Metabolomic variability & differential risk in primary biliary cholangitis

Abstract

Primary Biliary Cholangitis (PBC) is a progressive cholestatic autoimmune condition that can lead to end-stage liver disease (ESLD). The hallmark, anti-mitochondrial antibodies (AMA) are present in 95% of PBC patients. 10% of patients have AMA positivity but no symptoms and normal LFTs (AMANL). The symptoms associated with PBC can significantly impact patients' physical and psychological well-being. Unfortunately, there are only a limited number of treatment options available. This study aimed to identify metabolic signatures in serum, urine, and faeces that could differentiate PBC from AMANL and PBC patients with symptoms from asymptomatic patients. Healthy Volunteer controls and Primar Sclerosing Cholangitis (PSC) as cholestatic controls were included. We used high-throughput metabolomic techniques of Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS). Ethical approval was sought (REC: 15/EE/0455). Principal component analysis (PCA) followed by Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA) gave robust differentiating models, which were cross-validated with multivariate CV-ANOVA analysis. 51 PBC patients and 15 AMANL patients (median age: 64 years for PBC vs. 57 years for AMANL, p=0.12) participated in the study. Ninety percent of the PBC patients were receiving Ursodeoxycholic acid (UDCA) therapy. We found that total bile acids (BAs) were significantly higher in PBC patients compared to those with AMANL (p=0.001), with secondary BA levels also elevated (p=0.0001). The increase in serum BAs among PBC patients was linked to metabolites of UDCA and Lithocholic acid (LCA). Notably, LCA levels were also elevated in the faeces of the PBC group. We compared the profiles of PBC patients with pruritus to those without pruritus. Hyocholic acid (HCA) levels, a secondary BA produced by gut microbiota, were significantly higher in the serum of PBC patients with pruritus (median: 2036 vs. 395, p=0.0003). HCA levels were raised in both cholestatic groups PBC (561.5) and PSC (1080) when compared to HVs (300.6), p=0.003 and p=0.0003 respectively. There was no difference comparing PBC with PSC (p=0.25) and PSC with PBC pruritus (p=0.12). Additionally, no differences were observed when evaluating profiles of PBC patients experiencing fatigue or cognitive impairment compared to asymptomatic patients. The notably high levels of HCA in the PBC pruritus group raise questions about whether HCA is a direct cause of pruritus or a result of more complex metabolic alterations. It is important to note that due to the cross-sectional design of this study, we could not establish a "cause and effect" relationship. The study also lacks microbiome data, which may influence bile acid composition.