An Oligomannuronic Acid–Sialic Acid Conjugate Capable of Inhibiting Aβ42 Aggregation and Alleviating the Inflammatory Response of BV-2 Microglia

Oligomannuronic acid (MOS) from seaweed has antioxidant and anti-inflammatory activities. In this study, MOS was activated at the terminal to obtain three different graft complexes modified with sialic acid moiety (MOS-Sia). The results show that MOS-Sia addition can reduce the β-structure formation of Aβ42, and the binding effect of MOS-Sia3 is more obvious. MOS-Sia conjugates also have a better complexing effect with Ca2+ while reducing the formation of Aβ42 oligomers in solutions. MOS-Sia3 (25–50 μg/mL) can effectively inhibit the activation state of BV-2 cells stimulated by Aβ42, whereas a higher dose of MOS-Sia3 (>50 μg/mL) can inhibit the proliferation of BV-2 cells to a certain extent. A lower dose of MOS-Sia3 can also inhibit the expression of IL-1β, IL-6, TNF-α, and other proinflammatory factors in BV-2 cells induced by Aβ42 activation. In the future, the MOS-Sia3 conjugate can be used to treat Alzheimer’s disease.

Plasmodium infection induces cross-reactive antibodies to carbohydrate epitopes on the SARS-CoV-2 Spike protein

Individuals with acute malaria infection generated high levels of antibodies that cross-react with the SARS-CoV-2 Spike protein. Cross-reactive antibodies specifically recognized the sialic acid moiety on N-linked glycans of the Spike protein and do not neutralize in vitro SARS-CoV-2. Sero-surveillance is critical for monitoring and projecting disease burden and risk during the pandemic; however, routine use of Spike protein-based assays may overestimate SARS-CoV-2 exposure and population-level immunity in malaria-endemic countries.

Intramolecular Lactones of Sialic Acids

The so-called “sialo-chemical-biology” has become an attractive research area, as an increasing number of natural products containing a sialic acid moiety have been shown to play important roles in biological, pathological, and immunological processes. The intramolecular lactones of sialic acids are a subclass from this crucial family that could have central functions in the discrimination of physiological and pathological conditions. In this review, we report an in-depth analysis of the synthetic achievements in the preparation of the intramolecular lactones of sialic acids (1,4-, 1,7- and γ-lactones), in their free and/or protected form. In particular, recent advances in the synthesis of the 1,7-lactones have allowed the preparation of key sialic acid derivatives. These compounds could be used as authentic reference standards for their correct determination in biological samples, thus overcoming some of the limitations of the previous analytical procedures.

Alterations in sialic-acid O-acetylation glycoforms during murine erythrocyte development

ABSTRACT9-O-acetylation of sialic acid is a common modification that plays important roles in host-pathogen interactions. CASD1 has been described as a sialate-O-acetyltransferase and has been shown to be essential for 9-O-acetylation of sialic acid in some cell lines in vitro. In this study, we used knockout mice to confirm that CASD1 is indeed responsible for 9-O-acetylation of sialic acids in vivo. We observed a complete loss of 9-O-acetylation of sialic acids on the surface of myeloid, erythroid and CD4+ T cells in Casd1-deficient mice. Although 9-O-acetylation of sialic acids on multiple hematopoietic lineages was lost, there were no obvious defects in hematopoiesis. Interestingly, red blood cells from Casd1-deficient mice also lost reactivity to TER-119, a rat monoclonal antibody that is widely used to mark the murine erythroid lineage. The sialic acid glyco-epitope recognized by TER-119 on red blood cells was sensitive to the sialic acid O-acetyl esterase activity of the hemagglutinin esterase from bovine coronavirus but not to the corresponding enzyme from the influenza C virus. During erythrocyte development TER-119+ Ery-A and Ery-B cells could be stained by catalytically inactive bovine coronavirus hemaggutinin-esterase but not by the inactive influenza C hemagglutinin esterase, while TER-119+ Ery-C stage cells and mature erythrocytes were recognized by both virolectins. These results suggest that throughout murine erythrocyte development, cells of the erythroid lineage express a glycoconjugate bearing a modified 7,9-di-O-acetyl form of sialic acid, that is recognized specifically by the bovine coronavirus lectin and not by the influenza C hemagglutinin, and this modified sialic acid moiety is a component of the TER-119 epitope. As erythrocytes mature, the surface of Ery-C cells and mature erythrocytes also acquires a distinct CASD1-dependent 9-O-acetyl sialic acid moiety that can be recognized by virolectins from both influenza C and bovine coronavirus that are specific for 9-O-acetyl sialic acid.

Synthesis of a sialic acid derivative of ristocetin aglycone as an inhibitor of influenza virus

In order to promote attachment of the ristocetin aglycone molecule to the surface of the influenza virus, the aglycone was derivatized with a hemagglutinin ligand sialic acid moiety using a click reaction. The sialoristocetin derivative exhibited somewhat lower anti-influenza virus activity than ristocetin and aglycoristocetin.