Nitric oxide synthase-I containing cortical interneurons co-express antioxidative enzymes and anti-apoptotic Bcl-2 following focal ischemia: evidence for direct and indirect mechanisms towards their resistance to neuropathology

Neuronal nitric oxide-I is constitutively expressed in approximately 2% of cortical interneurons and is co-localized with gamma-amino butric acid, somatostatin or neuropeptide Y. These interneurons additionally express high amounts of glutamate receptors which mediate the glutamate-induced hyperexcitation following cerebral injury, under these conditions nitric oxide production increases contributing to a potentiation of oxidative stress. However, perilesional nitric oxide synthase-I containing neurons are known to be resistant to ischemic and excitotoxic injury. In vitro studies show that nitrosonium and nitroxyl ions inactivate N-methyl-D-aspartate receptors, resulting in neuroprotection. The question remains of how these cells are protected against their own high intracellular nitric oxide production after activation. In this study, we investigated immunocytochemically nitric oxide synthase-I containing cortical neurons in rats after unilateral, cortical photothrombosis. In this model of focal ischemia, perilesional, constitutively nitric oxide synthase-I containing neurons survived and co-expressed antioxidative enzymes, such as manganese- and copper-zinc-dependent superoxide dismutases, heme oxygenase-2 and cytosolic glutathione peroxidase. This enhanced antioxidant expression was accompanied by a strong perinuclear presence of the antiapoptotic Bcl-2 protein. No colocalization was detectable with upregulated heme oxygenase-1 in glia and the superoxide and prostaglandin G(2)-producing cyclooxygenase-2 in neurons. These results suggest that nitric oxide synthase-I containing interneurons are protected against intracellular oxidative damage and apoptosis by Bcl-2 and several potent antioxidative enzymes. Since nitric oxide synthase-I positive neurons do not express superoxide-producing enzymes such as cyclooxygenase-1, xanthine oxidase and cyclooxygenase-2 in response to injury, this may additionally contribute to their resistance by reducing their internal peroxynitrite, H(2)O(2)-formation and caspase activation.     

Molecular mechanisms of microglial activation

Microglial cells are brain macrophages which serve specific functions in the defense of the central nervous system (CNS) against microorganisms, the removal of tissue debris in neurodegenerative diseases or during normal development, and in autoimmune inflammatory disorders of the brain. In cultured microglial cells, several soluble inflammatory mediators such as cytokines and bacterial products like lipopolysaccharide (LPS) were demonstrated to induce a wide range of microglial activities, e.g. increased phagocytosis, chemotaxis, secretion of cytokines, activation of the respiratory burst and induction of nitric oxide synthase. Since heightened microglial activation was shown to play a role in the pathogenesis of experimental inflammatory CNS disorders, understanding the molecular mechanisms of microglial activation may lead to new treatment strategies for neurodegenerative disorders, multiple sclerosis and bacterial or viral infections of the nervous system.     

短期糖尿病雄性大鼠前列腺自由基和抗氧化水平变化研究

目的:研究短期糖尿病雄性大鼠前列腺氧自由基和抗氧化物酶的动态变化。方法:48只Wistar雄性大鼠随机分为6组(每组8只)。1组腹腔注射枸椽酸缓冲液作为正常对照组, 其余5组腹腔注射链脲菌素(STZ)制成糖尿病模型, 分别观察1d(D₁)、3d(D₃)、5d(D₅)、7d(D₇)和14d(D₁₄), 取前列腺组织制备组织匀浆, 分别测定组织中超氧化物歧化酶(SOD)、丙二醛(MDA)、谷胱甘肽(GSH)、谷胱甘肽转移酶(GST)、谷胱甘肽过氧化物酶(GSH-px)、一氧化氮(NO)及一氧化氮合酶(NOS)的水平。结果:糖尿病组前列腺MDA, GSH-px和NO水平显著高于正常组;SOD、GSH、GST和NOS水平呈现先升高后下降的趋势。结论:短期糖尿病雄性大鼠前列腺组织处于氧化应激状态。     

Selenium-dependent enzymes in endothelial cell function

Glutathione peroxidases and thioredoxin reductases are the main selenoproteins expressed by endothelial cells. These enzymes reduce hydroperoxides, their role in endothelial cell physiology, however, by far exceeds prevention of oxidative damage. Reactive oxygen and nitrogen species, especially superoxide, hydroperoxides, and nitric oxide, are crucial signaling molecules in endothelial cells. Their production is regulated by vascular NAD(P)H oxidases and the endothelial nitric oxide synthase. Their metabolism and physiological functions are coordinated by glutathione peroxidases and the thioredoxin/thioredoxin reductase system. Endothelial selenoproteins are involved in the regulation of the vascular tone by maintaining the superoxide anion/nitric oxide balance, of cell adhesion by controlling cell adhesion molecule expression, of apoptosis via inhibition/activation of apoptosis signal-regulating kinase-1, and of eicosanoid production by controlling the activity of cyclooxygenases and lipoxygenases. Accordingly, they regulate inflammatory processes and atherogenesis. The underlying mechanisms are various and differ between individual selenoproteins. Scavenging of hydroperoxides not only prevents oxidative damage, but also interferes with signaling cascades and enzymes involved. Modulation of proteins by hydroperoxide-driven thiol/disulfide exchange is a novel mechanism that needs to be further investigated. A better understanding of the complex interplay of selenoproteins in regulating endothelial cell functions will help to develop a rationale for an improvement of health by an optimum selenium supply.     

Cross talk of nitric oxide,oxygen radicals,and superoxide dismutase regulates the energy metabolism and cell death and determines the fates of aerobic life

Although oxygen is required for the energy metabolism in aerobic organisms, it generates reactive oxygen and nitrogen species that impair a wide variety of biological molecules, including lipids, proteins, and DNA, thereby causing various diseases. Because mitochondria are the major site of free radical generation, they are highly enriched with enzymes, such as Mn-type superoxide dismutase in matrix, and antioxidants including GSH on both sides of inner membranes, thus minimizing oxidative stress in and around this organelle. We recently showed that a cross talk of nitric oxide and oxygen radicals regulates the circulation, energy metabolism, reproduction, and remodeling of cells during embryonic development, and functions as a major defense system against pathogens. The present work shows that Cu/Zn-type superoxide dismutase, which has been postulated for a long time to be a cytosolic enzyme, also localizes bound to inner membranes of mitochondria, thereby minimizing oxidative stress in and around this organelle, while mitochondrial association decreases markedly with the variant types of the enzyme found in patients with familial amyotrophic lateral sclerosis. We also report that a cross talk of nitric oxide, superoxide, and molecular oxygen cooperatively regulates the fates of pathogens and their hosts and that oxidative stress in and around mitochondria also determines cell death in the development of animals and tissue injury caused by anticancer agents by some carnitine-inhibitable mechanism.     

Inflammatory Cytokine Induced Regulation of Superoxide Dismutase 3 Expression by Human Mesenchymal Stem Cells

Increasing evidence suggests that bone marrow derived-mesenchymal stem cells (MSCs) have neuroprotective properties and a major mechanism of action is through their capacity to secrete a diverse range of potentially neurotrophic or anti-oxidant factors. The recent discovery that MSCs secrete superoxide dismutase 3 (SOD3) may help explain studies in which MSCs have a direct anti-oxidant activity that is conducive to neuroprotection in both in vivo and in vitro. SOD3 attenuates tissue damage and reduces inflammation and may confer neuroprotective effects against nitric oxide-mediated stress to cerebellar neurons; but, its role in relation to central nervous system inflammation and neurodegeneration has not been extensively investigated. Here we have performed a series of experiments showing that SOD3 secretion by human bone marrow-derived MSCs is regulated synergistically by the inflammatory cytokines TNF-alpha and IFN-gamma, rather than through direct exposure to reactive oxygen species. Furthermore, we have shown SOD3 secretion by MSCs is increased by activated microglial cells. We have also shown that MSCs and recombinant SOD are able to increase both neuronal and axonal survival in vitro against nitric oxide or microglial induced damage, with an increased MSC-induced neuroprotective effect evident in the presence of inflammatory cytokines TNF-alpha and IFN-gamma. We have shown MSCs are able to convey these neuroprotective effects through secretion of soluble factors alone and furthermore demonstrated that SOD3 secretion by MSCs is, at least, partially responsible for this phenomenon. SOD3 secretion by MSCs maybe of relevance to treatment strategies for inflammatory disease of the central nervous system.     

The oxidative hypothesis of senescence

The oxidative hypothesis of senescence, since its origin in 1956, has garnered significant evidence and growing support among scientists for the notion that free radicals play an important role in ageing, either as "damaging" molecules or as signaling molecules. Age-increasing oxidative injuries induced by free radicals, higher susceptibility to oxidative stress in short-lived organisms, genetic manipulations that alter both oxidative resistance and longevity and the anti-ageing effect of caloric restriction and intermittent fasting are a few examples of accepted scientific facts that support the oxidative theory of senescence. Though not completely understood due to the complex "network" of redox regulatory systems, the implication of oxidative stress in the ageing process is now well documented. Moreover, it is compatible with other current ageing theories (e.g, those implicating the mitochondrial damage/mitochondrial-lysosomal axis, stress-induced premature senescence, biological "garbage" accumulation, etc). This review is intended to summarize and critically discuss the redox mechanisms involved during the ageing process: sources of oxidant agents in ageing (mitochondrial -electron transport chain, nitric oxide synthase reaction- and non-mitochondrial- Fenton reaction, microsomal cytochrome P450 enzymes, peroxisomal beta -oxidation and respiratory burst of phagocytic cells), antioxidant changes in ageing (enzymatic- superoxide dismutase, glutathione-reductase, glutathion peroxidase, catalase- and non-enzymatic glutathione, ascorbate, urate, bilirubine, melatonin, tocopherols, carotenoids, ubiquinol), alteration of oxidative damage repairing mechanisms and the role of free radicals as signaling molecules in ageing.     

Hepatitis C virus-core and non structural proteins lead to different effects on cellular antioxidant defenses

Chronic hepatitis C virus (HCV) infection leads to increased oxidative stress in the liver. Hepatic antioxidant enzymes provide an important line of defense against oxidative injury. To understand the antioxidant responses of hepatocytes to different HCV proteins, we compared changes in antioxidative enzymes in HCV-core and HCV-nonstructural protein expressing hepatocyte cell lines. We found that expression of HCV-core protein in hepatocyte cell lines leads to increased oxidative stress as determined by increased in the oxidant-sensitive probe 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-DCFH(2)) fluorescence, decreased reduced glutathione (GSH), and increased oxidation of thioredoxin (Trx). Although the expression of HCV-nonstructural (HCV-NS) proteins led to increased oxidative stress as well, the antioxidant enzymatic responses were different. Over-expression of HCV-NS proteins increased antioxidant enzymes (MnSOD and catalase), heme oxygenase-1 (HO-1), and GSH, indicating different mechanism(s) of prooxidative activity than HCV-core protein. Our findings show that different HCV proteins induce different antioxidant defense responses in hepatocytes. These findings may facilitate understanding the interaction of different HCV proteins with infected liver cells and help identify possible factors contributing to hepatocyte damage during HCV infection.     

H2S protects against methionine-induced oxidative stress in brain endothelial cells

Homocysteine (Hcy) causes cerebrovascular dysfunction by inducing oxidative stress. However, to date, there are no strategies to prevent Hcy-induced oxidative damage. Hcy is an H2S precursor formed from methionine (Met) metabolism. We aimed to investigate whether H2S ameliorated Met-induced oxidative stress in mouse brain endothelial cells (bEnd3). The bEnd3 cells were exposed to Met treatment in the presence or absence of NaHS (donor of H2S). Met-induced cell toxicity increased the levels of free radicals in a concentration-dependent manner. Met increased NADPH-oxidase-4 (NOX-4) expression and mitigated thioredxion-1(Trx-1) expression. Pretreatment of bEnd3 with NaHS (0.05 mM) attenuated the production of free radicals in the presence of Met and protected the cells from oxidative damage. Furthermore, NaHS enhanced inhibitory effects of apocynin, N-acetyl-l-cysteine (NAC), reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), Nomega-nitro-l-arginine methyl ester (L-NAME) on ROS production and redox enzymes levels induced by Met. In conclusion, the administration of H2S protected the cells from oxidative stress induced by hyperhomocysteinemia (HHcy), which suggested that NaHS/H2S may have therapeutic potential against Met-induced oxidative stress.     

Cardioprotective effects of aqueous extract of Oxalis corniculata in experimental myocardial infarction

The present study evaluated the protective potential of aqueous extract of Oxalis corniculata (OCE) against isoproterenol (ISO) induced myocardial infarction in rats. Myocardial infarction in rats was induced by isoproterenol (200 mg/kg) at an interval of 24 h for 2 days. OCE was given to rats as pretreatment for 30 days orally using an intragastric tube. Isoproterenol caused a significant increase in the activity of cardiac injury marker enzymes like creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) and increased the concentration of serum lipids. OCE pretreatment significantly reduced the concentration of CPK, LDH, serum total cholesterol, LDL cholesterol and triglycerides. OCE also reduced the activity of lipogenic enzyme, glucose-6-phosphate dehydrogenase in ISO administered rats. Oxidative stress produced by isoproterenol was significantly lowered by the administration of OCE which was evident from increased activities of antioxidant enzymes (catalase and superoxide dismutase) and reduced concentration of lipid peroxidation products (TBARS and conjugated dienes). Concentration of vitamin C, protein sulfhydryl groups and reduced glutathione (GSH) was also high in OCE pretreated rats. Histopathology of heart of ISO administered rat pretreated with OCE showed normal myocardium with very little evidence of inflammatory infiltration. Results of our in vitro findings also confirmed that OCE exhibits significant antioxidant and radical scavenging activity against DPPH, superoxide and nitric oxide radicals. These findings provided evidence that O. corniculata was found to be protecting the myocardium against ischemic insult and the protective effect could attribute to its antioxidative and antihyperlipidemic activities.     

Neurotoxicity of dichlorvos: effect on antioxidant defense system in the rat central nervous system.

The effect of dichlorvos exposure (5 mg kg-1 body wt, ip) on lipid peroxidation and antioxidant defense system in different regions of the rat central nervous system was studied. In the present paper an inhibition of acetylcholinesterase activity was used as an index of dichlorvos neurotoxicity. We observed significant increases in the activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase which were accompanied by a decrease in the values of lipid peroxidation. Dichlorvos exposure also resulted in a significant decrease in glutathione peroxidase activity. The decreased levels of both reduced and oxidized glutathione as observed on dichlorvos exposure affected the GSH/GSSG ratio. These results indicate that the enzymes SOD and catalase may enhance the disposal of potentially toxic radicals. Furthermore, the decrease in GSH levels may be a mechanism for the detoxification of dichlorvos in the brain.     

Evidence of neuronal oxidative damage in Alzheimer's disease.

Oxidative stress has been proposed as a pathogenetic mechanism in Alzheimer's disease. One mechanism of oxidative damage is the nitration of tyrosine residues in proteins, mediated by peroxynitrite breakdown. Peroxynitrite, a reaction product of nitric oxide and superoxide radicals, has been implicated in N-methyl-D-aspartate receptor-mediated excitotoxic damage. Reported evidence of oxidative stress in Alzheimer's disease includes increased iron, alterations in protective enzymes, and markers of oxidative damage to proteins and lipids. In this report, we demonstrate the presence of nitrotyrosine in neurofibrillary tangles of Alzheimer's disease. Nitrotyrosine was not detected in controls lacking neurofibrillary tangles. Immunolabeling was demonstrated to be specific nitrotyrosine in a series of control experiments. These observations link oxidative stress with a key pathological lesion of Alzheimer's disease, the neurofibrillary tangle, and demonstrate a pathogenetic mechanism in common with the other major neurodegenerative diseases of aging, Parkinson's disease and amyotrophic lateral sclerosis. These findings further implicate nitric oxide expression and excitotoxicity in the pathogenesis of cell death in Alzheimer's disease.     

Artemisia campestris leaf extract alleviates early diabetic nephropathy in rats by inhibiting protein oxidation and nitric oxide end products

Chronic hyperglycemia in diabetes leads to free radicals overproduction, which contributes to the development of diabetic nephropathy. The present study investigated the effects of Artemisia campestris (Ac), a plant of the Asteraceae family, on renal impairment and oxidative stress in alloxan-induced diabetic rats. Diabetes was induced by a single subcutaneous injection of alloxan (120 mg kg(-1)) in rats. Ac (200 mg kg(-1)) was administered to diabetic rats for 3 weeks. Diabetic renal injury was associated with hyperglycemia, increased serum creatinine, urea and uric acid levels. This nephropathophysiology was associated with a surproduction of nitric oxide (NO), malondialdehyde (MDA) and advanced oxidation protein products (AOPP) levels and a decrease in glutathione (GSH) levels. In addition, hyperglycemia increased the activities of antioxidant enzymes, such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx), in the kidney of diabetic rats. Treatment with Ac effectively ameliorated diabetic renal dysfunction by reducing oxidative and nitrosative stress. Histological studies also supported the experimental findings. The results suggested that Ac might act as a beneficial agent against renal dysfunctions developed in alloxan-induced diabetes.     

Reactive oxygen and nitrogen species and cellular and organismal decline: amelioration with melatonin

Cellular and organismal decline is, in part, believed to be a consequence of oxygen and nitrogen-based reactants which persistently damage macromolecules throughout a lifetime. The resulting accumulation of damaged molecules eventually seriously compromises essential functions of cells leading to their death. Excessive cellular loss causes deterioration of organ function and inevitably to the demise of the organism. The sequence of events, known as the free radical theory of aging, is widely espoused by biological gerontologists. Antioxidants are commonly employed to combat molecular damage mediated by oxygen and nitrogen-based reactants. One of these protective agents is melatonin. Melatonin has several distinct advantages as a preserver of organelle structure and function. It is widely distributed in organisms and within cells. It works via a number of mechanisms to reduce oxidative damage. Thus, melatonin scavenges a number of reactants including the hydroxyl radical (*OH), hydrogen peroxide (H(2)O(2)), nitric acid (NO*), peroxynitrite (ONOO(-)) and peroxynitrous acid (ONOOH). One of the products of melatonin's interaction with H(2)O(2), i.e., N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), is also a highly efficient radical scavenger. The cascade of reactions where the secondary metabolites are also effective scavenges is believed to contribute to melatonin's high efficacy in reducing oxidative damage. Besides its direct scavenging actions, melatonin stimulates several antioxidative enzymes including superoxide dismutase, glutathione peroxidase and glutathione reductase in addition to inhibiting a proxidative enzyme, nitric oxide synthase. This combination of actions assists melatonin in protecting cells from the degenerative changes normally associated with aging and age-related diseases.     

Analysis of the parameters of oxidative stress in patients with Parkinson’s disease

The increasing data provides enough evidences confirming the involvement of free radicals and other reactive oxygen species (ROS) superoxide radical ( ^. O ₂ ^? ), nitric oxide (NO ^. ), hydrogen peroxide (H₂O₂) and hydroxyl radicals ( ^. OH) in a number of physiological and pathological processes. Imbalance between levels of ROS resulting in the body and the capacity of antioxidant defense mechanisms occur oxidative stress (OS). OS is related to a number of structural and functional damages to cells and is involved in the pathogenesis of many diseases, including neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease (PD), amyotrophic lateral sclerosis, and Huntington disease. Defects in oxidative phosphorylation and oxidative damage play an important role in neurodegenerative diseases. The aim of this study was to investigate some biomarkers of OS such as the level of lipid peroxidation measured as malondialdehyde (MDA) reactive products and activity of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) in the blood of PD patients compared with control group of healthy volunteers. By the present research we report higher levels of MDA products and an imbalance in SOD and CAT enzyme activities in PD patients compared to the control group.     

Effects of obstructive jaundice on the antioxidative capacity of human red blood cells

Transient haemolysis and shortened erythrocyte lifespan are reported in association with extrahepatic biliary tract obstruction. An increase in lipid peroxidation has been noted as evidence of oxidative damage in red cells due to cholestasis. The influence of surgical relief on the antioxidative capacity of the erythrocyte is less well defined. The ability of erythrocytes to regenerate the antioxidative capacity after side-to-side choledo-choduodenostomy was assessed by measuring the two principal antioxidant enzymes, namely superoxide dismutase (SOD) and catalase (CAT), as well as the glutathione (GSH) content in the red blood cells (RBC) taken from patients with obstructive jaundice. A comparison of patients and healthy volunteers revealed a consistent decrease in enzyme activities (pSOD = 0.01, pCAT = 0.0002) and glutathione concentrations (PGSH = 0.0000) in cholestatic patients. Statistical analysis proved a clear correlation between the surgical relief of common bile duct obstruction and restored antioxidative capacity of red cells. These observations suggest that the red cells from patients with multiple common bile duct stones almost completely regenerated their antioxidative capacity four weeks after side-to-side choledochoduodenostomy.     

Free radicals in the physiological control of cell function.

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.     

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".     

The microglial NADPH oxidase complex as a source of oxidative stress in Alzheimer's disease

Alzheimer's disease is the most common cause of dementia in the elderly, and manifests as progressive cognitive decline and profound neuronal loss. The principal neuropathological hallmarks of Alzheimer's disease are the senile plaques and the neurofibrillary tangles. The senile plaques are surrounded by activated microglia, which are largely responsible for the proinflammatory environment within the diseased brain. Microglia are the resident innate immune cells in the brain. In response to contact with fibrillar beta-amyloid, microglia secrete a diverse array of proinflammatory molecules. Evidence suggests that oxidative stress emanating from activated microglia contribute to the neuronal loss characteristic of this disease. The source of fibrillar beta-amyloid induced reactive oxygen species is primarily the microglial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. The NADPH oxidase is a multicomponent enzyme complex that, upon activation, produces the highly reactive free radical superoxide. The cascade of intracellular signaling events leading to NADPH oxidase assembly and the subsequent release of superoxide in fibrillar beta-amyloid stimulated microglia has recently been elucidated. The induction of reactive oxygen species, as well as nitric oxide, from activated microglia can enhance the production of more potent free radicals such as peroxynitrite. The formation of peroxynitrite causes protein oxidation, lipid peroxidation and DNA damage, which ultimately lead to neuronal cell death. The elimination of beta-amyloid-induced oxidative damage through the inhibition of the NADPH oxidase represents an attractive therapeutic target for the treatment of Alzheimer's disease.     

Toxoplasma gondii prevents neuron degeneration by interferon-gamma-activated microglia in a mechanism involving inhibition of inducible nitric oxide synthase and transforming growth factor-beta1 production by infected microglia

Interferon (IFN)-gamma, the main cytokine responsible for immunological defense against Toxoplasma gondii, is essential in all infected tissues, including the central nervous system. However, IFN-gamma-activated microglia may cause tissue injury through production of toxic metabolites such as nitric oxide (NO), a potent inducer of central nervous system pathologies related to inflammatory neuronal disturbances. Despite potential NO toxicity, neurodegeneration is not commonly found during chronic T. gondii infection. In this study, we describe decreased NO production by IFN-gamma-activated microglial cells infected by T. gondii. This effect involved strong inhibition of iNOS expression in IFN-gamma-activated, infected microglia but not in uninfected neighboring cells. The inhibition of NO production and iNOS expression were parallel with recovery of neurite outgrowth when neurons were co-cultured with T. gondii-infected, IFN-gamma-activated microglia. In the presence of transforming growth factor (TGF)-beta1-neutralizing antibodies, the beneficial effect of the parasite on neurons was abrogated, and NO production reverted to levels similar to IFN-gamma-activated uninfected co-cultures. In addition, we observed Smad-2 nuclear translocation, a hallmark of TGF-beta1 downstream signaling, in infected microglial cultures, emphasizing an autocrine effect restricted to infected cells. Together, these data may explain a neuropreservation pattern observed during immunocompetent host infection that is dependent on T. gondii-triggered TGF-beta1 secretion by infected microglia.