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.