Serum mBDNF and ProBDNF Expression Levels as Diagnosis Clue for Early Stage Parkinson's Disease

Parkinson's disease (PD) is one of the most common chronic, progressive, and neurodegenerative diseases characterized clinically by resting tremor, bradykinesia, rigidity, and postural instability. As this disease is usually detected in the later stages, the cure is often delayed, ultimately leading to disability due to the lack of early diagnostic techniques. Therefore, it is of great importance to identify reliable biomarkers with high sensitivity and specificity for the early diagnosis of PD. In this study, we aimed to investigate whether serum expressions of mature brain-derived neurotrophic factor (mBDNF) and proBDNF can serve as biomarkers for the diagnosis of PD at early stage. One hundred and fifty-six patients with limb tremor and/or bradykinesia meeting the inclusion criteria were assigned to either ex-PD group (PD cases) or ex-NPD group (non-PD cases) and then reassigned to either po-PD group (with PD) or po-NPD group (without PD) at 1-year follow-up based on the results of the rediagnoses as performed in accordance with MDS Parkinson's diagnostic criteria. To improve early diagnostic accuracy, grouping (PD group and non-PD group) at initial visit and follow-up was performed differently and independently. Serum mBDNF and proBDNF levels were measured by enzyme-linked immunosorbent assays. The results demonstrated that serum levels of mBDNF and mBDNF/proBDNF were significantly lower in the ex-PD group (19.73 ± 7.31 and 0.09 ± 0.05 ng/ml) as compared with the ex-NPD group (23.47 ± 8.21 and 0.15 ± 0.12 ng/ml) (p < 0.01 for both) and in the po-PD group (19.24 ± 7.20 and 0.09 ± 0.05 ng/ml) as compared with the po-NPD group (25.05 ± 7.67 and 0.16 ± 0.14 ng/ml) (p < 0.01 for both). However, a significantly higher serum level of proBDNF was noted in the ex-PD group (235.49 ± 60.75 ng/ml) as compared with the ex-NPD group (191.75 ± 66.12 ng/ml) (p < 0.01) and in the po-PD group (235.56 ± 60.80 ng/ml) as compared with the po-NPD group (188.42 ± 65.08 ng/ml) (p < 0.01). In conclusion, mBDNF/proBDNF can be used as biomarkers for early stage Parkinson's disease; in addition, mBDNF plus proBDNF has better diagnostic value than mBDNF alone in the diagnosis of PD.