A recent study published in Frontiers in Medicine described anti-post-translational modification (PTM) antibodies in patients with autoimmune-mediated and cholestatic liver diseases (AILD).
AILD represents a group of hepatocellular and cholestatic diseases, such as autoimmune hepatitis (AIH), primary sclerosing cholangitis (PSC), and primary biliary cholangitis (PBC). PBC and AIH are characterized by autoantibodies and increased immunoglobulin G (IgG) or IgM levels. Autoantibody testing in standard liver disease diagnosis is not disease-specific.
Autoantibodies often target proteins with PTMs, such as carbamylation (CarP) and citrullination (Cit), in rheumatoid arthritis. Previously, the authors detected antibodies against advanced glycation end-products (AGEs) and malondialdehyde-acetaldehyde adducts (MAAs) in systemic lupus erythematosus patients.
AGE, MAA, lysine acetylation (AL), and tyrosine nitration (NT) occur under oxidative stress. Oxidative stress is more frequent in AIH than cholestatic liver disease (CLD). These PTMs are highly immunogenic and can induce anti-PTM antibodies. Nevertheless, there is limited evidence of anti-PTM antibodies in AILD.
About the study
In the present study, researchers explored anti-PTM autoantibodies in AILD. Patients visiting the hepatology and gastroenterology department at the Leiden University and Erasmus Medical Centers from 1996 to 2020 were included. Participants were stratified into AILD (PSC, PBC, or AIH), non-AILD (other chronic liver diseases), and healthy control (HC) groups.
Electronic records were accessed for data on sex, age, comorbidities, liver cirrhosis, disease duration, arthralgia, and medications. Data on treatment response, liver transplantation, complete biochemical response (CBR), and mortality were also obtained. CBR was the normalization of IgG and aminotransferases. Time to CBR was the period between treatment initiation and the first CBR.
Enzyme-linked immunosorbent assay (ELISA) was used to detect anti-PTM antibodies. Chi-squared and Kruskal-Wallis tests examined group differences in anti-PTM antibody levels. Spearman rank analysis and point biserial correlation determined correlations of anti-PTM antibodies with continuous and dichotomous clinical variables, respectively.
The team included 207 patients, comprising AILD and non-AILD cohorts, with 106 and 101 subjects, respectively. On average, patients in the AILD and non-AILD cohorts were aged 48.2 and 54 years, respectively. In the AILD cohort, 66 patients had AIH, 30 had PSC, and 10 had PBC. The AILD cohort was further stratified into CLD (PSC and PBC) and AIH sub-cohorts.
Cirrhosis was diagnosed in 56.4% of non-AILD and 39.6% of AILD patients. The researchers observed substantial heterogeneity in the levels of anti-AGE, anti-MAA, anti-AL, and anti-CarP antibodies between HCs and AILD subjects. The AILD cohort showed higher median levels of these antibodies than non-AILD patients.
Further, only anti-CarP and anti-MAA antibodies were significantly elevated in non-AILD subjects relative to HCs. Median anti-Cit and anti-NT antibodies only differed between HCs and the AILD cohort. The frequency of having at least one type of anti-PTM antibodies was higher in AILD patients than HCs and non-AILD subjects.
AILD individuals were also more likely to have multiple antibodies. Among AILD sub-cohorts, AIH patients displayed higher antibodies against AL, CarP, AGE, and MAA than non-AILD patients. They were also more often positive for anti-AGE, anti-Cit, anti-MAA, and anti-CarP antibodies than CLD patients.
Furthermore, in untreated AIH patients, anti-MAA and anti-CarP antibodies correlated with serum IgG and anti-nuclear antibody (ANA) levels. A negative correlation was observed between the time to CBR and anti-PTM antibodies in AIH patients. Anti-AGE and anti-MAA antibodies were positively correlated with CBR at three months.
In contrast, anti-AGE, anti-MAA, and anti-CarP antibodies were positively correlated with CBR at one year. Patients harboring at least three anti-PTM antibodies had significantly higher levels of IgG (at diagnosis) and aminotransferases. Significantly more patients with AIH with at least three anti-PTM antibodies reached CBR after three-month treatment, which remained significant at one year.
Twenty-five AIH patients had clinical data from before and during treatment, with a median interval of 65 months. Anti-MAA, anti-CarP, anti-AL, and anti-AGE antibodies declined significantly over time. Changes in anti-AL levels were associated with changes in aspartate and alanine aminotransferases. Likewise, changes in anti-AGE antibodies were associated with IgG changes.
In sum, the researchers noted that antibodies against AL, MAA, CarP, and AGE were more prevalent in AILD patients than HCs or non-AILD patients. AILD subjects, particularly AIH patients, often showed multiple anti-PTM antibodies. Also, more AIH patients with at least three anti-PTM antibodies reached CBR one year after treatment.
Of note, several anti-PTM antibodies were detected in AIH patients seronegative for classical autoantibodies (i.e., ANAs), suggesting that anti-PTM antibodies may be detected before conventional autoantibodies. Future work should evaluate the possibility of implementing anti-PTM antibody assessment in AIH diagnosis.
- Van Den Beukel MD, Stoelinga AEC, Van Der Meer AJ, et al. (2023). Antibodies against multiple post-translationally modified proteins aid in diagnosis of autoimmune hepatitis and associate with complete biochemical response to treatment. Front Med. doi: 10.3389/fmed.2023.1195747