Methamphetamine-induced inhibition of mitochondrial complex II: roles of glutamate and peroxynitrite

Long-term methamphetamine self-administration increases mesolimbic mitochondrial oxygen consumption and decreases striatal glutathione

Neurotoxic regimens of methamphetamine (METH) are known to increase reactive oxygen species (ROS), affect redox homeostasis, and lead to damage in dopamine neurons. Functional changes induced by long-term METH self-administration on mitochondrial respiratory metabolism and redox homeostasis are less known. To fill this gap, we implanted a jugular catheter into adult male mice and trained them to nose poke for METH infusions. After several weeks of METH exposure, we collected samples of the ventral striatum (vST) and the ventral midbrain (vMB). We used HPLC to determine the levels of the ROS scavenger glutathione in its reduced (GSH) and oxidized forms. Then, we used high-resolution respirometry to determine the oxygen consumption rate (OCR) of mitochondrial complexes. Finally, using in vivo electrophysiology, we assessed changes in dopamine neuron firing activity in the VTA. METH self-administration produced a decrease of the GSH pool in vST, correlating with lifetime METH intake. We observed increased mitochondrial respiration across the two mesolimbic regions. METH self-administration decreases firing rate and burst activity but increases the number of spontaneously active dopamine neurons per track. We conclude that METH self-administration progressively decreased the antioxidant pool in sites of higher dopamine release and produced an increase in mitochondrial metabolism in the mesolimbic areas, probably derived from the increased number of dopamine neurons actively firing. However, dopamine neuron firing activity is decreased by METH self-administration, reflecting a new basal level of dopamine neurotransmission.

Effect of methamphetamine on ultraweak photon emission and level of reactive oxygen species in male rat brain

All living cells, including neurons, generate ultra-weak photon emission (UPE) during biological activity, and in particular, in the brain, it has been shown that UPE is correlated with neuronal activity and associated metabolic processes. Various intracellular factors, as well as external factors, can reduce or increase the intensity of UPE. In this study, we have used Methamphetamine (METH) as one potentially effective external factor, which is a substance that has the property of stimulating the central nervous system. METH can impair mitochondrial function by causing toxicity via various pathways, including an increase in the number of mitochondria, hyperthermia, the increased metabolic activity of the brain, and the production of glutamate and excess calcium. In addition to mitochondrial dysfunction, METH alters cellular homeostasis, leading to cell damage and the production of excess ROS. The aim of this study is to measure and compare the UPE intensity and reactive oxygen species (ROS) levels of the prefrontal, motor, and visual cortex before and after METH administration. Twenty male rats were randomly assigned to two groups, the control, and METH groups. In the control group, 2 h after injection of normal saline and without any intervention, and in the experimental group 2 h after IP injection of 20 mg/kg METH, sections were prepared from three areas: prefrontal, motor, and V1-V2 cortex, which were used to evaluate the emission of UPE using a photomultiplier tube (PMT) device and to evaluate the amount of ROS. The results showed that the amount of ROS and UPE in the experimental group in all three areas significantly increased compared to the control group. So, METH increases UPE and ROS in the prefrontal, motor, and visual regions, and there is a direct relationship between UPE intensity and ROS production. Therefore, UPE may be used as a dynamic reading tool to monitor oxidative metabolism in physiological processes related to ROS and METH research. Also, the results of this experiment may create a new avenue to test the hypothesis that the excess in UPE generation may lead to the phenomenon of phosphene and visual hallucinations.

Effect of the Sargassum angustifolium Extract on Methamphetamine-Induced Cytotoxicity in SH-SY5Y Cells

This study aimed to assess the effect of the Sargassum angustifolium extract in methamphetamine-induced SH-SY5Y cells death. The brown algae S. angustifolium was extracted with 80% ethanol. The SH-SY5Y cells were treated with different concentrations of methamphetamine to measure IC50 $\mathrm{..}$ The MTT test was used to assess the toxic effect of the S. angustifolium extract in SH-SY5Y cells. SH-SY5Y cells’ survival was measured while cells were treated with different concentrations of methamphetamine and S. angustifolium extract simultaneously. A specific kit measured intracellular ROS levels. Western blot analysis evaluated the expression of cytochrome C and Bax/Bcl2 ratio. The results showed that 5 mM methamphetamine approximately killed 50% of the cells, so it is considered IC50. The MTT test showed no toxicity effect for the S. angustifolium extract. 80, 160, 320, and 640 μg/ml of S. angustifolium extract prevented the occurrence of methamphetamine toxic effects in SH-SY5Y cells after 24 hours. Moreover, the S. angustifolium extract decreased ROS levels and cytochrome C release and reduced BaX/Bcl2 ratio in cells treated by methamphetamine. On the whole, it seems that the S. angustifolium hydroalcoholic extract has the potential to increase cell survival through in vitro antioxidant and antiapoptotic activities.

Alterations of Mitochondrial Structure in Methamphetamine Toxicity

Recent evidence shows that methamphetamine (METH) produces mitochondrial alterations that contribute to neurotoxicity. Nonetheless, most of these studies focus on mitochondrial activity, whereas mitochondrial morphology remains poorly investigated. In fact, morphological evidence about the fine structure of mitochondria during METH toxicity is not available. Thus, in the present study we analyzed dose-dependent mitochondrial structural alterations during METH exposure. Light and transmission electron microscopy were used, along with ultrastructural stoichiometry of catecholamine cells following various doses of METH. In the first part of the study cell death and cell degeneration were assessed and they were correlated with mitochondrial alterations observed using light microscopy. In the second part of the study, ultrastructural evidence of specific mitochondrial alterations of crests, inner and outer membranes and matrix were quantified, along with in situ alterations of mitochondrial proteins. Neurodegeneration induced by METH correlates significantly with specific mitochondrial damage, which allows definition of a scoring system for mitochondrial integrity. In turn, mitochondrial alterations are concomitant with a decrease in fission/mitophagy protein Fis1 and DRP1 and an increase in Pink1 and Parkin in situ, at the mitochondrial level. These findings provide structural evidence that mitochondria represent both direct and indirect targets of METH-induced toxicity

A Non-Canonical Role for IRE1α Links ER and Mitochondria as Key Regulators of Astrocyte Dysfunction: Implications in Methamphetamine use and HIV-Associated Neurocognitive Disorders

Astrocytes are one of the most numerous glial cells in the central nervous system (CNS) and provide essential support to neurons to ensure CNS health and function. During a neuropathological challenge, such as during human immunodeficiency virus (HIV)-1 infection or (METH)amphetamine exposure, astrocytes shift their neuroprotective functions and can become neurotoxic. Identifying cellular and molecular mechanisms underlying astrocyte dysfunction are of heightened importance to optimize the coupling between astrocytes and neurons and ensure neuronal fitness against CNS pathology, including HIV-1-associated neurocognitive disorders (HAND) and METH use disorder. Mitochondria are essential organelles for regulating metabolic, antioxidant, and inflammatory profiles. Moreover, endoplasmic reticulum (ER)-associated signaling pathways, such as calcium and the unfolded protein response (UPR), are important messengers for cellular fate and function, including inflammation and mitochondrial homeostasis. Increasing evidence supports that the three arms of the UPR are involved in the direct contact and communication between ER and mitochondria through mitochondria-associated ER membranes (MAMs). The current study investigated the effects of HIV-1 infection and chronic METH exposure on astrocyte ER and mitochondrial homeostasis and then examined the three UPR messengers as potential regulators of astrocyte mitochondrial dysfunction. Using primary human astrocytes infected with pseudotyped HIV-1 or exposed to low doses of METH for 7 days, astrocytes had increased mitochondrial oxygen consumption rate (OCR), cytosolic calcium flux and protein expression of UPR mediators. Notably, inositol-requiring protein 1α (IRE1α) was most prominently upregulated following both HIV-1 infection and chronic METH exposure. Moreover, pharmacological inhibition of the three UPR arms highlighted IRE1α as a key regulator of astrocyte metabolic function. To further explore the regulatory role of astrocyte IRE1α, astrocytes were transfected with an IRE1α overexpression vector followed by activation with the proinflammatory cytokine interleukin 1β. Overall, our findings confirm IRE1α modulates astrocyte mitochondrial respiration, glycolytic function, morphological activation, inflammation, and glutamate uptake, highlighting a novel potential target for regulating astrocyte dysfunction. Finally, these findings suggest both canonical and non-canonical UPR mechanisms of astrocyte IRE1α. Thus, additional studies are needed to determine how to best balance astrocyte IRE1α functions to both promote astrocyte neuroprotective properties while preventing neurotoxic properties during CNS pathologies.

Therapeutic Targets for Regulating Oxidative Damage Induced by Ischemia-Reperfusion Injury: A Study from a Pharmacological Perspective

Ischemia-reperfusion (I-R) injury is damage caused by restoring blood flow into ischemic tissues or organs. This complex and characteristic lesion accelerates cell death induced by signaling pathways such as apoptosis, necrosis, and even ferroptosis. In addition to the direct association between I-R and the release of reactive oxygen species and reactive nitrogen species, it is involved in developing mitochondrial oxidative damage. Thus, its mechanism plays a critical role via reactive species scavenging, calcium overload modulation, electron transport chain blocking, mitochondrial permeability transition pore activation, or noncoding RNA transcription. Other receptors and molecules reduce tissue and organ damage caused by this pathology and other related diseases. These molecular targets have been gradually discovered and have essential roles in I-R resolution. Therefore, the current study is aimed at highlighting the importance of these discoveries. In this review, we inquire about the oxidative damage receptors that are relevant to reducing the damage induced by oxidative stress associated with I-R. Several complications on surgical techniques and pathology interventions do not mitigate the damage caused by I-R. Nevertheless, these therapies developed using alternative targets could work as coadjuvants in tissue transplants or I-R-related pathologies

Mitochondrial function influences expression of methamphetamine-induced behavioral sensitization

Repeated methamphetamine use leads to long lasting brain and behavioral changes in humans and laboratory rats. These changes have high energy requirements, implicating a role for mitochondria. We explored whether mitochondrial function underpins behaviors that occur in rats months after stopping methamphetamine self-administration. Accordingly, rats self-administered intravenous methamphetamine for 3 h/day for 14 days. The mitochondrial toxin rotenone was administered as (1 mg/kg/day for 6 days) via an osmotic minipump starting at 0, 14 or 28 days of abstinence abstinence. On abstinence day 61, expression of methamphetamine-induced behavioral sensitization was obtained with an acute methamphetamine challenge in rotenone-free rats. Rotenone impeded the expression of sensitization, with the most robust effects obtained with later abstinence exposure. These findings verified that self-titration of moderate methamphetamine doses results in behavioral (and thus brain) changes that can be revealed months after exposure termination, and that the meth-initiated processes progressed during abstinence so that longer abstinence periods were more susceptible to the consequences of exposure to a mitochondrial toxin.

Dopamine and Methamphetamine Differentially Affect Electron Transport Chain Complexes and Parkin in Rat Striatum: New Insight into Methamphetamine Neurotoxicity

Methamphetamine (METH) is a highly abused psychostimulant that is neurotoxic to dopaminergic (DAergic) nerve terminals in the striatum and increases the risk of developing Parkinson’s disease (PD). In vivo, METH-mediated DA release, followed by DA-mediated oxidative stress and mitochondrial dysfunction in pre- and postsynaptic neurons, mediates METH neurotoxicity. METH-triggered oxidative stress damages parkin, a neuroprotective protein involved in PD etiology via its involvement in the maintenance of mitochondria. It is not known whether METH itself contributes to mitochondrial dysfunction and whether parkin regulates complex I, an enzymatic complex downregulated in PD. To determine this, we separately assessed the effects of METH or DA alone on electron transport chain (ETC) complexes and the protein parkin in isolated striatal mitochondria. We show that METH decreases the levels of selected complex I, II, and III subunits (NDUFS3, SDHA, and UQCRC2, respectively), whereas DA decreases the levels only of the NDUFS3 subunit in our preparations. We also show that the selected subunits are not decreased in synaptosomal mitochondria under similar experimental conditions. Finally, we found that parkin overexpression does not influence the levels of the NDUFS3 subunit in rat striatum. The presented results indicate that METH itself is a factor promoting dysfunction of striatal mitochondria; therefore, it is a potential drug target against METH neurotoxicity. The observed decreases in ETC complex subunits suggest that DA and METH decrease activities of the ETC complexes via oxidative damage to their subunits and that synaptosomal mitochondria may be somewhat “resistant” to DA- and METH-induced disruption in mitochondrial ETC complexes than perikaryal mitochondria. The results also suggest that parkin does not regulate NDUFS3 turnover in rat striatum.

Influence of psychostimulants and opioids on epigenetic modification of class III histone deacetylase (HDAC)-sirtuins in glial cells

Substance abuse affects the central nervous system (CNS) and remains a global health problem. Psychostimulants, such as cocaine and methamphetamine (METH), and opioids affect neuronal function and lead to behavioral impairments via epigenetic modification. Epigenetic changes occur via classical pathways, especially the class III histone deacetylase (HDAC)-sirtuin (SIRT) family, that act as cellular sensors to regulate energy homeostasis and coordinate cellular responses to maintain genome integrity. However, SIRT family (1-7)-associated neurodegeneration has not been elucidated in the context of energy metabolism. The present study examined the effects of psychostimulants, such as cocaine and METH, and opioids, such as morphine, on SIRT family (1-7) [class I, II, III and IV] expression and cellular translocation-mediated dysfunction in astrocytes and microglial cells. The "nootropic" drug piracetam played a preventative role against psychostimulant- and opioid-induced SIRT (1-7) expression in astrocytes. These results indicate that cocaine, METH, and morphine affected deacetylation and cellular function, and these changes were prevented by piracetam in astrocytes.

Neurotoxicity of methamphetamine: Main effects and mechanisms

Methamphetamine (METH) is an illicit psychostimulant that is abused throughout the world. METH addiction is also a major public health concern and the abuse of large doses of the drug is often associated with serious neuropsychiatric consequences that may include agitation, anxiety, hallucinations, paranoia, and psychosis. Some human methamphetamine users can also suffer from attention, memory, and executive deficits. METH-associated neurological and psychiatric complications might be related, in part, to METH-induced neurotoxic effects. Those include altered dopaminergic and serotonergic functions, neuronal apoptosis, astrocytosis, and microgliosis. Here we have endeavored to discuss some of the main effects of the drug and have presented the evidence supporting certain of the molecular and cellular bases of METH neurotoxicity. The accumulated evidence suggests the involvement of transcription factors, activation of dealth pathways that emanate from mitochondria and endoplasmic reticulum (ER), and a role for neuroinflammatory mechanisms. Understanding the molecular processes involved in METH induced neurotoxicity should help in developing better therapeutic approaches that might also serve to attenuate or block the biological consequences of use of large doses of the drug by some humans who meet criteria for METH use disorder.

Parkin-deficient rats are resistant to neurotoxicity of chronic high-dose methamphetamine

Methamphetamine (METH) is a highly addictive and powerful central nervous system psychostimulant with no FDA-approved pharmacotherapy. Parkin is a neuroprotective protein and its loss of function contributes to Parkinson's disease. This study used 3-month-old homozygous parkin knockout (PKO) rats to determine whether loss of parkin protein potentiates neurotoxicity of chronic METH to the nigrostriatal dopamine pathway. PKO rats were chronically treated with 10 mg/kg METH for 10 consecutive days and assessed for neurotoxicity markers in the striatum on the 5th and 10th day of withdrawal from METH. The PKO rats showed higher METH-induced hyperthermia; however, they did not display augmented deficits in dopaminergic and serotonergic neurotoxicity markers, astrocyte activation or decreased mitochondrial enzyme levels as compared to wild-type (WT) rats. Interestingly, saline-treated PKO rats had lower levels of dopamine (DA) as well as mitochondrial complex I and II levels while having increased basal levels of glial fibrillary acidic protein (GFAP), a marker of gliosis. These results indicate PKO display a certain resistance to METH neurotoxicity, possibly mediated by lowered DA levels and downregulated mitochondria.

Methamphetamine-induced dopaminergic neurotoxicity as a model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with a high prevalence, approximately 1 % in the elderly population. Numerous studies have demonstrated that methamphetamine (MA) intoxication caused the neurological deficits and nigrostriatal damage seen in Parkinsonian conditions, and subsequent rodent studies have found that neurotoxic binge administration of MA reproduced PD-like features, in terms of its symptomatology and pathology. Several anti-Parkinsonian medications have been shown to attenuate the motor impairments and dopaminergic damage induced by MA. In addition, it has been recognized that mitochondrial dysfunction, oxidative stress, pro-apoptosis, proteasomal/autophagic impairment, and neuroinflammation play important roles in inducing MA neurotoxicity. Importantly, MA neurotoxicity has been shown to share a common mechanism of dopaminergic toxicity with that of PD pathogenesis. This review describes the major findings on the neuropathological features and underlying neurotoxic mechanisms induced by MA and compares them with Parkinsonian pathogenesis. Taken together, it is suggested that neurotoxic binge-type administration of MA in rodents is a valid animal model for PD that may provide knowledge on the neuropathogenesis of PD.

Autophagy as a gateway for the effects of methamphetamine: From neurotransmitter release and synaptic plasticity to psychiatric and neurodegenerative disorders

As a major eukaryotic cell clearing machinery, autophagy grants cell proteostasis, which is key for neurotransmitter release, synaptic plasticity, and neuronal survival. In line with this, besides neuropathological events, autophagy dysfunctions are bound to synaptic alterations that occur in mental disorders, and early on, in neurodegenerative diseases. This is also the case of methamphetamine (METH) abuse, which leads to psychiatric disturbances and neurotoxicity. While consistently altering the autophagy machinery, METH produces behavioral and neurotoxic effects through molecular and biochemical events that can be recapitulated by autophagy blockade. These consist of altered physiological dopamine (DA) release, abnormal stimulation of DA and glutamate receptors, as well as oxidative, excitotoxic, and neuroinflammatory events. Recent molecular insights suggest that METH early impairs the autophagy machinery, though its functional significance remains to be investigated. Here we discuss evidence suggesting that alterations of DA transmission and autophagy are intermingled within a chain of events underlying behavioral alterations and neurodegenerative phenomena produced by METH. Understanding how METH alters the autophagy machinery is expected to provide novel insights into the neurobiology of METH addiction sharing some features with psychiatric disorders and parkinsonism.

The Role of Chinese Herbal Therapy in Methamphetamine Abuse and its Induced Psychiatric Symptoms

Repeated intake of methamphetamine (METH) leads to drug addiction, the inability to control intake, and strong drug cravings. It is also likely to cause psychiatric impairments, such as cognitive impairment, depression, and anxiety. Because the specific neurobiological mechanisms involved are complex and have not been fully and systematically elucidated, there is no established pharmacotherapy for METH abuse. Studies have found that a variety of Chinese herbal medicines have significant therapeutic effects on neuropsychiatric symptoms and have the advantage of multitarget comprehensive treatment. We conducted a systematic review, from neurobiological mechanisms to candidate Chinese herbal medicines, hoping to provide new perspectives and ideas for the prevention and treatment of METH abuse.

The Role of α-Synuclein in Methamphetamine-Induced Neurotoxicity

Methamphetamine (METH), a highly addictive psychostimulant, is the second most widely used illicit drug. METH produces damage dopamine neurons and apoptosis via multiple inter-regulating mechanisms, including dopamine overload, hyperthermia, oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, protein degradation system dysfunction, and neuroinflammation. Increasing evidence suggests that chronic METH abuse is associated with neurodegenerative changes in the human brain and an increased risk of Parkinson's disease (PD). METH use and PD may share some common steps in causing neurotoxicity. Accumulation of α-synuclein, a presynaptic protein, is the pathological hallmark of PD. Intriguingly, α-synuclein upregulation and aggregation are also found in dopaminergic neurons in the substantia nigra in chronic METH users. This suggests α-synuclein may play a role in METH-induced neurotoxicity. The mechanism of α-synuclein cytotoxicity in PD has attracted considerable attention; however, how α-synuclein affects METH-induced neurotoxicity has not been reviewed. In this review, we summarize the relationship between METH use and PD, interdependent mechanisms that are involved in METH-induced neurotoxicity and the significance of α-synuclein upregulation in response to METH use. The identification of α-synuclein overexpression and aggregation as a contributor to METH-induced neurotoxicity may provide a novel therapeutic target for the treatment of the deleterious effect of this drug and drug addiction.

TBHQ-Overview of Multiple Mechanisms against Oxidative Stress for Attenuating Methamphetamine-Induced Neurotoxicity

Methamphetamine is a derivative of amphetamines, a highly addictive central stimulant with multiple systemic toxicity including the brain, heart, liver, lung, and spleen. It has adverse effects such as apoptosis and breakdown of the blood-brain barrier. Methamphetamine is a fatal and toxic chemical substance, and its lethal mechanism has been widely studied in recent years. The possible mechanism is that methamphetamine can cause cardiotoxicity and neurotoxicity mainly by inducing oxidative stress so as to generate heat, eliminate people's hunger and thirst, and maintain a state of excitement so that people can continue to exercise. According to many research, there is no doubt that methamphetamine triggers neurotoxicity by inducing reactive oxygen species (ROS) production and redox imbalance. This review summarized the mechanisms of methamphetamine-induced neurotoxicity including apoptosis and blood-brain barrier breakdown through oxidative stress and analyzed several possible antioxidative mechanisms of tert-butylhydroquinone (TBHQ) which is a kind of food additive with antioxidative effects. As a nuclear factor E2-related factor 2 (Nrf2) agonist, TBHQ may inhibit neurotoxicity caused by oxidative stress through the following three mechanisms: the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, the astrocytes activation, and the glutathione pathway. The mechanism about methamphetamine's toxic effects and its antioxidative therapeutic drugs would become a research hotspot in this field and has very important research significance.

Systems Biology Analysis of the Antagonizing Effects of HIV-1 Tat Expression in the Brain over Transcriptional Changes Caused by Methamphetamine Sensitization

Methamphetamine (Meth) abuse is common among humans with immunodeficiency virus (HIV). The HIV-1 regulatory protein, trans-activator of transcription (Tat), has been described to induce changes in brain gene transcription that can result in impaired reward circuitry, as well as in inflammatory processes. In transgenic mice with doxycycline-induced Tat protein expression in the brain, i.e., a mouse model of neuroHIV, we tested global gene expression patterns induced by Meth sensitization. Meth-induced locomotor sensitization included repeated daily Meth or saline injections for seven days and Meth challenge after a seven-day abstinence period. Brain samples were collected 30 min after the Meth challenge. We investigated global gene expression changes in the caudate putamen, an area with relevance in behavior and HIV pathogenesis, and performed pathway and transcriptional factor usage predictions using systems biology strategies. We found that Tat expression alone had a very limited impact in gene transcription after the Meth challenge. In contrast, Meth-induced sensitization in the absence of Tat induced a global suppression of gene transcription. Interestingly, the interaction between Tat and Meth broadly prevented the Meth-induced global transcriptional suppression, by maintaining regulation pathways, and resulting in gene expression profiles that were more similar to the controls. Pathways associated with mitochondrial health, initiation of transcription and translation, as well as with epigenetic control, were heavily affected by Meth, and by its interaction with Tat in anti-directional ways. A series of systems strategies have predicted several components impacted by these interactions, including mitochondrial pathways, mTOR/RICTOR, AP-1 transcription factor, and eukaryotic initiation factors involved in transcription and translation. In spite of the antagonizing effects of Tat, a few genes identified in relevant gene networks remained downregulated, such as sirtuin 1, and the amyloid precursor protein (APP). In conclusion, Tat expression in the brain had a low acute transcriptional impact but strongly interacted with Meth sensitization, to modify effects in the global transcriptome.

Psychotropic and neurological medication effects on mitochondrial complex I and IV in rodent models

Mitochondrial complex I (NADH-dehydrogenase) and complex IV (cytochrome-c-oxidase) are reported to be affected by drugs used to treat psychiatric or neurodegenerative diseases, including antidepressants, antipsychotics, anxiolytics, mood stabilizers, stimulants, antidementia, and antiparkinsonian drugs. We conducted meta-analyses examining the effects of each drug category on complex I and IV. The electronic databases Pubmed, EMBASE, CENTRAL, and Google Scholar were searched for studies published between 1970 and 2018. Of 3105 screened studies, 68 articles covering 53 drugs were included in the meta-analyses. All studies assessed complex I and IV in rodent brain at the level of enzyme activity. Results revealed that selected antidepressants increase or decrease complex I and IV, antipsychotics and stimulants decrease complex I but increase complex IV, whereas anxiolytics, mood stabilizers, antidementia, and antiparkinsonian drugs preserve or even enhance both complex I and IV. Potential contributions to the drug effects were found to be related to the drugs' neurotransmitter receptor profiles with adrenergic (α1B), dopaminergic (D1/2), glutaminergic (NMDA1,3), histaminergic (H1), muscarinic (M1,3), opioid (OP1-3), serotonergic (5-HT_2A, 5-HT_2C, 5-HT_3A) and sigma (σ1) receptors having the greatest effects. The findings are discussed in relation to pharmacological mechanisms of action that might have relevance for clinical and research applications.

Thyroid hormone treatment alleviates the impairments of neurogenesis, mitochondrial biogenesis and memory performance induced by methamphetamine

Chronic use of methamphetamine (MA), a neurotoxic psychostimulant, leads to long-lasting cognitive dysfunctions in humans and animal models. Thyroid hormones (THs) have several physiological actions and are crucial for normal behavioral, intellectual and neurological development. Considering the importance of THs in the cognitive processes, the present study was designed to evaluate the therapeutic effects of THs on cognitive and neurological impairments induced by MA. Escalating doses of MA (1-10 mg/kg, IP) were injected twice daily for 10 consecutive days in rats and cognitive functions were evaluated using behavioral tests. The expression of factors involved in neurogenesis (NES and DCX), mitochondrial biogenesis (PGC-1α, NRF-1, and TFAM), neuroinflammation (GFAP, Iba-1, and COX-2) as well as Reelin and NT-3 (synaptic plasticity and neurotrophic factor, respectively) was measured in the hippocampus of MA-treated animals. The effects of three different doses of T4 (20, 40 or 80 μg/kg; intraperitoneally) or T3 (20, 40 or 80 μg/rat; 2.5 μl/nostril; intranasal) treatment, once a day for one week after MA cessation, were assessed in MA-treated rats. After the last behavioral test, serum T4 and T3 levels were measured using radioimmunoassay. The results revealed that repeated escalating regimen of MA impaired cognitive functions concomitant with neurogenesis and synaptic plasticity impairments, mitochondrial dysfunction, and neuroinflammation. T4 or T3 treatment partially decreased the alterations induced by MA. These findings suggest that THs can be considered as potential candidates for the reduction of MA abuse related neurocognitive disturbances.

mTOR Modulates Methamphetamine-Induced Toxicity through Cell Clearing Systems

Methamphetamine (METH) is abused worldwide, and it represents a threat for public health. METH exposure induces a variety of detrimental effects. In fact, METH produces a number of oxidative species, which lead to lipid peroxidation, protein misfolding, and nuclear damage. Cell clearing pathways such as ubiquitin-proteasome (UP) and autophagy (ATG) are involved in METH-induced oxidative damage. Although these pathways were traditionally considered to operate as separate metabolic systems, recent studies demonstrate their interconnection at the functional and biochemical level. Very recently, the convergence between UP and ATG was evidenced within a single organelle named autophagoproteasome (APP), which is suppressed by mTOR activation. In the present research study, the occurrence of APP during METH toxicity was analyzed. In fact, coimmunoprecipitation indicates a binding between LC3 and P20S particles, which also recruit p62 and alpha-synuclein. The amount of METH-induced toxicity correlates with APP levels. Specific markers for ATG and UP, such as LC3 and P20S in the cytosol, and within METH-induced vacuoles, were measured at different doses and time intervals following METH administration either alone or combined with mTOR modulators. Western blotting, coimmunoprecipitation, light microscopy, confocal microscopy, plain transmission electron microscopy, and immunogold staining were used to document the effects of mTOR modulation on METH toxicity and the merging of UP with ATG markers within APPs. METH-induced cell death is prevented by mTOR inhibition, while it is worsened by mTOR activation, which correlates with the amount of autophagoproteasomes. The present data, which apply to METH toxicity, are also relevant to provide a novel insight into cell clearing pathways to counteract several kinds of oxidative damage.

Methamphetamine Induces Apoptosis of Microglia via the Intrinsic Mitochondrial-Dependent Pathway

Methamphetamine (METH) is a drug of abuse, the acute and chronic use of which induces neurotoxic responses in the human brain, ultimately leading to neurocognitive disorders. Our goals were to understand the impact of METH on microglial mitochondrial respiration and to determine whether METH induces the activation of the mitochondrial-dependent intrinsic apoptosis pathway in microglia. We assessed the expression of pro- apoptosis genes using qPCR of RNA extracted from a human microglial cell line (HTHU). We examined the apoptosis-inducing effects of METH on microglial cells using digital holographic microscopy (DHM) to quantify real-time apoptotic volume decrease (AVD) in microglia in a noninvasive manner. METH treatment significantly increased AVD, activated Caspase 3/7, increased the gene expression levels of the pro- apoptosis proteins, APAF-1 and BAX, and decreased mitochondrial DNA content. Using immunofluorescence analysis, we found that METH increased the expression of the mitochondrial proteins cytochrome c and MCL-1, supporting the activation of mitochondrion-dependent (intrinsic) apoptosis pathway. Cellular bio-energetic flux analysis by Agilent Seahorse XF Analyzer revealed that METH treatment increased both oxidative and glycolytic respiration after 3 h, which was sustained for at least 24 h. Several events, such as oxidative stress, neuro-inflammatory responses, and mitochondrial dysfunction, may converge to mediate METH-induced apoptosis of microglia that may contribute to neurotoxicity of the CNS. Our study has important implications for therapeutic strategies aimed at preserving mitochondrial function in METH abusing patients.

Epigenetic Effects Induced by Methamphetamine and Methamphetamine-Dependent Oxidative Stress

Methamphetamine is a widely abused drug, which possesses neurotoxic activity and powerful addictive effects. Understanding methamphetamine toxicity is key beyond the field of drug abuse since it allows getting an insight into the molecular mechanisms which operate in a variety of neuropsychiatric disorders. In fact, key alterations produced by methamphetamine involve dopamine neurotransmission in a way, which is reminiscent of spontaneous neurodegeneration and psychiatric schizophrenia. Thus, understanding the molecular mechanisms operated by methamphetamine represents a wide window to understand both the addicted brain and a variety of neuropsychiatric disorders. This overlapping, which is already present when looking at the molecular and cellular events promoted immediately after methamphetamine intake, becomes impressive when plastic changes induced in the brain of methamphetamine-addicted patients are considered. Thus, the present manuscript is an attempt to encompass all the molecular events starting at the presynaptic dopamine terminals to reach the nucleus of postsynaptic neurons to explain how specific neurotransmitters and signaling cascades produce persistent genetic modifications, which shift neuronal phenotype and induce behavioral alterations. A special emphasis is posed on disclosing those early and delayed molecular events, which translate an altered neurotransmitter function into epigenetic events, which are derived from the translation of postsynaptic noncanonical signaling into altered gene regulation. All epigenetic effects are considered in light of their persistent changes induced in the postsynaptic neurons including sensitization and desensitization, priming, and shift of neuronal phenotype.

The Main Molecular Mechanisms Underlying Methamphetamine- Induced Neurotoxicity and Implications for Pharmacological Treatment

Methamphetamine (METH) is a popular new-type psychostimulant drug with complicated neurotoxicity. In spite of mounting evidence on METH-induced damage of neural cell, the accurate mechanism of toxic effect of the drug on central nervous system (CNS) has not yet been completely deciphered. Besides, effective treatment strategies toward METH neurotoxicity remain scarce and more efficacious drugs are to be developed. In this review, we summarize cellular and molecular bases that might contribute to METH-elicited neurotoxicity, which mainly include oxidative stress, excitotoxicity, and neuroinflammation. We also discuss some drugs that protect neural cells suffering from METH-induced neurotoxic consequences. We hope more in-depth investigations of exact details that how METH produces toxicity in CNS could be carried out in future and the development of new drugs as natural compounds and immunotherapies, including clinic trials, are expected.

The Role of Mitochondria in Methamphetamine-induced inhibitory effects on osteogenesis of Mesenchymal Stem Cells

Methamphetamine (METH) abuse causes significant physical, psychological, and social concerns. Therefore, in this study, we investigated its effects on osteogenic differentiation of mesenchymal stem cells (MSCs). We found that METH dose-dependently affected MSCs viability. Upon osteogenic induction, the 3 and 30 µmol/l METH dosages without deleterious effects on MSCs viability resulted in the down-regulation of osteoblastic marker genes (Alp, Bglap, and Runx2), suppression of the protein expression of RUNX2, and decreased ALP activity and mineralization ability. Mitochondria are essential during osteogenesis of MSCs. Our analysis on mitochondrial function revealed that METH decreased ATP production, suppressed the oxygen consumption rate, and depolarized the mitochondrial membrane potential, but it had no significant effects on the protein expression of the five complexes on the respiratory chain. Additionally, METH could impair mitochondrial biogenesis, as demonstrated by decreased mtDNA and down-regulated biogenesis factors. Mitochondrial fusion regulators were also decreased at the mRNA and protein levels. However, mitochondrial fission and mitophagy were not affected. In conclusion, our study revealed that exposure to METH could result in decreased mitochondrial biogenesis and fusion as well as mitochondrial dysfunction, and thus it suppressed the osteogenesis of MSCs.

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.

The neurotoxic mechanisms of amphetamine: Step by step for striatal dopamine depletion

Amphetamine (AMPH) is a commonly abused psychostimulant that induces neuronal cell death/degeneration in humans and experimental animals. Although multiple neurotoxic mechanisms of AMPH have been intensively investigated, the interplay between these mechanisms has remained elusive. In this study, we used a rat model of AMPH-induced long-lasting striatal dopamine (DA) depletion and identified mechanisms of neurotoxicity, energy failure, excitotoxicity, and oxidative stress. Pretreatment with nicotinamide (NAM, a co-factor for the electron transport chain) blocked AMPH-induced free radical formation, energy failure, and striatal DA decrease. Also, MK-801 (a NMDA receptor antagonist) blocked AMPH-induced free radical formation and striatal DA but not energy failure decrease, indicating excitotoxicity may occur before free radical formation and after energy failure. Thus, these results show that during AMPH intoxication, energy failure, excitotoxicity, and free radical formation are orchestrated consecutively to mediate the depletion of striatal DA.

Escalating Methamphetamine Regimen Induces Compensatory Mechanisms, Mitochondrial Biogenesis, and GDNF Expression, in Substantia Nigra

Methamphetamine (MA) produces long-lasting deficits in dopaminergic neurons in the long-term use via several neurotoxic mechanisms. The effects of MA on mitochondrial biogenesis is less studied currently. So, we evaluated the effects of repeated escalating MA regimen on transcriptional factors involved in mitochondrial biogenesis and glial-derived neurotrophic factor (GDNF) expression in substantia nigra (SN) and striatum of rat. In male Wistar rats, increasing doses of MA (1-14 mg/kg) were administrated twice a day for 14 days. At the 1st, 14th, 28th, and 60th days after MA discontinuation, we measured the PGC1α, TFAM and NRF1 mRNA levels, indicator of mitochondrial biogenesis, and GDNF expression in SN and striatum. Furthermore, we evaluated the glial fibrillary acidic protein (GFAP) and Iba1 mRNA levels, and the levels of tyrosine hydroxylase (TH) and α-synuclein (α-syn) using immunohistochemistry and real-time polymerase chain reaction (PCR). We detected increments in PGC1α and TFAM mRNA levels in SN, but not striatum, and elevations in GDNF levels in SN immediately after MA discontinuation. We also observed increases in GFAP and Iba1 mRNA levels in SN on day 1 and increases in Iba1 mRNA on days 1 and 14 in striatum. Data analysis revealed that the number of TH⁺ cells in the SN did not reduce in any time points, though TH mRNA levels was increased on day 1 after MA discontinuation in SN. These data show that repeated escalating MA induces several compensatory mechanisms, such as mitochondrial biogenesis and elevation in GDNF in SN. These mechanisms can reverse MA-induced neuroinflammation and prevent TH-immunoreactivity reduction in nigrostriatal pathway. J. Cell. Biochem. 118: 1369-1378, 2017. © 2016 Wiley Periodicals, Inc.

Fatty acid nitroalkenes induce resistance to ischemic cardiac injury by modulating mitochondrial respiration at complex II

Nitro-fatty acids (NO₂-FA) are metabolic and inflammatory-derived electrophiles that mediate pleiotropic signaling actions. It was hypothesized that NO₂-FA would impact mitochondrial redox reactions to induce tissue-protective metabolic shifts in cells. Nitro-oleic acid (OA-NO₂) reversibly inhibited complex II-linked respiration in isolated rat heart mitochondria in a pH-dependent manner and suppressed superoxide formation. Nitroalkylation of Fp subunit was determined by BME capture and the site of modification by OA-NO₂ defined by mass spectrometric analysis. These effects translated into reduced basal and maximal respiration and favored glycolytic metabolism in H9C2 cardiomyoblasts as assessed by extracellular H⁺ and O₂ flux analysis. The perfusion of NO₂-FA induced acute cardioprotection in an isolated perfused heart ischemia/reperfusion (IR) model as evidenced by significantly higher rate-pressure products. Together these findings indicate that NO₂-FA can promote cardioprotection by inducing a shift from respiration to glycolysis and suppressing reactive species formation in the post-ischemic interval.

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Nitro-oleic acid (OA-NO₂) reversibly inhibits complex II-linked respiration.

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Nitrated fatty acid favor a switch from beta oxidation to glycolysis in cardiomyoblasts.

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Nitrated fatty acid induce cardioprotection in a heart ischemia/reperfusion model.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

Mitochondria: key players in the neurotoxic effects of amphetamines

Amphetamines are a class of psychotropic drugs with high abuse potential, as a result of their stimulant, euphoric, emphathogenic, entactogenic, and hallucinogenic properties. Although most amphetamines are synthetic drugs, of which methamphetamine, amphetamine, and 3,4-methylenedioxymethamphetamine ("ecstasy") represent well-recognized examples, the use of natural related compounds, namely cathinone and ephedrine, has been part of the history of humankind for thousands of years. Resulting from their amphiphilic nature, these drugs can easily cross the blood-brain barrier and elicit their well-known psychotropic effects. In the field of amphetamines' research, there is a general consensus that mitochondrial-dependent pathways can provide a major understanding concerning pathological processes underlying the neurotoxicity of these drugs. These events include alterations on tricarboxylic acid cycle's enzymes functioning, inhibition of mitochondrial electron transport chain's complexes, perturbations of mitochondrial clearance mechanisms, interference with mitochondrial dynamics, as well as oxidative modifications in mitochondrial macromolecules. Additionally, other studies indicate that amphetamines-induced neuronal toxicity is closely regulated by B cell lymphoma 2 superfamily of proteins with consequent activation of caspase-mediated downstream cell death pathway. Understanding the molecular mechanisms at mitochondrial level involved in amphetamines' neurotoxicity can help in defining target pathways or molecules mediating these effects, as well as in developing putative therapeutic approaches to prevent or treat the acute- or long-lasting neuropsychiatric complications seen in human abusers.

Methamphetamine effects on blood-brain barrier structure and function

Methamphetamine (Meth) is a widely abuse psychostimulant. Traditionally, studies have focused on the neurotoxic effects of Meth on monoaminergic neurotransmitter terminals. Recently, both in vitro and in vivo studies have investigated the effects of Meth on the BBB and found that Meth produces a decrease in BBB structural proteins and an increase in BBB permeability to various molecules. Moreover, preclinical studies are validated by clinical studies in which human Meth users have increased concentrations of toxins in the brain. Therefore, this review will focus on the structural and functional disruption of the BBB caused by Meth and the mechanisms that contribute to Meth-induced BBB disruption. The review will reveal that the mechanisms by which Meth damages dopamine and serotonin terminals are similar to the mechanisms by which the blood-brain barrier (BBB) is damaged. Furthermore, this review will cover the factors that are known to potentiate the effects of Meth (McCann et al., 1998) on the BBB, such as stress and HIV, both of which are co-morbid conditions associated with Meth abuse. Overall, the goal of this review is to demonstrate that the scope of damage produced by Meth goes beyond damage to monoaminergic neurotransmitter systems to include BBB disruption as well as provide a rationale for investigating therapeutics to treat Meth-induced BBB disruption. Since a breach of the BBB can have a multitude of consequences, therapies directed toward the treatment of BBB disruption may help to ameliorate the long-term neurodegeneration and cognitive deficits produced by Meth and possibly even Meth addiction.

Amphetamine- and methamphetamine-induced hyperthermia: Implications of the effects produced in brain vasculature and peripheral organs to forebrain neurotoxicity

The adverse effects of amphetamine- (AMPH) and methamphetamine- (METH) induced hyperthermia on vasculature, peripheral organs and peripheral immune system are discussed. Hyperthermia alone does not produce amphetamine-like neurotoxicity but AMPH and METH exposures that do not produce hyperthermia (≥40°C) are minimally neurotoxic. Hyperthermia likely enhances AMPH and METH neurotoxicity directly through disruption of protein function, ion channels and enhanced ROS production. Forebrain neurotoxicity can also be indirectly influenced through the effects of AMPH- and METH- induced hyperthermia on vasculature. The hyperthermia and the hypertension produced by high doses amphetamines are a primary cause of transient breakdowns in the blood-brain barrier (BBB) resulting in concomitant regional neurodegeneration and neuroinflammation in laboratory animals. This BBB breakdown can occur in the amygdala, thalamus, striatum, sensory and motor cortex and hippocampus. Under these conditions, repetitive seizures greatly enhance neurodegeneration in hippocampus, thalamus and amygdala. Even when the BBB is less disrupted, AMPH- or METH- induced hyperthermia effects on brain vasculature may play a role in neurotoxicity. In this case, striatal and cortical vascular function are adversely affected, and even greater ROS, immune and damage responses are seen in the meninges and cortical surface vasculature. Finally, muscle and liver damage and elevated cytokines in blood can result when amphetamines produce hyperthermia. Proteins, from damaged muscle may activate the peripheral immune system and exacerbate liver damage. Liver damage can further increase cytokine levels, immune system activation and increase ammonia levels. These effects could potentially enhance vascular damage and neurotoxicity.

Differential effects of binge methamphetamine injections on the mRNA expression of histone deacetylases (HDACs) in the rat striatum

Methamphetamine use disorder is characterized by recurrent binge episodes. Humans addicted to methamphetamine experience various degrees of cognitive deficits and show evidence of neurodegenerative processes in the brain. Binge injections of METH to rodents also cause significant toxic changes in the brain. In addition, this pattern of METH injections can alter gene expression in the dorsal striatum. Gene expression is regulated, in part, by histone deacetylation. We thus tested the possibility that METH toxic doses might cause changes in the mRNA levels of histone deacetylases (HDACs). We found that METH did produce significant decreases in the mRNA expression of HDAC8, which is a class I HDAC. METH also decreased expression of HDAC6, HDAC9, and HDAC10 that are class II HDACs. The expression of the class IV HDAC, HDAC11, was also suppressed by METH. The expression of Sirt2, Sirt5, and Sirt6 that are members of class III HDACs was also downregulated by METH injections. Our findings implicate changes in HDAC expression may be an early indicator of impending METH-induced neurotoxicity in the striatum. This idea is consistent with the accumulated evidence that some HDACs are involved in neurodegenerative processes in the brain.

Keto amphetamine toxicity-focus on the redox reactivity of the cathinone designer drug mephedrone

The β-keto amphetamine (cathinone, β-KA) designer drugs such as mephedrone (4-methylmethcathinone, 4-MMC) show a large degree of structural similarity to amphetamines like methamphetamine (METH). However, little is currently known about whether these substances also share the potential neurotoxic properties of their non-keto amphetamine counterparts, or what mechanisms could be involved. Here, we evaluate the cytotoxicity of β-KAs in SH-SY5Y cells using lactate dehydrogenase (LDH) assays, assess the redox potential of a range of β-KAs and non-keto amphetamines using the sensitive redox indicator 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1), and explore the effect of 4-MMC on the formation of protein adducts using ultra-high performance liquid chromatography/high-resolution time-of-flight mass spectrometry (UHPLC-HR-TOFMS) and on the mitochondrial respiratory chain using high-resolution respirometry. We show that treatment with β-KAs increases LDH release. Further, we demonstrate that even under physiological pH, β-KAs are effective and selective-as compared with their non-keto analogues-reductants in the presence of electron acceptors. Increased pH (range 7.6-8.0) greatly enhanced the reactivity up to sixfold. We found no evidence of protein adduct formation, suggesting the reactivity is due to direct electron transfer by the β-KAs. Finally, we show that 4-MMC and METH produce dissimilar effects on the respiratory chain. Our results indicate that β-KAs such as 4-MMC possess cytotoxic properties in vitro. Furthermore, in the presence of an electron-accepting redox partner, the ketone moiety of β-KAs is vital for pH-dependent redox reactivity. Further work is needed to establish the importance of β-KA redox properties and its potential toxicological importance in vivo.

Psychostimulants and brain dysfunction: a review of the relevant neurotoxic effects

Psychostimulants abuse is a major public concern because is associated with serious health complications, including devastating consequences on the central nervous system (CNS). The neurotoxic effects of these drugs have been extensively studied. Nevertheless, numerous questions and uncertainties remain in our understanding of these toxic events. Thus, the purpose of the present manuscript is to review cellular and molecular mechanisms that might be responsible for brain dysfunction induced by psychostimulants. Topics reviewed include some classical aspects of neurotoxicity, such as monoaminergic system and mitochondrial dysfunction, oxidative stress, excitotoxicity and hyperthermia. Moreover, recent literature has suggested new phenomena regarding the toxic effects of psychostimulants. Thus, we also reviewed the impact of these drugs on neuroinflammatory response, blood-brain barrier (BBB) function and neurogenesis. Assessing the relative importance of these mechanisms on psychostimulants-induced brain dysfunction presents an exciting challenge for future research efforts. This article is part of the Special Issue entitled 'CNS Stimulants'.

Co-administration of betulinic acid and methamphetamine causes toxicity to dopaminergic and serotonergic nerve terminals in the striatum of late adolescent rats

Psychostimulant methamphetamine (METH) is toxic to striatal dopaminergic and serotonergic nerve terminals in adult, but not in the adolescent, brain. Betulinic acid (BA) and its derivatives are promising anti-HIV agents with some toxic properties. Many METH users, particularly young men, are HIV-positive; therefore, they might be treated with BA or its derivative for HIV infection. It is not known whether BA, or any of its derivatives, are neurotoxic in combination with METH in the adolescent brain. The present study investigated the effects of BA and binge METH in the striatum of late adolescent rats. BA or METH alone did not decrease the levels of dopaminergic or serotonergic markers in the striatum whereas BA and METH together decreased these markers in a BA dose-dependent manner. BA+METH also caused decreases in the levels of mitochondrial complex I in the same manner; BA alone only slightly decreased the levels of this enzyme in striatal synaptosomes. BA or METH alone increased cytochrome c. METH alone decreased parkin, increased complex II and striatal BA levels. These results suggest that METH in combination with BA can be neurotoxic to striatal dopaminergic and serotonergic nerve terminals in the late adolescent brain via mitochondrial dysfunction and parkin deficit. We report a synergistic neurotoxicity of betulinic acid (BA) and methamphetamine (METH) to monoaminergic terminals in the striatum of male late adolescent rats. BA contribution to the neurotoxicity is decreasing mitochondrial complex I whereas METH contribution is decreasing parkin and increasing brain concentration of BA. We propose that clinical use of BA in young male METH users can be neurotoxic.

Induction of mitochondrial permeability transition (MPT) pore opening and ROS formation as a mechanism for methamphetamine-induced mitochondrial toxicity

During the past 10 years, the use of methamphetamine (METH) has significantly increased in Iran and around the world. The widespread use of 3,4-methylenedioxymethamphetamine as a recreational drug has been responsible for the incidence of several cases of liver failure in young people. This issue made researchers focus on METH toxicity due to the lack of effective treatment and human health risk assessment. There are several reports showing that its long-term use increases the risk for dopamine depletion, but the toxicity mechanisms of METH in liver are not well understood. Therefore, we aimed to investigate the mitochondrial toxicity mechanisms of METH on isolated mitochondria. Rat liver mitochondria were obtained by differential ultracentrifugation, and the isolated mitochondria were then incubated with different concentrations of METH (2.5-20 μM). Our results showed that this agent could induce oxidative stress via rising in mitochondrial reactive oxygen species (ROS) formation, lipid peroxidation, mitochondrial membrane potential collapse, and mitochondrial swelling. In addition, collapse of mitochondrial membrane potential, mitochondrial swelling, and release of cytochrome c following METH treatment were well inhibited by pretreatment of mitochondria with cyclosporin A and butylated hydroxytoluene. Finally, it is suggested that METH could interact with respiratory complexes (II and III) and METH-induced liver toxicity may be the result of its disruptive effect on mitochondrial respiratory chain that is the obvious cause of ROS formation, mitochondrial membrane potential decline, and cytochrome c expulsion which start cell death signaling.

Neurotoxicity of methamphetamine and 3,4-methylenedioxymethamphetamine

Amphetamines are a class of psychostimulant drugs that are widely abused for their stimulant, euphoric, empathogenic and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, methamphetamine and 3,4 methylenedioxymethamphetamine (MDMA) produce persistent damage to dopamine and serotonin nerve terminals. This review summarizes the numerous interdependent mechanisms including excitotoxicity, mitochondrial damage and oxidative stress that have been demonstrated to contribute to this damage. Emerging non-neuronal mechanisms by which the drugs may contribute to monoaminergic terminal damage, as well as the neuropsychiatric consequences of this terminal damage are also presented. Methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) have similar chemical structures and pharmacologic properties compared to other abused substances including cathinone (khat), as well as a relatively new class of novel synthetic amphetamines known as 'bath salts' that have gained popularity among drug abusers.

Methamphetamine decreases levels of glutathione peroxidases 1 and 4 in SH-SY5Y neuronal cells: protective effects of selenium

Methamphetamine interferes with dopamine reuptake, and the resulting increased dopamine oxidation that creates oxidative stress can lead to degeneration of dopaminergic terminals. Previous studies have shown that the trace element selenium protects against methamphetamine toxicity. However, the specific selenoproteins responsible for protection have not been elucidated. Glutathione peroxidases 1 and 4 (GPx1 and GPx4) incorporate selenium into the amino acid selenocysteine, and their known antioxidant functions make them good candidates for protection from methamphetamine-induced oxidative damage. We differentiated SH-SY5Y neuronal cells in serum-free media with defined supplement containing 0, 10 and 100 nM selenium, and then challenged the cells with a 24-h exposure to methamphetamine. We found that 100 μM methamphetamine decreased GPx1 and GPx4 protein levels. However, both proteins were upregulated with increasing media selenium concentration. GPx enzymatic activity was also increased by selenium and decreased by methamphetamine and correlated with GPx protein levels. Total glutathione levels were reduced by methamphetamine at lower selenium conditions, while the oxidized fraction of GSH was increased at higher selenium levels. Additionally, we observed an increased generation of reactive oxygen species with methamphetamine exposure in media with 0 nM selenium, which was ameliorated by selenium supplementation. These results show that methamphetamine increases oxidative stress by reducing GPx levels, and this can be reversed with addition of selenium. These findings have important implications for treating patients with acute methamphetamine toxicity.

The role of dopamine receptors in the neurotoxicity of methamphetamine

Methamphetamine is a synthetic drug consumed by millions of users despite its neurotoxic effects in the brain, leading to loss of dopaminergic fibres and cell bodies. Moreover, clinical reports suggest that methamphetamine abusers are predisposed to Parkinson's disease. Therefore, it is important to elucidate the mechanisms involved in methamphetamine-induced neurotoxicity. Dopamine receptors may be a plausible target to prevent this neurotoxicity. Genetic inactivation of dopamine D1 or D2 receptors protects against the loss of dopaminergic fibres in the striatum and loss of dopaminergic neurons in the substantia nigra. Protection by D1 receptor inactivation is due to blockade of hypothermia, reduced dopamine content and turnover and increased stored vesicular dopamine in D1R(-/-) mice. However, the neuroprotective impact of D2 receptor inactivation is partially dependent on an effect on body temperature, as well as on the blockade of dopamine reuptake by decreased dopamine transporter activity, which results in reduced intracytosolic dopamine levels in D2R(-/-) mice.

Evaluating the role of neuronal nitric oxide synthase-containing striatal interneurons in methamphetamine-induced dopamine neurotoxicity

Production of nitric oxide (NO) has been implicated in methamphetamine (METH)-induced dopamine (DA) neurotoxicity. The source of this NO has not been clearly delineated, but recent evidence suggests that it arises from activation of neuronal nitric oxide synthase (nNOS), which is selectively expressed in a subpopulation of striatal interneurons. Our objective was to determine whether inhibiting activation of nNOS-containing interneurons in the striatum blocks METH-induced neurotoxicity. These interneurons selectively express the neurokinin-1 (NK-1) receptor, which is activated by substance P. One particular toxin, a conjugate of substance P to the ribosome-inactivating protein saporin (SSP-SAP), selectively destroys neurons expressing the NK-1 receptor. Thus, we examined the extent to which depletion of the nNOS-containing interneurons alters production of NO and attenuates METH-induced neurotoxicity. The SSP-SAP lesions resulted in significant loss of nNOS-containing interneurons throughout striatum. Surprisingly, this marked deletion did not confer resistance to METH-induced DA neurotoxicity, even in areas devoid of nNOS-positive cells. Furthermore, these lesions did not attenuate NO production, even in areas lacking nNOS. These data suggest that nNOS-containing interneurons either are not necessary for METH-induced DA neurotoxicity or produce NO that can diffuse extensively through striatal tissue and thereby still mediate neurotoxicity.

Decreased frontal lobe phosphocreatine levels in methamphetamine users

BACKGROUND

Mitochondria-related mechanisms have been suggested to mediate methamphetamine (METH) toxicity. However, changes in brain energetics associated with high-energy phosphate metabolism have not been investigated in METH users. Phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS) was used to evaluate changes in mitochondrial high energy phosphates, including phosphocreatine (PCr) and β-nucleoside triphosphate (β-NTP, primarily ATP in brain) levels. We hypothesized that METH users would have decreased high-energy PCr levels in the frontal gray matter.

METHODS

Study participants consisted of 51 METH (age=32.8±6.7) and 23 healthy comparison (age=31.1±7.5) subjects. High-energy phosphate metabolite levels were compared between the groups and potential gender differences were explored.

RESULTS

METH users had lower ratios of PCr to total pool of exchangeable phosphate (PCr/TPP) in the frontal lobe as compared to the healthy subjects (p=.001). The lower PCr levels in METH subjects were significantly associated with lifetime amount of METH use (p=.003). A sub-analysis for gender differences revealed that female METH users, who had lower daily amounts (1.1±1.0g) of METH use than males (1.4±1.7g), had significantly lower PCr/TPP ratios than male METH users, controlling for the amount of METH use (p=.02).

CONCLUSIONS

The present findings suggest that METH compromises frontal lobe high-energy phosphate metabolism in a dose-responsive manner. Our findings also suggest that the abnormality in frontal lobe high-energy phosphate metabolism might be more prominent in female than in male METH users. This is significant as decreased PCr levels have been associated with depressive symptoms, and poor responses to antidepressant treatment have been reported in those with decreased PCr levels.

Chronic exposure to corticosterone enhances the neuroinflammatory and neurotoxic responses to methamphetamine

Up-regulation of proinflammatory cytokines and chemokines in brain ("neuroinflammation") accompanies neurological disease and neurotoxicity. Previously, we documented a striatal neuroinflammatory response to acute administration of a neurotoxic dose of methamphetamine (METH), i.e. one associated with evidence of dopaminergic terminal damage and activation of microglia and astroglia. When we used minocycline to suppress METH-induced neuroinflammation, indices of dopaminergic neurotoxicity were not affected, but suppression of neuroinflammation was incomplete. Here, we administered the classic anti-inflammatory glucocorticoid, corticosterone (CORT), in an attempt to completely suppress METH-related neuroinflammation. METH alone caused large increases in striatal proinflammatory cytokine/chemokine mRNA and subsequent astrocytic hypertrophy, microglial activation, and dopaminergic nerve terminal damage. Pre-treatment of mice with acute CORT failed to prevent neuroinflammatory responses to METH. Surprisingly, when mice were pre-treated with chronic CORT in the drinking water, an enhanced striatal neuroinflammatory response to METH was observed, an effect that was accompanied by enhanced METH-induced astrogliosis and dopaminergic neurotoxicity. Chronic CORT pre-treatment also sensitized frontal cortex and hippocampus to mount a neuroinflammatory response to METH. Because the levels of chronic CORT used are associated with high physiological stress, our data suggest that chronic CORT therapy or sustained physiological stress may sensitize the neuroinflammatory and neurotoxicity responses to METH.

Prevention of methamphetamine-induced microglial cell death by TNF-α and IL-6 through activation of the JAK-STAT pathway

Background

It is well known that methamphetamine (METH) is neurotoxic and recent studies have suggested the involvement of neuroinflammatory processes in brain dysfunction induced by misuse of this drug. Indeed, glial cells seem to be activated in response to METH, but its effects on microglial cells are not fully understood. Moreover, it has been shown that cytokines, which are normally released by activated microglia, may have a dual role in response to brain injury. This led us to study the toxic effect of METH on microglial cells by looking to cell death and alterations of tumor necrosis factor-alpha (TNF-α) and interleukine-6 (IL-6) systems, as well as the role played by these cytokines.

Methods

We used the N9 microglial cell line, and cell death and proliferation were evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay and incorporation of bromodeoxyuridine, respectively. The TNF-α and IL-6 content was quantified by enzyme-linked immunosorbent assay, and changes in TNF receptor 1, IL-6 receptor-alpha, Bax and Bcl-2 protein levels by western blotting. Immunocytochemistry analysis was also performed to evaluate alterations in microglial morphology and in the protein expression of phospho-signal transducer and activator of transcription 3 (pSTAT3).

Results

METH induced microglial cell death in a concentration-dependent manner (EC₅₀ = 1 mM), and also led to significant morphological changes and decreased cell proliferation. Additionally, this drug increased TNF-α extracellular and intracellular levels, as well as its receptor protein levels at 1 h, whereas IL-6 and its receptor levels were increased at 24 h post-exposure. However, the endogenous proinflammatory cytokines did not contribute to METH-induced microglial cell death. On the other hand, exogenous low concentrations of TNF-α or IL-6 had a protective effect. Interestingly, we also verified that the anti-apoptotic role of TNF-α was mediated by activation of IL-6 signaling, specifically the janus kinase (JAK)-STAT3 pathway, which in turn induced down-regulation of the Bax/Bcl-2 ratio.

Conclusions

These findings show that TNF-α and IL-6 have a protective role against METH-induced microglial cell death via the IL-6 receptor, specifically through activation of the JAK-STAT3 pathway, with consequent changes in pro- and anti-apoptotic proteins.