Emerging aspects of gut sulfur amino acid metabolism.

PURPOSE OF REVIEW: This review discusses the recent evidence indicating that sulfur amino acid metabolism in gastrointestinal tissues may be linked to human health and gut disease. RECENT
FINDINGS: Studies indicate that the gastrointestinal tract metabolizes 20% of dietary methionine and that its main metabolic fate is transmethylation to homocysteine and transsulfuration to cysteine. The gastrointestinal tract accounts for approximately 25% of whole-body transmethylation and transsulfuration and is a site of net homocysteine release. The production of homocysteine within the intestinal mucosa may contribute to the inflammatory response and endothelial cell dysfunction in patients with inflammatory bowel disease. Studies also show that the availability of S-adenosylmethionine as a precursor for methylation reactions and polyamines plays a key role in epigenetic DNA methylation, gene expression and colon carcinogenesis. Cysteine derived from the diet and methionine transsulfuration is a functional constituent of antioxidant systems and impacts several elements of redox status that regulate epithelial intracellular signaling, proliferation and survival.
SUMMARY: Further studies are warranted to establish how local production of homocysteine, S-adenosylmethionine and antioxidants contributes to the development of gastrointestinal diseases and whether dietary intervention with folate and cysteine is an efficacious approach to prevention and treatment.