Petra Obermayer-Straub

Polymorphic Gene Regulation and Interindividual Variation of UDP-glucuronosyltransferase Activity in Human Small Intestine

UDP-glucuronosyltransferases (UGTs) convert dietary constituents, drugs, and environmental mutagens to inactive hydrophilic glucuronides. Recent studies have shown that the expression of the UGT1 and UGT2 gene families is regulated in a tissue-specific fashion. Human small intestine represents a major site of resorption of dietary constituents and orally administered drugs and plays an important role in extrahepatic UGT directed metabolism. Expression of 13 UGT1A and UGT2Bgenes coupled with functional and catalytic analyses were studied using 18 small intestinal and 16 hepatic human tissue samples. Hepatic expression of UGT gene transcripts was without interindividual variation. In contrast, a polymorphic expression pattern of all the UGT genes was demonstrated in duodenal, jejunal, and ileal mucosa, with the exception of UGT1A10.To complement these studies, interindividual expression of UGT proteins and catalytic activities were also demonstrated. Hyodeoxycholic acid glucuronidation, catalyzed primarily by UGT2B4 and UGT2B7, showed a 7-fold interindividual variation in small intestinal duodenal samples, in contrast to limited variation in the presence of 4-methylumbelliferone, a substrate glucuronidated by mostUGT1A and UGT2B gene products. Linkage of RNA expression patterns to protein abundance were also made with several mono-specific antibodies to the UGTs. These results are in contrast to a total absence of polymorphic variation in gene expression, protein abundance, and catalytic activity in liver. In addition, the small intestine exhibits considerable catalytic activity toward most of the different classes of substrates accepted for glucuronidation by the UGTs, which is supported by immunofluorescence analysis of UGT1A protein in the mucosal cell layer of the small intestine. Thus, tissue-specific and interindividual polymorphic regulation ofUGT1A and UGT2B genes in small intestine is identified and implicated as molecular biological determinant contributing to interindividual prehepatic drug and xenobiotic metabolism in humans.

The genetic background of autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy and its autoimmune disease components

Autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy (APECED) is a rare autosomal recessive disorder characterized by an immune-mediated destruction of endocrine tissues, chronic candidiasis, and additional ectodermal disorders. In contrast to many other autoimmune diseases, APECED is associated with mutations of a single gene, designated autoimmune regulator (AIRE). To date, 45 different mutations of the AIRE gene have been identified and are distributed throughout the entire coding region. Several of the AIRE mutations predict the transcription and translation of a truncated protein, which may be nonfunctional. In contrast to the genetic background of APECED, in all of the autoimmune conditions typically associated with APECED the conclusive role of a single genetic locus capable of providing insight into the etiology of the disease has not been identified. Here we provide an overview of the current clinical and genetic features of APECED in comparison to the genetic background of the frequently associated disease components of APECED.

Two cytochromes P450 are major hepatocellular autoantigens in autoimmune polyglandular syndrome type 1

BACKGROUND & AIMS Liver disease has been described in 10%-15% of patients with autoimmune polyglandular syndrome type 1 (APS-1). After the discovery of cytochrome P450 1A2 (CYP1A2) as a hepatocellular autoantigen in liver-kidney microsomal autoantibody (LKM)-positive patients with APS-1, the investigation of antiliver antibodies was extended to 11 Sardinian patients with APS-1. METHODS Indirect immunofluorescence and Western blotting analysis were performed to study the antiliver antibodies. RESULTS Immunofluorescence revealed LKM antibodies in 3 patients with APS-1, 1 of whom died of fulminant hepatitis. Western blotting showed a liver microsomal protein band of approximately 51 kilodaltons in the LKM-positive sera of these 3 patients. Western blotting performed with recombinant cytochrome P450 enzymes allowed the identification of CYP2A6 as a specific target antigen. CONCLUSIONS LKM antibodies in APS-1 sera are specifically directed against CYP1A2 or CYP2A6, but their diagnostic and prognostic significance for liver disease remain to be determined.

Epitope mapping of cytochrome P4502D6 autoantigen in patients with chronic hepatitis C during α-interferon treatment

BACKGROUND/AIMS Cytochrome P450 2D6 (CYP2D6) has been documented as the major target antigen of liver kidney microsomal autoantibodies type-1 (anti-LKM-1) in both autoimmune hepatitis type-2 (AIH-2) and hepatitis C (HCV). In HCV/anti-LKM-1-positive patients, the choice between alpha-interferon (alpha-IFN) or immunosuppression may be difficult. This study was conducted to evaluate the course and outcome of alpha-IFN therapy in HCV/anti-LKM-1-positive and -negative patients and the alterations in these autoantibody titers by the indirect immunofluorescence and a novel radioligand assay. Epitope mapping was also performed to screen for a potential shift in anti-LKM-1 binding towards small linear epitopes, which are more often detected in AIH-2 patients. METHODS Twenty-one patients with HCV infection received alpha-IFN. Seven patients were anti-LKM-1 positive (study group) and 14 patients were anti-LKM-1 negative (disease control group). Anti-CYP2D6 detection was based on immunoprecipitation of [35S]-methionine-labeled CYP2D6 recombinant protein (rCYP2D6) produced by in vitro transcription/translation. RESULTS Four out of seven (57%) patients in the study group and 5/14 (36%) in the disease control group initially responded, but subsequently relapsed. During follow-up, alanine aminotransferase significantly increased in the study group compared to the disease control group (p<0.01). A slight increase, followed by a plateau of autoantibody titers was recorded by the radioligand assay and by indirect immunofluorescence during therapy and follow-up in most cases. In one patient, however, gamma-globulins and anti-LKM-1 titers increased, reaching very high levels (1:40 960). alpha-IFN was interrupted and immunosuppression was started. HCV/anti-CYP2D6 positive sera recognized CYP2D6 expressed in E. coli and two truncated proteins (aa 250-494 and 321-494). Two out of seven sera, in addition reacted with a small linear epitope of aa 257-269 (one of which also reacted with a C-terminal domain of aa 350-494). CONCLUSIONS A rather mild deterioration in liver disease was observed in only 1/7 HCV/anti-LKM-1-positive patients during alpha-IFN treatment. This patient showed high anti-CYP2D6 titers before the initiation of therapy, a sharp increase in anti-LKM-1 titers during treatment, and reactivities to a small linear epitope and an infrequently recognized C-terminal domain of CYP2D6. After switching to immunosuppressive treatment, a complete and sustained response was recorded. Further prospective studies from many centers are needed to define whether these features have general, clinical significance or not.

Development of cytochrome P450 2D6-specific LKM-autoantibodies following liver transplantation for Wilson's disease -- possible association with a steroid-resistant transplant rejection episode.

BACKGROUND/AIMS Antibodies to cytochrome P450 2D6, also known as LKM1-autoantibodies, are characteristic for a subgroup of patients with autoimmune hepatitis, but can also occasionally be found in hepatitis C. We observed the occurrence of LKM1-autoantibodies 4 months after liver transplantation for Wilsons disease, in close association with a steroid-resistant rejection episode, in the absence of evidence for autoimmune hepatitis or hepatitis C. METHODS Sera from several time points prior to and following transplantation were tested for LKM-reactivity by immunofluorescence, ELISA and Western blotting. Antigen specificity was confirmed by Western blotting analysis on different cytochrome P450 isoenzymes. The absence of viral hepatitis C and hepatitis G virus infection was confirmed by polymerase chain reaction. The serum of the organ donor was also tested. RESULTS All the sera prior to transplantation and up to 4 months after transplantation were LKM-negative by all assay systems used. In the course of a steroid-resistant rejection episode at this time, the patient developed LKM antibodies at high titre (70% in inhibition ELISA) and has remained positive since (now more than 4 years). Reactivity was exclusively to the cytochrome isoenzyme 2D6. Hepatitis C infection never occurred, but hepatitis G was transiently present many years prior to transplantation. The donor serum was negative for all autoantibodies and for hepatitis C and G virus infection. DISCUSSION We here describe a patient developing LKM1-autoantibodies without evidence of autoimmune or viral hepatitis. The close temporal association with a transplant rejection episode suggests immunological mechanisms of rejection together with hepatocellular injury as a pathogenetic mechanism.

Increased incidence of anti-LKM autoantibodies in a consecutive cohort of hepatitis C patients from central Greece.

Objectives In Greece, there are insufficient data regarding the presence of non-organ and liver-related autoantibodies in hepatitis C patients. This study in a consecutive cohort of 39 such patients from central Greece investigates (1) the prevalence of non-organ and liver-related autoantibodies, and (2) the reactivity of anti-liver–kidney microsomal type 1 antibodies (in the case of positivity with at least one of the methods used) against their molecularly defined antigens. Design All serum samples were tested by standard and molecular assays for the presence of anti-nuclear antibodies, smooth muscle antibodies, anti-liver–kidney microsomal type 1 antibodies, antibodies against parietal cells, anti-CYP2A6, anti-CYP1A2 and anti-CYP2D6 autoantibodies. Methods Indirect immunofluorescence, competitive enzyme-linked immunosorbent assays, immunoblotting and novel radioligand assays based on immunoprecipitation of [35S]-methionine labelled recombinant CYP2A6, CYP1A2 and CYP2D6 His-taq fusion proteins produced by in vitro transcription/translation were used. Results Seven out of 39 patients (17.9%) tested positive for smooth muscle antibodies, 2/39 (5.1%) tested positive for anti-nuclear antibodies, 1/39 (2.5%) tested positive for parietal cell antibodies, and 4/39 (10.3%) were found to be anti-liver–kidney microsomal positive (with at least one of the methods used). All sera were negative for anti-CYP2A6 and anti-CYP1A2 autoantibodies. Three out of four anti-liver–kidney microsomal positive samples had the typical liver–kidney microsomal staining pattern shown by indirect immunofluorescence. However, none tested positive for anti-CYP2D6 autoantibodies using the competitive CYP2D6 enzyme-linked immunosorbent assay, the specific CYP2D6 radioligand assay, and western blot using either human microsomes or recombinant CYP2D6. The fourth patient tested negative for anti-liver–kidney autoantibodies by either indirect immunofluorescence or the competitive enzyme-linked immunosorbent assay, but was repeatedly positive for anti-CYP2D6 autoantibodies by the sensitive and specific radioligand assay. Western blot experiments using human microsomes in this patient serum revealed two bands of 50 kDa and 55 kDa that documented as anti-CYP2D6 and anti-uridine triphosphate glucuronosyltransferase autoantibodies when recombinant CYP2D6 and recombinant uridine triphosphate glucuronosyltransferase autoantigens were used for immunoblot, respectively. Conclusions A relatively high incidence of anti-liver–kidney microsomal autoantibodies (10.3%) was found in a consecutive sample of Greek patients with hepatitis C. The expanded panel of assays, however, failed to document CYP2D6 as the target autoantigen of anti-liver–kidney microsomal autoantibodies in most patients. We report for the first time the detection of parietal cell antibodies and both anti-CYP2D6 (anti-liver–kidney microsomal type 1) and anti-uridine triphosphate glucuronosyltransferase (anti-liver–kidney microsomal type 3) autoantibodies in patients who were hepatitis C positive/hepatitis D negative. Further studies are needed to confirm our findings and to determine whether these preliminary results have a clinical importance or not.

Identification of cyclosporine A and tacrolimus glucuronidation in human liver and the gastrointestinal tract by a differentially expressed UDP-glucuronosyltransferase: UGT2B7

BACKGROUND/AIMS The oral administration of the major transplant immunosuppressants cyclosporine A and tacrolimus leads to unpredictable drug levels requiring drug monitoring. Hepatic and extrahepatic metabolism of cyclosporine A and tacrolimus by cytochrome P450 proteins has been analyzed but metabolism and inactivation by glucuronidation has not been investigated. METHODS Cyclosporine A and tacrolimus glucuronidation was measured in hepatic and gastrointestinal microsomal protein, and with 11 recombinant hepatic and extrahepatic family 1 and 2 UDP-glucuronosyltransferases. UDP-glucuronosyltransferase transcripts were determined by polymerase chain reaction. RESULTS Significant cyclosporine and tacrolimus glucuronidation activity was present in endoplasmic reticulum from liver, duodenum, jejunum, ileum and colon, but was absent in stomach. Specific cyclosporine A glucuronidation activity was highest in liver and colon, tacrolimus glucuronidation was highest in liver. Analyses using recombinant UDPglucuronosyltransferases identified UGT2B7 as a human UDP-glucuronosyltransferase with specific activity toward cyclosporine A and tacrolimus. The hepato-gastrointestinal distribution of immunosuppressant glucuronidation activity corresponded to the differential expression pattern of UGT2B7 mRNA. CONCLUSIONS This study provides conclusive evidence of hepatic and extrahepatic immunosuppressant glucuronidation by human UGT2B7 which was identified to be differentially expressed in the human hepatogastrointestinal tract. Hepatic and extrahepatic glucuronidation may influence the therapeutic efficacy of transplant immunosuppressants.

Cytochrome P450 2A6: a new hepatic autoantigen in patients with chronic hepatitis C virus infection

BACKGROUND/AIMS Cytochromes P4502A6 (CYP2A6) and P4501A2 (CYP1A2) were described as hepatic autoantigens in the autoimmune polyglandular syndrome type-1 (APS-1). We evaluated the significance of anti-CYP2A6 and anti-CYP1A2 in several hepatic diseases in the absence of APS-1. METHODS A radioligand assay (RLA) based on immunoprecipitation of [(35)S]-methionine-labeled CYP2A6 and CYP1A2 was used. Four hundred and thirty subjects with chronic viral hepatitis (n=185), autoimmune liver diseases (n=181), autoimmune rheumatic diseases (ARD, n=31) and healthy (n=33) were tested. RESULTS Seven out of 366 patients with liver diseases were anti-CYP2A6 positive. Neither healthy nor ARD patients showed anti-CYP2A6. One out of 181 patients with autoimmune liver diseases tested anti-CYP2A6 positive. A significantly higher prevalence of anti-CYP2A6 (P<0.05) was detected with six out of seven patients positive in the viral hepatitis group. The latter were infected by flaviviruses (1 HGV/GBVC, 5 HCV). 4/5 HCV/anti-CYP2A6 positive sera were positive for anti-LKM-1 by immunofluorescence and for anti-CYP2D6 by RLA. None of the 430 sera recognized CYP1A2. CONCLUSIONS For the first time CYP2A6 is reported as a hepatic autoantigen in patients with viral hepatitis caused by flaviviruses and in particular in HCV/anti-LKM-1 positive patients. Multicenter studies are needed in order to investigate the clinical importance of this novel finding. This study further supports that anti-CYP2A6 in the absence of flavivirus is rather limited to APS-1.

A Major CYP2D6 Autoepitope in Autoimmune Hepatitis Type 2 and Chronic Hepatitis C is a Three-dimensional Structure Homologous to Other Cytochrome P450 Autoantigens

Liver-kidney microsomal antibodies type 1 (LKM) are a diagnostic marker for autoimmune hepatitis type 2 (AIH-2), however, LKM autoantibodies are also detected in a small percentage of patients with chronic hepatitis C. The major target of LKM antibodies as evidenced by indirect immunofluorescence is cytochrome P4502D6 (CYP2D6). Anti-CYP2D6 titers of 62 LKM positive sera, 196 sera of patients with hepatic and rheumatic diseases and 33 sera of healthy blood donors (BD) were determined by an in vitro transcription/in vitro translation assay (ITT). Twenty five out of 26 AIH-2 sera and 33/36 LKM positive hepatitis C virus (HCV) sera were anti-CYP2D6 positive by ITT and antibody titers were similar in both patient groups. Epitope mapping experiments were performed by a series of truncated CYP2D6 proteins and by single epitopes of 257-269, 321-351, 373-389 and 410-419 amino acid (aa) expressed as DHFR-fusion proteins in Escherichia coli. The major linear epitope consists of 257-269 aa. This epitope is recognized with a significantly higher prevalence (64%) in AIH-2 than in LKM sera from patients with chronic hepatitis C (24%) (p lt; 0.001). None of the other autoepitopes showed significant differences in the prevalence of recognition by sera from both patient groups. Minor binding sites consisted of 321-351 aa, which was recognized by less than 20% of LKM sera and in the C-terminal region of 350-494 aa, which was recognized by less than 5% of LKM sera. Our study revealed an epitope of 321-379 aa on CYP2D6, which was shown to be conformation dependent. It was recognized by the vast majority of LKM sera, specifically by 76% of sera from HCV positive LKM patients and also by 76% of sera from patients with AIH-2. This epitope is homologous to three-dimensional epitopes detected by autoantibodies directed against hepatic cytochromes P450s in drug induced hepatitis and to an autoepitope on CYP21B associated with adrenal failure.

Autoimmunity in liver diseases

ConclusionThe characterization of B-cell epitopes using a variety of molecular biological tools has served to further a distinction between genuine autoimmune hepatitis and autoimmunity associated with ongoing viral hepatitis (Tables 1 and 2). This has been possible through the identification and characterization of antibody reactivity with a number of antigens belonging to the the cytochrome P450 and UGT1A super families of proteins. As a short-term effect, these studies help to define the regimens of treatment—corticosteroids in genuine AIH, interferon in viral hepatitis—and thus contribute to treatment safety. From the collection of data available, it appears that HDV and HCV infection additionally may be model diseases for virus-associated autoimmunity in humans.