Changes in avidity and specificity of IgG during electro-oxidation. Relevance of binding of antibodies to β2-GPI

A novel method for in silico assessment of Methionine oxidation risk in monoclonal antibodies: Improvement over the 2-shell model

Over the past decade, therapeutic monoclonal antibodies (mAbs) have established their role as valuable agents in the treatment of various diseases ranging from cancers to infectious, cardiovascular and autoimmune diseases. Reactive groups of the amino acids within these proteins make them susceptible to many kinds of chemical modifications during manufacturing, storage and in vivo circulation. Among these reactions, the oxidation of methionine residues to their sulfoxide form is a commonly observed chemical modification in mAbs. When the oxidized methionine is in the complementarity-determining region (CDR), this modification can affect antigen binding and thus abrogate biological activity. For these reasons, it is essential to identify oxidation liabilities during the antibody discovery and development phases. Here, we present an in silico method, based on protein modeling and molecular dynamics simulations, to predict the oxidation-liable residues in the variable region of therapeutic antibodies. Previous studies have used the 2-shell water coordination number descriptor (WCN) to identify methionine residues susceptible to oxidation. Although the WCN descriptor successfully predicted oxidation liabilities when the residue was solvent exposed, the method was much less accurate for partially buried methionine residues. Consequently, we introduce a new descriptor, WCN-OH, that improves the accuracy of prediction of methionine oxidation susceptibility by extending the theoretical framework of the water coordination number to incorporate the effects of polar amino acids side chains in close proximity to the methionine of interest.

Oxidative Modifications Switch Modulatory Activities of Urinary Proteins From Inhibiting to Promoting Calcium Oxalate Crystallization, Growth, and Aggregation

The incidence/prevalence of kidney stone disease has been increasing around the globe, but its pathogenic mechanisms remained unclear. We evaluated effects of oxidative modifications of urinary proteins on calcium oxalate (CaOx) stone formation processes. Urinary proteins derived from 20 healthy individuals were modified by performic oxidation, and the presence of oxidatively modified urinary proteins was verified, quantified, and characterized by Oxyblot assay and tandem MS (nanoLC-electrospray ionization-linear trap quadrupole-Orbitrap-MS/MS). Subsequently, activities of oxidatively modified urinary proteins on CaOx stone formation processes were examined. Oxyblot assay confirmed the marked increase in protein oxidation level in the modified urine. NanoLC-electrospray ionization-linear trap quadrupole-Orbitrap-MS/MS identified a total of 193 and 220 urinary proteins in nonmodified and modified urine samples, respectively. Among these, there were 1121 and 5297 unambiguous oxidatively modified peptides representing 42 and 136 oxidatively modified proteins in the nonmodified and modified urine samples, respectively. Crystal assays revealed that oxidatively modified urinary proteins significantly promoted CaOx crystallization, crystal growth, and aggregation. By contrast, the nonmodified urinary proteins had inhibitory activities. This is the first direct evidence demonstrating that oxidative modifications of urinary proteins increase the risk of kidney stone disease by switching their modulatory activities from inhibiting to promoting CaOx crystallization, crystal growth, and aggregation.

Label-Free Method Development for Hydroxyproline PTM Mapping in Human Plasma Proteome

Post-translational modifications (PTMs) impart structural heterogeneities that can alter plasma proteins' functions in various pathophysiological processes. However, the identification and mapping of PTMs in untargeted plasma proteomics is still a challenge due to the presence of diverse components in blood. Here, we report a label-free method for identifying and mapping hydroxylated proteins using tandem mass spectrometry (MS/MS) in the human plasma sample. Our untargeted proteomics approach led us to identify 676 de novo sequenced peptides in human plasma that correspond to 201 proteins, out of which 11 plasma proteins were found to be hydroxylated. Among these hydroxylated proteins, Immunoglobulin A1 (IgA1) heavy chain was found to be modified at residue 285 (Pro²⁸⁵ to Hyp²⁸⁵), which was further validated by MS/MS study. Molecular dynamics (MD) simulation analysis demonstrated that this proline hydroxylation in IgA1 caused both local and global structural changes. Overall, this study provides a comprehensive understanding of the protein profile containing Hyp PTMs in human plasma and shows the future perspective of identifying and discriminating Hyp PTM in the normal and the diseased proteomes.

Sepsis and septic shock: Pathogenesis and treatment perspectives

The majority of bacteremias do not develop to sepsis: bacteria are cleared from the bloodstream. Oxygen released from erythrocytes and humoral immunity kill bacteria in the bloodstream. Sepsis develops if bacteria are resistant to oxidation and proliferate in erythrocytes. Bacteria provoke oxygen release from erythrocytes to arterial blood. Abundant release of oxygen to the plasma triggers a cascade of events that cause: 1. oxygen delivery failure to cells; 2. oxidation of plasma components that impairs humoral regulation and inactivates immune complexes; 3. disseminated intravascular coagulation and multiple organs' failure. Bacterial reservoir inside erythrocytes provides the long-term survival of bacteria and is the cause of ineffectiveness of antibiotics and host immune reactions. Treatment perspectives that include different aspects of sepsis development are discussed.

Oxidatively altered IgG with increased immunoreactivity to β2-glycoprotein I and its peptide clusters influence human coronary artery endothelial cells

Oxidative stress has been shown to play a role in modifying antibodies in favor of higher auto-immunoreactivity. We studied the immunoreactivity of oxidized IgG (oxIgG) to β2-glycoprotein I (β2GPI), six peptide sequences corresponding to amino acid clusters on its different domains, to determine their effects on human coronary artery endothelial cells (HCAEC). Human IgG was purified from seven donors, electro-oxidized and checked for immunoreactivity and avidity to β2GPI and to peptides by ELISA. Conformational stability and antibody-antigen complex formation of oxIgG was analyzed by fluorescence spectroscopy and dynamic light scattering. Resting and activated sub-confluent HCAEC were stimulated with oxIgG or IgG. Secreted cytokines were measured by ELISA. Immunoreactivity of seven oxIgG samples increased to 7.5-fold against β2GPI and to 3.8-fold against six peptides as compared to IgG. oxIgG showed low avidity "properties." Conformational changes and exposure of protein hydrophobic regions were confirmed by an elevation in fluorescence (2.4- to 5.0-fold) on bis-ANS dye binding to oxIgG. oxIgG significantly elevated the release of GROα and IL-8 in resting and activated states of HCAEC. Oxidation alters IgG in favor of autoreactivity toward whole β2GPI and corresponding peptides on different domains of β2GPI and could lead to dysfunction of arterial endothelium by upregulation of chemokines.

Platelet and endothelial activation in catastrophic and quiescent antiphospholipid syndrome

Antiphospholipid antibodies (aPL) seem to induce a prothrombotic state by activating endothelium and platelets, but no studies have evaluated systematically the effects of aPL from patients with the antiphospholipid syndrome (APS) in quiescent versus catastrophic phase. Our aims were to evaluate the in vitro effects on platelet activation of anti-β2 glycoprotein I (anti-β2GPI) antibodiesisolated from APS patientin either quiescent or catastrophic phase and to investigate ex vivo platelet and endothelial activation in patients with quiescent or catastrophic APS. Anti-β2GPI antibodies were isolated from plasma of a pregnant woman in two different stages of APS (quiescent and catastrophic, respectively). They were co-incubated with washed platelets from healthy controls that were then challenged with TRAP-6 (thrombin receptor activating peptide 6) and the expression of P- selectin (P-sel) on platelets was assessed by flow cytometry. Moreover, plasma samples from six patients with quiescent, four with catastrophic APS and 10 controls were assessed for several markers of platelet and endothelial activation. The results showed that purified anti-β2GPI antibodies co-incubated with platelets enhanced TRAP-6- induced platelet P-sel expression. Notably, anti-β2GPI antibodies isolated during the catastrophic phase enhanced platelet P-sel expression more than antibodies isolated from the same patient in the quiescent stage of disease. Moreover, APS patients had significantly higher plasma levels of soluble (s) Psel, sCD40 ligand, soluble vascular cell adhesion molecule 1 and monocyte chemoattractant protein 1 than control subjects. In addition, sP-sel and von Willebrand factor activity were significantly higher during catastrophic than in quiescent phase.

The avidity of anti-β2-glycoprotein I antibodies in patients with or without antiphospholipid syndrome: a collaborative study in the frame of the European forum on antiphospholipid antibodies

Objective. The objective of this study was to extend the findings of the preliminary study by measuring the avidity of IgG anti-β2-glycoprotein I antibodies (anti-β2-GPI) on a larger group of patients with primary or secondary antiphospholipid syndrome (APS) and anti-β2-GPI positive patients without APS in the frame of the European Forum on antiphospholipid antibodies (aPL).

Methods. Serum from 137 patients with primary APS, APS associated with autoimmune diseases, and patients with autoimmune diseases other than APS from five EU rheumatology centres were tested for anti-β2-GPI antibodies. The 109 patients who were sera positive for anti-β2-GPI by the in-house anti-β2-GPI enzyme-linked immunosorbent assay (ELISA) at the Immunology Laboratory, UMC Ljubljana were selected for further testing on avidity with chaotropic anti-β2-GPI ELISA.

Results. High, low and heterogeneous avidity IgG anti-β2-GPI was found in 32/109, 17/109 and 60/109 patients respectively. Significantly more patients with APS were in the high avidity than in the low avidity anti-β2-GPI group, while the opposite was observed for non-APS (both p < 0.001). The most common clinical feature among patients with high avidity anti-β2-GPI was thrombosis, mainly due to venous thrombosis ( p < 0.01 and p < 0.001, versus low avidity anti-β2-GPI group).

Conclusion. Patients with or without APS had anti-β2-GPI of high, low or heterogeneous avidity. High avidity anti-β2-GPI was associated with thrombosis and APS, while in the low avidity anti-β2-GPI group non-APS (predominantly SLE) patients prevailed. Determination of anti-β2-GPI avidity should be considered in the analytical strategies for further differentiation of patients with anti-β2-GPI antibodies.

Autoimmune reactivity of IgM acquired after oxidation

OBJECTIVES

Redox-reactive antibodies, mainly of the IgG class, gained a wide area of interest after their autoimmune reactivity was revealed following the application of chemical and physiological oxidants. In this study, we examined the susceptibility of IgMs to oxidation and evaluated their binding to the autoantigens important in some autoimmune diseases.

METHODS

IgM and IgG fractions, isolated from healthy individuals' sera, were oxidized using direct electric current or physiological oxidant hemin. Specificities towards beta-2-glycoprotein I (β(2)-GPI), cardiolipin (CL), and rheumatoid factor were evaluated with the enzyme-linked immunosorbent assays (ELISAs). Post-translational modification was investigated by 2,4-dinitrophenylhydrazine reaction.

RESULTS

Electrochemically oxidized IgM fractions exhibited altered immunoreactivity - low to medium titers in anti-CL and low positive titers in anti-β(2)-GPI ELISA but exhibited no rheumatoid factor reactivity. Oxidized IgG and IgM fractions exhibited 2.5- and 5-fold increase in the carbonyl content, respectively.

DISCUSSION

An increase in the carbonyl content along with increased immunoreactivity after oxidation suggests modifications of the IgM paratopes. These results point towards possible modifications of native IgMs to their autoimmune state despite the fact that IgMs were less susceptible to oxidation than IgGs. The importance of an individual's redox status in maintenance of autoimmune reactions was emphasized by in vitro diagnostic tests.

Redox-reactive autoantibodies in Alzheimer's patients' cerebrospinal fluids: Preliminary studies

Oxidation of cerebrospinal fluid (CSF) causes differential unmasking of autoantibodies in control CSF vs. that obtained from postmortem CSF samples from autopsy confirmed Alzheimer's disease (AD) cases. This study demonstrates that normal CSF from both living patients and from non-demented autopsy cases contains redox-reactive autoantibodies with specificities that include antiphospholipid antibodies (aPL). In contrast, CSF from autopsy confirmed AD subjects contained little or no redox-reactive aPL autoantibodies. Tests using an in vitro rat synaptosome model showed that the oxidized CSF autoantibodies from a normal individual can cause ERK1/2 phosphorylation at a level consistent with reports of pathogenic changes found in brain tissues from AD patients. The decrease or absence of redox-reactive antibodies in CSF from Alzheimer's patients suggests that these antibodies may have been previously unmasked by the oxidative conditions that exist in the CNS in AD patients. These unmasked autoantibodies could then bind to neuronal tissues and possibly participate in the initial cascade leading to the dementia in Alzheimer's. To our knowledge, this is the first description of resident autoantibodies with the potential to cause brain cell damage documented in CSF without a breech in the blood-brain barrier. The untimely and inappropriate physiological unmasking of these redox-reactive autoantibodies in AD patients CSF may represent a valuable biomarker for diagnosis and progression of this and perhaps other neurodegenerative diseases which also have oxidative stress components. These novel autoantibody observations may stimulate thoughts about additional therapeutic approaches and warrant similar studies for other neurodegenerative diseases.

Systemic lupus erythematosus in the elderly

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease, characterized by multisystemic involvement. Late onset SLE represents a specific sub-group of the disorder, beginning above 50-65 years of age. The incidence of late onset SLE ranges in the interval of 12-18% and the course of the disease is considered to be more benign. According to several authors, skin manifestations, photosensitivity, arthritis and nephritis, occur rarely in the elderly patients with late SLE onset; prevalence of serositis, lung involvement and Sjögren's syndrome were observed more often. Late onset SLE patients manifested higher rate of positive findings of rheumatoid factors, as well as of anti-Ro and anti-La antibodies; and the lower occurrence of anti-RNP antibodies and hypocomplementaemia. A slow onset of the disorder, non-specific manifestations at the beginning of the illness and less frequent prevalence of SLE in the elderly often result in late diagnosis. Treatment of the disease depends on its clinical manifestations. NSAID's, antimalarials or low doses of glucocorticoids are used for the less severe forms. Immunosuppressives and higher doses of glucocorticoids are the treatments of choice for more severe organ involvements and complications. A multidisciplinary approach is recommended for the treatment of late onset SLE patients.