Biotransformation of Corn-Derived N1,N10-di-p-Coumaroyl Spermidine in Mice and by Human Gut Microbiota Reveals Novel Reduced Metabolites.

While candidate biomarkers have been proposed for several cereals and pseudocereals, no validated biomarkers have been established for whole grain (WG) corn. As an initial step toward biomarker development, this study investigated the biotransformation of N1,N10-di-p-coumaroyl spermidine (diCouSpd), a major corn phenolamide, using an integrated approach combining chemical synthesis, LC-MS- and NMR-based structural elucidation, in vitro human fecal fermentation, and in vivo mouse studies. Three previously unreported hydrogenated metabolites were identified: N1-dihydro-p-coumaroyl-N10-p-coumaroyl-spermidine (1), N1-p-coumaroyl-N10-dihydro-p-coumaroyl-spermidine (2), and N1,N10-bis(dihydro-p-coumaroyl)-spermidine (3). Fecal and urine analyses from mice administrated diCouSpd or corn extracts prepared from two or four servings of WG corn confirmed the formation of these reduced metabolites. Human fecal fermentation revealed a putative stepwise hydrogenation pathway involving sequential reduction of p-coumaroyl moieties in diCouSpd. Collectively, these findings provide new insights into the reductive metabolism of corn phenolamides and support diCouSpd and its metabolites as potential exposure biomarkers of WG corn intake.