Pro-inflammatory cytokines levels in tears and dry eye disease in Parkinson’s disease

Background:Neuroinflammation is an essential event in Parkinson’s disease(PD).Identifying affordable and less invasive biomarkers to make an early diagnosis and monitor therapeutic strategies should be a priority among researchers.The study’s objective was to measure tear levels of cytokines in subjects with PD and their association with motor features and the presence of dry eye symptoms.Methods:A total of 16 subjects with PD and 16 age-and sex-matched controls were included.Movement Disorders Society-Unified Parkinson’s Disease Rating Scale(MDS-UPDRS),Hoehn and Yahr(HY)stage scale,Montreal Cognitive Assessment(MoCA),tear break-up time(TBUT),blink rate(BR),Dry Eye Questionnaire 5(DEQ-5)were examined,and pro-inflammatory cytokines[interleukin(IL)-1β,IL-6,IL-8,IL-10,IL-12p70 and tumor necrosis factor-alpha(TNF-α)]were quantified in tears using the BD Cytometric Bead Array Human Inflammatory Cytokine Kit.Results:Higher tear TNF-αwere quantified in PD compared to controls(2.94±3.95 vs.0.33±0.49 pg/mL,P=0.008).According to DEQ-5,50.0%(n=8)of PD subjects and 12.5%(n=2)controls had dry eye disease(DED).No differences were found in cytokines concentrations between PD patients with DED compared to those without DED.IL-8 was associated with the HY stage,TBUT,DEQ-5,and a better MoCA score.A higher BR correlated moderately with a lower HY stage(r=−0.645,P=0.007),and DED patients have lower BR in PD(12.14±2.54 vs.9.0±2.06 blinks/minute,P=0.031).Conclusions:PD patients have higher levels of TNF-αin tears than age-and sex-matched HC.IL-8 in tears may be both involved in the severity of the disease and in the development of DED in PD.In addition,our findings suggest that as HY stage increases,indicating a more advanced stage,BR decreases,indicating greater motor impairment.Conversely,the presence of DED is associated with higher levels of bradykinesia in PD patients,suggesting a potential relationship between DED and motor impairment severity.