Abstract 3678: Pilot walnut intervention study in human volunteers to establish and justify criteria for future screening and clinical intervention trials
Authors: Owen Robert W. , Pfundstein Beate , Hull William E. , Haubner Roswitha , Ulrich Cornelia M. 
Published: June 2012

A two-stage pilot intervention study with walnuts was conducted in human volunteers (n = 4) to establish the bioavailability of urolithins which are the terminal end-products of ellagitannin metabolism by the faecal flora. Biosamples (blood, faeces and urine) were evauated for their cancer chemopreventive potential in a range of in vitro assays (DPPH, FRAP, ORAC). Urolithin metabolites were identified and quantitated by HPLC-ESI-MS. Furthermore individual metabolites were isolated and purified by semi-preparative HPLC and characterized by HPLC-ESI-MS, nano-ESI-MS-MS and NMR (600 MHz). These were urolithin-A glucuronide, urolithin-B glucuronide (four isomers), urolithin-C glucuronide (two isomers) and urolithin-D glucuronide (four isomers). Additionally the following free urolithins were characterized namely urolithin-A, urolithin-B (two isomers), urolihin-C (two isomers), urolithin-D and methyl urolithin-D. The concentrations of glucuronidated urolithins measured in urine and calculated per g/walnuts were volunteer-1 (female) 69.9 µM, volunteer-2 (male) 60.4 µM, volunteer-3 (female) 15.7 µM and volunteer-4 (male) 20.0 µM. There was a wide inter-individual variation in gastrointestinal polyphenol metabolism, among the four volunteers, as judged by the profiles in urine: volunteer-1 excreted mainly di-, tri- and tetrahydroxyurolithin glucuronides, volunteer-2 excreted mainly mono- and di-hydroxyurolithin glucuronides, volunteer-3 mainly trihydroxyurolithin glucuronide and volunteer-4 only dihydroxyurolithin glucuronides. In one individual the concentration of total urolithin glucuronides rose in plasma to 186 µM and then slowly declined 24 h after ingestion. The distribution in plasma followed a gaussian curve. The major dibenzopyrone excreted in feces was tetrahydroxydibenzopyran-(6)-one with the highest concentration at 299 mg/day day on day 3 and 414 mg on day 10, respectively. The second was trihydroxydibenzopyrone excreted in highest concentration on day 4 (two days after ingestion) in feces (60.3 mg/day) followed by day 9 (88.4 mg/day) (one day after ingestion). The antioxidant capacity of the glucuronidated urolithins was weak in the DPPH and FRAP assays whereas in the more biologically relevant ORAC assay the antioxidant capacity was strong. However a strong positive correlation was only evident with uric acid concentration in urine across the assays. The free urolithins displayed high antioxidant capacity in the DPPH and ORAC assays and this correlated positively with the concentration of urolithins (especially tetrahydroxydibenzopyran-(6)-one) in the fecal extracts. The data indicates that free urolithins may be protective against oxidation in the large intestine. Preclinical trials are warranted to assess the efficacy of urolithins as protective agents against colorectal cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3678. doi:10.1158/1538-7445.AM2011-3678