Salivary biomarkers in dementia

Introduction: The incidence of dementia is increasing yearly. Alzheimer's disease accounts for about 70% of all cases. Neurodegenerative dementias are currently incurable. The first significant symptoms occur in an advanced stage. Caring for patients places a heavy burden on both the families and the healthcare system. During the COVID-19 pandemic, SARS-CoV-2 infection caused further rapid progression in the condition of patients with dementia. The aim of our study was to identify effective, early, non-invasive biomarkers in the diagnosis of dementia.

Materials and methods: 25 SARS-CoV-2 negative patients with moderate to severe dementia participated in the study and peripheral blood, saliva and oral mucosa smears were taken. The severity of dementia was classified based on the MMSE (mini mental state examination-mini mental test), and patient data were systematically organized. The level of immunoglobulin A (IgA), secretory IgA (sIgA), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8) and osteopontin (OPN) were determined from serum and rest mixed saliva with ELISA and ECLIA methods. Additional tests were performed on peripheral blood (e.g., APOE genotyping). A questionnaire summarizing COVID vaccinations and past infections was also completed. Cariological and periodontal status of the patients was also recorded. The obtained results were compared with age- and sex-matched healthy controls (n=10). Kolmogorov-Smirnov, Wilcoxon, Mann-Whitney and t-tests were used to analyze the data. We had the required ethical approvals for the experiments (DE RKEB/IKEB: 5395-2019).

Results: Levels of both serum IgA and salivary sIgA, OPN, IL-6, IL-8, IL-1β, TNF-α differed significantly (p≤0.05) between each investigated groups (control vs moderate and severe dementia; moderate dementia vs severe dementia).

Conclusion: Immunoglobulins and interleukins in saliva reflect well the acute and chronic inflammatory processes in the body. Taking other local and systemic modifying factors into account, they may be suitable as part of oral diagnostics to judge the severity of dementia and follow its progression.