Colonic oligosaccharide structures deduced from lectin-binding studies before and after desialylation

Abstract

Dolichos biflorus agglutinin (DBA) binds N-acetylgalactosamine (GalNAc), and peanut agglutinin (PNA) binds Galβ(1–3)GalNAc residues (Gal = galactose). We used these lectins with neuraminidase to probe colonic oligosaccharides. Tissues included normal epithelium, adenocarcinomas (T) with contiguous transitional (TM) and normal mucosae (RM), and adenomatous polyps. Except for DBA binding in carcinomas, neuraminidase digestion increased DBA and PNA binding in all epithelia. In untreated specimens, reciprocal gradients for binding by DBA (T < TM and TM < RM) and PNA (T > TM and T > RM) were seen. After neuraminidase, all gradients were abolished except for T < TM and T < RM with DBA. We conclude that (1) qualitative as well as quantitative differences may exist between the mucins of benign and neoplastic colonic epithelium, (2) the NeuAc-GalNAc dimer is a widely prevalent terminal oligosaccharide in benign epithelium at all stages of differentiation (NeuAc = sialic acid), and (3) in contrast with evidence from recent biochemical studies, the Galβ(1–3)GalNAc dimer is a common masked oligosaccharide in benign epithelium.