Hai-Quyen Tran

Role of Mitochondria in Methamphetamine-Induced Dopaminergic Neurotoxicity: Involvement in Oxidative Stress, Neuroinflammation, and Pro-apoptosis—A Review

Methamphetamine (MA), an amphetamine-type psychostimulant, is associated with dopaminergic toxicity and has a high abuse potential. Numerous in vivo and in vitro studies have suggested that impaired mitochondria are critical in dopaminergic toxicity induced by MA. Mitochondria are important energy-producing organelles with dynamic nature. Evidence indicated that exposure to MA can disturb mitochondrial energetic metabolism by inhibiting the Krebs cycle and electron transport chain. Alterations in mitochondrial dynamic processes, including mitochondrial biogenesis, mitophagy, and fusion/fission, have recently been shown to contribute to dopaminergic toxicity induced by MA. Furthermore, it was demonstrated that MA-induced mitochondrial impairment enhances susceptibility to oxidative stress, pro-apoptosis, and neuroinflammation in a positive feedback loop. Protein kinase Cδ has emerged as a potential mediator between mitochondrial impairment and oxidative stress, pro-apoptosis, or neuroinflammation in MA neurotoxicity. Understanding the role and underlying mechanism of mitochondrial impairment could provide a molecular target to prevent or alleviate dopaminergic toxicity induced by MA.

Current understanding of methamphetamine-associated dopaminergic neurodegeneration and psychotoxic behaviors

Clinical and preclinical studies have indicated that chronic methamphetamine (MA) use is associated with extensive neurodegeneration, psychosis, and cognitive impairment. Evidence from animal models has suggested a considerable role of excess dopamine or glutamate, oxidative stress, neuroinflammation, and apoptosis in MA-induced neurotoxicity, and that protein kinase Cδ might mediate the interaction among these factors. In addition, the relatively long-lasting and recurrent nature of MA psychosis has been reproduced in animals treated with various dosing regimens of MA, which have shown behavioral sensitization, sociability deficits, and impaired prepulse inhibition. Genetic predisposition as well as dopaminergic and glutamatergic alterations might be important in the development of MA psychosis. Neuroimaging studies have identified functional and morphological changes related to the cognitive dysfunction shown in chronic MA users. Failure in the task-evoked phosphorylation of extracellular signal-related kinase likely underlies MA-induced memory impairment. Recent progress has suggested certain roles of oxidative stress and neuroinflammation in the psychosis and cognitive deficits induced by repeated low doses of MA. This review provides a comprehensive description of pertinent findings from human and animal studies, with an emphasis on the current understanding of the underlying mechanisms of MA neuropsychotoxicity and its relevance to Parkinson’s disease or schizophrenia.

PKCδ-dependent p47 phox activation mediates methamphetamine-induced dopaminergic neurotoxicity

ABSTRACT Protein kinase C (PKC) has been recognized to activate NADPH oxidase (PHOX). However, the interaction between PKC and PHOX in vivo remains elusive. Treatment with methamphetamine (MA) resulted in a selective increase in PKC&dgr; expression out of PKC isoforms. PKC&dgr; co‐immunoprecipitated with p47phox, and facilitated phosphorylation and membrane translocation of p47phox. MA‐induced increases in PHOX activity and reactive oxygen species were attenuated by knockout of p47phox or PKC&dgr;. In addition, MA‐induced impairments in the Nrf‐2‐related glutathione synthetic system were also mitigated by knockout of p47phox or PKC&dgr;. Glutathione‐immunoreactivity was co‐localized in Iba‐1‐labeled microglial cells and in NeuN‐labeled neurons, but not in GFAP‐labeled astrocytes, reflecting the necessity for self‐protection against oxidative stress by mainly microglia. Buthionine‐sulfoximine, an inhibitor of glutathione biosynthesis, potentiated microglial activation and pro‐apoptotic changes, leading to dopaminergic losses. These neurotoxic processes were attenuated by rottlerin, a pharmacological inhibitor of PKC&dgr;, genetic inhibitions of PKC&dgr; [i.e., PKC&dgr; knockout mice (KO) and PKC&dgr; antisense oligonucleotide (ASO)], or genetic inhibition of p47phox (i.e., p47phox KO or p47phox ASO). Rottlerin did not exhibit any additive effects against the protective activity offered by genetic inhibition of p47phox. Therefore, we suggest that PKC&dgr; is a critical regulator for p47phox activation induced by MA, and that Nrf‐2‐dependent GSH induction via inhibition of PKC&dgr; or p47phox, is important for dopaminergic protection against MA insult. Graphical abstract Figure. No caption available. HighlightsInterplay between PKC and PHOX in vivo in the neurotoxic condition remains unclear.PKC&dgr; co‐immunoprecipitated with p47phox and facilitated the potential of p47phox.Methamphetamine‐induced Nrf‐2 system was mitigated by inhibition of p47phox or PKC&dgr;.BSO potentiated microgliosis and apoptotic changes, leading to dopaminergic losses.PKC&dgr; is a critical regulator for p47phox activation induced by methamphetamine.

The role of system Xc− in methamphetamine-induced dopaminergic neurotoxicity in mice

&NA; The cystine/glutamate antiporter (system Xc−, Sxc) transports cystine into cell in exchange for glutamate. Since xCT is a specific subunit of Sxc, we employed xCT knockout mice and investigated whether this antiporter affected methamphetamine (MA)‐induced dopaminergic neurotoxicity. MA treatment significantly increased striatal oxidative burdens in wild type mice. xCT inhibitor [i.e., S‐4‐carboxy‐phenylglycine (CPG), sulfasalazine] or an xCT knockout significantly protected against these oxidative burdens. MA‐induced increases in Iba‐1 expression and Iba‐1‐labeled microglial immunoreactivity (Iba‐1‐IR) were significantly attenuated by CPG or sulfasalazine administration or xCT knockout. CPG or sulfasalazine significantly attenuated MA‐induced TUNEL‐positive cell populations in the striatum of Taconic ICR mice. The decrease in excitatory amino acid transporter‐2 (or glutamate transporter‐1) expression and increase in glutamate release were attenuated by CPG, sulfasalazine or xCT knockout. In addition, CPG, sulfasalazine or xCT knockout significantly protected against dopaminergic loss (i.e., decreases in tyrosine hydroxylase expression and immunoreactivity, and an increase in dopamine turnover rate) induced by MA. However, CPG, sulfasalazine or xCT knockout did not significantly affect the impaired glutathione system [i.e., decrease in reduced glutathione (GSH) and increase in oxidized glutathione (GSSG)] induced by MA. Our results suggest that Sxc mediates MA‐induced neurotoxicity via facilitating oxidative stress, microgliosis, proapoptosis, and glutamate‐related toxicity. HighlightsGenetic or pharmacologic inhibition of xCT exhibits protective potentials against MA.xCT inhibition exerts antioxidant and antiapoptotic effects against MA neurotoxicity.xCT inhibition attenuates microglial activation and glutamate toxicity induced by MA.xCT inhibition does not affect glutathione system impairment induced by MA.

Treatment with Mountain-Cultivated Ginseng Alleviates Trimethyltin-Induced Cognitive Impairments in Mice via IL-6-Dependent JAK2/STAT3/ERK Signaling

Panax ginseng is the most widely used herbal medicine for improving cognitive functions. The pharmacological activity and underlying mechanisms of mountain-cultivated ginseng, however, have yet to be clearly elucidated, in particular, against trimethyltin-induced cognitive dysfunction. We previously reported that interleukin-6 plays a protective role against trimethyltin-induced cognitive dysfunction. Because of this, we have implemented a study system that uses interleukin-6 null (-/-) and wild-type mice. Interestingly, mountain-cultivated ginseng significantly upregulated interleukin-6 expression. With this study, we sought to determine whether the interleukin-6-dependent modulation of the Janus kinase 2/signal transducer activator of transcription 3 and extracellular signal-regulated kinase signaling network is also associated with the pharmacological activity of mountain-cultivated ginseng against trimethyltin-induced cognitive dysfunction. Trimethyltin treatment (2.4 mg/kg, intraperitoneal) causes the downregulation of Janus kinase 2/signal transducer activator of transcription 3, extracellular signal-regulated kinase signaling, and impairment of the cholinergic system. We found that mountain-cultivated ginseng treatment (50 mg/kg, intraperitoneal) significantly attenuated cognitive impairment normally induced by trimethyltin by upregulating p-Janus kinase 2/signal transducer activator of transcription 3, p-extracellular signal-regulated kinase signaling, and the cholinergic system. Trimethyltin-induced cognitive impairments were more pronounced in interleukin-6 (-/-) mice than wild-type mice, and they were markedly reduced by treatment with either mountain-cultivated ginseng or recombinant interleukin-6 protein (6 ng, intracerebroventricular). Additionally, treatment with either AG490 (20 mg/kg, intraperitoneal), a Janus kinase 2/signal transducer activator of transcription 3 inhibitor, or U0126 (2 µg/head, intracerebroventricular), an extracellular signal-regulated kinase inhibitor, reversed the effects of mountain-cultivated ginseng treatment. The effects of mountain-cultivated ginseng treatment were comparable to those of recombinant interleukin-6 protein in interleukin-6 (-/-) mice. Our results, therefore, suggest that mountain-cultivated ginseng acts through interleukin-6-dependent activation of Janus kinase 2/signal transducer activator of transcription 3/extracellular signal-regulated kinase signaling in order to reverse cognitive impairment caused by trimethyltin treatment.

Role of dopamine D1 receptor in 3-fluoromethamphetamine-induced neurotoxicity in mice

&NA; 3‐Fluoromethamphetamine (3‐FMA) is an illegal designer drug of methamphetamine (MA) derivative. Up to date, little is known about the neurotoxic potential of 3‐FMA. In the present study, we investigated the role of dopamine receptors in neurotoxicity induced by 3‐FMA in comparison with MA (35 mg/kg, i.p.) as a control drug. Here we found that 3‐FMA (40, 60 or 80 mg/kg, i.p.) produced mortality in a dose‐dependent manner in mice. Treatment with 3‐FMA (40 mg/kg, i.p.) resulted in significant hyperthermia, oxidative stress and microgliosis (microglial differentiation into M1 phenotype) followed by pro‐apoptotic changes and the induction of terminal deoxynucleotidyl transferase dUDP nick end labeling (TUNEL)‐positive cells. Moreover, 3‐FMA significantly produced dopaminergic impairments [i.e., increase in dopamine (DA) turnover rate and decreases in DA level, and in the expression of tyrosine hydroxylase (TH), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT‐2)] with behavioral impairments. These dopaminergic neurotoxic effects of 3‐FMA were comparable to those of MA. SCH23390, a dopamine D1 receptor antagonist, but not sulpiride, a dopamine D2 receptor antagonist significantly attenuated 3‐FMA‐induced neurotoxicity. Although both SCH23390 and sulpiride attenuated MA‐induced dopaminergic neurotoxicity, sulpiride is more effective than SCH23390 on the dopaminergic neurotoxicity. Interestingly, SCH23390 treatment positively modulated 3‐FMA‐induced microglial activation (i.e., SCH23390 inhibited M1 phenotype from 3‐FMA insult, but activated M2 phenotype). Therefore, our results suggest that the activation of dopamine D1 receptor is critical to 3‐FMA‐induced neurotoxicity, while both dopamine D1 and D2 receptors (dopamine D2 receptor > dopamine D1 receptor) mediate MA‐induced dopaminergic neurotoxicity.

MK-801, but not naloxone, attenuates high-dose dextromethorphan-induced convulsive behavior: Possible involvement of the GluN2B receptor

&NA; Dextromethorphan (DM) is a dextrorotatory isomer of levorphanol, a typical morphine‐like opioid. When administered at supra‐antitussive doses, DM produces psychotoxic and neurotoxic effects in humans. Although DM abuse has been well‐documented, few studies have examined the effects of high‐dose DM. The present study aimed to explore the effects of a single high dose of DM on mortality and seizure occurrence. After intraperitoneal administration with a high dose of DM (80 mg/kg), Sprague–Dawley rats showed increased seizure occurrence and intensity. Hippocampal expression levels of N‐methyl‐D‐aspartate (NMDA) receptor subunits (GluN1 < GluN2A < GluN2B), c‐Fos and pro‐apoptotic factors (Bax and cleaved caspase‐3) were upregulated by DM treatment; while levels of anti‐apoptotic factors (Bcl‐2 and Bcl‐xL) were downregulated. Consistently, DM also induced ultrastructural degeneration in the hippocampus. A non‐competitive NMDA receptor antagonist, MK‐801, attenuated these effects of high‐dose DM, whereas an opioid antagonist, naloxone, did not affect DM‐induced neurotoxicity. Moreover, pretreatment with a highly specific GluN2B subunit inhibitor, traxoprodil, was selectively effective in preventing DM‐induced c‐Fos expression and apoptotic changes. These results suggest that high‐dose DM produces convulsive behaviors by activating GluN2B/NMDA signaling that leads to pro‐apoptotic changes. HighlightsHigh‐dose (a supra antitussive dose) DM produces seizure behaviors.Intraperitoneal route (i.p.) is critical for induction of DM neurotoxicity.NMDA receptor antagonist, but not opioid receptor antagonist, attenuates DM seizures.GluN2B/NMDA signaling mediates DM‐induced neurotoxicity.

Ginsenoside Re protects methamphetamine-induced dopaminergic neurotoxicity in mice via upregulation of dynorphin-mediated κ-opioid receptor and downregulation of substance P-mediated neurokinin 1 receptor

BackgroundWe previously reported that ginsenoside Re (GRe) attenuated against methamphetamine (MA)-induced neurotoxicity via anti-inflammatory and antioxidant potentials. We also demonstrated that dynorphin possesses anti-inflammatory and antioxidant potentials against dopaminergic loss, and that balance between dynorphin and substance P is important for dopaminergic neuroprotection. Thus, we examined whether GRe positively affects interactive modulation between dynorphin and substance P against MA neurotoxicity in mice.MethodsWe examined changes in dynorphin peptide level, prodynorphin mRNA, and substance P mRNA, substance P-immunoreactivity, homeostasis in enzymatic antioxidant system, oxidative parameter, microglial activation, and pro-apoptotic parameter after a neurotoxic dose of MA to clarify the effects of GRe, prodynorphin knockout, pharmacological inhibition of κ-opioid receptor (i.e., nor-binaltorphimine), or neurokinin 1 (NK1) receptor (i.e., L-733,060) against MA insult in mice.ResultsGRe attenuated MA-induced decreases in dynorphin level, prodynorphin mRNA expression in the striatum of wild-type (WT) mice. Prodynorphin knockout potentiated MA-induced dopaminergic toxicity in mice. The imbalance of enzymatic antioxidant system, oxidative burdens, microgliosis, and pro-apoptotic changes led to the dopaminergic neurotoxicity. Neuroprotective effects of GRe were more pronounced in prodynorphin knockout than in WT mice. Nor-binaltorphimine, a κ-opioid receptor antagonist, counteracted against protective effects of GRe. In addition, we found that GRe significantly attenuated MA-induced increases in substance P-immunoreactivity and substance P mRNA expression in the substantia nigra. These increases were more evident in prodynorphin knockout than in WT mice. Although, we observed that substance P-immunoreactivity was co-localized in NeuN-immunreactive neurons, GFAP-immunoreactive astrocytes, and Iba-1-immunoreactive microglia. NK1 receptor antagonist L-733,060 or GRe selectively inhibited microgliosis induced by MA. Furthermore, L-733,060 did not show any additive effects against GRe-mediated protective activity (i.e., antioxidant, antimicroglial, and antiapoptotic effects), indicating that NK1 receptor is one of the molecular targets of GRe.ConclusionsOur results suggest that GRe protects MA-induced dopaminergic neurotoxicity via upregulatgion of dynorphin-mediated κ-opioid receptor and downregulation of substance P-mediated NK1 R.

Role of protein kinase Cδ in dopaminergic neurotoxic events

The pro-apoptotic role of Protein kinase Cδ (PKCδ), a member of the novel PKC subfamily, has been well-documented in various pathological conditions. In the central nervous system, the possible role of PKCδ has been studied, mainly in the condition of dopaminergic loss. It has been suggested that the phosphorylation of PKCδ at tyrosine 311 residue (Tyr311) by redox-sensitive Src family kinases (SFKs) is critical for the caspase-3-mediated proteolytic cleavage, which produces the constitutively active cleaved form of PKCδ. Mitochondrial translocation of cleaved PKCδ has been suggested to facilitate mitochondria-derived apoptosis and oxidative burdens. Moreover, it has been suggested that PKCδ contribute to neuroinflammation through the transformation of microglia into the pro-inflammatory M1 phenotype and the assembly of membrane NADPH oxidase in dopaminergic impairments. Interestingly, mitochondrial respiratory chain inhibitors or neuroinflammogens have shown to induce PKCδ activation in dopaminergic systems. Thus, PKCδ activation may be one of the pivotal causes of neuropathologic events, and could amplify these processes further in a positive feedback manner. Furthermore, PKCδ may play an intermediary role in connecting each neuropathologic event. This review affords insight into the role of PKCδ in various dopaminergic neurotoxic models, which could provide a potential target for mitigating dopaminergic neurotoxicity.

5-HT1A receptor agonist 8-OH-DPAT induces serotonergic behaviors in mice via interaction between PKCδ and p47phox

Serotonin syndrome is an adverse reaction due to increased serotonin (5-hydroxytryptophan: 5-HT) concentrations in the central nervous system (CNS). The full 5-HT1A receptor (5-HT1AR) agonist (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT) has been recognized to elicit traditional serotonergic behaviors. Treatment with 8-OH-DPAT selectively increased PKCδ expression out of PKC isoforms and 5-HT turnover rate in the hypothalamus of wild-type mice. Treatment with 8-OH-DPAT resulted in oxidative burdens, co-immunoprecipitation of 5-HT1AR and PKCδ, and phosphorylation and membrane translocation of p47phox. Importantly, p47phox also interacted with 5-HT1AR or PKCδ in the presence of 8-OH-DPAT. Consistently, the interaction and oxidative burdens were attenuated by 5-HT1AR antagonism (i.e., WAY100635), PKCδ inhibition (i.e., rottlerin and genetic depletion of PKCδ), or NADPH oxidase/p47phox inhibition (i.e., apocynin and genetic depletion of p47phox). However, WAY100635, apocynin, or rottlerin did not exhibit any additive effects against the protective effect by inhibition of PKCδ or p47phox. Furthermore, apocynin, rottlerin, or WAY100635 also significantly protected from pro-inflammatory/pro-apoptotic changes induced by 8-OH-DPAT. Therefore, we suggest that 8-OH-DPAT-induced serotonergic behaviors requires oxidative stress, pro-inflammatory, and pro-apoptotic changes, that PKCδ or p47phox mediates the serotonergic behaviors induced by 8-OH-DPAT, and that the inhibition of PKCδ-dependent p47phox activation is critical for protecting against serotonergic behaviors.