Mohammed Bourdi

Epidemic of liver disease caused by hydrochlorofluorocarbons used as ozone-sparing substitutes of chlorofluorocarbons.

BACKGROUND Hydrochlorofluorocarbons (HCFCs) are used increasingly in industry as substitutes for ozone-depleting chlorofluorocarbons (CFCs). Limited studies in animals indicate potential hepatotoxicity of some of these compounds. We investigated an epidemic of liver disease in nine industrial workers who had had repeated accidental exposure to a mixture of 1,1-dichloro-2,2,2-trifluoroethane (HCFC 123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC 124). All nine exposed workers were affected to various degrees. Both compounds are metabolised in the same way as 1-bromo-1-chloro-2,2,2-trifluoroethane (halothane) to form reactive trifluoroacetyl halide intermediates, which have been implicated in the hepatotoxicity of halothane. We aimed to test whether HCFCs 123 and 124 can result in serious liver disease. METHODS For one severely affected worker liver biopsy and immunohistochemical stainings for the presence of trifluoroacetyl protein adducts were done. The serum of six affected workers and five controls was tested for autoantibodies that react with human liver cytochrome-P450 2E1 (P450 2E1) and P58 protein disulphide isomerase isoform (P58). FINDINGS The liver biopsy sample showed hepatocellular necrosis which was prominent in perivenular zone three and extended focally from portal tracts to portal tracts and centrilobular areas (bridging necrosis). Trifluoroacetyl-adducted proteins were detected in surviving hepatocytes. Autoantibodies against P450 2E1 or P58, previously associated with halothane hepatitis, were detected in the serum of five affected workers. INTERPRETATION Repeated exposure of human beings to HCFCs 123 and 124 can result in serious liver injury in a large proportion of the exposed population. Although the exact mechanism of hepatotoxicity of these agents is not known, the results suggest that trifluoroacetyl-altered liver proteins are involved. In view of the potentially widespread use of these compounds, there is an urgent need to develop safer alternatives.

Macrophage migration inhibitory factor in drug-induced liver injury: a role in susceptibility and stress responsiveness

Idiosyncratic drug-induced hepatitis may depend upon many factors including a balance between pro- and anti-inflammatory mediator production levels. Using a guinea pig model of liver injury induced by bioactivation of the anesthetic drug, halothane, we found that toxicity was commensurate with an increase in serum macrophage migration inhibitory factor (MIF), a pro-inflammatory signal and counter-regulator of glucocorticoids, but only in susceptible animals. The pathogenic role of MIF was further investigated using a murine model in which liver injury was induced by the reactive metabolite of another drug, acetaminophen (APAP). MIF leakage from the liver into the sera preceded peak increases in toxicity following APAP administration. MIF null (-/-) mice were significantly less susceptible to this toxicity at 8 h. At 48 h following a 300 mg/kg dose, complete lethality was observed in wild-type mice, while 46% survival was noted in MIF-/- mice. The decreased hepatic injury in MIF-/- mice correlated with a reduction in mRNA levels of interferon-gamma and a significant increase in heat shock protein expression, but was unrelated to the APAP-protein adduct formation in the liver. These findings support MIF as a critical pro-toxicant signal in drug-induced liver injury with potentially important and novel effects on heat shock protein responsiveness.

SIRT3-dependent deacetylation exacerbates acetaminophen hepatotoxicity.

Acetaminophen/paracetamol‐induced liver failure—which is induced by the binding of reactive metabolites to mitochondrial proteins and their disruption—is exacerbated by fasting. As fasting promotes SIRT3‐mediated mitochondrial‐protein deacetylation and acetaminophen metabolites bind to lysine residues, we investigated whether deacetylation predisposes mice to toxic metabolite‐mediated disruption of mitochondrial proteins. We show that mitochondrial deacetylase SIRT3−/− mice are protected from acetaminophen hepatotoxicity, that mitochondrial aldehyde dehydrogenase 2 is a direct SIRT3 substrate, and that its deacetylation increases acetaminophen toxic‐metabolite binding and enzyme inactivation. Thus, protein deacetylation enhances xenobiotic liver injury by modulating the binding of a toxic metabolite to mitochondrial proteins.

Mispairing C57BL/6 substrains of genetically engineered mice and wild-type controls can lead to confounding results as it did in studies of JNK2 in acetaminophen and concanavalin A liver injury.

C57BL/6 mice are widely used in biomedical research for the background of genetically engineered mice (GEM) and wild-type controls with the belief that the genetic background of GEM and control mice differ significantly by only one or more altered genes. This principle, however, does have limitations due in part to the existence of multiple substrains of C57BL/6 mice that should not be used interchangeably as they can differ both genetically and phenotypically. We show here that these mispairings do occur frequently and can lead to inaccurate and conflicting findings.

Knockdown of ERp57 increases BiP/GRP78 induction and protects against hyperoxia and tunicamycin-induced apoptosis.

Supplemental oxygen therapy (hyperoxia) in preterm babies with respiratory stress is associated with lung injury and the development of bronchopulmonary dysplasia. Endoplasmic reticulum (ER) homeostasis plays critical roles in maintaining cellular functions such as protein synthesis, folding, and secretion. Interruption of ER homeostasis causes ER stress and triggers the unfolded protein response, which can lead to apoptosis in persistently stressed cells. ERp57 is an ER protein and is associated with calreticulin and calnexin in protein glycosylation. In this study, we found hyperoxia downregulated ERp57 in neonatal rat lungs and cultured human endothelial cells. Transient transfection of ERp57 small interfering RNA significantly knocked down ERp57 expression and reduced hyperoxia- or tunicamycin-induced apoptosis in human endothelial cells. Apoptosis was decreased from 26.8 to 9.9% in hyperoxia-exposed cells and from 37.8 to 5.0% in tunicamycin-treated cells. The activation of caspase-3 induced by hyperoxia or tunicamycin was diminished and immunoglobulin heavy chain-binding protein/glucose-regulated protein 78-kDa (BiP/GRP78) induction was increased in ERp57 knockdown cells. Overexpression of ERp57 exacerbated hyperoxia- or tunicamycin-induced apoptosis in human endothelial cells. Apoptosis was increased from 10.1 to 14.3% in hyperoxia-exposed cells and from 14.0 to 21.2% in tunicamycin-treated cells. Overexpression of ERp57 also augmented tunicamycin-induced caspase-3 activation and reduced BiP/GRP78 induction. Our results demonstrate that ERp57 can regulate apoptosis in human endothelial cells. It appears that knockdown of ERp57 confers cellular protection against hyperoxia- or tunicamycin-induced apoptosis by inhibition of caspase-3 activation and stimulation of BiP/GRP78 induction.

Protective role of c-Jun N-terminal kinase 2 in acetaminophen-induced liver injury.

Recent studies in mice suggest that stress-activated c-Jun N-terminal protein kinase 2 (JNK2) plays a pathologic role in acetaminophen (APAP)-induced liver injury (AILI), a major cause of acute liver failure (ALF). In contrast, we present evidence that JNK2 can have a protective role against AILI. When male C57BL/6J wild type (WT) and JNK2(-/-) mice were treated with 300mg APAP/kg, 90% of JNK2(-/-) mice died of ALF compared to 20% of WT mice within 48h. The high susceptibility of JNK2(-/-) mice to AILI appears to be due in part to deficiencies in hepatocyte proliferation and repair. Therefore, our findings are consistent with JNK2 signaling playing a protective role in AILI and further suggest that the use of JNK inhibitors as a potential treatment for AILI, as has been recommended by other investigators, should be reconsidered.

Endogenous interleukin-4 regulates glutathione synthesis following acetaminophen-induced liver injury in mice.

In a recent study, we reported that interleukin (IL)-4 had a protective role against acetaminophen (APAP)-induced liver injury (AILI), although the mechanism of protection was unclear. Here, we carried out more detailed investigations and have shown that one way IL-4 may control the severity of AILI is by regulating glutathione (GSH) synthesis. In the present studies, the protective role of IL-4 in AILI was established definitively by showing that C57BL/6J mice made deficient in IL-4 genetically (IL-4(-/-)) or by depletion with an antibody, were more susceptible to AILI than mice not depleted of IL-4. The increased susceptibility of IL-4(-/-) mice was not due to elevated levels of hepatic APAP-protein adducts but was associated with a prolonged reduction in hepatic GSH that was attributed to decreased gene expression of γ-glutamylcysteine ligase (γ-GCL). Moreover, administration of recombinant IL-4 to IL-4(-/-) mice postacetaminophen treatment diminished the severity of liver injury and increased γ-GCL and GSH levels. We also report that the prolonged reduction of GSH in APAP-treated IL-4(-/-) mice appeared to contribute toward increased liver injury by causing a sustained activation of c-Jun-N-terminal kinase (JNK) since levels of phosphorylated JNK remained significantly higher in the IL-4(-/-) mice up to 24 h after APAP treatment. Overall, these results show for the first time that IL-4 has a role in regulating the synthesis of GSH in the liver under conditions of cellular stress. This mechanism appears to be responsible at least in part for the protective role of IL-4 against AILI in mice and may have a similar role not only in AILI in humans but also in pathologies of the liver caused by other drugs and etiologies.

Drug‐induced allergic hepatitis develops in mice when myeloid‐derived suppressor cells are depleted prior to halothane treatment

Clinical evidence suggests that many cases of serious idiosyncratic drug‐induced liver injury are mediated by the adaptive immune system in response to hepatic drug‐protein adducts, also referred to as “drug‐induced allergic hepatitis”; but detailed mechanistic proof has remained elusive due to the lack of animal models. We have hypothesized that drug‐induced allergic hepatitis is as rare in animals as it is in humans due at least in part to the tolerogenic nature of the liver. We provide evidence that immune tolerance can be overcome in a murine model of halothane‐induced liver injury initiated by trifluoroacetylated protein adducts of halothane formed in the liver. Twenty‐four hours after female Balb/cJ mice were initially treated with halothane, perivenous necrosis and an infiltration of CD11b+Gr‐1high cells were observed in the liver. Further study revealed a subpopulation of myeloid‐derived suppressor cells within the CD11b+Gr‐1high cell fraction that inhibited the proliferation of both CD4+ and CD8+ T cells. When CD11b+Gr‐1high cells were depleted from the liver with Gr‐1 antibody treatment, enhanced liver injury was observed at 9 days after halothane rechallenge. Toxicity was associated with increased serum levels of interleukin‐4 and immunoglobulins G1 and E directed against hepatic trifluoroacetylated protein adducts, as well as increased hepatic infiltration of eosinophils and CD4+ T cells, all features of an allergic reaction. When hepatic CD4+ T cells were depleted 5 days after halothane rechallenge, trifluoroacetylated protein adduct–specific serum immunoglobulin and hepatotoxicity were reduced. Conclusion: Our data provide a rational approach for developing animal models of drug‐induced allergic hepatitis mediated by the adaptive immune system and suggest that impaired liver tolerance may predispose patients to this disease. (Hepatology 2015;62:546–557

Eosinophils mediate the pathogenesis of halothane-induced liver injury in mice†‡

Drug‐induced liver injury (DILI) is a major health issue, as it remains difficult to predict which new drugs will cause injury and who will be susceptible to this disease. This is due in part to the lack of animal models and knowledge of susceptibility factors that predispose individuals to DILI. In this regard, liver eosinophilia has often been associated with DILI, although its role remains unclear. We decided to investigate this problem in a murine model of halothane‐induced liver injury (HILI). When female Balb/cJ mice were administered halothane, eosinophils were detected by flow cytometry in the liver within 12 hours and increased thereafter proportionally to liver damage. Chemokines, eotaxin‐1 (CCL11) and eotaxin‐2 (CCL24), which are known to attract eosinophils, increased in response to halothane treatment. The severity of HILI was decreased significantly when the study was repeated in wildtype mice made deficient in eosinophils with a depleting antibody and in eosinophil lineage‐ablated ΔdblGata−/− mice. Moreover, depletion of neutrophils by pretreating animals with Gr‐1 antibody prior to halothane administration failed to reduce the severity of HILI at antibody concentrations that did not affect hepatic eosinophils. Immunohistochemical staining for the granule protein, major basic protein, revealed that eosinophils accumulated exclusively around areas of hepatocellular necrosis. Conclusion: Our findings indicate that eosinophils have a pathologic role in HILI in mice and suggest that they may contribute similarly in many clinical cases of DILI. (HEPATOLOGY 2013)

Pathologic role of stressed-induced glucocorticoids in drug-induced liver injury in mice

UNLABELLED We previously reported that acetaminophen (APAP)-induced liver injury (AILI) in mice is associated with a rise in serum levels of the glucocorticoid (GC), corticosterone. In the current study, we provide evidence that endogenous GC play a pathologic role in AILI. Specifically, pretreatment of mice with the GC receptor (GCR) inhibitor, RU486 (mifepristrone), protected normal but not adrenalectomized mice from AILI, while pretreatment with dexamethasone, a synthetic GC, exacerbated AILI. RU486 did not affect the depletion of whole liver reduced GSH or the formation of APAP-protein adducts. It also had no effects on the formation of reactive oxygen species or the depletion of mitochondrial GSH or ATP. While RU486 pretreatment also protected against halothane-induced liver injury, it exacerbated concanavalin A (ConA)- and carbon tetrachloride (CCl(4))-induced liver injury, demonstrating the complexity of GC effects in different types of liver injury. CONCLUSION These results suggest that under certain conditions, elevated levels of GC might represent a previously unappreciated risk factor for liver injury caused by APAP and other drugs through the diverse biological processes regulated by GCR.