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.     

Mitochondria as targets for chemotherapy

Mitochondrial malfunctioning is implicated in the pathogenesis of a variety of disorders, including cancer and multiple neurodegenerative diseases, such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and Huntington’s disease. Disturbance of mitochondrial vital functions, e.g., production of ATP, calcium buffering capacity, and generation of reactive oxygen species, can be potentially involved in disease pathogenesis. Neurological disorders caused by mitochondrial deterioration are often associated with cell loss within specific brain regions. In contrast, mitochondrial alterations in tumor cells and the “Warburg effect” might lead to cell survival and resistance of tumor cells to chemotherapy. This review is devoted to the role of mitochondria in neurodegeneration and tumor formation, and describes how targeting of mitochondria can be beneficial in the therapy of these diseases, which affect a large human population.     

The Sirtuin-2 Inhibitor AK7 Is Neuroprotective in Models of Parkinson’s Disease but Not Amyotrophic Lateral Sclerosis and Cerebral Ischemia

Sirtuin deacetylases regulate diverse cellular pathways and influence disease processes. Our previous studies identified the brain-enriched sirtuin-2 (SIRT2) deacetylase as a potential drug target to counteract neurodegeneration. In the present study, we characterize SIRT2 inhibition activity of the brain-permeable compound AK7 and examine the efficacy of this small molecule in models of Parkinson’s disease, amyotrophic lateral sclerosis and cerebral ischemia. Our results demonstrate that AK7 is neuroprotective in models of Parkinson’s disease; it ameliorates alpha-synuclein toxicity in vitro and prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopamine depletion and dopaminergic neuron loss in vivo. The compound does not show beneficial effects in mouse models of amyotrophic lateral sclerosis and cerebral ischemia. These findings underscore the specificity of protective effects observed here in models of Parkinson’s disease, and previously in Huntington’s disease, and support the development of SIRT2 inhibitors as potential therapeutics for the two neurodegenerative diseases.     

Free Copper,Ferroxidase and SOD1 Activities,Lipid Peroxidation and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Content in the CSF. A Different Marker Profile in Four Neurodegenerative Diseases

The understanding of oxidative damage in different neurodegenerative diseases could enhance therapeutic strategies. Our objective was to quantify lipoperoxidation and other oxidative products as well as the activity of antioxidant enzymes and cofactors in cerebrospinal fluid (CSF) samples. We recorded data from all new patients with a diagnosis of either one of the four most frequent neurodegenerative diseases: Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD) and lateral amyotrophic sclerosis (ALS). The sum of nitrites and nitrates as end products of nitric oxide (NO) were increased in the four degenerative diseases and fluorescent lipoperoxidation products in three (excepting ALS). A decreased Cu/Zn-dependent superoxide dismutase (SOD) activity characterized the four diseases. A significantly decreased ferroxidase activity was found in PD, HD and AD, agreeing with findings of iron deposition in these entities, while free copper was found to be increased in CSF and appeared to be a good biomarker of PD.     

Modeling human neurodegenerative diseases in transgenic systems

Transgenic systems are widely used to study the cellular and molecular basis of human neurodegenerative diseases. A wide variety of model organisms have been utilized, including bacteria (Escherichia coli), plants (Arabidopsis thaliana), nematodes (Caenorhabditis elegans), arthropods (Drosophila melanogaster), fish (zebrafish, Danio rerio), rodents (mouse, Mus musculus and rat, Rattus norvegicus) as well as non-human primates (rhesus monkey, Macaca mulatta). These transgenic systems have enormous value for understanding the pathophysiological basis of these disorders and have, in some cases, been instrumental in the development of therapeutic approaches to treat these conditions. In this review, we discuss the most commonly used model organisms and the methodologies available for the preparation of transgenic organisms. Moreover, we provide selected examples of the use of these technologies for the preparation of transgenic animal models of neurodegenerative diseases, including Alzheimer’s disease (AD), frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD) and Parkinson’s disease (PD) and discuss the application of these technologies to AD as an example of how transgenic modeling has affected the study of human neurodegenerative diseases.     

Genes and the Environment in Neurodegeneration

Neurodegenerative diseases are a heterogeneous group of pathologies which includes complex multifactorial diseases, monogenic disorders and disorders for which inherited, sporadic and transmissible forms are known. Factors associated with predisposition and vulnerability to neurodegenerative disorders may be described usefully within the context of gene–environment interplay. There are many identified genetic determinants for neurodegeneration, and it is possible to duplicate many elements of recognized human neurodegenerative disorders in animal models of the disease. However, there are similarly several identifiable environmental influences on outcomes of the genetic defects; and the course of a progressive neurodegenerative disorder can be greatly modified by environmental elements. In this review we highlight some of the major neurodegenerative disorders (Alzheimer’s disease, Parkinson’s disease, Amyotrophic lateral sclerosis, Huntington’s disease, and prion diseases.) and discuss possible links of gene–environment interplay including, where implicated, mitochondrial genes.     

Ubiquitin/proteasome pathway impairment in neurodegeneration: therapeutic implications

The ubiquitin/proteasome pathway is the major proteolytic quality control system in cells. In this review we discuss the impact of a deregulation of this pathway on neuronal function and its causal relationship to the intracellular deposition of ubiquitin protein conjugates in pathological inclusion bodies in all the major chronic neurodegenerative disorders, such as Alzheimer’s, Parkinson’s and Huntington’s diseases as well as amyotrophic lateral sclerosis. We describe the intricate nature of the ubiquitin/proteasome pathway and discuss the paradox of protein aggregation, i.e. its potential toxic/protective effect in neurodegeneration. The relations between some of the dysfunctional components of the pathway and neurodegeneration are presented. We highlight possible ubiquitin/proteasome pathway-targeting therapeutic approaches, such as activating the proteasome, enhancing ubiquitination and promoting SUMOylation that might be important to slow/treat the progression of neurodegeneration. Finally, a model time line is presented for neurodegeneration starting at the initial injurious events up to protein aggregation and cell death, with potential time points for therapeutic intervention.     

Defective Protein Folding and Aggregation as the Basis of Neurodegenerative Diseases: The Darker Aspect of Proteins

Abstract  

The ability of a polypeptide to fold into a unique, functional, and three-dimensional structure depends on the intrinsic properties of the amino acid sequence, function of the molecular chaperones, proteins, and enzymes. Every polypeptide has a finite tendency to misfold and this forms the darker side of the protein world. Partially folded and misfolded proteins that escape the cellular quality control mechanism have the high tendency to form inter-molecular hydrogen bonding between the same protein molecules resulting in aggregation. This review summarizes the underlying and universal mechanism of protein folding. It also deals with the factors responsible for protein misfolding and aggregation. This article describes some of the consequences of such behavior particularly in the context of neurodegenerative conformational diseases such as Alzheimer’s, Parkinson’s, Huntington’s, amyotrophic lateral sclerosis and other non-neurodegenerative conformational diseases such as cancer and cystic fibrosis etc. This will encourage a more proactive approach to the early diagnosis of conformational diseases and nutritional counseling for patients.     

Heteromeric complexes of heat shock protein 70 (HSP70) family members,including Hsp70B′, in differentiated human neuronal cells

Human neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis have been termed “protein misfolding disorders.” Upregulation of heat shock proteins that target misfolded aggregation-prone proteins has been proposed as a potential therapeutic strategy to counter neurodegenerative disorders. The heat shock protein 70 (HSP70) family is well characterized for its cytoprotective effects against cell death and has been implicated in neuroprotection by overexpression studies. HSP70 family members exhibit sequence and structural conservation. The significance of the multiplicity of HSP70 proteins is unknown. In this study, coimmunoprecipitation was employed to determine if association of HSP70 family members occurs, including Hsp70B′ which is present in the human genome but not in mouse and rat. Heteromeric complexes of Hsp70B′, Hsp70, and Hsc70 were detected in differentiated human SH-SY5Y neuronal cells. Hsp70B′ also formed complexes with Hsp40 suggesting a common co-chaperone for HSP70 family members.     

Stem cells and neurodegenerative diseases

Neurodegenerative diseases are characterized by the neurodegenerative changes or apoptosis of neurons involved in networks, which are important to specific physiological functions. With the de-velopment of old-aging society, the incidence of neurodegenerative diseases is on the increase. How-ever, it is difficult to diagnose for most of neurodegenerative diseases. At present, there are too few effective therapies. Advances in stem cell biology have raised the hope and possibility for the therapy of neurodegenerative diseases. Recently, stem cells have been widely attempted to treat neurodegen-erative diseases of animal model. Here we review the progress and prospects of various stem cells, including embryonic stem cells, mesenchymal stem cell and neural stem cells and so on, for the treatments of neurodegenerative diseases, such as Parkinson’s disease, Alzheimer’s disease, Hunt-ington’s disease and Amyotrophic lateral sclerosis/Lou Gehrig’s disease.     

RNAi: a potential new class of therapeutic for human genetic disease

Dominant negative genetic disorders, in which a mutant allele of a gene causes disease in the presence of a second, normal copy, have been challenging since there is no cure and treatments are only to alleviate the symptoms. Current therapies involving pharmacological and biological drugs are not suitable to target mutant genes selectively due to structural indifference of the normal variant of their targets from the disease-causing mutant ones. In instances when the target contains single nucleotide polymorphism (SNP), whether it is an enzyme or structural or receptor protein are not ideal for treatment using conventional drugs due to their lack of selectivity. Therefore, there is a need to develop new approaches to accelerate targeting these previously inaccessible targets by classical therapeutics. Although there is a cooling trend by the pharmaceutical industry for the potential of RNA interference (RNAi), RNAi and other RNA targeting drugs (antisense, ribozyme, etc.) still hold their promise as the only drugs that provide an opportunity to target genes with SNP mutations found in dominant negative disorders, genes specific to pathogenic tumor cells, and genes that are critical for mediating the pathology of various other diseases. Because of its exquisite specificity and potency, RNAi has attracted a considerable interest as a new class of therapeutic for genetic diseases including amyotrophic lateral sclerosis, Huntington’s disease (HD), Alzheimer’s disease (AD), Parkinson’s disease (PD), spinocerebellar ataxia, dominant muscular dystrophies, and cancer. In this review, progress and challenges in developing RNAi therapeutics for genetic diseases will be discussed.     

Functional genomics approaches to neurodegenerative diseases

Many of the neurodegenerative diseases that afflict humans are characterised by the protein aggregation in neurons. These include complex diseases like Alzheimer’s disease and Parkinson’s disease, and Mendelian diseases caused by polyglutamine expansion mutations [like Huntington’s disease (HD) and various spinocerebellar ataxias (SCAs), like SCA3]. A range of functional genomic strategies have been used to try to elucidate pathways involved in these diseases. In this minireview, I focus on how modifier screens in organisms from yeast to mice may be of value in helping to elucidate pathogenic pathways.     

Neuroglial Roots of Neurodegenerative Diseases?

Neuroglia is critically important for controlling the brain homeostasis and for mounting the brain defence against pathological insults. Here, we overview recent data about the role of neuroglia in various types of neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease, fronto-temporal dementia, Wernicke encephalopathy, amyotrophic lateral sclerosis and immunodeficiency virus-1-associated dementia). In all these forms of neurodegeneration, astroglia undergoes complex morphological and functional changes. The early and mid-term stages of neurodegenerative processes, and specifically of Alzheimer’s disease, are associated with generalised atrophy of astroglia, whereas the later stages are characterised with an astrogliosis and microglial activation linked to neuropathological lesions such as senile plaques. Atrophic changes in astroglia may contribute to the initial cognitive deficits due to reduced glial synaptic coverage and decreased neuroprotection.     

Astrocytes in Neurodegenerative Disease

Astrocytes contribute to the maintenance of the health and function of the central nervous system (CNS). Thus, it is not surprising that these multifunctional cells have been implicated in the onset and progression of several neurodegenerative diseases. The involvement of astrocytes in the neuropathology of these diseases is likely a consequence of both the loss of normal homeostatic functions and gain of toxic functions. Intracellular aggregates in astrocytes are a common feature of various neurodegenerative diseases, and these aggregates perturb normal astrocytic functions in ways that can be harmful to neuronal viability. Here, we review the role of astrocytes in neurodegenerative diseases, focusing on their dysfunction in Huntington’s disease (HD), Parkinson’s disease (PD), Alzheimer’s disease (AD), and amyotrophic lateral sclerosis (ALS).     

Neuroprotective Effects of IGF-I Following Kainic Acid-Induced Hippocampal Degeneration in the Rat

Insulin-like growth factor I (IGF-I) has been shown to act as a neuroprotectant both in in vitro studies and in in vivo animal models of ischemia, hypoxia, trauma in the brain or the spinal cord, multiple and amyotrophic lateral sclerosis, Alzheimer’s and Parkinson’s disease. In the present study, we investigated the neuroprotective potential of IGF-I in the “kainic acid-induced degeneration of the hippocampus” model of temporal lobe epilepsy. Increased cell death—as detected by FluoroJade B staining—and extensive cell loss—as determined by cresyl violet staining—were observed mainly in the CA3 and CA4 areas of the ipsilateral and contralateral hippocampus, 7 days following intrahippocampal administration of kainic acid. Kainic acid injection also resulted in intense astrogliosis—as assessed by the number of glial fibrillary acidic protein (GFAP) immunopositive cells—in both hemispheres, forming a clear astroglial scar ipsilaterally to the injection site. Heat-shock protein 70 (Hsp70) immunopositive cells were also observed in the ipsilateral dentate gyrus (DG) following kainic acid injection. When IGF-I was administered together with kainic acid, practically no signs of degeneration were detected in the contralateral hemisphere, while in the ipsilateral, there was a smaller degree of cell loss, reduced number of FluoroJade B-stained cells, decreased reactive gliosis and fewer Hsp70-positive cells. Our present results extend further the cases in which IGF-I is shown to exhibit neuroprotective properties in neurodegenerative processes in the CNS.     

Human stem cells for CNS repair

Although most peripheral tissues have at least a limited ability for self-repair, the central nervous system (CNS) has long been known to be relatively resistant to regeneration. Small numbers of stem cells have been found in the adult brain but do not appear to be able to affect any significant recovery following disease or insult. In the last few decades, the idea of being able to repair the brain by introducing new cells to repair damaged areas has become an accepted potential treatment for neurodegenerative diseases. This review focuses on the suitability of various human stem cell sources for such treatments of both slowly progressing conditions, such as Parkinson’s disease, Huntington’s disease and multiple sclerosis, and acute insult, such as stroke and spinal cord injury. Despite stem cell transplantation having now moved a step closer to the clinic with the first trials of autologous mesenchymal stem cells, the effects shown are moderate and are not yet at the stage of development that can fulfil the hopes that have been placed on stem cells as a means to replace degenerating cells in the CNS. Success will depend on careful investigation in experimental models to enable us to understand not just the practicalities of stem cell use, but also the underlying biological principles.     

Exploring the therapeutic role of creatine supplementation

Creatine (Cr) plays a central role in energy provision through a reaction catalyzed by phosphorylcreatine kinase. Furthermore, this amine enhances both gene expression and satellite cell activation involved in hypertrophic response. Recent findings have indicated that Cr supplementation has a therapeutic role in several diseases characterized by atrophic conditions, weakness, and metabolic disturbances (i.e., in the muscle, bone, lung, and brain). Accordingly, there has been an evidence indicating that Cr supplementation is capable of attenuating the degenerative state in some muscle disorders (i.e., Duchenne and inflammatory myopathies), central nervous diseases (i.e., Parkinson’s, Huntington’s, and Alzheimer’s), and bone and metabolic disturbances (i.e., osteoporosis and type II diabetes). In light of this, Cr supplementation could be used as a therapeutic tool for the elderly. The aim of this review is to summarize the main studies conducted in this field and to highlight the scientific and clinical perspectives of this promising therapeutic supplement.     

The effect of formalin fixation on the levels of brain transition metals in archived samples

Reports that iron, zinc and copper homeostasis are in aberrant homeostasis are common for various neurodegenerative diseases, particularly for Huntington’s disease, Parkinson’s disease, and Alzheimer’s disease. Manipulating the levels of these elements in the brain through the application of chelators has been and continues to be tested therapeutically in clinical trials with mixed results. Much of the data indicating that these metals are abnormally concentrated in Alzheimer’s disease and Parkinson’s disease brain tissue was generated through the analysis of post-mortem human tissue which was archived in formalin. In this study, we evaluated the effect of formalin fixation of brain on the levels of three important transition metals (iron, copper, and zinc) by atomic absorption spectroscopy. Paired brain specimens were obtained at autopsy for each case; one was conserved by formalin archival (averaging four years), the other was rapidly frozen. Both white and grey matter samples were analyzed and the concentrations of iron and zinc were found to decrease with fixation. Iron was reduced by 40% (P < 0.01), and zinc by 77% (P < 0.0001); copper concentrations increased by 37% (P < 0.05) by the paired T-test. The increase in copper is likely due to contamination from trace copper in the formalin. These results indicate that transition metal data obtained from fixed tissue may be heavily distorted and care should be taken in interpreting this data.     

Effects of Mitochondrial Toxins on the Brain Amino Acid Concentrations

In the pathogenesis of Parkinson’s disease and Huntington’s disease excitotoxicity may play an important role. The common toxin model for Parkinson’s disease is MPTP, while for Huntington’s disease it is 3-NP. These toxins inhibit the mitochondrial respiratory chain, resulting in an energy deficit. In the central nervous system, the amino acids act as neurotransmitters and neuromodulators. The energy deficit caused by these neurotoxins may alter the concentrations of amino acids. Thus, it can be claimed that the aminoacidergic neurotransmission can be changed by neurotoxins. To test this hypothesis we studied the amino acid concentrations in different brain regions following MPTP or 3-NP administration. The two toxins were found to produce similar changes. We detected marked decreases in most of the amino acid concentrations in the striatum and in the cortex, while the levels in the cerebellum increased significantly. The decreased amino acid levels can be explained by the reduced levels of ATP produced by these neurotoxins. In the cerebellum, where there is no detectable ATP loss, the elevated amino acid levels may reflect a compensation of the altered neurotransmission.     

Redox Regulation of Cellular Stress Response in Aging and Neurodegenerative Disorders: Role of Vitagenes

Reduced expression and/or activity of antioxidant proteins lead to oxidative stress, accelerated aging and neurodegeneration. However, while excess reactive oxygen species (ROS) are toxic, regulated ROS play an important role in cell signaling. Perturbation of redox status, mutations favoring protein misfolding, altered glyc(osyl)ation, overloading of the product of polyunsaturated fatty acid peroxidation (hydroxynonenals, HNE) or cholesterol oxidation, can disrupt redox homeostasis. Collectively or individually these effects may impose stress and lead to accumulation of unfolded or misfolded proteins in brain cells. Alzheimer’s (AD), Parkinson’s and Huntington’s disease, amyotrophic lateral sclerosis and Friedreich’s ataxia are major neurological disorders associated with production of abnormally aggregated proteins and, as such, belong to the so-called “protein conformational diseases”. The pathogenic aggregation of proteins in non-native conformation is generally associated with metabolic derangements and excessive production of ROS. The “unfolded protein response” has evolved to prevent accumulation of unfolded or misfolded proteins. Recent discoveries of the mechanisms of cellular stress signaling have led to new insights into the diverse processes that are regulated by cellular stress responses. The brain detects and overcomes oxidative stress by a complex network of “longevity assurance processes” integrated to the expression of genes termed vitagenes. Heat-shock proteins are highly conserved and facilitate correct protein folding. Heme oxygenase-1, an inducible and redox-regulated enzyme, has having an important role in cellular antioxidant defense. An emerging concept is neuroprotection afforded by heme oxygenase by its heme degrading activity and tissue-specific antioxidant effects, due to its products carbon monoxide and biliverdin, which is then reduced by biliverdin reductase in bilirubin. There is increasing interest in dietary compounds that can inhibit, retard or reverse the steps leading to neurodegeneration in AD. Specifically any dietary components that inhibit inappropriate inflammation, AβP oligomerization and consequent increased apoptosis are of particular interest, with respect to a chronic inflammatory response, brain injury and β-amyloid associated pathology. Curcumin and ferulic acid, the first from the curry spice turmeric and the second a major constituent of fruit and vegetables, are candidates in this regard. Not only do these compounds serve as antioxidants but, in addition, they are strong inducers of the heat-shock response. Food supplementation with curcumin and ferulic acid are therefore being considered as a novel nutritional approach to reduce oxidative damage and amyloid pathology in AD. We review here some of the emerging concepts of pathways to neurodegeneration and how these may be overcome by a nutritional approach. Special issue dedicated to John P. Blass.