O-acetylated sialic acids -: Their detection, biological significance and alteration in diseases

Sialic acids are acidic, 9-carbon carboxylated monosaccharides, typically expressed on the outermost end of the sugar chains of membrane and secreted glycoconjugates. This particular location provides it accessibility reflected in its regulation of a multitude of cellular and molecular interactions. Amongst the diverse structural variations that occur, the commonest is O-acetylation at C-(4,7,8) and (9) carbon positions. This diversity in O-acetylated sialic acid (O-AcSA) derivatives is attributed to their linkage to the underlying sugar chain, the carbon position that gets O-acetylated and nature of the glycoconjugates to which they are attached. Steady refinement of analytical techniques has allowed for identification of O-AcSA derivatives in several diseases leading to a shift in focus towards understanding the biological importance of this modification. The present review deals primarily with the recently evolved information regarding detection of altered O-acetylation in various pathophysiological conditions and their biological relevance. Particular attention is focused on two diverse diseases, namely, Acute Lymphoblastic Leukemia (ALL) and Visceral Leishmaniasis (VL) in which 9-O acetylated sialoglycoconjugates (9-OAcSGs) have proved to be effective biomarkers for monitoring their clinical status.