Biochemical and histochemical effects of perorally applied endotoxin on intestinal mucin glycoproteins of the common carp Cyprinus carpio

Mucins are high molecular weight glycoproteins produced by goblet cells and secreted on mucosal surfaces. We investigated biochemical and histochemical properties of intestinal mucins of virus- and parasite-free common carp Cyprinus carpio in response to a single peroral application of endotoxin (lipopolysaccharide = LPS). Intracellular mucins were quantified histochemically by their carbohydrate content and characterized by specific, lectin-based methods. In addition, secreted epithelial (intracellular) and luminal (extracellular) mucins were isolated and separated by downward gel filtration. Carbohydrate and protein content were determined photometrically. Subsequently, terminal glycosylation was characterized by a lectin-binding assay. A peroral endotoxin application altered intestinal secretion and composition of intestinal mucin glycoproteins in common carp. A statistically significant decrease in mature luminal mucins was demonstrated, linked to a new biosynthesis of intracellular mucin glycoproteins. Simultaneous changes in the glycosylation pattern of isolated mucins were found. The intestinal mucosal system is purported to provide a removal mechanism for bacterial noxes by increasing secretion of mucins inducing a flushing-out effect, in combination with altered glycosylation patterns that change adhesion properties. Consequently, pseudofaeces of fish, which are a common sign of intestinal parasitical infections, may also be interpreted as an elimination mechanism for strong bacterial noxes.