RESEARCH ARTICLE www.mnf-journal.com Monomeric Flavanols Are More Efficient Substrates for Gut Microbiota Conversion to Hydroxyphenyl- -Valerolactone Metabolites Than Oligomeric Procyanidins: A Randomized, Placebo-Controlled Human Intervention Trial Wendy J Hollands, Mark Philo, Natalia Perez-Moral, Paul W Needs, George M Savva, and Paul A Kroon* Scope: The majority of ingested flavanols reach the colon where they are catabolized by the microbiota to form hydroxyphenyl- -valerolactones (HGVLs). It is not known if the HGVLs are catabolic products of monomeric (epi)catechins (EPC), oligomeric procyanidins (OPCs), or both. Using data from a randomized, double-blind, placebo-controlled crossover trial the relative contributions of catechins and OPC to the bioavailable pool of HGVLs are estimated. Methods and results: Participants ingested an apple extract once daily for 28 days that delivered the following: i) 70 mg EPC and 65 mg OPC (low dose EPC), ii) 140 mg EPC and 130 mg OPC (high dose EPC), iii) 6 mg EPC and 130 mg OPC (OPC), and iv) a placebo control. Urine is collected over a 24-h period before and after treatments. The median urinary excretion of HGVLs after ingestion of the high dose EPC is tenfold higher than that excreted after ingestion of the OPC that provided an equivalent dose of PC. Approximately 22% of catechins are converted to HGVLs in contrast to PC, for which there is limited conversion. Conclusion: Monomeric catechins are efficiently converted to derived HGVLs that are absorbed and excreted in human urine, whereas oligomeric PCs are much less efficiently converted. W. J Hollands, M. Philo, Dr. N. Perez-Moral, Dr. P. W Needs, Dr. P. A Kroon Food Innovation and Health Programme Quadram Institute Bioscience Norwich, NR4 7UQ, UK E-mail: paul.kroon@quadram.ac.uk G. M Savva Core Research Services Quadram Institute Bioscience Norwich, NR4 7UQ, UK © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. DOI: 10.1002/mnfr.201901135 1. Introduction Human intervention trials with flavanol- rich foods and beverages have shown im- provements in biomarkers of cardiovas- cular disease (CVD) after ingestion. [1–3] Cocoa and some apple varieties are rich dietary sources of both monomeric flavanols, ((‒)-epicatechin (EC) and (+)-catechin) and procyanidins (PC); oligomers/polymers of epicatechin and catechin. Yet whether the observed ben- eficial effects of consuming flavanol-rich foods are due to the monomeric flavanols or the oligomeric/polymeric PC is not known. To exert the physiological effects ob- served in human intervention trials a compound must be bioavailable. Like all flavonoids, absorption and metabolism of flavanols is influenced by both chem- ical structure and molecular weight. The complex absorption and metabolism of low molecular weight monomeric catechins has been well described. [4] After ingestion, monomeric catechins are predominantly ab- sorbed in the small intestine after which they are metabolised by phase II conjugating enzymes to appear in plasma as sulfated and glucuronidated derivatives of epicatechin and methylepi- catechins. In humans, circulating metabolites of monomeric (epi)catechins have been reported to reach peak plasma concen- trations of 3.5–9 µmols L -1 within 30–90 min of ingestion with corresponding urinary excretion rates ranging between 88 and 200 µmols per day, depending upon the dose of (epi)catechins ingested. [5] Monomeric (epi)catechins that have not been subject to absorption in the small intestine, or otherwise effluxed back into the small intestine from the liver through bile excretion, will reach the colon. The metabolic fate of higher molecular weight oligomeric/polymeric PC on the other hand is less well under- stood. While PC have been shown to be stable during gut transit in humans, [6] they are poorly absorbed with only PC dimers detected in human plasma and at concentrations ≈100-fold lower when compared with the monomeric (epi)catechins. [7–9] Mol. Nutr. Food Res. 2020, 64, 1901135 1901135 (1 of 8) © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim