Most Cited Articles:

Abstracts


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Disulfiram: An Old Therapeutic with New Applications
Kelly S. Barth and Robert J. Malcolm.

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.


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Effectiveness and Safety of Baclofen in the Treatment of Alcohol Dependent Patients
Lorenzo Leggio, James C. Garbutt and Giovanni Addolorato.

Both preclinical and clinical research studies have shown the GABA B 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).


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Assessing activation states in microglia
Carol A. Colton and Donna M. Wilcock.

Since the original identification of microglia as a principal player in the brain's innate immune response, microglial activation has been widely studied. Recent studies suggest that microglial responses are heterogeneous, requiring a more precise definition of the functional outcomes of their participation in disease. Similarly to other tissue macrophages, microglia respond to inflammatory or injurious stimuli in the CNS in a pre-programmed manner that is designed to both kill and to set the stage for repair and resolution of the disease. In vitro studies on acute immune responses have provided key information on the initiation, signaling pathways and products of activated macrophages. However, in chronic neurodegenerative diseases such as Alzheimer's disease where in vivo analyses are critical to understanding the long-term disease processes, our knowledge of the integrated tissue immune response and the outcome of this immune activity to neurons and other glia over the extended course of disease is more limited. This is due in part to the complexity of microglial activation states and to the location of microglia in a dense neuronal network. Classical activation, alternative activation and acquired deactivation are each found in the brain during chronic neuroinflammatory diseases and may demonstrate regional differences in expression levels. This review will identify "markers" that can be used to explore inflammatory states in the brain and will discuss the likely functional outcomes when these cytoactive factors are expressed. A broad-based functional view is provided that is designed to more fully explore the balance between inflammo-toxic and inflammo-resolution factors that govern chronic disease progression.


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Microglia and inflammation in Alzheimer's disease
Shweta Mandrekar-Colucci and Gary E. Landreth.

One hundred and fifty years have elapsed since the original discovery of the microglial cell by Virchow. While this cell type has been well studied, the role of microglia in the pathology of many central nervous system diseases still remains enigmatic. It is widely accepted that microglial-mediated inflammation contributes to the progression of Alzheimer's disease (AD); however, the precise mechanisms through which these cells contribute to AD-related inflammation remains to be elucidated. In the AD brain, microglial cells are found in close association with amyloid β (Aβ) deposits. Histological examination of AD brains as well as cell culture studies have shown that the interaction of microglia with fibrillar Aβ leads to their phenotypic activation. The conversion of these cells into a classically 'activated' phenotype results in production of chemokines, neurotoxic cytokines and reactive oxygen and nitrogen species that are deleterious to the CNS. However, microglia also exert a neuroprotective role through their ability to phagocytose Aβ particles and clear soluble forms of Aβ. These cells have been documented to play integral roles in tissue repair and inflammation, and in recent years it has been appreciated that this cell type is capable of facilitating a more complex response to pathogens by changing their activation status. A variety of new findings indicate that their role in the central nervous system is far more complex than previously appreciated. In this review we discuss the role of microglia in the normal brain and their phenotypic heterogeneity and how this may play a role in ADrelated pathophysiology. We touch on what is known about their ability to recognize and clear Aβ peptides as well as more controversial topics, including various activation states of microglia and the ability of peripheral macrophages or monocytes to infiltrate the brain.


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Non-Steroidal Anti-Inflammatory Drugs and Alzheimer's Disease: The Epidemiological Evidence
C.A. Szekely and P.P. Zandi.

Alzheimer's disease imposes a significant public health burden that will only worsen as the population ages. Thus, there is considerable motivation to develop effective strategies to treat, or more ideally, prevent the disease. Epidemiologic evidence has suggested that non-steroidal anti-inflammatory drugs (or NSAIDs) may be neuro-protective. However, this evidence is controversial. Observational studies in humans have found that the use of NSAIDs is associated with a lower risk of developing Alzheimer's disease. By contrast, randomized trials have reported that NSAIDs are not effective in treating patients with clinically established disease nor in preventing the onset of dementia among those who are cognitively normal or have mild cognitive impairment. In this article, we review the existing epidemiologic evidence on the relationship between NSAIDs and Alzheimer's disease and discuss several hypotheses to explain the divergent findings.


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Amyloid-β Immunotherapy for Alzheimer's Disease
H.J. Fu, B. Liu, J.L. Frost and C.A. Lemere.

Alzheimer's disease (AD) is a progressive, degenerative disorder of the brain and the most common form of dementia among the elderly. As the population grows and lifespan is extended, the number of AD patients will continue to rise. Current clinical therapies for AD provide partial symptomatic benefits for some patients; however, none of them modify disease progression. Amyloid-β (Aβ) peptide, the major component of senile plaques in AD patients, is considered to play a crucial role in the pathogenesis of AD thereby leading to Aβ as a target for treatment. Aβ immunotherapy has been shown to induce a marked reduction in amyloid burden and an improvement in cognitive function in animal models. Although preclinical studies were successful, the initial human clinical trial of an active Aβ vaccine was halted due to the development of meningoencephalitis in ~ 6% of the vaccinated AD patients. Some encouraging outcomes, including signs of cognitive stabilization and apparent plaque clearance, were obtained in subset of patients who generated antibody titers. These promising preliminary data support further efforts to refine Aβ immunotherapy to produce highly effective and safer active and passive vaccines for AD. Furthermore, some new human clinical trials for both active and passive Aβ immunotherapy are underway. In this review, we will provide an update of Aβ immunotherapy in animal models and in human beings, as well as discuss the possible mechanisms underlying Aβ immunotherapy for AD.


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Mechanisms of Oxidative Glutamate Toxicity: The Glutamate/Cystine Antiporter System xc¯ as a Neuroprotective Drug Target
Philipp Albrecht, Jan Lewerenz, Sonja Dittmer, Rebecca Noack, Pamela Maher and Axel Methner.

The glutamate/cystine antiporter system xc̄ transports cystine into cells in exchange for the important neurotransmitter glutamate at a ratio of 1:1. It is composed of a specific light chain, xCT, and a heavy chain, 4F2, linked by a disulfide bridge. Both subunits are localized prominently in the mouse and human brain especially in border areas between the brain and periphery including vascular endothelial cells, ependymal cells, choroid plexus, and leptomeninges. Glutamate exported by system xc̄ is largely responsible for the extracellular glutamate concentration in the brain, whereas the imported cystine is required for the synthesis of the major endogenous antioxidant, glutathione. System xc̄ thus connects the antioxidant defense with neurotransmission and behavior. Disturbances in the function of system xc̄ have been implicated in nerve cell death due to increased extracellular glutamate and reduced intracellular glutathione. In vitro, inhibition of cystine import through system xc̄ leads to cell death by a mechanism called oxidative glutamate toxicity or oxytosis, which includes depletion of intracellular glutathione, activation of 12-lipoxygenase, accumulation of intracellular peroxides, and the activation of a cyclic guanosine monophosphate (cGMP)-dependent calcium channel towards the end of the death cascade. Cell death caused by oxytosis is distinct from classical apoptosis. In this contribution, we discuss the function of system xc̄ in vitro and in vivo, the role of xCT as an important but due to its dual role probably ambivalent drug target, and the relevance of oxytosis as an in vitro assay for the identification of novel neuroprotective proteins and signaling pathways.


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Clinical Trials for Neuroprotection in ALS
G. Siciliano, C. Carlesi, L. Pasquali, S. Piazza, S. Pietracupa, F. Fornai, S. Ruggieri and L. Murri.

Owing to uncertainty on the pathogenic mechanisms underlying motor neuron degeneration in amyotrophic lateral sclerosis (ALS) riluzole remains the only available therapy, with only marginal effects on disease survival. Here we review some of the recent advances in the search for disease-modifying drugs for ALS based on their putative neuroprotective effetcs. A number of more or less established agents have recently been investigated also in ALS for their potential role in neuroprotection and relying on antiglutamatergic, antioxidant or antiapoptotic strategies. Among them Talampanel, beta-lactam antibiotics, Coenzyme Q10, and minocycline have been investigated. Progress has also been made in exploiting growth factors for the treatment of ALS, partly due to advances in developing effective delivery systems to the central nervous system. A number of new therapies have also been identified, including a novel class of compounds, such as heat-shock protein co-inducers, which upregulate cell stress responses, and agents promoting autophagy and mitochondriogenesis, such as lithium and rapamycin. More recently, alterations of mRNA processing were described as a pathogenic mechanism in genetically defined forms of ALS, as those related to TDP-43 and FUS-TLS gene mutations. This knowledge is expected to improve our understanding of the pathogenetic mechanism in ALS and developing more effective therapies.


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Drosophila melanogaster in the Study of Human Neurodegeneration
Frank Hirth.

Human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people. The majority of the diseases are associated with pathogenic oligomers from misfolded proteins, eventually causing the formation of aggregates and the progressive loss of neurons in the brain and nervous system. Several of these proteinopathies are sporadic and the cause of pathogenesis remains elusive. Heritable forms are associated with genetic defects, suggesting that the affected protein is causally related to disease formation and/or progression. The limitations of human genetics, however, make it necessary to use model systems to analyse affected genes and pathways in more detail. During the last two decades, research using the genetically amenable fruitfly has established Drosophila melanogaster as a valuable model system in the study of human neurodegeneration. These studies offer reliable models for Alzheimer's, Parkinson's, and motor neuron diseases, as well as models for trinucleotide repeat expansion diseases, including ataxias and Huntington's disease. As a result of these studies, several signalling pathways including phosphatidylinositol 3-kinase (PI3K)/Akt and target of rapamycin (TOR), c-Jun N-terminal kinase (JNK) and bone morphogenetic protein (BMP) signalling, have been shown to be de- regulated in models of proteinopathies, suggesting that two or more initiating events may trigger disease formation in an age-related manner. Moreover, these studies also demonstrate that the fruitfly can be used to screen chemical compounds for their potential to prevent or ameliorate the disease, which in turn can directly guide clinical research and the development of novel therapeutic strategies for the treatment of human neurodegenerative diseases.


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Oxidative Stress and Altered Mitochondrial Function in Neurodegenerative Diseases: Lessons >From Mouse Models
J.C. Fernandez-Checa, A. Fernandez, A. Morales, M. Mari, C. Garcia-Ruiz and A. Colell.

Oxidative stress has been consistently linked to ageing-related neurodegenerative diseases leading to the generation of lipid peroxides, carbonyl proteins and oxidative DNA damage in tissue samples from affected brains. Studies from mouse models that express disease-specific mutant proteins associated to the major neurodegenerative processes have underscored a critical role of mitochondria in the pathogenesis of these diseases. There is strong evidence that mitochondrial dysfunction is an early event in neurodegeneration. Mitochondria are the main cellular source of reactive oxygen species and key regulators of cell death. Moreover, mitochondria are highly dynamic organelles that divide, fuse and move along axons and dendrites to supply cellular energetic demands; therefore, impairment of any of these processes would directly impact on neuronal viability. Most of the disease-specific pathogenic mutant proteins have been shown to target mitochondria, promoting oxidative stress and the mitochondrial apoptotic pathway. In addition, disease-specific mutant proteins may also impair mitochondrial dynamics and recycling of damaged mitochondria via autophagy. Collectively, these data suggest that ROS-mediated defective mitochondria may accumulate during and contribute to disease progression. Strategies aimed to improve mitochondrial function or ROS scavenging may thus be of potential clinical relevance.