Microbiome-generated antifolates

The folate biosynthesis activity of the human microbiome provides reduced folate metabolites that are readily absorbed from the gastrointestinal (GI) tract. The bacterial folate biosynthesis enzyme dihydropteroate synthase (DHPS), which adds p-aminobenzoate (pABA) to an activated pterin precursor, is an important antibiotic target. Both the broad-spectrum p-aminobenzenesulfonamide antibiotics, and the drug p-aminosalicylate (PAS, 2-hydroxy-pABA) with high selectivity for Mycobacterium tuberculosis, are competitive DHPS substrates. The adducts formed from these drugs, DHP-sulfonamides (sulfapterins) and 2'-hydroxyfolate metabolites, respectively, have been reported to exhibit antifolate activity in studies of microorganisms. The presence of these DHP-adducts and their effects on the host organism are largely undetermined; however, their close structural relationship to dihydrofolate (DHF) suggests that they are likely to mediate some side effects reported for these antibiotics. Naturally occurring pABA analogs that probably function similar to DHPS-targeted antibiotics have been identified in carrots and bacteria. Impact statement pABA analogs represent an important class of antibiotics, that are converted into dihydrofolate analogs by organisms present in the human microbiome. These analogs may mediate reported side-effects associated with these antibiotics. Several naturally occurring pABA mimics have been identified that are likely to exhibit antibiotic activity.