Comprehensive Analyses of Quercetin Conjugates by LC/MS/MS Revealed That Isorhamnetin-7-O-glucuronide-4′-O-sulfate Is a Major Metabolite in Plasma of Rats Fed with Quercetin Glucosides

Quercetin glycosides in the diet are absorbed and converted to glucuronides, sulfates, or mixed conjugates of glucuronide and sulfate in plasma. Physiological effects of quercetin conjugates (Q-conjugates) differ depending on the type and position of conjugation. We developed a comprehensive analysis of Q-conjugates, including mixed conjugates, by LC/MS/MS. The whole species of Q-conjugates in tail blood plasma was measured on days 1, 3, and 12 in rats fed a 0.24% quercetin glucoside-containing diet. Twenty-three Q-conjugate molecules were detected, and 16 Q-conjugates among these were quantified using standard compounds. The most abundant metabolite in the plasma was mixed conjugates, comprising isorhamnetin-7-O-glucuronide-4'-O-sulfate, followed by quercetin-7-O-glucuronide-4'-O-sulfate; together, they accounted for 86% of total Q-conjugates on day 12. The profile of quercetin conjugate species did not significantly change during 12 days. The total Q-conjugate molecules quantified by our method was comparable with the total Q-conjugates quantified using an enzymatic deconjugation method.