Targeting NADPH oxidase and phospholipases A2 in Alzheimer's disease. Mol Neurobiol. 2010;41:73-86. [PMID: 20195796 DOI: 10.1007/s12035-010-8107-7]

Amyloid beta-activated alpha-1-syntrophin has ramifications on Rac1 activation, ROS production and neuronal cell death

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of β-amyloid (Aβ)-containing extracellular neuritic plaques and phosphorylated tau-containing intracellular neurofibrillary tangles. It remains the primary neuropathological criteria for the diagnosis of AD. Additionally, several other processes are currently being recognized as significant risk factors for AD development, including the brain's susceptibility to reactive oxygen species (ROS). The ROS production is among the early signs in the progression of AD. However, the underlying mechanisms behind increased ROS production in AD remain poorly understood. We have observed SNTA1 plays critical role in regulating ROS levels in different pathological conditions. Here, we wanted to gain further insight into the role of SNTA1 in the development of AD by using IMR32 cell line. Our results show that the accumulation of Aβ plaques in Alzheimer's model neuroblastoma cells significantly increases the expression and activation of SNTA1 and MKK6 kinase. The activation of MKK6 results in the phosphorylation of SNTA1, creating a binding site for Rac1, leading to its activation and subsequent production of ROS. Excessive ROS production leads to cell cycle arrest in the G2/M phase, a hallmark of AD. Our study provides new insight into the mechanism of Aβ-mediated cell death in AD and suggests that MKK6-mediated activation of alpha-1-syntrophin promotes ROS production in neuronal cells, resulting in cell death. This study presents a mechanistic insight into Aβ-mediated cell death and could serve as a paradigm for reducing neuronal cell death in AD.

Upregulation of NADPH-oxidase, inducible nitric oxide synthase and apoptosis in the hippocampus following impaired insulin signaling in the rats: Development of sporadic Alzheimer's disease

NADPH-oxidase (NOX) is a multi-subunit enzyme complex. The upregulation of NOX causes massive production of superoxide (O2¯), which avidly reacts with nitric oxide (NO) and increases cellular reactive oxygen/nitrogen species (ROS/RNS). Increased ROS/RNS plays pivotal role in the sporadic Alzheimer's disease (sAD) development and brain damage following impaired insulin signaling. Hence, this study aimed to examine early-time course of changes in NOX and NOS expression, and apoptotic proteins in the rats hippocampi following insulin signaling impairment [induced by STZ injection; intraperitoneal (IP) or in cerebral ventricles (ICV)]. Early effects (1, 3, or 6 weeks) on the NOX activity, translocation of NOX subunits from cytosol to the membrane, NO-synthases [neuronal-, inducible- and endothelial-NOS; nNOS, iNOS and eNOS], The Rac-1 protein expression, levels of NO and O2¯, cytochrome c release, caspase-3 and 9 activations (cleavage) were studied. STZ injection (in both models) increased NOX activity, O2¯ production, and enhanced cytosolic subunits translocation into membrane. The iNOS but not nNOS and eNOS expression and NO levels were increased in STZ treated rats. Finally, STZ injection increased cytochrome c release, caspase-3 and 9 activations in a manner that was significantly associated with levels of O2¯ and NO in the hippocampus. ICV-STZ administration resulted in significant profound changes over the IP route. In conclusion, impairment in insulin function induces early changes in ROS/RNS contents through NOX and iNOS upregulation and neuronal apoptosis in the hippocampus. Our results could mechanistically explain the role of impaired insulin function in the development of sAD.

Blackberry-Loaded AgNPs Attenuate Hepatic Ischemia/Reperfusion Injury via PI3K/Akt/mTOR Pathway

Liver ischemia-reperfusion injury (IRI) is a pathophysiological insult that often occurs during liver surgery. Blackberry leaves are known for their anti-inflammatory and antioxidant activities. Aims: To achieve site-specific delivery of blackberry leaves extract (BBE) loaded AgNPs to the hepatocyte in IRI and to verify possible molecular mechanisms. Methods: IRI was induced in male Wister rats. Liver injury, hepatic histology, oxidative stress markers, hepatic expression of apoptosis-related proteins were evaluated. Non-targeted metabolomics for chemical characterization of blackberry leaves extract was performed. Key findings: Pre-treatment with BBE protected against the deterioration caused by I/R, depicted by a significant improvement of liver functions and structure, as well as reduction of oxidative stress with a concomitant increase in antioxidants. Additionally, BBE promoted phosphorylation of antiapoptotic proteins; PI3K, Akt and mTOR, while apoptotic proteins; Bax, Casp-9 and cleaved Casp-3 expressions were decreased. LC-HRMS-based metabolomics identified a range of metabolites, mainly flavonoids and anthocyanins. Upon comprehensive virtual screening and molecular dynamics simulation, the major annotated anthocyanins, cyanidin and pelargonidin glucosides, were suggested to act as PLA2 inhibitors. Significance: BBE can ameliorate hepatic IRI augmented by BBE-AgNPs nano-formulation via suppressing, oxidative stress and apoptosis as well as stimulation of PI3K/Akt/mTOR signaling pathway.

Intertwined associations between oxidative and nitrosative stress and endocannabinoid system pathways: Relevance for neuropsychiatric disorders

The endocannabinoid system (ECS) appears to regulate metabolic, cardiovascular, immune, gastrointestinal, lung, and reproductive system functions, as well as the central nervous system. There is also evidence that neuropsychiatric disorders are associated with ECS abnormalities as well as oxidative and nitrosative stress pathways. The goal of this mechanistic review is to investigate the mechanisms underlying the ECS's regulation of redox signalling, as well as the mechanisms by which activated oxidative and nitrosative stress pathways may impair ECS-mediated signalling. Cannabinoid receptor (CB)1 activation and upregulation of brain CB2 receptors reduce oxidative stress in the brain, resulting in less tissue damage and less neuroinflammation. Chronically high levels of oxidative stress may impair CB1 and CB2 receptor activity. CB1 activation in peripheral cells increases nitrosative stress and inducible nitric oxide (iNOS) activity, reducing mitochondrial activity. Upregulation of CB2 in the peripheral and central nervous systems may reduce iNOS, nitrosative stress, and neuroinflammation. Nitrosative stress may have an impact on CB1 and CB2-mediated signalling. Peripheral immune activation, which frequently occurs in response to nitro-oxidative stress, may result in increased expression of CB2 receptors on T and B lymphocytes, dendritic cells, and macrophages, reducing the production of inflammatory products and limiting the duration and intensity of the immune and oxidative stress response. In conclusion, high levels of oxidative and nitrosative stress may compromise or even abolish ECS-mediated redox pathway regulation. Future research in neuropsychiatric disorders like mood disorders and deficit schizophrenia should explore abnormalities in these intertwined signalling pathways.

Renal tubular injury induced by glyphosate combined with hard water: the role of cytosolic phospholipase A2

Background

The combined effects of glyphosate and hard water on chronic kidney disease of unknown etiology (CDKu) have attracted much interest, but the mechanisms remain unknown. Cytoplasmic phospholipase A₂ (cPLA₂) plays a key role in the acute and chronic inflammatory reactions. This study explored the effect of glyphosate combined with hard water on renal tubules and the possible targets and mechanisms involved.

Methods

In vivo experiments were conducted to investigate the synergistic effects and potential mechanisms of glyphosate and hard water on renal tubular injury in mice.

Results

Administration of glyphosate in mice resulted in elevated levels of β2-microglobulin (β₂-MG), albumin (ALB), and serum creatinine (SCr) compared to control mice. This increase was more pronounce when glyphosate was combined with hard water. In the glyphosate-treated mice, small areas of the kidney revealed fibroblast proliferation and vacuolar degeneration, particularly at the higher dose of 400 mg/kg glyphosate. However, the combination of glyphosate and hard water induced an even greater degree of pathological changes in the kidney. Immunofluorescence and western blot analyses showed that glyphosate and hard water had a coordinated effect on calcium ions (Ca²⁺)-activated phospholipase A₂ and the activation may play a key role in inflammation and renal tubular injury. Exposure to glyphosate alone or glyphosate plus hard water increased the levels of oxidative stress markers and inflammatory biomarkers, namely, thromboxane A₂ (TX-A₂), leukotriene B₄ (LTB₄), prostaglandin E₂ (PGE₂), nitric oxide synthase (NOS), and nitric oxide (NO). Parameters of oxidative stress, including the levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were decreased. Further analysis showed that the levels of these biomarkers were significantly different between the mice treated with glyphosate plus hard water and the mice treated with glyphosate alone.

Conclusions

These findings suggested that hard water combined with glyphosate can induce renal tubular injury in mice, and this may involve mitogen-activated protein kinases (MAPK)/cytosolic phospholipase A₂ (cPLA₂)/arachidonic acid (AA) and its downstream factors.

Potential Role of Fluoride in the Etiopathogenesis of Alzheimer's Disease

The etiopathogenesis of Alzheimer's disease has not been fully explained. Now, the disease is widely attributed both to genetic and environmental factors. It is believed that only a small percentage of new AD cases result solely from genetic mutations, with most cases attributed to environmental factors or to the interaction of environmental factors with preexistent genetic determinants. Fluoride is widespread in the environment and it easily crosses the blood⁻brain barrier. In the brain fluoride affects cellular energy metabolism, synthesis of inflammatory factors, neurotransmitter metabolism, microglial activation, and the expression of proteins involved in neuronal maturation. Finally, and of specific importance to its role in Alzheimer's disease, studies report fluoride-induced apoptosis and inflammation within the central nervous system. This review attempts to elucidate the potential relationship between the effects of fluoride exposure and the pathogenesis of Alzheimer's disease. We describe the impact of fluoride-induced oxidative stress and inflammation in the pathogenesis of AD and demonstrate a role for apoptosis in disease progression, as well as a mechanism for its initiation by fluoride. The influence of fluoride on processes of AD initiation and progression is complex and warrants further investigation, especially considering growing environmental fluoride pollution.

Cerebrovascular β-amyloid deposition and associated microhemorrhages in a Tg2576 Alzheimer mouse model are reduced with a DHA-enriched diet

Cerebral amyloid angiopathy (CAA) is a major contributor to Alzheimer's disease (AD) pathogenesis. Like AD, CAA is often accompanied by marked inflammation, aggravating associated vasculopathies. No evidence-based prevention or treatment strategies are available. Here, we evaluate the possible beneficial effect of a diet enriched with docosahexaenoic acid (DHA), which is known to attenuate inflammation in CAA. Tg2576 mice, a transgenic model of AD/CAA, were fed a DHA-enriched diet starting at 2 mo of age and ending at 10, 14, or 18 mo of age. β-Amyloid (Aβ)-peptide deposition and bleeding were visualized by immunohistochemistry or histochemistry on coronal sections of the brain. DHA, arachidonic acid, and eicosanoid levels were measured by liquid chromatography/mass spectrometry or GC-MS. DHA-enriched diet throughout aging limits the accumulation of vascular Aβ peptide deposits as well as the likelihood of microhemorrhages. There is a strong correlation between systemic 12-hydroxyeicosatetraenoic acid (HETE) levels and the size of the area affected by both vascular amyloid deposits and hemorrhages. The lowest levels of 12-HETE, a lipid-derived proinflammatory product of 12-lipoxygenase (LOX), were found in DHA-fed mice. In vitro experiments performed on amyloid vascular smooth muscle cells showed that a 12-LOX inhibitor almost completely blocked the Aβ_1-40 peptide-induced apoptosis of these cells. This study yet again highlights the important role of inflammation in CAA pathogenesis and identifies potential new targets for preventive care.-Hur, J., Mateo, V., Amalric, N., Babiak, M., Béréziat, G., Kanony-Truc, C., Clerc, T., Blaise, R., Limon, I. Cerebrovascular β-amyloid deposition and associated microhemorrhages in a Tg2576 Alzheimer mouse model are reduced with a DHA-enriched diet.

Analyzing Nicotinamide Adenine Dinucleotide Phosphate Oxidase Activation in Aging and Vascular Amyloid Pathology

In aging individuals, both protective as well as regulatory immune functions are declining, resulting in an increased susceptibility to infections as well as to autoimmunity. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2-deficiency in immune cell subsets has been shown to be associated with aging. Using intravital marker-free NAD(P)H-fluorescence lifetime imaging, we have previously identified microglia/myeloid cells and astrocytes as main cellular sources of NADPH oxidase (NOX) activity in the CNS during neuroinflammation, due to an overactivation of NOX. The overactivated NOX enzymes catalyze the massive production of the highly reactive O2−, which initiates in a chain reaction the overproduction of diverse reactive oxygen species (ROS). Age-dependent oxidative distress levels in the brain and their cellular sources are not known. Furthermore, it is unclear whether in age-dependent diseases oxidative distress is initiated by overproduction of ROS or by a decrease in antioxidant capacity, subsequently leading to neurodegeneration in the CNS. Here, we compare the activation level of NOX enzymes in the cerebral cortex of young and aged mice as well as in a model of vascular amyloid pathology. Despite the fact that a striking change in the morphology of microglia can be detected between young and aged individuals, we find comparable low-level NOX activation both in young and old mice. In contrast, aged mice with the human APP^E693Q mutation, a model for cerebral amyloid angiopathy (CAA), displayed increased focal NOX overactivation in the brain cortex, especially in tissue areas around the vessels. Despite activated morphology in microglia, NOX overactivation was detected only in a small fraction of these cells, in contrast to other pathologies with overt inflammation as experimental autoimmune encephalomyelitis (EAE) or glioblastoma. Similar to these pathologies, the astrocytes majorly contribute to the NOX overactivation in the brain cortex during CAA. Together, these findings emphasize the role of other cellular sources of activated NOX than phagocytes not only during EAE but also in models of amyloid pathology. Moreover, they may strengthen the hypothesis that microglia/monocytes show a diminished potential for clearance of amyloid beta protein.

Imaging hydrogen peroxide in Alzheimer's disease via cascade signal amplification

In brains of Alzheimer’s disease (AD), reactive oxygen species (ROS) levels are significantly higher than that of healthy brains. Evidence suggests that, during AD onset and progression, a vicious cycle revolves around amyloid beta (Aβ) production, aggregation, plaque formation, microglia/immunological responses, inflammation, and ROS production. In this cycle, ROS species play a central role, and H₂O₂ is one of the most important ROS species. In this report, we have designed a fluorescent imaging probe CRANAD-88, which is capable of cascade amplifying near infrared fluorescence (NIRF) signals at three levels upon interacting with H₂O₂ in AD brains. We demonstrated that the amplification was feasible in vitro and in vivo. Remarkably, we showed that, for the first time, it was feasible to monitor the changes of H₂O₂ concentrations in AD brains before and after treatment with an H₂O₂ scavenger. Our method opens new revenues to investigate H₂O₂ in AD brains and can be very instructive for drug development.

Anti-oxidant and anti-hyperlipidemic activity of Hemidesmus indicus in rats fed with high-fat diet

OBJECTIVE

Dietary changes play major risk roles in oxidative stress and cardiovascular disease and modulate normal metabolic function. The present study was designed to investigate the ameliorative potential of different extracts of Hemidesmus indicus to experimental high-fat diet in wistar rats, and their possible mechanism of action.

MATERIALS AND METHODS

Male wistar rats were divided into 6 groups (n=6/group) and fed with a standard diet (control), high-fat diet (HFD), high-fat diet supplemented with different extracts and positive control for 9 weeks. High-fat diet induced changes in average body weight and oxidative stress and elevated levels of plasma lipid profile in rats.

RESULTS

Oral administration of methanolic extract of H. indicus (200 mg/kg) offered a significant dose-dependent protection against HFD-induced oxidative stress, as reflected in the levels of catalase (p<0.001 in the aorta, heart and liver), superoxide dismutase (p<0.001 in the aorta, heart and liver), and glutathione peroxidase (p<0.001 in the aorta, heart and liver). Hyperlipidemia condition assessed in terms of body weight, total cholesterol, free cholesterol, ester cholesterol, phospholipids, triglycerides, and atherogenic index and the results showed significant differences between HFD and non-HFD fed rats (p<0.001). High-fat diet treated rats showed changes in hepatic tissue architecture such as micro and macrovascular steatosis, increased fatty infiltration, and inflammation.

CONCLUSION

The present study revealed that the methanolic extract of H. indicus protects against oxidative stress, hyperlipidemia and liver damage.

Redox-active biflavonoids from Garcinia brasiliensis as inhibitors of neutrophil oxidative burst and human erythrocyte membrane damage

ETHNOPHARMACOLOGICAL RELEVANCE

Garcinia brasiliensis, a plant native to the Brazilian Amazon Rainforest, is used in traditional medicine to treat inflammation of the urinary tract, peptic ulcers, arthritis and other conditions.

AIM OF THE STUDY

The purposes of this study were to analyze the chemical constituents of G. brasiliensis branches and leaves and to evaluate the potential of isolated compounds to act as inhibitors of both the oxidative burst of stimulated neutrophils and oxidative damage in human erythrocyte membranes to verify the antioxidant and anti-inflammatory effects of this plant.

MATERIALS AND METHODS

Neutrophils were isolated from the blood of healthy donors by Ficoll-Paque density gradient centrifugation. Superoxide anion and total reactive oxygen species (ROS) produced by stimulated neutrophils were measured by WST-1 reduction and luminol-enhanced chemiluminescence assays, respectively. Radical-induced lipoperoxidation and hemolysis were performed using erythrocytes from the blood of healthy donors. Compounds were isolated from G. brasiliensis branches and leaves by HPLC microfractionation, and structure elucidation of the isolated compounds was performed based on NMR and HR-MS analyses.

RESULTS

The biflavonoids procyanidin, fukugetin, amentoflavone and podocarpusflavone isolated from G. brasiliensis showed potent inhibitory effects on the oxidative burst of human neutrophils, inhibiting ROS production by 50% at 1 μmol L(-1). These biflavonoids also proved to be potent inhibitors of hemolysis (with 88 ± 7% inhibition at 50 µmol L(-1) for procyanidin) and lipid peroxidation in human erythrocytes, with a malondialdehyde level (a biomarker of oxidative stress) of 8.5 ± 0.3 nmol/mg Hb at 50 µmol L(-1) for procyanidin.

CONCLUSIONS

These findings indicate that the biflavonoids extracted from G. brasiliensis branches and leaves modulate oxidative stress via inhibition of NADPH oxidase and ROS production by stimulated human neutrophils. Furthermore, the biflavonoids exhibited potent inhibition of oxidant hemolysis and lipid peroxidation induced by AAPH in human erythrocytes. Therefore, these studies suggest the use of G. brasiliensis extract as an antioxidant and anti-inflammatory agent.

Association of the p22phox polymorphism C242T with the risk of late-onset Alzheimer's disease in a northern Han Chinese population

The C242T polymorphism of the CYBA gene that encodes p22phox, a component of nicotinamide adenine dinucleotide phosphate oxidase, has been found to modulate reactive oxygen species (ROS) production. Oxidative stress is thought to play a pivotal role in the pathophysiology of Alzheimer's disease (AD), which is manifested as increased availability of ROS because of an imbalanced redox state. Therefore, the aim of this study was to investigate potential associations of the p22phox C242T polymorphism with the risk of late-onset AD (LOAD) in a northern Han Chinese population. Patients with LOAD (n = 276) and 320 control subjects were recruited for the study. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the genotypes. No significant differences were found between LOAD and p22phox C242T polymorphism, but a significant association was obtained in the genotype and allele distributions of p22phox C242T between LOAD patients and controls in apolipoprotein E (ApoE) ϵ4 carriers. These results suggested that p22phox C242T polymorphism has a possible role in changing the genetic susceptibility to LOAD in ApoE ϵ4 carriers of this northern Han Chinese population.

Synthetic and natural inhibitors of phospholipases A2: their importance for understanding and treatment of neurological disorders

Phospholipases A2 (PLA2) are a diverse group of enzymes that hydrolyze membrane phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is metabolized to eicosanoids (prostaglandins, leukotrienes, thromboxanes), and lysophospholipids are converted to platelet-activating factors. These lipid mediators play critical roles in the initiation, maintenance, and modulation of neuroinflammation and oxidative stress. Neurological disorders including excitotoxicity; traumatic nerve and brain injury; cerebral ischemia; Alzheimer's disease; Parkinson's disease; multiple sclerosis; experimental allergic encephalitis; pain; depression; bipolar disorder; schizophrenia; and autism are characterized by oxidative stress, inflammatory reactions, alterations in phospholipid metabolism, accumulation of lipid peroxides, and increased activities of brain phospholipase A2 isoforms. Several old and new synthetic inhibitors of PLA2, including fatty acid trifluoromethyl ketones; methyl arachidonyl fluorophosphonate; bromoenol lactone; indole-based inhibitors; pyrrolidine-based inhibitors; amide inhibitors, 2-oxoamides; 1,3-disubstituted propan-2-ones and polyfluoroalkyl ketones as well as phytochemical based PLA2 inhibitors including curcumin, Ginkgo biloba and Centella asiatica extracts have been discovered and used for the treatment of neurological disorders in cell culture and animal model systems. The purpose of this review is to summarize information on selective and potent synthetic inhibitors of PLA2 as well as several PLA2 inhibitors from plants, for treatment of oxidative stress and neuroinflammation associated with the pathogenesis of neurological disorders.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging

SIGNIFICANCE

Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection.

RECENT ADVANCES

Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging.

CRITICAL ISSUES

Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit.

FUTURE DIRECTIONS

Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

P2Y receptors in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 10% of people over the age of 65. Age is the greatest risk factor for AD, although a combination of genetic, lifestyle and environmental factors also contribute to disease development. Common features of AD are the formation of plaques composed of beta-amyloid peptides (Aβ) and neuronal death in brain regions involved in learning and memory. Although Aβ is neurotoxic, the primary mechanisms by which Aβ affects AD development remain uncertain and controversial. Mouse models overexpressing amyloid precursor protein and Aβ have revealed that Aβ has potent effects on neuroinflammation and cerebral blood flow that contribute to AD progression. Therefore, it is important to consider how endogenous signalling in the brain responds to Aβ and contributes to AD pathology. In recent years, Aβ has been shown to affect ATP release from brain and blood cells and alter the expression of G protein-coupled P2Y receptors that respond to ATP and other nucleotides. Accumulating evidence reveals a prominent role for P2Y receptors in AD pathology, including Aβ production and elimination, neuroinflammation, neuronal function and cerebral blood flow.

Caffeic Acid phenethyl ester: consequences of its hydrophobicity in the oxidative functions and cytokine release by leukocytes

Numerous anti-inflammatory properties have been attributed to caffeic acid phenethyl ester (CAPE), an active component of propolis. NADPH oxidases are multienzymatic complexes involved in many inflammatory diseases. Here, we studied the importance of the CAPE hydrophobicity on cell-free antioxidant capacity, inhibition of the NADPH oxidase and hypochlorous acid production, and release of TNF-α and IL-10 by activated leukocytes. The comparison was made with the related, but less hydrophobic, caffeic and chlorogenic acids. Cell-free studies such as superoxide anion scavenging assay, triene degradation, and anodic peak potential (E_pa) measurements showed that the alterations in the hydrophobicity did not provoke significant changes in the oxidation potential and antiradical potency of the tested compounds. However, only CAPE was able to inhibit the production of superoxide anion by activated leukocytes. The inhibition of the NADPH oxidase resulted in the blockage of production of hypochlorous acid. Similarly, CAPE was the more effective inhibitor of the release of TNF-α and IL-10 by Staphylococcus aureus stimulated cells. In conclusion, the presence of the catechol moiety and the higher hydrophobicity were essential for the biological effects. Considering the involvement of NADPH oxidases in the genesis and progression of inflammatory diseases, CAPE should be considered as a promising anti-inflammatory drug.

Characterization of the expression and inflammatory activity of NADPH oxidase after spinal cord injury

Reactive oxygen species (ROS) and the NADPH oxidase (NOX) enzyme are both up-regulated after spinal cord injury (SCI) and play significant roles in promoting post-injury inflammation. However, the cellular and temporal expression profile of NOX isotypes, including NOX2, 3, and 4, after SCI is currently unclear. The purpose of this study was to resolve this expression profile and examine the effect of inhibition of NOX on inflammation after SCI. Briefly, adult male rats were subjected to moderate contusion SCI. Double immunofluorescence for NOX isotypes and CNS cellular types was performed at 24 h, 7 days, and 28 days post-injury. NOX isotypes were found to be expressed in neurons, astrocytes, and microglia, and this expression was dependent on injury status. NOX2 and 4 were found in all cell types assessed, while NOX3 was positively identified in neurons only. NOX2 was the most responsive to injury, increasing in both microglia and astrocytes. The biggest increases in expression were observed at 7 days post-injury and increased expression was maintained through 28 days. NOX2 inhibition by systemic administration of gp91ds-tat at 15 min, 6 h or 7 days after injury reduced both pro-inflammatory cytokine expression and evidence of oxidative stress in the injured spinal cord. This study therefore illustrates the regional and temporal influence on NOX isotype expression and the importance of NOX activation in SCI. This information will be useful in future studies of understanding ROS production after injury and therapeutic potentials.

New insights on NOX enzymes in the central nervous system

SIGNIFICANCE

There is increasing evidence that the generation of reactive oxygen species (ROS) in the central nervous system (CNS) involves the NOX family of nicotinamide adenine dinucleotide phosphate oxidases. Controlled ROS generation appears necessary for optimal functioning of the CNS through fine-tuning of redox-sensitive signaling pathways, while overshooting ROS generation will lead to oxidative stress and CNS disease.

RECENT ADVANCES

NOX enzymes are not only restricted to microglia (i.e. brain phagocytes) but also expressed in neurons, astrocytes, and the neurovascular system. NOX enzymes are involved in CNS development, neural stem cell biology, and the function of mature neurons. While NOX2 appears to be a major source of pathological oxidative stress in the CNS, other NOX isoforms might also be of importance, for example, NOX4 in stroke. Globally speaking, there is now convincing evidence for a role of NOX enzymes in various neurodegenerative diseases, cerebrovascular diseases, and psychosis-related disorders.

CRITICAL ISSUES

The relative importance of specific ROS sources (e.g., NOX enzymes vs. mitochondria; NOX2 vs. NOX4) in different pathological processes needs further investigation. The absence of specific inhibitors limits the possibility to investigate specific therapeutic strategies. The uncritical use of non-specific inhibitors (e.g., apocynin, diphenylene iodonium) and poorly validated antibodies may lead to misleading conclusions.

FUTURE DIRECTIONS

Physiological and pathophysiological studies with cell-type-specific knock-out mice will be necessary to delineate the precise functions of NOX enzymes and their implications in pathomechanisms. The development of CNS-permeant, specific NOX inhibitors will be necessary to advance toward therapeutic applications.

Cellular and temporal expression of NADPH oxidase (NOX) isotypes after brain injury

BACKGROUND

Brain injury results in an increase in the activity of the reactive oxygen species generating NADPH oxidase (NOX) enzymes. Preliminary studies have shown that NOX2, NOX3, and NOX4 are the most prominently expressed NOX isotypes in the brain. However, the cellular and temporal expression profile of these isotypes in the injured and non-injured brain is currently unclear.

METHODS

Double immunofluorescence for NOX isotypes and brain cell types was performed at acute (24 hours), sub-acute (7 days), and chronic (28 days) time points after controlled cortical impact-induced brain injury or sham-injury in rats.

RESULTS

NOX2, NOX3, and NOX4 isotypes were found to be expressed in neurons, astrocytes, and microglia, and this expression was dependent on both cellular source and post-injury time. NOX4 was found in all cell types assessed, while NOX3 was positively identified in neurons only, and NOX2 was identified in microglia and neurons. NOX2 was the most responsive to injury, increasing primarily in microglia in response to injury. Quantitation of this isotype showed a significant increase in NOX2 expression at 24 hours, with reduced expression at 7 days and 28 days post-injury, although expression remained above sham levels at later time points. Cellular confirmation using purified primary or cell line culture demonstrated similar patterns in microglia, astrocytes, and neurons. Further, inhibition of NOX, and more specifically NOX2, reduced pro-inflammatory activity in microglia, demonstrating that NOX is not only up-regulated after stimulation, but may also play a significant role in post-injury neuroinflammation.

CONCLUSIONS

This study illustrates the expression profiles of NOX isotypes in the brain after injury, and demonstrates that NOX2, and to a lesser extent, NOX4, may be responsible for the majority of oxidative stress observed acutely after traumatic brain injury. These data may provide insight into the design of future therapeutic approaches.

Antioxidant treatment strategies for hyperphenylalaninemia

Hyperphenylalaninemia (HPA) leads to increased oxidative stress in patients with phenylketonuria (PKU) and in animal models of PKU. Early diagnosis and immediate adherence to a phenylalanine-restricted diet prevents HPA and, consequently, severe brain damage. However, treated adolescent and adult PKU patients have difficulties complying with the diet, leading to an oscillation of phenylalanine levels and associated oxidative stress. The brain is especially susceptible to reactive species, and oxidative stress might add to the impaired cognitive function found in these patients. The restricted PKU diet has a very limited nutrient content from natural foods and almost no animal protein, which reduces the intake of important compounds. These specific compounds can act as scavengers of reactive species and can be co-factors of antioxidant enzymes. Supplementation with nutrients, vitamins, and tetrahydropterin has given quite promising results in patients and animal models. Antioxidant supplementation has been studied in HPA, however there is no consensus about its always beneficial effects. In this way, regular exercise could be a beneficial addition on antioxidant status in PKU patients. A deeper understanding of PKU molecular biochemistry, and genetics, as well as the need for improved targeted treatment options, could lead to the development of new therapeutic strategies.

The role of secretory phospholipase A₂ in the central nervous system and neurological diseases

Secretory phospholipase A2 (sPLA2s) are small secreted proteins (14-18 kDa) and require submillimolar levels of Ca(2+) for liberating arachidonic acid from cell membrane lipids. In addition to the enzymatic function, sPLA2 can exert various biological responses by binding to specific receptors. Physiologically, sPLA2s play important roles on the neurotransmission in the central nervous system and the neuritogenesis in the peripheral nervous system. Pathologically, sPLA2s are involved in the neurodegenerative diseases (e.g., Alzheimer's disease) and cerebrovascular diseases (e.g., stoke). The common pathology (e.g., neuronal apoptosis) of Alzheimer's disease and stroke coexists in the mixed dementia, suggesting common pathogenic mechanisms of the two neurological diseases. Among mammalian sPLA2s, sPLA2-IB and sPLA2-IIA induce neuronal apoptosis in rat cortical neurons. The excess influx of calcium into neurons via L-type voltage-dependent Ca(2+) channels mediates the two sPLA2-induced apoptosis. The elevated concentration of intracellular calcium activates PKC, MAPK and cytosolic PLA2. Moreover, it is linked with the production of reactive oxygen species and apoptosis through activation of the superoxide producing enzyme NADPH oxidase. NADPH oxidase is involved in the neurotoxicity of amyloid β peptide, which impairs synaptic plasticity long before its deposition in the form of amyloid plaques of Alzheimer's disease. In turn, reactive oxygen species from NADPH oxidase can stimulate ERK1/2 phosphorylation and activation of cPLA2 and result in a release of arachidonic acid. sPLA2 is up-regulated in both Alzheimer's disease and cerebrovascular disease, suggesting the involvement of sPLA2 in the common pathogenic mechanisms of the two diseases. Thus, our review presents evidences for pathophysiological roles of sPLA2 in the central nervous system and neurological diseases.

NOX-mediated MAPK and PI3K/Akt signaling pathways and liver fibrosis

Hepatic satellite cells (HSCs) are the main cell type involved in the development of liver fibrosis and have been recognized as the important cellular source of extracellular matrix (ECM). NADPH oxidase (NOX) catalyzes the generation of reactive oxygen species (ROS), regulates signal transduction in HSCs, and thereby plays a key role in the pathogenesis of hepatic fibrosis. ROS generated by NOX promotes proliferation and inhibits apoptosis of HSCs by activation of mitogen-activated protein kinase and phosphatidylinositol-3 kinase/Akt signaling pathways, thus contributing to the development of liver fibrosis. Inhibition of NOX activation to generate ROS and NOX-mediated signal transduction induces HSC apoptosis. Therefore, drugs that target specific NOX can be expected to be useful in arresting the progression of liver fibrosis.

Redox regulation of protein misfolding, mitochondrial dysfunction, synaptic damage, and cell death in neurodegenerative diseases

The loss or injury of neurons associated with oxidative and nitrosative redox stress plays an important role in the onset of various neurodegenerative diseases. Specifically, nitric oxide (NO), can affect neuronal survival through a process called S-nitrosylation, by which the NO group undergoes a redox reaction with specific protein thiols. This in turn can lead to the accumulation of misfolded proteins, which generally form aggregates in Alzheimer's, Parkinson's, and other neurodegenerative diseases. Evidence suggests that S-nitrosylation can also impair mitochondrial function and lead to excessive fission of mitochondria and consequent bioenergetic compromise via effects on the activity of the fission protein dynamin-related protein 1 (Drp1). This insult leads to synaptic dysfunction and loss. Additionally, high levels of NO can S-nitrosylate a number of aberrant targets involved in neuronal survival pathways, including the antiapoptotic protein XIAP, inhibiting its ability to prevent apoptosis.

NADPH oxidases as therapeutic targets in ischemic stroke

Reactive oxygen species (ROS) act physiologically as signaling molecules. In pathological conditions, such as ischemic stroke, ROS are released in excessive amounts and upon reperfusion exceed the body's antioxidant detoxifying capacity. This process leads to brain tissue damage during reoxygenation. Consequently, antioxidant strategies have long been suggested as a therapy for experimental stroke, but clinical trials have not yet been able to promote the translation of this concept into patient treatment regimens. As an evolution of this concept, recent studies have targeted the sources of ROS generation-rather than ROS themselves. In this context, NADPH oxidases have been identified as important generators of ROS in the cerebral vasculature under both physiological conditions in general and during ischemia/reoxygenation in particular. Inhibition of NADPH oxidases or genetic deletion of certain NADPH oxidase isoforms has been found to considerably reduce ischemic injury in experimental stroke. This review focuses on recent advances in the understanding of NADPH oxidase-mediated tissue injury in the cerebral vasculature, particularly at the level of the blood-brain barrier, and highlights promising inhibitory strategies that target the NADPH oxidases.

Targeting NOX enzymes in the central nervous system: therapeutic opportunities

Among the pathogenic mechanisms underlying central nervous system (CNS) diseases, oxidative stress is almost invariably described. For this reason, numerous attempts have been made to decrease reactive oxygen species (ROS) with the administration of antioxidants as potential therapies for CNS disorders. However, such treatments have always failed in clinical trials. Targeting specific sources of reactive oxygen species in the CNS (e.g. NOX enzymes) represents an alternative promising option. Indeed, NOX enzymes are major generators of ROS, which regulate progression of CNS disorders as diverse as amyotrophic lateral sclerosis, schizophrenia, Alzheimer disease, Parkinson disease, and stroke. On the other hand, in autoimmune demyelinating diseases, ROS generated by NOX enzymes are protective, presumably by dampening the specific immune response. In this review, we discuss the possibility of developing therapeutics targeting NADPH oxidase (NOX) enzymes for the treatment of different CNS pathologies. Specific compounds able to modulate the activation of NOX enzymes, and the consequent production of ROS, could fill the need for disease-modifying drugs for many incurable CNS pathologies.

Integrating cytosolic phospholipase A₂ with oxidative/nitrosative signaling pathways in neurons: a novel therapeutic strategy for AD

The pathophysiology of Alzheimer's disease (AD) is comprised of complex metabolic abnormalities in different cell types in the brain. To date, there are not yet effective drugs that can completely inhibit the pathophysiological event, and efforts have been devoted to prevent or minimize the progression of this disease. Much attention has focused on studies to understand aberrant functions of the ionotropic glutamate receptors, perturbation of calcium homeostasis, and toxic effects of oligomeric amyloid beta peptides (Aβ) which results in production of reactive oxygen and nitrogen species and signaling pathways, leading to mitochondrial dysfunction and synaptic impairments. Aberrant phospholipase A(2) (PLA(2)) activity has been implicated to play a role in the pathogenesis of many neurodegenerative diseases, including AD. However, mechanisms for their modes of action and their roles in the oxidative and nitrosative signaling pathways have not been firmly established. In this article, we review recent studies providing a metabolic link between cytosolic PLA(2) (cPLA(2)) and neuronal excitation due to stimulation of ionotropic glutamate receptors and toxic Aβ peptides. The requirements for Ca(2+) binding together with its posttranslational modifications by protein kinases and possible by the redox-based S-nitrosylation, provide strong support for a dynamic role of cPLA(2) in serving multiple functions to neurons and glial cells under abnormal physiological and pathological conditions. Therefore, understanding mechanisms for cPLA(2) in the oxidative and nitrosative pathways in neurons will allow the development of novel therapeutic targets to mitigate the detrimental effects of AD.

The neuroprotective effects of apocynin

The recognition of health benefits of phytomedicines and herbal supplements lead to an increased interest to understand the cellular and molecular basis of their biological activities. Apocynin (4-hydroxy-3-methoxy-acetophenone) is a constituent of the Himalayan medicinal herb Picrorhiza kurroa which is regarded as an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, a superoxide-producing enzyme. NADPH oxidase appears to be especially important in the modulation of redox-sensitive signaling pathways and also has been implicated in neuronal dysfunction and degeneration, and neuroinflammmation in diseases ranging from stroke, Alzheimer's and Parkinson's diseases to psychiatric disorders. In this review, we aim to give an overview of current literature on the neuroprotective effects of apocynin in the prevention and treatment of neurodegenerative disorders. Particular attention is given to in vivo studies.

Cobalt(II) β-ketoaminato complexes as novel inhibitors of neuroinflammation

Neuroinflammation contributes to the pathogenesis of neurological disorders including stroke, head trauma, multiple sclerosis, amyotrophic lateral sclerosis as well as age-associated neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Therefore, anti-inflammatory drugs could be used to slow the progression of these diseases. We studied the anti-neuroinflammatory activity of four novel square planar cobalt(II) compounds bearing tetradentate β-ketoaminato ligands with variation in the number of CF(3) ligand substituents, as well as their corresponding unmetallated organic ligands. Cobalt (Co) complexes were consistently more active than their corresponding ligands. One of the complexes, L(3)Co at concentrations (1-10 μM) that were not toxic to cells, significantly reduced cytotoxic secretions by human monocytic THP-1 cells, astrocytoma U-373 MG cells, and primary human microglia. This anti-neurotoxic action of L(3)Co was reduced by SP600125 and PD98059, selective inhibitors of c-Jun NH2-terminal kinase (JNK) and extracellular signal regulated kinase (ERK) kinase (MEK)1/2 respectively. L(3)Co had no effect on secretion of monocyte chemotactic protein-1 (MCP-1) by THP-1 cells, but it inhibited the NADPH oxidase-dependent respiratory burst activity of differentiated human HL-60 cells. L(3)Co upregulated heme oxygenase-1 (HOX-1) expression by THP-1 cells, which may be one of the molecular mechanisms responsible for its anti-inflammatory properties. Two of the Co compounds tested showed activity only at high concentrations (50 μM), but L(2)Co was highly toxic to all cell types used. Select Co complexes, such as L(3)Co, may exhibit pharmacological properties beneficial in human diseases involving neuroinflammatory processes. Further studies of the in vivo efficacy, safety and pharmacokinetics of L(3)Co are warranted.

Phospholipases A2 and neural membrane dynamics: implications for Alzheimer's disease

Phospholipases A(2) (PLA(2)s) are essential enzymes in cells. They are not only responsible for maintaining the structural organization of cell membranes, but also play a pivotal role in the regulation of cell functions. Activation of PLA(2) s results in the release of fatty acids and lysophospholipids, products that are lipid mediators and compounds capable of altering membrane microdomains and physical properties. Although not fully understood, recent studies have linked aberrant PLA(2) activity to oxidative signaling pathways involving NADPH oxidase that underlie the pathophysiology of a number of neurodegenerative diseases. In this paper, we review studies describing the involvement of cytosolic PLA(2) in oxidative signaling pathways leading to neuronal impairment and activation of glial cell inflammatory responses. In addition, this review also includes information on the role of cytosolic PLA(2) and exogenous secretory PLA(2) on membrane physical properties, dynamics, and membrane proteins. Unraveling the mechanisms that regulate specific types of PLA(2)s and their effects on membrane dynamics are important prerequisites towards understanding their roles in the pathophysiology of Alzheimer's disease, and in the development of novel therapeutics to retard progression of the disease.

Altered microglial copper homeostasis in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive neurodegeneration associated with the aggregation and deposition of β-amyloid (Aβ(40) and Aβ(42) ) peptide in senile plaques. Recent studies suggest that copper may play an important role in AD pathology. Copper concentrations are elevated in amyloid plaques and copper binds with high affinity to the Aβ peptide and promotes Aβ oligomerization and neurotoxicity. Despite this connection between copper and AD, it is unknown whether the expression of proteins involved in regulating copper homeostasis is altered in this disorder. In this study, we demonstrate that the copper transporting P-type ATPase, ATP7A, is highly expressed in activated microglial cells that are specifically clustered around amyloid plaques in the TgCRND8 mouse model of AD. Using a cultured microglial cell line, ATP7A expression was found to be increased by the pro-inflammatory cytokine interferon-gamma, but not by TNF-α or IL-1β. Interferon-gamma also elicited marked changes in copper homeostasis, including copper-dependent trafficking of ATP7A from the Golgi to cytoplasmic vesicles, increased copper uptake and elevated expression of the CTR1 copper importer. These findings suggest that pro-inflammatory conditions associated with AD cause marked changes in microglial copper trafficking, which may underlie the changes in copper homeostasis in AD. It is concluded that copper sequestration by microglia may provide a neuroprotective mechanism in AD.