Overestimation of flavonoid aglycones as a result of the ex vivo deconjugation of glucuronides by the tissue β-glucuronidase

Tissue β-glucuronidase hydrolyzes flavonoid glucuronides to their aglycones during tissue extraction, resulting in higher reported tissue levels of aglycone. β-Glucuronidase inhibitor d-saccharic acid 1,4-lactone (SL) blocks the ex vivo deconjugation of flavonoid glucuronides. SL at concentration of 15 μmol/g liver tissue decreases quercetin (Q) and methyl-quercetin (Me-Q) deconjugated from glucuronides by 87% and 84%, respectively (**p < 0.01).