Involvement of oxidative and L-arginine-NO pathways in the neurotoxicity of drugs of abuse in vitro

Total antioxidant capacity is significantly lower in cocaine-dependent and methamphetamine-dependent patients relative to normal controls: results from a preliminary study

BACKGROUND

Oxidative stress can result in damage to the brain and other organs. To protect from oxidative damage, the human body possesses molecular defense systems, based on the activity of antioxidants, and enzymatic defense systems, including the enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Although pre-clinical research has shown that stimulant use is associated with oxidative damage, oxidative stress and the antioxidant defense systems have not been evaluated in clinical samples of stimulant-dependent patients.

OBJECTIVES

This study aimed to investigate the link between stimulant dependence and oxidative stress.

METHODS

Peripheral blood samples from 174 methamphetamine (n = 48) and/or cocaine-dependent (n = 126) participants as well as 30 normal control participants were analyzed for the enzyme activities of CAT, SOD, and GSH-Px in the erythrocytes and the total antioxidant capacity and the malondialdehyde concentration in the plasma.

RESULTS

We could show an association of stimulant dependence with a depletion of total antioxidant capacity to 54.6 ± 4.7%, which correlates with a reduced activity of the SOD to 71.3 ± 0.03% compared with healthy control participants (100%).

CONCLUSION

Stimulant-dependent patients had significantly lower antioxidant capacity relative to controls, suggesting that they may be at greater risk for oxidative damage to the brain and other organs.

Synergism between methamphetamine and the neuropeptide substance P on the production of nitric oxide in the striatum of mice

Our laboratory has been investigating the participation of striatal neurokinin-1 receptors in the methamphetamine (METH)-induced loss of striatal neurons. Signaling through these receptors exacerbates the METH-induced striatal apoptosis. METH induces the synthesis of nitric oxide (NO) and the latter has been linked to the activation of neurodegenerative cascades. In the present study, we assessed the role of the neurokinin-1 receptor in the production of striatal 3-nitrotyrosine (3-NT) and l-citrulline (indirect indices of NO production). To that end, we injected male mice with a bolus of METH (30 mg/kg, ip) and visualized striatal neuronal nitric oxide synthase (NOS)-positive cells by immunohistochemistry and protein levels by Western blot. The expression of neuronal NOS or protein levels at 2, 4 and 8 hours post-METH was unchanged. Next, we assessed 3-NT and l-citrulline by immunohistochemistry. At 4 hours post-METH, striatal 3-NT and l-citrulline levels were increased 30- and 5-fold, respectively, relative to controls and the selective neurokinin-1 receptor antagonist WIN-51,708 attenuated these increases. Intrastriatal infusion of the neurokinin-1 receptor agonist GR-73632 induced striatal 3-NT production that was attenuated with systemic injection of WIN-51,708 or 7-nitroindazole (7-NI, an inhibitor of neuronal NOS). Moreover, infusion of calmidazolium (calmodulin inhibitor) with GR-73632 prevented the production of 3-NT. These data are consistent with the hypothesis that METH-induced production of NO is modulated by the striatal neurokinin-1 receptors and that this receptor may participate in the biochemical activation of neuronal NOS.

Enhanced tau phosphorylation in the hippocampus of mice treated with 3,4-methylenedioxymethamphetamine ("Ecstasy")

3,4-Methylenedioxymethamphetamine (MDMA) ("Ecstasy") produces neurotoxic effects, which result into an impairment of learning and memory and other neurological dysfunctions. We examined whether MDMA induces increases in tau protein phosphorylation, which are typically associated with Alzheimer's disease and other chronic neurodegenerative disorders. We injected mice with MDMA at cumulative doses of 10-50 mg/kg intraperitoneally, which are approximately equivalent to doses generally consumed by humans. MDMA enhanced the formation of reactive oxygen species and induced reactive gliosis in the hippocampus, without histological evidence of neuronal loss. An acute or 6 d treatment with MDMA increased tau protein phosphorylation in the hippocampus, revealed by both anti-phospho(Ser(404))-tau and paired helical filament-1 antibodies. This increase was restricted to the CA2/CA3 subfields and lasted 1 and 7 d after acute and repeated MDMA treatment, respectively. Tau protein was phosphorylated as a result of two nonredundant mechanisms: (1) inhibition of the canonical Wnt (wingless-type MMTV integration site family) pathway, with ensuing activation of glycogen synthase kinase-3beta; and (2) activation of type-5 cyclin-dependent kinase (Cdk5). MDMA induced the expression of the Wnt antagonist, Dickkopf-1, and the expression of the Cdk5-activating protein, p25. In addition, the increase in tau phosphorylation was attenuated by strategies that rescued the Wnt pathway or inhibited Cdk5. Finally, an impairment in hippocampus-dependent spatial learning was induced by doses of MDMA that increased tau phosphorylation, although the impairment outlasted this biochemical event. We conclude that tau hyperphosphorylation in the hippocampus may contribute to the impairment of learning and memory associated with MDMA abuse.

DNA fragmentation and oxidative stress in the hippocampal formation: a bridge between 3,4-methylenedioxymethamphetamine (ecstasy) intake and long-lasting behavioral alterations

Intake of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) in humans leads to marked behavioral alterations. In a recent paper, we demonstrated that chronic MDMA intake produces a latent hippocampal hyperexcitability that parallels a reduced threshold for limbic seizures and a slowing of electroencephalographic activity. These phenomena suggest an alteration in hippocampal function. So far, only a few studies have focused on the hippocampal formation as a potential target for the effects induced by MDMA. In this study we sought to evaluate whether the intrinsic cells of the hippocampus might be modified chronically by ecstasy intake. In particular, we examined whether administration of MDMA, at doses producing hippocampal hyperexcitability also produces rearrangements of DNA strands measured by the comet assay. We found that MDMA, at very low doses, comparable with those self-administered by humans, produces acute oxidative stress and DNA single and double-strand breaks, which persist together with long-lasting metabolic changes in the hippocampal formation. These persisting effects are accompanied by behavioral sensitization, reduced seizure threshold and long-lasting slowing of electroencephalographic activity, and hyperexcitability of the hippocampus, without affecting the basal ganglia. The present data indicate that the intake of very low doses of MDMA, comparable to those consumed by humans, produces selective hippocampal alterations which may underlie cognitive impairment and seizure susceptibility.

Evidence for the Involvement of Nitric Oxide in 3,4-Methylenedioxymethamphetamine-Induced Serotonin Depletion in the Rat Brain

Production of reactive oxygen and/or nitrogen species has been thought to contribute to the long-term depletion of brain dopamine and serotonin (5-HT) produced by amphetamine derivatives, i.e., methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA). In the present study, the effects of nitric-oxide synthase (NOS) inhibitors were examined on the long-term depletion of striatal dopamine and/or 5-HT produced by the local perfusion of malonate and MDMA or the systemic administration of MDMA. The effect of MDMA on nitric oxide formation and nitrotyrosine concentration also was determined. Perfusion with MDMA and malonate resulted in a 34% reduction of 5-HT and 49% reduction of dopamine concentrations in the striatum. The systemic administration of NOS inhibitors, N(omega)-nitro-l-arginine methyl ester hydrochloride and S-methyl-l-thiocitrulline (S-MTC), and the peroxynitrite decomposition catalyst Fe(III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride attenuated the MDMA- and malonate-induced depletion of striatal dopamine and 5-HT. S-MTC also attenuated the depletion of 5-HT in the striatum produced by the systemic administration of MDMA without attenuating MDMA-induced hyperthermia. Additionally, the systemic administration of MDMA significantly increased the formation of nitric oxide and the nitrotyrosine concentration in the striatum. These results support the conclusion that MDMA produces reactive nitrogen species in the rat that contribute to the neurotoxicity of this amphetamine analog.

Inhibitory effects of flavonoids from Hypericum perforatum on nitric oxide synthase

The inhibitory effects of six flavonoids from Hypericum perforatum were assessed spectrophotometrically using nitric oxide synthase (NOS) in blood and cerebral homogenate of rats. Of the assayed compounds, quercetin and hyperoside showed concentration-dependent enzyme inhibitory actions. The IC50 values of quercetin for inhibiting NOS in rat cerebral homogenate and blood were 63.06 and 57.54 microM, and those of hyperoside 56.23 and 158.49 microM, respectively. The competitive patterns were discerned with the inhibition of the two flavonoids on NOS in serum and cerebral homogenate (except a mixed type inhibition was observed with quercetin in inhibiting cerebral NOS). Furthermore, similar inhibitions were found for quercetin upon NOS in cerebral homogenate and blood. However, a stronger inhibitory effect of hyperoside on the enzyme was discerned in cerebrum than in blood. These results suggested that the galactose moiety in hyperoside may be associated with the selectivity of the NOS inhibition.

A study of the mechanisms involved in the neurotoxic action of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') on dopamine neurones in mouse brain

1. Administration of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') to mice produces acute hyperthermia and long-term degeneration of striatal dopamine nerve terminals. Attenuation of the hyperthermia decreases the neurodegeneration. We have investigated the mechanisms involved in producing the neurotoxic loss of striatal dopamine. 2. MDMA produced a dose-dependent loss in striatal dopamine concentration 7 days later with 3 doses of 25 mg kg(-1) (3 h apart) producing a 70% loss. 3. Pretreatment 30 min before each MDMA dose with either of the N-methyl-D-aspartate antagonists AR-R15896AR (20, 5, 5 mg kg(-1)) or MK-801 (0.5 mg kg(-1)x3) failed to provide neuroprotection. 4. Pretreatment with clomethiazole (50 mg kg(-1)x3) was similarly ineffective in protecting against MDMA-induced dopamine loss. 5. The free radical trapping compound PBN (150 mg kg(-1)x3) was neuroprotective, but it proved impossible to separate neuroprotection from a hypothermic effect on body temperature. 6. Pretreatment with the nitric oxide synthase (NOS) inhibitor 7-NI (50 mg kg(-1)x3) produced neuroprotection, but also significant hypothermia. Two other NOS inhibitors, S-methyl-L-thiocitrulline (10 mg kg(-1)x3) and AR-R17477AR (5 mg kg(-1)x3), provided significant neuroprotection and had little effect on MDMA-induced hyperthermia. 7. MDMA (20 mg kg(-1)) increased 2,3-dihydroxybenzoic acid formation from salicylic acid perfused through a microdialysis tube implanted in the striatum, indicating increased free radical formation. This increase was prevented by AR-R17477AR administration. Since AR-R17477AR was also found to have no radical trapping activity this result suggests that MDMA-induced neurotoxicity results from MDMA or dopamine metabolites producing radicals that combine with NO to form tissue-damaging peroxynitrites.

Methamphetamine potentiates ischemia/reperfusion insults after transient middle cerebral artery ligation

BACKGROUND AND PURPOSE

Previous studies have indicated that both methamphetamine (MA) and ischemia/reperfusion injuries involve reactive oxygen species formation and activation of apoptotic mechanism. That MA could have a synergistic or additive effect with stroke-induced brain damage is possible. The purpose of the present study was to investigate whether administration of MA in vivo would potentiate ischemic brain injury.

METHODS

Adult CD-1 mice were pretreated with MA or saline. Each animal later was anesthetized with chloral hydrate and placed in a stereotaxic frame. A subset of animals received intracerebral administration of glial cell line-derived neurotrophic factor (GDNF). The right middle cerebral artery and bilateral carotids were transiently occluded for 45 minutes. Regional cerebral blood flow was measured by laser Doppler. Animals were sacrificed for triphenyltetrazolium chloride staining and p53 mRNA Northern blot assay after 24 hours of reperfusion. Cortical and striatal GDNF levels were assayed by ELISA.

RESULTS

We found that pretreatment with MA increased ischemia-induced cerebral infarction. Ischemia or MA alone enhanced p53 mRNA expression. Moreover, MA potentiated expression of p53 mRNA in the ischemic mouse brain. MA pretreatment decreased GDNF levels in ischemic striatum. Intracerebral administration of GDNF before ischemia reduced MA-facilitated infarction.

CONCLUSIONS

Our data indicate that MA exacerbates ischemic insults in brain, perhaps through the inhibition of GDNF-mediated pathways and suggest that MA may antagonize endogenous neuroprotective pathways as part of its mechanism of action.

Free radical scavengers: chemical concepts and clinical relevance

Free radicals are involved in the pathology of many CNS disorders, like Parkinson's disease, Alzheimer's disease, or stroke. This discovery lead to the development of many radical scavengers for the clinical treatment of neurodegenerative diseases. In this review, the different chemical concepts for free radical scavenging will be discussed: nitrons, thiols, iron chelators, phenols, and catechols. Especially catechols, like the naturally occurring flavonols, the synthetic drug nitecapone, or the endogenous catacholamines and their metabolites, are of great interest, as they combine iron chelating with radical scavenging activity. We present data on the radical scvenging activity of dopamine and apomorphine, which prevent lipid peroxidation in rat brain mitochondria and protect PC12 cells against H2O2-toxicity.

Amphetamines induce apoptosis and regulation of bcl-x splice variants in neocortical neurons

Amphetamineanalogs have emerged as popular recreational drugs of abuse. The number of reports of these substances producing severe acute toxicity and death is increasing. In 'Ecstasy' -associated deaths, focal necrosis in the liver and individual myocytic necrosis has been reported. Furthermore, serotonergic and dopaminergic neuronal cell damage has been observed in experimental amphetamine intoxication in laboratory animals. Here we demonstrate that subchronic exposure to D-amphetamine, methamphetamine, methylenedioxyamphetamine, and methylenedioxymethamphetamine ('Ecstasy') results in significant neurotoxicity in rat neocortical neurons in vitro. This neuronal cell death is accompanied by endonucleosomal DNA cleavage and differential expression of anti- and proapoptotic bcl-xL/S splice variants. In addition, we observed pronounced induction of cell stress-associated transcription factor c-jun and translation initiation inhibitor p97 after amphetamine treatment. These data support that the neurotoxic effects of different amphetamines are extended to rat neocortical neurons and that apoptotic pathways are involved in amphetamine-induced neurotoxicity.

Role of brain nitric oxide in (+/-)3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity in rats

The role of nitric oxide (NO) in the long-term serotoninergic neurotoxicity induced by (+/-)3,4-methylenedioxymethamphetamine (MDMA) in rats was investigiated. Pretreatment with Nomega-nitro-L-arginine (L-NOARG) (10 mg kg-1), a nitric oxide synthase (NOS) inhibitor, partially protected against long-term serotonin (5-HT) depletion induced by MDMA (40 mg kg-1) in frontal cortex and parietal cortex, but not in other brain regions examined. Brain NOS activities in these two regions were significantly elevated at 6 h after MDMA administration. Moreover, L-NOARG pretreatment caused significant inhibition of brain NOS activity but did not affect the acute 5-HT and dopamine (DA) changes or the hyperthermia induced by MDMA. These results suggest that it is the NOS inhibitory properties of L-NOARG, rather than its effects on the acute monoamine changes or the hyperthermia induced by MDMA, that are responsible for the prevention of neurotoxicity. The regional differences on the protection of L-NOARG and on the activation of NOS by MDMA indicate the unequal role that NO may play in MDMA-induced neurotoxicity in different brain regions.

Methamphetamine-induced hyperthermia in mice: examination of dopamine depletion and heat-shock protein induction

Methamphetamine (METH) is a common drug of abuse and a clinical anoretic which is known to cause neurotoxicity in rodents as evidenced by a depletion of dopamine (DA) and by decreased numbers of DA uptake sites in the striatum. It is also known to cause hyperthermia which is believed to induce the production of the 72-kDa heat-shock protein (HSP-72). In the present study, we evaluated whether METH induced the production of HSP-72 in both the mouse hippocampus and striatum and also attempted to correlate this induction with monoamine depletion. Adult male C57BL/6N mice received METH (20 mg/kg, i.p.) in an ambient temperature of 27 degrees C and body temperatures were monitored up to 240 min after treatment. Animals were sacrificed 12, 18, 24, 39, and 48 h after treatment. One striatum was examined for DA, DOPAC, and HVA levels using HPLC-EC and the contralateral striatum, along with the hippocampus, was prepared for immunoblotting. HPLC-EC analysis revealed a significant depletion of DA, DOPAC, and HVA at all time points. There was, however, a significant increase in DA at 48 vs. 39 h. A biphasic production of HSP-72, in both the hippocampus and striatum, was detected by immunoblot. HSP-72 production was strong at 12 h which corresponds to neuronal induction. However, at 18 h in the striatum and 24 h in the hippocampus, the induction appears to be reduced. A second phase of HSP-72 induction occurred at 39 h in both regions. In a second experiment, mice were dosed according to the same paradigm and were perfused at 18 h after treatment for immunohistochemical analysis. HSP-72 immunoreactivity was found in neurons of the CA1 and CA4 regions of the hippocampus; however, no detectable response was evident in the striatum. In conclusion, these data demonstrate that a single injection of METH can lead to hyperthermia which may then result in both the induction of HSP-72 and depletion of DA concentration.

Molecular mechanism of the inactivation of tryptophan hydroxylase by nitric oxide: attack on critical sulfhydryls that spare the enzyme iron center

Tryptophan hydroxylase (TPH), the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin (5-HT), is irreversibly inactivated by nitric oxide (NO). We have expressed brain TPH as a recombinant glutathione-S-transferase fusion protein and delineated the catalytic domain of the enzyme as the region spanning amino acids 99-444. Highly purified TPH catalytic core, like the native enzyme from brain, is inactivated by NO in a concentration-dependent manner. Removal of iron from TPH produces an apoenzyme with low activity that can be reconverted to its highly active holo-form by the addition of ferrous iron. Apo-TPH exposed to NO cannot be reactivated by iron. Treatment of holo-TPH (iron-loaded) with the disulfide 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB) causes an inactivation of TPH that is readily reversed by dithiothreitol (DTT). DTNB-treated TPH [sulfhydryl (SH)-protected] exposed to NO is returned to full activity by thiol reduction with DTT. The inactivation of native TPH by NO cannot be reversed by either iron or DTT. These data indicate that NO inactivates TPH by selective action on critical SH groups (i.e., cysteine residues) while sparing catalytic iron sites within the enzyme. The results are interpreted with reference to the substituted amphetamines, which are neurotoxic to 5-HT neurons, that inactivate TPH in vivo and are now known to produce NO and other reactive oxygen species in vivo.