The Detergent Effect of Mesalazine Interferes with Phosphatidylcholine Binding to Mucin 2.

OBJECTIVES: Therapeutically applied delayed-release phosphatidylcholine (PC) revealed mucosa protection and clinical improvement of ulcerative colitis. However, a recent trial with simultaneous application of delayed-release PC and mesalazine showed lack of efficacy. It is hypothesized that mesalazine acts as detergent to prohibit PC integration into mucus as target compartment, thus preventing topical mucus protection. METHODS: In vitro PC-binding studies with mucin 2 and intestinally differentiated CaCo2 cells as well as outcome analysis of a therapeutic trial with delayed-release PC and additional mesalazine. RESULTS: Choline-containing phospholipids, in particular PC, bind to mucin 2 as main scaffold protein of intestinal mucus to establish a hydrophobic barrier towards microbiota in the intestinal lumen. PC also binds to the apical surface of polarized CaCo2 cells with membrane-anchored mucin 3. Mesalazine removes mucin-bound PC and, thus, reduces transepithelial resistance. A post hoc analysis of patients from a previous multicenter phase IIB trial with delayed-release PC revealed that those without mesalazine showed a PC dose-dependent outcome with regard to achievement of partial and complete remission (p < 0.05 for 1.6 and 3.2 g PC daily) whereas those treated simultaneously with mesalazine showed no PC dose dependency. CONCLUSION: Mesalazine solubilizes PC and, thus, prevents the protective action of therapeutically applied delayed-release PC within mucus.