How Dentists Are Poised to Unlock the Potential of Molecular Salivary Testing

Dr. Jack Martin

About Author

Scientific Background

Saliva has been shown to have a rich biomarker alphabet which includes DNA, RNA, proteins, metabolites and microbes.¹ The mechanisms by which the salivary gland alters it secretion in the presence of disease in a topic of ongoing investigation, but some elements such as transcription factors and exosomes have been identified.^2,3

The National Institutes of Health and the National Institute of Dental and Craniofacial Research have heavily supported the development of the science of salivary diagnostics for more than a decade.

The messenger RNAs or transcriptome reflect gene expression which has been demonstrated in animal models of melanoma and lung cancer to change in response to systemic disease.³ These biomarkers also have been shown in humans to have a distinct molecular footprint for a variety of systemic diseases including oral cancer and other malignancies, as well as in Sjogren’s syndrome and diabetes.^4-12 A host of other biomarker constituents also have been shown to be altered in these conditions as well as in periodontal disease.^13-15

The Scope of Salivary Diagnostics

Saliva is a convenient body fluid for diagnostic applications and can be obtained quickly and painlessly by untrained personnel.¹⁶ Transport media has been developed that can stabilize the constituents for transport to a central laboratory for analysis, and automated high throughput laboratory methodology allows for affordable and cost effective applications of this breakthrough technology.

Point of care testing capability is also under development and is suitable for some chairside applications in the future. This technology also holds promise for the use of saliva for infectious disease applications including the potential for a true handheld device for applications in biodefense.^9,17

Saliva is currently used in clinical practice for genotyping as well as for detection of HIV and HPV infections. The SaliMark OSCC saliva test for oral squamous cell cancer will be the first salivary multi-marker molecular panel. This test incorporates several genes into a composite score that helps to quantitate the risk of cancer in patients with suspicious oral lesions.

These markers were identified in initial studies at UCLA, verified in international studies in other ethnic groups, validated by the National Cancer Institute Early Detection Research Network and subsequently further validated in a prospective blinded study at several academic institutions in Michigan.^4,5,8,9,18 The initial intended use is to aid in the decision for biopsy in patients with oral lesions detected on screening examinations.

Biomarkers for Sjogren’s syndrome have been identified and pre-validated in a subsequent study in the Netherlands.^10,11 A further validations study is underway in the United States with collaboration of the Sjogren’s Syndrome Foundation. These discriminatory markers have the potential to aid in the diagnosis of this disease that has a constellation of nonspecific symptoms and often goes undetected for many years.

Additional studies are underway to identify salivary biomarkers for early detection of lung cancers. These studies could lead far more effective and less invasive testing.

Diabetes and pre-diabetes is in epidemic proportions in the United States and worldwide. There is a strong association of oral disease in patients with diabetes and the treatment of oral disease can influence systemic inflammation and diabetes control. Patients with diabetes and pre-diabetes often go undetected until severe end organ damage has occurred.

For example, many patients presenting with myocardial infarctions have undetected pre-diabetes and type 2 diabetes.¹⁹ Because many patients see their dentist more regularly than their medical doctor, dentistry can play a critical role in early detection and prevention of this disease. While recent studies advocate testing bold glucose in dental offices, saliva is more readily obtained than blood.

Furthermore, early in the disease process blood glucose and hemoglobin A1c levels are often in the normal range while increased insulin production compensates for the insulin resistance state. Preliminary studies indicate salivary biomarkers can potentially identify the metabolic derangements that occur early in this disease process.¹² Ongoing investigations are needed to further explore the potential of salivary markers for diabetes detection and surveillance.

Conclusion

Dentistry has a rich history of preventive care. Salivary diagnostics holds the potential to advance this role of the oral practitioner to a new level and to enhance the collaboration between dentists and medical doctors that has been long advocated but not fully realized.²⁰ 

References

1. Wong DT. Salivary Diagnostics: Amazing as it might seem, doctors can detect and monitor diseases using molecules found in a sample of spit. Am Sci. Jan 1 2008;96(1):37-43.
2. Palanisamy V, Sharma S, Deshpande A, Zhou H, Gimzewski J, Wong DT. Nanostructural and transcriptomic analyses of human saliva derived exosomes. Plos one 2010 Jan 5;5(1):e8577.       
3. Gao, et al. Systemic Disease-Induced Salivary Biomarker Profiles in Mouse Models of Melanoma and Non-Small Cell Lung Cancer. PLoS ONE 4(6): e5875.
4. Elashoff D, et al. (2012) Prevalidation of salivary biomarkers for oral cancer Detection. Cancer Epidemiol Biomarkers Prev 21(4): 664–72.
5. Li Y, St John MA, Zhou X, et al. Salivary transcriptome diagnostics for oral cancer detection. Clin Cancer Res. Dec 15 2004;10(24):8442-8450.
6. Zhang L, et al.Development of transcriptomic biomarker signature in human saliva to detect lung cancer Cell. Mol. Life Sci. 2012; 69(19):3341-50.
7. Zhang L, et al. Salivary Transcriptomic Biomarkers for Detection of Resectable Pancreatic Cancer. Gastroenterology 2010;138:949–957.
8. Brinkmann O, et al. Oral squamous cell carcinoma detection by salivary biomarkers in a Serbian population Oral Oncol. 2011; 47(1): 51–55.
9. Wei F, et al.Electrochemical Sensor for Multiplex Biomarkers Detection. Clin Cancer Res 2009;15:4446-4452.
10. Shen Hu, Jianghua Wang, Jiska Meijer, Sonya Ieong, Yongming Xie, Tianwei Yu, Hui Zhou, Sharon Henry, Arjan Vissink, Justin Pijpe, Cees Kallenberg, David Elashoff, Joseph A. Loo, and David T. Wong. Salivary Proteomic and Genomic Biomarkers for Primary Sjögren's Syndrome. Arthritits and Rheumatism 2007; 56 (11), 3588–3600.
11. Hu, S., Gao, K., Pollard, R., Arellano-Garcia, M. et al., Preclinical validation of salivary biomarkers for primary Sjögren's syndrome. Arthritis Care Res. 2010; 62, 1633–1638.
12. Wong, DT personal communication.
13. Greenberg BL, et al. Saliva as a diagnostic tool for periodontal disease: current state and future directions. Periodontology 2000, Vol. 50, 2009, 52–64. 
14. Hu S, Arellano M, Boontheung P, et al. Salivary proteomics for oral cancer biomarker discovery. Clin Cancer Res 2008;14:6246–52.
15. Xiao H, et al. Proteomic Analysis of Human Saliva From Lung Cancer Patients Using Two-Dimensional Difference Gel Electrophoresis and Mass Spectrometry. Molecular & Cellular Proteomics 2012; 11(2):M111.012112, 1–12.
16. Greenberg BL, Glick M, Frantsve-Hawley J and Kantor ML. Dentists’ attitudes toward chairside screening for medical conditions. JADA 2010; 141(1): 52-62.
17. Lillehoj PB, Wei F, Ho CM. A self-pumping lab-on-a-chip for rapid detection of botulinum toxin. Lab chip 2010; 10 (17):2265-70.
18. Martin J, et al. Evaluation of salivary transcriptome markers for the early detection of oral squamous cell cancer in a prospective blinded trial. Compend Contin Educ Dent. in press.
19. Conaway DG. Frequency of undiagnosed diabetes mellitus in patients with acute coronary syndrome. Am J Cardiol 2005: 96; 363-365.
20. Friedwald VE, et al.  The American Journal of Cardiology and Journal of Periodontology Editors’ Consensus: Periodontitis and Atherosclerotic Cardiovascular Disease. J Periodontol 2009; 80: 1021-2032.