Triterpene glycosides from Blighia welwitschii and evaluation of their antibody recognition capacity in multiple sclerosis

Multiple sclerosis (MS) in a multifactorial autoimmune disease in which reliable biomarkers are needed for therapeutic monitoring and diagnosis. Autoantibodies (autoAbs) are known biomarker candidates although their detection in biological fluids requires a thorough characterization of their associated antigens. Over the past twenty years, a reverse chemical-based approach aiming to screen putative autoantigens has underlined the role of glycans, in particular glucose, in MS. Despite the progress achieved, a lack of consensus regarding the nature of innate antigens as well as difficulties proposing new synthetic glucose-based structures have proved to be obstacles. Here is proposed a strategy to extend the current methodology to the field of natural glycosides, in order to dramatically increase the diversity of glycans that could be tested. Triterpene saponins from the Sapindaceace family represent an optimal starting material as their abundant description in the literature has revealed a prevalence of glucose-based oligosaccharides. Blighia welwitschii (Sapindaceae) was thus selected as a case study and twelve triterpene saponins were isolated and characterized. Their structures were elucidated on the basis of 1D and 2D NMR as well as mass spectrometry, revealing seven undescribed compounds. A selection of natural glycosides exhibiting various oligosaccharide moieties were then tested as antigens in enzyme-linked immunosorbent assay (ELISA) to recognize IgM antibodies (Abs) in MS patients' sera. Immunoassay results indicated a correlation between the glycan structures and their antibody recognition capacity, allowing the determination of structure-activity relationships that were coherent with previous studies. This approach might help to identify sugar epitopes putatively involved in MS pathogenesis, which remains poorly understood.

Keywords: Antibody recognition; Blighia welwitschii; ELISA; Multiple sclerosis; Sapindaceae; Triterpene saponins.