Saliva is a biological fluid produced in the oral cavity by three pairs of major glands and up to 1000 minor salivary glands. In recent years, a lot has been studied with respect to salivary proteins.
The study of salivary metabolites has been confined to only a few selected analytes. This has revealed important knowledge about these metabolites, such as the role of urea in the maintenance of salivary pH or lactate in the aetiology of dental caries.
Despite the advantages such as ease of collection and preparation, saliva is comparatively less studied by metabolic profiling compared to fluids such as urine and plasma.
The functional roles of salivary metabolites remain largely unexplored. Areas of emerging research today include the quest towards understanding the role of oral and host-microbiome interactions that might alter the salivary metabolite profile of an individual. The role of salivary metabolites in physiological oral activities such as taste perception is also frequently studied.
Systematic metabolite profiling of saliva is a relatively recent avenue of research. The potential for salivary metabolites as diagnostic biomarkers is promising. Preliminary studies of salivary metabolites were focused on characterizing and identifying the metabolites that can be measured. Nevertheless, studies looking at the dynamic nature of salivary metabolites have been published and these are increasing in number.
Most of the studies on salivary metabolic composition have focused on salivary metabolite profiling as a means of biomarker discovery, e.g., oral cancer, periodontitis, Alzheimer’s disease, etc.
Another emerging area of salivary metabolomics research is in sports and exercise physiology.
While the studies follow a broadly similar approach in their attempt to find differences between diseased individuals and healthy controls, there is considerable variation in the, sample collection and preparation methods, analytical platforms used, and statistical methods employed.
What Needs To Be Done:
For biomarkers to become clinically accepted and diagnostically useful, systemic reviews of large multicentric trials must be performed. There is a need for both a consensus on sample handling as well as cross-validation of analytical equipment between different centres working on such projects.
Future Directions for Salivary Metabolomics
At present, very few studies have studied saliva using both sequencing and metabolomics technologies.
The future of salivary metabolomics lies in the adoption or omics – genomics, transcriptomics, proteomics, etc. Gene sequencing technologies previously revolutionized oral microbiology. Using genomics, it became apparent that half of the microbial species occupying the oral cavity are non-culturable.
There is a clear need for future work to reconcile the functional information provided by metabolomics with the oral microbial composition and host factors that may modify the latter. Therefore, further studies with a combined analytical approach will be essential in future.
Salivary metabolomics is gaining recognition as a valuable source of biological information.