Elevated levels of salivary interleukin-34 in patients suffering from Alzheimer's disease.

Objectives: To investigate interleukin (IL)-34 and colony-stimulating factor (CSF)-1 levels in saliva, cerebrospinal fluid, and plasma in different stages of cognitive impairment. The study also examines the relationship between these biomarkers and periodontal status across different stages of cognitive impairment.

Material and methods: A total of 230 individuals diagnosed with Alzheimer's disease (AD, n = 52), mild cognitive impairment (MCI, n = 51), subjective cognitive impairment (SCI, n = 51), and controls (n = 76) were enrolled. Participants underwent clinical and radiological oral examinations. Cerebrospinal fluid samples were collected from all groups except controls. Stimulated saliva and blood were collected during oral examination. IL-34 and CSF-1 levels were assessed using enzyme-linked immunosorbent assays.

Results: Salivary IL-34 levels were increased in AD compared to SCI (p = 0.010) and controls (p < 0.001), and in MCI compared to controls (p < 0.001). Elevated salivary CSF-1 levels were observed in AD compared to SCI (p = 0.003). Salivary IL-34 was inversely associated with Mini-Mental State Examination (MMSE) scores (p < 0.010) and body mass index (p = 0.040), while CSF-1 was associated with age (p = 0.015). IL-34 and CSF-1 levels did not differ in cerebrospinal fluid between groups, and periodontal status did not affect the levels in any biofluid measured.

Conclusion: Salivary IL-34 is increased in AD patients and is associated with MMSE scores.

Clinical relevance: Identifying reliable biomarkers for AD is crucial for early detection and intervention. This study suggests that salivary IL-34 could serve as a potential biomarker for AD.