Immunogenic properties of rapidly digested food proteins following gavage exposure of mice: a comparison of ovalbumin with a potato acid phosphatase preparation

The ability of food proteins to resist digestion in simulated gastric fluid (SGF) correlates with allergenic potential. The purpose of the current investigations was to determine whether this association is due solely to the failure of unstable proteins to elicit an immune response when administered orally. We have examined immune responses induced in BALB/c mice by gavage administration of ovalbumin (OVA) and a crude potato protein extract (PPE) containing acid phosphatase activity. The stability of OVA and PPE in SGF was measured using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The ability of these proteins to stimulate specific IgG and IgE antibody production in mice following parenteral (intraperitoneal; ip) or oral (gavage) exposure was compared using enzyme-linked immunosorbent and homologous passive cutaneous anaphylaxis assays, respectively. Both OVA and PPE induced specific IgG antibody responses when administered either by gavage or by ip injection. Parenteral, but not gavage, exposure to OVA was associated with robust IgE antibody responses. Administration of PPE failed to stimulate strong IgE production via either route of exposure. Differential stability in SGF was observed, with PPE being digested extremely rapidly (within 1 min), whereas OVA was more resistant. The strong association reported by others between stability in SGF and allergenic potential is unlikely to be solely due to orally-ingested labile proteins failing to provoke immune responses due to degradation in the stomach.

Interindividual variability in P450-dependent generation of neoantigens in halothane hepatitis

Halothane hepatitis occurs because susceptible patients mount immune responses to trifluoroacetylated protein antigens, formed following cytochrome P450-mediated bioactivation of halothane to trifluoroacetyl chloride. In the present study, an in vitro approach has been used to investigate the cytochrome P450 isozyme(s) which catalyze neoantigen formation and to explore the protective role of non-protein thiols (cysteine and reduced glutathione). Significant levels of trifluoroacetyl protein antigens were generated when human liver microsomes, and also microsomes from livers of rats pre-treated with isoniazid, phenobarbital or beta-naphtoflavone, were incubated with halothane plus a nicotinamide adenine dinucleotidephosphate (NADPH) generating system. Immunoblotting studies revealed that the major trifluoroacetyl antigens expressed in vitro exhibited molecular masses of 50-55 kDa and included 60 and 80 kDa neoantigens recognized by antibodies from patients with halothane hepatitis. Much lower concentrations of halothane were required to produce maximal antigen generation in isoniazid-induced rat microsomes, as compared with phenobarbital or isosafrole-induced microsomes (0.5 vs 12.5 microl/ml). In isoniazid-induced microsomes, antigen generation was inhibited > 90% by the nucleophiles cysteine and glutathione and by the CYP2E1-selective inhibitors diallylsulfide and p-nitrophenol, but was unaffected by inhibitors of other P450 isozymes (furafylline, sulfaphenazole or triacetyloleandomycin). Neoantigen formation in six human liver microsomal preparations was inhibited in the presence of diallylsulfide, but not by furafylline, sulfaphenazole or triacetyloleandomycin, and exhibited marked variability which correlated with CYP2E1 levels. These results suggest that the balance between metabolic bioactivation by CYP2E1 and detoxication of reactive metabolites by cellular nucleophiles could be an important metabolic risk factor in halothane hepatitis.

Gallstones and isoflurane hepatitis

This report is of a case of a previously fit 65-year-old woman who developed postoperative liver dysfunction following an anaesthetic involving isoflurane. Biliary ultrasound demonstrated gallstones. However, serum antibodies to trifluoroacetylated proteins were detected, suggesting that immune sensitisation to the anaesthetic could have contributed to the impaired liver function.

Immunochemical identification of hepatic protein adducts derived from estragole

Hepatic protein adducts derived from the allylbenzene food flavor estragole, which is hepatocarcinogenic when given to rodents at high doses, have been identified using immunochemical approaches. Male Fischer 344 rats were given estragole orally and hepatic protein adducts were detected by immunoblotting, using antisera raised by immunizing rabbits with 4-methoxycinnamic acid-modified rabbit serum albumin. A major 155-kDa adduct was expressed in livers of animals that had been treated with estragole at 100, 300, or 500 mg/kg. Levels of expression of the adduct increased disproportionately with respect to dose, and other adducts (170, 100, 44, and 35 kDa) were detected also in the high-dose group. Rats given estragole for 5 days, at 300 mg/kg/day, expressed predominantly 155- and 44-kDa adducts. The 155-, 100-, 44-, and 35-kDa adducts were detected in greatest abundance in liver microsomal fractions, while the 170-kDa adduct was most abundant in the nuclear fraction. Interestingly, whereas the 170-, 155-, 100-, and 35-kDa adducts were detected in cytosolic fractions, relatively low levels of the 44-kDa adduct were detected in nuclear fractions but not in cytosolic fractions. The various adducts were solubilized when microsomal fractions were extracted with sodium carbonate and were digested by trypsin. This implies that the target proteins are peripheral membrane proteins bound to the outer surface of microsomal membranes. Experiments undertaken with isolated rat hepatocytes and with V79 cells transfected with human monoamine phenol sulfotransferase cDNA revealed that adduct formation required 1'-hydroxylation of estragole, followed by sulfation. The pattern of adducts expressed when the transfected V79 cells were incubated with 1'-hydroxyestragole was very similar to that expressed in livers of estragole-treated rats. These cells should constitute a valuable in vitro model system for investigation of toxicological consequences arising from estragole-induced protein adduct formation.

Cytochrome P450 mediated bioactivation of methyleugenol to 1'-hydroxymethyleugenol in Fischer 344 rat and human liver microsomes

Cytochrome P450 mediated metabolism of methyleugenol to the proximate carcinogen 1'-hydroxymethyleugenol has been investigated in vitro. Kinetic studies undertaken in liver microsomes from control male Fischer 344 rats revealed that this reaction is catalyzed by high affinity (Km of 74.9 +/- 9.0 microM, Vmax of 1.42 +/- 0.17 nmol/min/nmol P450) and low affinity (apparent Km several mM) enzymic components. Studies undertaken at low substrate concentration (20 microM) with microsomes from livers of rats treated with the enzyme inducers phenobarbital, dexamethasone, isosafrole and isoniazid indicated that a number of cytochrome P450 isozymes can catalyze the high affinity component. In control rat liver microsomes, 1'-hydroxylation of methyleugenol (assayed at 20 microM substrate) was inhibited significantly (P < 0.05) by diallylsulfide (40%), p-nitrophenol (55%), tolbutamide (30%) and alpha-naphthoflavone (25%) but not by troleandomycin, furafylline, quinine or cimetidine. These results suggested that the reaction is catalyzed by CYP 2E1 and by another as yet unidentified isozyme(s) (most probably CYP 2C6), but not by CYP 3A, CYP 1A2, CYP 2D1 or CYP 2C11. Administration of methyleugenol (0-300 mg/kg/day for 5 days) to rats in vivo caused dose-dependent auto-induction of 1'-hydroxylation of methyleugenol in vitro which could be attributed to induction of various cytochrome P450 isozymes, including CYP 2B and CYP 1A2. Consequently, high dose rodent carcinogenicity studies are likely to over-estimate the risk to human health posed by methyleugenol. The rate of 1'-hydroxylation of methyleugenol in vitro in 13 human liver samples varied markedly (by 37-fold), with the highest activities being similar to the activity evident in control rat liver microsomes. This suggests that the risk posed by dietary ingestion of methyleugenol could vary markedly in the human population.

Immunochemical identification of mouse hepatic protein adducts derived from the nonsteroidal anti-inflammatory drugs diclofenac, sulindac, and ibuprofen

Reactive metabolite-modified hepatic protein adducts have been proposed to play important roles in the mechanism(s) of hepatotoxicity of nonsteroidal anti-inflammatory drugs (NSAIDs). In the present study, immunochemical techniques have been used to compare the patterns of drug-protein adducts expressed in livers of mice given single doses of one or other of three different NSAIDs. These were diclofenac and sulindac, which are widely used but potentially hepatotoxic drugs, and ibuprofen, which is considered to be nonhepatotoxic. Specific polyclonal antisera were produced by immunization of rabbits with conjugates prepared by coupling each of the NSAIDs to the carrier protein keyhole limpet hemocyanin. Immunoblotting studies revealed dose-dependent formation of major 110 kDa polypeptide adducts in livers from mice sacrificed 6 h after administration of single doses of either diclofenac (0-300 mg/kg) or sulindac (0-100 mg/kg). Lower levels of several other adducts, of 140 and 200 kDa, were also expressed in livers from these animals. In contrast, livers from mice treated with ibuprofen (0-200 mg/kg) predominantly expressed a 60 kDa adduct and only relatively low levels of a 110 kDa adduct. The various adducts were shown by differential centrifugation to be concentrated in the nuclear fraction of liver homogenates. Those derived from diclofenac and sulindac were further localized, by Percoll density gradient centrifugation, to a subfraction which contained a high activity of the bile canalicular marker enzyme alkaline phosphatase. This suggests that they are concentrated in the bile canalicular domain of hepatocytes. The different patterns of adduct formation raise the possibility that formation of certain NSAID protein adducts, particularly 110 kDa adducts, has toxicological significance.

Cytochrome P450 2E1 is a cell surface autoantigen in halothane hepatitis

Recent studies have shown that cytochrome P450 2E1 (CYP2E1) is a major catalyst of formation of trifluoroacetylated proteins, which have been implicated as target antigens in the mechanism of halothane hepatitis. In the present investigation, trifluoroacetylated CYP2E1 was detected immunochemically in livers of rats treated with halothane. Furthermore, high levels of autoantibodies that recognized purified rat CYP2E1 but not purified rat CYP3A were detected by enzyme-linked immunosorbent assay in 14 of 20 (70%) sera from patients with halothane hepatitis. Only very low levels of such antibodies were detected in sera from healthy controls, from patients anesthetized with halothane without developing hepatitis, or from patients with other liver diseases. The intracellular distribution of CF3CO-adducts was studied in highly differentiated FGC4 rat hepatoma cell cultures. High levels of adducts were found after 22-hr culture in the presence of halothane, and their generation was dependent on the expression of CYP2E1. Adducts were predominantly located in the endoplasmic reticulum but also, to a minor extent, on the cell surface, as detected by immunofluorescence. A very similar distribution was found for CYP2E1 in FGC4 cells, and immunoprecipitation experiments performed in cultures of FGC4-related Fao hepatoma cells suggest that surface immunoreactivity originates from a small fraction of intact CYP2E1 apoprotein. Human CYP2E1, expressed in V79 cells after cDNA transfection, was also detected to a minor extent in the plasma membrane, whereas no immunofluorescence was evident in parental V79 cells. It is suggested that immune responses to cell surface CYP2E1 could be involved in the pathogenesis of halothane hepatitis.

Sevoflurane degradation by soda lime in a circle breathing system

Sevoflurane is degraded by soda lime to a vinyl ether commonly referred to as compound A. We measured the concentration of compound A in the circle breathing system of 31 patients receiving sevoflurane anaesthesia. Inspiratory and expiratory gas samples were analysed using gas chromatography and flame ionisation detection. The end-tidal sevoflurane concentration and soda lime temperature were recorded. The peak compound A concentration ranged between 10 to 32 ppm in the inspiratory limb and 7 to 26 ppm in the expiratory limb. There was a positive correlation between the peak compound A concentration and the end-tidal sevoflurane concentration (r2 = 0.545, p < 0.0001) and the soda lime temperature (r2 = 0.301, p = 0.0014). We conclude that the end-tidal concentration of sevoflurane and the temperature of the soda lime are important variables in determining concentration of compound A in a circle system.

Immunochemical detection of covalently modified protein adducts in livers of rats treated with methyleugenol

Methyleugenol is an allylbenzene food flavoring which has been shown to form DNA and protein adducts, and to cause hepatotoxicity and carcinogenicity in rodents. In order to investigate the nature of the protein adducts, specific antisera were raised by immunizing rabbits with conjugates prepared by coupling 1'-acetoxymethyleugenol, or its acidic congener 3,4-dimethoxycinnamic acid, to rabbit serum albumin (RSA). These polyclonal antisera were shown by enzyme linked immunosorbent assay (ELISA) to contain antibodies which recognized the 3,4-dimethoxyphenyl ring portion of methyleugenol. Analysis of livers from rats given methyleugenol i.p. for 5 days, at doses between 10 and 300 mg/kg/day, revealed dose-dependent formation of novel protein adducts which were recognized by the antisera. The adducts were detected by ELISA and by immunoblotting and were concentrated in the microsomal fraction, and were shown in inhibition studies to be derived from methyleugenol. A 44 kDa adduct was the only protein adduct detected in livers of rats given low loses of methyleugenol (10 or 30 mg/kg/day) and was the major adduct detected in rats given high doses of the compound (100 and 300 mg/kg/day). This adduct was solubilized when microsomal fractions were extracted using 0.1 M sodium carbonate, implying that it is a peripheral membrane protein. A pattern of protein adducts which mirrored the in vivo situation was generated when rat hepatocytes were incubated with 1'-hydroxymethyleugenol in vitro, but could not be reproduced in experiments undertaken using liver microsomes or postmitochondrial supernatants. These findings imply that generation of protein adducts in livers of rats given methyleugenol in vivo proceeds via the 1'-hydroxy metabolite and requires crucial cofactors, and/or structural features, which are present in intact hepatocytes but not in broken cell preparations and which remain to be defined.

Detection of autoantibodies directed against human hepatic endoplasmic reticulum in sera from patients with halothane-associated hepatitis

1. Previous studies have demonstrated the presence of antibodies to trifluoroacetylated hepatic proteins (TFA-proteins) in sera from patients with the severe form of halothane-associated hepatitis (halothane hepatitis). The TFA-proteins are produced via cytochrome P450-mediated metabolism of halothane to the reactive species TFA-chloride. 2. To investigate the presence of autoantibodies (which recognize various non-TFA-modified human hepatic polypeptides) in patients with halothane hepatitis immunoblotting experiments were performed using microsomal fractions prepared freshly from livers of five different (halothane-free) tissue donors. Blots were developed using 15 well-characterised sera from patients with halothane hepatitis. 3. Autoantibodies to human hepatic polypeptides were detected in most, but not all, of the patients' sera. The pattern of antibody reactivity varied markedly between sera. Although no common pattern of antibody recognition was observed, polypeptides of molecular mass between 60 and 80 kDa were the predominant targets. A similar protein recognition pattern was seen when each positive serum was tested against the five individual human liver samples. 4. Such autoantibodies were not detected in sera from 16 normal human blood donors, but were detected in three of six sera from patients exposed to halothane without developing hepatitis. 5. The autoantibodies are thought to arise in patients exposed to halothane as a consequence of a halothane-induced immune response to chemically-modified proteins. Such antibodies could contribute to the complex pathological processes involved in halothane hepatitis.

The lipoic acid containing components of the 2-oxoacid dehydrogenase complexes mimic trifluoroacetylated proteins and are autoantigens associated with halothane hepatitis

Anti-CF3CO antibodies, monospecific toward trifluoroacetylated proteins (CF3CO-proteins), which are elicited in experimental animals and humans exposed to the anesthetic agent halothane, cross-react with an unknown protein of approximately 52 kDa, constitutively expressed in tissues of experimental animals and humans not previously exposed to the agent. Using anti-CF3CO antibody, the protein(s) of 52 kDa could be immunoprecipitated from solubilized rat heart homogenate. Two-dimensional gel electrophoretic analysis revealed the presence of distinct major (P1, P2) and minor (P3, P4, P5) protein components with apparent molecular masses of 52 kDa. From each of the components P1 and P2, the amino acid sequences of three peptides were determined and found to exhibit 100% identity with the corresponding amino acid sequences of the E2 subunit of the rat 2-oxoglutarate dehydrogenase complex (OGDC). Additionally to the E2 subunit of OGDC, anti-CF3CO antibody also recognized on immunoblots the purified E2 subunit of the branched chain 2-oxoacid dehydrogenase complex (BCOADC) and protein X, a constituent of the pyruvate dehydrogenase complex (PDC), in a manner sensitive to competition by N6-(trifluoroacetyl)-L-lysine (CF3CO-Lys), 6(RS)-lipoic acid, and N6-(6(RS)-lipoyl)-L-lysine (lipoyl-Lys). Furthermore, a discrete population of autoantibodies was identified in sera of patients with halothane hepatitis which could not discriminate between the lipoylated target epitope present on the E2 subunit of OGDC and epitopes on CF3CO-RSA, used as model for CF3CO-proteins. These data suggest that the autoantigenicity of these proteins in halothane hepatitis is based on the molecular mimicry of CF3CO-Lys by lipoic acid, the prosthetic group common to protein X and the E2 subunits of OGDC and BCOADC.

Circulating antibodies to cardiac protein-acetaldehyde adducts in alcoholic heart muscle disease

1. Serum samples from patients with alcoholic heart muscle disease and from control subjects with and without heart disease who did not drink to excess were screened by Western immunoblotting for antibodies to acetaldehyde-modified cardiac cytosolic proteins. 2. Two of the 64 control samples (from subjects with and without heart disease who were not drinking and from subjects with alcoholic liver disease) had detectable (IgG) antibody to acetaldehyde-modified cardiac proteins. 3. By contrast, 7 of 21 (33%) patients with alcoholic heart muscle disease had antibodies against cyanoborohydride-stabilized, acetaldehyde-modified human cardiac cytosolic protein antigens (P < 0.001). 4. Antibodies were of IgG class in six patients and IgA class in five. The molecular sizes of the protein antigens observed ranged from 58 to 120 kDa. 5. These results suggest that a proportion of patients with alcoholic heart muscle disease develop immunogenic cardiac protein-acetaldehyde adducts. The presence of antibodies to these adducts may be a marker for the diagnosis of this heart disease, or possibly for its pathogenesis.

Sera from patients with halothane hepatitis contain antibodies to halothane-induced liver antigens which are not detectable by immunoblotting

In previous studies, immune responses to novel, halothane-induced hepatic antigens have been implicated in the mechanism of halothane hepatitis. Experiments performed using the technique of immunoblotting have indicated that the halothane-induced antigens comprise a group of halothane metabolite-modified microsomal proteins (trifluoroacetylated proteins). In the present report, we describe detection of an additional and quite distinct group of halothane-induced antigens. The novel halothane-induced antigens were expressed in microsomal fractions from livers of halothane-treated rats and could be detected by enzyme-linked immunosorbent assay (ELISA), but not by immunoblotting. In contrast to the major trifluoroacetyl-protein antigens detectable by immunoblotting, which were soluble in buffer containing 0.1% sodium deoxycholate, the novel antigens detectable by ELISA were not soluble in 0.1% sodium deoxycholate but were soluble in 2% sodium deoxycholate. Expression of the novel antigens was reduced markedly when rats were treated with deuterated halothane, in place of halothane. This suggests that their expression requires metabolism of halothane via the same oxidative, cytochrome P450-mediated pathway known to be responsible for generation of the antigens detectable by immunoblotting. Both the antigens detectable by ELISA and the antigens detected by immunoblotting were expressed slowly in livers of halothane-treated rats and were long-lived. Overall, these results indicate that the technique of immunoblotting is of limited value for detection and characterization of antigens involved in immune-mediated adverse drug reactions.

Formation of trifluoroacetylated protein antigens in cultured rat hepatocytes exposed to halothane in vitro

Immune responses to novel, halothane metabolite-modified protein antigens (tri-fluoroacetylated proteins; TFA-proteins) have been implicated in the pathogenesis of halothane hepatitis. The aim of the present study was to investigate and characterize expression of TFA-proteins in cultures of rat hepatocytes which were exposed to halothane in vitro. Following exposure to halothane, the hepatocytes were harvested, then subcellular fractions were prepared and were analysed by immunoblotting for expression of antigens recognized by a rabbit anti-TFA antiserum, and by antibodies in sera from two patients with halothane hepatitis. Hepatocytes exposed to halothane in vitro were shown to express novel microsomal protein antigens, which exhibited molecular masses that were identical to the molecular masses of the major TFA-protein antigens expressed in vivo, in livers of halothane-treated rats (100, 80 and 60 kDa). Experiments in which hepatocytes were exposed to halothane in the presence of SKF-525A, or were exposed to deuterated halothane in place of halothane, confirmed that these novel antigens were TFA-modified proteins whose generation required cytochrome P450-mediated metabolism of halothane. The maximal levels of TFA-antigens expressed in vitro were about 30% of the levels expressed in halothane-treated rats in vivo. Maximal expression of the TFA-antigens in vitro occurred when hepatocytes were exposed to halothane at doses which yielded concentrations of the drug in culture medium of about 13 microM. Expression of the antigens in vitro occurred slowly, with an apparent half-time of about 8 hr. Overall, these results demonstrate that the properties of the TFA-antigens expressed in cultured hepatocytes in vitro closely resemble the properties exhibited by the antigens expressed in vivo, in livers of halothane-treated rats.

Identification of the dihydrolipoamide acetyltransferase subunit of the human pyruvate dehydrogenase complex as an autoantigen in halothane hepatitis. Molecular mimicry of trifluoroacetyl-lysine by lipoic acid

Trifluoroacetylated (CF3CO-) proteins, elicited upon exposure of animals or humans to halothane, were recognized by anti-CF3CO antibody, monospecific for the hapten derivative N6-trifluoroacetyl-L-lysine. Anti-CF3CO antibodies cross-reacted with the dihydrolipoamide acetyltransferase (E2 subunit) of pyruvate dehydrogenase, indicating that epitopes on the E2 subunit of pyruvate dehydrogenase molecularly mimic those on CF3CO-proteins. Lipoic acid, the prosthetic group of the E2 subunit of pyruvate dehydrogenase was essential in this process, in that only the lipoylated form of the recombinantly expressed inner lipoyl domain of the human E2 subunit of pyruvate dehydrogenase, but not the unlipolyated form, was recognized by anti-CF3CO antibody. Furthermore, based on a high degree of structural relatedness, both CF3CO-Lys and (6RS)-lipoic acid, as well as the lipoylated peptide ETDK(lipoyl)ATIG specifically inhibited the recognition by anti-CF3CO antibody of the E2 subunit of pyruvate dehydrogenase, of trifluoroacetylated rabbit serum albumin and of human liver CF3CO-proteins. In sera of patients with halothane hepatitis, autoantibodies with properties identical to those of anti-CF3CO antibody were identified which could not discriminate between CF3CO-proteins and the E2 subunit of pyruvate dehydrogenase. These data suggest that the E2 subunit pyruvate of dehydrogenase is an autoantigen in halothane hepatitis and that molecular mimicry of CF3CO-proteins by the E2 subunit of pyruvate dehydrogenase is due to the similar structures of CF3CO-Lys and lipoic acid.

Autoantibodies to hepatic microsomal carboxylesterase in halothane hepatitis

Halothane hepatitis can be life-threatening, and this severe adverse reaction may arise via an immune process. We have detected autoantibodies to purified human liver microsomal carboxylesterase in sera of 17 out of 20 patients with halothane hepatitis (85%) but not in 9 halothane-exposed controls and in only 2 (at low levels) of 33 patients with liver disease due to other causes. Immunohistochemical studies localised the carboxylesterase predominantly to the centrilobular region of liver sections, which is consistent with the area affected by halothane hepatitis. Human hepatic microsomal carboxylesterase is a target antigen in halothane hepatitis, and an immune response to this protein may be involved in the liver damage observed.

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.

Serum antibodies from halothane hepatitis patients react with the rat endoplasmic reticulum protein ERp72

Immunoblotting studies have previously shown that serum antibodies from halothane hepatitis patients react with several liver microsomal proteins that have been modified by the trifluoroacetyl halide metabolite of halothane. In this study, an 80-kDa protein recognized by the patients' antibodies has been purified from rat liver microsomes and characterized. When the purified trifluoroacetylated 80-kDa and native 80-kDa proteins were employed as test antigens in an enzyme-linked immunosorbent assay, serum antibodies from halothane hepatitis patients reacted with both of these proteins to a significantly greater extent than did serum antibodies from control patients. Amino acid sequence analyses of several hydrolytic peptide fragments of the 80-kDa protein showed that the protein was 99% identical to the deduced amino acid sequence of a murine cDNA of the luminal endoplasmic reticulum protein ERp72. These results indicate that trifluoroacetylated ERp72 in the liver of halothane hepatitis patients may induce immune responses against epitopes present on the covalently altered protein and those present on the native protein and may have a role in halothane hepatitis. In addition, immunoblot and immunohistochemical studies revealed that the 80-kDa protein was present in all tissues studied, but was in highest concentration in liver, adipose tissue, ovaries, and testes and was enriched in specific cells of some organs. In the future, these findings should help define the physiological function of ERp72.

Molecular mimicry of trifluoroacetylated human liver protein adducts by constitutive proteins and immunochemical evidence for its impairment in halothane hepatitis

A monospecific antibody (anti-CF3CO antibody) was obtained by affinity chromatography on a N epsilon-trifluoroacetyl-L-lysine (CF3CO-Lys) matrix of a rabbit polyclonal antiserum, directed against trifluoroacetylated protein adducts (CF3CO-proteins). The anti-CF3CO antibody recognized distinct CF3CO-proteins on immunoblots of a liver biopsy obtained from a human individual 10 h after halothane anaesthesia. Cross-reactive proteins of 52 kDa and 64 kDa were recognized on immunoblots of livers obtained from human individuals not exposed to halothane. Recognition of both CF3CO-proteins and the 52-kDa and 64-kDa cross-reactive proteins was abolished in the presence of 1 mM CF3CO-Lys. Anti-CF3CO antibody, affinity-adsorbed to the 52-kDa or the 64-kDa cross-reactive proteins of human liver, recognized the majority of target CF3CO-proteins on immunoblots of the human liver biopsy of an individual exposed to halothane. Liver biopsies of 5 out of 7 (71%) patients with halothane hepatitis exhibited an absence or low amounts of immunorecognizable 52-kDa and/or 64-kDa cross-reactive proteins. In contrast, of 22 control human individuals tested, all liver tissue samples were positive for the 52-kDa and/or the 64-kDa cross-reactive proteins. These data indicate that epitopes on the cross-reactive proteins of 52 kDa and 64 kDa of human liver bear strong immunochemical resemblance to epitopes on human liver CF3CO-proteins. Low-level expression of the cross-reactive proteins of 52 kDa and 64 kDa is discussed as one possible factor in human susceptibility to halothane hepatitis.

Immunoglobulin A antibody to a 200-kilodalton cytosolic acetaldehyde adduct in alcoholic hepatitis

Considerable clinical and experimental evidence points to the importance of immune responses in the development of alcoholic liver disease. In the present study it was investigated whether circulating antibodies from patients with alcoholic liver disease recognize acetaldehyde-liver protein adducts. Cytosolic and microsomal fractions from livers of Wistar rats or from normal human liver were incubated with acetaldehyde (0.5-2.5 mmol/L) and/or cyanoborohydride (100 mmol/L) then analysed by immunoblotting. Cytosolic fractions that had been incubated with acetaldehyde and cyanoborohydride expressed a 200-kilodalton protein antigen not present in untreated fractions or fractions incubated with acetaldehyde or cyanoborohydride alone. The 200-kilodalton antigen was recognized by immunoglobulin (Ig)A antibodies in a large proportion of sera from patients with alcoholic hepatitis (70%, n = 23), but in significantly smaller proportions of sera from patients with alcoholic cirrhosis without hepatitis (30%, n = 10; P < 0.05), heavy drinkers without overt liver disease (20%, n = 10; P < 0.02), patients with nonalcoholic liver disease (35%, n = 17; P < 0.05), or normal control subjects consuming moderate quantities of alcohol (25%, n = 20%; P < 0.005). These results indicate that IgA antibodies to a 200-kilodalton acetaldehyde-protein adduct are present in a large proportion of patients with alcoholic liver disease and in a significantly smaller proportion of other individuals.

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.