D -Penicillamine modulates hydrogen sulfide (H₂S) pathway through selective inhibition of cystathionine-γ-lyase

Background and Purpose Hydrogen sulfide (H₂S) is a gasotransmitter produced from l-cysteine through the enzymatic action of cystathionine-γ-lyase (CSE) and/or cystathionine-β-synthase. d-Penicillamine is the d isomer of a dimethylated cysteine and has been used for the treatment of rheumatoid arthritis. As d-penicillamine is structurally very similar to cysteine, we have investigated whether d-penicillamine, as a cysteine analogue, has an effect on the H₂S pathway. Experimental Approach We tested the effect of d-penicillamine (0.01-1 mM) in mouse aortic rings mounted in isolated organ baths and determined whether it could affect H₂S biosynthesis. In particular, we investigated any possible inhibitor or donor behaviour by using recombinant enzyme-based assays and an in vivo approach. Key Results d-Penicillamine, per se, showed little or no vasodilator effect, and it cannot be metabolized as a substrate in place of l-cysteine. However, d-penicillamine significantly reduced l-cysteine-induced vasodilatation in a concentration-dependent manner through inhibition of H₂S biosynthesis, and this effect occurred at concentrations 10 times lower than those needed to induce the release of H₂S. In particular, d-penicillamine selectively inhibited CSE in a pyridoxal-5′-phospate-dependent manner. Conclusions and Implications Taken together, our results suggest that d-penicillamine acts as a selective CSE inhibitor, leading to new perspectives in the design and use of specific pharmacological tools for H₂S research. In addition, the inhibitory effect of d-penicillamine on CSE could account for its beneficial action in rheumatoid arthritis patients, where H₂S has been shown to have a detrimental effect.