In this study, the protective effect of melatonin on kainic acid (KA)-induced neurotoxicity involving autophagy and α-synuclein aggregation was investigated in the hippocampus of C57/BL6 mice. Our data showed that intraperitoneal injection of KA (20 mg/kg) increased LC3-II levels (a hallmark protein of autophagy) and reduced mitochondrial DNA content and cytochrome c oxidase levels (a protein marker of mitochondria). Atg7 siRNA transfection prevented KA-induced LC3-II elevations and mitochondria loss. Furthermore, Atg7 siRNA attenuated KA-induced activation of caspases 3/12 (biomarkers of apoptosis) and hippocampal neuronal loss, suggesting a pro-apoptotic role of autophagy in the KA-induced neurotoxicity. Nevertheless, KA-induced α-synuclein aggregation was not affected in the Atg7 siRNA-transfected hippocampus. The neuroprotective effect of melatonin (50 mg/kg) orally administered 1 hr prior to KA injection was studied. Melatonin was found to inhibit KA-induced autophagy-lysosomal activation by reducing KA-induced increases in LC3-II, lysosomal-associated membrane protein 2 (a biomarker of lysosomes) and cathepsin B (a lysosomal cysteine protease). Subsequently, KA-induced mitochondria loss was prevented in the melatonin-treated mice. At the same time, melatonin reduced KA-increased HO-1 levels and α-synuclein aggregation. Our immunoprecipitation study showed that melatonin enhanced ubiquitination of α-synuclein monomers and aggregates. The anti-apoptotic effect of melatonin was demonstrated by attenuating KA-induced DNA fragmentation, activation of caspases 3/12, and neuronal loss. Taken together, our study suggests that KA-induced neurotoxicity may be mediated by autophagy and α-synuclein aggregation. Moreover, melatonin may exert its neuroprotection via inhibiting KA-induced autophagy and a subsequent mitochondrial loss as well as reducing α-synuclein aggregation by enhancing α-synuclein ubiquitination in the CNS.

Platonin, a photosensitizing dye, is known to possess antioxidant and anti-inflammatory activity. Platonin has been used to treat trauma, ulcers and some acute inflammations and it also reported to improve blood circulation and reduce mortality in endotoxin-induced rat models. Our previous studies established that platonin suppresses the lipopolysaccharides (LPS)-induced inflammatory cytokines, including interleukin-1β (IL-1β-+), IL-6, tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS). Nuclear factor-kB (NF-kB) and activator protein-1 (AP-1) transcription factors are reported to be essential in mediating the endotoxin-induced production of inflammatory molecules. In vivo studies from our groups revealed that platonin has potential effects on inhibiting pyrogen release, tissue damage and ischemia during heatstroke, ischemia reperfusion injury in lungs and also improve the survival of skin allografts in rats. Clinically, this compound has been proven to cure juvenile rheumatoid arthritis (JRA) and polyarteritis nodosa (PN). In this review, we summarize the pharmacological and clinical effects of platonin via describing the potential molecular mechanism of regulation of inflammatory molecules of mitogen-activated protein kinases (MAPKs), including extracellular regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 MAPK and also NF-kB activation. Moreover, this paper discusses the signaling pathways expedited by NF-kB, AP-1, MAPKs and NO/NOS, these all have been reflected in inflammatory processes, and could be the encouraging molecular targets for the design of pharmaceutical drugs targeting antiinflammatory therapy.