Central effects of acamprosate: part 2. Acamprosate modifies the brain in-vivo proton magnetic resonance spectrum in healthy young male volunteers

Neuroimaging markers of glutamatergic and GABAergic systems in drug addiction: Relationships to resting-state functional connectivity

Drug addiction is characterized by widespread abnormalities in brain function and neurochemistry, including drug-associated effects on concentrations of the excitatory and inhibitory neurotransmitters glutamate and gamma-aminobutyric acid (GABA), respectively. In healthy individuals, these neurotransmitters drive the resting state, a default condition of brain function also disrupted in addiction. Here, our primary goal was to review in vivo magnetic resonance spectroscopy and positron emission tomography studies that examined markers of glutamate and GABA abnormalities in human drug addiction. Addicted individuals tended to show decreases in these markers compared with healthy controls, but findings also varied by individual characteristics (e.g., abstinence length). Interestingly, select corticolimbic brain regions showing glutamatergic and/or GABAergic abnormalities have been similarly implicated in resting-state functional connectivity deficits in drug addiction. Thus, our secondary goals were to provide a brief review of this resting-state literature, and an initial rationale for the hypothesis that abnormalities in glutamatergic and/or GABAergic neurotransmission may underlie resting-state functional deficits in drug addiction. In doing so, we suggest future research directions and possible treatment implications.

Ethanol withdrawal-induced brain metabolites and the pharmacological effects of acamprosate in mice lacking ENT1

Acamprosate is clinically used to treat alcohol-dependent patients. While the molecular and pharmacological mechanisms of acamprosate remain unclear, it has been shown to regulate γ-aminobutyric acid (GABA) or glutamate levels in the cortex and striatum. To investigate the effect of acamprosate on brain metabolites in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc), we employed in vivo 16.4 T proton magnetic resonance spectroscopy. We utilized type 1 equilibrative nucleoside transporter (ENT1) null mice since acamprosate attenuates ethanol drinking in these mice. Our findings demonstrated that ethanol withdrawal reduced GABA levels and increased phosphorylated choline compounds in the mPFC of both wild-type and ENT1 null mice. Notably, acamprosate normalized these withdrawal-induced changes only in ENT1 null mice. In the NAc, ethanol withdrawal increased glutamate and glutamine (Glx) levels only in wild-type mice. Interestingly, acamprosate reduced Glx levels in the NAc compared to the withdrawal state in both genotypes. These results provide a molecular basis for the pharmacological effect of acamprosate in the cortical-striatal circuit.

Acamprosate reduces ethanol drinking behaviors and alters the metabolite profile in mice lacking ENT1

Acamprosate is clinically used to treat alcoholism. However, the precise molecular functionality of acamprosate in the central nervous system remains unclear, although it is known to antagonize glutamate action in the brain. Since elevated glutamate signaling, especially in the nucleus accumbens (NAc), is implicated in several aspects of alcoholism, we utilized mice lacking type 1 equilibrative nucleoside transporter (ENT1), which exhibit increased glutamate levels in the NAc as well as increased ethanol drinking behaviors. We found that acamprosate significantly reduced ethanol drinking of mice lacking ENT1 (ENT1(-/-)) while having no such effect in wild-type littermates. We then analyzed the basal and acamprosate-treated accumbal metabolite profiles of ENT1(-/-) and wild-type mice using in vivo 16.4T proton magnetic resonance spectroscopy (MRS). Our data show that basal glutamate+glutamine (Glx), glutamate, glutamine and N-acetylaspartatic acid (NAA) levels are increased in the nucleus accumbens (NAc) of ENT1(-/-) compared to wild-type mice. We then found that acamprosate treatment significantly reduced Glx and glutamine levels while increasing taurine levels in the NAc of only ENT1(-/-) compared to their saline-treated group while normalizing other metabolite compared to wild-type mice. This study will be useful in the understanding of the molecular basis of acamprosate in the brain.

Effect of acamprosate on magnetic resonance spectroscopy measures of central glutamate in detoxified alcohol-dependent individuals: a randomized controlled experimental medicine study

CONTEXT

Acamprosate is approved for the treatment of alcoholism, but its mechanism of action remains unclear. Results of animal studies suggest that a persistent hyperglutamatergic state contributes to the pathogenesis of alcoholism and that acamprosate may exert its actions by intervening in this process. Human translation of these findings is lacking.

OBJECTIVE

To examine whether acamprosate modulates indices of central glutamate levels in recently abstinent alcohol-dependent patients as measured using proton nuclear magnetic resonance spectroscopy (¹H-MRS).

DESIGN

A 4-week, double-blind, placebo-controlled, randomized controlled experimental medicine study, with ¹H-MRS measures obtained on days 4 and 25.

SETTING

An inpatient research unit at the NIH Clinical Center. Patients Thirty-three patients who met the DSM-IV criteria for alcohol dependence and who were admitted for medically supervised withdrawal from ongoing alcohol use. Intervention Four weeks of acamprosate (initial oral loading followed by 1998 mg daily) or matched placebo, initiated at the time of admission.

MAIN OUTCOME MEASURES

The glutamate to creatine ratio as determined using single-voxel ¹H-MRS in the anterior cingulate. Exploratory neuroendocrine, biochemical, and behavioral outcomes were also collected, as were safety- and tolerability-related measures.

RESULTS

There was a highly significant suppression of the glutamate to creatine ratio across time by acamprosate (time × treatment interaction: F₁(,)₂₉ = 13.5, P < .001). Cerebrospinal fluid levels of glutamate obtained in a subset of patients 4 weeks into abstinence were uncorrelated with the MRS measures and unaffected by treatment but were strongly correlated (R² = 0.48, P < .001) with alcohol dependence severity. Other exploratory outcomes, including repeated dexamethasone-corticotropin-releasing hormone tests, and psychiatric ratings were unaffected. Among tolerability measures, gastrointestinal symptoms were significantly greater in acamprosate-treated individuals, in agreement with the established profile of acamprosate.

CONCLUSION

The MRS measures of central glutamate are reduced across time when acamprosate therapy is initiated at the onset of alcohol abstinence.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00106106.

Emerging drugs to treat alcoholism

IMPORTANCE OF THE FIELD

Alcoholism is a widespread disorder with substantial mortality and negative treatment outcomes. To date, few medications have been found to reduce relapse rates or drinking in alcohol-dependent patients.

AREAS COVERED IN THIS REVIEW

This review focuses on drugs that have been clinically tested for the treatment of alcohol dependence in clinical trials, pilot trials or which are considered to have a clinical perspective. For this purpose, a detailed Medline search was conducted on this issue. Although the neurochemical basis of alcoholism and the neuronal circuitry mediating its psychotropic effects have been explored in great detail in recent years, few drugs have emerged for the treatment of alcohol dependence, also because pharmaceutical companies have only a limited interest in this area of research. Acamprosate and the opioid antagonist naltrexone have been found to be effective, although data are mixed. A depot formula of naltrexone and the alternate opioid antagonist nalmefene have been studied in clinical trials and will presumably be introduced in the markets soon. Other emerging drugs are topiramate, novel acetaldehyde dehydrogenase (ALDH) inhibitors, baclofen, a combination therapy of gababentin and flumazenil and drugs targeting the cortitropin-releasing factor/neuropeptide Y mediated stress axis.

WHAT THE READER WILL GAIN

Insights on the neurochemical basis of alcohol dependence and possible targets of medications.

TAKE HOME MESSAGE

Acamprosate, naltrexone and the ALDH inhibitor disulfiram are proven medications for the treatment of alcohol dependence with modest efficacy. Novel alternate medications, a depot formulation of the opioid antagonist naltrexone and another oral opioid antagonist, nalmefene, are available now with good evidence for clinical efficacy. Novel ALDH inhibitors, antiepileptic drugs such as topiramate and drugs targeting the stress axis are currently among the most promising emerging drugs.

Role of altered structure and function of NMDA receptors in development of alcohol dependence

Long-term alcohol exposure gives rise to development of physical dependence on alcohol in consequence of changes in certain neurotransmitter functions. Accumulating evidence suggests that the glutamatergic neurotransmitter system, especially the N-methyl-D-aspartate (NMDA) type of glutamate receptors is a particularly important site of ethanol's action, since ethanol is a potent inhibitor of the NMDA receptors (NMDARs) and prolonged ethanol exposition leads to a compensatory "upregulation" of NMDAR mediated functions supposedly contributing to the occurrence of ethanol tolerance, dependence as well as the acute and delayed signs of ethanol withdrawal.Recently, expression of different types of NMDAR subunits was found altered after long-term ethanol exposure. Especially, the expression of the NR2B and certain splice variant forms of the NR1 subunits were increased in primary neuronal cultures treated intermittently with ethanol. Since NMDA ion channels with such an altered subunit composition have increased permeability for calcium ions, increased agonist sensitivity, and relatively slow closing kinetics, the abovementioned alterations may underlie the enhanced NMDAR activation observed after long-term ethanol exposure. In accordance with these changes, the inhibitory potential of NR2B subunit-selective NMDAR antagonists is also increased, demonstrating excellent potency against alcohol withdrawal-induced in vitro cytotoxicity. Although in vivo data are few with these compounds, according to the effectiveness of the classic NMDAR antagonists in attenuation, not only the physical symptoms, but also some affective and motivational components of alcohol withdrawal, novel NR2B subunit selective NMDAR antagonists may offer a preferable alternative in the pharmacotherapy of alcohol dependence.

Alcoholism: A Systems Approach From Molecular Physiology to Addictive Behavior

Alcohol consumption is an integral part of daily life in many societies. The benefits associated with the production, sale, and use of alcoholic beverages come at an enormous cost to these societies. The World Health Organization ranks alcohol as one of the primary causes of the global burden of disease in industrialized countries. Alcohol-related diseases, especially alcoholism, are the result of cumulative responses to alcohol exposure, the genetic make-up of an individual, and the environmental perturbations over time. This complex gene × environment interaction, which has to be seen in a life-span perspective, leads to a large heterogeneity among alcohol-dependent patients, in terms of both the symptom dimensions and the severity of this disorder. Therefore, a reductionistic approach is not very practical if a better understanding of the pathological processes leading to an addictive behavior is to be achieved. Instead, a systems-oriented perspective in which the interactions and dynamics of all endogenous and environmental factors involved are centrally integrated, will lead to further progress in alcohol research. This review adheres to a systems biology perspective such that the interaction of alcohol with primary and secondary targets within the brain is described in relation to the behavioral consequences. As a result of the interaction of alcohol with these targets, alterations in gene expression and synaptic plasticity take place that lead to long-lasting alteration in neuronal network activity. As a subsequent consequence, alcohol-seeking responses ensue that can finally lead via complex environmental interactions to an addictive behavior.

Acamprosate in the treatment of alcohol dependence: clinical and economic considerations

Acamprosate has been commercially available in the USA since 2004 to treat alcohol dependence. Its safety and efficacy have been demonstrated in a number of clinical trials worldwide, which overall have shown significant improvements in abstinence compared with placebo. As with all alcoholism pharmacotherapies, acamprosate is used in conjunction with psychosocial interventions. One frequently described mechanism stipulates that acamprosate supports abstinence by normalizing the often protracted dysregulation of NMDA-mediated glutamatergic neurotransmission that follows chronic heavy alcohol use and withdrawal. This article reviews the clinical safety and efficacy of acamprosate, as well as results from recent pharmacoeconomic and human laboratory studies. These data elucidate the economic benefits of acamprosate, as well as its effects on cognition and alcohol-related sleep disturbances.

Update on neuropharmacological treatments for alcoholism: scientific basis and clinical findings

The past decade has seen an expansion of research and knowledge on pharmacotherapy for the treatment of alcohol dependence. The Food and Drug Administration (FDA)-approved medications naltrexone and acamprosate have shown mixed results in clinical trials. Oral naltrexone and naltrexone depot formulations have generally demonstrated efficacy at treating alcohol dependence, but their treatment effect size is small, and more research is needed to compare the effects of different doses on drinking outcome. Acamprosate has demonstrated efficacy for treating alcohol dependence in European trials, but with a small effect size. In U.S. trials, acamprosate has not proved to be efficacious. Research continues to explore which types of alcohol-dependent individual would benefit the most from treatment with naltrexone or acamprosate. The combination of the two medications demonstrated efficacy for treating alcohol dependence in one European study but not in a multi-site U.S. study. Another FDA-approved medication, disulfiram, is an aversive agent that does not diminish craving for alcohol. Disulfiram is most effective when given to those who are highly compliant or who are receiving their medication under supervision. Of the non-approved medications, topiramate is among the most promising, with a medium effect size in clinical trials. Another promising medication, baclofen, has shown efficacy in small trials. Serotonergic agents such as selective serotonin reuptake inhibitors and the serotonin-3 receptor antagonist, ondansetron, appear to be efficacious only among certain genetic subtypes of alcoholic. As neuroscientific research progresses, other promising medications, as well as medication combinations, for treating alcohol dependence continue to be explored.

Effects of acamprosate on sleep during alcohol withdrawal: A double-blind placebo-controlled polysomnographic study in alcohol-dependent subjects

BACKGROUND

Sleep disturbances are frequently encountered in alcohol-dependent patients. Drugs improving sleep during abstinence from alcohol may play an important role in the recovery process.

METHODS

In the present study, the effects of acamprosate, a drug successfully used in maintaining abstinence following alcohol withdrawal, were assessed by polysomnographic recordings. A parallel double-blind placebo-controlled study was conducted in 24 male DSM-IV alcohol-dependent subjects aged 35.9+/-1.2 years. Treatments (2 tablets of 333 mg acamprosate vs placebo t.i.d.) were initiated 8 days before alcohol withdrawal and continued during the 15 days following alcohol withdrawal. Polysomnographic assessments were recorded during acute withdrawal (the first 2 nights following withdrawal) and during postwithdrawal abstinence (the last 2 nights of the trial).

RESULTS

Results show that, compared with placebo, acamprosate decreased wake time after sleep onset and increased stage 3 and REM sleep latency (all treatment effects with a p < 0.05 significance). Withdrawal effects themselves were also demonstrated as sleep efficiency (p < 0.01) and total sleep time (p < 0.05) were lower in abstinence nights versus withdrawal nights, whereas no significant treatment x withdrawal effect could be evidenced. Acamprosate was well tolerated during the entire course of the study.

CONCLUSIONS

The present study shows that acamprosate ameliorates both sleep continuity and sleep architecture parameters classically described as disturbed in alcohol-dependent patients. From a clinical perspective, it suggests that an 8-day acamprosate prewithdrawal treatment is well tolerated and can attenuate the sleep disturbances engendered by alcohol withdrawal in alcohol-dependent subjects.

Acamprosate for the treatment of alcohol dependence

BACKGROUND

Both inpatient and outpatient treatment centers that focus solely on psychosocial therapies for the treatment of alcohol dependence have high relapse rates. Thus, extensive research has focused on the development of pharmacologic moieties to attenuate the craving for alcohol after acute alcohol detoxification. Three drug therapies are currently approved by the US Food and Drug Administration (FDA) for this purpose: disulfiram, naltrexone, and acamprosate. The latter was approved by the FDA in 2004.

OBJECTIVE

This article describes the pharmacologic properties and clinical usefulness of acamprosate for the treatment of alcohol dependence.

METHODS

Relevant information was identified through searches of MEDLINE (1966 to March 2005), International Pharmaceutical Abstracts (1970-2005), Current Contents (1996-2005), and Cumulative Index to Nursing and Allied Health Literature (1982-Week 2, 2004) using the key words acamprosate, alcohol dependence, and alcoholism (MeSH).

RESULTS

Acamprosate limited to randomized, controlled clinical trials yielded 33 hits in MEDLINE. Twenty-two articles were reviewed for efficacy end points, and 10 were reviewed for pharmacology and pharmacokinetics data. Acamprosate plus pharmacokinetics and pharmacodynamics yielded 19 hits, some of which were duplicates from the previously described search. Acamprosate plus meta-analysis (MeSH) yielded 5 hits, naltrexone plus meta-analysis (MeSH) yielded 9 hits, and disulfiram plus meta-analysis yielded 3 hits. The most recent review articles and their reference lists were assessed to ensure completeness of literature searches. Based on these searches, acamprosate is known to be an analogue of taurine and gamma-aminobutyric acid (GABA), 2 central nervous system neuromodulators. Acamprosate is thought to share some of the cellular actions of taurine affecting GABA and glutaminergic receptors in the nucleus accumbens, a brain region that may be responsible for the reinforcing effects received after alcohol consumption. Acamprosate is thought to also suppress excitation-induced calcium entry that results from chronic alcohol exposure, thereby altering the conformation of the N-methyl-d-aspartate receptors. The percentage of patients taking acamprosate who were completely abstinent throughout the different durations of the studies varied from approximately 18% to 61%, compared with 4% to 45% with placebo. Diarrhea was the most common adverse effect accompanying acamprosate therapy, and this was generally described as dose related and transient.

CONCLUSIONS

Acamprosate is associated with modest treatment effects. Its efficacy is similar to naltrexone, and the combination of acamprosate and naltrexone appears to be more efficacious than acamprosate alone, when combined with psychosocial interventions.

Sleep disturbances, psychiatric disorders, and psychotropic drugs

Brain neurotransmitter dysfunctions involved in the pathophysiological processes of psychiatric disorders are likely to be reflected by concomitant alterations in sleep continuity and architecture. Since the corrective effects of psychotropic drugs on dysfunctional neurotransmission systems can be evidenced through polysomnographic recordings, one may consider sleep as a kind of “window” on the neurobiology of psychiatric disorders. During the last 10 years, major breakthroughs in our understanding of sleep-wake mechanisms have provided some indications on how psychotropic drugs could influence the sleep-wake cycle. In this review, recent inroads into the understanding of sleep regulatory neural mechanisms are introduced and discussed in terms of the effects of psychotropic drugs. The relationship between the patho-physiological process of a disease, its consequence on sleep, and the corrective effect of a psychotropic drug are exemplified by two psychopathological states: substance withdrawal and major depression. One may conclude that polysomnographic recordings are a unique noninvasive tool to analyze brain functioning, and are particularly well suited to evaluating the objective effects of new psychotropic drugs.

Addiction and its brain science

AIMS

To illustrate how modern neurobiological approaches will help to identify the neurocircuits and genes involved in addictive behavior.

BACKGROUND

The current disorder concept of addiction includes neurobiological foundations and neurobiological research assuming irreversible molecular and structural changes within the brain dopamine reinforcement system, constituting the 'molecular and structural switch' from controlled drug intake to compulsive drug abuse. However, those irreversible changes have not so far been identified and it is suggested that in addition to the mesolimbic dopamine system, other brain systems including the mesocortical and nigrostriatal pathways as well as their non-dopaminergic feedback-loops might be involved in addictive behavior. NEUROBIOLOGICAL APPROACH: A three-step neurobiological approach is described that allows in a first step via novel animal models and imaging techniques to identify the neuroanatomical sites mediating voluntary drug intake, reinstatement of drug-seeking behavior, relapse, loss of control and drug intake despite negative consequences. In a subsequent step, forward genetic approaches including quantitative trait loci (QTL)-analysis and gene expression profiling are helpful in identifying so-called candidate genes. In a final step, conditional animal mutants and selective pharmacological tools are used to functionally validate candidate genes. Following this validation process, the transfer to the human situation has to be made and candidate genes have to be verified further in well-phenotyped cohorts of addicted patients.

CONCLUSION

This three-step neurobiological approach, that must involve an interdisciplinary team including experimental psychologists, geneticists, molecular biologists and finally clinical addiction researchers, will allow us to understand where and how the addicted brain goes awry.

Neuroprotective and abstinence-promoting effects of acamprosate: elucidating the mechanism of action

Acamprosate is an abstinence-promoting drug widely used in the treatment of alcohol dependence but which has a mechanism of action that has remained obscure for many years. Recently, evidence has emerged that this drug may interact with excitatory glutamatergic neurotransmission in general and as an antagonist of the metabotropic glutamate receptor subtype 5 (mGluR5) in particular. These findings provide, for the first time, a satisfactory, unifying hypothesis that can bring together and explain the diverse neurochemical effects of acamprosate. Glutamic acid is involved in several aspects of alcohol dependence and withdrawal, many of which can be modified by acamprosate. For example, during chronic exposure to alcohol, the glutamatergic system becomes upregulated, leaving the brain exposed to excessive glutamatergic activity when alcohol is abruptly withdrawn. The surge in glutamic acid release that occurs following alcohol withdrawal can be attenuated by acamprosate. The elevated extracellular levels of glutamic acid observed in withdrawal, together with supersensitivity of NMDA receptors, may expose vulnerable neurons to excitotoxicity, possibly contributing to the neuronal loss sometimes observed in chronic alcohol dependence. In vitro studies suggest that the excitotoxicity produced by ethanol can effectively be blocked by acamprosate. Moreover, glutamatergic neurotransmission plays an important role in the acquisition of cue-elicited drinking behaviours, which again can be modulated by acamprosate. In conclusion, the glutamatergic hypothesis of the mechanism of action of acamprosate helps explain many of its effects in human alcohol dependence and points the way to potential new activities, such as neuroprotection, that merit exploration in the clinic.

Acamprosate Calcium Delayed-Release Tablets

Each month, subscribers to The Formulary Monograph Service receive five to six well-documented monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. With a subscription, the monographs are sent to you in print and CD ROM forms and are available online. Monographs can be customized to meet the needs of your facility. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The November 2004 monograph topics are erlotinib hydrochloride, clodronate, oxypurinol sodium, pegaptanib sodium injection, and ramelteon. The DUE is on ezetimibe/simvastatin.

Use of acamprosate and opioid antagonists in the treatment of alcohol dependence: a European perspective

In thirteen of sixteen placebo-controlled trials in Europe, acamprosate increased abstinence in detoxified alcohol-dependent patients. It is approved in most EU countries. Its action at N-methyl-D-aspartate (NMDA) receptors appears to account for many of its effects. The number needed to treat in the fifteen trials suitable for meta-analysis has been calculated at 8.15. Trials of naltrexone in Europe have shown less clear evidence of efficacy than trials of acamprosate, whether abstinence or relapse to heavy drinking is used as the outcome criterion. With reduction in heavy drinking days as the criterion, naltrexone compared favorably to acamprosate in an open study in moderate alcohol dependence; one double-blind study has pointed to an advantage of the combination of naltrexone with acamprosate over either drug. To date, there are no trials published of nalmefene in European clinics. While many centers routinely offer a trial of acamprosate to newly detoxified patients aiming for abstinence, naltrexone usage varies. Some centers suggest naltrexone not only for patients aiming for abstinence but also for patients for whom continued drinking is a therapeutic possibility or a clinical inevitability.

Synthesis and assessment of [11C]acetylhomotaurine as an imaging agent for the study of the pharmacodynamic properties of acamprosate by positron emission tomography

Acetylhomotaurine was labeled with (11)C via N-acetylation with [(11)C]acetyl chloride. The synthesis yielded 48.2+/-3.8%, decay corrected to end of bombardment. The specific activity of the (radio)chemically pure product was 20.8+/-2.0 GBq/micromol at EOS. In vivo studies revealed a very fast clearance of the tracer from the blood and a uniform distribution in the different brain regions. Unfortunately, the poor passage through the blood brain barrier makes the tracer not suitable for PET studies.

Acamprosate for the adjunctive treatment of alcohol dependence

OBJECTIVE

To review the literature related to the treatment of alcohol dependence with acamprosate, a synthetic compound structurally similar to the naturally occurring amino acid, homotaurine.

DATA SOURCES

Primary literature and review articles were identified by MEDLINE search (1966-June 2003). Abstracts from recent meetings were also reviewed.

DATA SYNTHESIS

Acamprosate has been marketed in 24 countries. Although the precise mechanism of acamprosate in the treatment of alcohol-dependent patients is unclear, it may restore the balance between inhibitory and excitatory neurotransmission in the central nervous system. European trials have shown consistent increases in abstinence rates compared with placebo when acamprosate use was paired with appropriate psychosocial and behavioral therapies. Decreased direct and indirect healthcare costs associated with acamprosate treatment have also been reported.

CONCLUSIONS

Acamprosate is a promising medication for the treatment of alcohol dependence in the US.

Effects of acamprosate on excitatory amino acids during multiple ethanol withdrawal periods

BACKGROUND

Our previous studies on the effects of acamprosate on enhanced locomotion during repeated withdrawals are now extended to the effects of acamprosate on excitatory amino acids in the hippocampus during repeated ethanol withdrawals.

METHODS

In this study, Wistar rats were made ethanol dependent by 4 weeks of vapor inhalation. After this first cycle of chronic ethanol treatment, rats underwent repeated and alternate cycles of 24 hr withdrawals and 1 week of chronic ethanol treatment. The microdialysis technique was used together with high-performance liquid chromatography and electrochemical detection to quantify different amino acids such as aspartate and glutamate.

RESULTS

An intraperitoneal administration of acamprosate (400 mg/kg) to naïve rats did not alter aspartate or glutamate levels compared with the saline groups. During the first cycle of ethanol withdrawal, the administration of acamprosate (400 mg/kg, intraperitoneally) 2 hr after the commencement of ethanol withdrawal decreased both aspartate and glutamate microdialysate levels when compared with their respective saline group. Acamprosate administration also significantly decreased glutamate levels during the third withdrawal compared with the saline group, whereas no changes were seen in aspartate levels.

CONCLUSION

The results of this work demonstrate that acamprosate reduced the excitatory amino acid glutamate increase observed during repeated ethanol withdrawal. These effects of acamprosate may provide a protective mechanism against neurotoxicity by reducing excitatory amino acids, particularly glutamate.

Human models as tools in the development of psychotropic drugs

Despite the growing means devoted to research and development (R α D) and refinements in the preclinical stages, the efficiency of central nervous system (CMS) drug development is disappointing. Many drugs reach patient studies with an erroneous therapeutic indication andlor in incorrect doses. Apart from the first clinical studies, which are conducted in healthy volunteers and focus only on safety, iolerability, and pharmacokinetics, drug development mostly relies on patient studies. Psychiatric disorders are characterized by heterogeneity and a high rate of comorbidity. It is becoming increasingly difficult to recruit patients for clinical trials and there are many confounding factors in this population, for example, those related to treatments. In order to keep patient exposure and financial expenditure to a minimum, it is important to avoid ill-designed and inconclusive studies. This risk could be minimized by gathering pharmacodynamic data earlier in development and considering that the goal of a phase 1 plan is to reach patient studies with clear ideas about the compound's pharmacodynamic profile, its efficacy in the putative indication (proof of concept), and pharmacokinetic/pharmacodynamic relationships, in addition to safety, tolerability, and pharmacokinetics. Human models in healthy volunteers may be useful tools for this purpose, but their use necessitates a global adaptation of the phase scheme, favoring pharmacodynamic assessments without neglecting safety. We are engaged in an R α D program aimed to adapt existing models and develop new paradigms suitable for early proof of concept substantiation.

Effects of ethanol and of alcohol dehydrogenase inhibitors on the reduction of N-acetylaspartate levels of brain in mice in vivo: a search for substances that may have therapeutic value in the treatment of Canavan disease

N-Acetylaspartate (NAA) is an important osmolyte in the vertebrate brain that participates in an intercompartmental metabolic cycle. It is synthesized primarily in neurons from L-aspartate (Asp) and acetyl-CoA and, after its regulated release, it is hydrolysed by aspartoacylase in an oligodendrocyte compartment to produce Asp and acetate. NAA also gives a strong 1H magnetic resonance spectroscopic signal, which has led to its widespread use as a neuronal marker. Utilizing this noninvasive technique, the NAA concentrations in normal brain and in brains exhibiting a variety of CNS disease syndromes have been studied. In normal individuals, the concentration of NAA has been observed to be relatively stable over long periods. However, in many CNS disease processes there are long-term changes in the level of NAA that have been considered to signal changes in neuron density or function. We report that the concentration of NAA in brain is malleable and that, in addition to normal endogenous variation or changes due to disease processes, it can be modified by a variety of exogenous drugs and other substances. As a result of this investigation, we have also been able to identify a new class of NAA-active compounds--pyrazole and pyrazole derivatives--that have the ability to reduce brain NAA concentrations in normal mice. The importance of these findings in understanding the NAA intercompartmental cycle, and its role in Canavan disease, a genetic aspartoacylase deficiency disease, are discussed.

Ethanol and amino acids in the central nervous system: assessment of the pharmacological actions of acamprosate

Ethanol induces alterations in the central nervous system by differentially interfering with a number of neurotransmitter systems, although the mechanisms by which such effects are executed are not well understood. The present review therefore, is designed to ascertain the effect of ethanol on both excitatory and inhibitory amino acid neurotransmitters, as well as the sulphonated amino acid taurine, assayed by the microdialysis technique within specific brain regions of rat during different types of alcohol intoxication, acute and chronic, as well as during the withdrawal period. Such an understanding of these pharmacological actions of ethanol on neurotransmitters is essential in order to provide the impetus for the development of appropriate therapeutic intervention to ameliorate the multitude of neurochemical disorders induced by ethanol. In addition the possible mode of action of a new therapeutic drug for the treatment of alcoholism, acamprosate will be discussed. The first part of this review will be limited to studies of the effect of ethanol on both amino acid neurotransmitters and the sulphonated amino acid taurine, a possible neuromodulator. While, the second part will seek to establish the possible mechanism of action of a new therapeutic drug, acamprosate, which is used to combat the effects of ethanol, particularly during the craving period, as well as maintaining abstinence in weaned alcoholics.