Change of tryptophan-niacin metabolism in D-galactosamine induced liver injury in rat

Abstract

The change of tryptophan-niacin metabolism in D-galactosamine (D-galN) injected rats was investigated. Rats fed with niacin-free diets containing 40% casein for 11 days were injected with D-ga1N (0.8 g/kg body weight). The urinary excretions of nicotinamide and its metabolites, and the activity of liver α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) (EC 4.1.1.45), a key enzyme of tryptophan-niacin metabolism, were assayed. As the result, the urinary excretions of N1- methylnicotinamide (MNA), N1-methyl- 2-pyridone-5-carboxamide (2-Py), N1-methyl-4-pyridone-3-carboxamide (4-Py) and their sum (nicotinamide+MNA+2-Py+4-Py) were higher in the DgalN-injected group than in the control group. Hepatic ACMSD activity in the D-galN- injected group was lower than that of the control group. These results suggest that the increase in urinary excretion of nicotinamide and its metabolites after the injection of D-galN is considered to be attributable to a decrease in liver ACMSD activity.