Conjugation of dinitrofluorobenzene to plasma proteins in vivo in the rat

The extent of protein dinitrophenylation was determined in plasma and other tissues of anesthetized rats after administration of the model immunogen [3H]dinitrofluorobenzene (DNFB) (25 mg/kg; 5-25 microCi). DNFB was given by the intravenous, intraportal, intramuscular, or oral route. Irreversible binding was determined radiometrically after exhaustive solvent extraction of plasma or organ proteins. The extent of binding was high in plasma after parenteral administration (approximately 1% dose/ml plasma), but less (approximately 0.1% dose/ml) if DNFB was given orally. Low levels of radioactivity were bound irreversibly in liver (0.01-0.13% dose/g) and kidney (0.03-0.10% dose/g) and only residual amounts in other organs. Western blotting was used to identify target proteins in plasma, liver, and kidney using a specific antidinitrophenyl antiserum. No dinitrophenylation could be detected in liver or kidney samples, but strong recognition of two protein bands was observed in plasma. Bands with the same apparent molecular masses (67 and 44 kDa) were seen when DNFB was incubated with rat plasma in vitro. Preliminary evidence for these proteins being albumin and alpha 1-acid glycoprotein, respectively, is presented. The latter may be important for interindividual variability in immune responsiveness, because it is an acute phase protein whose levels fluctuate widely during disease states.

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.

The calcium-binding protein calreticulin is covalently modified in rat liver by a reactive metabolite of the inhalation anesthetic halothane

A general procedure is presented for the isolation of several liver microsomal target proteins of the reactive trifluoroacetyl halide metabolite of halothane. It was found that most of these proteins could be selectively extracted from microsomes with 0.1% sodium deoxycholate and separated into partially purified fractions by DEAE-Sepharose anion-exchange chromatography. Using this method, we describe the isolation and identification of a 63-kDa target protein of halothane in rat liver. Amino acid sequences of the N-terminal and of several internal peptides of the protein, as well as the deduced amino acid sequence of a nearly full-length rat liver cDNA clone of the protein, showed 98% identity with a reported murine cDNA that encodes for calreticulin, a major calcium-binding protein of the lumen of endoplasmic reticulum. Although it remains to be determined what role calreticulin has in the development of halothane hepatitis, this study has shown that calreticulin can be a target of reactive metabolites of xenobiotics.

Factors affecting the expression of trifluoroacetylated liver microsomal protein neoantigens in rats treated with halothane

Previous studies have shown that antibodies in the sera of halothane hepatitis patients recognize trifluoroacetylated liver microsomal proteins (neoantigens) of 100 kDa, 76 kDa, 59 kDa, 57 kDa, and 54 kDa. In the present investigation, factors that might affect the level of expression of the neoantigens were investigated. A study of the time course of neoantigen expression in halothane-treated rats revealed that the 100 kDa, 76 kDa, 59 kDa, and 57 kDa neoantigens were longer-lived than the 54 kDa neoantigen and could be detected in the liver up to a week after the administration of halothane. Pretreatment of rats with isoniazid, which is known to induce cytochrome P-450 IIE1, appeared to increase the expression of each of the neoantigens, whereas inducers of several other forms of cytochrome P-450 had either very little effect or decreased the expression of several of the neoantigens. Female rats appeared to express some of the neoantigens at a higher level than that found in males. Examination of the organ distribution of the trifluoroacetylated neoantigens showed that, of the tissues examined, only the liver contained appreciable levels of the neoantigens. These results indicate that the level of expression and possibly the immunogenicity of the trifluoroacetylated liver neoantigens may be influenced by their half-lives and the repertoire of cytochrome P-450 present in the liver.

Antibody assays for the detection of patients sensitized to halothane

Sera from patients with a clinical diagnosis of halothane hepatitis have been shown to contain antibodies that react with liver microsomal proteins (100, 76, 59, 57, and 54 kDa) covalently altered by the trifluoroacetyl (TFA) halide metabolite of halothane. In the present study, rapid and sensitive enzyme-linked immunosorbent assays for the detection of these antibodies have been evaluated. A recently described method that utilizes TFA-rabbit serum albumin as test antigen was studied employing a large population of halothane hepatitis and control patients. Several problems were discovered with the assay that were not previously recognized. The assay was then compared directly with methods that utilize as test antigens either liver microsomes or purified TFA proteins from halothane-treated rats. Sixty-seven percent of patients with a clinical diagnosis of halothane hepatitis tested positive for antibodies when the test antigens were either TFA-rabbit serum albumin or liver microsomes. This value was increased to 79% when the purified TFA-57 kDa, TFA-76 kDa, and TFA-100 kDa proteins were used as test antigens. These results indicate that the specificity and sensitivity of enzyme-linked immunosorbent assay methods for the detection of patients' antibodies may be increased significantly by utilizing the purified TFA microsomal proteins as test antigens.

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.

Enflurane metabolism produces covalently bound liver adducts recognized by antibodies from patients with halothane hepatitis

The existence of a rare syndrome of "enflurane hepatitis" similar to that described for halothane and of a cross-sensitization between halothane and enflurane has been controversial, largely due to equivocal clinical case reports and a lack of a plausible molecular mechanism for the hepatotoxicity. The present study suggests a possible hypersensitivity basis for enflurane hepatitis and the apparent cross-sensitization between halothane and enflurane involving covalently bound liver microsomal adducts. Immunoblotting studies have revealed that antibodies in the sera of six patients with halothane hepatitis recognize liver microsomal antigens of Mr = 100,000, or both 100,000 and 76,000, formed in rats treated with enflurane or halothane. These antigens were not detected in microsomes from isoflurane- or sesame oil-treated rats. The recognition of these antigens could be abolished by preincubation of the sera with microsomes from halothane-treated rats. These data suggest that the difluoromethoxydifluoroacetyl halide metabolite of enflurane, as well as the trifluoroacetyl halide metabolite of halothane, covalently bind to similar hepatic proteins, and may become immunogens in susceptible patients. This mechanism may also account for the apparent cross-sensitization between halothane and enflurane anesthesia, and the development of hepatic necrosis.

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.

Metabolic basis for a drug hypersensitivity: antibodies in sera from patients with halothane hepatitis recognize liver neoantigens that contain the trifluoroacetyl group derived from halothane

Previous studies have demonstrated that antibodies in sera from patients with halothane hepatitis recognize halothane-induced liver microsomal polypeptide neoantigens, and have suggested that these antibodies may play a role in the pathogenesis of the hepatitis. In the present study, the mechanism of neoantigen generation was investigated. Liver microsomes from rats treated in vivo with halothane or deuterated halothane were tested by immunoblotting for reactivity with patients' sera and with an antiserum specific for the covalently bound trifluoroacetyl (TFA) halide metabolite of halothane. Rat liver microsomes incubated aerobically or anaerobically with halothane or deuterated halothane in vitro, +/- NADPH and/or NADH, were also analyzed. The results obtained demonstrate that neoantigen expression involves oxidative halothane metabolism by cytochromes P-450 to TFA halide and covalent binding of the TFA group to the proteins. Incubation of microsomes from halothane-treated rats with 1 M piperidine cleaved the TFA groups from the proteins and abolished antigenicity, confirming this conclusion. Recognition of the neoantigens by the patients' antibodies was inhibited only partially using the hapten derivative N-E-TFA-L-lysine. It appears that the patients' antibodies recognize epitopes consisting of the TFA group plus associated structural features of the protein carriers (100 kDa, 76 kDa, 59 kDa, 57 kDa and 54 kDa), not the TFA hapten alone. To our knowledge, this constitutes the first characterization of drug metabolite-tissue protein neoantigens implicated in a drug hypersensitivity. The approach described may be of general utility for characterization of drug-induced neoantigens associated with other drug hypersensitivities.

Measurement of ferritin in serum by an indirect competitive enzyme-linked immunosorbant assay

This indirect competitive enzyme-linked immunosorbant assay (ELISA) for ferritin, unlike other currently available ELISAS, does not require use of an anti-ferritin antibody-enzyme conjugate. Designed for use on microtiter plates, the method has a precision and sensitivity similar to those of other immunoassays. The detection limit is 20 pg of ferritin per test (corresponding to 2.0 micrograms/L in serum samples). Comparison of results obtained on serum from 57 patients by this method with those from a conventional radioimmunoassay gave a correlation coefficient of 0.92.

Measurement of ferritin in serum by an indirect competitive enzyme-linked immunosorbant assay

This indirect competitive enzyme-linked immunosorbant assay (ELISA) for ferritin, unlike other currently available ELISAS, does not require use of an anti-ferritin antibody-enzyme conjugate. Designed for use on microtiter plates, the method has a precision and sensitivity similar to those of other immunoassays. The detection limit is 20 pg of ferritin per test (corresponding to 2.0 micrograms/L in serum samples). Comparison of results obtained on serum from 57 patients by this method with those from a conventional radioimmunoassay gave a correlation coefficient of 0.92.

Potential metabolic basis for enflurane hepatitis and the apparent cross-sensitization between enflurane and halothane

Clinical case reports of unexplained hepatic dysfunction following enflurane and isoflurane anesthesia led to the hypothesis that oxidative metabolism of these drugs by cytochromes P-450 produces immunoreactive, covalently bound acylated protein adducts similar to those implicated in the genesis of halothane-induced hepatic necrosis. Microsomal adducts were detected by enzyme-linked immunosorbent assay and immunoblotting techniques utilizing specific anti-trifluoroacetyl (TFA) IgG hapten antibodies in rat liver following enflurane, isoflurane, or halothane administration. Preincubation of the antibodies with microsomes from halothane-pretreated rats or with 500 microM TFA-lysine, markedly inhibited adduct recognition, while preincubation with 500 microM acetyllysine had no effect. The relative amounts of immunoreactive protein adducts formed were halothane much greater than enflurane much greater than isoflurane and correlates directly with the relative extents of metabolism of these agents. These results support the view that acyl metabolites of the volatile anesthetics may become covalently bound to hepatic proteins, thus serving as antigens, and thereby account for the apparent cross-sensitization and idiosyncratic hepatotoxicity reported for these drugs.

Specific antibodies to halothane-induced liver antigens in halothane-associated hepatitis

Antibodies to halothane-altered liver cell determinants (halothane antibodies) have previously been detected in serum of patients with fulminant hepatic failure after halothane anaesthesia. However, their diagnostic value has not been reported in patients with non-fulminant hepatitis. Sera from 39 patients who developed hepatitis following halothane anaesthesia between January 1983 and December 1985 were tested for antibodies to halothane-induced liver antigens using an ELISA; 22 of these patients had hepatitis without encephalopathy. Nineteen of the sera were from patients anaesthetized during 1985; four of the patients were aged 15 yr or less. All patients had undergone previous anaesthesia 17 days to 13 yr (median 3 yr) earlier. In 19 of the patients the final operation was a minor surgical procedure, lasting less than 45 min. In 13 patients a previous adverse reaction to halothane was documented in the case records. Twelve of the patients died. Halothane antibodies were detected in 12 of the 16 (75%) patients with hepatic encephalopathy and 16 of the 23 (70%) who did not develop encephalopathy, demonstrating that halothane antibodies are detectable in a wider spectrum of halothane-associated liver damage than previously appreciated.

Identification by immunoblotting of three halothane-induced liver microsomal polypeptide antigens recognized by antibodies in sera from patients with halothane-associated hepatitis

Previous studies have demonstrated that sera from patients with severe liver damage after halothane anesthesia ("halothane hepatitis") contain antibodies reacting with novel antigenic determinants expressed on hepatocytes from rabbits exposed previously to halothane. To determine the structure of the halothane-induced antigen(s), immunoblotting experiments were performed using patient sera and rabbit liver subcellular fractions. Three polypeptide antigens (Mr 100,000, 76,000 and 57,000) expressed in liver fractions from animals sacrificed 16 hr after exposure to 1% halothane in oxygen for 45 min, but not in fractions from unexposed animals, were identified. Analysis of fractions prepared by differential and sucrose density gradient centrifugation, and characterized by enzyme marker analysis, localized all three antigens to a microsomal subfraction relatively enriched in glucose-6-phosphatase activity, therefore, presumably derived from the endoplasmic reticulum. Antibodies to these antigens were detected in 19 of 24 sera from patients with halothane hepatitis, and four distinct patterns of antibody specificity were observed: 100,000 + 76,000 (seven patients), 100,000 alone (seven patients), 76,000 alone (three patients) and 57,000 alone (two patients). Such antibodies were not detectable in sera from 24 normal blood donors or 36 control patients. Thus, halothane induces expression of three distinct polypeptide antigens in liver, and patients with halothane hepatitis differ in patterns of recognition of these antigens by circulating antibodies.

Halothane hepatitis in children

It is often stated that halothane hepatitis in children is nonexistent or extremely rare. This syndrome occurred in seven children aged between 11 months and 15 years, one of whom, a 3 1/2 year old boy, died with fulminant hepatic failure. All the children had received multiple halothane anaesthetics (range 2-6, median 3). In all cases other causes of liver diseases were excluded, and in all but one the diagnosis was confirmed serologically by antibodies to halothane altered liver cell membrane antigens. These findings suggest that halothane hepatitis occurs in children, and the risk of halothane hepatitis should therefore be considered when choosing which agents to use in children who require multiple anaesthetics.

Halothane hepatitis: attempt to develop an animal model

Patients with liver damage following halothane anaesthesia (halothane hepatitis) have circulating antibodies reacting with plasma membrane determinants present on hepatocytes isolated from rabbits previously exposed to halothane. In an attempt to develop an animal model of halothane hepatitis, rabbits were immunised with hepatocytes isolated from litter mates previously exposed to halothane; this resulted in the generation of antibodies to both normal and halothane related liver cell determinants detected by both immunofluorescence and indirect cytotoxicity. Exposure of these immunised rabbits to halothane resulted in the disappearance of the halothane-related antibody, presumably due to its reaction with the liver-cell membrane halothane-related antigen; this, however, could not be proved since immunisation with halothane hepatocytes induced the presence of antibodies on the recipient hepatocytes. Although both human and rabbit lymphocytes were directly cytotoxic in vitro to these antibody coated hepatocytes, no evidence of liver damage could be detected. Thus, if immune mechanisms are involved in the pathogenesis of halothane hepatitis, other factors, probably related to idiosyncratic host immune responses, must be implicated.

Halothane-associated liver damage and renal failure in a young child

A case of halothane-associated liver damage and renal failure is described in an 18-month-old girl after her third halothane anaesthetic. There had been two uneventful enflurane anaesthetics. The diagnosis was confirmed by detecting antibodies specific for halothane-associated liver failure using a recently developed enzyme-linked immunosorbent assay.

Methods for reducing non-specific antibody binding in enzyme-linked immunosorbent assays

Enzyme-linked immunosorbent assays were used to study (i) binding of rabbit antibodies (raised against litter mate liver plasma membrane fraction) to the immunizing membrane fraction, and (ii) binding of human antibodies to liver membrane fractions and to liver-specific lipoprotein (a liver membrane-derived antigen complex). When assays were conducted using the non-ionic detergent Tween 20 as blocking agent, high non-specific binding was encountered. With the low titre rabbit antisera high binding of non-immune test antibody and of second antibody (anti-rabbit IgG) to the immunogen, and also directly to the solid phase, was found. This was abolished by replacement of Tween 20 in the antibody diluent buffers by a non-reactive protein, casein proving to be a more effective blocking agent than either bovine serum albumin or gelatin. With human sera, high binding of human IgG to the solid phase was noted. This too was blocked by casein, but only when the anti-microbial agent Thimerosal was included in the casein buffer, and when Tween 20 in the wash buffer was replaced by casein-Thimerosal so that the solid phase was exposed to casein before incubation with the test serum. The casein buffers described may prove of general value in solid-phase assays where high non-specific binding is encountered.