Effect of nitric oxide on naphthoquinone toxicity in endothelial cells: role of bioenergetic dysfunction and poly (ADP-ribose) polymerase activation

Vitamin E Attenuates Red-Light-Mediated Vasodilation: The Benefits of a Mild Oxidative Stress

Red light (670 nm) energy controls vasodilation via the formation of a transferable endothelium-derived nitric oxide (NO)-precursor-containing substance, its intracellular traffic, and exocytosis. Here we investigated the underlying mechanistic effect of oxidative stress on light-mediated vasodilation by using pressure myography on dissected murine arteries and immunofluorescence on endothelial cells. Treatment with antioxidants Trolox and catalase decreased vessel dilation. In the presence of catalase, a lower number of exosomes were detected in the vessel bath. Light exposure resulted in increased cellular free radical levels. Mitochondrial reactive oxygen species were also more abundant but did not alter cellular ATP production. Red light enhanced the co-localization of late exosome marker CD63 and cellular S-nitrosoprotein to a greater extent than high glucose, suggesting that a mild oxidative stress favors the localization of NO precursor in late exosomes. Exocytosis regulating protein Rab11 was more abundant after irradiation. Our findings conclude that red-light-induced gentle oxidative stress facilitates the dilation of blood vessels, most likely through empowering the traffic of vasodilatory substances. Application of antioxidants disfavors this mechanism.

β-cell-selective inhibition of DNA damage response signaling by nitric oxide is associated with an attenuation in glucose uptake

Nitric oxide (NO) plays a dual role in regulating DNA damage response (DDR) signaling in pancreatic β-cells. As a genotoxic agent, NO activates two types of DDR signaling; however, when produced at micromolar levels by the inducible isoform of NO synthase, NO inhibits DDR signaling and DDR-induced apoptosis in a β-cell-selective manner. DDR signaling inhibition by NO correlates with mitochondrial oxidative metabolism inhibition and decreases in ATP and NAD+. Unlike most cell types, β-cells do not compensate for impaired mitochondrial oxidation by increasing glycolytic flux, and this metabolic inflexibility leads to a decrease in ATP and NAD+. Here, we used multiple analytical approaches to determine changes in intermediary metabolites in β-cells and non-β-cells treated with NO or complex I inhibitor rotenone. In addition to ATP and NAD+, glycolytic and tricarboxylic acid cycle intermediates as well as NADPH are significantly decreased in β-cells treated with NO or rotenone. Consistent with glucose-6-phosphate residing at the metabolic branchpoint for glycolysis and the pentose phosphate pathway (NADPH), we show that mitochondrial oxidation inhibitors limit glucose uptake in a β-cell-selective manner. Our findings indicate that the β-cell-selective inhibition of DDR signaling by NO is associated with a decrease in ATP to levels that fall significantly below the KM for ATP of glucokinase (glucose uptake) and suggest that this action places the β-cell in a state of suspended animation where it is metabolically inert until NO is removed, and metabolic function can be restored.

Regulation of ATR-dependent DNA damage response by nitric oxide

We have shown that nitric oxide limits ataxia-telangiectasia mutated signaling by inhibiting mitochondrial oxidative metabolism in a β-cell selective manner. In this study, we examined the actions of nitric oxide on a second DNA damage response transducer kinase, ataxia-telangiectasia and Rad3-related protein (ATR). In β-cells and non-β-cells, nitric oxide activates ATR signaling by inhibiting ribonucleotide reductase; however, when produced at inducible nitric oxide synthase-derived (low micromolar) levels, nitric oxide impairs ATR signaling in a β-cell selective manner. The inhibitory actions of nitric oxide are associated with impaired mitochondrial oxidative metabolism and lack of glycolytic compensation that result in a decrease in β-cell ATP. Like nitric oxide, inhibitors of mitochondrial respiration reduce ATP levels and limit ATR signaling in a β-cell selective manner. When non-β-cells are forced to utilize mitochondrial oxidative metabolism for ATP generation, their response is more like β-cells, as nitric oxide and inhibitors of mitochondrial respiration attenuate ATR signaling. These studies support a dual role for nitric oxide in regulating ATR signaling. Nitric oxide activates ATR in all cell types examined by inhibiting ribonucleotide reductase, and in a β-cell selective manner, inducible nitric oxide synthase-derived levels of nitric oxide limit ATR signaling by attenuating mitochondrial oxidative metabolism and depleting ATP.

The Role of Thioredoxin/Peroxiredoxin in the β-Cell Defense Against Oxidative Damage

Oxidative stress is hypothesized to play a role in pancreatic β-cell damage, potentially contributing to β-cell dysfunction and death in both type 1 and type 2 diabetes. Oxidative stress arises when naturally occurring reactive oxygen species (ROS) are produced at levels that overwhelm the antioxidant capacity of the cell. ROS, including superoxide and hydrogen peroxide, are primarily produced by electron leak during mitochondrial oxidative metabolism. Additionally, peroxynitrite, an oxidant generated by the reaction of superoxide and nitric oxide, may also cause β-cell damage during autoimmune destruction of these cells. β-cells are thought to be susceptible to oxidative damage based on reports that they express low levels of antioxidant enzymes compared to other tissues. Furthermore, markers of oxidative damage are observed in islets from diabetic rodent models and human patients. However, recent studies have demonstrated high expression of various isoforms of peroxiredoxins, thioredoxin, and thioredoxin reductase in β-cells and have provided experimental evidence supporting a role for these enzymes in promoting β-cell function and survival in response to a variety of oxidative stressors. This mini-review will focus on the mechanism by which thioredoxins and peroxiredoxins detoxify ROS and on the protective roles of these enzymes in β-cells. Additionally, we speculate about the role of this antioxidant system in promoting insulin secretion.

Inhibition of oxidative metabolism by nitric oxide restricts EMCV replication selectively in pancreatic beta-cells

Environmental factors, such as viral infection, are proposed to play a role in the initiation of autoimmune diabetes. In response to encephalomyocarditis virus (EMCV) infection, resident islet macrophages release the pro-inflammatory cytokine IL-1β, to levels that are sufficient to stimulate inducible nitric oxide synthase (iNOS) expression and production of micromolar levels of the free radical nitric oxide in neighboring β-cells. We have recently shown that nitric oxide inhibits EMCV replication and EMCV-mediated β-cell lysis and that this protection is associated with an inhibition of mitochondrial oxidative metabolism. Here we show that the protective actions of nitric oxide against EMCV infection are selective for β-cells and associated with the metabolic coupling of glycolysis and mitochondrial oxidation that is necessary for insulin secretion. Inhibitors of mitochondrial respiration attenuate EMCV replication in β-cells, and this inhibition is associated with a decrease in ATP levels. In mouse embryonic fibroblasts (MEFs), inhibition of mitochondrial metabolism does not modify EMCV replication or decrease ATP levels. Like most cell types, MEFs have the capacity to uncouple the glycolytic utilization of glucose from mitochondrial respiration, allowing for the maintenance of ATP levels under conditions of impaired mitochondrial respiration. It is only when MEFs are forced to use mitochondrial oxidative metabolism for ATP generation that mitochondrial inhibitors attenuate viral replication. In a β-cell selective manner, these findings indicate that nitric oxide targets the same metabolic pathways necessary for glucose stimulated insulin secretion for protection from viral lysis.

Nitric Oxide Circumvents Virus-Mediated Metabolic Regulation during Human Cytomegalovirus Infection

Nitric oxide is a versatile and critical effector molecule that can modulate many cellular functions. Although recognized as a regulator of infections, the inhibitory mechanism of nitric oxide against human cytomegalovirus (HCMV) replication remains elusive. We demonstrate that nitric oxide attenuates viral replication by interfering with HCMV-mediated modulation of several cellular processes. Nitric oxide exposure reduced HCMV genome synthesis and infectious viral progeny with cell-type-dependent differences observed. Mitochondrial respiration was severely reduced in both uninfected and HCMV-infected cells during exposure with little impact on ATP levels indicating changes in cellular metabolism. Metabolomics identified significantly altered small molecules in multiple pathways during nitric oxide exposure including nucleotide biosynthesis, tricarboxylic acid (TCA) cycle, and glutamine metabolism. Glutathione metabolites were increased coinciding with a reduction in the glutathione precursor glutamine. This shift was accompanied by increased antioxidant enzymes. Glutamine deprivation mimicked defects in HCMV replication and mitochondrial respiration observed during nitric oxide exposure. These data suggest that nitric oxide limits glutaminolysis by shuttling glutamine to glutathione synthesis. In addition, lipid intermediates were severely altered, which likely contributes to the observed increase in defective viral particles. Nitric oxide disrupts multiple cellular processes, and we had limited success in rescuing replication defects by supplementing with metabolic intermediates. Our studies indicate that nitric oxide attenuation of HCMV is multifactorial with interference in viral manipulation of cellular metabolism playing a central role.IMPORTANCE Human cytomegalovirus is a prevalent pathogen that can cause serious disease in patients with compromised immune systems, including transplant patients and during congenital infection. HCMV lytic replication likely occurs in localized sites of infection with immune cells infiltrating and releasing nitric oxide with other effector molecules. This nonspecific immune response results in both uninfected and infected cells exposed to high levels of nitric oxide. The absence of nitric oxide synthase has been associated with lethal HCMV infection. We demonstrate that nitric oxide inhibition of HCMV replication is multifactorial and cell type dependent. Our results indicate that nitric oxide controls replication by interfering with viral modulation of cellular metabolism while also affecting proliferation and mitochondrial respiration of neighboring uninfected cells. These studies identify the mechanism and contribution of nitric oxide during immune control of HCMV infection and provide insight into its role in other viral infections.

Inhibition of mitochondrial oxidative metabolism attenuates EMCV replication and protects β-cells from virally mediated lysis

Viral infection is one environmental factor that may contribute to the initiation of pancreatic β-cell destruction during the development of autoimmune diabetes. Picornaviruses, such as encephalomyocarditis virus (EMCV), induce a pro-inflammatory response in islets leading to local production of cytokines, such as IL-1, by resident islet leukocytes. Furthermore, IL-1 is known to stimulate β-cell expression of iNOS and production of the free radical nitric oxide. The purpose of this study was to determine whether nitric oxide contributes to the β-cell response to viral infection. We show that nitric oxide protects β-cells against virally mediated lysis by limiting EMCV replication. This protection requires low micromolar, or iNOS-derived, levels of nitric oxide. At these concentrations nitric oxide inhibits the Krebs enzyme aconitase and complex IV of the electron transport chain. Like nitric oxide, pharmacological inhibition of mitochondrial oxidative metabolism attenuates EMCV-mediated β-cell lysis by inhibiting viral replication. These findings provide novel evidence that cytokine signaling in β-cells functions to limit viral replication and subsequent β-cell lysis by attenuating mitochondrial oxidative metabolism in a nitric oxide-dependent manner.

Peroxiredoxin 1 plays a primary role in protecting pancreatic β-cells from hydrogen peroxide and peroxynitrite

Both reactive nitrogen and oxygen species (RNS and ROS), such as nitric oxide, peroxynitrite, and hydrogen peroxide, have been implicated as mediators of pancreatic β-cell damage during the pathogenesis of autoimmune diabetes. While β-cells are thought to be vulnerable to oxidative damage due to reportedly low levels of antioxidant enzymes, such as catalase and glutathione peroxidase, we have shown that they use thioredoxin reductase to detoxify hydrogen peroxide. Thioredoxin reductase is an enzyme that participates in the peroxiredoxin antioxidant cycle. Peroxiredoxins are expressed in β-cells and, when overexpressed, protect against oxidative stress, but the endogenous roles of peroxiredoxins in the protection of β-cells from oxidative damage are unclear. Here, using either glucose oxidase or menadione to continuously deliver hydrogen peroxide, or the combination of dipropylenetriamine NONOate and menadione to continuously deliver peroxynitrite, we tested the hypothesis that β-cells use peroxiredoxins to detoxify both of these reactive species. Either pharmacological peroxiredoxin inhibition with conoidin A or specific depletion of cytoplasmic peroxiredoxin 1 (Prdx1) using siRNAs sensitizes INS 832/13 cells and rat islets to DNA damage and death induced by hydrogen peroxide or peroxynitrite. Interestingly, depletion of peroxiredoxin 2 (Prdx2) had no effect. Together, these results suggest that β-cells use cytoplasmic Prdx1 as a primary defense mechanism against both ROS and RNS.

The Role of Metabolic Flexibility in the Regulation of the DNA Damage Response by Nitric Oxide

In this report, we show that nitric oxide suppresses DNA damage response (DDR) signaling in the pancreatic β-cell line INS 832/13 and rat islets by inhibiting intermediary metabolism. Nitric oxide is known to inhibit complex IV of the electron transport chain and aconitase of the Krebs cycle. Non-β cells compensate by increasing glycolytic metabolism to maintain ATP levels; however, β cells lack this metabolic flexibility, resulting in a nitric oxide-dependent decrease in ATP and NAD+ Like nitric oxide, mitochondrial toxins inhibit DDR signaling in β cells by a mechanism that is associated with a decrease in ATP. Non-β cells compensate for the effects of mitochondrial toxins with an adaptive shift to glycolytic ATP generation that allows for DDR signaling. Forcing non-β cells to derive ATP via mitochondrial respiration (replacing glucose with galactose in the medium) and glucose deprivation sensitizes these cells to nitric oxide-mediated inhibition of DDR signaling. These findings indicate that metabolic flexibility is necessary to maintain DDR signaling under conditions in which mitochondrial oxidative metabolism is inhibited and support the inhibition of oxidative metabolism (decreased ATP) as one protective mechanism by which nitric oxide attenuates DDR-dependent β-cell apoptosis.

Pancreatic β-cells detoxify H2O2 through the peroxiredoxin/thioredoxin antioxidant system

Oxidative stress is thought to promote pancreatic β-cell dysfunction and contribute to both type 1 and type 2 diabetes. Reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, are mediators of oxidative stress that arise largely from electron leakage during oxidative phosphorylation. Reports that β-cells express low levels of antioxidant enzymes, including catalase and GSH peroxidases, have supported a model in which β-cells are ill-equipped to detoxify ROS. This hypothesis seems at odds with the essential role of β-cells in the control of metabolic homeostasis and organismal survival through exquisite coupling of oxidative phosphorylation, a prominent ROS-producing pathway, to insulin secretion. Using glucose oxidase to deliver H₂O₂ continuously over time and Amplex Red to measure extracellular H₂O₂ concentration, we found here that β-cells can remove micromolar levels of this oxidant. This detoxification pathway utilizes the peroxiredoxin/thioredoxin antioxidant system, as selective chemical inhibition or siRNA-mediated depletion of thioredoxin reductase sensitized β-cells to continuously generated H₂O₂ In contrast, when delivered as a bolus, H₂O₂ induced the DNA damage response, depleted cellular energy stores, and decreased β-cell viability independently of thioredoxin reductase inhibition. These findings show that β-cells have the capacity to detoxify micromolar levels of H₂O₂ through a thioredoxin reductase-dependent mechanism and are not as sensitive to oxidative damage as previously thought.

The effects of pro- and anti-atherosclerotic factors on intracellular nucleotide concentration in murine endothelial cells

Endothelial cell activation and dysfunction could lead to endothelial injury that is an important factor in the development of vascular diseases. Vascular injury is strongly associated with disturbed endothelial cell energetics and pyridine nucleotide pool. This study aimed to evaluate the effects of inflammatory stimuli (IL-6, LPS), uric acid, hyperglycemia, fatty acids, flavonoids, statins and nonsteroidal anti-inflammatory drugs on cellular concentration of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide (NAD⁺) in cultured endothelial cells. Murine-immortalized heart endothelial cells (H5V cells) were treated with different concentrations of pro- and anti-atherosclerotic factors and intracellular concentration of nucleotides were measured using high performance liquid chromatography. Intracellular ATP concentration in H5V cells was not changed by inflammatory stimuli (IL-6 and LPS), uric acid, glucose, atorvastatin, acetylsalicylic acid, monounsaturated and polyunsaturated fatty acids. Only high concentration of palmitic acid (1 mM) and kaempferol (>0.1 mM) decreased intracellular ATP concentration. The concentration of intracellular ADP has not been altered by any of tested compounds. In turn, intracellular NAD⁺ pool was modified only by polyunsaturated fatty acids and atorvastatin. Linoleic acid, docosahexaenoic acid and atorvastatin increased cellular NAD⁺ concentration. Tested compounds have a small influence on murine endothelial cell energetics, but polyunsaturated fatty acids and atorvastatin increased intracellular NAD⁺ concentration that could be an important protective mechanism against endothelial cell injury.

Dual Role of Nitric Oxide in Regulating the Response of β Cells to DNA Damage

SIGNIFICANCE

Cytokines released in and around pancreatic islets during islet inflammation are believed to contribute to impaired β cell function and β cell death during the development of diabetes. Nitric oxide, produced by β cells in response to cytokine exposure, controls many of the responses of β cells during islet inflammation. Recent Advances: Although nitric oxide has been shown to inhibit insulin secretion and oxidative metabolism and induce DNA damage in β cells, it also activates protective pathways that promote recovery of insulin secretion and oxidative metabolism and repair of damaged DNA. Recent studies have identified a novel role for nitric oxide in selectively regulating the DNA damage response in β cells.

CRITICAL ISSUES

Does nitric oxide mediate cytokine-induced β cell damage, or is nitric oxide produced by β cells in response to cytokines to protect β cells from damage?

FUTURE DIRECTIONS

β cells appear to be the only islet endocrine cell type capable of responding to proinflammatory cytokines with the production of nitric oxide, and these terminally differentiated cells have a limited capacity to regenerate. It is likely that there is a physiological purpose for this response, and understanding this could open new areas of study regarding the loss of functional β cell mass during diabetes development.

Cardiomyocyte Differentiation Promotes Cell Survival During Nicotinamide Phosphoribosyltransferase Inhibition Through Increased Maintenance of Cellular Energy Stores

To address concerns regarding the tumorigenic potential of undifferentiated human pluripotent stem cells (hPSC) that may remain after in vitro differentiation and ultimately limit the broad use of hPSC‐derivatives for therapeutics, we recently described a method to selectively eliminate tumorigenic hPSC from their progeny by inhibiting nicotinamide phosphoribosyltransferase (NAMPT). Limited exposure to NAMPT inhibitors selectively removes hPSC from hPSC‐derived cardiomyocytes (hPSC‐CM) and spares a wide range of differentiated cell types; yet, it remains unclear when and how cells acquire resistance to NAMPT inhibition during differentiation. In this study, we examined the effects of NAMPT inhibition among multiple time points of cardiomyocyte differentiation. Overall, these studies show that in vitro cardiomyogenic commitment and continued culturing provides resistance to NAMPT inhibition and cell survival is associated with the ability to maintain cellular ATP pools despite depletion of NAD levels. Unlike cells at earlier stages of differentiation, day 28 hPSC‐CM can survive longer periods of NAMPT inhibition and maintain ATP generation by glycolysis and/or mitochondrial respiration. This is distinct from terminally differentiated fibroblasts, which maintain mitochondrial respiration during NAMPT inhibition. Overall, these results provide new mechanistic insight into how regulation of cellular NAD and energy pools change with hPSC‐CM differentiation and further inform how NAMPT inhibition strategies could be implemented within the context of cardiomyocyte differentiation. Stem Cells Translational Medicine2017;6:1191–1201

Aloe vera toxic effects: expression of inducible nitric oxide synthase (iNOS) in testis of Wistar rat

OBJECTIVES

Nitric oxide (NO), a product of inducible nitric oxide synthase (iNOS), contributes in germ cell apoptosis. This study was aimed to evaluate the effects of Aloe vera gel (AVG) on male Wistar rat reproductive organ, serum NO level, and expression of iNOS gene in leydig cells.

MATERIALS AND METHODS

Adult male Wistar rats (n=36) were used for experiments in three groups. The experimental groups were orally administered with the AVG extract solution once-daily as follow: 150 mg.kg(-1); group A, 300 mg.kg(-1); group B, and only normal saline; group C (control group). They were mated with untreated females and the reproductive and chemical parameters were assessed for each group, including semen quality, serum testosterone, sperm fertility, gonad and body weight, serum NO concentration (by the Griess method), and iNOS gene expression (using RT-PCR).

RESULTS

The testes weight, serum testosterone, as well as sperm count and fertility of the AVG treated groups were significantly reduced when compared to the control (P<0.001). Concentration of serum NO was significantly increased (37.1±4.63 µM) in the administrated group with higher AVG concentration, compared to the control group (P<0.001; 10.19±0.87 µM); however, iNOS mRNA expression was increased in the treated animals (P<0.001).

CONCLUSION

iNOS may play a functional role in spermatogenesis via apoptosis, reducing sperm count, but further studies are needed to illustrate the mechanisms by which AVG exerts its negative effects on spermatogenesis and sperm quality.

ATM facilitates mouse gammaherpesvirus reactivation from myeloid cells during chronic infection

Gammaherpesviruses are cancer-associated pathogens that establish life-long infection in most adults. Insufficiency of Ataxia-Telangiectasia mutated (ATM) kinase leads to a poor control of chronic gammaherpesvirus infection via an unknown mechanism that likely involves a suboptimal antiviral response. In contrast to the phenotype in the intact host, ATM facilitates gammaherpesvirus reactivation and replication in vitro. We hypothesized that ATM mediates both pro- and antiviral activities to regulate chronic gammaherpesvirus infection in an immunocompetent host. To test the proposed proviral activity of ATM in vivo, we generated mice with ATM deficiency limited to myeloid cells. Myeloid-specific ATM deficiency attenuated gammaherpesvirus infection during the establishment of viral latency. The results of our study uncover a proviral role of ATM in the context of gammaherpesvirus infection in vivo and support a model where ATM combines pro- and antiviral functions to facilitate both gammaherpesvirus-specific T cell immune response and viral reactivation in vivo.

PARP-1 involvement in neurodegeneration: A focus on Alzheimer's and Parkinson's diseases

DNA damage is the prime activator of the enzyme poly(ADP-ribose)polymerase1 (PARP-1) whose overactivation has been proven to be associated with the pathogenesis of numerous central nervous system disorders, such as ischemia, neuroinflammation, and neurodegenerative diseases. Under oxidative stress conditions PARP-1 activity increases, leading to an accumulation of ADP-ribose polymers and NAD(+) depletion, that induces energy crisis and finally cell death. This review aims to explain the contribution of PARP-1 in neurodegenerative diseases, focusing on Alzheimer's and Parkinson's disease, to stimulate further studies on this issue and thereby engage a new perspective regarding the design of possible therapeutic agents or the identification of biomarkers.

Inhibition of an NAD⁺ salvage pathway provides efficient and selective toxicity to human pluripotent stem cells

The tumorigenic potential of human pluripotent stem cells (hPSCs) is a major limitation to the widespread use of hPSC derivatives in the clinic. Here, we demonstrate that the small molecule STF-31 is effective at eliminating undifferentiated hPSCs across a broad range of cell culture conditions with important advantages over previously described methods that target metabolic processes. Although STF-31 was originally described as an inhibitor of glucose transporter 1, these data support the reclassification of STF-31 as a specific NAD⁺ salvage pathway inhibitor through the inhibition of nicotinamide phosphoribosyltransferase (NAMPT). These findings demonstrate the importance of an NAD⁺ salvage pathway in hPSC biology and describe how inhibition of NAMPT can effectively eliminate hPSCs from culture. These results will advance and accelerate the development of safe, clinically relevant hPSC-derived cell-based therapies.

How the location of superoxide generation influences the β-cell response to nitric oxide

Cytokines impair the function and decrease the viability of insulin-producing β-cells by a pathway that requires the expression of inducible nitric oxide synthase (iNOS) and generation of high levels of nitric oxide. In addition to nitric oxide, excessive formation of reactive oxygen species, such as superoxide and hydrogen peroxide, has been shown to cause β-cell damage. Although the reaction of nitric oxide with superoxide results in the formation of peroxynitrite, we have shown that β-cells do not have the capacity to produce this powerful oxidant in response to cytokines. When β-cells are forced to generate peroxynitrite using nitric oxide donors and superoxide-generating redox cycling agents, superoxide scavenges nitric oxide and prevents the inhibitory and destructive actions of nitric oxide on mitochondrial oxidative metabolism and β-cell viability. In this study, we show that the β-cell response to nitric oxide is regulated by the location of superoxide generation. Nitric oxide freely diffuses through cell membranes, and it reacts with superoxide produced within cells and in the extracellular space, generating peroxynitrite. However, only when it is produced within cells does superoxide attenuate nitric oxide-induced mitochondrial dysfunction, gene expression, and toxicity. These findings suggest that the location of radical generation and the site of radical reactions are key determinants in the functional response of β-cells to reactive oxygen species and reactive nitrogen species. Although nitric oxide is freely diffusible, its biological function can be controlled by the local generation of superoxide, such that when this reaction occurs within β-cells, superoxide protects β-cells by scavenging nitric oxide.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

Neuroinflammation and demyelination from the point of nitrosative stress as a new target for neuroprotection

The role of nitrosative stress in the early pathogenesis of neuroinflammation and demyelination is undoubtedly wide. This review summarizes and integrates the results, found in previously performed studies, which have evaluated nitrosative stress participation in neuroinflammation. The largest number of studies indicates that the supply of nitrosative stress inhibitors has led to the opposite clinical effects in experimental studies. Some results claim that attributing the protective role to nitric oxide, outside the total changes of redox oxidative processes and without following the clinical and paraclinical correlates of neuroinflammation, is an overrated role of this mediator. The fact is that the use of nitrosative stress inhibitors would be justified in the earlier phases of neuroinflammation. The ideal choice would be a specific inducible nitric oxide synthase (iNOS) inhibitor, because its use would preserve the physiological features of nitric oxide produced by the effects of constitutive NOS. This review discusses the antinitrosative therapy as a potential mode of therapy that aims to control neuroinflammation in early phases, delaying its later phases, which are accompanied with irreversible neurological disabilities. Some parameters of nitrosative stress might serve as surrogate biomarkers for neuroinflammation intensity and its radiological and clinical correlates.

Energy and oxygen metabolism disorder during septic acute kidney injury

BACKGROUND/AIMS

Acute kidney injury (AKI) during septic shock, which is one of the most common clinical syndromes in the intensive care unit (ICU), has a high mortality rate and poor prognosis, partly because of a poor understanding of the pathogenesis of renal dysfunction during septic shock. Although ischemic injury of the kidney has been reported to result from adenosine triphosphate (ATP) depletion, increasing evidence has demonstrated that AKI occurs in the absence of renal hypoperfusion and even occurs during normal or increased renal blood flow (RBF); nevertheless, whether energy metabolism disorder is involved in septic AKI and whether it changes according to renal hemodynamics have not been established. Moreover, tubular cell apoptosis, which is closely related to ATP depletion, rather than necrosis, has been shown to be the major form of cell injury during AKI.

METHODS

We used canine endotoxin shock models to investigate the hemodynamics, renal energy metabolism, renal oxygen metabolism, and pathological changes during septic AKI and to explore the underlying mechanisms of septic AKI.

RESULTS

The present results revealed that the nicotinamide adenine dinucleotide (NAD+) pool and the ATP/adenosine diphosphate (ADP) ratio were significantly decreased during the early phase of septic AKI, which is accompanied by a decreased renal oxygen extraction ratio (O2ER%) and decreased renal oxygen consumption (VO2). Furthermore, significant apoptosis was observed following renal dysfunction. RBF and renal oxygen delivery were not significantly altered.

CONCLUSION

These results suggest that imbalanced energy metabolism, rather than tubular cell apoptosis, may be the initiator of renal dysfunction during septic shock.

L-carnosine alters some hemorheologic and lipid peroxidation parameters in nephrectomized rats

Background

Chronic kidney disease (CKD) is a major health problem worldwide. Oxidative stress is one of the mediators of this disease. Systemic complications of oxidative stress are involved in the pathogenesis of hypertension, endothelial dysfunction, shortened erythrocyte lifespan, deformability, and nitric oxide (NO) dysfunction. L-carnosine is known as an antioxidant. In this study, our aim was to investigate the effect of carnosine on hemorheologic and cardiovascular parameters in CKD-induced rats.

Material/Methods

We used 4-month-old male Sprague-Dawley rats divided into 4 groups of 6 rats each. Three days after subtotal nephrectomy and sham operations, the surviving rats were divided into the 4 groups; 1) Sham (S), 2) Sham+Carnosine (S-C), 3) Subtotal nephrectomy (Nx), and 4) Subtotal nephrectomy + Carnosine (N-C). Carnosine was injected intraperitoneally (i.p.) (50 mg/kg) for 15 days. The control group received the same volume of physiological saline.

Results

In CKD rats, malondialdehyde (MDA) levels were increased, and NO and RBC deformability were decreased compared to Sham. Carnosine treatment decreased MDA levels, improved RBC (red blood cell) ability to deform, and increased NO levels. However, carnosine did not affect blood pressure levels in these rats.

Conclusions

We found that carnosine has beneficial effects on CKD in terms of lipid peroxidation and RBC deformability. Carnosine may have a healing effect in microcirculation level, but may not have any effect on systemic blood pressure in CKD-induced rats.

Do β-cells generate peroxynitrite in response to cytokine treatment?

The purpose of this study was to determine the reactive species that is responsible for cytokine-mediated β-cell death. Inhibitors of inducible nitric oxide synthase prevent this death, and addition of exogenous nitric oxide using donors induces β-cell death. The reaction of nitric oxide with superoxide results in the generation of peroxynitrite, and this powerful oxidant has been suggested to be the mediator of β-cell death in response to cytokine treatment. Recently, coumarin-7-boronate has been developed as a probe for the selective detection of peroxynitrite. Using this reagent, we show that addition of the NADPH oxidase activator phorbol 12-myristate 13-acetate to nitric oxide-producing macrophages results in peroxynitrite generation. Using a similar approach, we demonstrate that cytokines fail to stimulate peroxynitrite generation by rat islets and insulinoma cells, either with or without phorbol 12-myristate 13-acetate treatment. When forced to produce superoxide using redox cyclers, this generation is associated with protection from nitric oxide toxicity. These findings indicate that: (i) nitric oxide is the likely mediator of the toxic effects of cytokines, (ii) β-cells do not produce peroxynitrite in response to cytokines, and (iii) when forced to produce superoxide, the scavenging of nitric oxide by superoxide is associated with protection of β-cells from nitric oxide-mediated toxicity.