Drug-metabolising enzymes are down-regulated by hypoxia in differentiated human hepatoma HepaRG cells: HIF-1alpha involvement in CYP3A4 repression

Effect of hypoxia on aquaporins and hepatobiliary transport systems in human hepatic cells

OBJECTIVES

Hepatic ischemia and hypoxia are accompanied by reduced bile flow, biliary sludge and cholestasis. Hepatobiliary transport systems, nuclear receptors and aquaporins were studied after hypoxia and reoxygenation in human hepatic cells.

METHODS

Expression of Aquaporin 8 (AQP8), Aquaporin 9 (AQP9), Pregnane X receptor (PXR), Farnesoid X receptor (FXR), Organic anion transporting polypeptide 1 (OATP1), and the Multidrug resistance-associated protein 4 (MRP4) were investigated in induced pluripotent stem cells (iPSCs) derived hepatic cells and the immortalized hepatic line HepG2. HepG2 was subjected to combined oxygen and glucose deprivation for 4 h followed by reoxygenation.

RESULTS

Expression of AQP8 and AQP9 increased during differentiation in iPSC-derived hepatic cells. Hypoxia did not alter mRNA levels of AQP8, but reoxygenation caused a marked increase in AQP8 mRNA expression. While expression of OATP1 had a transient increase during reoxygenation, MRP4 showed a delayed downregulation. Knock-down of FXR did not alter the expression of AQP8, AQP9, MRP4, or OATP1. Post-hypoxic protein levels of AQP8 were reduced after 68 h of reoxygenation compared to normoxic controls.

CONCLUSIONS

Post-transcriptional mechanisms rather than reduced transcription cause reduction in AQP8 protein concentration after hypoxia-reoxygenation in hepatic cells. Expression patterns differed between hepatobiliary transport systems during hypoxia and reoxygenation.

IMPACT

Expression of AQP8 and AQP9 increased during differentiation in induced pluripotent stem cells. Expression of hepatobiliary transporters varies during hypoxia and reoxygenation. Post-hypoxic protein levels of AQP8 were reduced after 68 h of reoxygenation. Post-transcriptional mechanisms rather than reduced transcription cause reduction in AQP8 protein concentration after hypoxia-reoxygenation in hepatic cells. Hypoxia and reoxygenation may affect aquaporins in hepatic cells and potentially affect bile composition.

Regulatory role of oxidative stress in retrorsine - Induced apoptosis and autophagy in primary rat hepatocytes

Pyrrolizidine alkaloids (PAs) are a group of naturally occurring alkaloids widely present in plants. PAs are highly hepatotoxic and have been documented to cause many incidents of human and animal poisoning. Retrorsine (RTS) is a pyrrolizidine alkaloid (PA) derived from the Compositae Senecio, which has been shown to cause hepatotoxicity. Human liver poisoning occurs through the consumption of RTS-contaminated food, and animals can also be poisoned by ingesting RTS-containing toxic plants. The mechanism of RTS-induced liver toxicity is not fully understood. In this study, we demonstrated that RTS-induced oxidative stress plays a pivotal role in RTS-induced liver toxicity involving apoptosis and autophagy. The results showed that RTS treatment in the cultured Primary rat hepatocytes caused cytotoxicity and release of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in a time- and dose-dependent manner. Our study showed that treatment of RTS induced ROS and MDA (malondialdehyde, a lipid peroxidation marker) in the hepatocytes, and reduced antioxidant capacity (GSH content, SOD activity), suggesting RTS treatment caused oxidative stress response in the hepatocytes. Furthermore, we found that RTS induced apoptosis and autophagy in the hepatocytes, and RTS-induced apoptosis and autophagy could be alleviated by ROS scavenger N-acetylcysteine (NAC) and the MAPK pathway inhibitors suggesting ROS/MAPK signaling pathway plays a role in RTS induced apoptosis and autophagy. Collectively, this study reveals the regulatory mechanism of oxidative stress in RTS-induced apoptosis and autophagy in the hepatocytes, providing important insights of molecular mechanisms of hepatotoxicity induced by RTS and related pyrrolizidine alkaloids in liver. This mechanism provides a basis for the prevention and treatment of PA poisoning in humans and animals.

Role of Hypoxia and Rac1 Inhibition in the Metastatic Cascade

The hypoxic condition has a pivotal role in solid tumors and was shown to correlate with the poor outcome of anticancer treatments. Hypoxia contributes to tumor progression and leads to therapy resistance. Two forms of a hypoxic environment might have relevance in tumor mass formation: chronic and cyclic hypoxia. The main regulators of hypoxia are hypoxia-inducible factors, which regulate the cell survival, proliferation, motility, metabolism, pH, extracellular matrix function, inflammatory cells recruitment and angiogenesis. The metastatic process consists of different steps in which hypoxia-inducible factors can play an important role. Rac1, belonging to small G-proteins, is involved in the metastasis process as one of the key molecules of migration, especially in a hypoxic environment. The effect of hypoxia on the tumor phenotype and the signaling pathways which may interfere with tumor progression are already quite well known. Although the role of Rac1, one of the small G-proteins, in hypoxia remains unclear, predominantly, in vitro studies performed so far confirm that Rac1 inhibition may represent a viable direction for tumor therapy.

New in vitro screening system to detect drug-induced liver injury using a culture plate with low drug sorption and high oxygen permeability

Drug-induced liver injury (DILI) is a major factor underlying drug withdrawal from the market. Therefore, it is important to predict DILI during the early phase of drug discovery. Metabolic activation and mitochondrial toxicity are good indicators of the potential for DILI. However, hepatocyte function, including drug-metabolizing enzyme activity and mitochondrial function, reportedly decreases under conventional culture conditions; therefore, these conditions fail to precisely detect metabolic activation and mitochondrial toxicity-induced cell death. To resolve this issue, we employed a newly developed cell culture plate with high oxygen permeability and low drug sorption (4-polymethyl-1-pentene [PMP] plate). Under PMP plate conditions, cytochrome P450 (CYP) activity and mitochondrial function were increased in primary rat hepatocytes. Following l-buthionine-sulfoximine-induced glutathione depletion, acetaminophen-induced cell death significantly increased under PMP plate conditions. Additionally, 1-aminobenzotriazole reduced cell death. Moreover, mitochondrial toxicity due to mitochondrial complex inhibitors (ketoconazole, metformin, and phenformin) increased under PMP plate conditions. In summary, PMP plate conditions could improve CYP activity and mitochondrial function in primary rat hepatocytes and potentially detect metabolic activation and mitochondrial toxicity.

Evaluation of Drug-Drug Interaction Potential of Enarodustat (JTZ-951) Using a Cytochrome P450 Probe Cocktail

The drug interaction potential of enarodustat (doses: 25, 50 mg) on the activity of cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6, and 3A4 was evaluated after once-daily administration for 15 days in a phase 1 multiple-ascending-dose study in healthy subjects. Probe substrates specific for the enzymes, i.e., caffeine (CYP1A2), tolbutamide (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), and midazolam (CYP3A4), were administered orally as a cocktail with (day 15) and without (day -3) enarodustat. Drug interaction was based on geometric mean maximum plasma concentration (Cmax ) and area under the plasma concentration-time curve from the time of dosing to infinity (AUCinf ) ratios (day 15/day -3) for CYP1A2, 2C9, 2C19, 2D6, 3A4, and urinary excretion of dextromethorphan metabolite dextrorphan for CYP2D6. At the 2 enarodustat doses, for caffeine, the geometric mean ratios (range) for Cmax and AUCinf were 0.99-1.06 and 1.61-1.63, respectively. The ratios for peak concentrations and total exposures were 0.98-1.07 and 0.71-1.78 for tolbutamide and omeprazole, respectively. For dextrorphan the Cmax and AUCinf ratios were 0.83-0.90 and 1.02-1.04, respectively. The mean dextrorphan cumulative amount excreted into the urine from the time of dosing to 24 hours values on day -3 and day 15 were 8.25 mg and 8.20 mg at the lower dose, and 9.40 mg and 9.51 mg at the higher dose. The ratios for midazolam Cmax and AUCinf were 1.42-1.63. Overall, there was a lack of enarodustat dose dependency regarding the geometric mean ratios and 90% confidence intervals and urinary excretion of dextrorphan. There were some cases where the 90% confidence intervals at the 2 enarodustat doses were outside the 0.80-1.25 range, but changes in the geometric mean ratios were all <2-fold.

The effects of hexabromocyclododecane on the transcriptome and hepatic enzyme activity in three human HepaRG-based models

The disruption of thyroid hormone homeostasis by hexabromocyclododecane (HBCD) in rodents is hypothesized to be due to HBCD increasing the hepatic clearance of thyroxine (T4). The extent to which these effects are relevant to humans is unclear. To evaluate HBCD effects on humans, the activation of key hepatic nuclear receptors and the consequent disruption of thyroid hormone homeostasis were studied in different human hepatic cell models. The hepatoma cell line, HepaRG, cultured as two-dimensional (2D), sandwich (SW) and spheroid (3D) cultures, and primary human hepatocytes (PHH) cultured as sandwich were exposed to 1 and 10 µM HBCD and characterized for their transcriptome changes. Pathway enrichment analysis showed that 3D models, followed by SW, had a stronger transcriptome response to HBCD, which is explained by the higher expression of hepatic nuclear receptors but also greater accumulation of HBCD measured inside cells in these models. The Pregnane X receptor pathway is one of the pathways most upregulated across the three hepatic models, followed by the constitutive androstane receptor and general hepatic nuclear receptors pathways. Lipid metabolism pathways had a downregulation tendency in all exposures and in both PHH and the three cultivation modes of HepaRG. The activity of enzymes related to PXR/CAR induction and T4 metabolism were evaluated in the three different types of HepaRG cultures exposed to HBCD for 48 h. Reference inducers, rifampicin and PCB-153 did affect 2D and SW HepaRG cultures' enzymatic activity but not 3D. HBCD did not induce the activity of any of the studied enzymes in any of the cell models and culture methods. This study illustrates that for nuclear receptor-mediated T4 disruption, transcriptome changes might not be indicative of an actual adverse effect. Clarification of the reasons for the lack of translation is essential to evaluate new chemicals' potential to be thyroid hormone disruptors by altering thyroid hormone metabolism.

The role of drug-metabolizing enzymes in synthetic lethality of cancer

Drug-metabolizing enzymes (DMEs) have shown increasing importance in anticancer therapy. It is not only due to their effect on activation or deactivation of anticancer drugs, but also because of their extensive connections with pathological and biochemistry changes during tumorigenesis. Meanwhile, it has become more accessible to discovery anticancer drugs that selectively targeted cancer cells with the development of synthetic lethal screen technology. Synthetic lethal strategy makes use of unique genetic markers that different cancer cells from normal tissues to discovery anticancer agents. Dysregulation of DMEs has been found in various cancers, making them promising candidates for synthetic lethal strategy. In this review, we will systematically discuss about the role of DMEs in tumor progression, the application of synthetic lethality strategy in drug discovery, and a link between DMEs and synthetic lethal of cancer.

High-altitude Hypoxia Influences the Activities of the Drug-Metabolizing Enzyme CYP3A1 and the Pharmacokinetics of Four Cardiovascular System Drugs

(1) Background: High-altitude hypoxia has been shown to affect the pharmacokinetic properties of drugs. Although there is a high incidence of cardiovascular disease among individuals living in high-altitude areas, studies on the effect of high-altitude hypoxia on the pharmacokinetic properties of cardiovascular drugs are limited. (2) Methods: The aim of this study was to evaluate the pharmacokinetics of nifedipine, bosentan, simvastatin, sildenafil, and their respective main metabolites, dehydronifedipine, hydroxybosentan, simvastatin hydroxy acid, and N-desmethyl sildenafil, in rats exposed to high-altitude hypoxia. Additionally, the protein and mRNA expression of cytochrome P450 3A1 (CYP3A1), a drug-metabolizing enzyme, were examined. (3) Results: There were significant changes in the pharmacokinetic properties of the drugs in rats exposed to high-altitude hypoxia, as evidenced by an increase in the area under the curve (AUC) and the half-life (t_1/2z) and a decrease in total plasma clearance (CL_z/F). However, most of these changes were reversed when the rats returned to a normoxic environment. Additionally, there was a significant decrease in CYP3A1 expression in rats exposed to high-altitude hypoxia at both the protein and mRNA levels. (4) Conclusions: High-altitude hypoxia suppressed the metabolism of the drugs, indicating that the pharmacokinetics of the drugs should be re-examined, and the optimal dose should be reassessed in patients living in high-altitude areas.

The Role of Catecholamines in Pathophysiological Liver Processes

Over the last few years, the number of research publications about the role of catecholamines (epinephrine, norepinephrine, and dopamine) in the development of liver diseases such as liver fibrosis, fatty liver diseases, or liver cancers is constantly increasing. However, the mechanisms involved in these effects are not well understood. In this review, we first recapitulate the way the liver is in contact with catecholamines and consider liver implications in their metabolism. A focus on the expression of the adrenergic and dopaminergic receptors by the liver cells is also discussed. Involvement of catecholamines in physiological (glucose metabolism, lipids metabolism, and liver regeneration) and pathophysiological (impact on drug-metabolizing enzymes expression, liver dysfunction during sepsis, fibrosis development, or liver fatty diseases and liver cancers) processes are then discussed. This review highlights the importance of understanding the mechanisms through which catecholamines influence liver functions in order to draw benefit from the adrenergic and dopaminergic antagonists currently marketed. Indeed, as these molecules are well-known drugs, their use as therapies or adjuvant treatments in several liver diseases could be facilitated.

Gut Microbiota as the Potential Mechanism to Mediate Drug Metabolism Under High-Altitude Hypoxia

BACKGROUND

The characteristics of pharmacokinetics and the activity and expression of drug-metabolizing enzymes and transporters significantly change under a high-altitude hypoxic environment. Gut microbiota is an important factor affecting the metabolism of drugs through direct or indirect effects, changing the bioavailability, biological activity, or toxicity of drugs and further affecting the efficacy and safety of drugs in vivo. A high-altitude hypoxic environment significantly changes the structure and diversity of gut microbiota, which may play a key role in drug metabolism under a high-altitude hypoxic environment.

METHODS

An investigation was carried out by reviewing published studies to determine the role of gut microbiota in the regulation of drug-metabolizing enzymes and transporters. Data and information on expression change in gut microbiota, drug-metabolizing enzymes and transporters under a high-altitude hypoxic environment were explored and proposed.

RESULTS

High-altitude hypoxia is an important environmental factor that can adjust the structure of the gut microbiota and change the diversity of intestinal microbes. It was speculated that the gut microbiota could regulate drug-metabolizing enzymes through two potential mechanisms, the first being through direct regulation of the metabolism of drugs in vivo and the second being indirect, i.e., through the regulation of drug-metabolizing enzymes and transporters, thereby affecting the activity of drugs.

CONCLUSION

This article reviews the effects of high-altitude hypoxia on the gut microbiota and the effects of these changes on drug metabolism.

Molecular Networking for Drug Toxicities Studies: The Case of Hydroxychloroquine in COVID-19 Patients

Using drugs to treat COVID-19 symptoms may induce adverse effects and modify patient outcomes. These adverse events may be further aggravated in obese patients, who often present different illnesses such as metabolic-associated fatty liver disease. In Rennes University Hospital, several drug such as hydroxychloroquine (HCQ) have been used in the clinical trial HARMONICOV to treat COVID-19 patients, including obese patients. The aim of this study is to determine whether HCQ metabolism and hepatotoxicity are worsened in obese patients using an in vivo/in vitro approach. Liquid chromatography high resolution mass spectrometry in combination with untargeted screening and molecular networking were employed to study drug metabolism in vivo (patient’s plasma) and in vitro (HepaRG cells and RPTEC cells). In addition, HepaRG cells model were used to reproduce pathophysiological features of obese patient metabolism, i.e., in the condition of hepatic steatosis. The metabolic signature of HCQ was modified in HepaRG cells cultured under a steatosis condition and a new metabolite was detected (carboxychloroquine). The RPTEC model was found to produce only one metabolite. A higher cytotoxicity of HCQ was observed in HepaRG cells exposed to exogenous fatty acids, while neutral lipid accumulation (steatosis) was further enhanced in these cells. These in vitro data were compared with the biological parameters of 17 COVID-19 patients treated with HCQ included in the HARMONICOV cohort. Overall, our data suggest that steatosis may be a risk factor for altered drug metabolism and possibly toxicity of HCQ.

Tumor Microenvironment Alters Chemoresistance of Hepatocellular Carcinoma Through CYP3A4 Metabolic Activity

Variations in tumor biology from patient to patient combined with the low overall survival rate of hepatocellular carcinoma (HCC) present significant clinical challenges. During the progression of chronic liver diseases from inflammation to the development of HCC, microenvironmental properties, including tissue stiffness and oxygen concentration, change over time. This can potentially impact drug metabolism and subsequent therapy response to commonly utilized therapeutics, such as doxorubicin, multi-kinase inhibitors (e.g., sorafenib), and other drugs, including immunotherapies. In this study, we utilized four common HCC cell lines embedded in 3D collagen type-I gels of varying stiffnesses to mimic normal and cirrhotic livers with environmental oxygen regulation to quantify the impact of these microenvironmental factors on HCC chemoresistance. In general, we found that HCC cells with higher baseline levels of cytochrome p450-3A4 (CYP3A4) enzyme expression, HepG2 and C3Asub28, exhibited a cirrhosis-dependent increase in doxorubicin chemoresistance. Under the same conditions, HCC cell lines with lower CYP3A4 expression, HuH-7 and Hep3B2, showed a decrease in doxorubicin chemoresistance in response to an increase in microenvironmental stiffness. This differential therapeutic response was correlated with the regulation of CYP3A4 expression levels under the influence of stiffness and oxygen variation. In all tested HCC cell lines, the addition of sorafenib lowered the required doxorubicin dose to induce significant levels of cell death, demonstrating its potential to help reduce systemic doxorubicin toxicity when used in combination. These results suggest that patient-specific tumor microenvironmental factors, including tissue stiffness, hypoxia, and CYP3A4 activity levels, may need to be considered for more effective use of chemotherapeutics in HCC patients.

Identification of a Novel Metastasis-Related miRNAs-Based Signature for Predicting the Prognosis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common internal malignancies worldwide and is associated with a poor prognosis. Abnormal expression of miRNAs is believed to play a role in the recurrent metastasis of HCC. However, limited studies on the role of miRNAs in HCC metastasis have been carried out. Therefore, this study is aimed at exploring the potential value of metastasis-related miRNAs (MRMs) in HCC. We retrieved MRMs were from the Human Cancer Metastasis Database. Differential miRNAs were identified for tumor samples of HCC patients and normal samples based on the TCGA database. Further, univariate and multivariate Cox regression analyses were used to screen MRMs known to be independent prognostic factors in HCC. These MRMs were then used to build a prognostic signature. All patients were classified into high-risk and low-risk groups based on the median of the signature scores. Moreover, GO and KEGG pathway enrichment analyses were performed to predict the function of these MRMs. Finally, a nomogram was constructed to predict the OS of patients at 1, 2, and 3 years. In our study, a total of seven prognostic MRMs (miR-140-3p, miR-9-5p, miR-942-5p, miR-324-3p, miR-29c-5p, miR-551a, and miR-149-5p) were identified and used for constructing the prognostic signature based on the training cohort. Patients in the low-risk HCC group showed better overall survival (OS) than those in the high-risk group. The results were validated using the validation cohort. In summary, the findings of this study provide evidence that MRMs-based prognostic signature is an independent biomarker in the prognosis of HCC patients.

Downregulation of CYP1A2, CYP2B6, and CYP3A4 in Human Hepatocytes by Prolyl Hydroxylase Domain 2 Inhibitors via Hypoxia-Inducible Factor-α Stabilization

Hypoxia-inducible factor (HIF) is associated with the expression of CYP, but the underlying mechanism remains uncertain. In this study, we investigated the effect of HIF-α stabilization caused by novel prolyl hydroxylase domain (PHD) 2 inhibitors, which are HIF-α stabilizers that mimic hypoxia, on the expressions of CYP1A2, CYP2B6, and CYP3A4 in human hepatocytes. An mRNA expression analysis of human hepatocytes treated with PHD2 inhibitors for 72 hours showed the downregulation of genes encoding CYP1A2, CYP2B6, and CYP3A4. The mRNA repressions were accompanied with an increase in erythropoietin protein, a marker of HIF-α stabilization, indicating that HIF-α stabilization was involved in the downregulation of the CYP isoforms. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors [aryl hydrocarbon receptor (AhR), AhR nuclear translocator (ARNT), constitutive androstane receptor (CAR), pregnane X receptor (PXR), and retinoid X receptor (RXR)] in human hepatocytes treated with the HIF-α stabilizers. As a result, the mRNA level of AhR did not decrease, although ARNT expression was repressed. On the other hand, the mRNA expression levels of CAR, PXR, and RXR were repressed and closely associated with those of CYP2B6 and CYP3A4. Although the underlying mechanism of the downregulation for CYP1A2 remains unclear, the presently reported results suggest that the downregulation of CYP2B6 and CYP3A4 via HIF-α stabilization is caused by a decrease in the expressions of CAR, PXR, and RXR. SIGNIFICANCE STATEMENT: We showed that hypoxia-inducible factor (HIF)-α stabilization downregulates CYP1A2, CYP2B6, and CYP3A4 using prolyl hydroxylase domain 2 inhibitors, which are HIF-α stabilizers, as a new tool to mimic hypoxia in human hepatocytes. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors. Our findings would contribute to a better understanding of the hypoxia-triggered regulatory mechanism of drug-metabolizing enzymes in human hepatocytes.

Transcriptional regulation of CYP3A4 by nuclear receptors in human hepatocytes under hypoxia

The human hepatic cytochrome P-450 3A4 (CYP3A4), recognized as a multifunctional enzyme, has a wide range of substrates including commonly used drugs. Previous investigations demonstrated that the expression of CYP3A4 in human hepatocytes could be regulated by some nuclear receptors (NRs) at transcriptional level under diverse situations. The significance of oxygen on CYP3A4-mediated metabolism seems notable while the regulatory mode of CYP3A4 in the particular case still remains elusive. Recently, striking evidence has emerged that both CYP3A4 and its regulator NR could be inhibited by exposure to hypoxia. Therefore, it is of great importance to elucidate whether and how these NRs act in the transcriptional regulation of CYP3A4 in human hepatocytes under hypoxic conditions. In this review, we mainly summarized transcriptional regulation of the pivotal enzyme CYP3A4 by NRs and explored the possible regulatory pathways of CYP3A4 via these major NRs under hypoxia, expecting to provide favorable evidence for further clinical guidance under such pathological situations.

[Effects of acute hypoxia on expression of pregnane X receptor in liver tissues of rats exposed to high altitude]

OBJECTIVE

To investigate the effects of high-altitude hypoxic environment on the expression of pregnane X receptor (PXR) in rat liver and related mechanism.

METHODS

Wistar rats were randomly divided into five groups with 8 rats in each group, the rats were exposed to high-plateau hypoxia for 0 (control group), 12, 24, 36 and 48 h, respectively. Abdominal aortic blood samples were collected for blood gas analysis. HE staining was used to observe the pathological changes of liver tissue. The expression levels of PXR mRNA in liver tissues were determined by RT-PCR. Western blot analysis was performed to determine the protein expression of PXR and protease SUG1 in liver tissues of rats.

RESULTS

Compared with the control group, the blood pH of the rats decreased after 12 h of acute hypoxia. After 24 h exposed to hypoxia, SaO2 was lower than 80%, PaO2 was lower than 60 mmHg (1 mmHg=0.133 kPa); and PaCO2 increased after 48 h exposed to hypoxia (P<0.05). There was obvious edema in the central vein of the liver tissue at 12 h and 24 h after exposure to hypoxia. The liver tissue of the rats exposed to hypoxia for 36 h and 48 h showed inflammatory infiltration. The expression of PXR mRNA was significantly decreased by 63%, 96%, 86%, and 85%at 12, 24, 36 h, and 48 h after exposure to hypoxia (all P<0.05), respectively. The protein expression of PXR was significantly up-regulated by 93%and 99%after 36 h and 48 h exposure to hypoxia (all P<0.05), respectively. The protein expression of proteinase SUG1 decreased by 14%, 34%and 46%after 24, 36 and 48 h after hypoxia (all P<0.01).

CONCLUSIONS

Acute hypoxia at high altitude can affect the expression of nuclear receptor PXR in rat liver, and protease SUG1 may be a regulatory factor for PXR expression in hypoxia.

Role of the Aryl Hydrocarbon Receptor/ARNT/Cytochrome P450 System in Pulmonary Vascular Diseases

RATIONALE

CYPs (cytochrome p450) are critically involved in the metabolism of xenobiotics and toxins. Given that pulmonary hypertension is strongly associated with environmental exposure, we hypothesize that CYPs play a role in the development and maintenance of pathological vascular remodeling.

OBJECTIVE

We sought to identify key CYPs that could link drug or hormone metabolism to the development of pulmonary hypertension.

METHODS AND RESULTS

We searched in Medline (PubMed) database, as well as http://www.clinicaltrials.gov, for CYPs associated with many key aspects of pulmonary arterial hypertension including, but not limited to, severe pulmonary hypertension, estrogen metabolism, inflammation mechanisms, quasi-malignant cell growth, drug susceptibility, and metabolism of the pulmonary arterial hypertension-specific drugs.

CONCLUSIONS

We postulate a hypothesis where the AhR (aryl hydrocarbon receptor) mediates aberrant cell growth via expression of different CYPs associated with estrogen metabolism and inflammation.

Cytochrome P450 1A1/2, 2B6 and 3A4 HepaRG Cell-Based Biosensors to Monitor Hepatocyte Differentiation, Drug Metabolism and Toxicity

Human hepatoma HepaRG cells express most drug metabolizing enzymes and constitute a pertinent in vitro alternative cell system to primary cultures of human hepatocytes in order to determine drug metabolism and evaluate the toxicity of xenobiotics. In this work, we established novel transgenic HepaRG cells transduced with lentiviruses encoding the reporter green fluorescent protein (GFP) transcriptionally regulated by promoter sequences of cytochromes P450 (CYP) 1A1/2, 2B6 and 3A4 genes. Here, we demonstrated that GFP-biosensor transgenes shared similar expression patterns with the corresponding endogenous CYP genes during proliferation and differentiation in HepaRG cells. Interestingly, differentiated hepatocyte-like HepaRG cells expressed GFP at higher levels than cholangiocyte-like cells. Despite weaker inductions of GFP expression compared to the strong increases in mRNA levels of endogenous genes, we also demonstrated that the biosensor transgenes were induced by prototypical drug inducers benzo(a)pyrene and phenobarbital. In addition, we used the differentiated biosensor HepaRG cells to evidence that pesticide mancozeb triggered selective cytotoxicity of hepatocyte-like cells. Our data demonstrate that these new biosensor HepaRG cells have potential applications in the field of chemicals safety evaluation and the assessment of drug hepatotoxicity.

Hypoxia increases chemoresistance in human medulloblastoma DAOY cells via hypoxia‑inducible factor 1α‑mediated downregulation of the CYP2B6, CYP3A4 and CYP3A5 enzymes and inhibition of cell proliferation

Medulloblastomas are among the most frequently diagnosed pediatric solid tumors, and drug resistance remains as the principal cause of treatment failure. Hypoxia and the subsequent activation of hypoxia-inducible factor 1α (HIF-1α) are considered key factors in modulating drug antitumor effectiveness, but the underlying mechanisms in medulloblastomas have not yet been clearly understood. The aim of the present study was to determine whether hypoxia induces resistance to cyclophosphamide (CPA) and ifosfamide (IFA) in DAOY medulloblastoma cells, whether the mechanism is dependent on HIF-1α, and whether involves the modulation of the expression of cytochromes P450 (CYP)2B6, 3A4 and 3A5 and the control of cell proliferation. Monolayer cultures of DAOY medulloblastoma cells were exposed for 24 h to moderate (1% O₂) or severe (0.1% O₂) hypoxia, and protein expression was evaluated by immunoblotting. Cytotoxicity was studied with the MTT assay and by Annexin V/PI staining and flow cytometry. Cell proliferation was determined by the trypan-blue exclusion assay and cell cycle by propidium iodide staining and flow cytometry. Hypoxia decreased CPA and IFA cytotoxicity in medulloblastoma cells, which correlated with a reduction in the protein levels of CYP2B6, CYP3A4 and CYP3A5 and inhibition of cell proliferation. These responses were dependent on hypoxia-induced HIF-1α activation, as evidenced by chemical inhibition of its transcriptional activity with 2-methoxyestradiol (2-ME), which enhanced the cytotoxic activity of CPA and IFA and increased apoptosis. Our results indicate that by stimulating HIF-1α activity, hypoxia downregulates the expression of CYP2B6, CYP3A4 and CYP3A5, that in turn leads to decreased conversion of CPA and IFA into their active forms and thus to diminished cytotoxicity. These results support that the combination of HIF-1α inhibitors and canonical antineoplastic agents provides a potential therapeutic alternative against medulloblastoma.

Decreased expression of hepatic cytochrome P450 1A2 (CYP1A2) in a chronic intermittent hypoxia mouse model

Background

Hepatic cytochrome P450 (CYP) isoforms, CYP1A2, is one of important enzymes for many drugs metabolism. Studies have confirmed that sustained hypoxia can influence the expression of hepatic CYP, including CYP1A2. The impact of chronic intermittent hypoxia (CIH), a marked characteristic of sleep apnea, on CYP1A2 remains unclear. The aim of the present study was to evaluate the effect of CIH on the expression of hepatic CYP1A2 in a mouse model with sleep apnea.

Methods

Twenty four old male (6-8 weeks) C57BL/6J mice (n=12 in each group) were randomly assigned to either normoxia group or CIH group. Mice in CIH group underwent 12 weeks intermittent hypoxia exposure. The different gene expression of hepatic CYP1A2 between two groups was analyzed by quantity real-time polymerase chain reaction. The protein levels of hepatic CYP1A2 in each group were observed by using western blotting and immunohistochemistry.

Results

After 12 weeks of exposure to intermittent hypoxia, the expression of hepatic CYP1A2, at the mRNA and protein levels was decreased more significantly in the CIH group than the normoxia group (P<0.01).

Conclusions

CIH contributes to inhibiting the expression of hepatic CYP1A2. This implies that the dosage of drugs metabolized by CYP1A2, should be adjusted in patients with sleep apnea.

Efficient transfection of Xenobiotic Responsive Element-biosensor plasmid using diether lipid and phosphatidylcholine liposomes in differentiated HepaRG cells

In this study, we evaluated cationic liposomes prepared from diether-NH₂ and egg phosphatidylcholine (EPC) for in vitro gene delivery. The impact of the lipid composition, i.e. the EPC and Diether-NH₂ molar ratio, on in vitro transfection efficiency and cytotoxicity was investigated using the human HEK293T and hepatoma HepaRG cells known to be permissive and poorly permissive cells for liposome-mediated gene transfer, respectively. Here, we report that EPC/Diether-NH₂-based liposomes enabled a very efficient transfection with low cytotoxicity compared to commercial transfection reagents in both HEK293T and proliferating progenitor HepaRG cells. Taking advantage of these non-toxic EPC/Diether-NH₂-based liposomes, we developed a method to efficiently transfect differentiated hepatocyte-like HepaRG cells and a biosensor plasmid containing a Xenobiotic Responsive Element and a minimal promoter driving the transcription of the luciferase reporter gene. We demonstrated that the luciferase activity was induced by a canonical inducer of cytochrome P450 genes, the benzo[a]pyrene, and two environmental contaminants, the fluoranthene, a polycyclic aromatic hydrocarbon, and the endosulfan, an organochlorine insecticide, known to induce toxicity and genotoxicity in differentiated HepaRG cells. In conclusion, we established a new efficient lipofection-mediated gene transfer in hepatocyte-like HepaRG cells opening new perspectives in drug evaluation relying on xenobiotic inducible biosensor plasmids.

Bisphenol a induces steatosis in HepaRG cells using a model of perinatal exposure

Human exposure to bisphenol A (BPA) could favor obesity and related metabolic disorders such as hepatic steatosis. Investigations in rodents have shown that these deleterious effects are observed not only when BPA is administered during the adult life but also with different protocols of perinatal exposure. Whether perinatal BPA exposure could pose a risk in human is currently unknown, and thus appropriate in vitro models could be important to tackle this major issue. Accordingly, we determined whether long-term BPA treatment could induce steatosis in human HepaRG cells by using a protocol mimicking perinatal exposure. To this end, the kinetics of expression of seven proteins differentially expressed during liver development was determined during a 4-week period of cell culture required for proliferation and differentiation. By analogy with data reported in rodents and humans, our results indicated that the period of cell culture around day 15 and day 18 after seeding could be considered as the "natal" period. Consequently, HepaRG cells were treated for 3 weeks with BPA (from 0.2 to 2000 nM), with a treatment starting during the proliferating period. BPA was able to induce steatosis with a nonmonotonic dose response profile, with significant effects on neutral lipids and triglycerides observed for the 2 nM concentration. However, the expression of many enzymes involved in lipid and carbohydrate homeostasis was unchanged in exposed HepaRG cells. The expression of other potential BPA targets and enzymes involved in BPA biotransformation was also determined, giving answers as well as new questions regarding the mechanisms of action of BPA. Hence, HepaRG cells provide a valuable model that can prove useful for the toxicological assessment of endocrine disruptors on hepatic metabolisms, in particular in the developing liver. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1024-1036, 2017.

Evaluation of genotoxicity using automated detection of γH2AX in metabolically competent HepaRG cells

The in situ detection of γH2AX was recently reported to be a promising biomarker of genotoxicity. In addition, the human HepaRG hepatoma cells appear to be relevant for investigating hepatic genotoxicity since they express most of drug metabolizing enzymes and a wild type p53. The aim of this study was to determine whether the automated in situ detection of γH2AX positive HepaRG cells could be relevant for evaluation of genotoxicity after single or long-term repeated in vitro exposure compared to micronucleus assay. Metabolically competent HepaRG cells were treated daily with environmental contaminants and genotoxicity was evaluated after 1, 7 and 14 days. Using these cells, we confirmed the genotoxicity of aflatoxin B1 and benzo(a)pyrene and demonstrated that dimethylbenzanthracene, fipronil and endosulfan previously found genotoxic with comet or micronucleus assays also induced γH2AX phosphorylation. Furthermore, we showed that fluoranthene and bisphenol A induced γH2AX while no effect had been previously reported in HepG2 cells. In addition, induction of γH2AX was observed with some compounds only after 7 days, highlighting the importance of studying long-term effects of low doses of contaminants. Together, our data demonstrate that automated γH2AX detection in metabolically competent HepaRG cells is a suitable high-through put genotoxicity screening assay.

Resistance to cancer chemotherapy: failure in drug response from ADME to P-gp

Cancer chemotherapy resistance (MDR) is the innate and/or acquired ability of cancer cells to evade the effects of chemotherapeutics and is one of the most pressing major dilemmas in cancer therapy. Chemotherapy resistance can arise due to several host or tumor-related factors. However, most current research is focused on tumor-specific factors and specifically genes that handle expression of pumps that efflux accumulated drugs inside malignantly transformed types of cells. In this work, we suggest a wider and alternative perspective that sets the stage for a future platform in modifying drug resistance with respect to the treatment of cancer.

Incidence and risk of hand-foot skin reaction with cabozantinib, a novel multikinase inhibitor: a meta-analysis

BACKGROUND

Cabozantinib is approved in the treatment of progressive, metastatic medullary thyroid cancer (MTC). It is a small molecule inhibitor, which targets multiple receptors, including vascular endothelial growth factor receptor, tyrosine kinase with Ig and epidermal growth factor homology domains-2 and the proto-oncogenes MET (mesenchymal-epithelial transition factor) and RET (rearranged during transfection). The drug is currently in phase I/II/III clinical trials for a number of other solid tumours and haematological malignancies. The adverse event (AE) profile is similar to that of other newer angiogenesis inhibitors. Hand-foot skin reaction (HFSR) is an important dose-limiting dermatological adverse event of this class of drugs.

AIM

To ascertain the incidence and risk of HFSR in patients with cancer during treatment with cabozantinib.

METHODS

Electronic databases (PubMed, Web of Science) and the American Society of Clinical Oncology Meeting Library were queried from inception to July 2014. Only phase II/III studies investigating cabozantinib for the treatment of cancer were shortlisted. The incidence, relative risk (RR) and 95% CI were calculated using random- or fixed-effects models, depending on the heterogeneity of the included studies.

RESULTS

We included 831 patients treated with cabozantinib for various solid malignancies in the analysis. The overall incidence was 35.3% (95% CI 27.9-43.6%) for all-grade and 9.5% (95% CI 7.6-11.7%) for high-grade HFSR. The RR of all-grade and high-grade HFSR with cabozantinib, compared with controls, was increased for both all-grade (27.3; 95% CI 6.9-108.3; P < 0.001) and high-grade (28.1; 95% CI 1.7-457; P < 0.02) HFSR, respectively.

CONCLUSIONS

The incidence and risk of developing HFSR with cabozantinib are high. Timely recognition of this dose-limiting AE is critical to direct supportive care efforts including patient counselling, and to institute preventative and/or treatment interventions.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Hypoxia interferes with aryl hydrocarbon receptor pathway in hCMEC/D3 human cerebral microvascular endothelial cells

The expression of aryl hydrocarbon receptor (AhR) transcription factor was detected at transcript level in freshly isolated human brain microvessels and in the hCMEC/D3 human cerebral microvascular endothelial cell line. Recent studies have demonstrated that AhR pathway is able to crosstalk with other pathways such as hypoxia signaling pathway. Therefore, we used the hCMEC/D3 cell line to investigate the potential crosstalk between AhR and hypoxia signaling pathways. First, we performed two different hypoxia-like procedures in hCMEC/D3 cells; namely, exposition of cells to 150 μM deferoxamine or to glucose and oxygen deprivation for 6 h. These two procedures led to hypoxia-inducible factor (HIF)-1α and HIF-2α proteins accumulation together with a significant induction of the two well-known hypoxia-inducible genes VEGF and GLUT-1. Both HIF-1α and -2α functionally mediated hypoxia response in the hCMEC/D3 cells. Then, we observed that a 6 h exposure to 25 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin, a strong AhR ligand, up-regulated CYP1A1 and CYP1B1 expression, and that this effect was AhR dependent. Regarding AhR and hypoxia crosstalk, our experiments revealed that an asymmetric interference between these two pathways effectively occurred in hCMEC/D3 cells: hypoxia pathway interfered with AhR signaling but not the other way around. We studied the putative crosstalk of AhR and hypoxia pathways in hCMEC/D3 human cerebral microvascular endothelial cells. While hypoxia decreased the expression of the two AhR target genes CYP1A1 and CYP1B1, AhR activation results in no change in hypoxia target gene expression. This is the first sign of AhR and hypoxia pathway crosstalk in an in vitro model of the human cerebral endothelium.

Altered CYP2C9 activity following modulation of CYP3A4 levels in human hepatocytes: an example of protein-protein interactions

Cytochrome P450 (P450) protein-protein interactions resulting in modulation of enzyme activities have been well documented using recombinant isoforms. This interaction has been less clearly demonstrated in a more physiologic in vitro system such as human hepatocytes. As an expansion of earlier work (Subramanian et al., 2010), in which recombinant CYP2C9 activity decreased with increasing levels of CYP3A4, the current study modulated CYP3A4 content in human hepatocytes to determine the impact on CYP2C9. Modulation of CYP3A4 levels in situ was enabled by the use of a long-term human hepatocyte culture model (HepatoPac) shown to retain phenotypic hepatocyte function over a number of weeks. The extended period of culture allowed time for knockdown of CYP3A4 protein by small interfering RNA (siRNA) with subsequent recovery, as well as upregulation through induction with a recovery period. CYP3A4 gene silencing resulted in a 60% decrease in CYP3A4 activity and protein levels with a concomitant 74% increase in CYP2C9 activity, with no change in CYP2C9 mRNA levels. Upon removal of siRNA, both CYP2C9 and CYP3A4 activities returned to pre-knockdown levels. Importantly, modulation of CYP3A4 protein levels had no impact on cytochrome P450 reductase activities or levels. However, the possibility for competition for limiting reductase cannot be ruled out. Interestingly, lowering CYP3A4 levels also increased UDP-glucuronosyltransferase 2B7 activity. These studies clearly demonstrate that alterations in CYP3A4 levels can modulate CYP2C9 activity in situ and suggest that further studies are warranted to evaluate the possible clinical consequences of these findings.

Regulatory crosstalk and interference between the xenobiotic and hypoxia sensing pathways at the AhR-ARNT-HIF1α signaling node

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the responses to toxic environmental chemicals such as TCDD or dioxin-like PCBs. To regulate gene expression, the AhR requires its binding partner, the aryl hydrocarbon receptor nuclear translocator (ARNT). ARNT is also required by the hypoxia-inducible factor-1α (HIF-1α), a crucial regulator of responses to conditions of reduced oxygen. The important role of ARNT in both the AhR and HIF-1α signaling pathways establishes a meaningful foundation for a possible crosstalk between these two vitally important signaling pathways. This crosstalk might lead to interference between the two signaling pathways and thus might play a role in the variety of cellular responses after exposure to AhR ligands and reduced oxygen availability. This review focuses on studies that have analyzed the effect of low oxygen environments and hypoxia-mimetic agents on AhR signaling and conversely, the effect of AhR ligands, with a special emphasis on PCBs, on HIF-1α signaling. We highlight studies that assess the role of ARNT, elucidate the mechanism of the crosstalk, and discuss the physiological implications for exposure to AhR-inducing compounds in the context of hypoxia.

Metabolism and disposition of acetaminophen: recent advances in relation to hepatotoxicity and diagnosis

Acetaminophen (APAP) is one of the most widely used drugs. Though safe at therapeutic doses, overdose causes mitochondrial dysfunction and centrilobular necrosis in the liver. The first studies of APAP metabolism and activation were published more than 40 years ago. Most of the drug is eliminated by glucuronidation and sulfation. These reactions are catalyzed by UDP-glucuronosyltransferases (UGT1A1 and 1A6) and sulfotransferases (SULT1A1, 1A3/4, and 1E1), respectively. However, some is converted by CYP2E1 and other cytochrome P450 enzymes to a reactive intermediate that can bind to sulfhydryl groups. The metabolite can deplete liver glutathione (GSH) and modify cellular proteins. GSH binding occurs spontaneously, but may also involve GSH-S-transferases. Protein binding leads to oxidative stress and mitochondrial damage. The glucuronide, sulfate, and GSH conjugates are excreted by transporters in the canalicular (Mrp2 and Bcrp) and basolateral (Mrp3 and Mrp4) hepatocyte membranes. Conditions that interfere with metabolism and metabolic activation can alter the hepatotoxicity of the drug. Recent data providing novel insights into these processes, particularly in humans, are reviewed in the context of earlier work, and the effects of altered metabolism and reactive metabolite formation are discussed. Recent advances in the diagnostic use of serum adducts are covered.

Cimetidine-associated patent ductus arteriosus is mediated via a cytochrome P450 mechanism independent of H2 receptor antagonism

Persistent patency of the ductus arteriosus (PDA) is a common problem in preterm infants. The antacid cimetidine is a potent antagonist of the H2 histamine receptor but it also inhibits certain cytochrome P450 enzymes (CYPs), which may affect DA patency. We examined whether cimetidine contributes to PDA and is mediated by CYP inhibition rather than H2 blockade. Analysis of a clinical trial to prevent lung injury in premature infants revealed a significant association between cimetidine treatment and PDA. Cimetidine and ranitidine, both CYP inhibitors as well as H2 blockers, caused relaxation of the term and preterm mouse DA. CYP enzymes that are inhibited by cimetidine were expressed in DA subendothelial smooth muscle. The selective CYP3A inhibitor ketoconazole induced greater DA relaxation than cimetidine, whereas famotidine and other H2 antagonists with less CYP inhibitory effects caused less dilation. Histamine receptors were developmentally regulated and localized in DA smooth muscle. However, cimetidine caused DA relaxation in histamine-deficient mice, consistent with CYP inhibition, not H2 antagonism, as the mechanism for PDA. Oxygen-induced DA constriction was inhibited by both cimetidine and famotidine. These studies show that antacids and other compounds with CYP inhibitory properties pose a significant and previously unrecognized risk for PDA in critically ill newborn infants.

Highly efficient SiRNA and gene transfer into hepatocyte-like HepaRG cells and primary human hepatocytes: new means for drug metabolism and toxicity studies

The metabolically competent hepatocyte-like human HepaRG cells represent a suitable alternative in vitro cell model to human primary hepatocytes. Here, we describe the culture procedure required to expand progenitor HepaRG cells and to differentiate them into hepatocyte-like cells. Transient transfection of gene and siRNA into cultured cells, using nonviral strategies, is an invaluable technique to decipher gene functions. In this chapter, we detail transfection protocols for efficient transfer of plasmid DNA or siRNAs into proliferating progenitor or quiescent differentiated HepaRG cells as well as into primary hepatocytes.

Phase 1 and phase 2 drug metabolism and bile acid production of HepaRG cells in a bioartificial liver in absence of dimethyl sulfoxide

The human liver cell line HepaRG has been recognized as a promising source for in vitro testing of metabolism and toxicity of compounds. However, currently the hepatic differentiation of these cells relies on exposure to dimethylsulfoxide (DMSO), which, as a side effect, has a cytotoxic effect and represses an all-round hepatic functionality. The AMC-bioartificial liver (AMC-BAL) is a three-dimensional bioreactor that has previously been shown to upregulate various liver functions of cultured cells. We therefore cultured HepaRG cells in the AMC-BAL without DMSO and characterized the drug metabolism. Within 14 days of culture, the HepaRG-AMC-BALs contained highly polarized viable liver-like tissue with heterogeneous expression of CYP3A4. We found a substantial metabolism of the tested substrates, ranging from 26% (UDP-glucuronosyltransferase 1A1), 47% (CYP3A4), to 240% (CYP2C9) of primary human hepatocytes. The CYP3A4 activity could be induced 2-fold by rifampicin, whereas CYP2C9 activity remained equally high. The HepaRG-AMC-BAL secreted bile acids at 43% the rate of primary human hepatocytes and demonstrated hydroxylation, conjugation, and transport of bile salts. Concluding, culturing HepaRG cells in the AMC-BAL yields substantial phase 1 and phase 2 drug metabolism, while maintaining high viability, rendering DMSO addition superfluous for the promotion of drug metabolism. Therefore, AMC-BAL culturing makes the HepaRG cells more suitable for testing metabolism and toxicity of drugs.

Nitric oxide pathway-related gene alterations in inflammatory bowel disease

OBJECTIVE

To reveal specific gene activation in nitric oxide (NO)-related inflammation we studied differential gene expression in inflammatory bowel disease (IBD).

METHODS

Total RNA was isolated from 20 biopsies of inflamed mucosa from Crohn's disease (CD) and ulcerative colitis (UC) patients each as well as from six controls, labeled with (32)P-dCTP and hybridized to a human NO gene array. Significant genes were analyzed for functional gene interactions and heatmaps generated by hierarchical clustering. A selection of differentially expressed genes was further evaluated with immunohistochemical staining.

RESULTS

Significant gene expression differences were found for 19 genes in CD and 23 genes in UC compared to controls, both diseases with high expression of ICAM1 and IL-8. Correlation between microarray expression and corresponding protein expression was significant (r = 0.47, p = 0.002). Clustering analysis together with functional gene interaction analysis revealed clusters of coregulation and coexpression in CD and UC: transcripts involved in angiogenesis, inflammatory response mediated by the transcription factor hypoxia-inducible factor 1, and tissue fibrosis. Also, a fourth cluster with transcripts regulated by the transcription factor Sp1 was found in UC.

CONCLUSIONS

Expression analysis in CD and UC revealed disease-specific regulation of NO-related genes, which might be involved in perpetuating inflammatory disease activity in IBD.

Diminished toxicity of C-1748, 4-methyl-9-hydroxyethylamino-1-nitroacridine, compared with its demethyl analog, C-857, corresponds to its resistance to metabolism in HepG2 cells

The narrow "therapeutic window" of anti-tumour therapy may be the result of drug metabolism leading to the activation or detoxification of antitumour agents. The aim of this work is to examine (i) whether the diminished toxicity of a potent antitumour drug, C-1748, 9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine, compared with its 4-demethyl analogue, C-857, results from the differences between the metabolic pathways for the two compounds and (ii) the impact of reducing and/or hypoxic conditions on studied metabolism. We investigated the metabolites of C-1748 and C-857 formed in rat and human liver microsomes, with human P450 reductase (POR) and in HepG2 cells under normoxia and hypoxia. The elimination rate of C-1748 from POR knockout mice (HRN) was also evaluated. Three products, 1-amino-9-hydroxyethylaminoacridine, 1-aminoacridinone and a compound with an additional 6-membered ring, were identified for C-1748 and C-857 in all studied metabolic systems. The new metabolite was found in HepG2 cells. We showed that metabolic rate and the reactivity of metabolites of C-1748 were considerably lower than those of C-857, in all investigated metabolic models. Compared with metabolism under normoxia, cellular metabolism under hypoxia led to higher levels of 1-aminoacridine and aza-acridine derivatives of both compounds and of the 6-membered ring metabolite of C-1748. In conclusion, the crucial role of hypoxic conditions and the direct involvement of POR in the metabolism of both compounds were demonstrated. Compared with C-857, the low reactivity of C-1748 and the stability of its metabolites are postulated to contribute significantly to the diminished toxicity of this compound observed in animals.

Optimization of the HepaRG cell model for drug metabolism and toxicity studies

The HepaRG cell line is the first human cell line able to differentiate in vitro into mature hepatocyte-like cells. Our main objective within the framework of the EEC-LIINTOP project was to optimize the use of this cell line for drug metabolism and toxicity studies, especially after repeat treatments. The main results showed that differentiated HepaRG cells: (i) retained their drug metabolism capacity (major CYPs, phase 2 enzymes, transporters and nuclear receptors) and responsiveness to prototypical inducers at relatively stable levels for several weeks at confluence. The levels of several functions, including some CYPs such as CYP3A4, were dependent on the addition of dimethyl sulfoxide in the culture medium; (ii) sustained the different types of chemical-induced hepatotoxicity, including steatosis, phospholipidosis and cholestasis, after acute and/or repeat treatment with reference drugs. In particular, drug-induced vesicular steatosis was demonstrated in vitro for the first time. In conclusion, our results from the LIINTOP project, together with other studies reported concomitantly or more recently in the literature, support the conclusion that the metabolically competent human HepaRG cells represent a surrogate to primary human hepatocytes for investigating drug metabolism parameters and both acute and chronic effects of xenobiotics in human liver.

The HepaRG cell line: a unique in vitro tool for understanding drug metabolism and toxicology in human

INTRODUCTION

HepaRG is a unique cell line showing a great plasticity, which differentiates to both canaliculae-like and hepatocyte-like cells. The long-term stability of key cell functions, for example, the drug-metabolizing cytochrome P450 (CYP) enzyme activities, in culture is especially useful in drug metabolism, disposition and toxicity studies.

AREAS COVERED

This review describes features of the HepaRG cells focusing on drug-metabolizing enzymes and drug transporters, their functionality and regulation. Several applications in drug discovery studies are discussed and the use of HepaRG, as a human relevant predictive in vitro CYP induction model, is described. In addition, promising studies using HepaRG cells for understanding liver toxicity mechanisms by drug compounds are also discussed.

EXPERT OPINION

HepaRG cells exhibit features which make them useful as an in vitro model for drug metabolism, disposition and toxicity studies, and could, for many studies, replace the requirement for primary human hepatocytes. Care should be taken since HepaRG cells are of a specific genotype which is reflected in the expression of drug processing proteins. The finding that HepaRG cells form tight junctions provides the basis for formation of functional canalicular structures and this should be investigated further to aid development of human relevant hepatic in vitro 2D and 3D models.

Effects of hypoxia-inducible factor-1α chemical stabilizer, CoCl(2) and hypoxia on gene expression of CYP3As in human fetal liver cells

Distinctive response patterns of CYP3A4 and CYP3A7 to cobalt chloride (CoCl(2)) in human fetal liver (HFL) cells were observed and compared with those under hypoxic conditions. The expression levels of CYP3A4 and CYP3A7 mRNAs were decreased by CoCl(2) and hypoxia, although significance could not be determined in HFL cells cultured under 3% O(2). The hypoxia-inducible factor-1α (HIF-1α) protein content in HFL cells was significantly increased by CoCl(2) and 3% O(2). Transcriptional activities of CYP3A4 and CYP3A7 were not altered by 3% O(2) when reporter plasmids containing the promoter region ranging up to about 10 kb and 12 kb upstream, respectively, were transfected into HFL cells, although the activity was significantly suppressed by CoCl(2). These results suggested that the mechanisms controlling CYP3A gene expression of HIF-1α chemical stabilizer in fetal hepatocytes might be different from those in adult hepatocytes, and that HIF-1α is not directly involved in regulation of CYP3A4 or CYP3A7 expression.