Association of primary biliary cirrhosis with the allele HLA-DPB1*0301 in a German population

Mechanism-based target therapy in primary biliary cholangitis: opportunities before liver cirrhosis?

Primary biliary cholangitis (PBC) is an immune-mediated liver disease characterized by cholestasis, biliary injuries, liver fibrosis, and chronic non-suppurative cholangitis. The pathogenesis of PBC is multifactorial and involves immune dysregulation, abnormal bile metabolism, and progressive fibrosis, ultimately leading to cirrhosis and liver failure. Ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) are currently used as first- and second-line treatments, respectively. However, many patients do not respond adequately to UDCA, and the long-term effects of these drugs are limited. Recent research has advanced our understanding the mechanisms of pathogenesis in PBC and greatly facilitated development of novel drugs to target mechanistic checkpoints. Animal studies and clinical trials of pipeline drugs have yielded promising results in slowing disease progression. Targeting immune mediated pathogenesis and anti-inflammatory therapies are focused on the early stage, while anti-cholestatic and anti-fibrotic therapies are emphasized in the late stage of disease, which is characterized by fibrosis and cirrhosis development. Nonetheless, it is worth noting that currently, there exists a dearth of therapeutic options that can effectively impede the progression of the disease to its terminal stages. Hence, there is an urgent need for further research aimed at investigating the underlying pathophysiology mechanisms with potential therapeutic effects. This review highlights our current knowledge of the underlying immunological and cellular mechanisms of pathogenesis in PBC. Further, we also address current mechanism-based target therapies for PBC and potential therapeutic strategies to improve the efficacy of existing treatments.

HLA, gut microbiome and hepatic autoimmunity

Genetic susceptibility to autoimmune liver diseases is conferred mainly by polymorphisms of genes encoding for the human leukocyte antigens (HLA). The strongest predisposition to autoimmune hepatitis type 1 (AIH-1) is linked to the allele DRB1*03:01, possession of which is associated with earlier disease onset and more severe course. In populations where this allele is very rare, such as in Asia, and in DRB1*03-negative patients, risk of AIH-1 is conferred by DRB1*04, which is associated with later disease onset and milder phenotype. AIH type 2 (AIH-2) is associated with DRB1*07. The pediatric condition referred to as autoimmune sclerosing cholangitis (ASC), is associated with the DRB1*13 in populations of Northern European ancestry. DRB1*1501 is protective from AIH-1, AIH-2 and ASC in Northern European populations. Possession of the DRB1*08 allele is associated with an increased risk of primary biliary cholangitis (PBC) across different populations. DRB1*03:01 and B*08:01 confer susceptibility to primary sclerosing cholangitis (PSC), as well as DRB1*13 and DRB1*15 in Europe. The hepatic blood supply is largely derived from the splanchnic circulation, suggesting a pathophysiological role of the gut microbiome. AIH appears to be associated with dysbiosis, increased gut permeability, and translocation of intestinal microbial products into the circulation; molecular mimicry between microbial and host antigens may trigger an autoaggressive response in genetically-predisposed individuals. In PBC an altered enteric microbiome may affect intestinal motility, immunological function and bile secretion. Patients with PSC have a gut microbial profile different from health as well as from patients with inflammatory bowel disease without PSC.

Amino acid residues in five separate HLA genes can explain most of the known associations between the MHC and primary biliary cholangitis

Primary Biliary Cholangitis (PBC) is a chronic autoimmune liver disease characterised by progressive destruction of intrahepatic bile ducts. The strongest genetic association is with HLA-DQA1*04:01, but at least three additional independent HLA haplotypes contribute to susceptibility. We used dense single nucleotide polymorphism (SNP) data in 2861 PBC cases and 8514 controls to impute classical HLA alleles and amino acid polymorphisms using state-of-the-art methodologies. We then demonstrated through stepwise regression that association in the HLA region can be largely explained by variation at five separate amino acid positions. Three-dimensional modelling of protein structures and calculation of electrostatic potentials for the implicated HLA alleles/amino acid substitutions demonstrated a correlation between the electrostatic potential of pocket P6 in HLA-DP molecules and the HLA-DPB1 alleles/amino acid substitutions conferring PBC susceptibility/protection, highlighting potential new avenues for future functional investigation.

Association of Estrogen Receptor Gene Polymorphisms and Primary Biliary Cirrhosis in a Chinese Population: A Case-Control Study

Background:

Primary biliary cirrhosis (PBC) is a chronic and slowly progressive cholestatic liver disease characterized by destruction of the interlobular bile ducts and a striking female predominance. The aim of this study was to identify associations between estrogen receptor (ESR) gene polymorphisms with the risk of developing PBC and abnormal serum liver tests in a Chinese population.

Methods:

Thirty-six patients with PBC (case group) and 35 healthy individuals (control group) from the First Hospital of Jilin University were studied. Whole genomic DNA was extracted from all the participants. Three single-nucleotide polymorphisms (rs2234693, rs2228480, and rs3798577) from ESR1 and two (rs1256030 and rs1048315) from ESR2 were analyzed by a pyrosequencing method. Demographic data and liver biochemical data were collected.

Results:

Subjects with the T allele at ESR2 rs1256030 had 1.5 times higher risk of developing PBC than those with the C allele (odds ratio [OR] = 2.1277, 95% confidence interval [CI] = 1.1872–4.5517). Haplotypes TGC of ESR1 rs2234693, rs2228480, and rs3798577 were risk factors for having PBC. The C allele at ESR1 rs2234693 was associated with abnormal alkaline phosphatase (OR = 5.2469, 95% CI = 1.3704–20.0895) and gamma-glutamyl transferase (OR = 3.4286, 95% CI = 1.0083–13.6578) levels in PBC patients.

Conclusions:

ESR2 rs1256030 T allele may be a significant risk factor for the development of PBC. Screening for patients with gene polymorphisms may help to make early diagnoses in patients with PBC.

Vitamin D deficiency in patients with liver cirrhosis

There is ongoing evidence that vitamin D is related to the pathophysiology of cirrhosis. Although the incidence of vitamin D deficiency in chronic liver diseases and cirrhosis is strongly documented, its pathogenic association with advanced liver fibrosis remains controversial. There is evidence of a significant relation of 25(OH)D levels with the degree of liver dysfunction, considering that an inverse correlation of 25(OH)D levels with both Child-Pugh score and Model for End-Stage Liver Disease has been reported. In addition, vitamin D deficiency has been shown to increase the risk for overall mortality and infections in patients with cirrhosis. Vitamin D deficiency has been also associated with advanced stages of hepatocellular carcinoma and poor prognosis. Finally, there are studies suggesting that patients with chronic hepatitis C and normal vitamin D levels have higher virological response to treatment. However, there are not enough studies conducted in cirrhotic-only populations. The association between vitamin D and cirrhosis demonstrates a great potential for clinical application. The relation between vitamin D deficiency and the degree of liver function, degree of fibrosis and infectious complications could support its use as a prognostic index and a diagnostic tool.

Association of human leukocyte antigen class II with susceptibility to primary biliary cirrhosis: a systematic review and meta-analysis

Purpose

Several previous studies suggested that HLA-ClassII may be associated with susceptibility to primary biliary cirrhosis (PBC), but data from individual studies remain controversial. Therefore, a systematic review and meta-analysis is needed to comprehensively evaluate the association between HLA-ClassII and PBC risk.

Methods

All published reports of an association between HLA class II and PBC risk were searched in PubMed, EMBASE (updated to 22 May 2012). ORs with 95% confidence intervals (CIs) were extracted from each included study and the meta-analysis was performed using the fixed- or random-effects model.

Results

A total of 3,732 PBC patients and 11,031 controls from 34 studies were included in the meta-analysis. An assessment of study quality revealed that the majority of studies included (18 studies) were of high quality. The serological group DR8 was found to be a risk factor for PBC (OR = 2.82, 95%CI: 1.84–4.30). At the allelic level, HLA-DR*08 and HLA-DR*0801 were identified as risk factors for PBC (OR = 2.30, 95%CI: 1.76-3.00; OR = 3.23, 95%CI: 2.22–4.70, respectively), whereas HLA-DR*11 and HLA-DR*13 were potent protective factors (OR = 0.31, 95%CI: 0.27-0.38; OR = 0.62, 95%CI: 0.48-0.81, respectively). HLA-DQB1 and HLA-DQB1*0402 conferred a predisposition to PBC development (OR = 3.47, 95%CI: 2.35–5.13), whereas HLA-DQB1*0604 was protective against PBC (OR = 0.3, 95%CI: 0.18–0.58). No HLA-DPB1 allele was observed to be associated with PBC susceptibility (P > 0.05).

Conclusions

The present study revealed that HLA-ClassII components are closely associated with the development of PBC.

The role of vitamin d in primary biliary cirrhosis: possible genetic and cell signaling mechanisms

Primary biliary cirrhosis (PBC) is an immune-mediated chronic inflammatory disease of the liver of unknown etiology. Vitamin D deficiency is highly prevalent in patients with PBC, and many studies have demonstrated the significant effect of calcitriol on liver cell physiology. Vitamin D has antiproliferative and antifibrotic effects on liver fibrosis. Genetic studies have provided an opportunity to determine which proteins link vitamin D to PBC pathology (e.g., the major histocompatibility complex class II molecules, the vitamin D receptor, toll-like receptors, apolipoprotein E, Nramp1, and cytotoxic T lymphocyte antigen-4). Vitamin D also exerts its effect on PBC through cell signaling mechanisms, that is, matrix metalloproteinases, prostaglandins, reactive oxygen species, and the transforming growth factor betas. In conclusion, vitamin D may have a beneficial role in the treatment of PBC. The best form of vitamin D for use in the PBC is calcitriol because it is the active form of vitamin D3 metabolite, and its receptors are present in the sinusoidal endothelial cells, Kupffer cells, and stellate cells of normal livers, as well as in the biliary cell line.

Classical HLA-DRB1 and DPB1 alleles account for HLA associations with primary biliary cirrhosis

Susceptibility to primary biliary cirrhosis (PBC) is strongly associated with human leukocyte antigen (HLA)-region polymorphisms. To determine if associations can be explained by classical HLA determinants, we studied Italian, 676 cases and 1440 controls, genotyped with dense single-nucleotide polymorphisms (SNPs) for which classical HLA alleles and amino acids were imputed. Although previous genome-wide association studies and our results show stronger SNP associations near DQB1, we demonstrate that the HLA signals can be attributed to classical DRB1 and DPB1 genes. Strong support for the predominant role of DRB1 is provided by our conditional analyses. We also demonstrate an independent association of DPB1. Specific HLA-DRB1 genes (*08, *11 and *14) account for most of the DRB1 association signal. Consistent with previous studies, DRB1*08 (P=1.59 × 10(-11)) was the strongest predisposing allele, whereas DRB1*11 (P=1.42 × 10(-10)) was protective. Additionally, DRB1*14 and the DPB1 association (DPB1*03:01; P=9.18 × 10(-7)) were predisposing risk alleles. No signal was observed in the HLA class 1 or class 3 regions. These findings better define the association of PBC with HLA and specifically support the role of classical HLA-DRB1 and DPB1 genes and alleles in susceptibility to PBC.

Genomic variants associated with primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune hepatobiliary disease characterized by immune-mediated injury of small and medium-sized bile ducts, eventually leading to liver cirrhosis. Several studies have addressed PBC immunopathology, and the data support an immune activation leading to autoantibodies and autoreactive T cells acting against the lipoylated 2-oxoacid dehydrogenase complexes. The causes of the disease remain unknown, but environmental factors and genetic susceptibility both contribute to its onset. Over the past two decades several association studies have addressed the role of genetic polymorphisms in PBC pathogenesis and have reported multiple associations. However, only a few studies had sufficient statistical power, and in most cases results were not independently validated. A genome-wide association study has recently been reported, but this too awaits independent confirmation. The aim of this present work is to critically review the numerous studies dedicated to revealing genetic associations in PBC, and to predict the potential for future studies based on these data.

Genetics and genomics of primary biliary cirrhosis

The etiologic and pathogenic factors contributing to primary biliary cirrhosis (PBC) development, progression, response to treatment, and outcome remain a mystery. Recognition of the genomic regions harboring risk factors is hindered by the rarity and late onset of PBC. Recent advancements in genomics hold promise for understanding, prevention, and therapy of PBC. Large registries and biospecimen repositories of patients who have PBC, their family members, and controls are needed. Haplotype mapping-based association studies are necessary for defining genetic predisposition. Experimental data will provide the means for fine mapping studies, resequencing efforts, functional experimentation, and elucidation of gene-environment and gene-gene interaction.

Clinical pathology and HLA-DRB1 allele associations of primary biliary cirrhosis and autoimmune cholangitis in Han Chinese

AIM: To analyze the clinical and pathological characte-ristics of both primary biliary cirrhosis (PBC) and auto- immune cholangitis (AIC), and to explore their associ-ations with HLA-DRB1 alleles in Han Chinese.

METHODS: Of 94 patients diagnosed with PBC, 12 cases of AIC and 9 cases of overlap syndrome of PBC and au-toimmune hepatitis (AIH) were identified. The clinical manifestations and pathological changes exhibited in the liver biopsies from AIC, pure PBC and overlap syndrome were comparatively analyzed. The frequencies of HLA-DRB1 alleles were determined in AIC and PBC patients and healthy controls by polymerase chain reaction with sequence specific primers.

RESULTS: The age, sex, clinical manifestations, bio-chemical markers and histological findings were not significantly different between the AIC and pure PBC patients. However, the score for AIH and the positive rate of serum antinuclear antibody and/or smooth muscle antibody were higher in patients (8.8±0.9 vs 4.6±0.8, t = 17.45, P <0.01; 84.6% vs 22.2%, χ² = 17.003 9, P <0.01). The serum levels of alanine aminotransferase (ALT), aspartate transaminase (AST) and immunoglobulin G in AIC patients were markedly lower than those in the overlap syndrome patients (t = 3.44, P <0.01; t = 2.83, P <0.01; t = 2.18, P <0.05). Higher allele frequency of HLA-DRB1*08 was found in pure PBC patients, versus controls (9.7% vs 3.3%, RR = 4.42, P <0.05), and the allele frequency of HLA-DRB1*08 tended to increase in pure PBC patients.

CONCLUSION: Except the pretreatment score for AIH and the types of immunoserological marker, there were no differences between AIC and pure PBC. AIC may only be a variant pattern of PBC, rather than a separate disease.

Genetic association of cytokines polymorphisms with autoimmune hepatitis and primary biliary cirrhosis in the Chinese

AIM: To characterize gene polymorphism of several cytokine gene in-patients with AIH and PBC and to analyze the difference of the polymorphism distribution between Chinese patients and healthy controls.

METHODS: The study population consisted of 62 patients with AIH, and 77 patients with PBC. The genetic profile of four cytokines was analyzed by restriction fragment length polymorphism after specific PCR amplification (PCR-RFLP) or sequence-specific primers PCR (SSP-PCR). The analyzed gene polymorphism included interleukin-1 (IL-1) (at position +3 953 and IL-1RN intron 2), IL-6 (at position -174), IL-10 promoter (at position -1082, -819, and -592). The control group consisted of 160 healthy blood donors.

RESULTS: The majority of Chinese people including patients and healthy controls exhibited IL-1B 1,1 genotype, and there was no significant difference in AIH, PBC patients and controls. There were highly statistically significant differences in the distribution of the IL-1RN gene polymorphism between the patients with PBC compared with controls. The frequency of IL-1RN 1,1 was significantly higher (90.9% vs 79.4%, P = 0.03) and the frequency of IL-1RN 1,2 was significantly lower in PBC patients (6.5% vs 17.5%, P = 0.01). No statistical difference was observed between AIH patients and controls. All of the 160 healthy controls and 62 cases of AIH patients exhibited IL-6-174GG genotype, and there were four cases, which expressed IL-6-174GC genotype in 77 cases of PBC patients. The frequency of IL-6-174GC was markedly significantly higher in PBC patients compared with controls (5.2% vs 0%, P = 0.004). No statistically significant difference was found in the distribution of IL-10 promoter genotype in AIH and PBC patients compared with controls.

CONCLUSION: The polymorphisms of IL-1RN and IL-6 -174G/C appear to be associated with PBC in Chinese patients.