Evaluation of Inhibitory Antibodies against the Muscarinic Acetylcholine Receptor Type 3 in Patients with Primary Biliary Cholangitis and Primary Sclerosing Cholangitis

Abstract

Background: Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) constitute rare chronic inflammatory biliary diseases which likely comprise genetic, environmental and autoimmune factors. Specific inhibitory (auto-) antibodies against the muscarinic acetylcholine receptor type 3 (mAChR3 auto-ab) may contribute to the pathogenesis of chronic biliary inflammation by modulating mAChR3- mediated signaling.

Aims: The aim of this study was to analyze the prevalence and relevance of inhibitory mAChR3 auto-ab (mAChR3inh+ auto-ab) in a large cohort of PBC patients from two independent tertiary centers in Berlin and Leipzig in comparison to a large PSC cohort. Baseline parameters and response rates to standard treatment with ursodeoxycholic acid (UDCA) were characterized with respect to the individual mAChR3 auto-ab status.

Methods: In total, the study population comprised 437 PBC patients, 187 PSC patients and 80 healthy controls. Clinical and laboratory baseline characteristics were retrieved from medical records. The response to ursodeoxycholic acid (UDCA) therapy after 12 months of treatment was available in 176 PBC and 45 PSC patients.

Results: The prevalence of mAChR3inh+ auto-ab was significantly higher among PBC patients (11.2%, 49/437; p = 0.008 vs. healthy controls) and PSC patients (33.6%, 63/187; p < 0.0001 vs. healthy controls) compared to healthy controls (2.5%, 2/80), respectively. PBC patients with mAChR3inh+ auto-ab exhibited significantly higher levels of alkaline phosphatase (ALP) and bilirubin, which constitute established parameters for PBC risk stratification. Moreover, mAChR3inh+ PBC patients tended to show decreased response rates to UDCA therapy compared to PBC patients without mAChR3inh+ auto-ab (mAChR3- PBC). In contrast, PSC patients with mAChR3inh+ auto-ab showed no significant differences in laboratory findings compared to mAChR3 auto-ab negative (mAChR3-) PSC patients.

Conclusion: MAChR3inh+ auto-ab might be involved in the pathogenesis and treatment response of chronic biliary inflammation in patients with PBC but not in patients with PSC.

Keywords: biliary bicarbonate umbrella; chronic biliary inflammation; muscarinic acetylcholine receptor type 3; primary biliary cholangitis; primary sclerosing cholangitis; ursodeoxycholic acid.

Figure 1

Study flow diagram. In total 437 patients with primary biliary cholangitis (PBC) and 187 patients with primary sclerosing cholangitis (PSC) from two independent fulfilled all diagnostic criteria and were included in the study.

Figure 2

Prevalence of functional mAChR3 auto-ab in 187 PSC patients, 437 PBC patients and 80 healthy controls. A range between 80 and 120 calcium-induced relative luminescence units (RLU) was defined as normal. An RLU < 80 was defined as inhibitory effect due to mAChR3inh+ auto-ab. An RLU > 120 was defined as stimulatory effect due to mAChR3stim+ auto-ab. * p < 0.05, **** p < 0.0001; Analysis was done using Kruskal–Wallis test.

Figure 3

Treatment response in PBC patients 12 months after treatment initiation with UDCA according to functional mAChR3 auto-ab status. (A) alkaline phosphatase (ALP), (B) gamma glutamyltransferase (GGT), (C) bilirubin (D) Aspartate aminotransferase (AST), (E) Alanine aminotransferase (ALT) according to mAChR3 auto-ab status. ULN, upper limit of normal, p* = Analysis was done using Student’s t-Test, p** = Analysis was done using Mann–Whitney U Test.

Figure 4

Comparison of treatment response in mAChR3inh+ and mAChR3− PBC patients 12 months after initiation of UDCA therapy according to the Rochester criterion (AP ≥ 2 × ULN or Mayo-Score ≥ 4.5), Rotterdam criterion (Bilirubin ≥ 1 × ULN and/or Albumin < 1 × ULN), Paris II criterion (ALP ≥ 1.5 × ULN or AST ≥ 1.5 × ULN or Bilirubin >1 mg/dL), Paris I criterion (ALP ≥ 3 × ULN or AST ≥ 2 × ULN or Bilirubin >1 mg/dL) and ALP normalization (ALP < 1 × ULN). Patients with similar disease stage at baseline were compared between mAChR3inh+ and mAChR3− based on ultrasound with absence of fibrosis classified as early stage and clear signs of fibroses classified as advanced stage. p = Analysis was done using Fisher’s exact test, n.s. = not significant.

Figure 5

Comparison of UK-PBC risk score according to the functional mAChR3− status, p = Analysis was done using Mann–Whitney U Test.

Figure 6

Comparison of Amsterdam-Oxford PSC score according to functional mAChR3− status. Analysis was done using Mann-Whitney U Test.