Discovery of oral fluid biomarkers for human oral cancer by mass spectrometry.

Proteomic analysis of human oral fluid (whole saliva) holds promise as a non-invasive method to identify biomarkers for human oral cancer, a high impact local disease in the oral cavity affecting 38,000 Americans and with 350,000 cases worldwide annually. In this study, matrix-assisted laser desorption/ionization--mass spectrometry (MALDI-MS) was used to profile oral fluid samples from oral cancer and control subjects, and 46 peptides/proteins were found at significantly different levels between the two groups. To identify a candidate protein biomarker, oral fluid samples were separated by liquid chromatography (LC) using a C4 reversed-phase column. The collected LC fractions were monitored by MALDI-MS and the fraction containing the candidate biomarker was digested for LC-MS/MS analysis to identify it. The use of nanospray MS/MS for the identification of candidate peptide biomarkers was also demonstrated. This approach can be useful for the identification of protein or peptide biomarkers following MALDI-MS or surface-enhanced laser desorption/ionization MS profiling of clinical samples. This study clearly demonstrated that oral fluid contains proteomic signatures that may serve as biomarkers for human diseases such as oral cancer. Once discovered and validated on a large and independent clinical cohort, oral fluid proteomic biomarkers may be extensively used for future disease diagnosis.