Methamphetamine-induced neurotoxicity: structure activity relationships

Examining the Impact of Individual, Community, and Market Factors on Methamphetamine Use: A Tale of Two Cities

Although prior studies have monitored the trends in methamphetamine use and reported its increase over the years, few studies have considered how community-level characteristics affect the use of methamphetamine. In this study, we utilize data from the Arrestee Drug Abuse Monitoring (ADAM) program from two cities to examine how individual-level, community-level, and drug market factors influence methamphetamine use. Results indicate that both individual and community-level data significantly influence methamphetamine use. Also, findings show that predictors of methamphetamine use (at the individual and community-level) differ significantly from marijuana, cocaine, and opiate use. Policy implications regarding law enforcement suppression and the treatment of methamphetamine users are discussed.

Neurologic Complications of Psychomotor Stimulant Abuse

Psychomotor stimulants are drugs that act on the central nervous system (CNS) to increase alertness, elevate mood, and produce a sense of well-being. These drugs also decrease appetite and the need for sleep. Stimulants can enhance stamina and improve performance in tasks that have been impaired by fatigue or boredom. Approved therapeutic applications of stimulants include attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. These agents also possess potent reinforcing properties that can result in excessive self-administration and abuse. Chronic use is associated with adverse effects including psychosis, seizures, and cerebrovascular accidents, though these complications usually occur in individuals with preexisting risk factors. This chapter reviews the adverse neurologic consequences of chronic psychomotor stimulant use and abuse, with a focus on two prototypical stimulants methamphetamine and cocaine.

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.

Neurochemical and behavioural characterisation of alkoxyamphetamine derivatives in rats

The clinical utility of amphetamine and amphetamine analogues has been jeopardized by a number of side effects and toxicity, partly due to complex mechanisms of action. While some of the analogues have been individually characterised, there is still need for comparative studies, in particularly on their efficacy to release dopamine and 5-hydroxytryptamine, further enlightening some of the synaptic mechanisms conveying their actions. Thus, we have compared four alkoxyamphetamine derivatives, i.e., p-methoxyamphetamine; p-methoxymethamphetamine; methylenedioxyamphetamine, methylenedioxymethamphetamine, using methamphetamine, and D-amphetamine, as reference substances, on rotational behaviour and releasing mechanisms studied with in vivo microdialysis in rats. All alkoxylated-derivatives produced a long-lasting rotational behaviour at 10 mg/kg s.c., but the reference substances produced a strong rotation already at 2 mg/kg s.c. in 6-hydroxydopamine-lesioned rats. At the concentration of 100 micromolar, the alkoxylated-derivatives were equipotent to evoke dopamine and 5-hydroxytryptamine release in rat neostriatum, while D-amphetamine and methamphetamine were more efficient on dopamine release. Pre-treatment with methamphetamine or the alkoxylated-derivatives produced a remarkable decrease of the effect of K+ -depolarisation on both dopamine and 5-hydroxytryptamine release. The insertion of a methoxy or a methylenedioxy group on the benzene ring of D-amphetamine or methamphetamine, or N-methylation of the D-amphetamine molecule alters the selectivity of the compounds. The efficacy of the alkoxylated-derivatives on dopamine and 5-hydroxytryptamine release was similar, but stimulated less dopamine release and produced less rotational behaviour than D-amphetamine and methamphetamine. The lower efficacy of K+ -depolarisation following pre-treatments with the derivatives suggests an impairment of releasable monoamine stores. The present observations can enlighten the mechanisms of action of drugs showing a high risk for abuse among young populations.

Safety of intravenous methamphetamine administration during treatment with bupropion

RATIONALE

Methamphetamine dependence is a growing problem for which no medication treatments have proven effective.

OBJECTIVES

We evaluated bupropion, an antidepressant with beneficial effects for the treatment of nicotine dependence, in patients with methamphetamine dependence, to assess the safety and tolerability of methamphetamine administration during bupropion treatment.

METHODS

Twenty-six participants entered the study and 20 completed the protocol. Participants received intravenous methamphetamine (0, 15, and 30 mg) before and after randomization to twice-daily bupropion (150 mg SR) or matched placebo. Dependent measures included cardiovascular effects of methamphetamine, methamphetamine and amphetamine pharmacokinetics, and peak and trough plasma concentrations of bupropion and its metabolites.

RESULTS

Bupropion treatment was well tolerated, with bupropion- and placebo-treated groups reporting similar rates of adverse events. Methamphetamine administration was associated with expected stimulant cardiovascular effects, and these were not accentuated by bupropion treatment. Instead, there was a trend for bupropion to reduce methamphetamine-associated increases in blood pressure and a statistically significant reduction in methamphetamine-associated increases in heart rate. Pharmacokinetic analysis revealed that bupropion treatment reduced the plasma clearance of methamphetamine and also reduced the appearance of amphetamine in the plasma. Methamphetamine administration did not alter the peak and trough plasma concentrations of bupropion or its metabolites.

CONCLUSIONS

Methamphetamine administration was well tolerated during bupropion treatment. There was no evidence of additive cardiovascular effects when the drugs were coadministered. This study provides initial evidence for the safety of prescribing bupropion for the treatment of methamphetamine abuse and dependence. The impact of bupropion treatment in patients who abuse larger doses of methamphetamine remains undetermined.

Neurocognitive performance of methamphetamine users discordant for history of marijuana exposure

Abuse of the stimulant drug methamphetamine is associated with neural injury and neuropsychological (NP) deficits, while the residual effects of marijuana use remain uncertain. We sought to determine if methamphetamine dependent persons who also met criteria for marijuana abuse or dependence evidenced different NP performance than those with dependence for methamphetamine alone. We examined three groups that did not differ significantly on important demographic factors: (1) subjects with a history of methamphetamine dependence and history of marijuana abuse/dependence (METH+/MJ+, n=27); (2) methamphetamine dependent subjects without history of marijuana abuse/dependence (METH+/MJ-, n=26); (3) a control group with minimal or no drug use (n=41). A comprehensive NP battery was administered and performance was quantified for five cognitive ability areas. The METH+/MJ- group generally demonstrated the greatest NP impairment, with statistically significant differences observed between the METH+/MJ- and control group in learning, retention/retrieval, and a summary score of global NP performance. The METH+/MJ+ group did not differ significantly from the control or METH+/MJ- group on any NP ability. However, there was a significant linear trend in the global NP score suggesting that the METH+/MJ+ performed intermediate to the control and METH+/MJ- groups. Based on these findings, we cannot conclude that there is a protective effect of marijuana use in methamphetamine users; however, marijuana use clearly did not appear to exacerbate methamphetamine neurotoxicity. Further investigations are needed to determine if the emerging literature, suggesting that certain cannabinoids might have neuroprotective actions, is generalizable to community-dwelling substance abusers.

Designer drugs: how dangerous are they?

Of the designer drugs, the amphetamine analogues are the most popular and extensively studied, ecstasy (3,4-methylenedioxymethamphetamine; MDMA) in particular. They are used recreationally with increasing popularity despite animal studies showing neurotoxic effects to serotonin (5-HT) and/or dopamine (DA) neurones. However, few detailed assessments of risks of these drugs exist in humans. Previously, there were no methods available for directly evaluating the neurotoxic effects of amphetamine analogues in the living human brain. However, development of in vivo neuroimaging tools have begun to provide insights into the effects of MDMA in human brain. In this review, contributions of brain imaging studies on the potential 5-HT and/or DA neurotoxic effects of amphetamine analogues will be highlighted in order to delineate the risks these drugs engender in humans, focusing on MDMA. An overview will be given of PET, SPECT and MR Spectroscopy studies employed in human users of these drugs. Most of these studies provide suggestive evidence that MDMA is neurotoxic to 5-HT neurones, and (meth)amphetamine to DA neurones in humans. These effects seem to be dose-related, leading to functional impairments such as memory loss, and are reversible in several brain regions. However most studies have had a retrospective design, in which evidence is indirect and differs in the degree to which any causative links can be implied between drug use and neurotoxicity. Therefore, at this moment, it cannot be ascertained that humans are susceptible to MDMA-induced 5-HT injury or (meth)amphetamine-induced DA injury. Finally, although little is known about other amphetamine analogues there are important questions as to the safety of these designer drugs as well, in view of the fact that they are chemically closely related to MDMA and some have been shown to be 5-HT neurotoxins in animals.

Ibogaine signals addiction genes and methamphetamine alteration of long-term potentiation

The mapping of the human genetic code will enable us to identify potential gene products involved in human addictions and diseases that have hereditary components. Thus, large-scale, parallel gene-expression studies, made possible by advances in microarray technologies, have shown insights into the connection between specific genes, or sets of genes, and human diseases. The compulsive use of addictive substances despite adverse consequences continues to affect society, and the science underlying these addictions in general is intensively studied. Pharmacological treatment of drug and alcohol addiction has largely been disappointing, and new therapeutic targets and hypotheses are needed. As the usefulness of the pharmacotherapy of addiction has been limited, an emerging potential, yet controversial, therapeutic agent is the natural alkaloid ibogaine. We have continued to investigate programs of gene expression and the putative signaling molecules used by psychostimulants such as amphetamine in in vivo and in vitro models. Our work and that of others reveal that complex but defined signal transduction pathways are associated with psychostimulant administration and that there is broad-spectrum regulation of these signals by ibogaine. We report that the actions of methamphetamine were similar to those of cocaine, including the propensity to alter long-term potentiation (LTP) in the hippocampus of the rat brain. This action suggests that there may be a "threshold" beyond which the excessive brain stimulation that probably occurs with compulsive psychostimulant use results in the occlusion of LTP. The influence of ibogaine on immediate early genes (IEGs) and other candidate genes possibly regulated by psychostimulants and other abused substances requires further evaluation in compulsive use, reward, relapse, tolerance, craving and withdrawal reactions. It is therefore tempting to suggest that ibogaine signals addiction gene products.

Methamphetamine neurotoxicity: necrotic and apoptotic mechanisms and relevance to human abuse and treatment

Research into methamphetamine-induced neurotoxicity has experienced a resurgence in recent years. This is due to (1) greater understanding of the mechanisms underlying methamphetamine neurotoxicity, (2) its usefulness as a model for Parkinson's disease and (3) an increased abuse of the substance, especially in the American Mid-West and Japan. It is suggested that the commonly used experimental one-day methamphetamine dosing regimen better models the acute overdose pathologies seen in humans, whereas chronic models are needed to accurately model human long-term abuse. Further, we suggest that these two dosing regimens will result in quite different neurochemical, neuropathological and behavioral outcomes. The relative importance of the dopamine transporter and vesicular monoamine transporter knockout is discussed and insights into oxidative mechanisms are described from observations of nNOS knockout and SOD overexpression. This review not only describes the neuropathologies associated with methamphetamine in rodents, non-human primates and human abusers, but also focuses on the more recent literature associated with reactive oxygen and nitrogen species and their contribution to neuronal death via necrosis and/or apoptosis. The effect of methamphetamine on the mitochondrial membrane potential and electron transport chain and subsequent apoptotic cascades are also emphasized. Finally, we describe potential treatments for methamphetamine abusers with reference to the time after withdrawal. We suggest that potential treatments can be divided into three categories; (1) the prevention of neurotoxicity if recidivism occurs, (2) amelioration of apoptotic cascades that may occur even in the withdrawal period and (3) treatment of the atypical depression associated with withdrawal.

3,4-Methylenedioxy analogues of amphetamine: defining the risks to humans

The 3,4-methylenedioxy analogues of amphetamine [MDMA ("Ecstasy", "Adam"), MDA ("Love") and MDE ("Eve")] are recreational drugs that produce feelings of euphoria and energy and a desire to socialize, which go far to explain their current popularity as "rave drugs". In addition to these positive effects, the drugs are relatively inexpensive to purchase and have the reputation of being safe compared to other recreational drugs. Yet there is mounting evidence that these drugs do not deserve this reputation of being safe. This review examines the relevant human and animal literature to delineate the possible risks MDMA, MDA and MDE engender with oral consumption in humans. Following a summary of the behavioral and cognitive effects of MDMA, MDA and MDE, risks will be discussed in terms of toxicity, psychopathology, neurotoxicity, abuse potential and the potential for drug-drug interactions associated with acute and chronic use.

The discriminative stimulus effects of methamphetamine in pigeons

This experiment was designed to elucidate the neurotransmitter systems that mediate the discriminative stimulus effects of methamphetamine. Four pigeons were trained to peck one key following saline injections and a second key following methamphetamine injections (1.0 or 1.7 mg/kg, IM). Substitution tests revealed drug-appropriate responding following administration of the psychomotor stimulants methamphetamine, amphetamine and cocaine, the dopamine (DA) reuptake inhibitor bupropion, norepinephrine (NE) reuptake inhibitors imipramine and tomoxetine, and the serotonin (5-HT) releaser fenfluramine. Saline-key responding occurred following administration of the D1 agonist SKF-38393, the D1 antagonist SCH-23390, the alpha 2 receptor agonist clonidine, the alpha 1 antagonist prazosin, a nonselective beta-antagonist propranolol and the selective 5-HT reuptake inhibitor fluoxetine. The D2/D3 agonist quinpirole produced drug-appropriate responding in two pigeons and partial substitution in the remaining two pigeons. The 5HT1A agonist 8-OH-DPAT produced drug-appropriate responding at higher doses (0.3-1.0 mg/kg), whereas much lower doses (0.003-1.0 mg/kg) antagonized the methamphetamine stimulus. The stimulus effects of methamphetamine were attenuated by pretreatment with prazosin, SCH-23390 and eticlopride, whereas pretreatment with propranolol and the 5-HT3 antagonist, MDL 72222, failed reliably to attenuate drug key responding. These results suggest that NE and DA reuptake inhibition and 5-HT release mediate the discriminative stimulus effects of methamphetamine as do the 5-HT1A and DA D1 and D2 receptors.

Influence of naloxone upon motor activity induced by psychomotor stimulant drugs

Naloxone, an opioid receptor antagonist, attenuates a wide range of behavioral effects of d-amphetamine, such as the stimulation of motor activity. To investigate the pharmacological selectivity of the naloxone/amphetamine interaction, we assessed the effects of naloxone (5.0 mg/kg SC) upon motor activity induced in rats by a range of psychomotor stimulant drugs with a mechanism of action either similar to or different from that of d-amphetamine. Each of the drugs tested caused dose-dependent increases in both gross and fine activity. Naloxone attenuated the gross but not the fine activity response to d- and l-amphetamine, but had no influence upon the other catecholamine-releasing drugs, methamphetamine and phendimetrazine. In contrast, naloxone increased the gross but not the fine activity response to the catecholamine uptake inhibitors cocaine and mazindol, but had no effects upon the motor response to methylphenidate. The responses to other stimulant drugs (apomorphine, caffeine, scopolamine) were unaffected by naloxone pretreatment. The present findings extend the range of conditions under which naloxone and, by inference, endogenous opioid systems, modulate the behavioral response to psychomotor stimulants. However, the differential effects of naloxone upon the motor response to individual stimulant drugs support previous suggestions of fundamental differences in mechanisms of action among these compounds.