PJ contains multiple phenolic compounds such as anthocyanins and ETs. However, ETs comprise most of the polyphenols found in commercial PJ, POMxp, and POMxl. Therefore the metabolism of these compounds, i.e.
, ETs, were the focus of this study.7,11
In our prior study, we demonstrated that EA appears in plasma after consumption of PJ.7
PJ consumed daily can have significant effects on cardiovascular biomarkers3,4
and on circulating prostate-specific antigen in prostate cancer patients,6
which is assumed to be due to the actions of EA derived from ETs and of EA metabolites, including UAG. In the present study, we compared the absorption of EA from PJ, POMxl, and POMxp and the excretion of urinary UAG.
The present study confirmed the rapid absorption of EA from PJ, POMxl, and POMxp and demonstrated that UAG was excreted in the urine for up to 48 hours after administration of PJ, POMxl, and POMxp. EA metabolites have been previously reported to be present in human urine up to 56 hours after PJ intake.9
Urinary EA metabolites, such as urolithins, arise from biotransformation of EA by the intestinal microflora, which then undergo conjugation with methyl, glucuronyl, and sulfate groups and are excreted in the urine.7,9
In the present study, UAG was the most commonly found urinary metabolite of EA. Other urinary metabolites, including sulfated and methylated forms of urolithin-A, were also detected in this study (data not shown) but with considerable interindividual variability as previously reported.7,9
Urolithin metabolism may be dependent on bowel transit time or intestinal flora as has been defined for soy isoflavones,12
and this deserves further study. Nevertheless, this research provides valuable knowledge about pomegranates and metabolomics (the integrated study of molecules produced by metabolism). It is known that the large-bowel microflora produce many of the food or dietary supplement compounds absorbed, metabolized, and passed through the blood and secreted in urine and saliva.13
In summary, we were able to demonstrate that the consumption of pomegranate polyphenols delivered by PJ, POMxl, and POMxp resulted in similar absorption of EA. However, the time course of POMxp absorption was different from that of the beverages, PJ and POMxl, and clustered around two different delayed peaks of 2 hours and 3 hours compared to approximately 1 hour for PJ and POMxl. However, despite the delayed appearance, the AUC of plasma EA was not statistically different with PJ, POMxl, and POMxp treatment. The delayed plasma appearance of EA observed by our group in this study is similar to a finding from our prior study comparing a green tea extract supplement versus tea beverages.14
In that study, polyphenol absorption following consumption of a green tea extract supplement was delayed by greater than 1 hour when compared to tea beverages with similar amounts of total tea polyphenols.14
POMxp was administered in a gel capsule, and it is possible that the delayed absorption was due to the time necessary to dissolve the capsule material and release the contents. There are a number of possible explanations for the delayed absorption, but the clustering among different individuals of plasma EA at time to peak concentration of either 2 or 3 hours is interesting. There may be differences in gut motility, in gut bacteria, or in the hydrolysis of ETs within the stirred layer of intestinal epithelial cells.