Protection of Dopaminergic Neurons in Hemiparkinsonian Monkeys by Flavouring Ingredient Glyceryl Tribenzoate

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and this study underlines the significance of a small molecule glyceryl tribenzoate (GTB), a FDA approved food additive, in preventing parkinsonian pathologies in MPTP-induced animal models. The study conducted in MPTP-induced mice demonstrated dose-dependent protection of nigral tyrosine hydroxylase (TH) and striatal dopamine level by GTB oral treatment and the optimum dose was found to be 50 mg/kg/d. In the next phase, the study was carried out in MPTP-injected hemiparkinsonian monkeys, which recapitulate better clinical parkinsonian syndromes. GTB inhibited MPTP-driven induction of glial inflammation, which was evidenced by reduced level of GTP-p21 and phospho-p65 in SN of monkeys. It led to decreased expression of inflammatory markers such as IL-1β and iNOS. Simultaneously, GTB oral treatment protected nigral TH cells, striatal dopamine, and improved motor behaviour of hemiparkinsonian monkeys. Presence of sodium benzoate, a GTB metabolite and a FDA-approved drug for urea cycle disorders and glycine encephalopathy, in the brain suggests that the neuroprotective effect imparted by GTB might be mediated by sodium benzoate. Although the mechanism of action of GTB is poorly understood, the study sheds light on the therapeutic possibility of a food additive GTB in PD.