S-Methyl-L-cysteine sulphoxide: the Cinderella phytochemical?

Many vegetables considered beneficial to human health contain the amino acid derivative, S-methyl-L-cysteine sulphoxide. This plant secondary metabolite functions as a phytoalexin with strong antimicrobial activity preventing pathogenesis in growing plants. The potent biological activity of S-methyl-L-cysteine sulphoxide was first identified in ruminant animals as a toxicant, where it was demonstrated to be the 'kale anaemia factor'. Contrary to this toxicity, scattered reports in the literature have since shown anti-carcinogenic, anti-diabetic and cardiovascular effects in experimental animals. It has also recently been identified as a biomarker of cruciferous vegetable intake in a human dietary intervention study and a potentially significant constituent of the human metabolome. Considering the abundance and wide distribution of S-methyl-L-cysteine sulphoxide it is surprising that it has not been the subject of greater scrutiny as a chemoprotective agent and significant contributor to the purported health benefits of various plant foods. This review aims to consolidate current knowledge surrounding this amino acid derivative and provide an impetus for its further examination.