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Polyphenol Phase‐II Metabolites are Detectable in Human Plasma after Ingestion of 13C Labeled Spinach—a Pilot Intervention Trial in Young Healthy Adults

Passon, Maike, Bühlmeier, Judith, Zimmermann, Benno F., Stratmann, Anja, Latz, Stefan, Stehle, Peter, Galensa, Rudolf
Molecular nutrition & food research 2018 v.62 no.10 pp. e1701003
Spinacia oleracea, adults, carbon, freeze drying, isotope labeling, men, metabolites, microorganisms, pharmacokinetics, polyphenols, spinach, stable isotopes
SCOPE: After intrinsic labeling of spinach (Spinacia oleracea L., Chenopodiaceae) with ¹³CO₂, 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 ¹³C 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 ¹³C/¹²C ratio. Additionally, ¹³C 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 ¹²C₁¹³C₁₆ and ¹³C₁₇ isotopologs, were tentatively identified. Plasma concentration of TMM‐glucuronide and TMM‐sulfate reached cₘₐₓ from 19.1–54.3 and 22.5–125.5 nmol L–¹, respectively, 7–9 h post‐ingestion. CONCLUSION: It seems likely that ¹³C 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 ¹³C labeled polyphenol metabolites are detectable and quantifiable in human plasma.