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Digestive Health Summit – March 2005: Abstracts
Polyphenols Ins and Out - Metabolism and Uptake From The Gut
Stephen Barnes, PhD
University of Alabama at Birmingham School of Medicine
The diet has numerous types of polyphenols derived from plants. The gastrointestinal tract is exposed to these compounds and their metabolites in concentrations substantially larger than in peripheral tissues. Polyphenols come in forms varying from very hydrophobic (the methoxy flavonoids tangeritin and nobelitin) to hydrophilic (glycosides of polyhydroxylated flavonoids). The mechanisms of uptake from the gut generally first require hydrolysis of the O-glycosides, either by bacterial glycosidases or lactose phlorizin hydrolase in the apical enterocytes. It is possible that the polyphenol glucosides are taken up by Na+-dependent glucose transporters followed by hydrolysis in the enterocyte. In the case of C-glucoside conjgates, they are resistant to hydrolysis and are rapidly taken up without any metabolism. Within the enterocyte, polyphenol aglycones are glucuronidated Although they can pass through the enterocyte basolateral membrane and hence into the vascular system, they are also transferred back into the luminal compartment by P-glycoprotein and multi-drug resistance proteins (MDR1, MRP1, MDR2). Overall uptake of an individual polyphenol depends on its rate of glucuronidation and substrate specificity for the transporter. The overall pathway of uptake and metabolism of polyphenols is carried out using a combined strategy of intact animals, isolated perfused intestine, and cultured Caco-2 cells, a human colonic cancer cell line. Some polyphenols are either too hydrophilic or have a high molecular weight and remain within the gastrointestinal tract. A potential consequence of this is regulation of the intestinal microflora within the colon. In summary, metabolism of polyphenols and their uptake are complex processes that occur at many levels of the intestines and may have an important role in gut health.
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