Characterization of methylglyoxal-modified human IgG by physicochemical methods

Glycoxidation of mammalian whole histone generates highly immunogenic aggregates: Sera of SLE patients contain autoantibodies against aggregates

Non-enzymatic glycation and oxidation of self-proteins, causing formation and accumulation of advanced glycation end products (AGEs), have been reported in an array of pathologies, including systemic lupus erythematosus (SLE). Such modifications may generate neo-epitopes, break immunological tolerance, and induce antibody response. In this study, we have first analysed the structural modifications of whole histone in the presence of deoxyribose followed by oxidation with hydroxyl radicals. Changes in the secondary and tertiary structure of the whole histone were determined by spectroscopic techniques and biochemical assays. Fluorescence spectroscopy and UPLC-MS showed the generation of AGEs such as carboxymethyl lysine and pentosidine, while DLS and TEM indicated the presence of amorphous AGE-aggregates. Moreover, rabbits immunized with these histone-AGEs exhibited enhanced immunogenicity and ELISA and western immunoblot of IgG antibodies from SLE patients' sera showed a significantly higher specificity towards modified histone-AGEs than the native histone.

Antibodies against 4 Atypical Post-Translational Protein Modifications in Patients with Rheumatoid Arthritis

Patients with rheumatoid arthritis (RA) show autoantibodies against post-translational protein modifications (PTMs), such as anti-citrullinated protein antibodies. However, the range of recognized PTMs is unknown. Here, we addressed four PTMs: chlorination, non-enzymatic glycation, nitration, and homocysteinylation, identified as targets of atypical RA autoantibodies in studies whose protocols we have followed. The modified antigens included collagen type II, an extract of synovial proteins and a selection of peptides. We interpreted the results according to the optical density (OD) obtained in an enzyme-linked immunosorbent assay ( ELISA) with the modified antigen and the corrected OD obtained after subtracting the reactivity against the unmodified antigen. The results showed evidence of specific antibodies against glycated collagen type II, as the corrected ODs were higher in the 182 patients with RA than in the 164 healthy controls (p = 0.0003). However, the relevance of these antibodies was doubtful because the magnitude of the specific signal was small (median OD = 0.072 vs. 0.027, respectively). There were no specific antibodies against any of the other three PTMs. Therefore, our results showed that the four PTMs are not inducing a significant autoantibody response in patients with RA. These results indicated that the repertoire of PTM autoantigens in RA is restricted.

Interaction of silica nanoparticles with tau proteins and PC12 cells: Colloidal stability, thermodynamic, docking, and cellular studies

Study on the side effects of the nanoparticles (NPs) can provide useful information regarding their biological and medical applications. Herein, the colloidal stability of the silicon dioxide NPs (SiO₂ NPs) in the absence and presence of tau was investigated by TEM and DLS techniques. Afterwards, the thermodynamic parameters of interaction between SiO₂ NPs and tau were determined by fluorescence spectroscopy and docking studies. Finally, the cytotoxic effects of SiO₂ NPs on the viability of PC12 cells were investigated by MTT, AO/EB staining and flow cytometry assays. TEM, DLS, and zeta potential investigations revealed that tau can reduce the colloidal stability of SiO₂ NPs. Fluorescence spectroscopy study indicated that SiO₂ NPs bound to the tau with high affinity through hydrogen bonds and van der Waals interactions. Docking study also determined that Ser, Thr and Tyr residues provide a polar microenvironment for SiO₂ NPs/tau interaction. Cellular studies demonstrated that SiO₂ NPs can induce cell mortality through both apoptosis and necrosis mechanisms. Therefore, it may be concluded that the biological systems such as nervous system proteins can affect the colloidal stability of NPs and vice versa NPs in the biological systems can bind to proteins and cell membranes non-specifically and may induce toxicity.