3,3'-Diindolylmethane induces CYP1A2 in cultured precision-cut human liver slices

Drug-Drug Interactions Involving Intestinal and Hepatic CYP1A Enzymes

Cytochrome P450 (CYP) 1A enzymes are considerably expressed in the human intestine and liver and involved in the biotransformation of about 10% of marketed drugs. Despite this doubtless clinical relevance, CYP1A1 and CYP1A2 are still somewhat underestimated in terms of unwanted side effects and drug–drug interactions of their respective substrates. In contrast to this, many frequently prescribed drugs that are subjected to extensive CYP1A-mediated metabolism show a narrow therapeutic index and serious adverse drug reactions. Consequently, those drugs are vulnerable to any kind of inhibition or induction in the expression and function of CYP1A. However, available in vitro data are not necessarily predictive for the occurrence of clinically relevant drug–drug interactions. Thus, this review aims to provide an up-to-date summary on the expression, regulation, function, and drug–drug interactions of CYP1A enzymes in humans.

Transcriptomic analysis of the mode of action of the candidate anti-fouling compound di(1H-indol-3-yl)methane (DIM) on a marine biofouling species, the bryozoan Bugula neritina

Di(1H-indol-3-yl)methane (DIM) was previously suggested to be an environmentally friendly antifouling compound, but it was also reported that the compound was highly stable in natural seawater. The present study reported that 3 h DIM treatments at 4 μg mL^-1 or higher concentration and 12 h DIM treatments at 2 μg mL^-1 or higher concentration induced significant larval mortality and metamorphic abnormality in the bryozoan Bugula neritina. The bioassay results correlated with the dose-dependent up-regulation of HSP family proteins, pro-apoptotic proteins, ubiquitination protein, and the dose-dependent down-regulation of anti-apoptotic genes and developmental genes. Unexpectedly, genes involved in fatty acid biosynthesis and protein synthesis were up-regulated in response to DIM treatment, but, in general, the effects of DIM on B. neritina larvae were comparable to that reported in human cancer cell lines. DIM also induced changes in steroid hormone biosynthesis genes in B. neritina larvae, leading to the concern that DIM might have long-term effects on marine lives. Overall, the present study suggested that application of DIM to the bryozoan larvae would trigger a major transcriptomic response, which might be linked to the observed larval mortality and abnormality. We suggest that application of DIM as an antifouling ingredient should be proceeded with great cautions.

Diindolylmethane, a naturally occurring compound, induces CYP3A4 and MDR1 gene expression by activating human PXR

Activation of human pregnane X receptor (hPXR)-regulated expression of cytochrome P450 3A4 (CYP3A4) and multidrug resistance protein 1 (MDR1) plays an important role in mediating adverse drug interactions. Given the common use of natural products as part of adjunct human health behavior, there is a growing concern about natural products for their potential to induce undesired drug interactions through the activation of hPXR-regulated CYP3A4 and MDR1. Here, we studied whether 3,3'-diindolylmethane (DIM), a natural health supplement, could induce hPXR-mediated regulation of CYP3A4 and MDR1 in human hepatocytes and intestinal cells. DIM, at its physiologically relevant concentrations, not only induced hPXR transactivation of CYP3A4 promoter activity but also induced gene expression of CYP3A4 and MDR1. DIM decreased intracellular accumulation of MDR1 substrate rhodamine 123, suggesting that DIM induces the functional expression of MDR1. Pharmacologic inhibition or genetic knockdown of hPXR resulted in attenuation of DIM induced CYP3A4 and MDR1 gene expression, suggesting that DIM induces CYP3A4 and MDR1 in an hPXR-dependent manner. Together, these results support our conclusion that DIM induces hPXR-regulated CYP3A4 and MDR1 gene expression. The inductive effects of DIM on CYP3A4 and MDR1 expression caution the use of DIM in conjunction with other medications metabolized and transported via CYP3A4 and MDR1, respectively.

The Use of Long-term Hepatocyte Cultures for Detecting Induction of Drug Metabolising Enzymes: The Current Status

In this report, metabolically competent in vitro systems have been reviewed, in the context of drug metabolising enzyme induction. Based on the experience of the scientists involved, a thorough survey of the literature on metabolically competent long-term culture models was performed. Following this, a prevalidation proposal for the use of the collagen gel sandwich hepatocyte culture system for drug metabolising enzyme induction was designed, focusing on the induction of the cytochrome P450 enzymes as the principal enzymes of interest. The ultimate goal of this prevalidation proposal is to provide industry and academia with a metabolically competent in vitro alternative for long-term studies. In an initial phase, the prevalidation study will be limited to the investigation of induction. However, proposals for other long-term applications of these systems should be forwarded to the European Centre for the Validation of Alternative Methods for consideration. The prevalidation proposal deals with several issues, including: a) species; b) practical prevalidation methodology; c) enzyme inducers; and d) advantages of working with independent expert laboratories. Since it is preferable to include other alternative tests for drug metabolising enzyme induction, when such tests arise, it is recommended that they meet the same level of development as for the collagen gel sandwich long-term hepatocyte system. Those tests which do so should begin the prevalidation and validation process.

Using molecular features of xenobiotics to predict hepatic gene expression response

Despite recent advances in molecular medicine and rational drug design, many drugs still fail because toxic effects arise at the cellular and tissue level. In order to better understand these effects, cellular assays can generate high-throughput measurements of gene expression changes induced by small molecules. However, our understanding of how the chemical features of small molecules influence gene expression is very limited. Therefore, we investigated the extent to which chemical features of small molecules can reliably be associated with significant changes in gene expression. Specifically, we analyzed the gene expression response of rat liver cells to 170 different drugs and searched for genes whose expression could be related to chemical features alone. Surprisingly, we can predict the up-regulation of 87 genes (increased expression of at least 1.5 times compared to controls). We show an average cross-validation predictive area under the receiver operating characteristic curve (AUROC) of 0.7 or greater for each of these 87 genes. We applied our method to an external data set of rat liver gene expression response to a novel drug and achieved an AUROC of 0.7. We also validated our approach by predicting up-regulation of Cytochrome P450 1A2 (CYP1A2) in three drugs known to induce CYP1A2 that were not in our data set. Finally, a detailed analysis of the CYP1A2 predictor allowed us to identify which fragments made significant contributions to the predictive scores.

Influence of environmental and genetic factors on CYP1A2 activity in individuals of South Asian and European ancestry

The drug-metabolizing enzyme CYP1A2 contributes to the metabolism of a number of commonly used medicines and displays wide interindividual variability. The aim of this study was to investigate CYP1A2 activity in a population of South Asian ancestry and compare it with a population of European ancestry. CYP1A2 activity was determined using the 4 h paraxanthine/caffeine saliva concentration ratio following a 100-mg oral dose of caffeine in healthy individuals of South Asian (n = 166) and European (n = 166) ancestry. Participants were surveyed for extrinsic ethnic factors and genotyped for polymorphisms in CYP1A2 and related genes. Significantly lower CYP1A2 activity was observed in South Asian participants (median: 0.42; range: 0.10-1.06) as compared with European participants (0.54; 0.12-1.64) (P < 0.01). Multiple linear regression indicated that 41% of the variability in CYP1A2 activity could be explained by the diet, lifestyle, and genetic factors studied.

Attenuation of multi-targeted proliferation-linked signaling by 3,3'-diindolylmethane (DIM): from bench to clinic

Emerging evidence provide credible support in favor of the potential role of bioactive products derived from ingesting cruciferous vegetables such as broccoli, brussel sprouts, cauliflower and cabbage. Among many compounds, 3,3'-diindolylmethane (DIM) is generated in the acidic environment of the stomach following dimerization of indole-3-carbinol (I3C) monomers present in these classes of vegetables. Both I3C and DIM have been investigated for their use in preventing, inhibiting, and reversing the progression of cancer - as a chemopreventive agent. In this review, we summarize an updated, wide-ranging pleiotropic anti-tumor and biological effects elicited by DIM against tumor cells. It is unfeasible to point one single target as basis of cellular target of action of DIM. We emphasize key cellular and molecular events that are effectively modulated in the direction of inducing apoptosis and suppressing cell proliferation. Collectively, DIM orchestrates signaling through Ah receptor, NF-κB/Wnt/Akt/mTOR pathways impinging on cell cycle arrest, modulation of key cytochrome P450 enzymes, altering angiogenesis, invasion, metastasis and epigenetic behavior of cancer cells. The ability of DIM to selectively induce tumor cells to undergo apoptosis has been observed in preclinical models, and thus it has been speculated in improving the therapeutic efficacy of other anticancer agents that have diverse molecular targets. Consequently, DIM has moved through preclinical development into Phase I clinical trials, thereby suggesting that DIM could be a promising and novel agent either alone or as an adjunct to conventional therapeutics such as chemo-radio and targeted therapies. An important development has been the availability of DIM formulation with superior bioavailability for humans. Therefore, DIM appears to be a promising chemopreventive agent or chemo-radio-sensitizer for the prevention of tumor recurrence and/or for the treatment of human malignancies.

CYP1A2, GSTM1, and GSTT1 polymorphisms and diet effects on CYP1A2 activity in a crossover feeding trial

Cytochrome P-450 1A2 (CYP1A2) is a biotransformation enzyme that activates several procarcinogens. CYP1A2 is induced by cruciferous and inhibited by apiaceous vegetable intake. Using a randomized, crossover feeding trial in humans, we investigated the dose effects of cruciferous vegetables and the effects of any interaction between cruciferous and apiaceous vegetables on CYP1A2 activity. We also investigated whether response varied by CYP1A2*1F, GSTM1, and GSTT1 genotypes (glutathione S-transferases that metabolize crucifer constituents) and whether CYP1A2 activity rebounds after apiaceous vegetables are removed from the diet. Participants (N = 73), recruited based on genotypes, consumed four diets for two weeks each: low-phytochemical diet (basal), basal plus single dose of cruciferous (1C), basal plus double dose of cruciferous (2C), and basal plus single dose of cruciferous and apiaceous vegetables (1C+A). CYP1A2 activity was determined by urine caffeine tests administered at baseline and the end of each feeding period. Compared with basal diet, the 1C diet increased CYP1A2 activity (P < 0.0001) and the 2C diet resulted in further increases (P < 0.0001), with men experiencing greater dose-response than women. The 1C+A diet decreased CYP1A2 activity compared with the 1C and 2C diets (P < 0.0001 for both). Although there was no overall effect of CYP1A2*1F or GSTM1-null/GSTT1-null genotypes or genotype-by-diet interactions, there were significant diet response differences within each genotype. Additionally, CYP1A2 activity recovered modestly one day after the removal of apiaceous vegetables. These results suggest complex interactions among dietary patterns, genetic variation, and modulation of biotransformation that may not be apparent in observational studies.

Induction of CYP2B and CYP2E1 in precision-cut rat liver slices cultured in defined medium

Many drugs and endogenous substances undergo biotransformation by cytochrome P450s (CYPs), and some drugs are also capable of modulating the expression of various CYPs. Knowledge of the potential of a drug to modulate CYPs is useful to help predict potential drug interactions. This study utilized precision-cut rat liver slices in dynamic organ culture to assess the effects of various media on the viability of rat liver slices and the expression of CYP2B and CYP2E1 when the slices are exposed to phenobarbital and isoniazid, which are drugs capable of inducing these respective CYPs. Liver slices were maintained in serum supplemented Waymouths medium and two different serum-free media, Hepatozyme (Life Technologies) and a new defined medium, which is named BPM. While Hepatozyme is considered a suitable medium to support primary hepatocyte cultures, this product did not maintain viable liver slices, even for 24 h. The serum containing and new defined media maintained viable liver slices for up to 96 h in culture. Phenobarbital (0.5 mM) and isoniazid (0.1 or 0.6 mM) did not affect viability in this model. In the absence of phenobarbital or isoniazid, liver slices maintained for 96 h in the new BPM medium maintained the respective levels of CYP2B and 2E1 protein at 1.8 and 1.9-fold higher than in slices maintained in the serum-containing medium. Phenobarbital exposure (0.5 mM) for 96 h induced CYP2B protein 5.2-fold in the BPM medium and 2.5-fold in the serum-containing medium. Isoniazid exposure (0.1 and 0.5 mM) for 96 h induced CYP2E1 protein 1.9 and 2.1-fold (respectively) in the BPM medium and 2.1 and 2.0-fold in the serum-containing medium. The respective CYP enzymatic activities were also increased by these drugs in a similar manner. Thus, the new defined BPM medium provides suitable conditions for maintaining CYP2B and 2E1 in liver slices and supports the investigation of drug-induced modulation of these enzymes.

3,3'-diindolylmethane is a novel topoisomerase IIalpha catalytic inhibitor that induces S-phase retardation and mitotic delay in human hepatoma HepG2 cells

Epidemiological evidence suggests that high consumption of Brassica genus vegetables, such as broccoli, cabbage, and Brussels sprouts, is very effective in reducing the risks of several types of cancers. 3,3'-Diindolylmethane (DIM), one of the most abundant and biologically active dietary compounds derived from Brassica genus vegetables, displays remarkable antitumor activity against several experimental tumors. In the present study, we demonstrate for the first time that DIM is a novel catalytic topoisomerase IIalpha inhibitor. In supercoiled DNA relaxation assay and kinetoplast DNA decatenation assay, DIM strongly inhibited DNA topoisomerase IIalpha and also partially inhibited DNA topoisomerases I and IIbeta. DIM did not stabilize DNA cleavage complex and did not prevent etoposide-induced DNA cleavage complex formation. Further experiments showed that DIM inhibited topoisomerase IIalpha-catalyzed ATP hydrolysis, which is a necessary step for the enzyme turnover. In cultured human hepatoma HepG2 cells, DIM blocked DNA synthesis and mitosis in a concentration-dependent manner, which was consistent with the outcome of topoisomerase inhibition in these cell-cycle phases. Our results identified a new mode of action for this intriguing dietary component that might be exploited for therapeutic development.

Phytochemical-induced changes in gene expression of carcinogen-metabolizing enzymes in cultured human primary hepatocytes

1. The naturally occurring compounds curcumin (CUR), 3,3'-diindolylmethane (DIM), isoxanthohumol (IXN), 8-prenylnaringenin (8PN), phenethyl isothiocyanate (PEITC) and sulforaphane (SFN) protect animals against chemically induced tumours. Putative chemoprotective mechanisms include modulated expression of hepatic biotransformation enzymes. However, few, if any, studies have used human primary cells as test models. 2. The present study investigated the effects of these phytochemicals on the expression of four carcinogenesis-relevant enzymes--cytochrome P450 (CYP)1A1 and 1A2, NAD(P)H:quinone oxidoreductase (NQO1) and glutathione S-transferase A1 (GSTA1)--in primary cultures of freshly isolated human hepatocytes. 3. Quantitative RT-PCR analyses demonstrated that CYP1A1 was up-regulated by PEITC and DIM in a dose-dependent manner. CYP1A2 transcription was significantly activated following DIM, IXN, 8PN and PEITC treatments. DIM exhibited a remarkably effective induction response of CYP1A1 (474-, 239- and 87-fold at 50, 25 and 10 microM, respectively) and CYP1A2 (113-, 70- and 31-fold at 50, 25 and 10 microM, respectively), that was semiquantitatively reflected in protein levels. NQO1 expression responded to PEITC (11 x at 25 microM), DIM (4.5 x at 50 microM) and SFN (5 x at 10 microM) treatments. No significant effects on GSTA1 transcription were seen. 4. The findings show novel and unexpected effects of these phytochemicals on the expression of human hepatic biotransformation enzymes that play key roles in chemical-induced carcinogenesis.

Quantitative PCR assay for cytochromes P450 2B and 3A induction in rat precision-cut liver slices: correlation study with induction in vivo

INTRODUCTION

In drug development, new chemical entities that cause cytochrome P450 induction are considered to be undesirable since P450 induction is linked to tumor formation and may compromise the evaluation of drug safety when autoinduction results in poor drug exposure.

METHODS

We evaluated the use of the precision-cut liver slice as a model for measuring induction of cytochrome P450 in rats. Quantitative real-time reverse-transcription polymerase chain reaction was used to analyze the induction of selected forms of cytochrome P450 at the mRNA level. Firstly, the system was validated against known inducers of CYP2B and 3A. Subsequently, 26 proprietary compounds were tested in rat liver slices and rats in vivo for CYP2B and 3A induction.

RESULTS

Exposure of liver slices to the known CYP2B inducers phenobarbital, benzoyl-pyridine, cabarmazepine, metyrapone, RU486 and dexamethasone caused elevation of CYP2B1/2 expression 10- to 40-fold compared to the control values. The CYP3A inducers PCN, dexamethasone, nicardipine, nifedipine, clotrimazole and RU486 induced a 4- to 50-fold expression of CYP3A14. For 26 proprietary compounds, a correlation with an R(2) value of 0.74 was established between the induction of CYP2B expression in liver slices and that in rats in vivo. When liver slice results were used to predict the induction of CYP2B in rats in vivo, the success rate was 91%. The induction of CYP3A in rats in vivo was analyzed by Western blot, then quantified by densitometry. There was a good correlation between CYP3A induction in liver slices and induction in vivo as assessed by Western blot, with an 86% positive prediction rate.

DISCUSSION

The use of liver slices in combination with TaqMan technology provides a good model for predicting CYP induction in the rat. This method is useful for identifying compounds with CYP2B and 3A induction liability in the early phase of drug discovery.

Comparative studies on the cytochrome p450-associated metabolism and interaction potential of selegiline between human liver-derived in vitro systems

Selegiline was used as a model compound in a project aimed at comparing, evaluating, and integrating different in vitro approaches for the prediction of cytochrome p450 (p450)-catalyzed hepatic drug metabolism in humans (EUROCYP). Metabolic predictions were generated using homology modeling, cDNA-expressed p450 enzymes, human liver microsomes, primary cultured human hepatocytes, and precision-cut human liver slices. All of the in vitro systems correctly indicated the formation of two dealkylated metabolites, desmethylselegiline and methamphetamine. The metabolic instability of selegiline was demonstrated by all of the in vitro systems studied. Estimates of clearance varied from 16 l/h to 223 l/h. With the exception of one approach, all systems underpredicted the in vivo clearance in humans (236 l/h). Despite this, all approaches successfully classified selegiline as a high clearance compound. Homology modeling suggested the participation of CYP2B6 in the demethylation of selegiline and of CYP2D6 in the depropargylation of the drug. Studies with recombinant expressed enzymes and with human hepatic microsomal fraction supported the involvement of CYP2B6 but not of CYP2D6. These techniques also suggested the involvement of CYP1A2, CYP2C8, and CYP2C19 in the biotransformation of selegiline. In vitro, CYP2B6 was the most active form of p450 involved in selegiline metabolism. Metabolism by several enzymes operating in parallel implies a low interaction potential for the drug. None of the techniques alone was able to predict all aspects of the metabolic and kinetic behavior of selegiline in vivo. However, when used as an integrated package, all significant characteristics were predictable.

The conduct of in vitro and in vivo drug-drug interaction studies: a Pharmaceutical Research and Manufacturers of America (PhRMA) perspective

Current regulatory guidances do not address specific study designs for in vitro and in vivo drug-drug interaction studies. There is a common desire by regulatory authorities and by industry sponsors to harmonize approaches, to allow for a better assessment of the significance of findings across different studies and drugs. There is also a growing consensus for the standardization of cytochrome P450 (P450) probe substrates, inhibitors and inducers and for the development of classification systems to improve the communication of risk to health care providers and to patients. While existing guidances cover mainly P450-mediated drug interactions, the importance of other mechanisms, such as transporters, has been recognized more recently, and should also be addressed. This article was prepared by the Pharmaceutical Research and Manufacturers of America (PhRMA) Drug Metabolism and Clinical Pharmacology Technical Working Groups and represents the current industry position. The intent is to define a minimal best practice for in vitro and in vivo pharmacokinetic drug-drug interaction studies targeted to development (not discovery support) and to define a data package that can be expected by regulatory agencies in compound registration dossiers.

An update on in vitro test methods in human hepatic drug biotransformation research: pros and cons

The liver is the predominant organ in which biotransformation of foreign compounds takes place, although other organs may also be involved in drug biotransformation. Ideally, an in vitro model for drug biotransformation should accurately resemble biotransformation in vivo in the liver. Several in vitro human liver models have been developed in the past few decades, including supersomes, microsomes, cytosol, S9 fraction, cell lines, transgenic cell lines, primary hepatocytes, liver slices, and perfused liver. A general advantage of these models is a reduced complexity of the study system. On the other hand, there are several more or less serious specific drawbacks for each model, which prevents their widespread use and acceptance by the regulatory authorities as an alternative for in vivo screening. This review describes the practical aspects of selected in vitro human liver models with comparisons between the methods.

Induction of cytochrome P450 2B6 and 3A4 expression by phenobarbital and cyclophosphamide in cultured human liver slices

PURPOSE

To examine the potential of cultured human liver slices to predict cytochrome P450 (CYP) inducibility, regarding global and zonal CYP expression, together with drug-induced histologic changes.

METHODS

We first assessed whether CYP2B6, 3A4, and 2C9 expression was maintained in cultured liver slices. Cultured hepatocytes were used as the reference culture system. Then we tested the effects of phenobarbital and cyclophosphamide on CYP expression in both models.

RESULTS

Morphologic features are preserved in slices. Basal CYP expression declines with time in culture in both models. Slices display the same region specificity of CYP2B6, 2C9, and 3A4 expression as intact liver. CYP2B6 and 3A4 mRNA, apoprotein, and enzyme-related activities were induced by phenobarbital and cyclophosphamide, whereas CYP2C9 apoprotein was not. Their immunoreactivities were also increased, while their zonal distribution was preserved on slice tissue sections. Microsomal enzyme induction was confirmed by histology.

CONCLUSIONS

Cultured human liver slices are an attractive alternative to hepatocyte culture for the prediction of human CYP isoenzyme induction by xenobiotics.

Induction of cytochrome P450 enzymes in cultured precision-cut human liver slices

Precision-cut human liver slices obtained from 11 donors were cultured for 72 h in a defined medium (serum free Williams' medium E) supplemented with 0.1 microM insulin and 0.1 microM dexamethasone (DEX). Liver slices were treated with 50 microM concentrations of beta -naphthoflavone (BNF), lansoprazole, rifampicin (RIF), DEX and methylclofenapate and 500 microM sodium phenobarbital (NaPB). The relative apoprotein levels of 12 cytochrome P450 (P450) enzymes were determined in liver slice microsomes using a panel of antipeptide antibodies. Treatment with BNF significantly induced mean levels of CYP1A2 apoprotein to 160% of levels in 72-h control (no test compound) human liver slice microsomes. NaPB significantly induced levels of CYP3A4 apoprotein to 255% of control and RIF significantly induced levels of CYP2C19 and CYP3A4 apoproteins to 265 and 330% of control, respectively. In addition, treatment with RIF increased levels of CYP2A6 apoprotein to 205% of control, and treatment with both NaPB and RIF increased levels of CYP2B6 apoprotein to 370 and 615% of control, respectively. However, these increases were not statistically significant, owing to a variable response between liver slice preparations from different subjects, this being apparent for all inducible P450s. In contrast, none of the compounds examined significantly increased levels of CYP2C8, CYP2C9, CYP2D6, CYP2E1, and CYP4A11 apoproteins. Levels of CYP1A1 apoprotein were not detected in any liver slice sample, either before or after treatment with the model inducers. Overall, these results demonstrate the utility of cultured human liver slices for assessing the effects of chemicals on P450 enzymes.

Metabolism of zaleplon by human liver: evidence for involvement of aldehyde oxidase

1. The metabolism of Zaleplon (CL-284,846; ZAL) has been studied in precision-cut human liver slices and liver cytosol preparations. 2. Human liver slices metabolized ZAL to a number of products including 5-oxo-ZAL (M2), N-desethyl-5-oxo-ZAL (M1) and N-desethyl-ZAL (DZAL), the latter metabolite being known to be formed by CYP3A forms. 3. Human liver cytosol preparations catalysed the metabolism of ZAL to M2. Kinetic analysis of three cytosol preparations revealed mean (+/- SEM) K(m) and V(max) of 93 +/- 18 mm and 317 +/- 241 pmol/min/mg protein, respectively. 4. Using 16 individual human liver cytosol preparations a 33-fold variability in the metabolism of 80 micro M ZAL to M2 was observed. Correlations were observed between M2 formation and the metabolism of the aldehyde oxidase substrates phenanthridine (r(2) = 0.774) and phthalazine (r(2) = 0.460). 5. The metabolism of 80 micro M ZAL to M2 in liver cytosol preparations was markedly inhibited by the aldehyde oxidase inhibitors chlorpromazine, promethazine, hydralazine and menadione. Additional kinetic analysis suggested that chlorpromazine and promethazine were non-competitive inhibitors of M2 formation with K(i) of 2.3 and 1.9 micro M, respectively. ZAL metabolism to M2 was also inhibited by cimetidine. 6. Incubations conducted with human liver cytosol and H(2)(18)O demonstrated that the oxygen atom incorporated into ZAL and DZAL to form M2 and M1, respectively, was derived from water and not from molecular oxygen. 7. In summary, by correlation analysis, chemical inhibition and H(2)(18)O incorporation studies, ZAL metabolism to M2 in human liver appears to be catalysed by aldehyde oxidase. With human liver slices, ZAL was metabolized to products dependent on both aldehyde oxidase and CYP3A forms.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Lack of effect of furfural on unscheduled DNA synthesis in the in vivo rat and mouse hepatocyte DNA repair assays and in precision-cut human liver slices

The ability of furfural to induce unscheduled DNA synthesis (UDS) in hepatocytes of male and female B6C3F(1) mice and male F344 rats after in vivo administration and in vitro in precision-cut human liver slices has been studied. Preliminary toxicity studies established the maximum tolerated dose (MTD) of furfural to be 320 and 50 mg/kg in the mouse and rat, respectively. Furfural was dosed by gavage at levels of 0 (control), 50, 175 and 320 mg/kg to male and female mice and 0, 5, 16.7 and 50 mg/kg to male rats. Hepatocytes were isolated by liver perfusion either 2-4 h or 12-16 h after treatment, cultured in medium containing [3H]thymidine for 4 h and assessed for UDS by grain counting of autoradiographs. Furfural treatment did not produce any statistically significant increase or any dose-related effects on UDS in mouse and rat hepatocytes either 2-4 h or 12-16 h after dosing. In contrast, UDS was markedly induced in mice and rats 2-4 h after treatment with 20 mg/kg dimethylnitrosamine and 12-16 h after treatment of mice and rats with 200 mg/kg o-aminoazotoluene and 50 mg/kg 2-acetylaminofluorene (2-AAF), respectively. Precision-cut human liver slices from four donors were cultured for 24 h in medium containing [3H]thymidine and 0-10 mM furfural. Small increases in the net grain count (i.e. nuclear grain count less mean cytoplasmic grain count) observed with 2-10 mM furfural were not due to any increase in the nuclear grain count. Rather, it was the result of concentration-dependent decreases in the mean cytoplasmic grain counts and to a lesser extent in nuclear grain counts, due to furfural-induced cytotoxicity. In contrast, marked increases in UDS (both net grain and nuclear grain counts) were observed in human liver slices treated with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM aflatoxin B(1) and 0.005 and 0.05 mM 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. This study demonstrates that furfural does not induce UDS in the hepatocytes of male and female B6C3F(1) mice and male F344 rats after oral treatment at doses up to the MTDs. Moreover, human liver slice studies suggest that furfural is also not a genotoxic agent in human liver.

Carbamazepine: a 'blind' assessment of CVP-associated metabolism and interactions in human liver-derived in vitro systems

1. The ability of various in vitro systems for CYP enzymes (computer modelling, human liver microsomes, precision-cut liver slices, hepatocytes in culture, recombinant enzymes) to predict various aspects of in vivo metabolism and kinetics of carbamazepine (CBZ) was investigated. 2. The study was part of the EUROCYP project that aimed to evaluate relevant human in vitro systems to study drug metabolism. 3. CBZ was given to the participating laboratories without disclosing its chemical nature. 4. The most important enzyme (CYP3A4) and metabolic route (10,11-epoxidation) were predicted by all the systems studied. 5. Minor enzymes and routes were predicted to a different extent by various systems. 6. Prediction of a clearance class, i.e. slow clearance, was correctly predicted by microsomes, slices, hepatocytes and recombinant enzymes (CYP3A4). 7. The 10,11-epoxidation of CBZ by the recombinant CYP3A4 was enhanced by the addition of exogenous cytochrome-b5, leading to a considerable over-prediction. 8. Induction potency of CBZ was predicted in cultured hepatocytes in which 7-ethoxycoumarin O-deethylase was used as an index activity. 9. It seems that for a principally CYP-metabolized substance such as CBZ, all liver-derived systems provide useful information for prediction of metabolic routes, rates and interactions.

3,3'-diindolylmethane, a major condensation product of indole-3-carbinol, is a potent estrogen in the rainbow trout

Indole-3-carbinol (I3C), a compound found in Brassica vegetables has been widely studied for its chemopreventive properties. I3C has been shown to block tumor initiation and promotion; however, it also acts as a tumor promoter. I3C and some of its acid condensation products, particularly 3,3'-diindolylmethane (I33'), have exhibited antiestrogenic properties. We report that I33' acts as an estrogen in the rainbow trout liver in vitro and in vivo by inducing vitellogenin (Vg), a well-characterized biomarker for estrogens. Precision-cut liver slices from male rainbow trout, Oncorhynchus mykiss, were incubated at 14 degrees C for 96 h in media containing I3C, I33', or a mixture of I3C acid condensation products (RXN) (0-250 microM). I33' and RXN increased Vg levels in rainbow trout liver slices by over 300- and 20-fold, respectively, vs vehicle. The efficacy of I33' induction of Vg was comparable to 17 beta-estradiol (E(2)) with 2500-fold less potency. I33' and E(2) cotreatment resulted in additive Vg induction. Tamoxifen completely inhibited I33'-induced Vg induction, suggesting that Vg induction by I33' is entirely through the estrogen receptor. In vivo, juvenile male rainbow trout were fed I3C, RXN (0-2000 mg/kg), or I33' (0-250 mg/kg) for 2 weeks. At 2000 mg/kg, I3C induced Vg by over 100,000-fold compared to controls, which was comparable to 5 mg/kg 17 beta-estradiol (the dose resulting in maximum induction). I33' was five times as potent as I3C with equal efficacy. The potency of RXN was only 5% of I3C. Again, I33' and E(2) cotreatment resulted in additive Vg induction. I33' may have accounted for Vg increases observed in trout fed I3C as it is present in liver after oral dosing at concentrations (70 microM) expected to maximally induce Vg. In trout, results in vitro and in vivo document that I33' is estrogenic, consistent with our hypothesis that I3C promotes liver cancer in trout by estrogenic pathways.

Effect of some indole derivatives on xenobiotic metabolism and xenobiotic-induced toxicity in cultured rat liver slices

In this study the effect of some indole derivatives on xenobiotic metabolizing enzymes and xenobiotic-induced toxicity has been examined in cultured precision-cut liver slices from male Sprague-Dawley rats. While treatment of rat liver slices for 72 hours with 2-200 microM of either indole-3-carbinol (I3C) or indole-3-acetonitrile (3-ICN) had little effect on cytochrome P-450 (CYP)-dependent enzyme activities, enzyme induction was observed after in vivo administration of I3C. The treatment of rat liver slices with 50 microM 3,3'-diindolylmethane (DIM; a dimer derived from I3C under acidic conditions) for 72 hours resulted in a marked induction of CYP-dependent enzyme activities. DIM appears to be a mixed inducer of CYP in rat liver slices having effects on CYP1A, CYP2B and CYP3A subfamily isoforms. Small increases in liver slice reduced glutathione levels and glutathione S-transferase activity were also observed after DIM treatment. While aflatoxin B1 and monocrotaline produced a concentration-dependent inhibition of protein synthesis in 72-hour-cultured rat liver slices, cytotoxicity was markedly reduced in liver slices cultured with 50 microM DIM. These results demonstrate that cultured rat liver slices may be employed to evaluate the effects of chemicals derived from cruciferous and other vegetables on CYP isoforms. In addition, liver slices can also be utilized to examine the ability of such chemicals to modulate xenobiotic-induced toxicity.

Time- and concentration-dependent induction of CYP1A1 and CYP1A2 in precision-cut rat liver slices incubated in dynamic organ culture in the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin

In a previous 24-h study, precision-cut rat liver slices were validated as a useful in vitro model for assessing the dose-related induction of CYP1A1 and CYP1A2 in rat liver following exposure to 2, 3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Further assessment of the utility of this model was accomplished by initially exposing rat liver slices to medium containing TCDD (0.01 nM) for 24 h and incubating the slices up to an additional 72 h in TCDD-free medium. The slices remained viable throughout the incubation period with an intracellular potassium content varying from 45.2 +/- 2.3 micromol/g at 48 h to 50.0 +/- 1.6 micromol/g at 72 h. In TCDD-exposed slices, CYP1A1 protein and its respective enzymatic activity, the O-deethylation of ethoxyresorufin (EROD), significantly increased with time over the 96-h incubation period, with EROD activity increasing from 63.6 +/- 14.2 at 24 h to 905 +/- 291 pmol/mg/min at 96 h. Under identical incubation conditions, but in the absence of TCDD, the EROD activity for the control liver slices ranged from 14. 3 +/- 4.3 to 44.9 +/- 11.9 pmol/min/mg. Conversely, the level of CYP1A2 protein and its respective activity (acetanilide hydroxylation) transiently decreased from 24 to 96 h with no significant differences observed between the control (0 nM TCDD) and treatment group (0.01 nM TCDD). The concentration-effect relationship at 96 h was characterized by incubating rat liver slices for the initial 24 h in medium containing TCDD at concentrations ranging from 0.1 pM to 10 nM. Induction of CYP1A1 protein and EROD activity was observed for all treatment groups with the 10 nM TCDD treatment group displaying greater than 100-fold induction compared to control (0 nM TCDD). Immunohistochemical localization of CYP1A1 protein within liver slices supported the time- and concentration-dependent induction of EROD activity by TCDD. The induction of CYP1A1 was initially observed to be centrilobular, with increased expression due to both elevated CYP1A1 within cells and the recruitment of additional cells expressing CYP1A1 throughout the entire liver slice. Additionally, the immunohistochemical analysis of the liver slices demonstrated the conservation of tissue architecture following up to 96 h of incubation in dynamic organ culture and provided further evidence for maintenance of tissue viability. In comparison to CYP1A1, the induction of CYP1A2 at 96 h was a less sensitive response, with significant induction of CYP1A2 protein and its respective activity occurring at a medium concentration of 0.1 nM TCDD (686 pg/g liver). In general, increasing the incubation period from 24 to 96 h markedly increased TCDD-induced expression of CYP1A1 and minimally enhanced CYP1A2 expression. Moreover, extending the incubation period to 96 h resulted in in vitro induction profiles for CYP1A1 and CYP1A2 that were qualitatively and quantitatively similar to that previously observed following in vivo exposure to TCDD (Drahushuk et al., Toxicol. Appl. Pharmacol. 140, 393-403, 1996).