PROTEIN-METABOLISM IN HUMAN COLON CARCINOMAS - IN-VIVO INVESTIGATIONSUSING A MODIFIED TRACER TECHNIQUE WITH L-[1-C-13]LEUCINE

To quantify the protein anabolism of tumors it is not sufficient simpl y to determine the level of protein synthesis. The decisive factor is the net balance. This is the first attempt to establish this parameter in human tumors in vivo. Intraoperative tumor leucine/protein metabol ism was studied in 15 patients with resectable malignant colon tumors using a balance model and L[1-C-13]leucine as the tracer substance. Co mparative measurements were also carried out simultaneously for periph eral tissue (forearm); in addition, protein kinetics parameters were e stablished for the whole body using a proven two-pool model (with the same tracer as above). In view of the frequently conflicting data on a mino acid metabolism in tumors, the tumoral and peripheral exchange ra tes of 20 amino acids were also determined. In tumors, essential and b ranched-chain amino acid uptakes were found to be 1.68 +/- 0.59 (SE) a nd 1.52 +/- 0.23 mu mol/100 g tissue/min, respectively; in peripheral tissue there was overall an amino acid release [-0.11 +/- 0.06 and -0. 05 +/- 0.04 mu mol/100 g/min; in either case P < 0.01 (tumor versus pe riphery)]. Tracer analyses yielded a net retention for the tumors but a protein loss for peripheral tissue (8.941 +/- 3.113 versus -0.557 +/ - 0.53 g/kg/24 h; P < 0.01) and for the whole body (-0.363 +/- 0.04 g/ kg/24 h). The tumors were divided into two prognostic groups on the ba sis of their histology. Significant differences were found between the two groups in terms of the net retention rate for 10 amino acids, inc luding leucine; retention was elevated in tumors with an unfavorable p rognosis, possibly due to a higher amino acid requirement because of m ore rapid growth or for export processes (mucus production). The prote in balance model used here has proved satisfactory for our purposes an d could also be used to directly evaluate dietary measures (e.g., adju vant parenteral nutrition in connection with chemotherapy).