Serum Clusterin Concentration and Its Glycosylation Changes as Potential New Diagnostic Markers of SARS-CoV-2 Infection and Recovery Process

Abstract

COVID-19 is an infectious disease caused by the SARS-CoV-2 virus. Glycoprotein clusterin (CLU) has many functions such as phagocyte recruitment, complement system inhibition, apoptosis inhibition, hormone and lipid transport, as well as in the immune response. The study aimed to assess the changes in CLU concentrations and the profile and degree of CLU glycosylation between patients with severe COVID-19, convalescents, and healthy subjects (control). The profile and degree of serum CLU N-glycosylation were analyzed using lectin-ELISA with specific lectins. CLU concentrations were significantly lower and relative reactivities of CLU glycans with SNA (Sambucus nigra agglutinin) were significantly higher in severe COVID-19 patients in comparison to convalescents and the control group. The relative reactivities of CLU glycans with MAA (Maackia amurensis agglutinin), together with relative reactivity with LCA (Lens culinaris agglutinin), were also significantly higher in patients with severe COVID-19 than in convalescents and the control group, but they also significantly differed between convalescents and control. The development of acute inflammation in the course of severe COVID-19 is associated with a decrease in CLU concentration, accompanied by an increase in the expression of α2,3-linked sialic acid, and core fucose. Both of these parameters can be included as useful glycomarkers differentiating patients with severe COVID-19 from convalescents and the control group, as well as convalescents and healthy subjects.

Keywords: COVID-19; lectin-ELISA; serum clusterin glycosylation.

Figure 1

Clusterin concentrations (A) and relative reactivities of serum clusterin glycans with specific lectins (B–F). Significant differences between healthy subjects (control) vs. ¹ patients with severe COVID-19 and ² convalescents. CLU glycan relative reactivities with lectins SNA (Sambucus nigra agglutinin), MAA (Maackia amurensis agglutinin), LCA (Lens culinaris agglutinin), LTA (Lotus tetragonolobus agglutinin), and UEA (Ulex europaeus agglutinin) were expressed in absorbance units (AU). The exact specificity of the lectins used can be found in Section 4.4. A two-tailed p-value (probability value) of less than 0.05 was considered significant.

Figure 2

ROC curve analysis for clusterin concentrations (A) and relative reactivities of CLU glycans with lectins (B–H). Only the parameters for which the values of area under the curve (AUC) were ≥0.704 (moderate and high clinical value) were presented. For the determination of cut-off points, the Youden index method was used. The reference line is marked in red, the receiver operating characteristics for analyzed parameter in blue, and the cut-off point in green. CLU—blood serum clusterin concentrations; SNA—CLU glycan relative reactivity with Sambucus nigra agglutinin; MAA—CLU glycan relative reactivity with Maackia amurensis agglutinin; LCA—CLU glycan relative reactivity with Lens culinaris agglutinin. Significant differences were accepted for a p-value (probability value) of less than 0.05. The exact specificity of the lectins used can be found in Section 4.4.