Saliva: an emerging biofluid for early detection of diseases

Abstract

The capability to assess physiological states, detect morbidity initiation and progression, and monitor posttreatment therapeutic outcomes through a noninvasive approach is one of the most desirable goals for healthcare research and delivery. Saliva, a multi-constituent oral fluid, has high potential for the surveillance of general health and disease. To reach the above goal through saliva-based diagnostics, two prerequisites must be fulfilled: (1) discovering biomarker(s) for different diseases among the complicated components of saliva, and (2) advancing sensitivity and specificity of biomarker(s) through persistent development of technologies. Under the support and research blueprint initiated by the National Institute of Dental and Craniofacial Research (NIDCR), salivary diagnostics has not only steadily progressed with respect to accuracy and availability, but has also bridged up-to-date nanotechnology to expand the areas of application. With collective efforts over several years, saliva has been demonstrated to be a promising bodily fluid for early detection of diseases, and salivary diagnostics has exhibited tremendous potential in clinical applications. This review presents an overview of the value of saliva as a credible diagnostic tool, the discovery of salivary biomarkers, and the development of salivary diagnostics now and in the future.

Fig. 1

Mechanism of molecular transport from serum into salivary gland ducts. A. Active transport.B. Passive diffusion. C. Simple filtration. D. Acinar cells actively pump sodium ions (Na+) into the duct. E. Duct cells pump Na+ ions back into blood. F. Cell membrane. G. Pore on the cell membrane. H. Intracellular space. I. Acinar cell. (This figure was adapted from Haeckel and Hanecke with permission of Walter de Gruyter GmbH & Co. Copyrighted and used with permission of Mayo Foundation for Medical Education and Research, all rights reserved).

Fig. 2

Collection of whole saliva by the Salivette (absorbent) method. (a) Saliva is collected by chewing a cotton wool swab. (b) The swab containing saliva is placed in the tube of Salivette. (c) Centrifugation of the assemblage. (d) Saliva is separated from the swab and is ready for analysis.

Fig. 3

2D gel electrophoretograms of human whole saliva proteins. Proteins were separated in the 1st dimension immobilized pH gradients (IPG) followed by SDS-PAGE. Speckles were visualized by SYPRO Ruby stain. The arrows indicate five isoforms of carbonate dehydratase VI precursor. Targets of interest will be identified by subsequent MS analysis.

Fig. 4

Oral Fluid NanoSensor Test (OFNASET), a point-of-care, automated, easy-to-use integrated system that will enable simultaneous, accurate, and rapid detection of multiple salivary protein and nucleic acid biomarkers.