S-Carboxymethyl-L-cysteine

Abstract

S-carboxymethyl-L-cysteine, the side-chain carboxymethyl derivative of the sulfur-containing amino acid, cysteine, has been known and available for almost 80 years. During this time, it has been put to a variety of uses, but it is within the field of respiratory medicine that, presently, it has found a clinical niche. Early studies indicated that this compound underwent a rather simplistic, predictable pattern of metabolism, whereas later investigations alluded to more subtle interactions with the pathways of intermediary metabolism, as may be expected for an amino acid derivative. In addition, suggestions of polymorphic influences and circadian rhythms within metabolic profiles have emerged. These latter factors may underlie the conflicting reports regarding the therapeutic efficacy of this compound: that it appears to work well in some patients, but has no measurable effects in others. The relevant literature pertaining to the fate of this compound within living systems has been reviewed and a comprehensive précis advanced. Hopefully, this article will serve as a vade mecum for those interested in S-carboxymethyl-L-cysteine and as a catalyst for future research.

Keywords::

• Cysteine
• mucolytic
• sulfoxidation
• circadian rhythm
• cysteine dioxygenase
• phenylalanine hydroxylase

Acknowledgments

The authors thank all of those who have been involved with this compound over the years and, in a modest way, echo the sentiment expressed at the begining of J.W. Mellor’s magnum opus (“A Comprehensive Treatise on Inorganic and Theoretical Chemistry”), which reads: “Dedicated to the Privates in the great army of workers in chemistry; their names have been forgotten, their work remains.”

Declaration of interest

The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper.