NADPH oxidase mediates radiation-induced oxidative stress in rat brain microvascular endothelial cells

Role of cerebral endothelial cells in the astrocyte swelling and brain edema associated with acute hepatic encephalopathy

Brain edema is an important complication of acute hepatic encephalopathy (AHE), and astrocyte swelling is largely responsible for its development. Elevated blood and brain ammonia levels have been considered as major etiological factors in this edema. In addition to ammonia, recent studies have suggested that systemic infection, inflammation (and associated cytokines (CKs)), as well as endotoxin (lipopolysaccharide (LPS)) are also involved in AHE-associated brain edema. As endothelial cells (ECs) are the first resident brain cells exposed to blood-borne "noxious agents" (i.e., ammonia, CKs, LPS) that are present in AHE, these cells may be in a critical position to react to these agents and trigger a process resulting in astrocyte swelling/brain edema. We therefore examined the effect of conditioned media (CM) from ammonia, LPS and cytokine-treated cultured brain ECs on cell swelling in cultured astrocytes. CM from ammonia-treated ECs when added to astrocytes caused significant cell swelling, and such swelling was potentiated when astrocytes were exposed to CM from ECs treated with a combination of ammonia, LPS and CKs. We also found an additive effect when astrocytes were exposed to ammonia along with CM from ammonia-treated ECs. Additionally, ECs treated with ammonia showed a significant increase in the production of oxy-radicals, nitric oxide (NO), as well as evidence of oxidative/nitrative stress and activation of the transcription factor nuclear factor kappa B (NF-κB). CM derived from ECs treated with ammonia, along with antioxidants (AOs) or the NF-κB inhibitor BAY 11-7082, when added to astrocytes resulted in a significant reduction in cell swelling, as compared to the effect of CM from ECs-treated only with ammonia. We also identified increased nuclear NF-κB expression in rat brain cortical ECs in the thioacetamide (TAA) model of AHE. These studies suggest that ECs significantly contribute to the astrocyte swelling/brain edema in AHE, likely as a consequence of oxidative/nitrative stress and activation of NF-κB.

NADPH oxidase subunit 4 mediates cycling hypoxia-promoted radiation resistance in glioblastoma multiforme

Cycling hypoxia is a well-recognized phenomenon within animal and human solid tumors. It mediates tumor progression and radiotherapy resistance through mechanisms that involve reactive oxygen species (ROS) production. However, details of the mechanism underlying cycling hypoxia-mediated radioresistance remain obscure. We have previously shown that in glioblastoma, NADPH oxidase subunit 4 (Nox4) is a critical mediator involved in cycling hypoxia-mediated ROS production and tumor progression. Here, we examined the impact of an in vivo tumor microenvironment on Nox4 expression pattern and its impact on radiosensitivity in GBM8401 and U251, two glioblastoma cell lines stably transfected with a dual hypoxia-inducible factor-1 (HIF-1) signaling reporter construct. Furthermore, in order to isolate hypoxic tumor cell subpopulations from human glioblastoma xenografts based on the physiological and molecular characteristics of tumor hypoxia, several techniques were utilized. In this study, the perfusion marker Hoechst 33342 staining and HIF-1 activation labeling were used together with immunofluorescence imaging and fluorescence-activated cell sorting (FACS). Our results revealed that Nox4 was predominantly highly expressed in the endogenous cycling hypoxic areas with HIF-1 activation and blood perfusion within the solid tumor microenvironment. Moreover, when compared to the normoxic or chronic hypoxic cells, the cycling hypoxic tumor cells derived from glioblastoma xenografts have much higher Nox4 expression, ROS levels, and radioresistance. Nox4 suppression in intracerebral glioblastoma-bearing mice suppressed tumor microenvironment-mediated radioresistance and enhanced the efficiency of radiotherapy. In summary, our findings indicated that cycling hypoxia-induced Nox4 plays an important role in tumor microenvironment-promoted radioresistance in glioblastoma; hence, targeting Nox4 may be an attractive therapeutic strategy for blocking cycling hypoxia-mediated radioresistance.

Radiation-induced c-Jun activation depends on MEK1-ERK1/2 signaling pathway in microglial cells

Radiation-induced normal brain injury is associated with acute and/or chronic inflammatory responses, and has been a major concern in radiotherapy. Recent studies suggest that microglial activation is a potential contributor to chronic inflammatory responses following irradiation; however, the molecular mechanism underlying the response of microglia to radiation is poorly understood. c-Jun, a component of AP-1 transcription factors, potentially regulates neural cell death and neuroinflammation. We observed a rapid increase in phosphorylation of N-terminal c-Jun (on serine 63 and 73) and MAPK kinases ERK1/2, but not JNKs, in irradiated murine microglial BV2 cells. Radiation-induced c-Jun phosphorylation is dependent on the canonical MEK-ERK signaling pathway and required for both ERK1 and ERK2 function. ERK1/2 directly interact with c-Jun in vitro and in cells; meanwhile, the JNK binding domain on c-Jun is not required for its interaction with ERK kinases. Radiation-induced reactive oxygen species (ROS) potentially contribute to c-Jun phosphorylation through activating the ERK pathway. Radiation stimulates c-Jun transcriptional activity and upregulates c-Jun-regulated proinflammatory genes, such as tumor necrosis factor-α, interleukin-1β, and cyclooxygenase-2. Pharmacologic blockade of the ERK signaling pathway interferes with c-Jun activity and inhibits radiation-stimulated expression of c-Jun target genes. Overall, our study reveals that the MEK-ERK1/2 signaling pathway, but not the JNK pathway, contributes to the c-Jun-dependent microglial inflammatory response following irradiation.

PAI-1-dependent endothelial cell death determines severity of radiation-induced intestinal injury

Normal tissue toxicity still remains a dose-limiting factor in clinical radiation therapy. Recently, plasminogen activator inhibitor type 1 (SERPINE1/PAI-1) was reported as an essential mediator of late radiation-induced intestinal injury. However, it is not clear whether PAI-1 plays a role in acute radiation-induced intestinal damage and we hypothesized that PAI-1 may play a role in the endothelium radiosensitivity. In vivo, in a model of radiation enteropathy in PAI-1 −/− mice, apoptosis of radiosensitive compartments, epithelial and microvascular endothelium was quantified. In vitro, the role of PAI-1 in the radiation-induced endothelial cells (ECs) death was investigated. The level of apoptotic ECs is lower in PAI-1 −/− compared with Wt mice after irradiation. This is associated with a conserved microvascular density and consequently with a better mucosal integrity in PAI-1 −/− mice. In vitro, irradiation rapidly stimulates PAI-1 expression in ECs and radiation sensitivity is increased in ECs that stably overexpress PAI-1, whereas PAI-1 knockdown increases EC survival after irradiation. Moreover, ECs prepared from PAI-1 −/− mice are more resistant to radiation-induced cell death than Wt ECs and this is associated with activation of the Akt pathway. This study demonstrates that PAI-1 plays a key role in radiation-induced EC death in the intestine and suggests that this contributes strongly to the progression of radiation-induced intestinal injury.

Oxidative Stress Induced by MnSOD-p53 Interaction: Pro- or Anti-Tumorigenic?

The formation of reactive oxygen species (ROS) is a result of incomplete reduction of molecular oxygen during cellular metabolism. Although ROS has been shown to act as signaling molecules, it is known that these reactive molecules can act as prooxidants causing damage to DNA, proteins, and lipids, which over time can lead to disease propagation and ultimately cell death. Thus, restoring the protective antioxidant capacity of the cell has become an important target in therapeutic intervention. In addition, a clearer understanding of the disease stage and molecular events that contribute to ROS generation during tumor promotion can lead to novel approaches to enhance target specificity in cancer progression. This paper will focus on not only the traditional routes of ROS generation, but also on new mechanisms via the tumor suppressor p53 and the interaction between p53 and MnSOD, the primary antioxidant enzyme in mitochondria. In addition, the potential consequences of the p53-MnSOD interaction have also been discussed. Lastly, we have highlighted clinical implications of targeting the p53-MnSOD interaction and discussed recent therapeutic mechanisms utilized to modulate both p53 and MnSOD as a method of tumor suppression.

PROBING THE IMPACT OF GAMMA-IRRADIATION ON THE METABOLIC STATE OF NEURAL STEM AND PRECURSOR CELLS USING DUAL-WAVELENGTH INTRINSIC SIGNAL TWO-PHOTON EXCITED FLUORESCENCE

Two-photon excited fluorescence (TPEF) spectroscopy and imaging were used to investigate the effects of gamma-irradiation on neural stem and precursor cells (NSPCs). While the observed signal from reduced nicotinamide adenine dinucleotide (NADH) was localized to the mitochondria, the signal typically associated with oxidized flavoproteins (Fp) was distributed diffusely throughout the cell. The measured TPEF emission and excitation spectra were similar to the established spectra of NAD(P)H and Fp. Fp fluorescence intensity was markedly increased by addition of the electron transport chain (ETC) modulator menadione to the medium, along with a concomitant decrease in the NAD(P)H signal. Three-dimensional (3D) neurospheres were imaged to obtain the cellular metabolic index (CMI), calculated as the ratio of Fp to NAD(P)H fluorescence intensity. Radiation effects were found to differ between low-dose (≤ 50 cGy) and high-dose (≥ 50 cGy) exposures. Low-dose irradiation caused a marked drop in CMI values accompanied by increased cellular proliferation. At higher doses, both NAD(P)H and Fp signals increased, leading to an overall elevation in CMI values. These findings underscore the complex relationship between radiation dose, metabolic state, and proliferation status in NSPCs and highlight the ability of TPEF spectroscopy and imaging to characterize metabolism in 3D spheroids.

Involvement of NADPH oxidase in up-regulation of plasminogen activator inhibitor-1 and heat shock factor-1 in mouse embryo fibroblasts induced by oxidized LDL and in apolipoprotein E-deficient mice

The present study demonstrated that oxidized LDL (oLDL) increased the generation of superoxide and hydrogen peroxide (H(2)O(2)), the abundances of NADPH oxidase (NOX)4, NOX2, p22-phox and lectin-like oLDL receptor-1 (LOX-1) in wild-type or heat shock factor-1 (HSF1)-deficient mouse embryo fibroblasts (MEF). LOX-1 antibody inhibited LDL or oLDL-induced expression of NOX components in MEF. Abundance of HSF1 or plasminogen activator inhibitor-1 (PAI-1) was increased by oLDL in wild-type, but not in HSF1-deficient MEF. Diphenyleneiodonium or siRNA for NOX or p22-phox inhibited oLDL-induced increases of HSF1, PAI-1 and H(2)O(2) in MEF. Increased NOX4, NOX2, LOX1, HSF1 and PAI-1 were detected in aortae and hearts of apolipoprotein E-knockout (apoE-KO) mice compared to controls, which were associated with increased serum cholesterol or plasma PAI-1. The results suggest that NOX is required for oLDL-induced HSF1 or PAI-1 expression in MEF, which was supported by the up-regulation of NOX, LOX-1, HSF1 and PAI-1 in apoE-KO mice.

Melatonin in mitochondrial dysfunction and related disorders

Mitochondrial dysfunction is considered one of the major causative factors in the aging process, ischemia/reperfusion (I/R), septic shock, and neurodegenerative disorders like Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Increased free radical generation, enhanced mitochondrial inducible nitric oxide (NO) synthase activity, enhanced NO production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pore all have been suggested as factors responsible for impaired mitochondrial function. Melatonin, the major hormone of the pineal gland, also acts as an antioxidant and as a regulator of mitochondrial bioenergetic function. Both in vitro and in vivo, melatonin was effective for preventing oxidative stress/nitrosative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. In addition, melatonin is known to retard aging and to inhibit the lethal effects of septic shock or I/R lesions by maintaining respiratory complex activities, electron transport chain, and ATP production in mitochondria. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other antioxidants. Melatonin has thus emerged as a major potential therapeutic tool for treating neurodegenerative disorders such as PD or AD, and for preventing the lethal effects of septic shock or I/R.

NADPH oxidase inhibition attenuates total body irradiation-induced haematopoietic genomic instability

Ionising radiation (IR) is a known carcinogen and poses a significant risk to the haematopoietic system for the development of leukaemia in part by induction of genomic instability. Induction of chronic oxidative stress has been assumed to play an important role in mediating the effect of IR on the haematopoietic system. However, there was no direct evidence to support this hypothesis prior to our studies. In our recent studies, we showed that exposure of mice to total body irradiation (TBI) induces persistent oxidative stress selectively in haematopoietic stem cells (HSCs) at least in part via up-regulation of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 4. Now, we found that post-TBI treatment with diphenylene iodonium (DPI), a pan NOX inhibitor, not only significantly reduces TBI-induced increases in reactive oxygen species (ROS) production, oxidative DNA damage and DNA double-strand breaks in HSCs but also dramatically decreases the number of cells with unstable chromosomal aberrations in the clonal progeny of irradiated HSCs. The effects of DPI are comparable to Mn (III) meso-tetrakis (N-ethylpyridinium-2-yl) porphyrin, a superoxide dismutase mimetic and a potent antioxidant. These findings demonstrate that increased production of ROS by NOX in HSCs mediates the induction of haematopoietic genomic instability by IR and that NOX may represent a novel molecular target to inhibit TBI-induced genomic instability.

NFkappaB-dependent regulation of urokinase plasminogen activator by proanthocyanidin-rich grape seed extract: effect on invasion by prostate cancer cells

Tumor invasion and metastasis present major obstacles to successful control of androgen-independent prostate cancer. Cell migration is a fundamental aspect of cancer cell metastasis. Urokinase plasminogen activator (uPA) system is implicated in cell migration and cancer metastasis and has potential to be developed as therapeutic target. In recent years, efficacy of dietary nutrients in preventing and curing cancer has gained increasing attention. One such promising candidate is proanthocyanidin-rich grape seed extract (GSE). We investigated the efficacy of GSE in regulating uPA expression and cell migration using highly metastatic androgen-independent PC3 prostate cancer cells as a model. GSE down-regulated uPA as a function of concentration. Additional studies showed that GSE inhibited DNA-binding activity of the transcription factor nuclear factor kappa B (NFkappaB), which in turn decreased NFkappaB-dependent uPA transcription. Invasion assays revealed the inhibitory effect of GSE on PC3 cell migration. These in-vitro experiments demonstrate the therapeutic property of GSE as an antimetastatic agent by targeting uPA.

NADPH oxidase-mediated redox signaling: roles in cellular stress response, stress tolerance, and tissue repair

NADPH oxidase (Nox) has a dedicated function of generating reactive oxygen species (ROS). Accumulating evidence suggests that Nox has an important role in signal transduction in cellular stress responses. We have reviewed the current evidence showing that the Nox system can be activated by a collection of chemical, physical, and biological cellular stresses. In many circumstances, Nox activation fits to the cellular stress response paradigm, in that (1) the response can be initiated by various forms of cellular stresses; (2) Nox-derived ROS may activate mitogen-activated protein kinases (extracellular signal-regulated kinase, p38) and c-Jun NH(2)-terminal kinase, which are the core of the cell stress-response signaling network; and (3) Nox is involved in the development of stress cross-tolerance. Activation of the cell survival pathway by Nox may promote cell adaptation to stresses, whereas Nox may also convey signals toward apoptosis in irreversibly injured cells. At later stage after injury, Nox is involved in tissue repair by modulating cell proliferation, angiogenesis, and fibrosis. We suggest that Nox may have an integral role in cell stress responses and the subsequent tissue repair process. Understanding Nox-mediated redox signaling mechanisms may be of prominent significance at the crossroads of directing cellular responses to stress, aiming at either enhancing the stress resistance (in such situations as preventing ischemia-reperfusion injuries and accelerating wound healing) or sensitizing the stress-induced cytotoxicity for proliferative diseases such as cancer. Therefore, an optimal outcome of interventions on Nox will only be achieved when this is dealt with in a timely and disease-and stage-specific manner.

Renin-angiotensin system blockers and modulation of radiation-induced brain injury

Radiation-induced brain injury remains a major cause of morbidity in cancer patients with primary or metastatic brain tumors. Approximately 200,000 individuals/year are treated with fractionated partial or whole-brain irradiation, and > half will survive long enough (≤6 months) to develop radiation-induced brain injury, including cognitive impairment. Although short-term treatments have shown efficacy, no long-term treatments or preventive approaches are presently available for modulating radiation-induced brain injury. Based on previous preclinical studies clearly demonstrating that renin-angiotensin system (RAS) blockers can modulate radiation-induced late effects in the kidney and lung, we and others hypothesized that RAS blockade would similarly modulate radiation-induced brain injury. Indeed, studies in the last 5 years have shown that both angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor antagonists (AT(1)RAs) can prevent/ameliorate radiation-induced brain injury, including cognitive impairment, in the rat. The mechanistic basis for this RAS blocker-mediated effect remains the subject of ongoing investigations. Putative mechanisms include, i] blockade of Ang II/NADPH oxidase-mediated oxidative stress and neuroinflammation, and ii] a change in the balance of angiotensin (Ang) peptides from the pro-inflammatory and pro-oxidative Ang II to the anti-inflammatory and anti-oxidative Ang-1-7). However, given that both ACEIs and AT(1)RAs are 1] well-tolerated drugs routinely prescribed for hypertension, 2] exhibit some antitumor properties, and 3] can prevent/ameliorate radiation-induced brain injury, they appear to be ideal drugs for future clinical trials, offering the promise of improving the quality of life of brain tumor patients receiving brain irradiation.

Manganese superoxide dismutase is not protective in bovine pulmonary artery endothelial cells at systemic oxygen levels

Bovine pulmonary artery endothelial cells (BPAEC) are extremely sensitive to oxygen, mediated by superoxide production. Ionizing radiation is known to generate superoxide in oxygenated aqueous media; however, at systemic oxygen levels (3%), no oxygen enhancement is observed after irradiation. A number of markers (cell growth, alamarBlue, mitochondrial membrane polarization) for metabolic activity indicate that BPAEC maintained under 20% oxygen grow and metabolize more slowly than cells maintained under 3% oxygen. BPAEC cultured in 20% oxygen grow better when they are transiently transfected with either manganese superoxide dismutase (MnSOD) or copper zinc superoxide dismutase (CuZnSOD) and exhibit improved survival after irradiation (0.5-10 Gy). Furthermore, X irradiation of BPAEC grown in 20% oxygen results in very diffuse colony formation, which is completely ameliorated by either growth in 3% oxygen or overexpression of MnSOD. However, MnSOD overexpression in BPAEC grown in 3% oxygen provides no further radioprotection, as judged by clonogenic survival curves. Radiation does not increase apoptosis in BPAEC but inhibits cell growth and up-regulates p53 and p21 at either 3% or 20% oxygen.

Sustained expression of NADPH oxidase 4 by p38 MAPK-Akt signaling potentiates radiation-induced differentiation of lung fibroblasts

Radiation-induced fibrosis (RIF) is a long-term adverse effect of curative radiotherapy; however, the distinct molecular mechanisms of RIF in neighboring normal tissue are not fully understood. We investigated the mechanisms underlying radiation-induced fibroblast differentiation into myofibroblasts. Lung fibroblasts produced reactive oxygen species (ROS) immediately after irradiation, the level of which remained increased for 24 h. The NADPH oxidase inhibitor, diphenyleneiodonium (DPI), suppressed ROS production and significantly decreased the radiation-induced expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin (FN). The mRNA and protein expression of Nox4 was increased by radiation, and siRNA knockdown of Nox4 reduced alpha-SMA and FN levels. Increased phosphorylation of p38MAPK, Erk, and PI3k/Akt was observed after irradiation. Inhibitors of p38 MAPK and Akt, but not of Erk, reduced radiation-induced fibroblast differentiation and Nox4 expression. Notably, DPI partially decreased phosphorylation of p38MAPK and Akt, suggesting that p38MAPK, Akt, and Nox4 may cooperate in a positive feedback loop. Nox4 expression was also increased during bleomycin-induced fibroblast differentiation, and downregulation of Nox4 reduced alpha-SMA levels and extracellular matrix (ECM) accumulation. These results demonstrate that interfering Nox4 activation can be a potential strategy to disrupt fibrotic process.

The induction of reactive oxygen species and loss of mitochondrial Omi/HtrA2 is associated with S-nitrosoglutathione-induced apoptosis in human endothelial cells

The pathophysiological relevance of S-nitrosoglutathione (GSNO)-induced endothelial cell injury remains unclear. The main objective of this study was to elucidate the molecular mechanisms of GSNO-induced oxidative stress in endothelial cells. Morphological evaluation through DAPI staining and propidium iodide (PI) flow cytometry was used to detect apoptosis. In cultured EA.hy926 endothelial cells, exposure to GSNO led to a time- and dose-dependent apoptotic cascade. When intracellular reactive oxygen species (ROS) production was measured in GSNO-treated cells with the fluorescent probes 5-(and-6)-carboxy-2',7'-dichlorofluorescein diacetate, we observed elevated ROS levels and a concomitant loss in mitochondrial membrane potential, indicating that GSNO-induced death signaling is mediated through a ROS-mitochondrial pathway. Importantly, we found that peroxynitrite formation and Omi/HtrA2 release from mitochondria were involved in this phenomenon, whereas changes of death-receptor dependent signaling were not detected in the same context. The inhibition of NADPH oxidase activation and Omi/HtrA2 by a pharmacological approach provided significant protection against caspase-3 activation and GSNO-induced cell death, confirming that GSNO triggers the death cascade in endothelial cells in a mitochondria-dependent manner. Taken together, our results indicate that ROS overproduction and loss of mitochondrial Omi/HtrA2 play a pivotal role in reactive nitrogen species-induced cell death, and the modulation of these pathways can be of significant therapeutic benefit.

Total body irradiation causes residual bone marrow injury by induction of persistent oxidative stress in murine hematopoietic stem cells

Ionizing radiation (IR) and/or chemotherapy causes not only acute tissue damage but also late effects including long-term (or residual) bone marrow (BM) injury. The induction of residual BM injury is primarily attributable to the induction of hematopoietic stem cell (HSC) senescence. However, the molecular mechanisms by which IR and/or chemotherapy induces HSC senescence have not been clearly defined, nor has an effective treatment been developed to ameliorate the injury. Thus, we investigated these mechanisms in this study. The results from this study show that exposure of mice to a sublethal dose of total body irradiation (TBI) induced a persistent increase in reactive oxygen species (ROS) production in HSCs only. The induction of chronic oxidative stress in HSCs was associated with sustained increases in oxidative DNA damage, DNA double-strand breaks (DSBs), inhibition of HSC clonogenic function, and induction of HSC senescence but not apoptosis. Treatment of the irradiated mice with N-acetylcysteine after TBI significantly attenuated IR-induced inhibition of HSC clonogenic function and reduction of HSC long-term engraftment after transplantation. The induction of chronic oxidative stress in HSCs by TBI is probably attributable to the up-regulation of NADPH oxidase 4 (NOX4), because irradiated HSCs expressed an increased level of NOX4, and inhibition of NOX activity with diphenylene iodonium but not apocynin significantly reduced TBI-induced increases in ROS production, oxidative DNA damage, and DNA DSBs in HSCs and dramatically improved HSC clonogenic function. These findings provide the foremost direct evidence demonstrating that TBI selectively induces chronic oxidative stress in HSCs at least in part via up-regulation of NOX4, which leads to the induction of HSC senescence and residual BM injury.

Neuroprotection by radical avoidance: search for suitable agents

Neurodegeneration is frequently associated with damage by free radicals. However, increases in reactive oxygen and nitrogen species, which may ultimately lead to neuronal cell death, do not necessarily reflect its primary cause, but can be a consequence of otherwise induced cellular dysfunction. Detrimental processes which promote free radical formation are initiated, e.g., by disturbances in calcium homeostasis, mitochondrial malfunction, and an age-related decline in the circadian oscillator system. Free radicals generated at high rates under pathophysiological conditions are insufficiently detoxified by scavengers. Interventions at the primary causes of dysfunction, which avoid secondary rises in radical formation, may be more efficient. The aim of such approaches should be to prevent calcium overload, to reduce mitochondrial electron dissipation, to support electron transport capacity, and to avoid circadian perturbations. L-theanine and several amphiphilic nitrones are capable of counteracting excitotoxicity and/or mitochondrial radical formation. Resveratrol seems to promote mitochondrial biogenesis. Mitochondrial effects of leptin include attenuation of electron leakage. Melatonin combines all the requirements mentioned, additionally regulates anti- and pro-oxidant enzymes and is, with few exceptions, very well tolerated. In this review, the perspectives, problems and limits of drugs are compared which may be suitable for reducing the formation of free radicals.

Oxidative stress upregulates the NMDA receptor on cerebrovascular endothelium

N-methyl-d-aspartate receptor (NMDA-R)-mediated oxidative stress has been implicated in blood-brain barrier (BBB) disruption in a variety of neuropathological diseases. Although some interactions between both phenomena have been elucidated, possible influences of reactive oxygen species (ROS) on the NMDA-R itself have so far been neglected. The objective of this study was to examine how the cerebroendothelial NMDA-R is affected by exposure to oxidative stress and to assess possible influences on BBB integrity. RT-PCR confirmed several NMDA-R subunits (NR1, NR2B-D) expressed in the bEnd3 cell line (murine cerebrovascular endothelial cells). NR1 protein expression after exposure to ROS was observed via in-cell Western. The functionality of the expressed NMDA-R was determined by measuring DiBAC fluorescence in ROS-preexposed cells upon stimulation with the specific agonist NMDA. Finally, the effects on barrier integrity were evaluated using the ECIS system to detect changes in monolayer impedance upon NMDA-R stimulation after exposure to ROS. The expression of NR1 significantly (p<0.001) increased 72 h after 30 min exposure to superoxide (+33.8+/-7.5%), peroxynitrite (+84.9+/-10.7%), or hydrogen peroxide (+92.8+/-7.6%), resulting in increased cellular response to NMDA-R stimulation and diminished monolayer impedance. We conclude that oxidative stress upregulates NMDA-R on cerebrovascular endothelium and thus heightens susceptibility to glutamate-induced BBB disruption.

Radiation nephropathy is not mitigated by antagonists of oxidative stress

Abstract Persistent, chronic oxidative injury may play a mechanistic role in late radiation injury. Thus antioxidants may be useful as mitigators of radiation injury. The antioxidants deferiprone, genistein and apocynin were tested in a rat radiation nephropathy model that uses single-fraction total-body irradiation (TBI) followed by syngeneic bone marrow transplant. Deferiprone was added to the drinking water at 1.0 or 2.5 g/liter, starting 3 days after the TBI. Urinary bleomycin-detectable iron, which could enhance production of oxygen radicals, was reduced in the rats on deferiprone compared to untreated rats, but deferiprone did not mitigate radiation nephropathy. Genistein added to the chow at 750 mg/kg starting immediately after TBI did not mitigate radiation nephropathy. Apocynin added to the drinking water at 250 mg/liter immediately after TBI did not mitigate radiation nephropathy. Thus three different types of antioxidants, when used at doses consistent with an antioxidant effect, had no mitigation efficacy against radiation nephropathy.

Role of PPARs in Radiation-Induced Brain Injury

Whole-brain irradiation (WBI) represents the primary mode of treatment for brain metastases; about 200 000 patients receive WBI each year in the USA. Up to 50% of adult and 100% of pediatric brain cancer patients who survive >6 months post-WBI will suffer from a progressive, cognitive impairment. At present, there are no proven long-term treatments or preventive strategies for this significant radiation-induced late effect. Recent studies suggest that the pathogenesis of radiation-induced brain injury involves WBI-mediated increases in oxidative stress and/or inflammatory responses in the brain. Therefore, anti-inflammatory strategies can be employed to modulate radiation-induced brain injury. Peroxisomal proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the steroid/thyroid hormone nuclear receptor superfamily. Although traditionally known to play a role in metabolism, increasing evidence suggests a role for PPARs in regulating the response to inflammation and oxidative injury. PPAR agonists have been shown to cross the blood-brain barrier and confer neuroprotection in animal models of CNS disorders such as stroke, multiple sclerosis and Parkinson's disease. However, the role of PPARs in radiation-induced brain injury is unclear. In this manuscript, we review the current knowledge and the emerging insights about the role of PPARs in modulating radiation-induced brain injury.

Oxygen toxicity and reactive oxygen species: the devil is in the details

Reactive oxygen species (ROS) serve as cell signaling molecules for normal biologic processes. However, the generation of ROS can also provoke damage to multiple cellular organelles and processes, which can ultimately disrupt normal physiology. An imbalance between the production of ROS and the antioxidant defenses that protect cells has been implicated in the pathogenesis of a variety of diseases, such as cancer, asthma, pulmonary hypertension, and retinopathy. The nature of the injury will ultimately depend on specific molecular interactions, cellular locations, and timing of the insult. This review will outline the origins of endogenous and exogenously generated ROS. The molecular, cellular, pathologic, and physiologic targets will then be discussed with a particular emphasis on aspects relevant to child development. Finally, antioxidant defenses that scavenge ROS and mitigate associated toxicities will be presented, with a discussion of potential therapeutic approaches for the prevention and/or treatment of human diseases using enzymatic and nonenzymatic antioxidants.

N-acetylcysteine inhibits alveolar epithelial-mesenchymal transition

The ability of transforming growth factor-beta1 (TGF-beta1) to induce epithelial-mesenchymal transition (EMT) in alveolar epithelial cells (AEC) in vitro and in vivo, together with the demonstration of EMT in biopsies of idiopathic pulmonary fibrosis (IPF) patients, suggests a role for TGF-beta1-induced EMT in disease pathogenesis. We investigated the effects of N-acetylcysteine (NAC) on TGF-beta1-induced EMT in a rat epithelial cell line (RLE-6TN) and in primary rat alveolar epithelial cells (AEC). RLE-6TN cells exposed to TGF-beta1 for 5 days underwent EMT as evidenced by acquisition of a fibroblast-like morphology, downregulation of the epithelial-specific protein zonula occludens-1, and induction of the mesenchymal-specific proteins alpha-smooth muscle actin (alpha-SMA) and vimentin. These changes were inhibited by NAC, which also prevented Smad3 phosphorylation. Similarly, primary alveolar epithelial type II cells exposed to TGF-beta1 also underwent EMT that was prevented by NAC. TGF-beta1 decreased cellular GSH levels by 50-80%, whereas NAC restored them to approximately 150% of those found in TGF-beta1-treated cells. Treatment with glutathione monoethyl ester similarly prevented an increase in mesenchymal marker expression. Consistent with its role as an antioxidant and cellular redox stabilizer, NAC dramatically reduced intracellular reactive oxygen species production in the presence of TGF-beta1. Finally, inhibition of intracellular ROS generation during TGF-beta1 treatment prevented alveolar EMT, but treatment with H2O2 alone did not induce EMT. We conclude that NAC prevents EMT in AEC in vitro, at least in part through replenishment of intracellular GSH stores and limitation of TGF-beta1-induced intracellular ROS generation. We speculate that beneficial effects of NAC on pulmonary function in IPF may be mediated by inhibitory effects on alveolar EMT.

PPARalpha ligands inhibit radiation-induced microglial inflammatory responses by negatively regulating NF-kappaB and AP-1 pathways

Whole-brain irradiation (WBI) can lead to cognitive impairment several months to years after irradiation. Studies on rodents have shown a rapid and sustained increase in activated microglia (brain macrophages) following brain irradiation, contributing to a chronic inflammatory response and a corresponding decrease in hippocampal neurogenesis. Thus, alleviating microglial activation following radiation represents a key strategy to minimize WBI-induced morbidity. We hypothesized that pretreatment with peroxisomal proliferator-activated receptor (PPAR)alpha agonists would ameliorate the proinflammatory responses seen in the microglia following in vitro radiation. Irradiating BV-2 cells (a murine microglial cell line) with single doses (2-10 Gy) of (137)Cs gamma-rays led to increases in (1) the gene expression of IL-1beta and TNFalpha, (2) Cox-2 protein levels, and (3) intracellular ROS generation. In addition, an increase in the DNA-binding activity of redox-regulated proinflammatory transcription factors AP-1 and NF-kappaB was observed. Pretreating BV-2 cells with the PPARalpha agonists GW7647 and Fenofibrate significantly inhibited the radiation-induced microglial proinflammatory response, in part, via decreasing (i) the nuclear translocation of the NF-kappaB p65 subunit and (ii) phosphorylation of the c-jun subunit of AP-1 in the nucleus. Taken together, these data support the hypothesis that activation of PPARalpha can modulate the radiation-induced microglial proinflammatory response.