Promising applications of human-derived saliva biomarker testing in clinical diagnostics

Abstract

Saliva testing is a vital method for clinical applications, for its noninvasive features, richness in substances, and the huge amount. Due to its direct anatomical connection with oral, digestive, and endocrine systems, clinical usage of saliva testing for these diseases is promising. Furthermore, for other diseases that seeming to have no correlations with saliva, such as neurodegenerative diseases and psychological diseases, researchers also reckon saliva informative. Tremendous papers are being produced in this field. Updated summaries of recent literature give newcomers a shortcut to have a grasp of this topic. Here, we focused on recent research about saliva biomarkers that are derived from humans, not from other organisms. The review mostly addresses the proceedings from 2016 to 2022, to shed light on the promising usage of saliva testing in clinical diagnostics. We recap the recent advances following the category of different types of biomarkers, such as intracellular DNA, RNA, proteins and intercellular exosomes, cell-free DNA, to give a comprehensive impression of saliva biomarker testing.

Fig. 1

The scheme of the review organized by different types of biomarkers. Some categories were listed specifically, such as C-reaction protein, because the research is relatively dominant. The figure is created with BioRender.com

Fig. 2

The timeline of salivary hormones. The time was determined by the publishing year of the oldest and most relevant papers. Not all hormones were included since there was no evidence showing the existence of them in saliva or the poor correlation of the concentration between saliva and target organ, such as follicle-stimulating hormone (FSH). The figure is created with BioRender.com