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1. The natural polyphenol gossypol possesses many therapeutic benefits. Here we aim to determine the elimination pathways of gossypol in vivo and in vitro. 2. Metabolite elucidation of gossypol was performed using UPLC-QTOF/MS coupled with Metabolynx analysis. Clearance of gossypol was evaluated in bile duct cannulated rats and in the single-pass perfused rat intestine model. In vitro glucuronidation of gossypol was characterized using liver and intestine microsomes as well as recombinant UDP-glucuronosyltransferase (UGT) enzymes. 3. Analysis of rat plasma, urine, and feces revealed glucuronidation as the only metabolic pathway for gossypol. In bile duct cannulated rats, considerable amounts of glucuronides (G1, G2 and G3; 58.8-83.2% of dose) and parent compound (5.0-20%) were excreted into bile after IV administration. In the perfused rat intestine model, gossypol was well absorbed with a [Formula: see text] (the dimensionless effective permeability) value of 4.4. Significant amounts of glucuronides (G1, G2 and G3) were excreted into the gut lumen (2.5%) and into the bile (4.8%). Biliary excretion of unchanged gossypol (6.0%) was comparable to that of glucuronides. Further, gossypol was subjected to rapid glucuronidation by liver and intestine microsomes. Reaction phenotyping showed that multiple UGT1A enzymes (including UGT1A1, 1A3, 1A7 and 1A8) are mainly responsible for gossypol metabolism. 4. In conclusion, glucuronidation was the only metabolic pathway for gossypol in rats. Excretion of unchanged gossypol into bile was also an important clearance mechanism.

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-39-O-sulfate (H-39-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 mM, and K si = 58.1 mM for H-39-S; V max = 0.29 nmol/min per mg, K m = 14.8 mM, and K si = 49.1 mM for H-7-S). The pan-multidrug resistance-associated protein (MRP) inhibitor MK-571 at 20 mM essentially abolished cellular excretion of both H-39-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-39-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.

1. Niclosamide is an old anthelmintic drug that shows potential in fighting against cancers. Here, we characterized the metabolism of niclosamide by cytochrome P450 enzymes (CYPs) and UDP-glucuronosyltransferases (UGTs) using human liver microsomes (HLM) and expressed enzymes. 2. NADPH-supplemented HLM (and liver microsomes from various animal species) generated one hydroxylated metabolite (M1) from niclosamide; and UDPGA-supplemented liver microsomes generated one mono-O-glucuronide (M2). The chemical structures of M1 (3-hydroxy niclosamide) and M2 (niclosamide-2-O-glucuronide) were determined through LC-MS/MS and/or NMR analyses. 3. Reaction phenotyping revealed that CYP1A2 was the main enzyme responsible for M1 formation. The important role of CYP1A2 in niclosamide metabolism was further confirmed by activity correlation analyses as well as inhibition experiments using specific inhibitors. 4. Although seven UGT enzymes were able to catalyze glucuronidation of niclosamide, UGT1A1 and 1A3 were the enzymes showed the highest metabolic activities. Activity correlation analyses demonstrated that UGT1A1 played a predominant role in hepatic glucuronidation of niclosamide, whereas the role of UGT1A3 was negligible. 5. In conclusion, niclosamide was subjected to efficient metabolic reactions hydroxylation and glucuronidation, wherein CYP1A2 and UGT1A1 were the main contributing enzymes, respectively.