Halothane hepatitis: a model of immune mediated drug hepatotoxicity

Exogenous NADPH ameliorates myocardial ischemia-reperfusion injury in rats through activating AMPK/mTOR pathway

Our previous study shows that nicotinamide adenine dinucleotide phosphate (NADPH) plays an important role in protecting against cerebral ischemia injury. In this study we investigated whether NADPH exerted cardioprotection against myocardial ischemia/reperfusion (I/R) injury. To induce myocardial I/R injury, rats were subjected to ligation of the left anterior descending branch of coronary artery for 30 min followed by reperfusion for 2 h. At the onset of reperfusion, NADPH (4, 8, 16 mg· kg⁻¹· d⁻¹, iv) was administered to the rats. We found that NADPH concentrations in plasma and heart were significantly increased at 4 h after intravenous administration. Exogenous NADPH (8−16 mg/kg) significantly decreased myocardial infarct size and reduced serum levels of lactate dehydrogenase (LDH) and cardiac troponin I (cTn-I). Exogenous NADPH significantly decreased the apoptotic rate of cardiomyocytes, and reduced the cleavage of PARP and caspase-3. In addition, exogenous NADPH reduced mitochondrial vacuolation and increased mitochondrial membrane protein COXIV and TOM20, decreased BNIP3L and increased Bcl-2 to protect mitochondrial function. We conducted in vitro experiments in neonatal rat cardiomyocytes (NRCM) subjected to oxygen–glucose deprivation/restoration (OGD/R). Pretreatment with NADPH (60, 500 nM) significantly rescued the cell viability and inhibited OGD/R-induced apoptosis. Pretreatment with NADPH significantly increased the phosphorylation of AMPK and downregulated the phosphorylation of mTOR in OGD/R-treated NRCM. Compound C, an AMPK inhibitor, abolished NADPH-induced AMPK phosphorylation and cardioprotection in OGD/R-treated NRCM. In conclusion, exogenous NADPH exerts cardioprotection against myocardial I/R injury through the activation of AMPK/mTOR pathway and inhibiting mitochondrial damage and cardiomyocyte apoptosis. NADPH may be a potential candidate for the prevention and treatment of myocardial ischemic diseases.

The histopathological evaluation of drug-induced liver injury

Drug-induced liver injury (DILI) presents unique challenges to the pathologist. It is not only an uncommon reason for liver biopsy, but the pathology of DILI is spread across the entire spectrum of hepatic injury patterns. It is important for the pathologist to suspect DILI when the histological changes are unusual or out of synchronicity with the patient's history. A systematic evaluation approach will yield the most information. It begins with the characterization of the general pattern of injury which, for most cases, will be found in a handful of necroinflammatory and cholestatic patterns. A careful assessment of the severity of injury across the various anatomic compartments will provide information on the probable natural history of the injury. Correlation of liver injury with the patient's medication history and clinical findings will help to narrow the differential diagnosis, particularly when it is recognized that most drugs have a limited range of histological findings and vary in their propensity to cause injury. This review provides an overview of the assessment of the liver biopsy and its use to confirm or exclude particular drugs as contributing to the patient's liver injury.

Lost in Translation (LiT): IUPHAR Review 6

Translational medicine is a roller coaster with occasional brilliant successes and a large majority of failures. Lost in Translation 1 ('LiT1'), beginning in the 1950s, was a golden era built upon earlier advances in experimental physiology, biochemistry and pharmacology, with a dash of serendipity, that led to the discovery of many new drugs for serious illnesses. LiT2 saw the large-scale industrialization of drug discovery using high-throughput screens and assays based on affinity for the target molecule. The links between drug development and university sciences and medicine weakened, but there were still some brilliant successes. In LiT3, the coverage of translational medicine expanded from molecular biology to drug budgets, with much greater emphasis on safety and official regulation. Compared with R&D expenditure, the number of breakthrough discoveries in LiT3 was disappointing, but monoclonal antibodies for immunity and inflammation brought in a new golden era and kinase inhibitors such as imatinib were breakthroughs in cancer. The pharmaceutical industry is trying to revive the LiT1 approach by using phenotypic assays and closer links with academia. LiT4 faces a data explosion generated by the genome project, GWAS, ENCODE and the 'omics' that is in danger of leaving LiT4 in a computerized cloud. Industrial laboratories are filled with masses of automated machinery while the scientists sit in a separate room viewing the results on their computers. Big Data will need Big Thinking in LiT4 but with so many unmet medical needs and so many new opportunities being revealed there are high hopes that the roller coaster will ride high again.

Drug-induced autoimmune-like hepatitis

The clinical phenotype of classical autoimmune hepatitis can be mimicked by idiosyncratic drug-induced liver injury, and differentiation can be difficult. The goals of this review are to enumerate the major agents of drug-induced autoimmune-like hepatitis, describe the clinical findings and risk factors associated with it, detail the clinical tools by which to assess causality, discuss putative pathogenic mechanisms, and describe treatment and outcome. The frequency of drug-induced autoimmune-like hepatitis among patients with classical features of autoimmune hepatitis is 9%. Minocycline and nitrofurantoin are implicated in 90% of cases. Female predominance, acute onset, and absence of cirrhosis at presentation are important clinical manifestations. Genetic factors affecting phase I and phase II transformations of the drug, polymorphisms that protect against cellular oxidative stress, and human leukocyte antigens that modulate the immune response may be important pathogenic components. Clinical judgment is the mainstay of diagnosis as structured diagnostic methods for drug-induced liver injury are imperfect. The covalent binding of a reactive drug metabolite to a hepatocyte surface protein (commonly a phase I or phase II enzyme), formation of a neoantigen, activation of CD8 T lymphocytes with nonselective antigen receptors, and deficient immune regulatory mechanisms are the main bases for a transient loss of self-tolerance. Discontinuation of the offending drug is the essential treatment. Spontaneous improvement usually ensues within 1 month. Corticosteroid therapy is warranted for symptomatic severe disease, and it is almost invariably effective. Relapse after corticosteroid withdrawal probably does not occur, and its absence distinguishes drug-induced disease from classical autoimmune hepatitis.

Generation of T cell responses targeting the reactive metabolite of halothane in mice

Immune-mediated adverse drug reactions (IADRs) represent a significant problem in clinical practice and drug development. Studies of the underlying mechanisms of IADRs have been hampered by the lack of animal models. Halothane causes severe allergic hepatitis with clinical features consistent with an IADR. Our ultimate goal is to develop a mouse model of halothane hepatitis. Evidence suggests that adaptive immune responses targeting liver protein adducts of the reactive metabolite (trifluoroacetyl (TFA)) play an important role in the pathogenesis. The present study demonstrated that the combination of an anti-CD40 antibody (Ab) and a Toll-like receptor (TLR) agonist served as a potent adjuvant in generating TFA-specific T cell responses in mice. Both CD4(+) and CD8(+) subsets of T cells were activated and the TFA-specific responses were detected not only in the spleen but also in the liver of mice immunized with mouse serum albumin adducts of TFA (TFA-MSA) plus the combined CD40/TLR agonist. Whereas all three TLR agonists examined were effective in eliciting TFA-specific immune responses in BALB/cByJ mice, only polyI:C was effective in DBA/1 mice and none of the TLR agonists could aid the generation of TFA-specific T cells in C57BL/6J mice. This result, combined with our previous finding that BALB/cByJ mice were the most susceptible to halothane-induced acute liver injury, provides the basis for employing this strain in future studies. Collectively, our data demonstrated the successful completion of a crucial first step in the development of a murine model of halothane hepatitis.

Drug-induced liver injury

Many drugs and environmental chemicals are capable of evoking some degree of liver injury. The liver represents a primary target for adverse drug reactions due to its central role in biotransformation and excretion of foreign compounds, its portal location within the circulation exposing it to a wide variety of substances, and its anatomic and physiologic structure. Drug-induced liver injury (DILI) remains the single most common adverse indication leading to drug candidate failure or withdrawal from the market. However, the absolute incidence of DILI is low, and this presents a challenge to mechanistic studies. DILI remains unpredictable making prevention very difficult. In this chapter, we focus on the current understanding of DILI. We begin with an overview regarding the significance and epidemiology of DILI and then examine the clinical presentation and susceptibility factors related to DILI. This is followed by a review of the current literature regarding the proposed pathogenesis of DILI, which involves the participation of a drug, or most often a reactive metabolite of the drug, that either directly affects cellular function or elicits an immune response. It is our hope that this chapter will shed light on the major problems associated with DILI in regards to the pharmaceutical industry, drug regulatory agencies, physicians and pharmacists, and patients.

Retrospective study of post-anesthetic mild liver disorder associated with inhalation anesthetics, halothane and enflurane

The incidence of post-anesthetic mild liver disorder (PAMLD) was compared between 928 patients administered halothane and 1766 patients administered enflurane. They were selected from 19 504 surgical patients administered general anesthesia at Kyushu University Hospital over the past 6 years and 4 months. They had had normal liver function before operation and had no history of blood transfusion. Alanine aminotransferase (ALT) levels exceeding 70 IU. l(-1) within 180 days after operation were found in 226 patients in the halothane group (24.4%), and in 250 patients in the enflurane group (14.2%) ( P < 0.01). Both maximum ALT levels and duration of ALT elevation were higher and longer in the halothane group ( P < 0.01). These results suggest that, not only in the development of fulminant hepatitis but also in PAMLD, enflurane is less hepatotoxic than halothane.

Xenobiotic-induced hepatotoxicity: mechanisms of liver injury and methods of monitoring hepatic function

Xenobiotic-induced liver injury is a clinically important etiology of hepatic disease that, if not recognized, can lead to hepatic failure. In this article we discuss the mechanisms of xenobiotic-induced liver injury, various factors that can alter the risk and severity of injury, the clinical and laboratory manifestations of injury, and the methods used to detect the presence of injury and (or) functioning liver mass.

Halothane-induced liver injury in guinea-pigs: importance of cytochrome P450 enzyme activity and hepatic blood flow

The basis for susceptibility to halothane-induced liver necrosis in guinea-pigs was examined. In hepatic microsomes, the following were similar in susceptible and resistant animals: total cytochrome (CYP) P450 (P450), phenobarbital-inducible pathways of mixed function oxidation (androstenedione 6 beta- and 16 beta-hydroxylase activities) and the CyP2E1-catalysed pathway of N-nitrosodimethylamine N-demethylase activity. Similarly, immunohistochemical staining of CYP2E1 protein was equivalent in livers from susceptible and resistant guinea-pigs. Prior treatment with the P450-inhibitors, metyrapone and SKF-525A ameliorated halothane-induced liver damage in susceptible animals. Conversely, in resistant guinea-pigs, stimulation of hepatic CYP2E1 activity by treatment with 4-methylpyrazole produced severe hepatotoxicity after re-exposure to halothane. These results confirm the conclusions of others, that P450-mediated metabolism produces halothane-induced liver necrosis in the guinea-pig model but, as in other work, the data fail to explain why no difference in activity of these enzymes could be found between susceptible and resistant guinea-pigs. To establish whether a differential effect on hepatic blood flow between susceptible and resistant guinea-pigs could explain this paradox, studies were performed using a radiolabelled microsphere technique. The effect of halothane on lowering cardiac output was identical in both groups of animals and halothane significantly reduced hepatic arterial but not portal blood flow. The effect on arterial blood flow was more profound in susceptible guinea-pigs (0.67 +/- 0.17% of injected microspheres) than in resistant animals (0.99 +/- 0.13%; P < 0.005). It is concluded that P450-catalysed metabolism and reduced hepatic blood flow are both necessary to produce halothane-induced liver injury in susceptible guinea-pigs, but it is the effect of halothane on hepatic arterial blood flow that differs between susceptible and resistant animals.

Trifluoroacetylation potentiates the humoral immune response to halothane in the guinea pig

Halothane hepatitis appears to result from an inappropriate immune response to the products of halothane metabolism. Attempts to produce an animal model for halothane hepatitis have been largely unsuccessful. Although guinea pigs produce neoantigens following treatment with halothane, the subsequent antibody response is weak, possibly accounting for the failure to produce halothane hepatitis in these animals. In order to increase the antibody response to halothane neoantigens, three methods for trifluoroacetylating proteins were used. Guinea pigs were either treated with S-ethylthiotrifluoroacetate, autologous lymphocytes trifluoroacetylated ex vivo, or immunized with trifluoroacetylated mycobacterial protein, followed by exposure to halothane, and examined for anti-halothane metabolite antibodies (anti-TFA antibodies). Animals treated with S-ethylthiotrifluoroacetate developed anti-TFA antibodies, and following exposure to halothane exhibited an enhanced antibody response. Treatment with trifluoroacetylated lymphocytes also resulted in an enhanced anti-TFA antibody response following halothane exposure. Immunization with trifluoroacetylated mycobacterial proteins resulted in very high anti-TFA antibody titers. However, subsequent exposure to halothane had no observable effect on specific antibody titers. Exposure to halothane, regardless of treatment, resulted in the production of anti-microsomal protein antibodies. Signs of halothane hepatitis were not observed, indicating that enhancement of the humoral immune response does not appear to be sufficient for production of halothane hepatitis.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

Species variation in the bioactivation of tacrine by hepatic microsomes

1. The metabolite profile of tacrine (1,2,3,4-tetrahydro-9-amino acridine) was similar in hepatic microsomes from man, rat, dog, rabbit, mouse and hamster. Major metabolites were 1-, 2-, 4- and 7-OH tacrine. Only quantitative differences in metabolite profile were evident between species. 2. Bioactivation to protein-reactive metabolite(s) was seen in microsomes from all species. 3. 7-Methyl tacrine was found to undergo significantly less bioactivation than either 7-OH tacrine or tacrine itself. 4. In the presence of hepatic microsomes and thiol-containing agents protein-reactive metabolite formation was significantly reduced. With mercaptoethanol present a stable thioether adduct was generated from both tacrine and 7-OH tacrine. 5. Analysis of the thioether adduct by mass spectrometry yielded a molecular ion of m/z 290 consistent with the presence of a covalent adduct of 7-OH tacrine complexed in a 1:1 molar ratio with mercaptoethanol. 6. We have therefore provided further evidence for a two-step mechanism in the bioactivation of tacrine involving an initial 7-hydroxylation followed by a postulated 2-electron oxidation to yield a reactive quinone methide. This mechanism of bioactivation appears to be identical in human and animal hepatic microsomes.

Absence of anti-trifluoroacetate antibody after halothane anaesthesia in patients exhibiting no or mild liver damage

It has been shown that the circulating antibodies, which bind to rat hepatic microsomal proteins obtained after in vivo exposure to halothane, are detectable by immunoblotting in patients with "halothane hepatitis (HH)," and that rabbit immunized anti-sera against trifluoroacetylated rabbit serum albumin (TFA-RSA) recognizes rat microsomal distorted polypeptides in almost the same way as do sera from patients with HH. In this paper, we report first the development of a novel method of synthesizing TFA-RSA using p-nitrophenyl TFA, and second the results of tests for circulating anti-TFA antibodies in the serum of 86 patients who had received halothane anaesthesia and developed no (67 patients) or mild (19 patients, the maximum activity of serum alanine aminotransaminase 519 IU.L-1) liver damage. Serum was selected from stored sera of post-transfusion patients. The new method of synthesizing TFA-RSA was convenient and was able to be done at neutral pH. Rabbit sera obtained after immunization with the newly synthesized TFA-RSA recognized the same polypeptides (109 kDa, 92 kDa, 80 kDa, 76 kDa, 64 kDa and 59 kDa) as the established anti-sera against TFA-RSA, and these reactions were inhibited in the presence of TFA-lysine. Circulating antibodies were not detected in our patients who had developed no or mild liver damage. The present finding supports the hypothesis that the appearance of circulating antibodies against microsomal distorted proteins are specific to patients with HH. Furthermore, we have shown here that the halothane-induced mild increase in ALT activity is not associated with the appearance of those circulating antibodies, supporting the pathophysiological difference between HH and halothane-induced mild hepatic damage.

Association of anti-58 kDa endoplasmic reticulum antibodies with halothane hepatitis

We recently showed that when rats were administered the inhalation anesthetic halothane, a 58 kDa liver endoplasmic reticulum protein became covalently trifluoroacetylated by the trifluoroacetyl chloride metabolite of halothane. Although the 58 kDa protein showed 99% identity to that of the deduced amino acid sequence of a cDNA reported to correspond to phosphatidylinositol-specific phospholipase C-alpha, it did not have phosphatidylinositol-specific phospholipase C activity. It was concluded that the reported cDNA of phosphatidylinositol-specific phospholipase C-alpha actually encoded for the 58 kDa endoplasmic reticulum protein of unknown function. Other researchers have come to the same conclusion and have shown that the 58 kDa protein has protein disulfide-isomerase and protease activities. We now report that patients with halothane hepatitis have serum antibodies that react with both purified trifluoroacetylated and native rat liver 58 kDa proteins. These results suggest that when patients are exposed to halothane a human liver orthologue of the rat liver trifluoroacetylated-58 kDa protein is formed. In certain patients, this protein may become immunogenic and lead to the formation of specific antibodies and or specific T-cells, which may react with both trifluoroacetylated and native 58 kDa proteins, and ultimately be responsible, at least in part, for the hepatitis caused by halothane.

Halothane hepatitis patients have serum antibodies that react with protein disulfide isomerase

Clinical and laboratory evidence suggests that the fulminant liver failure sometimes associated with the inhalation anesthetic halothane may be an immune-mediated toxicity. Most importantly, the vast majority of patients with a clinical diagnosis of halothane hepatitis have serum antibodies, which react with one or more specific liver microsomal proteins that have been covalently altered by the trifluoroacetyl chloride metabolite of halothane. The serum antibodies are specific to halothane hepatitis patients and are not seen in sera of patients with other types of liver pathology. In this study, a 57-kD trifluoroacetylated liver microsomal neoantigen associated with halothane hepatitis and native 57-kD protein were purified from liver microsomes of halothane-treated and -untreated rats, respectively. When the purified trifluoroacetylated 57-kD and native 57-kD proteins were used as test antigens in an enzyme-linked immunosorbent assay, serum antibodies from halothane hepatitis patients (n = 40) reacted with both of these proteins to a significantly greater extent than did serum antibodies from control patients (n = 32). On the basis of its apparent monomeric molecular mass, isoelectric point and NH2-terminal amino acid and tryptic peptide sequences, the 57-kD protein has been identified as rat liver protein disulfide isomerase. Antibodies raised against rat liver protein disulfide isomerase also reacted with a protein of approximately 58-kD in human liver microsomes. The results of this investigation suggest that trifluoroacetylated protein disulfide isomerase is one of the immunogens associated with halothane hepatitis. In certain patients it might lead either to specific antibodies or, possibly, to specific T cells, which could be responsible for halothane hepatitis.

An investigation into the formation of stable, protein-reactive and cytotoxic metabolites from tacrine in vitro. Studies with human and rat liver microsomes

Tacrine (1,2,3,4-tetrahydro-9-aminoacridine hydrochloride; THA) is known to undergo extensive oxidative metabolism to a variety of mono- and dihydroxylated metabolites in animals and humans. The potential for tacrine to undergo metabolism to stable, protein-reactive and cytotoxic metabolites has been investigated in incubations with human and rat liver microsomes. Using lymphocytes as sensitive markers to quantify cytotoxicity, THA (50 microM) underwent NADPH-dependent bioactivation to a cytotoxic metabolite(s). NADPH-dependent cytotoxicity in the presence of rat and human microsomes was 9.8 +/- 3.1% (P < 0.05 cf. -NADPH control) and 6.2 +/- 2.0% (P < 0.05 cf. -NADPH control), respectively. Stable and protein-reactive metabolites were also formed in microsomes from both species. These accounted for 28.2 +/- 12.7% and 1.22 +/- 0.79% of incubated radioactivity in human microsomes and 6.4 +/- 2.2% and 0.4 +/- 0.1% of incubated radioactivity in rat microsomes. In microsomes pooled from six human livers the NADPH-dependent cytotoxicity was 9.4 +/- 1.1%. Formation of stable and protein-reactive metabolites accounted for 29.2 +/- 2.3% and 1.2 +/- 1.0% of incubated radioactivity. Reduced glutathione (500 microM) completely blocked NADPH-dependent cytotoxicity and inhibited protein-reactive metabolite formation by 60% (P < 0.05). Ascorbic acid (500 microM) inhibited the generation of cytotoxic and protein-reactive metabolites by 75% (P < 0.05) and 35% (P < 0.05), respectively. Cyclohexene oxide was without effect. Human serum albumin was found to protect the lymphocytes against toxicity. In microsomes prepared from the livers of four donors known to have been smokers there were no significant differences in the generation of metabolites from THA compared with microsomes prepared from livers of non-smokers. Enoxacin, a specific inhibitor of cytochrome P450 1A2 significantly inhibited all routes of THA metabolism. We have therefore demonstrated that THA may be oxidatively metabolized to stable, protein-reactive and cytotoxic metabolites in human and rat liver microsomes. A number of inhibitors may affect these process, whilst inhibition by enoxacin indicates a role for cytochrome P450 1A2 in THA metabolism.

The topography of trifluoroacetylated protein antigens in liver microsomal fractions from halothane treated rats

Sera from patients with halothane hepatitis contain immunoglobulin G (IgG) antibodies to trifluoroacetylated liver microsomal proteins of 100, 76, 59, 57 and 54 kDa, which are produced as a consequence of metabolism of halothane to trifluoroacetyl halide by cytochrome(s) P450. In the present study, the membrane topographies of the various antigens in rat liver microsomal fractions were investigated. Liver microsomal fractions from rats treated with halothane in vivo, and rat liver microsomal fractions which had been incubated with halothane in vitro, were used as the source of trifluoroacetyl antigens. The antigens were detected by immunoblotting. Whereas the 100, 76, 59 and 57 kDa antigens were solubilized from the microsomal membrane by either 0.1 M sodium carbonate or 0.1% (w/v) sodium deoxycholate, the 54 kDa antigen was not solubilized by 0.1% (w/v) sodium deoxycholate. In intact microsomal fractions, the 100, 76, 59 and 57 kDa antigens were not degraded appreciably by trypsin unless detergent was added to permeabilize the microsomal membrane. These results indicate that the 54 kDa antigen is an integral membrane protein, whereas the 100, 76, 59 and 57 kDa antigens are peripheral membrane proteins situated within the lumen of microsomal vesicles, and hence presumably located within the lumen of the endoplasmic reticulum in vivo.

Postoperative elevation of serum transaminases following isoflurane anesthesia

Halogenated inhalational anesthetics have been implicated in hepatotoxicity. Halothane hepatitis results from the biotransformation of the drug to a metabolite that binds to liver proteins, which creates a hapten, which, in turn, causes an immunologic response in the liver. Case reports of hepatic injury resulting from isoflurane, which has a decreased biotransformation compared with that of halothane, have received much criticism. We describe a patient who had elevated liver enzymes and a positive trifluoroacetyl antibody titer following an anesthetic regimen that included isoflurane.

Metabolism of ciamexon by human liver microsomes: an investigation into the formation of stable, chemically reactive and cytotoxic metabolites

1. The in vitro generation of stable, protein-reactive and cytotoxic metabolites from ciamexon by human liver microsomes has been assessed. Stable metabolites were characterized by h.p.l.c./mass spectrometry, protein reactive metabolites by radiometric analysis and cytotoxic metabolites by assessment of cell viability after exposure to metabolites formed in situ. 2. Human livers were obtained from renal transplant donors. All 16 livers investigated metabolized ciamexon in a NADPH-dependent reaction, the major metabolite being the 6-hydroxy-methyl derivative. The hydroxylase activity of the livers varied from 34-577 pmol mg-1 min-1, with a mean activity of 306 +/- 156 pmol mg-1 min-1. The further oxidation product, 6-carboxy ciamexon, was also detected in some incubations. A third, unidentified, polar metabolite was present in all incubations (3.34-11.11% of incubated radioactivity). 3. Only very low levels (less than 1%) of radioactivity became irreversibly bound to microsomal protein, which suggests that ciamexon undergoes little or no oxidative bioactivation in vitro. 4. Human liver microsomes did not metabolize ciamexon to a cytotoxic species, whereas microsomes prepared from mouse livers did generate a cytotoxic species. The degree of toxicity was enhanced if animals were pre-treated with either phenobarbitone or beta-naphthoflavone.

Drug-induced jaundice

A large number of drugs may be associated with impaired bile flow. Drug-associated cholestasis presents like other forms of cholestasis with pale stools, dark urine, pruritus and jaundice. Abdominal pain may be present in some instances and can be so severe as to lead to a false diagnosis of acute cholecystitis. Biochemically, drug-associated cholestasis resembles other forms of cholestasis although the presence of eosinophilia may suggest drug involvement. Many types of drug-induced cholestasis run a benign course with resolution of signs and symptoms within 3 months but occasionally the jaundice can take a year or more to resolve. Progression to cirrhosis is uncommon. Some patients may develop a syndrome resembling primary biliary cirrhosis. The mechanisms of drug-associated cholestasis are uncertain but may arise from alteration of bile formation within the hepatocyte or bile excretion at the level of the canaliculus or the extrahepatic ducts. Histological examination of the liver may be helpful in classifying the types of jaundice but the diagnosis of drug-induced cholestasis is usually one of temporal association and exclusion of other causes.

Human anti-endoplasmic reticulum antibodies in sera of patients with halothane-induced hepatitis are directed against a trifluoroacetylated carboxylesterase

Previous studies have demonstrated that patients with halothane-induced hepatitis have serum antibodies that are directed against novel liver microsomal neoantigens and have suggested that these neoantigens may play an immunopathological role in development of the patients' liver damage. These investigations have further revealed that the antibodies are directed against distinct polypeptide fractions (100 kDa, 76 kDa, 59 kDa, 57 kDa, 54 kDa) that have been covalently modified by the reactive trifluoroacetyl halide metabolite of halothane. In this paper, the trifluoroacetylated (TFA) 59-kDa neoantigen (59-kDa-TFA) recognized by the patients' antibodies was isolated from liver microsomes of halothane-treated rats by chromatography on an immunoaffinity column of anti-TFA IgG. Antibodies were raised against the 59-kDa-TFA protein and were used to purify the native protein from liver microsomes of untreated rats. Based upon its apparent monomeric molecular mass, NH2-terminal amino acid sequence, catalytic activity, and other physical properties, the protein has been identified as a previously characterized microsomal carboxylesterase (EC 3.1.1.1). A similar strategy may be used to purify and characterized neoantigens associated with other drug toxicities that are believed to have an immunopathological basis.

Evidence for expression in human liver of halothane-induced neoantigens recognized by antibodies in sera from patients with halothane hepatitis

Previous investigations have shown that antibodies in sera from patients with halothane hepatitis recognize neoantigens, expressed in livers of halothane-exposed rabbits and rats, which consist of a halothane metabolite bound covalently to specific microsomal proteins. These studies have suggested that the patients' antibodies may play a role in the pathogenesis of the hepatitis. In the present investigation, human liver biopsy samples were analyzed using an immunoblotting method to seek evidence for expression of halothane-induced neoantigens in humans. Sera from four patients with halothane hepatitis, which recognized halothane-induced rabbit liver neoantigens of 100, 76 and 57 kD, reacted strongly with antigens of very similar molecular weights that were expressed in livers from two patients who had died of cardiac failure following recent anesthesia with halothane. The antigens were not expressed in normal human liver or in livers from three patients who died of cardiac failure following anesthesia with agents other than halothane. The human antigens were not recognized by antibodies present in various control sera. Recognition of the 100- and 76-kD human antigens by the patients' antibodies was greatly reduced by absorption of sera with liver microsomes from halothane-exposed rabbits, but not by absorption of sera with control rabbit microsomes. These results indicate that humans exposed to halothane express liver neoantigens which are analogous to the halothane metabolite-protein neoantigens characterized previously in halothane-exposed animals.