Detection of anti-LKM-1(anti-CYP2D6) by an enzyme-linked immunosorbent assay in adult patients with chronic liver diseases

Identification of new autoantigens by protein array indicates a role for IL4 neutralization in autoimmune hepatitis

Autoimmune hepatitis (AIH) is an unresolving inflammation of the liver of unknown cause. Diagnosis requires the exclusion of other conditions and the presence of characteristic features such as specific autoantibodies. Presently, these autoantibodies have relatively low sensitivity and specificity and are identified via immunostaining of cells or tissues; therefore, there is a diagnostic need for better and easy-to-assess markers. To identify new AIH-specific autoantigens, we developed a protein microarray comprising 1626 human recombinant proteins, selected in silico for being secreted or membrane associated. We screened sera from AIH patients on this microarray and compared the reactivity with that of sera from healthy donors and patients with chronic viral hepatitis C. We identified six human proteins that are specifically recognized by AIH sera. Serum reactivity to a combination of four of these autoantigens allows identification of AIH patients with high sensitivity (82%) and specificity (92%). Of the six autoantigens, the interleukin-4 (IL4) receptor fibronectin type III domain of the IL4 receptor (CD124), which is expressed on the surface of both lymphocytes and hepatocytes, showed the highest individual sensitivity and specificity for AIH. Remarkably, patients' sera inhibited STAT6 phosphorylation induced by IL4 binding to CD124, demonstrating that these autoantibodies are functional and suggesting that IL4 neutralization has a pathogenetic role in AIH.

Novel autoimmune hepatitis-specific autoantigens identified using protein microarray technology

Autoimmune hepatitis (AIH) is a chronic necroinflammatory disease of the liver with a poorly understood etiology. Detection of nonorgan-specific and liver-related autoantibodies using immunoserological approaches has been widely used for diagnosis and prognosis. However, unambiguous and accurate detection of the disease requires the identification and characterization of disease-specific autoantigens. In the present study, we have profiled the autoantigen repertoire of patients with AIH versus those with other liver diseases, identifying and validating three novel and highly specific biomarkers for AIH. In phase I, we fabricated a human protein chip of 5011 nonredundant proteins and used it to quickly identify 11 candidate autoantigens with relative small serum collection. In phase II, we fabricated an AIH-specific protein chip and obtained autoimmunogenic profiles of serum samples from 44 AIH patients, 50 healthy controls, and 184 additional patients suffering from hepatitis B, hepatitis C, systemic lupus erythematosus, primary Sjogren's syndrome, rheumatoid arthritis, or primary biliary cirrhosis. With this two-phase approach, we identified three new antigens, RPS20, Alba-like, and dUTPase, as highly AIH-specific biomarkers, with sensitivities of 47.5% (RPS20), 45.5% (Alba-like), and 22.7% (dUTPase). These potential biomarkers were further validated with additional AIH samples in a double-blind design. Finally, we demonstrated that these new biomarkers could be readily applied to ELISA-based assays for use in clinical diagnosis/prognosis.

New insights into the structural characteristics and functional relevance of the human cytochrome P450 2D6 enzyme

To date, the crystal structures of at least 12 human CYPs (1A2, 2A6, 2A13, 2C8, 2C9, 2D6, 2E1, 2R1, 3A4, 7A1, 8A1, and 46A1) have been determined. CYP2D6 accounts for only a small percentage of all hepatic CYPs (< 2%), but it metabolizes approximately 25% of clinically used drugs with significant polymorphisms. CYP2D6 also metabolizes procarcinogens and neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroquinoline, and indolealkylamines. Moreover, the enzyme utilizes hydroxytryptamines and neurosteroids as endogenous substrates. Typical CYP2D6 substrates are usually lipophilic bases with an aromatic ring and a nitrogen atom, which can be protonated at physiological pH. Substrate binding is generally followed by oxidation (5-7 A) from the proposed nitrogen-Asp301 interaction. A number of homology models have been constructed to explore the structural features of CYP2D6, while antibody studies also provide useful structural information. Site-directed mutagenesis studies have demonstrated that Glu216, Asp301, Phe120, Phe481, and Phe483 play important roles in determining the binding of ligands to CYP2D6. The structure of human CYP2D6 has been recently determined and shows the characteristic CYP fold observed for other members of the CYP superfamily. The lengths and orientations of the individual secondary structural elements in the CYP2D6 structure are similar to those seen in other human CYP2 members, such as CYP2C9 and 2C8. The 2D6 structure has a well-defined active-site cavity located above the heme group with a volume of approximately 540 A(3), which is larger than equivalent cavities in CYP2A6 (260 A(3)), 1A2 (375 A(3)), and 2E1 (190 A(3)), but smaller than those in CYP3A4 (1385 A(3)) and 2C8 (1438 A(3)). Further studies are required to delineate the molecular mechanisms involved in CYP2D6 ligand interactions and their implications for drug development and clinical practice.

Frequency and significance of anti-glutathione S-transferase autoantibody (anti-GST A1-1) in autoimmune hepatitis

Several phase I and phase II multi-drug metabolizing enzymes, such as CYP2D6, 3A4, and UGTA1, were reported to act as immunotargets in a subset of autoimmune hepatitis and hepatic autoimmunity. However, it is uncertain whether glutathione S-transferase (GST) A1-1, one of the phase II multi-drug metabolizing enzymes, is also an immunotarget in autoimmune hepatitis. So, in the present study, we investigated the frequency and significance of anti-GST A1-1 in sera from patients with autoimmune hepatitis. A total of 74 serum samples from patients with autoimmune hepatitis were examined in the present study. As controls, 20 serum samples from patients with primary biliary cirrhosis, 10 serum samples from patients with primary sclerosing cholangitis, 40 serum samples from patients with liver cirrhosis type B and C, 32 serum samples from patients with systemic lupus erythematosus, and 20 serum samples from normal controls were used. Anti-GST A1-1 antibody was determined by immunoblotting using the recombinant full-length GST A1-1 protein as the antigen. The immunofluorescent staining pattern of anti-GST A1-1 was investigated using rat liver and kidney sections. We compared clinicopathologic findings between anti-GST A1-1-positive and -negative autoimmune hepatitis patients. Anti-GST A1-1 was detected in 12 (16%) of 74 patients with autoimmune hepatitis, however, it was not detected in any control serum samples except for two patients with primary biliary cirrhosis. The immunofluorescence staining pattern of anti-GST A1-1 was found to be unique and different from those of anti-mitochondrial antibody or anti-liver-kidney microsome type 1 antibody. Anti-GST A1-1 coexisted with other autoantibodies such as anti-nuclear or anti-smooth muscle antibodies, but did not coexist with anti-soluble liver antigen/liver pancreas. Anti-GST A1-1-positive autoimmune hepatitis patients had severe clinical features and a poor prognosis compared with anti-GST A1-1-negative patients. These findings suggested that despite the low frequency, anti-GST A1-1 might be the marker of an early progression in autoimmune hepatitis.

Evaluating molar CYP1A level in fish hepatic microsomes by competitive ELISA using recombinant membrane-free CYP1A standard protein

Fish cytochrome P4501A (CYP1A) is a widely accepted environmental biomarker, detecting biological effects of several xenobiotic groups present in aquatic environments, when evaluated in target tissues of a biosensor species. However, appropriate utilization of its protein level as a routine environmental diagnostic tool requires evaluation of properly normalized molar levels, mitigating comparison among different laboratories, during a multi-annual time scale and over a variety of tested populations of the biosensor species. A competitive enzyme-linked immunosorbent assay (ELISA) was developed for determination of CYP1A of the striped sea bream, Lithognathus mormyrus, using our previously described antibody raised to a trout CYP1A synthetic peptide, and a recombinant L. mormyrus CYP1A as a competitor. The L. mormyrus CYP1A-cDNA was cloned and modified by truncating its 5' hydrophobic membrane anchor, as well as by addition of 4x histidine tag, permitting its partial purification on a nickel-NTA column. The modified cDNA was ligated into the PCWOri+ vector and heterologously produced in Escherichia coli as a cytosolic, membrane-free protein, retaining its immuno-affinity with the anti-CYP1A antibody in the presence of the detergent Triton X-100. The detergent was added to the ELISA solution during the competitive step, rendering the microsomal CYP1A more accessible to the antibody. ELISA components, including coated levels of the modified standard CYP1A, and the concentrations of the Triton X-100, CYP1A-specific antibody, and the range of dissolved CYP1A standard protein, were optimized. Hypothesized immuno-affinity differences between the microsomal and the recombinant CYP1As, and among microsomal samples, as well as assay accuracy, were examined and discussed. This ELISA can serve for more efficient utilization of fish CYP1A as a pollution biomarker, and also as a model for establishing competitive ELISAs aimed at quantification of many different microsomal P450 proteins.

Anti-CYP2D6 antibodies detected by quantitative radioligand assay and relation to antibodies to liver-specific arginase in patients with autoimmune hepatitis

BACKGROUND

Antibodies to cytochrome P4502D6 (CYP2D6) were measured and their prevalence compared with that of antibodies to liver-specific arginase in patients with autoimmune hepatitis (AIH).

METHODS

Anti-CYP2D6 antibodies were measured by sensitive radioligand assay and enzyme-linked immunosorbent assay (ELISA), and anti-arginase antibodies were measured by ELISA in 132 patients (definite AIH 11, probable AIH 36, hepatitis C 20, hepatitis B 23, other autoimmune diseases 42) and 50 healthy controls.

RESULTS

CYP2D6 index (radioligand assay) was significantly higher in all groups of patients than those in healthy controls. A higher index than the cut-off value (mean+3 S.D. in healthy controls) was found in 36.4%, 44.4%, 25.0%, 17.4% and 28.6% of patients with definite AIH, probable AIH, hepatitis C, hepatitis B and other autoimmune diseases, respectively. CYP2D6 index was not related to serum IgG, anti-nuclear antibody or AIH scores, and was weakly correlated with anti-arginase antibody activity. When CYP2D6 index and anti-arginase antibodies were combined, 55.3% of AIH patients were positive for either one or both antibodies.

CONCLUSIONS

Anti-CYP2D6 antibodies by radioligand assay were frequently present in patients with AIH. Combined tests for anti-CYP2D6 radioligand assay and anti-arginase antibodies resulted in detection of 55% of AIH patients.

Differences in anti-LKM-1 autoantibody immunoreactivity to CYP2D6 antigenic sites between hepatitis C virus-negative and -positive patients

Anti-liver kidney microsome type 1 autoantibodies (anti-LKM-1) are known to be present in sera of autoimmune hepatitis type II and a subset of chronic hepatitis C patients. The autoantigen to anti-LKM-1 has been identified to be cytochrome P450 IID6 (CYP2D6) and the most frequently cited CYP2D6 antigenic sites of anti-LKM-1 in sera from autoimmune hepatitis type II patients spans the region aa 256-269. Other antigenic sites on CYP2D6 exist and have been identified in the two patient groups. However, most of these sites are concentrated on the carboxyl-terminal side of the protein, and the amino-terminal region has not been thoroughly investigated. Here, we have studied the antigenicity of the CYP2D6 amino region and compared reactivities between hepatitis C virus (HCV)-negative and -positive Japanese patient groups. A total of 34 anti-LKM-1-positive sera (eight with autoimmune hepatitis type II and 26 with chronic hepatitis C) were included. The immunoreactivity of patients' sera was examined against four conformational and one linear CYP2D6 peptide fragments. A defined antigenic site spanning aa 181-245 was found to react with 88% (7/8) of autoimmune hepatitis type II patients, as opposed to only 38% (10/26) of chronic hepatitis C patients. This was a significant difference (P< 0.043). Among these positively reacting samples, five of the seven autoimmune hepatitis type II sera and four of the ten chronic hepatitis C sera also reacted with a synthetic peptide spanning aa 256-269. Anti-LKM-1 thus may be able to recognize simultaneously at least two antigenic sites on the CYP2D6 protein, and reactivities against individual epitopes may differ according to HCV infectivity status.

Effect of interferon therapy on Japanese chronic hepatitis C virus patients with anti-liver/kidney microsome autoantibody type 1

AIM

The aim of this study was to determine the prevalence of anti-liver/kidney microsome autoantibody type 1 (anti-LKM-1) among hepatitis C virus (HCV)-infected Japanese patients at various stages (chronic hepatitis, liver cirrhosis and hepatocellular carcinoma), and to assess the influence of anti-LKM-1 on interferon therapy.

METHODS

A total of 390 serum samples from 215 HCV-infected patients with chronic hepatitis (HCV-CH), 81 HCV-infected patients with liver cirrhosis (HCV-LC), and 94 HCV-HCC infected patients were subjected to examination. Ninety-one HBsAg-positive patients and 137 healthy subjects served as controls. Anti-liver/kidney microsome autoantibody type 1 was determined by using a newly developed ELISA using recombinant cytochrome P450 IID6 as the antigen.

RESULTS

Anti-liver/kidney microsome autoantibody type 1 was detected in six of the 390 (1.5%) chronic HCV-infected patients (four were HCV-CH and two were HCV-LC); in contrast, it was not detected in control groups. Among the 110 HCV-CH patients treated with interferon (IFN), four were positive for anti-LKM-1. No change in anti-LKM-1 immunoreactivity from negative to positive during interferon therapy was observed. Moreover, no increase in the serum alanine aminotransferase level was observed in these four patients with anti-LKM-1.

CONCLUSION

Our study indicates that: (i) anti-LKM-1 does not aggravate the liver disease associated with HCV infection; and (ii) no change in anti-LKM-1 immunoreactivity from negative to positive or no aggravations of liver dysfunction were observed among HCV-CH patients during the IFN therapy for Japanese patients with liver disease.

Immunoreactivity to various human cytochrome P450 proteins of sera from patients with autoimmune hepatitis, chronic hepatitis B, and chronic hepatitis C

Numerous human Cytochrome P450 enzymes (CYPs) associated with 'phase I' drug metabolism have been identified. Among them, CYP2D6 is thought to be the major target autoantigen to anti-liver kidney microsome (LKM)-1 autoantibody, a characteristic feature of autoimmune hepatitis (AIH) type II. In this study, we were able to clone CYP2D6 cDNA from a human liver cDNA library and express the CYP2D6 recombinant protein, and also to prepare four other representative human CYP proteins (CYP1A2, 2C9, 2E1, and 3A4). These preparations were used to assay the immunoreactivity of patients with AIH type I (n=35) and type II (n=9). As comparison groups, sera from patients with chronic hepatitis B (n=15), chronic hepatitis C (n=55; 24 anti-LKM-1-positive, 31 anti-LKM-1-negative), and from normal controls (n=30) were included. The five CYP proteins did not react with sera from normal controls nor from patients with chronic hepatitis B. CYP2D6 reacted with sera from 100% (9/9) of AIH type II patients, 79% (19/24) of patients with anti-LKM-1-positive chronic hepatitis C, and 6.5% (2/31) of patients with anti-LKM-1-negative chronic hepatitis C. In contrast, CYP1A2 reacted with serum from one patient with AIH type I, CYP2E1 reacted with sera from two patients with AIH type I, one patient with anti-LKM-1-positive chronic hepatitis C, and two patients with anti-LKM-1-negative chronic hepatitis C, and CYP3A4 reacted with sera from one patient with AIH type II and one patient with anti-LKM-1-positive chronic hepatitis C. CYP2C9 did not react with any of the sera included in this study. From these results, it is suggested that CYPs other than CYP2D6 can function as immunotargets in certain disease conditions.

Autoimmune liver disease

Regional differences in the manifestations of autoimmune hepatitis underscore the importance of genetic and/or environmental factors in its expression. The -308 polymorphism of TNF-A increases susceptibility to type 1 autoimmune hepatitis; HLA DRB1*13 is an important risk factor in South America; and DRB1*07 characterizes type 2 autoimmune hepatitis. Minocycline and mesalazine can trigger the disease, and interferon therapy can accentuate autoimmune manifestations. Autoimmune cholangitis in Japan is similar to primary biliary cirrhosis, and assays for carbonic anhydrase II lack diagnostic specificity. Perinuclear antineutrophil cytoplasmic antibodies are reactive to diverse nuclear antigens, but high mobility nonhistone chromosomal proteins may be important targets in autoimmune hepatitis. T cells can cross-react with viral and host peptides, and the candidacy of glutathione S-transferases as target autoantigens has been weakened. A murine model of PBC will be useful in studying mechanisms of autoreactivity, and cyclosporine has shown promise in the treatment of children with autoimmune hepatitis. Recurrence after liver transplantation is common, and it may require retransplantation. The human transplantation model will be valuable in understanding the host-and organ-specific contributions to disease expression.

CYP2D6 polymorphism and the presence of anti-LKM-1 in patients with chronic hepatitis C

Anti-LKM-1 autoantibodies are directed mostly at cytochrome P450 2D6 (CYP2D6) autoantigen, whose activity ranges from "complete deficiency" to "extensive metabolism" due to genetic polymorphism. We aimed to find any relevance of CYP2D6 alleles to the presence/absence of anti-LKM-1 in Japanese patients with chronic hepatitis C. The frequency of an extensive metabolizer-type allele (CYP2D6*1) in anti-LKM-1-positive patients was higher than that in anti-LKM-1-negative patients (0.800 vs 0.431; P = 0.0035), while the CYP2D6*10 allele with moderately reduced activity was less frequent in the former than the latter (0.050 vs 0.389; P = 0.0069). Moreover, the rate of homozygosity for CYP2D6*1 showed a striking difference between the two groups (70% vs 19%; P = 0.0021). These findings suggest that a genetic predisposition to produce the enzyme CYP2D6 of extensive metabolizer-type is associated with the induction of anti-LKM-1 in chronic hepatitis C patients.