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Melatonin is synthetized by the mitochondria, which in turn are the main intracellular targets of the indoleamine [1,2]. Due to the impairment of mitochondria in Parkinson's disease (PD), and its relationship with neuroinflammation, we analyzed the mitochondrial bioenergetics and melatonin effects in two models of parkinsonism, mouse and zebrafish. The participation of inflammation on mitochondria disfunction was analyzed in iNOS and nNOS deficient mice. Mitochondria were prepared from substantia nigra and striatum of control and MPTP-treated mice, and bioenergetics analyzed in an Oxygraph-2K respirometer . Our results showed that MPTP increased iNOS activity in substantia nigra and striatum, whereas it sharply reduced complex I activity and mitochondrial bioenergetics in all strains. In the presence of MPTP, mice lacking iNOS showed similar restricted mitochondrial function than wild type or mice lacking nNOS. Therefore, neuroinflammation and mitochondrial dysregulation seem to act in parallel in the MPTP model of PD. Melatonin administration counteracted these effects, preventing from the drastic changes in mitochondrial oxygen consumption, and neuroinflammation, recovering normal locomotor activity of mice. The protective effects of melatonin on mitochondria are also independent of its anti-inflammatory properties, but both effects are required for an effective anti-parkinsonian activity of the indoleamine as reported in this study.
In the second study, we studied the capacity of melatonin to recover from a parkinsonian phenotype . Here, 24 to 72 hpf zebrafish were treated with MPTP and ''in vivo'' respiration was measured in a Seahorse respirometer. A reduction in electron transfer system capacity, ATP turnover, and increased proton leak, were observed at 72 hpf in MPTP-treated embryos. These changes were followed by neuroinflammation and autophagy impairment. After removing MPTP from the treatment at 72 hpf, these bioenergetic deficiencies persisted up to 120 hpf. The administration of melatonin to zebrafish embryos at 72 hpf, when mitochondrial dysfunction is already present, restored the respiratory capacity and ATP production, reduced neuroinflammation, and normalized autophagy. Melatonin, added together with MPTP or added once MPTP was removed, prevented and recovered, respectively, the parkinsonian phenotype once it was established, restoring gene expression and normal function of the parkin/PINK1/DJ-1/MUL1 loop and also the normal motor activity of the embryos. the normal motor activity of the embryos.