Abstract
In this study we explored whether the impaired flux of substrates for H2S synthesis and/or deficient enzyme activities alter production of hydrogen sulfide in patients with homocystinurias using thioethers as an indirect measure of H2S synthesis. In patients with classical homocystinuria we observed significantly decreased cystathionine and lanthionine concentrations in plasma (46% and 74% of median control levels, respectively) and significantly lower cystathionine in fibroblasts (8% of median control concentrations) indicating that H2S production from cysteine and homocysteine may be also impaired.
In contrast, the grossly elevated plasma levels of homolanthionine in plasma from CBS deficient patients (32-times elevation compared to median of controls) clearly demonstrates a simultaneous overproduction of H2S from homocysteine by CTH. In the remethylation defects the accumulation of homocysteine and the increased flux of metabolites through the transsulfuration pathway resulted in elevation of cystathionine and homolanthionine (857% and 400% of median control values, respectively) indicating possibly an increased biosynthesis of H2S by both CBS and CTH.
This study shows clearly disturbed thioether concentrations in homocystinurias, and modeling using these data indicates that H2S synthesis may be increased in these conditions. Further studies are needed to explore the possible implications of these findings for pathophysiology of these disorders.