Identification of glucocorticoid-inducible cytochromes P-450 in the intestinal mucosa of rats and man

Cytochrome P450 pharmacogenetics as a predictor of toxicity and clinical response to pulse cyclophosphamide in lupus nephritis

OBJECTIVE

Pulse cyclophosphamide is the treatment of choice for severe lupus nephritis. However, not all patients respond to this therapy, and gonadal toxicity is of particular concern. Cyclophosphamide is a prodrug that requires activation by cytochrome P450 (CYP) enzymes. We conducted a retrospective cohort study to test whether genetic polymorphisms of these enzymes are associated with the toxicity of, and clinical response to, cyclophosphamide in patients with lupus nephritis.

METHODS

Sixty-two patients with proliferative lupus nephritis treated with cyclophosphamide were genotyped for common variant alleles of CYP2B6, 2C19, 2C9, and 3A5. We examined the association between these genotypes and the following clinical end points: development of premature ovarian failure, end-stage renal disease (ESRD), doubling of serum creatinine level, and achievement of complete renal response.

RESULTS

The observed frequencies of the variant alleles CYP2B6*5, CYP2C19*2, CYP2C9*2, and CYP3A5*3 were 12.1%, 25.0%, 4.0%, and 75.8%, respectively. Patients who were either heterozygous or homozygous for CYP2C19*2 had a significantly lower risk of developing premature ovarian failure (relative risk 0.10; 95% confidence interval 0.02-0.52), after adjustment for age and total number of cyclophosphamide pulses received. In a survival analysis, patients homozygous for CYP2B6*5 (n = 3) or CYP2C19*2 (n = 4) had a higher probability of reaching ESRD (P = 0.0005) and of doubling the creatinine level (P = 0.0005) as well as a trend toward a lower probability of achieving a complete renal response (P = 0.051).

CONCLUSION

Determination of selected cytochrome P450 enzyme genotypes may be valuable for predicting the risk of premature ovarian failure in lupus nephritis patients treated with cyclophosphamide. The association of these genotypes with renal response needs further validation.

Sex-Related Differences in the Pharmacokinetics of Once-Daily Saquinavir Soft-Gelatin Capsules Boosted with Low-Dose Ritonavir in Patients Infected with Human Immunodeficiency Virus Type 1

STUDY OBJECTIVES

To compare the steady-state pharmacokinetics and safety of saquinavir soft-gelatin capsules (SGC) plus low-dose ritonavir administered once/day in antiretroviral-naive adult patients infected with the human immunodeficiency virus type 1 (HIV-1) and to evaluate any sex-related differences.

DESIGN

Single-center, open-label, pharmacokinetic study.

SETTING

University-affiliated outpatient HIV clinic.

PATIENTS

Six men and seven women with HIV-1.

INTERVENTION

Each patient received saquinavir SGC 1600 mg and ritonavir 100 mg for a 14-day course of therapy. Nine serial blood samples during 24 hours were collected on day 14 of therapy

MEASUREMENTS AND MAIN RESULTS

Plasma saquinavir and ritonavir concentrations were measured by high-performance liquid chromatography. Standard noncompartmental methods were used to calculate the pharmacokinetic parameters. The unpaired Student t test was used for the statistical comparison of pharmacokinetic parameters between male and female patients. Once-daily saquinavir SGC plus ritonavir was generally well tolerated. Pharmacokinetic data from five men and five women were evaluable. The median saquinavir area under the concentration-time curve from 0-24 hours (AUC0-24) in the female patients (82,300 ng x hr/ml) was significantly (p=0.036) higher than that in the male patients (47,400 ng x hr/ml). This relationship remained significant for weight-adjusted saquinavir AUC0-24 values. Ritonavir's apparent oral clearance in the women was significantly (p=0.023) lower than that in the men.

CONCLUSION

Significantly higher plasma concentrations of saquinavir were achieved in female compared with male HIV-infected patients receiving once-daily saquinavir SGC 1600 mg plus ritonavir 100 mg.

Genetics of the Variable Expression of CYP3A in Humans

CYP3A isozymes participate in the metabolism of 45-60% of currently used drugs and of a variety of other compounds such as steroid hormones, toxins, and carcinogens. The CYP3A expression status is a major determinant of drug efficacy and safety, and it may also affect an individual's predisposition to certain cancers. The inter- and intraindividual expression of CYP3A is variable because of a complex interplay between genetic and environmental factors. Markers predictive of the individual CYP3A activity could improve therapies with CYP3A substrates by personalised dose adjustments, but their development has been slower than for other drug-metabolizing enzymes. Here we summarize the recent progress in genomics and regulation of CYP3A. The recently described markers of the CYP3A5 and CYP3A7 polymorphisms should facilitate the development of isozyme-specific activity markers for the individual CYP3A isozymes, including CYP3A4.

Identification of a novel polymorphic enhancer of the human CYP3A4 gene

CYP3A4, the most abundant form of cytochrome P450 in the human adult liver, shows wide interindividual variation in its activity. This variability is thought to be caused largely by transcriptional and genetic factors, yet the underlying mechanisms are poorly understood. The purpose of this study was to clarify the mechanisms controlling the CYP3A4 gene transcription and to search for genetic polymorphisms in the 5'-flanking region of the CYP3A4 gene. Transient transfection of human hepatoma HepG2 cells and of normal human hepatocytes with a series of CYP3A4 promoter-luciferase reporter plasmids revealed that a region from -11.4 to -10.5 kilobases, designated the constitutive liver enhancer module of CYP3A4 (CLEM4), was important for the constitutive activation of the CYP3A4 gene. Gel shift assay using nuclear extracts prepared from HepG2 cells showed that HNF-1alpha, HNF-4alpha, USF1, and AP-1 interacted with CLEM4. Furthermore, the introduction of mutations into their binding sites demonstrated that essentially all sites were required for the maximal enhancer activity. Screening for genetic polymorphisms within CLEM4 in genomic DNA from French persons, we identified the novel variant, TGT insertion between -11,129 and -11,128 (-11,129_-11,128insTGT), whose allele frequency was 3.1%. The -11,129_-11,128insTGT resulted in the disruption of USF1 binding and a 36% reduction of the enhancer activity. These results suggest that CLEM4 is a constitutive enhancer of the CYP3A4 gene in the liver and that -11,129_-11,128insTGT may at least partly contribute to the interindividual variability of CYP3A4 expression.

Pharmacokinetic Optimisation of Treatment with Oral Etoposide

Etoposide is a derivative of podophyllotoxin widely used in the treatment of several neoplasms, including small cell lung cancer, germ cell tumours and non-Hodgkin's lymphomas. Prolonged administration of etoposide aims for continuous inhibition of topoisomerase II, the intracellular target of etoposide, thus preventing tumour cells from repairing DNA breaks. However, the clinical advantages of extended schedules as compared with conventional short-term infusions remain unclear. Oral administration of etoposide represents the most feasible and economic strategy to maintain effective concentrations of drug for extended times. Nevertheless, the efficacy of oral etoposide therapy is contingent on circumventing pharmacokinetic limitations, mainly low and variable bioavailability. Inhibition of small bowel and hepatic metabolism of etoposide with specific cytochrome P450 inhibitors or inhibition of the intestinal P-glycoprotein efflux pump have been attempted to increase the bioavailability of oral etoposide, but the best results were obtained with daily oral administration of low etoposide doses (50-100 mg/day for 14-21 days). Saturable absorption of etoposide was reported for doses greater than 200 mg/day, whereas lower doses were associated with increased bioavailability, although they were characterised by high inter- and intrapatient variability. Pharmacokinetic parameters such as plasma trough concentration between two oral administrations (C(24,trough)), drug exposure time above a threshold value and area under the plasma concentration-time curve have been correlated with the pharmacodynamic effect of oral etoposide. Pharmacokinetic-pharmacodynamic relationships indicate that severe toxicity is avoided when peak plasma concentrations do not exceed 3-5 mg/L and C(24,trough) is under the threshold limit of 0.3 mg/L. To maintain effective etoposide plasma concentrations during prolonged oral administration, pharmacokinetic variability must be monitored in each patient, taking account of factors from many pharmacokinetic studies of etoposide, including absorption, distribution, protein binding, metabolism and elimination. Dosage reduction is generally useful to avoid haematological toxicity in patients with renal dysfunction (creatinine clearance <50 mL/min). The need for dosage adjustment based on liver function in patients with liver dysfunction is not completely defined, but generally is not indicated in patients with minor liver dysfunction. Adaptive dosage adjustment based on individual pharmacokinetic parameters, estimated using limited sampling strategies and population pharmacokinetic models, is more appropriate. This approach has been used with success in different clinical trials to increase the etoposide dosage, without significantly increasing toxicity. Various pharmacodynamic models have been proposed to guide etoposide oral dosage. However, they lack precision and accuracy and need to be refined by considering other predictor variables in order to extend their application in current clinical practice.

Role of c-Myc in nitric oxide-mediated suppression of cytochrome P450 3A4

Cytochrome P450 (CYP) 3A4, which is abundant in human liver and small intestine and participates in the metabolism of various drugs and xenochemicals, is known to be induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in the colon carcinoma cell line Caco-2 cells. Nitric oxide (NO) is able to inhibit CYP3A4 expression and catalytic activity. In this study, we investigated the mechanism of suppression by NO of 1,25(OH)2D3-induced CYP3A4 expression in Caco-2 cells. Caco-2 cells were exposed for 36 h to 400 nM 1,25(OH)2D3, and the induction of CYP3A4 mRNA expression was detected by real-time PCR. Because c-Myc regulates the expression of several genes, we examined its effect on the CYP3A4 expression induced by 1,25(OH)2D3. The expression of c-myc mRNA was increased in the early stage but decreased 36 h after the treatment of Caco-2 cells with 1,25(OH)2D3. The NO donor NOR-4 suppressed CYP3A4 expression induced by 1,25(OH)2D3 in Caco-2 cells in contrast, it significantly induced c-myc gene expression. Treatment of Caco-2 cells with the c-myc antisense oligonucleotide reversed the inhibitory effect of NOR-4 on CYP3A4 expression induced by 1,25(OH)2D3. These results suggest that the suppression of 1,25(OH)2D3-induced CYP3A4 expression by NO is due to c-myc expression.

Hepatic drug metabolism and transport in patients with kidney disease

The disposition of many drugs is altered in patients with acute (AKD) and chronic kidney disease (CKD). A decline in renal clearance of several drugs has been correlated significantly with residual renal function (ie, creatinine clearance) of subjects. Reductions in nonrenal clearance of some compounds also have been reported and associated with clearance of markers of oxidative and/or conjugative metabolism or P-glycoprotein-mediated transport. Although initial accounts of reduced hepatic microsomal cytochrome P-450 (CYP) content and activity in animal models of AKD and CKD were published almost 25 years ago, it is only in the last decade that technical advances in molecular biology and clinical pharmacology have enabled researchers to begin to characterize the phenotypic expression of individual enzymes and, importantly, distinguish the molecular and/or genetic basis for these changes. The selective modulation of hepatic CYP enzyme activity observed in kidney disease is caused, at least in part, by differentially altered expression of several CYP isoforms. This review summarizes data available through June 2003 regarding the effect of AKD and CKD on drug metabolism. Knowledge of the impact and nature of these alterations associated with kidney disease may facilitate the individualization of medication management in this patient population.

Expression profiles of drug-metabolizing enzyme CYP3A and drug efflux transporter multidrug resistance 1 subfamily mRNAS in small intestine

The purpose of this study is to examine the expression profiles of CYP3A1, CYP3A2, CYP3A9, and CYP3A18 mRNAs as well as multidrug resistance (mdr)1a and mdr1b mRNAs in the liver and small intestine of normal male Wistar rats using a reverse transcription-polymerase chain reaction (PCR). In the rat liver, the PCR products for CYP3A1, CYP3A2, and CYP3A18 were readily detectable, whereas CYP3A9 was slightly and mdr1a and mdr1b barely detected. Surprisingly, no PCR products for CYP3A1 and CYP3A2 were detected in the small intestine, but those for CYP3A9, CYP3A18, and mdr1a were readily detectable, and a faint band for mdr1b was also observed. Both CYP3A9 and CYP3A18 levels were found to be high in the duodenum and decreased from the top to bottom of the gut, indicating regional differences in both CYP3A9 and CYP3A18 expression in the small intestine. In contrast, mdr1a expression increased gradually from the upper to lower intestine. Consequently, it was suggested that drug metabolism in the small intestine of normal rats was mediated by CYP3A9 and CYP3A18 rather than CYP3A1 and CYP3A2. Also, regional differences of CYP3A9, CYP3A18, and mdr1a expression were found in the small intestine. The distributions of CYP3A9 and CYP3A18 were different from the distribution of mdr1a, suggesting the cooperative action of drug clearance pathways. This information is important to drug metabolism research based on ex vivo and in vivo studies using rats.

Human extrahepatic cytochromes P450: function in xenobiotic metabolism and tissue-selective chemical toxicity in the respiratory and gastrointestinal tracts

Cytochrome P450 (CYP) enzymes in extrahepatic tissues often play a dominant role in target tissue metabolic activation of xenobiotic compounds. They may also determine drug efficacy and influence the tissue burden of foreign chemicals or bioavailability of therapeutic agents. This review focuses on xenobiotic-metabolizing CYPs of the human respiratory and gastrointestinal tracts, including the lung, trachea, nasal respiratory and olfactory mucosa, esophagus, stomach, small intestine, and colon. Many CYPs are expressed in one or more of these organs, including CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2A13, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP2F1, CYP2J2, CYP2S1, CYP3A4, CYP3A5, and CYP4B1. Of particular interest are the preferential expression of certain CYPs in the respiratory tract and the regional differences in CYP expression profile in different parts of the gastrointestinal tract. Current research activities on the characterization of CYP expression, function, and regulation in these tissues, as well as future research needs, are discussed.

Exposure-dependent inhibition of intestinal and hepatic CYP3A4 in vivo by grapefruit juice

Consumption of typical quantities of grapefruit juice (GFJ) increases the oral bioavailability of several CYP3A4 substrates without affecting their elimination, consistent with selective inhibition of intestinal but not hepatic CYP3A4. However, increases in the AUCs of CYP3A4 substrates recently associated with the consumption of large amounts of GFJ were similar to those observed with potent inhibitors of hepatic CYP3A4. The current study compared the effects of consuming large quantities and more typical amounts of GFJ on the activity of hepatic and intestinal cytochrome P450 3A4 in vivo, employing the erythromycin breath test (EBT) and oral midazolam pharmacokinetics. This was a two-phase, randomized, placebo-controlled crossover study, with each phase conducted with a separate panel of subjects. In Phase I, 8 male volunteers were randomized to the order of receiving one glass (240 mL) of water (placebo) or double-strength (DS) GFJ tid for 2 days and then 90, 60, and 30 minutes prior to administration of probe drugs on the 3rd day. In Phase II, 16 male volunteers were randomized to the order of receiving one glass of (1) single-strength (SS) GFJ, (2) DS GFJ, and (3) water (placebo). All treatments were administered in a fasted state. There was at least a 7-day washout period between treatments. Probe drugs, administered 30 minutes or 1 hour following each treatment in Phase I or II, respectively, consisted of oral midazolam (2 mg) coadministered with IV [14G N-methyl] erythromycin (0.03 mg). The EBT was performed 20 minutes following erythromycin administration. Blood was collected during the 24 hours following probe drug administration for the analysis of midazolam pharmacokinetics. In Phase I, consumption of one glass of DS GFJ tid for 3 days increased the Cmax of midazolam 3-fold, the AUC 6-fold, and the t1/2 2-fold and decreased the amount of exhaled 14CO2 in all 8 subjects, with a mean decrease in EBT of 18%. In Phase II, consumption of one glass of DS GFJ significantly increased the AUC and Cmax of midazolam approximately 2-fold without a significant effect on the t1/2 of midazolam or the EBT. The effects of consuming one glass of SS GFJ on midazolam pharmacokinetics and the EBT were not significantly different from those of one glass of DS GFJ. It was concluded that consumption of one glass of DS GFJ tid for 3 days significantly increased the AUC, Cmax, and t1/2 of midazolam and reduced EBT values, reflecting inhibition of both hepatic and intestinal CYP3A4. In contrast, consumption of one glass of SS or DS GFJ increased midazolam AUC and Cmax, with little effect on the midazolam t1/2 and EBT values, reflecting preferential inhibition of intestinal CYP3A4. Alterations of midazolam AUC and Cmax induced by nine glasses of DS GFJ were significantly greater than those produced by one glass of SS or DS GFJ. These data suggest that GFJ inhibits intestinal and hepatic CYP3A4 in an exposure-dependent fashion and that patients taking medications that are CYP3A4 substrates are at risk for developing drug-related adverse events if they consume large amounts of grapefruit juice.

Timed-release formulation to avoid drug-drug interaction between diltiazem and midazolam

The purpose of this study was to investigate whether the use of a timed-release (TR) drug formulation can avoid unfavorable pharmacokinetic drug-drug interactions in vivo. First, the effects of the time interval between administration of midazolam and diltiazem on the known drug-drug interaction between these drugs were investigated in dogs. When dogs were given midazolam orally at the same time they were orally given an aqueous diltiazem solution, the area under the plasma concentration-time curves of midazolam increased significantly compared with that of midazolam given orally in the absence of diltiazem. However, there was no significant difference in pharmacokinetics of midazolam when the diltiazem solution was administered 1-2 h after midazolam. Tests on a TR formulation containing diltiazem demonstrated that the first appearance of diltiazem in plasma occurs at 2.6 +/- 0.5 h in dogs. Subsequent tests showed that the plasma concentration-time profile of midazolam after concurrent oral administration of the diltiazem TR formulation was almost the same as that of midazolam administered alone. These results demonstrate that a TR formulation of diltiazem can avoid the interaction between diltiazem and midazolam by creating a time interval between absorption of drugs in vivo, without the need for closely controlling the time of drug administration.

Predicting inductive drug-drug interactions

Until recently, inductive drug-drug interactions have proved difficult to predict prior to formal pharmacokinetic studies in man. Even then, important interactions have often gone unrecognized until clinical sequelae have occurred in the postmarketing phase. Recent advances in the molecular and cellular biology of nuclear receptors have revealed that there are 'sensors' for xenobiotics, which in turn transactivate genes involved in drug metabolism and excretion. Knowledge of these mechanisms has allowed the development of assay systems that detect the potential of drugs to cause gene induction, well before human studies are contemplated.

Regulation of P450 genes by liver-enriched transcription factors and nuclear receptors

Cytochrome P450s (P450s) constitute a superfamily of heme-proteins that play an important role in the activation of chemical carcinogens, detoxification of numerous xenobiotics as well as in the oxidative metabolism of endogenous compounds such as steroids, fatty acids, prostaglandins, and leukotrienes. In addition, some P450s have important roles in physiological processes, such as steroidogenesis and the maintenance of bile acid and cholesterol homeostasis. Given their importance, the molecular mechanisms of P450 gene regulation have been intensely studied. Direct interactions between transcription factors, including nuclear receptors, with the promoters of P450 genes represent one of the primary means by which the expression of these genes is controlled. In this review, several liver-enriched transcription factors that play a role in the tissue-specific, developmental, and temporal regulation of P450s are discussed. In addition, the nuclear receptors that play a role in the fine control of cholesterol and bile acid homeostasis, in part, through their modulation of specific P450s, are discussed.

Improvement of oral drug treatment by temporary inhibition of drug transporters and/or cytochrome P450 in the gastrointestinal tract and liver: an overview

The oral bioavailability of many cytotoxic drugs is low and/or highly variable. This can be caused by high affinity for drug transporters and activity of metabolic enzymes in the gastrointestinal tract and liver. In this review, we will describe the main involved drug transporters and metabolic enzymes and discuss novel methods to improve oral treatment of affected substrate drugs. Results of preclinical and clinical phase I and II studies will be discussed in which affected substrate drugs, such as paclitaxel, docetaxel, and topotecan, are given orally in combination with an inhibitor of drug transport or drug metabolism. Future randomized studies will, hopefully, confirm that this strategy for oral treatment is at least as equally effective and safe as standard intravenous administration of these drugs.

Catalytic activities of cytochrome P450 enzymes and UDP-glucuronosyltransferases involved in drug metabolism in rat everted sacs and intestinal microsomes

1. The use of everted sacs of the small intestine as an enzyme source for studying the metabolism of xenobiotics by cytochrome P450 (P450, CYP) enzymes and UDP-glucuronosyltransferases has been investigated. 2. Most of the drug oxidation activities for testosterone, bufuralol, ethoxyresorufin and 7-ethoxycoumarin resided in the upper part of the everted sacs and in intestinal microsomes. Testosterone 6 beta-hydroxylase activities in the everted sacs were about two times higher than those in the intestinal microsomes. By freezing and thawing treatment, the testosterone 6 beta- and 16 alpha-hydroxylase activities of the everted sacs were considerably decreased, and those of the intestinal microsomes were abolished. 3. Microsomal testosterone 6 beta-hydroxylation, bufuralol 1'-hydroxylation, and pentoxyresorufin and ethoxyresorufin O-dealkylation were inhibited by ketoconazole, quinine, metyrapone and alpha-naphthoflavone respectively. Immunoreactive proteins using anti-CYP2B1 and anti-CYP3A2 antibodies were detected in the upper and middle parts of the rat small intestine. 4. Except for morphine 3-glucuronidation, glucuronidation activities in intestinal microsomes or everted sacs were not dependent on the intestinal region. The lower part of the everted sacs exhibited about 10 times higher morphine-3-glucuronidation activities compared with those of the upper part. The glucuronidation activities of 4-nitrophenol in the everted sacs were 10 times higher than those in microsomes. 5. These results demonstrated that the upper part of rat small intestine serves as the major site for intestinal P450-mediated first-pass metabolism. CYP3A enzymes in rat intestinal microsomes may not be stable but probably play an important role in drug oxidations. The high activity of glucuronidation in the rat small intestine should also be considered in terms of drug metabolism.

Metabolism of N,N-Dipropyl-2-[4-Methoxy-3-(2-Phenyl-Ethoxy)-Phenyl]-Ethyl-Amine-Monohydrochloride (NE-100), A Novel Sigma Ligand: Contribution of Cytochrome P450 Forms Involved in the Formation of Individual Metabolites in Human Liver and Small Intestine

In the present study, human cytochrome P450 (CYP) forms involved in producing the primary metabolites of NE-100 were identified. Major metabolites of NE-100 in human liver microsomes (HLM) were N-depropylation of NE-100 (NE-098), p-hydroxylation of phenyl group of NE-100 (NE-152), m-hydroxylation of phenyl group of NE-100 (NE-163) and O-demethylation of NE-100 (NE-125). Judging from the correlation and inhibition studies, NE-125 and NE-152+163mix formations were predominantly mediated by CYP2D6 and NE-098 formation was mediated by multiple CYP forms at a low NE-100 concentration (0.1 microM) in the HLM. According to relative activity factor (RAF) approaches, all these reactions were predominantly catalyzed by CYP2D6 at a substrate concentration assuming a plasma level of NE-100 (K(m)>>S) in case of the human liver. Depending on the increase in NE-100 concentrations, the rate of contribution for NE-098 and NE-152+163mix formations increased in CYP3A4, although the predominant contribution of CYP2D6 for NE-125 formation did not change. In human intestinal microsomes (HIM), NE-100 was mainly metabolized to NE-098 and NE-152+163mix by CYP3A4. The intrinsic clearance for their formations in HIM was 3.2 and 14.9 times less than those in HLM, respectively, and no formation of NE-125 was observed in HIM. These results strongly suggest that CYP2D6 is the predominant form for NE-100 metabolism in the human liver in in vivo conditions (K(m)>>S) and the liver plays a more important role than does the small intestine in the first pass metabolism.

Differences in cytochrome P450 forms involved in the metabolism of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100), a novel sigma ligand, in human liver and intestine

N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100) has been developed to treat subjects with schizophrenia. This drug is mainly excreted in the form of oxidative metabolites. In the present study, identification of p450 forms involved in the metabolism was carried out using human livers and intestinal microsomes (HLM and HIM). Eadie-Hofstee plots for NE-100 disappearance in HLM were biphasic, thus indicating the involvement of at least two p450 forms. The metabolism of NE-100 was mediated with recombinant CYP1A1, CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. A significant correlation was observed between activities of NE-100 metabolism and dextromethorphan O-demethylation (a specific activity for CYP2D6) or testosterone 6beta-hydroxylation (a specific activity for CYP3A4) in HLM. The activity of NE-100 metabolism was inhibited by approximately 80% by an anti-CYP2D6 antibody and only by quinidine among the p450-selective inhibitors at a low substrate concentration (0.1 microM). In contrast, with a high substrate concentration (10 microM), the activity was inhibited by an anti-CYP3A4 antibody and by ketoconazole. On the other hand, in HIM, the Eadie-Hofstee plots for NE-100 disappearance were monophasic, and the metabolism was strongly inhibited by an anti-CYP3A4 antibody and by ketoconazole but not by other inhibitors used. These results strongly suggest that NE-100 has different profiles regarding metabolism between liver and intestine. During absorption, NE-100 is mainly metabolized by CYP3A4 in the intestine and thereafter by CYP2D6 in the liver in the presence of therapeutic doses.

The Intestinal First-pass Metabolism of Substrates of CYP3A4 and P-glycoprotei—Quantitative Analysis Based on Information from the Literature

It is suggested that the bioavailability of CYP3A4 substrates might be low due to first-pass metabolism in the small intestine, and it is possible that P-glycoprotein (P-gp) may influence first-pass metabolism in a co-operative manner. We have collected information of the pharmacokinetics of CYP3A4 substrates to evaluate the fraction absorbed (Fa), intestinal availability (Fg) and hepatic availability (Fh) and have investigated the intestinal first-pass metabolism and the effect of P-gp on this. The pharmacokinetic data involved ten compounds metabolized by CYP3A4 in humans, with and without an inhibitor or inducer. FaFg, which is the product of Fa and Fg, and Fh were calculated using three liver blood flow rates (17.1, 21.4, 25.5 mL/min/kg) in consideration of variations in the liver flow rate. Co-administration with an inhibitor of CYP3A4 and treatment of an inducer of CYP3A4 caused an increase and decrease in the FaFg of CYP3A4 substrates, regardless of the liver blood flow, indicating that CYP3A4 substrates exhibit a first-pass effect in their metabolism. This holds true regardless of whether the compounds are P-gp substrates or not. No relationship was observed between FaFg and Fh, regardless of the hepatic blood flow rate and the P-gp substrates. The FaFg of both P-gp and non P-gp substrates decreased as the hepatic intrinsic clearance increased. FaFg was markedly reduced when the hepatic intrinsic clearance was more than 100 mL/min/kg. This in vivo intrinsic clearance corresponds to an in vitro intrinsic clearance of 78 muL/min/mg human hepatic microsomal protein, equivalent to a half-life of 8.9 min for the substrate in a commonly used metabolic stability test with human microsomes (1 mgMs protein/mL). This phenomenon was not observed in substrates of CYP isoforms other than CYP3A4. In conclusion, it is suggested that CYP3A4 substrates which have a hepatic intrinsic clearance of 100 mL/min/kg exhibit a low bioavailability due to intestinal first-pass metabolism, regardless of whether they are substrates of P-gp or not.

Is quinine a suitable probe to assess the hepatic drug-metabolizing enzyme CYP3A4?

AIMS

To evaluate the antimalarial agent quinine as a potential in vivo probe for hepatic cytochrome P450 (CYP) 3A4 activity.

METHODS

Ten healthy adult volunteers received, by randomized crossover design, either a single oral dose of quinine sulphate (600 mg) alone, or quinine sulphate (600 mg) plus the CYP3A4 inhibitor troleandomycin (TAO; 500 mg every 8 h). Plasma and urine samples were collected before quinine administration, and up to 48 h thereafter, then analysed by h.p.l.c. for both quinine and its CYP3A4-generated metabolite, 3-hydroxyquinine. During both phases, the erythromycin breath test (ERMBT) was administered at specific times to assess hepatic CYP3A4 activity.

RESULTS

Compared with control, TAO treatment significantly decreased the mean time-averaged ERMBT result by 77% (95% CI, 68, 85%), the mean apparent oral clearance of quinine (CL/F ) by 45% (95% CI, 39, 52%), and the mean apparent formation clearance of 3-hydroxyquinine (CL3-OH) by 81% (95% CI, 76, 87%). There was no correlation between the TAO-mediated percent decrease in the time-averaged ERMBT result and the percent decrease in CL/F or in CL3-OH. When TAO and control treatments were analysed separately, there were no significant correlations between the time-averaged ERMBT result and CL/F, CL3-OH, or single plasma quinine concentration at 12, 24, and 48 h.

CONCLUSIONS

Quinine may be a useful probe to detect inhibition of liver CYP3A4 activity within an individual. Further studies are needed to determine whether it can provide a quantitative measure of CYP3A4 activity suitable for intersubject comparison.

Molecular cloning and characterization of mouse CYP2J6, an unstable cytochrome P450 isoform

A cDNA encoding a new cytochrome P450 was cloned from a mouse liver library. Sequence analysis revealed that this 2046-bp cDNA encodes a 501-amino acid polypeptide that is 72-94% identical to other CYP2J subfamily P450s and is designated CYP2J6. Northern analysis demonstrated that CYP2J6 transcripts are abundant in the small intestine and present at lower levels in other mouse tissues. In situ hybridization revealed that CYP2J6 mRNAs are present in luminal epithelial cells of the gastrointestinal mucosa. The CYP2J6 cDNA was expressed in Sf9 cells using baculovirus. The heterologously expressed CYP2J6 protein displayed a typical P450 CO-difference spectrum; however, the protein was unstable as evidenced by the loss of the Soret maxima at 450nm and the appearance of a 420nm peak when CYP2J6-expressing cells were disrupted by mechanical homogenization, sonication, or freeze-thaw. Immunoblotting of mouse microsomes with the anti-human CYP2J2 IgG, which cross-reacts with rodent CYP2Js, demonstrated the presence of multiple distinct murine CYP2J immunoreactive proteins in various tissues. Immunoblotting with an antibody to a CYP2J6-specific peptide detected a prominent 55-57kDa protein in Sf9 cell extracts expressing recombinant CYP2J6 but did not detect a protein of similar molecular mass in mouse small intestinal microsomes. Mixing experiments demonstrated that recombinant CYP2J6 is degraded rapidly in the presence of small intestinal microsomes consistent with proteolysis at highly sensitive sites. Sf9 cells, which express both CYP2J6 and NADPH-P450 oxidoreductase, metabolized benzphetamine but not arachidonic acid. We conclude that CYP2J6 is an unstable P450 that is active in the metabolism of benzphetamine, but not arachidonic acid.

Differential induction of midazolam metabolism in the small intestine and liver by oral and intravenous dexamethasone pretreatment in rat

1. Midazolam is metabolized in the rat by CYP3A enzymes to 4-OH-midazolam (4-OH-MDZ) and 1'-OH-midazolam (1'-OH-MDZ). The induction of midazolam metabolism was studied in male Wistar rats treated with dexamethasone (50 mg kg(-1) day(-1)) during 4 days via the oral or intravenous routes. Microsomes were prepared from the liver and the proximal small intestine and in vitro metabolism of midazolam was determined. In addition, CYP3A1- and CYP3A2-like protein levels were measured by gel electrophoresis and immunoblotting. 2. The V(max)'s (mean SEM) for 4-OH-MDZ and 1'-OH-MDZ formation were much lower in intestinal (0.078 +/- 0.002 and 0.074 +/- 0.002 microM min(-1) mg(-1) protein, respectively) compared with hepatic microsomes prepared from the uninduced rat (0.870 +/- 0.007 and 0.310 +/- 0.020 microM min(-1) mg(-1) protein, respectively). Induction by oral or intravenous dexamethasone pretreatment led to significant increases in V(max) for 4-OH-MDZ and 1'-OH-MDZ by both intestinal and hepatic microsomes. Oral dexamethasone pretreatment via the oral route resulted in a more pronounced increase in V(max) compared with intravenous administration of the inducer. 3. CYP3A1 and CYP3A2 protein levels in liver microsomes were significantly increased following oral (3.7- and 3.2-fold, respectively) or intravenous (2.6- and 2.1-fold, respectively) pretreatment with dexamethasone. On the contrary, only oral dexamethasone pretreatment resulted in a significant change in intestinal CYP3A2-like protein (7.3-fold). A slight difference in the migration distance of the immunoreactive band for CYP3A2 was also observed for intestinal microsomes. 4. These results suggest that intestinal CYP3A enzymes in the rat differ from hepatic CYP3A1 and CYP3A2. They also demonstrate that systemic dexamethasone administration can induce intestinal microsome activity.

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

Reversible and irreversible inhibition of CYP3A enzymes by tamoxifen and metabolites

1. Preliminary studies have identified cytochrome P450 (CYP) 3A4 and CYP1B1 as the human CYPs inhibited by tamoxifen. To quantify the inhibitory potency of tamoxifen and its major metabolites, the metabolism of three substrates of CYP3A, midazolam, diltiazem and testosterone, and 7-ethoxyresorufin as a substrate of CYP1B1 were examined in catalytic assays carried out using human liver microsomes and cDNA-expression systems. 2. Tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen and 3-hydroxytamoxifen reversibly inhibited midazolam 1'-hydroxylation, diltiazem N-demethylation and testosterone 6beta-hydroxylation with K(i) ranging from 3 to 37 micro M in human liver microsomes. Tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen and 3-hydroxytamoxifen also reversibly inhibited the activity of cDNA-expressed CYP3A4, CYP3A5 and CYP1B1. 3. Tamoxifen and N-desmethyltamoxifen exhibited time-dependent inactivation of testosterone 6beta-hydroxylation by cDNA-expressed CYP3A4 (+ cytochrome b5) yielding k(inact) and K(i) of 0.04 min(-1) and 0.2 micro M for tamoxifen and 0.08 min(-1) and 2.6 micro M for N-desmethyltamoxifen. A metabolic intermediate complex (MIC) was also formed by tamoxifen and N-desmethyltamoxifen with CYP3A4 (+ cytochrome b5) and CYP3A4 but not with CYP3A5 or CYP3A7. Pre-incubation with 4-hydroxytamoxifen and 3-hydroxytamoxifen did not result in any CYP3A inactivation or detectable MIC formation. There was no detectable time-dependent inactivation or MIC formation with tamoxifen or metabolites with CYP1B1. 4. These data indicate that tamoxifen and its three major metabolites are effective inhibitors of CYP3A in vitro and that tamoxifen and N-desmethyltamoxifen are effective mechanism-based inhibitors. Thus, caution should be exercised when tamoxifen is coadministered with other CYP3A substrates.

Alteration of cellular phosphorylation state affects vitamin D receptor-mediated CYP3A4 mRNA induction in Caco-2 cells

Expression of cytochrome P450 3A4 (CYP3A4) is induced by 1,25-dihydroxyvitamin D(3)(1,25(OH)(2)D(3)) in Caco-2 cells. However, since a typical vitamin D responsive element has not been found in the 5(')-flanking region of the CYP3A4 gene, the mechanism of 1,25(OH)(2)D(3)-induced CYP3A4 mRNA expression is poorly understood. In the present study, we demonstrated that vitamin D receptor (VDR) is a critical factor for the induction using the antisense oligonucleotide technique. In addition, we found that treatment of Caco-2 cells with the protein kinase C (PKC) inhibitors, staurosporine and GF109203X, and the tyrosine kinase inhibitor, genistein, but not with the protein kinase A inhibitor, H-89, suppressed CYP3A4 mRNA induction by 1,25(OH)(2)D(3). The depletion of PKC by prolonged treatment with phorbol ester abolished the induction. On the other hand, protein kinase inhibitors used had no effects on the constitutive expression of VDR mRNA. Therefore, these observations suggest that 1,25(OH)(2)D(3)-induced CYP3A4 mRNA expression might be involved in phosphorylation events in addition to transcriptional regulation via VDR. However, 1,25(OH)(2)D(3) did not rapidly activate PKC in the Caco-2 cells used, while the treatment with staurosporine and GF109203X, but not genistein, decreased basal PKC activity by approximately 30% of the controls. Taken together, these findings suggest that the change in the phosphorylation state via PKC and tyrosine kinase might, at least in part, modulate 1,25(OH)(2)D(3)-induced CYP3A4 mRNA expression via VDR.

Piperine, a major constituent of black pepper, inhibits human P-glycoprotein and CYP3A4

Dietary constituents (e.g., in grapefruit juice; NaCl) and phytochemicals (e.g., St. John's wort) are important agents modifying drug metabolism and transport and thereby contribute to interindividual variability in drug disposition. Most of these drug-food interactions are due to induction or inhibition of P-glycoprotein and/or CYP3A4. Preliminary data indicate that piperine, a major component of black pepper, inhibits drug-metabolizing enzymes in rodents and increases plasma concentrations of several drugs, including P-glycoprotein substrates (phenytoin and rifampin) in humans. However, there are no direct data whether piperine is an inhibitor of human P-glycoprotein and/or CYP3A4. We therefore investigated the influence of piperine on P-glycoprotein-mediated, polarized transport of digoxin and cyclosporine in monolayers of Caco-2 cells. Moreover, by using human liver microsomes we determined the effect of piperine on CYP3A4-mediated formation of the verapamil metabolites D-617 and norverapamil. Piperine inhibited digoxin and cyclosporine A transport in Caco-2 cells with IC(50) values of 15.5 and 74.1 microM, respectively. CYP3A4-catalyzed formation of D-617 and norverapamil was inhibited in a mixed fashion, with K(i) values of 36 +/- 8 (liver 1)/49 +/- 6 (liver 2) and 44 +/- 10 (liver 1)/77 +/- 10 microM (liver 2), respectively. In summary, we showed that piperine inhibits both the drug transporter P-glycoprotein and the major drug-metabolizing enzyme CYP3A4. Because both proteins are expressed in enterocytes and hepatocytes and contribute to a major extent to first-pass elimination of many drugs, our data indicate that dietary piperine could affect plasma concentrations of P-glycoprotein and CYP3A4 substrates in humans, in particular if these drugs are administered orally.

Ursodeoxycholic acid (UDCA) prevents DCA effects on male mouse liver via up-regulation of CYP [correction of CXP] and preservation of BSEP activities

To investigate whether ursodeoxycholic acid (UDCA) can prevent metabolic impairment induced by deoxycholic acid (DCA), we evaluated the effects of these bile acids on murine CYP enzymes and the relationship with canalicular bile salt export pump (Bsep) expression. In Swiss Albino CD1 mice, UDCA and DCA were injected intraperitoneally either singly, concurrently, or sequentially (UDCA 1 hour before DCA) at equimolar 24.4 mg/kg body weight (BW) doses. CYP content, NADPH-CYP-c-reductase, and individual mixed function oxidases (MFO) were measured 24 hours later. Modulations were observed mainly in males: whereas DCA decreased MFO activities to various isoenzymes with respect to controls (up to 43%, CYP1A2-linked activity), UDCA boosted them (up to 6-fold, testosterone 16 beta-hydroxylase); concurrent administration of UDCA and DCA provided a preventive effect, enhancing MFO activity with respect to single administration of DCA by up to 4.4-fold in the CYP3A1/2 and CYP2B1/2 (6 beta-hydroxylase) and by 2.1-fold in the CYP2E1 (p-nitrophenol hydroxylase). In males (but not females), sequential administration (UDCA then DCA) produced a rather similar protective pattern, but the extent of recovery was generally smaller. Western immunoblotting results for the most affected isoenzymes (CYP3A1/2 and CYP2E1) and Bsep confirmed that UDCA can both prevent and reduce the CYP-dependent MFO inactivation and Bsep down-regulation caused by DCA. These findings may shed further light on the mechanisms responsible for UDCA's protective role in the treatment of cholestatic liver disease.

The mucosa of the small intestine: how clinically relevant as an organ of drug metabolism?

The intestinal mucosa is capable of metabolising drugs via phase I and II reactions. Increasingly, as a result of in vitro and in vivo (animal and human) data, the intestinal mucosa is being implicated as a major metabolic organ for some drugs. This has been supported by clinical studies of orally administered drugs (well-known examples include cyclosporin, midazolam, nifedipine and tacrolimus) where intestinal drug metabolism has significantly reduced oral bioavailability. This review discusses the intestinal properties and processes that contribute to drug metabolism. An understanding of the interplay between the processes controlling absorption, metabolism and P-glycoprotein-mediated efflux from the intestinal mucosa into the intestinal lumen facilitates determination of the extent of the intestinal contribution to first-pass metabolism. The clinical relevance of intestinal metabolism, however, depends on the relative importance of the metabolic pathway involved, the therapeutic index of the drug and the inherent inter- and intra-individual variability. This variability can stem from genetic (metabolising enzyme polymorphisms) and/or non-genetic (including concomitant drug and food intake, route of administration) sources. An overwhelming proportion of clinically relevant drug interactions where the intestine has been implicated as a major contributor to first-pass metabolism involve drugs that undergo cytochrome P450 (CYP) 3A4-mediated biotransformation and are substrates for the efflux transporter P-glycoprotein. Much work is yet to be done in characterising the clinical impact of other enzyme systems on drug therapy. In order to achieve this, the first-pass contributions of the intestine and liver must be successfully decoupled.

Dose-dependent increase of saquinavir bioavailability by the pharmaceutic aid cremophor EL

AIMS

Bioavailability of orally administered drugs depends on several factors including active excretion, e.g. by P-glycoprotein (PGP), and presystemic metabolism, e.g. by cytochrome P450 3A (CYP3A), in both gastrointestinal tract and liver. Many drugs including saquinavir are substrates of both PGP and CYP3A. It was the aim of this study to test whether the extremely low bioavailability of saquinavir can be increased dose-dependently in vivo by cremophor EL, an 'inactive' pharmaceutic aid known to inhibit PGP in vitro.

METHODS

In a randomized, placebo-controlled, double-blind, four phase cross-over design single doses of oral saquinavir (Invirase, 600 mg, without food) were administered with increasing single doses of oral cremophor EL (up to 5000 mg) to eight healthy, male individuals. Saquinavir plasma concentrations were determined by LC/MS/MS up to 48 h after intake. Main outcome measures were area under the plasma concentration time curve (AUC), peak concentration (Cmax), time to reach Cmax (tmax) and terminal elimination half-life (t(1/2)).

RESULTS

Cremophor EL dose-dependently increased Cmax, AUC(0,4 h), and AUC(0,infinity) of saquinavir. As compared with placebo, the increment observed after 5000 mg cremophor EL was 13-fold for both Cmax and AUC(0,4 h) and 5-fold for AUC(0,infinity). The terminal half-life and the time to reach Cmax (tmax) were unchanged.

CONCLUSIONS

Cremophor EL increased the systemic availability of saquinavir without affecting its elimination suggesting that cremophor EL is not devoid of pharmacological action and acts as a modulator of the absorption process, probably by inhibiting intestinal PGP.

Intestinal metabolism promotes regional differences in apical uptake of indinavir: coupled effect of P-glycoprotein and cytochrome P450 3A on indinavir membrane permeability in rat

The purpose of this study was to investigate transport and metabolism contributions to low indinavir permeability in rat ileum and enhanced drug permeability in the jejunum. Permeability models utilized included single pass in situ rat intestinal perfusion and rat intestinal tissue mounted in Ussing chambers. Intestinal metabolism was measured by fractional appearance of metabolite (F(met)), determined as the percentage of the predominant metabolite M6 over luminal loss of indinavir in the perfusion model. Among the results, indinavir exhibited bidirectional transport across rat ileum. Verapamil and cyclosporin A inhibited net flux by 37 and 38%, respectively. Intestinal metabolism of indinavir was most significant in upper jejunum (F(met) = 65.78 +/- 19.02%), decreasing in midjejunum (F(met) = 31.58 +/- 5.63%). M6 was not detectable in ileum or colon. Western blot analysis of rat intestinal mucosal tissue samples confirmed that the axial expression of CYP3A was consistent with the regional pattern of formation of M6. Intestinal metabolism was saturable and could be inhibited by the CYP3A inhibitor, ketoconazole. A low luminal concentration of indinavir (1 microM) was associated with high F(met) (87.90 +/- 14.30%), whereas a high luminal concentration of indinavir (50 microM) was associated with low F(met) (35.84 +/- 11.59%). In the presence of ketoconazole, both F(met) and permeability of indinavir were reduced in the jejunum. These results suggest that 1) intracellular metabolism of indinavir enhances apical uptake of indinavir in the rat jejunum as a function of the increased concentration gradient generated across the epithelial cell membrane and 2) the efflux transporter P-glycoprotein limits apical uptake of indinavir in the ileum, resulting in low apparent permeability.

Regulation of cyp3a gene transcription by the pregnane x receptor

The pregnane X receptor (PXR) is a promiscuous nuclear receptor that has evolved to protect the body from toxic chemicals. PXR is activated by a structurally diverse collection of xenobiotics, including several widely used prescription drugs. Various lipophilic compounds produced by the body, such as bile acids and steroids, also activate PXR. PXR stimulates the transcription of cytochrome P450 3A monooxygenases and other genes involved in the detoxification and elimination of these potentially harmful chemicals. Assays that detect PXR activation have important implications for the design of future drugs in two respects. On the one hand, PXR activation assays can be used to determine whether candidate drugs are likely to induce CYP3A gene expression and interact with other medicines. On the other hand, PXR agonists may prove useful in the treatment of diseases in which toxic metabolites accumulate, such as cholestatic liver disease.

Roles of the jejunum and ileum in the first-pass effect as absorptive barriers for orally administered tacrolimus

BACKGROUND

The immunosuppressant tacrolimus shows poor and variable bioavailability following oral administration in clinical use. Recently, the hepatic and intestinal metabolisms, or first-pass effect, of tacrolimus have been suggested to be responsible for its bioavailability. In the present study, we investigated the respective contribution of the jejunum and ileum to the first-pass effect of tacrolimus in rats.

METHODS

The metabolism of tacrolimus in everted sacs of the duodenum, jejunum, and ileum was examined. Tacrolimus was administered intravenously or intraintestinally to sham-operated, jejunum-resected, or ileum-resected rats. Blood samples were collected over a 240-min period, and whole-blood tacrolimus concentrations were measured by semiautomated microparticle enzyme immunoassay. The pharmacokinetic parameters of tacrolimus in each group were estimated.

RESULTS

The metabolic activity of tacrolimus appeared to be the highest in the everted sacs of the duodenum. The bioavailability of tacrolimus in the jejunum- or ileum-resected rats was higher than that in sham-operated controls. On the other hand, the time to peak concentration in the jejunum-resected rats was about twofold slower than those in ileum-resected and sham-operated rats.

CONCLUSIONS

These results suggested that the first-pass effect of tacrolimus in the small intestine shows regional differences and the extraction of tacrolimus in the small intestine consists of the amount of extraction in the jejunum and ileum. In addition, the ileum rather than the jejunum as a graft of segmental small bowel transplantation would be useful to avoid the adverse effects of tacrolimus.

Effect of oral ketoconazole on first-pass effect of nifedipine after oral administration in dogs

The long-term oral ketoconazole (KTZ) treatment extensively inhibits hepatic CYP3A activity. We investigated the effect of the KTZ treatment on hepatic and intestinal extraction of nifedipine (NIF) using beagle dogs. Four dogs were given orally KTZ for 20 days (200 mg, bid). NIF was administered either intravenously (0.5 mg/kg) or orally (20 mg) 10 and 20 days before the KTZ treatment and 10 and 20 days after start of KTZ treatment. CLtot of NIF after intravenous administration decreased to about 50% during the KTZ treatment. C(max) and AUC after oral administration increased to 2.5-fold and fourfold, respectively, by the KTZ treatment. The hepatic extraction ratio of NIF decreased to about a half by KTZ. A significant decrease in intestinal extraction ratio was not observed. In conclusion, the KTZ treatment inhibits hepatic extraction more profoundly than intestinal extraction of NIF. Therefore, inhibition of hepatic extraction of NIF by the KTZ treatment mainly results in substantial increase in systemic bioavailability in dogs. Because KTZ inhibits human CYP3A activities similar to canine CYP3A activities, the long-term oral KTZ treatment may dramatically increase bioavailability of NIF or other CYP3A substrates in humans.

Unmasking the dynamic interplay between intestinal P-glycoprotein and CYP3A4

Drug efflux by intestinal P-glycoprotein (P-gp) is known to decrease the oral bioavailability of many CYP3A4 substrates. We hypothesized that the interplay occurring between P-gp and CYP3A4 at the apical membrane would increase the opportunity for drug metabolism. To define the roles of P-glycoprotein (P-gp) and CYP3A4 in controlling the extent of intestinal absorption and metabolism, two substrates were tested. The transport, metabolism, and intracellular levels of N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K77, a cysteine protease inhibitor; P-gp and CYP3A4 substrate) and felodipine (CYP3A4 substrate only) were measured across CYP3A4-transfected Caco-2 cells in the presence of an inhibitor of CYP3A4 and P-gp, cyclosporine (CsA), or an inhibitor of P-gp and not CYP3A4, GG918 (N-[4-[2-(1,2,3,4-tetrahydro-6,7- dimethoxy-2-isoquinolinyl)-ethyl]-phenyl]-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamine). The extent of metabolism was measured by calculating the extraction ratio (ER) across the cells, while accounting for intracellular changes occurring with P-gp inhibition. The (A)pical to (B)asolateral and B-->A ERs for K77 were 0.33 and 0.06, respectively. These changed with GG918 to 0.14 and 0.12 and with CsA to 0.06 and 0.04. Felodipine ERs were similar in both directions, 0.26 and 0.24 (A-->B and B-->A), and were unchanged in the presence of GG918 but decreased with CsA (0.14 and 0.11). The K77 absorption rate was increased 5 and 4.2-fold in the presence of CsA and GG918, respectively, whereas no change was observed for felodipine absorption. The decreased A-->B ER and increased absorption of K77 with GG918 suggest that P-gp influences the extent of drug metabolism in the intestine via prolonging the access of drugs to CYP3A4 near the apical membrane and decreasing transport across the cells.

Investigation of the coordinated functional activities of cytochrome P450 3A4 and P-glycoprotein in limiting the absorption of xenobiotics in Caco-2 cells

The coordination of the functional activities of intestinal CYP3A4 and P-gp in limiting the absorption of xenobiotics in Caco-2 cells was investigated. Growing Caco-2 cells were exposed to increasing concentrations of doxorubicin (1-2 microM) in plastic flasks to encourage a subpopulation of cells, that displayed an intrinsically higher multidrug resistance (mdr) phenotype than the parent cells, to survive and grow. Doxorubicin-exposed (hereinafter referred to as type I cells) and nonexposed Caco-2 cells (parent cells) on collagen-coated inserts were also treated with either 0 (control) or 0.25 microM 1alpha,25-dihydroxyvitamin D(3) to promote cellular CYP3A4 expression. Increased P-gp protein expression, as detected by Western blotting, was noted in type I cells (213 +/- 54.35%) compared to that of parent cells (100 +/- 6.05%). Furthermore, they retained significantly less [(3)H]vincristine sulphate (p < 0.05), a P-gp substrate, after efflux (272.89 +/- 11.86 fmol/mg protein) than the parent cells (381.39 +/- 61.82 fmol/mg protein). The expression of CYP3A4 in parental cells after 1alpha,25-dihydroxyvitamin D(3) treatment was quantified to be 76.2 +/- 7.6 pmol/mg protein and comparable with that found in human jejunal enterocytes (70.0 +/- 20.0 pmol/mg protein). Type I cells, however, expressed a very low quantity of CYP3A4 both before and after the treatment that was beyond the minimum detection limit of Western blotting. Functionally, the rates of 1-hydroxylation of midazolam by CYP3A for both cell types ranged from 257.0 +/- 20.0 to 1057.0 +/- 46.0 pmol/min/mg protein. Type I cells, although having a higher P-gp expression and activity comparatively, metabolized midazolam less extensively than the parent cells. The results suggested that there were noncoordinated functional activities of intestinal CYP3A4 and P-gp in Caco-2 cells, although they both functioned independently to minimize intestinal epithelial absorption of xenobiotics.

The effects of an oral contraceptive containing ethinyloestradiol and norgestrel on CYP3A activity

AIMS

To examine the effects of an oral contraceptive containing ethinyloestradiol and norgestrel on intestinal and hepatic CYP3A activity using midazolam as a probe substrate.

METHODS

In a nonblinded sequential study, nine healthy women received simultaneous doses of intravenous midazolam (0.05 mg kg(-1)) and oral 15N3-midazolam (3 mg) on days 0, 4, 6, 8, and 14. On study day 5, Ovral(50 microg ethinyloestradiol/500 microg norgestrel) was administered for 10 days. Serum and urine samples were assayed for midazolam, 15N3-midazolam and metabolites by liquid chromatography-mass spectrometry. A Digit Symbol Substitution Test (DSST) was used to assess changes in the pharmacodynamic activity of midazolam.

RESULTS

Moderate (% CV 26-46) interindividual variability in the pharmacokinetics of midazolam were observed. Compared with baseline, AUC(0,infinity)iv ratios (95% CIs) after 2, 4, and 10 days treatment with OC were 89% (79, 101), 96% (85, 109), and 88% (77, 99), respectively. The AUC(0,infinity)oral ratios (95% CIs) were 101% (82, 125), 105% (85, 130), and 114% (92, 141), respectively, after 2, 4, and 10 days OC treatment compared with baseline. Concomitant administration of the oral contraceptive, Ovral for 2, 4 or 10 days did not significantly alter the area under the curve, clearance, or half-life of midazolam after either oral or intravenous administration. No alterations in pharmacodynamic effects of midazolam were observed between treatment days. Mean DSST scores strongly correlated with mean total midazolam blood concentrations (r = -0.936).

CONCLUSIONS

Administration of Ovral for 10 days had no impact on intestinal or hepatic CYP3A activity as determined by midazolam metabolism.

Induction of multidrug resistance-1 and cytochrome P450 mRNAs in human mononuclear cells by rifampin

Reverse transcription-polymerase chain reaction (RT-PCR) and quantitative, competitive RT-PCR were used to examine the capability of rifampin to induce the expression of mRNA derived from multidrug resistance-1 (MDR1) and drug-metabolizing cytochrome P450 (P450) genes in the mononuclear fraction (lymphocytes) of human blood. A total of 50 healthy volunteers (age, 18-74) participated in two studies in which 600 mg of rifampin was administered orally once daily in the evening for 7 days. Twenty of these individuals also received fexofenadine before and after rifampin dosing. MDR1 and CYP2C8 mRNAs were expressed in 100% (50 of 50) and 95% (35 of 37) of individuals, respectively, at baseline. A significant (P < 0.05; n = 37) increase in the expression of MDR1 mRNA from 176,900 +/- 122,000 to 248,500 +/- 162,300 molecules/microg of RNA was observed following rifampin administration in the human lymphocytes. There was no significant (P > 0.05) difference in MDR1 mRNA expression between males and females at baseline. Interestingly, 58% of the individuals (n = 29) demonstrated a 120% increase [95% confidence interval (CI); 120%; range, 81-153%; responders] in MDR1 mRNA expression. In contrast, the remaining 42% of individuals (n = 21) exhibited a mean decrease of -5.2% (95% CI; -5.2%; range, -15 to +4%; nonresponders). Rifampin steady-state trough serum concentrations were not significantly different (P > 0.05) between responders and nonresponders. Likewise, there was no relationship between the observed induction in MDR1 mRNA expression in lymphocytes and the observed increase in fexofenadine oral clearance in twenty volunteers. The mRNA of CYP2E1, CYP3A5, CYP3A7, CYP4A11, and CYP4B1 genes were variably expressed at baseline and following rifampin treatment. In contrast, CYP2C9 and CYP3A4 mRNAs were undetectable in lymphocytes both before and after rifampin dosing. Interindividual variability in baseline expression and inducibility of MDR1 and P450 mRNA in human lymphocytes appeared to be substantial and may not reflect the expression of these enzymes in other tissues.

Immunohistochemical localization and differential expression of cytochrome P450 3A27 in the gastrointestinal tract of rainbow trout

In mammals the cytochrome P450 3A (CYP3A) subfamily isoforms are primarily expressed in liver and intestines with lesser amounts found in other tissues. The aim of this study was to examine the cellular localization and the expression pattern of CYP3A27 in the gastrointestinal tract (GI tract) of a freshwater teleost species, the rainbow trout (Oncorhynchus mykiss), a fish model used extensively for toxicological and carcinogenesis research. Using an avidin biotinylated enzyme complex and 3,3'-diaminobenzidine staining, strong cytoplasmic immunohistochemical staining was observed for CYP3A27 protein in hepatocytes and in enterocytes of the intestinal ceca and the proximal descending intestine when probed with a polyclonal antibody raised against rainbow trout P450 LMC5, a CYP3A protein. The intensity of epithelial staining decreased distally along the GI tract with faint staining observed in the epithelial cells examined near the vent. Western blot analysis was supportive of the immunohistochemistry results. Northern blot analysis also demonstrated that CYP3A27 mRNA was expressed along the entire GI tract. The major area of CYP3A27 mRNA expression was in the intestinal ceca, followed by the proximal descending intestine, at levels that were about three- to five-fold and two- to four-fold, respectively, greater than seen in the liver of the fish studied. Monooxygenase activities of intestinal ceca microsomes against testosterone and progesterone confirmed the presence of active CYP3A enzyme in this tissue. These results suggest that the intestine of rainbow trout may possesses substantial capacity for first-pass metabolism of xenobiotics by CYP3A27, which makes it an excellent model in which to study the consequence of such metabolism.

CYP3A4, CYP3A5, and MDR1 in human small and large intestinal cell lines suitable for drug transport studies

The aim of this study was to find a cell culture model of the intestinal epithelium for use in studies of CYP3A4-mediated first-pass metabolism of drugs and also for studies of the interplay between CYP3A4 metabolism and P-glycoprotein efflux. For this purpose, the expression of CYP3A4, CYP3A5, and MDR1 mRNA was studied in three cell lines of the normal human intestinal epithelium and three transformed cell lines of colonic (Caco-2) origin. Surprisingly, only transformed cell lines were induced by 1alpha,25-dihydroxy vitamin D3 (D3) to express high amounts of CYP3A4. In contrast to the original findings for this model, the monolayer integrity was maintained during D3 treatment. Levels of CYP3A mRNA expression in Caco-2 and TC7 cells differed dramatically. The highest levels of CYP3A4 and lowest levels of CYP3A5 mRNA expression were observed in D3 treated Caco-2 cells of high passage numbers, resulting in a CYP3A4/3A5 expression ratio greater than fourfold higher than that seen in TC7 cells. Functional studies, using the CYP3A probe testosterone, showed that CYP3A activity was completely absent only in uninduced Caco-2 cells. After D3 induction, high levels of the metabolite were produced in both cell lines (149.4 +/- 12.3 and 86.5 +/- 3.8 pmol 6beta-OH testosterone/min/mg cellular protein from 75 microM testosterone in Caco-2 and TC7 cells, respectively). The maximum velocity (Vmax) and the apparent Michaelis constant (Km) for the 6beta-hydroxylation of testosterone by CYP3A4 in intact Caco-2 monolayers were similar to those obtained from human intestinal microsomes. Only minor changes in P-glycoprotein activity were observed when the metabolically stable P-glycoprotein substrate celiprolol was used. In conclusion, these results show that the features of the generally available Caco-2 cell line from American Type Culture Collection make it suitable for studies of CYP3A4-mediated first-pass metabolism and also for studies of the interplay between CYP3A4 and drug efflux mechanisms.

Strategies to overcome simultaneous P-glycoprotein mediated efflux and CYP3A4 mediated metabolism of drugs

Cytochrome P450 3A4 (CYP3A4), abundant in both the liver and upper intestinal enterocytes, limits the systemic bioavailability of xenobiotics. P-glycoprotein (P-gp), the MDR1 gene product, is also known to reduce the oral bioavailability of the drug molecules. High cellular expression of P-gp and CYP3A4 in mature intestinal enterocytes and their similar substrate specificity suggest that the function of these proteins may be complementary and may form a co-ordinated intestinal barrier. Various ongoing preclinical and clinical studies have demonstrated that the oral bioavailability of various P-gp and/or CYP3A4 substrates can be increased by simultaneous administration of P-gp and/or CYP3A4 inactivators. The current review describes the background and summarises several proposed hypotheses in modifying oral bioavailability by various drug-inhibitor interactions.

The gut as a barrier to drug absorption: combined role of cytochrome P450 3A and P-glycoprotein

Intestinal phase I metabolism and active extrusion of absorbed drug have recently been recognised as major determinants of oral bioavailability. Cytochrome P450 (CYP) 3A, the major phase I drug metabolising enzyme in humans, and the multidrug efflux pump, P-glycoprotein, are present at high levels in the villus tip of enterocytes in the gastrointestinal tract, the primary site of absorption for orally administered drugs. The importance of CYP3A and P-glycoprotein in limiting oral drug delivery is suggested to us by their joint presence in small intestinal enterocytes, by the significant overlap in their substrate specificities, and by the poor oral bioavailability of joint substrates for these 2 proteins. These proteins are induced or inhibited by many of the same compounds. A growing number of preclinical and clinical studies have demonstrated that the oral bioavailability of many CYP3A and/or P-glycoprotein substrate drugs can be increased by concomitant administration of CYP3A inhibitors and/or P-glycoprotein inhibitors. We believe that further understanding the physiology and biochemistry of the interactive nature of intestinal CYP3A and P-glycoprotein will be important in defining, controlling, and improving oral bioavailability of CYP3A/P-glycoprotein substrates.

Saquinavir and ritonavir pharmacokinetics following combined ritonavir and saquinavir (soft gelatin capsules) administration

AIMS

To investigate the influence of combined ritonavir (RTV) and saquinavir (soft-gelatin capsule formulation; SQV) on systemic exposure to SQV with a view to optimizing the dosing regimen of combined RTV and SQV antiretroviral therapy.

METHODS

In this open labelled, randomized, parallel group study, SQV and RTV were administered twice daily for 14 days to groups of eight healthy subjects. The two antiretrovirals were either administered alone (800 mg SQV, regimen A, and 400 mg RTV, B) or in combination at various dose levels (RTV : SQV: 400 : 400 mg, C; 300 : 600 mg, D; 200 : 800 mg, E; 300 : 800 mg, F; 400 : 800 mg, G; and 400 : 600 mg, H). Pharmacokinetic parameters of saquinavir and ritonavir were determined and adverse events, vital signs, and clinical laboratory variables recorded.

RESULTS

RTV substantially increased the plasma concentration of saquinavir for all dose combinations, compared with SQV alone. Based on the primary statistical analysis there was an overall 17-, 22-, and 23-fold increase in saquinavir AUC(0,24 h) on day 14 with regimens E, F, and G, respectively (with confidence intervals of 10-30, 13-37, and 13-39). The lowest combination dose of RTV (200 : 800 mg; E) significantly increased the saquinavir AUC(0,24 h) from below 5 to 57 microg ml(-1) h, which was higher than the exposure obtained with the 400 : 400 mg twice daily regimen (i.e. 36 microg ml(-1) h). RTV also reduced intersubject variability in AUC(0,24 h) for saquinavir from 105% to 32-68%, and C(max)(0,24 h) from 124% to 30-49%. In contrast, SQV showed no clinically significant effect on the pharmacokinetics of ritonavir. The combination regimens were well tolerated, with the least number of adverse events recorded for the 200 : 800 mg (RTV : SQV) combination regimen.

CONCLUSIONS

RTV significantly increases saquinavir exposure as a consequence of inhibiting SQV metabolism and possibly P-glycoprotein efflux. Pharmacokinetic and safety profiles obtained in the current study indicate that the use of a combination with a lower dose of RTV and a higher dose of SQV than the 400 : 400 mg combination frequently used in clinical practice should be further explored.

Cooperative regulation of CYP3A5 gene transcription by NF-Y and Sp family members

The purpose of this study was to clarify the mechanism(s) responsible for the transcriptional regulation of the human CYP3A5 gene. It was found that a region from nucleotides -90 to -40 was involved in the transcriptional activity of the CYP3A5 gene by transfection of a series of 5'-truncated promoter-luciferase chimeric genes into human hepatoma HepG2 cells. A gel shift assay using nuclear extracts prepared from HepG2 cells showed that nuclear factor-Y (NF-Y) and specificity protein (Sp) 1 and Sp3 bound to CCAAT box (-78/-68) and a basic transcription element (BTE) (-67/-46) in the CYP3A5 gene. Furthermore, introduction of mutations in the CCAAT box, the BTE, or both elements decreased the transcriptional activity to 10, 21, or 4% of that seen with the intact gene. Thus, we conclude that the transcription of the CYP3A5 gene is cooperatively regulated by NF-Y, Sp1, and Sp3 in HepG2 cells.

Characterizing the expression of CYP3A4 and efflux transporters (P-gp, MRP1, and MRP2) in CYP3A4-transfected Caco-2 cells after induction with sodium butyrate and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate

PURPOSE

To examine the changes in expression levels of CYP3A4 and efflux transporters in CYP3A4-transfected Caco-2 (colon carcinoma) cells in the presence of the inducers sodium butyrate (NaB) and 12-O-tetradecanoylphorbol-13-acetate (TPA). To characterize the transport of [3H]-digoxin and the metabolism of midazolam in the cells under different inducing conditions.

METHODS

CYP3A4-Caco-2 cells were seeded onto cell culture inserts and were grown for 13-14 days. Transport and metabolism studies were performed on cells induced with NaB and/or TPA for 24 h. The expression and localization of P-gp, MRP1, MRP2, and CYP3A4 were examined by Western blot and confocal microscopy.

RESULTS

In the presence of both inducers, CYP3A4 protein levels were increased 40-fold over uninduced cells, MRP2 expression was decreased by 90%, and P-gp and MRP1 expression were unchanged. Midazolam 1-OH formation exhibited a rank order correlation with increased CYP3A4 protein, whereas [3H]-digoxin transport (a measure of P-gp activity) was unchanged with induction. P-gp and MRP2 were found on the apical membrane, whereas MRP1 was found perinuclear within the cell. CYP3A4 displayed a punctate pattern of expression consistent with endoplasmic reticulum localization and exhibited preferential polarization towards the apical side of the cell.

CONCLUSIONS

The present study characterized CYP3A4-Caco-2 cell monolayers when induced for 24 h in the presence of both NaB and TPA. These conditions provide intact cells with significant CYP3A4 and P-gp expression suitable for the concurrent study of transport and metabolism.

Intestinal first-pass metabolism of eperisone in the rat

PURPOSE

The purpose of this study was to clarify quantitatively the contribution of the intestine to the first-pass metabolism of eperisone in rats.

METHODS

The systemic availabilities of eperisone were estimated by administering the drug into the duodenum, portal vein, and femoral vein in rats in vivo. The first-pass metabolism of eperisone was confirmed in the perfused rat small intestine in situ. Metabolism of eperisone to an omega-1-hydroxylated metabolite (HMO), the first step of eperisone metabolism, was studied using rat intestinal microsomes in vitro.

RESULTS

The bioavailabilities in the intestine were 0.176 and 0.0879 at administration rates of 100 and 25 mg/h/kg, respectively, whereas those in the liver were 0.532 and 0.486, respectively. In the intestinal perfusion experiment, the appearance clearance to the portal vein from the intestinal lumen was much lower than the elimination clearance from the intestinal lumen, resulting in high metabolic clearance of eperisone in the small intestine. Eperisone was biotransformed to HMO by rat intestinal microsomes, and this was inhibited by alpha-naphthoflavone and an anti-rat CYP1A antibody.

CONCLUSIONS

Those data strongly suggest that eperisone may be metabolized to HMO by CYP1A in rat intestinal microsomes during the first-pass through the epithelium of the small intestine.

Induction of intestinal cytochrome P450 (CYP3A) by rifampicin in beagle dogs

Both male and female beagle dogs (four dogs/sex) were orally treated with rifampicin (Rif) at the dose of 10 mg/kg/day for 7 days and an additional eight dogs (four dogs/sex) were used as a control. The inducible effect of Rif on intestinal cytochrome P450, especially CYP3A enzyme, was investigated by measuring microsomal testosterone 6beta-hydroxylation (6beta-OHT) activity, immunoblot and ELISA analysis. In male dogs, microsomal 6beta-OHT activity in the duodenum, upper, middle and lower part of the jejunum and the ileum of the control was 229, 204, 194, 129 and 57 pmol/min/mg protein, while the activity of the Rif-treated dogs significantly increased to 456, 486, 430, 192 and 138 pmol/min/mg protein, respectively. The activity of intestinal 6beta-OHT in the control and Rif-treated female dogs showed almost similar levels to those observed in the corresponding male dogs. The activity of intestinal 6beta-OHT in both control and Rif-treated dogs was specifically inhibited by anti-CYP3A12 antiserum. The apparent K(m) value for 6beta-OHT activity in all sections of the small intestine was comparable with that in the liver, and no significant changes were observed in between control and Rif-treated dogs. In both control and Rif-treated dogs, immunoblotting of intestinal microsomes with anti-CYP3A12 antiserum produced a band indistinguishable from that of purified CYP3A12 or of immunoreactive CYP3A12 in liver microsomes. A significant increase in intestinal CYP3A content by Rif treatment was quantitatively verified by the ELISA analysis and the magnitude of its increase correlated well with that of 6beta-OHT activity elevation. Furthermore, the results of immunohistochemistry using the anti-CYP3A12 antiserum indicated that CYP3A protein was specifically distributed in epithelial cells throughout the small intestine and appeared to be predominant at the apical side of villus cells. These results demonstrate that Rif induces not only hepatic CYP3A12 but also intestinal CYP3A in dogs.

Enterocytic CYP3A4 in a paediatric population: developmental changes and the effect of coeliac disease and cystic fibrosis

AIMS

To investigate the effects of age and disease states on the expression and activity of intestinal CYP3A4 in a paediatric population.

METHODS

Duodenal biopsies and surgical sections were collected from 104 paediatric patients (age range 2 weeks to 17 years) and from 11 foetuses. An S9 fraction was prepared in each case. CYP3A4 expression was assessed by Western blotting and by immunohistochemistry; activity was measured by the rate of formation of 6beta-hydroxytestosterone from testosterone. Villin expression was used as a marker of enterocyte harvest to normalize CYP3A4 expression and activity data.

RESULTS

In the 74 histologically normal paediatric biopsies there were statistically significant increases in CYP3A4 expression (r2 = 0.19, P = 0.001) and activity (r2 = 0.17, P = 0.02) with age. CYP3A4 was practically absent in fetal duodenum and was expressed at relatively low levels in neonates (P < 0.05 between neonates and children > 5 years). Active coeliac disease resulted in significant (P < 0.001) decreases in CYP3A4 expression and activity.

CONCLUSIONS

Duodenal CYP3A4 is present at significantly lower levels in neonates and in patients with active coeliac disease. This may have clinical significance with respect to the oral bioavailability of CYP3A4 substrates.

Cytokines influence mRNA expression of cytochrome P450 3A4 and MDRI in intestinal cells

Inflammation and infection may have the potential to increase the bioavailability of drugs. This effect could be because of a reduced metabolism of xenobiotics in the liver and/or the intestines, or because of alterations in small intestinal permeability, mucosal flow, and expression of drug efflux transporters such as P-glycoprotein (Pgp). To assess the impact on intestinal epithelium of some proinflammatory cytokines and macrophages on permeability and mRNA expression of CYP3A4 and MDRI (multidrug resistance, coding for Pgp), we used the Caco-2 cell line as a model. Exposure to proinflammatory cytokines and macrophages decreased the mRNA expression of CYP3A4 and increased the expression of MDR1 mRNA in the Caco-2 cells. In parallel, the cell layer permeability, as measured by sodium fluorescein flux, increased for all cytokine and macrophage treatments, whereas the effect on transepithelial electrical resistance (TEER) varied. Our findings suggest that inflammation and infection trigger several different cellular responses that may affect drug bioavailability; that is hampered CYP3A4 expression, increased permeability of the epithelial cell layer, and enhanced Pgp-mediated counteractive transport.