The effect of mucin on bacterial translocation in I-407 fetal and Caco-2 adult enterocyte cultured cell lines

Abstract

Although the intestinal mucosa forms a crucial barrier between the host and the environment, bacterial translocation (BT) occurs frequently in neonates and may be a source of sepsis. The intestinal mucous gel layer is thought to be a vital component of the gut barrier and is composed, in part, of a family of glycoproteins known as mucins. Our aim was to study the effects of mucin on BT in an enterocyte cell-culture model using a fetal (I-407) and an adult (Caco-2) intestinal cell line. I-407 and Caco-2 cells were grown to confluence on porous filters in a two-chamber Transwell system. The integrity of the monolayers was confirmed by transepithelial electrical resistance (TEER) and permeability using the macromolecule dextran blue. Cells were treated with mucin (40 mg/ml) prior to inoculation of 1 x 10(6) Escherichia coli C25. The magnitude of BT was determined quantitatively by culturing the samples from the basal chamber of the wells and was expressed as log 10 [Colony Forming Units (CFU)/ml]. Statistical analysis was performed by the Mann-Whitney U test with statistical significance at P < 0.05. Mucin inhibited BT across both fetal and adult cultured enterocyte monolayers; however, the inhibitory effect was less on the fetal cells compared to the adult cells. Dextran-blue studies showed that monolayers were intact throughout the experiments. Despite 98% inhibition of BT, mucin had a statistically significant effect on post-bacterial inoculation TEER in Caco-2 cells and no effect in I-407 cells. The ability of mucin, a mucous-barrier glycoprotein, to inhibit BT across immature intestinal enterocytes, as in the neonate, may be diminished compared to mature adult enterocytes.

Intrauterine Growth Restriction Alters Postnatal Colonic Barrier Maturation in Rats

“…MUC2 also plays a critical role in mucosal protection by preventing bacterial pathogens from gaining access to the epithelium. Indeed, the protective effect of probiotics on bacterial translocation is associated with MUC2 over expression (39), and the application of mucins to the surface of neonatal epithelial cell line was shown to inhibit bacterial translocation (40). In patients with Hirschsprung's disease, a decrease in the expression of MUC2 has been linked to the development of associated enterocolitis (15).…”

New insights into the pathogenesis of Hirschsprung’s associated enterocolitis

“…Yet, those patients who developed HAEC had mucin turnover rates that were seven times lower than those without enterocolitis [35]. Gork et al [36] showed mucin-inhibited bacterial translocation in vitro across both foetal and adult-cultured intact enterocyte monolayers. Also in this study, they demonstrated that the inhibitory effect on translocation was lower on the foetal cells compared to the adult cells.…”

Protection of the Neonate by the Innate Immune System of Developing Gut and of Human Milk

“…A major physical barrier of the gut is the thick mucin-rich glycocalyx that lines the entire alimentary canal (12). In the intestine and colon, the epithelial monolayer is 93%-95% absorptive enterocytes (13), whose surface area is further increased by microvilli on apical surfaces.…”

“…The amount of lysozyme in human milk varies, but is often approximately 100 g/L and is found in the feces of breast-fed infants (68), indicating that it survives intestinal digestion sufficiently to potentially break down the more vulnerable cell walls of Gram-negative bacteria. Haptocorrin, a human milk protein that chelates vitamin B 12 , is resistant to digestion and inhibits enterotoxigenic E. coli.…”