A Systematic Review on the Feasibility of Salivary Biomarkers for Alzheimer's Disease

Early AD diagnosis is critical for ameliorating prognosis and treatment. The analysis of CSF biomarkers yields accurate results, but it necessitates a lumbar puncture procedure. Screening for peripheral biomarkers in saliva is advantageous since this medium is noninvasive and inexpensive to obtain. The objective of this systematic review is to analyze saliva biomarker studies which aim to diagnose AD. Titles, abstracts, and reference lists for publications from January 2004 to February 2020 were screened for by searching Google Scholar and PubMed. The inclusion criteria involved published studies that consisted of both AD and control groups. 88 studies were screened, and 20 publications fulfilled the inclusion criteria. These selected publications were scrutinized and included in this review. A beta 42, tau, certain metabolites, and oral microbiota might serve as reliable biomarkers for AD diagnosis. These results showcase the legitimate feasibility of proteomic, metabolomic, and microbiotic compounds in saliva for AD diagnostics in the near future. Supplemental studies must consider standardizing the analytical methods of measuring salivary biomarkers to establish coherence for the selection of valid AD biomarkers. Validation studies will require a large sample size of biomarker-diagnosed individuals for independent populations. This ensures accuracy and rigidity for receiver operating characteristic (ROC) curves that can be set for the most optimal salivary biomarkers in future clinical settings.