Neuroinflammation in amyotrophic lateral sclerosis: role of glial activation in motor neuron disease

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS) are characterised by the appearance of reactive microglial and astroglial cells, a process referred to as neuroinflammation. In transgenic mouse models of mutant SOD1-associated familial ALS, reactive microglial cells and astrocytes actively contribute to the death of motor neurons. The biological processes that drive this glial reaction are complex and have both beneficial and deleterious effects on motor neurons. Therapeutic interventions targeting these cells are being explored. An improved understanding of the biological processes that cause neuroinflammation will help to define its medical importance and to identify the therapeutic potential of interfering with this reaction.     

Lipid peroxidation and oxidative imbalance: early functional events in Alzheimer's disease

Alzheimer's disease (AD) is a growing public health problem worldwide. Clinically, AD is a progressive neurodegenerative disorder characterized by a global cognitive decline. Accumulating evidence indicates that reactive oxygen species-mediated reactions, particularly of neuronal lipids, are extensive in those AD brain areas directly involved in the disease processes. Traditional views claim that oxidative-mediated tissue injury in the AD brain is the result of neurodegeneration. In recent years, numerous investigations have pointed to the functional importance of oxidative imbalance as a crucial event in mediating AD pathogenesis. The availability of specific and sensitive markers to monitor in vivo oxidative stress, in combination with studies performed in living patients with clinical diagnosis of AD are helping us to elucidate these issues. The evidence we have accumulated so far clearly indicates that oxidative imbalance and subsequent oxidative stress are early events during the evolution of the disease, and secondary to specific mechanism(s) present in AD but not in other neurodegenerative diseases. These new concepts implicate that this phenomenon may play a more important role in AD pathogenesis than previously anticipated, and that any therapeutic intervention targeting oxidative stress should be initiated at the earliest possible stage of the disease.     

Rutin inhibits β-amyloid aggregation and cytotoxicity, attenuates oxidative stress, and decreases the production of nitric oxide and proinflammatory cytokines

Alzheimer's disease (AD) is a complex, multi-factorial neurodegenerative disease. The aggregation of soluble β-amyloid (Aβ) into fibrillar deposits is a pathological hallmark of AD. The Aβ aggregate-induced neurotoxicity, inflammatory reactions, oxidative stress, and nitric oxide (NO) generation are strongly linked to the etiology of AD. Here, we show that the common dietary flavonoid, rutin, can dose-dependently inhibit Aβ42 fibrillization and attenuate Aβ42-induced cytotoxicity in SH-SY5Y neuroblastoma cells. Moreover, rutin decreases the formation of reactive oxygen species (ROS), NO, glutathione disulfide (GSSG), and malondialdehyde (MDA), reduces inducible nitric oxide synthase (iNOS) activity, attenuates mitochondrial damage, increases the glutathione (GSH)/GSSG ratio, enhances the activities of super oxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), and modulates the production of proinflammatory cytokines by decreasing TNF-α and IL-1β generation in microglia. Taken together, the actions of rutin on multiple pathogenic factors deserves further investigation for the prevention and treatment of AD.     

Age-related macular degeneration (AMD): Alzheimer's disease in the eye?

Age-related macular degeneration (AMD) is a late-onset, neurodegenerative retinal disease that shares several clinical and pathological features with Alzheimer's disease (AD), including stress stimuli such as oxidative stress and inflammation. In both diseases, the detrimental intra- and extracellular deposits have many similarities. Aging, hypercholesterolaemia, hypertension, obesity, arteriosclerosis, and smoking are risk factors to develop AMD and AD. Cellular aging processes have similar organelle and signaling association in the retina and brain tissues. However, it seems that these diseases have a different genetic background. In this review, differences and similarities of AMD and AD are thoroughly discussed.     

Alzheimer's disease: cerebrovascular dysfunction, oxidative stress, and advanced clinical therapies

Many lines of independent research have provided convergent evidence regarding oxidative stress, cerebrovascular disease, dementia, and Alzheimer's disease (AD). Clinical studies spurred by these findings engage basic and clinical communities with tangible results regarding molecular targets and patient outcomes. Focusing on recent progress in characterizing age-related diseases specifically highlights oxidative stress and mechanisms for therapeutic action in AD. Oxidative stress has been investigated independently for its relationship with aging and cardiovascular and neurodegenerative diseases and provides evidence of shared pathophysiology across these conditions. The mechanisms by which oxidative stress impacts the cerebrovasculature and blood-brain barrier are of critical importance for evaluating antioxidant therapies. Clinical research has identified homocysteine as a relevant risk factor for AD and dementia; basic research into molecular mechanisms associated with homocysteine metabolism has revealed important findings. Oxidative stress has direct implications in the pathogenesis of age-related neurodegenerative diseases and careful scrutiny of oxidative stress in the CNS has therapeutic implications for future clinical trials. These mechanisms of dysfunction, acting independently or in concert, through oxidative stress may provide the research community with concise working concepts and promising new directions to yield new methods for evaluation and treatment of dementia and AD.     

Curcumins promote monocytic gene expression related to β-amyloid and superoxide dismutase clearance

Neurodegenerative diseases are associated with accumulation of modified proteins or peptides including amyloid-β (Aβ) in Alzheimer's disease (AD), and misfolded superoxide dismutase-1 (SOD-1) in amyotrophic lateral sclerosis (ALS). Clearance of Aβ or SOD-1 by the innate immune system may be important for controlling or preventing disease onset. Curcumins restore Aβ phagocytosis by peripheral blood mononuclear cells (PBMCs) from AD patients and Aβ clearance with upregulation of key genes including MGAT3, vitamin D receptor (VDR) and Toll-like receptors (TLRs). Certain curcumins inhibit inflammatory processes of PBMCs from ALS patients. We developed an in vitro system using human monocytes from patients and monocytic cell lines (i.e. U-937, THP-1) for evaluating curcuminoid potency of innate immune cell stimulation. Bisdemethoxycurcumin and certain analogs potentiated MGAT3,VDR and TLR gene expression 3- to 300-fold in U-937 cells. The effect of curcumins on inflammation in monocytes from patients with ALS was examined. Recursive medicinal chemistry was applied to identify compounds that stimulate the innate immune system for use in the clearance of Aβ in AD and the reversal of neuroinflammation and defective SOD-1 accumulation in ALS.     

Increased susceptibility to plasma lipid peroxidation in Alzheimer disease patients

Oxidative stress, linked to Abeta-lipid interactions, plays a pathogenetic role in Alzheimer's disease. We investigated modifications of lipid peroxidation products in plasma of 52 AD patients, 42 healthy controls and 16 patients with amyotrophic lateral sclerosis, a neurodegenerative disease where oxidative stress also plays a pathogenetic role. Final lipid peroxidation products were measured in plasma by thiobarbituric acid reactive substances (TBARS) assay before and after ex vivo oxidative stress catalysed by copper. There were no significant changes at basal conditions, but after copper-induced oxidation TBARS levels were higher in AD patients (19.0 microM +/- 2.2) versus both controls (5.2 microM +/- 0.8, p<0.001) and ALS patients (7.6 microM +/- 2.1, p<0.01). Stimulated TBARS levels were significantly higher in mild and moderate AD (p<0.0001) with respect to controls, but not in severe AD patients, with a significant inverse correlation between disease severity and lipid peroxidation (p<0.005, r2=0.21). Treatment of a subgroup (13) of mild and moderate AD patients with vitamin C and E for three months decreased plasma lipoperoxidation susceptibility by 60%. Thus, oxidative stress, expressed as ex vivo susceptibility to lipid peroxidation, appears to be an early phenomenon, probably related to AD pathogenetic mechanisms.     

The role of the phosphoinositide signalling system in the pathogenesis of sporadic Alzheimer's disease: a hypothesis

Great advances have been made in recent years in our knowledge of the genetic mutations found in early onset familial Alzheimer's disease (AD) and their pathological consequences. The pathogenesis of sporadic AD, on the other hand, is less clear, although a central role of oxidative stress is indicated. In the AD brain, severe dysfunctions in the phosphoinositide signalling pathway have been reported. In view of the fact that (a) oxidative stress can adversely affect phosphoinositide breakdown and hence diacylglycerol-mediated activation of protein kinase C and (b) protein kinase C activation reduces the production of β-amyloid peptide from amyloid precursor protein, it is possible that this represents a pathogenic pathway whereby oxidative stress can lead to amyloid deposition and the development of the disease.     

Review: Iron metabolism and the role of iron in neurodegenerative disorders

Iron plays a role for the biogenesis of two important redox‐reactive prosthetic groups of enzymes, iron sulphur clusters (ISC) and heme. A part of these biosynthetic pathways takes plays in the mitochondria. While several important proteins of cellular iron uptake and storage and of mitochondrial iron metabolism are well‐characterized, limited knowledge exists regarding the mitochondrial iron importers (mitoferrins). A disturbed distribution of iron, hampered Fe‐dependent biosynthetic pathways and eventually oxidative stress resulting from an increased labile iron pool are suggested to play a role in several neurodegenerative diseases. Friedreich's ataxia is associated with mitochondrial iron accumulation and hampered ISC/heme biogenesis due to reduced frataxin expression, thus representing a monogenic mitochondrial disorder, which is clearly elicited solely by a disturbed iron metabolism. Less clear are the controversially discussed impacts of iron dysregulation and iron‐dependent oxidative stress in the most common neurodegenerative disorders, i.e. Alzheimer's disease (AD) and Parkinson's disease (PD). Amyotrophic lateral sclerosis (ALS) may be viewed as a disease offering a better support for a direct link between iron, oxidative stress and regional neurodegeneration. Altogether, despite significant progress in molecular knowledge, the true impact of iron on the sporadic forms of AD, PD and ALS is still uncertain. Here we summarize the current knowledge of iron metabolism disturbances in neurodegenerative disorders.     

Neuroinflammation and oxidative stress act in concert to promote neurodegeneration in the diabetic retina and optic nerve:galectin-3 participation

Diabetes is a lifelong disease characterized by glucose metabolic imbalance,in which low insulin levels or impaired insulin signaling lead to hyperglycemic state.Within 20 years of diabetes progression,95%of patients will have diabetic retinopathy,the leading cause of visual defects in working-age people worldwide.Although diabetes is considered a microvascular disease,recent studies have shown that neurodegeneration precedes vascular changes within the diabetic visual system,albeit its mechanisms are still under investigation.Neuroinflammation and oxidative stress are intrinsically related phenomena,since macrophage/microglia and astrocytes are the main sources of reactive oxygen species during central nervous system chronic degenerative diseases,and both pathological processes are increased in the visual system during diabetes.The present review will focus on recent findings of the contribution of oxidative stress derived from neuroinflammation in the early neurodegenerative aspects of the diabetic visual system and their relationship with galectin-3.     

Clinical and Pathological Benefit of Twendee X in Alzheimer's Disease Transgenic Mice with Chronic Cerebral Hypoperfusion

BackgroundMultiple pathogeneses are involved in Alzheimer's disease (AD), such as amyloid-β accumulation, neuroinflammation, and oxidative stress. The pathological impact of chronic cerebral hypoperfusion on Alzheimer's disease is still poorly understood.MethodsAPP23 mice were implanted to bilateral common carotid arteries stenosis with ameroid constrictors for slowly progressive chronic cerebral hypoperfusion (CCH). The effects of the administration of Twendee X (TwX) were evaluated by behavioral analysis, immunohistochemical analysis, and immunofluorescent histochemistry.ResultsIn the present study, chronic cerebral hypoperfusion, which is commonly found in aged Alzheimer's disease, significantly exacerbated motor dysfunction of APP23 mice from 5 months and cognitive deficit from 8 months of age, as well as neuronal loss, extracellular amyloid-β plaque and intracellular oligomer formations, and amyloid angiopathy at 12 months. Severe upregulations of oxidative markers and inflammatory markers were found in the cerebral cortex, hippocampus, and thalamus at 12 months. Twendee X treatment (20 mg/kg/d, from 4.5 to 12 months) substantially rescued the cognitive deficit and reduced the above amyloid-β pathology and neuronal loss, alleviated neuroinflammation and oxidative stress.ConclusionsThe present findings suggested a potential therapeutic benefit of Twendee X for Alzheimer's disease with chronic cerebral hypoperfusion.     

Antioxidant protection and neurodegenerative disease: the role of amyloid-beta and tau

In Alzheimer's disease (AD), the major components of senile plaques and neurofibrillary tangles, amyloid-beta and tau, respectively, are thought by many to play a key role in disease initiation and progression. However, herein we propose that rather than being initiators of disease pathogenesis, the lesions that characterize AD, senile plaques and neurofibrillary pathology, occur consequent to oxidative stress and, importantly, function as a primary line of antioxidant defense. Importantly, this paradigm shift in thinking about the role of lesions in disease also provides an explanation for the appearance of both amyloid-beta and tau in control individuals given the increased levels of oxidative stress associated with the aged brain. In AD, oxidative stress is not only high but chronic and is superimposed upon an age-related vulnerable environment. Therefore, one would predict, successfully, an increased lesion load in patients with AD above and beyond that seen in normal aging. The notion that amyloid-beta and tau accumulations indicate adaptation and, likely, physiological processes sheds light on the pathological expression of disease and calls into question the rationale of current therapeutic efforts targeted toward lesion removal.     

Mitochondrial failures in Alzheimer's disease

Mitochondrial dysfunction and free radical-induced oxidative damage have been implicated in the pathogenesis of several different neurodegenerative diseases such as Parkinson disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and Alzheimer's disease (AD). The defective adenosine triphosphate (ATP) production and increased oxygen radicals may induce mitochondria-dependent cell death because damaged mitochondria are unable to maintain the energy demands of the cell. The role of vascular hypoperfusion-induced mitochondria failure in the pathogenesis of AD now has been widely accepted. However, the exact cellular mechanisms behind vascular lesions and their relation to oxidative stress markers identified by RNA oxidation, lipid peroxidation, or mitochondrial DNA (mtDNA) deletion remain unknown. Future studies comparing the spectrum of mitochondrial damage and the relationship to oxidative stress-induced damage during the aging process or, more importantly, during the maturation of AD pathology are warranted.     

Nitric Oxide-Mediated Oxidative Damage and the Progressive Demise of Motor Neurons in ALS

Oxidative damage is a common and early feature of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and other neurodegenerative disorders. Dr. Mark Smith and his colleagues have built the case for oxidative stress being a primary progenitor rather than a secondary end-stage epiphenomenon of neurodegeneration. They proposed that reactive oxygen species contribute to the "age-related cascade of neurodegeneration," whereby accumulative oxidative damage with age promotes other characteristic pathological changes in afflicted brain regions, including protein aggregation, metabolic deficiencies, and inflammation. Nitric oxide (NO) likely plays a critical role in this age-related cascade. NO is a major signaling molecule produced in the central nervous system to modulate neurological activity through stimulating cyclic GMP synthesis. However, the same physiological concentrations of NO, relevant in cellular signaling, may also initiate and amplify oxidative damage by diffusion-limited reactions with superoxide (O (2) ( ?- ) ) to produce peroxynitrite (ONOO( - )). This is perhaps best illustrated in ALS where physiological levels of NO promote survival of motor neurons, but the same concentrations can stimulate motor neuron apoptosis and glial cell activation under pathological conditions. While these changes represent a complex mechanism involving multiple cell types in the pathogenesis of ALS, they also reveal general processes underlying neurodegeneration.     

NF-E2-related factor 2 activation boosts antioxidant defenses and ameliorates inflammatory and amyloid properties in human Presenilin-1 mutated Alzheimer's disease astrocytes

Alzheimer's disease (AD) is a common dementia affecting a vast number of individuals and significantly impairing quality of life. Despite extensive research in animal models and numerous promising treatment trials, there is still no curative treatment for AD. Astrocytes, the most common cell type of the central nervous system, have been shown to play a role in the major AD pathologies, including accumulation of amyloid plaques, neuroinflammation, and oxidative stress. Here, we show that inflammatory stimulation leads to metabolic activation of human astrocytes and reduces amyloid secretion. On the other hand, the activation of oxidative metabolism leads to increased reactive oxygen species production especially in AD astrocytes. While healthy astrocytes increase glutathione (GSH) release to protect the cells, Presenilin-1-mutated AD patient astrocytes do not. Thus, chronic inflammation is likely to induce oxidative damage in AD astrocytes. Activation of NRF2, the major regulator of cellular antioxidant defenses, encoded by the NFE2L2 gene, poses several beneficial effects on AD astrocytes. We report here that the activation of NRF2 pathway reduces amyloid secretion, normalizes cytokine release, and increases GSH secretion in AD astrocytes. NRF2 induction also activates the metabolism of astrocytes and increases the utilization of glycolysis. Taken together, targeting NRF2 in astrocytes could be a potent therapeutic strategy in AD.     

Exosomes: a novel therapeutic target for Alzheimer's disease?

Extracellular exosomes are formed inside the cytoplasm of cells in compartments known as multivesicular bodies. Thus, exosomes contain cytoplasmic content. Multivesicular bodies fuse with the plasma membrane and release exosomes into the extracellular environment. Comprehensive research suggests that exosomes act as both inflammatory intermediaries and critical inducers of oxidative stress to drive progression of Alzheimer's disease. An important role of exosomes in Alzheimer's disease includes the formation of neurofibrillary tangles and beta-amyloid production, clearance, and accumulation. In addition, exosomes are involved in neuroinflammation and oxidative stress, which both act as triggers for beta-amyloid pathogenesis and tau hyperphosphorylation. Further, it has been shown that exosomes are strongly associated with beta-amyloid clearance. Thus, effective measures for regulating exosome metabolism may be novel drug targets for Alzheimer's disease.     

Neuroinflammation in Alzheimer's disease and prion disease

Alzheimer's disease (AD) and prion disease are characterized neuropathologically by extracellular deposits of Abeta and PrP amyloid fibrils, respectively. In both disorders, these cerebral amyloid deposits are co-localized with a broad variety of inflammation-related proteins (complement factors, acute-phase protein, pro-inflammatory cytokines) and clusters of activated microglia. The present data suggest that the cerebral Abeta and PrP deposits are closely associated with a locally induced, non-immune-mediated chronic inflammatory response. Epidemiological studies indicate that polymorphisms of certain cytokines and acute-phase proteins, which are associated with Abeta plaques, are genetic risk factors for AD. Transgenic mice studies have established the role of amyloid associated acute-phase proteins in Alzheimer amyloid formation. In contrast to AD, there is a lack of evidence that cytokines and acute-phase proteins can influence disease progression in prion disease. Clinicopathological and neuroradiological studies have shown that activation of microglia is a relatively early pathogenetic event that precedes the process of neuropil destruction in AD patients. It has also been found that the onset of microglial activation coincided in mouse models of prion disease with the earliest changes in neuronal morphology, many weeks before neuronal loss and subsequent clinical signs of disease. In the present work, we review the similarities and differences between the involvement of inflammatory mechanisms in AD and prion disease. We also discuss the concept that the demonstration of a chronic inflammatory-like process relatively early in the pathological cascade of both diseases suggests potential therapeutic strategies to prevent or to retard these chronic neurodegenerative disorders.     

Vascular inflammatory, oxidative and protease-based processes: implications for neuronal cell death in Alzheimer's disease

A substantial literature demonstrates activation of inflammatory processes in the Alzheimer's disease (AD) brain and an association between inflammation and oxidative stress. We have shown that brain microvessels from AD patients express high levels of inflammatory proteins and that these proteins evoke release of the neurotoxic protease thrombin from brain endothelial cells. The objective of this study was to determine the effects of inflammatory proteins on brain endothelial cell reactive oxygen species generation, protease release and cell apoptosis. Also, the effects of inflammatory proteins on neuronal reactive oxygen species generation, injury and apoptosis were assessed. Treatment of cultured brain endothelial cells with inflammatory proteins (LPS, IL-1beta, IL-6, IFN-gamma, TNF-alpha) resulted in a significant increase (p < 0.01) in intracellular levels of reactive oxygen species by 1 h. Inflammatory proteins also caused release of tissue plasminogen activator and increased apoptosis by 24 h in these cells. In cultured neurons, inflammatory proteins caused an increase in reactive oxygen species, membrane fluidity, and apoptosis by 24 h, as detected by fluorescent microscopy. Taken together, these data support the hypothesis that vascular inflammatory, oxidative and protease-based processes contribute to neuronal cell death, and suggest that therapies targeted at these mediators and processes could be effective in AD.