Cysteine dioxygenase and γ-glutamylcysteine synthetase activities in primary cultured hepatocytes respond to sulfur amino acid supplementation in a reciprocal manner

Hepatocytes were cultured for 3 days as spheroids (aggregates) or as monolayers in basal medium and in sulfur amino acid-supplemented media. Cultured hepatocytes had low levels of cysteine dioxygenase (CDO) activity and normal levels of γ-glutamylcysteine synthetase (GCS) and cysteinesulfinate decarboxylase (CSDC) activities compared to freshly isolated cells. CDO activity increased and GCS activity decreased in a dose-response manner in cells cultured in either methionine- or cysteine-supplemented media. CSDC activity was not significantly affected by methionine supplementation. Changes in CDO and GCS were associated with changes in cysteine catabolism to taurine plus sulfate and in synthesis of glutathione, respectively. These responses are similar to those observed in liver of intact rats fed diets supplemented with sulfur amino acids. A near-maximal response of CDO or GCS activity was observed when the medium contained 1.0 mmol/L of methionine plus cyst(e)ine. Changes in CDO and GCS activities did not appear to be mediated by changes in the intracellular glutathione concentration. Cultured hepatocytes offer a useful model for further studies of cysteine metabolism and its regulation in response to sulfur amino acid availability.