Protein and mucin retention on oral mucosal surfaces in dry mouth patients

Oral homeostasis depends largely on proteins and mucins present in saliva that coat all oral surfaces. The present study compared the protein composition of residual fluid on mucosal surfaces in subjects with normal salivary flow with that of patients with dry mouth caused by salivary hypofunction. Samples of residual mucosal fluid were collected using paper strips and then analysed by protein electrophoresis and immunoblotting. In both patients and controls, residual fluids on mucosal surfaces (except the anterior tongue in control subjects) had higher protein concentrations than unstimulated whole-mouth saliva. High-molecular-weight mucin (MUC5B) was present in greater amounts on the anterior tongue than on other surfaces in control subjects. In dry mouth patients who were unable to provide a measurable saliva sample, MUC5B was often still present on all mucosal surfaces but in reduced amounts on the anterior tongue. The membrane-bound mucin, MUC1, was prominent on buccal and labial surfaces in patients and controls. Statherin was still present on surfaces that were dried to remove salivary fluid, suggesting that it may be adsorbed as a protein pellicle. It is concluded that oral mucosal surfaces in dry mouth patients can retain MUC5B and other salivary proteins, although the functional integrity of these proteins is uncertain.