Vitamin Effects on Tryptophan-Niacin Metabolism in Primary Hepatoma Patients

Abstract

Metabolism of ¹⁴C-labeled tryptophan and 3-hydroxyanthranilic acid were administered to early hepatoma patients to evaluate the conversion of these precursors to niacin metabolites and to assess the effect of dietary supplementation with vitamin B-6, riboflavin, thiamin and vitamin C on the extent of conversion. Expired labeled carbon dioxide and urinary excretion of picolinic acid (PA), quinolinic acid (QA), nicotinic acid (NA), N₁₋ methylnicotinamide (N₁MeNAm) and N₁₋methyl-2-pyridone-5-carboxamide (MPCA) were measured by carrier isolations. There were no consistent statistical differences in these conversions before and after vitamin supplementation, suggesting that the patients’ nutrition was adequate and that none of the vitamins were rate-limiting under these conditions.