Metabolites of ellagitannins and their antioxidant activity

Various biological activities such as antioxidant, antiviral and antitumor activities were reported for different types of ellagitannins [1,2]. Nevertheless, there are little definitive studies on the absorption and metabolism of ellagitannins. We describe the characterization of urinary and intestinal microbial metabolites in rats after ingestion of geraniin, which is a typical ellagitannin isolated from Geranium thunbergii, an anti-diarrheic in Japan. Seven metabolites (M1-M7) were isolated from the suspension of rat intestinal microflora and rat urine samples. The structures of M1 (urolithin A), M2 (3,8,9-trihydroxy-6H-dibenzo[b,d]pyran-6-one), M3 (3,8-dihydroxy-9-methoxy-6H-dibenzo[b,d]pyran-6-one), M4 (3,9-dihydroxy-8-methoxy-6H-dibenzo[b,d]pyran-6-one), M5 (3,4,8,9,10-pentahydroxy-6H-dibenzo[b,d]pyran-6-one), M6 (3,8,9, 10-tetrahydroxy-6H-dibenzo[b,d]pyran-6-one), and M7 (3,8,10-trihydroxy-6H-dibenzo[b,d]pyran-6-one) were determined based on spectroscopic data. [3]. Furthermore, four major metabolites (M1-M4) were evaluated for antioxidant activity. These metabolites showed more potent antioxidant activity than intact ellagitannins such as geraniin in the ORAC assay, suggesting that the metabolites may contribute to the health benefits of ellagitannins as an antioxidant in the body.

References: 1. Okuda T. et al. (2009) Chemistry and biology of ellagitannins – An underestimated class of bioactive plant polyphenols-, World Scientific, Singapore: 1–54.

2. Yoshida T. et al. (2009) Chemistry and biology of ellagitannins – An underestimated class of bioactive plant polyphenols-, World Scientific, Singapore: 55–93.

3. Ito, H. et al. (2008)J. Agric. Food Chem. 56:393–400.