Nitric oxide inhibits iron-induced lipid peroxidation in HL-60 cells

Pro-Tumor Activity of Endogenous Nitric Oxide in Anti-Tumor Photodynamic Therapy: Recently Recognized Bystander Effects

Various studies have revealed that several cancer cell types can upregulate inducible nitric oxide synthase (iNOS) and iNOS-derived nitric oxide (NO) after moderate photodynamic treatment (PDT) sensitized by 5-aminolevulinic acid (ALA)-induced protoporphyrin-IX. As will be discussed, the NO signaled cell resistance to photokilling as well as greater growth and migratory aggressiveness of surviving cells. On this basis, it was predicted that diffusible NO from PDT-targeted cells in a tumor might enhance the growth, migration, and invasiveness of non- or poorly PDT-targeted bystander cells. This was tested using a novel approach in which ALA-PDT-targeted cancer cells on a culture dish were initially segregated from non-targeted bystander cells of the same type via impermeable silicone-rimmed rings. Several hours after LED irradiation, the rings were removed, and both cell populations were analyzed in the dark for various responses. After a moderate extent of targeted cell killing (~25%), bystander proliferation and migration were evaluated, and both were found to be significantly enhanced. Enhancement correlated with iNOS/NO upregulation in surviving PDT-targeted cancer cells in the following cell type order: PC3 > MDA-MB-231 > U87 > BLM. If occurring in an actual PDT-challenged tumor, such bystander effects might compromise treatment efficacy by stimulating tumor growth and/or metastatic dissemination. Mitigation of these and other negative NO effects using pharmacologic adjuvants that either inhibit iNOS transcription or enzymatic activity will be discussed.

The role of nutritional-immunological indices in estimating serum LPS and antioxidant enzyme activity and sepsis status in female dogs with pyometra caused by E. coli

The aim of this study was to diagnose pyometra and related sepsis status using cost-effective nutritional-immunological indices, antioxidants, and toxin levels in dogs and to investigate the utility of the indices in predicting toxin and antioxidant status. A total of 29 dogs were enrolled into the present study. Among these, 9 female dogs in their diestrus stages, were allocated for elective ovariohysterectomy. The pyometra group was also separated into two subgroups as Sepsis (+) and Sepsis (-). Blood samples were collected into two tubes containing EDTA for hematological analysis; without anticoagulant for serum progesterone, LPS concentration, and antioxidant levels at the time of diagnosis. Bacteriological and tissue samples of the uterus were collected after the ovariohysterectomy. Antioxidant activity, progesterone, and toxin concentration were determined by using commercial ELISA kits. Statistical analyses were performed using Stata version 16.1 and MedCalc 16 statistical software. Receiver operating characteristics curves were used for the threshold for evaluating pyometra and sepsis status. Pairwise comparisons were carried out of the area under the curve (AUC) for thresholds of nutritional immunologic indices (hemoglobin, albumin, lymphocyte, platelet (HALP) score; prognostic nutritional index (PNI); Albumin hemoglobin index (AHI)), serum LPS and antioxidant activity. Linear regression model was used for the estimation of serum LPS and antioxidant activity by using indices. Mean serum progesterone, LPS concentrations, and Nitric Oxide (NO) production were greater, while serum superoxide dismutase (SOD), tissue SOD, and glutathione peroxidase (GPx) activities were lower in dogs with pyometra. All nutritional-immunologic indices were lower in pyometra cases. Nutritional-immunologic indices (AUC of HALP:0.759; PNI:0.981; AHI 0.994), NO (AUC: 0.787) and SOD (AUC: 0.784) levels were useful for pyometra diagnosis. AHI and LPS were useful for the determination of sepsis status with the AUC values of 0.850 and 0.740, respectively. While AHI was useful for the estimation of serum LPS and NO concentration (p < 0.001), PNI was useful for serum SOD concentration (p = 0.003). In conclusion, PNI, HALP and AHI can be used in the diagnosis of pyometra, however, only AHI and LPS levels can be used in the diagnosis of sepsis. SOD and NO can be used to determine pyometra but have no effect on determining sepsis status. Additionally, the estimation of the levels of serum LPS, NO, and SOD activities can be done using the AHI and PNI values.

Targeted delivery of Nitric Oxide triggered by α-Glucosidase to Ameliorate NSAIDs-induced Enteropathy

Nonsteroidal anti-inflammatory drugs (NSAIDs) increase risks of severe small intestinal injuries. Development of effective therapeutic strategies to overcome this issue remains challenging. Nitric oxide (NO) as a gaseous mediator plays a protective role in small intestinal injuries. However, small intestine-specific delivery systems for NO have not been reported yet. In this study, we reported a small intestine-targeted polymeric NO donor (CS-NO) which was synthesized by covalent grafting of α-glucosidase-activated NO donor onto chitosan. In vitro and in vivo experiments demonstrated that CS-NO could be activated by intestinal α-glucosidase to release NO in the small intestine. Pre-treatment of mice with CS-NO significantly alleviated small intestinal damage induced by indomethacin, as demonstrated by down-regulation of the levels of pro-inflammatory cytokines and chemokines CXCL1/KC. Moreover, CS-NO also attenuated indomethacin-induced gut barrier dysfunction as evidenced by up-regulation of the levels of tight junction proteins and restoration of the levels of goblet cells and MUC2 production. Meanwhile, CS-NO effectively restored the defense function of Paneth cells against pathogens in small intestine. Our present study paves the way to develop NO-based therapeutic strategy for NSAIDs-induced small intestinal injuries.

Indirect Antioxidant Effects of the Nitrite Anion: Focus on Xanthine Oxidase

One electron reduction of nitrite (NO₂ ^-) has been determined to be a significant, noncanonical source of nitric oxide (NO) with molybdopterin enzymes being identified as critical to this process. Of the molybdopterin enzymes identified as NO₂ ^- reductases, xanthine oxidoreductase (XOR) is the most extensively studied. Paradoxically, XOR generates oxidants and thus can contribute to oxidative stress under inflammatory conditions when the oxidase form (XO) of XOR is abundant. However, under similar inflammatory conditions XO has been associated with NO generation, especially when NO₂ ^- levels are elevated which begs the question: if reaction of nitrite with XO consumes electrons, then does it subsequently reduce oxidant generation? To address this question, electron paramagnetic resonance (EPR) was used, under controlled O₂ tensions, to assess superoxide (O₂ ^•-) generation by endothelial-bound XO plus xanthine and the resultant impact of introducing NO₂ ^-. Nitrite diminished XO-derived O₂ ^•- under hypoxia (1% O₂) whereas at 21% O₂, it had no impact. To confirm these results and discount contributions from the reaction of NO with O₂ ^•-, molecular O₂ consumption was assessed. The presence of NO₂ ^- decreased the rate of XO/xanthine-dependent O₂ consumption in a concentration-dependent manner with greater impact under hypoxic conditions (1% O₂) compared to 21% O₂. In a more biologic setting, NO₂ ^- also diminished XO-dependent H₂O₂ formation in murine liver homogenates supplemented with xanthine. Interestingly, nitrate (NO₃ ^-) did not alter XO-dependent O₂ consumption at either 21% or 1% O₂; yet it did slightly impact nitrite-mediated effects when present at 2:1 ratio vs. NO₂ ^-. When combined, these data: 1) show a significant indirect antioxidant function for NO₂ ^- by decreasing oxidant generation from XO, 2) demonstrate that both XO-derived H₂O₂ and O₂ ^•- production are diminished by the presence of NO₂ ^- and 3) incentivize further exploration of the difference between XO reaction with NO₂ ^- vs. NO₃ ^-.

Photodynamic Therapy as an Oxidative Anti-Tumor Modality: Negative Effects of Nitric Oxide on Treatment Efficacy

Anti-tumor photodynamic therapy (PDT) is a unique oxidative stress-based modality that has proven highly effective on a variety of solid malignancies. PDT is minimally invasive and generates cytotoxic oxidants such as singlet molecular oxygen (¹O₂). With high tumor site-specificity and limited off-target negative effects, PDT is increasingly seen as an attractive alternative or follow-up to radiotherapy or chemotherapy. Nitric oxide (NO) is a short-lived bioactive free radical molecule that is exploited by many malignant tumors to promote cell survival, proliferation, and metastatic expansion. Typically generated endogenously by inducible nitric oxide synthase (iNOS/NOS2), low level NO can also antagonize many therapeutic interventions, including PDT. In addition to elevating resistance, iNOS-derived NO can stimulate growth and migratory aggressiveness of tumor cells that survive a PDT challenge. Moreover, NO from PDT-targeted cells in any given population is known to promote such aggressiveness in non-targeted counterparts (bystanders). Each of these negative responses to PDT and their possible underlying mechanisms will be discussed in this chapter. Promising pharmacologic approaches for mitigating these NO-mediated responses will also be discussed.

Nitric Oxide-elicited Resistance to Antitumor Photodynamic Therapy via Inhibition of Membrane Free Radical-mediated Lipid Peroxidation

This review focuses on the ability of nitric oxide (NO) to antagonize antitumor photodynamic therapy (PDT). NO's anti-PDT effects were recognized relatively recently and require a better mechanistic understanding for developing new strategies to improve PDT efficacy. Many PDT sensitizers (PSs) are amphiphilic and tend to localize in membrane compartments of tumor cells. Unsaturated lipids in these compartments can undergo peroxidative degradation after PS photoactivation. Primary Type I (free radical) vs. Type II (singlet oxygen) photochemistry of lipid peroxidation is discussed, along with light-independent turnover of primary lipid hydroperoxides to free radical species. Chain lipid peroxidation mediated by the latter exacerbates membrane damage and cytotoxicity after a PDT challenge. Our studies have shown that NO from chemical donors can suppress chain peroxidation by intercepting lipid-derived free radical intermediates, thereby protecting cancer cells against photokilling. More recent evidence has revealed that inducible NO synthase (iNOS) is dramatically upregulated in several cancer cell types after a photodynamic challenge, and that iNOS-derived NO enhances resistance as well as growth and migratory aggressiveness of surviving cells. Chain breaking by NO and other possible NO-based resistance mechanisms are discussed, along with novel pharmacologic approaches for overcoming these negative effects.

Oxidative resistance of leukemic stem cells and oxidative damage to hematopoietic stem cells under pro-oxidative therapy

Leukemic stem cells (LSCs) and hematopoietic stem cells (HSCs) are both dependent on the hypoxic bone marrow (BM) microenvironment (also known as the BM niche). There is always fierce competition between the two types of cells, and the former exhibits a greater competitive advantage than the latter via multiple mechanisms. Under hypoxia, the dynamic balance between the generation and clearing of intracellular reactive oxygen species (ROS) is conducive to maintaining a quiescent state of cells. Quiescent LSCs can reside well in the BM niche, avoiding attack by chemotherapeutic agents, which is the cause of chemotherapeutic resistance and relapse in leukemia. HSCs acquire energy mainly through anaerobic glycolysis, whereas LSCs achieve energy metabolism largely through mitochondrial oxidative respiration. Mitochondria are the primary site of ROS generation. Thus, in theory, mitochondria-mediated respiration will cause an increase in ROS generation in LSCs and a higher intracellular oxidative stress level. The sensitivity of the cells to pro-oxidant drugs increases as well, which allows for the selective clearing of LSCs by pro-oxidative therapy. However, HSCs are also highly sensitive to changes in ROS levels, and the toxic effects of pro-oxidant drugs on HSCs poses a major challenge to pro-oxidative therapy in leukemia. Given the above facts, we reviewed studies on the oxidative resistance of LSCs and the oxidative damage to HSCs under pro-oxidative therapy. An in-depth investigation into the oxidative stress status and regulatory mechanisms of LSCs and HSCs in hypoxic environments will promote our understanding of the survival strategy employed by LSCs and the mechanism of the oxidative damage to HSCs in the BM niche, thus facilitating individualized treatment of leukemia patients and helping eliminate LSCs without disturbing normal hematopoietic cells.

Modulation of the Anti-Tumor Efficacy of Photodynamic Therapy by Nitric Oxide

Nitric oxide (NO) produced by nitric oxide synthase (NOS) enzymes is a free radical molecule involved in a wide variety of normophysiologic and pathophysiologic processes. Included in the latter category are cancer promotion, progression, and resistance to therapeutic intervention. Animal tumor photodynamic therapy (PDT) studies several years ago revealed that endogenous NO can reduce PDT efficacy and that NOS inhibitors can alleviate this. Until relatively recently, little else was known about this anti-PDT effect of NO, including: (a) the underlying mechanisms; (b) type(s) of NOS involved; and (c) whether active NO was generated in vascular cells, tumor cells, or both. In addressing these questions for various cancer cell lines exposed to PDT-like conditions, the author's group has made several novel findings, including: (i) exogenous NO can scavenge lipid-derived free radicals arising from photostress, thereby protecting cells from membrane-damaging chain peroxidation; (ii) cancer cells can upregulate inducible NOS (iNOS) after a PDT-like challenge and the resulting NO can signal for resistance to photokilling; (iii) photostress-surviving cells with elevated iNOS/NO proliferate and migrate/invade more aggressively; and (iv) NO produced by photostress-targeted cells can induce greater aggressiveness in non-targeted bystander cells. In this article, the author briefly discusses these various means by which NO can interfere with PDT and how this may be mitigated by use of NOS inhibitors as PDT adjuvants.

Role of nitric oxide in pathological responses of the lung to exposure to environmental/occupational agents

Conflicting evidence exists as to whether nitric oxide expresses damaging/inflammatory or antioxidant/anti-inflammatory properties. Data presented in this review indicate that in vitro or in vivo exposure to selected environmental or occupational agents, such as asbestos, silica, ozone or lipopolysaccharide, can result in up-regulation of inducible nitric oxide synthase by alveolar macrophages and pulmonary epithelial cells. In the case of silica exposure, evidence consistently supports a damaging/inflammatory role of nitric oxide and/or peroxynitrite in the pathogenesis of lung disease. Although conflicting data have been reported, the majority of published studies suggest that nitric oxide plays a damaging role in pulmonary injury resulting from exposure to ozone or asbestos. In contrast, most information supports an anti-inflammatory role of nitric oxide following exposure to lipopolysaccharide. Further investigation is required to elucidate fully the mechanisms involved in determining the role of nitric oxide in the initiation and progression of various pulmonary diseases.

Modification of DNA damage mechanisms by nitric oxide during ionizing radiation

Nitric oxide ((•)NO) is a very effective radiosensitizer of hypoxic mammalian cells. In vivo (•)NO may have effects on tumor vasculature and hence on tumor oxygenation and it may also interact with radiation-produced radicals to modify DNA lesions. Few studies have addressed this last aspect, and we report here specific base modifications that result from reaction of (•)NO with radicals in DNA bases and in plasmid DNA after irradiation. 2'-Deoxyxanthosine monophosphate and 2'-deoxy-8-azaguanosine monophosphate (8azadGMP) are formed upon γ-irradiation of 2'-deoxyguanosine monophosphate (dGMP) in the presence of micromolar levels of (•)NO in anoxia. In addition, the presence of (•)NO at physiological pH inhibits the formation of the well-described (•)OH-induced oxidation product of dGMP, 8-oxo-2'-deoxyguanosine monophosphate. Single-strand breaks are induced in plasmid DNA when γ-irradiated in anoxia, whereas in the presence of (•)NO the number of breaks is reduced by approximately threefold, and evidence is shown for the formation of 8azadGMP in these plasmids. The consequence of the base modifications by (•)NO are as yet unknown although additional breaks are revealed in irradiated plasmid DNA after treatment with glycosylases involved in base excision repair. V79-4 cells irradiated in anoxia show an enhancement in the number of γH2AX foci when (•)NO is present, particularly evident a few hours postirradiation, indicative of the formation of replication-induced DNA damage. We propose that the consequence of (•)NO-induced base modifications in anoxia contributes to its radiosensitization of cells.

Molecular Imaging of Brain Lipid Environment of Lymphocytes in Amyotrophic Lateral Sclerosis Using Magnetic Resonance Imaging and SECARS Microscopy

This paper highlights some of the key technologies of using two innovative molecular imaging modalites, magnetic resonance imaging (MRI) and nonlinear optical microscopy, for imaging intravenously injected ultra small paramagnetic iron oxide nanoparticles cross linked with antibodies (CLUSPIO) in the amyotrophic lateral sclerosis (ALS) experimental model in vivo or ex vivo, respectively. Intensive efforts have been made in investigating the causes of abnormalities in lipid metabolism, monitored in some neurodegenerative disorders systems. It has been shown that an abnormal accumulation of some common lipids in motor nerve cells may play a critical role in the development of amyotrophic lateral sclerosis. The presented experiments were performed on brain specimens from the transgenic rat model expressing multiple copies of mutated (G93A) human SOD-1 gene, after CD4+ lymphocytes were magnetically labeled with i.v.i. CLUSPIO antibodies. In vivo MRI revealed marked signal intensity enhancements in specific pathological regions of the ALS rat brain as compared to the wild type. Surface-enhanced coherent anti-Stokes Raman scattering (SECARS) microscopy indicated cellular interactions based on lipids association to anti-CD4 CLUSPIO.

The effects of moderately oxidised dietary oil with or without vitamin E supplementation on performance, nutrient digestibility, some blood traits, lipid peroxidation and antioxidant defence of male broilers

BACKGROUND

The experiment was conducted to determine the effects of dietary supplementation of oxidised oil with or without vitamin E on performance, nutrient digestibility, some blood traits, lipid peroxidation and antioxidant defence system of male broilers.

RESULTS

The supplementation of oxidised oil with or without vitamin E to the grower diets did not significantly affect performance, the pH and viscosity values of excreta and nutrient digestibilities in male broilers. Oxidised oil supplementation slightly increased plasma triglyceride and cholesterol concentrations but did not alter plasma glucose concentration. Although malondialdehyde (MDA) and nitric oxide concentrations tended to be higher in the oxidised oil group, these increases were not significant. Birds fed the diet containing oxidised oil had significantly lower superoxide dismutase (SOD) activity. However, no differences were observed in glutathione peroxidase (GSH-Px) activity and uric acid concentrations of broilers fed oxidised oil as compared to the control group. Dietary vitamin E supplementation decreased MDA concentration whereas increasing SOD activity, suggesting that vitamin E supplementation reduced susceptibility to lipid peroxidation.

CONCLUSION

The results showed that a milder oxidative stress occurred by supplementation of moderately oxidised oil to the diet of broilers and vitamin E supplementation had been helpful in alleviating lipid peroxidation.

Dietary flavonoid quercetin stimulates vasorelaxation in aortic vessels

Considerable epidemiological evidence indicates that dietary consumption of moderate levels of polyphenols decreases both the incidence of cardiovascular disease and the mortality associated with myocardial infarction. Molecular mechanisms of this cardiovascular protection remain uncertain but can involve changes in rates of nitric oxide (NO) generation by endothelial nitric oxide synthase (eNOS). We examined the vascular responses to quercetin using a combination of biochemical and vessel function criteria. Quercetin treatment for 30min enhanced relaxation of rat aortic ring segments. Moreover, the addition of L-NAME (100muM) or charybdotoxin (ChTx) blocked quercetin-mediated vasorelaxation thus demonstrating the effect was partially dependent on NOS and endothelium-derived hyperpolarizing factor (EDHF). Additionally, bovine aortic endothelial cells (BAEC) treated with quercetin showed a rapid increase of intracellular Ca(2+) concentrations as well as a dose- and time-dependent stimulation of eNOS phosphorylation with a concomitant increase in NO production. These results demonstrate that quercetin-mediated stimulation of eNOS phosphorylation increases NO bioavailability in endothelial cells and can thus play a role in the vascular protective effects associated with improved endothelial cell function.

Exploring mechanism of pioglitazone-induced memory restorative effect in experimental dementia

The present study was undertaken to investigate possible mechanism of pioglitazone-induced beneficial effect in memory deficits associated with experimental dementia. Dementia was induced in Swiss albino mice by administration of streptozotocin (STZ; 3 mg/kg administered intracerebroventricularly on 1st & 3rd day). Morris Water-Maze test was employed to assess learning and memory of the animals. Brain acetylcholinesterase (AChE) activity was measured by Ell Mann's method. Brain thiobarbituric acid reactive species (TBARS) levels and reduced glutathione (GSH) levels were measured by Ohokawa's and Beutler's method respectively to assess total oxidative stress. Blood glucose level was also measured. Streptozotocin (STZ) produced a significant decrease in water-maze performance of mice hence reflecting loss of learning and memory. Pioglitazone (20 mg/kg p.o. daily for 14 days) successfully attenuated STZ-induced memory deficits, without any significant per se effect on blood glucose levels. Higher levels of brain AChE activity, TBARS and lower levels of GSH were observed in STZ treated animals, which were significantly attenuated by pioglitazone. Further, the noted beneficial effect of pioglitazone on STZ-induced dementia was significantly abolished by pre-treatment of nitric oxide (NO) synthase inhibitor L-NAME (3 mg/kg i.p.) manifested in the terms of decrease in water-maze performance and increase in brain AChE activity as well as oxidative stress. It is concluded that anti-dementic effect of pioglitazone may involve central cholinergic, oxidative and NO pathways.

Inhibitory and enhancing effects of NO on H(2)O(2) toxicity: dependence on the concentrations of NO and H(2)O(2)

Nitric oxide (NO) has been shown to both enhance hydrogen peroxide (H(2)O(2)) toxicity and protect cells against H(2)O(2) toxicity. In order to resolve this apparent contradiction, we here studied the effects of NO on H(2)O(2) toxicity in cultured liver endothelial cells over a wide range of NO and H(2)O(2) concentrations. NO was generated by spermine NONOate (SpNO, 0.001-1 mM), H(2)O(2) was generated continuously by glucose/glucose oxidase (GOD, 20-300 U/l), or added as a bolus (200 microM). SpNO concentrations between 0.01 and 0.1 mM provided protection against H(2)O(2)-induced cell death. SpNO concentrations >0.1 mM were injurious with low H(2)O(2) concentrations, but protective at high H(2)O(2) concentrations. Protection appeared to be mainly due to inhibition of lipid peroxidation, for which SpNO concentrations as low as 0.01 mM were sufficient. SpNO in high concentration (1 mM) consistently raised H(2)O(2) steady-state levels in line with inhibition of H(2)O(2) degradation. Thus, the overall effect of NO on H(2)O(2) toxicity can be switched within the same cellular model, with protection being predominant at low NO and high H(2)O(2) levels and enhancement being predominant with high NO and low H(2)O(2) levels.

NO* chemistry: a diversity of targets in the cell

NO(*) alone is a poorly reactive species; however, it is able to undergo secondary reactions to form highly oxidizing and nitrating species, NO(2)(*), N(2)O(3), and ONOO(-). These secondary reactive nitrogen species (RNS) are capable of modifying a diversity of biomolecular structures in the cell. The chemical properties of individual RNS will be discussed, along with their ability to react with amino acids, metal cofactors, lipids, cholesterol, and DNA bases and sugars. Many of the identified RNS-induced modifications have been observed both in vitro and in vivo. Several of these chemical modifications have been attributed with a functional role in the cell, such as the modulation of enzyme activity. Other areas in the field will be discussed, including the ability of RNS to react with metabolites, RNA, and substrates in the mitochondrion, and the cellular removal/repair of RNS-modified structures.

Nitric oxide-induced resistance to lethal photooxidative damage in a breast tumor cell line

The long-term effects of nitric oxide (NO) on cell susceptibility to photodynamic killing have been studied, using a human breast tumor line (COH-BR1). Subconfluent cells were exposed to a nonlethal dose of spermine NONOate (SPNO, 0.2 mM) and 20 h later were metabolically sensitized with protoporphyrin IX (PpIX) by incubating with 5-aminolevulinic acid. PpIX overproduced in mitochondria was allowed to diffuse to peripheral sites, including plasma membrane, after which a photooxidative challenge was imposed. Active (but not decomposed) SPNO made cells substantially more resistant to necrotic photokilling than non-SPNO-treated controls. A similar response to a tert-butyl hydroperoxide challenge was observed. Hyperresistance was detected approximately 8 h post-SPNO, maximized after approximately 20 h, and reflected diminished oxidant accumulation, as determined with 2',7'-dichlorofluorescein. Intracellular free iron determined with the fluorescent probe calcein rose to approximately 160% of the control level 6 h after SPNO, but declined to approximately 70% after 24 h. Immunoblot analyses revealed a rapid early (approximately 2 h post-NO) increase in heme oxygenase-1 level, followed by a gradual (4-20 h post-NO) increase in ferritin. Upregulation of these proteins is consistent with a cytoprotective mechanism involving mobilization of "signaling" iron. Preactivated RAW 264.7 macrophages on microporous inserts also induced a long-term photoresistance in underlying PpIX-sensitized COH-BR1 cells. This response was abolished by L-NAME, indicating that NO from induced nitric oxide synthase was involved. The NO effects described are entirely novel in the context of photooxidative stress and provide new insights into how NO might affect antitumor photodynamic therapy (PDT).

Nitric oxide consumption through lipid peroxidation in brain cell suspensions and homogenates

Mechanisms which inactivate NO (nitric oxide) are probably important in governing the physiological and pathological effects of this ubiquitous signalling molecule. Cells isolated from the cerebellum, a brain region rich in the NO signalling pathway, consume NO avidly. This property was preserved in brain homogenates and required both particulate and supernatant fractions. A purified fraction of the particulate component was rich in phospholipids, and NO consumption was inhibited by procedures that inhibited lipid peroxidation, namely a transition metal chelator, the vitamin E analogue Trolox and ascorbate oxidase. The requirement for the supernatant was accounted for by its content of ascorbate which catalyses metal-dependent lipid peroxidation. The NO-degrading activity of the homogenate was mimicked by a representative mixture of brain lipids together with ascorbate and, under these conditions, the lipids underwent peroxidation. In a suspension of cerebellar cells, there was a continuous low level of lipid peroxidation, and consumption of NO by the cells was decreased by approx. 50% by lipid-peroxidation inhibitors. Lipid peroxidation was also abolished when NO was supplied at a continuously low rate (approximately 100 nM/min), which explains why NO consumption by this process is saturable. Part of the activity remaining after the inhibition of lipid peroxidation was accounted for by contaminating red blood cells, but there was also another component whose activity was greatly enhanced when the cells were maintained under air-equilibrated conditions. A similar NO-consuming process was present in cerebellar glial cells grown in tissue culture but not in blood platelets or leucocytes, suggesting a specialized mechanism.

Nitric oxide as a cellular antioxidant: a little goes a long way

Nitric oxide (NO*) is an effective chain-breaking antioxidant in free radical-mediated lipid oxidation (LPO). It reacts rapidly with peroxyl radicals as a sacrificial chain-terminating antioxidant. The goal of this work was to determine the minimum threshold concentration of NO* required to inhibit Fe2+ -induced cellular lipid peroxidation. Using oxygen consumption as a measure of LPO, we simultaneously measured nitric oxide and oxygen concentrations with NO* and O2 electrodes. Ferrous iron and dioxygen were used to initiate LPO in docosahexaenoic acid-enriched HL-60 and U937 cells. Bolus addition of NO* (1.5 microM) inhibited LPO when the NO* concentration was greater than 50 nM. Similarly, using (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate as a NO* donor we found that an average steady-state NO* concentration of at least 72 +/- 9 nM was required to blunt LPO. As long as the concentration of NO* was above 13 +/- 8 nM the inhibition was sustained. Once the concentration of NO* fell below this value, the rate of lipid oxidation accelerated as measured by the rate of oxygen consumption. Our model suggests that a continuous production of NO* that would yield a steady-state concentration of only 10-20 nM is capable of inhibiting Fe2+ -induced LPO.

Early onset of lipofuscin accumulation in dystrophin-deficient skeletal muscles of DMD patients and mdx mice

Lipofuscin, the so-called ageing pigment, is formed by the oxidative degradation of cellular macromolecules by oxygen-derived free radicals and redox-active metal ions. Usually it accumulates in post-mitotic, long-lived cells such as neurons and cardiac muscle cells. In contrast, it is rarely seen in either normal or diseased skeletal muscle fibres. In this paper, we report that lipofuscin accumulates at an early age in both human and murine dystrophic muscles. Autofluorescent lipofuscin granules were localized, using confocal laser scanning microscopy and electron microscopy, in dystrophin-deficient skeletal muscles of X chromosome-linked young Duchenne muscular dystrophy (DMD) patients and of mdx mice at various ages after birth. Age-matched normal controls were studied similarly. Autofluorescent lipofuscin granules were observed in dystrophic biceps brachii muscles of 2-7-year-old DMD patients where degeneration and regeneration of myofibres are active, but they were rarely seen in age-matched normal controls. In normal mice, lipofuscin first appears in diaphragm muscles nearly 20 weeks after birth but in mdx muscles it occurs much earlier, 4 weeks after birth, when the primary degeneration of dystrophin-deficient myofibres is at a peak. Lipofuscin accumulation increases with age in both mdx and normal controls and is always higher in dystrophic muscles than in age-matched normal controls. At the electron microscopical level, it was confirmed that the localisation of autofluorescent granules observed by light microscopy in dystrophin-deficient skeletal muscles coincided with lipofuscin granules in myofibres and myosatellite cells, and in macrophages accumulating around myofibres and in interstitial connective tissue. Our results agree with previous biochemical and histochemical data implying increased oxidative damages in DMD and mdx muscles. They indicate that dystrophin-deficient myofibres are either more susceptible to oxidative stress, or are subjected to higher intra- or extracellular oxidative stress than normal controls, or both.

Direct Measurement of Nitric Oxide and Oxygen Partitioning into Liposomes and Low Density Lipoprotein

Nitric oxide (*NO) has been proposed to play a relevant role in modulating oxidative reactions in lipophilic media like biomembranes and lipoproteins. Two factors that will regulate *NO reactivity in the lipid milieu are its diffusion and solubility, but there is no data concerning the actual diffusion (D) and partition coefficients (KP) of *NO in biologically relevant hydrophobic phases. Herein, a "equilibrium-shift" method was designed to directly determine the *NO and O2 partition coefficients in liposomes and low density lipoprotein (LDL) relative to water. It was found that *NO partitions 4.4- and 3.4-fold in liposomes and LDL, respectively, whereas O2 behaves similarly with values of 3.9 and 2.9, respectively. In addition, actual diffusion coefficients in these hydrophobic phases were determined using fluorescence quenching and found that *NO diffuses approximately 2 times slower than O2 in the core of LDL and 12 times slower than in buffer (DNOLDL=3.9 x 10(-6) cm2 s(-1),DO2LDL=7.0 x 10(-6) cm2 s(-1),DNObuffer=DO2buffer=4.5 x 10(-5) cm2 s(-1)). The influence of *NO and O2 partitioning and diffusion in membranes and lipoproteins on *NO reaction with lipid radicals and auto-oxidation is discussed. Particularly, the 3-4-fold increase in O2 and *NO concentration within biological hydrophobic phases provides quantitative support for the idea of an accelerated auto-oxidation of *NO in lipid-containing structures, turning them into sites of enhanced local production of oxidant and nitrosating species.

Effects of triazolopyrimidine on lipid peroxidation and nitric oxide levels in the corticosteroid-impaired healing of rat tracheal anastomoses

Corticosteroids are used to reduce the oedema and prevent scar tissue formation of the upper airways by their ability to inhibit influx of inflammatory cells, limit capillary permeability and block collagen synthesis in the early stages of wound healing. Triazolopyrimidine (Trapidil) is an antiplatelet agent that acts in part as a phosphodiesterase inhibitor and as a competitive inhibitor of the platelet-derived growth factor (PDGF) receptor. Trapidil, with its vasodilator and NO releasing effect may have some potential to diminish the tissue injury. This study was carried out to evaluate the effects of trapidil (triazolopyrimidine) on lipid peroxidation and nitric oxide in the corticosteroid-impaired healing of tracheal anastomoses. Thirty-four adult Wistar rats were divided into five groups. The animals underwent tracheal transection and primary anastomoses. The groups were assigned as follows: group I, control, (GI, n = 6); group II, sham, (GII, n = 6); group III, dexamethasone, 0.1 mg kg(-1) twice daily intramuscularly, (GIII, n = 8); group IV, trapidil, 6 mg kg(-1) twice daily intraperitoneally (GIV, n = 7); group V, dexamethasone, 0.1 mg kg(-1) plus trapidil, 6 mg kg(-1) twice daily (GV, n = 7), for 1 week. After 1 week, anastomotic healing was assessed by measurement of bursting pressure, evaluation of histopathology, measurement of MDA and nitrite/nitrate levels. In GIII, GIV and GV bursting pressures resulted in significantly reduced anastomotic strength compared to the controls (p < 0.001 for all groups). The difference between bursting pressures of GIII and GIV was not found to be statistically significant (p = 0.966). In regard to fibroblast proliferation and collagen content, a significant difference was found between GIII and GI (p < 0.01), A significant difference was also found when GIV and GV were compared to GIII (p < 0.01). MDA and nitrite/nitrate levels were found to be higher in GIII when compared to all other groups. MDA levels of GIV and GV rats were found to be lower than GIII (p < 0.001, for both groups). The nitrite/nitrate levels of GIV and GV rats were found to be lower than GIII (p < 0.05), and higher than GI (p < 0.001). Trapidil may be useful for its preventive effects on lipid peroxidation and possible increases in NO in cases with corticosteroid-impaired healing of trachea anastomoses.

The nitric oxide synthase inhibitor N(G)-nitro-L-arginine decreases defibrillation-induced free radical generation

OBJECTIVES

to demonstrate that nitric oxide (NO) contributes to free radical generation after epicardial shocks and to determinethe effect of a nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NNA), on free radical generation.

BACKGROUND

Free radicals are generated by direct current shocks for defibrillation. NO reacts with the superoxide (O2*-) radical to for peroxynitrite (O = NOO-), which is toxic and initiates additional free radical generation. The contribution of NO to free radical generation after defibrillation is not fully defined.

METHODS AND RESULTS

Fourteen open chest dogs were studied. In the initial eight dogs, 40 J damped sinusoidal monophasic epicardial shocks was administered. Using electron paramagnetic resonance, we monitored the coronary sinus concentration of ascorbate free radical (Asc*-), a measure of free radical generation (total oxidative flux). Epicardial shocks were repeated after L-NNA, 5 mg/kg IV. In six additional dogs, immunohistochemical staining was done to identify nitrotyrosine, a marker of reactive nitrogen species-mediated injury, in post-shock myocardial tissue. Three of these dogs received L-NNA pre-shock. After the initial 40 J shock, Asc*- rose 39 +/- 2.5% from baseline. After L-NNA infusion, a similar 40 J shock caused Asc*- to increase only 2 +/- 3% form baseline (P < 0.05, post-L-NNA shock versus initial shock). Nitrotyrosine staining was more prominent in control animals than dogs receiving L-NNA, suggesting prevention of O = NOO- formation.

CONCLUSION

NO contributes to free radical generation and nitrosative injury after epicardial shocks; NOS inhibitors decrease radical generation by inhibiting the production of O = NOO-.

Endogenous production and exogenous exposure to nitric oxide augment doxorubicin cytotoxicity for breast cancer cells but not cardiac myoblasts

We studied the effect of nitric oxide (*NO) on the anticancer activity of doxorubicin. When MCF-7 human breast cancer cells were exposed to an aqueous solution of *NO delivered as a bolus 30 min prior to doxorubicin, the cytotoxic effect as measured in a clonogenic assay was increased (doxorubicin alone, 40% survival, doxorubicin plus *NO, 5% survival). The *NO donor diethylamine nitric oxide, but not inactivated donor, also yielded an increase in doxorubicin cytotoxicity. The sequence was important since the simultaneous application of *NO with doxorubicin yielded only a small augmentation of effect, and the exposure of the cells to doxorubicin prior to the *NO obliterated the augmentation. Prior depletion of glutathione by incubation of the cells for 24h with D,L-buthionine-S,R-sulfoximine (BSO) further increased the cytotoxicity so that BSO plus *NO plus doxorubicin killed all of the clones. MCF-7 cells transduced with inducible nitric oxide synthase gene (iNOS) through an adenoviral vector overexpressed iNOS and produced increased amounts of nitrite, an indicator of increased *NO production. These iNOS transduced cells were more susceptible to doxorubicin than vector control or wild-type cells. Cell cycle progression of iNOS transduced cells was not different from controls. Likewise, iNOS transduction resulted in no change in cellular glutathione levels. For comparison, we examined the effect of iNOS transduction on the sensitivity of MCF-7 to edelfosine, a membrane-localizing anticancer drug without direct DNA interaction. Insertion of the iNOS had no effect on killing of the MCF-7 cells by this ether lipid class drug. We also tested the effect of iNOS transduction on doxorubicin sensitivity of H9c2 rat heart-derived myoblasts. We found no augmentation of cytotoxicity by *NO, and this observation offers potential therapeutic tumor selectivity by using *NO with doxorubicin. Therefore, we conclude that *NO produced intracellularly by iNOS overexpression or delivered as a bolus sensitizes human breast cancer cells in culture to doxorubicin, but not to a cardiac cell line or to edelfosine. This augmentation is not due to a modulation of cell cycle distribution or measurable cellular glutathione resulting from the transduction.

Prevention of doxorubicin-induced damage to rat heart myocytes by arginine analog nitric oxide synthase inhibitors and their enantiomers

The clinical use of the widely used anticancer drug doxorubicin is limited by a dose-dependent cardiotoxicity. Doxorubicin can be reduced to its semiquinone free radical form by nitric oxide synthases (NOS). The release of lactate dehydrogenase (LDH) from doxorubicin-treated neonatal cardiac rat myocytes was used as a model of doxorubicin-induced cardiotoxicity. The NOS inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA) protected myocytes from doxorubicin as did their non-inhibitory enantiomers D-NAME and D-NMMA. Thus, these agents did not protect by inhibiting NOS. L-NAME, which does not act at the reductase domain of NOS, also had no effect on the production of the doxorubicin semiquinone by myocytes. Nitric oxide (NO) EPR spin trapping experiments showed that L-NAME reacted with various biological reducing agents to produce NO. Ascorbic acid was highly effective in reacting with L-NAME to produce NO, while glutathione, NADPH, and NADH were much less effective. Thus, these guanadino-substituted analogs of L-arginine likely protected through their ability to slowly produce NO by reaction with intracellular ascorbic acid. Thus, some caution must be exercised in their use. NO may exert its protective effects either by directly acting as an antioxidant or through some other NO-dependent pathway.

The effect of L-carnitine on the prevention of experimentally induced myringosclerosis in rats

The objective of this study was to investigate the possible effect of L-carnitine on the prevention of experimentally induced myringosclerosis. Twenty Sprague-Dawley rats were bilaterally myringotomized. The rats were divided into two groups randomly: group 1 which were intraperitoneally administered saline and group 2 which were intraperitoneally administered L-carnitine. Blood samples were collected for biochemical evaluation and the tympanic membranes were harvested after 28 days. Histopathological and immunohistochemical evaluation were done under light microscopy. The mean malondialdehyde levels were 3.9+/-0.9 in group 2, and 7.9+/-1.1 in group 1 (P<0.001), nitric oxide levels were 25.6+/-6.4 in group 2 and 30.8+/-8.2 in group 1 (P=0.14) and acetylcholinesterase was 1035+/-60 in group 2 and 678+/-35 in group 1 (P=0.001). Myringosclerosis was more frequent and severe in group 1 than group 2 (P<0.007). Immunoreactivity was seen in 16 of 20 tympanic membranes in group 2 and six of 20 tympanic membranes in group 1 (P=0.005). We conclude that L-carnitine diminishes the occurrence of myringosclerosis in rats after myringotomy possibly by antioxidant activity and decreasing the formation of reactive oxygen species.

Is nitric oxide (NO) an antioxidant or a prooxidant for lipid peroxidation?

Antioxidant and prooxidant effects of nitric oxide (NO) on lipid peroxidation in aqueous and non-aqueous media were examined. In an aqueous solution, NO did not induce peroxidation of unoxidized methyl linoleate (ML) and suppressed the radical initiator-induced oxidation of ML. NO suppressed the Fe(II) ion-induced oxidation of mouse liver microsomes. NO reduced the O2 consumption during the radical initiator-induced oxidation of linoleic acid in an aqueous medium. NO conversion into NO2- in an aqueous medium was not affected by unoxidized ML and was slightly reduced by peroxidizing ML. On the other hand, as well as pure NO2, NO induced peroxidation of unoxidized ML in n-hexane in a dose-dependent fashion. NO did not suppress the radical initiator-induced oxidation of ML in n-hexane. Nitrogen oxide species (NO2 or N2O3) formed by autoxidation was dramatically lost in n-hexane in the presence of unoxidized ML. The results indicated that NO terminated lipid peroxidation in an aqueous medium, whereas NO induced lipid peroxidatiton in a non-aqueous medium. Hence, NO showed both antioxidant and prooxidant effects on lipid peroxidation depending on the solvents.

Effects of iNOS-related NO on hearts exposed to liposoluble iron

Inducible nitric oxide synthase (iNOS) protects heart against ischemia/reperfusion injury. However, it is unknown whether the beneficial effects of iNOS are mediated by the interaction of NO with radical oxygen species (ROS). To address this issue, we examined the effects of liposoluble iron-induced ROS generation in isolated perfused hearts from rats treated with lipopolysaccharide (LPS). LPS administration (10 mg/kg, i.p., 6 h before heart removal) induced iNOS expression and increased NO production as indicated by a 3-fold elevation of nitrite level in coronary effluents relative to control hearts. An enhanced expression of hemeoxygenase 1 protein was also observed in septic hearts compared to control. Iron-induced perfusion and contractile deficits were ameliorated by LPS with more important coronary than myocardial benefits. In iron-loaded hearts, oxidative stress as measured by the 2,3 dihydroxybenzoic acid/salicylic acid concentration ratio in cardiac tissue was 23% lower in septic than in control heart although the difference did not reach significance. In addition, the presence of the NO synthase inhibitor N-nitro-L-arginine in the perfusion medium totally blocked NO production but did not reverse the protective effects of LPS. The results indicate that LPS protects from iron-induced cardiac dysfunction by mechanisms independent on ex vivo NO production and suggest that NO acts as a trigger rather than a direct mediator of the cardioprotective effects of LPS in heart exposed to iron.

NO-aspirin: mechanism of action and gastrointestinal safety

Nitric oxide-releasing aspirins are new chemical entities obtained by adding a nitric oxide-releasing moiety to aspirin. NCX-4016 is the prototype of this family of molecules. NCX-4016 consists of the parent molecule (aspirin) linked to a 'spacer' via an ester linkage, which is in turn connected to a nitric oxide-releasing moiety. Both aspirin and nitric oxide moieties of NCX-4016 contribute to its effectiveness, the latter occurring via both cyclic guanosyl monophosphate-dependent and -independent mechanisms. In vitro studies have shown that NCX-4016 inhibits platelet aggregation induced by aspirin-sensitive (arachidonic acid) and aspirin-insensitive (thrombin) agonist. In contrast to aspirin, NCX-4016 exerts a multilevel regulation of inflammatory target, including caspase-1 and NF-kappaB. This broad spectrum of activities translates to an increased potency of this drug in modulating cardiovascular inflammation. Human studies have shown, that while nitric oxide-aspirin maintains its anti-thrombotic activity, it spares the gastrointestinal tract. Indeed, a 7-day course of NCX-4016 results in 90% reduction of gastric damage caused by equimolar doses of aspirin. Further studies are ongoing to define whether this superior anti-inflammatory and anti-thrombotic profile translates in clinical benefits in patients with cardiovascular diseases.

The nitric oxide synthase inhibitor N(G)-nitro-L-arginine decreases defibrillation-induced free radical generation

OBJECTIVES

To demonstrate that nitric oxide (NO) contributes to free radical generation after epicardial shocks and to determine the effect of a nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NNA), on free radical generation.

BACKGROUND

Free radicals are generated by direct current shocks for defibrillation. NO reacts with the superoxide (O(2).(-)) radical to form peroxynitrite (O=NOO(-)), which is toxic and initiates additional free radical generation. The contribution of NO to free radical generation after defibrillation is not fully defined.

METHODS AND RESULTS

Fourteen open chest dogs were studied. In the initial eight dogs, 40 J damped sinusoidal monophasic epicardial shocks was administered. Using electron paramagnetic resonance, we monitored the coronary sinus concentration of ascorbate free radical (Ascz.(-)), a measure of free radical generation (total oxidative flux). Epicardial shocks were repeated after L-NNA, 5 mg/kg IV. In six additional dogs, immunohistochemical staining was done to identify nitrotyrosine, a marker of reactive nitrogen species-mediated injury, in post-shock myocardial tissue. Three of these dogs received L-NNA pre-shock. After the initial 40 J shock, Ascz.(-) rose 39+/-2.5% from baseline. After L-NNA infusion, a similar 40 J shock caused Ascz.(-) to increase only 2+/-3% from baseline (P<0.05, post-L-NNA shock versus initial shock). Nitrotyrosine staining was more prominent in control animals than dogs receiving L-NNA, suggesting prevention of O=NOO(-) formation.

CONCLUSIONS

NO contributes to free radical generation and nitrosative injury after epicardial shocks; NOS inhibitors decrease radical generation by inhibiting the production of O=NOO(-).

Chain-breaking Antioxidant and Cytoprotective Action of Nitric Oxide on Photodynamically Stressed Tumor Cells¶

Nitric oxide (.NO) has a multitude of physiological roles, including the ability to protect cells against oxidant-induced killing, e.g. by inhibiting caspase-mediated apoptosis or by intercepting damaging free radicals derived from membrane lipids. The purpose of this study was to test the hypothesis that low flux .NO acting in the latter fashion can enhance tumor-cell resistance to photodynamic killing, specifically that sensitized by 5-aminolevulinic acid (ALA)-derived protoporphyrin IX (PpIX). Preliminary model experiments with iron-ascorbate-treated, PpIX-sensitized liposomes showed that spermine NONOate (SPER/NO)-derived .NO had no effect on photoinduced accumulation of primary singlet oxygen adducts, e.g. the cholesterol hydroperoxide 5 alpha-OOH, but dose-dependently inhibited the buildup of free radical-generated oxidation products arising from one-electron turnover of primary peroxides. In subsequent studies, breast tumor COH-BR1 cells in serum-free medium were treated with 1 mM ALA for 15 min and then without ALA for 3.75 h, allowing biogenerated PpIX to diffuse to extramitochondrial sites, including plasma membrane. Cells were irradiated in the absence or presence of SPER/NO and compared for peroxidative damage and Hoechst-assessed viability after 5 h in the dark. Iron-stimulated necrotic photo-killing and accumulation of chain lipid peroxidation products were observed, and this was inhibited strongly by SPER/NO, but not by decomposed SPER/NO, confirming that .NO was the active agent. When introduced after irradiation, .NO became progressively less inhibitory, consistent with ongoing but waning free-radical activity. These findings provide new insights into the possible role of .NO in tumor resistance to ALA-photodynamic therapy and other photo-dynamic treatments.

The effects of dexamethasone on lipid peroxidation and nitric oxide levels on the healing of tracheal anastomoses: an experimental study in rats

Corticosteroids are shown to have deleterious effects on wound healing for various tissues. Arginine metabolism and nitric oxide (NO) synthesis play an important role in many aspects of inflammation and wound healing. The study was designed to evaluate the relationship of dexamethasone impaired healing of tracheal anastomoses to NO metabolism and lipid peroxidation. Forty-two adult Wistar rats were randomly divided into five groups. The animals underwent tracheal transection and primary anastomoses. The groups were assigned as follows: Group I (GI) (sham, N = 6); Group II (GII) (control, N = 6); Group III (GIII), dexamethasone, 0.1 mg kg(-1) per day, intramuscularly for a week (N = 10); Group IV (GIV), dexamethasone, 1 mg kg(-1) per day, intramuscularly for a week (N = 10); Group V (GV), dexamethasone, 6 mg kg(-1) intramuscularly as a single dose (N = 10). After 7 days, bursting pressure was used to evaluate anastomotic healing. Serum nitrite/nitrate and malondialdehyde (MDA) levels were measured as an index of NO synthesis and lipid peroxidation, respectively. The bursting pressure significantly decreased in GIII and GIV when compared to the control group. The difference between GIII and GIV was also statistically significant. Nitrite/nitrate and MDA levels of GIII were found to be significantly higher than the control group. Also, the difference was found to be statistically significant between GIII and GIV in regard to nitrite/nitrate levels. The present study demonstrates that daily administration of dexamethasone for a week inhibits NO synthesis in a dose-dependent manner on tracheal anastomotic healing. Besides the generally accepted evaluation parameters including bursting pressure and hydoxyproline content; NO and MDA levels may be helpful in the assessment of wound healing especially for the investigation of impairment mechanism.

Vascular protective actions of a nitric oxide aspirin analog in both in vitro and in vivo models of diabetes mellitus

BACKGROUND

Defective endothelium-dependent relaxation is observed in experimental and human diabetes mellitus. The nature of this defect is not fully understood but may involve decreased nitric oxide (NO) bioactivity due to enhanced production of reactive oxygen species (ROS). In this paper, we examine the benefits and actions of a novel NO-donating, antioxidant called 2-acetoxybenzoic acid 2-(2-nitrooxymethyl) phenyl ester, and denoted as NCX4016, on NO-mediated endothelium-dependent relaxation in normal arteries exposed to acute elevations in glucose or in arteries derived from chronic diabetic animals.

MATERIAL AND METHODS

Intrinsic free radical scavenging by NO-NSAIDs in solution were evaluated using electron paramagnetic resonance (EPR) spectroscopy and spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In acute studies, normal rat aortas were exposed in tissue culture for 18 h to 5.5 mM or 40 mM in the presence or absence of NCX4016, a NO-donating NSAID unrelated to aspirin (NCX2216) or aspirin. Vascular reactivity of thoracic aortic rings to endothelium-dependent relaxation to acetylcholine in vitro was determined. For chronic hyperglycemia, diabetes was induced in rats by intravenous injection with streptozotocin. Vascular reactivity of thoracic aortic rings to endothelium-dependent relaxation to acetylcholine in vitro was determined after 8 wks in untreated animals or animals chronically-treated with NCX4016. Antioxidant efficacy in vivo was determined by measurement of plasma isoprostanes and by nuclear binding activity of NF-kappaB in nuclear fractions of aortae.

RESULTS

Incubation with NCX4016 and NCX2216 produced a concentration-dependent inhibition of DMPO-OH formation indicating scavenging of hydroxyl radicals (HO(*)). In contrast, little efficacy to scavenge superoxide anion radicals was noted. Acute incubation of normal arteries with elevated glucose concentration caused inhibition of normal relaxation to acetylcholine. This impairment was prevented by co-incubation with NCX4106 but not by mannitol, the parent compound (aspirin) or by NCX2216. In addition, chronic treatment with NCX4016 prevented the development of defective endothelium-dependent relaxation to acetylcholine. This protection did not occur as a result to any changes in blood glucose concentration or hemoglobin glycation. Treatment with NCX4016 did decrease the elevation in plasma isoprostanes and normalized the diabetes-induced increase in NF-kappaB binding activity in nuclear fractions derived from aortic tissue.

CONCLUSIONS

Collectively, these studies suggest that antioxidant interventions using NO-donating NSAIDs may provide an important novel therapeutic strategy to protect the diabetic endothelium.

Comparing beta-carotene, vitamin E and nitric oxide as membrane antioxidants

Singlet oxygen initiates lipid peroxidation via a nonfree radical mechanism by reacting directly with unsaturated lipids to form lipid hydroperoxides (LOOHs). These LOOHs can initiate free radical chain reactions leading to membrane leakage and cell death. Here we compare the ability and mechanism by which three small-molecule membrane antioxidants (beta-carotene, alpha-tocopherol and nitric oxide) inhibit lipid peroxidation in membranes. We demonstrate that beta-carotene provides protection against singlet oxygen-mediated lipid peroxidation, but does not slow free radical-mediated lipid peroxidation. Alpha-Tocopherol does not protect cells from singlet oxygen, but does inhibit free radical formation in cell membranes. Nitric oxide provides no direct protection against singlet oxygen exposure, but is an exceptional chain-breaking antioxidant as evident from its ability to blunt oxygen consumption during free radical-mediated lipid peroxidation. These three small-molecule antioxidants appear to have complementary mechanisms for the protection of cell membranes from detrimental oxidations.

Protection of primary glial cells by grape seed proanthocyanidin extract against nitrosative/oxidative stress

Previous studies showed that proanthocyanidins provide potent protection against oxidative stress. Here we investigate the effects of grape seed proanthocyanidin extract (GSPE) as a novel natural antioxidant on the generation and fate of nitric oxide (NO) in rat primary glial cell cultures. GSPE treatment (50 mg/L) increased NO production (measured by NO(2-) assay) by stimulation of the inducible isoform of NOS. However, GSPE failed to affect the LPS/IFN-gamma-induced NO production or iNOS expression. Similar responses were found in the murine macrophage cell line RAW264.7. GSPE did not show any effect on dihydrodichlorofluorescein fluorescence (ROS marker with high sensitivity toward peroxynitrite) either in control or in LPS/IFN-gamma-induced glial cultures even in the presence of a superoxide generator (PMA). GSPE treatment alone had no effect on the basal glutathione (GSH) status in glial cultures. Whereas the microglial GSH level declined sharply after LPS/IFN-gamma treatment, the endogenous GSH pool was protected when such cultures were treated additionally with GSPE, although NO levels did not change. Glial cultures pretreated with GSPE showed higher tolerance toward application of hydrogen peroxide (H(2)O(2)) and tert-butylhydroperoxide. Furthermore, GSPE-pretreated glial cultures showed improved viability after H(2)O(2)-induced oxidative stress demonstrated by reduction in lactate dehydrogenase release or propidium iodide staining. We showed that, in addition to its antioxidative property, GSPE enhances low-level production of intracellular NO in primary rat astroglial cultures. Furthermore, GSPE pretreatment protects the microglial GSH pool during high output NO production and results in an elevation of the H(2)O(2) tolerance in astroglial cells.

Mechanisms of circulatory and intestinal barrier dysfunction during whole body hyperthermia

This work tested the hypotheses that splanchnic oxidant generation is important in determining heat tolerance and that inappropriate.NO production may be involved in circulatory dysfunction with heat stroke. We monitored colonic temperature (T(c)), heart rate, mean arterial pressure, and splanchnic blood flow (SBF) in anesthetized rats exposed to 40 degrees C ambient temperature. Heating rate, heating time, and thermal load determined heat tolerance. Portal blood was regularly collected for determination of radical and endotoxin content. Elevating T(c) from 37 to 41.5 degrees C reduced SBF by 40% and stimulated production of the radicals ceruloplasmin, semiquinone, and penta-coordinate iron(II) nitrosyl-heme (heme-.NO). Portal endotoxin concentration rose from 28 to 59 pg/ml (P < 0.05). Compared with heat stress alone, heat plus treatment with the nitric oxide synthase (NOS) antagonist N(omega)-nitro-L-arginine methyl ester (L-NAME) dose dependently depressed heme-.NO production and increased ceruloplasmin and semiquinone levels. L-NAME also significantly reduced lowered SBF, increased portal endotoxin concentration, and reduced heat tolerance (P < 0.05). The NOS II and diamine oxidase antagonist aminoguanidine, the superoxide anion scavenger superoxide dismutase, and the xanthine oxidase antagonist allopurinol slowed the rates of heme-.NO production, decreased ceruloplasmin and semiquinone levels, and preserved SBF. However, only aminoguanidine and allopurinol improved heat tolerance, and only allpourinol eliminated the rise in portal endotoxin content. We conclude that hyperthermia stimulates xanthine oxidase production of reactive oxygen species that activate metals and limit heat tolerance by promoting circulatory and intestinal barrier dysfunction. In addition, intact NOS activity is required for normal stress tolerance, whereas overproduction of.NO may contribute to the nonprogrammed splanchnic dilation that precedes vascular collapse with heat stroke.

Detailed methods for the quantification of nitric oxide in aqueous solutions using either an oxygen monitor or EPR

The interest in nitric oxide has grown with the discovery that it has many biological functions. This has heightened the need for methods to quantify nitric oxide. Here we report two separate methods for the quantification of aqueous stock solutions of nitric oxide. The first is a new method based on the reaction of nitric oxide with oxygen in liquid phase (*NO + O2 + 2H2O --> 4HNO2); an oxygen monitor is used to measure the consumption of oxygen by nitric oxide. This method offers the advantages of being both simple and direct. The presence of nitrite or nitrate, frequent contaminants in nitric oxide stock solutions, does not interfere with the quantification of nitric oxide. Measuring the disappearance of dissolved oxygen, a reactant, in the presence of known amounts of nitric oxide has provided verification of the 4:1 stoichiometry of the reaction. The second method uses electron paramagnetic resonance spectroscopy (EPR) and the nitric oxide trap [Fe2+-(MGD)2], (MGD = N-methyl-D-glucamine dithiocarbamate). The nitrosyl complex is stable and easily quantitated as a room temperature aqueous solution. These two methods are validated with Sievers 280 Nitric Oxide Analyzer and cross-checked with standards using UV-Vis spectroscopy. The practical lower limits for measuring the concentration of nitric oxide using the oxygen monitor approach and EPR are approximately 3 microM and 500 nM, respectively. Both methods provide straightforward approaches for the standardization of nitric oxide in solution.

Glutathione-dependent regulation of nitric oxide production in isolated rat hepatocyte suspensions

Freshly isolated suspensions of rat parenchymal liver cells (hepatocytes) spontaneously produce large amounts of nitrite following collagenase isolation. Our previous studies indicate that nitrite production is associated with the expression of inducible nitric oxide synthase (iNOS) and reflects NO production. Depletion of glutathione (GSH) with diethylmaleate (DEM) inhibited nitrite production, and this inhibition was time-dependent. DEM was more effective in blocking nitrite production if it was added within the first 1 hr of the start of the incubation. The reducing agent dithiothreitol (DTT) and the alkylating agent ethyl methanesulfonate (EMS) also inhibited hepatocyte nitrite production, and this inhibition was also greatest if they were added within 1 hr of initiating the incubation. However, EMS added at 3 hr still reduced 6-hr nitrite production by about 70%. This reduction in nitrite production by EMS added at 3 hr may be due to the direct modification of thiol groups on the iNOS protein because we have determined that iNOS activity is inhibited by the sulfhydryl modifying reagent N-ethylmaleimide (NEM). Western blots also indicate that the iNOS protein is expressed when EMS is added at 3 hr. The addition of DEM, DTT, or EMS at 0 time greatly reduced the levels of cellular iNOS mRNA relative to controls as determined by quantitative RT-PCR. Based on our results with mRNA levels, both DTT and depletion of cellular GSH appear to inhibit the early signaling events leading to iNOS expression and suggest that the control of iNOS induction in hepatocytes is sensitive to the thiol redox status of the cell.