Regioselective hydroxylation of an antiarrhythmic drug, propafenone, mediated by rat liver cytochrome P450 2D2 differs from that catalyzed by human P450 2D6

Cytochrome P450s in chimeric mice with humanized liver

Chimeric mice with humanized livers (humanized liver mice) are attractive experimental animal models for drug metabolism and pharmacokinetic studies. The "humanized liver" is a mature and functional liver with zonal position-specific expressions of human cytochrome P450 (P450) enzymes and a global gene expression pattern consistent with that of the mature human liver. Most P450-dependent drug oxidation activities were comparable between microsomes from livers of human and humanized liver mice based on similar expression levels of human P450 enzymes; however, some differences were observed between the two species, including considerable variations in activities of bufuralol 1'-hydroxylation and propafenone 4'-hydroxylation. Human disproportionate and/or unique metabolites of P450 substrate drugs were produced in humanized liver mice. Plasma concentration profiles of typical P450 substrate drugs in humans could be extrapolated from the corresponding data in humanized liver mice using simplified physiologically based pharmacokinetic modeling. Drug-drug interaction-mediated hepatic human CYP3A/2C induction by rifampicin (a human pregnane X receptor agonist) was observed in humanized liver mice. The major role of human CYP2C9 in in vivo diclofenac 4'-hydroxylation were determined using human CYP2C9-inactivated chimeric mice using a mechanism-based inhibitor, tienilic acid. Overall, based on the functional characteristics of hepatic human P450 enzymes, humanized liver mice are valuable experimental animals for studying metabolite profiling, pharmacokinetics, and drug interactions.

Comparison of mouse and human cytochrome P450 mediated-drug metabolizing activities in hepatic and extrahepatic microsomes

1. Despite the importance of mice as a preclinical species in drug testing, their hepatic and extrahepatic drug-metabolizing characteristics are poorly understood. Here, we compared the P450-dependent drug oxidation activity in tissue microsomes and distribution patterns of P450 protein/mRNA between humans and mice.2. The activities of midazolam 1'-/4-hydroxylation in the liver and intestine and chlorzoxazone 6-hydroxylation in the liver were similar in humans and mice. The activities of coumarin 7-hydroxylation, flurbiprofen 4'-hydroxylation, and S-mephenytoin 4'-hydroxylation in the liver were higher in humans than in mice. The activities of 7-ethoxyresorufin O-deethylation in the liver, 7-pentoxyresorufin O-depentylation in the lung/liver/intestine, bufuralol 1'-hydroxylation in the liver/intestine, propafenone 4'-hydroxylation in liver/intestine, and diazepam N-demethylation in the liver/intestine were higher in mice than in humans.3. CYP1A2/2E1 mRNAs were mainly expressed in the livers of humans and mice. Cyp2b9/2b10 mRNAs were abundant in the mouse lung/liver/intestine, but CYP2B6 was mainly expressed in the human liver. CYP2C/2D/3A mRNAs were expressed in the liver and intestine, with the respective proteins detected in tissue microsomes of both humans and mice.4. These information on P450-dependent drug-metabolizing characteristics in hepatic and extrahepatic tissues is useful to understand the similarities and differences between humans and mice in drug metabolism.

Metabolites Identification of Chemical Constituents From the Eggplant (Solanum melongena L.) Calyx in Rats by UPLC/ESI/qTOF-MS Analysis and Their Cytotoxic Activities

Eggplant (Solanum melongena L.) Calyx is a medicinal and edible traditional Chinese medicine with anti-inflammatory, anti-oxidant, and anti-cancer properties. However, the pharmacodynamic components and metabolic characteristics remain unclear. Amide and phenylpropanoid were the two main constituents, and four amides, including n-trans-p-coumaroyltyramine (1), n-trans-p-coumaroyloctopamine (2), n-trans-p-coumaroylnoradrenline (3), n-trans-feruloyloctopamine (4), and a phenylpropanoid neochlorogenic acid (5) were selected. In this study, these five representative compounds showed cytotoxic activities on A549, HCT116, and MCF7 cells. In addition, the metabolites of 1–5 from the eggplant calyx in rats were identified. In total, 23, 37, 29, and 17 metabolites were separately characterized in rat plasma, urine, feces, and livers, by UPLC/ESI/qTOF-MS analysis. The metabolism of amides and phenylpropanoid was mainly involved in hydroxylation, methylation, glucuronidation, or sulfation reactions. Two hydroxylated metabolites (1-M2 and 2-M3) were clearly identified by comparison with reference standards. Rat liver microsome incubation experiments indicated that P450 enzymes could hydroxylate 1–5, and the methylation reaction of the 7-hydroxyl was also observed. This is the first study on the in vivo metabolism of these compounds, which lays a foundation for follow-up studies on pharmacodynamic evaluations and mechanisms.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.