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glycosidic forms (49). Quercetin derivatives are deconjugated and converted to hydroxyphenylacetic acids by the colonic microbiota in vitro (50). Confirming these observations, recent in vitro studies revealed the production of 3-hydroxyphenylacetic acid and 3-(hydroxyphenyl)-propionic acid from rutin (a representative glycoside of quercetin) in human gut microbiota fermentation studies (31). An important observation in these studies was that the pattern of degradation varied considerably between donor fecal microbiota samples and with concentration of the initial substrate. This is significant since many of the compounds produced in this degradative process may have enhanced biological properties. 3,4-dihydroxyphenylacetic acid and 4-hydroxyphenylacetic acid have more effective antiplatelet aggregation activity than their precursors rutin and quercetin (51).

Compositional variations in the microbiota may have a significant impact on the final metabolic products of flavonol metabolism. Indeed reports of studies designed to confirm these observations are now appearing. Eubacterium ramulus is capable of metabolizing quercetin both in vitro and in rats associated with the organism (8). In both cases, the isolate was capable of releasing quercetin from its glycosidic form and was then able to cleave the ring system of quercetin and produce mainly 3,4-dihydroxyphenylacetic acid. Further studies in humans revealed that E. ramulus is a common member of the human gut microbiota (52); its resident population level is dependant on flavonoid intake and the production of secondary metabolites of flavonoids (such as 3,4-dihydroxyphe-nylacetic acid) was greatest when E. ramulus populations where increased (15). Meanwhile E. ramulus has also been tested for its abilities to degrade other structurally related flavonoids including other flavonols, flavones, flavan-3-ols, and flavonones, and in certain cases, significant metabolism can occur (53). Clostridium orbiscindens, which is an obligate anaerobe commonly found in the intestinal tract, is also capable of cleaving the C3-C4 bond of quercetin to give 3,4-dihydroxyphenylacetic acid (54). In recent studies, it was also shown to degrade a range of other flavonols and flavanones in vitro and that it was present in 8 of 10 volunteers at levels of 1.87 X 108 to 2.5 X 109 cells/ g (55). At present, these are the most extensively published reports on the influence of microbiota composition in polyphenol metabolism and set the benchmark for future studies in other polyphenol classes.

Pregnancy And Childbirth

Pregnancy And Childbirth

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