Influence of D-galactosamine on the synthesis of sugar nucleotides and glycoconjugates in rat hepatocytes

Abstract

Rat hepatocytes were incubated in the presence of a high concentration of the hepatopathogenic agent D-galactosamine (GalN), and the effect on the cellular concentrations of pyrimidine nucleotides and nucleotide sugars was determined. The UTP pool became depleted. The pools of UMP and CMP in RNA decreased to 72%, indicative for an inhibition of RNA synthesis. UDP-HexNAc (where HexNAc is GlcNAc+GalNAc) and UDP-HexN (where HexN is GlcN+GalN) levels increased, and those of UDP-hexose and UDP-GlcA (where GlcA is glucuronic acid) decreased. The cellular concentration of CTP did not change, whereas that of CMP-NeuAc (where NeuAc is N-acetylneuraminic acid) showed a 2-fold increase. Labelling with [14C]orotic acid and [3H]cytidine showed that the metabolic flow via the de novo pathway was not changed. The depletion of the so-called overflow pool of UTP [Pels Rijcken et al., Biochem. J., 293, 207-213, 1993] caused a release of the feedback inhibition by UTP and thus an increased flow through the salvage pathway. Finally, it appeared that GalN, when added to hepatocytes, gives rise to a pool of UDP-GlcNAc (where GlcNAc is N-acetylglucosamine) that is separate from the pool of UDP-GlcNAc that is derived from GlcN.