CNS & Neurological Disorders - Drug Targets (Formerly Current Drug Targets - CNS & Neurological Disorders) - Volume 9, Issue 1, 2010

Drug delivery to the central nervous system remains a vexing problem because of the presence of the blood-brain barrier (BBB), whose endothelial cell tight junctions limit the paracellular flux of hydrophilic molecules. One solution may be vector-mediated delivery to the brain. This employs chimeric peptide technology, wherein the drug is conjugated to a molecular carrier of protein nature (e.g. cationized albumin or a transferrin receptor antibody). Transferrin receptor antibodies selectively target BBB endothelium due to the high levels of receptor expressed by these cells, thereby triggering receptor-mediated transport across the BBB via transcytosis. Chitosan, a naturally occurring, abundant, and biocompatible polysaccharide has found widespread pharmaceutical application. In particular, the cationic nature of chitosan facilitates its interaction with negative charges on the brain endothelium, Building on their previous work on brain-deliverable chitosan-polyethylene glycol nanoparticles functionalized with monoclonal anti-transferrin antibody, Karatas and colleagues have now designed caspase-3 inhibitor-loaded chitosan nanospheres conjugated with an anti-mouse transferrin receptor monoclonal antibody that selectively recognizes the transferrin receptor type 1 on the cerebral vasculature. Caspase-3 has been implicated in neuronal cell death in cerebral ischemia, as well as in the pathophysiology of other neurological disorders. When given intravenously, the caspase-3-loaded nanospheres were rapidly transported across the BBB and dose-dependently decreased infarct volume, neurological deficit, and ischemiainduced caspase-3 activity in mice subjected to focal cerebral ischemia/reperfusion. Because significant opening of the BBB starts only 6 h after ischemia/reperfusion, the rapid transfer of nanospheres to the brain was not likely caused by an increased permeability of the BBB. Similarly, nanospheres inhibited physiological caspase-3 activity during development in the neonatal mouse cerebellum on postnatal day 17, after closure of the BBB. These observations convincingly demonstrate that transferrin monoclonal antibody-conjugated chitosan nanospheres are an efficient delivery system for bringing neuroprotective, small peptide drugs into the brain. This opens intriguing new avenues for the treatment of central nervous system disorders in which the administration of therapeutic agents is handicapped by insufficient diffusion across the BBB. Further studies are eagerly awaited to see if this technology will be applicable to polypeptide factors, for example, brain-derived neurotrophic factor and ciliary neurotrophic factor.

Alcoholism and other alcohol use disorders are major public health problems, and the success rates of non-pharmacological treatment of these disorders such as psychotherapy, cognitive-behavioral therapy, group therapy, or residential treatment programs, remain only modest at best. High rates of recidivism (relapse) in alcoholics attempting to remain abstinent are prevalent worldwide. In recent years abundant evidence has accumulated demonstrating that alcoholism is a complex and multifaceted disease of the brain caused by numerous genetic, neurobiological, developmental, environmental, and socioeconomic factors that are still not yet fully understood. There is thus a great need to improve the success rates of all forms of treatment of alcoholism not only in preventing relapse, but curbing active alcohol consumption and craving. The development of improved pharmacotherapies that could be used as adjuncts to the aforementioned non-pharmacological treatment approaches is one avenue of great interest to the scientific community and the general public. Currently there are only three medications approved by the U.S. Food and Drug Administration (FDA) for use in the treatment of alcohol abuse and alcoholism - disulfiram, naltrexone, and acamprosate. Yet medication compliance issues and the modest efficacy of these compounds leave substantial room for improvement. This special issue is devoted to reviewing the current status of these FDAapproved medications in the treatment of alcoholism. In addition, preclinical and clinical evidence suggesting that other classes of medications might also be of potential use are reviewed, including anticonvulsants, GABAB receptor agonists, cholinergic receptor partial agonists, corticotropin-releasing factor and cannabinoid CB1 receptor antagonists, nociceptin receptor ligands, and the novel antipsychotic aripiprazole.

Disulfiram treatment, despite its limitations, remains a viable option as a treatment for alcohol dependence and has shown recent promise in treating (1) those with co-morbid alcohol dependence and post-traumatic stress disorder, (2) those with co-morbid cocaine- and alcohol-dependence, and (3) those with cocaine-dependence alone. Although disulfiram's mechanism of action in alcohol dependence was long thought to be its effects as a psychological deterrent, more recent studies have uncovered potential anti-craving effects as well as direct effects of disulfiram on cocaine abuse, highlighting a few of the many potential and unique benefits disulfiram may have through its inhibition of dopamine β-hydroxylase. This article will review the major clinical trials of disulfiram spanning nearly 60 years. We will discuss the pharmacodynamics and pharmacokinetics of disulfiram, indications and limitations of its use, suggestions for appropriate patient populations, and monitoring for compliance and adverse effects. We will also review recent literature on newer potential applications for disulfiram use via its unique action on dopamine β-hydroxylase.

Naltrexone is an opioid receptor antagonist with established efficacy, albeit moderate, for the treatment of alcohol dependence. This manuscript provides a critical review of the literature on naltrexone as a pharmacotherapy for alcoholism by covering the following areas: (a) clinical findings from treatment studies; (b) pharmacokinetics and safety data; (c) medication compliance and persistence; and (d) neurobiological and biobehavioral mechanisms of action of naltrexone for the indication of alcohol dependence. This review will then focus on the emerging literature on naltrexone pharmacogenetics, which has the potential to identify responders on the basis of genetic variation and to use genetic tools to individualize the use of this medication. Limitations and future directions in the research and practice of naltrexone for alcoholism are also outlined.

Alcoholism is one of the most prevalent substance dependence disorders in the world. Advances in research in the neurobiological mechanisms underlying alcohol dependence have identified specific neurotransmitter targets for the development of pharmacological treatments. Acamprosate, marketed under the brand name Campral, is an orally administered drug available by prescription in the U.S. and throughout much of the world for treating alcohol dependence. Its safety and efficacy have been demonstrated in numerous clinical trials worldwide. Here we provide an overview of acamprosate in the context of the neurobiological underpinnings of alcohol dependence. We propose that unlike previously available pharmacotherapies, acamprosate represents a prototypical neuromodulatory approach in the treatment of alcohol dependence. A neuromodulatory approach seeks to restore the disrupted changes in neurobiology resulting from chronic alcohol intake. We believe that a neuromodulatory approach will provide a heuristic framework for developing more effective pharmacotherapies for alcohol dependence.

Both preclinical and clinical research studies have shown the GABAB receptor agonist baclofen represents a promising treatment for alcohol dependence. Preliminary clinical studies indicate that baclofen is able to suppress withdrawal symptoms in alcoholdependent patients affected by the alcohol withdrawal syndrome. Moreover, baclofen has shown efficacy and safety in promoting alcohol abstinence in alcohol dependent patients in two placebo-controlled trials including one in alcohol-dependent patients with liver cirrhosis. These trials also demonstrated that baclofen was associated with reductions in withdrawal-related anxiety and alcohol craving. However, more work is needed to clearly demonstrate the efficacy of baclofen and to ascertain whether efficacy is limited to certain subtypes of alcoholic patients. For example, a recent US trial failed to demonstrate a robust effect of baclofen in treating alcohol-dependent patients though the relative moderate severity of alcohol-dependence in that trial has been suggested as one factor that may have contributed to the finding. In the present review, the authors will summarize the published clinical studies on the role of baclofen in alcohol dependence and will also present some unpublished secondary analyses. Finally, the authors will discuss possible future directions to further investigate the role of baclofen in alcohol dependence (e.g., baclofen's biobehavioral mechanisms, different baclofen doses, differences in severity and in alcoholic subtypes, different formulations of baclofen, possible combination of baclofen with other medications).

Alcohol dependence is a major health problem worldwide. Various pharmacological agents have been used in the management of alcohol dependence. This review looks at the role of topiramate and other anticonvulsants in the management of alcohol dependence. Topiramate is the most widely used anticonvulsant in the treatment of alcohol dependence. The literature on topiramate is reviewed and critically analyzed, along with its proposed mechanism of action in alcohol dependence. A review of data available on other anticonvulsants like carbamazepine, oxcarbazepine, sodium valproate, gabapentin and levetiracetam are presented and their potential in the treatment of alcohol dependence is considered, together with future research directions.

Alcohol dependence is a costly and socially devastating illness. The dopamine system has received increased attention due to the consensus that dopaminergic dysfunction is at the core of the addiction process. Agents that modulate this system might be beneficial in reducing craving, reward, and relapse. Aripiprazole is a 3rd generation atypical antipsychotic U.S. Food and Drug Administrationapproved for the treatment of schizophrenia, bipolar disorder, and treatment-resistant major depression. Its principal mechanism of action appears to be associated with partial agonism at the D2 dopamine receptor. Nevertheless, relatively recent pre-clinical data shows that aripiprazole might exert its action by way of agonism, partial agonism, and antagonism at both dopamine and serotonin receptors. In animal models of alcoholism aripiprazole produced an overall decrease in drinking behavior. Clinical trials with aripiprazole in alcoholics have shown some positive, but inconsistent, results. Given aripiprazole's putative activity on frontal-subcortical circuits subserving reward/craving and impulsive behavior, it might prove to be beneficial for neuropsychiatric conditions in which dysregulation of reward and impulsivity, among them alcoholism, are at the core of the syndrome. This article proposes a potential role for aripiprazole in alcoholism treatment, and suggests that more randomized controlled trials should be designed at appropriate doses to better understand aripiprazole's potential role as a treatment option. More options are needed to treat alcoholics that fall into different subgroups (e.g., those with impulsive disorders), or non-responsive to available treatments. Early results with aripiprazole are promising and warrant further exploration.

The present paper summarizes the results of a number of pharmacological studies implicating the cannabinoid CB1 receptor in the neural circuitry regulating different alcohol-related behaviors in rodents. Specifically, cannabinoid CB1 receptor antagonists - including the prototype, rimonabant - have been reported to suppress: (a) acquisition and maintenance of alcohol drinking behavior under the 2-bottle “alcohol vs water” choice regimen; (b) the increase in alcohol intake occurring after a period of alcohol abstinence (an experimental model of alcohol relapse); (c) alcohol's reinforcing and motivational properties measured in rats trained to perform a specific task (e.g., lever-pressing) to access alcohol; (d) reinstatement of extinguished alcohol-seeking behavior triggered in rats by a nicotine challenge or presentation of cues previously associated to alcohol availability (another model of alcohol relapse). Additional data indicate that the opioid receptor antagonists, naloxone and naltrexone, synergistically potentiate the suppressing effect of rimonabant on alcohol intake and alcohol's motivational properties in rats. Conversely, the two clinical studies conducted to date (one in alcoholdependent individuals and one in nontreatment-seeking heavy alcohol drinkers) yielded less conclusive results. Unfortunately, the recent discontinuation - due to the occurrence of some psychiatric adverse effects - of all trials with cannabinoid CB1 receptor antagonists apparently hinders further investigations on the potential of rimonabant in the treatment of alcohol dependence.

Alcohol use disorders (AUDs) are complex and developing effective treatments will require the combination of novel medications and cognitive behavioral therapy approaches. Epidemiological studies have shown there is a high correlation between alcohol consumption and tobacco use, and the prevalence of smoking in alcoholics is as high as 80% compared to about 30% for the general population. Both preclinical and clinical data provide evidence that nicotine administration increases alcohol intake and nonspecific nicotinic receptor antagonists reduce alcohol-mediated behaviors. As nicotine interacts specifically with the neuronal nicotinic acetylcholine receptor (nAChR) system, this suggests that nAChRs play an important role in the behavioral effects of alcohol. In this review, we discuss the importance of nAChRs for the treatment of AUDs and argue that the use of FDA approved nAChR ligands, such as varenicline and mecamylamine, approved as smoking cessation aids may prove to be valuable treatments for AUDs. We also address the importance of combining effective medications with behavioral therapy for the treatment of alcohol dependent individuals.

Alcoholism is a chronic disorder characterized by cycling periods of excessive ethanol consumption, withdrawal, abstinence and relapse, which is associated with progressive changes in central corticotropin-releasing factor (CRF) receptor signaling. CRF and urocortin peptides act by binding to the CRF type 1 (CRF1R) or the CRF type 2 (CRF2R) receptors, both of which have been implicated in the regulation of neurobiological responses to ethanol. The current review provides a comprehensive overview of preclinical evidence from studies involving rodents that when viewed together, suggest a promising role for CRFR antagonists in the treatment of alcohol abuse disorders. CRFR antagonists protect against excessive ethanol intake resulting from ethanol dependence without influencing ethanol intake in non-dependent animals. Similarly, CRFR antagonists block excessive binge-like ethanol drinking in non-dependent mice but do not alter ethanol intake in mice drinking moderate amounts of ethanol. CRFR antagonists also protect against increased ethanol intake and relapse-like behaviors precipitated by exposure to a stressful event. Additionally, CRFR antagonists attenuate the negative emotional responses associated with ethanol withdrawal. The protective effects of CRFR antagonists are modulated by CRF1R. Finally, recent evidence has emerged suggesting that CRF2R agonists may also be useful for treating alcohol abuse disorders.

Nociceptin (known also as orphanin FQ) is the most recently discovered member of the endogenous opioid peptide family, albeit nearly 15 years ago. Nociceptin renders or influences many behavioral, psychological and neurobiological processes, including memory, anxiety, stress and reward. Since its discovery, results of a steady stream of studies have suggested that endogenous nociceptin might be involved in responses to addictive drugs, and that targeting the nociceptin system may be beneficial in treating addictions. The current review summarizes and critically appraises those studies, particularly those that point to an application in treating alcoholism. Overall, most studies suggest that the endogenous nociceptin system has a physiological role in mediating or regulating behavioral responses to alcohol, and that activating nociceptin receptors suppresses ongoing alcohol consumption or reinstatement of responding for alcohol. These findings encourage the development of therapies targeted at the nociceptin system for the treatment of alcoholism in humans, though a minor number of studies showing continuous activation of the nociceptin receptor can produce increased, rather than reduced, alcohol consumption emphasize the necessity of further investigation.

Calcium is an essential intracellular messenger and serves critical cellular functions in both excitable and non-excitable cells. Most of the physiological functions in these cells are uniquely regulated by changes in cytosolic Ca2+ levels ([Ca2+]i), which are achieved via various mechanisms. One of these mechanism(s) is activated by the release of Ca2+ from the endoplasmic reticulum (ER), followed by Ca2+ influx across the plasma membrane (PM). Activation of PM Ca2+ channels is essential for not only refilling of the ER Ca2+ stores, but is also critical for maintaining [Ca2+]i that regulates biological functions, such as neurosecretion, sensation, long term potentiation, synaptic plasticity, gene regulation, as well as cellular growth and differentiation. Alterations in Ca2+ homeostasis have been suggested in the onset/progression of neurological diseases, such as Parkinson's, Alzheimer's, bipolar disorder, and Huntington's diseases. Available data on transient receptor potential conical (TRPC) protein indicate that these proteins initiate Ca2+ entry pathways and are essential in maintaining cytosolic, ER, and mitochondrial Ca2+ levels. A number of biological functions have been assigned to these TRPC proteins. Silencing of TRPC1 and TRPC3 has been shown to inhibit neuronal proliferation and loss of TRPC1 is implicated in neurodegeneration. Thus, TRPC channels not only contribute towards normal physiological processes, but are also implicated in several human pathological conditions. Overall, it is suggested that these channels could be used as potential therapeutic targets for many of these neurological diseases. Thus, in this review we have focused on the functional implication of TRPC channels in neuronal cells along with the elucidation of their role in neurodegeneration.

Mitochondrial metabolism is a highly orchestrated phenomenon in which many enzyme systems cooperate in a variety of pathways to dictate cellular fate. As well as its vital role in cellular energy metabolism (ATP production), mitochondria are powerful organelles that regulate reactive oxygen species production, NAD+/NADH ratio and programmed cell death. In addition, mitochondrial abnormalities have been well-recognized to contribute to degenerative diseases, like Parkinson's disease (PD). Particularly a deficiency in the mitochondrial respiratory chain complex I and cristae disruption have been consistently described in PD. Moreover, the products of PD-familial genes, including α-synuclein, Parkin, PINK1, DJ-1, LRRK2 and HTR2A, were shown to localize to the mitochondria under certain conditions. It seems that PD has a mitochondrial component so events that would modulate normal mitochondrial functions may compromise neuronal survival. However, it remains an open question whether alterations of these pathways lead to different aspects of PD or whether they converge at a point that is the common denominator of PD pathogenesis. In this review we will focus on mitochondrial metabolic control and its implications on sirtuins activation, microtubule dynamics and the autophagic-lysosomal pathway. We will address mitochondrial metabolism modulation as a new promising therapeutic tool for PD.

The active form of the serine/threonine kinase cRaf-1 is upregulated postmortem in the brains of Alzheimer's disease (AD) patients and in transgenic mouse models of AD pathology. The persistent activation of cRaf-1 can activate the proinflammatory factor NFκB and consequently, upregulate the expression of several of its downstream factors such as the amyloid precursor protein (APP), Cox-2 and iNOS. These factors have been found upregulated in numerous neurodegenerative conditions including AD, epilepsy, brain trauma, and psychological stress. The Raf kinase inhibitors, GW5074 and ZM336372, are neuroprotective against many different neurotoxic insults in vitro, including the A.. peptide, glutamate and glutathione depletion. Recently, we have reported that the multikinase and potent Raf inhibitor sorafenib reversed memory impairment and reduced the expression of APP, Cox-2, and iNOS in the brain of the transgenic mouse model of AD, APPswe. Similar improvement of behavioral outcome was attained after acute treatment with GW5074 in a mouse model of Huntington's disease. Several Raf inhibitors have been developed to treat aggressive forms of cancer showing an upregulation of Raf kinases. These Raf inhibitors offer a great promise as therapeutic tools against neurological disorders. The negative and positive aspects of these inhibitors as anti-neurodegenerative agents are discussed.