LKM-positive autoimmune hepatitis in the western United States: a case series

OBJECTIVE

LKM-positive, or type 2, autoimmune hepatitis is characterized by the presence of antibodies directed against liver-kidney microsomes (LKM1). Although described frequently in southern Europe and the Mediterranean, this subtype of autoimmune liver disease seems to be extremely rare in northern Europe and in the United States. We report here five cases of LKM-positive autoimmune hepatitis that were seen at our center in the period 1989-1999.

METHODS

We reviewed the medical records of all patients with the diagnosis of AIH in our institution during the period 1989-1999, and found that five patients had type 2 AIH. All patients were female; four of five were young, and four of five presented with overt cirrhosis.

RESULTS

One patient died, one underwent liver transplantation and two are currently awaiting liver transplantation. Response to conventional immunosuppressive therapy was poor and two patients required treatment with cyclosporine and tacrolimus respectively. Four of five patients had at least one associated autoimmune disorder, including IgE-induced IgA deficiency, idiopathic thrombocytopenic purpura (ITP), and arthritis. HLA class II DR4 was present in two patients.

CONCLUSIONS

LKM-positive autoimmune hepatitis seems to be a subset of autoimmune hepatitis with distinct clinical features; although rare, it is occasionally encountered in the western United States. Prompt diagnosis and appropriate immunosuppressive treatment are recommended, as well as early referral to transplantation centers. Clinicians should be aware of this condition in the setting of young female patients with unexplained severe liver disease.

Comparative immunoreactivity of anti-trifluoroacetyl (TFA) antibody and anti-lipoic acid antibody in primary biliary cirrhosis: searching for a mimic

Previous studies documenting the existence of cross-reactivity between the lipoated (but not unlipoated) forms of the inner lipoyl domain (E2L2) of PDC-E2 [the major autoantigen in Primary biliary cirrhosis (PBC)] and trifluoroacetylated (TFA) proteins, led us to hypothesize that PBC may be due to an initial insult with an environmental agent that cross-reacts with TFA. Therefore, we performed a comparative study of the reactivity of rabbit anti-TFA antibody and anti-lipoic acid (LA) antibody against the mitochondrial autoantigens of human PBC and various TFA and LA conjugated proteins. Whereas both anti-TFA and anti-LA reacted with PDC-E2, the wild-type lipoated form of E2L2, OGDC-E2, E3-BP and LA-KLH, neither reacted with BCOADC-E2 or the non-lipoated form of E2L2. Of interest was that while anti-TFA reacted with PDC-E2, TFA-RSA and LA-KLH, it failed to inhibit PDC-E2 enzyme function. In contrast, anti-LA demonstrated cytoplasmic and mitochondrial staining, and inhibited PDC enzyme activity. Hence, although considerable cross reactivity exists between anti-TFA and anti-LA, the molecular nature of the interaction is clearly different. One of 14 PBC sera reacted weakly with TFA-albumin, whereas four of 14 PBC sera reacted with LA-KLH. Immunohistochemically, both anti-TFA and anti-LA antibodies reacted focally with periportal hepatocytes and bile ducts in both PBC and controls. However, anti-LA produced much stronger focalized staining of the bile ducts of diseased liver. This study suggests that while anti-TFA antibody recognizes lipoic acid-linked enzymes and proteins, the epitope recognized differs from that of anti-LA antibody and PBC autoantibodies. It is unlikely that a response to TFA is the triggering event in PBC. Anti-LA antibodies share a higher degree of similarity to PBC sera providing suggestive evidence that anti-LA antibodies or anti-LA like antibodies (mimotopes) may help define the initiator of the autoimmune response.

Autoantibodies associated with acute rejection after liver transplantation for type-2 autoimmune hepatitis

Autoantibodies, markers of autoimmune diseases, can also be detected in chronic allograft rejection. However, the appearance of these autoantibodies in acute rejection after orthotopic liver transplantation has not yet been reported. Liver-kidney-microsome type-1 (LKM-1) antibodies directed against the autoantigen cytochrome CYP2D6 define a group of patients with autoimmune hepatitis type-2 (AIH-2), distinct from autoimmune hepatitis type-1 (AIH-1) in which anti-nuclear antibodies and anti-smooth muscle antibodies (SMA) with actin specificity are present in patient sera. Autoantibodies were studied by the quantitative CYP2D6 radioligand assay (RLA) that uses a radiolabeled CYP2D6 as antigen, immunoblotting using recombinant CYP2D6 protein and human liver microsomal and cytosolic fractions, and indirect immunofluorescence (IIF) using rat kidney-stomach-liver cryostat sections. In addition, the specificity of anti-SMA was detected by IIF on HEp2 cell line harvested with colchicin. This report describes the time course of CYP2D6 antibodies and the appearance of anti-SMA (without anti-actin, cytokeratin and vimentin reactivity) associated with acute rejection during a 2-year follow-up, in a patient who underwent transplantation at end-stage type 2 autoimmune hepatitis. In addition, we report a new reactivity against an unknown 40-kDa protein using a rat cytosolic fraction. The detection of autoantibodies in sequential samples may be important to better predict rejection or relapse, and to establish adequate therapy.

The Long Evans Cinnamon (LEC) rat develops hepatocellular damage in the absence of antimicrosomal antibodies

Long Evans Cinnamon (LEC) rats are an inbred strain with a mutation affecting a copper transporter. As a result, hepatic copper levels rise and the rats spontaneously develop hepatitis that is fatal in about 40% of the rats. The rats that die have been reported to develop anti-microsomal antibodies, most frequently against protein disulfide isomerase (PDI), prior to the onset of liver damage. The association between the presence of antibodies and death of the LEC rats, along with the detection of antibodies prior to the detection of liver damage suggested that the antibodies may have a role in the pathogenesis of liver damage. The objective of this study was to more clearly delineate the temporal relationship between antibody production and the onset of liver damage and copper accumulation. Serum was screened for the presence of anti-microsomal antibodies by immunoblotting. Liver damage was assessed by serum biochemistry and histological examination on rats between 6 and 12 weeks of age (four per group). Copper accumulation in the liver was determined by biochemistry and histological examination. Evidence of liver damage was detectable by serum biochemistry and histopathology by 11.5 weeks. Copper was rarely detected in hepatocytes, although it was detected in macrophages. Sera from only one of seven rats with evidence of liver damage had detectable anti-microsomal protein antibodies. The protein recognized was not PDI. The development of anti-microsomal autoantibodies did not precede the development of significant liver damage, suggesting that they play only a secondary role, if any, in the pathogenesis of hepatitis in this rat strain.

Treatment of autoimmune and extra-hepatic manifestations of HCV infection

Hepatitis C virus (HCV) infects mononuclear cells and may, like other viruses, cause immunological disorders. Immunological abnormalities observed in HCV infections are usually nonspecific (e.g. cryoglobulinemia, immune complex deposits, autoantibodies). There is a clear association between cryoglobulinemia and hepatitis C and cryoglobulinemia related symptoms are usually improved by treatment with interferon alpha, although patients usually relapse after treatment end. The relationships between hepatitis C and other immunological abnormalities are unclear. The association between chronic hepatitis C and anti-smooth muscle or anti-nuclear antibodies does not appear to be significantly different from that in other hepatic disorders, particularly hepatitis B. Conversely, patients with hepatitis C have significantly more often anti-liver kidney microsomal (LKM1) antibodies than patients with other causes of liver diseases. When clinical, histological and biological findings are indicative of HCV infection with chronic hepatitis, interferon alpha or combination therapy with ribavirin are treatments options. Conversely, when clinical context and results of laboratory tests are in favor of an autoimmune disorder or of overlap-syndromes (i.e. both autoimmune and viral hepatitis), interferon should not be given in first intention, since revelation or exacerbation of autoimmune hepatitis have been reported under interferon. An important prevalence of anti-HCV antibodies has also been reported in patients with sialadenitis, lichen planus and thyroiditis. It has been clearly demonstrated that interferon may induce or worsen such immunological diseases, but there are very few studies showing improvement of these manifestations under interferon. In conclusion, interferon may be appropriate in patients with HCV infection and extrahepatic manifestations linked to immune complex deposition, whereas, in other cases, careful assessment of patients with autoimmune processes is necessary before choosing any treatment strategy.

Decrease in brain cytochrome P450 enzyme activities during infection and inflammation of the central nervous system

The effect of infection and inflammation of the central nervous system (CNS) on cytochrome-P450-dependent activities in brain, spinal cord and liver microsomes was determined. For this, two models were used: (1) the intracerebroventricularly injected lipopolysaccharide (LPS) model and (2) the experimental auto-immune encephalomyelitis (EAE) model. In the LPS model, aminopyrine N-demethylase (AMND) and ethoxycoumarin O-deethylase (ECOD) activities (both P450 dependent) were significantly decreased (35 and 20%, respectively) in brain microsomes. In the EAE model, only ECOD activity was significantly lower (18%). In the liver, a decrease in total P450, AMND and ECOD activities was only observed in the LPS model. In both models, tumour necrosis factor (TNF) was significantly elevated in brain and spinal cord tissues. In serum, TNF was only detectable in the LPS model. It is concluded that an infection or inflammation located in the CNS, which is accompanied by high TNF levels, results in a decrease in P450-dependent metabolism not only in the liver but in the brain as well.

Autoantigen characterization in liver/kidney microsome positive hepatitis

Liver/kidney microsome autoantibodies are detectable in different forms of chronic hepatitis, namely autoimmune, viral, and drug-induced hepatitis and in hepatitis associated with Type 1 autoimmune polyglandular syndrome. Based on the aetiology of chronic hepatitis, liver/kidney microsome autoantibodies are directed against different enzymes with very little overlap. Thus, the simple Indirect Immunofluorescence test, which is universally used as a screening test to detect autoantibodies, does not allow subtyping of liver/kidney microsome autoantibodies. This brief review stresses the need to use methods such as Western-Blotting and enzyme-linked immunosorbent assay together with Indirect Immunofluorescence to characterize the liver/kidney microsome autoantibodies. Identification of the liver/kidney microsome target antigens, when possible, makes differential diagnosis easier and, at times, may help the clinician to choose the best approach to treatment.

Overlapping but distinct specificities of anti-liver-kidney microsome antibodies in autoimmune hepatitis type II and hepatitis C revealed by recombinant native CYP2D6 and novel peptide epitopes

Anti-liver-kidney microsome antibodies (anti-LKM) occur in autoimmune hepatitis (AIH) type II and in a subset of patients with hepatitis C. Anti-LKM1 in AIH are directed against cytochrome P4502D6 (CYP2D6), but conflicting data exist concerning the specificity of anti-LKM in hepatitis C. The aim of this study was to evaluate binding specificities of anti-LKM antibodies in both diseases using novel test antigens as well as their inhibitory capacity on CYP2D6 enzyme activity. Sera from 22 patients with AIH type II and 17 patients with hepatitis C being anti-LKM-positive in the immunofluorescence test were investigated for binding to native recombinant CYP2D6 and liver microsomes by ELISA and immunoblotting, and to synthetic peptides covering the region 254-339 (254-273, 257-269, 270-294, 291-310, 307-324, 321-339, 373-389) as well as the novel peptide 196-218 by ELISA. Furthermore, all sera were tested for inhibition of CYP2D6-dependent bufuralol 1'-hydroxylase activity. Twenty of the 22 AIH type II sera (91%) and nine of the 17 hepatitis C sera (53%) were positive for CYP2D6 by ELISA and/or immunoblotting. The previously described major peptide epitope comprising CYP2D6 amino acids 257-269 was recognized by 16 of the 22 AIH sera but by only one hepatitis C serum. A further epitope, 196-218, could be defined for the first time as another immunodominant epitope for AIH because it was recognized by 15 of the 22 AIH (68%) but only three of the 17 hepatitis C sera (18%). With the exception of the peptide 254-273, the other peptides showed no significant reactivity. Analysing the inhibitory properties of anti-LKM antibodies it emerged that 95% of AIH sera and 88% of hepatitis C sera inhibited enzyme function. These data indicate that anti-LKM antibodies in AIH and hepatitis C react with CYP2D6, as shown by their inhibitory activity, and that besides the known epitope 257-269 a further immunodominant epitope exists on CYP2D6 which is recognized by sera from patients with AIH II but hardly by sera from patients with hepatitis C.

Sera of children with hepatitis C infection and anti-liver-kidney microsome-1 antibodies recognize different CYP2D6 epitopes than adults with LKM+/HCV+ sera

BACKGROUND

Liver-kidney microsome type 1 (LKM1) antibodies are specific markers of autoimmune hepatitis (AIH) type 2. Antibodies to LKM1 have been found in 2% to 3% of adults infected with hepatitis C virus (HCV) without AIH. Thirty percent of these antibodies are directed against linear sequences of CYP2D6 protein. LKM1 antibodies in HCV+/LKM1+ sera and in sera of AIH patients do not recognize the same CYP2D6 epitopes. The current study was conducted to determine whether LKM1 antibodies in HCV+/LKM1+ children's sera are the result of the same immune response as the antibodies described in AIH type 2 and in HCV+/LKM1+ adult patients.

METHODS

Sera from 10 HCV+/LKM1+ children were tested against human liver microsomal and cytosolic proteins by Western blot analysis and against synthetic peptides of the CYP2D6 sequence between amino acids 200 and 429 by dot blot. The same sera were tested against radiolabeled CYP2D6 by immunoprecipitation.

RESULTS

Four of 10 sera tested by Western blot analysis showed immunoglobulin (Ig) G-type antibodies against CYP2D6, and 2 had antibodies against proteins of 58, 66, and 84 kDa. One of the sera also contained IgM-type anti-66-kDa and 84-kDa proteins. The radioligand test detected anti-CYP2D6 antibodies in 9 of 10 patients. Five of the anti-CYP2D6-positive sera recognized a peptide between amino acids 200 and 429 including amino acids 254-271.

CONCLUSIONS

Most HCV+/LKM1+ sera from children recognize conformational epitopes of the CYP2D6 antigen, and half recognize linear epitopes. Some HCV+/LKM1+ sera demonstrated antibodies against the AIH type 2 main antigenic site of the CYP2D6. Screening of HCV RNA should be performed before starting treatment of presumed autoimmune hepatitis associated with LKM1.

Prevalence of GBV-C/HGV-RNA, virus genotypes, and anti-E2 antibodies in autoimmune hepatitis

OBJECTIVE

We investigated the prevalence of hepatitis G-RNA (GBV-C/HGV-RNA), a recently cloned new flavivirus, and of antibodies to the envelope 2 antigen (anti-E2), a marker of past infection, in patients with autoimmune hepatitis, and compared it with the prevalence in patients with chronic viral hepatitis and healthy control individuals.

METHODS

Sera of 63 patients with autoimmune hepatitis were studied for the presence of GBV-C/HGV-RNA by reverse-transcription polymerase chain reaction and for anti-E2 by enzyme-linked immunosorbent assay. GBV-C/HGV genotypes were determined by genome sequencing.

RESULTS

Patients with autoimmune hepatitis had a similar high prevalence of GBV-C/HGV-RNA and anti-E2 antibodies as patients with chronic viral hepatitis B or C. GBV-C/HGV-RNA was found significantly more often in patients with autoimmune hepatitis (11%, p = 0.045), hepatitis B (16%, p = 0.004), or hepatitis C (21%, p = 0.001) than in healthy controls (2%). The prevalence of anti-E2 antibodies in patients with autoimmune hepatitis was not different from healthy controls (17% vs 13%, NS). The various subtypes of autoimmune hepatitis had similar prevalence rates of GBV-C/HGV-RNA as patients with liver-kidney microsomal antibody-positive hepatitis C. All of our anti-E2+ (GBV-C/HGV-RNA-) patients were positive for anti-smooth-muscle antibody, whereas only 29% of GBV-C/HGV-RNA+ (anti-E2-) patients were positive (p = 0.025). All seven of the GBV-C/HGV-RNA+ patients with autoimmune hepatitis had genotype 2a, which is also the most prevalent genotype in our region.

CONCLUSION

The prevalence of GBV-C/HGV-RNA is significantly increased in patients with autoimmune hepatitis, compared with healthy controls, and is similar to the increased prevalence seen in chronic hepatitis B or C patients. Anti-E2 positivity was associated with antibodies against smooth-muscle antigen in all cases. All GBV-C/HGV+ autoimmune hepatitis patients were infected with genotype 2a.

A novel assay for detecting antibodies to cytochrome P4502D6, the molecular target of liver kidney microsomal antibody type 1

Liver Kidney Microsomal type 1 (LKM1) antibody, the diagnostic marker of autoimmune hepatitis type 2, is also found in a proportion of patients with hepatitis C virus infection (HCV). It is detected conventionally by the subjective immunofluorescence technique. Our aim was to establish a simple and objective enzyme-linked immunosorbent assay (ELISA) that measures antibodies to cytochrome P4502D6 (CYP2D6), the target of LKM1. An indirect ELISA using eukaryotically expressed CYP2D6 was designed. Absorbance values obtained against a reference microsomal preparation were subtracted from those obtained against a microsomal preparation over-expressing CYP2D6, thus removing the non-CYP2D6-specific reaction. Sera from 51 LKM1 positive patients (21 autoimmune hepatitis and 30 with HCV infection), 111 LKM1 negative patients with chronic liver disease (including 20 with HCV infection) and 43 healthy controls were tested. Of 51 patients positive by immunofluorescence, 48 were also positive by ELISA while all the 154 LKM1 negative subjects were also negative by ELISA. There was a high degree of association between IFL and ELISA as demonstrated by a kappa reliability value of 0.96. The absorbance values by ELISA correlated with immunofluorescence LKM1 titres both in autoimmune hepatitis (r = 0.74, p < 0.001) and HCV infection (r = 0.67, p < 0.001). The simple, objective ELISA described has the potential to replace the standard immunofluorescence technique.

Autoantibodies against cytochromes P-4502E1 and P-4503A in alcoholics

Autoantibodies against soluble liver enzymes have been reported among alcoholics, but the targets of self-reactivity toward membrane proteins of the liver have not been characterized. Previously, among alcoholics, we found antibodies against ethanol-derived radical protein adducts that are dependent on cytochrome P-4502E1 (CYP2E1) for their formation. To further investigate autoantibodies against cytochrome P-450s during alcohol abuse, sera of rats chronically treated with ethanol in the total enteral nutrition model and sera from alcoholics with or without alcohol liver disease and from control subjects were analyzed by enzyme-linked immunosorbent assay and Western blotting for the presence of IgG against rat and human CYP2E1, rat CYP3A1, and human CYP3A4. A time-dependent appearance of IgG against rat CYP3A1 and CYP2E1 was evident during chronic ethanol feeding of rats. Anti-CYP2E1 reactivity showed positive correlation with the levels of hepatic CYP2E1 and was inhibited by the CYP2E1 transcriptional inhibitor chlormethiazole. Screening of the human sera by enzyme-linked immunosorbent assay revealed reactivity against CYP3A4 and CYP2E1 in about 20 to 30% and 10 to 20% of the alcoholic sera, respectively. No difference were noted between sera from alcoholics with or without hepatitis C virus infection, and only very little reactivity was seen in sera from control subjects. Western blotting analysis revealed anti-human CYP2E1 reactivity in 8 of 85 alcoholic sera and 3 of 58 control sera, whereas anti-CYP3A4 reactivity was detected in 18 of 85 alcoholic sera and 4 of 58 control sera, which were different from the sera reactive with CYP2E1. Immunoblot reactivity of CYP3A4-positive alcoholic sera was found against glutathione-S-transferase fusion proteins containing truncated forms of CYP3A4, and such sera were also able to immunoprecipitate in vitro translated CYP3A4. Seven of eight sera showed reactivity toward domains C-terminal of position Ser281, and 1 of 8 sera recognized autoepitopes within the region Thr207-Ser281. These findings indicate that alcoholics develop autoantibodies against CYP2E1 and CYP3A4 that the CYP3A4 C-terminal domain is a target for the autoantibody reactions among a subset of alcoholics. The novel finding of CYP3A4 autoantibodies and their significant expression among alcoholics warrants further investigation. Attention should be given to immune toxicity associated with CYP3A4 autoantibodies and cases of alcohol abuse that are accompanied by exposure to drugs and substances that are CYP3A substrates.

Effect of 3-methylcholanthrene administration on expression of cytochrome P-450 isoforms induced by phenobarbital in rat hepatocytes

The effects of an inducer on expression of cytochrome P-450 (P-450) isoforms induced antecedently by another inducer are unknown. Thus, we examined the amount of phenobarbital (PB)-inducible P-450 isoforms (P-450 2B1/2B2) in hepatocytes from rats injected first with PB and then with 3-methylcholanthrene (MC) (PB+MC-treated animals) by quantitative immunohistochemistry. In addition, expression of P-450 2B2 mRNA was examined by in situ hybridization. In PB-treated animals, P-450 2B1/2B2 content increased in perivenular and midzonal hepatocytes. In PB+MC-treated animals, however, the PB-induced increase in 2B1/2B2 content was suppressed in perivenular hepatocytes but promoted in midzonal hepatocytes. The hybridization signal for P-450 2B2 mRNA appeared almost exclusively in perivenular hepatocytes after 24 hr of PB injection and disappeared after 48 hr of injection. In PB+MC-treated animals, however, strong hybridization signal was observed in midzonal and perivenular hepatocytes after 48 hr of PB injection. The promotion of the increase in P-450 2B1/2B2 content in midzonal hepatocytes in PB+MC-treated animals probably corresponds to the strong hybridization signal, whereas there appeared to be a divergence between the intensity of the signal and the content in perivenular hepatocytes. The results indicate that MC administration drastically influences the pattern of expression of P-450 isoforms induced by PB in perivenular and midzonal hepatocytes.

Autoantibodies in Estonia and Sweden, populations with different responses to allergens

BACKGROUND

There are substantial differences in immune-mediated disease prevalence between different countries and populations which cannot be explained by genetic variability.

AIMS

To compare the prevalence of antinuclear (ANA), antimitochondrial, antireticulin, liver-kidney microsomal, parietal cell, thyroid microsomal and double-stranded DNA (dsDNA) antibodies among adults aged 20-44 years in two towns, i.e. in Tartu, Estonia (n = 448) and in Uppsala, Sweden (n = 532) with a low and a high prevalence of allergy.

METHODS

For autoantibody detection, standard indirect immunofluorescence tests on tissue and Chritidia lucilia antigenic preparations were used (sera were diluted starting from 1:10).

RESULTS

The prevalence of ANA was lower in Tartu than in Uppsala (3 vs. 10% among males and 11 vs. 16% among females; p<0.01 and p<0.1, respectively). Furthermore, dsDNA antibody-positive cases were only identified in Uppsala. The largest difference between the two populations was revealed for IgM type ANA, both among males (1 vs. 6%; p<0.02) and females (5 vs. 11%; p<0.01). In addition, the antibody titers were lower in Tartu than in Uppsala (p<0.05). The prevalence of other autoantibodies was similar in the two towns.

CONCLUSIONS

The findings could support that Th2-like immune responses are commoner in Sweden than in Estonia, as previously suggested by the higher prevalence of allergy.

Ethylmorphine N-demethylase activity as a marker for cytochrome P450 CYP3A activity in rat hepatic microsomes

The purpose of this study was to evaluate the selectivity and sensitivity of ethylmorphine N-demethylase (EMD) as an indicator of chemically-induced cytochrome P450 CYP3A activity in liver microsomes of rats following treatment with selective enzyme inducers. Male and female Sprague-Dawley (CD) rats were dosed with either pregnenolone-16alpha-carbonitrile (PCN; 50 mg/kg per day for 5 days), phenobarbital (PB; 100 mg/kg per day for 4 days), beta-naphthoflavone (betaNF; 100 mg/kg per day for 3 days), clofibrate (CF; 300 mg/kg per day for 14 days), isoniazid (ISO; 100 mg/kg per day for 3 days), or dexamethasone (DEX; 50 mg/kg per day for 4 days). Microsomes were isolated, frozen and subsequently assayed for protein, cytochrome P450 content and EMD activity. In males, significant elevations (P < 0.01) in EMD activity were observed in microsomes from PB-, DEX- and PCN-dosed animals compared with untreated controls. Microsomes from ISO- and betaNF-dosed males showed a reduction (P < 0.05) in EMD activity when compared with control microsomes, and CF was without effect. In females, EMD activities were significantly increased in microsomes from PCN, DEX and PB-dosed but not betaNF, ISO, or CF-dosed animals. As expected on the basis of sex-related differences in gene expression, EMD activities in untreated animals were considerably higher in males than females, attributable to constitutive CYP3A and CYP2C11 activities. The selectivity of EMD for induced CYP3A was confirmed on the basis of inhibition studies with selected steroid substrates of CYP3A, polyclonal anti-CYP3A1 antibodies and triacetyloleandomycin (TAO), a selective inhibitor of CYP3A. In conclusion, for both sexes, the greatest elevations (approximately 3-13-fold) in EMD activity were observed in microsomes from rats dosed with DEX, a potent archetypal inducer with lesser but significant increases noted for PCN and PB, indicating that EMD is a reliable indicator of induced rat hepatic cytochrome P450 CYP3A activity.

Autoimmune disease is not a feature of hepatitis C infection in Ireland

To determine the prevalence of autoimmune disease, autoantibody positivity, or both in Irish persons with hepatitis C, we surveyed 98 such patients (55 recipients of anti-D, 25 intravenous drug abusers, and 18 blood transfusion recipients). We studied them clinically and tested for anti-nuclear, anti-smooth muscle, and anti-mitochondrial, liver-kidney microsomal, thyroid microsomal, thyroid globulin, and gastric parietal antibodies; and also for rheumatoid factor. In the anti-D antibody group (all female), two patients reported generalized musculoskeletal symptoms but had no demonstrable physical signs. We did not find cryoglobulins in any patient. We detected thyroid microsomal antibodies in only 6 of 55 (10.9%) patients. (In two of these, thyroid globulin antibodies were also positive). These patients were all clinically euthyroid, but two had borderline low-normal thyroid function tests. Titers for anti-nuclear antibodies were weakly positive in 5 of 55 (9.1%) patients, and gastric parietal antibodies were positive in 5 of 55 (9.1%) patients. In particular, we noted no antibodies to liver-kidney microsome. Rheumatoid factor was detected in eight patients. Forty-seven of 55 patients were genotype 1b, and 8 of 55 were genotype 3. In the intravenous drug abusers (8 women, 17 men), we detected no autoantibodies. Seven of the 25 genotypes were tested; three were genotype 3 and four were genotype 1b. In the transfusion group (10 women, 8 men), we detected no autoantibodies apart from weak anti-nuclear antibody Titers (1:10), which we found three patients. Five of 10 genotypes tested were of genotype 3 and the other five were of genotype 1b. These findings suggest that in Irish patients with hepatitis C, neither genotype nor source (and dose) of inoculum contributes to the development of autoimmune disease. How hepatitis C virus is associated with autoimmune disease in other studies remains unknown. The answer may, at least in part, be found in genetic; HLA typing studies should provide useful information.

Effects of co-administration of butylated hydroxytoluene, butylated hydroxyanisole and flavonoids on the activation of mutagens and drug-metabolizing enzymes in mice

Effects of co-administration of food additives and naturally occurring food components were studied on the activation of mutagens. Male mice (ddY) were given diets containing butylated hydroxytoluene (BHT) or butylated hydroxyanisole (BHA) and flavone or flavanone (2,3-dihydroflavone) for two weeks and the ability of hepatic microsomes to activate aflatoxin B1, benzo[a]pyrene and N-nitrosodimethylamine was determined by the mutagenicity test. Co-administration of an antioxidant (0.1% BHT or 0.2% BHA in diet) and a flavonoid (0.1% flavone or 0.1% flavanone) resulted in additive effects on the activation of aflatoxin B1 and benzo[a]pyrene, while the activation of N-nitrosodimethylamine was not elevated significantly by the co-administration. To understand the mechanism for the additive effects, induction of specific isozymes of cytochrome P450 involved in the activation of the mutagens was studied. Co-administration of BHT (0.1%) and flavone (0.1%) increased markedly the levels of proteins and the activities of the enzymes related to the isozymes of CYP2A and CYP2B, while co-administration of BHA (0.2%) and flavanone (0.1%) elevated those related to CYP1A. Further, the activation of aflatoxin B1 and benzo[a]pyrene in hepatic microsomes was inhibited by the antibodies against these isozymes, which suggested that the enhanced activation of the mutagens by the co-administration might be mediated by the induction of these isozymes.

Specific inhibition of human CYP1A2 using a targeted antibody

The structural similarity of related forms of P450 makes selective immunoinhibition of individual forms notoriously difficult to achieve. We report the use of a targeted antibody to overcome this problem. An antibody was raised against the synthetic peptide, Ser-Lys-Lys-Gly-Pro-Arg-Ala-Ser-Gly-Asn-Leu-Ile, corresponding to residues 291-302 of human CYP1A2. This sequence of human CYP1A2 is located in a similar position to a proinhibitory region previously identified in rat CYP1A1 and CYP1A2. The antibody bound strongly and specifically to CYP1A2 in human hepatic microsomal fraction. Binding was unaffected by denaturation of the protein. The specificity of the antibody was demonstrated by immunoblotting of human hepatic microsomal fraction where a single immunoreactive band was identified at Mr 54,000. The intensity of this band correlated strongly with high-affinity phenacetin O-deethylase activity of the microsomal fractions. In addition, the antibody bound to a single protein at Mr 54,000 in the microsomal fraction of lymphoblastoid cells expressing human CYP1A2, but not to any other recombinant P450 enzyme. CYP1A2-dependent activity (high-affinity phenacetin O-deethylase) of human hepatic microsomal fraction was inhibited >90% by whole antiserum or purified immunoglobulin. This decrease in activity represents complete inhibition of CYP1A2 activity, residual phenacetin O-deethylase activity being due to low-affinity enzymes. In contrast, the antibody, which does not bind to rat CYP1A2, had no effect on CYP1A2-dependent activity (high-affinity phenacetin O-deethylase) of rat hepatic microsomal fraction. The antiserum also had no effect on human hepatic microsomal debrisoquine 4-hydroxylase (CYP2D6) or coumarin 7-hydroxylase (CYP2A6) activities, indicating that inhibition was specific to human CYP1A2. These results demonstrate the importance of the region comprising residues 291-302 of human CYP1A2 in the catalytic activity of this enzyme.

Bioactivation of monocrotaline by P-450 3A in rat liver

Monocrotaline (MCT) is bioactivated in liver cytochrome P-450s to MCT pyrrole (MCTP), which primarily injures the lung endothelium to result in the development of pulmonary hypertension (PH) in rats. However, whether there is a relation between the degree of PH and the activity of liver cytochrome P-450 to convert MCT to MCTP remains unclear. To examine the relation between these physiological and biochemical changes, we first measured the severity of MCT-induced (20 mg/kg) PH in male, female, castrated male, and phenobarbital (PB, liver P-450s inducer)-pretreated male rats. The degree of right ventricular hypertrophy was more severe in PB-pretreated male than in control male rats. It was also more severe in male than in either female or castrated male rats, suggesting that sex-specific P-450s could be involved in the metabolic pathways of MCT in the liver. Further to explore which of the isozymes (2A2, 2C11, and 3A) of P-450s in the liver is responsible for the bioactivation of MCT, we measured the rate of MCTP production in hepatic microsomes by a modified Mattock's method. Treatment of male rats with PB and pregnenolone 16alpha-carbonitrile (PCN), which is the specific inducer of P-450 3A, increased the rate of MCTP production, suggesting that P-450 3A may contribute to the conversion to pyrrole. Therefore we measured the amount of P-450 3A protein by immunoblotting and attempted to inhibit MCT metabolism by using antibodies to P-450 3A. P-450 3A was significantly induced by PCN (6.5-fold) and PB (4.6-fold) treatment and reduced by castration (0.38-fold). The amount of P-450 3A was closely correlated with the production of MCTP, and the conversion of MCT to MCTP was strongly inhibited by antibodies against P-450 3A. These results indicated that P-450 3A was predominantly responsible for the metabolism of MCT to MCTP in rat liver and suggested a tight linkage between the degree of PH and the activity of liver P-450 3A.

Plasma membrane hydroxyethyl radical adducts cause antibody-dependent cytotoxicity in rat hepatocytes exposed to alcohol

BACKGROUND & AIMS

We reported previously that patients with alcoholic liver disease (ALD) have circulating immunoglobulins reacting with cytochrome P4502E1 (CYP2E1) complexed with hydroxyethyl free radicals. The aim of this study was to investigate whether hydroxyethyl radical adducts are present on the plasma membranes of ethanol-treated hepatocytes and their role in antibody-dependent cytotoxicity.

METHODS

Immunofluorescence confocal laser microscopy, Western blotting, and antibody-dependent cell-mediated cytotoxicity assay were used.

RESULTS

Isolated rat hepatocytes incubated in vitro with ethanol or obtained from ethanol-treated animals showed strong surface fluorescence when exposed to rabbit anti-hydroxyethyl radical serum or sera from patients with ALD. No surface fluorescence was evident on control hepatocytes or after scavenging hydroxyethyl radicals with 4-pyridyl-1-oxide-t-butyl nitrone. The presence of CYP2E1-hydroxyethyl radical adducts on hepatocyte plasma membranes was shown by Western blot and by immunofluorescence using double staining for human and rabbit anti-CYP2E1 immunoglobulin G. Cytotoxicity was observed in ethanol-treated hepatocytes incubated with immunoglobulin G from patients with ALD and normal human blood mononuclear cells. This effect was blocked by preabsorbing the sera with human albumin complexed with hydroxyethyl radicals, which also eliminated the antibody reaction with the plasma membranes.

CONCLUSIONS

Hydroxyethyl radicals bound to CYP2E1 on hepatocyte plasma membranes can target immune reactions triggered by alcohol abuse.

Epitope mapping of human CYP1A2 in dihydralazine-induced autoimmune hepatitis

Dihydralazine-induced hepatitis is characterized by the presence of anti-liver microsomal (anti-LM) autoantibodies in the sera of patients. Cytochrome P450 1A2 (CYP1A2), involved in the metabolism of dihydralazine, was shown to be a target for autoantibodies. In order to investigate further the relationship between drug metabolism and the pathogenesis of this drug-induced autoimmune disease, and since the specificity of anti-LM autoantibodies towards CYP1A2 has been determined, the antigenic site was further localized. By constructing fragments derived from CYP1A2 cDNA and probing the corresponding proteins with several anti-LM sera, we were able to define a region (amino acid 335-471) which was immunoreactive with 100% of sera. An internal deletion in this region led to the loss of recognition by anti-LM autoantibodies, confirming that the epitope was conformational. Epitope mapping studies had previously been performed for CYP2D6, CYP17, CYP21A2, and recently for CYP3A1 and CYP2C9. Those data were compared with results obtained in the present study for CYP1A2.

Inhibitory anti-peptide antibody against human CYP3A4

An inhibitory anti-peptide antibody was raised against a 21-amino acid peptide (VKRMKESRLEDTQKHRVDFLQ) corresponding to residues 253-273 of human cytochrome P450 3A4. High titer antibodies were produced by rabbits immunized with this peptide coupled to keyhole limpet hemocyanin, as judged by ELISA. Anti-peptide antibody recognized a single protein band in microsomes prepared from cells expressing recombinant human CYP3A4 in immunoblotting analysis. No immunodetectable proteins were found in microsomes containing other cytochrome P450 isoforms. In addition, the antibody did not recognize CYP3A5, a closely related isoform in the CYP3A family. In human liver microsomes, only one protein band which comigrated with human CYP3A4 was recognized by this antibody and the relative blotting intensity of this protein band correlated significantly with human CYP3A4-catalyzed testosterone 6 beta-hydroxylase activities (r = 0.96). More importantly, this antibody exhibited greater than 90-95% inhibition of testosterone 6 beta-hydroxylation, while other cytochrome P450-mediated reactions in human liver microsomes were not inhibited. Because of its specificity and inhibitory potency, this anti-peptide antibody should be a valuable tool in evaluating the role of CYP3A in mediating in vitro metabolism of therapeutic agents.