d ‐Penicillamine modulates hydrogen sulfide ( H 2 S ) pathway through selective inhibition of cystathionine‐γ‐lyase

Background and Purpose Hydrogen sulfide (H 2 S) 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 H 2 S 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 H 2 S 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 H 2 S biosynthesis, and this effect occurred at concentrations 10 times lower than those needed to induce the release of H 2 S. 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 H 2 S research. In addition, the inhibitory effect of d ‐penicillamine on CSE could account for its beneficial action in rheumatoid arthritis patients, where H 2 S has been shown to have a detrimental effect.