreased the viability of C2C12 myotubes, especially at concentrations of 20–25 μg.mL-1. There was an increase in the content of the pro-oxidant malondialdehyde, and a decrease in antioxidant enzyme activity. Myotubes protein synthesis decreased and protein degradation increased together with an enhanced in the chymotrypsin-like enzyme activity, a measure of functional proteasome activity, after treatment with WF. Morphological alterations such as cell retraction and the presence of numerous cells in suspension were observed, particularly at high WF concentrations.These results indicate that WF has similar effects to those of proteolysis-inducing factor, but is less potent than the latter. Further studies are required to determine the precise role of WF in this experimental model.The most common manifestation of advanced malignant disease is the development of cancer cachexia, which is a strong independent cause of mortality in this disease [1]. The abnormalities associated with cancer cachexia include anorexia, loss of body weight and muscle mass, as well as alterations in carbohydrate, lipid, and protein metabolism [2,3].Atrophy of skeletal muscle results from increased protein catabolism (hypercatabolism) and decreased protein synthesis (hypoanabolism), both of which may occur simultaneously and result in intense muscular atrophy [4,5]. Cytokines, particularly TNF-α, IL-6, and interferon-γ, have been suggested to be responsible for the metabolic changes associated with tissue loss in cancer wasting [6-8]. In addition to humoral factors, tumour-derived molecules have also been proposed as mediators of cancer cachexia. Todorov et al. [9] purified and