Proteomic analysis of cells in saliva from oral cancer patients

Objectives: Whole human saliva possesses tremendous potential in clinical diagnostics, particularly for conditions localized within the oral cavity, such as oral squamous cell carcinoma(OSCC) . Although many have studied the soluble fraction of whole saliva, few have taken advantage of the diagnostic potential of the cells present in saliva, and none have used proteomic capabilities for their study. Methods: Saliva was collected by standard techniques (Rhodus, 2004) from 4 patients with OSCC as well as 4 with epithelial dysplasia and 4 controls. Using three dimensions of peptide fractionation by combining these steps: preparative IEF using Free Flow Electrophoresis; strong cation exchange step-gradient chromatography; and microcapillary reverse-phase liquid chromatography, we determined that the whole saliva samples contained enough cells, mostly exfoliated epithelial cells, so that adequate amounts of total protein were available for proteomic analysis using our method. Results: From a mixture of OSCC saliva samples, the analysis resulted in a catalogue of over 1900 identified human proteins, including numerous proteins which play a role in OSSC signaling and tumorigenesis pathways. Additionally, 134 proteins from over 30 different bacteria were identified, some of which putatively contribute to cancer development. Conclusions: For detecting salivary markers of oral cancer, and possibly other conditions of the oral cavity, the results confirm both the potential of analyzing the cells in whole saliva with our proteomic method as well as significant differences in saliva from patients with oral cancer or precancer as compared to controls.