Further exploring the absorption and enterocyte metabolism of quercetin forms in the Caco-2 model using nano-LC-TOF-MS

When using the Caco-2 intestinal model, the low uptake, intracellular presence at low levels as well as generation of trace metabolites may limit the analysis of flavonoids. To overcome these limitations, we performed a simple but sensitive methodology based on nano-LC-TOF-MS, using an on-line trapping step. The analytical method was validated for quercetin, quercetin 3-O-glucoside, and quercetin 3-O-glucuronide and the reliability for characterization using lock-mass calibration was also assessed along the linear range. Afterwards, the in vitro absorption, metabolism, and cellular occurrence were explored with the proposed methodology. The apparent permeability coefficient in the absorptive direction and the cellular accumulation were higher for quercetin aglycone, with a value of 2.61 × 10(-6) cm/s and relative amounts of 0.73 and 1.17% in the cytosolic and solid particle fraction at the end of the assay, respectively. Alternatively, the net efflux ratio was lower for quercetin than for their derivatives. Moreover, depending on the structure of the parent compound, metabolites were generated by glucuronidation, sulfation, and methylation.