Systemic administration of d-amphetamine induces long-lasting oxidative stress in the rat striatum

Role of nitric oxide in psychostimulant-induced neurotoxicity

In recent decades, consumption of psychostimulants has been significantly increased all over the world, while exact mechanisms of neurochemical effects of psychomotor stimulants remained unclear. It is assumed that the neuronal messenger nitric oxide (NO) may be involved in mechanisms of neurotoxicity evoked by psychomotor stimulants. However, possible participation of NO in various pathological states is supported mainly by indirect evidence because of its short half-life in tissues. Aim of this review is to describe the involvement of NO and the contribution of lipid peroxidation (LPO) and acetylcholine (ACH) release in neurotoxic effects of psychostimulant drugs. NO was directly determined in brain structures by electron paramagnetic resonance (EPR). Both NO generation and LPO products as well as release of ACH were increased in brain structures following four injections of amphetamine (AMPH). Pretreatment of rats with the non-selective inhibitor of NO-synthase (NOS) N-nitro-L-arginine or the neuronal NOS inhibitor 7-nitroindazole significantly reduced increase of NO generation as well as the rise of ACH release induced by AMPH. Both NOS inhibitors injected prior to AMPH had no effect on enhanced levels of LPO products. Administration of the noncompetitive NMDA receptor antagonist dizocilpine abolished increase of both NO content and concentration of LPO products induced by of the psychostimulant drug. Dizocilpine also eliminated the influence of AMPH on the ACH release. Moreover, the neurochemical and neurotoxic effects of the psychostimulant drug sydnocarb were compared with those of AMPH. Single injection of AMPH showed a more pronounced increase in NO and TBARS levels than after an equimolar concentration of sydnocarb. The findings demonstrate the crucial role of NO in the development of neurotoxicity elicited by psychostimulants and underline the key role of NOS in AMPH-induced neurotoxicity.

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.

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'.

Toxicity of amphetamines: an update

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review.

Pharmacologic Management of Parkinson Disease: Choice of Initial Therapy in Early Disease

The most efficacious symptomatic agent for Parkinson's disease is levodopa; however, the development of motor complications with long-term therapy is concerning. In the modern day treatment of Parkinson's disease, non-levodopa agents (eg, dopamine agonists, monoamine oxidase type B inhibitors) should be considered as appropriate initial treatments. In early Parkinson's disease, dopamine agonists provide effective symptomatic therapy, reduce the risk for motor complications, and delay the need to initiate levodopa. However, the dopamine agonists are associated with impulse control disorders and behaviors that are concerning. Monoamine oxidase type B inhibitors are also effective as monotherapy for early stage Parkinson's disease. Clinical data demonstrate that early initiation of rasagiline (in the absence of functional impairment) is associated with improved outcomes as opposed to delayed initiation. Selegiline can delay the need for levodopa, albeit its clinical effectiveness as monotherapy is equivocal. When selecting initial therapy for early Parkinson's disease, clinicians must consider both short-term and long-term benefits and risks.

Proteomic profiling of proteins associated with methamphetamine-induced neurotoxicity in different regions of rat brain

It is well documented that methamphetamine (MA) can cause obvious damage to the brain, but the exact mechanism is still unknown. In the present study, proteomic methods of two-dimensional gel electrophoresis in combination with mass spectrometry analysis were used to identify global protein profiles associated with MA-induced neurotoxicity. For the first time, 30 protein spots have been found differentially expressed in different regions of rat brain, including 14 in striatum, 12 in hippocampus and 4 in frontal cortex. The proteins identified by tandem mass spectrometry were Cu, Zn superoxide dismutase, dimethylarginine dimethylaminohydrolase 1, alpha synuclein, ubiquitin-conjugating enzyme E2N, stathmin 1, calcineurin B, cystatin B, subunit of mitochondrial H-ATP synthase, ATP synthase D chain, mitochondrial, NADH dehydrogenase(ubiquinone) Fe-S protein 8, glia maturation factor, beta, Ash-m, neurocalcin delta, myotrophin, profiling IIa, D-dopachrome tautomerase, and brain lipid binding protein. The known functions of these proteins were related to the pathogenesis of MA-induced neurotoxicity, including oxidative stress, degeneration/apoptosis, mitochontrial/energy metabolism and others. Of these proteins, alpha-synuclein was up-regulated, and ATP synthase D chain, mitochondrial was down-regulated in all brain regions. Two proteins, Cu, Zn superoxide dismutase, subunit of mitochondrial H-ATPsynthase were down-regulated and Ubiquitin-conjugating enzyme E2N, NADH dehydrogenase (ubiquinone) Fe-S protein 8 were up-regulated simultaneously in striatum and hippocaltum. The expression of dimethylarginine dimethylaminohydrolase 1 (DDAH 1) increased both in striatum and frontal cortex. The parallel expression patterns of these proteins suggest that the pathogenesis of MA neurotoxicity in different brain regions may share some same pathways.

Levels of 4-Hydroxynonenal and Malondialdehyde Are Increased in Brain of Human Chronic Users of Methamphetamine

Animal studies suggest that the widely used psychostimulant drug methamphetamine (MA) can harm brain dopamine neurones, possibly by causing oxidative damage. However, evidence of oxidative damage in brain of human MA users is lacking. We tested the hypothesis that levels of two "gold standard" products generated from lipid peroxidation, 4-hydroxynonenal (one of the most reactive lipid peroxidation aldehyde products) and malondialdehyde, would be elevated in post mortem brain of 16 dopamine-deficient chronic MA users compared with those in 21 matched control subjects. Derivatized aldehyde concentrations were determined by gas chromatography-mass spectrometry. In the MA group, we found significantly increased levels of 4-hydroxynonenal and malondialdehyde in the dopamine-rich caudate nucleus (by 67 and 75%, respectively) and to a lesser extent in frontal cortex (48 and 36%, respectively) but not in the cerebellar cortex. Approximately half of the MA users had levels of 4-hydroxynonenal falling above the upper limit of the control range in caudate and frontal cortex. A subgroup of MA users with high brain drug levels had higher concentrations of the aldehydes. Our data suggest that MA exposure in human causes, as in experimental animals, above-normal formation of potentially toxic lipid peroxidation products in brain. This provides evidence for involvement of oxygen-based free radicals in the action of MA in both dopamine-rich (caudate) and -poor (cerebral cortex) areas of human brain.

The effects of exposure to extremely low-frequency magnetic field and amphetamine on the reduced glutathione in the brain

Continuous exposure to extremely low-frequency magnetic field (ELF-MF, 50 Hz, 0.5 mT) alone and combined with D-amphetamine (1.5 mg/kg) affected the reduced glutathione content in brain regions of rats. Compared to sham-exposed rats, the glutathione content in the forebrain cortex of the ELF-MF-exposed rats decreased (P < 0.001), but this reverted after giving amphetamine upon ELF-MF exposure. In this group, the glutathione content was increased in the brain stem and cerebellum (P < 0.05 compared to the sham-exposed, ELM-MF-exposed, and amphetamine-treated groups). It is suggested that biogenic monoamines are involved in the reduced glutathione changes observed. The changes are not uniform in the brain regions examined.

Increased oxidative stress in submitochondrial particles after chronic amphetamine exposure

Previous studies have suggested that reactive oxygen species (ROS) production may play a role in the pathophysiology of many neuropsychiatric disorders, such as bipolar disorder (BD) and schizophrenia (SCZ). In addition, there is an emerging body of data indicating that BD and SCZ may be associated with mitochondrial dysfunction. We studied the effects of acute and chronic d-amphetamine on ROS production in submitochondrial particles of rat brain. Male Wistar rats were divided in two experimental groups: acute and chronic treatment. In the acute treatment, rats received one single IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline (control group). In the chronic treatment, rats received one daily IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline for 7 days. Locomotor activity was assessed with the open field task, and thiobarbituric acid reactive substances (TBARS) and superoxide production were measured in submitochondrial particles of the prefrontal cortex and hippocampus. Both acute and chronic amphetamine treatment increased locomotor behavior. Chronic amphetamine exposure induced a 3- to 6-fold increase of TBARS and a 1.5- to 2-fold increase of superoxide production in submitochondrial particles of prefrontal cortex and hippocampus (P < 0.05). No effects on superoxide or TBARS were observed with acute treatment. These findings suggest that amphetamine-induced mitochondrial ROS generation may be a useful model to investigate the hypothesis of altered brain energy metabolism associated with BD and SCZ. Further studies assessing the effects of mood stabilizers and antipsychotics in preventing mitochondrial oxidative stress are necessary.

Effects of alpha-phenyl-N-tert-butyl nitrone and N-acetylcysteine on hydroxyl radical formation and dopamine depletion in the rat striatum produced by d-amphetamine

Previous studies have shown that treatment with free radical scavengers attenuated the D-amphetamine (AMPH) neurotoxicity. But several of these agents also prevent AMPH-induced elevation of body temperature in the rat. Thus, further studies are needed to determine if blockade of the production of free radical or hypothermia are related to the neuroprotective mechanism of the free radical scavengers for AMPH neurotoxicity. In the present study, we examined the effects of the free radical scavengers alpha-phenyl-N-tert-butyl nitrone (PBN) and N-acetylcysteine (NAC) on long-term depletion of striatal dopamine (DA) and lipid peroxidation formation and on hyperthermia induced by AMPH. We also determined their effects on acute hydroxyl radical formation after direct intrastriatal infusion of AMPH. The results showed that both significantly attenuated long-term DA depletion and lipid peroxidation formation in the rat striatum at the dose range that did not block hyperthermia induced by AMPH. These agents also completely inhibited the production of hydroxyl radical after AMPH infusion into the striatum. Our results suggest that free radical scavengers such as PBN and NAC could protect against AMPH-induced oxidative stress and DAergic terminal toxicity via their free radical removing property independent of lowering the core body temperature of rats, and imply that supplement with antioxidants is a potential strategy in the treatment of AMPH neurotoxicity.

Effect of acute and chronic psychostimulant drugs on redox status, AP-1 activation and pro-enkephalin mRNA in the human astrocyte-like U373 MG cells

In order to approach the astroglial implication of addictive and neurotoxic processes associated with psychostimulant drug abuse, the effects of amphetamine or cocaine (1-100 microM) on redox status, AP-1 transcription factor and pro-enkephalin, an AP-1 target gene, were investigated in the human astrocyte-like U373 MG cells. We demonstrated an early increase in the generation of radical oxygen species and in the formation of 4-hydroxynonenal-adducts reflecting the pro-oxidant action of both substances. After 1 h or 96 h of treatment, Fos and Jun protein levels were altered and the DNA-binding activity of AP-1 was increased in response to both substances. Using supershift experiments, we observed that the composition of AP-1 dimer differed according to the substance and the duration of treatment. FRA-2 protein represented the main component of the chronic amphetamine- or cocaine-activated complexes, which suggests its relevance in the long-term effects of psychostimulant drugs. Concomitantly, the pro-enkephalin gene was differently regulated by either 6 h or 96 h of treatment. Because astrocytes interact extensively with the neurons in the brain, our data led us to conclude that oxidation-regulated AP-1 target genes may represent one of the molecular mechanisms underlying neuronal adaptation associated with psychostimulant dependence.

Pharmacological properties of the anti-Parkinson drug rasagiline; modification of endogenous brain amines, reserpine reversal, serotonergic and dopaminergic behaviours

Rasagiline [N-propargyl-1R(+)-aminoindan; TVP1012] is a potent irreversible monoamine oxidase (MAO) inhibitor with selectivity for type B of the enzyme, which is being developed for treatment of Parkinson's disease. In this study we examined effects of rasagiline on CNS monoamine levels, modification of behavioural response to L-tryptophan, fluoxetine and L-DOPA, and reversal of reserpine syndrome. Reserpine-induced ptosis was reversed by rasagiline at doses above 2 mg x kg(-1) i.p., which inhibit MAO-A as well as MAO-B, but not at MAO-B-selective doses. However, combination of rasagiline (10 mg x kg(-1) i.p.) with L-DOPA or L-tryptophan (50 mg x kg(-1) i.p.), or rasagiline (10 mg x kg(-1) p.o.) with fluoxetine (10 mg x kg(-1) p.o.), did not induce the behavioural hyperactivity syndrome which is seen following inhibition of both MAO-A and MAO-B by tranylcypromine together with the monoamine precursors. Following oral administration, levels of noradrenaline (NA), 5-hydroxytryptamine (5-HT) and dopamine (DA) were unaffected in hippocampus and striatum after single doses of rasagiline up to 2 mg x kg(-1). Following chronic oral administration (21 days, one dose daily), levels of NA, 5-HT and DA in hippocampus and striatum were unaffected by rasagiline at doses up to 1 mg x kg(-1). Rasagiline does not modify CNS monoamine tissue levels or monoamine-induced behavioural syndromes at doses which selectively inhibit MAO-B but not MAO-A.

Free radicals mediate amphetamine-induced acute pulmonary edema in isolated rat lung

Intravenous amphetamine abuse may cause serious cardiopulmonary complications via unknown mechanisms. We investigated the role of free radicals in the amphetamine-induced lung injury using isolated rat lungs. Adding amphetamine into the perfusate caused dose-dependent increases in perfusion pressure and lung weight. Amphetamine increased the filtration coefficient (K(f)) by 90 +/- 20% and 210 +/- 10% at doses of 10 microM and 50 microM, respectively, as compared to the baseline level. Pretreatment with dimethylthiourea (DMTU), an oxygen radical scavenger, abolished the pulmonary hypertension, lung weight gain, and permeability changes. We also examined the effect of amphetamine on free radical generation in polymorphonuclear leukocytes (PMN). Adding phorbol myristate acetate (PMA, 1 nM) enhanced the chemiluminescence indicating the functional viability of the isolated PMN. Amphetamine (50 microM) significantly enhanced the chemiluminescence generation of PMN by 152 +/- 26% as compared with the baseline value. Combination of amphetamine and PMA increased free radical formation by 360 +/- 85%. In summary, our results showed that amphetamine may cause acute lung injury by overproduction of free radicals. Although amphetamine can activate PMN, the source of free radicals remains to be determined.

Dopamine transporter-dependent induction of C-Fos in HEK cells

The psychostimulants cocaine and amphetamine increase expression of the immediate early gene (IEG) c-fos indirectly, via D1 dopamine receptor activation. To determine whether dopamine transporter substrates and inhibitors can affect c-Fos expression directly, we investigated their effects on c-Fos protein and c-fos mRNA in HEK-293 (HEK) cells transfected with the human dopamine transporter (hDAT). In untransfected HEK cells, methylphenidate and cocaine produced a small but statistically significant increase in c-Fos, whereas dopamine and amphetamine did not. In hDAT cells, DAT substrates (dopamine, amphetamine) increased c-Fos immunoreactivity 6- and 3-fold (respectively). The DAT inhibitors cocaine, methylphenidate, and bupropion also increased c-Fos approximately 3-fold in hDAT cells. If coincubated with dopamine, the inhibitors attenuated dopamine-induced c-Fos in hDAT cells. The magnitude of c-fos mRNA induction by substrates and inhibitors paralleled induction of c-Fos protein immunoreactivity. The results indicate that substrates or inhibitors of the DAT can trigger induction of IEG expression in the absence of D1 dopamine receptor. For substrates, IEG induction is DAT-dependent, but for certain DAT inhibitors the cellular response can be elicited in the absence of the DAT in HEK cells. Oxidative stress may partly, but not fully, account for the DA-induced c-Fos induction as an inhibitor of oxidative stress Trolox C, attenuated DA-induced c-Fos induction. Protein kinase C (PKC) may also partially account for c-Fos induction as a specific inhibitor of PKC Bisindolylmaleimide I (BIS) attenuated DA-induced c-Fos by 50%. DAT substrate and inhibitor effects on IEGs, other fos-related antigens, and possible mechanisms that contribute to c-Fos induction warrant investigation in presynaptic neurons as a potential contribution to the long-term effects of psychostimulants.

The polychlorinated biphenyl mixture aroclor 1254 induces death of rat cerebellar granule cells: the involvement of the N-methyl-D-aspartate receptor and reactive oxygen species

Polychlorinated biphenyls (PCBs) are widespread persistent environmental contaminants that display a complex spectrum of toxicological properties, including neurotoxicity. The present study investigates the effects of the PCB mixtures Aroclor 1242 (A1242) and Aroclor 1254 (A1254), and the PCB congeners 126 (3,3',4,4',5,-PeCB) and 153 (2,2',4,4',5,5'-HxCB) on formation of reactive oxygen species (ROS) and cell death in cultured rat cerebellar granule cells. The increase of ROS and induction of cell death were assayed using the fluorescent probe 2,7-dichlorofluorescin diacetate (DCFH-DA) and the trypan blue exclusion assay, respectively. A1242 and A1254 and PCB 153 induced a concentration-dependent increase in cell death and ROS formation. A1254 was selected for mechanistic studies. When the cerebellar granule cells were exposed to 15 microM A1254 for 12 h, 95% of the cells died. Both PCB-mediated cell death and the increase of the ROS formation were inhibited by MK-801, demonstrating the importance of the N-methyl-D-aspartate receptor. Inhibitors of nitric oxide synthase and phospholipase A2 led to a significant reduction of the DCF fluorescence and cell death. The mitochondrial permeability transition pore blocker cyclosporin A and the antioxidant vitamin E also increased survival and reduced ROS formation. The results show a connection between cell death and free radical formation.

Parallel increases in lipid and protein oxidative markers in several mouse brain regions after methamphetamine treatment

The neurotoxic actions of methamphetamine (METH) may be mediated in part by reactive oxygen species (ROS). Methamphetamine administration leads to increases in ROS formation and lipid peroxidation in rodent brain; however, the extent to which proteins may be modified or whether affected brain regions exhibit similar elevations of lipid and protein oxidative markers have not been investigated. In this study we measured concentrations of TBARs, protein carbonyls and monoamines in various mouse brain regions at 4 h and 24 h after the last of four injections of METH (10 mg/kg/injection q 2 h). Substantial increases in TBARs and protein carbonyls were observed in the striatum and hippocampus but not the frontal cortex nor the cerebellum of METH-treated mice. Furthermore, lipid and protein oxidative markers were highly correlated within each brain region. In the hippocampus and striatum elevations in oxidative markers were significantly greater at 24 h than at 4 h. Monoamine levels were maximally reduced within 4 h (striatal dopamine [DA] by 95% and serotonin [5-HT] in striatum, cortex and hippocampus by 60-90%). These decrements persisted for 7 days after METH, indicating effects reflective of nerve terminal damage. Interestingly, NE was only transiently depleted in the brain regions investigated (hippocampus and cortex), suggesting a pharmacological and non-toxic action of METH on the noradrenergic nerve terminals. This study provides the first evidence for concurrent formation of lipid and protein markers of oxidative stress in several brain regions of mice that are severely affected by large neurotoxic doses of METH. Moreover, the differential time course for monoamine depletion and the elevations in oxidative markers indicate that the source of oxidative stress is not derived directly from DA or 5HT oxidation.