Biochemical studies on the age-related toxicity of galactosamine in primary rat hepatocyte cultures

Galactosamine (GalN) induces liver injury by depletion of uracil nucleotides. The objectives of this study were to investigate the age-related hepatotoxicity of GalN and to find out the mechanism(s) governing this toxicity in primary rat hepatocyte cultures. Hepatocyte cultures were established from foetal (day 20 of gestation), neonatal (3-day), adult (5-month) and aged (30-month) rat livers, and were exposed to 5 mm-GalN 24 hr after seeding. UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal) and glycogen were measured as indicators of disturbances in uracil nucleotides at 1, 12, 24, 48 and 60 hr after the addition of GalN. Additionally, UDP-glucosamine (UDP-GlcN) and UDP-galactosamine (UDP-GalN) were measured as uracil-trapping metabolites of GalN. Furthermore, the uptake of [(3)H]GalN by hepatocyte cultures of different ages also was determined after incubation of cell cultures with radioactive GalN. UDP-Glc, UDP-Gal and glycogen were decreased significantly at 24, 48 and 60 hr after treatment of adult hepatocyte monolayers. Although the concentrations of UDP metabolites of glucose, galactose and glycogen were decreased in aged liver cells, the decreases were considerably smaller than those in the adult cells. Measurement of the same biochemicals in foetal and neonatal cells did not reveal any significant decrease in their concentrations. The uracil-trapping metabolites, UDP-GlcN and UDP-GalN, were detected at significant concentrations in adult hepatocytes. Although these metabolites were detected in cells of other ages, their levels were significantly lower than in the adult cells. Even though the uptake of [(3)H]GalN by the cells reached a maximum at 30 min in all four ages, it was significantly higher in adult cells followed by aged, foetal and neonatal hepatocytes. A significantly lower uracil trapping by GalN metabolites in foetal and neonatal hepatocytes might be mitigated by further metabolism to non-toxic metabolites by foetal and neonatal cells. This could also be a direct result of much lower GalN uptake by these cells. These studies suggest that the age difference in GalN toxicity demonstrable in vitro may be related to the rate of GalN uptake and further metabolism of uracil-trapping metabolites such as UDP-GlcN and UDP-GalN.