Forms Of Liver Injury Research Articles

Isoniazid hepatotoxicity: Progress in understanding the immunologic component

Isoniazid hepatotoxicity: Progress in understanding the immunologic component

Detection of anti-isoniazid and anti-cytochrome P450 antibodies in patients with isoniazid-induced liver failure

Isoniazid (INH)-induced hepatotoxicity remains one of the most common causes of drug-induced idiosyncratic liver injury and liver failure. This form of liver injury is not believed to be immune-mediated because it is not usually associated with fever or rash, does not recur more rapidly on rechallenge, and previous studies have failed to identify anti-INH antibodies (Abs). In this study, we found Abs present in sera of 15 of 19 cases of INH-induced liver failure. Anti-INH Abs were present in 8 sera; 11 had anti–cytochrome P450 (CYP)2E1 Abs, 14 had Abs against CYP2E1 modified by INH, 14 had anti-CYP3A4 antibodies, and 10 had anti-CYP2C9 Abs. INH was found to form covalent adducts with CYP2E1, CYP3A4, and CYP2C9. None of these Abs were detected in sera from INH-treated controls without significant liver injury. The presence of a range of antidrug and autoAbs has been observed in other drug-induced liver injury that is presumed to be immune mediated. Conclusion: These data provide strong evidence that INH induces an immune response that causes INH-induced liver injury. (Hepatology 2014;59:1084–1093)

A Multifactorial Approach to Hepatobiliary Transporter Assessment Enables Improved Therapeutic Compound Development

The bile salt export pump (BSEP) is expressed at the canalicular domain of hepatocytes, where it serves as the primary route of elimination for monovalent bile acids (BAs) into the bile canaliculi. The most compelling evidence linking dysfunction in BA transport with liver injury in humans is found with carriers of mutations that render BSEP nonfunctional. Based on mounting evidence, there appears to be a strong association between drug-induced BSEP interference and liver injury in humans; however, causality has not been established. For this reason, drug-induced BSEP interference is best considered a susceptibility factor for liver injury as other host- or drug-related properties may contribute to the development of hepatotoxicity. To better understand the association between BSEP interference and liver injury in humans, over 600 marketed or withdrawn drugs were evaluated in BSEP expressing membrane vesicles. The example of a compound that failed during phase 1 human trials is also described, AMG 009. AMG 009 showed evidence of liver injury in humans that was not predicted by preclinical safety studies, and BSEP inhibition was implicated. For 109 of the drugs with some effect on in vitro BSEP function, clinical use, associations with hepatotoxicity, pharmacokinetic data, and other information were annotated. A steady state concentration (C(ss)) for each of these annotated drugs was estimated, and a ratio between this value and measured IC₅₀ potency values were calculated in an attempt to relate exposure to in vitro potencies. When factoring for exposure, 95% of the annotated compounds with a C(ss)/BSEP IC₅₀ ratio ≥ 0.1 were associated with some form of liver injury. We then investigated the relationship between clinical evidence of liver injury and effects to multidrug resistance-associated proteins (MRPs) believed to play a role in BA homeostasis. The effect of 600+ drugs on MRP2, MRP3, and MRP4 function was also evaluated in membrane vesicle assays. Drugs with a C(ss)/BSEP IC₅₀ ratio ≥ 0.1 and a C(ss)/MRP IC₅₀ ratio ≥ 0.1 had almost a 100% correlation with some evidence of liver injury in humans. These data suggest that integration of exposure data, and knowledge of an effect to not only BSEP but also one or more of the MRPs, is a useful tool for informing the potential for liver injury due to altered BA transport.

DILI: New Insights into Diagnosis and Management

Drug-induced liver injury continues to have a significant impact. With over 1000 drugs now registered as causing DILI, this form of liver injury is the most cited reason for withdrawal of a drug from the marketplace. Despite this, the diagnosis of DILI continues to rely on subjective measures and expert opinion with results that are both difficult to verify and reproduce. However, recent developments in DILI research may provide new insights to improve diagnosis and treatment in the future.

Translating an Understanding of the Pathogenesis of Hepatic Fibrosis to Novel Therapies

The response to injury is one of wound healing and fibrogenesis, which ultimately leads to fibrosis. The fibrogenic response to injury is a generalized one across virtually all organ systems. In the liver, the injury response, typically occurring over a prolonged period of time, leads to cirrhosis (although it should be pointed out that not all patients with liver injury develop cirrhosis). The fact that many different diseases result in cirrhosis suggests a common pathogenesis. The study of hepatic fibrogenesis over the past 2 decades has been remarkably active, leading to a considerable understanding of this process. It clearly has been shown that the hepatic stellate cell is a central component in the fibrogenic process. It also has been recognized that other effector cells are important in the fibrogenic process, including resident fibroblasts, bone marrow-derived cells, fibrocytes, and even perhaps cells derived from epithelial cells (ie, through epithelial to mesenchymal transition). A key aspect of the biology of fibrogenesis is that the fibrogenic process is dynamic; thus, even advanced fibrosis (or cirrhosis) is reversible. Together, an understanding of the cellular basis for liver fibrogenesis, along with multiple aspects of the basic pathogenesis of fibrosis, have highlighted many exciting potential therapeutic opportunities. Thus, although the most effective antifibrotic therapy is simply treatment of the underlying disease, in situations in which this is not possible, specific antifibrotic therapy is likely not only to become feasible, but will soon become a reality. This review highlights the mechanisms underlying fibrogenesis that may be translated into future antifibrotic therapies and to review the current state of clinical development.

Current Challenges and Controversies in Drug-Induced Liver Injury

Current key challenges and controversies encountered in the identification of potentially hepatotoxic drugs and the assessment of drug-induced liver injury (DILI) are covered in this article. There is substantial debate over the classification of DILI itself, including the definition and validity of terms such as 'intrinsic' and 'idiosyncratic'. So-called idiosyncratic DILI is typically rare and requires one or more susceptibility factors in individuals. Consequently, it has been difficult to reproduce in animal models, which has limited the understanding of its underlying mechanisms despite numerous hypotheses. Advances in predictive models would also help to enable preclinical elimination of drug candidates and development of novel biomarkers. A small number of liver laboratory tests have been routinely used to help identify DILI, but their interpretation can be limited and confounded by multiple factors. Improved preclinical and clinical biomarkers are therefore needed to accurately detect early signals of liver injury, distinguish drug hepatotoxicity from other forms of liver injury, and differentiate mild from clinically important liver injury. A range of potentially useful biomarkers are emerging, although so far most have only been used preclinically, with only a few validated and used in the clinic for specific circumstances. Advances in the development of genomic biomarkers will improve the prediction and detection of hepatic injury in future. Establishing a definitive clinical diagnosis of DILI can be difficult, since it is based on circumstantial evidence by excluding other aetiologies and, when possible, identifying a drug-specific signature. DILI signals based on standard liver test abnormalities may be affected by underlying diseases such as hepatitis B and C, HIV and cancer, as well as the concomitant use of hepatotoxic drugs to treat some of these conditions. Therefore, a modified approach to DILI assessment is justified in these special populations and a suggested framework is presented that takes into account underlying disease when evaluating DILI signals in individuals. Detection of idiosyncratic DILI should, in some respects, be easier in the postmarketing setting compared with the clinical development programme, since there is a much larger and more varied patient population exposure over longer timeframes. However, postmarketing safety surveillance is currently limited by the quantity and quality of information available to make an accurate diagnosis, the lack of a control group and the rarity of cases. The pooling of multiple healthcare databases, which could potentially contain different types of patient data, is advised to address some of these deficiencies.

The effect of SAMe and betaine on Hepa 1–6, C34 and E47 liver cell survival in vitro

In recent years, methyl one-carbon metabolism has received a great deal of attention because the disruption of methyl balance in a variety of genetically modified mice is associated with the development of various forms of liver injury, namely fatty liver disease and hepatocellular carcinoma (HCC). In addition, patients with liver disease often have an abnormal expression of key genes involved in methionine metabolism as well as elevated serum levels of methionine and homocysteine (Hcy). S-adenosylmethionine (SAMe) has rapidly moved from being a methyl donor to a key metabolite that regulates hepatocyte proliferation, necrosis and differentiation. Biosynthesis of SAMe occurs in all mammalian cells as the first step in methionine catabolism in a reaction catalyzed by methionine adenosyltransferase (MAT). Decreased hepatic SAMe biosynthesis is a consequence of numerous forms of chronic liver injury. In an animal model of chronic liver SAMe deficiency, the liver is predisposed to further injury and develops spontaneous steatohepatitis and HCC. SAMe treatment in experimental animal models of liver injury shows hepatoprotective properties. Meta-analyses also showed that it is effective in the treatment of patients with cholestatic liver diseases. We studied the survival of liver cells treated with SAMe and betaine using Hepa 1–6 and E47/C34 cell lines. We showed that exogenous SAMe decreased the number of Hepa 1–6 and E47/C34 cells, and increased the number of dead cells in vitro. Betaine had no significant effect on the number of surviving cells and the number of dead cells. The combination of both methyl donors significantly increased the survival of liver cells and reduced necrosis, compared to SAMe alone. This study showed the inhibition of the proliferation and increased necrosis in response to SAMe on liver cancer cell lines Hepa 1–6 and C34.

Gut Microbiota, Intestinal Permeability, Obesity‐Induced Inflammation, and Liver Injury

Obesity and its metabolic complications are major health problems in the United States and worldwide, and increasing evidence implicates the microbiota in these important health issues. Indeed, it appears that the microbiota function much like a metabolic "organ," influencing nutrient acquisition, energy homeostasis, and, ultimately, the control of body weight. Moreover, alterations in gut microbiota, increased intestinal permeability, and metabolic endotoxemia likely play a role in the development of a chronic low-grade inflammatory state in the host that contributes to the development of obesity and associated chronic metabolic diseases such as nonalcoholic fatty liver disease. Supporting these concepts are the observations that increased gut permeability, low-grade endotoxemia, and fatty liver are observed in animal models of obesity caused by either high-fat or high-fructose feeding. Consistent with these observations, germ-free mice are protected from obesity and many forms of liver injury. Last, many agents that affect gut flora/permeability, such as probiotics/prebiotics, also appear to affect obesity and certain forms of liver injury in animal model systems. Here the authors review the role of the gut microbiota and metabolic endotoxemia-induced inflammation in the development of obesity and liver injury, with special reference to the intensive care unit setting.

Enumeration, isolation, and electron microscopic study of hematopoietic stem cells in Egyptian patients with chronic liver diseases

The contribution of hematopoietic stem cells (HSCs) to liver regeneration in different forms of liver injury remains debatable. Many studies tried to verify whether various liver lesions can activate bone marrow by mobilizing peripheral blood HSCs (CD34/CD133+cells) putatively able to induce liver repopulation. The aim of this work was to determine the degree of mobilization of BM-derived HSCs into the peripheral blood of chronic hepatic affection patients and correlating it with various grades of liver damage. This study was conducted on 30 patients with Child A, B, and C grades of chronic liver disease (ten patients for each stage) as well as ten age- and sex-matched normal healthy subjects were enrolled as a control group. The percent of circulating HSCs was determined by flow cytometry. Also, the isolation of such cells was done by magnetic cell-sorting technique for further ultrastructural assessment by transmission electron microscopy (TEM). Our study revealed that chronic liver disease patients compared to healthy control group, exhibited insignificant difference in the percentage of circulating CD133+ cells. Regarding the level of CD34+ cells, a significant increase was found between Child A chronic liver disease patients and the control group (p = 0.02). However, an insignificant difference was found between Child B and C patients and control group or between each other (p > 0.05). The ultrastructural characteristics of isolated cells were compared in healthy subjects and hepatic patients, the cells were similar in appearance in both groups with no evidence of structural changes. TEM analysis revealed typical features of immaturity. Our study showed that chronic lesions of any degree of severity did not evoke bone marrow to mobilize HSCs into the circulation.

Evidence-Based Liver Chemistry Monitoring in Drug Development

Background: Liver safety issues affect patients and may result in compound termination during drug development or drug withdrawal postmarketing. While liver chemistries are monitored to protect patient safety, the frequency and timing of monitoring is largely empirically determined. Objective: To determine the optimal timing of liver chemistry monitoring in phase I–III drug development. Setting: Liver chemistries and safety were analysed from six GlaxoSmithKline (GSK) clinical development programmes discontinued with liver safety issues, marketed products and five products withdrawn from the market because of liver safety issues. Methods of assessment: Retrospective analysis of the temporal appearance, incidence, form of liver injury and severity of liver chemistry elevations and adverse outcomes observed with medication use. Results: In the phase I–III clinical studies, all six GSK compounds exhibited hepatocellular injury and/or jaundice in the first treatment month. Alanine aminotransferase (ALT) ≥3 × the upper limit of normal occurred within the first 2 weeks to 4 months in 2–50% of treated subjects. By contrast, drugs withdrawn from the market exhibited a more severe pattern of injury with a lower incidence of liver chemistry elevations observed after 3 days to >24 months of treatment. Conclusions: Liver chemistry monitoring appears to be most productive in the first few months of drug initiation. Evaluating the incidence of liver chemistry elevations proactively identifies whether there is a compound liver safety signal that requires further assessment.

Discernment of possible mechanisms of hepatotoxicity via biological processes over-represented by co-expressed genes

BackgroundHepatotoxicity is a form of liver injury caused by exposure to stressors. Genomic-based approaches have been used to detect changes in transcription in response to hepatotoxicants. However, there are no straightforward ways of using co-expressed genes anchored to a phenotype or constrained by the experimental design for discerning mechanisms of a biological response.ResultsThrough the analysis of a gene expression dataset containing 318 liver samples from rats exposed to hepatotoxicants and leveraging alanine aminotransferase (ALT), a serum enzyme indicative of liver injury as the phenotypic marker, we identified biological processes and molecular pathways that may be associated with mechanisms of hepatotoxicity. Our analysis used an approach called Coherent Co-expression Biclustering (cc-Biclustering) for clustering a subset of genes through a coherent (consistency) measure within each group of samples representing a subset of experimental conditions. Supervised biclustering identified 87 genes co-expressed and correlated with ALT in all the samples exposed to the chemicals. None of the over-represented pathways related to liver injury. However, biclusters with subsets of samples exposed to one of the 7 hepatotoxicants, but not to a non-toxic isomer, contained co-expressed genes that represented pathways related to a stress response. Unsupervised biclustering of the data resulted in 1) four to five times more genes within the bicluster containing all the samples exposed to the chemicals, 2) biclusters with co-expression of genes that discerned 1,4 dichlorobenzene (a non-toxic isomer at low and mid doses) from the other chemicals, pathways and biological processes that underlie liver injury and 3) a bicluster with genes up-regulated in an early response to toxic exposure.ConclusionWe obtained clusters of co-expressed genes that over-represented biological processes and molecular pathways related to hepatotoxicity in the rat. The mechanisms involved in the response of the liver to the exposure to 1,4-dichlorobenzene suggest non-genotoxicity whereas the exposure to the hepatotoxicants could be DNA damaging leading to overall genomic instability and activation of cell cycle check point signaling. In addition, key pathways and biological processes representative of an inflammatory response, energy production and apoptosis were impacted by the hepatotoxicant exposures that manifested liver injury in the rat.

Noninvasive diagnosis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease, affecting approximately 30% of Western populations and a frequent indication for liver transplantation. The histologic spectrum of NAFLD includes simple steatosis, which has a benign prognosis, and nonalcoholic steatohepatitis, a more aggressive form of liver injury that may progress to cirrhosis and its complications. At present, the only widely accepted means of differentiating these lesions, including the severity of hepatic fibrosis, is liver biopsy. However, due to the invasiveness of this procedure, the rising prevalence of NAFLD, and the expected availability of effective therapies for this condition, the identification of noninvasive tools for the diagnosis and staging of NAFLD has emerged as a major clinical and research priority. This review summarizes important advances in this field during the past decade, including the development of biomarkers of hepatic fibrosis, apoptosis, and inflammation; novel imaging techniques such as transient elastography; and high-throughput technologies including proteomics and genomics. Future studies must focus on the development of accurate, inexpensive, and reliable tools that can differentiate the major histologic determinants of NAFLD; are responsive to changes in NAFLD severity due to therapeutic intervention and time; and have prognostic significance. Until such tools are developed, liver biopsy remains an important tool in the assessment of patients with NAFLD.

An inhibitor of c- Jun NH2-terminal kinase, SP600125, protects mice from d-galactosamine/lipopolysaccharide-induced hepatic failure by modulating BH3-only proteins

Fulminant hepatic failure (FHF) is a dramatic clinical syndrome characterized by massive hepatocyte apoptosis and very high mortality. The c- Jun-N-terminal kinase (JNK) pathway is an important stress-responsive kinase activated by several forms of liver injury. The aim of this study is to assess the role of JNK during d-galactosamine (GalN)/lipopolysaccharide (LPS)-induced liver injury, an experimental model of FHF, using SP600125, a small molecule JNK-specific inhibitor. Mice were given an intraperitoneal dose of GalN (800 μg/g body weight)/LPS (100 ng/g body weight) with and without subcutaneous SP600125 (50 mg/kg body weight) treatment (at 6 and 2 h before and 2 h after GalN/LPS administration). GalN/LPS treatment induced sustained JNK activation. Administration of SP600125 diminished JNK activity, suppressed lethality and the elevation of both serum alanine aminotransferase and aspartate aminotransferase, but had no effect on serum tumor necrosis factor-α, and reduced hepatocyte apoptosis after GalN/LPS administration. In support of the role of JNK in promoting the mitochondria-mediated apoptosis pathway, SP600125 prevented cytochrome c release, caspase-9 and caspase-3 activity. Moreover, SP600125 downregulated the mRNA and protein expression of Bad in the early periods following GalN/LPS injection and prevented Bid cleavage in the late periods. These results confirm the role of JNK as a critical apoptotic mediator in GalN/LPS-induced FHF. SP600125 has the potential to protect FHF by downregulating Bad and inhibiting Bid cleavage.

The Prevalence of Nonalcoholic Steatohepatitis is Greater in Morbidly Obese Men Compared to Women

Nonalcoholic steatohepatitis (NASH) is a form of liver injury that is common in morbidly obese subjects. It has been shown that gender differences exist in the spectrum of nonalcoholic fatty liver disease (NAFLD). The focus of this study was to further characterize these gender differences based on ATP III criteria used to diagnose the metabolic syndrome (MS). We retrospectively assessed NAFLD 58 men and 307 women who underwent gastric bypass, for the presence of NASH, MS, and positive predictors of NASH. There was no statistical difference in age, gender, or the presence of diabetes. The prevalence of NASH in men and women was 60.3% and 30.9%, respectively (P<0.001). Multivariate logistic analysis showed an association of male gender with NASH (2.7; 95% CI, 1.3-5.6, P=0.006) as well as age, AST, and diabetes. MS was diagnosed in 91.4% and 76.2% of men and women (P=0.008), and men tended to have more criteria for MS compared to women. The only positive predictor of MS that was statistically significant between genders was high triglycerides (P=0.003). Controlling for BMI and excess body weight produced similar results. Gender differences do exist within NAFLD and MS, that may be associated with free fatty acid flow to the liver.

Role of the Peroxynitrite - Poly (ADP-Ribose) Polymerase Pathway in the Pathogenesis of Liver Injury

Oxidative and nitrosative stress triggers DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP). One of the key triggers of DNA single strand breakage in pathophysiological conditions is peroxynitrite, a reactive species produced from the reaction of nitric oxide and superoxide. Activation of PARP can dramatically lower the intracellular concentration of its substrate, nicotinamide adenine dinucleotide, thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. Here we review the role of PARP in various forms of liver injury.

Long-term culture of cholangiocytes from liver fibro-granulomatous lesions

BackgroundExtensive bile duct proliferation is a key feature of the tissue reaction to clinical and experimental forms of liver injury. Experimental infection of mice by Schistosoma mansoni is a well-studied model of liver fibrosis with bile duct hyperplasia. However, the regulatory mechanisms of bile duct changes are not well understood. In this study we report the reproducible isolation of long-term cultures of cholangiocytes from mice livers with schistosomal fibrosis.MethodsWe have isolated a cholangiocyte cell line from Schistosoma-induced liver granulomas using a combination of methods including selective adhesion and isopyknic centrifugation in Percoll.ResultsThe cell line was characterized by morphological criteria in optical and transmission electron microscopy, ability to form well differentiated ductular structures in collagen gels and by a positive staining for cytokeratin 18 and cytokeratin 19. To our knowledge, this is the first murine cholangiocyte cell line isolated from schistosomal fibrosis reported in the literature.ConclusionAfter 9 months and 16 passages this diploid cell line maintained differentiated characteristics and a high proliferative capacity. We believe the method described here may be a valuable tool to study bile duct changes during hepatic injury.

TWEAK induces liver progenitor cell proliferation

Progenitor ("oval") cell expansion accompanies many forms of liver injury, including alcohol toxicity and submassive parenchymal necrosis as well as experimental injury models featuring blocked hepatocyte replication. Oval cells can potentially become either hepatocytes or biliary epithelial cells and may be critical to liver regeneration, particularly when hepatocyte replication is impaired. The regulation of oval cell proliferation is incompletely understood. Herein we present evidence that a TNF family member called TWEAK (TNF-like weak inducer of apoptosis) stimulates oval cell proliferation in mouse liver through its receptor Fn14. TWEAK has no effect on mature hepatocytes and thus appears to be selective for oval cells. Transgenic mice overexpressing TWEAK in hepatocytes exhibit periportal oval cell hyperplasia. A similar phenotype was obtained in adult wild-type mice, but not Fn14-null mice, by administering TWEAK-expressing adenovirus. Oval cell expansion induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) was significantly reduced in Fn14-null mice as well as in adult wild-type mice with a blocking anti-TWEAK mAb. Importantly, TWEAK stimulated the proliferation of an oval cell culture model. Finally, we show increased Fn14 expression in chronic hepatitis C and other human liver diseases relative to its expression in normal liver, which suggests a role for the TWEAK/Fn14 pathway in human liver injury. We conclude that TWEAK has a selective mitogenic effect for liver oval cells that distinguishes it from other previously described growth factors.

Expression of hepatocyte growth factor and its receptor c-met, correlates with severity of pathological injury in experimental alcoholic liver disease

Expression of hepatocyte growth factor (HGF) and its receptor, c-met is up-regulated in various forms of liver injury. This study evaluated the relationship between HGF and c-met expression and pathological changes in experimental alcoholic liver disease. Rats (5 per group) were fed ethanol and a diet containing saturated fat corn oil or fish oil by intragastric infusion. Dextrose isocalorically replaced ethanol in controls. In a second set of experiments, Kupffer cells, endothelial cells and hepatocytes were isolated from rats in each group. Pathological evaluation and analysis of HGF and c-met expression were performed in liver and the different cell types. Increased expression of HGF and c-met expression was detected in the liver of rats showing necroinflammatory changes. The Kupffer and endothelial cells were primarily responsible for the increase in HGF, c-met expression was seen only in hepatocytes. Thus, up-regulation of HGF and c-met occurred in the presence of the necrosis and inflammation suggesting that HGF may be acting to protect against liver injury or accelerate the regenerative process.

Pathophysiology of Cholangiopathies

The diseases of the intrahepatic biliary tree are a large group of potentially evolutive congenital and acquired liver disorders affecting both the adult and pediatric populations. They represent a relevant cause of liver-related morbidity and mortality and an important indication for liver transplantation, particularly in children. While the practical approach to patients affected by biliary tree diseases has not significantly changed yet, the conceptual approach to the pathophysiology of cholangiopathies has witnessed important advances that will be discussed. The primary cell target of the pathogenetic sequence of these disorders is the biliary epithelium. Cholangiocytes have multifaceted functions, not limited to bile production. Their capability to secrete a range of different pro-inflammatory mediators, cytokines, and chemokines indicates a major role of cholangiocytes in the inflammatory reaction. Furthermore, paracrine secretion of growth factors and peptides mediates an extensive cross-talk with other liver cell types, including hepatocytes, stellate, and endothelial and inflammatory cells. Cholangiopathies share a number of pathogenetic mechanisms, including inflammation, cholestasis, fibrosis, apoptosis, altered development, and neoplastic transformation. These basic disease mechanisms will be discussed in detail, along with the distinct features of a number of cholangiopathies. Furthermore, an increase in the biliary cell compartment is a common response to many forms of liver injury, from cholangiopathies to viral and fulminant hepatitis. Elucidation of these pathophysiologic mechanisms will likely provide clues for future therapeutic strategies. Furthermore, understanding the role of cholangiocytes in liver regeneration/repair and the mechanisms of cholangiocyte activation and their relationship with liver progenitor cell will be of further interest.

Uroporphyria and hepatic carcinogenesis induced by polychlorinated biphenyls–iron interaction: Absence in the Cyp1a2(− /− ) knockout mouse

Aryl hydrocarbon receptor ligands, such as polychlorinated biphenyls (PCBs), cause inhibition of the heme biosynthesis enzyme, uroporphyrinogen decarboxylase; this leads to uroporphyria and hepatic tumors, which are markedly enhanced by iron overload in C57BL/10 and C57BL/6 strains of mice. Cyp1a2(− /− ) knockout mice were used to compare the effects of CYP1A2 expression on uroporphyria and liver carcinogenesis. PCBs in the diet (100 ppm) of Cyp1a2(+/+) wild-type mice caused hepatic uroporphyria, which was strongly increased by iron–dextran (800 mg Fe/kg). In contrast, uroporphyria was not detected in Cyp1a2(− /− ) knockout mice, although expression of CYP1A1 and CYP2B10 was greatly induced. After 57 weeks on this diet, hepatic preneoplastic foci and tumors were seen in the Cyp1a2(+/+) mice; numbers and severity were enhanced by iron. No foci or tumors were detected in Cyp1a2(− /− ) mice, although evidence for other forms of liver injury was observed. Our findings suggest a link not only between CYP1A2, iron metabolism, and the induction of uroporphyria by PCBs, but also with subsequent hepatocarcinogenesis.