Effect of methionine-free total parenteral nutrition and insulin-like growth factor I on tumor growth in rats

The objectives of this study were to evaluate the effect of insulin-like growth factor I (IGF-I) on the fractional synthesis rate (FSR) of muscle and whole body protein breakdown rate (WPBR) during methionine-free total parenteral nutrition (MTPN). We also determined whether the inhibition of endogenous methionine availability reduced tumor protein synthesis. AH109A hepatoma cells were inoculated onto the backs of Donryu rats on day 0. On day 10, the rats were catheterized for TPN and assigned to one of four groups: 1) standard TPN (STPN), 2) STPN + IGF-I, 3) MTPN, or 4) MTPN + IGF-I. The addition of IGF-I to MTPN reduced the loss of body weight by both increasing muscle FSR and reducing WPBR. The tumor FSR did not differ between MTPN + IGF-I and MTPN. The methionine extraction ratio from the liver was negative with MTPN + IGF-I but positive in the other groups. We concluded that IGF-I blockage of endogenous methionine release from peripheral protein sites was associated with a shift to liver-derived methionine, with no change in tumor growth in MTPN-treated rats.