Metabolism Of Some Flavonoids By Human Intestinal Microflora

Flavonoids, found largely distributed in plants, constitute the most abundant phenolic compounds in human diet with an estimated daily intake of 500 to 1000 mg in the U.S, mainly as glycosides. [1] Studies on these compounds based mainly on in vitro experiments have suggested many health benefits through cell signaling pathways and antioxidant activity. [1] Human tissues with the exception of intestinal lining, come in contact with flavonoids via blood. As such, the tissues often receive molecules that are different from those found in the food due to extensive modification by first-pass metabolism during and after absorption. [2] Further, the flavonoids that are not absorbed in the small intestine are subjected to microbial activity mainly in the colon yielding reductive and ring-fission metabolites. [3,4] Thus, it is essential to trace the fate of these compounds to evaluate their biological activities.

In our ongoing studies to characterize human intestinal microbial metabolites of flavonoids, we were able to transform 2'-hydroxyflavanone and 7-hydroxyflavone to 2, 2'-dihydroxydihydrochalcone and 7-hydroxyflavanone together with catechol, respectively. These catabolic transformations are comparable to flavonoid conversions brought about by the key anaerobic intestinal bacterium, Eubacterium ramulus. [5] Catechol is a known NF-kB inhibitor [6] and Dihydroxy dihydrochalcones have been shown to exhibit antitumor activity. [7] Two other compounds, silybin and 5-hydroxyflavanone failed to yield metabolites with the intestinal microbial flora.

Acknowledgements: This research is supported in part by Science Based Authentication of Dietary Supplements and Botanical Dietary Supplement Research funded by the Food and Drug Administration grant numbers 1U01FD004246 – 05 and 1U01FD003871 – 01, and the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No.58 – 6408 – 1-603 – 07.

References:

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[2] Kroon P.A., Clifford M.N., et al. (2004) Am. J. Clin. Nutr. 80(1):15 – 21.

[3] Williamson G, Day A.J., et al. (2000) Biochem. Soc. Trans., 28(2):16 – 22.

[4] Yang C.S., Landau J.M. et al. (2001) Annu. Rev. Nutr., 21:381 – 406.

[5] Braune A., Gütschow M., et al., (2001) Appl. Environ. Microbiol. 67(12): 5558 – 5567.

[6] Knuth S., Schubel et al., (2011) Planta Med., 77:1024 – 1026.

[7] Szliszka E., Czuba Z.P. et al. (2010) Molecules, 15(8): 5336 – 5353.