Mycobacterial DNA not detected in liver sections from patients with primary biliary cirrhosis

No rise in incidence but geographical heterogeneity in the occurrence of primary biliary cirrhosis in North East England

In this study, we examined temporal changes in the incidence of primary biliary cirrhosis (PBC) and investigated associations between PBC incidence and sociodemographic factors and spatial clustering. We included 982 patients aged ≥40 years from North East England with incident PBC diagnosed during 1987–2003. Age-standardized incidence rates with 95% confidence intervals were calculated. Negative binomial regression was used to analyze incidence and socioeconomic deprivation. Clustering analysis was performed using point process methods, testing the null hypothesis that disease risk does not vary spatially and that PBC cases occur independently. The age-standardized incidence rate was 53.50 per million persons per year (95% confidence interval: 48.65, 58.35) in 1987–1994 and 45.09 per million persons per year (95% confidence interval: 41.10, 49.07) in 1995–2003. Risk of PBC increased in areas with higher levels of socioeconomic deprivation (P = 0.035). More specifically, risk increased in areas with higher levels of overcrowded homes (P = 0.040), higher levels of households without cars (P < 0.001), and higher levels of non-owner-occupied homes (P < 0.001). Overall, there was evidence of spatial clustering (P = 0.001). The findings confirm that overall incidence of PBC did not rise over time, but sociodemographic variations suggest that certain aspects of deprivation are involved in its etiology.

Tracing environmental markers of autoimmunity: introducing the infectome

We recently introduced the concept of the infectome as a means of studying all infectious factors which contribute to the development of autoimmune disease. It forms the infectious part of the exposome, which collates all environmental factors contributing to the development of disease and studies the sum total of burden which leads to the loss of adaptive mechanisms in the body. These studies complement genome-wide association studies, which establish the genetic predisposition to disease. The infectome is a component which spans the whole life and may begin at the earliest stages right up to the time when the first symptoms manifest, and may thus contribute to the understanding of the pathogenesis of autoimmunity at the prodromal/asymptomatic stages. We provide practical examples and research tools as to how we can investigate disease-specific infectomes, using laboratory approaches employed from projects studying the “immunome” and “microbiome”. It is envisioned that an understanding of the infectome and the environmental factors that affect it will allow for earlier patient-specific intervention by clinicians, through the possible treatment of infectious agents as well as other compounding factors, and hence slowing or preventing disease development.

Primary biliary cirrhosis does not increase the risk of UTIs following diagnosis compared to other chronic liver diseases?

BACKGROUND

Urinary Tract Infections (UTIs) occur more frequently in patients with Primary Biliary Cirrhosis (PBC). Previous studies have compared UTI occurrence in PBC and general population controls, however, it remains unclear if UTI is a feature of all chronic liver diseases (CLD)s, or is specific to PBC, or if this is a cause or consequence of PBC.

AIMS

We aimed to determine if UTIs are more common after a diagnosis of PBC compared to general population and CLD controls.

METHODS

A cohort study was conducted using the General Practice Research Database. We selected all cases of PBC plus 10 age- and sex-matched general population controls, and an unmatched group with other CLDs. We formed a Cox-proportional hazard model of time to first UTI following diagnosis.

RESULTS

Two hundred and forty-eight (24.6%) of PBC cases had a UTI event compared with 2127 (21.1%) of matched and 2131 (11.7%) of the unmatched CLD controls. Comparing PBC with matched controls showed an approximately 30% increased risk of UTI [hazard ratio (HR) 1.33 confidence interval (CI) 1.17-1.52]. Adjusting for diabetes, smoking and previous UTI reduced this (HR 1.25 CI 1.09-1.42). The Hazard Ratio comparing PBC with unmatched CLD controls was 2.00 (CI 1.76-2.28), but this became non-significant when adjusting for age, sex, diabetes, smoking and previous UTI 0.98 (0.86-1.12).

CONCLUSIONS

There is increased risk of UTI in PBC patients compared to general population controls, but not compared to CLD controls suggesting that this association is not specific to PBC after diagnosis.

Infectome: a platform to trace infectious triggers of autoimmunity

The "exposome" is a term recently used to describe all environmental factors, both exogenous and endogenous, which we are exposed to in a lifetime. It represents an important tool in the study of autoimmunity, complementing classical immunological research tools and cutting-edge genome wide association studies (GWAS). Recently, environmental wide association studies (EWAS) investigated the effect of environment in the development of diseases. Environmental triggers are largely subdivided into infectious and non-infectious agents. In this review, we introduce the concept of the "infectome", which is the part of the exposome referring to the collection of an individual's exposures to infectious agents. The infectome directly relates to geoepidemiological, serological and molecular evidence of the co-occurrence of several infectious agents associated with autoimmune diseases that may provide hints for the triggering factors responsible for the pathogenesis of autoimmunity. We discuss the implications that the investigation of the infectome may have for the understanding of microbial/host interactions in autoimmune diseases with long, pre-clinical phases. It may also contribute to the concept of the human body as a superorganism where the microbiome is part of the whole organism, as can be seen with mitochondria which existed as microbes prior to becoming organelles in eukaryotic cells of multicellular organisms over time. A similar argument can now be made in regard to normal intestinal flora, living in symbiosis within the host. We also provide practical examples as to how we can characterise and measure the totality of a disease-specific infectome, based on the experimental approaches employed from the "immunome" and "microbiome" projects.

Role for mycobacterial infection in pathogenesis of primary biliary cirrhosis?

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterized by the immune-mediated destruction of biliary epithelial cells in small intrahepatic bile ducts. The disease is characterized by circulating antimitochondrial antibodies (AMAs) as well as disease-specific antinuclear antibodies, cholestatic liver function tests, and characteristic histological features, including granulomas. A variety of organisms are involved in granuloma formation, of which mycobacteria are the most commonly associated. This has led to the hypothesis that mycobacteria may be involved in the pathogenesis of PBC, along with other infectious agents. Additionally, AMAs are found in a subgroup of patients with mycobacterial infections, such as leprosy and pulmonary tuberculosis. Antibodies against species-specific mycobacterial proteins have been reported in patients with PBC, but it is not clear whether these antibodies are specific for the disease. In addition, data in support of the involvement of the role of molecular mimicry between mycobacterial and human mitochondrial antigens as triggers of cross-reactive immune responses leading to the loss of immunological tolerance, and the induction of pathological features have been published. Thus, antibodies against mycobacterial heat shock protein appear to cross-recognize AMA-specific autoantigens, but it is not clear whether these autoantibodies are mycobacterium-species-specific, and whether they are pathogenic or incidental. The view that mycobacteria are infectious triggers of PBC is intriguing, but the data provided so far are not conclusive.

Tuberculosis Is Not a Risk Factor for Primary Biliary Cirrhosis: A Review of the Literature

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterised serologically by cholestasis and the presence of high-titre antimitochondrial antibodies, and histologically by chronic nonsuppurative cholangitis and granulomata. As PBC is a granulomatous disease andMycobacterium tuberculosisis the most frequent cause of granulomata, a causal relation between tuberculosis and PBC has been suggested. Attempts to find serological evidence of PBC-specific autoantibodies such as AMA have been made and, conversely, granulomatous livers from patients with PBC have been investigated for molecular evidence ofMycobacterium tuberculosis. This paper discusses in detail the reported data in support or against an association betweenMycobacterium tuberculosisinfection and PBC. We discuss the immunological and microbiological data exploring the association of PBC with exposure toMycobacterium tuberculosis. We also discuss the findings of large epidemiologic studies investigating the association of PBC with preexistent or concomitant disorders and the relevance of these findings with tuberculosis. Genome-wide association studies in patients with tuberculosis as well as in patients with PBC provide conclusive hints regarding the assumed association between exposure to this mycobacterium and the induction of PBC. Analysis of these data suggest thatMycobacterium tuberculosisis an unlikely infectious trigger of PBC.

Are transient environmental agents involved in the cause of primary biliary cirrhosis? Evidence from space-time clustering analysis

The cause of primary biliary cirrhosis (PBC) is unclear. Both genetic and environmental factors are likely to contribute. Some studies have suggested that one or more infectious agents may be involved. To examine whether infections may contribute to the cause of PBC, we have analyzed for space-time clustering using population-based data from northeast England over a defined period (1987-2003). Space-time clustering is observed when excess cases of a disease are found within limited geographical areas at limited periods of time. If present, it is suggestive of the involvement of one or more environmental components in the cause of a disease and is especially supportive of infections. A second-order procedure based on K-functions was used to test for global space-time clustering using residential addresses at the time of diagnosis. The Knox method determined the spatiotemporal range over which global clustering was strongest. K-function tests were repeated using nearest neighbor thresholds to adjust for variations in population density. Individual space-time clusters were identified using Kulldorff's scan statistic. Analysis of 1015 cases showed highly statistically significant space-time clustering (P < 0.001). Clustering was most marked for cases diagnosed within 1-4 months of one another. A number of specific space-time clusters were identified. In conclusion, these novel results suggest that transient environmental agents may play a role in the cause of PBC.

Chlamydia pneumoniae replicates in Kupffer cells in mouse model of liver infection

AIM: To develop an animal model of liver infection with Chlamydia pneumoniae (C. pneumoniae) in intraperitoneally infected mice for studying the presence of chlamydiae in Kupffer cells and hepatocytes.

METHODS: A total of 80 BALB/c mice were inoculated intraperitoneally with C. pneumoniae and sacrificed at various time points after infection. Chlamydiae were looked for in liver homogenates as well as in Kupffer cells and hepatocytes separated by liver perfusion with collagenase. C. pneumoniae was detected by both isolation in LLC-MK2 cells and fluorescence in situ hybridization (FISH). The releasing of TNFA-α by C. pneumoniae in vitro stimulated Kupffer cells was studied by enzyme-linked immunosorbent assay.

RESULTS: C. pneumoniae isolation from liver homogenates reached a plateau on d 7 after infection when 6 of 10 animals were positive, then decreased, and became negative by d 20. C. pneumoniae isolation from separated Kupffer cells reached a plateau on d 7 when 5 of 10 animals were positive, and became negative by d 20. The detection of C. pneumoniae in separated Kupffer cells by FISH, confirmed the results obtained by culture. Isolated hepatocytes were always negative. Stimulation of Kupffer cells by alive C. pneumoniae elicited high TNF-α levels.

CONCLUSION: A productive infection by C. pneumoniae may take place in Kupffer cells and C. pneumoniae induces a local pro-inflammatory activity. C. pneumoniae is therefore, able to act as antigenic stimulus when localized in the liver. One could speculate that C. pneumoniae infection, involving cells of the innate immunity such as Kupffer cells, could also trigger pathological immune reactions involving the liver, as observed in human patients with primary biliary cirrhosis.

[Seropositivity for Chlamydia pneumoniae in patients with primary biliary cirrhosis]

INTRODUCTION

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease characterized by inflammatory injury and bile duct destruction. Recent studies suggest that Chlamydia pneumoniae could be associated with the development of PBC. The aim of this study was to determine the seroprevalence of C. pneumoniae in a cohort of patients with PBC.

PATIENTS AND METHODS

The presence of IgG antibodies against C. pneumoniae was investigated in 46 patients with PBC and in 105 subjects without cirrhosis.

RESULTS

Twenty-one patients (46%) with PBC had antibodies against C. pneumoniae compared with 74 subjects (71%) in the control group (OR = 0.6; 95% CI, 0.3-1.2; p = NS). Subanalysis of the PBC group showed that patients with C. pneumoniae antibodies had a higher frequency of advanced Child-Pugh stages (24% A, 52% B and 24% C vs 64% A, 32% B and 4% C; p = 0.01), a higher score on the Mayo Clinic Prognostic Index (7.8 +/- 2.1 vs 5.6 +/- 1.2; p = 0.004), a higher frequency of ascites (29% vs 4%; OR = 9.6; 95% CI, 1-87; p = 0.02), higher total bilirubin levels (4.5 +/- 2.5 mg/dl vs 2.4 +/- 4.3 mg/dl, p = 0.001) and lower serum albumin levels (2.6 +/- 0.9 g/dl vs 3.3 +/- 0.6 g/dl, p = 0.02).

CONCLUSION

No association was found between C. pneumoniae infection and PBC in this study. An association was found between the severity of PBC and C. pneumoniae, which may suggest a deleterious effect of C. pneumoniae infection or a predisposition in advanced stages of PBC to acquire infection with this microorganism.

Primary biliary cirrhosis: an infectious disease caused by Chlamydia pneumoniae?

BACKGROUND/AIMS

The etiology and pathogenesis of primary biliary cirrhosis (PBC) remain elusive. Both an infectious etiology and molecular mimicry have been implicated. The aim is to study the prevalence of Chlamydial antigens and RNA in the liver tissue of patients with PBC.

METHODS

We compared the prevalence of Chlamydial antigen and RNA in 25 explants with PBC who underwent orthotopic liver transplantation with 105 explanted livers from other chronic liver disease. We also studied 14 liver biopsies from patients with early stages of PBC. Donor livers were also studied.

RESULTS

In all 39 patients with PBC, Chlamydia pneumoniae antigens were present but not Chlamydia trachomatis, and only 9/105 (8.5%) of patients in the other categories were positive (P<0.01) for C. pneumoniae. Eight explanted PBC livers were tested for C. pneumoniae 16S RNA by in situ hybridization and were positive.

CONCLUSIONS

The presence of C. pneumoniae antigen and RNA in liver tissue of patients with PBC suggests that C. pneumoniae antigen may trigger an immune response based on molecular mimicry.

Immunization with a xenobiotic 6-bromohexanoate bovine serum albumin conjugate induces antimitochondrial antibodies

The E2 subunit of pyruvate dehydrogenase complex (PDC-E2) is the major autoantigen recognized by antimitochondrial Abs (AMA) in primary biliary cirrhosis (PBC). Recently, we replaced the lipoic acid moiety of PDC-E2 with a battery of synthetic structures designed to mimic a xenobiotically modified lipoyl hapten on a 12-aa peptide that was found within the immunodominant autoepitope of PDC-E2 and demonstrated that AMA in PBC reacted against several organic modified mimotopes as well as, or sometimes significantly better than, the native lipoyl domain. Based on this data, we immunized rabbits with one such xenobiotic organic compound, 6-bromohexanoate, coupled to BSA. One hundred percent of immunized rabbits developed AMA that have each and every characteristic of human AMAs with reactivity against PDC-E2, E2 subunit of branched chain 2-oxo-acid dehydrogenase, and E2 subunit of 2-oxoglutarate dehydrogenase complex. The rabbit AMA also inhibited enzymatic function of PDC-E2 and, importantly, binds to peptide sequences not present in the xenobiotic carrier immunogen. In contrast, BSA-immunized controls did not produce such activity. Our observation that animals immunized with a xenobiotic BSA complex produce autoantibodies that react not only with the xenobiotic, but also with mitochondrial autoantigens recognized by autoimmune PBC sera, suggests that environmental xenobiotic agents can be a risk factor for the induction of PBC.

Expected developments in hepatology

It is very difficult to predict new developments in hepatology so we have decided to analyse the most important issues related to three clinical conditions in hepatology. The first is chronic hepatitis. Here, we discuss the relevance of occult forms of hepatitis B virus infection in the development of cryptogenic liver disease and hepatocellular carcinoma. In addition, the role of genotyping in hepatitis B is analysed, indicating that patients with genotype A have a better prognosis than those with genotype D. The treatment of hepatitis B virus infection is also reviewed, and it has been suggested that research should be directed towards the development of new anti-viral agents to suppress virus replication. The natural history of hepatitis C virus infection is considered, emphasizing the need to know the progression of fibrosis in these patients. The chapter also suggests that treatment of hepatitis C virus infection with pegilated interferon and ribavirin is currently relatively effective. New therapeutic strategies will be required in the future, the most important challenge being the development of a hepatitis C virus vaccine. The second section is on chronic cholestasis. The role of anti-mitochondrial antibodies in primary biliary cirrhosis is considered. The possible infectious agents implicated as potential triggers of primary biliary cirrhosis are also discussed, suggesting that several infections may play a role in the pathogenesis of this condition. Other aetiopathogenic factors, for example organic compounds, drugs and chemicals, are indicated. It is possible that, in the near future, the precise sequence and molecular basis by which infectious agents or xenobiotics may initiate the cascade of the autoimmune response will be defined. One of the most important challenges in primary sclerosing cholangitis concerns the mechanisms that may induce the development of this disease. Up until now, genetic factors have been suggested, recent data reporting a clear-cut association between primary sclerosing cholangitis and the tumour necrosis factor-alpha(2) allele. The third part of this chapter includes recent progress achieved in hepatocellular carcinoma, discussing developments in the knowledge of hepatocellular carcinogenesis. Hepatocellular carcinomas appear so far to be genetically heterogeneous neoplasms, and this heterogeneity may correlate with the variety of aetiological factors involved. The risk factors and primary, secondary and tertiary prevention of the condition are also analysed. Finally, the development of new therapeutic strategies for hepatocellular carcinoma is evaluated by evidence-based studies.

Hepatic manifestations of gastrointestinal diseases. Inflammatory bowel disease, celiac disease, and Whipple's disease

The gastrointestinal tract and the liver are closely related anatomically, physiologically, and pathologically. Some disease associations are well documented, such as PSC in association with IBD, whereas others are less well defined. A heightened clinical suspicion is required in these patients who do not present with the classical disease associations. The underlying causes of their diseases are the subject of much debate and research, and their diagnosis and management remain challenging.

Amplification and sequence analysis of partial bacterial 16S ribosomal RNA gene in gallbladder bile from patients with primary biliary cirrhosis

BACKGROUND/AIMS

The etiopathogenesis of bile duct lesion in primary biliary cirrhosis is unknown, though the participation of bacteria and/or their components and products is suspected. In this study, we tried to detect and identify bacteria in the bile of patients with primary biliary cirrhosis by polymerase chain reaction using universal bacterial primers of the 16S ribosomal RNA gene.

METHODS

Gallbladder bile samples from 15 patients with primary biliary cirrhosis, 5 with primary sclerosing cholangitis, 5 with hepatitis C virus-related liver cirrhosis, 11 with cholecystolithiasis, and from 12 normal adult gallbladders were used. In addition to the culture study, partial bacterial 16S ribosomal RNA gene was amplified by polymerase chain reaction (PCR) taking advantage of universal primers that can amplify the gene of almost all bacterial species, and the amplicons were cloned and sequenced. Sequence homology with specific bacterial species was analyzed by database research. Bacterial contamination at every step of the bile sampling, DNA extraction and PCR study was avoided. Furthermore, to confirm whether bacterial DNA is detectable in liver explants, the same analysis was performed using 10 liver explants of patients with primary biliary cirrhosis.

RESULTS

In primary biliary cirrhosis, 75% (p<0.0001) of 100 clones were identified as so-called gram-positive cocci while these cocci were positive in only 5% in cholecystolithiasis (p<0.0001). In cholecystolithiasis gram-negative rods were predominant instead. One bacterial species detected in a normal adult was not related to those detected in primary biliary cirrhosis and cholecystolithiasis patients. No bacterial DNA was detected by PCR amplification in 10 liver explants of patients with primary biliary cirrhosis.

CONCLUSIONS

The present results raise several possible roles of gram-positive bacteria in bile in the etiopathogenesis of primary biliary cirrhosis. However, these results could also reflect an epiphenomenon due to decreased bile flow in the patients with primary biliary cirrhosis at an advanced stage.

Primary biliary cirrhosis, primary sclerosing cholangitis, and autoimmune cholangitis

Primary biliary cirrhosis (PBC), and autoimmune cholangitis are presumed to be autoimmune cholestatic diseases, but the relevant antigens are unknown. Primary biliary cirrhosis is diagnosed by a positive serum mitochondrial antibody test. It usually affects women and has a very long course, culminating in liver transplantation or death. Ursodeoxycholic acid is probably the appropriate treatment. Primary sclerosing cholangitis (PSC) is marked by progressive destruction of extrahepatic and intrahepatic bile ducts. There is no specific diagnostic test or treatment. Cholangiocarcinoma is the dreaded complication and precludes liver transplantation, the only chance of a cure. Autoimmune cholangitis overlaps PBC and autoimmune chronic hepatitis. It is a rare condition, resembling PBC but with a negative serum mitochondrial antibody test; however, serum antinuclear antibodies and smooth muscle antibodies are present in high titers.

Are infectious agents involved in primary biliary cirrhosis? A PCR approach

BACKGROUND/AIMS

A variety of data suggest that microbial infections and, in particular, atypical mycobacteria infections, may either initiate and/or be associated with the pathogenesis of primary biliary cirrhosis.

METHODS

To address this hypothesis, use was made of polymerase chain reaction techniques and primers specific for the 16s rRNA gene of Eubacteria, Archaeabacteria, Mycobacteria and Helicobacter to determine if such sequences were detectable in liver tissue specimens from 29 patients with primary biliary cirrhosis. Similar liver tissues from patients with primary sclerosing cholangitis, chronic hepatitis, alcoholic liver disease and otherwise normal donors were analyzed in parallel. Genomic DNA was extracted from each of these liver tissue specimens using sterile techniques to avoid possible laboratory contamination. The DNA was subjected to polymerase chain reaction amplification using bacterial genus specific primers and the amplified products cloned and sequenced. Sequence data were analyzed by searching for homology to existing genes.

RESULTS

Sequences from primary biliary cirrhosis and control livers corresponded to those found in a variety of bacteria, but no consensus sequence was found in primary biliary cirrhosis specimens. Neither Archaeabacteria nor Mycobacteria products were detected in liver specimens of patients with primary biliary cirrhosis, and Helicobacter pylori DNA was detected in only one primary biliary cirrhosis patient.

CONCLUSIONS

Although bacterial infection, particularly with intracellular organisms, has been suggested to play a role in the initiation of primary biliary cirrhosis, there is no evidence from this study to suggest an ongoing chronic infectious process.

Cholestatic syndromes

Recent advances in cholestatic liver disease have occurred in several areas. Molecular cloning of hepatobiliary transport systems has resulted in the identification of the molecular basis of hereditary and acquired cholestatic syndromes. Apoptosis has been identified as an important mechanism of cholestatic liver injury and bile duct loss. New insights into the pathogenesis of pruritus and fatigue have resulted in new treatment strategies for these debilitating symptoms. Important new studies have been published about pathogenesis, clinical features, and treatment of primary biliary cirrhosis, primary sclerosing cholangitis, cholestasis of pregnancy, and drug-induced cholestasis.