Analysis of Residual and Minor Saliva on Oral Mucosal Surfaces

Saliva serves to moisten, lubricate, and act as a protective barrier. It is produced by three pairs of major salivary glands (submandibular, parotid and sublingual) and numerous minor salivary glands distributed throughout the mouth. Unstimulated whole mouth saliva (UWMS) is the basal secretion from all glands and residual saliva remains on the mucosal surfaces after swallowing. Minor saliva is the viscous fluid secreted by the minor salivary glands. Objective: to identify glycoproteins and mucins in residual and minor saliva from oral mucosal surfaces using sodium dodecyl sulphate-polyacrylamide elctrophoresis (SDS-PAGE) and different detection techniques. Methods: unstimulated whole mouth saliva (UWMS) was collected from healthy volunteers for 10 minutes. Residual saliva was collected at four mucosal surfaces: anterior hard palate (AHP), buccal (BUC), anterior tongue (AT) and labial (LL), using sterile sialopaper™ strips applied for 10 seconds. Minor saliva was collected from the dried labial mucosa using a sterile sialopaper™ strip applied for 60 seconds. Proteins were eluted from the strips using an LDS buffer and electrophoresed on 4-12% gradient Bis-Tris SDS-PAGE gels. Resolved glycoproteins were either stained with periodate Schiff reagent (PAS), followed by a silver stain, or were western blotted. Results: PAS demonstrated a number of high molecular weight glycoproteins which were identified by western blotting. High and low molecular weight mucins, MG1 (muc5B) and MG2 (muc7) were present in all residual and minor saliva samples. The glycoprotein, agglutinin (GP340) was more abundant in UWMS. Additional glycoproteins, muc1 and gp230, were present in BUC, LL and LL minor saliva, but absent in UWMS. Conclusion: filter paper sampling followed by SDS-PAGE is an effective way to analyse and compare the glycoproteins and mucins of saliva from different oral mucosal surfaces. Acknowledgements: Gift of anti-sera from D. Swallow (UCL, London), J. Hilkens (Cancer Inst, Amsterdam) and U. Mandel (Copenhagen Univ, Denmark).