Effects of benzimidazole derivatives on cytochrome P450 1A1 expression in a human hepatoma cell line

Revisiting the Therapeutic Potential of Bothrops jararaca Venom: Screening for Novel Activities Using Connectivity Mapping

Snake venoms are sources of molecules with proven and potential therapeutic applications. However, most activities assayed in venoms (or their components) are of hemorrhagic, hypotensive, edematogenic, neurotoxic or myotoxic natures. Thus, other relevant activities might remain unknown. Using functional genomics coupled to the connectivity map (C-map) approach, we undertook a wide range indirect search for biological activities within the venom of the South American pit viper Bothrops jararaca. For that effect, venom was incubated with human breast adenocarcinoma cell line (MCF7) followed by RNA extraction and gene expression analysis. A list of 90 differentially expressed genes was submitted to biosimilar drug discovery based on pattern recognition. Among the 100 highest-ranked positively correlated drugs, only the antihypertensive, antimicrobial (both antibiotic and antiparasitic), and antitumor classes had been previously reported for B. jararaca venom. The majority of drug classes identified were related to (1) antimicrobial activity; (2) treatment of neuropsychiatric illnesses (Parkinson’s disease, schizophrenia, depression, and epilepsy); (3) treatment of cardiovascular diseases, and (4) anti-inflammatory action. The C-map results also indicated that B. jararaca venom may have components that target G-protein-coupled receptors (muscarinic, serotonergic, histaminergic, dopaminergic, GABA, and adrenergic) and ion channels. Although validation experiments are still necessary, the C-map correlation to drugs with activities previously linked to snake venoms supports the efficacy of this strategy as a broad-spectrum approach for biological activity screening, and rekindles the snake venom-based search for new therapeutic agents.

Microbial metabolites of omeprazole activate murine aryl hydrocarbon receptor in vitro and in vivo

Omeprazole (OME), a proton pump inhibitor used to treat gastritis, is also an aryl hydrocarbon receptor (AhR) activator. OME activates AhR in human hepatocytes and hepatoma cells, but not in mice in vivo or in vitro. We recently discovered that this species-specific difference results from a difference in a few amino acids in the ligand-binding domain of AhR. However, OME activates both mouse and human AhRs in the yeast reporter assay system. Nevertheless, the cause of this discrepancy in OME responses remains unknown. Here, we report that CYP1A1 mRNA expression in mouse cecum was elevated after OME administration, although the mouse is regarded as an OME-unresponsive animal. Using the yeast reporter assay system with human and murine AhRs, we found AhR agonist-like activity in the cecal extracts of OME-treated mice. We speculated that OME metabolites produced by cecal bacteria might activate murine AhRs in vivo. In high-performance liquid chromatography (HPLC) analysis, AhR agonist-like activity of cecal bacterial culture and cecal extracts were detected at the same retention time. AhR agonist-like activity was also detected in the HPLC fractions of yeast culture media containing OME. This unknown substance could induce reporter gene expression via mouse and human AhRs. The agonist-like activity of the OME metabolite was reduced by concomitant α-naphthoflavone exposure. These results indicate that a yeast-generated OME metabolite elicited the response of mouse AhR to OME in the yeast system, and that bacterial OME metabolites may act as AhR ligands in human and mouse intestines.

Identification of amino acid residues in the ligand-binding domain of the aryl hydrocarbon receptor causing the species-specific response to omeprazole: possible determinants for binding putative endogenous ligands

Omeprazole (OME) induces the expression of genes encoding drug-metabolizing enzymes, such as CYP1A1, via activation of the aryl hydrocarbon receptor (AhR) both in vivo and in vitro. However, the precise mechanism of OME-mediated AhR activation is still under investigation. While elucidating species-specific susceptibility to dioxin, we found that OME-mediated AhR activation was mammalian species specific. Moreover, we previously reported that OME has inhibitory activity toward CYP1A1 enzymes. From these observations, we speculated that OME-mediated AhR target gene transcription is due to AhR activation by increasing amounts of putative AhR ligands in serum by inhibition of CYP1A1 activity. We compared the amino acid sequences of OME-sensitive rabbit AhR and nonsensitive mouse AhR to identify the residues responsible for the species-specific response. Chimeric AhRs were constructed by exchanging domains between mouse and rabbit AhRs to define the region required for the response to OME. OME-mediated transactivation was observed only with the chimeric AhR that included the ligand-binding domain (LBD) of the rabbit AhR. Site-directed mutagenesis revealed three amino acids (M328, T353, and F367) in the rabbit AhR that were responsible for OME-mediated transactivation. Replacing these residues with those of the mouse AhR abolished the response of the rabbit AhR. In contrast, substitutions of these amino acids with those of the rabbit AhR altered nonsensitive mouse AhR to become sensitive to OME. These results suggest that OME-mediated AhR activation requires a specific structure within LBD that is probably essential for binding with enigmatic endogenous ligands.

Expression of Cytochromes P-450 2E1, 3A4 and 1A1/1A2 in Growing and Confluent Human HepG2 Hepatoma Cells-Effect of Ethanol

In cultured human hepatoma HepG2 cells, cytochrome (CYP) 1A-associated 7-ethoxyresorufin-O-deethylase (EROD), CYP 3A-associated benzyloxyresorufin O-debenzylase (BROD) and CYP 2E1-associated p-nitrophenol-hydroxylase (PNPH) decreased during time in culture. The enzyme activities in cells at confluence were 35-60% of the activities in cells 24 hours after seeding. Similarly, CYP 3A and CYP 2E1 proteins were present at higher concentrations in growing (G) than in confluent (C) HepG2 cells. CYP 1A1/1A2 protein was not detected, neither in G nor in C HepG2 cells but was strongly induced by 3-methylcholanthrene (3-MC) treatment. Ethanol (EtOH) was shown to increase CYP 2E1 and CYP 3A proteins and CYP 1A1/1A2-, CYP 2E1- and CYP 3A-associated mixed-function oxidase activities (MFOs) in HepG2 cells, as has been previously reported for primary cultures of human hepatocytes. These effects were observed only at the beginning of culture, in growing HepG2 cells, demonstrating the influence of the growth stage of HepG2 cells on their response to EtOH treatment. This is, to our knowledge, the first report on increases in CYP proteins and associated MFOs by EtOH in HepG2 cells. It suggests that growing HepG2 cells provide a useful in vitro model system in which to study the regulation of human CYPs by EtOH.

Transcriptional modulation of the NAD(P)H:quinone oxidoreductase 1 by mercury in human hepatoma HepG2 cells

NAD(P)H:quinone oxidoreductase (NQO1)-mediated detoxification of quinones plays a critical role in cancer prevention. Heavy metals such as mercury (Hg(2+)) alter the carcinogenicity of aryl hydrocarbon receptor ligands, mainly by modifying various xenobiotic-metabolizing enzymes such as NQO1. Therefore, we examined the effect of Hg(2+) on the expression of NQO1 in human hepatoma HepG2 cells. For this purpose HepG2 cells were incubated with various concentrations of Hg(2+) (2.5, 5, and 10μM) in the presence and absence of two NQO1 inducers, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and isothiocyanate sulforaphane (SUL), as bifunctional and monofunctional inducers, respectively. Analysis of the time-dependent effect of Hg(2+) revealed that Hg(2+) increased the expression of NQO1 mRNA in a time-dependent manner. In addition, Hg(2+) increased NQO1 at the mRNA, protein, and activity levels in the presence and absence of both NQO1 inducers, TCDD and SUL, which coincided with increased nuclear accumulation of Nrf2 protein. Investigating the effect of Hg(2+) at the transcriptional level revealed that Hg(2+) significantly induced the antioxidant-responsive element-dependent luciferase reporter gene expression in the absence and the presence of both NQO1 inducers. NQO1 mRNA and protein decay experiments revealed a lack of posttranscriptional and posttranslational mechanisms. Transfecting HepG2 cells with siRNA for Nrf2 significantly decreased the Hg(2+)-mediated induction of NQO1 mRNA and catalytic activity by approximately 90%. In conclusion, we demonstrated that Hg(2+) regulates the expression of the NQO1 gene through a transcriptional mechanism in human hepatoma HepG2 cells. In addition, Nrf2 is involved in the modulation of NQO1 by Hg(2+).

Omeprazole attenuates hyperoxic lung injury in mice via aryl hydrocarbon receptor activation and is associated with increased expression of cytochrome P4501A enzymes

Hyperoxia contributes to lung injury in experimental animals and bronchopulmonary dysplasia (BPD) in preterm infants. Cytochrome P4501A (CYP1A) enzymes, which are regulated by the aryl hydrocarbon receptor (AhR), have been shown to attenuate hyperoxic lung injury in rodents. Omeprazole, a proton pump inhibitor, used in humans to treat gastric acid-related disorders, induces hepatic CYP1A in vitro. However, the mechanism by which omeprazole induces CYP1A and its impact on CYP1A expression in vivo and hyperoxic lung injury are unknown. Therefore, we tested the hypothesis that omeprazole attenuates hyperoxic lung injury in adult wild-type (WT) C57BL/6J mice by an AhR-mediated induction of pulmonary and hepatic CYP1A enzymes. Accordingly, we determined the effects of omeprazole on pulmonary and hepatic CYP1A expression and hyperoxic lung injury in adult WT and AhR dysfunctional (AhRd) mice. We found that omeprazole attenuated lung injury in WT mice. Attenuation of lung injury by omeprazole paralleled enhanced pulmonary CYP1A1 and hepatic CYP1A2 expression in the omeprazole-treated mice. On the other hand, omeprazole failed to enhance pulmonary CYP1A1 and hepatic CYP1A2 expression and protect against hyperoxic lung injury in AhRd mice. In conclusion, our results suggest that omeprazole attenuates hyperoxic lung injury in mice by AhR-mediated mechanisms, and this phenomenon is associated with induction of CYP1A enzymes. These studies have important implications for the prevention and/or treatment of hyperoxia-induced disorders such as BPD in infants and acute respiratory distress syndrome in older children and adults.

CYP Induction-Mediated Drug Interactions: in Vitro Assessment and Clinical Implications

Cytochrome P450 (CYP) induction-mediated interaction is one of the major concerns in clinical practice and for the pharmaceutical industry. There are two major issues associated with CYP induction: a reduction in therapeutic efficacy of comedications and an induction in reactive metabolite-induced toxicity. Because CYP induction is a metabolic liability in drug therapy, it is highly desirable to develop new drug candidates that are not potent CYP inducer to avoid the potential of CYP induction-mediated drug interactions. For this reason, today, many drug companies routinely include the assessment of CYP induction at the stage of drug discovery as part of the selection processes of new drug candidates for further clinical development. The purpose of this article is to review the molecular mechanisms of CYP induction and the clinical implications, including pharmacokinetic and pharmacodynamic consequences. In addition, factors that affect the degree of CYP induction and extrapolation of in vitro CYP induction data to in vivo situations will also be discussed. Finally, assessment of the potential of CYP induction at the drug discovery and development stage will be discussed.

Vinclozolin, a widely used fungizide, enhanced BaP-induced micronucleus formation in human derived hepatoma cells by increasing CYP1A1 expression

Vinclozolin, a widely used fungicide, can be identified as a residue in numerous vegetable and fruit samples. To get insight in its genetic toxicity, we investigated the genotoxic effect of vinclozolin in the human derived hepatoma cell line HepG2 using the micronucleus (MN) assay. Additionally, to evaluate the co- or anti-mutagenic potency of vinclozolin, we treated HepG2 cells with different concentrations of vinclozolin for 24 h. Subsequently, the cells were exposed to benzo[a]pyrene (BaP) for 1h. Exposure of HepG2 cells to 50-400 microM vinclozolin alone did not cause any induction of micronuclei. However, a pronounced co-mutagenic effect was observed. MN frequencies caused by BaP increased by 30.6%, 52.8% and 65.3% after pretreatment of the cell cultures with 50, 100 and 200 microM vinclozolin, respectively. The highest concentration (400 microM) of vinclozolin tested caused cytotoxicity. Therefore, micronuclei were not considered for that concentration. To clarify the mechanism of cogenotoxicity, we assayed cytochrome P450 1A1 (CYP1A1), which plays a pivotal role in activation of BaP. Cells exposed to vinclozolin led to significant increase of CYP1A1 expression in Western blot. The result suggested that induction of CYP1A1 by vinclozolin account for its enhancing effect on genotoxicity caused by BaP.

Organochlorine insecticides: impacts on human HepG2 cytochrome P4501A, 2B activities and glutathione levels

This study examined the effects of the organochlorine (OC) insecticides chlordane, o,p'-DDT, dieldrin, endosulfan, kepone, methoxychlor, and toxaphene on human HepG2 cytochrome P450 (1A-EROD and 2B-PROD) activities and glutathione (GSH) levels. Cells were exposed for 24 h at high concentrations (1, 5 or 10 mM) and for 48 h at lower concentrations ranging from 0.01 to 1 mM to evaluate dose responses. Our results show that after 48 h all but dieldrin significantly induced both P4501A and 2B. P4502B responses were greater at all exposure concentrations and times. Mixed responses in GSH levels were observed. All OCs except dieldrin and MXC significantly depleted GSH after 24 h. At 48 h, chlordane, endosulfan and toxaphene significantly increased GSH at low levels and decreased GSH at high levels, while kepone and methoxychlor produced significant declines in GSH at all concentrations. These results support findings of OC insecticides inducing CYP1A, 2B in rats, with CYP2B responses more important. GSH levels declined when P4502B activity was significantly elevated and were significantly increased in the absence of significant P450 activity, suggesting that GSH levels influence the catalytic activity of the cytochrome P450s and the cytochrome P450s influence the cell's ability to regulate GSH.

CYP35: xenobiotically induced gene expression in the nematode Caenorhabditis elegans

Although over 80 cytochrome P450 (CYP) encoding genes have been identified in the genome of the nematode Caenorhabditis elegans very little is known about their involvement in biotransformation. This paper demonstrates a concentration-dependent relationship of C. elegans CYP35A1, A2, A5, and C1 gene expression in response to four organic xenobiotics, namely atrazine, PCB52, fluoranthene, and lansoprazole. The toxicity of these xenobiotics was determined using a reproduction assay. CYP-specific messenger RNA expression was analyzed by semi-quantitative RT-PCR resulting in a strongly increasing, concentration-dependent induction well below the EC50 for reproduction. For PCB52, approximately 0.5% of the EC50 induces a 2-fold increase of CYP35 gene expression. Using a double mutant and multiple RNAi of CYP35A/C it was possible to diminish the reproduction decline caused by PCB52 and fluoranthene.

Involvement of cytochrome P450 1A in sanguinarine detoxication

Sanguinarine (SA), a member of the benzo[c]phenanthridine alkaloids, is a potent anti-microbial agent with anti-inflammatory and anti-neoplastic properties. However, toxicity of the alkaloid severely limits its medical applications. Recent report by Williams et al. implicated rat hepatic cytochrome P450 (CYP) 1A2 as a likely modulator of SA toxicity. Indeed, the in vitro toxicity of SA in primary culture of rat hepatocytes and human hepatic cell line HepG2, demonstrated as lactate dehydrogenase leakage and metabolic capability (MTT assay), was diminished following induction of CYP1A by 2,3,7,8-tetrachlorodibenzo-p-dioxin, 3-methylcholanthrene, and beta-naphtoflavone. Using microsomes containing recombinant CYP1A1 or CYP1A2 we show that SA causes non-competitive inhibition of the former and competitive inhibition of the latter as assessed by ethoxyresorufin de-ethylation (EROD). In human hepatic microsomes SA exhibits competitive inhibition of EROD activity with apparent K(i) of 2 microM, a value identical to that observed for CYP1A2 inhibition in recombinant system. Pre-incubation of SA with human liver microsomes resulted in time-dependent, but not dose-dependent decline in EROD activity suggesting CYP1A2 inhibition is not mechanism based. SA also inhibits activity of NADPH:CYP reductase, an enzyme required for CYP activity, with IC(50) very similar to that observed for EROD inhibition. Tentative mechanism for CYP1A involvement in decreased in vitro SA toxicity is discussed.

Benzimidazole drugs and modulation of biotransformation enzymes

Benzimidazole drugs (e.g., anthelmintics albendazole, fenbendazole, oxfenbendazole, thiabendazole, mebendazole; inhibitors of proton pump omeprazole, lansoprasole, pantoprasole) represent substances used in both human and veterinary medicine; however, from the point of view of induction and inhibition of biotransformation enzymes, research has been carried out mainly due to the initiative of human pharmacologists. The purpose of the present review is to inform about inductive and inhibitive effects of benzimidazole drugs in man, animals and cell cultures. Pharmacological and toxicological consequences of modulation of biotransformation enzymes are discussed and the significance of studies in the field of modulation of biotransformation enzymes in food-producing animals is explained. Since the modulating effect of benzimidazoles strongly varies depending on structure of the individual substances, the particular attention is paid to structure-modulation relationships.

The effects of benzimidazole anthelmintics on P4501A in rat hepatocytes and HepG2 cells

Benzimidazole anthelmintics including albendazole, fenbendazole, and mebendazole are widely used in veterinary medicine. The effects of these benzimidazoles on cytochrome P4501A were investigated in primary cultures of rat hepatocytes and in the HepG2 cell line. After incubation of rat hepatocytes and HepG2 for 24-, 48-, and 72-h cells with drugs at various concentrations (0.1-50 microM), the enzyme activities associated with P4501A1/2 (7-ethoxyresorufin O-deethylation and 7-methoxyresorufin O-demethylation) were measured. The P4501A1/2 protein levels in both model systems were determined by Western blotting. Although all benzimidazoles provoked a significant increase of P4501A1/2 protein levels and P4501A activities, large differences in the induction response were found which was dependent on drug structure, concentration, and model system used. Based on the results, relationships between induction potency and structure of drug were demonstrated, as well as differences between the in vitro systems used. Therefore, pharmacological and toxicological consequences of cytochrome P4501A induction by benzimidazole drugs should be taken into account in veterinary therapy.

The effects of mebendazole on P4501A activity in rat hepatocytes and HepG2 cells. Comparison with tiabendazole and omeprazole

Mebendazole is a benzimidazole anthelmintic widely used in veterinary and human therapy. Among benzimidazole derivatives, several drugs with inducing effect on cytochromes P450 can be found. However, the induction capacity of mebendazole on P450s has not been explored yet. In this study, the effects of mebendazole on P4501A activity was tested in primary cultures of rat hepatocytes and in human hepatoma HepG2 cell line. Two known P4501A inducers with benzimidazole structure, tiabendazole and omeprazole, were also included in the experiments with the aim of studying structure-induction relationships. After 24-, 48- and 72-h incubation of rat hepatocytes and HepG2 cells with drugs in various concentrations (0.1-100 microM), enzyme activity associated with P4501A1/2 (EROD, MROD) was measured. In addition, the P4501A1/2 protein levels in both in-vitro systems were determined by Western-blotting. Mebendazole provoked a significant increase in P4501A1/2 protein expression and P4501A activity in both in-vitro systems. Omeprazole caused a significant dose-dependent increase of P4501A activity only in HepG2 cells. Although tiabendazole treatment led to significant increase of P4501A protein level, no effect on P4501A activity was observed in either system. The results demonstrate that mebendazole possesses the ability to significantly induce P4501A. Thus, pharmacological and toxicological consequences of P4501A induction should be taken into account in human therapy. The structure-induction relationships and differences between in-vitro systems used are discussed.

Differential drug-induced mRNA expression of human CYP3A4 compared to CYP3A5, CYP3A7 and CYP3A43

Drug-mediated regulation of mRNA expression of all members of the cytochrome P450 3A (CYP3A) subfamily has been measured by reverse transcription-polymerase chain reaction (RT-PCR) in the human hepatocellular carcinoma cell line, HepG2. Transcriptional regulation was proved by inhibition of induction with actinomycin D. Besides the positive control dexamethasone, the H(+)/K(+)-ATPase inhibitors omeprazole, lansoprazole, pantoprazole, and rabeprazole, and the herbal antidepressant St. John's wort (Hypericum extract) were studied. All CYP3A mRNAs were induced by dexamethasone. CYP3A4 was the only CYP3A isoform that was induced by all of the four benzimidazole derivatives, while CYP3A5, CYP3A7, and CYP3A43 were unaffected or even slightly downregulated by these drugs. St. John's wort also increased CYP3A4 mRNA exclusively, leaving CYP3A5 and CYP3A43 unaffected, whereas CYP3A7 was decreased. Depending on the inducer, expression of CYP3A4 is differently regulated from CYP3A5, CYP3A7, and CYP3A43.

Time-dependent transcriptional induction of CYP1A1, CYP1A2 and CYP1B1 mRNAs by H+/K+ -ATPase inhibitors and other xenobiotics

1. Xenobiotic-mediated regulation of mRNA expression of all members of the human cytochrome P450 (CYP) 1 family has been measured by RT-PCR in the hepatoma cell line, HepG2. Besides the positive control beta -naphthoflavone, the H(+)/K(+)-ATPase inhibitors omeprazole, lansoprazole, pantoprazole and rabeprazole and the anti-malaria drug primaquine were included in this study. 2. beta-Naphthoflavone, primaquine, omeprazole and lansoprazole increased mRNA levels of CYP1A1, CYP1A2 and CYP1B1. Induction by rabeprazole was significant only for CYP1A1 and CYP1A2, whereas none of the CYP1 mRNAs was induced by pantoprazole. This result was confirmed in primary human hepatocytes. 3. Transcriptional regulation was proved by inhibition of induction with actinomycin D. 4. Increase of CYP1 mRNA was significant after 1 h and maximal after 4 h. CYP1B1, but not CYP1A1 or CYP1A2, was dramatically down-regulated between 4 and 24 h. This decrease was prevented by treatment of cells with actinomycin D after induction, indicating an active transcription-dependent mechanism of CYP1B1 mRNA degradation. 5. In conclusion, xenobiotics inducing CYP1A1 mRNA expression have been shown also to induce CYP1A2 and CYP1B1, differing only with regard to level and time course of induction.

Induction of cytochrome P4501A1 by autoclavable culture medium change in HepG2 cells

1. Without the addition of xenobiotics, only by changing the culture medium can one induce extensively and transiently cytochrome P4501A1 (CYP1A1) protein and mRNA in human hepatoma HepG2 cells. The induction was aryl hydrocarbon receptor (AhR)-dependent, and was proven by: (1) the medium change activated the AhR, as judged by a electrophoretic mobility shift assay; and (2) the AhR inhibitor alpha-naphthoflavone inhibited the medium change-mediated induction. 2. Induction of CYP1A1 was related to medium prepared by autoclaving. By screening the ingredients in the medium, the serum had no effect on CYP1A1 induction, whereas both photo-oxidized and autoclaved tryptophan were shown to induce CYP1A1, as indicated by CYP1A1 protein or ethoxyresorufin-O-deethylase activity. The autoclaved tryptophan contained in an autoclavable medium was a more potent inducer of CYP1A1 than photo-oxidized tryptophan. 3. The results provide some practical suggestions with experiments related to CYP1A1.

Musk ketone enhances benzo(a)pyrene induced mutagenicity in human derived Hep G2 cells

Musk ketone is a widely used artificial fragrance which has been identified in human fatty tissue and milk. The mutagenic and comutagenic effects of this compound were studied in micronucleus tests with a human derived hepatoma cell line (Hep G2). Exposure of the cells to MK alone in the range between 5 and 5000 ng/ml did not cause induction of MN. When the cells were treated simultaneously with MK (5-5000 ng/ml) and 0.2 microg/ml benzo(a)pyrene, no synergistic effects were detected; benzo(a)pyrene (B(a)P) itself caused an 1.5-fold increase of MN over the spontaneous background frequency (60 versus 39 MN/1000 binucleated cells). In a third experimental series, the cells were pretreated with MK for 28h and subsequently exposed to 0.2 microg/ml B(a)P. In this case, a pronounced comutagenic effect was observed: The LOAEL for MK was 0.05 microg/ml. With higher doses (0.5, 1.0 and 5.0 microg MK/ml), a significant increase of B(a)P induced MN frequencies was measured, the induction rates being 50, 66, and 88%, respectively. Additional measurements of 7-ethoxyresorufin deethylase indicated that MK induces cytochrome P450 isoenzymes (1A1) which play a key role in the activation of B(a)P. The results of the present study show that MK amplifies the genotoxic effects of B(a)P in human derived cells and indicate that exposure of humans to MK might increase their susceptibility to the health hazards of B(a)P and other polycyclic aromatic hydrocarbons.

Clinical experience with pantoprazole in gastroesophageal reflux disease

BACKGROUND

Pantoprazole is a new proton pump inhibitor indicated for the treatment of erosive esophagitis associated with gastroesophageal reflux disease (GERD) and is available in both oral and intravenous (IV) formulations.

OBJECTIVE

This paper reviews the pharmacologic properties of pantoprazole and summarizes the findings from clinical studies of this drug.

METHODS

This review was compiled from the published literature, abstracts from clinical trials, and data on file with the manufacturer of pantoprazole.

RESULTS

Pantoprazole selectively accumulates in the acidic environment of gastric parietal cells and acts at the final step of acid secretion by binding 2 key cysteine residues of the proton pump involved in gastric acid production. The bioavailability of pantoprazole is not altered by concomitant administration of food or antacids or with repeated dosing. Both oral and IV formulations of pantoprazole exhibit linear pharmacokinetics. Several clinical trials have proved pantoprazole superior to histamine-2-receptor antagonists (H2RAs) in reducing acid secretion and elevating gastric pH levels. Pantoprazole has been shown to be more effective than ranitidine (P < 0.05), famotidine (P < 0.001), and nizatidine (P < 0.05), and at least as effective as omeprazole, in healing erosive esophagitis and relieving associated symptoms of GERD, including regurgitation. Pantoprazole is also more effective than the H2RA nizatidine for the treatment of nighttime heartburn (P < 0.05). Studies have shown pantoprazole to be well tolerated; adverse events, including headache, diarrhea, flatulence, abdominal pain, eructation, nausea, and rash, occurred in < or = 6% of patients. The oral and IV formulations of pantoprazole are equally potent in inhibiting gastric acid secretion; thus, switching between formulations requires no dosage adjustments. Special patient populations, including the elderly and patients with renal or mild to moderate hepatic impairment, can take pantoprazole without an adjustment in dosage.

CONCLUSIONS

Because of its unique pharmacokinetic properties, mechanism of action, and reduced potential for producing cytochrome P-450-based drug interactions, pantoprazole in both oral and IV formulations is effective over a full 24 hours and is well tolerated in a variety of patient types.

Prediction of aryl hydrocarbon receptor-mediated enzyme induction of drugs and chemicals by mRNA quantification

Enzyme-specific testing for drug interactions by in vitro techniques has become a routine practice in drug development. With many drugs, enzyme induction has similar importance for the prediction of drug-drug interactions. We developed a method for recognizing enzyme induction mediated via the aryl hydrocarbon receptor. This type of induction may be clinically important since experimental data suggest a higher rate of toxification in induced subjects. Twenty-four drugs and environmental chemicals, selected as prototype inducers or being chemically related to known inducers, including HIV protease inhibitors nelfinavir, saquinavir, ritonavir, and indinavir, were tested for their potency to induce cytochrome P450 1A1 mRNA in human Hela cell cultures by a quantitative reverse transcriptase polymerase chain reaction. Known prototype inducers such as beta-naphthoflavone and 3-methylcholanthrene exhibited the highest inducing potency quantified with an Imax value (maximal induction of cytochrome P450 1A1 mRNA synthesis) of 5.48 and 10.7 x 10(6) mRNA molecules per 150 ng of total RNA, respectively. The enzyme-inducing efficacy of some compounds such as resveratrol (2.92 x 10(6)) and the protease inhibitors was not much lower (2.23-3.08 x 10(6)). All compounds that were structurally similar to benzimidazoles exhibited some extent of enzyme induction; e.g., Imax values were 0.86 x 10(6), 0.20 x 10(6), and 0.14 x 10(6) for omeprazole, lansoprazole, and losartan, respectively. To predict the clinical relevance of these inducing effects, the concentration at half-maximal induction IM was estimated; the plasma concentrations of these drug substances were within 1 order of magnitude of the IM values, upon usual dosage. In conclusion, cytochrome P450 1A1 enzyme induction by drugs is a common phenomenon, though there is a great range in the inducing efficacy. In vitro prediction of enzyme induction may be useful for explaining or foreseeing drug interactions, drug side effects, or toxicity by xenobiotics.

An evaluation of the cytochrome P450 induction potential of pantoprazole in primary human hepatocytes

Primary human hepatocytes contain a full complement of human drug-metabolizing enzymes and therefore represent a relevant experimental system for the evaluation of pharmacokinetic drug-drug interaction potential in human. In this study, the cytochrome P450 (CYP) induction potential of pantoprazole (PAN) was evaluated and compared to two other proton pump inhibitors (PPIs), omeprazole (OM) and lansoprazole (LAN). Primary human hepatocytes from three donors were studied. The hepatocytes were cultured for 3 days, followed by treatment for 3 days with the PPIs at 2, 5 and 10 microM. Two other known CYP inducers, 3-methylcholanthrene at 1 microM and rifampin at 50 microM, were also evaluated. Induction potentials of these chemicals for CYP1A and CYP3A were evaluated by isozyme activity and isozyme content. 7-Ethoxyresorufin-O-deethylase and testosterone 6beta-hydroxylase activities were used as endpoints for CYP1A and CYP3A, respectively. Isozyme protein contents of CYP1A and CYP3A were evaluated via Western blotting. The results showed that for CYP1A induction, the rank ordering in induction potential was consistently OM > LAN > PAN. CYP3A induction by the PPI's were observed in two of the three hepatocyte cultures, with no apparent differences in induction potency for the three compounds. Our results on CYP1A induction suggest that PAN has a lower drug-drug interaction potential than OM and LAN.

Molecular modelling and quantitative structure-activity relationship studies on the interaction of omeprazole with cytochrome P450 isozymes

Molecular modelling of the anti-ulcerative agent, omeprazole, with the putative active sites of cytochromes P4503A4 and P4502C19, enzymes which are the major catalysts of omeprazole metabolism in man, are reported. Interactive docking of omeprazole in both CYP3A4 and CYP2C19 gives rise to binding orientations which are consistent with both the known sites of metabolism reported for these isoforms and with evidence from site-directed mutagenesis experiments on CYP2C19, a P450 associated with genetic polymorphism in human drug metabolism. The potential P450 enzymic interactions, inhibition and induction of omeprazole are discussed in the light of molecular modelling and QSAR (quantitative structure-activity relationship) studies on related compounds.