Salivary Aβ 1–42 may be a quick-tested biomarker for clinical use in Alzheimer’s disease: a meta-analysis

Objective Alzheimer’s disease (AD) is the most prevalent form of dementia among the aging population. Cumulative studies aim to find non-invasive biomarkers in the early stages of AD. Saliva can be obtained easily, and salivary biomarkers have been proven effective in detecting neurodegenerative diseases. To find effective biomarkers in saliva and to help the diagnosis of AD, we performed a meta-analysis focusing on the salivary biomarkers (β-amyloid 1–42 (Aβ 1–42 ), total tau (t-tau), phosphorylated tau (p-tau) and acetylcholinesterase (AChE)) in AD. Methods We conducted a systematic online search for eligible studies reporting data on salivary biomarkers reflecting Aβ 1–42 , t-tau, p-tau, and AChE in AD cohorts versus controls. Biomarkers’ performance was assessed in a random-effects meta-analysis with the ratio of mean (RoM). Results A total of thirteen studies were included in the meta-analysis, of them seven involved salivary Aβ 1–42 (271 AD and 489 controls), five involved salivary t-tau (324 AD and 252 controls), four involved salivary p-tau (130 AD and 161 controls), and three involved salivary AChE (81 AD and 54 controls). AD showed significantly higher salivary Aβ 1–42 levels than control (ROM = 1.90 (95% CI 1.28–2.81, P = 0.001), while AD and control did not differ significantly on salivary t-tau, p-tau and AChE (ROM = 0.94, 95% CI 0.67–1.31, P = 0.72; ROM = 0.91, 95% CI 0.56–1.45, P = 0.68; ROM = 0.83, 95% CI 0.24–2.88, P = 0.77; respectively). Conclusion The pooled results provide evidence that salivary Aβ 1–42 may serve as a sensitive biomarker for AD; nevertheless, larger AD cohorts are required to further confirm the sensitivity and specificity of salivary Aβ 1–42 for AD diagnosis.