A Label-Free SARS-CoV-2 Surrogate Virus Neutralization Test and a Longitudinal Study of Antibody Characteristics in COVID-19 Patients

Background. The laboratory-based methods to measure the SARS-CoV-2 humoral response include virus neutralization tests (VNTs) to determine antibody neutralization potency. For ease of use and universal applicability, surrogate virus neutralization tests (sVNTs) based on antibody-mediated blockage of molecular interactions have been proposed. Methods. A surrogate virus neutralization test established on a label-free immunoassay platform (LF-sVNT). The LF-sVNT analyzes the binding ability of RBD to ACE2 after neutralizing RBD with antibodies in serum. Results. The LF-sVNT neutralizing antibody titers (IC50) were determined from serum samples (n=246) from COVID-19 patients (n=113), as well as the IgG concentrations and the IgG avidity indices. Although there is variability in the kinetics of the IgG concentrations and neutralizing antibody titers between individuals, there is an initial rise, plateau and then in some cases a gradual decline at later timepoints after 40 days post-symptom onset. The IgG avidity indices, in the same cases, plateau after the initial rise and did not show a decline. Conclusions. The LF-sVNT can be a valuable tool in clinical laboratories for the assessment of the presence of neutralizing antibodies to COVID-19. This study is the first to provide longitudinal neutralizing antibody titers beyond 200 days post-symptom onset. Despite the decline of IgG concentration and neutralizing antibody titer, IgG avidity index increases, reaches a plateau and then remains constant up to 8 months post-infection. The decline of antibody neutralization potency can be attributed to the reduction in antibody quantity rather than the deterioration of antibody avidity, a measure of antibody quality.

Kinetics of SARS-CoV-2 Antibody Avidity Maturation and Association with Disease Severity

The kinetics of IgG avidity maturation during SARS-CoV-2 infection was studied. The IgG avidity assay used a novel label-free immunoassay technology. It was found that there was a strong correlation between IgG avidity and days since symptom onset, and peak readings were significantly higher in severe than mild disease cases.

Elevated level of carbonyl compounds correlates with insulin resistance in type 2 diabetes

<p><b>INTRODUCTION</b>Recent periodicals direct that reactive carbonyl compounds are formed due to existing oxidative stress in type 2 diabetes mellitus, which further nonenzymatically react with proteins and lipids to form irreversible advanced glycation end products (AGE) and advanced lipoxidation end products (ALE). In type 2 diabetes mellitus, insulin resistance plays a pivotal role in hyperglycaemia. In this study, we tried to fi nd the relation between insulin resistance and carbonyl stress.</p><p><b>MATERIALS AND METHODS</b>Forty-seven patients of type 2 diabetes mellitus (age 51 ± 5.06 years) were selected and fasting plasma glucose, serum insulin, total carbonyl compounds, HbA1c, thiobarbituric acid reacting substances (TBARS) and Trolox equivalent antioxidant capacity (TEAC) were estimated using standard protocols. Homeostatic model assessement of insulin resistance (HOMA-IR) was evaluated from fasting plasma glucose and serum insulin levels.</p><p><b>RESULTS</b>We found highly significant correlations of carbonyl compounds with HOMA-IR, fasting plasma glucose and glycated haemoglobin (HbA1c). Correlations of lipid peroxidation end product, TBARS were not so significant.</p><p><b>CONCLUSION</b>Findings from this study indicate that the level of carbonyl compounds can be a biomarker of insulin resistance in type 2 diabetes mellitus.</p>

Non-haem iron-mediated oxidative stress in haemoglobin E beta-thalassaemia

<p><b>INTRODUCTION</b>Haemoglobin (Hb) E beta-thalassaemia is a common thalassaemic disorder in Southeast Asia and is very common in the eastern and north-eastern parts of India. The disease cause rapid erythrocyte destruction due to the free radical mediated injury but factors for the oxidative injury are not clearly known. We investigated the free reactive iron (non-haem) mediated insult in Hb E beta-thalassaemia.</p><p><b>MATERIALS AND METHODS</b>Thirty Hb E beta-thalassaemic patients (age range, 3 to 15 years) who had undergone blood transfusion at least 1 month prior to sampling and 32 normal healthy individuals (age range, 18 to 30 years) were included in this study. We estimated the ferrozine detected intracellular erythrocytic free reactive iron (nonhaem iron), reduced glutathione (GSH), glutathione reductase activity, cellular damage marker serum thiobarbituric acid reacting substances (TBARS) and also serum ferritin using standard methods.</p><p><b>RESULTS</b>We found that the erythrocytic free reactive iron was significantly higher (P <0.001) in Hb E beta patients and was about 30% more than in controls. The elevated level of erythrocytic non-haem iron was associated with a high level of serum TBARS which was about 86% higher in patients than in controls. The serum ferritin level was also significantly higher (P <0.001) compared to controls. The erythrocytic reduced glutathione level was significantly lower (P <0.001) at about 65% less in the patients' group and the erythrocytic glutathione reductase enzyme was also found to be significantly lower (P <0.001) in Hb E beta-thalassaemia.</p><p><b>CONCLUSIONS</b>We concluded that a significantly elevated level of erythrocytic free reactive iron and lipid peroxidation end product was associated with low erythrocytic GSH level. This reflects non-haem iron mediated cellular damage in Hb E beta-thalassaemia.</p>