Metabolic alterations in cancer. Part II. Protein and fat metabolism.

Intracellular changes in protein metabolism within cancer cells may facilitate cell reduplication, and this may be supported by changes in enzymes responsible for protein synthesis and degradation. Synthesis of ectopic hormones probably reflects genetic de-repression. Increased muscle proteolysis has been reported by some workers in cancer patients, and this may be associated with muscle cells, increased glucocorticoid secretion by the adrenal cortex, increased gluconeogenesis or impaired muscle glycolysis. Decreased proteogenesis has also been reported to occur in the muscles of cancer patients. Although tumour tissue may inhibit muscle proteogenesis, there are as yet no data to suggest a direct tumour-derived ectopic substance which affects muscle proteolysis or proteogenesis. Data regarding serum levels of free fatty acids (FFA) in weight-losing cancer patients are conflicting, although it is likely that abnormally high values are due to liver dysfunction rather than enhanced peripheral lipolysis. Nevertheless, since serum levels may be normal if FFA consumption is increased to the same extent as release, these levels need not indicate overall FFA turnover. If enhanced FFA release from fat stores does occur, this may provide the liver with an energy source required for its increased commitment to gluconeogenesis.