Detergent induces the formation of IgG aggregates: a multi-methodological approach

Chaperone and Immunoglobulin-Binding Activities of Skp Protein from Yersinia pseudotuberculosis

Here, we determined qualitative and quantitative characteristics of the chaperone and immunoglobulin-binding activities of recombinant Skp protein (rSkp) from Yersinia pseudotuberculosis using the methods of dynamic light scattering and surface plasmon resonance. Commercial human polyclonal IgG and Fc and Fab fragments of human IgG were used as substrate proteins. The activity of rSkp strongly depended on the medium pH. The most stable low-molecular-weight complexes with a hydrodynamic radius up to 10 nm were formed by rSkp and protein substrates at acidic pH values. Under these conditions, rSkp exhibited the lowest propensity to self-association and the highest affinity for human IgG and its Fc and Fab fragments, as well as prevented their aggregation most efficiently (i.e., demonstrated the maximal chaperone activity). As the medium pH increased, the affinity of rSkp for IgG and its fragments decreased; rSkp was not able to completely prevent the aggregation of protein substrates, but significantly slowed it down. The obtained information may be of practical interest, since the stability of therapeutic IgG preparations affects their safety and efficacy in medical applications.

Structural and immunological characterization of hydroxyl radical modified human IgG: Clinical correlation in rheumatoid arthritis

Structural alterations in proteins under oxidative stress have been widely implicated in the immuno-pathology of various disorders. This study has evaluated the extent of damage in the conformational characteristics of IgG by hydroxyl radical (OH) and studied its implications in the immuno-pathology of rheumatoid arthritis (RA). Using various biophysical and biochemical techniques, changes in aromatic microenvironment of the IgG and the protein aggregation became evident after treatment with OH. The SDS-PAGE study confirmed the protein aggregation while far ultraviolet circular dichroism spectroscopy (Far-UV CD) and fourier transform infrared spectroscopy (FTIR) inferred towards the alterations in secondary structure of IgG under OH stress. Dynamic light scattering showed that the modification increased the hydrodynamic radius and polydispersity of IgG. The free arginine and lysine content reduced upon modification. OH induced aggregation was confirmed by enhanced thioflavin-T (ThT) fluorescence and red shift in the congo red (CR) absorbance. The study on experimental animals reiterates the earlier findings of enhanced immunogenicity of OH treated IgG (OH-IgG) compared to that of native IgG. OH-IgG strongly interacted with the antibodies derived from the serum of 80 rheumatoid arthritis (RA) patients. The overwhelming and strong tendency of OH-IgG to bind the antibodies derived from the serum of RA patients points towards the modification of IgG under patho-physiological conditions in RA that generate neo-epitopes and eventually cause the generation of auto antibodies that circulate in the patient sera. Further studies on this aspect may possibly lead to the development of a biomarker for RA.

Estimating Extrinsic Dyes for Fluorometric Online Monitoring of Antibody Aggregation in CHO Fed-Batch Cultivations

Multi-wavelength fluorescence spectroscopy was evaluated in this work as tool for real-time monitoring of antibody aggregation in CHO fed-batch cultivations via partial least square (PLS) modeling. Therefore, we used the extrinsic fluorescence dyes 1-anilinonaphthalene-8-sulfonate (ANS), 4,4′-bis-1-anilinonaphthalene-8-sulfonate (Bis-ANS), or Thioflavin T (ThT) as medium additives. This is a new application area, since these dyes are commonly used for aggregate detection during formulation development. We determined the half maximum inhibitory concentrations of ANS (203 ± 11 µmol·L⁻¹), Bis-ANS (5 ± 0.5 µmol·L⁻¹), and ThT (3 ± 0.2 µmol·L⁻¹), and selected suitable concentrations for this application. The results showed that the emission signals of non-covalent dye antibody aggregate interaction superimposed the fluorescence signals originating from feed medium and cell culture. The fluorescence datasets were subsequently used to build PLS models, and the dye-related elevated fluorescence signals dominated the model calibration. The soft sensors based on ANS and Bis-ANS signals showed high predictability with a low error of prediction (1.7 and 2.3 mg·mL⁻¹ aggregates). In general, the combination of extrinsic dye and used concentration influenced the predictability. Furthermore, the ThT soft sensor indicated that the intrinsic fluorescence of the culture might be sufficient to predict antibody aggregation online.

Neo-Epitopes Generated on Hydroxyl Radical Modified GlycatedIgG Have Role in Immunopathology of Diabetes Type 2

Glycoxidation plays a crucial role in diabetes and its associated complications. Among the glycoxidation agents, methylglyoxal (MG) is known to have very highglycationpotential witha concomitant generation of reactive oxygen species (ROS) during its synthesis and degradation. The presentstudy probes the MG and ROSinduced structural damage to immunoglobulin G (IgG) and alterations in its immunogenicity in diabetes type 2 patients (T2DM). Human IgG was first glycated with MG followed by hydroxyl radical (OH•) modification. Glycoxidation mediated effects on IgG were evaluated by various physicochemical techniques likeultraviolet (UV) and fluorescence spectroscopy, 8-anilinonaphthalene-1-sulfonic acid (ANS) binding studies, carbonyl andfree sulfhydryl groups assay, matrix assisted laser desorption ionization mass spectrometry-time of flight (MALDI-TOF), red blood cell (RBC) haemolysis assay, Congored (CR) staining analysis and scanning electron microscopy (SEM). The results revealed hyperchromicityin UV, advanced glycation end product (AGE)specific and ANS fluorescence, quenching in tyrosine and tryptophan fluorescence intensity,enhanced carbonyl content,reduction in free sulfhydryl groups,pronounced shift in m/z value of IgGand decrease in antioxidant activity in RBC induced haemolysis assayupon glycoxidation. SEM and CRstaining assay showed highly altered surface morphology in glycoxidised sample as compared to the native. Enzyme linked immunosorbent assay (ELISA) and band shift assay were performed to assess the changes in immunogenicity of IgG upon glyoxidation and its role in T2DM. The serum antibodies derived from T2DM patients demonstrated strong affinity towards OH• treated MG glycatedIgG (OH•-MG-IgG) when compared to native IgG (N-IgG) or IgGs treated with MG alone (MG-IgG) or OH• alone (OH•-IgG). This study shows the cumulating effect of OH• on the glycation potential of MG. The results point towards the modification of IgG in diabetes patients under the effect of glycoxidative stress, leading to the generation of neo-epitopes on theIgG molecule and rendering it immunogenic.