Endoplasmic Reticulum Of Hepatocytes Research Articles

Single nucleotide polymorphism-mediated translational suppression of endoplasmic reticulum mannosidase I modifies the onset of end-stage liver disease in alpha1-antitrypsin deficiency.

Inappropriate accumulation of the misfolded Z variant of alpha1-antitrypsin in the hepatocyte endoplasmic reticulum (ER) is a risk factor for the development of end-stage liver disease. However, the genetic and environmental factors that contribute to its etiology are poorly understood. ER mannosidase I (ERManI) is a quality control factor that plays a critical role in the sorting and targeting of misfolded glycoproteins for proteasome-mediated degradation. In this study, we tested whether genetic variations in the human ERManI gene influence the age at onset of end-stage liver disease in patients homozygous for the Z allele (ZZ). We sequenced all 13 exons in a group of unrelated Caucasian ZZ transplant recipients with different age at onset of the end-stage liver disease. Homozygosity for the minor A allele at 2484G/A (refSNP ID number rs4567) in the 3'-untranslated region was prevalent in the infant ZZ patients. Functional studies indicated that rs4567(A), but not rs4567(G), suppresses ERManI translation under ER stress conditions. These findings suggest that the identified single-nucleotide polymorphism can accelerate the onset of the end-stage liver disease associated with alpha1-antitrypsin deficiency and underscore the contribution of biosynthetic quality control as a modifier of genetic disease.

Autophagy in aging, disease and death: the true identity of a cell death impostor

Although strictly speaking, the term autophagy merely means ‘self-eating’, many presume that this cellular self-eating is inevitably a form of cellular self-destruction. Indeed, within the cell death research field, autophagy has also long been defined as a form of non-apoptotic, or type II, programmed cell death. However, as revealed in this issue of Cell Death and Differentiation, which contains nine review papers on the topic of Autophagy in Aging, Disease and Death1–9 and one article outlining the recommendations of the Nomenclature Committee on Cell Death 2009,10 a consensus is emerging that autophagy is largely a cell death impostor which, in reality, functions primarily to promote cellular and organismal health.

Endoplasmic Reticulum Stress Markers Are Associated with Obesity in Nondiabetic Subjects

Adipocyte and hepatocyte endoplasmic reticulum (ER) stress response is activated in dietary and genetic models of obesity in mice. We hypothesized that ER stress was also activated and associated with reduced insulin sensitivity (SI) in human obesity. We recruited 78 healthy, nondiabetic individuals over a spectrum of body mass index (BMI) who underwent oral and iv glucose tolerance tests, and fasting sc adipose and muscle biopsies. We tested expression of 18 genes and levels of total and phosphorylated eukaryotic initiation factor 2alpha, c-jun, and c-Jun N-terminal kinase 1 in adipose tissue. We compared gene expression in stromal vascular and adipocyte fractions in paired samples from 22 individuals, and tested clustering on gene and protein markers. Adipocyte expression of most markers of ER stress, including chaperones downstream of activating transcription factor 6, were significantly correlated with BMI and percent fat (r>0.5; P<0.00001). Phosphorylation of eukaryotic initiation factor 2alpha but not of c-Jun N-terminal kinase 1 or c-jun was increased with obesity. ER stress response (as elsewhere) was also increased with obesity in a second set of 86 individuals, and in the combined sample (n=161). The increase was only partially attributable to the stromal vascular fraction and macrophage infiltration. ER stress markers were only modestly correlated with S(I). Clustering algorithms supported ER stress activation with high BMI but not low SI. Multiple markers of ER stress are activated in human adipose with obesity, particularly for protective chaperones downstream of activating transcription factor 6alpha.

Autophagic disposal of the aggregation-prone protein that causes liver inflammation and carcinogenesis in α-1-antitrypsin deficiency

Alpha-1-antitrypsin (AT) deficiency is a relatively common autosomal co-dominant disorder, which causes chronic lung and liver disease. A point mutation renders aggregation-prone properties on a hepatic secretory protein in such a way that the mutant protein is retained in the endoplasmic reticulum of hepatocytes rather than secreted into the blood and body fluids where it ordinarily functions as an inhibitor of neutrophil proteases. A loss-of-function mechanism allows neutrophil proteases to degrade the connective tissue matrix of the lung causing chronic emphysema. Accumulation of aggregated mutant AT in the endoplasmic reticulum of hepatocytes causes liver inflammation and carcinogenesis by a gain-of-toxic function mechanism. However, genetic epidemiology studies indicate that many, if not the majority of, affected homozygotes are protected from liver disease by unlinked genetic and/or environmental modifiers. Studies performed over the last several years have demonstrated the importance of autophagy in disposal of mutant, aggregated AT and raise the possibility that predisposition to, or protection from, liver injury and carcinogenesis is determined by the balance of de novo biogenesis of the mutant AT molecule and its autophagic disposal.

Transgenic mice replicating hepatitis B virus but lacking expression of the major HBsAg

Hepatitis B Virus (HBV) transgenic mice replicating the viral genome at high level but lacking expression of the small envelope protein (HBsAg) have been produced using a terminally redundant viral DNA construct (HBV 1.4). The generation of viable infectious progeny was dependent on sex and age of mice. Viral mRNA was abundant in liver and kidneys and at low levels in other organs of the mice. No viral particles or HBV envelope proteins could be detected in sera of mice. Despite expression of non-secreted LHBs and MHBs proteins in the liver, there was no accumulation of viral particles in the endoplasmic reticulum of hepatocytes and no necroinflammatory hepatitis was observed. Therefore, these mice represent an excellent model for studies of the role of HBsAg in viral assembly, antiviral immune responses, the further understanding of HBV immunopathogenesis, and the development of antiviral vaccines.

Alpha‐1 antitrypsin deficiency: A conformational disease associated with lung and liver manifestations

Alpha-1 antitrypsin (A1AT) is a serine anti-protease produced chiefly by the liver. A1AT deficiency is a genetic disorder characterized by serum levels of less than 11 mumol/L and is associated with liver and lung manifestations. The liver disease, which occurs in up to 15% of A1AT-deficient individuals, is a result of toxic gain-of-function mutations in the A1AT gene, which cause the A1AT protein to fold aberrantly and accumulate in the endoplasmic reticulum of hepatocytes. The lung disease is associated with loss-of-function, specifically decreased anti-protease protection on the airway epithelial surface. The so-called 'Z' mutation in A1AT deficiency encodes a glutamic acid-to-lysine substitution at position 342 in A1AT and is the most common A1AT allele associated with disease. Here we review the current understanding of the molecular pathogenesis of A1AT deficiency and the best clinical management protocols.

Microsomal Triglyceride Transfer Protein Activity Is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in McA-RH7777 Cells

We previously demonstrated that the N-terminal 1000 amino acid residues of human apolipoprotein (apo) B (designated apoB:1000) are competent to fold into a three-sided lipovitellin-like lipid binding cavity to form the apoB "lipid pocket" without a structural requirement for microsomal triglyceride transfer protein (MTP). Our results established that this primordial apoB-containing particle is phospholipid-rich (Manchekar, M., Richardson, P. E., Forte, T. M., Datta, G., Segrest, J. P., and Dashti, N. (2004) J. Biol. Chem. 279, 39757-39766). In this study we have investigated the putative functional role of MTP in the initial lipidation of apoB:1000 in stable transformants of McA-RH7777 cells. Inhibition of MTP lipid transfer activity by 0.1 microm BMS-197636 and 5, 10, and 20 microm of BMS-200150 had no detectable effect on the synthesis, lipidation, and secretion of apoB:1000-containing particles. Under identical experimental conditions, the synthesis, lipidation, and secretion of endogenous apoB100-containing particles in HepG2 and parental untransfected McA-RH7777 cells were inhibited by 86-94%. BMS-200150 at 40 microm nearly abolished the secretion of endogenous apoB100-containing particles in HepG2 and parental McA-RH cells but caused only 15-20% inhibition in the secretion of apoB: 1000-containing particles. This modest decrease was attributable to the nonspecific effect of a high concentration of this compound on hepatic protein synthesis, as reflected in a similar (20-25%) reduction in albumin secretion. Suppression of MTP gene expression in stable transformants of McA-RH7777 cells by micro-interfering RNA led to 60-70% decrease in MTP mRNA and protein levels, but it had no detectable effect on the secretion of apoB:1000. Our results provide a compelling argument that the initial addition of phospholipids to apoB:1000 and initiation of apoB-containing lipoprotein assembly occur independently of MTP lipid transfer activity.

Alpha-1-antitrypsin mutant Z protein content in individual hepatocytes correlates with cell death in a mouse model

Alpha-1-antitrypsin (a1AT) deficiency is caused by homozygosity for the a1AT mutant Z gene and occurs in 1 in 2000 births. The Z mutation confers an abnormal conformation on the protein, resulting in an accumulation within the endoplasmic reticulum of hepatocytes rather than appropriate secretion. The accumulation of the mutant protein is strikingly heterogeneous within the liver. Homozygous ZZ children and adults have an increased risk of chronic liver disease, which is thought to result from this variable intracellular accumulation of the a1AT mutant Z protein. Previous reports have suggested that autophagy, mitochondrial injury, apoptosis, and other pathways may be involved in the mechanism of hepatocyte injury, although the interplay of these mechanisms in vivo is unclear. In this study, we examine a well-characterized in vivo model of a1AT mutant Z liver injury, the PiZ mouse, to better understand the pathways involved in this disease. The results show an increase in the stimulation of the apoptotic cascade in hepatocytes, the magnitude of which strongly correlates to the absolute amount of the a1AT mutant Z protein accumulated within the individual cell. Increases in apoptotic regulatory proteins are also detected. These data, combined with previous work, permit for the first time the construction of a hypothetical hepatocellular injury cascade for this disease involving mitochondrial injury, caspase activation, and apoptosis, which takes into account the heterogeneous nature of the mutant Z protein accumulation within the liver. Further development of this hypothetical cascade will focus future research on this and other metabolic liver diseases.

The Selective Advantage of α1-Antitrypsin Deficiency

The S- and Z-deficiency alleles of alpha1-antitrypsin are found in more than 20% of some white populations. This high gene frequency suggests that these mutations confer a selective advantage, but the biologic mechanism of this has remained obscure. It is now well recognized that the S and Z alleles result in a conformational transition within the alpha1-antitrypsin molecule and the formation of polymers that are retained within the endoplasmic reticulum of hepatocytes. Polymers of mutant alpha1-antitrypsin can also form within the alveoli and small airways of the lung where they may drive the inflammation that underlies emphysema in individuals with alpha1-antitrypsin deficiency. This local production of polymers by mutant S and Z alpha1-antitrypsin may have also provided protection against infectious disease in the preantibiotic era by focusing and amplifying the inflammatory response to limit invasive respiratory and gastrointestinal infection. It is only since the discovery of antibiotics, the widespread adoption of smoking, and increased longevity that these protective, proinflammatory properties of alpha1-antitrypsin mutants have become detrimental to cause the emphysema and systemic inflammatory diseases associated with alpha1-antitrypsin deficiency.

Indomethacin increases liver damage in a murine model of liver injury from alpha‐1‐antitrypsin deficiency†

Homozygous (PIZZ) alpha-1-antitrypsin (alpha(1)-AT) deficiency is associated with the development of liver damage in children as well as chronic liver injury and hepatocellular carcinoma in adults. The alpha(1)-AT mutant Z gene encodes a mutant protein that accumulates in the endoplasmic reticulum of hepatocytes rather than being secreted appropriately into serum. Liver injury is caused by the accumulation of alpha(1)-AT mutant Z protein in hepatocytes, which triggers downstream intracellular injury pathways. However, development of clinical liver disease among PIZZ homozygotes is highly variable, suggesting other genetic or environmental factors contribute to liver injury. In this study, we tested whether nonsteroidal anti-inflammatory drugs (NSAIDs) could be a comorbid factor in the development of liver injury in alpha(1)-AT deficiency using the PiZ mouse. This mouse model is transgenic for the mutant Z allele of the human alpha(1)-AT gene, in which alpha(1)-ATZ expression is regulated by the human promoter regulatory sequences. Our results showed that administration of indomethacin to PiZ mice resulted in increased hepatic injury, indicated by increased hepatocellular proliferation and increased activation of caspase 9. This indomethacin-induced injury was associated with activation of IL-6-STAT3 signaling, increased expression of alpha(1)-AT mRNA, and greater accumulation of mutant polymerized alpha(1)-ATZ protein in livers of indomethacin-treated PiZ mice compared to vehicle-treated PiZ animals. In conclusion, environmental factors, such as exogenous medication administration, can significantly potentiate the liver injury associated with alpha(1)-ATZ hepatic accumulation; NSAIDs may be especially injurious to patients with alpha(1)-AT deficiency, possibly by increasing the expression and accumulation of the hepatotoxic mutant protein.

A Toxicologist's Guide to the Preclinical Assessment of Hepatic Microsomal Enzyme Induction

The assessment of hepatic microsomal enzyme induction at the completion of preclinical toxicology studies in rodents and large mammals provides a wealth of information to the toxicologist and pharmacokineticist regarding how the drug-metabolizing system of the hepatocyte endoplasmic reticulum responded to high-dose levels of a xenobiotic designed for a specific pharmacological target in any of several target organs. The interpretation of these data can be greatly enhanced by a clear understanding of how this system functions and what the immediate and long-term ramifications are to organs and organ systems. This review focuses on how drugs modify the hepatic cytochrome P450 system, how those modifications are detected, the various consequences of these modifications, and some differences in the induction response among species.

Fibrinogen storage disease without hypofibrinogenemia associated with estrogen therapy

BackgroundCytoplasmic inclusion bodies within hepatocytes may have different etiologies, including the Endoplasmic Reticulum Storage Diseases (ERSDs). ERSD is a pathological condition characterized by abnormal accumulation of proteins destined for secretion in the endoplasmic reticulum of hepatocytes; it may be congenital (primary) or acquired (secondary). Fibrinogen storage disease is a form of ERSD.Case PresentationWe present a case of fibrinogen storage disease secondary to estrogen replacement therapy. Its causal relationship to the drug is shown by histological, immunohistochemical and ultrastructural studies of paired liver biopsies obtained during and after the drug therapy.ConclusionThe liver biopsies of patients with idiopathic liver enzyme abnormalities should be carefully evaluated for cytoplasmic inclusion bodies and, although rare, fibrinogen deposits.

Latent S49P Neuroserpin Forms Polymers in the Dementia Familial Encephalopathy with Neuroserpin Inclusion Bodies

The serpinopathies result from conformational transitions in members of the serine proteinase inhibitor superfamily with aberrant tissue deposition or loss of function. They are typified by mutants of neuroserpin that are retained within the endoplasmic reticulum of neurons as ordered polymers in association with dementia. We show here that the S49P mutant of neuroserpin that causes the dementia familial encephalopathy with neuroserpin inclusion bodies (FENIB) forms a latent species in vitro and in vivo in addition to the formation of polymers. Latent neuroserpin is thermostable and inactive as a proteinase inhibitor, but activity can be restored by refolding. Strikingly, latent S49P neuroserpin is unlike any other latent serine proteinase inhibitor (serpin) in that it spontaneously forms polymers under physiological conditions. These data provide an alternative method for the inactivation of mutant neuroserpin as a proteinase inhibitor in FENIB and demonstrate a second pathway for the formation of intracellular polymers in association with disease.

P0214 PHENOTYPIC EXPRESSION OF LIVER DISEASE IN FAMILIES WITH PIZZ ALPHA-1-ANTITRYPSIN DEFICIENCY

Introduction: PiZZ alpha-one-antitrypsin deficiency (A1ATD) is the commonest genetic cause of chronic liver disease leading to liver transplantation in children. The pathogenic mechanism appears to involve abnormal loop sheet polymerisation of the aberrant PiZ alpha-1-antitrypsin and its retention in the hepatocyte endoplasmic reticulum, with consequent progression to chronic inflammation and cirrhosis. Only 10–15% of PiZZ individuals develop clinical symptoms and additional genetic and environmental modifiers have been postulated. Methods: The database of 279 children diagnosed with A1ATD at our centre between 1978–2002 was reviewed to identify families in which there was more than one child with the PiZZ phenotype. A retrospective analysis of their notes was carried out to assess the severity of their liver disease. Results: Forty-two children (24 boys) from twenty-one families were identified, including 2 pairs of monozygotic and 1 pair of dizygotic twins. The children were followed up for a median of 66 months (range, 8–185 months). The patients were divided into the following categories: (A) asymptomatic/family screening –4.8%; (B) no clinical liver disease after neonatal biochemical dysfunction – 30.9%; (C) mild ongoing liver dysfunction – 35.7%; (D) moderate chronic liver disease – 19.1% and (E) end stage liver disease/liver transplant – 9.5%. There were no significant differences in the length of breastfeeding or frequency of infection between the siblings. Only 5/21 sibling pairs (23.8%) were within the same category. Of note, of those children requiring liver transplant 3/4 had siblings within categories A or B. Of the three pairs of twins identified, the twins were in different categories in 2 out of 3. Six out of 12 children in the D and E categories were male. Amongst the families where a child had end stage liver disease (E), 6 sought an antenatal diagnosis. Two of the foetuses were PiZZ and the pregnancies were terminated, the remainder were heterozygotes. Two of the families with moderate chronic liver disease (D) were also tested antenatally: one was a heterozygote and the other a PiZZ foetus was lost as a consequence of a mid-trimester spontaneous abortion. Conclusion: In the relatively small sample of families reviewed, the clinical course of liver disease within siblings with PiZZ A1ATD was highly variable. This observation, if confirmed in a larger sample, is important because antenatal diagnosis of PiZZ A1ATD may not predict the extent of liver involvement in families where one child has been affected by end stage liver disease, as has been previously reported.

155. Non-Viral Gene Therapy for Type 1 Diabetes by Electrotransfer of Insulin and Glucokinase Genes to Skeletal Muscle

Alpha1-antitrypsin (α1-AT) deficiency is caused by mutations in the α1-AT gene, a protease inhibitor, and can result in emphysema and/or liver disease. The lung disease is caused by a decrease in secreted α1-AT enzyme, a loss-of-function which results in tissue damage from unchecked leukocyte proteases. In contrast, the liver disease occurs by a gain-of-function, whereby mutant protein polymers are retained in the endoplasmic reticulum of hepatocytes. In persuit of an alternative to the only current treatment for the liver disease, to transplant the organ, we are investigating a genetic therapy that would combine the technologies of RNA interference (RNAi) with the Sleeping Beauty transposon system. The RNAi pathway consists of endogenous enzymes that destroy mRNAs selectively in response to small RNAs that are complimentary in sequence. Small inhibitory RNAs (siRNAs), which can be transcribed from plasmid constructs introduced into cells, have been shown to mediate RNAi in vitro and in vivo. Moreover, siRNAs can mediate long-term repression of a target gene if they are constitutively expressed from the genome. The Sleeping Beauty (SB) transposon system can integrate DNA transgenes into the genome for long-term expression in vitro and in vivo, and is being developed as a novel, non-viral gene therapy tool. A SB transposon vector was constructed to express siRNAs that target human α1-AT mRNA. The results demonstrate that siRNA transposons can be used to reduce wildtype and mutant α1-AT expression in cultured cells, whereas the house-keeping gene GAPDH was not affected. Next, we plan to test these siRNA transposons in vivo, in the transgenic mouse model of α1-AT liver disease. This gene therapy model combines two technologies, RNAi and the SB transposon, for a potential new therapeutic for the liver disease associated with mutant α1-AT.

CD1d function is regulated by microsomal triglyceride transfer protein.

CD1d is a major histocompatibility complex (MHC) class I-related molecule that functions in glycolipid antigen presentation to distinct subsets of T cells that express natural killer receptors and an invariant T-cell receptor-alpha chain (invariant NKT cells). The acquisition of glycolipid antigens by CD1d occurs, in part, in endosomes through the function of resident lipid transfer proteins, namely saposins. Here we show that microsomal triglyceride transfer protein (MTP), a protein that resides in the endoplasmic reticulum of hepatocytes and intestinal epithelial cells (IECs) and is essential for lipidation of apolipoprotein B, associates with CD1d in hepatocytes. Hepatocytes from animals in which Mttp (the gene encoding MTP) has been conditionally deleted, and IECs in which Mttp gene products have been silenced, are unable to activate invariant NKT cells. Conditional deletion of the Mttp gene in hepatocytes is associated with a redistribution of CD1d expression, and Mttp-deleted mice are resistant to immunopathologies associated with invariant NKT cell-mediated hepatitis and colitis. These studies indicate that the CD1d-regulating function of MTP in the endoplasmic reticulum is complementary to that of the saposins in endosomes in vivo.

Detection of Circulating and Endothelial Cell Polymers of Z and Wild Type α1-Antitrypsin by a Monoclonal Antibody

Globular inclusions of abnormal alpha1-antitrypsin (AAT) in the endoplasmic reticulum of hepatocytes are a characteristic feature of AAT deficiency of the PiZZ phenotype. Monoclonal antibodies, which contain constant specificity and affinity, are often used for the identification of Z-mutation carriers. A mouse monoclonal antibody (ATZ11) raised against PiZZ hepatocytic AAT was successfully used in enzyme-linked immunosorbent assays (ELISA) and in identification of Z-related AAT globular inclusions by immunohistochemical techniques. Using electrophoresis, Western blotting, and ELISA procedures, we have shown in the present study that this monoclonal antibody specifically detects a conformation-dependent neoepitope on both polymerized and elastase-complexed molecular forms of AAT. The antibody has no apparent affinity for native, latent, or cleaved forms of AAT. The antibody ATZ11 illustrates the structural resemblance between the polymerized form of AAT and its complex with elastase and provides evidence that Z-homozygotes beyond the native form may have at least one more circulating molecular form of AAT, i.e. its polymerized form. In addition, staining of endothelial cells with ATZ11 antibody in both M- and Z-AAT individuals shows that AAT attached to endothelial cells is in a polymerized form. The antibody can be a powerful tool for the study of the molecular profile of AAT, not only in Z-deficiency cases but also in other (patho)physiological conditions.

Farnesol as an inhibitor and substrate for rabbit liver microsomal P450 enzymes

Farnesol and the related isoprenoids, geranylgeraniol, geranylgeranyl pyrophosphate, and farnesyl pyrophosphate, are produced in the endoplasmic reticulum of hepatocytes in mammals, and each serve important biological functions. Of these compounds, only farnesol was shown to significantly inhibit rabbit liver microsomal cytochrome P450 enzymes. The observed inhibition appeared to be reversible, and was not strictly competitive, but rather mixed in nature. Of the activities examined, ethoxycoumarin de-ethylase and diclofenac-4-hydroxylase activities were most sensitive to farnesol, with K I and K I ′ values between 11 and 40 μM . Caffeine-8-hydroxylation and taxol-6-hydroxylation were not inhibited at all by farnesol. Farnesol appeared to be a P450 substrate, as well as an inhibitor, as indicated by the NADPH-dependent decrease in farnesol concentration in microsomal incubations, and the metabolism was inhibited by CO, which pointed to the involvement of P450 isozymes.

Hepatic synthesis, maturation and complex formation between retinol-binding protein and transthyretin.

The retinol/retinol-binding protein/transthyretin complex, that carries and delivers hydrophobic retinol molecules to target cells, is assembled in the hepatocyte endoplasmic reticulum. In this paper, we review data related to events that lead to the formation of this complex, including transthyretin oligomerization and retinol-binding protein secretion. Our studies on transthyretin oligomerization have demonstrated that cleavage of signal peptide and the environment of endoplasmic reticulum influence transthyretin oligomerization. In vitro, mutated transthyretin without signal sequence fails to form dimers, while wild-type transthyretin is translocated into the microsomes where it forms dimers and small amounts of tetramers. In vivo, tetramers were detected in HepG2 cells but not in transfected Cos cells, suggesting that tissue-specific factors affect tetramer stability. In vitamin A deficiency, retinol-binding protein secretion is blocked and the protein accumulates in the endoplasmic reticulum, from where it is promptly released after retinol repletion. We use MMH cells to identify factors involved in complex formation, retention and secretion, the crucial steps to understand the molecular mechanisms underlying vitamin A homeostasis. In parallel, studies on vitamin A transport in fish are in progress; retinol-binding protein and transthyretin have already been characterized in different fish species.

Interactions alcool–xénobiotiques. Rôle du cytochrome P450 2E1

Alcohol and xenobiotics share the same oxidative microsomal pathway, which is mainly located in the endoplasmic reticulum of hepatocytes. This pathway involves enzymes that belong to the super family of cytochrome P450 and allows to explain a lot of pharmacokinetic or toxic interactions between alcohol and xenobiotics. Cytochrome P450 2E1 (CYP2E1) is the key enzyme of the microsomal pathway of ethanol oxidation. It is inducible by chronic ethanol consumption and its activity is increased by three to five fold in liver from alcoholics subjects. This induction involves to a lesser extent cytochromes P450 3A4 and 1A2 and contributes to the metabolic tolerance of alcohol and drugs observed in alcoholics. The metabolic tolerance persits several days after ethanol withdrawal. Furthermore, CYP2E1 has a high capacity to activate numerous xenobiotics into toxic or carcinogenic compounds. Drugs currently used such as paracetamol, anesthetics (enflurane, halothane), industrial solvents (benzene or its derivatives), halogenated solvents (CCl 4, trichlorethylene) and nitrosamines which are present in food or tobacco smoke are included. Therefore, heavy consumption of alcohol, which results in CYP2E1 induction, increases individual susceptibility to the toxic or carcinogenic effects of these xenobiotics.