RESUMEN
Clinical applications of prenatal genetic screening currently focus on detection of aneuploidy and other genetic diseases in the developing fetus. Growing evidence suggests that the fetal genome may also be informative about fetal exposures through contributions to placental transport as well as placental and fetal metabolism. Possible clinical applications of prenatal pharmacogenomic screening include prospective optimization of medication selection and dosage, as well as retrospective assessment of whether a fetus was previously exposed to significant risk. Newly available noninvasive methods of prenatal genetic screening mean that relevant fetal genotypes could be made available to obstetricians for use in management of a current pregnancy. This promising area for research merits more attention than it has thus far received.The Pharmacogenomics Journal advance online publication, 10 May 2016; doi:10.1038/tpj.2016.33.
Asunto(s)
Investigación Biomédica/métodos , Sistema Enzimático del Citocromo P-450/genética , Proteínas de Transporte de Membrana/genética , Farmacogenética/métodos , Pruebas de Farmacogenómica , Variantes Farmacogenómicas , Diagnóstico Prenatal/métodos , Animales , Biotransformación , Sistema Enzimático del Citocromo P-450/metabolismo , Femenino , Feto/metabolismo , Genotipo , Humanos , Proteínas de Transporte de Membrana/metabolismo , Fenotipo , Placenta/metabolismo , EmbarazoRESUMEN
Large interindividual variability has been observed in the metabolism of CYP2C19 substrates in vivo. The study aimed to evaluate sources of this variability in CYP2C19 activity, focusing on CYP2C19 diplotypes and the cytochrome P450 oxidoreductase (POR). CYP2C19 gene analysis was carried out on 347 human liver samples. CYP2C19 activity assayed using human liver microsomes confirmed a significant a priori predicted rank order for (S)-mephenytoin hydroxylase activity of CYP2C19*17/*17 > *1B/*17 > *1B/*1B > *2A/*17 > *1B/*2A > *2A/*2A diplotypes. In a multivariate analysis, the CYP2C19*2A allele and POR protein content were associated with CYP2C19 activity. Further analysis indicated a strong effect of the CYP2C19*2A, but not the *17, allele on both metabolic steps in the conversion of clopidogrel to its active metabolite. The present study demonstrates that interindividual variability in CYP2C19 activity is due to differences in both CYP2C19 protein content associated with gene diplotypes and the POR concentration.The Pharmacogenomics Journal advance online publication, 1 September 2015; doi:10.1038/tpj.2015.58.
Asunto(s)
Citocromo P-450 CYP2C19/genética , Citocromo P-450 CYP2C19/metabolismo , Sistema Enzimático del Citocromo P-450/metabolismo , Hígado/enzimología , Mefenitoína/metabolismo , Variantes Farmacogenómicas/genética , Ticlopidina/análogos & derivados , Activación Metabólica , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Niño , Preescolar , Clopidogrel , Femenino , Regulación Enzimológica de la Expresión Génica , Frecuencia de los Genes , Genotipo , Humanos , Hidroxilación , Lactante , Recién Nacido , Cinética , Modelos Lineales , Masculino , Microsomas Hepáticos/enzimología , Persona de Mediana Edad , Análisis Multivariante , Oxidación-Reducción , Fenotipo , Especificidad por Sustrato , Ticlopidina/metabolismo , Adulto JovenRESUMEN
BACKGROUND AND AIMS: In previous analyses, we identified three dietary patterns from food frequency questionnaire data among a sample of Yup'ik Alaska Native people living in Southwest Alaska: a "subsistence foods" dietary pattern and two market-based dietary patterns "processed foods" and "fruits and vegetables". In this analysis, we aimed to characterize the association between the dietary patterns and cardiometabolic (CM) risk factors (lipids, blood pressure, glucose, adiposity). METHODS AND RESULTS: We used multilevel linear regression to estimate the mean of each CM risk factor, comparing participants in the 4th to the 1st quartile of each dietary pattern (n = 637). Models were adjusted for age, sex, past smoking, current smoking, and physical activity. Mean log triglyceride levels were significantly higher among participants in the 4th compared to the 1st quartile of the processed foods dietary pattern (ß = 0.11). Mean HbA1c percent was significantly lower (ß = -0.08) and mean diastolic blood pressure (DBP) mm Hg was significantly higher (ß = 2.87) among participants in the 4th compared to the 1st quartile of the fruits and vegetables dietary pattern. Finally, mean log triglyceride levels and mean DBP mm Hg were significantly lower among participants in the 4th compared to the 1st quartile of the subsistence foods dietary pattern (ß = -0.10 and ß = -3.99 respectively). CONCLUSIONS: We found increased CM risk, as reflected by increased triglycerides, associated with eating a greater frequency of processed foods, and reduced CM risk, as reflected by lower triglycerides and DBP, associated with eating a greater frequency of subsistence foods.
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Enfermedades Cardiovasculares/epidemiología , Registros de Dieta , Dieta , Conducta Alimentaria/etnología , Síndrome Metabólico/epidemiología , Adulto , Factores de Edad , Anciano , Alaska/epidemiología , Enfermedades Cardiovasculares/prevención & control , Estudios Transversales , Femenino , Humanos , Inuk , Estilo de Vida , Modelos Lineales , Masculino , Síndrome Metabólico/prevención & control , Persona de Mediana Edad , Análisis Multivariante , Medición de Riesgo , Factores Sexuales , Encuestas y CuestionariosRESUMEN
Tacrolimus is the mainstay immunosuppressant drug used after solid organ and hematopoietic stem cell transplantation. Individuals who express CYP3A5 (extensive and intermediate metabolizers) generally have decreased dose-adjusted trough concentrations of tacrolimus as compared with those who are CYP3A5 nonexpressers (poor metabolizers), possibly delaying achievement of target blood concentrations. We summarize evidence from the published literature supporting this association and provide dosing recommendations for tacrolimus based on CYP3A5 genotype when known (updates at www.pharmgkb.org).
Asunto(s)
Citocromo P-450 CYP3A/genética , Inmunosupresores/administración & dosificación , Tacrolimus/administración & dosificación , Pruebas Genéticas , Genotipo , Trasplante de Células Madre Hematopoyéticas , Humanos , Trasplante de ÓrganosRESUMEN
The influence of warfarin pharmacogenomics on major bleeding risk has been little studied in long-term users and non-specialist care settings. We conducted a case-control study to evaluate associations between CYP2C9*2/*3, VKORC1(1173), and CYP4F2*3 variants and major bleeding among patients treated with warfarin in a community setting. We calculated major bleeding odds ratios, adjusting for race, duration of warfarin use, age, gender, and body mass index. In 265 cases and 305 controls with 3.4 and 3.7 mean years of warfarin use, respectively, CYP4F2*3 was associated with decreased major bleeding risk (odds ratio: 0.62; 95% confidence interval: 0.43-0.91). CYP2C9*2/*3 and VKORC1(1173) had null associations overall, but there was a nonsignificant increase in major bleeding risk in patients with duration <6 months (odds ratio: 1.30; 95% confidence interval: 0.60-2.83; odds ratio: 1.23; 95% confidence interval: 0.57-2.64, respectively). In summary, in the largest study of warfarin pharmacogenomics and major bleeding to date, we found a 38% lower risk in patients with CYP4F2*3, potentially reflecting interaction with warfarin and dietary vitamin K intake and warranting additional evaluation.
Asunto(s)
Anticoagulantes/efectos adversos , Hemorragia/inducido químicamente , Hemorragia/genética , Warfarina/efectos adversos , Anciano , Hidrocarburo de Aril Hidroxilasas/genética , Hidrocarburo de Aril Hidroxilasas/metabolismo , Estudios de Casos y Controles , Citocromo P-450 CYP2C9 , Sistema Enzimático del Citocromo P-450/genética , Sistema Enzimático del Citocromo P-450/metabolismo , Familia 4 del Citocromo P450 , Dieta , Interacciones Farmacológicas , Etnicidad , Femenino , Estudios de Asociación Genética , Hemorragia/epidemiología , Humanos , Relación Normalizada Internacional , Masculino , Factores de Riesgo , Caracteres Sexuales , Washingtón/epidemiologíaRESUMEN
We evaluated the hypothesis that cytochrome P450 3A5 (CYP3A5) expression can affect intrarenal tacrolimus accumulation. Tacrolimus was administered orally to 24 healthy volunteers who were selected on the basis of their CYP3A5 genotype. As compared with CYP3A5 nonexpressors, expressors had a 1.6-fold higher oral tacrolimus clearance and 2.0- to 2.7-fold higher metabolite/parent area under the curve (AUC) ratios for 31-desmethyl tacrolimus (31-DMT), 12-hydroxy tacrolimus, and 13-desmethyl tacrolimus (13-DMT). In addition, the apparent urinary tacrolimus clearance was 36% lower in CYP3A5 expressors as compared with nonexpressors. To explore the mechanism behind this observation, we developed a semiphysiological model of renal tacrolimus disposition and predicted that tacrolimus exposure in the renal epithelium of CYP3A5 expressors is 53% of that for CYP3A5 nonexpressors, when normalized to blood AUC. These data suggest that, at steady state, intrarenal accumulation of tacrolimus and its primary metabolites will depend on the CYP3A5 genotype of the liver and kidneys. This may contribute to interpatient differences in the risk of tacrolimus-induced nephrotoxicity.
Asunto(s)
Citocromo P-450 CYP3A/genética , Inmunosupresores/farmacocinética , Tacrolimus/farmacocinética , Adulto , Algoritmos , Área Bajo la Curva , Biotransformación , ADN/genética , Femenino , Variación Genética , Genotipo , Semivida , Heterocigoto , Humanos , Inmunosupresores/orina , Riñón/metabolismo , Masculino , Modelos Genéticos , Reacción en Cadena de la Polimerasa , Polimorfismo de Nucleótido Simple , Tacrolimus/orinaRESUMEN
The allosteric effect of fluconazole (effector) on the formation of 1'-hydroxymidazolam (1'-OH-MDZ) and 4-hydroxymidazolam (4-OH-MDZ) from midazolam (MDZ), a substrate of CYP3A4/5--members of the cytochrome P450 superfamily of enzymes--was examined in healthy volunteers. Following pretreatment with fluconazole, the ratio of the areas under the curve (AUCs) for 4-OH-MDZ and MDZ (AUC(4-OH)/AUC(MDZ)) increased by 35-62%, whereas the ratio AUC(1'-OH)/AUC(MDZ) decreased by 5-37%; the ratio AUC(1'-OH)/AUC(4-OH) decreased by 46-58% after fluconazole administration and had no association with the CYP3A5 genotype. The in vitro formation of 1'-OH-MDZ was more susceptible to inhibition by fluconazole than that of 4-OH-MDZ. Fluconazole decreased the intrinsic formation-clearance ratio of 1'-OH-MDZ/4-OH-MDZ to an extent that was quantitatively comparable to in vivo observations. The elimination clearance of MDZ metabolites appeared unaffected by fluconazole. This study demonstrated that fluconazole alters formation of MDZ metabolites, both in vivo and in vitro, in a manner consistent with an allosteric interaction. The 1'-OH-MDZ/4-OH-MDZ ratio may serve as a biomarker of such interactions among MDZ, CYP3A4/5, and other putative effectors.
Asunto(s)
Citocromo P-450 CYP3A/metabolismo , Fluconazol/farmacología , Midazolam/farmacocinética , Regulación Alostérica , Área Bajo la Curva , Biomarcadores/metabolismo , Citocromo P-450 CYP3A/genética , Interacciones Farmacológicas , Humanos , Midazolam/análogos & derivados , Midazolam/metabolismo , Midazolam/farmacologíaRESUMEN
An endogenous probe for CYP3A activity would be useful for early identification of in vivo cytochrome P450 (CYP) 3A4 inhibitors. The aim of this study was to determine whether formation clearance (CL(f)) of the sum of 6ß-hydroxycortisol and 6ß-hydroxycortisone is a useful probe of CYP3A4 inhibition in vivo. In human liver microsomes (HLMs), the formation of 6ß-hydroxycortisol and 6ß-hydroxycortisone was catalyzed by CYP3A4, and itraconazole inhibited these reactions with half maximal inhibitory concentration (IC(50))(,u) values of 3.1 nmol/l and 3.4 nmol/l, respectively. The in vivo IC(50,u) value of itraconazole for the combined CL(f) of 6ß-hydroxycortisone and 6ß-hydroxycortisol was 1.6 nmol/l. The greater inhibitory potency in vivo is probably due to circulating inhibitory itraconazole metabolites. The maximum in vivo inhibition was 59%, suggesting that f(m,CYP3A4) for cortisol and cortisone 6ß-hydroxylation is ~60%. Given the significant decrease in CL(f) of 6ß-hydroxycortisone and 6ß-hydroxycortisol after 200-mg and 400-mg single doses of itraconazole, this endogenous probe can be used to detect moderate and potent CYP3A4 inhibition in vivo.
Asunto(s)
Cortisona/análogos & derivados , Inhibidores del Citocromo P-450 CYP3A , Citocromo P-450 CYP3A/biosíntesis , Hidrocortisona/análogos & derivados , Sondas Moleculares/metabolismo , Cortisona/antagonistas & inhibidores , Cortisona/metabolismo , Citocromo P-450 CYP3A/metabolismo , Combinación de Medicamentos , Evaluación Preclínica de Medicamentos/métodos , Humanos , Hidrocortisona/antagonistas & inhibidores , Hidrocortisona/biosíntesis , Hidrocortisona/metabolismo , Itraconazol/metabolismo , Itraconazol/farmacología , Microsomas Hepáticos/efectos de los fármacos , Microsomas Hepáticos/enzimología , Microsomas Hepáticos/metabolismo , Reproducibilidad de los ResultadosRESUMEN
Pharmacogenetic research offers the potential to improve the safety and efficacy of drug prescribing. Assuring that the benefits of this research reach indigenous and other medically underserved people is an important justice concern. First, however, a legacy of mistrust, derived from traditional research practices that disempower communities, must be overcome. Linking pharmacogenetic research to collaborative, power-sharing research partnerships provides a valuable opportunity to develop new and positive precedents for genetic research in indigenous communities.
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Investigación Genética/ética , Indígenas Norteamericanos , Preparaciones Farmacéuticas/administración & dosificación , Farmacogenética/ética , Investigación Participativa Basada en la Comunidad/organización & administración , Conducta Cooperativa , Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos , Accesibilidad a los Servicios de Salud , Humanos , Área sin Atención Médica , Farmacogenética/organización & administración , Pautas de la Práctica en Medicina , Confianza , Estados UnidosRESUMEN
Inhibitory drug metabolites may contribute to drug-drug interactions (DDIs). The aim of this study was to determine the importance of inhibitory metabolites of itraconazole (ITZ) in in vivo cytochrome P450 (CYP) 3A4 inhibition. The pharmacokinetics of ITZ and midazolam (MDZ) were determined in six healthy volunteers in four sessions after administration of MDZ with and without oral ITZ. After doses of 50, 200, and 400 mg of ITZ, the clearance of orally administered MDZ decreased by 27, 74, and 83%, respectively. The in vivo half maximal inhibitory concentration (IC(50)) for ITZ ranged from 5 to 132 nmol/l in the six subjects. The metabolites of ITZ were estimated to account for ~50% of the total CYP3A4 inhibition, with the relative contribution increasing with time after ITZ dosing. Of the total of 18 interactions observed, 15 (84%) could be predicted within a twofold error margin, with improved accuracy observed when ITZ metabolites were included in the predictions. This study shows that the metabolites of ITZ contribute to CYP3A4 inhibition and need to be accounted for in quantitative rationalization of ITZ-mediated DDIs.
Asunto(s)
Inhibidores del Citocromo P-450 CYP3A , Inhibidores Enzimáticos/farmacología , Itraconazol/farmacología , Midazolam/farmacocinética , Adulto , Área Bajo la Curva , Citocromo P-450 CYP3A , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Femenino , Humanos , Técnicas In Vitro , Concentración 50 Inhibidora , Masculino , Tasa de Depuración Metabólica , Adulto JovenRESUMEN
The small intestine and liver express high levels of cytochrome P450 3A (CYP3A), an enzyme subfamily that contributes significantly to drug metabolism. In patients with cirrhosis, reduced metabolism of drugs is typically attributed to decreased liver function, but it is unclear whether drug metabolism in the intestine is also compromised. In this study, we compared CYP3A protein expression and in vitro midazolam hydroxylation in duodenal mucosal biopsies from subjects with normal liver function (controls; n = 20) and subjects with various levels of severity of cirrhosis (n = 23). In samples from subjects with cirrhosis, duodenal CYP3A expression and total midazolam hydroxylation were lower by 47 and 34%, respectively, as compared with samples from controls. Greater decreases in CYP3A expression were seen in subjects with more severe cirrhosis. Therefore, patients with advanced cirrhosis may have greater drug exposure following oral dosing as a result of both impaired liver function and decreased intestinal CYP3A expression and activity.
Asunto(s)
Citocromo P-450 CYP3A/biosíntesis , Duodeno/enzimología , Regulación Enzimológica de la Expresión Génica/fisiología , Cirrosis Hepática/enzimología , Adulto , Anciano , Catálisis/efectos de los fármacos , Citocromo P-450 CYP3A/análisis , Duodeno/efectos de los fármacos , Activación Enzimática/genética , Femenino , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Humanos , Mucosa Intestinal/efectos de los fármacos , Mucosa Intestinal/enzimología , Cirrosis Hepática/tratamiento farmacológico , Masculino , Midazolam/farmacocinética , Midazolam/uso terapéutico , Persona de Mediana EdadRESUMEN
The US Food and Drug Administration (FDA) is currently developing a guidance for industry to replace a previous guidance, "Pharmacokinetics in Patients With Impaired Renal Function--Study Design, Data Analysis, and Impact on Dosing and Labeling" (renal guidance) issued in May 1998. The impact of the 1998 renal guidance was assessed following a survey of 94 new drug applications (NDAs) for small-molecule new molecular entities (NMEs) approved over the past 5 years (2003-2007). The survey results indicate that 57% of these NDAs included renal impairment study data, that 44% of those with renal data included evaluation in patients on hemodialysis, and that 41% of those with renal data resulted in recommendation of dose adjustment in renal impairment. In addition, the survey results provided evidence that renal impairment can affect the pharmacokinetics of drugs that are predominantly eliminated by nonrenal processes such as metabolism and/or active transport. The latter finding supports our updated recommendation to evaluate pharmacokinetic/pharmacodynamic alterations in renal impairment for those drugs that are mainly eliminated by nonrenal processes, in addition to those that are mainly excreted unchanged by the kidney.
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Drogas en Investigación/administración & dosificación , Drogas en Investigación/metabolismo , Aplicación de Nuevas Drogas en Investigación , Enfermedades Renales/metabolismo , Drogas en Investigación/efectos adversos , Humanos , Enfermedades Renales/inducido químicamente , Guías de Práctica Clínica como Asunto/normasRESUMEN
The objectives of the study were to evaluate the effects of pregnancy on CYP3A and P-glycoprotein (P-gp) activities, as measured by disposition of midazolam and digoxin, respectively. Thirteen women received digoxin (0.25 mg p.o.) and midazolam (2 mg p.o.) in random order, separated by 1-2 weeks at 28-32 weeks gestation, and the same order was repeated at 6-10 weeks postpartum. Plasma and urine concentrations were determined by liquid chromatography-mass spectrometry and analyzed by noncompartmental methods. Midazolam CL/F(unbound) (593 +/- 237 l/min vs. 345 +/- 103 l/min; P = 0.007), digoxin CL(Renal, unbound) (272 +/- 45 ml/min vs. 183 +/- 37 ml/min; P < 0.002) and digoxin CL(secretion,) (unbound) (109 +/- 34 ml/min vs. 58 +/- 22 ml/min; P < 0.002) were higher during pregnancy than postpartum. These data are consistent with increased hepatic and/or intestinal CYP3A and renal P-gp activities during pregnancy.
Asunto(s)
Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/metabolismo , Citocromo P-450 CYP3A/metabolismo , Digoxina/farmacocinética , Midazolam/farmacocinética , Periodo Posparto/metabolismo , Embarazo/metabolismo , Adulto , Anestésicos Intravenosos/farmacocinética , Ansiolíticos/farmacocinética , Antiarrítmicos/farmacocinética , Área Bajo la Curva , Cardiotónicos/farmacocinética , Creatinina/orina , Digoxina/sangre , Digoxina/orina , Inhibidores Enzimáticos/farmacocinética , Femenino , Cromatografía de Gases y Espectrometría de Masas , Genotipo , Humanos , Hipnóticos y Sedantes/farmacocinética , Midazolam/sangre , Midazolam/orina , Tercer Trimestre del Embarazo/metabolismoRESUMEN
Itraconazole (ITZ) is metabolized in vitro to three inhibitory metabolites: hydroxy-itraconazole (OH-ITZ), keto-itraconazole (keto-ITZ), and N-desalkyl-itraconazole (ND-ITZ). The goal of this study was to determine the contribution of these metabolites to drug-drug interactions caused by ITZ. Six healthy volunteers received 100 mg ITZ orally for 7 days, and pharmacokinetic analysis was conducted at days 1 and 7 of the study. The extent of CYP3A4 inhibition by ITZ and its metabolites was predicted using this data. ITZ, OH-ITZ, keto-ITZ, and ND-ITZ were detected in plasma samples of all volunteers. A 3.9-fold decrease in the hepatic intrinsic clearance of a CYP3A4 substrate was predicted using the average unbound steady-state concentrations (C(ss,ave,u)) and liver microsomal inhibition constants for ITZ, OH-ITZ, keto-ITZ, and ND-ITZ. Accounting for circulating metabolites of ITZ significantly improved the in vitro to in vivo extrapolation of CYP3A4 inhibition compared to a consideration of ITZ exposure alone.
Asunto(s)
Antifúngicos/farmacología , Inhibidores Enzimáticos del Citocromo P-450 , Inhibidores Enzimáticos/farmacología , Itraconazol/análogos & derivados , Itraconazol/farmacología , Hígado/efectos de los fármacos , Administración Oral , Adulto , Antifúngicos/administración & dosificación , Antifúngicos/farmacocinética , Biotransformación , Citocromo P-450 CYP3A , Sistema Enzimático del Citocromo P-450/metabolismo , Interacciones Farmacológicas , Inhibidores Enzimáticos/administración & dosificación , Inhibidores Enzimáticos/farmacocinética , Femenino , Glucurónidos/metabolismo , Humanos , Itraconazol/administración & dosificación , Itraconazol/farmacocinética , Hígado/enzimología , Masculino , Modelos BiológicosRESUMEN
BACKGROUND: Cytochrome P4502E1(CYP2E1)-mediated oxidation of halothane to a reactive intermediate (trifluoroacyl chloride) that covalently binds to hepatic proteins forming trifluoroacetylated neoantigens is believed to be the initiating event in a complex immunologic cascade culminating in antibody formation and severe hepatic necrosis ('halothane hepatitis') in susceptible patients. Trifluoroacyl chloride may also hydrolyze to the stable metabolite trifluoroacetic acid (TFA). CYP2E1 inactivation by disulfiram or its primary metabolite, diethyldithiocarbamate, inhibits human halothane oxidation to TFA in vitro and in vivo. Nevertheless, disulfiram effects on hepatic protein trifluoroacetylation by halothane in vivo are unknown. This investigation tested the hypotheses that disulfiram prevents halothane-dependent protein trifluoroacetylation in vivo, and that TFA represents a biomarker for hepatic protein trifluoroacetylation. METHODS: Rats were pretreated with isoniazid (CYP2E1 induction), isoniazid followed by disulfiram (CYP2E1 inhibition), or nothing (controls), then anesthetized with halothane or nothing (controls). Plasma and urine TFA were quantified by ion HPLC; hepatic microsomal TFA-proteins were analyzed by Western blot. RESULTS: CYP2E1 induction increased both TFA and TFA-protein formation compared with uninduced halothane-treated rats. Disulfiram, even after CYP2E1 induction, nearly abolished both TFA and TFA-protein formation. Pretreatments similarly affected both TFA and TFA-protein formation across all groups. CONCLUSIONS: Disulfiram inhibition of CYP2E1-mediated halothane oxidation prevents hepatic protein trifluoroacetylation. Based on the concordance between TFA and TFA-protein formation, TFA appears to be a valid biomarker for TFA-protein formation. Disulfiram inhibition of human halothane oxidation in vivo, previously assessed by diminished TFA formation, probably also confers inhibition of hepatic TFA-protein formation.
Asunto(s)
Anestésicos por Inhalación/metabolismo , Disulfiram/farmacología , Halotano/metabolismo , Hígado/metabolismo , Proteínas/metabolismo , Ácido Trifluoroacético/metabolismo , Animales , Western Blotting , Bromuros/metabolismo , Cromatografía Líquida de Alta Presión , Inhibidores del Citocromo P-450 CYP2E1 , Inducción Enzimática/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Isoniazida/farmacología , Hígado/efectos de los fármacos , Masculino , Oxidación-Reducción , Ratas , Ratas Sprague-DawleyRESUMEN
PURPOSE: To evaluate the potential pharmacokinetic interactions between topiramate (TPM) and phenytoin (PHT) in patients with epilepsy by studying their pharmacokinetics (PK) after monotherapy and concomitant TPM/PHT treatment. METHODS: Twelve patients with epilepsy stabilized on PHT monotherapy were enrolled in this study, with 10 and seven patients completing the phases with 400 and 800 mg TPM daily doses, respectively. TPM was added at escalating doses, and after stabilization at the highest tolerated TPM dose, PHT doses were tapered. Serial blood and urine samples were collected for PK analysis during the monotherapy phase or the lowest PHT dose after taper and the concomitant TPM/PHT phase. Potential metabolic interaction between PHT and TPM also was studied in vitro in human liver microsomal preparations. RESULTS: In nine of the 12 patients, PHT plasma concentrations remained stable, with a mean (+/-SD) area under the curve (AUC) ratio (combination therapy/monotherapy) of 1.13 +/- 0.17 (range, 0.89-1.23). Three patients had AUC ratios of 1.25, 1.39, and 1.55, respectively, and with the addition of TPM (800, 400, and 400 mg daily, respectively), their peak PHT plasma concentrations increased from 15 to 21 mg/L, 28 to 36 mg/L, and 27 to 41 mg/L, respectively. Human liver microsomal studies with S-mephenytoin showed that TPM partially inhibited CYP2C19 at very high concentrations of 300 microM (11% inhibition) and 900 microM (29% inhibition). Such high plasma concentrations would correspond to doses in humans that are 5 to 15 times higher than the recommended dose (200-400 mg). TPM clearance was approximately twofold higher during concomitant TPM/PHT therapy CONCLUSIONS: This study provides evidence that the addition of TPM to PHT generally does not cause clinically significant PK interaction. PHT induces the metabolism of TPM, causing increased TPM clearance, which may require TPM dose adjustments when PHT therapy is added or is discontinued. TPM may affect PHT concentrations in a few patients because of inhibition by TPM of the CYP2C19-mediated minor metabolic pathway of PHT.
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Anticonvulsivantes/farmacocinética , Hidrocarburo de Aril Hidroxilasas , Epilepsia/tratamiento farmacológico , Fructosa/farmacocinética , Fenitoína/farmacocinética , Adolescente , Adulto , Anticonvulsivantes/uso terapéutico , Citocromo P-450 CYP2C19 , Sistema Enzimático del Citocromo P-450/efectos de los fármacos , Sistema Enzimático del Citocromo P-450/metabolismo , Relación Dosis-Respuesta a Droga , Esquema de Medicación , Interacciones Farmacológicas , Quimioterapia Combinada , Epilepsia/metabolismo , Femenino , Fructosa/análogos & derivados , Fructosa/uso terapéutico , Humanos , Masculino , Persona de Mediana Edad , Oxigenasas de Función Mixta/efectos de los fármacos , Oxigenasas de Función Mixta/metabolismo , Fenitoína/uso terapéutico , TopiramatoRESUMEN
We investigated whether a single plasma midazolam concentration could serve as an accurate predictor of total midazolam clearance, an established in-vivo probe measure of cytochrome P450 3A (CYP3A) activity. In a retrospective analysis of data from 224 healthy volunteers, non-compartmental pharmacokinetic parameters were estimated from plasma concentration-time curves following intravenous (IV) and/or oral administration. Based on statistical moment theory, the concentration at the mean residence time (MRT) should be the best predictor of the total area under the curve (AUC). Following IV or oral midazolam administration, the average MRT was found to be approximately 3.5 h, suggesting that the optimal single sampling time to predict AUC was between 3 and 4 h. Since a 4-h data point was common to all studies incorporated into this analysis, we selected this time point for further investigation. The concentrations of midazolam measured 4 h after an IV or oral dose explained 80 and 91% of the constitutive interindividual variability in midazolam AUC, respectively. The 4-h midazolam measurement was also an excellent predictor of drug-drug interactions involving CYP3A induction and inhibition. Compared with baseline values, the direction and magnitude of change in midazolam AUC and the 4-h concentration were completely concordant for all study subjects. We conclude that a single 4-h midazolam concentration following IV or oral administration represents an accurate marker of CYP3A phenotype under constitutive and modified states. Moreover, the single-point approach offers an efficient means to phenotype and identify individuals with important genetic polymorphisms that affect CYP3A activity.
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Sistema Enzimático del Citocromo P-450/análisis , Midazolam/sangre , Administración Oral , Adulto , Anciano , Área Bajo la Curva , Asiático/genética , Población Negra/genética , Sistema Enzimático del Citocromo P-450/genética , Femenino , Semivida , Hispánicos o Latinos/genética , Humanos , Inyecciones Intravenosas , Masculino , Tasa de Depuración Metabólica , Microsomas Hepáticos/enzimología , Microsomas Hepáticos/metabolismo , Midazolam/administración & dosificación , Midazolam/farmacocinética , Persona de Mediana Edad , Fenotipo , Estudios Retrospectivos , Población Blanca/genéticaRESUMEN
It was previously shown that CYP3A4 is induced in the human intestinal Caco-2 cell model by treatment with 1alpha,25-dihydroxy vitamin D3 (1,25-D3). We demonstrate the vitamin D analog, 19-nor-1alpha,25-dihydroxy vitamin D2, is also an effective inducer of CYP3A4 in Caco-2 cells, but with half the potency of 1,25-D3. We report that treatment of LS180 cells, a human intestinal cell line, with 1 to 10 nM 1,25-D3 dose dependently increased CYP3A4 protein and CYP3A4 mRNA expression. CYP3A4- and CYP3A23-promoter-Luciferase reporter constructs transiently transfected into LS180 cells were transcriptionally activated in a dose-dependent manner by 1,25-D3, whereas mutation of the nuclear hormone receptor binding motif (ER6) in the CYP3A4 promoter abrogated 1,25-D3 activation of CYP3A4. Although the CYP3A4 ER6 promoter element has been shown to bind the pregnane X receptor (PXR), this receptor does not mediate 1,25-D3 induction of CYP3A4 because a) PXR is not expressed in Caco-2 cells; b) PXR mRNA expression is not induced by 1,25-D3 treatment of LS180 cells; and c) the ligand binding domain of human PXR was not activated by 1,25-D3. 1,25-D3 uses the vitamin D receptor to induce CYP3A4 because a) the vitamin D receptor (VDR)-retinoid X receptor (RXR) heterodimer binds specifically to the CYP3A4 ER6; b) selective mutation of the CYP3A4 ER6 disrupted the binding of VDR-RXR; and c) reporter constructs containing only three copies of the CYP3A4 ER6 linked to a TK-CAT reporter were activated by 1,25-D3 only in cells cotransfected with a human VDR expression plasmid. These data support the hypothesis that 1,25-D3 and VDR induce expression of intestinal CYP3A by binding of the activated VDR-RXR heterodimer to the CYP3A PXR response element and promoting gene transcription.
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Calcitriol/farmacología , Sistema Enzimático del Citocromo P-450/biosíntesis , Intestinos/efectos de los fármacos , Oxigenasas de Función Mixta/biosíntesis , Transcripción Genética/efectos de los fármacos , Animales , Células COS , Células CACO-2 , Células Cultivadas , Citocromo P-450 CYP3A , Sistema Enzimático del Citocromo P-450/genética , Dimerización , Relación Dosis-Respuesta a Droga , Inducción Enzimática , Ergocalciferoles/farmacología , Haplorrinos , Humanos , Intestinos/enzimología , Luciferasas/genética , Oxigenasas de Función Mixta/genética , Receptor X de Pregnano , Unión Proteica , Receptores de Calcitriol/genética , Receptores de Calcitriol/metabolismo , Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Ácido Retinoico/metabolismo , Receptores de Esteroides/metabolismo , Receptores X Retinoide , Factores de Tiempo , Factores de Transcripción/metabolismo , Activación TranscripcionalRESUMEN
Under certain culture conditions, exposure of the human colon adenocarcinoma cell line Caco-2 to 1,25-(OH)(2)-D(3) induces expression of CYP3A4 to levels comparable to that in human small intestinal epithelium. To determine whether 1,25-(OH)(2)-D(3) could be used to restore CYP3A expression in other culture models, we examined several cell lines derived from malignancies of human tissues known to express CYP3A enzymes: Hep G2 (liver), LS180 (colon), HPAC (pancreas), Hs746T (stomach). Primary cultures of human hepatocytes from two donors were also examined. 1,25-(OH)(2)-D(3) increased CYP3A catalytic activity in LS180 (15-fold), HPAC (6-fold), and hepatocytes (2- to 3-fold); this was accompanied by induction of CYP3A4 mRNA and CYP3A immunoreactive protein. However, 1,25-(OH)(2)-D(3) had no effect on CYP3A expression in Hs746T or Hep G2. Known ligands for pregnane X receptor (PXR) (rifampin, dexamethasone, and dexamethasone t-butyl acetate) markedly induced CYP3A4 expression in human hepatocytes. In contrast, these ligands had little or no effect on CYP3A4 expression in Caco-2 cells, even at concentrations 1 to 2 orders of magnitude greater than effective concentrations of 1,25-(OH)(2)-D(3) or two other vitamin D receptor (VDR) ligands (25-OH-D(3) and 1-OH-D(3)). The retinoic acid receptor ligand all-trans-retinoic acid augmented the 1,25-(OH)(2)-D(3)-mediated induction of CYP3A4 catalytic activity up to 2-fold in Caco-2 cells, while having no demonstrable effect on levels of CYP3A4 mRNA or protein. The retinoid X receptor ligand 9-cis-retinoic acid appeared to slightly reduce CYP3A4 catalytic activity. We conclude that 1,25-(OH)(2)-D(3) can be used to increase CYP3A4 expression in some, but not all, human cell lines derived from tissues known to express CYP3A enzymes. The mechanisms involved in this induction are unlikely to involve PXR and may involve VDR.
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Calcitriol/farmacología , Agonistas de los Canales de Calcio/farmacología , Sistema Enzimático del Citocromo P-450/biosíntesis , Oxigenasas de Función Mixta/biosíntesis , Receptores Citoplasmáticos y Nucleares/fisiología , Receptores de Esteroides/fisiología , Células CACO-2/efectos de los fármacos , Células CACO-2/enzimología , Calcitriol/análogos & derivados , Células Cultivadas , Citocromo P-450 CYP3A , Inducción Enzimática/efectos de los fármacos , Hepatocitos/efectos de los fármacos , Hepatocitos/enzimología , Humanos , Receptor X de PregnanoRESUMEN
OBJECTIVE: To investigate putative differences in CYP3A activity between European American and Japanese subjects using midazolam as an in vivo probe. METHODS: Midazolam was administered orally (2 mg) to 22 young healthy Japanese men and, on a separate occasion, to 19 of these by the intravenous route (1 mg). The disposition of the drug and its 1'-hydroxy metabolite were determined and compared with data collected in a similar fashion in 20 young healthy European American men. RESULTS: Plasma concentrations of midazolam, especially those attained soon after drug administration, were higher after intravenous injection in Japanese subjects than those in European American men. This observation was associated with smaller initial (2.5-fold) and steady-state (1.8-fold) volumes of distribution for the drug; normalization for body weight only modestly reduced these differences. The systemic clearance value of midazolam was 25% lower (P < .03) in Japanese subjects, but this difference was not apparent after accounting for the smaller body weights of that group. No statistical differences were noted in the elimination half-life (t 1/2) of midazolam between European American and Japanese subjects. Much greater interindividual variability was observed after oral administration compared with intravenous administration, but significant differences were not found between the 2 groups with respect to the maximum midazolam plasma level or its oral clearance. Absolute oral bioavailability and its associated gastrointestinal and hepatic extraction ratios also showed no statistically significant interracial differences. CONCLUSIONS: On average, hepatic CYP3A, as measured by the metabolism of midazolam, is lower in young healthy Japanese men compared with similar European Americans. However, there is considerable interindividual variability, and body size appears to be an important determinant. After oral administration, even greater variability in the plasma level-time profile of midazolam is present, and no statistically significant or clinically important interracial/ethnic difference is present. Possibly because of smaller body mass and differences in body composition, midazolam has a smaller distribution volume(s) in Japanese men than in European American men that might be an important factor when drugs are administered intravenously.