Iron released by sodium nitroprusside contributes to heme oxygenase-1 induction via the cAMP-protein kinase A-mitogen-activated protein kinase pathway in RAW 264.7 cells

Nitric oxide augments signaling for contraction in hypoxic pulmonary arterial smooth muscle—Implications for hypoxic pulmonary hypertension

Introduction: Hypoxic persistent pulmonary hypertension in the newborn (PPHN) is usually treated with oxygen and inhaled nitric oxide (NO), both pulmonary arterial relaxants. But treatment failure with NO occurs in 25% of cases. We previously demonstrated that 72 h exposure to hypoxia, modeling PPHN, sensitized pulmonary artery smooth muscle cells (PASMC) to the contractile agonist thromboxane and inhibited relaxant adenylyl cyclase (AC) activity.

Methods: In this study, we examined the effects of sodium nitroprusside (SNP), as NO donor, on the thromboxane-mediated contraction and NO-independent relaxation pathways and on reactive oxygen species (ROS) accumulation in PASMC. In addition, we examined the effect of the peroxynitrite scavenger 5,10,15,20-Tetrakis (4-sulfonatophenyl)porphyrinato Iron (III) (FeTPPS) on these processes.

Results: Exposure of PASMC to 72 h hypoxia increased total intracellular ROS compared to normoxic control cells and this was mitigated by treatment of cells with either SNP or FeTPPS. Total protein nitrosylation was increased in hypoxic PASMC compared to controls. Both normoxic and hypoxic cells treated with SNP exhibited increased total protein nitrosylation and intracellular nitrite; this was reduced by treatment with FeTPPS. While cell viability and mitochondrial number were unchanged by hypoxia, mitochondrial activity was decreased compared to controls; addition of FeTPPS did not alter this. Basal and maximal mitochondrial metabolism and ATP turnover were reduced in hypoxic PASMC compared to controls. Hypoxic PASMC had higher basal Ca2+, and a heightened peak Ca2+ response to thromboxane challenge compared to controls. Addition of SNP further elevated the peak Ca2+ response, while addition of FeTPPS brought peak Ca2+ response down to control levels. AC mediated relaxation was impaired in hypoxic PASMC compared to controls but was normalized following treatment with FeTPPS. Addition of SNP inhibited adenylyl cyclase activity in both normoxic and hypoxic PASMC. Moreover, addition of the Ca2+ chelator BAPTA improved AC activity, but the effect was minimal.

Discussion: We conclude that NO independently augments contraction and inhibits relaxation pathways in hypoxic PASMC, in part by a mechanism involving nitrogen radical formation and protein nitrosylation. These observations may partially explain impaired effectiveness of NO when treating hypoxic pulmonary hypertension.

Direct reprogramming of cardiomyocytes into cardiac Purkinje-like cells

Currently, there are no treatments that ameliorate cardiac cell death, the underlying basis of cardiovascular disease. An unexplored cell type in cardiac regeneration is cardiac Purkinje cells; specialized cells from the cardiac conduction system (CCS) responsible for propagating electrical signals. Purkinje cells have tremendous potential as a regenerative treatment because they may intrinsically integrate with the CCS of a recipient myocardium, resulting in more efficient electrical conduction in diseased hearts. This study is the first to demonstrate an effective protocol for the direct reprogramming of human cardiomyocytes into cardiac Purkinje-like cells using small molecules. The cells generated were genetically and functionally similar to native cardiac Purkinje cells, where expression of key cardiac Purkinje genes such as CNTN2, ETV1, PCP4, IRX3, SCN5a, HCN2 and the conduction of electrical signals with increased velocity was observed. This study may help to advance the quest to finding an optimized cell therapy for heart regeneration.

The effects of gasotransmitters on bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), which remains a major clinical problem for preterm infants, is caused mainly by hyperoxia, mechanical ventilation and inflammation. Many approaches have been developed with the aim of decreasing the incidence of or alleviating BPD, but effective methods are still lacking. Gasotransmitters, a type of small gas molecule that can be generated endogenously, exert a protective effect against BPD-associated lung injury; nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) are three such gasotransmitters. The protective effects of NO have been extensively studied in animal models of BPD, but the results of these studies are inconsistent with those of clinical trials. NO inhalation seems to have no effect on BPD, although side effects have been reported. NO inhalation is not recommended for BPD treatment in preterm infants, except those with severe pulmonary hypertension. Both CO and H₂S decreased lung injury in BPD rodent models in preclinical studies. Another small gas molecule, hydrogen, exerts a protective effect against BPD. The nuclear factor erythroid-derived 2 (Nrf2)/heme oxygenase-1 (HO-1) axis seems to play a central role in the protective effect of these gasotransmitters on BPD. Gasotransmitters play important roles in mammals, but further clinical trials are needed to explore their effects on BPD.

Role of GS28 in sodium nitroprusside-induced cell death in cervical carcinoma cells

Golgi S-nitro-N-acetylpenicillamine receptor complex 1 (GS28) has been implicated in Golgi vesicle transport. We examined the role of GS28 and its molecular mechanisms in sodium nitroprusside (SNP)-induced cell death using GS28 siRNA (siGS28)-transfected HeLa cells. Significant inhibition of cytotoxicity was observed in the cells treated with SNP, and photodegraded SNP showed equal cytotoxicity to SNP. Pretreatment with an ERK inhibitor or siErk1 cotransfection blocked the inhibition in cytotoxicity. Additionally, increased phosphorylation of ERK was maintained in the cells treated with SNP, and Nrf2 level was dependent on ERK phosphorylation. However, pretreatment with a pan-caspase inhibitor had no effect on cytotoxicity or procaspase-3 level. Pretreatment with an autophagy inhibitor or siATG5 cotransfection blocked the inhibition of cytotoxicity. The changes of LC3 corresponded to that in siErk1-cotransfected cells. These data suggest that GS28 has an inductive role in SNP-induced cell death via inhibition of ERK, leading to inhibition of autophagic processes in HeLa cells.

Burkholderia pseudomallei modulates host iron homeostasis to facilitate iron availability and intracellular survival

Background

The control over iron homeostasis is critical in host-pathogen-interaction. Iron plays not only multiple roles for bacterial growth and pathogenicity, but also for modulation of innate immune responses. Hepcidin is a key regulator of host iron metabolism triggering degradation of the iron exporter ferroportin. Although iron overload in humans is known to increase susceptibility to Burkholderia pseudomallei, it is unclear how the pathogen competes with the host for the metal during infection. This study aimed to investigate whether B. pseudomallei, the causative agent of melioidosis, modulates iron balance and how regulation of host cell iron content affects intracellular bacterial proliferation.

Principal findings

Upon infection of primary macrophages with B. pseudomallei, expression of ferroportin was downregulated resulting in higher iron availability within macrophages. Exogenous modification of iron export function by hepcidin or iron supplementation by ferric ammonium citrate led to increased intracellular iron pool stimulating B. pseudomallei growth, whereas the iron chelator deferoxamine reduced bacterial survival. Iron-loaded macrophages exhibited a lower expression of NADPH oxidase, iNOS, lipocalin 2, cytokines and activation of caspase-1. Infection of mice with the pathogen caused a diminished hepatic ferroportin expression, higher iron retention in the liver and lower iron levels in the serum (hypoferremia). In vivo administration of ferric ammonium citrate tended to promote the bacterial growth and inflammatory response, whereas limitation of iron availability significantly ameliorated bacterial clearance, attenuated serum cytokine levels and improved survival of infected mice.

Conclusions

Our data indicate that modulation of the cellular iron balance is likely to be a strategy of B. pseudomallei to improve iron acquisition and to restrict antibacterial immune effector mechanisms and thereby to promote its intracellular growth. Moreover, we provide evidence that changes in host iron homeostasis can influence susceptibility to melioidosis, and suggest that iron chelating drugs might be an additional therapeutic option.

Iron is an essential nutrient for many bacterial pathogens. A sufficient availability is linked to bacterial proliferation and pathogenicity. The host requires iron for cellular functions including innate immune defense mechanisms. Consequently, the control over iron homeostasis plays an important role in the course of infection. Burkholderia pseudomallei is an environmental bacterium ubiquitous in soil and water surfaces causing the disease melioidosis with a wide range of signs and symptoms including localized, pulmonary, or bloodstream infections. Conditions with increased iron stores, such as thalassemia, are considered to increase the risk to acquire melioidosis. Here we show that infection with the pathogen triggers downregulation of the major cellular iron exporter inducing intracellular iron retention and stimulation of bacterial proliferation. Experimental iron overload appears to predispose to infection with B. pseudomallei, whereas iron deficiency confers relative resistance to melioidosis. These effects of changed iron metabolism on the course of infection may be ascribed to modifications in the host immune response and direct effects on bacterial growth, respectively. Thus, the B. pseudomallei-driven alteration of cellular iron traffic leading to increased iron availability can promote its intracellular growth, and treatment with iron chelators together with antibiotics might be an appropriate strategy to control infection.

Signaling through reactive oxygen and nitrogen species is differentially modulated in sunflower seedling root and cotyledon in response to various nitric oxide donors and scavengers<sup/>

Sodium nitroprusside (SNP), diethylenetriamine NONOate (DETA), S-nitroso-n-acetyl-D,L- penicillamine (SNAP), and 4-(p-methoxyphenyl)-1,3,2- Oxathiazolylium-5-olate (CAY) exhibit differential NO releasing ability in aqueous solution and hemoglobin is a more efficient NO quencher than cPTIO in solution. DETA releases 16% more NO compared with SNP in solution. Various NO donors (SNP, DETA, SNAP, and CAY) also bring about a differential but concentration-dependent increase in endogenous NO in seedling cotyledons and roots. Two-day old, dark-grown seedling roots exhibit 95%, 77%, 59% and 45% increase in NO content in presence of each of 500 µM of DETA, SNAP, CAY and SNP, respectively, relative to control. NO accumulation in the tissue system as a response to NO donors is reflected in terms of corresponding peroxynitrite accumulation. Release of cyanide and free iron as byproducts of SNP dissociation in solution limits its usefulness as an NO donor. SNP leads to profuse ROS generation in sunflower seedling roots. Light is not a pre-requisite for NO generation from SNP. Present work also demonstrates the usefulness of hemoglobin over cPTIO as NO scavenger. Hemoglobin brings about increasing NO quenching with its increasing concentration from 2.5 to 10 µM. Greater sensitivity of the root system to the NO donor/scavenger treatments is evident, it being in direct contact with the molecules in the incubation/ growth medium. This differential effect does not seem to be significantly transmitted to the cotyledons (long-distance signaling).

Dominant roles of Fenton reaction in sodium nitroprusside-induced chondrocyte apoptosis

Sodium nitroprusside (SNP) has been widely used as an exogenous nitric oxide (NO) donor to explore the molecular mechanism of NO-mediated chondrocyte apoptosis during the latest two decades. We have recently found that NO-independent ROS play a key role in SNP-induced apoptosis in rabbit chondrocytes. This study aims to investigate what kind of ROS and how the reliable ROS mediators mediate the SNP-induced apoptosis. Data shows that SNP and NO-exhausted SNP (SNPex) induced ROS production or cytotoxicity to identically degree. SNP induced a marked increase in iron ions, superoxide anion (O2(•-)), hydrogen peroxide (H2O2) and hydroxyl radical ((•)OH) level. H2O2 scavenger (CAT) and (•)OH scavenger (DMSO) significantly inhibited SNP-induced chondrocyte apoptosis. Iron ions chelator (DFO) entirely prevented SNP-induced chondrocyte apoptosis. In contrast, O2(•-) scavenger (SOD) and glutathione depletion agent (BSO) promoted SNP-induced cytotoxicity. K3[Fe(CN)6] exhibited no cytotoxicity, and H2O2 alone up to 250µM or iron ions alone up to 90µM is non-cytotoxic to chondrocytes. Combination of 25µM FeSO4 and 100µM H2O2 in the presence of BSO induced chondrocyte death similar to SNP treatment. Fetal bovine serum (FBS) enhanced iron ions release from SNP and the cytotoxicity of SNP. Our data shows that the extracellular Fenton reaction between iron ions released from SNP and H2O2 induced by SNP plays a key role in SNP-induced chondrocyte apoptosis. Overall, our results indicate that the potential of SNP to increase iron ions and ROS should be especially considered for some biological functions and, possibly, also for clinical applications of this drug.

Efficient Generation of Cardiac Purkinje Cells from ESCs by Activating cAMP Signaling

Dysfunction of the specialized cardiac conduction system (CCS) is associated with life-threatening arrhythmias. Strategies to derive CCS cells, including rare Purkinje cells (PCs), would facilitate models for mechanistic studies and drug discovery and also provide new cellular materials for regenerative therapies. A high-throughput chemical screen using CCS:lacz and Contactin2:egfp (Cntn2:egfp) reporter embryonic stem cell (ESC) lines was used to discover a small molecule, sodium nitroprusside (SN), that efficiently promotes the generation of cardiac cells that express gene profiles and generate action potentials of PC-like cells. Imaging and mechanistic studies suggest that SN promotes the generation of PCs from cardiac progenitors initially expressing cardiac myosin heavy chain and that it does so by activating cyclic AMP signaling. These findings provide a strategy to derive scalable PCs, along with insight into the ontogeny of CCS development.

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A chemical screen was carried out for compounds that induce cardiac conduction cells

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Two ESC reporter lines were used to identify lead hits

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Sodium nitroprusside efficiently generated scalable amounts of PC-like cells

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By activating cAMP signaling, PCs are derived from cardiac progenitors

Sodium nitroprusside suppresses male fertility in vitro

Sodium nitroprusside is a nitric oxide donor involved in the regulation of the motility, hyperactivation, capacitation, and acrosome reaction (AR) of spermatozoa. However, the molecular mechanism underlying this regulation has not yet been elucidated. Therefore, this study was designed to evaluate the molecular basis for the effects of sodium nitroprusside on different processes in spermatozoa and its consequences on subsequent oocyte fertilization and embryo development. In this in vitro study, mouse spermatozoa were incubated with various concentrations of sodium nitroprusside (1, 10, and 100 μM) for 90 min. Our results showed that sodium nitroprusside inhibited sperm motility and motion kinematics in a dose-dependent manner by significantly enhancing intracellular iron and reactive oxygen species (ROS), and decreasing Ca(2+), and adenosine triphosphate levels in spermatozoa. Moreover, short-term exposure of spermatozoa to sodium nitroprusside increased the tyrosine phosphorylation of sperm proteins involved in PKA-dependent regulation of intracellular calcium levels, which induced a robust AR. Finally, sodium nitroprusside significantly decreased the rates of fertilization and blastocyst formation during embryo development. Based on these results, we propose that sodium nitroprusside increases ROS production and precocious AR may alter overall sperm physiology, leading to poor fertilization and compromised embryonic development.

Acetylcholinesterase inhibitory activity of pigment echinochrome A from sea urchin Scaphechinus mirabilis

Echinochrome A (EchA) is a dark-red pigment of the polyhydroxynaphthoquinone class isolated from sea urchin Scaphechinus mirabilis. Acetylcholinesterase (AChE) inhibitors are used in the treatment of various neuromuscular disorders, and are considered as strong therapeutic agents for the treatment of Alzheimer's disease (AD). Although EchA is clinically used to treat ophthalmic diseases and limit infarct formation during ischemia/ reperfusion injury, anti-AChE effect of EchA is still unknown. In this study, we investigated the anti-AChE effect of EchA in vitro. EchA and its exhausted form which lost anti-oxidant capacity did not show any significant cytotoxicy on the H9c2 and A7r5 cells. EchA inhibited AChE with an irreversible and uncompetitive mode. In addition, EchA showed reactive oxygen species scavenging activity, particularly with nitric oxide. These findings indicate new therapeutic potential for EchA in treating reduced acetylcholine-related diseases including AD and provide an insight into developing new AChE inhibitors.

Identification of nitric oxide as an endogenous inhibitor of 26S proteasomes in vascular endothelial cells

The 26S proteasome plays a fundamental role in almost all eukaryotic cells, including vascular endothelial cells. However, it remains largely unknown how proteasome functionality is regulated in the vasculature. Endothelial nitric oxide (NO) synthase (eNOS)-derived NO is known to be essential to maintain endothelial homeostasis. The aim of the present study was to establish the connection between endothelial NO and 26S proteasome functionality in vascular endothelial cells. The 26S proteasome reporter protein levels, 26S proteasome activity, and the O-GlcNAcylation of Rpt2, a key subunit of the proteasome regulatory complex, were assayed in 26S proteasome reporter cells, human umbilical vein endothelial cells (HUVEC), and mouse aortic tissues isolated from 26S proteasome reporter and eNOS knockout mice. Like the other selective NO donors, NO derived from activated eNOS (by pharmacological and genetic approach) increased O-GlcNAc modification of Rpt2, reduced proteasome chymotrypsin-like activity, and caused 26S proteasome reporter protein accumulation. Conversely, inactivation of eNOS reversed all the effects. SiRNA knockdown of O-GlcNAc transferase (OGT), the key enzyme that catalyzes protein O-GlcNAcylation, abolished NO-induced effects. Consistently, adenoviral overexpression of O-GlcNAcase (OGA), the enzyme catalyzing the removal of the O-GlcNAc group, mimicked the effects of OGT knockdown. Finally, compared to eNOS wild type aortic tissues, 26S proteasome reporter mice lacking eNOS exhibited elevated 26S proteasome functionality in parallel with decreased Rpt2 O-GlcNAcylation, without changing the levels of Rpt2 protein. In conclusion, the eNOS-derived NO functions as a physiological suppressor of the 26S proteasome in vascular endothelial cells.

Suppression of Heme Oxygenase-1 by Prostaglandin E2-Protein Kinase A-A-Kinase Anchoring Protein Signaling Is Central for Augmented Cyclooxygenase-2 Expression in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

PURPOSE

Prostaglandin (PG) E2 is an immunomodulatory lipid mediator generated mainly via the cyclooxygenase-2 (COX-2) pathway from arachidonic acid at sites of infection and inflammation. A positive feedback loop of PGE2 on COX-2 expression is critical for homeostasis during toll-like receptor (TLR)-mediated inflammatory processes. The mechanism of PGE2-regulated COX-2 expression remains poorly understood. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) contributes to the anti-inflammatory, anti-oxidant and anti-apoptotic response against environmental stress.

METHODS

We explored the involvement of HO-1 on PGE2 regulation of LPS-induced COX-2 expression in RAW 264.7 macrophages.

RESULTS

LPS-induced COX-2 expression in RAW 264.7 macrophages was enhanced by exogenous PGE2 or cyclic AMP (cAMP) analogue and was suppressed by a COX inhibitor (indomethacin), a protein kinase A (PKA) inhibitor (KT5720), and A kinase anchoring protein (AKAP) disruptors (Ht31 and RIAD). This result suggests that the stimulatory effects of endogenous and exogenous PGE2 on COX-2 expression are mediated by a cAMP-PKA-AKAP-dependent pathway. The induction of HO-1 was observed in LPS-stimulated RAW 264.7 macrophages. This induction was suppressed by exogenous PGE2 and enhanced by blockage of the endogenous PGE2 effect by the PKA inhibitor or AKAP disruptors. In addition, HO-1 induction by the HO activator copper protoporphyrin suppressed LPS-induced COX-2 expression, which was restored by the addition of exogenous PGE2. The induction of HO-1 inhibited LPS-induced NF-κB p-65 nuclear expression and translocation.

CONCLUSIONS

AKAP plays an important role in PGE2 regulation of COX-2 expression, and the suppression of HO-1 by PGE2-cAMP-PKA-AKAP signaling helps potentiate the LPS-induced COX-2 expression through a positive feedback loop in RAW 264.7 macrophages.

Paradoxical protection from atherosclerosis and thrombosis in a mouse model of sickle cell disease

Sickle cell disease (SCD) is associated with vascular complications including premature stroke. The role of atherothrombosis in these vascular complications is unclear. To determine the effect of SCD on atherosclerosis and thrombosis, mice with SCD along with controls were generated by transplantation of bone marrow from mice carrying the homozygous sickle cell mutation (Hbb(hβs/hβs) ) or wild-type mice (Hbb(+/+) ) into C57BL6/J or apolipoprotein E deficient (Apoe(-/-) ) recipient mice. At the time of sacrifice, 23-28 weeks following bone marrow transplantation, anaemia, reticulocytosis, and splenomegaly were present in mice receiving Hbb(hβs/hβs) bone marrow compared with control mice. Analysis of atherosclerosis involving the aortic root revealed reduced atherosclerotic lesion area with reduced macrophage content and increased collagen content in Apoe(-/-) , Hbb(hβs/hβs) mice compared to Apoe(-/-) , Hbb(+/+) mice. In a carotid thrombosis model, the time to thrombosis was prolonged in Hbb(hβs/hβs) mice compared to Hbb(+/+) mice. This apparent protective effect of SCD on atherosclerosis and thrombosis was diminished by inhibition of heme oxygenase-1 (HMOX1) using zinc protoporphyrin IX. We conclude that SCD in mice is paradoxically protective against atherosclerosis and thrombosis, highlighting the complexity of vascular events in SCD. This protective effect is at least partially mediated by induction of HMOX1.

Nitric oxide donors as neuroprotective agents after an ischemic stroke-related inflammatory reaction

Cerebral ischemia initiates a cascade of detrimental events including glutamate-associated excitotoxicity, intracellular calcium accumulation, formation of Reactive oxygen species (ROS), membrane lipid degradation, and DNA damage, which lead to the disruption of cellular homeostasis and structural damage of ischemic brain tissue. Cerebral ischemia also triggers acute inflammation, which exacerbates primary brain damage. Therefore, reducing oxidative stress (OS) and downregulating the inflammatory response are options that merit consideration as potential therapeutic targets for ischemic stroke. Consequently, agents capable of modulating both elements will constitute promising therapeutic solutions because clinically effective neuroprotectants have not yet been discovered and no specific therapy for stroke is available to date. Because of their ability to modulate both oxidative stress and the inflammatory response, much attention has been focused on the role of nitric oxide donors (NOD) as neuroprotective agents in the pathophysiology of cerebral ischemia-reperfusion injury. Given their short therapeutic window, NOD appears to be appropriate for use during neurosurgical procedures involving transient arterial occlusions, or in very early treatment of acute ischemic stroke, and also possibly as complementary treatment for neurodegenerative diseases such as Parkinson or Alzheimer, where oxidative stress is an important promoter of damage. In the present paper, we focus on the role of NOD as possible neuroprotective therapeutic agents for ischemia/reperfusion treatment.

Cellular signalling pathways mediating dilation of porcine pial arterioles to adenosine A₂A receptor activation

AIMS

Adenosine is a potent vasodilator contributing to cerebral blood flow regulation during metabolic stress. However, the distribution of adenosine receptor subtypes and underlying signalling mechanisms for dilation of pial arterioles remain unclear. The present study aimed at addressing these issues.

METHODS AND RESULTS

Isolated porcine pial arterioles were subjected to study of vasomotor function, localization of adenosine receptors, and production of nitric oxide (NO). Concentration-dependent vasodilation to adenosine was inhibited by A₂A receptor antagonist ZM241385 but not by A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. A₂A receptors were detected in endothelium and smooth muscle of pial arterioles via immunohistochemistry. Adenosine significantly increased arteriolar production of NO, and the induced dilation was insensitive to KATP channel blocker glibenclamide but was attenuated by endothelial denudation, NO synthase inhibitor L-NAME, or guanylyl cyclase inhibitor ODQ in a similar manner. Both inward rectifier potassium (Kir) channel inhibitor barium and cAMP signalling inhibitor Rp-8-Br-cAMPS attenuated adenosine-induced dilation. In the presence of L-NAME or the absence of endothelium, addition of Rp-8-Br-cAMPS but not barium further reduced adenosine-induced responses. Barium diminished endothelium-independent vasodilation to NO donor sodium nitroprusside. Comparable to the adenosine-induced response, vasodilation to A₂A receptor agonist CGS21680 was attenuated by endothelial removal, ZM241385, L-NAME, barium, or Rp-8-Br-cAMPS, but not by glibenclamide.

CONCLUSION

Adenosine evokes dilation of porcine pial arterioles via parallel activation of endothelial and smooth muscle A₂A receptors. Stimulation of endothelial NO production activates smooth muscle guanylyl cyclase for vasodilation by opening Kir channels. Adenosine also activates smooth muscle cAMP signalling leading to vasodilation.

Sodium nitroprusside toxicity in Drosophila melanogaster: delayed pupation, reduced adult emergence, and induced oxidative/nitrosative stress in eclosed flies

The toxicity of sodium nitroprusside (SNP) was tested on the Drosophila melanogaster model system. Fly larvae were raised on food supplemented with SNP at concentrations of 0.01-1.5 mM. Food supplementation with SNP caused a developmental delay in flies and reduced adult eclosion. Biochemical analyses such as levels of oxidative stress markers and activities of antioxidant and associated enzymes were carried out on 2-day-old flies emerged from control and SNP-fed larvae. Larval exposure to SNP resulted in lower activities of aconitase and catalase in adult flies relative to the control cohort. However, larval treatment with SNP led to higher carbonyl protein content and higher activities of superoxide dismutase, glucose-6-phosphate dehydrogenase, thioredoxin reductase, and glutathione-S-transferase in flies. Among the parameters tested, aconitase activity and developmental end points may be useful early indicators of toxicity caused by SNP. The study also suggests that the toxicity of SNP may arise not just from its direct effects, but also from its decomposition products such as nitric oxide and iron ions.

H(2)O(2) preferentially synergizes with nitroprusside to induce apoptosis associated with superoxide dismutase dysregulation in human melanoma irrespective of p53 status: Antagonism by o-phenanthroline

The pro-oxidant hydrogen peroxide (H(2)O(2)) is converted to a reactive oxygen species by transition metals like iron. Since mutations in the p53 tumor suppressor gene contribute to drug resistance, we used genetically-matched human C8161 melanoma harbouring wt or DN-R175H mutant p53, to investigate the influence of p53 status on the potentiation of H(2)O(2) toxicity by: (a) intact sodium nitroprusside or nitroferricyanide (SNP), (b) its light-exhausted NO-depleted form (lex-SNP), (c) potassium ferricyanide, or (d) ferric ammonium sulphate. Whereas single treatments with SNP or H(2)O(2) were partly cytotoxic, preferentially potentiation of H(2)O(2) toxicity was evidenced with intact or lex-SNP. No comparable increase of H(2)O(2) toxicity was induced by ferricyanide, ferric ammonium sulphate or S-nitroso-N-acetyl penicillamine (SNAP), a known NO donor lacking iron. Immune blotting revealed apoptosis-associated PARP cleavage induced by [SNP+H(2)O(2)] irrespective of p53 status. This correlated with an eightfold induction of [Mn-SOD; SOD2] in wt p53 melanoma cells, and with a super-induction of the same enzyme reciprocal with loss of [Cu,Zn-SOD; SOD1], in mutant p53 cells. All these changes were antagonized by the anti-oxidant N-acetylcysteine or the iron chelator o-phenanthroline. We hypothesize that superoxide dismutase imbalance and iron-dependent redox changes involving OH species generated from a Fenton reaction between [SNP+H(2)O(2)], may be important in this anti-tumor activity. Although tumor drug resistance is frequently associated with DN-p53 mutations, our data shows for the first time the preferential ability of SNP to enhance H(2)O(2) toxicity, irrespective of p53 status.

Regulation of P-glycoprotein in renal proximal tubule epithelial cells by LPS and TNF-alpha

During endotoxemia, the ATP-dependent drug efflux pump P-glycoprotein (Abcb1/P-gp) is upregulated in kidney proximal tubule epithelial cells. The signaling pathway through which lipopolysaccharide (LPS) or tumor necrosis factor-α (TNF-α) regulates P-gp expression and activity was investigated further in the present study. Exposure of rat kidney proximal tubule cells to TNF-α alone or TNF-α and LPS increased P-gp gene and protein expression levels and efflux activity, suggesting de novo P-gp synthesis. Upon exposure to TNF-α in combination with LPS, P-gp activity in renal proximal tubule cells is increased under influence of nitric oxide (NO) produced by inducible NO synthase. Upon exposure to TNF-α alone, P-gp upregulation seems to involve TLR4 activation and nuclear factor kappaB (NF-κB) translocation, a pathway that is likely independent of NO. These findings indicate that at least two pathways regulate P-gp expression in the kidney during endotoxemia.

Lipocalin-2 is an autocrine mediator of reactive astrocytosis

Astrocytes, the most abundant glial cell type in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. In response to a brain injury, astrocytes proliferate and become hypertrophic with an increased expression of intermediate filament proteins. This process is collectively referred to as reactive astrocytosis. Lipocalin 2 (lcn2) is a member of the lipocalin family that binds to small hydrophobic molecules. We propose that lcn2 is an autocrine mediator of reactive astrocytosis based on the multiple roles of lcn2 in the regulation of cell death, morphology, and migration of astrocytes. lcn2 expression and secretion increased after inflammatory stimulation in cultured astrocytes. Forced expression of lcn2 or treatment with LCN2 protein increased the sensitivity of astrocytes to cytotoxic stimuli. Iron and BIM (Bcl-2-interacting mediator of cell death) proteins were involved in the cytotoxic sensitization process. LCN2 protein induced upregulation of glial fibrillary acidic protein (GFAP), cell migration, and morphological changes similar to characteristic phenotypic changes termed reactive astrocytosis. The lcn2-induced phenotypic changes of astrocytes occurred through a Rho-ROCK (Rho kinase)-GFAP pathway, which was positively regulated by nitric oxide and cGMP. In zebrafishes, forced expression of rat lcn2 gene increased the number and thickness of cellular processes in GFAP-expressing radial glia cells, suggesting that lcn2 expression in glia cells plays an important role in vivo. Our results suggest that lcn2 acts in an autocrine manner to induce cell death sensitization and morphological changes in astrocytes under inflammatory conditions and that these phenotypic changes may be the basis of reactive astrocytosis in vivo.

Role of heme oxygenase-1 in the cardioprotective effects of erythropoietin during myocardial ischemia and reperfusion

We have recently demonstrated that erythropoietin (EPO) protects cardiomyocytes from apoptosis during myocardial ischemia-reperfusion (I/R). The objective of the present study was to investigate the role of heme oxygenase (HO)-1 in the antiapoptotic effects of EPO. Primary cultures of neonatal mouse cardiomyocytes were subjected to anoxia-reoxygenation (A/R). Pretreatment with EPO significantly reduced apoptosis in A/R-treated cells. This reduction in apoptosis was preceded by an increase in the mRNA and protein expression of HO-1. Selective inhibition of HO-1 using chromium mesoporphyrin (CrMP) significantly diminished the ability of EPO to inhibit apoptosis. Cotreatment of EPO with SB-202190, an inhibitor of p38 activation, blocked the EPO-mediated HO-1 expression and antiapoptotic effects, suggesting a p38-dependent mechanism. The in vivo significance of p38 and HO-1 as mediators of EPO's cardioprotection was investigated in mice subjected to myocardial I/R. Pretreatment with EPO decreased infarct size as well as I/R-induced apoptosis in wild-type mice. However, these effects were significantly diminished in HO-1(-/-) mice. Furthermore, EPO given during ischemia reduced infarct size in mice subjected to I/R, and this effect was blocked by CrMP treatment in wild-type mice. Moreover, inhibition of p38 diminished the cardioprotective effects of EPO. We conclude that upregulation of HO-1 expression via p38 signaling contributes to EPO-mediated cardioprotection during myocardial I/R.

Reactive oxygen species mediate p53 activation and apoptosis induced by sodium nitroprusside in SH-SY5Y cells

Sodium nitroprusside (SNP) is a water-soluble iron nitrosyl complex clinically used as a powerful vasodilator for treatment of hypertension; and, in basic research, it has been used to mainly investigate the cytotoxic effects of nitrosative stress. Although NO is considered a pharmacologically active molecule, not all of the biological effects of SNP are dependent on its NO moiety. To elucidate the molecular executioner(s) responsible for SNP cytotoxicity, this study determines the involvement of oxidative stress in p53 activation and apoptotic induction elicited by SNP in SH-SY5Y neuroblastoma cells. We demonstrate that proapoptotic activity of SNP is independent of NO production, because SNP and its 2-day light-exhausted compound SNP(ex) trigger apoptosis to the same extent. We provide evidence for the occurrence of oxidative stress and oxidative damage during both SNP and SNP(ex) exposure and demonstrate that iron-derived reactive oxygen species (ROS) are the genuine mediators of their cytotoxicity. We show that p53 is equally activated upon both SNP and SNP(ex) treatments. Moreover, as demonstrated by small interfering RNA experiments, we indicate its primary role in the induction of apoptosis, suggesting the ineffectiveness of NO in its engagement. The attenuation of p53 levels, obtained by oxy-radical scavengers, is consistent with the recovery of cell viability and ROS decrease, demonstrate that SNP-mediated p53 activation is an event triggered by ROS and/or ROS-mediated damages. Together, our results suggest that investigations of the physiopathological effects of SNP should consider the role of ROS, other than NO, particularly in some conditions such as apoptotic induction and p53 activation.

A dual role of lipocalin 2 in the apoptosis and deramification of activated microglia

Activated microglia are thought to undergo apoptosis as a self-regulatory mechanism. To better understand molecular mechanisms of the microglial apoptosis, apoptosis-resistant variants of microglial cells were selected and characterized. The expression of lipocalin 2 (lcn2) was significantly down-regulated in the microglial cells that were resistant to NO-induced apoptosis. lcn2 expression was increased by inflammatory stimuli in microglia. The stable expression of lcn2 as well as the addition of rLCN2 protein augmented the sensitivity of microglia to the NO-induced apoptosis, while knockdown of lcn2 expression using short hairpin RNA attenuated the cell death. Microglial cells with increased lcn2 expression were more sensitive to other cytotoxic agents as well. Thus, inflammatory activation of microglia may lead to up-regulation of lcn2 expression, which sensitizes microglia to the self-regulatory apoptosis. Additionally, the stable expression of lcn2 in BV-2 microglia cells induced a morphological change of the cells into the round shape with a loss of processes. Treatment of primary microglia cultures with the rLCN2 protein also induced the deramification of microglia. The deramification of microglia was closely related with the apoptosis-prone phenotype, because other deramification-inducing agents such as cAMP-elevating agent forskolin, ATP, and calcium ionophore also rendered microglia more sensitive to cell death. Taken together, our results suggest that activated microglia may secrete LCN2 protein, which act in an autocrine manner to sensitize microglia to the self-regulatory apoptosis and to endow microglia with an amoeboid form, a canonical morphology of activated microglia in vivo.

The effect of nitric oxide on heme oxygenase gene expression in soybean leaves

Heme oxygenase (HO, EC 1.14.99.3) catalyzes the oxidative conversion of heme to biliverdin IXalpha with the concomitant release of carbon monoxide and iron. Recently, HO has been involved in the protection against oxidative stress in plants. The fact that nitric oxide (NO), an endogenous signaling molecule in animals and plants mediates responses to abiotic and biotic stresses, prompted us to study whether this molecule could modulate HO-1 gene transcription. To fulfill this objective leaves of soybean (Glycine max L.) plants were stimulated with Cd, employing an acute intoxication model. Cadmium caused dehydration, chlorophyll loss and ion leakage. Semi-quantitative RT-PCR analysis showed no augmentation of HO-1 transcript levels with respect to controls. Pretreatment with 100 microM sodium nitroprussiate (SNP), a well-known NO donor, prevented the effects caused by Cd. When the HO-1 mRNA levels were analyzed, a significant augmentation (54%) was observed with respect to Cd-treated plants. On the other hand, 50 or 300 microM SNP did not fully prevent the effects elicited by Cd. When HO-1 transcript levels were analyzed, no significant enhancement or a down-regulation was observed. The potassium salt of 2-(4-carboxylphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, arrested NO-mediated protective effects against to Cd-induced oxidative damage. These data provide an understanding of one of the possible roles that NO can play against an oxidative insult. NO is cytoprotective depending on its concentration, and it was further demonstrated that this protection could be, at least in part, mediated by an enhancement of HO-1 mRNA, as it happens with genes associated with the antioxidant defense system.

Change of heme oxygenase-1 expression in lung injury induced by chrysotile asbestos in vivo and in vitro

Oxidative stress is thought to be the pathogenesis of pulmonary fibrosis induced by asbestos, and heme oxygenase-1 (HO-1) protects lung tissue against oxidative stress. We hypothesized that HO-1 is also associated with oxidative lung injury caused by exposure to chrysotile asbestos. This study was conducted to investigate the HO-1 expression of lungs in lung injury by chrysotile asbestos in vivo and in vitro. Male Wistar rats were administered 1 mg or 2 mg chrysotile suspended in saline by a single intratracheal instillation and were sacrificed at 3 days, 1 wk, 1 mo, 3 mo, and 6 mo of recovery time. The expression of HO-1 was observed by Western blot analysis, reverse-transcription polymerase chain reaction, and immunostaining. Protein levels of HO-1 increased at from 3 days to 6 mo following intratracheal instillation of 1 or 2 mg chrysotile. The mRNA levels of HO-1 increased at 3 mo and 6 mo following intratracheal instillation of 1 or 2 mg chrysotile. HO-1-positive cells were mainly found in the alveolar macrophages during immunostaining. We then examined HO-1 protein expression in human alveolar epithelial cells (A549). A549 cells were incubated with chrysotile at concentrations of 0, 12.5, 25, 50, and 100 microg/ml over 24 h. Increased expression of HO-1 protein was found following exposure to 25 or 50 microg/ml of chrysotile. Increased expression of HO-1 was also found at 6, 12, 24, and 48 h after exposure to 50 microg/ml of chrysotile with a peak at 24 h. These findings suggest that HO-1 is related to lung injury arising from exposure to chrysotile asbestos in vivo and in vitro.

Nitric oxide stimulates heme oxygenase-1 gene transcription via the Nrf2/ARE complex to promote vascular smooth muscle cell survival

OBJECTIVE

Previous studies from our laboratory and others found that NO is a potent inducer of heme oxygenase-1 (HO-1) gene transcription in vascular smooth muscle cells (SMC), however, the mechanism responsible for the induction of HO-1 gene expression has not been elucidated. In the present study, we determined the signaling pathway responsible for the induction of HO-1 and its biological significance.

METHODS

Cultured rat aortic SMC were exposed to nitrosative stress by treating cells with various NO donors or with inflammatory cytokines.

RESULTS

Nitrosative stress stimulated an increase in HO-1 mRNA expression and promoter activity in vascular SMC. However, mutation of the antioxidant response element (ARE) in the HO-1 promoter or overexpression of a dominant-negative mutant of NF-E2-related factor-2 (Nrf2) abrogated the activation by NO. Electromobility shift assays using an ARE probe detected a complex that was significantly increased in intensity by NO. In addition, the migration of this complex was retarded by using an antibody directed against Nrf2. NO also increased Nrf2 mRNA expression, total and nuclear Nrf2 levels, and the binding of Nrf2 to the HO-1 promoter. Finally, treatment of SMC with NO stimulated apoptosis that was increased by HO-1 inhibition.

CONCLUSIONS

These results demonstrate that nitrosative stress induces HO-1 gene transcription through the activation of the Nrf2/ARE complex to counteract NO-induced apoptosis of vascular SMC. The capacity of nitrosative stress to activate Nrf2 and stimulate HO-1 gene transcription may represent a critical adaptive response to maintain cell viability at sites of vascular inflammation and atherosclerosis.

Characterization of transcriptional regulation of neurogranin by nitric oxide and the role of neurogranin in SNP-induced cell death: implication of neurogranin in an increased neuronal susceptibility to oxidative stress

Neurogranin (Ng), a calmodulin (CaM)-binding protein kinase C (PKC) substrate, regulates the availability of Ca²⁺/CaM complex and modulates the homeostasis of intracellular calcium in neurons. Previous work showed Ng oxidation by NO donor induces increase in [Ca²⁺]_i. The current study demonstrated that the gene transcription of Ng could be up-regulated by various nitric oxide (NO) donors via a NO-soluble guanylyl cyclase (sGC)-mediated pathway. Furthermore, ectopic expression of neuronal nitric oxide synthase (nNOS) in human embryonic kidney 293 cells (HEK 293) exhibited a nNOS-concentration-dependent biphasic regulatory effect on Ng gene transcription. One of the NO donors, sodium nitroprusside (SNP), however, induced cell death of neuroblastoma Neuro-2a cells. The potency of SNP-induced cell death was shown to be higher in Neuro-2a cells expressing recombinant Ng, as compared with Neuro-2a control cells without Ng expression in cell viability and apoptosis assays. Single-cell fluorescence imaging and site-directed mutagenesis studies suggest that Ng promotes SNP-induced cell death through an amplification of calcium-mediated signaling, which requires the interaction between CaM and IQ motif of Ng. Increased neuronal susceptibility rendered by Ng in response to pathophysiological NO production is suggested to be involved in the selective vulnerability of neurons to oxidative insults in the CNS.

No nitric oxide for HO-1 from sodium nitroprusside

Nitric oxide (NO) and NO donors were among the first reported inducers of the tissue-protective protein heme oxygenase-1 (HO-1) with a potential for eventual use in humans. Besides other clinically established NO releasing drugs, sodium nitroprusside (SNP) has frequently been employed as an experimental tool to explore effects of NO on HO-1 and other biological targets. In this issue of Molecular Pharmacology, Kim et al. (p. 1633) demonstrate that the effects of SNP on expression of HO-1 are mainly due to free iron released from SNP in aqueous solution, whereas NO plays a negligible role, if any, as the mediator of response to SNP. Downstream effects of iron, after being dissociated from SNP, include increases in intracellular cAMP that are causally linked to subsequent phosphorylation of specific MAPK targets and enhanced HO-1 protein levels. Based on the data reported by Kim et al. (2006), the use of SNP as an experimental tool to mimic intracellular effects of NO should be avoided in the future. This work not only helps revise concepts in NO and HO-1 research but also may direct future efforts to the role of iron and reactive oxygen species in the regulation of adenylyl cyclase.