Enzymatic hemisynthesis of metabolites and conjugates of anthocyanins

This work aims to study the phase II metabolization of anthocyanins that is likely to occur in vivo. Anthocyanins (delphinidin, cyanidin, and malvidin-3-glucosides) were incubated with phase II enzymes in the presence of activated cofactors in order to obtain glutathionyl conjugates, methylated and glucuronydated compounds. Overall, the three anthocyanins tested were metabolized in vitro. Two compounds were detected by HPLC after incubation of human liver cytosolic fraction with cyanidin-3-glucoside and one compound with delphinidin-3-glucoside. These compounds were identified as monomethylated products. LC-MS analysis yielded mass data that fit with the anthocyanin structures bearing an additional methyl group in ring B. Several compounds were detected by HPLC after incubation of human liver microsomes with malvidin, cyanidin, and delphinidin-3-glucosides. These compounds were identified as monoglucuronides products after HPLC analysis. Conjugation with glutathione also occurred as proved by the mass data obtained. However, in this case, two anthocyanin equilibrium forms (flavylium and chalcone or water adducts) conjugated with glutathione were detected. Overall, the data of the present work shows the feasibility of the in vitro enzymatic hemisynthesis of metabolites and glutathione conjugates of anthocyanins. This first experimental approach may further allow the achievement of new purified forms of anthocyanins, some of which do not occur in nature, and also the determination of whether these compounds are the bioactive forms responsible for some of the biological activities reported for anthocyanins.