Evidence for elevation of cytochrome P4502E1 (alcohol-inducible form) mRNA levels in rat kidney following pyridine administration

Effects of dioxane on cytochrome P450 enzymes in liver, kidney, lung and nasal mucosa of rat

The effect of acute and chronic dioxane administration on hepatic, renal, pulmonary and nasal mucosa P450 enzymes and liver toxicity were investigated in male rats. The acute treatment consisted of two doses (2 g/kg) of dioxane given for 2 days by gavage, whereas the chronic treatment consisted of 1.5% of dioxane in drinking water for 10 days. Both the acute and chronic dioxane treatments induced cytochrome P450 2B1/2- and P450 2E1-dependent microsomal monooxygenase activities (pentoxyresorufin O-depentylase and p-nitrophenol hydroxylase) in the liver, whereas in the kidney and nasal mucosa, only the 2E1 marker activities were enhanced. In addition in the liver, an induction of 2alpha-testosterone hydroxylase (associated with the constitutive and hormone-dependent P450 2C11) was also revealed, whereas the hepatic P450 4A-dependent omega-lauric acid hydroxylase was not enhanced by any dioxane treatment. These inductions were mostly confirmed by western blot analysis of liver, kidney and nasal mucosa microsomes. In the lung, no alteration of P450 activities was observed. To assess the mechanism of 2E1 induction, the hepatic, renal and nasal mucosa 2E1 mRNA levels were also examined. Following two kinds of dioxane administration, in the liver the 2E1 induction was not accompanied by a significant alteration of 2E1 mRNA levels, while both in the kidney and nasal mucosa the 2E1 mRNA increased about 2- to 3-fold, indicating an organ-specific regulation of this P450 isoform. Furthermore, dioxane was unable to alter the plasma alanine aminotransferase activity and hepatic glutathione (GSH) content, examined as an index of toxicity, when it was administered into rats with P450 2B1/2 and 2E1 preinduced by phenobarbital or fasting pretreatment. These results support the lack of or a poor formation of reactive and toxic intermediates during the biotrasformation of this solvent, even when its metabolism was enhanced by P450 inducers. The chronic administration of dioxane was also unable to induce the palmitoyl CoA oxidase, a marker of peroxisome proliferation, excluding this as a way to explain its toxicity. Thus, although the mechanism of dioxane carcinogenicity remains unclear, the present results suggest that the induction of 2E1 following a prolonged administration of dioxane might provide oxygen radical species, and thereby contribute to its organ-specific toxicity.

Tobacco smoke-dependent changes in cytochrome P450 1A1, 1A2, and 2E1 protein expressions in fetuses, newborns, pregnant rats, and human placenta

Tobacco smoke (TS) was described as a mixture of numerous cytochrome P450 (P450) substrates, inducers, and inhibitors. These inducers and inhibitors may modify drug clearance and xenobiotic or endogenous metabolism affecting P450s expression. In the present study, the effect of gestation and TS on: (1) cytochrome P450 CYP1A1, CYP1A2, and CYP2E1 protein expressions, and (2) cytochrome P450-linked microsomal enzyme activities, were studied in fetal rat liver, rat, and human placenta and in newborn and adult rat hepatic and extrahepatic tissues. Non-pregnant and pregnant 4-month-old female Wistar rats were exposed to TS (500, 1,000, or 1,500 mg carbon monoxide per m(3) air) in a toxicological chamber for 3 weeks (6 h daily, 5 days weekly). Human placentas were sampled from non-smoking, passive smoking, or active smoking primiparas. The efficacy of exposure was assessed by measuring urine cotinine levels. The TS-dependent inductory effect on the expression of CYP1A1 and 1A2 and related monooxygenase activities, and the inhibitory/inductory effect on CYP2E1 expression in rat tissues were observed. Pregnancy was associated with decreased levels of constitutive CYP1A1 and 2E1 in hepatic and extrahepatic tissues, TS-inducible CYP1A2 expression in the liver, and CYP1A1 expression in lungs and heart, but had no inhibitory effect on TS-inducible CYP1A1 and 2E1 expression, EROD, and P450-cooperated enzyme activities in the liver, kidney, and, in the latter case, in the heart. The presence of TS-induced CYP1A1 protein was confirmed in rat and human placenta and showed in newborn liver and lungs. CYP1A2 and 2E1 proteins were detectable in fetal rat liver. It was concluded that the expression of CYP1A1, 1A2, and 2E1, which metabolize some drugs and activate carcinogens, is controlled by age-, pregnancy-, and tissue-specific regulatory mechanisms in rats. Gestational differences in the regulation of expression of CYP1A subfamily members are not excluded. CYP1A1 and 2E1, but not CYP1A2 inductory mechanisms seem to be functional in fetal liver at day 21 of pregnancy but they appeared to be uninducible under a TS exposure. In TS-exposed pregnant females and fetuses the effects of metabolic activation of CYP1A1 and 1A2 substrates might be reduced because of lower CYP expressions or poor induction, respectively.

Immunohistochemical study of CYP2E1 in hepatocellular carcinoma carcinogenesis: examination with newly prepared anti-human CYP2E1 antibody

Cytochrome P450 2E1 (CYP2E1) is known as a heme-containing enzyme that produces abundant free radicals, and its involvement in carcinogenesis has been suggested in several organs in vivo. In this study, to clarify the involvement of CYP2E1 in liver cancer and its carcinogenesis process, we investigated the expression of CYP2E1 in 42 surgically resected or biopsied specimens of hepatocellular carcinomas (HCC) and 26 cases with other liver lesions immunohistochemically using a newly prepared anti-human CYP2E1 antibody. When intracellular CYP2E1 expression was investigated in three different regions of HCC specimens, the expression in hepatocytes of the peri-tumor region was the highest (p<0.001) compared with those in the tumor and non-peri-tumor regions. Histologically, the expression of CYP2E1 in tumor cells tended to decrease as the cells were less differentiated (p<0.0001) and was the lowest in poorly differentiated HCC (p<0.01). CYP2E1 expression was highest in the pseudo-glandular type and low in the thick trabecular and solid types of HCC (p<0.0001). In mature regenerative nodules of liver cirrhosis, adenomatous hyperplasia (AH) and atypical adenomatous hyperplasia (AAH) to early-HCC, CYP2E1 expression was notably high as compared with other legions. CYP2E1 has a strong free radical-producing ability, and the cell injury and DNA damages by the free radicals are considered to be involved in carcinogenesis. Therefore, our results suggest that the different expression of CYP2E1 in hepatocytes may play important roles in the multistep carcinogenic process and the histogenesis of hepatocellular carcinoma.

Increase in urea in conjunction with L-arginine metabolism in the liver leads to induction of cytochrome P450 2E1 (CYP2E1): the role of urea in CYP2E1 induction by acute renal failure

A number of xenobiotics and certain pathophysiological situations cause the induction of CYP2E1. The present study was designed to establish the role of plasma urea nitrogen and L-arginine on hepatic CYP2E1 expression in rats or rats with acute renal failure. Exposure of rats to a single intravenous dose of 5 mg/kg uranyl nitrate caused renal failure in 5 days (ARF), as evidenced by increases in plasma urea nitrogen level and kidney to body weight ratio. Northern and Western blot analyses revealed that hepatic CYP2E1 was 2- to 4-fold induced by ARF. Treatment of rats with either 10% glucose in drinking water for 5 days following a single injection of uranyl nitrate or two injections of recombinant growth hormone (5 units/kg, s.c., twice a day) on the 4th day after uranyl nitrate injection reduced both the rise in plasma urea nitrogen and the induction of CYP2E1. Exposure of rats to urea (approximately 225 mg/kg/day) in drinking water for 1 to 3 day(s) resulted in significant increases in CYP2E1 mRNA and protein. Furthermore, perfusion of the liver with 25 mM urea for 24 h resulted in CYP2E1 induction with an increase in the mRNA. The levels of CYP2E1 protein and mRNA were increased in rats perfused with 25 mM L-arginine for 24 h (i.e., a 4-fold increase). Hence, L-arginine, which is irreversibly hydrolyzed to urea and ornithine by arginase, also induced hepatic CYP2E1. The results of the present study provided evidence that increases in plasma urea in conjunction with L-arginine metabolism lead to the induction of CYP2E1 in the liver.

Promoter function and the role of cytokines in the transcriptional regulation of rabbit CYP2E1 and CYP2E2

Rabbit CYP2E1 and CYP2E2 show considerable similarity in the 5' flanking region, but a 32-base-pair element (32-BPE) that is repeated in 2E1 is present only as a single inexact copy in 2E2. In the present investigation, footprinting disclosed two specific binding sites for liver nuclear proteins, and the DNase I sensitivity profiles of the two genes were found to be different. Several positive and negative regulatory elements were identified by transfection with a series of constructs of upstream CYP2E sequences fused to the luciferase gene. Both genes have an HNF-1 consensus motif with one nucleotide mismatch, which affects binding affinity and promoter activity. Investigation of DNA-protein interactions revealed that Sp1 and NFkappaB bind exclusively to the 32-BPE of 2E1 and 2E2, respectively, suggesting a possible regulatory role for the 32-BPE. Interleukin-1alpha (IL-1alpha) gave rise to a 2.5-fold increase in the promoter activity of 2E1 in HepG2 cells, and the IL-1alpha-mediated induction of reporter gene expression was almost completely prevented when the 32-BPE was deleted. Increased DNA binding and Sp1 protein content as a result of IL-1alpha treatment, as well as cotransfection experiments with pPacSp1, suggest that Sp1 is a transcription activator for the induction of 2E1 by IL-1alpha in HepG2 cells.

Induction of cytochrome P450 enzymes in the livers of rats treated with the pyrrolizidine alkaloid retrorsine

Retrorsine is a member of the pyrrolizidine alkaloid (PA) family of naturally occurring compounds found in a large number of plant species worldwide. The cytotoxic, mutagenic, and antimitotic effects of PAs have made them targets for studies designed to determine their potential contributions to carcinogen esis and their usefulness for anticancer therapy. Evidence from the literature suggests that bioactivation of PAs by liver cytochrome P450 (CYP) enzymes is required for their toxicity. However, the specific CYP isozymes that are involved in retrorsine metabolism have not been identified. To address this issue, we administered retrorsine to a cohort of young adult male rats and examined induction or enhanced expression of mRNA and protein for widely studied hepatic CYP isoforms spanning four families together with the essential enzyme CYP reductase. The protein levels of normally expressed CYPs 1A2, 2B1/2, and 2E1 increase significantly in rat liver microsomes from retrorsine-treated rats compared to untreated control rats (P < 0. 05), but protein levels of CYP 4A3, CYP 3A1, and CYP reductase were unchanged after retrorsine treatment. In addition, CYP 1A1 mRNA and protein, which are not detectable in the livers of control rats, were induced after retrorsine exposure. The results of the present study demonstrate enhanced or induced expression of hepatic CYPs 1A1, 1A2, 2E1, and 2B1/2 in response to retrorsine exposure in rats, suggesting that one or more of these enzymes may be involved in retrorsine metabolism.

Cytochrome P450 2E1 mRNA in the rat prostate: detection and quantitation by competitive reverse transcription and polymerase chain reaction

Cytochrome P450 2E1 plays a pivotal role in the metabolic activation of a wide variety of low molecular weight environmental toxicants and procarcinogens. In the present study, expression of the P450 2E1 gene in the rat prostate gland was quantitated by competitive reverse transcription and the polymerase chain reaction. To assess accurately the induction level of P450 2E1 mRNA in the prostate after pyridine treatment of rats, a recombinant standard RNA was generated that is homologous to the sequence of P450 2E1 mRNA except for an internal deletion of 100 bases. The data indicate that P450 2E1 mRNA is present in the prostate of untreated animals and is induced about four-fold by treatment with pyridine. The results suggest that exposure to certain environmental chemicals and procarcinogens may increase P450 2E1 levels in the prostate gland and thus could enhance formation of reactive, carcinogenic metabolites.

The detection of cytochrome P450 2E1 and its catalytic activity in rat testis

Cytochrome P450 2E1 participates in the bioactivation of a wide variety of environmental and occupational pollutants. Such reactions may lead to the production of active carcinogenic metabolites. The presence of P450 2E1 in the testis and prostate has not yet been reported. In the present study, cytochrome P450 2E1 mRNA has been identified in the rat prostate and testis by reverse transcription PCR, southern blotting, and DNA sequencing. P450 2E1 protein from rat testis could be detected with immunoblot analysis, but was not detected in the prostate. The hydroxylation of p-nitrophenol, known to be mediated by P450 2E1, was demonstrated by HPLC measurement of product formation in microsomal fractions from the rat testis, but again not from prostate. Exposure of rats to pyridine resulted in a 2.9-fold increase of p-nitrophenol hydroxylation by testicular microsomes. Diethyldithiocarbamate, a selective mechanism-based inhibitor of P450 2E1, or a P450 2E1 monoclonal antibody, caused marked inhibition of testicular microsomal p-nitrophenol hydroxylase activity. These results indicate that cytochrome P450 2E1 is present in the rat testis, and that it is elevated by the treatment of the animals with pyridine. Thus, the presence and inducibility of cytochrome P450 2E1 in the testis may be of significance in the bioactivation of environmental chemicals to genotoxic metabolites.

Expression and distribution of cytochrome P450 enzymes in male rat kidney: effects of ethanol, acetone and dietary conditions

Ethanol, acetone, diet and starvation, known modulators of the hepatic cytochrome P450 (CYP)-dependent microsomal monooxygenase system, were assessed for their effects on cytochrome P450 isozyme content and monooxygenase activities in the male rat kidney. In acute experiments, rats were either treated with acetone, fasted or given a combination of the two treatments. Acetone treatment alone induced CYP2E1-dependent p-nitrophenol hydroxylase activity in kidney microsomes by 8-fold. This was accompanied by a 6-fold increase in CYP2E1 apoprotein as determined by Western blot analysis. There was, however, no significant increase in steady-state levels of CYP2E1 mRNA as measured by Northern blot analysis. Starvation also induced CYP2E1 apoprotein in the kidney and, as has been reported previously in the liver, had a synergistic inductive effect with acetone. CYP2B and CYP3A apoproteins were also induced by acetone, starvation and starvation/acetone combinations in the kidney. Immunohistochemical analysis revealed localization of CYP2E1 and CYP2B principally in the cortex associated with tubular cells. This distribution was maintained upon starvation/acetone treatment. Two induction experiments were performed in which the ethanol was administered as part of a system of total enteral nutrition (TEN). A short-term study was conducted in which ethanol was administered for 8 days in two liquid diets of different composition, and a chronic experiment was performed in which ethanol was administered for 35 days. A diet-independent 6-fold increase in CYP2E1 apoprotein was observed in the short-term experiment. Expression of CYP3A and CYP2A cross-reactive apoproteins in kidney microsomes appeared to be affected by alterations in diet but, were unaffected by ethanol treatment. In the chronic 35-day ethanol exposure experiment, CYP2E1 apoprotein was also elevated 6-fold and this was found to be accompanied by a significant 3-fold increase in CYP2E1 mRNA. In the same study, no ethanol effects were apparent on expression of CYP2B and CYP3A apoproteins. Thus, acetone induced a variety of renal cytochrome P450 forms in addition to CYP2E1, while ethanol appeared to be a much more specific renal CYP2E1 inducer. Furthermore, as reported in the liver, acetone and ethanol appeared to induce CYP2E1 in the kidney by different mechanisms.

Effect of pyridine on the expression of cytochrome P450 isozymes in primary rat hepatocyte culture

In vivo administration of pyridine has been shown to increase the activity and content of several forms of cytochrome P450 by transcriptional and posttranscriptional mechanisms. The effect of pyridine on CYP1A and CYP2E1 isozymes was studied in a rat hepatocyte culture model. Hepatocytes were isolated from non-induced rats and seeded onto matrigel-coated dishes and incubated in William's medium E containing 10% fetal calf serum, hormones, and essential metals. Cultures were treated with 0, 10 or 25 mM pyridine for 1-3 days and microsomes were isolated to determine catalytic activity and for immunoblot analysis, and total RNA was isolated for mRNA determinations. CYP2E1 content, CYP2E 1 mRNA, and CYP2E1 catalyzed oxidation of p-nitrophenol declined during culture to values of 3, 30 and 19% that of initial, non-cultured controls by day 3 of culture. Pyridine prevented this decline of CYP2E1 protein and activity such that 60-80% original activity remained after 3 days of culture in the presence of 25 mM pyridine. However, pyridine did not prevent the fall in CYP2E1 mRNA levels, nor did pyridine increase the content or activity of CYP2E1 above initial values of microsomes from freshly isolated hepatocytes. Pyridine increased the content of CYP1A2 and the oxidation of ethoxyresorufin 2-4 fold compared to cultures incubated without pyridine over the 3 day culture period. CYP1A1 levels, which rapidly declined, were induced and maintained in the presence of pyridine. Pyridine increased CYP1A content and activity 2-3 fold over initial values of freshly isolated hepatocytes. These increases were associated with corresponding increases in CYP1A mRNA levels. CYP1A2, but not CYP1A1, mRNA levels increased in the cultures incubated in the absence of pyridine. These results indicate that pyridine has different effects on CYP1A and CYP2E1 in this hepatocyte culture model. Pyridine appears to modulate CYP2E1 levels by posttranscriptional mechanisms as CYP2E1 activity and content were maintained in the presence of pyridine under conditions in which CYP2E1 mRNA levels declined. These mechanisms may involve increased translational efficiency of existing CYP2E1 mRNA or stabilization of CYP2E1 protein against degradation. Pyridine increased CYP1A1 and CYP1A2 content, activity and mRNA levels, either inducing CYP1A transcription or stabilizing CYP1A mRNA. Hepatocyte cultures may be a useful model to study the interaction of pyridine with P450 isozymes and their associated drug-mediated toxicity.

P450 2E1 expression in liver, kidney, and lung of rats treated with single or combined inducers

Ethanol consumption combined with smoking increase the risk of cancer in many tissues. Such a mechanism implies the involvement of cytochrome P450 alcohol (CYP2E1), which is regulated by numerous xenobiotics. The combination of P450 2E1 inducers (acetone or pyridine) and 3-methylcholanthrene during rat treatment was shown to decrease the liver P450 2E1 content while it enhanced its expression in kidney. It is suggested that this differential tissue response helps explain the organotropy of nitrosamine carcinogenicity.

Pyridine induction of Sprague-Dawley rat renal cytochrome P4502E1: immunohistochemical localization and quantitation

Previous research has shown that i.p. injection of rats with pyridine results in a significant increase in immunoreactive renal cytochrome P4502E1 (alcohol-inducible form) in a dose- and time-dependent manner. However, the cellular location of renal P4502E1 in rats was not reported. Thus, it was not known whether the pyridine-induced increase in renal P4502E1 resulted from increased production of the enzyme in cells which normally express P4502E1 or from de novo expression in cells normally devoid of the protein. To address these questions, rats were injected i.p. with either 200 mg pyridine/kg body wt./day for 1, 2, 3, or 4 days (n = 2/group) or injected once with an equal volume of sterile, pyrogen-free saline (control group; n = 2). Kidney tissue samples from saline- and pyridine-exposed rats were processed by light microscopy and were immunochemically stained to detect rat cytochrome P4502E1. Most of the immunoreactive P4502E1 was located within renal cortical epithelial cells lining proximal and distal tubules of the cortex with lesser--but consistent--amounts present in tubular epithelial cells within the inner and outer medulla. Pyridine exposure resulted in a 2-3-fold increase in P4502E1 immunoreactivity in proximal cortical tubules surrounding glomeruli and cortical blood vessels. The results of this study demonstrate a cell-specific distribution of cytochrome P4502E1 within the rat kidney and indicate that pyridine exposure results in a selective induction of immunoreactive P4502E1 in tubule epithelial cells which constitutively express this enzyme. The results of this study provide a morphologic basis for interpreting cell-specific nephrotoxicity due to xenobiotics that are biotransformed to toxic metabolites by renal P4502E1.

An NMR study of pyridine associated with DMPC liposomes and magnetically ordered DMPC-surfactant mixed micelles

With molecular dynamics simulations of phospholipid membranes becoming a reality, there is a growing need for experiments that provide the molecular details necessary to test these computational results. Pyridine is used here to explore the interaction of planar aromatic groups with the water-lipid interface of membranes. It is shown by magic angle spinning 13C nuclear magnetic resonance (NMR) to bind between the glycerol and choline groups of dimyristoylphosphatidylcholine (DMPC) liposomes. The axial pattern for the 31P NMR spectrum of DMPC liposomes is preserved even with more than half of the interfacial sites occupied, indicating that pyridine does not disrupt the lamellar phase of this lipid. 2H NMR experiments of liposomes in deuterium oxide demonstrate that pyridine might promote greater penetration of water into restricted regions in the interface. Magnetically oriented DMPC/surfactant micelles were investigated as a means for improving resolution and sensitivity in NMR studies of species bound to bilayers. The quadrupolar splittings in the 2H NMR spectra of d5-pyridine in DMPC liposomes and magnetically oriented DMPC/Trixon X-100 micelles indicate a common bound state for the two bilayer systems. The well resolved quadrupolar splittings of d5-pyridine in oriented micelles were used to establish the tilt of the pyridine ring relative to the bilayer plane.

Effects of P450 inhibition and induction on the olfactory toxicity of beta,beta'-iminodipropionitrile (IDPN) in the rat

In addition to the neurotoxic effects of beta,beta'-iminodipropionitrile (IDPN) which have been previously reported by other investigators, the olfactory toxicity of this compound has recently been uncovered in this laboratory. Due to the apparently conflicting observations that the IDPN-induced lesion in the olfactory mucosa is very focal in nature (suggesting site-specific activation) and the observation by other investigators that the behavioral effects of IDPN appear to be due to the parent compound, we initiated studies into the possible role of the cytochrome P450 enzymes in the olfactory toxicity of IDPN. Immunohistochemical studies with antibodies raised against several different P450 isoforms revealed good correlation between IDPN-induced olfactory mucosal degeneration and the localization of a protein immunoreacting with an antibody to P450 2E1. Enzymatic studies revealed that there is approximately five-fold more p-nitrophenol hydroxylation activity in the olfactory mucosa than in the liver on a per milligram microsomal protein basis. Administration of 1% acetone in the drinking water increased the levels of olfactory mucosal 2E1, and the increase in enzyme levels corresponded to increased olfactory toxicity of IDPN; inhibition of P450 activities with either metyrapone or carbon tetrachloride eliminated or significantly decreased the olfactory toxicity of IDPN, respectively. These studies suggest a role for cytochrome P450, specifically the 2E1 isoform, in the activation of IDPN within the nasal mucosa.