Autoantibodies against citrullinated serum albumin in patients with rheumatoid arthritis

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Albumin from sera of rheumatoid arthritis patients share multiple biochemical, biophysical and immunological properties with in vitro generated glyco-nitro-oxidized-albumin

The purpose of the present study is to explore the effects of endogenous stressors on structure and function of rheumatoid arthritis (RA) patients' albumin. In contrast to glycated-albumin or nitro-oxidized-albumin, high titre antibodies against glyco-nitro-oxidized-albumin were found in the sera of RA patients. Also, compared to the other two modified forms of albumin, glyco-nitro-oxidized-albumin showed highest percent inhibition. Albumin isolated from RA patients' sera displayed hyperchromicity and quenching of tyrosine and tryptophan fluorescence. Fluorescence spectroscopy studies also revealed the presence of dityrosine and advanced glycation end products in RA patient's albumin. RA patients' albumin showed weaker binding with 1-anilinonaphthalene-8-sulfonic acid dye. Secondary structure alterations were demonstrated by circular dichroism and Fourier transform infrared spectroscopy. Biochemical investigations revealed substantial decline in the availability of free side chains of amino acid residues; increased carbonyls and decreased sulfhydryls in RA patients' albumin. The functional impairment in RA patients' albumin was revealed by their low binding with bilirubin and cobalt. Liquid chromatography mass spectrometry analysis revealed the presence of Nε-(carboxymethyl) lysine and 3-nitrotyrosine in RA patients' albumin. The amyloidogenic aggregation of RA patients' albumin was confirmed by Congo red absorption and thioflavin-T fluorescence assays. The morphology of the aggregates was visualized under scanning and transmission electron microscope. From the above findings, we inferred that endogenous stress in RA patients have modified albumin and produce structural/functional abnormalities. Also, the presence of anti-glyco-nitro-oxidized-albumin antibodies along with other clinical features may be used as biomarker for the diagnosis and assessment of treatment responses in RA patients.Communicated by Ramaswamy H. Sarma.

Anemia in elderly rheumatoid arthritis patients: a cohort study

Introduction

Anemia is common in elderly patients with rheumatoid arthritis (RA). This study aimed to evaluate the current status and influencing factors of anemia in RA patients, to provide insights for clinical RA treatment and care.

Material and methods

This study included elderly patients with high RA activity treated in our hospital from June 1, 2021 to December 31, 2022 for analysis. The characteristics of RA patients were analyzed. Pearson correlation and logistic regression analysis were conducted to analyze the influencing factors of anemia in elderly patients with RA.

Results

A total of 285 RA patients were included. The incidence of anemia in high RA activity patients was 62.46%. There were significant differences in the course of RA, hemoglobin (Hb), low-density lipoprotein cholesterol (LDL-C), platelet/lymphocyte rate (PLR) and albumin (Alb) between RA patients with anemia and without anemia (all p < 0.05). Pearson correlation analysis indicated that course of RA (r = 0.522), Hb (r = 0.797), LDL-C (r = 0.558), PLR (r = 0.615) and Alb (r = 0.604) were correlated with anemia in patients with high RA activity (all p < 0.05). Logistic regression analysis indicated that course of RA ≥ 8 years (OR = 2.584, 95% CI: 1.822-3.647), LDL-C ≤ 2.8 mmol/l (OR = 3.202, 95% CI: 2.804-3.431), PLR ≥ 8 (OR = 2.183, 95% CI: 1.744-2.457), Alb ≤ 35 g/l (OR = 1.716, 95% CI: 1.401-2.006) were the risk factors of anemia in elderly patients with high RA activity (all p < 0.05).

Conclusions

Anemia in elderly patients with high RA activity is closely related to the course of RA, LDL-C, PLR and Alb. Close attention should be paid to the monitoring of those indicators to take early intervention measures to improve the prognosis of RA patients.

Molecular Dynamics Study of Citrullinated Proteins Associated with the Development of Rheumatoid Arthritis

Biological activity regulation by protein post-translational modification (PTM) is critical for cell function, development, differentiation, and survival. Dysregulation of PTM proteins is present in various pathological conditions, including rheumatoid arthritis (RA). RA is a systemic autoimmune disease that primarily affects joints, and there are three main types of protein PTMs associated with the development of this disease, namely, glycosylation, citrullination, and carbamylation. Glycosylation is important for the processing and presentation of antigen fragments on the cell surface and can modulate immunoglobulin activity. The citrullination of autoantigens is closely associated with RA, as evidenced by the presence of antibodies specific to citrullinated proteins in the serum of patients. Carbamylation and dysregulation have recently been associated with RA development in humans.In this study, we performed an overview analysis of proteins with post-translational modifications associated with the development of RA adverted in peer-reviewed scientific papers for the past 20 years. As a result of the search, a list of target proteins and corresponding amino acid sequences with PTM in RA was formed. Structural characteristics of the listed modified proteins were extracted from the Protein Data Bank. Then, molecular dynamics experiments of intact protein structures and corresponding structures with PTMs were performed regarding structures in the list announced in the ProtDB service. This study aimed to conduct a molecular dynamics study of intact proteins and proteins, including post-translational modification and protein citrullination, likely associated with RA development. We observed another exhibition of the fundamental physics concept, symmetry, at the submolecular level, unveiled as the autonomous repetitions of outside the protein structural motif performance globule corresponding to those in the whole protein molecule.

Autoantibodies Against Unmodified and Citrullinated Human Endogenous Retrovirus K Envelope Protein in Patients With Rheumatoid Arthritis

OBJECTIVE

Autoantibodies against proteins encoded by human endogenous retrovirus K (HERV-K) have been reported in patients with rheumatoid arthritis (RA), but their relevance, if any, has remained unresolved. We revisited this question and tested if such autoantibodies may react with citrullinated epitopes on the envelope (Env) protein of HERV-K.

METHODS

Immunoblotting and ELISAs were conducted with unmodified Env protein and with Env citrullinated by protein arginine deiminase 4 (PAD4). Sera from 100 patients with RA, plasma from 32 patients with juvenile idiopathic arthritis (JIA), and healthy adult and pediatric controls were included. Antibody reactivity was evaluated for correlations with clinical and laboratory variables of the patients.

RESULTS

We replicated and expanded upon published data suggesting that patients with RA or JIA have autoantibodies against HERV-K Env, some with high titers. Anti-HERV-K antibodies correlated with cigarette smoking and with circulating myeloperoxidase-DNA complexes indicative of nonapoptotic neutrophil cell death. Further, most of the patients with RA, but not those with JIA, had autoantibodies that reacted more strongly with Env that was citrullinated by PAD4. These anticitrullinated Env autoantibodies correlated with seropositivity and tended to be higher in patients with erosive disease.

CONCLUSION

Our data suggest that anti-HERV-K immunity is elevated in RA and JIA and may have a connection with pathogenic protein citrullination in RA.