B I Ghanayem

National Institutes of Health, Bethesda, MD, United States

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Publications (91)287.37 Total impact

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    ABSTRACT: Obesity and obesity-related illnesses are global epidemics impacting the health of adults and children. The purpose of the present work is to evaluate a genetically intact obese mouse model that more accurately reflects the impact of aging on diet-induced obesity and type 2 diabetes in humans. Male C57Bl/6J mice consumed either a control diet or one in which 60% kcal were due to lard beginning at 5-6 weeks of age. Body weight and fat measurements were obtained and necropsy performed at 15, 20, 30, and 40 weeks of age. Serum chemistry, histopathology, gene expression of the liver, and renal and hepatic function were also evaluated. In concert with significant increases in percent body fat and weight, mice fed the high-fat versus control diet had significantly increased levels of serum cholesterol. At ages 20 and 30 weeks, serum glucose was significantly higher in obese versus controls, while serum insulin levels were >/=4-fold higher in obese mice at ages 30 and 40 weeks. The effect of age exacerbated the effects of consuming a high-fat diet. In addition to being hyperinsulinemic and leptin resistant, older obese mice exhibited elevated hepatic PAI-1 and downregulation of GLUT4, G6PC, IGFBP-1, and leptin receptor mRNA in the liver, steatosis with subsequent inflammation, glomerular mesangial proliferation, elevated serum ALT, AST, and BUN, and increased numbers of pancreatic islets.
    Endocrine 09/2009; 36(2):311-25. · 3.53 Impact Factor
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    ABSTRACT: The prevalence of human obesity and related chronic disorders such as diabetes, cardiovascular diseases, and cancer is rapidly increasing. Human studies have shown a direct relationship between obesity and infertility. The objective of the current work was to examine the effect of diet-induced obesity on male fertility and the effect of obesity on susceptibility to chemical-induced reproductive toxicity. From 5 to 30 wk of age, genetically intact male C57Bl/6J mice were fed a normal diet or one in which 60% of the kilocalories were from lard. Obese mice exhibited significant differences in the mRNA of several genes within the testes in comparison to lean males. Pparg was increased 2.2-fold, whereas Crem, Sh2b1, Dhh, Igf1, and Lepr were decreased 6.7, 1.4, 3.2, 1.6, and 7.2-fold, respectively. The fertility of male mice was compared through mating with control females. Acrylamide (AA)-induced reproductive toxicity was assessed in obese or lean males treated with water or 25 mg AA kg(-1) day(-1) via gavage for 5 days and then mated to control females. Percent body fat and weight were significantly increased in mice fed a high-fat vs. a normal diet. Obesity resulted in significant reduction in plugs and pregnancies of control females partnered with obese vs. lean males. Serum leptin and insulin levels were each approximately 5-fold higher in obese vs. age-matched lean mice. Sperm from obese males exhibited decreased motility and reduced hyperactivated progression vs. lean mice. Treatment with AA exacerbated male infertility of obese and lean mice; however, this effect was more pronounced in obese mice. Further, females partnered with AA-treated obese mice exhibited a further decrease in the percentage of live fetuses, whereas the percentage of resorptions increased. This work demonstrated that diet-induced obesity in mice caused a significant reduction in male fertility and exacerbated AA-induced reproductive toxicity and germ cell mutagenicity.
    Biology of Reproduction 09/2009; 82(1):96-104. · 4.03 Impact Factor
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    Burhan I Ghanayem, Re Bai, Leo T Burka
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    ABSTRACT: Acrylamide (AA) is a known mutagen and animal carcinogen. Comparison of recent studies revealed significant quantitative differences in AA-induced germ cell mutagenicity. It was hypothesized that despite the administration of AA at similar doses, the discrepancy in the observed effects was most likely due to varying AA concentrations in the administered dosing solution. To test this hypothesis, AA was administered i.p. to mice at 50 mg/kg in a dose volume of 5 or 50 ml/kg, blood was collected at various time points, and AA and its metabolites were quantitated. Changes in dose volume resulted in significant differences in the toxicokinetics of AA and its metabolites and suggested that increased C(max) of AA led to increased metabolism. This theory, in conjunction with the fact that higher levels of AA-derived radioactivity were detected in the testes, may explain the greater toxicity of a 50 mg/kg dose when administered in 5 versus 50 ml/kg. The impact of dose volume on the toxicokinetics of 2-deoxy-d-glucose (DG), a nonreactive, nonmetabolizable substance, was also investigated. The areas under the curve for DG were not different for the two dose volumes; however, C(max) for the more concentrated dose was significantly higher. In conclusion, current studies show that the toxicokinetics of an administered xenobiotic and its metabolites is influenced by the concentration of the parent chemical in the dosing solution. Therefore, it is important to consider the concentration of an administered xenobiotic in the dosing solution because it may affect its toxicokinetics and metabolism and subsequently affect the biological effects of the administered chemical.
    Drug metabolism and disposition: the biological fate of chemicals 12/2008; 37(2):259-63. · 3.74 Impact Factor
  • Burhan I Ghanayem, Undi Hoffler
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    ABSTRACT: Cytochromes P450 (CYPs) comprise a number of enzyme subfamilies responsible for the oxidative metabolism of a wide range of therapeutic agents, environmental toxicants, mutagens, and carcinogens. In particular, cytochrome P450 2E1 (CYP2E1) is implicated in the oxidative bioactivation of a variety of small hydrophobic chemicals including a number of epoxide-forming drugs and environmentally important toxicants including urethane, acrylamide, acrylonitrile, benzene, vinyl chloride, styrene, 1-bromopropane, trichloroethylene, dichloroethylene, acetaminophen, and butadiene. Until recently, chemical modulators (inducers and inhibitors) were used in order to characterize the enzymatic basis of xenobiotic metabolism and the relationships between CYP-mediated bioactivation and chemical-induced toxicity/carcinogenicity. With the advent of genetically engineered knockout mice, the ability to evaluate the roles of specific CYPs in the metabolism of xenobiotics has become more attainable. The main focus of the current review is to present studies that characterized the enzymatic, metabolic, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity of various xenobiotics using Cyp2e1-/- mice. Data presented in this review demonstrated that the most comprehensive studies using Cyp2e1-/- mice, encompassing the entire paradigm of metabolism to toxicity, genotoxicity, and carcinogenicity were possible when a substrate was primarily metabolized via CYP2E1 (e.g. urethane and acrylamide). In contrast, when multiple CYP enzymes were prevalent in the oxidation of a particular substrate (e.g.: trichloroethylene, methacrylonitrile, crotononitrile), investigating the relationships between oxidative metabolism and biological activity became more complicated and required the use of chemical modulators. In conclusion, the current review showed that Cyp2e1-/- mice are a valuable animal model for the investigation of the metabolic and molecular basis of toxicity, genotoxicity, and carcinogenicity of xenobiotics.
    Current Drug Metabolism 11/2007; 8(7):728-49. · 4.41 Impact Factor
  • Burhan I Ghanayem
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    ABSTRACT: Urethane is an established animal carcinogen and has been classified as "reasonably anticipated to be a human carcinogen." Until recently, urethane metabolism via esterase was considered the main metabolic pathway of this chemical. However, recent studies in this laboratory showed that CYP2E1, and not esterase, is the primary enzyme responsible for urethane oxidation. Subsequent studies demonstrated significant inhibition of urethane-induced genotoxicity and cell proliferation in Cyp2e1-/- compared to Cyp2e1+/+ mice. Using Cyp2e1-/- mice, current studies were undertaken to assess the relationships between urethane metabolism and carcinogenicity. Urethane was administered via gavage at 1, 10, or 100 mg/kg/day, 5 days/week, for 6 weeks. Animals were kept without chemical administration for 7 months after which they were euthanized, and urethane carcinogenicity was assessed. Microscopic examination showed a significant reduction in the incidences of liver hemangiomas and hemangiosarcomas in Cyp2e1-/- compared to Cyp2e+/+ mice. Lung nodules increased in a dose-dependent manner and were less prevalent in Cyp2e1-/- compared to Cyp2e+/+ mice. Microscopic alterations included bronchoalveolar adenomas, and in one Cyp2e1+/+ mouse treated with 100 mg/kg urethane, a bronchoalveolar carcinoma was diagnosed. Significant reduction in the incidence of adenomas and the number of adenomas/lung were observed in Cyp2e1-/- compared to Cyp2e1+/+ mice. In the Harderian gland, the incidences of hyperplasia and adenomas were significantly lower in Cyp2e1-/- compared to Cyp2e+/+ mice at the 10 mg/kg dose, with no significant differences observed at the high or low doses. In conclusion, this work demonstrated a significant reduction of urethane-induced carcinogenicity in Cyp2e1-/- compared to Cyp2e1+/+ mice and proved that CYP2E1-mediated oxidation plays an essential role in urethane-induced carcinogenicity.
    Toxicological Sciences 03/2007; 95(2):331-9. · 4.33 Impact Factor
  • Dojung Kim, Burhan I Ghanayem
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    ABSTRACT: Trichloroethylene (TCE)1 is an important environmental contaminant, a well established rodent carcinogen, and a "probable human carcinogen". Metabolism of TCE occurs primarily via cytochrome P450 (P450)-dependent oxidation. In vitro studies suggested that CYP2E1 is the principal high-affinity enzyme responsible for TCE metabolism. The objective of the present work is to more directly assess the role of CYP2E1 in the metabolism and disposition of 1,2-14C-TCE administered at 250 or 1000 mg/kg (gavage) using Cyp2e1-/-[knockout (KO)] versus wild-type (WT) mice. After dosing, animals were individually placed in glass metabolism cages that allowed the collection of expired air, urine, and feces. Exhalation of TCE-derived 14CO2 increased in a dose-dependent manner in mice of both genotypes and was significantly higher in WT versus KO mice. A significantly greater percentage of the dose was exhaled in KO versus WT mice as organic volatiles (mainly as TCE). Urinary excretion was the major route of TCE metabolism in WT mice, and the percentage of dose eliminated in urine was significantly higher at the 250 versus 1000 mg/kg dose. Furthermore, urinary excretion and CO2 exhalation significantly decreased in KO versus WT mice. Pretreatment with 1-aminobenzotriazole clearly inhibited TCE metabolism as evident from increased exhalation of parent TCE, and decreased urinary excretion and CO2 exhalation in mice of both genotypes. In conclusion, these data showed that whereas CYP2E1 plays an important role in TCE metabolism and disposition, other P450s also play a significant role and may explain earlier results showing that TCE causes lung damage in KO and WT mice.
    Drug Metabolism and Disposition 01/2007; 34(12):2020-7. · 3.36 Impact Factor
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    ABSTRACT: This study was undertaken to test the hypothesis that bronchiolar damage induced by trichloroethylene (TCE) is associated with bioactivation within the Clara cells with the involvement of CYP2E1 and CYP2F2. Histopathology confirmed dose-dependent Clara cell injury and disintegration of the bronchiolar epithelium in CD-1 mice treated with TCE doses of 500 to 1000 mg/kg i.p. Immunohistochemical studies, using an antibody that recognizes dichloroacetyl lysine adducts, revealed dose-dependent formation of adducts in the bronchiolar epithelium. Localization of dichloroacetyl adducts in the Clara cells coincided with damage to this cell type in TCE-treated mice. Pretreatment of CD-1 mice with diallyl sulfone, an inhibitor of CYP2E1 and CYP2F2, abrogated the formation of the dichloroacetyl adducts and protected against TCE-induced bronchiolar cytotoxicity. Treatment of wild-type and CYP2E1-null mice with TCE (750 mg/kg i.p.) also elicited bronchiolar damage that correlated with the formation of adducts in the Clara cells. Immunoblotting, using lung microsomes from TCE-treated CD-1 mice, showed dose-dependent production of dichloroacetyl adducts that comigrated with CYP2E1 and CYP2F2. However, TCE treatment resulted in a loss of immunoreactive CYP2E1 and CYP2F2 proteins and p-nitrophenol hydroxylation, a catalytic activity associated with both cytochrome P450 enzymes. The TCE metabolite, chloral hydrate, was formed in incubations of TCE with lung microsomes from CD-1, wild-type, and CYP2E1-null mice. The levels were higher in CD-1 than in either wild-type or CYP2E1-null mice, although levels were higher in CYP2E1-null than in wild-type mice. These findings supported the contention that TCE bioactivation within the Clara cells, predominantly involving CYP2F2, correlated with bronchiolar cytotoxicity in mice.
    Journal of Pharmacology and Experimental Therapeutics 03/2006; 316(2):520-9. · 3.89 Impact Factor
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    ABSTRACT: Acrylamide (AA) is an animal carcinogen, neurotoxin, and reproductive toxin. AA is formed in baked and fried carbohydrate-rich foods. Metabolism of AA occurs via epoxidation to glycidamide (GA) or direct conjugation with glutathione. Using CYP2E1-null mice, recent studies in this laboratory demonstrated that induction of somatic and germ cell mutagenicity in AA-treated mice is dependent on CYP2E1. We hypothesized that AA metabolism to GA is a prerequisite for the induction of AA-induced mutagenicity. Current studies were undertaken to assess the role of CYP2E1 in the epoxidation of AA to GA and the formation of DNA and hemoglobin (HGB) adducts. AA was administered to CYP2E1-null or wild-type mice at 50 mg/kg ip. Mice were euthanized 6 h later and blood and tissues were collected. Using LC-ES/MS/MS, AA, GA, and DNA- and HGB-adducts were measured. While the plasma levels of AA and GA were 115 +/- 14.0 and 1.7 +/- 0.31 microM in CYP2E1-null mice, they were 0.84 +/- 0.80 and 33.0 +/- 6.3 microM in the plasma of AA-treated wild-type mice. Administration of AA to wild-type mice caused a large increase in N7-GA-Gua and N3-GA-Ade adducts in the liver, lung, and testes. While traces of N7-GA-Gua adducts were measured in the tissues of AA-treated CYP2E1-null mice, these levels were 52- to 66-fold lower than in wild-type mice. Significant elevation of both AA- and GA-HGB adducts was detected in AA-treated wild-type mice. In AA-treated CYP2E1-null mice, levels of AA-HGB adducts were roughly twice as high as those in wild-type mice. In conclusion, current work demonstrated that CYP2E1 is the primary enzyme responsible for the epoxidation of AA to GA, which leads to the formation of GA-DNA and HGB adducts.
    Toxicological Sciences 01/2006; 88(2):311-8. · 4.33 Impact Factor
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    ABSTRACT: Acrylamide, an animal carcinogen and germ cell mutagen present at low (ppm) levels in heated carbohydrate-containing foodstuffs, is oxidized by cytochrome P4502E1 (CYP2E1) to the epoxide glycidamide, which is believed to be responsible for the mutagenic and carcinogenic activity of acrylamide. We recently reported a comparison of the effects of acrylamide on the genetic integrity of germ cells of male wild-type and CYP2E1-null mice [B.I. Ghanayem, K.L. Witt, L. El-Hadri, U. Hoffler, G.E. Kissling, M.D. Shelby, J.B. Bishop, Comparison of germ-cell mutagenicity in male CYP2E1-null and wild-type mice treated with acrylamide: evidence supporting a glycidamide-mediated effect, Biol. Reprod. 72 (2005) 157-163]. In those experiments, dose-related increases in dominant lethal mutations were detected in uterine contents of female mice mated to acrylamide-treated wild-type males but not CYP2E1-null males, clearly implicating CYP2E1-mediated formation of glycidamide in the induction of genetic damage in male germ cells. We hypothesized that acrylamide-induced somatic cell damage is also caused by glycidamide. Therefore, to examine this hypothesis, female wild-type and CYP2E1-null mice were administered acrylamide (0, 25, 50mg/kg) by intraperitoneal injection once daily for 5 consecutive days. Twenty-four hours after the final treatment, blood and tissue samples were collected. Erythrocyte micronucleus frequencies were determined using flow cytometry and DNA damage was assessed in leukocytes, liver, and lung using the alkaline (pH>13) single cell gel electrophoresis (Comet) assay. Results were consistent with the earlier observations in male germ cells: significant dose-related increases in micronucleated erythrocytes and DNA damage in somatic cells were induced in acrylamide-treated wild-type but not in the CYP2E1-null mice. These results support the hypothesis that genetic damage in somatic and germ cells of mice-treated with acrylamide is dependent upon metabolism of the parent compound by CYP2E1. This dependency on metabolism has implications for the assessment of human risks resulting from occupational or dietary exposure to acrylamide. CYP2E1 polymorphisms and variability in CYP2E1 activity associated with, for example, diabetes, obesity, starvation, and alcohol consumption, may result in altered metabolic efficiencies leading to differential susceptibilities to acrylamide toxicities in humans.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 10/2005; 578(1-2):284-97. · 3.90 Impact Factor
  • Undi Hoffler, Burhan I Ghanayem
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    ABSTRACT: Urethane is a fermentation by-product and a potent animal carcinogen. Human exposure to urethane occurs through consumption of alcoholic beverages and fermented foods. Recently, CYP2E1 was identified as the primary enzyme responsible for the metabolism of [(14)C]carbonyl-labeled urethane. Subsequently, attenuation of urethane-induced cell proliferation and genotoxicity in CYP2E1-/- mice was reported. The present work compares the metabolism of single versus multiple exposures of CYP2E1-/- and CYP2E1+/+ mice to (14)C-ethyl-labeled urethane. Urethane was administered as a single 10 or 100 mg/kg gavage dose or at 100 mg/kg/day for 5 consecutive days. CYP2E1+/+ mice administered single or multiple doses exhaled 78 to 88% of dose as (14)CO(2)/day. CYP2E1-/- mice eliminated 30 to 38% of a single dose as (14)CO(2) in 24 h and plateaued after day 3 at approximately 52% of dose/day. The concentrations of urethane-derived radioactivity in plasma and tissues were dose-dependent, increased as a function of the number of doses administered, and were significantly higher in CYP2E1-/- versus CYP2E1+/+ mice. Whereas urethane was the main chemical found in the plasma and tissues of CYP2E1-/- mice, it was not detectable in CYP2E1+/+ mice. In conclusion, multiple dosing led to considerable bioaccumulation of urethane in mice of both genotypes; however, greater retention occurred in CYP2E1-/- versus CYP2E1+/+ mice. Furthermore, greater bioaccumulation of (14)C-ethyl-labeled than [(14)C]carbonyl-labeled urethane was observed in mice. Comparison of the metabolism of ethyl-versus carbonyl-labeled urethane was necessary for tracing the source of CO(2) and led us to propose for the first time that C-hydroxylation is a likely pathway of urethane metabolism.
    Drug Metabolism and Disposition 09/2005; 33(8):1144-50. · 3.36 Impact Factor
  • L El Hadri, B Chanas, B I Ghanayem
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    ABSTRACT: Methacrylonitrile (MAN) and acrylonitrile (AN) are metabolized via glutathione (GSH) conjugation or epoxide formation. We have recently shown that CYP2E1 is essential for AN epoxidation and subsequent cyanide liberation. Current studies were designed to compare the enzymatic basis of MAN vs. AN metabolism to cyanide using wild-type (WT), CYP2E1-, and mEH-null mice. Mice received a single gavage dose of 0.047, 0.095, 0.19, or 0.38 mmol/kg of MAN or AN, and blood cyanide was measured at 1 or 3 h later. Blood cyanide levels in WT mice treated with AN or MAN were dose and time dependent. At equimolar doses, significantly higher levels of cyanide were detected in the blood of MAN- vs. AN-treated mice. Further, while significant reduction in blood cyanide levels occurred in MAN-treated CYP2E1-null vs. WT mice, AN metabolism to cyanide was largely abolished in CYP2E1-null mice. Pretreatment of mice with 1-aminobenzotriazole (ABT, CYP inhibitor) demonstrated that CYPs other than CYP2E1 also contribute to MAN metabolism to cyanide. Blood cyanide levels in mEH-null mice treated with aliphatic nitriles are generally lower than levels in similarly treated WT mice. Western blot analysis showed that expression of sEH was greater in male vs. female mice. The role of various epoxide hydrolases (EHs) in the production of cyanide from aliphatic nitriles is apparently structure and dose dependent. Regardless of genotype, significantly higher levels of cyanide were measured in the blood of male vs. female mice treated with MAN or AN. In conclusion, these data showed that (1) at equimolar doses, higher blood cyanide levels were detected in mice treated with MAN vs. AN; (2) while CYP2E1 is the only enzyme responsible for AN metabolism to cyanide, other CYPs also contribute to MAN metabolism; and (3) significantly higher levels of cyanide were measured in the blood of male vs. female treated with either nitrile. Higher blood cyanide levels in male vs. female mice and in MAN- vs. AN-treated mice may explain the gender-related differences in the toxicity of these chemicals and the greater potency of MAN vs. AN.
    Toxicology and Applied Pharmacology 07/2005; 205(2):116-25. · 3.98 Impact Factor
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    ABSTRACT: Urethane is a multi-site animal carcinogen and was classified as "reasonably anticipated to be a human carcinogen." Urethane is a fermentation by-product and found at appreciable levels in alcoholic beverages and foods such as bread and cheese. Recent work in this laboratory demonstrated for the first time that CYP2E1 is the principal enzyme responsible for urethane metabolism. The current studies were undertaken to assess the relationships between CYP2E1-mediated metabolism and urethane-induced genotoxicity and cell proliferation as determined by induction of micronucleated erythrocytes (MN) and expression of Ki-67, respectively, using CYP2E1-null and wild-type mice. Urethane was administered at 0 (vehicle), 1, 10, or 100mg/kg/day (p.o.), 5 days/week for 6 weeks. A significant dose-dependent increase in MN was observed in wild-type mice; however, a slight increase was measured in the MN-polychromatic erythrocytes in CYP2E1-null mice treated with 100mg/kg. A significant increase in the expression of Ki-67 was detected in the livers and the lungs (terminal bronchioles, alveoli, and bronchi) of wild-type mice administered 100mg urethane/kg in comparison to controls. In contrast, CYP2E1-null mice administered this dose exhibited negligible alterations in Ki-67 expression in the livers and lungs compared to controls. Interestingly, while Ki-67 expression in the forestomach decreased in wild-type mice, it increased in CYP2E1-null mice. Subsequent comparative metabolism studies demonstrated that total urethane-derived radioactivity in the plasma, liver, and lung was significantly higher in CYP2E1-null versus wild-type mice and un-metabolized urethane constituted greater than 83% of the radioactivity in CYP2E1-null mice. Un-metabolized urethane was not detectable in the plasma, liver, and lung of wild-type mice. In conclusion, these data demonstrated that CYP2E1-mediated metabolism of urethane, presumably via epoxide formation, is necessary for the induction of genotoxicity, and cell proliferation in the liver and lung of wild-type mice.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 06/2005; 572(1-2):58-72. · 3.90 Impact Factor
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    ABSTRACT: Genetic variation in CYP3A activity may influence the rate of the metabolism and elimination of CYP3A substrates in humans. We previously reported four new CYP3A4 coding variants in three different racial groups. In the present study, we examined metabolism of nifedipine by the recombinant forms of these allelic variants. Metabolism of nifedipine by the L293P (CYP3A4*18), M445T (CYP3A4*3), and P467S (CYP3A4*19) allelic variants was not significantly different from wild-type CYP3A4*1. However, F189S (CYP3A4*17) exhibited a >99% decrease in both V(max) and CL(max) of nifedipine compared with CYP3A4*1. Of 72 racially diverse individuals, CYP3A4*17 was identified in 1 of 24 Caucasian samples [1:5 Eastern European (Adygei ethnic group)]. Genotyping of an extended set of 276 genomic DNAs of Caucasians (100 from the Coriell Repository and an additional 176 from the United States) for CYP3A4*17 detected no additional individuals containing the CYP3A4*17 allele. However, additional genotyping of four more Adygei samples available from Coriell detected an additional individual carrying the CYP3A4*17 allele. New specific polymerase chain reaction-restriction fragment length polymorphism genotyping procedures were developed for the major splice variant of CYP3A5 (CYP3A5*3) and CYP3A4*17. Genotyping revealed that the two individuals carrying CYP3A4*17 were either homozygous or heterozygous for the more frequent CYP3A5*3 allele, suggesting that the two alleles may exist on the same chromosome as a new putative CYP3A poor metabolizer haplotype. We predict that individuals who are homozygous for defective alleles of both of these genes would metabolize CYP3A substrates poorly. The new genetic tests will be useful in future clinical studies to investigate genotype/phenotype associations.
    Journal of Pharmacology and Experimental Therapeutics 04/2005; 313(1):302-9. · 3.89 Impact Factor
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    ABSTRACT: Acrylamide is an animal carcinogen and probable human carcinogen present in appreciable amounts in heated carbohydrate-rich foodstuffs. It is also a germ cell mutagen, inducing dominant lethal mutations and heritable chromosomal translocations in postmeiotic sperm of treated mice. Acrylamide's affinity for male germ cells has sometimes been overlooked in assessing its toxicity and defining human health risks. Previous investigations of acrylamide's germ cell activity in mice showed stronger effects after repeated administration of low doses compared with a single high dose, suggesting the possible involvement of a stable metabolite. A key oxidative metabolite of acrylamide is the epoxide glycidamide, generated by cytochrome P4502E1 (CYP2E1). To explore the role of CYP2E1 metabolism in the germ cell mutagenicity of acrylamide, CYP2E1-null and wild-type male mice were treated by intraperitoneal injection with 0, 12.5, 25, or 50 mg acrylamide (5 ml saline)(-1) kg(-1) day(-1) for 5 consecutive days. At defined times after exposure, males were mated to untreated B6C3F1 females. Females were killed in late gestation and uterine contents were examined. Dose-related increases in resorption moles (chromosomally aberrant embryos) and decreases in the numbers of pregnant females and the proportion of living fetuses were seen in females mated to acrylamide-treated wild-type mice. No changes in any fertility parameters were seen in females mated to acrylamide-treated CYP2E1-null mice. Our results constitute the first unequivocal demonstration that acrylamide-induced germ cell mutations in male mice require CYP2E1-mediated epoxidation of acrylamide. Thus, CYP2E1 polymorphisms in human populations, resulting in variable enzyme metabolic activities, may produce differential susceptibilities to acrylamide toxicities.
    Biology of Reproduction 02/2005; 72(1):157-63. · 4.03 Impact Factor
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    ABSTRACT: 1,1-Dichloroethylene (DCE) exposure to mice elicits lung toxicity that selectively targets bronchiolar Clara cells. The toxicity is mediated by DCE metabolites formed via cytochrome P450 metabolism. The primary metabolites formed are DCE epoxide, 2,2-dichloroacetaldehyde, and 2-chloroacetyl chloride. The major metabolite detected is 2-S-glutathionyl acetate [C], a putative conjugate of DCE epoxide with glutathione. In this investigation, studies were undertaken to test the hypothesis that CYP2E1 and CYP2F2 are involved in bioactivation of DCE to the epoxide in murine lung. We have developed a method using liquid chromatography/mass spectrometry (LC/MS) to evaluate the kinetics of the rates of production of conjugate [C] by recombinant CYP2E1 and CYP2F enzymes and lung microsomes. Concentration-dependent formation of conjugate [C] was found in incubations of DCE with recombinant CYP2E1 and CYP2F enzymes and lung microsomes from CD-1, wild-type (mixed 129/Sv and C57BL), and CYP2E1-null mice. Recombinant rat CYP2E1 exhibited greater affinity and catalytic efficiency for DCE metabolism than did recombinant human CYP2E1, mouse CYP2F2, goat CYP2F3 or rat CYP2F4. In the lung microsomal incubations, the rates of conjugate [C] production were higher in CD-1 mice than in either wild-type or CYP2E1-null mice; the level of [C] in CYP2E1-null mice was about 66% of that in wild-type mice. These results demonstrated that LC/MS analysis is a suitable method for detection and quantitation of conjugate [C], and that CYP2E1 and CYP2F2 catalyze the bioactivation of DCE to the epoxide in murine lung. The results also demonstrated that CYP2E1 is the high-affinity enzyme involved in DCE bioactivation.
    Drug Metabolism and Disposition 10/2004; 32(9):1032-9. · 3.36 Impact Factor
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    ABSTRACT: 1,1-Dichloroethylene (DCE) exposure evokes lung toxicity with selective damage to bronchiolar Clara cells. Recent in vitro studies have implicated CYP2E1 and CYP2F2 in the bioactivation of DCE to 2-S-glutathionyl acetate [C], a putative conjugate of DCE epoxide with glutathione. An objective of this study was to test the hypothesis that bioactivation of DCE is catalyzed by both CYP2E1 and CYP2F2 in murine lung. Western blot analysis of lung microsomal proteins from DCE-treated CD-1 mice showed time-dependent loss of immunodetectable CYP2F2 and CYP2E1 protein. Dose-dependent formation of conjugate [C] was observed in the lungs of CD-1 mice treated with DCE (75-225 mg/kg), but it was not detected after pretreatment with 5-phenyl-1-pentyne (5-PIP). Treatment of mice with 5-PIP and also with diallyl sulfone (DASO2) significantly inhibited hydroxylation of p-nitrophenol (PNP) and chlorzoxazone (CHZX). Incubation of recombinant CYP2F3 (a surrogate for CYP2F2) and recombinant CYP2E1 with PNP and CHZX confirmed that they are substrates for both of the recombinant enzymes. Incubation of the recombinant enzymes with DASO2 or 5-PIP significantly inhibited hydroxylation of both PNP and CHZX. Bronchiolar injury was elicited in CD-1 mice treated with DCE (75 mg/kg), but it was abrogated with 5-PIP pretreatment. Bronchiolar toxicity also was manifested in the lungs of CYP2E1-null and wild-type mice treated with DCE (75 mg/kg), but protection ensued after pretreatment with 5-PIP or DASO2. These results showed that bioactivation of DCE in murine lung occurred via the catalytic activities of both CYP2E1 and CYP2F2 and that bioactivation by these enzymes mediated the lung toxicity.
    Journal of Pharmacology and Experimental Therapeutics 10/2004; 310(3):855-64. · 3.89 Impact Factor
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    ABSTRACT: CYP2C9 is a clinically important enzyme, responsible for the metabolism of numerous clinically important therapeutic drugs. In the present study, we discovered 38 single nucleotide polymorphisms in CYP2C9 by resequencing of genomic DNA from 92 individuals from three different racial groups. Haplotype analysis predicted that there are at least 21 alleles of CYP2C9 in this group of individuals. Six new alleles were identified that contained coding changes: L19I (CYP2C9*7), R150H (CYP2C9*8), H251R (CYP2C9*9), E272G (CYP2C9*10), R335W(CYP2C9*11) and P489S (CYP2C9*12). When expressed in a bacterial cDNA expression system, several alleles exhibited altered catalytic activity. CYP2C9*11 appeared to be a putative poor metabolizer allele, exhibiting a three-fold increase in the Km and more than a two-fold decrease in the intrinsic clearance for tolbutamide. Examination of the crystal structure of human CYP2C9 reveals that R335 is located in the turn between the J and J' helices and forms a hydrogen-bonding ion pair with D341 from the J' helix. Abolishing this interaction in CYP2C9*11 individuals could destabilize the secondary structure and alter the substrate affinity. This new putative poor metabolizer (PM) allele was found in Africans. A second potentially PM allele CYP2C9*12 found in a racially unidentified sample also exhibited a modest decrease in the Vmax and the intrinsic clearance for tolbutamide in a recombinant system. Further clinical studies are needed to determine the effect of these new polymorphisms on the metabolism of CYP2C9 substrates.
    Pharmacogenetics 09/2004; 14(8):527-37.
  • Brian Chanas, Hongbing Wang, Burhan I Ghanayem
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    ABSTRACT: Acrylonitrile (AN) is a potent toxicant and a known rodent carcinogen. AN epoxidation to cyanoethylene oxide (CEO) via CYP2E1 and its subsequent metabolism via epoxide hydrolases (EH) to yield cyanide is thought to be responsible for the acute toxicity and mortality of AN. Recent reports showed that male mice are more sensitive than females to the acute toxicity/mortality of AN. The present work was undertaken to assess the metabolic and enzymatic basis for the greater sensitivity of male vs female mice to AN toxicity. Male and female wild-type and CYP2E1-null mice received AN at 0, 2.5, 10, 20, or 40 mg/kg by gavage. Cyanide concentrations were measured at 1 or 3 h after dosing. Current data demonstrated that cyanide levels in blood and tissues of AN-treated wild-type mice of both sexes were significantly greater than in vehicle-treated controls and increased in a dose-dependent manner. In contrast, cyanide levels in AN-treated CYP2E1-null mice were not statistically different from those measured in vehicle-treated controls. Furthermore, higher levels of cyanide were detected in male wild-type mice vs females in association with greater sensitivity of males to the acute toxicity/mortality of this chemical. Using Western blot analysis, negligible difference in CYP2E1 expression with higher levels of soluble and microsomal EH (sEH and mEH) was detected in the liver of male vs female mice. In kidneys, male mice exhibited higher expression of both renal CYP2E1 and sEH than did female mice. In conclusion, higher blood and tissue cyanide levels are responsible for the greater sensitivity of male vs female mice to AN. Further, higher expression of CYP2E1 and EH in male mice may contribute to greater formation of CEO and its subsequent metabolism to yield cyanide, respectively.
    Toxicology and Applied Pharmacology 01/2004; 193(2):293-302. · 3.98 Impact Factor
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    ABSTRACT: Genetic polymorphisms of cytochromes P450 (CYPs) are a principal reason for inter-individual variations in the metabolism of therapeutic drugs and environmental chemicals in humans. The present study identifies 34 single nucleotide polymorphisms (SNPs) of CYP3A5 including 27 previously unidentified SNPs by direct sequencing of the exons, intron-exon junctions and 5'-upstream region of CYP3A5 from 92 racially diverse individuals (24 Caucasians, 24 Africans, 24 Asians, and 20 individuals of unknown racial origin). Four new CYP3A5 SNPs produced coding changes: R28C, L82R, A337T, and F446S. CYP3A5 R28C occurred in African populations (allelic frequency of 4%). CYP3A5 A337T occurred in Asians (2% allelic frequency), CYP3A5 L82R (occurred in the racially unidentified group) and CYP3A5 F446S (identified in Caucasians with a 2% allelic frequency) were on an allele containing the splice change g.6986A>G known as CYP3A5*3. The newly identified allelic proteins were constructed by site-directed mutagenesis, expressed in Escherichia coli and purified. CYP3A5 L82R was expressed only as denatured CYP420, suggesting it may be unstable. CYP3A5*1 exhibited the highest maximal clearance for testosterone followed by CYP3A5 A337T > CYP3A5 R28C > CYP3A5 F446S. CYP3A5*1 exhibited a higher V(max) for nifedipine oxidation than CYP3A5 A337T > CYP3A5 R28C > CYP3A5 F446S. CYP3A5 A337T and CYP3A5 R28C exhibited a 42-64% lower V(max) for nifedipine oxidation than CYP3A5*1. CYP3A5 F446S exhibited a > 95% decrease in the intrinsic clearance for both 6beta-hydroxytestosterone and nifedipine oxidation. This study identifies four new potentially defective coding alleles. CYP3A5 F446S is predicted to be more catalytically defective than the splice change alone.
    Pharmacogenetics 08/2003; 13(8):461-72.
  • Undi Hoffler, Hisham A El-Masri, Burhan I Ghanayem
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    ABSTRACT: Urethane ([carbonyl-(14)C]ethyl carbamate) is a fermentation by-product in alcoholic beverages and foods and is classified as reasonably anticipated to be a human carcinogen. Early studies indicated that while CYP2E1 is involved, esterases are the primary enzymes responsible for urethane metabolism. Using CYP2E1-null (KO) mice, current studies were undertaken to elucidate CYP2E1's contribution to urethane metabolism. [Carbonyl-(14)C]urethane was administered by gavage to male CYP2E1-null and wild-type mice at 10 or 100 mg/kg and its metabolism and disposition were investigated. CO(2) was confirmed as the main metabolite of urethane. Significant inhibition of urethane metabolism to CO(2) occurred in CYP2E1-null versus wild-type mice. Pharmacokinetic modeling of (14)CO(2) exhalation data revealed that CYP2E1 is responsible for approximately 96% of urethane metabolism to CO(2) in wild-type mice. The contributions of other enzymes to urethane metabolism merely account for the remaining 4%. The half-life of urethane in wild-type and CYP2E1-null mice was estimated at 0.8 and 22 h, respectively. Additionally, the concentration of urethane-derived radioactivity in blood and tissues was dose-dependent and significantly higher in CYP2E1-null mice. High-performance liquid chromatography analysis showed only urethane in the plasma and liver extracts of CYP2E1-null mice. Because the lack of CYP2E1 did not completely inhibit urethane metabolism, the disposition of 10 mg/kg urethane was compared in mice pretreated with the P450 inhibitor, 1-aminobenzotriazole or the esterase inhibitor, paraoxon. Unlike paraoxon, 1-aminobenzotriazole resulted in significant inhibition of urethane metabolism to CO(2) in both genotypes. In conclusion, this work demonstrated that CYP2E1, not esterase, is the principal enzyme responsible for urethane metabolism.
    Journal of Pharmacology and Experimental Therapeutics 06/2003; 305(2):557-64. · 3.89 Impact Factor

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  • 1985–2009
    • National Institutes of Health
      • • Laboratory of Molecular Pharmacology
      • • Chemical Biology Laboratory
      • • Section on Human Iron Metabolism
      Bethesda, MD, United States
  • 1986–2007
    • National Institute of Environmental Health Sciences
      • Laboratory of Structural Biology (LSB)
      Durham, North Carolina, United States
  • 2006
    • Queen's University
      • Department of Anatomy and Cell Biology
      Kingston, Ontario, Canada
  • 2003–2005
    • Meharry Medical College
      • Department of Pharmacology
      Nashville, Tennessee, United States
  • 2001
    • Hebrew University of Jerusalem
      Yerushalayim, Jerusalem District, Israel
  • 1996–1999
    • National Eye Institute
      Maryland, United States
  • 1998
    • Research Triangle Park Laboratories, Inc.
      Raleigh, North Carolina, United States
  • 1982–1996
    • University of Texas Medical Branch at Galveston
      • • Department of Pathology
      • • Department of Pharmacology and Toxicology
      Galveston, TX, United States