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We have demonstrated that mitochondrial oxidative damage and PKCδ overexpression contribute to methamphetamine-induced dopaminergic degeneration. Although it is recognized that antioxidant melatonin is effective in preventing neurotoxicity induced by methamphetamine, its precise mechanism remains elusive. C57BL/6J wild-type mice exhibited a similar degree of dopaminergic deficit when methamphetamine was administered during light and dark phases. Furthermore, dopaminergic neuroprotection by genetic inhibition of PKCδ during the light phase was comparable to that during the dark phase. Thus, we have focused on the light phase to examine whether melatonin modulates PKCδ-mediated neurotoxic signaling after multiple high doses of methamphetamine. To enhance the bioavailability of melatonin, we applied liposomal melatonin. Treatment with methamphetamine resulted in hyperthermia, mitochondrial translocation of PKCδ, oxidative damage (mitochondria > cytosol), mitochondrial dysfunction, pro-apoptotic changes, ultrastructural mitochondrial degeneration, dopaminergic degeneration, and behavioral impairment in wild-type mice. Treatment with liposomal melatonin resulted in a dose-dependent attenuation against degenerative changes induced by methamphetamine in wild-type mice. Attenuation by liposomal melatonin might be comparable to that by genetic inhibition (using PKCδ((-/-)) mice or PKCδ antisense oligonucleotide). However, liposomal melatonin did not show any additional protective effects on the attenuation by genetic inhibition of PKCδ. Our results suggest that the circadian cycle cannot be a key factor in modulating methamphetamine toxicity under the current experimental condition and that PKCδ is one of the critical target genes for melatonin-mediated protective effects against mitochondrial burdens (dysfunction), oxidative stress, pro-apoptosis, and dopaminergic degeneration induced by methamphetamine.

BackgroundActivation of NADPH oxidase (PHOX) plays a critical role in mediating dopaminergic neuroinflammation. In the present study, we investigated the role of PHOX in methamphetamine (MA)-induced neurotoxic and inflammatory changes in mice.MethodsWe examined changes in mitogen-activated protein kinases (MAPKs), mitochondrial function [i.e., mitochondrial membrane potential, intramitochondrial Ca2+ accumulation, mitochondrial oxidative burdens, mitochondrial superoxide dismutase expression, and mitochondrial translocation of the cleaved form of protein kinase C delta type (cleaved PKCδ)], microglial activity, and pro-apoptotic changes [i.e., cytosolic cytochrome c release, cleaved caspase 3, and terminal deoxynucleotidyl transferase dUDP nick-end labeling (TUNEL) positive populations] after a neurotoxic dose of MA in the striatum of mice to achieve a better understanding of the effects of apocynin, a non-specific PHOX inhibitor, or genetic inhibition of p47phox (by using p47phox knockout mice or p47phox antisense oligonucleotide) against MA-induced dopaminergic neurotoxicity.ResultsPhosphorylation of extracellular signal-regulated kinases (ERK1/2) was most pronounced out of MAPKs after MA. We observed MA-induced phosphorylation and membrane translocation of p47phox in the striatum of mice. The activation of p47phox promoted mitochondrial stresses followed by microglial activation into the M1 phenotype, and pro-apoptotic changes, and led to dopaminergic impairments. ERK activated these signaling pathways. Apocynin or genetic inhibition of p47phox significantly protected these signaling processes induced by MA. ERK inhibitor U0126 did not exhibit any additional positive effects against protective activity mediated by apocynin or p47phox genetic inhibition, suggesting that ERK regulates p47phox activation, and ERK constitutes the crucial target for apocynin-mediated inhibition of PHOX activation.ConclusionsOur results indicate that the neuroprotective mechanism of apocynin against MA insult is via preventing mitochondrial burdens, microglial activation, and pro-apoptotic signaling process by the ERK-dependent activation of p47phox.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0478-x) contains supplementary material, which is available to authorized users.

Soybean polyunsaturated phosphatidylcholine (PC) is thought to exert anti-inflammatory activities and has potent effects in attenuating acute renal failure and liver dysfunction. The aim of this study was to investigate the effects of PC in protecting multiple organ injury (MOI) from lipopolysaccharide (LPS). Six groups of rats (N=8) were used in this study. Three groups acted as controls and received only saline, hydrocortisone (HC, 6 mg/kg, i.v.) or PC (600 mg/kg, i.p.) without LPS (15 mg/kg, i.p.) injections. Other 3 groups, as the test groups, were administered saline, HC or PC in the presence of LPS. Six hours after the LPS injection, blood and organs (lung, liver and kidney) were collected from each group to measure inflammatory cytokines and perform histopathology and myeloperoxidase (MPO) assessment. Serum cytokines (TNF-α, IL-6 and IL-10) and MPO activities were significantly increased, and significant histopathological changes in the organs were observed by LPS challenge. These findings were significantly attenuated by PC or HC. The treatment with PC or HC resulted in a significant attenuation on the increase in serum levels of TNF-α and IL-6, pro-inflammatory cytokines, while neither PC nor HC significantly attenuated serum levels of IL-10, anti-inflammatory cytokine. In the organs, the enhanced infiltration of neutrophils and expression of ED2 positive macrophage were attenuated by PC or HC. Inductions of MPO activity were also significantly attenuated by PC or HC. From the findings, we suggest that PC may be a functional material for its use as an anti-inflammatory agent.

Background:We demonstrated that oxidative stress plays a crucial role in cognitive impairment in klotho mutant mice, a genetic model of aging. Since down-regulation of melatonin due to aging is well documented, we used this genetic model to determine whether the antioxidant property of melatonin affects memory impairment.Methods:First, we examined the effects of melatonin on hippocampal oxidative parameters and the glutathione/oxidized glutathione (GSH/GSSG) ratio and memory dysfunction of klotho mutant mice. Second, we investigated whether a specific melatonin receptor is involved in the melatonin-mediated pharmacological response by application with melatonin receptor antagonists. Third, we examined phospho-extracellular-signal-regulated kinase (ERK) expression, nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation, Nrf2 DNA binding activity, and glutamate-cysteine ligase (GCL) mRNA expression. Finally, we examined effects of the ERK inhibitor SL327 in response to antioxidant efficacy and memory enhancement mediated by melatonin.Results:Treatment with melatonin resulted in significant attenuations of oxidative damage, a decrease in the GSH/GSSG ratio, and a significant amelioration of memory impairment in this aging model. These effects of melatonin were significantly counteracted by the selective MT2 receptor antagonist 4-P-PDOT. Importantly, 4-P-PDOT or SL327 also counteracted melatonin-mediated attenuation in response to the decreases in phospho-ERK expression, Nrf2 nuclear translocation, Nrf2 DNA-binding activity, and GCL mRNA expression in the hippocampi of klotho mutant mice. SL327 also counteracted the up-regulation of the GSH/GSSG ratio and the memory enhancement mediated by melatonin in klotho mutant mice.Conclusions:Melatonin attenuates oxidative stress and the associated memory impairment induced by klotho deficiency via signaling interaction between the MT2 receptor and ERK- and Nrf2-related antioxidant potential.

We investigated whether protein kinase C (PKC) is involved in trimethyltin (TMT)-induced neurotoxicity. TMT treatment (2.8 mg/kg, i.p.) significantly increased PKCδ expression out of PKC isozymes (i.e., α, βI, βII, δ, and ς) in the hippocampus of wild-type (WT) mice. Consistently, treatment with TMT resulted in significant increases in cleaved PKCδ expression. Genetic or pharmacological inhibition (PKCδ knockout or rottlerin) was less susceptible to TMT-induced seizures than WT mice. TMT treatment increased glutathione oxidation, lipid peroxidation, protein oxidation, and levels of reactive oxygen species. These effects were more pronounced in the WT mice than in PKCδ knockout mice. In addition, the ability of TMT to induce nuclear translocation of Nrf2, Nrf2 DNA-binding activity, and upregulation of γ-glutamylcysteine ligase was significantly increased in the PKCδ knockout mice and rottlerin (10 or 20 mg/kg, p.o. × 6)-treated WT mice. Furthermore, neuronal degeneration (as shown by nuclear chromatin clumping and TUNEL staining) in WT mice was most pronounced 2 days after TMT. At the same time, TMT-induced inhibition of phosphoinositol 3-kinase (PI3K)/Akt signaling was evident, thereby decreasing phospho-Bad, expression of Bcl-xL and Bcl-2, and the interaction between phospho-Bad and 14-3-3 protein, and increasing Bax expression and caspase-3 cleavage were observed. Rottlerin or PKCδ knockout significantly protected these changes in anti- and pro-apoptotic factors. Importantly, treatment of the PI3K inhibitor LY294002 (0.8 or 1.6 µg, i.c.v.) 4 h before TMT counteracted protective effects (i.e., Nrf-2-dependent glutathione induction and pro-survival phenomenon) of rottlerin. Therefore, our results suggest that down-regulation of PKCδ and up-regulations of Nrf2-dependent glutathione defense mechanism and PI3K/Akt signaling are critical for attenuating TMT neurotoxicity.

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