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.