A meta-analysis on the role of brain-derived neurotrophic factor in Parkinson's disease patients

Background. Brain-derived neurotrophic factor (BDNF) is essential for the development of dopaminergic neurons in the substantia nigra. Objectives. To investigate the level of BDNF among Parkinson's disease (PD) subjects and the influence of depression on BDNF levels. Materials and methods. A total of 1920 subjects were included in the analysis; of these, 1034 had PD and 886 were healthy controls. A thorough literature search up to May 2022 was conducted. The mean difference (MD) of BDNF levels and 95% confidence intervals (95% CIs) were calculated with random or fixed effects models. Results. Compared to healthy controls, levels of BDNF were significantly lower in patients with PD (MD = -1.60, 95% CI (-2.49, -0.70), p < 0.001). Patients with PD and depression had significantly lower levels of BDNF (MD = -3.39, 95% CI (-5.55, -1.23), p = 0.002), as well as those with PD without depression (MD = -0.80, 95% CI (-1.56, -0.03), p = 0.04). However, there was no discernible change in BDNF levels (MD = -0.82, 95% CI (1.75, 0.10), p = 0.08) between the participants with PD and depression compared to the PD patients alone. Conclusions. Compared with healthy controls, BDNF levels were significantly lower in the subjects with PD combined with depression, and PD without depression. However, there was no discernible difference in BDNF levels between subjects with PD with depression compared to those with PD without depression.