The aminosalicylate - folate connection

Abstract

Two aminosalicylate isomers have been found to possess useful pharmacological behavior: p-aminosalicylate (PAS, 4AS) is an anti-tubercular agent that targets M. tuberculosis, and 5-aminosalicylate (5AS, mesalamine, mesalazine) is used in the treatment of ulcerative colitis (UC) and other inflammatory bowel diseases (IBD). PAS, a structural analog of pABA, is biosynthetically incorporated by bacterial dihydropteroate synthase (DHPS), ultimately yielding a dihydrofolate (DHF) analog containing an additional hydroxyl group in the pABA ring: 2’-hydroxy-7,8-dihydrofolate. It has been reported to perturb folate metabolism in M. tuberculosis, and to selectively target M. tuberculosis dihydrofolate reductase (mtDHFR). Studies of PAS metabolism are reviewed, and possible mechanisms for its mtDHFR inhibition are considered. Although 5AS is a more distant structural relative of pABA, multiple lines of evidence suggest a related role as a pABA antagonist that inhibits bacterial folate biosynthesis. Structural data support the likelihood that 5AS is recognized by the DHPS pABA binding site, and its effects probably range from blocking pABA binding to formation of a dead-end dihydropterin-5AS adduct. These studies suggest that mesalamine acts as a gut bacteria-directed antifolate, that selectively targets faster growing, more folate-dependent species.

Keywords:

• Ulcerative colitis
• mesalamine
• 5-aminosalicylate
• tuberculosis
• p-aminosalicylate
• inflammatory bowel disease

Acknowledgments

The author is very grateful to Bill Beard, NIEHS, for many useful suggestions and a critical reading of this manuscript, and to Nora Weston, NIEHS for assistance with literature searches. This research was performed as part of the Intramural Research Program of the NIH and National Institute of Environmental Health Sciences (NIEHS), Research Project Number Z01-ES050111 to R.E.L.

Disclosure statement

The author declares that there are no competing interests associated with the manuscript.

Additional information

Funding

This work was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences, project number ZIA ES050111 to R.E.L.