Salivary Biomarkers and Diagnostics – Part 1: Introduction and Systemic Disease

Fiona Collins BDS, MBA, MA, FPFA

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Salivary Biomarkers and Diagnostics - Part 1: Introduction and Systemic Disease

Just as the eyes have been described as the mirror of the soul, saliva has been described as the mirror of the body1Cristaldi M, Mauceri R, Di Fede O, Giuliana G, Campisi G, Panzarella V. Salivary Biomarkers for Oral Squamous Cell Carcinoma Diagnosis and Follow-Up: Current Status and Perspectives. Front Physiol 2019;10:1476. doi:10.3389/fphys.2019.01476.. Salivary components include more than 2000 proteins, enzymes, electrolytes, small organic molecules such as bicarbonate, urea and metabolites, hormones, antimicrobials, and water.2Streckfus C, Dubinsky W, Bigler L, Bull J. Salivary biomarkers for the detection of cancer. January 2007. In book: Progress in Tumor Marker Research (pp.17-41). Nova Scientific Publishing, Inc. Ed: Swenson LI.,3Podzimek S, Vondrackova L, Duskova J, Janatova T, Broukal Z. Salivary markers for periodontal and general diseases. Disease Markers 2016;Article ID 9179632. https://doi.org/10.1155/2016/9179632. Whole saliva also contains plasma-derived components, sloughed epithelial cells, microorganisms and their associated products, gingival crevicular fluid, debris, and discharge from the nasopharynx.4Genco RJ. Salivary diagnostic tests. J Am Dent Assoc 2012;143(10 suppl):3S-5S. In addition, the content of saliva is influenced by exposure to microorganisms, chemicals, drugs and chemotherapeutics, by disease status and metabolic alterations.

The content of saliva is influenced by exposure to microorganisms, chemicals, drugs and chemotherapeutics, and by disease status and metabolic alterations.

Salivary testing and the associated technologies have been referred to as salivaomics.5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4. Given the range of salivary components, this includes proteomics, genomics, epigenomics, transcriptomics which studies mRNA in cells and organisms, metabolomics, and microbiology. Salivary diagnostics offers a noninvasive, available and easy method to collect samples in comparison to sampling blood, other body fluids and tissues.6Kaczor-Urbanowicz KE, Martin Carreras-Presas C, Aro K, Tu M, Garcia-Godoy F, Wong DT. Saliva diagnostics - Current views and directions. Exp Biol Med (Maywood) 2017;242(5):459-72. doi:10.1177/1535370216681550. Larger samples and repeat samples are also more easily obtained, and individuals can collect saliva samples at home without requiring assistance.1Cristaldi M, Mauceri R, Di Fede O, Giuliana G, Campisi G, Panzarella V. Salivary Biomarkers for Oral Squamous Cell Carcinoma Diagnosis and Follow-Up: Current Status and Perspectives. Front Physiol 2019;10:1476. doi:10.3389/fphys.2019.01476.,7Javaid MA, Ahmed AS, Durand R, Tran SD. Saliva as a diagnostic tool for oral and systemic diseases. J Oral Biol Craniofac Res 2016;6(1):66-75. doi:10.1016/j.jobcr.2015.08.006. That also reduces the risk of transmission of diseases since percutaneous injury is excluded as well as the risk of an individual releasing droplets or aerosols when samples are being taken. In the last two decades, we have seen more rapid developments in the use of salivary biomarkers,8Malamud D. Saliva as a diagnostic fluid. Dent Clin North Am 2011;55(1):159-78. doi:10.1016/j.cden.2010.08.004. which can be used to screen, help diagnose, predict prognoses, and monitor treatment outcomes for human disease, as well as for applications such as drug testing9FDA-NIH Biomarker Working Group. BEST (Biomarkers, EndpointS, and other Tools) Resource. Silver Spring (MD): Food and Drug Administration (US); Bethesda (MD): National Institutes of Health (US), www.ncbi.nlm.nih.gov/books/NBK326791/. and assessment of chemotherapeutics during drug development. This article contains information on salivary biomarkers, screening and systemic diseases.

Figure 1. Salivaomics and technology

Biomarkers and analytical methods

Various definitions have been used for biomarkers, depending on their intended purpose. The US. Food & Drug Administration and the National Institute of Health co-developed a definition, published in 2016 and updated in 2017.10Parikh R, Mathai A, Parikh S, Chandra Sekhar G, Thomas R. Understanding and using sensitivity, specificity and predictive values. Indian J Ophthalmol 2008;56(1):45-50. doi:10.4103/0301-4738.37595. This defines a biomarker as ‘A defined characteristic that is measured as an indicator of normal biological processes, pathogenic processes or responses to an exposure or intervention.’ Within this definition, subsets are provided that include Diagnostic, Monitoring, Pharmacodynamic/Response Biomarker, Predictive, Prognostic, Safety and Susceptibility/Risk Biomarkers. A further inclusion is ‘Reasonably Likely Surrogate Endpoint.’10Parikh R, Mathai A, Parikh S, Chandra Sekhar G, Thomas R. Understanding and using sensitivity, specificity and predictive values. Indian J Ophthalmol 2008;56(1):45-50. doi:10.4103/0301-4738.37595. Analytical methods for salivary testing as well as other body fluids include rapid and laboratory methods. In order to be useful, they must offer accuracy, high sensitivity (few false negatives) and high specificity (few false positives),11Slowey PD. Saliva collection devices and diagnostic platforms. In: Advances in Salivary Diagnostics (Ch. 3:p33-62). Springer. Ed: Charles F. Streckfus. reliability and repeatability. The ability to detect small amounts of a given biomarker (or any analyte) is also necessary to increase the level of detection. Examples of sensitive methods now used include polymerase chain reaction (PCR), quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA) which we became aware of in relation to screening for HIV, mass spectrometry and lateral flow technology.10Parikh R, Mathai A, Parikh S, Chandra Sekhar G, Thomas R. Understanding and using sensitivity, specificity and predictive values. Indian J Ophthalmol 2008;56(1):45-50. doi:10.4103/0301-4738.37595.

A biomarker has been described as ‘A defined characteristic that is measured as an indicator of normal biological processes, pathogenic processes or responses to an exposure or intervention.’

Systemic cancers

Salivary biomarkers are being researched and used as screening tools towards early detection of cancers, for diagnosis and tumor staging, to help determine prognoses and to assess treatment outcomes.1Cristaldi M, Mauceri R, Di Fede O, Giuliana G, Campisi G, Panzarella V. Salivary Biomarkers for Oral Squamous Cell Carcinoma Diagnosis and Follow-Up: Current Status and Perspectives. Front Physiol 2019;10:1476. doi:10.3389/fphys.2019.01476.,5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4.,7Javaid MA, Ahmed AS, Durand R, Tran SD. Saliva as a diagnostic tool for oral and systemic diseases. J Oral Biol Craniofac Res 2016;6(1):66-75. doi:10.1016/j.jobcr.2015.08.006. Biomarkers include salivary proteins such has tumor-associated antigens (TAs) and circulating tumor antigens (CTAs), salivary circulating tumor DNA, extracellular vesicles, and mRNAs.12Cheng J, Nonaka T, Wong DTW. Salivary exosomes as nanocarriers for cancer biomarker delivery. Materials (Basel) 2019;12(4):654. doi:10.3390/ma12040654. Further, in one review, 16 potential biomarkers were reported for lung cancer. When 5 of these were used in a multi-biomarker salivary biomarker panel, a sensitivity and specificity of almost 94% and 83%, respectively, was found.13Zhang L, Xiao H, Zhou H, Santiago S, Lee JM, Garon EB. Development of transcriptomic biomarker signature in human saliva to detect lung cancer. Cell Mol Life Sci 2012;69(19):3341-50. doi:10.1007/s00018-012-1027-0. In other research, a combination of extracellular RNAs demonstrated a sensitivity and specificity of 90% and 95%, respectively, in identifying patients with and without pancreatic cancer.14Zhang L, Farrell JJ, Zhou H. Salivary transcriptomic biomarkers for detection of resectable pancreatic cancer. Gastroenterology 2010;138:949-57. Further, a given biomarker may be applicable for multiple types of cancers.

Collectively, TAs may aid early diagnosis of several cancers, including breast, colorectal, gastric, lung and prostate cancer.15Antony F, Deantonio C, Cotella D, Soluri MF, Tarasiuk O, Raspagliesi F, et al. High-throughput assessment of the antibody profile in ovarian cancer ascitic fluids. OncoImmunol 2019;8:9. doi: 10.1080/2162402X.2019.1614856. Among these, CA-125, is applicable as a biomarker for breast, endometrial (uterine), gastrointestinal, lung and ovarian cancers.2Streckfus C, Dubinsky W, Bigler L, Bull J. Salivary biomarkers for the detection of cancer. January 2007. In book: Progress in Tumor Marker Research (pp.17-41). Nova Scientific Publishing, Inc. Ed: Swenson LI.,5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4. High salivary concentrations of CA-125 in patients with breast, ovarian and oral cancer have been reported.16Balan JJ, Rao RS, Premalatha BR, Patil S. Analysis of tumor marker CA 125 in saliva of normal and oral squamous cell carcinoma patients: a comparative study. J Contemp Dent Pract 2012;13(5):671-5. doi: 10.5005/jp-journals-10024-1207. In addition, an early study found that the diagnostic value of CA-125 for ovarian cancer was greater for salivary than serum samples.17Chen DX, Schwartz PE, Li FQ. Saliva and serum CA 125 assays for detecting malignant ovarian tumors. Obs Gyn 1990;75:701¬4. Several salivary biomarkers are used for breast cancer, including anti-p53 antibodies (pantropic p53), CA-153 (another TA), HER2/neu, epithelial group factor receptor (EGFR).5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4. The same substances are tumor markers for other cancers, e.g., anti-p53 levels are higher in patients with breast, esophageal, gastric and large intestine cancers, as well as oral squamous cell carcinoma.5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4. Another example is EGFR, which is also used as a biomarker for lung and pancreatic cancer.18Roi A, Rusu LC, Roi CI, Luca RE, Boia S, Munteanu RI. A new approach for the diagnosis of systemic and oral diseases based on salivary biomolecules. Dis Markers 2019:8761860. doi:10.1155/2019/8761860.,19Dumbrigue HB, Sandow PL, Nguyen KH, Humphreys-Beher MG. Salivary epidermal growth factor levels decrease in patients receiving radiation therapy to the head and neck. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:710-6.

Table 1. Examples of biomarkers for several cancers
Tumor-associated antigens May aid early diagnosis of several cancers, including lung, gastric, prostate, breast and colorectal cancer.
CA-125 Biomarker for breast, endometrial, gastrointestinal, and ovarian cancers.
Anti-p53 antibodies Biomarkers for breast, esophageal, gastric and large intestine cancers; squamous cell carcinoma.
EGFR A biomarker for lung and pancreatic cancer.

Monitoring treatment response
Salivary biomarkers can also be used to help predict and monitor treatment response. CA-125, for example, is used for detection purposes while it is mainly used for post-operative monitoring of patients with ovarian cancer.15 In one study, timing the administration of chemotherapy to coincide with the highest concentrations of salivary CA-125 appeared to maximize treatment efficacy.2Streckfus C, Dubinsky W, Bigler L, Bull J. Salivary biomarkers for the detection of cancer. January 2007. In book: Progress in Tumor Marker Research (pp.17-41). Nova Scientific Publishing, Inc. Ed: Swenson LI. CTAs are also believed to influence resistance to chemotherapy in ovarian cancer, and for metastatic breast cancer trastuzumab (Herceptin) is only used to treat patients who ae positive for human EGFR-2 gene.20Xie K, Fu C, Wang S, Hanzi Xu, Liu S, Shao Y, et al. Cancer-testis antigens in ovarian cancer: implication for biomarkers and therapeutic targets. J Ovarian Res 2019;12:1. https://doi.org/10.1186/s13048-018-0475-z.,21Knight ET, Murray Thomson W. A public health perspective on personalized periodontics. Periodontol 2000 2018;78(1):195-200. doi: 10.1111/prd.12228. These biomarkers, as noted above, are also found in saliva suggesting salivary testing as a simple method to help determine appropriate therapy.

Sjögren's Syndrome

Sjogren’s Syndrome (SS) is an autoimmune disease present in approximately 4 million individuals in the US.22García-Carrasco M, Ramos-Casals M, Rosas J, Pallarés L, Calvo-Alen J, Cervera R, et al. Primary Sjögren Syndrome: Clinical and immunologic disease patterns in a cohort of 400 patients. Medicine (Baltimore) 2002;81(4):270-80. Typically, SS affects the salivary and lacrimal glands, and results in dry eye and dry mouth that is often severe, alterations in salivary composition including increased levels of salivary interleukin-2 (IL-2), immunoglobulins and lactoferrin, decreased levels of IL-6, and changes in other components.6Kaczor-Urbanowicz KE, Martin Carreras-Presas C, Aro K, Tu M, Garcia-Godoy F, Wong DT. Saliva diagnostics - Current views and directions. Exp Biol Med (Maywood) 2017;242(5):459-72. doi:10.1177/1535370216681550. ,23Brito-Zerón P, Baldini C, Bootsma H, Bowman SJ, Jonsson R, Mariette X, et al. Sjögren syndrome. Nat Rev Dis Primers 2016;2:16047. doi: 10.1038/nrdp.2016.47. A connective tissue disorder may also be present , such as rheumatoid arthritis or lupus erythematosus, as well as conditions, and patients are at increased risk for lymphoma.23Brito-Zerón P, Baldini C, Bootsma H, Bowman SJ, Jonsson R, Mariette X, et al. Sjögren syndrome. Nat Rev Dis Primers 2016;2:16047. doi: 10.1038/nrdp.2016.47. The ability to obtain a definitive diagnosis without the need for biopsy or other invasive/uncomfortable procedures is desirable and a predictive screening tool has potential in enabling interventions to limit the potential sequalae of SS before the disease is clinically evident. Potential diagnostic biomarkers include a proteolytic peptide that was found in the unstimulated saliva of only patients with SS and an increased level of a B-cell chemokine (CXCL13) found in the salivary glands.24Zoukhri D, Rawe I, Singh M, Brown A, Kublin CL, Dawson K, et al. Discovery of putative salivary biomarkers for Sjogrens syndrome using high resolution mass spectrometry and bioinformatics. J Oral Sci 2012;54:61-70. Available at: https://www.jstage.jst.go.jp/article/josnusd/54/1/54_1_61/_pdf.,25Baker OJ, Edgerton M, Kramer JM, Ruhl S. Saliva-microbe interactions and salivary gland dysfunction. Adv Dent Res 2014;26(1):7-14. Other biomarkers include several mRNAs.5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4.,26Hu S, Gao K, Pollard R, Arellano-Garcia M, Zhou H, Zhang L, et al. Preclinical validation of salivary biomarkers for primary Sjögren's syndrome. Arthritis Care Res (Hoboken) 2010;62(11):1633-8. doi:10.1002/acr.20289. Among mRNAs, a combination of CPD, α-enolase and ß2m has been validated as an accurate method of identifying individuals with primary SS.26Hu S, Gao K, Pollard R, Arellano-Garcia M, Zhou H, Zhang L, et al. Preclinical validation of salivary biomarkers for primary Sjögren's syndrome. Arthritis Care Res (Hoboken) 2010;62(11):1633-8. doi:10.1002/acr.20289. Autoantibodies to Ro 60, Ro 52 and La are present in patients with SS, (anti-Ro/SSA and anti-La/SSB) and hold promise as a screening tool.27Theander E, Jonsson R, Sjöström B, Brokstad K, Olsson P, Henriksson G, et al. Prediction of sjogrens syndrome years before diagnosis and identification of patients with early onset and severe disease course by autoantibody profiling. Arthritis Rheumatol 2015;67(9):2427-36. One of these, Anti-Ro 52/SSA, was 100% predictive for both early onset and disease severity. In a recent study it was found that 82% of individuals had autoantibodies for up to 20 years (average 4 to 5 years), before receiving a definitive diagnosis.27Theander E, Jonsson R, Sjöström B, Brokstad K, Olsson P, Henriksson G, et al. Prediction of sjogrens syndrome years before diagnosis and identification of patients with early onset and severe disease course by autoantibody profiling. Arthritis Rheumatol 2015;67(9):2427-36.

A predictive screening tool has potential in enabling interventions to limit the potential sequalae of SS long before the disease is clinically evident.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is also an autoimmune disease, involving an inflammatory cascade and chronic inflammatory response.28Äyräväinen L, Heikkinen AM, Kuuliala A, Ahola K, Koivuniemi R, Laasonen L, et al. Inflammatory biomarkers in saliva and serum of patients with rheumatoid arthritis with respect to periodontal status. Ann Med 2018;50(4):333-44. doi: 10.1080/07853890.2018.1468922. In addition, RA and periodontitis share similarities. Both are multifactorial inflammatory conditions with commonality in the increased pro-inflammatory mediators, altered innate and adaptive immune responses, with common genetic traits including a specific human leukocyte antigen (HLA-DR).29Ancuta C, Iordache C, Ancuta E, Mihailov C. Rheumatoid arthritis and periodontal disease: A complex interplay. Ch 6, pp101-120. http://dx.doi.org/10.5772/65863. In: New Developments in the Pathogenesis of Rheumatoid Arthritis. InTech Open, 2017. These diseases are linked, with ongoing research on their relationship. Several body fluids and simple biomarkers such as autoantibodies and single proteins have been used as biomarkers for a number of decades. As noted in a recent review, these biomarkers may not be specific to a given condition, which may limit a biomarker’s usefulness.30Oderda GM, Lawless GC, Wright GC, Nussbaum SR, Elder R, Kim K, Brixner DI. The potential impact of monitoring disease activity biomarkers on rheumatoid arthritis outcomes and costs. Per Med 2018;15(4):291-301. https://doi.org/10.2217/pme-2018-0001. It has also been noted that a panel containing 12 protein biomarkers was an accurate predictive tool for disease activity.31Eastman PS, Manning WC, Qureshi F, Haney D, Cavet G, Alexander C, et al. Characterization of a multiplex, 12-biomarker test for rheumatoid arthritis. J Pharm Biomed Anal 2012;70:415-24. Multi-biomarker tests have been found to be more precise than solo biomarkers for RA and to better track disease activity.30Oderda GM, Lawless GC, Wright GC, Nussbaum SR, Elder R, Kim K, Brixner DI. The potential impact of monitoring disease activity biomarkers on rheumatoid arthritis outcomes and costs. Per Med 2018;15(4):291-301. https://doi.org/10.2217/pme-2018-0001. This corresponds with findings of a number of studies on biomarker accuracy in relation to cancers. However, in a recent study, salivary concentrations of C-reactive protein (CRP) and IL-6 were measured by immunoassays pre-treatment and 12 weeks post-treatment with anti-TNF-alpha therapy.32Sikorska D, Orzechowska Z, Rutkowski R, Prymas A, Mrall-Wechta M, Bednarek-Hatlińska D, et al. Diagnostic value of salivary CRP and IL-6 in patients undergoing anti-TNF-alpha therapy for rheumatic disease. J Inflammopharmacol 2018;26(5):1183-8. doi: 10.1007/s10787-018-0515-8. Salivary concentrations did not correlate with oral hygiene/oral health. Only the CRP concentration decreased substantially after an effective treatment response. In addition, CRP and IL-6 levels correlated for salivary and plasma concentrations.32Sikorska D, Orzechowska Z, Rutkowski R, Prymas A, Mrall-Wechta M, Bednarek-Hatlińska D, et al. Diagnostic value of salivary CRP and IL-6 in patients undergoing anti-TNF-alpha therapy for rheumatic disease. J Inflammopharmacol 2018;26(5):1183-8. doi: 10.1007/s10787-018-0515-8. In a study published this year, significantly higher salivary concentrations of human cathelicidin (LL-37) were found in individuals with RA and chronic periodontitis compared to those with RA alone.33Cheah CW, Al‐Maleki AR, Vadivelu J, Danaee M, Sockalingam S, Baharuddin NA, Vaithilingamet RD. Salivary and serum cathelicidin LL‐37 levels in individuals with rheumatoid arthritis and chronic periodontitis. Int J Rheum Dis 2020 Aug 2. doi: 10.1111/1756-185X.13919. Epub ahead of print. Comparisons were made for RA/No RA and patients with chronic periodontitis, gingivitis or a healthy periodontium. It was concluded that periodontal therapy needs to be included along with treatment received for RA itself. It can be anticipated that further research on biomarkers, including biomarkers related to the treatment of RA and PD, will help to further define their relationship and treatment.

Table 2. Recent findings for biomarkers and RA
Oderda et al (Per Med 2018)29Ancuta C, Iordache C, Ancuta E, Mihailov C. Rheumatoid arthritis and periodontal disease: A complex interplay. Ch 6, pp101-120. http://dx.doi.org/10.5772/65863. In: New Developments in the Pathogenesis of Rheumatoid Arthritis. InTech Open, 2017. Multi-biomarker tests more precise than solo biomarkers for RA and better able track disease activity.
Sikorska et al (Inflammopharmacol 2018)31Eastman PS, Manning WC, Qureshi F, Haney D, Cavet G, Alexander C, et al. Characterization of a multiplex, 12-biomarker test for rheumatoid arthritis. J Pharm Biomed Anal 2012;70:415-24. CRP concentration decreased substantially after an effective treatment response. Correlation for saliva and blood levels.
Cheah et al (Int J Rheum Dis 2020)32Sikorska D, Orzechowska Z, Rutkowski R, Prymas A, Mrall-Wechta M, Bednarek-Hatlińska D, et al. Diagnostic value of salivary CRP and IL-6 in patients undergoing anti-TNF-alpha therapy for rheumatic disease. J Inflammopharmacol 2018;26(5):1183-8. doi: 10.1007/s10787-018-0515-8. Significantly higher salivary concentrations of human cathelicidin (LL-37) in individuals with RA and CP compared to those with RA alone. Periodontal therapy needs to be included along with treatment received for RA itself.

Testing for Human Immunodeficiency Virus (HIV)

Salivary testing has enabled rapid point-of-care screening for HIV by dental professionals using an FDA-approved test kit. This test kit (OraQuick HIV ½; OraSure) is now also available to consumers to self-screen at home.9FDA-NIH Biomarker Working Group. BEST (Biomarkers, EndpointS, and other Tools) Resource. Silver Spring (MD): Food and Drug Administration (US); Bethesda (MD): National Institutes of Health (US), www.ncbi.nlm.nih.gov/books/NBK326791/. Screening does not confirm a diagnosis which requires use of an FDA-approved oral HIV ELISA laboratory test, known as the Western Blot test.

Salivary testing for SARS-CoV-2 (COVID-19)

Testing for COVID-19 can now be performed using oral/nasal swabs and either a molecular (RT-PCR) or antigen test. The current gold standard for sampling is nasopharyngeal swabs.34Czumbel LM, Kiss S, Farkas N, Mandel I, Hegyi A, Nagy Á, et al. Saliva as a candidate for COVID-19 diagnostic testing: A meta-analysis. Front Med (Lausanne) 2020;7:465. doi:10.3389/fmed.2020.00465. The use of saliva avoids the need for trained personnel, reduces the risk of transmission of SARS-CoV-2, and only requires the individual to spit in a collection tube rather than undergoing an uncomfortable naso-pharyngeal swab procedure. In preliminary research, the diagnostic accuracy for saliva samples using RT-qPCR was between 87% and 100% for COVID-19 patients, with the highest accuracy being 100% for ‘drooling saliva.’35Han P, Ivanovski S. Saliva-friend and foe in the COVID-19 outbreak. Diagnostics (Basel) 2020;10(5):290. doi: 10.3390/diagnostics10050290. In a meta-analysis of studies published from January through April 25, 2020, 91% and 98% sensitivity were found for saliva and nasopharyngeal swab tests, respectively. It was concluded that more studies were required to improve the sensitivity and specificity for salivary testing.34Czumbel LM, Kiss S, Farkas N, Mandel I, Hegyi A, Nagy Á, et al. Saliva as a candidate for COVID-19 diagnostic testing: A meta-analysis. Front Med (Lausanne) 2020;7:465. doi:10.3389/fmed.2020.00465.

In another study, salivary and nasopharyngeal samples were obtained from individuals working in COVID-19 wards in hospitals.36Wyllie AL, Fournier J, Casanovas-Massana A, Campbell M, Tokuyama M, Vijayakumar P. Saliva is more sensitive for SARS-CoV-2 detection in COVID-19 patients than nasopharyngeal swabs. Pre-print. Available at: https://www.medrxiv.org/content/10.1101/2020.04.16.20067835v1 The results obtained from the salivary samples offered superior sensitivity in detecting SARS-CoV-2 and less variability in sequential samples for a given individual. In addition, the amount of SARS-CoV-2 in salivary samples was much higher than for nasopharyngeal swabs. Rapid salivary testing tools continue to be researched and produced. The ability to rapidly screen and diagnose infection with SARS-CoV-2 offers opportunities for containment and tracing to minimize cross-infection, and potentially pre-emptive/early treatment with drugs that limit disease onset and severity.

Conclusions

Accurate, cost-effective mass screening using salivary biomarkers could enable prevention of some conditions and improve early diagnosis and treatment of others, reducing morbidity and mortality. Of note, depending on the specific process, traditional methods can be limited by intra- and inter-operator assessment, differences in methodology, variability in accuracy and reliability, cost or simply not be suitable for mass screening.5Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4.,29Ancuta C, Iordache C, Ancuta E, Mihailov C. Rheumatoid arthritis and periodontal disease: A complex interplay. Ch 6, pp101-120. http://dx.doi.org/10.5772/65863. In: New Developments in the Pathogenesis of Rheumatoid Arthritis. InTech Open, 2017. Given data showing that combining multiple biomarkers improved diagnostic value, research in this area can also be expected to accelerate. Further, dental professionals could play an increased role in screening patients for a variety of conditions using simple point-of-care salivary testing and collection of samples for laboratory testing. With a shift to personalized medicine and dentistry (4P), salivary and other biomarkers can be further developed for targeted healthcare. In conclusion, saliva is a promising biomarker fluid, and it can be anticipated that increased use of salivary diagnostics and testing by both dental and medical professionals will play a role in changing healthcare.

References

  • 1.Cristaldi M, Mauceri R, Di Fede O, Giuliana G, Campisi G, Panzarella V. Salivary Biomarkers for Oral Squamous Cell Carcinoma Diagnosis and Follow-Up: Current Status and Perspectives. Front Physiol 2019;10:1476. doi:10.3389/fphys.2019.01476.
  • 2.Streckfus C, Dubinsky W, Bigler L, Bull J. Salivary biomarkers for the detection of cancer. January 2007. In book: Progress in Tumor Marker Research (pp.17-41). Nova Scientific Publishing, Inc. Ed: Swenson LI.
  • 3.Podzimek S, Vondrackova L, Duskova J, Janatova T, Broukal Z. Salivary markers for periodontal and general diseases. Disease Markers 2016;Article ID 9179632. https://doi.org/10.1155/2016/9179632.
  • 4.Genco RJ. Salivary diagnostic tests. J Am Dent Assoc 2012;143(10 suppl):3S-5S.
  • 5.Wang X, Kaczor-Urbanowicz KE, Wong DT. Salivary biomarkers in cancer detection. Med Oncol 2017;34(1):7. doi:10.1007/s12032-016-0863-4.
  • 6.Kaczor-Urbanowicz KE, Martin Carreras-Presas C, Aro K, Tu M, Garcia-Godoy F, Wong DT. Saliva diagnostics - Current views and directions. Exp Biol Med (Maywood) 2017;242(5):459-72. doi:10.1177/1535370216681550.
  • 7.Javaid MA, Ahmed AS, Durand R, Tran SD. Saliva as a diagnostic tool for oral and systemic diseases. J Oral Biol Craniofac Res 2016;6(1):66-75. doi:10.1016/j.jobcr.2015.08.006.
  • 8.Malamud D. Saliva as a diagnostic fluid. Dent Clin North Am 2011;55(1):159-78. doi:10.1016/j.cden.2010.08.004.
  • 9.FDA-NIH Biomarker Working Group. BEST (Biomarkers, EndpointS, and other Tools) Resource. Silver Spring (MD): Food and Drug Administration (US); Bethesda (MD): National Institutes of Health (US), www.ncbi.nlm.nih.gov/books/NBK326791/.
  • 10.Parikh R, Mathai A, Parikh S, Chandra Sekhar G, Thomas R. Understanding and using sensitivity, specificity and predictive values. Indian J Ophthalmol 2008;56(1):45-50. doi:10.4103/0301-4738.37595.
  • 11.Slowey PD. Saliva collection devices and diagnostic platforms. In: Advances in Salivary Diagnostics (Ch. 3:p33-62). Springer. Ed: Charles F. Streckfus.
  • 12.Cheng J, Nonaka T, Wong DTW. Salivary exosomes as nanocarriers for cancer biomarker delivery. Materials (Basel) 2019;12(4):654. doi:10.3390/ma12040654.
  • 13.Zhang L, Xiao H, Zhou H, Santiago S, Lee JM, Garon EB. Development of transcriptomic biomarker signature in human saliva to detect lung cancer. Cell Mol Life Sci 2012;69(19):3341-50. doi:10.1007/s00018-012-1027-0.
  • 14.Zhang L, Farrell JJ, Zhou H. Salivary transcriptomic biomarkers for detection of resectable pancreatic cancer. Gastroenterology 2010;138:949-57.
  • 15.Antony F, Deantonio C, Cotella D, Soluri MF, Tarasiuk O, Raspagliesi F, et al. High-throughput assessment of the antibody profile in ovarian cancer ascitic fluids. OncoImmunol 2019;8:9. doi: 10.1080/2162402X.2019.1614856.
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