Salivary biomarkers for diagnosis of oral and systemic diseases

OBJECTIVES The purpose of this work is to re-port the recent researches on sal-ivary biomarkers potentially useful for the diagnosis of oral and systemic diseases, highlighting the procedures to perform saliva col-lection in a dental setting. MATERIALS AND METHODS The salivary sampling procedure should be carried out taking into consideration all factors potentially influencing presence and concentration of biomarkers in the oral fluid. In the preliminary phase, a thorough dental examination should be per-formed, in order to assess the presence of pathological conditions which could interfere with saliva composition. In such phase, the subject should also be instructed on the behaviors to adopt before saliva sampling. Subsequently, saliva should be collected, on the basis of the analytical examination. Three types are suitable for biomarkers analysis (whole saliva, parotid saliva, submandibular/sublingual saliva), each type possibly being either stimulated or unstimulated saliva. In the second part of the present work, a review of the relevant literature on salivary biomarkers for oral and systemic diseases is reported. Molecules have been classified into DNA, RNA, proteins and metabolites. RESULTS Most investigated salivary molecules for the diagnosis of oral cancer belong to the categories of DNA, messenger RNA (mRNA), microRNA (miRNA) and proteins. Few genetic panels have demon-strated some diagnostic accuracy in terms of sensitivity and specifici-ty. These include e the combination of the ECAD, MGMT, RARB and TMEFF2 genes and the combination of p16INK4a, RASSF1A, TIMP3 and PCQAP/MED15. Salivary mR-NA coding for interleukins IL8 and IL1B, have proven to be reliable in discriminating patients with oral carcinoma from healthy subjects. Several molecules have been de-scribed among salivary miRNAs, in-cluding miR-21, miR-31 and miR-24 (oncogenetic miRNA). Particu-larly, miR-302b-3p and miR-517b-3p appear to be present only in saliva of patients with oral cancer. The most reliable salivary proteins for the diagnosis of oral malignancy are some cytokines and chemok-ines (e.g. IL-8 and TNF-α). With regard to metabolites, 4 molecules (pyruvic acid, glycine, choline and proline) are currently being evaluated. Salivary molecules potentially useful as biomarkers for some systemic diseases have been investigated in a recent systematic review of the literature. The review analyzed 79 papers which met rigorous inclusion criteria. Among these, 51 (64%) were focused on malignant tumours, 14 (17.5%) on neurologic diseases and 14 (18.5%) on in-flammatory, metabolic and cardio-vascular diseases (18.5%). Among the studies evaluating malignant tu-mors, 12 (23.5%) were of “good quality” and 11 of these reported statistically significant associations between salivary molecules and the pathology. Similarly, a good quality study on neurological diseases reported promising results (correla-tion between Alzheimer’s disease and 2 salivary metabolites). Eventually, several salivary proteins (e.g. C-reactive protein and myo-globin) appear to be reliable diag-nostic markers in patients with acute myocardial infarction. CONCLUSIONS The development of analytical panels combining specific salivary markers, with high sensitivity and specificity, will be of great help in medicine and in dentistry. Dentists will, most probably, shortly face a diagnostic revolution based on salivary biomarkers for which it will be necessary to have a strong background of oral biology, bio-chemistry and physiology. CLINICAL SIGNIFICANCE According to current perspectives, the analysis of saliva will be able to substantially contribute to the concept of point of care, which will allow to acquire relevant information on the health status, through a non invasive, personalized and economically sustainable method.