Detection of an autoantibody directed against human liver microsomal protein in a patient with carbamazepine hypersensitivity

A 16-year old patient with carbamazepine-induced hepatotoxicity, associated with the hypersensitivity manifestations of fever, rash and eosinophilia, is described. Mononuclear leucocytes from the patient were more sensitive to oxidative metabolites of carbamazepine generated by induced murine and human hepatic microsomes, than cells from controls. On immunoblot analysis, serum from the patient recognised a single protein band (94 kDa) on human liver microsomes, but none out of 25 control sera recognised this band. No bands were recognised by the patient serum on human kidney microsomes or on microsomes from mouse and rat liver.

Catalytic and immunologic similarities between monkey and human liver cytochrome P-450db1 (human cytochrome P-450 2D6)

In vivo pharmacogenetic studies have suggested that the monkey may be an animal model for the human polymorphism of cytochrome P-450 2D6 (also called cytochrome P-450db1). In the present study, the catalytic, immunologic, and electrophoretic properties of cytochrome P-450db1 in liver microsomes from African green monkeys (Cercopithecus aethiops) were examined and compared with P-450db1 in human liver microsomes. Using sparteine as the substrate, the activity of microsomal P-450db1 from the two sources was indistinguishable in terms of the pattern of sparteine metabolites produced, the apparent Ki values of 8 competitive inhibitors (r = 0.94, p less than 0.001), and the extent of immunoinhibition by anti-rat P-450db1 antibody. Kinetic analyses demonstrated that the apparent KM values of the high affinity component of sparteine oxidation in monkey liver microsomes fell within the range observed in human livers; the Vmax of this component was as much as six times greater than the highest value reported for human liver. Western immunoblots showed a protein band in monkey liver microsomes that co-migrated with P-450db1 in human liver. The high degree of similarity observed here between P-450db1 of monkey and human liver microsomes suggests that the monkey will be a good animal model for P-450db1 enzyme studies, and possibly for studies of the role of this enzyme in drug abuse and dependence.

Screening for antibodies associated with halothane hepatitis

The diagnosis of halothane hepatitis (HH) may be assisted by detection of antibodies reacting to trifluoroacetylated proteins (anti-TFA antibodies). An enzyme-linked immunosorbent assay (ELISA) utilizing trifluoroacetylated rabbit serum albumin (TFA-RSA) as antigen detected anti-TFA antibodies in 67% of sera from patients for whom a clinical diagnosis of HH was made. Anti-TFA antibodies were detected in 33% of sera when using an ELISA with liver microsomal protein from halothane-treated rabbits as antigen. Absorption of the sera with untreated rabbit liver microsomal protein before using the microsomal protein ELISA resulted in detection of anti-TFA antibodies in 42% of sera. Using the presumptive hapten N-epsilon-trifluoroacetyl-1-lysine to block antibody binding in an ELISA resulted in positive detection in 50% of sera: the results did not always agree with the other ELISA methods. The TFA-RSA ELISA was the most sensitive method and, combined with the TFA-lysine blocking ELISA, resulted in 92% of sera from HH patients testing positive for HH-associated antibodies.

Detection of human hepatitis anti-liver kidney microsomes (LKM2) autoantibodies on rat liver sections is predominantly due to reactivity with rat liver P-450 IIC11

Anti-liver kidney microsomes (anti-LKM2) autoantibodies, appearing in patients treated with tienilic acid and suffering from hepatitis, react with proteins in rat liver sections. The nature of the rat proteins responsible for this recognition and detection of anti-LKM2 has been investigated. Immunoblot testing of the anti-LKM2 with liver microsomes from diversely treated rats and with purified rat liver cytochromes P450 (IA1, IA2, IIB1, IIB2, IIC6, IIC11 and IVA1) showed that these antibodies cross-reacted with cytochrome P450IIC11 and also with phenobarbital-induced cytochromes P450IIB1 and IIB2. Moreover, metabolic activation of tienilic acid and of a tienilic acid isomer by untreated rat liver microsomes was partially inhibited by anti-LKM2. On the other hand, monospecific polyclonal anti-rat P450IIC11 antibodies cross-reacted with human microsomal cytochromes P450 and recognized the same cytochromes P450 as anti-LKM2. This antibody also gave an immunofluorescence pattern on rat and mouse liver and kidney sections very similar to anti-LKM2. The data presented here show that anti-LKM2 recognize epitopes shared by rat P450 IIC11, and a human P450 of the family IIC. All the results indicate rat P450 IIC11, the major isoenzyme present in normal adult male rat liver, as the main antigen recognized by human anti-LKM2 autoantibodies; this is the basis of the immunofluorescence test for detection of these antibodies.

Occurrence of autoimmune antibodies to liver microsomal proteins in association with fulminant hepatitis in the LEC strain of rats

The Long Evans Cinnamon (LEC) rat, which has been established as a strain showing hereditary hepatitis and hepatic carcinoma, was found to possess autoimmune antibodies to liver microsomal proteins, particularly to a protein with the molecular weight of 56kD. The antibodies also recognized a protein(s) in liver microsomes from Long Evans Agouti and Sprague-Dawley rats. About 42 and 15 percent of respective female and male LEC rats died within a week after acute hepatitis; sera from all of the animals contained the antibodies. About 43 and 0 percent of the surviving female and male LEC rats possessed the antibodies, respectively. These results suggest that the autoantibodies occur in association with acute lethal hepatitis in the LEC rats.

Hepatitis C virus-related chronic liver disease with autoantibodies to liver-kidney microsomes (LKM). Clinical characterization from idiopathic LKM-positive disorders

This study was carried out on 33 patients who were sero-positive for liver-kidney microsomal antibodies (LKM) in order to examine clinical features and the presence of underlying hepatitis C virus infection. Twenty-four sera were positive for antibodies against HCV (anti-HCV) as detected by enzyme immunoassay and confirmed by recombinant immunoblot assay. These patients had chronic liver disease and the majority of those treated with interferon responded favourably. Three of the nine anti-HCV-negative patients had idiopathic chronic hepatitis and two responded favourably to steroids. Two patients were diagnosed as having toxic hepatitis and the other four had various extrahepatic disorders without evidence of liver involvement. The immunoblotting analysis showed reactivity with a 50 kDa microsomal protein which presumably corresponded to cytochrome P-450 db1 both in anti-HCV-positive and -negative sera. In addition a few anti-HCV-positive sera also reacted with a 35 kDa microsomal antigen. Autoimmune markers different from LKM were absent in both groups. The high prevalence of antibodies to the hepatitis C virus among LKM-positive sera confirms that this infection plays a role in forms of chronic hepatitis that had previously been labelled autoimmune. In patients with LKM the presence of anti-HCV may help to forecast a therapeutic response to interferon, while its absence may forecast response to steroid therapy.

Role of P450IID6, the target of the sparteine-debrisoquin oxidation polymorphism, in the metabolism of imipramine

The formation of three oxidative metabolites of imipramine, N-desmethylimipramine (desipramine), 2-hydroxyimipramine, and 10-hydroxyimipramine was studied in microsomes of an extensive metabolizer liver (KDL 26) and of a poor metabolizer liver (KDL 31) and in a homogenate of COS-1 cells in which the P450IID6 complementary deoxyribonucleic acid had been expressed. The following data support the role of P450IID6 in the 2-hydroxylation of imipramine: (1) The formation of 2-hydroxyimipramine was reduced to less than 20% of the control value when microsomes were incubated with serum containing inhibitory antibodies against P450IID6 (anti-LKM1), whereas no effect was seen with regard to formation of desipramine and 10-hydroxyimipramine, (2) quinidine and levomepromazine were potent competitive inhibitors of 2-hydroxylation of imipramine (ki approximately 70 nmol/L, and ki approximately 1 mumol/L, respectively) but had no effect on N-demethylation and 10-hydroxylation, and (3) in the COS-1 cell, homogenate, 10-hydroxyimipramine, 2-hydroxyimipramine, and desipramine were formed at rates of 48, 164, and 256 pmol per hour per milligram of homogenate protein, respectively. The P450 isozymes that are responsible for N-demethylation and 10-hydroxylation of imipramine have not yet been identified.

Anti-liver-kidney microsome antibody-positive autoimmune hepatitis associated with alopecia

A 14-year-old girl presented with anti-liver-kidney microsome autoimmune hepatitis preceded by alopecia 3 years earlier. Both pathologies were greatly improved by immunosuppressive therapy. Alopecia is a newly reported extrahepatic manifestation of type 2 autoimmune hepatitis. Its appearance could alert the clinician to an increased risk of autoimmune hepatitis in children.

Identification of human cytochrome P450s as autoantigens

Antimicrosomal antibodies in inflammatory liver diseases all seem to be directed against members of the cytochrome P450 family of proteins. These autoantigens seem to be genetically polymorphic, the autoantibodies are inhibitory, and the autoepitopes are generally conserved among species. Anti-P450 autoantibodies share these characteristics with other autoantibodies, for example, antinuclear antibodies in systemic lupus erythematosus. The identification of P450s as human autoantigens is clinically important. Diagnostic tests will be developed on the basis of cloned antigen, facilitating a better diagnosis of drug-induced and idiopathic autoimmune hepatitis. It is unknown what triggers autoantibody production against cytochrome P450 proteins. Furthermore, their pathogenetic role and thus their involvement in tissue destruction is unclear. In this context LKM1 autoantibodies may serve as a model. Although LKM1 antibodies are inhibitory, all LKM1 antibody-positive patients tested so far are extensive metabolizers for drug metabolism mediated by P450IID6 and express this protein in their livers. Thus, the inhibitory LKM1 autoantibody does not sufficiently penetrate through the intact liver cell membrane to inhibit enzyme function in vivo. Presumably, tissue destruction in autoimmune hepatitis is mediated by liver-infiltrating T lymphocytes. T lymphocytes have been cloned from liver tissue that specifically proliferate in the presence of recombinant cytochrome P450IID6. The construction of overlapping cDNA subclones is also valuable to identify immunodominant B cell as well as relevant T cell epitopes.

Anti-liver-kidney microsome antibody-positive autoimmune hepatitis presenting as fulminant liver failure

A 17-month-old girl presented with acute hepatitis, which took a fulminant course leading to death 2 months after onset. No known cause of fulminant liver failure could be identified. Postmortem examination of the liver showed massive multilobular necrosis and areas of severe piecemeal necrosis. A high level of total serum gamma-globulins raised the possibility of autoimmune hepatitis. Search for anti-liver-kidney microsome antibody in the patient's serum was positive by immunofluorescence and enzyme-linked immunosorbent assay. Western blot analysis showed reactivity of the antibody with a 50-kDa protein identical to that observed in children with autoimmune hepatitis. This patient's history strongly suggests that autoimmune hepatitis can present as fulminant liver failure in children. Early diagnosis in such a patient could lead to early immunosuppressive therapy.

Lack of response of peripheral blood mononuclear cells to thyroid microsomal antigen in nontoxic nodular goiters

The production of interferon gamma (IFN gamma) by peripheral blood mononuclear cells (PBMC) from patients with nontoxic nodular goiter (NTNG), autoimmune thyroid disease (AITD), and normal persons (NL) has been studied in vitro, with the express object of comparing NTNG and AITD. PBMC were cultured with thyroid microsomal antigen (TMc), thyroglobulin (Tg), and liver microsomal antigen (LMc) at concentrations of 0, 1, 10, 100, and 1000 ng/ml for two days. IFN gamma was measured by a spot-ELISA technique which determines the number of cells secreting IFN gamma. There were no significant differences in the basal numbers of IFN gamma secreting cells between NL, AITD, and NTNG PBMC in this study. In AITD PBMC, TMc antigen caused a significant increase in the number of IFN gamma secreting cells, compared with the numbers in unstimulated AITD PBMC (percent IFN gamma secreting cells), whereas Tg and LMc antigen caused a significant decrease in all groups. The maximal percentage change in IFN gamma secreting cells (i.e., compared to unstimulated PBMC) did not increase significantly in NTNG in response to TMc antigen, in contrast to the AITD PBMC. Based on these findings, it is concluded that NTNG PBMC are not sensitized to the thyroid antigens tested; this is unlike the findings from AITD PBMC.

[Cytochrome P-450 induction and the subsequent induction of an immune response in rats during the chronic administration of xenobiotics]

The long-term administration of xenobiotics carcinogens o-aminoazotoluene (o-AAT) and benz(a)pyrene (BP) to rats was found to cause induction of the liver cytochrome P-450 system which gradually decreases in spite of continued administration of the agents. Induction of microsomal oxygenases under these conditions is followed by induction of the immune response to o-AAT and BP. The data obtained correspond to the conception of the immunochemical functional system of homeostasis implying that the cytochrome-450 system and the immunity system are functionally linked and are elements of the common functional adaptive system of the organism.

Clinical and immunological heterogeneity of anti-liver-kidney microsome antibody-positive autoimmune hepatitis in children

A group of children with autoimmune hepatitis is characterized by the presence in their sera of anti-liver-kidney microsome antibody (LKMA) as defined by immunofluorescence. Immunoblot analysis of the sera of 21 such children using rat-liver microsome total proteins as antigen allowed separation into three groups--group 1, whose sera recognized a 50 kDa protein; group 2, whose sera recognized a 66 kDa protein; and group 3, whose sera recognized both proteins. Patients with the anti-66-kDa reactivity more often displayed an acute onset of the disease, less signs of portal hypertension, better sensitivity to immunosuppressive therapy, and less tendency to relapse. They also displayed a lower titer of anti-rat-liver microsome antibody in enzyme-linked immunosorbent assay (ELISA) and a serum reactivity with a rat-liver cytosolic protein. These results (a) indicate that the LKMA-positive autoimmune hepatitis of children is heterogeneous from both clinical and immunological view points, (b) suggest that children with anti-66-kDa reactivity could have a less severe disease than children with the 50-kDa reactivity, and (c) indicate that immunoblot analysis should be added to ELISA and immunofluorescence studies to achieve better characterization of these patients.

Intrahepatic assembly of very low density lipoproteins: immunologic characterization of apolipoprotein B in lipoproteins and hepatic membrane fractions and its intracellular distribution

Monoclonal antibodies, prepared against rat apoB, were used to examine apoB structure in serum lipoproteins and characterize the forms and localization of apoB in liver membrane fractions and cultured hepatocytes. Of the several antibodies obtained, four, having separate epitopes, were characterized. Western blot analysis showed that three (DB11, F4, and LB14) antibodies recognized both apoBL and apoBS. One antibody (HB41) recognized only apoBL. This antibody showed unusual properties. Competition ELISA assays showed that the epitope recognized by HB41 was more effectively expressed on low density lipoproteins (LDL) compared to very low density lipoproteins (VLDL). In addition, treatment of lipoproteins with detergents and sulfhydryl reducing agents also increased the expression of the HB41 epitope. Since HB41 has been found to inhibit LDL binding to hepatocyte receptors, these data indicate that the HB41 epitope is located on the carboxy-terminal side of the apoBS junction (probably within the LDL receptor binding domain). Western blotting hepatic microsomal subfractions showed that in the rough and smooth microsomes, HB41 recognized only apoBL, while in the Golgi it recognized both apoBL and a protein having a molecular weight slightly smaller. In contrast, Western blotting with a polyclonal antibody known to recognize both apoBL and apoBS showed that, in rough and smooth microsomes, proteins in addition to apoBL and apoBS having molecular weights between 120,000 and 30,000 were recognized. These proteins, likely to be proteolytic fragments of apoB, were barely detectable in the Golgi. Additional biosynthetic studies show that the [35S]methionine-labeled proteins smaller than apoB were immunoprecipitated from the rough microsome subfraction. Pulse-chase experiments show that these are produced with the same kinetics as full-size apoBL and apoBS, indicating that they are not incomplete nascent chains. Finally, immunofluorescence microscopy was used to determine the localization of monoclonal epitopes. ApoB monoclonal antibodies that recognized exclusively apoBL (HB41) and apoBL and apoBS (DB11) produced an immunofluorescence pattern characteristic of the endoplasmic reticulum, but not the Golgi. These data suggest that, in cultured rat hepatocytes, the majority of both molecular weight forms of apoB are localized in the endoplasmic reticulum, the initial site of VLDL assembly. The additional finding that proteolytic fragments of apoB are enriched in the microsomal fraction suggests that if the proteolysis occurs during subcellular fractionation, immature apoB is susceptible to proteolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Interspecies homology of cytochrome P-450: toxicological significance of cytochrome P-450 cross-reactive with anti-rat P-448-H antibodies in liver microsomes from dogs, monkeys and humans

The mutagenic activation of various promutagens by liver microsomes from dogs, monkeys and humans was investigated. Dog liver microsomes efficiently catalyzed the mutagenic activation of Trp-P-2 and Glu-P-1 followed by IQ and AAF. Monkey liver microsomes were most active in the activation of IQ followed by Glu-P-1, AAF and Trp-P-2. Although there were remarkable individual differences, human liver microsomes were found to be most active in the mutagenic activation of IQ followed by Trp-P-2, Glu-P-1 and AAF. Antibodies against rat P-448-H inhibited the mutagenic activation of Glu-P-1, Trp-P-2 and IQ in rat and dog liver microsomes, and Glu-P-1 and Trp-P-2 in monkey liver microsomes. The activation of Glu-P-1 and IQ in human liver microsomes was also strongly inhibited by anti-P-448-H antibodies. The amounts of cytochrome P-450 cross-reactive with anti-P-448-H antibodies in human liver microsomes highly correlated with the capacity to activate Glu-P-1, Trp-P-2 and IQ but not AAF.

Anti-liver-kidney microsome antibody type 1 recognizes human cytochrome P450 db1

Anti-liver-kidney microsome antibody type 1 (LKM1), present in the sera of a group of children with autoimmune hepatitis, was recently shown to recognize a 50 kDa protein identified as rat liver cytochromes P450 db1 and db2. High homology between these two members of the rat P450 IID subfamily and human P450 db1 suggested that anti-LKM1 antibody is directed against this human protein. To test this hypothesis, a human liver cDNA expression library in phage lambda GT-11 was screened using rat P450 db1 cDNA as a probe. Two human cDNA clones were found to be identical to human P450 db1 by restriction mapping. Immunoblot analysis using as antigen, the purified fusion protein from one of the human cDNA clones showed that only anti-LKM1 with anti-50 kDa reactivity recognized the fusion protein. This fusion protein was further used to develop an ELISA test that was shown to be specific for sera of children with this disease. These results: 1) identify the human liver antigen recognized by anti-LKM1 auto-antibodies as cytochrome P450 db1, 2) allow to speculate that mutation on the human P450 db1 gene could alter its expression in the hepatocyte and make it auto-antigenic, 3) provide a simple and specific diagnostic test for this disease.

A new antigen recognized by anti-liver-kidney-microsome antibody (LKMA)

Sera from 23 children with autoimmune chronic active hepatitis and positive for anti-liver-kidney-microsome antibody (LKMA), as defined by immunofluorescence, were analysed by Western blot (WB) and two-dimensional gel electrophoresis using rat liver microsomes as antigen, and by WB and dot-blot analysis with rat liver microsomal subfractions. Western blot analysis showed three patterns of reactivity: 13 sera recognized a 50 kD polypeptide, six sera a 66 kD polypeptide and four sera both of them. Two-dimensional gel electrophoresis, WB, and dot-blot analysis showed the 66 kD antigen to have a pI of 5.4 and to be located in the smooth domain of the endoplasmic reticulum. Western blot analysis using monospecific antisera against human IgG subclasses showed the LKMA directed against the 66 kD antigen to be mainly of the IgG1 subclass. These results indicate that LKMA associated with a subgroup of autoimmune hepatitis of children react with at least two different microsomal antigens in rat liver: (1) the 50 kD polypeptide, recently shown to be a cytochrome P-450 of the IID subfamily, and (2) a new antigen of 66 kD, the location of which suggests it may also be part of the mono-oxygenase complex.

Major antigen of liver kidney microsomal autoantibodies in idiopathic autoimmune hepatitis is cytochrome P450db1

Type 1, liver kidney microsomal autoantibodies (LKM-1) are associated with a subgroup of idiopathic autoimmune type, chronic active hepatitis (CAH). The antigenic specificity of LKM-1 autoantibodies from 13 patients was investigated by immunoblot analysis of human liver microsomal proteins. Polypeptides of 50, 55, and 64 kD were detected with these antisera. A high titer LKM-1 serum was selected to screen a human liver lambda gt11 cDNA expression library, resulting in the isolation of several complementary (c)DNA clones. Autoantibodies affinity purified from proteins expressed by two of the immunopositive cDNA clones, HLD8.2 and HLD13.2, specifically react with a 50-kD protein of human liver microsomes and display immunofluorescence staining of the proximal renal tubular epithelia characteristic of LKM-1 sera. Determination of the sequence of HLD8.2 revealed that it encodes a recently described cytochrome P450db1. A bacterial fusion protein constructed from HLD8.2 proved to be a specific and sensitive diagnostic reagent. All sera from patients with LKM-1 positive liver disease react with this fusion protein. No reaction was seen, however, for sera from patients with other types of autoimmune liver diseases, viral hepatitis, systemic immunological disorders, or healthy controls.

Cytochrome P-450 mediated metabolism in active murine systemic lupus erythematosus

In a comparison of NZB/NZW female mice either with active systemic lupus erythematosus (SLE) (28-33 weeks of age) or without overt SLE (7-13 weeks), the hepatic microsomal activities of ethoxycoumarin O-deethylation and aminopyrine N-demethylation were decreased 32% (p less than 0.05) and 28% (p less than 0.03), respectively, and cytochrome P-450 levels were decreased 34% (p less than 0.01) in the mice with active SLE. These changes were not associated with age differences alone in 2 nonautoimmune strains. Active murine SLE is thus associated with significant depressions in both hepatic cytochrome P-450 levels and microsomal enzyme activities. The metabolism of drugs and endogenous substrates may thus be impaired in active SLE.

A human cytochrome P-450 is recognized by anti-liver/kidney microsome antibodies in autoimmune chronic hepatitis

1- Anti-liver/kidney microsome autoantibodies type 1 (anti-LKM1), observed in some children with chronic active hepatitis, were used to isolate their antigen in human liver microsomes. A protein, called P-LKM1 was thus purified. This protein was recognized by a rabbit antiserum directed against the related human cytochromes P-450 bufI and P-450 bufII. 2- A human liver microsomal protein immunoprecipitated with anti-LKM1 sera was also recognized by anti cytochromes P-450 bufI/II antibodies. 3- Anti-LKM1 antibodies potently inhibited microsomal bufuralol 1'-hydroxylation. These results displayed the possible identity between cytochrome P-450 bufI/II and LKM1 antigen.

Immunochemical and catalytical characterization of the human liver NADPH-cytochrome P450 reductase

1. The NADPH-cytochrome P450 reductases (EC 1.6.2.4) from human and rabbit liver have been purified to electrophoretic homogeneity. The human reductase had an apparent monomeric molecular weight of 77,500 and the rabbit enzyme of 76,500. 2. Both flavoproteins exhibited typical flavoprotein spectra and contained equimolar quantities of FAD and FMN. The two reductases were catalytically active in reducing cytochrome c, ferricyanide and dichlorophenolindophenol, and in supporting rabbit liver cytochrome P450 Form 4 metabolism of 2-acetylaminofluorene. 3. An antibody raised in the goat against the human enzyme formed a precipitin line with the human reductase in a double-diffusion assay, but did not react with the rabbit reductase. Similarly, an antibody raised in the goat against the rabbit reductase formed a precipitin line with the rabbit enzyme, but did not cross-react with the human reductase. 4. Both antibodies inhibited cytochrome c reduction by the two reductases suggesting some immunochemical recognition. 5. Immunochemical cross-reactivity was confirmed when both reductases were subjected to the more sensitive immunoblot technique using either anti-human or anti-rabbit reductase IgG. 6. The human and rabbit reductases are essentially similar in amino acid composition, except that the former has larger amounts of serine and glycine.