Methylene blue protects dopaminergic neurons against MPTP‐induced neurotoxicity by upregulating brain‐derived neurotrophic factor

The relatively old, yet clinically used, drug methylene blue (MB) is known to possess neuroprotective properties by reducing aggregated proteins, augmenting the antioxidant response, and enhancing mitochondrial function and survival in various models of neurodegenerative diseases. In this study, we aimed to examine the effects of MB in Parkinson's disease (PD) in vivo and in vitro models by using 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)/1‐methyl‐4‐phenylpyridinium (MPP + ) with a focus on possible effects on induction of neurotrophic factors. Our results indicate that pretreatment with MB significantly attenuated MPTP‐induced loss of dopaminergic neurons, glial cell activation, and depletion of dopamine. We also found that MB upregulated brain‐derived neurotrophic factor (BDNF) and activated its downstream signaling pathways, suggesting that BDNF might be a contributor to MB‐associated neuroprotection. Specific inhibition of the BDNF receptor or extracellular signal‐regulated kinase (Erk) reversed the MB‐mediated protection against MPP + toxicity, thus implying a role for BDNF and the Erk pathway in the neuroprotective effects. Taken together, our data suggest that MB protects neurons from MPTP neurotoxicity via induction of BDNF. Further study to determine whether MB preserves dopaminergic neurons in the brains of PD patients is warranted.