Post-transcriptional regulation of rat CYP2E1 expression: role of CYP2E1 mRNA untranslated regions in control of translational efficiency and message stability

CYP2E1 in 1,4-dioxane metabolism and liver toxicity: insights from CYP2E1 knockout mice study

1,4-Dioxane (DX), an emerging water contaminant, is classified as a Group 2B liver carcinogen based on animal studies. Understanding of the mechanisms of action of DX liver carcinogenicity is important for the risk assessment and control of this environmental pollution. Previous studies demonstrate that high-dose DX exposure in mice through drinking water for up to 3 months caused liver mild cytotoxicity and oxidative DNA damage, a process correlating with hepatic CYP2E1 induction and elevated oxidative stress. To access the role of CYP2E1 in DX metabolism and liver toxicity, in the current study, male and female Cyp2e1-null mice were exposed to DX in drinking water (5000 ppm) for 1 week or 3 months. DX metabolism, redox and molecular investigations were subsequently performed on male Cyp2e1-null mice for cross-study comparisons to similarly treated male wildtype (WT) and glutathione (GSH)-deficient Gclm-null mice. Our results show that Cyp2e1-null mice of both genders were resistant to DX-induced hepatocellular cytotoxicity. In male Cyp2e1-null mice exposed to DX for 3 months, firstly, DX metabolism to β-hydroxyethoxyacetic acid was reduced to ~ 36% of WT levels; secondly, DX-induced hepatic redox dysregulation (lipid peroxidation, GSH oxidation, and activation of NRF2 antioxidant response) was substantially attenuated; thirdly, liver oxidative DNA damage was at a comparable level to DX-exposed WT mice, accompanied by suppression of DNA damage repair response; lastly, no aberrant proliferative or preneoplastic lesions were noted in DX-exposed livers. Overall, this study reveals, for the first time, that CYP2E1 is the main enzyme for DX metabolism at high dose and a primary contributor to DX-induced liver oxidative stress and associated cytotoxicity. High dose DX-induced genotoxicity may occur via CYP2E1-independent pathway(s), potentially involving impaired DNA damage repair.

Effect of SNPs in the Promoter Region on the Expression of Cytochrome P450 2E1 (CYP2E1) in Pig Liver

Boar taint, an unfavorable odor in the meat of intact male pigs, is caused primarily by the accumulation of two compounds: androstenone and skatole. This multifactorial trait is regulated by numerous dietary, management and genetic factors. At the mechanistic level, there are many genes known to be involved in boar taint metabolism. Cytochrome P450 2E1 (CYP2E1) impacts boar taint through the phase I metabolism of skatole. The aim of this study was to identify single-nucleotide polymorphisms (SNPs) within the CYP2E1 gene promoter and explore their relationship with the expression of CYP2E1 mRNA and protein. Sequencing of the promoter region using pools of genomic DNA identified seven promoter region SNPs at -159, -586, -1693, -1806, -2322, -2369 and -2514 bp upstream of the ATG start site. Genomic DNA was obtained from 65 boars from the three major swine breeds: Duroc, Landrace and Yorkshire, and individual animals were genotyped for the identified SNPs. RNA was isolated from liver tissue and quantitative PCR was performed to measure CYP2E1 gene expression, while levels of CYP2E1 protein in liver were measured by Western blotting. Significant within-breed variation in CYP2E1 protein and mRNA expression was observed, indicating significant differences in gene expression among individuals. However, levels of CYP2E1 mRNA and protein were not significantly correlated. Two SNPs within the promoter were significantly associated with CYP2E1 mRNA expression, but not with protein expression. This study provides evidence of additional mutations affecting the gene expression of CYP2E1 and suggests that factors that affect the differences in translation of CYP2E1 mRNA may also be important in affecting skatole metabolism.

Comparative transcriptomic and phenotypic analysis of induced pluripotent stem cell hepatocyte-like cells and primary human hepatocytes

Primary human hepatocytes (PHHs) are used extensively for in vitro liver cultures to study hepatic functions. However, limited availability and invasive retrieval prevent their widespread use. Induced pluripotent stem cells exhibit significant potential since they can be obtained non-invasively and differentiated into hepatic lineages, such as hepatocyte-like cells (iHLCs). However, there are concerns about their fetal phenotypic characteristics and their hepatic functions compared to PHHs in culture. Therefore, we performed an RNA-sequencing (RNA-seq) analysis to understand pathways that are either up- or downregulated in each cell type. Analysis of the RNA-seq data showed an upregulation in the bile secretion pathway where genes such as AQP9 and UGT1A1 were higher expressed in PHHs compared to iHLCs by 455- and 15-fold, respectively. Upon immunostaining, bile canaliculi were shown to be present in PHHs. The TCA cycle in PHHs was upregulated compared to iHLCs. Cellular analysis showed a 2-2.5-fold increase in normalized urea production in PHHs compared to iHLCs. In addition, drug metabolism pathways, including cytochrome P450 (CYP450) and UDP-glucuronosyltransferase enzymes, were upregulated in PHHs compared to iHLCs. Of note, CYP2E1 gene expression was significantly higher (21,810-fold) in PHHs. Acetaminophen and ethanol were administered to PHH and iHLC cultures to investigate differences in biotransformation. CYP450 activity of baseline and toxicant-treated samples was significantly higher in PHHs compared to iHLCs. Our analysis revealed that iHLCs have substantial differences from PHHs in critical hepatic functions. These results have highlighted the differences in gene expression and hepatic functions between PHHs and iHLCs to motivate future investigation.

A clinical experience-based Chinese herbal formula improves ethanol-induced drunken behavior and hepatic steatohepatitis in mice models

BACKGROUND

Bao-Gan-Xing-Jiu-Wan (BGXJW) is a clinical experience-based Chinese herbal formula. Its efficacy, pharmacological safety, targeted function, process quality, and other aspects have met the evaluation standards and the latest requirements of preparations. It could prevent and alleviate the symptoms of drunkenness and alcoholic liver injury clinically. The present work aims to elucidate whether BGXJW could protect against drunkenness and alcoholic liver disease in mice and explore the associated mechanism.

MATERIAL AND METHODS

We used acute-on-chronic (NIAAA) mice model to induce alcoholic steatosis, and alcohol binge-drinking model to reappear the drunk condition. BGXJW at indicated doses were administered by oral gavage respectively to analyze its effects on alcoholic liver injury and the associated molecular mechanisms.

RESULTS

BGXJW had no cardiac, hepatic, renal, or intestinal toxicity in mice. Alcoholic liver injury and steatosis in the NIAAA mode were effectively prevented by BGXJW treatment. BGXJW increased the expression of alcohol metabolizing enzymes ADH, CYP2E1, and ALDH2 to enhance alcohol metabolism, inhibited steatosis through regulating lipid metabolism, counteracted alcohol-induced upregulation of lipid synthesis related proteins SREBP1, FASN, and SCD1, meanwhile it enhanced fatty acids β-oxidation related proteins PPAR-α and CPT1A. Alcohol taken enhanced pro-inflammatory TNF-α, IL-6 and down-regulated the anti-inflammatory IL-10 expression in the liver, which were also reversed by BGXJW administration. Moreover, BGXJW significantly decreased the blood ethanol concentration and alleviated drunkenness in the alcohol binge-drinking mice model.

CONCLUSIONS

BGXJW could effectively relieve drunkenness and prevent alcoholic liver disease by regulating lipid metabolism, inflammatory response, and alcohol metabolism.

Drug-Metabolizing Cytochrome P450 Enzymes Have Multifarious Influences on Treatment Outcomes

Drug metabolism is a critical process for the removal of unwanted substances from the body. In humans, approximately 80% of oxidative metabolism and almost 50% of the overall elimination of commonly used drugs can be attributed to one or more of various cytochrome P450 (CYP) enzymes from CYP families 1-3. In addition to the basic metabolic effects for elimination, CYP enzymes in vivo are capable of affecting the treatment outcomes in many cases. Drug-metabolizing CYP enzymes are mainly expressed in the liver and intestine, the two principal drug oxidation and elimination organs, where they can significantly influence the drug action, safety, and bioavailability by mediating phase I metabolism and first-pass metabolism. Furthermore, CYP-mediated local drug metabolism in the sites of action may also have the potential to impact drug response, according to the literature in recent years. This article underlines the ability of CYP enzymes to influence treatment outcomes by discussing CYP-mediated diversified drug metabolism in primary metabolic sites (liver and intestine) and typical action sites (brain and tumors) according to their expression levels and metabolic activity. Moreover, intrinsic and extrinsic factors of personal differential CYP phenotypes that contribute to interindividual variation of treatment outcomes are also reviewed to introduce the multifarious pivotal role of CYP-mediated metabolism and clearance in drug therapy.

Constitutive expression of cytochrome P450 in foetal and adult porcine livers-Effects of body weight

The liver hosts a great number of enzymatically driven processes, including detoxification. The super-family of enzymes named cytochrome P450 (CYP) is the major participant in that process. The expression of CYPs is affected by several factors including life-stage (foetal vs. adult). In the present study we investigated the impact of birth-weight (high or low birth weight) and life-stage on constitutive expression of porcine hepatic CYP1A1, CYP1A2, CYP2A19, CYP2B22, CYP2C33, CYP2D25, CYP2E1 and CYP3A29, as well as the transcription factors controlling their expression; aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, C/EBP and hepatocyte nuclear factors 1 and 4. Both RT-PCR and western blotting showed a marked increase in the expression of the adult pigs compared with prenatal pigs. Moreover, CYP2E1 mRNA expression was 7.5 fold higher in foetuses with low birth weight compared with foetuses with high birth weight. Gender did not affect the mRNA expression within the different life-stages. These results indicate a similarity to what is observed in humans and porcine foetuses may therefore be a model for humans when studying expression of CYPs.

A dual inhibition: microRNA-552 suppresses both transcription and translation of cytochrome P450 2E1

MicroRNAs (miRNAs) can direct post-transcriptional or transcriptional gene silencing. Here, we report that miR-552 is in the nucleus and cytosol and inhibits human cytochrome P450 (CYP) 2E1 expression at both transcriptional and post-transcriptional levels. MiR-552 via its non-seed sequence forms hybrids with a loop hairpin of the cruciform structure in CYP2E1 promoter region to inhibit SMARCE1 and RNA polymerase II binding to the promoter and CYP2E1 transcription. Expressing SMARCE1 reverses the inhibitory effects of miR-552 on CYP2E1 mRNA expression. MiR-552 with mutations in non-seed region losses its transcriptional, but retains its post-transcriptional repression to CYP2E1. In contrast, mutation in miR-552 seed sequence suppresses its inhibitory effects on CYP2E1 expression at protein, but not at mRNA, levels. Our results suggest that miR-552 is a miRNA with a dual inhibitory ability at transcriptional and post-transcriptional levels leading to an effective inhibition.

2-Aminoacetophenone Is the Main Volatile Phase I Skatole Metabolite in Pietrain × Baden-Württemberg Hybrid Type Boars

Skatole metabolites have been considered as putative contributors to boar taint. Recently, 2-aminoacetophenone, a volatile phase I skatole metabolite, was identified in back fat samples from boars of Pietrain × Baden-Württemberg hybrid type. This paper addresses the question of the physiological origin of the observed 2-aminoacetophenone in these pigs. Microsomal fractions from nine boars were isolated, and formation of skatole metabolites was subsequently analyzed by stable-isotope dilution analysis (SIDA) using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS). Significant breed-related differences in phase I skatole metabolism were observed, explaining the high levels of 2-aminoacetophenone in Pietrain × Baden-Württemberg hybrid type boars.

Severely Impaired and Dysregulated Cytochrome P450 Expression and Activities in Hepatocellular Carcinoma: Implications for Personalized Treatment in Patients

This study aims to systematically determine the activities and expressions of cytochrome P450s (CYP) in hepatocellular carcinoma (HCC) patients to support their optimal use in personalized treatment of HCC. Activities of seven major drug-metabolizing CYP enzymes (CYP1A2, 2A6, 2C8, 2C9, 2D6, 2E1, and 3A4) were determined in tumors and pericarcinomatous tissues harvested from 26 patients with hepatitis B virus-positive HCC using probe substrates. Protein and mRNA levels of these CYPs were also measured using isotope label-free LC/MS-MS method and real-time PCR, respectively. Maximal metabolic velocity (Vmax) of CYP probe substrates was decreased by 2.5- to 30-fold in tumor microsomes, accompanied by a corresponding decrease in their protein and mRNA expression levels. However, Km values and turnover numbers of substrates in tumor microsomes were not changed. High correlations between activities and CYP protein levels were also observed, but the correlation between activities and mRNA levels was often poor. There was a major decrease in the degree of correlation in CYP expression in tumor tissues, suggesting that CYP expression levels are greatly disrupted by the tumorigenic process. Our unprecedented systemic study of the effects of HCC on CYPs demonstrated that activities of CYPs were seriously impaired and their expression patterns were severely altered by HCC. We proposed that determination of the CYP protein expression profile by LC/MS-MS in each patient is a promising approach that can be clinically used for individualized treatment of HCC.

Regulation of porcine hepatic cytochrome p450 - implication for boar taint

Cytochrome P450 (CYP450) is the major family of enzymes involved in the metabolism of several xenobiotic and endogenous compounds. Among substrates for CYP450 is the tryptophan metabolite skatole (3-methylindole), one of the major contributors to the off-odour associated with boar-tainted meat. The accumulation of skatole in pigs is highly dependent on the hepatic clearance by CYP450s. In recent years, the porcine CYP450 has attracted attention both in relation to meat quality and as a potential model for human CYP450. The molecular regulation of CYP450 mRNA expression is controlled by several nuclear receptors and transcription factors that are targets for numerous endogenously and exogenously produced agonists and antagonists. Moreover, CYP450 expression and activity are affected by factors such as age, gender and feeding. The regulation of porcine CYP450 has been suggested to have more similarities with human CYP450 than other animal models, including rodents. This article reviews the available data on porcine hepatic CYP450s and its implications for boar taint.

Differential expression of cytochrome P450 enzymes in normal and tumor tissues from childhood rhabdomyosarcoma

Intratumoral expression of genes encoding Cytochrome P450 enzymes (CYP) might play a critical role not only in cancer development but also in the metabolism of anticancer drugs. The purpose of this study was to compare the mRNA expression patterns of seven representative CYPs in paired tumor and normal tissue of child patients with rabdomyosarcoma (RMS). Using real time quantitative RT-PCR, the gene expression pattern of CYP1A1, CYP1A2, CYP1B1, CYP2E1, CYP2W1, CYP3A4, and CYP3A5 were analyzed in tumor and adjacent non-tumor tissues from 13 child RMS patients. Protein concentration of CYPs was determined using Western blot. The expression levels were tested for correlation with the clinical and pathological data of the patients. Our data showed that the expression levels of CYP1A1 and CYP1A2 were negligible. Elevated expression of CYP1B1 mRNA and protein was detected in most RMS tumors and adjacent normal tissues. Most cancerous samples exhibit higher levels of both CYP3A4 and CYP3A5 compared with normal tissue samples. Expression of CYP2E1 mRNA was found to be significantly higher in tumor tissue, however no relation was found with protein levels. CYP2W1 mRNA and/or protein are mainly expressed in tumors. In conclusion, we defined the CYP gene expression profile in tumor and paired normal tissue of child patients with RMS. The overexpression of CYP2W1, CYP3A4 and CYP3A5 in tumor tissues suggests that they may be involved in RMS chemoresistance; furthermore, they may be exploited for the localized activation of anticancer prodrugs.

Expression of selected cytochrome P450 isoforms and of cooperating enzymes in colorectal tissues in selected pathological conditions

The current interest in CYP expression in the colon results from its uniqueness as a target organ for cancer. To date, the CYP expression profiles in the colon have not yet been subject of comprehensive research. In this study, we investigated 40 patients with Crohn's disease, 40 with ulcerative colitis, and 40 healthy subjects as a control group. Colon tissues were fixed, dehydrated, cleared in xylene and embedded in paraffin. Sections were prepared from paraffin blocks for immunohistochemical staining with specific antibodies. We used antibodies to the human CYP1A1, CYP2B6, CYP2C9, CYP2E1 and CYP3A4 isoforms, as well as antibodies to the human glycoprotein P, glutathione-S transferase and antibody to the UDP-glucuronosyltransferase. The sections were stained immunohistochemically and examined using light microscopy. Cellular localization was determined, and computer image analysis was used. In all cases with Crohn's disease, the proteins studied showed at least a twofold expression. Ulcerative colitis showed a much weaker influence regarding the expression of the proteins studied but in case of CYP2C9 and UDP-glucuronosyltransferase, a decrease of expression was observed.

Cytochrome P450 2E1: its clinical aspects and a brief perspective on the current research scenario

Research on Cytochrome P450 2E1 (CYP2E1), a key enzyme in alcohol metabolism has been very well documented in literature. Besides the involvement of CYP2E1 in alcohol metabolism as illustrated through the studies discussed in the chapter, recent studies have thrown light on several other aspects of CYP2E1 i.e. its extrahepatic expression, its involvement in several diseases and pathophysiological conditions; and CYP2E1 mediated carcinogenesis and modulation of drug efficacy. Studies involving these interesting facets of CYP2E1 have been discussed in the chapter focusing on the recent observations or ongoing studies illustrating the crucial role of CYP2E1 in disease development and drug metabolism.

Efficient replication of primary or culture hepatitis C virus isolates in human liver slices: a relevant ex vivo model of liver infection

The development of human cultured hepatitis C virus (HCV) replication-permissive hepatocarcinoma cell lines has provided important new virological tools to study the mechanisms of HCV infection; however, this experimental model remains distantly related to physiological and pathological conditions. Here, we report the development of a new ex vivo model using human adult liver slices culture, demonstrating, for the first time, the ability of primary isolates to undergo de novo viral replication with the production of high-titer infectious virus as well as Japanese fulminant hepatitis type 1, H77/C3, and Con1/C3. This experimental model was employed to demonstrate HCV neutralization or HCV inhibition, in a dose-dependent manner, either by cluster of differentiation 81 or envelope protein 2-specific antibodies or convalescent serum from a recovered HCV patient or by antiviral drugs.

CONCLUSION

This new ex vivo model represents a powerful tool for studying the viral life cycle and dynamics of virus spread in native tissue and also allows one to evaluate the efficacy of new antiviral drugs.

Expression and activities of hepatic cytochrome P450 (CYP1A, CYP2A and CYP2E1) in entire and castrated male pigs

This study aimed to provide further insights into the mechanism of in vivo regulation of cytochrome P450 (CYP450) 1A, 2A and 2E1 activities in pigs with different levels of testicular steroids. Hepatic mRNA and protein expression and enzymatic activity of CYP1A, CYP2A and CYP2E1 were compared between entire male and castrated pigs. Castration was performed either surgically or immunologically. The pigs were divided into four groups. In the first group, piglets were surgically castrated without anaesthesia. Immunological castration was performed by vaccination with Improvac® (Pfizer Ltd). Vaccinated pigs were subdivided into two groups according to the vaccination regimen: early and standard vaccination. Pigs in the early vaccination group were vaccinated when aged 11 and 15 weeks. Pigs in the standard vaccination group were vaccinated when aged 17 and 21 weeks. In the control group, pigs remained intact throughout the study. Hepatic CYP450 mRNA expression, measured by real-time RT-PCR, differed significantly between groups for all isoforms measured: CYP1A2 (P = 0.002), 2A (P = 0.000) and 2E1 (P = 0.002). Lower CYP450 mRNA in entire male pigs suggests suppression of CYP1A2, CYP2A and CYP2E1 by testicular steroids at the transcriptional level. However, this suppression was not always reflected in decreased protein expression and activities of these isoforms, suggesting that at least some CYP450s (e.g. CYP2E1) are regulated by a post-transcriptional mechanism.

Effects of dietary inulin, statin, and their co-treatment on hyperlipidemia, hepatic steatosis and changes in drug-metabolizing enzymes in rats fed a high-fat and high-sucrose diet

Background

Rats fed a high-fat and high-sucrose (HF) diet develop hepatic steatosis and hyperlipidemia. There are several reports that a change in nutritional status affects hepatic levels of drug-metabolizing enzymes. Synthetic inulin is a dietary component that completely evades glucide digestion. Supplementing a HF diet with inulin ameliorates hypertriglycemia and hepatic steatosis, but not hypercholesterolemia. This study aimed at distinguishing the effects of synthetic inulin and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin), which inhibit cholesterol biosynthesis.

Methods

We examined effects of co-treatment with synthetic inulin (5%) and fluvastatin (0, 4, and 8 mg/kg, per os) on body weight, epidydimal white adipose tissue weight, serum and hepatic lipid profiles, and hepatic cytochrome P450 (CYP) mRNA and protein profiles in rats fed a standard diet or a HF diet for 3 weeks.

Results

Treatment with the synthetic inulin (5%) or fluvastatin at 4 mg/kg (lethal dose in rats fed the HF diet, 8 mg/kg) ameliorated the elevation in hepatic triacylglycerol and total cholesterol levels in rats fed the HF diet. Whereas co-treatment with the inulin (5%) and fluvastatin (4 mg/kg) had a tendency to more strongly suppress the elevation in serum levels of very low density lipoprotein triacylglycerol than either treatment alone, no additive or synergistic effect was found in decrease in hepatic lipid levels. Hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein and methoxyresorufin O-demethylase and ethoxyresorufin O-deethylase activities were reduced in rats fed the HF diet. The synthetic inulin alleviated the reduction in hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein more strongly than fluvastatin, and no synergistic effects were observed on co-treatment. Furthermore, hepatic levels of aryl hydrocarbon receptor mRNA were decreased in rats fed the HF diet and recovered to near normal values with the intake of dietary inulin, which correlated with change in CYP1A1/2.

Conclusions

Dietary inulin alone was effective to prevent the development of hepatic steatosis, ameliorate nutritional effects, and alleviate the hepatic change in the expression of CYP1A1/2 and CYP2E1, while co-treatment with statin did not have additive or synergistic effects and statin may cause adverse effects in rats fed the HF diet.

miRNAs: effectors of environmental influences on gene expression and disease

Discovered less than a decade ago, micro-RNAs (miRNAs) have emerged as important regulators of gene expression in mammals. They consist of short nucleic acids, on average approximately 22 nucleotides in length. The miRNAs exert their effect by binding directly to target messenger RNAs (mRNAs) and inhibiting mRNA stability and translation. Each miRNA can bind to multiple targets and many miRNAs can bind to the same target mRNA, allowing for a complex pattern of regulation of gene expression. Once bound to their targets, miRNAs can suppress translation of the mRNA by either sequestration or degradation of the message. Thus, miRNAs function as powerful and sensitive posttranscriptional regulators of gene expression. This review will summarize what is known about miRNA biogenesis, expression, regulation, function, mode of action, and role in disease processes with an emphasis on miRNAs in mammals. We discuss some of the methodology employed in miRNA research and the potential of miRNAs as therapeutic targets. The role of miRNAs in signal transduction and cellular stress is reviewed. Lastly, we identify new exciting avenues of research on the role of miRNAs in toxicogenomics and the possibility of epigenetic effects on gene expression.

Renal pathophysiology after systemic administration of recombinant adenovirus: changes in renal cytochromes P450 based on vector dose

Recombinant adenovirus (Ad) significantly alters hepatic cytochrome P450 (CYP). Because changes in renal function can alter hepatic CYP, the effect of Ad on renal CYPs 4A1, 4A2, 4F1, and 2E1 was evaluated. Male Sprague-Dawley rats were given one of six intravenous doses (5.7x10(6)-5.7x10(12) viral particles/kg [VP/kg]) of Ad expressing beta-galactosidase or saline. CYP protein, activity, gene expression, and serum creatinine (SCr) were evaluated 0.25, 1, 4, and 14 days later. Doses of 5.7x10(11) and 5.7x10(12) VP/kg increased CYP4A protein within 24 hr by 35 and 48%, respectively (p<0.05). A similar trend was observed on day 4. CYP4A1 mRNA doubled 6 hr after doses of 5.7x10(10)-10(12) VP/kg (p<0.01). Similar effects were observed 1 day after each dose tested. CYP4A2 gene expression was 20% above control 1 day after treatment with 5.7x10(10)-10(12) VP/kg and remained high through day 14. CYP4F1 expression was unaffected by all doses (p=0.08). CYP2E1 activity and gene expression were significantly suppressed 24 hr after administration of all doses and began to normalize by day 14 (p<0.01). SCr was significantly reduced (approximately 50%) throughout the study for doses at and below 5.7x10(11) VP/kg. SCr was increased by a factor of 3 by 5.7x10(12) VP/kg and glomerular filtration was significantly reduced (p<0.01). This suggests that changes in renal CYP and corresponding arachidonic acid metabolites may play a role in the documented toxicity associated with the systemic administration of recombinant Ad.

Cytochrome P450 levels are altered in patients with esophageal squamous-cell carcinoma

AIM: To investigate the role of cytochrome P450 (CYP) in the carcinogenesis of squamous-cell carcinoma (SCC) in human esophagus by determining expression patterns and protein levels of representative CYPs in esophageal tissue of patients with SCC and controls.

METHODS: mRNA expression of CYP2E1, CYP2C, CYP3A4, and CYP3A5 was determined using RT-PCR in both normal and malignant esophageal tissues of patients with untreated esophageal SCC (n = 21) and in controls (n = 10). Protein levels of CYP2E1, CYP2C8, CYP3A4, and CYP3A5 were measured by Western blot.

RESULTS: Within the group of SCC patients, mRNA expression of CYP 3A4 and CYP2C was significantly lower in malignant tissue (-39% and -74%, respectively, P < 0.05) than in normal tissue. Similar results were found in CYP3A4 protein levels. Between groups, CYP3A4, CYP3A5, and CYP2C8 protein concentration was significantly higher in non-malignant tissue of SCC patients (4.8-, 2.9-, and 1.9-fold elevation, P < 0.05) than in controls. In contrast, CYP2E1 protein levels were significantly higher in controls than in SCC patients (+46%, P < 0.05).

CONCLUSION: Significant differences exist in protein levels of certain CYPs in non-malignant esophageal tissue (e.g. CYP2C8, CYP3A4, CYP3A5, and CYP2E1) between SCC patients and healthy subjects and may contribute to the development of SCC in the esophagus.

In Vivo and in Vitro Characterization of Chlorzoxazone Metabolism and Hepatic CYP2E1 Levels in African Green Monkeys: Induction by Chronic Nicotine Treatment

CYP2E1 metabolizes compounds, including clinical drugs, organic solvents, and tobacco-specific carcinogens. Chlorzoxazone (CZN) is a probe drug used to phenotype for CYP2E1 activity. Smokers have increased CZN clearance during smoking compared with nonsmoking periods; however, it is unclear which cigarette smoke component is causing the increased activity. The relationships between in vivo CZN disposition, in vitro CZN metabolism, and hepatic CYP2E1 have not been investigated in a within-animal design. In control-treated monkeys (Cercopithecus aethiops), the in vivo CZN area under the curve extrapolated to infinity (AUC(inf)) was 19.7 +/- 4.5 microg x h/ml, t1/2 was 0.57 +/- 0.07 h, and terminal disposition rate constant calculated from last three to four points on the log-linear end of the concentration versus time curve was 1.2 +/- 0.2 /h. In vitro, the apparent Vmax was 3.48 +/- 0.02 pmol/min/mug microsomal protein, and the Km was 95.4 +/- 1.8 microM. Chronic nicotine treatment increased in vivo CZN disposition, as indicated by a 52% decrease in AUC(inf) (p < 0.01) and 52% decrease in Tmax (p < 0.05) compared with control-treated monkeys. The log metabolic ratios at 0.5, 1, 2, and 4 h significantly negatively correlated with CZN AUC(inf) (p = 0.01-0.0001). Monkey hepatic CYP2E1 levels significantly correlated with both in vivo AUC(inf) (p = 0.03) and in vitro (p = 0.004) CZN metabolism. Together, the data indicated that nicotine induction of in vivo CZN disposition is related to the rates of in vitro CZN metabolism and hepatic microsomal CYP2E1 protein levels. Nicotine is one component in cigarette smoke that can increase in vivo CZN metabolism via induction of hepatic CYP2E1 levels. Thus, nicotine exposure may affect the metabolism of CYP2E1 substrates such as acetaminophen, ethanol, and benzene.

Decreased expression of cytochrome P450 protein in non-malignant colonic tissue of patients with colonic adenoma

BACKGROUND

Cytochrome P450 (CYP) enzymes in epithelial cells lining the alimentary tract play an important role in both the elimination and activation of (pro-)carcinogens. To estimate the role of cytochrome P450 in carcinogenesis of the colon, expression patterns and protein levels of four representative CYPs (CYP2C, CYP2E1, CYP3A4 and CYP3A5) were determined in colon mucosa of normal and adenomatous colonic tissue of patients with adenomas and disease-free controls.

METHODS

Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 in colon mucosa of normal and adenomatous colonic tissue of patients with adenoma and disease-free controls was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot.

RESULTS

With the exception of CYP3A5, expression of CYP mRNA was similar among groups and tissues (e.g. normal colon mucosa and adenoma). CYP3A5 mRNA expression was significantly higher in adenoma in comparison to normal tissue of patients with adenoma (approximately 48%). When comparing protein concentrations of CYPs measured in adenomas with neighboring normal colonic mucosa no differences were found. However, in normal tissue of patients with adenomas, protein levels of CYP2C8, CYP3A4 and CYP3A5, but not that of CYP2E1, were significantly lower than in biopsies obtained from disease-free controls. Specifically, in normal colonic mucosa of patients protein concentrations of CYP2C8, CYP3A4, and CYP3A5 were approximately 86%, approximately 69%, and approximately 54%, respectively, lower than in disease-free controls.

CONCLUSION

In conclusion, among other factors, the altered protein levels of certain CYPs (e.g. CYP2C8, CYP3A4 and CYP3A5) in colon mucosa might contribute to the development of neoplasia in the colon.

Distribution of cytochrome P450 2C, 2E1, 3A4, and 3A5 in human colon mucosa

Background

Despite the fact that the alimentary tract is part of the body's first line of defense against orally ingested xenobiotica, little is known about the distribution and expression of cytochrome P450 (CYP) enzymes in human colon. Therefore, expression and protein levels of four representative CYPs (CYP2C(8), CYP2E1, CYP3A4, and CYP3A5) were determined in human colon mucosa biopsies obtained from ascending, descending and sigmoid colon.

Methods

Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 mRNA in colon mucosa was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot methods.

Results

Extensive interindividual variability was found for the expression of most of the genes. However, expression of CYP2C mRNA levels were significantly higher in the ascending colon than in the sigmoid colon. In contrast, mRNA levels of CYP2E1 and CYP3A5 were significantly lower in the ascending colon in comparison to the descending and sigmoid colon. In sigmoid colon protein levels of CYP2C8 were significantly higher by ~73% than in the descending colon. In contrast, protein concentration of CYP2E1 was significantly lower by ~81% in the sigmoid colon in comparison to the descending colon.

Conclusion

The current data suggest that the expression of CYP2C, CYP2E1, and CYP3A5 varies in different parts of the colon.

Acetoacetate induces CYP2E1 protein and suppresses CYP2E1 mRNA in primary cultured rat hepatocytes

The ketone body acetoacetate (AA) in the absence of insulin or in the presence of diabetic insulin levels decreases CYP2E1 mRNA expression in a concentration- and time-dependent manner in primary cultured rat hepatocytes. AA activates p70 ribosomal S6 kinase (p70S6K) and protein kinase C (PKC) by approximately 2- to 2.5-fold, respectively, following 6-h treatment. The AA-mediated activation of p70S6K, but not PKC, was abolished by inhibition of PI 3-K with LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] or wortmannin, in agreement with p70S6K being downstream of phosphatidylinositol 3-kinase (PI 3-K). Inhibition of PI 3-K, mTOR with rapamycin, or PKC with bisindolylmaleimide ameliorated the AA-mediated down-regulation of CYP2E1 mRNA expression. Neither the mitogen-activated protein kinase kinase inhibitor PD98059 (2'-amino-3'-methoxyflavone) nor the p38 mitogen-activated protein kinase inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole] ameliorated the AA-mediated suppression of CYP2E1 mRNA expression. Heterogeneous nuclear RNA analysis revealed that AA suppressed CYP2E1 gene transcription by approximately 50% and that inhibition of PI 3-K and PKC diminished this AA-mediated effect on transcription. CYP2E1 mRNA half-life slightly increased from approximately 24 h in untreated hepatocytes to approximately 32 h in AA-treated cells. Interestingly, AA increased CYP2E1 protein levels by approximately 2- and 2.5-fold at 24 and 48 h, respectively. DL-beta-hydroxybutyrate was without effect. Polysomal distribution studies revealed that AA increased the proportion of RNA associated with the actively translated polysomal fractions versus the 40S to 60S untranslated fractions by approximately 40%. CYP2E1 protein half-life increased from approximately 8 h in untreated hepatocytes to approximately 24 in AA-treated cells. These data show that AA decreases CYP2E1 mRNA expression through inhibition of gene transcription while simultaneously elevating CYP2E1 protein levels through increased translation and decreased protein degradation.

Primary acute lymphoblastic leukemia cells use a novel promoter and 5'noncoding exon for the human reduced folate carrier that encodes a modified carrier translated from an upstream translational start

The human reduced folate carrier (hRFC) is reported to be regulated by up to seven alternatively spliced noncoding exons (A1, A2, A, B, C, D, and E). Noncoding exon and promoter usage was analyzed in RNAs from 27 childhood acute lymphoblastic leukemia (ALL) specimens by real-time PCR and/or 5' rapid amplification of cDNA ends (5' RACE) assay. By real-time PCR, total hRFC transcripts in ALL spanned a 289-fold range. Over 90% of hRFC transcripts were transcribed with A1, A2, and B 5' untranslated regions (UTRs). Analysis of 5' RACE clones showed that the A1 + A2 5'UTRs contained A1 sequence alone or a fusion of A1 and A2, implying the existence of a single, alternatively spliced 1021-bp A1/A2 noncoding region. High frequency sequence polymorphisms (AGG deletion, C/T transition) identified in the A1/A2 region by 5'RACE were confirmed in normal DNAs. By reporter assays in HepG2 hepatoma and Jurkat leukemia cells, A1/A2 promoter activity was localized to a 134-bp minimal region. Translation from an upstream AUG in the A1/A2 noncoding region in-frame with the normal translation start resulted in synthesis of a larger ( approximately 7 kDa) hRFC protein with transport properties altered from those for wild-type hRFC. Although there was no effect on transcript or protein stabilities, in vitro translation from A1/A2 transcripts was decreased compared with those with the B 5'UTR. Our results document the importance of the hRFC A1/A2 upstream region in childhood ALL and an intricate transcriptional and posttranscriptional regulation of hRFC-A1/A2 mRNAs. Furthermore, they suggest that use of the A1/A2 5'UTR may confer a transport phenotype distinct from the other 5'UTRs due to altered translation efficiency and transport properties.

Transcriptional regulation of the human reduced folate carrier promoter C: synergistic transactivation by Sp1 and C/EBP beta and identification of a downstream repressor

The human reduced folate carrier (hRFC) is ubiquitously but differentially expressed in human tissues and its levels are regulated by up to six alternatively spliced non-coding regions (designated A1/A2, A, B, C, D, and E) and by at least four promoters. By transient transfections of HepG2 human hepatoma cells with 5' and 3' deletion constructs spanning 2883 bp of upstream sequence, a transcriptionally important region was localized to within 177 bp flanking the transcriptional start sites for exon C. By gel shift and chromatin immunoprecipitation assays, Sp1 and C/EBP beta transcription factors were found to bind consensus elements (GC-box, CCAAT-box) within this region. The functional importance of these elements was confirmed by transient tranfections of HepG2 cells with hRFC-C reporter constructs in which these elements were mutated, and by co-transfections of Drosophila SL-2 cells with wild-type hRFC-C promoter and expression constructs for Sp1 and C/EBP beta. Whereas both Sp1 and C/EBP beta transactivated hRFC-C promoter activity, C/EBP alpha and gamma were transcriptionally inert. Sp1 combined with C/EBP beta resulted in a synergistic transactivation. In HepG2 cells, transfections with Sp1 and C/EBP beta both increased endogenous levels of hRFC-C transcripts. By 3' deletion analysis, a repressor sequence was localized to within 71 bp flanking the minimal promoter. On gel shifts, a novel transcriptional repressor was localized to within 30 bp. Collectively, these results identify transcriptionally important regions in the hRFC-C minimal promoter that include a GC-box and CCAAT-box, and suggest that cooperative interactions between Sp1 and C/EBP beta are essential for hRFC-C transactivation. Another possible factor in the tissue-specific regulation of the hRFC-C region involves the downstream repressor flanking the minimal promoter.

Expression of genes encoding for drug metabolising cytochrome P450 enzymes and P-glycoprotein in the rat small intestine; comparison to the liver

The level of expression of genes encoding for nine major xenobiotic metabolising Cytochrome P450s (CYPs) and the P-glycoprotein (Pgp) was determined in three different regions of the small intestine of male and female Sprague Dawley rats and the expression was compared with that in the liver. A semi-quantitative RT-PCR method, using the total RNA from the tissues, was established for the determination of the level of gene expression. Four of the CYP genes: the CYP2B1, CYP2C6, CYP2C11 and CYP2D1 and the Pgp were expressed at as high levels in the small intestine as in the liver. The expression of the other CYP genes was remarkably different in the two organs. The CYP1A2, CYP2A3, CYP2E1 and CYP3A1 showed a strong expression in the liver but only a comparatively weak or no expression in the small intestine. The CYP1A1 on the other hand exhibited a stronger expression in the small intestine than in the liver. With the exception of the CYP2A3, none of the genes showed a clear regional distribution in their small intestinal expression. Furthermore, no obvious sex difference in the expression of the CYP and Pgp genes could be observed. Our results indicate that several of the enzymes, central for drug metabolism are differently expressed in the liver and in the small intestine of the rat which should be taken into account when using rat as a model for the bioavailability and organ specific toxicity studies of orally administered xenobiotics. The apparently strong small intestinal expression of the CYP2C genes suggests that these enzymes could play a key role in the intestinal drug metabolism in rats and therefore affect the bioavailability of those orally used drugs which are substrates of the CYP2Cs. This possibility should be investigated in more detail both in rats and humans.

Membrane transport of folates

The chapter reviews the current understanding of the transport mechanisms for folates in mammalian cells--their molecular identities and organization, tissue expression, regulation, structures, and their kinetic and thermodynamic properties. This encompasses a variety of diverse processes. Best characterized is the reduced folate carrier, a member of the SLC19 family of facilitative carriers. But other facilitative organic anion carriers (SLC21), largely expressed in epithelial tissues, transport folates as well. In addition to these bi-directional carrier systems are the membrane-localized folate receptors alpha and beta, that mediate folate uptake unidirectionally into cells via an endocytotic process. There are also several transporters, typified by the family of multidrug resistance-associated proteins, that unidirectionally export folates from cells. There are transport activities for folates, that function optimally at low pH, related in part to the reduced folate carrier, with at least one activity that is independent of this carrier. The reduced folate carrier-associated low-pH route mediates intestinal folate transport. This review considers how these different transport processes contribute to the generation of transmembrane folate gradients and to vectorial flows of folates across epithelia. The role of folate transporters in mouse development, as assessed by homologous deletion of folate receptors and the reduced folate carrier, is described. Much of the focus is on antifolate cancer chemotherapeutic agents that are often model surrogates for natural folates in transport studies. In particular, antifolate transport mediated by the reduced folate carrier is a major determinant of the activity of, and resistance to, these agents. Finally, many of the key in vitro findings on the properties of antifolate transporters are now beginning to be extended to patient specimens, thus setting the stage for understanding response to these drugs in the clinical setting at the molecular level.

Effects of prototypical microsomal enzyme inducers on cytochrome P450 expression in cultured human hepatocytes

Cultured human hepatocytes are a valuable in vitro system for evaluating new molecular entities as inducers of cytochrome P450 (P450) enzymes. The present study summarizes data obtained from 62 preparations of cultured human hepatocytes that were treated with vehicles (saline or dimethylsulfoxide, 0.1%), beta-naphthoflavone (33 microM), phenobarbital (100 or 250 microM), isoniazid (100 microM) and/or rifampin (20 or 50 microM), and examined for the expression of P450 enzymes based on microsomal activity toward marker substrates, or in the case of CYP2C8, the level of immunoreactive protein. The results show that CYP1A2 activity was markedly induced by beta-naphthoflavone (on average 13-fold, n = 28 preparations), and weakly induced by phenobarbital (1.9-fold, n = 25) and rifampin (2.3-fold, n = 22); CYP2A6 activity tended to be increased with phenobarbital (n = 7) and rifampin (n = 3) treatments, but the effects were not statistically significant; CYP2B6 was induced by phenobarbital (6.5-fold, n = 13) and rifampin (13-fold, n = 14); CYP2C8 was induced by phenobarbital (4.0-fold, n = 4) and rifampin (5.2-fold, n = 4); CYP2C9 was induced by phenobarbital (1.8-fold, n = 14) and rifampin (3.5-fold, n = 10); CYP2C19 was markedly induced by rifampin (37-fold, n = 10), but relatively modestly by phenobarbital (7-fold, n = 9); CYP2D6 was not significantly induced by phenobarbital (n = 5) or rifampin (n = 5); CYP2E1 was induced by phenobarbital (1.7-fold, n = 5), rifampin (2.2-fold, n = 5), and isoniazid (2.3-fold, n = 5); and, CYP3A4 was induced by phenobarbital (3.3-fold, n = 42) and rifampin (10-fold, n = 61), but not by beta-naphthoflavone. Based on these observations, we generalize that beta-naphthoflavone induces CYP1A2 and isoniazid induces CYP2E1, whereas rifampin and, to a lesser extent phenobarbital, tend to significantly and consistently induce enzymes of the CYP2A, CYP2B, CYP2C, CYP2E, and CYP3A subfamilies but not the 2D subfamily.

The human reduced folate carrier gene is regulated by the AP2 and sp1 transcription factor families and a functional 61-base pair polymorphism

Recently, our laboratory reported an intricate regulation of the human reduced folate carrier (hRFC) gene, involving multiple promoters and noncoding exons. We localized promoter activity to a 452-bp GC-rich region upstream of noncoding exon A, including a 47-bp basal promoter with a CRE/AP-1-like consensus element that bound the bZip family of DNA-binding proteins (e.g. CREB-1 and c-Jun). We now report that three nearly identical tandem repeats (49-61 bp) in the hRFC-A upstream region are involved in regulating promoter activity. By in vitro binding assays, multiple transcription factors (e.g. AP2 and Sp1/Sp3) bound this region. When AP2 was cotransfected with the hRFC-A reporter construct into HT1080 cells, promoter activity increased 3-fold. In Drosophila SL2 cells, Sp1 transactivated promoter A and showed synergism with CREB-1. However, c-Jun was antagonistic to the effects of Sp1. A sequence variant in the hRFC-A repeated region was identified, involving an exact duplication of a 61-bp sequence. This variant had an allelic frequency of 78% in 72 genomic DNAs and resulted in a 63% increase in promoter activity. These results identify important regions in the hRFC-A promoter and critical roles for AP2 and Sp1, in combination with the bZip transcription factors. Moreover, they document a functionally novel polymorphism that increases promoter activity and may contribute to interpatient variations in hRFC expression and effects on tissue folate homeostasis and antitumor response to antifolates.

The human reduced folate carrier gene is ubiquitously and differentially expressed in normal human tissues: identification of seven non-coding exons and characterization of a novel promoter

Our previous study identified two alternate non-coding upstream exons (A and B) in the human reduced folate carrier (hRFC) gene, each controlled by a separate promoter. Each minimal promoter was regulated by unique cis -elements and transcription factors, including stimulating protein (Sp) 1 and Sp3 and the basic leucine zipper family of proteins, suggesting opportunities for cell- and tissue-specific regulation. Studies were performed to explore the expression patterns of hRFC in human tissues and cell lines. Levels of hRFC transcripts were measured on a multi-tissue mRNA array from 76 human tissues and tumour cell lines and on a multi-tissue Northern blot of representative tissues, each probed with full-length hRFC cDNA. hRFC transcripts were ubiquitously expressed, with the highest level in placenta and the lowest level in skeletal muscle. By rapid amplification of cDNA 5'-ends assay from nine tissues and two cell lines, hRFC transcripts containing both A and B 5'-untranslated regions (UTRs) were identified. However, five additional 5'-UTRs (designated A1, A2, C, D and E) were detected, mapping over 35 kb upstream from the hRFC translation start site. The 5'-UTRs were characterized by multiple transcription start sites and/or alternative splice forms. At least 18 unique hRFC transcripts were detected. A novel promoter was localized to a 453 bp fragment, including 442 upstream of exon C and 11 bp of exon C. A 346 bp repressor flanked the 3'-end of this promoter. Our results suggest an intricate regulation of hRFC gene expression involving multiple promoters and non-coding exons. Moreover, they provide a transcriptional framework for understanding the role of hRFC in the pathophysiology of folate deficiency and antifolate drug selectivity.

Cytochrome P-450 mRNA expression in human liver and its relationship with enzyme activity

CYP activity and protein contents have been measured in human liver using different techniques. In contrast, CYP mRNA data are scarce and the relationships between CYP mRNA contents and activities have not been established. These studies deserve further attention because mRNA determinations by RT-PCR require a very small amount of material (e.g., liver needle biopsy) and could provide important data regarding CYP expression regulation. In this study we measured in 12 human liver samples the mRNA contents of 10 CYPs by quantitative RT-PCR and the metabolic activities using specific substrates. mRNA contents and activities showed high correlation coefficients for CYP1A1, CYP1A2, CYP3A4, CYP2D6, and CYP2B6 (0.96, 0.94, 0.69, 0.61, and 0.52, respectively), but no significant correlations were found for CYP2C9, CYP2A6, and CYP2E1. The results suggest that the regulation of CYP1A1, CYP1A2, CYP3A4, CYP2D6, and CYP2B6 expression is essentially pretranslational and that their mRNA levels could allow a good estimate of their activity.

Effect of 4-(4-chlorobenzyl)pyridine on rat hepatic microsomal cytochrome P450 and drug-metabolizing enzymes in vivo and in vitro

The effect of 4-(4-chlorobenzyl)pyridine (4-CBP) on rat hepatic microsomal cytochrome P450 (P450) and its molecular species (CYP2B1, 2E1, 3A2, 2C11, and 2C12), and on drug-metabolizing enzyme activities were examined in vivo and in vitro. Treatment of rats with 4-CBP resulted in the induction of P450 and drug-metabolizing enzymes in a dose-dependent manner, but it was markedly inhibitory at higher dose levels. Immunoblot analyses revealed that 4-CBP induces both CYP2B1 and 2E1; however, both were decreased by increasing the dose of 4-CBP. The in vitro inhibitory experiment revealed that 4-CBP strongly inhibited benzphetamine N-demethylase activity, but not dimethylnitrosamine N-demethylase activity. The present findings provide information on the induction and inhibition effect of chlorinated benzylpyridine on hepatic microsomal P450s and drug-metabolizing enzymes in vivo and in vitro.

The alcohol-inducible form of cytochrome P450 (CYP 2E1): role in toxicology and regulation of expression

Cytochrome P450 (CYP) 2E1 catalyzes the metabolism of a wide variety of therapeutic agents, procarcinogens, and low molecular weight solvents. CYP2E1-catalyzed metabolism may cause toxicity or DNA damage through the production of toxic metabolites, oxygen radicals, and lipid peroxidation. CYP2E1 also plays a role in the metabolism of endogenous compounds including fatty acids and ketone bodies. The regulation of CYP2E1 expression is complex, and involves transcriptional, post-transcriptional, translational, and post-translational mechanisms. CYP2E1 is transcriptionally activated in the first few hours after birth. Xenobiotic inducers elevate CYP2E1 protein levels through both increased translational efficiency and stabilization of the protein from degradation, which appears to occur primarily through ubiquitination and proteasomal degradation. CYP2E1 mRNA and protein levels are altered in response to pathophysiologic conditions by hormones including insulin, glucagon, growth hormone, and leptin, and growth factors including epidermal growth factor and hepatocyte growth factor, providing evidence that CYP2E1 expression is under tight homeostatic control.