Propargylglycine inhibits hypotaurine/taurine synthesis and elevates cystathionine and homocysteine concentrations in primary mouse hepatocytes

Our investigation showed that hepatocytes isolated from cysteine dioxygenase knockout mice (Cdo1(-/-)) had lower levels of hypotaurine and taurine than Cdo1 (+/+) hepatocytes. Interestingly, hypotaurine accumulates in cultured wild-type hepatocytes. DL-propargylglycine (PPG, inhibitor of cystathionine γ-lyase and H2S production) dramatically decreased both taurine and hypotaurine levels in wild-type hepatocytes compared to untreated cells. Addition of 2 mM PPG resulted in the decrease of the intracellular taurine levels: from 10.25 ± 5.00 observed in control, to 2.53 ± 0.68 nmol/mg protein (24 h of culture) and from 17.06 ± 9.40 to 2.43 ± 0.26 nmol/mg protein (control vs. PPG; 48 h). Addition of PPG reduced also intracellular hypotaurine levels: from 7.46 ± 3.55 to 0.31 ± 0.12 nmol/mg protein (control vs. PPG; 24 h) and from 4.54 ± 3.20 to 0.42 ± 0.11 nmol/mg protein (control vs. PPG; 48 h). The similar effects of PPG on hypotaurine and taurine levels were observed in culture medium. PPG blocked hypotaurine/taurine synthesis in wild-type hepatocytes, suggesting that it strongly inhibits cysteinesulfinate decarboxylase (pyridoxal 5'-phosphate-dependent enzyme) as well as cystathionine γ-lyase. In the presence of PPG, intracellular and medium cystathionine levels for both wild-type and Cdo1 (-/-) cells were increased. Addition of homocysteine or methionine resulted in higher intracellular concentrations of homocysteine, which is a cosubstrate for cystathionine β-synthase (CBS). It seems that PPG increases CBS-mediated desulfhydration by enhancing homocysteine levels in hepatocytes. There were no overall effects of PPG or genotype on intracellular or medium glutathione levels.