Effects of hydrogen gas inhalation on L-DOPA-induced dyskinesia

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia is a side effect of Parkinson's disease treatment and it is characterized by atypical involuntary movements. A link between neuroinflammation and L-DOPA-induced dyskinesia has been documented. Hydrogen gas (H₂) has neuroprotective effects in Parkinson's disease models and has a major anti-inflammatory effect. Our objective is to test the hypothesis that H₂ inhalation reduces L-DOPA-induced dyskinesia. 15 days after 6-hydroxydopamine lesions of dopaminergic neurons were made (microinjection into the medial forebrain bundle), chronic L-DOPA treatment (15 days) was performed. Rats were exposed to H₂ (2% gas mixture, 1 h) or air (controls) before L-DOPA injection. Abnormal involuntary movements and locomotor activity were conducted. Striatal microglia and astrocyte was analyzed and striatal and plasma samples for cytokines evaluation were collected after the abnormal involuntary movements analysis. H₂ inhalation attenuated L-DOPA-induced dyskinesia. The gas therapy did not impair the improvement of locomotor activity achieved by L-DOPA treatment. H₂ inhalation reduced activated microglia in the lesioned striatum, which is consistent with the observed reduced pro-inflammatory cytokines levels. Display of abnormal involuntary movements was positively correlated with plasma IL-1β and striatal TNF-α levels and negatively correlated with striatal IL-10 levels. Prophylactic H₂ inhalation decreases abnormal involuntary movements in a preclinical L-DOPA-induced dyskinesia model. The H₂ antidyskinetic effect was associated with decreased striatal and peripheral inflammation. This finding has a translational importance to L-DOPA-treated parkinsonian patients' well-being.