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

Migration inhibitory factor and cluster of differentiation 74-mediated dendritic cell apoptosis exacerbates acute acetaminophen-induced liver injury

INTRODUCTION

We investigated the role of macrophage migration inhibitory factor (MIF) on dendritic cells (DC) during acetaminophen (APAP)-induced acute liver injury (ALI) in mice.

METHODS

First, we randomly divided the mice into experimental (ALI model) and control groups, then intraperitoneally injected 600 mg/kg of APAP or phosphate-buffered saline, respectively. Then, we collected liver tissue and serum samples to evaluate liver inflammation using serum alanine aminotransferase level and hematoxylin and eosin (H&E) staining of liver tissues. Flow cytometry was used to identify changes in the quantity and percentage of DCs, as well as the expression of cluster of differentiation (CD) 74 and other apoptosis-related markers in the liver. Next, we randomly divided the mice into APAP-vehicles, APAP-bone marrow-derived dendritic cells (BMDCs), APAP-MIF, APAP-IgG (isotype immunoglobin G antibody) groups (four mice per group), after APAP injection, we injected control extracts, BMDCs, mouse recombinant MIF antibodies, or IgG antibodies into the tail vein. Lastly, the severity of the liver injury and the number of DCs were assessed.

RESULTS

The APAP-induced ALI mice had increased hepatic MIF expression but significantly lower amounts of hepatic DCs and apoptotic DCs than healthy mice; CD74 expression on the HDCs also increased markedly. Supplementing APAP-induced ALI mice with BMDCs or MIF antibodies significantly increased the number of hepatic DCs compared with the control mice, alleviating liver damage.

CONCLUSION

The MIF/CD74 signaling pathway may mediate hepatic DC apoptosis and promote liver damage.

Intrahepatic infiltration of activated CD8+ T cells and mononuclear phagocyte is associated with idiosyncratic drug-induced liver injury

Background

Idiosyncratic drug-induced liver injury (DILI) is caused by the interplay among drugs, their metabolites, and the host immune response. The characterization of infiltrated immune cells in the liver may improve the understanding of the pathogenesis of idiosyncratic DILI. This study investigated the phenotypes and clinical implications of liver-infiltrating immune cells in idiosyncratic DILI.

Methods

From January 2017 to June 2021, 53 patients with idiosyncratic DILI who underwent liver biopsy were prospectively enrolled in this study. Immunohistochemical staining and flow cytometry analyses were performed on the biopsy specimens. Serum levels of CXC chemokine ligand 10 (CXCL10) and soluble CD163 were measured. A multivariate cox proportional hazards model was used to evaluate predictors of DILI resolution within 30 days.

Results

The numbers of intrahepatic T cells and mononuclear phagocytes were positively correlated with serum levels of total bilirubin, alanine aminotransferase (ALT), and the model of end-stage liver disease score. The frequency of activated CD8+ T cells among liver-infiltrating CD8+ T cells in DILI livers was higher than that in healthy livers. Notably, the percentages of activated intrahepatic CD8+ T cells and mononuclear phagocytes in DILI livers showed a positive correlation with ALT. Additionally, serum CXCL10 level was positively correlated with intrahepatic T cell infiltration and ALT, and soluble CD163 level was positively correlated with intrahepatic mononuclear phagocyte infiltration and ALT. Thirty-six patients (70.6%) were treated with steroids. In multivariate analysis, total bilirubin and steroid use independently influenced DILI resolution within 30 days.

Conclusions

Activated CD8+ T cells and mononuclear phagocyte are associated with liver injury caused by drugs. Therefore, we suggest that steroids are a potential treatment option for idiosyncratic DILI.

The immunological mechanisms and therapeutic potential in drug-induced liver injury: lessons learned from acetaminophen hepatotoxicity

Acute liver failure caused by drug overdose is a significant clinical problem in developed countries. Acetaminophen (APAP), a widely used analgesic and antipyretic drug, but its overdose can cause acute liver failure. In addition to APAP-induced direct hepatotoxicity, the intracellular signaling mechanisms of APAP-induced liver injury (AILI) including metabolic activation, mitochondrial oxidant stress and proinflammatory response further affect progression and severity of AILI. Liver inflammation is a result of multiple interactions of cell death molecules, immune cell-derived cytokines and chemokines, as well as damaged cell-released signals which orchestrate hepatic immune cell infiltration. The immunoregulatory interplay of these inflammatory mediators and switching of immune responses during AILI lead to different fate of liver pathology. Thus, better understanding the complex interplay of immune cell subsets in experimental models and defining their functional involvement in disease progression are essential to identify novel therapeutic targets for the treatment of AILI. Here, this present review aims to systematically elaborate on the underlying immunological mechanisms of AILI, its relevance to immune cells and their effector molecules, and briefly discuss great therapeutic potential based on inflammatory mediators.

Macrophage Migration Inhibitory Factor as a Potential Biomarker in Acetaminophen Overdose: A Pilot Study

Introduction

Acetaminophen overdose is a leading cause of liver failure in the United States. Macrophage migration inhibitory factor (MIF) is a cytokine that is released early and promotes acetaminophen toxicity in preclinical models. This cytokine could prove a useful biomarker in emergency department (ED) patients immediately following an acute acetaminophen overdose.

Methods

We selected a convenience sample of thirteen patients from a prospective consecutive cohort of ED patients with suspected acute overdose. Research associates collected waste specimens for MIF analysis that remained after use for clinical care. Our team compared patients with confirmed acetaminophen overdose (n=9) to patients without acetaminophen exposure or liver injury (n=3) and a patient with liver injury in the absence of detectable acetaminophen (n=1).

Results

In our acetaminophen group, all nine patients had measurable acetaminophen concentrations. Median MIF serum concentrations were 16.08 ng/mL (IQR 2.06, 91.40) in the overdose group compared with the control group serum concentrations of 0.19 ng/mL (IQR 0.05, 0.32) (p = 0.0091).

Conclusion

In this pilot study, MIF was feasible to measure in specimens from an ED drug overdose cohort, and was significantly elevated in the acetaminophen group compared to non-acetaminophen controls without liver injury.

Protective effect of ISO-1 with inhibition of RIPK3 up-regulation and neutrophilic accumulation on acetaminophen-induced liver injury in mice

Overdose use of acetaminophen (APAP) often occurs a severe liver injury, and its liver injury is lethal in some cases. Macrophage migration inhibitory factor (MIF) is expressed in a variety of cells and has multifunctional roles. However, the role of MIF in APAP-induced liver injury has not been fully investigated. In this study, we investigated whether treatment with (S,R)-3-(4-hydroxyphenil)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1), a MIF inhibitor, protected mice from acute APAP-induced liver injury. Acute liver injury was induced by injection of APAP (300 mg/kg body weight). Mice were treated with a single injection of ISO-1(15 mg/kg body weight) 1 h (h) before APAP administration. Histological, biochemical and molecular analyses were performed in liver of mice 12 h after APAP administration. ISO-1 remarkably improved the histological findings of APAP-induced liver injury in mice. The increases in serum levels of alanine aminotransferase (ALT), and macrophage inflammatory protein-2 (MIP-2) by APAP were inhibited by ISO-1. In addition, ISO-1 reduced the increased number of the myeloperoxidase-staining cells and that of TUNEL-positive staining cells in the liver of mice with APAP-induced liver injury. Up-regulation of hepatic receptor interacting protein kinase (RIPK)3 and heat shock protein70 by APAP was suppressed in the liver of mice given ISO-1. These results provide the additional evidence that inhibition of MIF activity may be clinically effective for treatment of acute APAP-induced liver injury.

The effect of a mesenchymal stem cell conditioned medium fraction on morphological characteristics of hepatocytes in acetaminophen-induced acute liver failure: a preliminary study

Background: In our studies, it was shown that the effectiveness of the conditioned medium obtained by cultivating mesenchymal stem cells depends on the microenvironment conditions used to cultivate the cells. It was demonstrated that the conditioned medium obtained by culturing cells with low oxygen content (10%) has a much more pronounced protective effect.

Methods: Protein compositions obtained from MSCs cultured under hypoxic (10% O₂ hc-MSC) and normal (21% O₂ nc-MSC) conditions were used to treat acute liver failure (ALF) induced in mice by acetaminophen injection. Thus, we obtained fractions normalized by volume, which predominantly contained proteins with masses > 50, 50-30, 30-10, and 10-3 kDa.

Results: The data from biochemical studies have shown that only fractions from 10 to 30 kDa (hcMSC and ncMSC) significantly reduced the level of liver enzymes in the beginning of the acute period after acetaminophen administration. Mass spectrometry analysis of the proteins contained in the isolated fractions showed a sharp increase in the protein levels in the 10-30 kDa hcMSC fraction as compared with that in 10-30 kDa ncMSCs. The composition obtained from MSCs cultured at lower O₂ level (fraction 10-30 kDa hcMSC) was shown to be more potent than the composition prepared from normoxic cells.

Conclusion: The results have shown that a composition obtained by culturing the cells under a reduced content of O₂ (10%), significantly improves the biochemical parameters, and histological arrester reduces the degree of inflammation and stimulates regenerative processes in liver, compared to both the control group and group treated with the composition that was obtained by culturing the cells under normal oxygen content.

The Hippo Signaling Pathway in Regenerative Medicine

The major role of Hippo signaling is to inhibit their downstream effectors YAP/TAZ for organ size control during development and regeneration (Nat Rev Drug Discov 13(1):63-79, 2014; Dev Cell 19(4):491-505, 2010; Cell 163(4):811-828, 2015). We and others have demonstrated that the genetic disruption of kinases Mst1 and Mst2 (Mst1/2), the core components of Hippo signaling, results in YAP activation and sustained liver growth, thereby leading to an eight- to tenfold increase in liver size within 3 months and occurrence of liver cancer within 5 months (Curr Biol 17(23):2054-2060, 2007; Cancer Cell 16(5):425-438, 2009; Cell 130(6):1120-1133, 2007; Cancer Cell 31(5):669-684 e667, 2017; Nat Commun 6:6239, 2015; Cell Rep 3(5):1663-1677, 2013). XMU-MP-1, an Mst1/2 inhibitor, is able to augment mouse liver and intestinal repair and regeneration in both acute and chronic injury mouse models (Sci Transl Med 8:352ra108, 2016).In addition, YAP-deficient mice show an impaired intestinal regenerative response after DSS treatment or gamma irradiation (Proc Natl Acad Sci U S A 108(49):E1312-1320, 2011; Nature 493(7430):106-110, 2013; Genes Dev 24(21):2383-2388, 2010; J Vis Exp (111), 2010). IBS008738, a TAZ activator, facilitates muscle repair after cardiotoxin-induced muscle injury (Mol Cell Biol. 2014;34(9):1607-21). Deletion of Salvador (Sav) in mouse hearts enhances cardiomyocyte regeneration with reduced fibrosis and recovery of pumping function after myocardial infarction (MI) or resection of mouse cardiac apex (Development 140(23):4683-4690, 2013; Sci Signal 8(375):ra41, 2015; Nature 550(7675):260-264, 2017). This chapter provides a detailed description of procedures and important considerations when performing the protocols for the respective assays used to determine the effects of Hippo signaling on tissue repair and regeneration.

The effects of melatonin on liver functions in arsenic-induced liver damage

OBJECTIVE

Arsenic exposure is increasing in communities due to environmental pollution and industrial development. Arsenic is toxic to organ systems because it causes oxidative stress, enzymatic inhibition, and damage to protein structures. The liver, for example, is an organ that may be damaged by arsenic, and this damage may cause various clinical conditions like hepatic failure or cancer. Melatonin is a hormone that acts like an antioxidant, an anti-inflammatory agent, and a cytoprotective agent. In this study, we aimed to evaluate melatonin's protective effects on livers damaged by arsenic toxicity.

MATERIALS AND METHODS

Twenty-four Sprague-Dawley male rats were classified into three groups: a control group, an arsenic applied group, and an arsenic plus 10 mg/kg melatonin applied group. At the end of the fifteen-day experiment, the rats were sacrificed. Albumin, interleukin-6 (IL-6), total protein, alanine transaminase, aspartate transaminase, macrophage migration inhibitory factor, and monocyte chemotactic protein-1 measurements were obtained.

RESULTS

In rats with liver damage due to arsenic exposure, melatonin administration significantly decreased the levels of IL-6, macrophage migration inhibitory factor, and monocyte chemotactic protein-1 (p<0.001, p=0.02 and p=0.04, respectively).

CONCLUSION

After evaluating liver enzymes and inflammatory markers, this study determined that melatonin exposure improves liver tissue damage caused by arsenic exposure, with the degree of improvement varying based on the levels of arsenic exposure.

Characterization of chemical-induced sterile inflammation in vitro: application of the model compound ketoconazole in a human hepatic co-culture system

Liver injury as a result of a sterile inflammation is closely linked to the activation of immune cells, including macrophages, by damaged hepatocytes. This interaction between immune cells and hepatocytes is as yet not considered in any of the in vitro test systems applied during the generation of new drugs. Here, we established and characterized a novel in vitro co-culture model with two human cell lines, HepG2 and differentiated THP-1. Ketoconazole, an antifungal drug known for its hepatotoxicity, was used as a model compound in the testing of the co-culture. Single cultures of HepG2 and THP-1 cells were studied as controls. Different metabolism patterns of ketoconazole were observed for the single and co-culture incubations as well as for the different cell types. The main metabolite N-deacetyl ketoconazole was found in cell pellets, but not in supernatants of cell cultures. Global proteome analysis showed that the NRF2-mediated stress response and the CXCL8 (IL-8) pathway were induced by ketoconazole treatment under co-culture conditions. The upregulation and ketoconazole-induced secretion of several pro-inflammatory cytokines, including CXCL8, TNF-α and CCL3, was observed in the co-culture system only, but not in single cell cultures. Taking together, we provide evidence that the co-culture model applied might be suitable to serve as tool for the prediction of chemical-induced sterile inflammation in liver tissue in vivo.

Conceptual models for the initiation of hepatitis B virus-associated hepatocellular carcinoma

Although chronic hepatitis B virus (HBV) infection is a known risk factor for the development of hepatocellular carcinoma (HCC), the steps involved in the progression from normal liver to HCC are poorly understood. In this review, we apply five conceptual models, previously proposed by Vineis et al. to explain carcinogenesis in general, to explore the possible steps involved in the initiation and evolution of HBV-associated HCC. Available data suggest that the most suitable and inclusive model is based on evolution of hepatocyte subpopulations. In this evolutionary model, HCC-associated changes are driven by selection and subsequent clonal expansion of phenotypically altered hepatocyte subpopulations in the microenvironment of the HBV-infected liver. This model can incorporate the wide range of mechanisms proposed to play a role in the initiation of HCC including oncogenic HBV proteins, integration of HBV DNA and chronic inflammation of the liver. The model may assist in the early prevention, detection and treatment of HCC and may guide future studies of the initiation of HBV-associated HCC.

Albumin fusion prolongs the antioxidant and anti-inflammatory activities of thioredoxin in mice with acetaminophen-induced hepatitis

Overdoses of acetaminophen (APAP) are a major cause of acute liver failure. N-Acetylcysteine (NAC) is the standard therapy for patients with such an overdose because oxidative stress plays an important role in the pathogenesis of APAP-induced hepatitis. However, NAC is not sufficiently efficacious. We previously developed a recombinant human serum albumin (HSA)-thioredoxin 1 (Trx) fusion protein (HSA-Trx), designed to overcome the unfavorable pharmacokinetic and short pharmacological properties of Trx, an endogenous protein with antioxidative and anti-inflammatory properties. In this study, we investigated the therapeutic impact of HSA-Trx in mice with APAP-induced hepatitis. The systemic administration of HSA-Trx significantly improved the survival rate of mice treated with a lethal dose of APAP compared with saline. HSA-Trx strongly attenuated plasma transaminases in APAP-induced hepatitis mice compared with HSA or Trx, components of the fusion protein. HSA-Trx also markedly caused a diminution in the histopathological features of hepatic injuries and the number of apoptosis-positive hepatic cells. In addition, an evaluation of oxidative stress markers and plasma cytokine and chemokine levels clearly showed that HSA-Trx significantly improved the breakdown of hepatic redox conditions and inflammation caused by the APAP treatment. HSA-Trx also significantly decreased oxidative and nitrosative/nitrative stress induced by SIN-1 in vitro. Finally, HSA-Trx, but not the NAC treatment at 4 h after APAP injection, significantly inhibited the elevation in plasma transaminase levels. In conclusion, the findings suggest that HSA-Trx has considerable potential for use as a novel therapeutic agent for APAP-induced hepatitis, due to its long-lasting antioxidative and anti-inflammatory effects.

Human pluripotent stem cells for modeling toxicity

The development of xenobiotics, driven by the demand for therapeutic, domestic and industrial uses continues to grow. However, along with this increasing demand is the risk of xenobiotic-induced toxicity. Currently, safety screening of xenobiotics uses a plethora of animal and in vitro model systems which have over the decades proven useful during compound development and for application in mechanistic studies of xenobiotic-induced toxicity. However, these assessments have proven to be animal-intensive and costly. More importantly, the prevalence of xenobiotic-induced toxicity is still significantly high, causing patient morbidity and mortality, and a costly impediment during drug development. This suggests that the current models for drug safety screening are not reliable in toxicity prediction, and the results not easily translatable to the clinic due to insensitive assays that do not recapitulate fully the complex phenotype of a functional cell type in vivo. Recent advances in the field of stem cell research have potentially allowed for a readily available source of metabolically competent cells for toxicity studies, derived using human pluripotent stem cells harnessed from embryos or reprogrammed from mature somatic cells. Pluripotent stem cell-derived cell types also allow for potential disease modeling in vitro for the purposes of drug toxicology and safety pharmacology, making this model possibly more predictive of drug toxicity compared with existing models. This article will review the advances and challenges of using human pluripotent stem cells for modeling metabolism and toxicity, and offer some perspectives as to where its future may lie.

Ectopic expression of CD74 in Ikkβ-deleted mouse hepatocytes

CD74, a Type II membrane glycoprotein and MHC class II chaperone involved in antigen processing, is normally expressed by cells associated with the immune system. CD74 also forms heterodimers with CD44 to generate receptors to macrophage migration inhibitory factor (MIF), a proinflammatory cytokine. Following targeted Alb-Cre-mediated deletion of Ikkβ in Ikkβ(Δhep) mice (Ikkβ(F/F):Alb-Cre, a strain highly susceptible to chemically induced hepatotoxicity and hepatocarcinogenesis), CD74 is expressed abundantly by adult hepatocytes throughout liver acini, albeit more intensely in midzonal-to-centrilobular regions. By comparison, CD74 expression is not observed in Ikkβ(F/F) hepatocytes, nor is it augmented in the livers of Ikkβ(+/+):Alb-Cre mice; CD74 is barely detectable in cultured embryonic fibroblasts from Ikkβ(-/-) mice. Microarray profiling shows that constitutive CD74 expression in Ikkβ(Δhep) hepatocytes is accompanied by significantly augmented expression of CD44 and key genes associated with antigen processing and host defense, including MHC class II I-Aα, I-Aβ, and I-Eβ chains, CIITA and CD86. Taken together, these observations suggest that Ikkβ(Δhep) hepatocytes might express functional capacities for class II-restricted antigen presentation and heightened responsiveness to MIF-signaling, and also suggest further roles for intrahepatocellular IKKβ in the suppression or inactivation of molecules normally associated with the formation and differentiation of cells of the immune system.

Validity of plasma macrophage migration inhibitory factor for diagnosis and prognosis of hepatocellular carcinoma

We performed our study to determine whether plasma macrophage migration inhibitory factor (MIF) levels have diagnostic and prognostic value in hepatocellular carcinoma (HCC) patients. Enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry were used to measure the expression of MIF in plasma and tissues, respectively. Plasma MIF levels were compared to HCC occurrence, clinicopathological features and outcomes. Cutpoints of plasma MIF levels for diagnosis and prognosis were, respectively, determined by receiver operating characteristic analysis and X-tile in corresponding training cohort, and then were confirmed in the validation cohort. The postoperative plasma MIF levels of HCC patients were detected in an independent cohort (80 HCC patients). As a result, MIF expression in situ was mainly observed in the cytoplasm of HCC cells. Intratumoral MIF expression was positively correlated with plasma MIF levels (r = 0.759, p < 0.001). Compared to serum α-fetoprotein (AFP), plasma MIF had a higher diagnostic value for discrimination of HCC from controls at 35.3 ng/ml. With determined cutpoints, plasma MIF levels demonstrated a significant association with overall survival (OS) and disease-free survival (DFS) of HCC patients even in patients with normal serum AFP levels and Tumor Node Metastasis (TNM) stage I. In addition, the plasma MIF levels were identified as an independent factor for OS [hazard ratio (HR) = 1.754; p = 0.012] and DFS (HR = 2.121; p < 0.001). Plasma MIF levels decreased markedly within 30 days after tumor resection (p < 0.001). Therefore, plasma MIF levels have potential as a diagnostic and prognostic factor for HCC.

MIF: a key player in cutaneous biology and wound healing

Owing to its implication in a range of pathological conditions, including asthma, rheumatoid arthritis, atherosclerosis, inflammatory bowel disease and cancer, the pleiotropic cytokine macrophage migration inhibitory factor (MIF) has been the subject of intensive recent investigation. In the field of dermatology, MIF is believed to be a detrimental factor in diseases such as systemic sclerosis, atopic dermatitis, psoriasis, eczema and UV radiation damage. However, its contribution to other aspects of cutaneous biology is currently unclear. Although its expression in intact skin is well characterized, little is known about MIF's role in cutaneous homoeostasis. However, recent data do identify MIF as a key player in the immune privilege of hair follicles. Similarly, although MIF is rapidly released and its local expression significantly induced upon wounding, its primary role in the ensuing repair process remains a source of contention. MIF has been identified as being a key effector of the beneficial effects of estrogen on wound repair, yet studies employing Mif null mice, recombinant MIF, and neutralizing anti-MIF antibodies have failed to provide a consensus as to whether it benefits or inhibits healing. In fact MIF appears to be able to exert both positive and negative effects, with the cell-specific relevancy of MIF in wound healing still unclear. Thus, if MIF and/or its downstream targets are to be therapeutically useful in the context of cutaneous repair, more needs to be done to establish the nature and mechanism of action of MIF and its receptors in healing wounds.

Macrophage migration inhibitory factor contributes to development of nonsteroidal anti-inflammatory drugs-induced gastric injury in mice

Macrophage migration inhibitory factor (MIF) plays an important role in the development of inflammation. In this study, we evaluated the role of MIF in gastric injury induced by non-steroidal anti-inflammatory drugs (NSAIDs) in mice. To induce gastric injury, mice were intraperitnoneally injected with 35 mg/kg of indomethacin. The level of MIF protein was up-regulated and severe gastric injury with inflammatory infiltrate was observed in the stomach of wild-type (WT) mice treated with indomethacin. The severity of gastric injury in MIF-deficient mice was less than that in WT mice. Increase in TNF-α in gastric tissue of mice treated with indomethacin was suppressed in MIF-deficient mice. The expression of HSP70, which has a cytoprotective role, was remarkably up-regulated in the stomach of MIF-deficient mice compared with WT mice after indomethacin treatment. Our results suggest that MIF is essential for the development of gastric injury-induced by NSAIDs.

Role of monocytes and macrophages in experimental and human acute liver failure

Acute liver failure (ALF) is a devastating clinical syndrome characterised by progressive encephalopathy, coagulopathy, and circulatory dysfunction, which commonly leads to multiorgan failure and death. Central to the pathogenesis of ALF is activation of the immune system with mobilisation of cellular effectors and massive production of cytokines. As key components of the innate immune system, monocytes and macrophages are postulated to play a central role in the initiation, progression and resolution of ALF. ALF in humans follows a rapidly progressive clinical course that poses inherent difficulties in delineating the role of these pivotal immune cells. Therefore, a number of experimental models have been used to study the pathogenesis of ALF. Here we consider the evidence from experimental and human studies of ALF on the role of monocytes and macrophages in acute hepatic injury and the ensuing extrahepatic manifestations, including functional monocyte deactivation and multiple organ failure.

The role of cytokines in the mechanism of adverse drug reactions

Cytokines are thought to play a role in acute and/or immune-mediated adverse drug reactions (ADRs) due to their ability to regulate the innate and adaptive immune systems. This role is highly complex owing to the pluripotent nature of cytokines, which enables the same cytokine to play multiple roles depending on target organ(s) involved. As a result, the discussion of cytokine involvement in ADRs is organized according to target organ(s); specifically, ADRs targeting skin and liver, as well as ADRs targeting multiple organs, such as drug-induced autoimmunity and infusion-related reactions. In addition to discussing the mechanism(s) by which cytokines contribute to the initiation, propagation, and resolution of ADRs, we also discuss the usefulness and limitations of current methodologies available to conduct such mechanistic studies. While animal models appear to hold the most promise for uncovering additional mechanisms, this field is plagued by a lack of good animal models and, as a result, the mechanism of cytokine involvement in ADRs is often studied using less informative in vitro studies. The recent formation of the Drug-Induced Liver Injury Network, whose goal is collect thousands of samples from drug-induced liver injury patients, has enormous potential to advance knowledge in this field, by enabling large-scale cytokine polymorphism studies. In conclusion, we discuss how further advances in this field could be of significant benefit to patients in terms of preventing, predicting, and treating ADRs.

Hypothesis: Targeted Ikkβ deletion upregulates MIF signaling responsiveness and MHC class II expression in mouse hepatocytes

Macrophage migration inhibitory factor (MIF) is causally related to the pathogenesis of chronic liver disease but its hepatocellular mechanisms of action are largely unknown. Scattered reports in the literature hint at functional connections between the expression of MIF and major histocompatibility complex (MHC) Class II molecules. Not surprisingly, these relationships have not yet been explored in hepatocytes because MIF and MHC Class II cell surface receptors are commonly expressed by other cell types including various antigen presenting cells of the immune system. On the other hand, mounting evidence suggests that heteromeric MIF receptors share a common molecule with intracellular MHC Class II complexes, viz., CD74, which also serves as the MHC Class II chaperone; and, while it is unclear what cancer-related role(s) MHC Class II receptors might play, increasing evidence suggests that MIF and CD74 are also implicated in the biology of hepatocellular carcinoma. These reports are provocative for two reasons: firstly, Ikkβ^Δhep mice carrying hepatocyte-targeted deletions of Ikkβ, an IκB kinase complex subunit required for the activation of the transcription factor NF-κB (nuclear factor-κB), have been shown to display heightened susceptibilities to hepatotoxins and chemical hepatocarcinogens; secondly, microarray profiling observations indicate that Ikkβ^Δhep hepatocytes constitutively and “ectopically” overexpress genes, particularly CD74, CD44 (a MIF-receptor subunit) and MHC Class II I-A/E β and I-A α chains, and gene families that regulate host immune process and immune defense responses. These findings together suggest that Ikkβ^Δhep mice might express functional MIF and MHC Class II receptors, leading to increased hepatocellular sensitivity to MIF signaling as well as to the unusual property of antigen presentation; both functions might contribute to the heightened liver disease phenotypes of Ikkβ^Δhep mice. The findings raise questions about the potential existence of cohorts of human patients with genetic abnormalities of Ikkβ that might confer heightened susceptibility to liver disease including hepatocellular carcinoma.

The role of damage associated molecular pattern molecules in acetaminophen-induced liver injury in mice

The idiosyncratic nature, severity and poor diagnosis of drug-induced liver injury (DILI) make these reactions a major safety issue during drug development, as well as the most common cause for the withdrawal of drugs from the pharmaceutical market. Elucidation of the underlying mechanism(s) is necessary for identifying predisposing factors and developing strategies in the treatment and prevention of DILI. Acetaminophen (APAP) is a widely used over the counter therapeutic that is known to be effective and safe at therapeutic doses. However, in overdose situations fatal and non-fatal hepatic necrosis can result. Evidence suggests that the chemically reactive metabolite of the drug initiates hepatocyte damage and that inflammatory innate immune responses also occur within the liver, leading to the exacerbation and progression of tissue injury. Here we investigate whether following APAP-induced liver injury (AILI) damaged hepatocytes release "danger" signals or damage associated molecular pattern (DAMP) molecules, which induce pro-inflammatory activation of hepatic macrophages, further contributing to the progression of liver injury. Our study demonstrated a clear activation of Kupffer cells following early exposure to APAP (1h). Activation of a murine macrophage cell line, RAW cells, was also observed following treatment with liver perfusate from APAP-treated mice, or with culture supernatant of APAP-challenged hepatocytes. Moreover, in these media, the DAMP molecules, heat-shock protein-70 (HSP-70) and high mobility group box-1 (HMGB1) were detected. Overall, these findings reveal that DAMP molecules released from damaged and necrotic hepatocytes may serve as a crucial link between the initial hepatocyte damage and the activation of innate immune cells following APAP-exposure, and that DAMPs may represent a potential therapeutic target for AILI.

Liver tissue engineering in the evaluation of drug safety

Assessment of drug-liver interactions is an integral part of predicting the safety profile of new drugs. Existing model systems range from in vitro cell culture models to FDA-mandated animal tests. Data from these models often fail, however, to predict human liver toxicity, resulting in costly failures of clinical trials. In vitro screens based on cultured hepatocytes are now commonly used in early stages of development, but many toxic responses in vivo seem to be mediated by a complex interplay among several different cell types. We discuss some of the evolving trends in liver cell culture systems applied to drug safety assessment and describe an experimental model that captures complex liver physiology through incorporation of heterotypic cell-cell interactions, 3D architecture and perfused flow. We demonstrate how heterotypic interactions in this system can be manipulated to recreate an inflammatory environment and apply the model to test compounds that potentially exhibit idiosyncratic drug toxicity. Finally, we provide a perspective on how the range of existing and emerging in vitro liver culture approaches, from simple to complex, might serve needs across the range of stages in drug discovery and development, including applications in molecular therapeutics.

Understanding the role of reactive metabolites in drug-induced hepatotoxicity: state of the science

Drug-induced liver injury (DILI) represents a major impediment to the development of new drugs and is a leading cause of drug withdrawal. The occurrence of hepatotoxicity has been closely associated with the formation of chemically reactive metabolites. Huge investment has focused on the screening of chemically reactive metabolites to offer a pragmatic approach to produce safer drugs and also reduce drug attrition and prevent market place withdrawal. However, questions surrounding the importance of chemically reactive metabolites still remain. Increasing evidence now exists for the multi-factorial nature of DILI, in particular the role played by the host immune system or disease state in the pathogenesis of DILI. This review aims to evaluate the current measures for the prediction and diagnosis of DILI and to highlight investigations being made to understand the multidimensional nature. Some of the steps being made to generate improved physiological systems to identify more sensitive, reflective mechanism-based biomarkers to aid the earlier identification of DILI and develop safer medicines are also discussed.

Pathogenic role of natural killer T and natural killer cells in acetaminophen-induced liver injury in mice is dependent on the presence of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is commonly used in biological studies to dissolve drugs and enzyme inhibitors with low solubility. Although DMSO is generally thought of as being relatively inert, it can induce biological effects that are often overlooked. An example that highlights this potential problem is found in a recent report demonstrating a pathogenic role for natural killer T (NKT) and natural killer (NK) cells in acetaminophen-induced liver injury (AILI) in C57Bl/6 mice in which DMSO was used to facilitate acetaminophen (APAP) dissolution. We report that NKT and NK cells do not play a pathologic role in AILI in C57Bl/6 mice in the absence of DMSO. Although AILI was significantly attenuated in mice depleted of NKT and NK cells prior to APAP treatment in the presence of DMSO, no such effect was observed when APAP was dissolved in saline. Because of this unexpected finding, the effects of DMSO on hepatic NKT and NK cells were subsequently investigated. When given alone, DMSO activated hepatic NKT and NK cells in vivo as evidenced by increased NKT cell numbers and higher intracellular levels of the cytotoxic effector molecules interferon-gamma (IFN-gamma) and granzyme B in both cell types. Similarly, when used as a solvent for APAP, DMSO again increased NKT cell numbers and induced IFN-gamma and granzyme B expression in both cell types.

CONCLUSION

These data demonstrate a previously unappreciated effect of DMSO on hepatic NKT and NK cells, suggesting that DMSO should be used cautiously in experiments involving these cells.

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.

Role of extracellular nucleotide phosphohydrolysis in intestinal ischemia-reperfusion injury

Extracellular adenosine has been implicated as an innate antiinflammatory metabolite, particularly during conditions of limited oxygen availability such as ischemia. Because extracellular adenosine generation is primarily produced via phosphohydrolysis from its precursor molecule adenosine-monophosphate (AMP) through the enzyme ecto-5'-nucleotidase (CD73), we examined the contribution of CD73-dependent adenosine production in modulation of intestinal ischemia-reperfusion (IR) injury. Following transcriptional and translational profiling of intestinal tissue that revealed a prominent induction of murine CD73, we next determined the role of CD73 in protection against intestinal IR injury. Interestingly, pharmacological inhibition or targeted gene deletion of CD73 significantly enhanced not only local intestinal injury, but also secondary organ injury, following IR as measured by intestinal and lung myeloperoxidase, aspartate and alanine aminotransferase, interleukin (IL) -1, IL-6, and histological injury. To confirm the role of CD73 in intestinal adenosine production, we measured adenosine tissue levels and found that they were increased with IR injury. In contrast, CD73-deficient (cd73(-/-)) mice had lower adenosine levels at baseline and no increase with IR injury. Finally, reconstitution of cd73(-/-) mice or treatment of wild-type mice with soluble 5'-nucleotidase was associated with significantly lower levels of injury. These data reveal a previously unrecognized role of CD73 in attenuating intestinal IR-mediated injury.

Idiosyncratic drug reactions: current understanding

Clinical characteristics and circumstantial evidence suggest that idiosyncratic drug reactions are caused by reactive metabolites and are immune-mediated; however, there are few definitive data and there are likely exceptions. There are three principal hypotheses for how reactive metabolites might induce an immune-mediated idiosyncratic reaction: the hapten hypothesis, the danger hypothesis, and the PI hypothesis. It has been proposed that some idiosyncratic reactions, especially those involving the liver, represent metabolic idiosyncrasy; however, there are even less data to support this hypothesis. The unpredictable nature of these reactions makes mechanistic studies difficult. There is a very strong association with specific human leukocyte antigen (HLA) genes for certain reactions, but this has only been demonstrated for very few drugs. Animal models represent a very powerful tool for mechanistic studies, but the number of valid models is also limited. There may be biomarkers of risk; however, much more work needs to be done.

Resistance to experimental colitis depends on cytoprotective heat shock proteins in macrophage migration inhibitory factor null mice

Macrophage migration inhibitory factor plays an important role in inflammatory diseases. We investigated the role of macrophage migration inhibitory factor (MIF) in the development of dextran sulfate sodium (DSS)-induced colitis using MIF null ((-/-)) mice. MIF(-/-) mice given 3% DSS showed no clinical and histological feature of colitis in contrast to wild-type (WT) mice. Lack of MIF suppressed the up-regulation of TNF-alpha and IFN-gamma as Th1-derived cytokines, and increased the level of IL-4 as Th2-derived cytokine in the colon tissues. Moreover, we found that the expressions of heat shock protein (HSP)40 and HSP70 were markedly up-regulated in the colon of MIF(-/-) mice in response to DSS compared with WT mice. Additionally, quercetin, an inhibitor of HSP synthesis, inhibited the up-regulation of HSP40 and 70 expressions and developed DSS-induced colitis in MIF(-/-) mice. Our findings in this study provide more information in the role of MIF in colitis.

Role of inflammation in the mechanism of acetaminophen-induced hepatotoxicity

Acetaminophen (AAP) overdose and the resulting hepatotoxicity is an important clinical problem. In addition, AAP is widely used as a prototype hepatotoxin to study mechanisms of chemical-induced cell injury and to test the hepatoprotective potential of new drugs and herbal medicines. Because of its importance, the mechanisms of AAP-induced liver cell injury have been extensively investigated and controversially discussed for > 30 years. This review highlights recent new insight into intracellular events critical for liver cell death. In addition, the relevance of the inflammatory response is addressed, including cytotoxic and inflammatory mediators generated by activated inflammatory cells, that is, resident macrophages and lymphocytes as well as newly recruited blood-derived leukocytes. Inflammation is a critical component of the overall pathophysiology, not only as a potential factor that may aggravate cell damage, but more importantly as a vital response to limit cell injury, remove cell debris and promote regeneration.

Role of innate immunity in acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) hepatotoxicity is currently the single most important cause of acute liver failure in the US, and is associated with a significant number of deaths. The toxic response to APAP is triggered by a highly reactive metabolite N-acetyl-p-benzoquinone-imine. Following the hepatocellular initiation events, such as glutathione depletion and covalent binding, intracellular stress simultaneously activates signal transduction and transcription factor pathways that are protective or toxic (directly or through sensitisation). Subsequently, pro- and anti-inflammatory cascades of the innate immune system are simultaneously activated, the balance of which plays a major role in determining the progression and severity of APAP-induced hepatotoxicity. The threshold and susceptibility to APAP hepatotoxicity is determined by the interplay of injury promoting and inhibiting events downstream of the initial production of toxic metabolite. The environmental and genetic control of these intracellular and intercellular responses to toxic metabolites may be of critical importance in determining susceptibility to APAP hepatotoxicity and presumably idiosyncratic drug hepatotoxicity.

Lack of macrophage migration inhibitory factor protects mice against concanavalin A-induced liver injury

BACKGROUND

Macrophage migration inhibitory factor (MIF) is involved in inflammatory and immune-mediated diseases but the role of MIF in liver injury has not yet been elucidated.

METHODS

We investigated biochemically, histologically and immunologically the character of MIF in concanavalin A (Con A)-induced T-cell-mediated liver injury using MIF knockout (KO) mice and wild-type (WT) mice.

RESULTS

MIF KO mice showed significantly decreased serum alanine aminotransferase values and suppressed histological change with massive necrosis of the hepatic parenchymal cells and infiltration of inflammatory cells compared with their WT counterparts. This protection was not mediated by either tumor necrosis factor-alpha or interferon-gamma, which are critical mediators of Con A-induced liver injury, as their serum concentrations were shown to be similar in MIF KO and WT mice. On the other hand, a flow cytometric analysis demonstrated that the number of activated hepatic leukocytes decreased more in the MIF KO mice than in the WT mice.

CONCLUSIONS

A lack of MIF protected the mice from Con A-induced liver injury. Controlling the MIF activity may be a useful therapeutic strategy for treating such T-cell activation-associated liver diseases as autoimmune hepatitis and viral hepatitis.

Positive association of macrophage migration inhibitory factor gene-173G/C polymorphism with biliary atresia

BACKGROUND

Macrophage migration inhibitory factor (MIF) is a pleiotrophic lymphocyte and macrophage cytokine; it is likely to play an important role in innate immunity. Its expression was increased in several inflammatory diseases, and MIF gene polymorphisms have an effect on disease outcome and response to glucocorticoid treatment.

AIM

To investigate the role of the 173G/C polymorphism of the MIF gene for susceptibility to biliary atresia (BA).

METHOD

Between February 2002 and November 2004, 18 patients (mean age 1 +/- 0.4 years) diagnosed as having BA were studied. After informed consent, blood was collected, and DNA was obtained. MIF 173C/G polymorphism was detected using the polymerase chain reaction-restriction fragment length polymorphism based method. BA patients were compared with a group of chronic liver disease patients (CLD) (n = 36) and a group of unrelated healthy controls (n = 103).

RESULTS

MIF-173C allele frequency was significantly higher than both the CLD and healthy control groups (P = 0.03, odds ratio [OR] 4.4, 95% confidence interval [CI] 1.3-15.1; P = 0.000, OR 4.1, 95% CI 2.3-7.6, respectively). Univariate analysis showed that MIF-173G/C polymorphism was significantly associated with BA (for GC genotype, OR = 6, 95 % CI 2.8-11.5, P = 0.000). There was no significant correlation between pediatric end stage liver disease score and MIF genotypes both in BA and CLD groups.

CONCLUSION

Our results suggest that the -173C allele of the MIF gene might be associated with the susceptibility to BA.

Gastrointestinal ischemia-reperfusion injury is lectin complement pathway dependent without involving C1q

Complement activation plays an important role in local and remote tissue injury associated with gastrointestinal ischemia-reperfusion (GI/R). The role of the classical and lectin complement pathways in GI/R injury was evaluated using C1q-deficient (C1q KO), MBL-A/C-deficient (MBL-null), complement factor 2- and factor B-deficient (C2/fB KO), and wild-type (WT) mice. Gastrointestinal ischemia (20 min), followed by 3-h reperfusion, induced intestinal and lung injury in C1q KO and WT mice, but not in C2/fB KO mice. Addition of human C2 to C2/fB KO mice significantly restored GI/R injury, demonstrating that GI/R injury is mediated via the lectin and/or classical pathway. Tissue C3 deposition in C1q KO and WT, but not C2/fB KO, mice after GI/R demonstrated that complement was activated in C1q KO mice. GI/R significantly increased serum alanine aminotransferase, gastrointestinal barrier dysfunction, and neutrophil infiltration into the lung and gut in C1q KO and WT, but not C2/fB KO, mice. MBL-null mice displayed little gut injury after GI/R, but lung injury was present. Addition of recombinant human MBL (rhuMBL) to MBL-null mice significantly increased injury compared with MBL-null mice after GI/R and was reversed by anti-MBL mAb treatment. However, MBL-null mice were not protected from secondary lung injury after GI/R. These data demonstrate that C2 and MBL, but not C1q, are necessary for gut injury after GI/R. Lung injury in mice after GI/R is MBL and C1q independent, but C2 dependent, suggesting a potential role for ficolins in this model.

Identification of in vitro protein biomarkers of idiosyncratic liver toxicity

Drug-induced idiosyncratic hepatotoxicity continues to be an important safety issue for the pharmaceutical industry. This toxicity is due, in part, to the limited predictive nature of current pre-clinical study systems. A hypothesis was formed that treatment of existing in vitro hepatocyte cultures with drugs clinically linked to idiosyncratic hepatotoxicity would result in the release of extracellular protein biomarkers indicative of liver toxicity. To test this hypothesis, a combination of proteomic and immunological techniques were used to first identify, and subsequently verify, components of the protein-laden conditioned culture media from immortalized human hepatocytes which overexpressed cytochrome p450 3A4. These cells were treated separately with seven individual compounds made up of a combination of thiazolidinedione and l-tyrosine PPARgamma agonists and HIV protease inhibitors, plus a vehicle control (dimethyl sulfoxide). For each drug class, clinically determined hepatotoxic and non-hepatotoxic compounds were compared. Two proteins, BMS-PTX-265 and BMS-PTX-837, were reproducibly and significantly increased in the conditioned media from cells treated with each of the toxic compounds as compared to media from cells treated with the non-toxic compounds (and vehicle). This result supported the hypothesis, and so a series of successive assays (western blots and enzyme linked immunosorbent assays) were used to measure the response of these two proteins as a function of an expanded set of 20 compounds. For all 20 drugs, elevations of BMS-PTX-265 correlated exactly with the known safety profile; whereas changes in BMS-PTX-837 correctly predicted the safety profile in 19 of 20 drugs (one false negative). In summary, the data supports both the pre-clinical in vitro method as a means to identify new biomarkers of liver toxicity, as well as the validity of the biomarkers themselves.

Adverse hepatic drug reactions: inflammatory episodes as consequence and contributor

Susceptibility to drug toxicity is influenced by a variety of factors, both genetic and environmental. The focus of this article is the evidence addressing the hypothesis that inflammation is both a result of and a susceptibility factor for drug toxicity, with an emphasis on liver as a target organ. Results of studies suggesting a role for inflammatory mediators in the hepatotoxicity caused by acetaminophen or ethanol are discussed. For several drugs, the evidence from animal models that concurrent inflammation increases injury is presented. In addition, the occurrence of adverse drug reactions in people with preexisting inflammatory diseases is considered. The special case of idiosyncratic drug reactions is discussed and the potential raised for development of animal models for this type of drug toxicity. The conclusion is that inflammatory factors should be considered as determinants of sensitivity to adverse drug reactions.

Animal models of idiosyncratic drug reactions

Idiosyncratic drug reactions represent a major problem. In most cases the mechanisms of these reactions are unknown, but circumstantial evidence points to the involvement of reactive metabolites and the characteristics of the reactions suggest involvement of the immune system. If progress is to be made in dealing with these adverse reactions it is essential that we have a better understanding of their mechanisms, and it is hard to imagine testing mechanistic hypotheses without good animal models. Unfortunately, idiosyncratic reactions are also idiosyncratic in animals so few good models exist. The best models, in which a rodent develops a clinical syndrome similar to that which occurs in humans, appear to be penicillamine-induced autoimmunity in Brown Norway rats and nevirapine-induced skin rash in rats. Sulfamethoxazole-induced hypersensitivity in dogs and propylthiouracil-induced autoimmunity in cats are also similar to adverse reactions that occur in people, but they have practical limitations. Halothane-induced liver toxicity in guinea pigs and amodiaquine-induced bone marrow and liver toxicity in rats represent models in which there is an immune response and mild, reversible toxicity. It is possible that the development of immune tolerance is what limits the toxicity in these models, and if this is true, interventions that prevent tolerance might lead to good models. Although the history of developing animal models of idiosyncratic drug reactions is mostly one of failure, such models are essential. A better understanding of immune tolerance may greatly facilitate the development of better models; transgenic technology may also provide an important tool.

ACETAMINOPHEN-INDUCED HEPATOTOXICITY

The analgesic acetaminophen causes a potentially fatal, hepatic centrilobular necrosis when taken in overdose. The initial phases of toxicity were described in Dr. Gillette's laboratory in the 1970s. These findings indicated that acetaminophen was metabolically activated by cytochrome P450 enzymes to a reactive metabolite that depleted glutathione (GSH) and covalently bound to protein. It was shown that repletion of GSH prevented the toxicity. This finding led to the development of the currently used antidote N-acetylcysteine. The reactive metabolite was subsequently identified to be N-acetyl-p-benzoquinone imine (NAPQI). Although covalent binding has been shown to be an excellent correlate of toxicity, a number of other events have been shown to occur and are likely important in the initiation and repair of toxicity. Recent data have shown that nitrated tyrosine residues as well as acetaminophen adducts occur in the necrotic cells following toxic doses of acetaminophen. Nitrotyrosine was postulated to be mediated by peroxynitrite, a reactive nitrogen species formed by the very rapid reaction of superoxide and nitric oxide (NO). Peroxynitrite is normally detoxified by GSH, which is depleted in acetaminophen toxicity. NO synthesis (serum nitrate plus nitrite) was dramatically increased following acetaminophen. In inducible nitric oxide synthase (iNOS) knockout mice, acetaminophen did not increase NO synthesis or tyrosine nitration; however, histological evidence indicated no difference in toxicity. Acetaminophen did not cause hepatic lipid peroxidation in wild-type mice but did cause lipid peroxidation in iNOS knockout mice. These data suggest that NO may play a role in controlling lipid peroxidation and that reactive nitrogen/oxygen species may be important in toxicity. The source of the superoxide has not been identified, but our recent finding that NADPH oxidase knockout mice were equally sensitive to acetaminophen and had equal nitration of tyrosine suggests that the superoxide is not from the activation of Kupffer cells. It was postulated that NAPQI-mediated mitochondrial injury may be the source of the superoxide. In addition, the significance of cytokines and chemokines in the development of toxicity and repair processes has been demonstrated by several recent studies. IL-1beta is increased early in acetaminophen toxicity and may be important in iNOS induction. Other cytokines, such as IL-10, macrophage inhibitory protein-2 (MIP-2), and monocyte chemoattractant protein-1 (MCP-1), appear to be involved in hepatocyte repair and the regulation of proinflammatory cytokines.