Evaluation of anti α-d-Glc p-(1→4)-α-d-Glc p (GAGA4) IgM antibodies as a biomarker for multiple sclerosis

Abstract

The correct diagnosis of multiple sclerosis (MS) remains challenging due to the complex pathophysiological and clinical characteristics of the disease. Consequently, there has been immense interest in finding a non-invasive diagnostic test for MS. Recent studies found that serum anti-α-d-Glcp-(1→4)-α-d-Glcp (GAGA4) IgM antibodies were upregulated in MS patients, and this finding led to the development of a commercial diagnostic test (gMS® Dx test), although the test has poor selectivity and has not been independently validated. Herein, we developed an enzyme-linked immunosorbent assay (ELISA) to evaluate the use and reliability of several anti-glucose IgM antibodies, including those against GAGA4, as diagnostic biomarkers for MS. In contrast to previous studies, our results show that serum anti-GAGA4 IgM antibody levels are not significantly higher in MS patients, which could potentially explain the poor selectivity of the commercial test.

Fig. 1. Structure of GAGA4 with the cyanuric linker.

Fig. 2. Controls and antigens to be used in this study.

Fig. 3. Schematic representation of the ELISA protocol used in this study.

Scheme 1. Retrosynthetic analysis of glycoconjugate targets 2–7.

Scheme 2. Synthesis of the positive and negative control antigens.

Scheme 3. Synthesis of α-Glc based antigens 3 and 4.

Scheme 4. Synthesis of β-Glc based antigens 5–7.

Fig. 4. Serum anti-glycan IgM levels for healthy controls (HC, n = 10) and relapsing-remitting multiple sclerosis (RRMS, n = 40) patients (A); serum and plasma anti-glycan IgM levels for HC (n = 16) and MS patients (n = 48) (B). Data are expressed as median values and interquartile ranges, with bars above and below indicating the maximum and minimum ΔOD values, respectively. *p < 0.05 by Mann–Whitney U Test.