Studies on the age-dependent effects of galactosamine in primary rat hepatocyte cultures

Galactosamine (GalN) has been known to induce liver injury by depletion of uracil nucleotides. The objective of the present work was to examine age-dependent toxicity of GalN in primary hepatocyte cultures. Hepatocytes from fetal (Day 20 of gestation), neonatal (2.5-day), adult (5-month), and aged (30-month) rats were established as monolayered cultures. LDH leakage, cell viability, UTP, UDP, and UMP were measured as end points of toxicity in cultures exposed to 5 mM GalN. LDH leakage was increased and cell viability was decreased in adult rat hepatocytes at 48 and 60 hr after treatment. Although similar effects were observed in hepatocytes from aged rats, these cells appeared resilient to GalN toxicity as indicated by significantly less LDH leakage and cell death. Fetal and neonatal rat hepatocytes also exhibited greater resiliency to GalN based on the same end points. The UTP, UDP, and UMP levels of aged hepatocytes (30-month) were higher than control adult levels to begin with and dropped after GalN treatment. The level of UMP at 60 hr was similar to that of normal adult cells, but the UTP and UDP levels were significantly higher in aged hepatocytes in comparison to those of adult hepatocytes. The levels of uracil nucleotides in the fetal and neonatal cells were the same as those in adult cells, but did not decrease significantly after exposure to GalN. These findings show that aged rat hepatocytes have a higher set point for uracil nucleotides, which is consistent with the relative resiliency of these cells to GalN injury. Neonatal and fetal cells have the same set point for these nucleotides as adult rats, but are relatively resistant to GalN-induced depletion. In conclusion, the differences in toxicity of GalN may reside in age-related differences in the regulation of uracil nucleotide biochemistry.