Abstract

Sulfonation is an important metabolic pathway for hesperetin. However, the mechanisms for the cellular disposition of hesperetin and its sulfate metabolites are not fully established. In this study, disposition of hesperetin via the sulfonation pathway was investigated using human embryonic kidney (HEK) 293 cells overexpressing sulfotransferase 1A3. Two monosulfates, hesperetin-3′-O-sulfate (H-3′-S) and hesperetin-7-O-sulfate (H-7-S), were rapidly generated and excreted into the extracellular compartment upon incubation of the cells with hesperetin. Regiospecific sulfonation of hesperetin by the cell lysate followed the substrate inhibition kinetics (V_max = 0.66 nmol/min per mg, K_m = 12.9 μM, and K_si= 58.1 μM for H-3′-S; V_max = 0.29 nmol/min per mg, K_m = 14.8 μM, and K_si= 49.1 μM for H-7-S). The pan–multidrug resistance-associated protein (MRP) inhibitor MK-571 at 20 μM essentially abolished cellular excretion of both H-3′-S and H-7-S (the excretion activities were only 6% of the control), whereas the breast cancer resistance protein–selective inhibitor Ko143 had no effects on sulfate excretion. In addition, knockdown of MRP4 led to a substantial reduction (>47.1%; P < 0.01) in sulfate excretion. Further, H-3′-S and H-7-S were good substrates for transport by MRP4 according to the vesicular transport assay. Moreover, sulfonation of hesperetin and excretion of its metabolites were well characterized by a two-compartment pharmacokinetic model that integrated drug uptake and sulfonation with MRP4-mediated sulfate excretion. In conclusion, the exporter MRP4 controlled efflux transport of hesperetin sulfates in HEK293 cells. Due to significant expression in various organs/tissues (including the liver and kidney), MRP4 should be a determining factor for the elimination and body distribution of hesperetin sulfates.