Tear levels of tumor necrosis factor-alpha in patients with Parkinson's disease

Neuroinflammatory events mediated by the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) cause progressive neurodegeneration in dopaminergic neurons, and play an important role in the pathogenesis of Parkinson's disease (PD). The purpose of this study was to determine TNF-α levels in tear samples obtained from patients with PD and to analyze the relationship between TNF-α values and PD characteristics. Eighteen patients with PD and 17 healthy control subjects were included in the study. We examined the patient demographics, modified Hoehn and Yahr Staging Scale (mHY) stages, Unified Parkinson's disease rating scale (UPDRS) II and III scores, Mini Mental State Examination (MMSE) scores, and the predominant symptoms. We measured TNF-α using the multiplex immunobead assay in unstimulated tear samples, and determined the Schirmer's test and blink rate for each subject. Tear TNF-α values were significantly higher in patients with PD (196.9 ± 121.2 pg/ml) than in control subjects (110.7 ± 87.2 pg/ml; p = 0.02). We identified no relationship between tear TNF-α levels and age, sex, age at onset, PD duration, mHY stages, UPDRS II, UPDRS III, or MMSE scores. The higher TNF-α levels observed in the tears of patients with PD suggests neuroinflammation and TNF-α plays a role in the pathogenesis of PD. Tear TNF-α levels, however, were not related to the duration or severity of PD. Tears are a suitable method for measuring TNF-α levels, and can be used as a diagnostic measure to evaluate biomarkers in PD.