Phytochemicals Targeting Oxidative Stress,Interconnected Neuroinflammatory,and Neuroapoptotic Pathways Following Radiation

The radiation for therapeutic purposes has shown positive effects in different contexts; however, it can increase the risk of many age-related and neurodegenerative diseases such as Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD), and Parkinson’s disease (PD). These different outcomes highlight a dose-response phenomenon called hormesis. Prevailing studies indicate that high doses of radiation could play several destructive roles in triggering oxidative stress, neuroapoptosis, and neuroinflammation in neurodegeneration. However, there is a lack of effective treatments in combating radiation-induced neurodegeneration, and the present drugs suffer from some drawbacks, including side effects and drug resistance. Among natural entities, polyphenols are suggested as multi-target agents affecting the dysregulated pathogenic mechanisms in neurodegenerative disease. This review discusses the destructive effects of radiation on the induction of neurodegenerative diseases by dysregulating oxidative stress, apoptosis, and inflammation. We also describe the promising effects of polyphenols and other candidate phytochemicals in preventing and treating radiation-induced neurodegenerative disorders, aiming to find novel/potential therapeutic compounds against such disorders.     

Estrogen and cytokines production - the possible cause of gender differences in neurological diseases

Naturally occurring sexual dimorphism has been implicated in the risk, progression and recovery from numerous neurological disorders. These include head injury, multiple sclerosis (MS), stroke, and neurodegenerative diseases (Parkinson's disease (PD), Alzheimer's disease (AD) or amyotrophic lateral sclerosis (ALS). Accumulating evidence suggests that observed differences between men and women could result from estrogen's wide range of effects within the mammalian central nervous system (CNS), with it's neuroprotective effect being one of the most important. It seems possible that neuroprotective activity of estrogen could be partially a result of it's anti-inflammatory action. It has been well established that inflammation plays an important role in the etiopathogenesis and manifestation of brain pathological changes. In this regard, an important role has been suggested for pro-inflammatory cytokines produced by activated glial cells, neurons and immune cells that invade brain tissue. Within the CNS, cytokines stimulate inflammatory processes that may impair blood-brain barrier permeability as well as promote apoptosis of neurons, oligodendrocytes and induce myelin damage. Given that estrogen may modulate cytokine expression, coupled with the fact that gender differences of cytokine production are apparent in animal models of PD and MS, suggests an important connection between hormonal-cytokine link in neurodegeneration. Indeed, while MS patients and mice subjected to experimental autoimmune encephalomyelitis (EAE) display gender specific alterations of IFN-gamma and IL-12, variations of TNF and IL-6 were associated with PD. Also in case of more acute neurodegenerative conditions, such as stroke, the effect of IL-6 gene G-174C polymorphism was different in males and females. Given that our understanding of the role of estrogen on cytokine production and accompanying CNS pathological conditions is limited, the present reviews aims to present some of our recent findings in this area and further evaluate the evidence that may be relevant to the design of new hormonal anti-inflammatory treatment strategies for neurodegenerative diseases.     

Potential Role of Glucagon-Like Peptide-1 (GLP-1) in Neuroprotection

The current understanding of neurodegenerative processes in sporadic diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) or multiple sclerosis is very limited. Several risk factors have been identified that may shed light on the underlying mechanisms that initiate the neurodegeneration. Type 2 diabetes mellitus has been identified as a risk factor for AD and PD. In AD patients, desensitization of insulin receptors in the brain has been shown, even in non-diabetic patients. Insulin acts as a growth factor in the brain and supports neuronal repair, dendritic sprouting and synaptogenesis, and protection from oxidative stress. Importantly, several drugs have been developed to treat type 2 diabetes that re-sensitize insulin receptors and may be of use to prevent neurodegenerative processes. Glucagon-like peptide-1 (GLP-1) is a hormone that facilitates insulin release under high blood sugar conditions. Interestingly, GLP-1 also has very similar growth factor-like properties to insulin, and has been shown to reduce a range of degenerative processes. In pre-clinical studies, GLP-1 and longer-lasting protease-resistant analogues cross the blood-brain barrier, protect memory formation (AD) or motor activity (PD), protect synapses and synaptic functions, enhance neurogenesis, reduce apoptosis, protect neurons from oxidative stress, and reduce plaque formation and the chronic inflammation response in the brains of mouse models of AD, PD, amyotrophic lateral sclerosis, stroke and other degenerative diseases. GLP-1 signalling does not affect blood sugar levels in non-diabetic people and therapies that affect GLP-1 signalling have a good safety profile as shown by the chronic application of drugs currently on the market (liraglutide, Victoza?; NovoNordisk, Copenhagen, Denmark, and exendin-4, Byetta?; Amylin, San Diego, CA, USA). Based on the extensive evidence, several clinical trials are currently underway, testing liraglutide and exendin-4 in AD and PD patients. Therefore, GLP-1 analogues show great promise as a novel treatment for AD or other neurodegenerative conditions.     

From small to big molecules: how do we prevent and delay the progression of age-related neurodegeneration?

Age-related neurodegeneration in the brain and retina is complicated. It comprises a series of events encompassing different modes of degeneration in neurons, as well as inflammation mediated by glial cells. Systemic inflammation and risk factors can contribute to disease progression. Age-related conditions such as Alzheimer's disease (AD), Parkinson's disease (PD) and Age-related Macular Degeneration (AMD) affect patients for 5 to 20 years and are highly associated with risk factors such as hyperhomocysteinaemia, hypercholesterolaemia, hypertension, and symptoms of mood disorder. The long duration of the degeneration and the wide array of systemic factors provide the opportunity for nutraceutical intervention to prevent or delay disease progression. Small molecules such as phenolic compounds are candidates for neuroprotection because they have anti-oxidant activities and can modulate intracellular signaling pathways. Bigger entities such as oligosaccharides and polysaccharides have often been neglected because of their complex structure. However, certain big molecules can provide neuroprotective effects. They may also have a wide spectrum of action against risk factors. In this review we use an integrative approach to the potential uses of nutraceutical products to prevent age-related neurodegeneration. These include direct effects of phenolic compounds and polysaccharides on neurons to antagonize various neurodegenerative mechanisms in AD, PD and AMD, and indirect effects of these compounds on peripheral disease-related risk factors.     

Inhibition of Membrane-Bound Aminopeptidase P

The two most common neurodegenerative diseases are Alzheimer’s disease (AD) and Parkinson’s disease (PD). The symptoms are caused by the initially selective degeneration of neuronal subpopulations involved in memory (AD) or movement control (PD). The cause of both diseases is unknown, but ageing is an inevitable risk factor. The identification of disease-associated genes was a breakthrough for the understanding of molecular mechanisms of neurodegeneration and has provided the basis for the establishment of cell culture and animal model systems, instrumental for target validation and drug screening. Familial AD is caused by mutations in the β-amyloid precursor protein (βAPP) and in the gene products responsible for its proteolytic processing, namely the presenilins. Transgenic mice expressing these mutant genes develop characteristic AD plaques in an age-dependent manner. A reduction of plaque burden and amelioration of cognitive decline in these animals was recently achieved by vaccination with amyloid β-protein fibrils. The other hallmark lesion of AD, the neurofibrillary tangle, has been modelled recently in transgenic mice expressing mutant tau protein linked to frontotemporal dementia. PD is characterised by intraneuronal cytoplasmic deposits (Lewy bodies) of the PD-associated gene product α-synuclein. Transgenic expression of α-synuclein recreated hallmark features of PD in mice and fruit flies, establishing α-synuclein as PD-causing drug target. Moreover, environmental risk factors such as the pesticide rotenone have been used successfully to generate rodent models of PD. Lesion models of PD are being exploited for the development of experimental gene therapy and transplantation approaches.     

Role of sirtuins and calorie restriction in neuroprotection: implications in Alzheimer's and Parkinson's diseases

Aging is the major known risk factor for the onset of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Mitochondria play a central role in aging as mitochondrial dysfunction increases with age and produces harmful levels of reactive oxygen species which leads to cellular oxidative stress (free-radical theory of aging). Oxidative stress is highly damaging to cellular macromolecules and is also a major cause of the loss and impairment of neurons in neurodegenerative disorders. A growing body of evidence suggests that modulation of sirtuin activity and restricting calorie intake has a strong neuroprotective effect. SIRT1 induction by the use of pharmacological activators or by calorie restriction (CR) diet regimen has been shown to protect against neuronal loss and impairment in the cellular and animal models of AD and PD. Here, we review the current knowledge and recent data related to the role of sirtuins and CR in neurodegeneration and discuss the potential underlying signaling pathways of neuroprotection that might serve as attractive targets for the future therapeutic intervention of these age-related neurodegenerative diseases.     

The emerging utility of animal models of chronic neurodegenerative diseases

The two most common neurodegenerative diseases are Alzheimer's disease (AD) and Parkinson's disease (PD). The symptoms are caused by the initially selective degeneration of neuronal subpopulations involved in memory (AD) or movement control (PD). The cause of both diseases is unknown, but ageing is an inevitable risk factor. The identification of disease-associated genes was a breakthrough for the understanding of molecular mechanisms of neurodegeneration and has provided the basis for the establishment of cell culture and animal model systems, instrumental for target validation and drug screening. Familial AD is caused by mutations in the beta-amyloid precursor protein (betaAPP) and in the gene products responsible for its proteolytic processing, namely the presenilins. Transgenic mice expressing these mutant genes develop characteristic AD plaques in an age-dependent manner. A reduction of plaque burden and amelioration of cognitive decline in these animals was recently achieved by vaccination with amyloid beta-protein fibrils. The other hallmark lesion of AD, the neurofibrillary tangle, has been modelled recently in transgenic mice expressing mutant tau protein linked to frontotemporal dementia. PD is characterised by intraneuronal cytoplasmic deposits (Lewy bodies) of the PD-associated gene product alpha-synuclein. Transgenic expression of alpha-synuclein recreated hallmark features of PD in mice and fruit flies, establishing alpha-synuclein as PD-causing drug target. Moreover, environmental risk factors such as the pesticide rotenone have been used successfully to generate rodent models of PD. Lesion models of PD are being exploited for the development of experimental gene therapy and transplantation approaches.     

Transgenic animal models of neurodegenerative diseases and their application to treatment development

Neurodegenerative disorders of the aging population affect over 5 million people in the US and Europe alone. The common feature is the progressive accumulation of misfolded proteins with the formation of toxic oligomers. Previous studies show that while in Alzheimer's disease (AD) misfolded amyloid-beta protein accumulates both in the intracellular and extracellular space, in Lewy body disease (LBD), Parkinson's disease (PD), Multiple System Atrophy (MSA), Fronto-Temporal dementia (FTD), prion diseases, amyotrophic lateral sclerosis (ALS) and trinucleotide repeat disorders (TNRD), the aggregated proteins accumulate in the plasma membrane and intracellularly. Protein misfolding and accumulation is the result of an altered balance between protein synthesis, aggregation rate and clearance. Based on these studies, considerable advances have been made in the past years in developing novel experimental models of neurodegenerative disorders. This has been in part driven by the identification of genetic mutations associated with familial forms of these conditions and gene polymorphisms associated with the more common sporadic variants of these diseases. Transgenic and knock out rodents and Drosophila as well as viral vector driven models of Alzheimer's disease (AD), PD, Huntington's disease (HD) and others have been developed, however the focus for this review will be on rodent models of AD, FTD, PD/LBD, and MSA. Promising therapeutic results have been obtained utilizing amyloid precursor protein (APP) transgenic (tg) models of AD to develop therapies including use of inhibitors of the APP-processing enzymes beta- and gamma-secretase as well as vaccine therapies.     

Neurotoxicity as a Mechanism for Neurodegenerative Disorders: Basic and Clinical Aspects

This three day meeting focused on chronic neurodegenerative diseases such as Parkinson’s disease (PD), Alzheimer’s disease (AD) and amylotrophic lateral sclerosis (ALS). It attracted 69 participants from 10 countries with dominance of Chile and USA. Neurodegeneration and its prevention increasingly gain in importance as the number of people affected increases year-by-year. The meeting addressed various basic aspects having pragmatic implications such as: oxidative stress, inflammatory reaction, glial activation, role of glutamatergic system and apoptosis using a plethora of in vitro and in vivo methods.     

LPS-induced Murine Neuroinflammation Model: Main Features and Suitability for Pre-clinical Assessment of Nutraceuticals

Neuroinflammation is an important feature in the pathogenesis and progression of neurodegenerative diseases such as Alzheimer´s disease (AD), Parkinson´s disease (PD), frontotemporal dementia and amyotrophic lateral sclerosis. Based on current knowledge in the field, suggesting that targeting peripheral inflammation could be a promising additional treatment/prevention approach for neurodegenerative diseases, drugs and natural products with anti-inflammatory properties have been evaluated in animal models of neuroinflammation and neurodegeneration. In this review, we provide an extensive analysis of one of the most important and widely-used animal models of peripherally induced neuroinflammation and neurodegeneration - lipopolysaccharide (LPS)-treated mice, and address the data reproducibility in published research. We also summarize briefly basic features of various natural products, nutraceuticals, with known anti-inflammatory effects and present an overview of data on their therapeutic potential for reducing neuroinflammation in LPS-treated mice.     

NADPH oxidases: novel therapeutic targets for neurodegenerative diseases

Oxidative stress is a key pathologic factor in neurodegenerative diseases such as Alzheimer and Parkinson diseases (AD, PD). The failure of free-radical-scavenging antioxidants in clinical trials pinpoints an urgent need to identify and to block major sources of oxidative stress in neurodegenerative diseases. As a major superoxide-producing enzyme complex in activated phagocytes, phagocyte NADPH oxidase (PHOX) is essential for host defense. However, recent preclinical evidence has underscored a pivotal role of overactivated PHOX in chronic neuroinflammation and progressive neurodegeneration. Deficiency in PHOX subunits mitigates neuronal damage induced by diverse insults/stresses relevant to neurodegenerative diseases. More importantly, suppression of PHOX activity correlates with reduced neuronal impairment in models of neurodegenerative diseases. The discovery of PHOX and non-phagocyte NADPH oxidases in astroglia and neurons further reinforces the crucial role of NADPH oxidases in oxidative stress-mediated chronic neurodegeneration. Thus, proper modulation of NADPH oxidase activity might hold therapeutic potential for currently incurable neurodegenerative diseases.     

Apoptotic mechanisms involved in neurodegenerative diseases: experimental and therapeutic approaches

Alzheimer's disease (AD) and Parkinson's disease (PD) are two of the most significant neurodegenerative disorders in the developed world. However, although these diseases were described almost a century ago, the molecular mechanisms that lead to the neuronal cell death associated with these diseases are not yet clear, and vigorous research efforts have failed to identify effective treatment options. In the present review, we evaluate the potential mechanisms underlying apoptosis and neuronal death in neurodegenerative disorders. A role for mitochondria in the release of proapoptotic proteins, such as cytochrome c and apoptosis-inducing factor (AIF) etc., is discussed along with key processes involving oxidative stress and activation of glutamate receptors. We also deliberate the implication of DNA damage, primarily p53 induction and reentry in the cell cycle. Finally, we postulate that multitargeting therapies comprising antioxidants, cell cycle inhibitors and modulating agents of COX-2 or c-JUN kinase pathways could be suitable strategies to prevent or delay the process of neuronal cell death in neurodegenerative disorders. Thus, the aim of this review is to discuss the pathways involved in the pathogenesis of neurodegenerative diseases such as AD, PD and Huntington's disease (HD). Furthermore, current and future pharmacotherapeutics will be considered.     

Sphingosine kinase 1/sphingosine-1-phosphate receptors dependent signalling in neurodegenerative diseases. The promising target for neuroprotection in Parkinson’s disease

Parkinson’s disease (PD) is one of the most common serious neurodegenerative disorders in the world. The incidence of PD appears to be growing and this illness has an unknown pathogenesis. PD is characterized by selective loss of dopaminergic (DA) neurons in the substantia nigra (SN), with an enigmatic cause in most individuals. Current pharmacotherapies and surgery provide symptomatic relief but their effects against the progressive degeneration of neuronal cells are strongly limited if present at all. Therefore, uncovering novel molecular mechanisms of DA cell death and new potentially disease-modifying pharmacological targets is an important task for basic research. Significant progress has been made in understanding the role of disturbed sphingolipid metabolism, particularly relating to ceramide and sphingosine-1-phosphate (S1P) in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative diseases. Additionally, the neuroprotective potential of an S1P receptors (S1PR) modulator, fingolimod (FTY720), in multiple sclerosis (MS) and numerous other diseases has been observed over the past decade. In this review, we briefly summarise recent achievements in defining intracellular S1PR-dependent actions, discuss their significance to therapeutic approaches, and explore their neuroprotective potential as a target in PD treatment.     

Curcumin and neurodegenerative diseases: a perspective

INTRODUCTION: Curcumin, a dietary polyphenol found in the curry spice turmeric, possesses potent antioxidant and anti-inflammatory properties and an ability to modulate multiple targets implicated in the pathogenesis of chronic illness. Curcumin has shown therapeutic potential for neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). AREAS COVERED: This article highlights the background and epidemiological evidence of curcumin's health benefits and its pharmacodynamic and pharmacokinetic profile. Curcumin's ability to counteract oxidative stress and inflammation and its capacity to modulate several molecular targets is reviewed. We highlight the neuroprotective properties of curcumin including pre-clinical evidence for its pharmacological effects in experimental models of AD and PD. The bioavailability and safety of curcumin, the development of semi-synthetic curcuminoids as well as novel formulations of curcumin are addressed. EXPERT OPINION: Curcumin possesses therapeutic potential in the amelioration of a host of neurodegenerative ailments as evidenced by its antioxidant, anti-inflammatory and anti-protein aggregation effects. However, issues such as limited bioavailability and a paucity of clinical studies examining its therapeutic effectiveness in illnesses such as AD and PD currently limit its therapeutic outreach. Considerable effort will be required to adapt curcumin as a neuroprotective agent to be used in the treatment of AD, PD and other neurodegenerative diseases.     

Advances in tau-based drug discovery

INTRODUCTION: Tauopathies, including Alzheimer's disease (AD) and some frontotemporal dementias, are neurodegenerative diseases characterised by pathological lesions comprised of tau protein. There is currently a significant and urgent unmet need for disease-modifying therapies for these conditions and recently attention has turned to tau as a potential target for intervention. AREAS COVERED: Increasing evidence has highlighted pathways associated with tau-mediated neurodegeneration as important targets for drug development. Here, the authors review recently published papers in this area and summarise the genetic and pharmacological approaches that have shown efficacy in reducing tau-associated neurodegeneration. These include the use of agents to prevent abnormal tau processing and increase tau clearance, therapies targeting the immune system, and the manipulation of tau pre-mRNA to modify tau isoform expression. EXPERT OPINION: Several small molecule tau-based treatments are currently being assessed in clinical trials, the outcomes of which are eagerly awaited. Current evidence suggests that therapies targeting tau are likely, at least in part, to form the basis of an effective and safe treatment for Alzheimer's disease and related neurodegenerative disorders in which tau deposition is evident.     

Removing protein aggregates: the role of proteolysis in neurodegeneration

A common characteristic of neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) is the accumulation of protein aggregates. This reflects a severe disturbance of protein homeostasis, the proteostasis. Here, we review the involvement of the two major proteolytic machineries, the ubiquitin proteasome system (UPS) and the autophagy/lysosomal system, in the pathogenesis of neurodegenerative diseases. These proteolytic systems cooperate to maintain the proteostasis, as is indicated by intricate cross talk. In addition, the UPS and autophagy are regulated by stress pathways that are activated by disturbed proteostasis, like the unfolded protein response (UPR). We will specifically discuss how these proteolytic pathways are affected in neurodegenerative diseases. We will show that there is a differential involvement of the UPS and autophagy in different neurodegenerative disorders. In addition, the proteolytic impairment may be primary or secondary to the pathology. These differences have important implications for the design of therapeutic strategies. The opportunities and caveats of targeting the UPS and autophagy/lysosomal system as a therapeutic strategy in neurodegeneration will be discussed.     

Mitochondrial Biology and Neurological Diseases

Mitochondria are extremely active organelles that perform a variety of roles in the cell including energy production, regulation of calcium homeostasis, apoptosis, and population maintenance through fission and fusion. Mitochondrial dysfunction in the form of oxidative stress and mutations can contribute to the pathogenesis of various neurodegenerative diseases such as Parkinson’s (PD), Alzheimer’s (AD), and Huntington’s diseases (HD). Abnormalities of Complex I function in the electron transport chain have been implicated in some neurodegenerative diseases, inhibiting ATP production and generating reactive oxygen species that can cause major damage to mitochondriaMutations in both nuclear and mitochondrial DNA can contribute to neurodegenerative disease, although the pathogenesis of these conditions tends to focus on nuclear mutations. In PD, nuclear genome mutations in the PINK1 and parkin genes have been implicated in neurodegeneration [1], while mutations in APP, PSEN1 and PSEN2 have been implicated in a variety of clinical symptoms of AD [5]. Mutant htt protein is known to cause HD [2]. Much progress has been made to determine some causes of these neurodegenerative diseases, though permanent treatments have yet to be developed. In this review, we discuss the roles of mitochondrial dysfunction in the pathogenesis of these diseases.     

The many roles of chemokine receptors in neurodegenerative disorders: emerging new therapeutical strategies

Chemokines and chemokine receptors, primarily found to play a role in leukocyte migration to the inflammatory sites or to second lymphoid organs, have recently been found expressed on the resident cells of the central nervous system (CNS). These proteins are important for the development of the CNS and are involved in normal brain functions such as synaptic transmission. Increasing lines of evidence have implicated an involvement for chemokines and their receptors in several neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), human immunodeficiency virus-associated dementia (HAD), multiple sclerosis (MS), and stroke. Specific inhibition of the biological activities of chemokine receptors could gain therapeutic benefit for these neurodegenerative disorders. In recent years, non-peptide antagonists of chemokine receptors have been disclosed and tested in relevant pharmacological models and some of these inhibitors have entered clinical trials. The aim of this review is to outline the recent progress regarding the role of chemokines and their receptors in neurodegenerative diseases and the advancements in the development of chemokine receptor inhibitors as potential therapeutic approaches for these neurodegenerative diseases.