- Professor, Pharmacology and Toxicology
- Member of the Graduate Faculty
- Ph.D. Biological Chemistry
- University of Michigan, Ann Arbor, Michigan, United States
- Studies on Gonadotropin Receptor of Rat Ovary and Testis
No activities entered.
Drug Metabolism + DsptnCBIO 550 (Spring 2022)
Drug Metabolism + DsptnPCOL 550 (Spring 2022)
Clinical Pathophysiology IIPCOL 838B (Spring 2021)
Drug Dsptn+MetabolismCBIO 550 (Spring 2021)
Drug Dsptn+MetabolismPCOL 550 (Spring 2021)
Intro Molecular TherapeuticsCBIO 530 (Fall 2020)
Intro Molecular TherapeuticsCHEM 530 (Fall 2020)
Intro Molecular TherapeuticsPCOL 530 (Fall 2020)
Intro Molecular TherapeuticsPHSC 530 (Fall 2020)
Clinical Pathophysiology IIPCOL 838B (Spring 2020)
Drug Dsptn+MetabolismPCOL 550 (Spring 2020)
Clinical Pathophysiology IIPCOL 838B (Spring 2019)
DissertationPCOL 920 (Spring 2019)
Drug Dsptn+MetabolismCBIO 550 (Spring 2019)
Drug Dsptn+MetabolismPCOL 550 (Spring 2019)
Research ConferencePCOL 695A (Spring 2019)
ResearchPCOL 900 (Fall 2018)
Research ConferencePCOL 695A (Fall 2018)
Drug Dsptn+MetabolismCBIO 550 (Spring 2018)
Drug Dsptn+MetabolismPCOL 550 (Spring 2018)
Intro Phcl+Tox ResearchPCOL 586B (Spring 2018)
ResearchPCOL 900 (Spring 2018)
Research ConferencePCOL 695A (Spring 2018)
- Zhang, Q., & Ding, X. (2018). Enzyme Regulation. In Comprehensive Toxicology, 3rd Edition(pp 9-29). Oxford: Academic Press.
- Zhang, Q., Li, L., & Van Winkle, L. S. (2018). Biochemical Function of the Respiratory Tract: Metabolism of Xenobiotics. In Comprehensive Toxicology, 3rd Edition(pp 171-179). Oxford: Academic Press.
- Ding, L., Li, L., Liu, S., Bao, X., Dickman, K. G., Sell, S. S., Mei, C., Zhang, Q. Y., Gu, J., & Ding, X. (2020). Proximal Tubular Vacuolization and Hypersensitivity to Drug-Induced Nephrotoxicity in Male Mice With Decreased Expression of the NADPH-Cytochrome P450 Reductase. Toxicological sciences : an official journal of the Society of Toxicology, 173(2), 362-372.More infoThe effect of variations in the expression of cytochrome P450 reductase (CPR or POR) is determined in mice with decreased POR expression to identify potential vulnerabilities in people with low POR expression. There is an age-dependent appearance of increasing vacuolization in the proximal tubules of the renal cortex in 4- to 9-month-old male (but not female) Cpr-low (CL) mice. These mice have low POR expression in all cells of the body and upregulation of lysosome-associated membrane protein 1 expression in the renal cortex. Vacuolization is also seen in extrahepatic CL and extrarenal CL male mice, but not in mice with tissue-specific Por deletion in liver, intestinal epithelium, or kidney. The occurrence of vacuolization is accompanied by increases in serum blood-urea-nitrogen levels. Male CL mice are hypersensitive to cisplatin- and gentamicin-induced renal toxicity at 3 months of age, before proximal tubular (PT) vacuoles are detectable. At doses that do not cause renal toxicity in wild-type mice, both drugs cause substantial increases in serum blood-urea-nitrogen levels and PT vacuolization in male but not female CL mice. The hypersensitivity to drug-induced renal toxicity is accompanied by increases in circulating drug levels. These novel findings demonstrate deficiency of renal function in mice with globally reduced POR expression and suggest that low POR expression may be a risk factor for drug-induced nephrotoxicity in humans.
- Fan, X., Ding, X., & Zhang, Q. Y. (2020). Hepatic and intestinal biotransformation gene expression and drug disposition in a dextran sulfate sodium-induced colitis mouse model. Acta pharmaceutica Sinica. B, 10(1), 123-135.More infoWe examined the impact of gut inflammation on the expression of cytochrome P450 (P450) and other biotransformation genes in male mice using a dextran sulfate sodium (DSS)-induced colitis model. Several P450 isoforms, including CYP1A, CYP2B, CYP2C, and CYP3A, were down-regulated, accompanied by decreases in microsomal metabolism of diclofenac and nifedipine, in the liver and small intestine. The impact of the colitis on clearance of oral drugs varied for four different drugs tested: a small decrease for nifedipine, a relatively large decrease for lovastatin, but no change for pravastatin, and a large decrease in the absorption of cyclosporine A. To further assess the scope of influence of gut inflammation on gene expression, we performed genome-wide expression analysis using RNA-seq, which showed down-regulation of many CYPs, non-CYP phase-I enzymes, phase-II enzymes and transporters, and up-regulation of many other members of these gene families, in both liver and intestine of adult C57BL/6 mice, by DSS-induced colitis. Overall, our results indicate that gut inflammation suppresses the expression of many P450s and other biotransformation genes in the intestine and liver, and alters the pharmacokinetics for some but not all drugs, potentially affecting therapeutic efficacy or causing adverse effects in a drug-specific fashion.
- Fan, X., Li, H., Ding, X., & Zhang, Q. Y. (2019). Contributions of Hepatic and Intestinal Metabolism to the Disposition of Niclosamide, a Repurposed Drug with Poor Bioavailability. Drug metabolism and disposition: the biological fate of chemicals, 47(7), 756-763.More infoNiclosamide, an antiparasitic, has been repositioned as a potential therapeutic drug for systemic diseases based on its antiviral, anticancer, and anti-infection properties. However, low bioavailability limits its in vivo efficacy. Our aim was to determine whether metabolic disposition by microsomal P450 enzymes in liver and intestine influences niclosamide's bioavailability in vivo, by comparing niclosamide metabolism in wild-type, liver-Cpr-null (LCN), and intestinal epithelium-Cpr-null (IECN) mice. In vitro stability of niclosamide in microsomal incubations was greater in the intestine than in liver in the presence of NADPH, but it was much greater in liver than in intestine in the presence of UDPGA. NADPH-dependent niclosamide metabolism and hydroxy-niclosamide formation were inhibited in hepatic microsomes of LCN mice, but not IECN mice, compared with wild-type mice. In intestinal microsomal reactions, hydroxy-niclosamide formation was not detected, but rates of niclosamide-glucuronide formation were ∼10-fold greater than in liver, in wild-type, LCN, and IECN mice. Apparent Km and values for microsomal niclosamide-glucuronide formation showed large differences between the two tissues, with the intestine having higher Km (0.47 M) and higher (15.8) than the liver (0.09 M and 0.75, respectively). In vivo studies in LCN mice confirmed the essential role of hepatic P450 in hydroxy-niclosamide formation; however, pharmacokinetic profiles of oral niclosamide were only minimally changed in LCN mice, compared with wild-type mice, and the changes seem to reflect the compensatory increase in hepatic UDP-glucuronosyltransferase activity. SIGNIFICANCE STATEMENT: These results suggest that efforts to increase the bioavailability of niclosamide by blocking its metabolism by P450 enzymes will unlikely be fruitful. In contrast, inhibition of niclosamide glucuronidation in both liver and intestine may prove effective for increasing niclosamide's bioavailability, thereby making it practical to repurpose this drug for treating systemic diseases.
- Hartog, M., Zhang, Q. Y., & Ding, X. (2019). Role of mouse cytochrome P450 enzymes of the CYP2ABFGS subfamilies in the induction of lung inflammation by cigarette smoke exposure. Toxicological sciences : an official journal of the Society of Toxicology.More infoMany constituents of tobacco smoke (TS) require bioactivation to exert toxic effects; however, few studies have examined the role of bioactivation enzymes in the adverse effects of TS exposure. This knowledge gap is a major source of uncertainty for risk assessment and chemoprevention efforts.
- Jia, K., Zhang, D., Jia, Q., & Zhang, Q. Y. (2019). Regulation of Fgf15 expression in the intestine by glucocorticoid receptor. Molecular medicine reports, 19(4), 2953-2959.More infoFibroblast growth factor 15 (FGF15) was previously identified to be highly expressed in the ileum and functions as an endocrine factor to regulate bile acid synthesis in the liver. FGF15 targets its receptor fibroblast growth factor receptor 4 in the liver and serves important roles in energy metabolism, including bile acid homeostasis, glucose metabolism and protein synthesis. The expression of FGF15 is known to be regulated by the transcription factor farnesoid X receptor (FXR). In the present study, reverse transcription‑quantitative polymerase chain reaction was used for measuring Fgf15 expression from the animal and tissue culture experiments, and it was identified that dexamethasone, a drug widely used in anti‑inflammation therapy, and a classical inducer of glucocorticoid receptor (GR)‑ and pregnane X receptor (PXR)‑target genes, may downregulate Fgf15 expression in the ileum. GR was identified to be highly expressed in the ileum by western blot analysis. Furthermore, it was demonstrated that the downregulation of Fgf15 by dexamethasone is due to the repression of ileal FXR activity via GR; however, not PXR, in the ileum. The present results provide insight for a better understanding of the adverse effects associated with dexamethasone therapy.
- Kovalchuk, N., Zhang, Q. Y., Kelty, J., Van Winkle, L., & Ding, X. (2019). Toxicokinetic Interaction between Hepatic Disposition and Pulmonary Bioactivation of Inhaled Naphthalene Studied Using -Null and CYP2A13/2F1-Humanized Mice with Deficient Hepatic Cytochrome P450 Activity. Drug metabolism and disposition: the biological fate of chemicals, 47(12), 1469-1478.More infoPrevious studies using -null (lacking all genes of the , , , , and subfamilies), CYP2A13/2F1-humanized, and liver--null (LCN) mice showed that although hepatic cytochrome P450 (P450) enzymes are essential for systemic clearance of inhaled naphthalene (a possible human carcinogen), both hepatic and extrahepatic P450 enzymes may contribute to naphthalene-induced lung toxicity via bioactivation. Herein, we aimed to further understand the toxicokinetics of inhaled naphthalene in order to provide a basis for predicting the effects of variations in rates of xenobiotic disposition on the extent of target tissue bioactivation. We assessed the impact of a hepatic deficit in naphthalene metabolism on the toxicokinetics of inhaled naphthalene using newly generated -null-and-LCN and CYP2A13/2F1-humanized-and-LCN mice. We determined plasma, lung, and liver levels of naphthalene and naphthalene-glutathione conjugate, a biomarker of naphthalene bioactivation, over time after naphthalene inhalation. We found that the loss of hepatic naphthalene metabolism severely decreased naphthalene systemic clearance and caused naphthalene to accumulate in the liver and other tissues. Naphthalene release from tissue, as evidenced by the continued increase in plasma naphthalene levels after termination of active inhalation exposure, was accompanied by prolonged bioactivation of naphthalene in the lung. In addition, transgenic expression of human CYP2A13/2F1 in the respiratory tract caused a reduction in plasma naphthalene levels (by 40%, relative to -null-and-LCN mice) and corresponding decreases in naphthalene-glutathione levels in the lung in mice with hepatic P450 deficiency, despite the increase in local naphthalene-bioactivating P450 activity. Thus, the bioavailability of naphthalene in the target tissue has a significant effect on the extent of naphthalene bioactivation in the lung. SIGNIFICANCE STATEMENT: In this study, we report several novel findings related to the toxicokinetics of inhaled naphthalene, the ability of which to cause lung carcinogenesis in humans is a current topic for risk assessment. We show the accumulation of naphthalene in the liver and lung in mice with compromised hepatic cytochrome P450 (P450) activity; the ability of tissue-stored naphthalene to redistribute to the circulation after termination of active inhalation exposure, prolonging exposure of target tissues to naphthalene; and the ability of non-CYP2ABFGS enzymes of the lung to bioactivate naphthalene. These results suggest potentially large effects of deficiencies in hepatic P450 activity on naphthalene tissue burden and bioactivation in human lungs.
- Bissig, K. D., Han, W., Barzi, M., Kovalchuk, N., Ding, L., Fan, X., Pankowicz, F. P., Zhang, Q. Y., & Ding, X. (2018). P450-Humanized and Human Liver Chimeric Mouse Models for Studying Xenobiotic Metabolism and Toxicity. Drug metabolism and disposition: the biological fate of chemicals, 46(11), 1734-1744.More infoPreclinical evaluation of drug candidates in experimental animal models is an essential step in drug development. Humanized mouse models have emerged as a promising alternative to traditional animal models. The purpose of this mini-review is to provide a brief survey of currently available mouse models for studying human xenobiotic metabolism. Here, we describe both genetic humanization and human liver chimeric mouse models, focusing on the advantages and limitations while outlining their key features and applications. Although this field of biomedical science is relatively young, these humanized mouse models have the potential to transform preclinical drug testing and eventually lead to a more cost-effective and rapid development of new therapies.
- Li, L., Zhang, Q. Y., & Ding, X. (2018). A CYP2B6-humanized mouse model and its potential applications. Drug metabolism and pharmacokinetics, 33(1), 2-8.More infoCYP2B6 is a human microsomal cytochrome P450 enzyme with broad substrate selectivity. CYP2B6 is the only functional member of the human CYP2B gene subfamily, which differs from the situation in rodents, such as mouse, where multiple functional Cyp2b genes are expressed. Recent studies with Cyp2b knockout or knockdown mouse models have yielded insights into the in vivo roles of mouse CYP2B enzymes in drug disposition and xenobiotic toxicity. A CYP2B6-humanized mouse model (CYP2A13/2B6/2F1-transgenic/Cyp2abfgs-null), which expresses human CYP2B6 in the liver, and human CYP2A13 and CYP2F1 in the respiratory tract, but not any of the mouse Cyp2b genes, has also been established. In the CYP2B6-humanized mouse, the CYP2B6 transgene is expressed primarily in the liver, where it was found to be active toward prototype CYP2B6 substrate drugs. The regulatory elements of the CYP2B6 transgene appear to be compatible with mouse nuclear receptors that mediate CYP2B induction. Therefore, the CYP2B6-humanized mouse is a valuable animal model for studying the impact of CYP2B6 expression or induction on drug metabolism, drug efficacy, drug-drug interaction, and drug/xenobiotic toxicity. In this mini-review, we provide a brief background on CYP2B6 and the Cyp2b-knockout and CYP2B6-humanized mice, and discuss the potential applications and limitations of the current models.
- Li, Z., Sakamuru, S., Huang, R., Brecher, M., Koetzner, C. A., Zhang, J., Chen, H., Qin, C. F., Zhang, Q. Y., Zhou, J., Kramer, L. D., Xia, M., & Li, H. (2018). Erythrosin B is a potent and broad-spectrum orthosteric inhibitor of the flavivirus NS2B-NS3 protease. Antiviral research, 150, 217-225.More infoMany flaviviruses, such as Zika virus (ZIKV), Dengue virus (DENV1-4) and yellow fever virus (YFV), are significant human pathogens. Infection with ZIKV, an emerging mosquito-borne flavivirus, is associated with increased risk of microcephaly in newborns and Guillain-Barré syndrome and other complications in adults. Currently, specific therapy does not exist for any flavivirus infections. In this study, we found that erythrosin B, an FDA-approved food additive, is a potent inhibitor for flaviviruses, including ZIKV and DENV2. Erythrosin B was found to inhibit the DENV2 and ZIKV NS2B-NS3 proteases with IC in low micromolar range, via a non-competitive mechanism. Erythrosin B can significantly reduce titers of representative flaviviruses, DENV2, ZIKV, YFV, JEV, and WNV, with micromolar potency and with excellent cytotoxicity profile. Erythrosin B can also inhibit ZIKV replication in ZIKV-relevant human placental and neural progenitor cells. As a pregnancy category B food additive, erythrosin B may represent a promising and easily developed therapy for management of infections by ZIKV and other flaviviruses.
- Kovalchuk, N., Kelty, J., Li, L., Hartog, M., Zhang, Q. Y., Edwards, P., Van Winkle, L., & Ding, X. (2017). Impact of hepatic P450-mediated biotransformation on the disposition and respiratory tract toxicity of inhaled naphthalene. Toxicology and applied pharmacology, 329, 1-8.More infoWe determined whether a decrease in hepatic microsomal cytochrome P450 activity would impact lung toxicity induced by inhalation exposure to naphthalene (NA), a ubiquitous environmental pollutant. The liver-Cpr-null (LCN) mouse showed decreases in microsomal metabolism of NA in liver, but not lung, compared to wild-type (WT) mouse. Plasma levels of NA and NA-glutathione conjugates (NA-GSH) were both higher in LCN than in WT mice after a 4-h nose-only NA inhalation exposure at 10ppm. Levels of NA were also higher in lung and liver of LCN, compared to WT, mice, following exposure to NA at 5 or 10ppm. Despite the large increase in circulating and lung tissue NA levels, the level of NA-GSH, a biomarker of NA bioactivation, was either not different, or only slightly higher, in lung and liver tissues of LCN mice, relative to that in WT mice. Furthermore, the extent of NA-induced acute airway injury, judging from high-resolution lung histopathology and morphometry at 20h following NA exposure, was not higher, but lower, in LCN than in WT mice. These results, while confirming the ability of extrahepatic organ to bioactivate inhaled NA and mediate NA's lung toxicity, suggest that liver P450-generated NA metabolites also have a significant, although relatively small, contribution to airway toxicity of inhaled NA. This hepatic contribution to the airway toxicity of inhaled NA may be an important risk factor for individuals with diminished bioactivation activity in the lung.
- Li, L., Bao, X., Zhang, Q. Y., Negishi, M., & Ding, X. (2017). Role of CYP2B in Phenobarbital-Induced Hepatocyte Proliferation in Mice. Drug metabolism and disposition: the biological fate of chemicals, 45(8), 977-981.More infoPhenobarbital (PB) promotes liver tumorigenesis in rodents, in part through activation of the constitutive androstane receptor (CAR) and the consequent changes in hepatic gene expression and increases in hepatocyte proliferation. A typical effect of CAR activation by PB is a marked induction of expression in the liver; the latter has been suspected to be vital for PB-induced hepatocellular proliferation. This hypothesis was tested here by using a -null (null) mouse model in which all genes are deleted. Adult male and female wild-type (WT) and null mice were treated intraperitoneally with PB at 50 mg/kg once daily for 5 successive days and tested on day 6. The liver-to-body weight ratio, an indicator of liver hypertrophy, was increased by 47% in male WT mice, but by only 22% in male -null mice, by the PB treatment. The fractions of bromodeoxyuridine-positive hepatocyte nuclei, assessed as a measure of the rate of hepatocyte proliferation, were also significantly lower in PB-treated male null mice compared with PB-treated male WT mice. However, whereas few proliferating hepatocytes were detected in saline-treated mice, many proliferating hepatocytes were still detected in PB-treated male null mice. In contrast, female WT mice were much less sensitive than male WT mice to PB-induced hepatocyte proliferation, and PB-treated female WT and PB-treated female null mice did not show significant difference in rates of hepatocyte proliferation. These results indicate that CYP2B induction plays a significant, but partial, role in PB-induced hepatocyte proliferation in male mice.
- Li, L., Carratt, S., Hartog, M., Kovalchik, N., Jia, K., Wang, Y., Zhang, Q. Y., Edwards, P., Winkle, L. V., & Ding, X. (2017). Human CYP2A13 and CYP2F1 Mediate Naphthalene Toxicity in the Lung and Nasal Mucosa of CYP2A13/2F1-Humanized Mice. Environmental health perspectives, 125(6), 067004.More infoThe potential carcinogenicity of naphthalene (NA), a ubiquitous environmental pollutant, in human respiratory tract is a subject of intense debate. Chief among the uncertainties in risk assessment for NA is whether human lung CYP2A13 and CYP2F1 can mediate NA's respiratory tract toxicity.
- Sheng, J., Wang, Y., Turesky, R. J., Kluetzman, K., Zhang, Q. Y., & Ding, X. (2016). Novel Transgenic Mouse Model for Studying Human Serum Albumin as a Biomarker of Carcinogenic Exposure. Chemical research in toxicology, 29(5), 797-809.More infoAlbumin is a commonly used serum protein for studying human exposure to xenobiotic compounds, including therapeutics and environmental pollutants. Often, the reactivity of albumin with xenobiotic compounds is studied ex vivo with human albumin or plasma/serum samples. Some studies have characterized the reactivity of albumin with chemicals in rodent models; however, differences between the orthologous peptide sequences of human and rodent albumins can result in the formation of different types of chemical-protein adducts with different interaction sites or peptide sequences. Our goal is to generate a human albumin transgenic mouse model that can be used to establish human protein biomarkers of exposure to hazardous xenobiotics for human risk assessment via animal studies. We have developed a human albumin transgenic mouse model and characterized the genotype and phenotype of the transgenic mice. The presence of the human albumin gene in the genome of the model mouse was confirmed by genomic PCR analysis, whereas liver-specific expression of the transgenic human albumin mRNA was validated by RT-PCR analysis. Further immunoblot and mass spectrometry analyses indicated that the transgenic human albumin protein is a full-length, mature protein, which is less abundant than the endogenous mouse albumin that coexists in the serum of the transgenic mouse. The transgenic protein was able to form ex vivo adducts with a genotoxic metabolite of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, a procarcinogenic heterocyclic aromatic amine formed in cooked meat. This novel human albumin transgenic mouse model will facilitate the development and validation of albumin-carcinogen adducts as biomarkers of xenobiotic exposure and/or toxicity in humans.
- Liu, Z., Li, L., Wu, H., Hu, J., Ma, J., Zhang, Q. Y., & Ding, X. (2015). Characterization of CYP2B6 in a CYP2B6-humanized mouse model: inducibility in the liver by phenobarbital and dexamethasone and role in nicotine metabolism in vivo. Drug metabolism and disposition: the biological fate of chemicals, 43(2), 208-16.More infoThe aim of this study was to further characterize the expression and function of human CYP2B6 in a recently generated CYP2A13/2B6/2F1-transgenic (TG) mouse model, in which CYP2B6 is expressed selectively in the liver. The inducibility of CYP2B6 by phenobarbital (PB) and dexamethasone (DEX), known inducers of CYP2B6 in human liver, was examined in the TG mice, as well as in TG/Cyp2abfgs-null (or "CYP2B6-humanized") mice. Hepatic expression of CYP2B6 mRNA and protein was greatly induced by PB or DEX treatment in both TG and TG/Cyp2abfgs-null mice. Function of the transgenic CYP2B6 was first studied using bupropion as a probe substrate. In PB-treated mice, the rates of hepatic microsomal hydroxybupropion formation (at 50 μM bupropion) were >4-fold higher in TG/Cyp2abfgs-null than in Cyp2abfgs-null mice (for both male and female mice); the rate difference was accompanied by a 5-fold higher catalytic efficiency in the TG/Cyp2abfgs-null mice and was abolished by an antibody to CYP2B6. The ability of CYP2B6 to metabolize nicotine was then examined, both in vitro and in vivo. The rates of hepatic microsomal cotinine formation from nicotine were significantly higher in TG/Cyp2abfgs-null than in Cyp2abfgs-null mice, pretreated with PB or DEX. Furthermore, systemic nicotine metabolism was faster in TG/Cyp2abfgs-null than in Cyp2abfgs-null mice. Thus, the transgenic CYP2B6 was inducible and functional, and, in the absence of mouse CYP2A and CYP2B enzymes, it contributed to nicotine metabolism in vivo. The CYP2B6-humanized mouse will be valuable for studies on in vivo roles of hepatic CYP2B6 in xenobiotic metabolism and toxicity.
- Turesky, R. J., Konorev, D., Fan, X., Tang, Y., Yao, L., Ding, X., Xie, F., Zhu, Y., & Zhang, Q. Y. (2015). Effect of Cytochrome P450 Reductase Deficiency on 2-Amino-9H-pyrido[2,3-b]indole Metabolism and DNA Adduct Formation in Liver and Extrahepatic Tissues of Mice. Chemical research in toxicology, 28(12), 2400-10.More info2-Amino-9H-pyrido[2,3-b]indole (AαC), a carcinogen formed during the combustion of tobacco and cooking of meat, undergoes cytochrome P450 (P450) metabolism to form the DNA adduct N-(deoxyguanosin-8-yl)-2-amino-9H-pyrido[2,3-b]indole (dG-C8-AαC). We evaluated the roles of P450 expressed in the liver and intestine to bioactivate AαC by employing male B6 wild-type (WT) mice, liver-specific P450 reductase (Cpr)-null (LCN) mice, and intestinal epithelium-specific Cpr-null (IECN) mice. Pharmacokinetic parameters were determined for AαC, 2-amino-9H-pyrido[2,3-b]indol-3-yl sulfate (AαC-3-OSO3H), and N(2)-(β-1-glucosidurony1)-2-amino-9H-pyrido[2,3-b]indole (AαC-N(2)-Glu) with animals dosed by gavage with AαC (13.6 mg/kg). The uptake of AαC was rapid with no difference in the plasma half-lives (t1/2) of AαC, AαC-3-OSO3H, and AαC-N(2)-Glu among mouse models. The maximal plasma concentrations (Cmax) and the areas under concentration-time curve (AUC0-24h) of AαC and AαC-N(2)-Glu were 4-24-fold higher in LCN than in WT mice, but they were not different between WT and IECN mice. These findings are consistent with the ablation of hepatic P450 activity in LCN mice. However, the Cmax and AUC0-24h of AαC-3-OSO3H in plasma were not substantially different among the mouse models. Similar pharmacokinetic parameters were obtained with WT and LCN mice treated with a lower AαC dose (1.36 mg kg(-1)). dG-C8-AαC was detected at similar levels in the livers of all three mouse models at the high AαC dose; levels of dG-C8-AαC in colon, bladder, and lung were greater in LCN than in WT mice and were the same in colon of IECN and WT mice. At the low AαC dose, dG-C8-AαC occurred at ∼ 40% lower levels in liver of LCN mouse than in WT mouse liver, but adduct levels remained higher in extrahepatic tissues of LCN mice. Therefore, hepatic P450 plays an important role in detoxication of AαC, but other hepatic or extrahepatic enzymes contribute to the bioactivation of AαC. P450s expressed in the intestine do not appreciably contribute to bioactivation of AαC in mice.
- Zhu, Y., Xie, F., Ding, L., Fan, X., Ding, X., & Zhang, Q. Y. (2015). Intestinal epithelium-specific knockout of the cytochrome P450 reductase gene exacerbates dextran sulfate sodium-induced colitis. The Journal of pharmacology and experimental therapeutics, 354(1), 10-7.More infoThe potential involvement of intestinal microsomal cytochrome P450 (P450) enzymes in defending against colon inflammation and injury was studied in mice treated with dextran sulfate sodium (DSS) to induce colitis. Wild-type (WT) mice and mice with intestinal epithelium (IE)-specific deletion of the P450 reductase gene (IE-Cpr-null) were compared. IE-Cpr-null mice have little microsomal P450 activity in IE cells. DSS treatment (2.5% in drinking water for 6 days) caused more severe colon inflammation, as evidenced by the presence of higher levels of myeloperoxidase and proinflammatory cytokines [tumor necrosis factor-α, interleukin (IL)-6, and IL-1β], and greater weight loss, colonic tissue damage, and colon shortening, in IE-Cpr-null mice than in WT mice. The IE-Cpr-null mice were deficient in colonic corticosterone (CC) synthesis, as indicated by the inability of ex vivo cultured colonic tissues from DSS-treated IE-Cpr-null mice (in contrast to DSS-treated WT mice) to show increased CC production, compared with vehicle-treated mice, and by the ability of added deoxycorticosterone (DOC), a precursor of CC biosynthesis via mitochondrial CYP11B1, to restore ex vivo CC production by colonic tissues from DSS-treated null mice. Intriguingly, null (but not WT) mice failed to show increased serum CC levels following DSS treatment. Nevertheless, cotreatment of DSS-exposed mice with DOC, which did not restore DSS-induced increase in serum CC, abolished the hypersensitivity of IE-Cpr-null mice to DSS-induced colon injury. Taken together, our results strongly support the notion that microsomal P450 enzymes in the intestine play an important role in protecting colon epithelium from DSS-induced inflammation and injury, possibly through increased local CC synthesis in response to DSS challenge.
- Xie, F., Ding, X., & Zhang, Q. Y. (2016. An update on the role of intestinal cytochrome P450 enzymes in drug disposition(pp 374-383).More infoOral administration is the most commonly used route for drug treatment. Intestinal cytochrome P450 (CYP)-mediated metabolism can eliminate a large proportion of some orally administered drugs before they reach systemic circulation, while leaving the passage of other drugs unimpeded. A better understanding of the ability of intestinal P450 enzymes to metabolize various clinical drugs in both humans and preclinical animal species, including the identification of the CYP enzymes expressed, their regulation, and the relative importance of intestinal metabolism compared to hepatic metabolism, is important for improving bioavailability of current drugs and new drugs in development. Here, we briefly review the expression of drug-metabolizing P450 enzymes in the small intestine of humans and several preclinical animal species, and provide an update of the various factors or events that regulate intestinal P450 expression, including a cross talk between the liver and the intestine. We further compare various clinical and preclinical approaches for assessing the impact of intestinal drug metabolism on bioavailability, and discuss the utility of the intestinal epithelium-specific NADPH-cytochrome P450 reductase-null (IECN) mouse as a useful model for studying roles of intestinal P450 in the disposition of orally administered drugs.