[Amino acid uptake and release by colorectal cancer in man]

Little information is available regarding the amino acid exchange by human tumors. To characterize this exchange in vivo, 21 patients with resectable colorectal carcinomas were studied during curative operations. Concerning the amino acid uptake and release by peripheral tissues, 20 non-cancer patients served as controls. Both groups of subjects were well-nourished, as indicated by anthropometric and biochemical variables. In the cancer patients, we cannulated a peripheral artery and vein as well as a central tumor-draining vein and the portal vein. Plasma concentrations and concentration differences were determined in mumol/l and in percentages of the total amino acid amounts. Peripheral glutamate uptake per liter plasma was reduced in the cancer patients (p = 0.02). In these patients, the central tumor-draining vein contained less glutamine (p = 0.002) and more glutamate (p = 0.002) than the peripheral vein. Glutamine uptake by the tumor occurred more often than glutamine release, while glutamate had a negative balance across the tumor in all but three cases. The qualitative differences between the peripheral tissues and the tumors with respect to glutamine and glutamate exchange reached high levels of significance (p = 0.002 for both of the amino acids). In addition, the tumors released more glycine, ornithine, and tyrosine than the periphery. As to glutamine and glutamate metabolism, there was a significant difference between the tumors and the portal-drained organs (p greater than or equal to 0.05). The discussion of the results emphasizes the contributions made by the periphery and the tumor to the plasma amino pattern. The role of glutamine as a potential high importance energy source for neoplastic tissues is delineated.