Absorption and metabolism of flavonols

The consumption of flavonols, major sources of dietary flavonoids, have been linked to the reduction of risk factors for various chronic diseases. However, the bioavailability of flavonols would appear to be limited and not all compounds within the same subclass are absorbed with equal efficacy, thus compromising their nutritional relevance. The aim of this current study was to examine the absorption and metabolism of four major flavonols specifically quercetin, myricetin, kaempferol and galangin using both in vitro methods and healthy human volunteers to investigate how bioavailability was affected by the addition of other ingredients, specifically fat. Firstly, the enzymatic synthesis of flavonol metabolites was conducted using liver S9 homogenates, which demonstrated that all major flavonol aglycone generated several isomers of glucuronide or sulphate forms after the incubation period. The evidence for identification and characterisation of available authentic standards and synthesised flavonol metabolites using HPLC-DAD-MS-MS is presented. The success of this method was demonstrated through its application to assess the fate of flavonols in the cell culture transport experiments, which were examined using co-cultures of Caco-2 (enterocyte cell) and HT29-MTX (goblet cell) monolayers and the results partially substantiate that the absorption is most probably achieved by passive transport.