Journal of Indian Academy of Oral Medicine and Radiology

GUEST EDITORIAL
Year
: 2020  |  Volume : 32  |  Issue : 3  |  Page : 205--208

Review of salivary diagnostics – A current scenario


Sadaksharam Jayachandran 
 Department of Oral Medicine and Radiology, Tamil Nadu Government Dental College and Hospital, Tamil Nadu Dr. M.G.R. Medical University, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. Sadaksharam Jayachandran
Department of Oral Medicine and Radiology, Tamil Nadu Government Dental College and Hospital, Chennai, Tamil Nadu - 600003
India

Abstract

Human saliva is produced by the three major salivary glands (the parotid gland, submandibular gland, and sublingual glands) and minor salivary glands. It contains several hormones, antibodies, cytokines, proteins, enzymes, and antimicrobial constituents that act as biomarkers. It also contains variable amounts of gingival crevicular fluid (GCF), mucosal transudate, desquamated epithelial cells, bacteria, viruses, fungi, food debris, microorganisms, serum, and some blood derivatives. Saliva has simple collection methods (non-invasive), handling procedure, reliable sensitivity and specificity, good cooperation from patients, and the possibility to perform dynamic studies. Salivary analysis can determine various systemic diseases, metabolic disorders, and infections. Hence, it serves as a potential diagnostic and prognostic tool with widespread clinical and research applications in various fields of science and medicine.



How to cite this article:
Jayachandran S. Review of salivary diagnostics – A current scenario.J Indian Acad Oral Med Radiol 2020;32:205-208


How to cite this URL:
Jayachandran S. Review of salivary diagnostics – A current scenario. J Indian Acad Oral Med Radiol [serial online] 2020 [cited 2020 Nov 26 ];32:205-208
Available from: https://www.jiaomr.in/text.asp?2020/32/3/205/296577


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 Introduction



Human saliva harbors major biomolecules that are evident in blood or urine. The utilization of saliva to evaluate and monitor the health and disease states of an individual is the main goal for diagnosis, prognosis, and research.[1],[2] It is produced by the three major salivary glands (the parotid gland, submandibular gland, and sublingual glands) and minor salivary glands distributed throughout the mouth with a total volume of the saliva of 750–1000 mL daily.[3] The secretions of all the minor and major salivary glands contribute to the whole saliva, which is a hypotonic fluid composed of greater than 99% water and less than 1% proteins and salts.[4],[5] It also contains variable amounts of gingival crevicular fluid (GCF), mucosal transudate, desquamated epithelial cells, bacteria, viruses, fungi, food debris, microorganisms, serum, and some blood derivatives. The stimulated saliva or the mixed saliva collected from the mouth is a complex mixture, which is secreted in response to masticatory or gustatory stimulation. The resting flow rate of the whole saliva is 0.2-0.4 mL/min, and on stimulation, the rates increase to 0.2-0.6 mL/min for the whole saliva. The pH of the whole saliva varies from 6.4 to 7.4. The concentration and volume of saliva may be influenced by circadian rhythm, stimuli, and several functional secretory units.[3],[6] Salivary analysis can determine various disorders/diseases like Sjogren's syndrome, Cystic Fibrosis, acute myocardial infarct, cancer, periodontal disease, stress, calcium disorders, etc., They also aid in the detection of virus (Human Immunodeficiency Virus, Human Herpesvirus, Epstein-Barr virus, Cytomegalovirus, Hepatitis A, Hepatitis B, and Hepatitis C) and bacteria (Helicobacterpylori, Streptococcus species).[7]

Saliva is a biological fluid that has simple collection methods, handling procedure, reliable sensitivity and specificity, good cooperation from patients, and the possibility to perform dynamic studies.[8] It is a complex fluid that contains several hormones, antibodies, cytokines, proteins, enzymes, and antimicrobial constituents that facilitate their associations with various systemic diseases.[9] Human saliva also contains approximately 2400 compounds that can be specific biomarkers associated with cellular motility, with cell proliferation, signaling molecular pathways, and to the immune system.[8] The clinical application of salivary diagnosis is widespread in dentistry, oncology, forensic medicine, infectious diseases, autoimmune disease, endocrinology, cardiology, nephrology, pharmacology, pharmacotherapy, and epidemiology.

The whole saliva is collected by draining method, spitting, suction method, or swabbing method. The glandular saliva or gland specific saliva is collected according to the type of gland. The parotid saliva is collected using a cannula or Lashley cup, or modified Carlson Crittenden device. The submandibular saliva is collected using suction, cannulation or segregator method. Labial and buccal saliva can be collected using the periopaper/sialopaper absorbent method.[10] Sialometry is salivary flow rate measurements, and sialochemistry is an analysis of salivary composition.[11] Sialometry is used to compare the secretory capacities of the major salivary glands and secretory flow rates (unstimulated with stimulated flow rates).[12] Sialochemistry is used to determine gland dysfunction and its impact on the oral environment, including the mucosa. It also analyzes homeostatic fluctuations as a result of circulatory, innervations, or hormonal adjustments by the assessment of organic and inorganic elements.[13] Genomics, proteomics, transcriptomics, and metabolomics have aided in the discovery and development of salivary biomarkers, which have been studied with liquid chromatography (LC), capillary electrophoresis (CE), gel electrophoresis, nuclear magnetic resonance, enzyme-linked immunosorbent assay (ELISA), radioimmunoassays (RIA), lectin probe analysis, atomic absorption flame photometry, spectrophotometry, high-performance liquid chromatography, two-dimensional gel electrophoresis followed by mass spectrometry, reverse-phase LC, quantitative PCR (qPCR), reversed-phase liquid and hydrophilic interaction chromatography, and colorimetric assays.[7]

Saliva serves as a diagnostic tool in the early detection of various cancers such as oral cancer, lung cancer, pancreatic cancer, breast cancer, and stomach cancer.[14] The elevated levels of HER2/neu in the saliva are detected in breast cancer patients.[15] A logistic regression model with the combination of four messenger RNA salivary biomarkers (KRAS, MBD3L2, ACRV1, and DPM1) is used in the identification of pancreatic cancer.[16] Three salivary proteins have been linked to gastric cancer: triosephosphate isomerase (TPI1), cystatin B (CSTB), and deleted in malignant brain tumors 1 protein (DMBT1).[17] Three salivary tumor markers (tissue polypeptide antigen [TPA], Cyfra 21-1, and cancer antigen CA-125) are used in the detection of oral squamous cell carcinoma.[7] The increase in salivary IL-6 is present in leukoplakia and OSCC.[18] Seven mRNA transcripts [BRAF (v-raf murine sarcoma viral oncogene homolog B1), FGF19 (fibroblast growth factor 19), FRS2 (fibroblast growth factor receptor substrate 2), CCNI (cyclin I), GREB1 (growth regulation by estrogen in breast cancer 1), EGFR, and LZTS1 (leucine zipper, putative tumor suppressor 1)] are present in the saliva of lung cancer patients.[2] Spectroscopic analysis of saliva aids in discriminating oral premalignancy and malignancy.[19] NADH, FAD, and porphyrin levels and photophysical characteristics show significant molecular level changes during the transformation of normal into cancer.[20]

The saliva acts as an essential and emerging tool in forensic dentistry. The cells in saliva contain mitochondrial DNA and genomic DNA that are very useful in individual identification.[14] Cells present in the saliva can be used to determine the sex by detecting the presence of sex chromatin and also by determining sex hormone level.[21] Genetic fingerprinting of epithelial cells deposited in saliva can be used in ABO profiling.[22] Species identification is done using a monoclonal antibody to determine species salivary immunoglobulin A (sIgA) using the ELISA technique.[7] The amelogenin gene from saliva exhibits two bands in males (XY) and one band in females (XX). These differences in amelogenin gene expression allow for gender differentiation.[22]Streptococcus mutans is a common bacterium in oral microbiota. The strains of this organism are acquired during birth and persist throughout life. Subtyping this species can aid in identification methods.[22]

Cigarette consumption detection, organic substances detection, heavy metal intoxication detection, and hormone detection can be done using salivary analysis by Gas Chromatography or the ELISA technique. Cigarette consumption on the active smoker or nicotine intoxication on passive smoker can be detected by determining the salivary cotinine level using RIA or the ELISA technique.[7] Metals can be detected in saliva by using Atomic Absorption Spectroscopy or Mass Spectroscopy technique. Cadmium, Lead, Mercury, Nickel, Zinc, etc., can be analyzed through saliva.[23] RIA is used to detect the presence and determine the quantity of testosterone, progesterone, estradiol cortisol, and cortisone in saliva.[7],[21]

Salivaomics is the integrative study of saliva and its constituents, functions, and related techniques by genomics, transcriptomics, and proteomics.[24] Genomics extends its application to a salivary liquid biopsy which is used to detect mutations. The clinical testing of ctDNA (circulating tumor DNA) in body fluids is referred to as liquid biopsy that most noted is in lung cancer, where three mutations (L858R, exon 19del, and T790M) in the epidermal growth factor receptor (EGFR) gene can be therapeutically targeted to have an impact on the survival of patients with non-small cell lung carcinoma.[25] Genomics can also aid as a prognostic marker in HPV-related oral cancers and identify various HPV subtypes as low, medium, or high risk as an indicator of overall risk for HPV-related oral carcinoma.[2] Proteomic analysis of saliva is commonly used in the diagnostics of oral diseases and general disorders such as glossodynia, oral candidiasis, head and neck squamous cell cancer, Sjogren's syndrome, autism, acquired immunodeficiency syndrome, fibromyalgia, lung cancer, breast cancer, melanoma, and pancreatic cancer.[14] Salivary exRNAs have been identified to allow the detection of many various diseases like oral squamous cell carcinoma, resectable pancreatic cancer, lung cancer, ovarian cancer, and breast cancer.[14]

Salivary levels of creatinine is found to be higher in chronic kidney disease.[26] Salivary biomarkers have been recently explored as a screening tool for obesity and diabetes mellitus.[14] Salivary markers like TAU proteins are elevated in some neurodegenerative diseases like Alzheimer's disease.[27] Carbamazepine, digoxin, phenytoin, primidone, ethosuximide, irinotecan, cisplatin, diazepam, lithium, metoprolol, paracetamol, theophylline, procainamide, quinine, or valproic acid levels are detected in saliva.[28] Free fatty acid, ischemia modified albumin, intercellular adhesion molecule, troponin, creatine kinase, and myoglobin are detected in saliva in patients with cardiovascular disease. Cortisol levels are elevated in physiological stress and keratin levels in systemic sclerosis.[8] Three protein biomarkers (a-enolase, cathepsin D [CPD], and ß2-microglobulin [ß2m]) and three mRNA biomarkers (guanylate binding protein 2 [GBP-2], myeloid cell nuclear differentiation antigen [MNDA], and low-affinity IIIb receptor for the Fc fragment of IgG) were elevated in saliva of patients with primary Sjogren's syndrome.[14] Tissue anti transglutaminase antibodies are present in celiac disease.[29] Increased levels of prostaglandin PGE2 and decreased activity of protease and EGF are present in the saliva of cystic fibrosis patients.[7]

Helicobacterpylori is a bacteria commonly isolated from saliva. Cytomegalovirus, hepatitis A, hepatitis B, hepatitis C, herpes virus, Epstein Barr virus, Zika virus can be isolated from the saliva. Rarely, the level of salivary antibodies enables the detection of morbillivirus (measles), paramyxoviridae (mumps), and togaviridiae (rubella). Fungal local infections, like candidiasis, have been diagnosed in saliva. Low titers of Human Immunodeficiency (HIV-1) virus and high levels of HIV-1 RNA and antigens can routinely be measured in saliva. Secretory leukocyte protease inhibitor is a polypeptide found in saliva, antagonizes the HIV-1 infection and leads to low titers of infectious virus.[30] Oromucosal transudate can be used as a screening diagnostic tool for HIV.[31]

The production of SARS-CoV-specific secretory immunoglobulin A (sIgA) in the saliva has been seen in the animal models intranasally immunized.[32] SARS-CoV-2 has been detected in the saliva of confirmed patients with COVID-19, even up to the 11thday after hospitalization, in one of the cases.[32] The positive rate of COVID-19 in patients' saliva can reach 91.7%, and saliva samples can also cultivate the live virus.[33] The presence of coronavirus in the salivary fluid can be from either salivary glands or GCF or respiratory tract secretions.[34] The ACE2 epithelial cells of the salivary glands are an initial target for the SARS-CoV. Self-collected saliva samples have comparable SARS-CoV-2 detection sensitivity to nasopharyngeal swabs from mild and subclinical COVID-19 cases.[35] The sensitivity of SARS-CoV-2 detection from saliva is comparable, if not superior to nasopharyngeal swabs in early hospitalization and is more consistent during extended hospitalization and recovery.[36]

Age changes in the salivary glands are common and prominent in the parotid particularly. The gradual replacement of parenchyma with fatty tissue increased dryness, and the viscosity of saliva are common. Hypersalivation is a clinical feature of rabies, heavy metal poisoning, and during consumption of few drugs.[37] Hyposalivation is a clinical feature of Sjogren's syndrome, diabetes mellitus, diabetes insipidus, amyloidosis, sarcoidosis, and certain viral infections.[37] The salivary pH is altered in gastroesophageal reflux disease.[38] Salivary pH alters the growth of microorganisms which aids as an essential tool. Porphyromonas gingivalis grows at a pH of 6.5–7.0, Prevotella intermedia grows at a pH of 5.0–7.0, and Fusobacterium nucleatum grows at a pH of 5.5–7.0.[39] Salivary pH in patients with chronic generalized gingivitis is alkaline than with chronic generalized periodontitis which is more acidic.[39] Salivary flow rate, salivary viscosity, salivary pH, and salivary buffering capacity are lower in patients with high dental caries.[40] pH and amylase levels of saliva are found to be altered and prognostic factors in cancer. Lower pH decreased salivary flow, increased aciduric, and acidogenic lactobacilli are observed during radiotherapy.[41]

 Conclusion



Saliva reflects the physiological and pathological state of the body, and it is a biofluid that is emerging as a diagnostic and prognostic tool. Owing to the abundance of biomarkers present and noninvasive nature of the fluid, saliva can be potentially used as a diagnostic modality for various diseases and disorders. The newly emerging tools and rapidly developing technological perspectives can broadly widen the research area in salivary diagnostics.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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