RESEARCH ARTICLE Polyphenols www.mnf-journal.com Polyphenol Phase-II Metabolites are Detectable in Human Plasma after Ingestion of 13 C Labeled Spinach—a Pilot Intervention Trial in Young Healthy Adults Maike Passon,* Judith B¨ uhlmeier, Benno F. Zimmermann, Anja Stratmann, Stefan Latz, Peter Stehle, and Rudolf Galensa Scope: After intrinsic labeling of spinach (Spinacia oleracea L., Chenopodiaceae) with 13 CO 2 , we investigated if labeled polyphenol metabolites were detectable in human plasma. Methods and result: In a pilot intervention trial, five healthy men consumed 5 g freeze-dried 13 C labeled spinach, including a total amount of 160 μmol methoxyflavonols, including 70 μmol 5,3 ′ ,4 ′ -trihydroxy-3-methoxy-6, 7-methylendioxyflavone-4 ′ -glucuronide. Plasma samples of all subjects were analyzed with regard to their 13 C/ 12 C ratio. Additionally, 13 C labeled metabolites of patuletin, spinacetin, and 5,3 ′ ,4 ′ -trihydroxy-3-methoxy-6, 7-methylendioxyflavone (TMM) were analyzed in plasma samples in a subgroup of three subjects. TMM-glucuronide, TMM-sulfate, and spinacetin-glucuronide-sulfate, the latter as 12 C 1 13 C 16 and 13 C 17 isotopologs, were tentatively identified. Plasma concentration of TMM-glucuronide and TMM-sulfate reached c max from 19.1–54.3 and 22.5–125.5 nmol L –1 , respectively, 7–9 h post-ingestion. Conclusion: It seems likely that 13 C labeled TMM-glucuronide and TMM-sulfate are phase-II metabolites which were converted after colonic transformation. Variations in plasma kinetics were observed for these two metabolites and may be attributed to the individual composition of the microbiota. We conclude that 13 C labeled polyphenol metabolites are detectable and quantifiable in human plasma. Dr. M. Passon,Dr. B. F. Zimmermann Department of Nutrition and Food Sciences Molecular Food Technology University of Bonn R¨ omerstraße 164, 53117, Bonn, Germany E-mail: passon@uni-bonn.de Dr. J. B¨ uhlmeier, Prof. P. Stehle Department of Nutrition and Food Sciences Nutritional Physiology University of Bonn Nußallee 9, 53115, Bonn, Germany DOI: 10.1002/mnfr.201701003 1. Introduction There is convincing evidence from nu- merous observational studies that regu- lar consumption of plant-derived foods in comparably large quantities (500– 600 g d –1 ) essentially contribute to re- duce the overall risk of degenerative dis- eases such as cardiovascular disorders, specific forms of cancer, osteoporosis, or diabetes. [1,2] Polyphenols like flavonoids found in fruits, vegetables, cacao, and cof- fee in various amounts are seen as essen- tial mediators of the preventive effects of these food groups on human health. [3] In vitro, flavonoids exhibit high antioxidant capacity and can, thus, prevent oxida- tive cell damages. [4] Moreover, polyphe- nols and metabolites thereof can influ- ence cellular enzyme activities thereby affecting metabolic pathways. [5–7] In re- cent years, it became, however, clear that the bioavailability of dietary polyphenols in humans is influenced by several fac- tors, especially the food matrix, food pro- cessing, the compound concentration in the food item and the amount ingested. [8] Dr. J. B¨ uhlmeier Department of Child and Adolescent Psychiatry University Hospital Essen, University of Duisburg-Essen 45147, Essen, Germany Dr. B. F. Zimmermann Institut Kurz GmbH St¨ ockheimer Weg 1, 50829, K¨ oln, Germany A. Stratmann, Prof. R. Galensa Department of Nutrition and Food Sciences Food Chemistry University of Bonn Endenicher Allee 11–13, 53115, Bonn, Germany Dr. S. Latz Department of Urology University of Bonn Sigmund-Freud-Street 25, Bonn, 53127, Germany Mol. Nutr. Food Res. 2018, 1701003 C  2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1701003 (1 of 10)