Neuroprotective effects of creatine in a transgenic mouse model of Huntington's disease

Energy dysfunction in Huntington's disease: insights from PGC-1α, AMPK, and CKB

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. When the number of CAG repeats exceeds 36, the translated polyglutamine-expanded Htt protein interferes with the normal functions of many types of cellular machinery and causes cytotoxicity. Clinical symptoms include progressive involuntary movement disorders, psychiatric signs, cognitive decline, dementia, and a shortened lifespan. The most severe brain atrophy is observed in the striatum and cortex. Besides the well-characterized neuronal defects, recent studies showed that the functions of mitochondria and several key players in energy homeostasis are abnormally regulated during HD progression. Energy dysregulation thus is now recognized as an important pathogenic pathway of HD. This review focuses on the importance of three key molecular determinants (peroxisome proliferator-activated receptor-γ coactivator-1α, AMP-activated protein kinase, and creatine kinase B) of cellular energy homeostasis and their possible involvement in HD pathogenesis.

Therapeutic approaches to preventing cell death in Huntington disease

Neurodegenerative diseases affect the lives of millions of patients and their families. Due to the complexity of these diseases and our limited understanding of their pathogenesis, the design of therapeutic agents that can effectively treat these diseases has been challenging. Huntington disease (HD) is one of several neurological disorders with few therapeutic options. HD, like numerous other neurodegenerative diseases, involves extensive neuronal cell loss. One potential strategy to combat HD and other neurodegenerative disorders is to intervene in the execution of neuronal cell death. Inhibiting neuronal cell death pathways may slow the development of neurodegeneration. However, discovering small molecule inhibitors of neuronal cell death remains a significant challenge. Here, we review candidate therapeutic targets controlling cell death mechanisms that have been the focus of research in HD, as well as an emerging strategy that has been applied to developing small molecule inhibitors-fragment-based drug discovery (FBDD). FBDD has been successfully used in both industry and academia to identify selective and potent small molecule inhibitors, with a focus on challenging proteins that are not amenable to traditional high-throughput screening approaches. FBDD has been used to generate potent leads, pre-clinical candidates, and has led to the development of an FDA approved drug. This approach can be valuable for identifying modulators of cell-death-regulating proteins; such compounds may prove to be the key to halting the progression of HD and other neurodegenerative disorders.

Rodent motor and neuropsychological behaviour measured in home cages using the integrated modular platform SmartCage™

1. To facilitate investigation of diverse rodent behaviours in rodents' home cages, we have developed an integrated modular platform, the SmartCage(™) system (AfaSci, Inc. Burlingame, CA, USA), which enables automated neurobehavioural phenotypic analysis and in vivo drug screening in a relatively higher-throughput and more objective manner. 2, The individual platform consists of an infrared array, a vibration floor sensor and a variety of modular devices. One computer can simultaneously operate up to 16 platforms via USB cables. 3. The SmartCage(™) detects drug-induced increases and decreases in activity levels, as well as changes in movement patterns. Wake and sleep states of mice can be detected using the vibration floor sensor. The arousal state classification achieved up to 98% accuracy compared with results obtained by electroencephalography and electromyography. More complex behaviours, including motor coordination, anxiety-related behaviours and social approach behaviour, can be assessed using appropriate modular devices and the results obtained are comparable with results obtained using conventional methods. 4. In conclusion, the SmartCage(™) system provides an automated and accurate tool to quantify various rodent behaviours in a 'stress-free' environment. This system, combined with the validated testing protocols, offers powerful a tool kit for transgenic phenotyping and in vivo drug screening.

Mouse models of polyglutamine diseases: review and data table. Part I

Polyglutamine (polyQ) disorders share many similarities, such as a common mutation type in unrelated human causative genes, neurological character, and certain aspects of pathogenesis, including morphological and physiological neuronal alterations. The similarities in pathogenesis have been confirmed by findings that some experimental in vivo therapy approaches are effective in multiple models of polyQ disorders. Additionally, mouse models of polyQ diseases are often highly similar between diseases with respect to behavior and the features of the disease. The common features shared by polyQ mouse models may facilitate the investigation of polyQ disorders and may help researchers explore the mechanisms of these diseases in a broader context. To provide this context and to promote the understanding of polyQ disorders, we have collected and analyzed research data about the characterization and treatment of mouse models of polyQ diseases and organized them into two complementary Excel data tables. The data table that is presented in this review (Part I) covers the behavioral, molecular, cellular, and anatomic characteristics of polyQ mice and contains the most current knowledge about polyQ mouse models. The structure of this data table is designed in such a way that it can be filtered to allow for the immediate retrieval of the data corresponding to a single mouse model or to compare the shared and unique aspects of many polyQ models. The second data table, which is presented in another publication (Part II), covers therapeutic research in mouse models by summarizing all of the therapeutic strategies employed in the treatment of polyQ disorders, phenotypes that are used to examine the effects of the therapy, and therapeutic outcomes.

Mouse models of polyglutamine diseases in therapeutic approaches: review and data table. Part II

Mouse models of human diseases are created both to understand the pathogenesis of the disorders and to find successful therapies for them. This work is the second part in a series of reviews of mouse models of polyglutamine (polyQ) hereditary disorders and focuses on in vivo experimental therapeutic approaches. Like part I of the polyQ mouse model review, this work is supplemented with a table that contains data from experimental studies of therapeutic approaches in polyQ mouse models. The aim of this review was to characterize the benefits and outcomes of various therapeutic strategies in mouse models. We examine whether the therapeutic strategies are specific to a single disease or are applicable to more than one polyQ disorder in mouse models. In addition, we discuss the suitability of mouse models in therapeutic approaches. Although the majority of therapeutic studies were performed in mouse models of Huntington disease, similar strategies were also used in other disease models.

Tissue transglutaminase overexpression does not modify the disease phenotype of the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a devastating autosomal-dominant neurodegenerative disorder initiated by an abnormally expanded polyglutamine in the huntingtin protein. Determining the contribution of specific factors to the pathogenesis of HD should provide rational targets for therapeutic intervention. One suggested contributor is the type 2 transglutaminase (TG2), a multifunctional calcium dependent enzyme. A role for TG2 in HD has been suggested because a polypeptide-bound glutamine is a rate-limiting factor for a TG2-catalyzed reaction, and TG2 can cross-link mutant huntingtin in vitro. Further, TG2 is up regulated in brain areas affected in HD. The objective of this study was to further examine the contribution of TG2 as a potential modifier of HD pathogenesis and its validity as a therapeutic target in HD. In particular our goal was to determine whether an increase in TG2 level, as documented in human HD brains, modulates the well-characterized phenotype of the R6/2 HD mouse model. To accomplish this objective a genetic cross was performed between R6/2 mice and an established transgenic mouse line that constitutively expresses human TG2 (hTG2) under control of the prion promoter. Constitutive expression of hTG2 did not affect the onset and progression of the behavioral and neuropathological HD phenotype of R6/2 mice. We found no alterations in body weight changes, rotarod performances, grip strength, overall activity, and no significant effect on the neuropathological features of R6/2 mice. Overall the results of this study suggest that an increase in hTG2 expression does not significantly modify the pathology of HD.

Proteomic changes in the brains of Huntington's disease mouse models reflect pathology and implicate mitochondrial changes

Mouse models of Huntington's disease (HD) have been used extensively to recapitulate the pathological cascade of events in human HD. Mutant huntingtin interacts with many other proteins and has a well documented effect on gene expression. We were interested in whether changes in gene expression were translated into changes in the protein abundance in the brains of mouse models of HD. In two different HD knock in mouse models, the HdhQ150 and the HdhQ92, we detected changes in the abundance of proteins in mouse brain between wild-type and homozygous mutant animals. The numbers of changes detected rose with age and phenotypic severity. There were regional differences with most changes seen in the caudate and fewest in the cerebellum, reflecting the known pattern of gene expression changes in human HD and mouse models of HD and the known pathology. However, while some changes in the proteome followed changes in gene expression others did not directly reflect changes in gene expression seen in these animal models. Seven of the sixteen proteins detected have a known mitochondrial function, an enrichment of six-fold over that expected (p=0.001): these mitochondrial proteins show both increases and decreases in abundance implying that a straightforward alteration in mitochondrial number is unlikely to account for this finding.

Creatine metabolism and psychiatric disorders: Does creatine supplementation have therapeutic value?

Athletes, body builders, and military personnel use dietary creatine as an ergogenic aid to boost physical performance in sports involving short bursts of high-intensity muscle activity. Lesser known is the essential role creatine, a natural regulator of energy homeostasis, plays in brain function and development. Creatine supplementation has shown promise as a safe, effective, and tolerable adjunct to medication for the treatment of brain-related disorders linked with dysfunctional energy metabolism, such as Huntington's Disease and Parkinson's Disease. Impairments in creatine metabolism have also been implicated in the pathogenesis of psychiatric disorders, leaving clinicians, researchers and patients alike wondering if dietary creatine has therapeutic value for treating mental illness. The present review summarizes the neurobiology of the creatine-phosphocreatine circuit and its relation to psychological stress, schizophrenia, mood and anxiety disorders. While present knowledge of the role of creatine in cognitive and emotional processing is in its infancy, further research on this endogenous metabolite has the potential to advance our understanding of the biological bases of psychopathology and improve current therapeutic strategies.

Protein oxidation in Huntington disease

Huntington disease (HD) is an inherited neurodegenerative disorder caused by expansion of CAG repeats in the huntingtin gene, affecting initially the striatum and progressively the cortex. Oxidative stress, and consequent protein oxidation, has been described as important to disease progression. This review focuses on recent advances in the field, with a particular emphasis on the identified target proteins and the role that their oxidation has or might have in the pathophysiology of HD. Oxidation and the resulting inactivation and/or degradation of important proteins can explain the impairment of several metabolic pathways in HD. Oxidation of enzymes involved in ATP synthesis can account for the energy deficiency observed. Impairment of protein folding and degradation can be due to oxidation of several heat shock proteins and Valosin-containing protein. Oxidation of two enzymes involved in the vitamin B6 metabolism could result in decreased availability of pyridoxal phosphate, which is a necessary cofactor in transaminations, the kynurenine pathway and the synthesis of glutathione, GABA, dopamine and serotonin, all of which have a key role in HD pathology. In addition, protein oxidation often contributes to oxidative stress, aggravating the molecular damage inside the cell.

Sex-specific antidepressant effects of dietary creatine with and without sub-acute fluoxetine in rats

The potential role of metabolic impairments in the pathophysiology of depression is motivating researchers to evaluate the treatment efficacy of creatine, a naturally occurring energetic and neuroprotective compound found in brain and muscle tissues. Growing evidence is demonstrating the benefit of oral creatine supplements for reducing depressive symptoms in humans and animals. A novel question is whether dietary creatine, when combined with antidepressant drug therapy, would be more effective than either compound alone. To answer this question, four studies were conducted to investigate the behavioral effects of combined creatine and low-dose fluoxetine treatment using the forced swim test in male and female rats. Sprague-Dawley rats were fed powdered rodent chow supplemented with 0%, 2% or 4% w/w creatine monohydrate for 5 weeks. Rats were injected with fluoxetine (5.0 or 10.0 mg/kg) or saline according to a sub-acute dosing schedule. Female rats maintained on a 4% creatine diet displayed antidepressant-like effects compared to non-supplemented females prior to fluoxetine treatment. In contrast, creatine did not alter behavior reliably in males. Following drug treatment and a second forced swim trial, the antidepressant-like profile of creatine remained significant only in females co-administered 5.0 mg/kg fluoxetine. Moreover, in females only, supplementation with 4% creatine produced a more robust antidepressant-like behavioral profile compared to either dose of fluoxetine alone. Estrous cycle data indicated that ovarian hormones influenced the antidepressant-like effects of creatine. Addressing the issue of sex differences in response to treatment may affect our understanding of creatine, its relationship with depressive behavior, and may lead to sex-specific therapeutic strategies.

Metallothioneins protect cytosolic creatine kinases against stress induced by nitrogen-based oxidants

The formation of intracellular nitrogen-based oxidants has important physiological and pathological consequences. CK (creatine kinase), which plays a key role in intracellular energy metabolism, is a main target of low concentrations of oxidative and nitrative stresses. In the present study, the interaction between cytosolic CKs [MM-CK (muscle-type CK) and BB-CK (brain-type CK)] and MTs [metallothioneins; hMT2A (human MT-IIA) and hMT3 (human MT-III)] were characterized by both in vitro and intact-cell assays. MTs could successfully protect the cytosolic CKs against inactivation induced by low concentrations of PN (peroxynitrite) and NO both in vitro and in hMT2A-overexpressing H9c2 cells and hMT3-knockdown U-87 MG cells. Under high PN concentrations, CK formed granule-like structures, and MTs were well co-localized in these aggregated granules. Further analysis indicated that the number of cells containing the CK aggregates negatively correlated with the expression levels of MTs. In vitro experiments indicated that MTs could effectively protect CKs against aggregation during refolding, suggesting that MT might function as a chaperone to assist CK re-activation. The findings of the present study provide direct evidence of the connection between the two well-characterized intracellular systems: the precisely balanced energy homoeostasis by CKs and the oxidative-stress response system using MTs.

Huntington disease and the huntingtin protein

Huntington disease (HD) is a devastating neurodegenerative disease that derives from CAG repeat expansion in the huntingtin gene. The clinical syndrome consists of progressive personality changes, movement disorder, and dementia and can develop in children and adults. The huntingtin protein is required for human development and normal brain function. It is subject to posttranslational modification, and some events, such as phosphorylation, can play an enormous role in regulating toxicity of the huntingtin protein. The function of huntingtin in the cell is unknown, and it may play a role as a scaffold. Multiple mouse models of HD have now been created with fragments and full-length protein. The models show variable fidelity to the disease in terms of genetics, pathology, and rates of progression. Pathogenesis of HD involves cleavage of the protein and is associated with neuronal accumulation of aggregated forms. The potential mechanisms of neurodegeneration are myriad, including primary effects of protein homeostasis, gene expression, and mitochondrial dysfunction. Specific therapeutic approaches are similarly varied and include efforts to reduce huntingtin gene expression, protein accumulation, and protein aggregation.

Protein misfolding detected early in pathogenesis of transgenic mouse model of Huntington disease using amyloid seeding assay

Huntington disease (HD) is one of several fatal neurodegenerative disorders associated with misfolded proteins. Here, we report a novel method for the sensitive detection of misfolded huntingtin (HTT) isolated from the brains of transgenic (Tg) mouse models of HD and humans with HD using an amyloid seeding assay (ASA), which is based on the propensity of misfolded proteins to act as a seed and shorten the nucleation-associated lag phase in the kinetics of amyloid formation in vitro. Using synthetic polyglutamine peptides as the substrate for amyloid formation, we found that partially purified misfolded HTT obtained from end-stage brain tissue of two Tg HD mouse models and brain tissue of post-mortem human HD patients was capable of specifically accelerating polyglutamine amyloid formation compared with unseeded reactions and controls. Alzheimer and prion disease brain tissues did not do so, demonstrating the specificity of the ASA. It is unclear whether early intermediates or later conformational species in the protein misfolding process act as seeds in the ASA for HD. However, we were able to detect misfolded protein in the brains of YAC128 mice early in disease pathogenesis (11 weeks of age), whereas large inclusion bodies have not been observed in the brains of these mice by histology until 78 weeks of age, much later in the pathogenic process. The sensitive detection of misfolded HTT protein early in the disease pathogenesis in the YAC128 Tg mouse model strengthens the argument for a causative role of protein misfolding in HD.

Mitochondrial and metabolic-based protective strategies in Huntington's disease: the case of creatine and coenzyme Q

Huntington's disease (HD) is a neurodegenerative genetic disorder caused by an expansion of CAG repeats in the HD gene encoding for huntingtin (Htt), resulting in progressive death of striatal neurons, with clinical symptoms of chorea, dementia and dramatic weight loss. Metabolic and mitochondrial dysfunction caused by the expanded polyglutamine sequence have been described along with other mechanisms of neurodegeneration previously described in human tissues and animal models of HD. In this review, we focus on mitochondrial and metabolic disturbances affecting both the central nervous system and peripheral cells, including mitochondrial DNA damage, mitochondrial complexes defects, loss of calcium homeostasis and transcriptional deregulation. Glucose abnormalities have also been described in peripheral tissues of HD patients and in HD animal and cellular models. Moreover, there are no effective neuroprotective treatments available in HD. Thus, we briefly discuss the role of creatine and coenzyme Q10 that target mitochondrial dysfunction and impaired bioenergetics and have been previously used in HD clinical trials.

Early alterations of brain cellular energy homeostasis in Huntington disease models

Brain energy deficit has been a suggested cause of Huntington disease (HD), but ATP depletion has not reliably been shown in preclinical models, possibly because of the immediate post-mortem changes in cellular energy metabolism. To examine a potential role of a low energy state in HD, we measured, for the first time in a neurodegenerative model, brain levels of high energy phosphates using microwave fixation, which instantaneously inactivates brain enzymatic activities and preserves in vivo levels of analytes. We studied HD transgenic R6/2 mice at ages 4, 8, and 12 weeks. We found significantly increased creatine and phosphocreatine, present as early as 4 weeks for phosphocreatine, preceding motor system deficits and decreased ATP levels in striatum, hippocampus, and frontal cortex of R6/2 mice. ATP and phosphocreatine concentrations were inversely correlated with the number of CAG repeats. Conversely, in mice injected with 3-nitroproprionic acid, an acute model of brain energy deficit, both ATP and phosphocreatine were significantly reduced. Increased creatine and phosphocreatine in R6/2 mice was associated with decreased guanidinoacetate N-methyltransferase and creatine kinase, both at the protein and RNA levels, and increased phosphorylated AMP-dependent protein kinase (pAMPK) over AMPK ratio. In addition, in 4-month-old knock-in Hdh(Q111/+) mice, the earliest metabolic alterations consisted of increased phosphocreatine in the frontal cortex and increased the pAMPK/AMPK ratio. Altogether, this study provides the first direct evidence of chronic alteration in homeostasis of high energy phosphates in HD models in the earliest stages of the disease, indicating possible reduced utilization of the brain phosphocreatine pool.

Antioxidants in Huntington's disease

Huntington's disease (HD) is a prototypical neurodegenerative disease in which there is selective neuronal degeneration, which leads to progressive disability, manifesting itself as a movement disorder, with both psychiatric and cognitive impairment. The disease is caused by a cytosine-adenine-guanine (CAG) repeat expansion in the huntingtin gene, which causes an expanded polyglutamine repeat in the huntingtin protein, resulting in a protein with a novel gain of function. The mutant huntingtin protein causes neuronal dysfunction and eventual cell death in which transcriptional impairment, excitotoxicity, oxidative damage, inflammation, apoptosis and mitochondrial dysfunction are all implicated. A critical transcriptional impairment may be impaired expression and function of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), a master co-regulator of mitochondrial biogenesis and expression of antioxidant enzymes. A deficiency of PGC-1α leads to increased vulnerability to oxidative stress and to striatal degeneration. The extent and severity of the oxidative damage in HD are features well recognized but perhaps under-appreciated. Oxidative damage occurs to lipids, proteins and deoxyribonucleic acid (DNA), and it has been suggested that the latter may contribute to CAG repeat expansion during DNA repair [1]. A marked elevation of oxidized DNA bases occurs in patients' plasma, which may provide a biomarker of disease progression. Antioxidants are effective in slowing disease progression in transgenic mouse models of HD, and show promise in human clinical trials. Strategies to transcriptionally increase expression of antioxidant enzymes by modulating the Nrf-2/ARE pathway, or by increasing expression of PGC-1α hold great promise for developing new treatments to slow or halt the progression of HD. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Mutant huntingtin, abnormal mitochondrial dynamics, defective axonal transport of mitochondria, and selective synaptic degeneration in Huntington's disease

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease caused by expanded polyglutamine repeats in the HD gene. HD is characterized by chorea, seizures, involuntary movements, dystonia, cognitive decline, intellectual impairment and emotional disturbances. Research into mutant huntingtin (Htt) and mitochondria has found that mutant Htt interacts with the mitochondrial protein dynamin-related protein 1 (Drp1), enhances GTPase Drp1 enzymatic activity, and causes excessive mitochondrial fragmentation and abnormal distribution, leading to defective axonal transport of mitochondria and selective synaptic degeneration. This article summarizes latest developments in HD research and focuses on the role of abnormal mitochondrial dynamics and defective axonal transport in HD neurons. This article also discusses the therapeutic strategies that decrease mitochondrial fragmentation and neuronal damage in HD.

Synchrotron radiation Fourier-transform infrared and Raman microspectroscopy study showing an increased frequency of creatine inclusions in the rat hippocampal formation following pilocarpine-induced seizures

In the present work, synchrotron radiation Fourier-transform infrared (SRFTIR) and Raman microspectroscopies were used to evaluate a possible role of creatine in the pathogenesis and progress of pilocarpine-evoked seizures and seizure-induced neurodegenerative changes in the rat hippocampal tissue. The main goal of this study was to identify creatine deposits within the examined brain area, to analyze their frequency in epileptic animals and naive controls and to examine correlations between the number of inclusions in the hippocampal formation of epileptic rats and the quantitative parameters describing animal behavior during 6-h observation period after pilocarpine injection. The presence of creatine in the brain tissue was confirmed based on the vibrational bands specific for this compound in the infrared and Raman spectra. These were the bands occurring at the wavenumbers around 2800, 1621, 1398, and 1304 cm(-1) in IR spectra and around 1056, 908 and 834 cm(-1) in the Raman spectra. Creatine was detected in eight of ten analyzed epileptic samples and in only one of six controls under the study. The number of deposits in epileptic animals varied from 1 to 100 and a relative majority of inclusions were detected in the area of the Dentate Gyrus and in the multiform hippocampal layer. Moreover, the number of creatine inclusions was positively correlated with the total time of seizure activity.

The biological basis of injury and neuroprotection in the fetal and neonatal brain

A compromised intrauterine environment that delivers low levels of oxygen and/or nutrients, or is infected or inflammatory, can result in fetal brain injury, abnormal brain development and in cases of chronic compromise, intrauterine growth restriction. Preterm birth can also be associated with injury to the developing brain and affect the normal trajectory of brain growth. This review will focus on the effects that episodes of perinatal hypoxia (acute, chronic, associated with inflammation or as an antecedent of preterm birth) can have on the developing brain. In animal models of these conditions we have found that relatively brief (acute) periods of fetal hypoxemia can have significant effects on the fetal brain, for example death of susceptible neuronal populations (cerebellum, hippocampus, cortex) and cerebral white matter damage. Chronic placental insufficiency which includes fetal hypoxemia, nutrient restriction and altered endocrine status can result in fetal growth restriction and long-term deficits in neural connectivity in addition to altered postnatal function, for example in the auditory and visual systems. Maternal/fetal inflammation can result in fetal brain damage, particularly but not exclusively in the white matter; injury is more pronounced when associated with fetal hypoxemia. In the baboon, in which the normal trajectory of growth is affected by preterm birth, there is a direct correlation between a higher flux in oxygen saturation and a greater extent of neuropathological damage. Currently, the only established therapy for neonatal encephalopathy in full term neonates is moderate hypothermia although this only offers some protection to moderately but not severely affected brains. There is no accepted therapy for injured preterm brains. Consequently the search for more efficacious treatments continues; we discuss neuroprotective agents (erythropoietin, N-acetyl cysteine, melatonin, creatine, neurosteroids) which we have trialed in appropriate animal models. The possibility of combining hypothermia with such agents or growth factors is now being considered. A deeper understanding of causal pathways in brain injury is essential for the development of efficacious strategies for neuroprotection.

In vivo monitoring of recovery from neurodegeneration in conditional transgenic SCA1 mice

Reliable and objective markers of neuronal function and pathology that can directly assess the effects of neuroprotective treatments in the brain are urgently needed for clinical trials in neurodegenerative diseases. Here we assessed the sensitivity of high field proton magnetic resonance spectroscopy ((1)H MRS) to monitor reversal of neurodegeneration by taking advantage of a well characterized conditional mouse model of spinocerebellar ataxia type 1 (SCA1), where the cerebellar pathology and ataxic phenotype are reversible by doxycycline administration. Transgene expression was suppressed by feeding the mice with chow that contains doxycycline from 6 to 12 weeks of age in an early stage group and from 12 to 24 weeks in a mid-stage group. Cerebellar neurochemical profiles of treated and untreated conditional mice were measured at 9.4 tesla (T) before and after treatment and compared to those of wild type (WT) controls, as well as to histology measures (molecular layer thickness in the primary fissure and a global pathological severity score). Concentrations of N-acetylaspartate (NAA) and myo-inositol in the treated mice trended toward normalization to WT levels in both the early and mid-stage groups. The NAA-to-myo-inositol ratio was significantly different between the treated vs. untreated SCA1 mice and demonstrated partial reversal to WT values both at early and mid-stage, consistent with the histological measures. Taurine and total creatine levels were completely normalized in early and mid-stage treatment groups, respectively. The MRS markers were a more sensitive measure of treatment response than the histological measures from the same volume-of-interest in the early stage group. NAA, myo-inositol and taurine levels were significantly correlated with the histology measures in data combined from all groups. These data demonstrate that MRS markers reliably detect rescue from neuronal pathology and imply that the neurochemical levels measured by MRS accurately reflect treatment efficacy. Therefore this study presents an important step in validating MRS biomarkers as potential surrogate markers to evaluate therapeutics in pre-clinical and clinical trials in SCA1.

Endogenous neuroprotection in chronic neurodegenerative disorders: with particular regard to the kynurenines

Parkinson's disease (PD) and Huntington's disease (HD) are progressive chronic neurodegenerative disorders that are accompanied by a considerable impairment of the motor functions. PD may develop for familial or sporadic reasons, whereas HD is based on a definite genetic mutation. Nevertheless, the pathological processes involve oxidative stress and glutamate excitotoxicity in both cases. A number of metabolic routes are affected in these disorders. The decrease in antioxidant capacity and alterations in the kynurenine pathway, the main pathway of the tryptophan metabolism, are features that deserve particular interest, because the changes in levels of neuroactive kynurenine pathway compounds appear to be strongly related to the oxidative stress and glutamate excitotoxicity involved in the disease pathogenesis. Increase of the antioxidant capacity and pharmacological manipulation of the kynurenine pathway are therefore promising therapeutic targets in these devastating disorders.

Early defect of transforming growth factor β1 formation in Huntington's disease

A defective expression or activity of neurotrophic factors, such as brain- and glial-derived neurotrophic factors, contributes to neuronal damage in Huntington’s disease (HD). Here, we focused on transforming growth factor-β (TGF-β₁), a pleiotropic cytokine with an established role in mechanisms of neuroprotection. Asymptomatic HD patients showed a reduction in TGF-β₁ levels in the peripheral blood, which was related to trinucleotide mutation length and glucose hypometabolism in the caudate nucleus. Immunohistochemical analysis in post-mortem brain tissues showed that TGF-β₁ was reduced in cortical neurons of asymptomatic and symptomatic HD patients. Both YAC128 and R6/2 HD mutant mice showed a reduced expression of TGF-β₁ in the cerebral cortex, localized in neurons, but not in astrocytes. We examined the pharmacological regulation of TGF-β₁ formation in asymptomatic R6/2 mice, where blood TGF-β₁ levels were also reduced. In these R6/2 mice, both the mGlu2/3 metabotropic glutamate receptor agonist, LY379268, and riluzole failed to increase TGF-β₁ formation in the cerebral cortex and corpus striatum, suggesting that a defect in the regulation of TGF-β₁ production is associated with HD. Accordingly, reduced TGF-β₁ mRNA and protein levels were found in cultured astrocytes transfected with mutated exon 1 of the human huntingtin gene, and in striatal knock-in cell lines expressing full-length huntingtin with an expanded glutamine repeat. Taken together, our data suggest that serum TGF-β₁ levels are potential biomarkers of HD development during the asymptomatic phase of the disease, and raise the possibility that strategies aimed at rescuing TGF-β₁ levels in the brain may influence the progression of HD.

Mitochondrial dysfunction in epilepsy

Mitochondrial dysfunction has been identified as one potential cause of epileptic seizures. Impaired mitochondrial function has been reported for the seizure focus of patients with temporal lobe epilepsy and Ammon's horn sclerosis and of adult and immature animal models of epilepsy. Since mitochondrial oxidative phosphorylation provides the major source of ATP in neurons and mitochondria participate in cellular Ca(2+) homeostasis and generation of reactive oxygen species, their dysfunction strongly affects neuronal excitability and synaptic transmission. Therefore, mitochondrial dysfunction is proposed to be highly relevant for seizure generation. Additionally, mitochondrial dysfunction is known to trigger neuronal cell death, which is a prominent feature of therapy-resistant epilepsy. For this reason mitochondria have to be considered as promising targets for neuroprotective strategies in epilepsy.

Huntington's disease: can mice lead the way to treatment?

Mouse models for Huntington's Disease (HD) and HD patients demonstrate motor and behavioral dysfunctions, such as progressive loss of coordination and memory, and share similar transcriptional profiles and striatal neuron atrophy. Clear differences between the mouse and human diseases include almost complete striatal degeneration and rarity of intranuclear inclusions in HD, and the fact that mice expressing full-length mutant huntingtin do not demonstrate a shortened life span characteristic of HD. While no clinical interventions tested in mouse models to date have delayed disease progression, the mouse models provide an invaluable tool for both investigating the underlying pathogenic processes and developing new effective therapies. Inherent differences between humans and mice must be considered in the search for efficacious treatments for HD, but the striking similarities between human HD and mouse models support the view that these models are a biologically relevant system to support the identification and testing of potential clinical therapies.

Neuroprotective effects of creatine

There is a substantial body of literature, which has demonstrated that creatine has neuroprotective effects both in vitro and in vivo. Creatine can protect against excitotoxicity as well as against β-amyloid toxicity in vitro. We carried out studies examining the efficacy of creatine as a neuroprotective agent in vivo. We demonstrated that creatine can protect against excitotoxic lesions produced by N-methyl-D: -aspartate. We also showed that creatine is neuroprotective against lesions produced by the toxins malonate and 3-nitropropionic acid (3-NP) which are reversible and irreversible inhibitors of succinate dehydrogenase, respectively. Creatine produced dose-dependent neuroprotective effects against MPTP toxicity reducing the loss of dopamine within the striatum and the loss of dopaminergic neurons in the substantia nigra. We carried out a number of studies of the neuroprotective effects of creatine in transgenic mouse models of neurodegenerative diseases. We demonstrated that creatine produced an extension of survival, improved motor performance, and a reduction in loss of motor neurons in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). Creatine produced an extension of survival, as well as improved motor function, and a reduction in striatal atrophy in the R6/2 and the N-171-82Q transgenic mouse models of Huntington's disease (HD), even when its administration was delayed until the onset of disease symptoms. We recently examined the neuroprotective effects of a combination of coenzyme Q10 (CoQ10) with creatine against both MPTP and 3-NP toxicity. We found that the combination of CoQ and creatine together produced additive neuroprotective effects in a chronic MPTP model, and it blocked the development of alpha-synuclein aggregates. In the 3-NP model of HD, CoQ and creatine produced additive neuroprotective effects against the size of the striatal lesions. In the R6/2 transgenic mouse model of HD, the combination of CoQ and creatine produced additive effects on improving survival. Creatine may stabilize mitochondrial creatine kinase, and prevent activation of the mitochondrial permeability transition. Creatine, however, was still neuroprotective in mice, which were deficient in mitochondrial creatine kinase. Administration of creatine increases the brain levels of creatine and phosphocreatine. Due to its neuroprotective effects, creatine is now in clinical trials for the treatment of Parkinson's disease (PD) and HD. A phase 2 futility trial in PD showed approximately a 50% improvement in Unified Parkinson's Disease Rating Scale at one year, and the compound was judged to be non futile. Creatine is now in a phase III clinical trial being carried out by the NET PD consortium. Creatine reduced plasma levels of 8-hydroxy-2-deoxyguanosine in HD patients phase II trial and was well-tolerated. Creatine is now being studied in a phase III clinical trial in HD, the CREST trial. Creatine, therefore, shows great promise in the treatment of a variety of neurodegenerative diseases.

Creatine in mouse models of neurodegeneration and aging

The supplementation of creatine has shown a marked neuroprotective effect in mouse models of neurodegenerative diseases (Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis). This has been assigned to the known bioenergetic, anti-apoptotic, anti-excitotoxic and anti-oxidant properties of creatine. As aging and neurodegeneration share pathophysiological pathways, we investigated the effect of oral creatine supplementation on aging in 162 aged wild-type C57Bl/6J mice. The median healthy life span of creatine-fed mice was 9% higher than in their control littermates, and they performed significantly better in neurobehavioral tests. In brains of creatine-treated mice, there was a trend toward a reduction of reactive oxygen species and significantly lower accumulation of the "aging pigment" lipofuscin. Expression profiling showed an upregulation of genes implicated in neuronal growth, neuroprotection, and learning. These data showed that creatine improves health and longevity in mice. Creatine may, therefore, be a promising food supplement to promote healthy human aging. However, the strong neuroprotective effects in animal studies of creatine have not been reproduced in human clinical trials (that have been conducted in Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis). The reasons for this translational gap are discussed. One obvious cause seems to be that all previous human studies may have been underpowered. Large phase III trials over long time periods are currently being conducted for Parkinson's disease and Huntington's disease, and will possibly solve this issue.

Exercise-induced, but not creatine-induced, decrease in intramyocellular lipid content improves insulin sensitivity in rats

The effect of creatine supplementation, alone or in combination with exercise training, on insulin sensitivity, intramyocellular lipid content (IMCL) and fatty acid translocase (FAT)/CD36 content was investigated in rats fed a sucrose-rich cafeteria diet during 12 weeks. Five experimental conditions were CON, receiving normal pellets; CAF, fed the cafeteria diet; CAF(TR), fed the cafeteria diet together with exercise training in weeks 8-12 and CAF(CR) and CAF(CRT) that were analogous to CAF and CAF(TR), respectively, but which received daily 2.5% of creatine monohydrate. During intravenous glucose tolerance test, compared with CON, whole-body glucose tolerance was reduced in CAF and CAF(CR) but not in CAF(TR) and CAF(CRT). Insulin-stimulated glucose transport in perfused red gastrocnemius muscles was impaired in CAF and CAF(CR) but not in the trained groups. IMCL content in soleus and extensor digitorum longus muscles was higher in CAF than in CON, but not in CAF(TR), CAF(CR) and CAF(CRT). Compared with CON and CAF, FAT/CD36 protein content in m. soleus, was ~40% lower in CAF(CR), CAF(TR) and CAF(CRT). The fraction of fecal fat, as determined in a 3-week post hoc study, was 25% higher in CAF(CR) than in CON. Moreover, in CAF(CR), triglyceride concentration in blood and liver were significantly lower than in CAF. It is concluded that creatine supplementation in rats on a cafeteria diet inhibits IMCL accumulation via inhibition of gastrointestinal lipid absorption together with lower muscle FAT/CD36 content. Furthermore, exercise-induced but not creatine-induced reduction of IMCL is associated with improved insulin action on glucose transport in muscle cells.

Creatine for treating muscle disorders

BACKGROUND

Progressive muscle weakness is a main symptom of most hereditary and acquired muscle diseases. Creatine improves muscle performance in healthy individuals. This is an update of our 2007 Cochrane review that evaluated creatine treatment in muscle disorders.

OBJECTIVES

To evaluate the efficacy of creatine compared to placebo for the treatment of muscle weakness in muscle diseases.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Specialized Register (4 October 2010), the Cochrane Central Register of Controlled Trials (11 October 2010, Issue 4, 2010 in The Cochrane Library), MEDLINE (January 1966 to September 2010) and EMBASE (January 1980 to September 2010) for randomised controlled trials (RCT) of creatine used to treat muscle diseases.

SELECTION CRITERIA

RCTs or quasi-RCTs of creatine treatment compared to placebo in hereditary muscle diseases or idiopathic inflammatory myopathies.

DATA COLLECTION AND ANALYSIS

Two authors independently applied the selection criteria, assessed trial quality and extracted data. We obtained missing data from investigators.

MAIN RESULTS

The updated searches identified two new studies. A total of 14 trials, including 364 randomised participants, met the selection criteria. Meta-analysis of six trials in muscular dystrophies including 192 participants revealed a significant increase in muscle strength in the creatine group compared to placebo, with a weighted mean difference of 8.47%; (95% confidence intervals (CI) 3.55 to 13.38). Pooled data of four trials including 115 participants showed that a significantly higher number of patients felt better during creatine treatment compared to placebo with a risk ratio of 4.51 (95% CI 2.33 to 8.74). One trial in 37 participants with idiopathic inflammatory myopathies also showed a significant improvement in functional performance. No trial reported any clinically relevant adverse event. In metabolic myopathies, meta-analyses of three cross-over trials including 33 participants revealed no significant difference in muscle strength. One trial reported a significant deterioration of ADL (mean difference 0.54 on a 1 to 10 scale; 95% CI 0.14 to 0.93) and an increase in muscle pain during high-dose creatine treatment in McArdle disease.

AUTHORS' CONCLUSIONS

High quality evidence from RCTs shows that short- and medium-term creatine treatment increases muscle strength in muscular dystrophies. There is also evidence that creatine improves functional performance in muscular dystrophy and idiopathic inflammatory myopathy. Creatine is well tolerated in these people. High quality but limited evidence from RCTs does not show significant improvement in muscle strength in metabolic myopathies. High-dose creatine treatment impaired ADL and increased muscle pain in McArdle disease.

Structural MRI detects progressive regional brain atrophy and neuroprotective effects in N171-82Q Huntington's disease mouse model

Huntington's disease (HD) displays progressive striatal atrophy that occurs long before the onset of clinical motor symptoms. As there is no treatment for the disease once overt symptoms appear, it has been suggested that neuroprotective therapy given during this presymptomatic period might slow progression of the disease. This requires biomarkers that can reliably detect early changes and are sensitive to treatment response. In mouse models of HD, structural MRI measures have been shown to detect disease onset. To determine whether such measures could also be suitable biomarkers for following responses to treatment, we used T2-weighted MR imaging combined with automated morphological analyses and characterized changes in regional brain volumes longitudinally in the N171-82Q HD mouse model in a preclinical trial. We report here that N171-82Q HD mice exhibit adult-onset and progressive brain atrophy in the striatum and neocortex as well as in whole brain; the progressive atrophy in striatum and neocortex is positively correlated with motor deficits. Most notably, MRI also detected neuroprotective effects of sertraline treatment, a neuroprotective agent confirmed in our previous studies. Our present studies provide the first evidence that longitudinal structural MRI measures can detect the therapeutic effect in HD mice, suggesting that such measures in brain could be valuable biomarkers in HD clinical trials.

Brief ampakine treatments slow the progression of Huntington's disease phenotypes in R6/2 mice

Daily, systemic injections of a positive AMPA-type glutamate receptor modulator (ampakine) have been shown to reduce synaptic plasticity defects in rodent models of aging and early-stage Huntington's disease (HD). Here we report that long-term ampakine treatment markedly slows the progression of striatal neuropathology and locomotor dysfunction in the R6/2 HD mouse model. Remarkably, these effects were produced by an ampakine, CX929, with a short half-life. Injected once daily for 4-7 weeks, the compound increased protein levels of brain-derived neurotrophic factor (BDNF) in the neocortex and striatum of R6/2 but not wild-type mice. Moreover, ampakine treatments prevented the decrease in total striatal area, blocked the loss of striatal DARPP-32 immunoreactivity and reduced by 36% the size of intra-nuclear huntingtin aggregates in R6/2 striatum. The CX929 treatments also markedly improved motor performance of R6/2 mice on several measures (rotarod, vertical pole descent) but did not influence body weight or lifespan. These findings describe a minimally invasive, pharmacologically plausible strategy for treatment of HD and, potentially, other neuropathological diseases.

Energy deficit in Huntington disease: why it matters

Huntington disease (HD) is an autosomal dominant neurodegenerative disease with complete penetrance. Although the understanding of the cellular mechanisms that drive neurodegeneration in HD and account for the characteristic pattern of neuronal vulnerability is incomplete, defects in energy metabolism, particularly mitochondrial function, represent a common thread in studies of HD pathogenesis in humans and animal models. Here we review the clinical, biochemical, and molecular evidence of an energy deficit in HD and discuss the mechanisms underlying mitochondrial and related alterations.

Nrf2-ARE stress response mechanism: a control point in oxidative stress-mediated dysfunctions and chronic inflammatory diseases

Nrf2, a redox sensitive transcription factor, plays a pivotal role in redox homeostasis during oxidative stress. Nrf2 is sequestered in cytosol by an inhibitory protein Keap1 which causes its proteasomal degradation. In response to electrophilic and oxidative stress, Nrf2 is activated, translocates to nucleus, binds to antioxidant response element (ARE), thus upregulates a battery of antioxidant and detoxifying genes. This function of Nrf2 can be significant in the treatment of diseases, such as cancer, neurodegenerative, cardiovascular and pulmonary complications, where oxidative stress causes Nrf2 derangement. Nrf2 upregulating potential of phytochemicals has been explored, in facilitating cure for various ailments while, in cancer cells, Nrf2 upregulation causes chemoresistance. Therefore, Nrf2 emerges as a key regulator in oxidative stress-mediated diseases and Nrf2 silencing can open avenues in cancer treatment. This review summarizes Nrf2-ARE stress response mechanism and its role as a control point in oxidative stress-induced cellular dysfunctions including chronic inflammatory diseases.

Mitochondrial dysfunction in Parkinson's disease: pathogenesis and neuroprotection

Mitochondria are vitally important organelles involved in an array of functions. The most notable is their prominent role in energy metabolism, where they generate over 90% of our cellular energy in the form of ATP through oxidative phosphorylation. Mitochondria are involved in various other processes including the regulation of calcium homeostasis and stress response. Mitochondrial complex I impairment and subsequent oxidative stress have been identified as modulators of cell death in experimental models of Parkinson's disease (PD). Identification of specific genes which are involved in the rare familial forms of PD has further augmented the understanding and elevated the role mitochondrial dysfunction is thought to have in disease pathogenesis. This paper provides a review of the role mitochondria may play in idiopathic PD through the study of experimental models and how genetic mutations influence mitochondrial activity. Recent attempts at providing neuroprotection by targeting mitochondria are described and their progress assessed.

A phase I, pharmacokinetic, dosage escalation study of creatine monohydrate in subjects with amyotrophic lateral sclerosis

Creatine monohydrate (creatine) has potential neuroprotective properties and is a commonly used supplement in amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Minimum therapeutic and maximum tolerated dosages of creatine are not yet known, nor is it known what systemic plasma concentrations result from specific dosage regimens. The objectives of this study were to establish steady-state plasma pharmacokinetics of creatine at several dosages, and to evaluate the effects of creatine on brain metabolites using proton magnetic resonance spectroscopy ((1)H-MRS). Six participants with ALS received creatine at three weekly escalating oral dosages (5, 10, and 15 g b.i.d.). Plasma creatine levels and MR spectra were obtained at baseline and with each dosage increase. Mean pre-dose steady-state creatine plasma concentrations were 20.3, 39.3, and 61.5 ug/ml at 5, 10, and 15 g b.i.d., respectively. Creatine spectra increased by 8% (p = 0.06) and glutamate + glutamine signals decreased by 17% (p = 0.039) at higher dosages. There were no safety concerns at any of the dosages. In conclusion, creatine plasma concentrations increased in a dose-dependent manner. Creatine appears to cross the blood-brain barrier, and oral administration of 15 g b.i.d. is associated with increased in vivo brain creatine concentrations and decreased glutamate concentrations.

Electroconvulsive shock ameliorates disease processes and extends survival in huntingtin mutant mice

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by expanded polyglutamine repeats in the huntingtin (Htt) protein. Mutant Htt may damage and kill striatal neurons by a mechanism involving reduced production of brain-derived neurotrophic factor (BDNF) and increased oxidative and metabolic stress. Because electroconvulsive shock (ECS) can stimulate the production of BDNF and protect neurons against stress, we determined whether ECS treatment would modify the disease process and provide a therapeutic benefit in a mouse model of HD. ECS (50 mA for 0.2 s) or sham treatment was administered once weekly to male N171-82Q Htt mutant mice beginning at 2 months of age. Endpoints measured included motor function, striatal and cortical pathology, and levels of protein chaperones and BDNF. ECS treatment delayed the onset of motor symptoms and body weight loss and extended the survival of HD mice. Striatal neurodegeneration was attenuated and levels of protein chaperones (Hsp70 and Hsp40) and BDNF were elevated in striatal neurons of ECS-treated compared with sham-treated HD mice. Our findings demonstrate that ECS can increase the resistance of neurons to mutant Htt resulting in improved functional outcome and extended survival. The potential of ECS as an intervention in subjects that inherit the mutant Htt gene merits further consideration.

Mesenchymal stem cell transplantation and DMEM administration in a 3NP rat model of Huntington's disease: morphological and behavioral outcomes

Transplantation of mesenchymal stem cells (MSCs) may offer a viable treatment for Huntington's disease (HD). We tested the efficacy of MSC transplants to reduce deficits in a 3-nitropropionic acid (3NP) rat model of HD. Five groups of rats (Sham, 3NP, 3NP+vehicle, 3NP+TP(low), 3NP+TP(high)), were given PBS or 3NP intraperitoneally, twice daily for 42 days. On day 28, rats in all groups except Sham and 3NP, received intrastriatal injections of either 200,000 MSCs (TP(low)), 400,000 (TP(high)) MSCs or DMEM (VH, the vehicle for transplantation). MSCs survived 72 days without inducing a strong inflammatory response from the striatum. Behavioral sparing was observed on tests of supported-hindlimb-retraction, unsupported-hindlimb-retraction, visual paw placement and stepping ability for 3NP+TP(low) rats and on the unsupported-hindlimb-retraction and rotarod tasks for 3NP+VH rats. Relative to 3NP controls, all treated groups were protected from 3NP-induced enlargement of the lateral ventricles. In vitro, MSCs expressed transcripts for numerous neurotrophic factors. In vivo, increased striatal labeling in BDNF, collagen type-I and fibronectin (but not GDNF or CNTF) was observed in the brains of MSC-transplanted rats but not in DMEM-treated rats. In addition, none of the transplanted MSCs expressed neural phenotypes. These findings suggest that factors other than neuronal replacement underlie the behavioral sparing observed in 3NP rats after MSC transplantation.

Modulation of energy deficiency in Huntington's disease via activation of the peroxisome proliferator-activated receptor gamma

Huntington's disease (HD) is a neurodegenerative disease caused by the expansion of a CAG trinucleotide repeat in exon 1 of the huntingtin (HTT) gene. Here, we report that the transcript of the peroxisome proliferator-activated receptor-γ (PPARγ), a transcription factor that is critical for energy homeostasis, was markedly downregulated in multiple tissues of a mouse model (R6/2) of HD and in lymphocytes of HD patients. Therefore, downregulation of PPARγ seems to be a pathomechanism of HD. Chronic treatment of R6/2 mice with an agonist of PPARγ (thiazolidinedione, TZD) rescued progressive weight loss, motor deterioration, formation of mutant Htt aggregates, jeopardized global ubiquitination profiles, reduced expression of two neuroprotective proteins (brain-derived neurotrophic factor and Bcl-2) and shortened life span exhibited by these mice. By reducing HTT aggregates and, thus, ameliorating the recruitment of PPARγ into HTT aggregates, chronic TZD treatment also elevated the availability of the PPARγ protein and subsequently normalized the expression of two of its downstream genes (the glucose transporter type 4 and PPARγ coactivator-1 alpha genes). The protective effects described above appear to have been exerted, at least partially, via direct activation of PPARγ in the brain, as TZD was detected in the brains of mice treated with TZD and because a PPARγ agonist (rosiglitazone) protected striatal cells from mHTT-evoked energy deficiency and toxicity. We demonstrated that the systematic downregulation of PPARγ seems to play a critical role in the dysregulation of energy homeostasis observed in HD, and that PPARγ is a potential therapeutic target for this disease.

Molecular mechanisms and potential therapeutical targets in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the gene encoding for huntingtin protein. A lot has been learned about this disease since its first description in 1872 and the identification of its causative gene and mutation in 1993. We now know that the disease is characterized by several molecular and cellular abnormalities whose precise timing and relative roles in pathogenesis have yet to be understood. HD is triggered by the mutant protein, and both gain-of-function (of the mutant protein) and loss-of-function (of the normal protein) mechanisms are involved. Here we review the data that describe the emergence of the ancient huntingtin gene and of the polyglutamine trait during the last 800 million years of evolution. We focus on the known functions of wild-type huntingtin that are fundamental for the survival and functioning of the brain neurons that predominantly degenerate in HD. We summarize data indicating how the loss of these beneficial activities reduces the ability of these neurons to survive. We also review the different mechanisms by which the mutation in huntingtin causes toxicity. This may arise both from cell-autonomous processes and dysfunction of neuronal circuitries. We then focus on novel therapeutical targets and pathways and on the attractive option to counteract HD at its primary source, i.e., by blocking the production of the mutant protein. Strategies and technologies used to screen for candidate HD biomarkers and their potential application are presented. Furthermore, we discuss the opportunities offered by intracerebral cell transplantation and the likely need for these multiple routes into therapies to converge at some point as, ideally, one would wish to stop the disease process and, at the same time, possibly replace the damaged neurons.

Resveratrol protects against peripheral deficits in a mouse model of Huntington's disease

Sirtuins are NAD-dependent deacetylases that regulate important biologic processes including transcription, cell survival and metabolism. Activation of SIRT1, a mammalian sirtuin, extends longevity and increases neuronal survival. An important substrate of SIRT1 is peroxisome proliferator-activated receptor gamma co-activator-1alpha (PGC-1alpha), a principal regulator of energy metabolism, whose function is significantly impaired in Huntington's disease (HD). We studied the effects of a pharmacological preparation of the SIRT1 activator resveratrol (SRT501-M), in the N171-82Q transgenic mouse model of HD. We analyzed motor performance, survival, central and peripheral pathology and levels of PGC-1alpha expression. Administration of SRT501-M increased expression of PGC-1alpha, as well as its downstream targets, nuclear respiratory factor-1 (NRF-1) and uncoupling protein-1 (UCP-1) in brown adipose tissue (BAT), but there was no effect on PGC-1alpha, NRF-1 or the mitochondrial transcription factor (Tfam) in the striatum. SRT501-M administration also reduced BAT vacuolation and decreased elevated blood glucose levels. However, there was no significant improvement in weight loss, motor performance, survival and striatal atrophy. Activation of the PGC-1alpha signaling pathway via resveratrol-induced activation of SIRT1, therefore, is an effective therapy in BAT, but not in the central nervous system of HD transgenic mice.

Pharmacological therapy in Parkinson's disease: focus on neuroprotection

Although the number of available therapeutic approaches in Parkinson's disease (PD) is steadily increasing the search for effective neuroprotective agent is continuing. Such research is directed at influencing the key steps in the pathomechanism: the mitochondrial dysfunction, the oxidative stress, the neuroinflammatory processes and the final common apoptotic pathway. Earlier-developed symptomatic therapies were implicated to be neuroprotective, and promising novel disease modifying approaches were brought into the focus of interest. The current review presents a survey of our current knowledge relating to the pathomechanism of PD and discusses the putative neuroprotective therapy.