Incorporation of a Nitric Oxide Donating Motif into Novel PC-PLC Inhibitors Provides Enhanced Anti-Proliferative Activity

Inhibition of phosphatidylcholine-specific phospholipase C (PC-PLC) has previously been shown to be a potential target for novel cancer therapeutics. One downstream consequence of PC-PLC activity is the activation of NF-κB, a nuclear transcription factor responsible for transcribing genes related to oncogenic traits, such as proliferation, angiogenesis, metastasis, and cancer cell survival. Another biological pathway linked to NF-κB is the exogenous delivery of nitric oxide (NO), which decreases NF-κB activity through an apparent negative-feedback loop. In this study, we designed and synthesised 13 novel NO-releasing derivatives of our previously reported class of PC-PLC inhibitors, 2-morpholinobenzoic acids. These molecules contained a secondary benzylamine group, which was readily nitrosylated and subsequently confirmed to release NO in vitro using a DAF-FM fluorescence-based assay. It was then discovered that these NO-releasing derivatives possessed significantly improved anti-proliferative activity in both MDA-MB-231 and HCT116 cancer cell lines compared to their non-nitrosylated parent compounds. These results confirmed that the inclusion of an exogenous NO-releasing functional group onto a known PC-PLC inhibitor enhances anti-proliferative activity and that this relationship can be exploited in order to further improve the anti-proliferative activity of current/future PC-PLC inhibitors.

Extra-platelet low-molecular-mass thiols mediate the inhibitory action of S-nitrosoalbumin on human platelet aggregation via S-transnitrosylation of the platelet surface

Nitrosylation of sulfhydryl (SH) groups of cysteine (Cys) moieties is an important post-translational modification (PTM), often on a par with phosphorylation. S-Nitrosoalbumin (ALB-Cys³⁴SNO; SNALB) in plasma and S-nitrosohemoglobin (Hb-Cys^β93SNO; HbSNO) in red blood cells are considered the most abundant high-molecular-mass pools of nitric oxide (NO) bioactivity in the human circulation. SNALB per se is not an NO donor. Yet, it acts as a vasodilator and an inhibitor of platelet aggregation. SNALB can be formed by nitrosation of the sole reduced Cys group of albumin (Cys³⁴) by nitrosating species such as nitrous acid (HONO) and nitrous anhydride (N₂O₃), two unstable intermediates of NO autoxidation. SNALB can also be formed by the transfer (S-transnitrosylation) of the nitrosyl group (NO⁺) of a low-molecular-mass (LMM) S-nitrosothiol (RSNO) to ALB-Cys³⁴SH. In the present study, the effects of LMM thiols on the inhibitory potential of ALB-Cys³⁴SNO on human washed platelets were investigated. ALB-Cys³⁴SNO was prepared by reacting n-butylnitrite with albumin after selective extraction from plasma of a healthy donor on HiTrapBlue Sepharose cartridges. ALB-Cys³⁴SNO was used in platelet aggregation measurements after extended purification on HiTrapBlue Sepharose and enrichment by ultrafiltration (cutoff, 20 kDa). All tested LMM cysteinyl thiols (R-CysSH) including L-cysteine and L-homocysteine (at 10 µM) were found to mediate the collagen-induced (1 µg/mL) aggregation of human washed platelets by SNALB (range, 0-10 µM) by cGMP-dependent and cGMP-independent mechanisms. The LMM thiols themselves did not affect platelet aggregation. It is assumed that the underlying mechanism involves S-transnitrosylation of SH groups of the platelet surface by LMM RSNO formed through the reaction of SNALB with the thiols: ALB-Cys³⁴SNO + R-CysSH ↔ ALB-Cys³⁴SH + R-CysSNO. Such S-transnitrosylation reactions may be accompanied by release of NO finally resulting in cGMP-dependent and cGMP-independent mechanisms.

Receptor-independent modulation of cAMP-dependent protein kinase and protein phosphatase signaling in cardiac myocytes by oxidizing agents

The contraction and relaxation of the heart is controlled by stimulation of the β1-adrenoreceptor (AR) signaling cascade, which leads to activation of cAMP-dependent protein kinase (PKA) and subsequent cardiac protein phosphorylation. Phosphorylation is counteracted by the main cardiac protein phosphatases, PP2A and PP1. Both kinase and phosphatases are sensitive to intramolecular disulfide formation in their catalytic subunits that inhibits their activity. Additionally, intermolecular disulfide formation between PKA type I regulatory subunits (PKA-RI) has been described to enhance PKA's affinity for protein kinase A anchoring proteins, which alters its subcellular distribution. Nitroxyl donors have been shown to affect contractility and relaxation, but the mechanistic basis for this effect is unclear. The present study investigates the impact of several nitroxyl donors and the thiol-oxidizing agent diamide on cardiac myocyte protein phosphorylation and oxidation. Although all tested compounds equally induced intermolecular disulfide formation in PKA-RI, only 1-nitrosocyclohexalycetate (NCA) and diamide induced reproducible protein phosphorylation. Phosphorylation occurred independently of β1-AR activation, but was abolished after pharmacological PKA inhibition and thus potentially attributable to increased PKA activity. NCA treatment of cardiac myocytes induced translocation of PKA and phosphatases to the myofilament compartment as shown by fractionation, immunofluorescence, and proximity ligation assays. Assessment of kinase and phosphatase activity within the myofilament fraction of cardiac myocytes after exposure to NCA revealed activation of PKA and inhibition of phosphatase activity thus explaining the increase in phosphorylation. The data suggest that the NCA-mediated effect on cardiac myocyte protein phosphorylation orchestrates alterations in the kinase/phosphatase balance.

Chitosan chemically modified to deliver nitric oxide with high antibacterial activity

The aim of the current study is to report a simple and efficient method to chemically modify chitosan in order to form S-nitroso-chitosan for antibacterial applications. Firstly, commercial chitosan (CS) was modified to form thiolated chitosan (TCS) based on an easy and environmental-friendly method. TCS was featured based on physicochemical and morphological techniques. Results have confirmed that thiol groups in TCS formed after CS's primary amino groups were replaced with secondary amino groups. Free thiol groups in TCS were nitrosated to form S-nitrosothiol moieties covalently bond to the polymer backbone (S-nitroso-CS). Kinetic measurements have shown that S-nitroso-CS was capable of generating NO in a sustained manner at levels suitable for biomedical applications. The antibacterial activities of CS, TCS and S-nitroso-CS were evaluated based on the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves determined for Escherichia coli, Staphylococcus aureus and Streptococcus mutans. MIC/MBC values reached 25/25, 0.7/0.7 and 3.1/3.1 μg mL^-1 for CS/TCS and 3.1/3.1, 0.1/0.2, 0.1/0.2 μg mL^-1 for S-nitroso-CS, respectively. Decreased MIC and MBC values have indicated that S-nitroso-CS has higher antibacterial activity than CS and TCS. Time-kill curves have shown that the bacterial cell viability decreased 5-fold for E. coli and 2-fold for S. mutans in comparison to their respective controls, after 0.5 h of incubation with S-nitroso-CS. Together, CS backbone chemically modified with S-nitroso moieties have yielded a polymer capable of generating therapeutic NO concentrations with strong antibacterial effect.

Nitroso-hemoglobin-ginger conjugates effects on bacterial growth and color stability in a minced beef model

This study aims to enhance the color and microbiological qualities of a raw beef using natural ingredients. Nitroso-hemoglobin (NO-Hb) integrated with vitamin C (VC), calcium lactate, and ginger complexation were used as natural inhibitors against the growth of aerobic and pathogenic bacteria, namely (Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella. NO-Hb inhibited E. coli, S. aureus, and Salmonella, and enhanced the color stability more than nitrite in the minced beef model. After the multiexponential analysis of relaxation decays, the water component (T2b) was analyzed using the low-field NMR. The results indicated that, at the 7th d of cold-storage the third component (T2) was detected. Significant correlations were observed between T21 and T22 relaxation times and water-holding capacity in minced beef, implying that the LF-NMR measurements could be an efficient method for the determination and prediction of beef freshness. NO-Hb- ginger mixture, as a novel ingredient, could be used instead of nitrite in terms of meat safety.

Nitric Oxide Donor NOC-18-Induced Changes of Mitochondrial Phosphoproteome in Rat Cardiac Ischemia Model

Background and objective: Nitric oxide (NO) is known to exert cardioprotective effects against heart ischemic damage and may be involved in ischemic pre- and postconditioning. NO-triggered cardioprotective mechanisms are not well understood but may involve regulation of mitochondrial permeability transition pore (mPTP). In this study, we aimed to identify differentially phosphorylated mitochondrial proteins possibly involved in the NO/protein kinase G (PKG)/mPTP signaling pathway that can increase the resistance of cardiomyocytes to ischemic damage. Materials and methods: Isolated hearts from Wistar rats were perfused with NO donor NOC-18 prior to induction of stop–flow ischemia. To quantify and characterize the phosphoproteins, mitochondrial proteins were resolved and analyzed by two-dimensional gel electrophoresis followed by Pro-Q Diamond phosphoprotein gel staining, excision, trypsin digestions, and mass spectrometry. Quantitative proteomic analysis coupled with liquid chromatography–tandem mass spectrometry was also performed. Results: Mitochondrial protein phosphorylation patterns in NOC-18-pretreated ischemic hearts versus ischemic hearts were compared. Pretreatment of hearts with NOC-18 caused changes in mitochondrial phosphoproteome after ischemia which involved modifications of 10 mitochondrial membrane-bound and 10 matrix proteins. Among them, α-subunit of ATP synthase and adenine nucleotide (ADP/ATP) translocase 1, both of which are considered as potential structural components of mPTP, were identified. We also found that treatment of isolated non-ischemic mitochondria with recombinant PKG did not cause the same protein phosphorylation as pretreatment of hearts with NOC-18. Conclusions: Our study suggests that pretreatment of hearts with NOC-18 causes changes in mitochondrial phosphoproteome after ischemia which involves modifications of certain proteins thought to be involved in the regulation of mPTP opening and intracellular redox state. These proteins may be potential targets for pharmacological preconditioning of the heart.

Dapsone- and nitroso dapsone-specific activation of T cells from hypersensitive patients expressing the risk allele HLA-B*13:01

BACKGROUND

Research into drug hypersensitivity associated with the expression of specific HLA alleles has focussed on the interaction between parent drug and the HLA with no attention given to reactive metabolites. For this reason, we have studied HLA-B*13:01-linked dapsone hypersensitivity to (a) explore whether the parent drug and/or nitroso metabolite activate T cells and (b) determine whether HLA-B*13:01 is involved in the response.

METHODS

Peripheral blood mononuclear cells (PBMC) from six patients were cultured with dapsone and nitroso dapsone, and proliferative responses and IFN-γ release were measured. Dapsone- and nitroso dapsone-specific T-cell clones were generated and phenotype, function, HLA allele restriction, and cross-reactivity assessed. Dapsone intermediates were characterized by mass spectrometry.

RESULTS

Peripheral blood mononuclear cells from six patients and cloned T cells proliferated and secreted Th1/2/22 cytokines when stimulated with dapsone (clones: n = 395; 80% CD4+ CXCR3hi CCR4hi , 20% CD8+CXCR3hi CCR4hi CCR6hi CCR9hi CCR10hi ) and nitroso dapsone (clones: n = 399; 78% CD4+, 22% CD8+ with same chemokine receptor profile). CD4+ and CD8+ clones were HLA class II and class I restricted, respectively, and displayed three patterns of reactivity: compound specific, weakly cross-reactive, and strongly cross-reactive. Nitroso dapsone formed dimers in culture and was reduced to dapsone, providing a rationale for the cross-reactivity. T-cell responses to nitroso dapsone were dependent on the formation of a cysteine-modified protein adduct, while dapsone interacted in a labile manner with antigen-presenting cells. CD8+ clones displayed an HLA-B*13:01-restricted pattern of activation.

CONCLUSION

These studies describe the phenotype and function of dapsone- and nitroso dapsone-responsive CD4+ and CD8+ T cells from hypersensitive patients. Discovery of HLA-B*13:01-restricted CD8+ T-cell responses indicates that drugs and their reactive metabolites participate in HLA allele-linked forms of hypersensitivity.

Stimulation of constitutive nitric oxide uniquely and compensatorily regulates intestinal epithelial cell brush border membrane Na absorption

In the mammalian small intestine, sodium is primarily absorbed by Na+ /H+ exchange (NHE3) and Na-glucose cotransport (SGLT1) in the brush border membrane (BBM) of villus cells. However, how enhanced cellular constitutive nitric oxide (cNO) may affect NHE3 and SGLT1 remains unclear. Both in vivo in rabbit intestinal villus cells and in vitro IEC-18 cells, administration of NO donor, GSNAP, modestly increased cNO. GSNAP stimulated SGLT1 in villus and IEC-18 cells. The mechanism of stimulation was secondary to an increase in the affinity of SGLT1 for glucose. The change in SGLT1 was not secondary to altered Na-extruding capacity of the cell since Na+ /K+ -ATPase was decreased by GSNAP treatment. In contrast, GSNAP inhibited NHE3 activity in villus cell BBM. The mechanism of NHE3 inhibition was secondary to reduced BBM transporter numbers. These studies demonstrated that the physiological increase in cNO uniquely regulates mammalian small intestinal NHE3 and SGLT1 to maintain Na homeostasis.

X-Ray-Controlled Generation of Peroxynitrite Based on Nanosized LiLuF4 :Ce3+ Scintillators and their Applications for Radiosensitization

Peroxynitrite (ONOO^- ), the reaction product derived from nitric oxide (NO) and superoxide (O₂ ^-• ), is a potent oxidizing and nitrating agent that modulates complex biological processes and promotes cell death. Therefore, it can be expected that the overproduction of ONOO^- in tumors can be an efficient approach in cancer therapy. Herein, a multifunctional X-ray-controlled ONOO^- generation platform based on scintillating nanoparticles (SCNPs) and UV-responsive NO donors Roussin's black salt is reported, and consequently the mechanism of their application in enhanced therapeutic efficacy of radiotherapy is illustrated. Attributed to the radioluminescence and high X-ray-absorbing property of SCNPs, the nanocomposite can produce NO and O₂ ^-• simultaneously when excited by X-ray irradiation. Such simultaneous release of NO and O₂ ^-• ensures the efficient X-ray-controlled generation of ONOO^- in tumors. Meanwhile, the application of X-rays as the excitation source can achieve better penetration depth and induce radiotherapy in this nanotherapeutic platform. It is found that the X-ray-controlled ONOO^- -generation platform can efficiently improve the radiotherapy efficiency via directly damaging DNA, downregulating the expression of the DNA-repair enzyme, and overcoming the hypoxia-associated resistance in radiotherapy. Therefore, this SCNP-based platform may provide a new combinatorial strategy of ONOO^- and radiotherapy to improve cancer treatment.

Nitrosonifedipine, a Photodegradation Product of Nifedipine, Suppresses Pharmacologically Induced Aortic Aneurysm Formation

BACKGROUND/AIMS

We have reported that nitrosonifedipine (NO-NIF), a photodegradation product of nifedipine, has strong antioxidant and endothelial protective effects, and can suppress several cardiovascular diseases in animal models. The objective of the present study was to investigate the effects of NO-NIF on aortic aneurysm formation.

METHODS

The mice were infused with β-aminopropionitrile for 2 weeks and angiotensin II for 6 weeks to induce aortic aneurysm formation. The oxidative stress was measured by dihydroethidium staining and nitrotyrosine staining. The expressions of inflammation-related genes were assessed by quantitative real-time PCR and immunohistochemical staining. To clarify the mechanisms of how NO-NIF suppresses vascular cell adhesion molecule (VCAM)-1, endothelial cells were used in in vitro system.

RESULTS

NO-NIF suppressed pharmacologically induced the aortic aneurysm formation and aortic expansion without blood pressure changes. NO-NIF suppressed elastin degradation and matrix metalloproteinase-2 mRNA expression. NO-NIF suppressed the reactive oxygen species-cyclophilin A positive feedback loop. Upregulated mRNA expressions of inflammation-related genes and endothelial VCAM-1 were suppressed by NO-NIF co-treatment in aortae.

CONCLUSION

NO-NIF has the potential to be a new, nifedipine-derived therapeutic drug for suppressing aortic aneurysm formation by directly improving aortic structure with its strong ability to reduce oxidative stress and inflammation.

Midkine Controls Arteriogenesis by Regulating the Bioavailability of Vascular Endothelial Growth Factor A and the Expression of Nitric Oxide Synthase 1 and 3

Midkine is a pleiotropic factor, which is involved in angiogenesis. However, its mode of action in this process is still ill defined. The function of midkine in arteriogenesis, the growth of natural bypasses from pre-existing collateral arteries, compensating for the loss of an occluded artery has never been investigated. Arteriogenesis is an inflammatory process, which relies on the proliferation of endothelial cells and smooth muscle cells. We show that midkine deficiency strikingly interferes with the proliferation of endothelial cells in arteriogenesis, thereby interfering with the process of collateral artery growth. We identified midkine to be responsible for increased plasma levels of vascular endothelial growth factor A (VEGFA), necessary and sufficient to promote endothelial cell proliferation in growing collaterals. Mechanistically, we demonstrate that leukocyte domiciled midkine mediates increased plasma levels of VEGFA relevant for upregulation of endothelial nitric oxide synthase 1 and 3, necessary for proper endothelial cell proliferation, and that non-leukocyte domiciled midkine additionally improves vasodilation.

The data provided on the role of midkine in endothelial proliferation are likely to be relevant for both, the process of arteriogenesis and angiogenesis. Moreover, our data might help to estimate the therapeutic effect of clinically applied VEGFA in patients with vascular occlusive diseases.

•

Leukocyte domiciled midkine is decisive for collateral endothelial cell proliferation in arteriogenesis.

•

Midkine controls the bioavailability of VEGFA mediating endothelial Nos1 and Nos3 expression.

•

Nos1 and Nos3, relevant for endothelial cell proliferation, can substitute for each other.

Arteriogenesis is a life and tissue saving process as it compensates for the loss of an occluded artery. Decoding the underlying molecular mechanisms is a prerequisite for the development of novel therapeutic options to treat patients with vascular occlusive diseases. Lautz et al. identified midkine to be responsible for the increased bioavailability of VEGFA during arteriogenesis, necessary and sufficient to promote endothelial cell proliferation. These data might help to estimate the therapeutic effect of clinically applied VEGFA. As the identified mechanisms might also apply for angiogenesis, they are likely to be of broader relevance, e.g. in terms of tumor treatment.

Nitroso-sulfide coupled signaling triggers specific vasoactive effects in the intrarenal arteries of patients with arterial hypertension

In normotensive conditions, it has been confirmed that S-nitrosothiols (RSNO), can interact with hydrogen sulfide (H₂S) and create new substances with specific vasoactive effects. This interaction could also represent a new regulator signaling pathway in conditions of hypertension. Until now, these effects were studied only in normotensive rats, and they have not been carried out in humans yet. We investigated the vasoactive effects of the products of the H₂S/S-nitrosoglutathione (S/GSNO) interaction in lobar arteries (LA) isolated from the nephrectomized kidneys of patients suffering from arterial hypertension and in renal arteries (RA) of spontaneously hypertensive rats (SHR). The changes in the isometric tension of pre-contracted arteries were evaluated. Acetylcholine-induced vasorelaxation of LA was reduced compared to the effect induced by an NO donor, sodium nitroprusside suggesting an endothelium dysfunction. While 1 μmol/L Na2S had a minimal effect on the vascular tone, the concentration 20 μmol/L evoked a slight vasorelaxation. GSNO at 0.1 μmol/L induced vasorelaxation, which was less pronounced compared to the effect induced by 1 μmol/L. The S/GSNO products (final concentration 0.1 μmol/L) prepared as the mixture of GSNO (0.1 μmol/L) + Na2S (1 μmol/L) induced a higher vasorelaxation compared to GSNO (0.1 μmol/L) alone only in the 5^th minute and without the differences in the speed. On the other hand, the S/GSNO products (final concentration 1 μmol/L) prepared as the mixture of GSNO (1 μmol/L) + Na2S (10 μmol/L) induced a higher and faster vasorelaxation compared to the effect induced by GSNO (1 μmol/L) alone. In RA of SHR this S/GSNO products induced similar vasorelaxation (higher and faster than GSNO) with involvement of HNO (partially) and cGMP as mediators. However, the products of the H₂S/NO donor (DEA NONOate) manifested differently than S/GSNO indicating the unique interaction between GSNO and H₂S. In this study, we confirmed for the first time that specific vasoactive effects of coupled nitroso-sulfide signaling were also triggered in human arterial tissue. We suggest that in hypertension, H₂S in interaction with GSNO regulated a vasoconstrictor-induced increase in arterial tone towards a stronger vasorelaxation compared to GSNO alone or H₂S alone.

Synthesis and Biological Evaluation of N(2) -Substituted 2,4-Diamino-6-cyclohexylmethoxy-5-nitrosopyrimidines and Related 5-Cyano-NNO-azoxy Derivatives as Cyclin-Dependent Kinase 2 (CDK2) Inhibitors

The potent and selective cyclin-dependent kinase 2 (CDK2) inhibitor NU6027 (6-cyclohexylmethoxy-5-nitroso-2,4-diaminopyrimidine) was used as the lead for the synthesis of a series of analogues in order to provide further insight into the structure-activity relationships for 2,4-diaminopyrimidine CDK2 inhibitors. Aliphatic amino substituents were introduced at position 2. The use of linear or less sterically hindered amines gave rise to compounds endowed with slightly better activity than the lead; on the other hand, the compounds were less active if a bulkier amino substituent was used. Substitution of the 5-nitroso group with a 5-cyano-NNO-azoxy moiety afforded a new class of inhibitors, the activity of which against CDK2 was found to be similar to that of the nitroso series. The most active nitroso compound was 8 b ((2S)-2-[(4-amino-6-cyclohexylmethoxy-5-nitrosopyrimidin-2-yl)amino]propan-1-ol; IC50 =0.16 μm), while in the 5-cyano-NNO-azoxy series the most active compound was 9 b (4-amino-5-[(Z)-cyano-NNO-azoxy]-2-{[(2S)-1-hydroxypropan-2-yl]amino}-6-cyclohexylmethoxypyrimidine; IC50 =0.30 μm). Taken together, these new analogues of NU6027 enhance our understanding of the structure-activity relationships for 2,4-diaminopyrimidine CDK2 inhibitors.

Nitric Oxide Increases Arterial Endotheial Permeability through Mediating VE-Cadherin Expression during Arteriogenesis

Macrophage invasion is an important event during arteriogenesis, but the underlying mechanism is still only partially understood. The present study tested the hypothesis that nitric oxide (NO) and VE-cadherin, two key mediators for vascular permeability, contribute to this event in a rat ischemic hindlimb model. In addition, the effect of NO on expression of VE-caherin and endothelial permeability was also studied in cultured HUVECs. We found that: 1) in normal arteriolar vessels (NAV), eNOS was moderately expressed in endothelial cells (EC) and iNOS was rarely detected. In contrast, in collateral vessels (CVs) induced by simple femoral artery ligation, both eNOS and iNOS were significantly upregulated (P<0.05). Induced iNOS was found mainly in smooth muscle cells, but also in other vascular cells and macrophages; 2) in NAV VE-cadherin was strongly expressed in EC. In CVs, VE-cadherin was significantly downregulated, with a discontinuous and punctate pattern. Administration of nitric oxide donor DETA NONOate (NONOate) further reduced the amounts of Ve-cadherin in CVs, whereas NO synthase inhibitor L-NAME inhibited downregulation of VE-cadherin in CVs; 3) in normal rats Evans blue extravasation (EBE) was low in the musculus gracilis, FITC-dextron leakage was not detected in the vascular wall and few macrophages were observed in perivascular space. In contrast, EBE was significantly increased in femoral artery ligation rats, FITC-dextron leakage and increased amounts of macrophages were detected in CVs, which were further enhanced by administration of NONOate, but inhibited by L-NAME supplement; 4) in vitro experiments confirmed that an increase in NO production reduced VE-cadherin expression, correlated with increases in the permeability of HUVECs. In conclusion, our data for the first time reveal the expression profile of VE-cadherin and alterations of vascular permeability in CVs, suggesting that NO-mediated VE-cadherin pathway may be one important mechanism responsible, at least in part, for macrophage invasion during arteriogenesis.

Direct effects of hypoxia and nitric oxide on ecdysone secretion by insect prothoracic glands

Insect molting and metamorphosis are controlled by the molt stimulating hormone ecdysone. A recent study suggests that reduced tissue oxygenation correlates with the size-sensing mechanism responsible for triggering molting. When reared in hypoxia, larvae of Manduca sexta and Drosophila melanogaster initiate molting at lower weights than do larvae reared in normoxia. Furthermore, in Drosophila, the signaling gas nitric oxide (NO) appears to be required for normal developmental timing. As observed in Drosophila, NO signaling targets the nuclear hormone receptor beta fushi tarazu transcription factor 1 (βFTZ-F1) through activation of Drosophila hormone receptor 3 (DHR3), two key regulators of ecdysone production and metamorphic tissue progression. We set out to directly examine the effects of hypoxia and NO on ecdysone secretion using prothoracic glands from feeding fifth (last) larval stage M. sexta. Our results indicate that in vitro treatment of prothoracic glands with hypoxia (2% oxygen) or the NO donor DETA-NONOate significantly inhibit ecdysone secretion. Protein markers of glandular activity were also in keeping with an initial inhibition, measured a decrease in phosphorylated ERK (extracellular signal regulated kinase) and an increase in non-phosphorylated 4EBP (eukaryotic initiation factor 4E binding protein). Additionally, gene expression levels of Manduca hormone receptor 3 (mhr3), βftz-f1, nitric oxide synthase (nos), and the PTTH receptor torso, were quantified using real-time PCR. NO treatment increased mhr3 expression and decreased nos expression. Hypoxia increased mhr3 transcription after 2 hr, but decreased transcription after 12 hr, with no effect on nos expression. Both NO and hypoxia had small effects on βftz-f1 expression, yet strongly increased torso transcription. Our results demonstrate that, in isolated prothoracic glands, hypoxia and NO signaling directly inhibit ecdysteroid secretion, but at the same time alter aspects of prothoracic gland function that may enhance secretory response.

Cholinergic neurons of the basal forebrain mediate biochemical and electrophysiological mechanisms underlying sleep homeostasis

The tight coordination of biochemical and electrophysiological mechanisms underlies the homeostatic sleep pressure (HSP) produced by sleep deprivation (SD). We have reported that during SD the levels of inducible nitric oxide synthase (iNOS), extracellular nitric oxide (NO), adenosine [AD]ex , lactate [Lac]ex and pyruvate [Pyr]ex increase in the basal forebrain (BF). However, it is not clear whether all of them contribute to HSP leading to increased electroencephalogram (EEG) delta activity during non-rapid eye movement (NREM) recovery sleep (RS) following SD. Previously, we showed that NREM delta increase evident during RS depends on the presence of BF cholinergic (ChBF) neurons. Here, we investigated the role of ChBF cells in coordination of biochemical and EEG changes seen during SD and RS in the rat. Increases in low-theta power (5-7 Hz), but not high-theta (7-9 Hz), during SD correlated with the increase in NREM delta power during RS, and with the changes in nitrate/nitrite [NOx ]ex and [AD]ex . Lesions of ChBF cells using IgG 192-saporin prevented increases in [NOx ]ex , [AD]ex and low-theta activity, during SD, but did not prevent increases in [Lac]ex and [Pyr]ex . Infusion of NO donor DETA NONOate into the saporin-treated BF failed to increase NREM RS and delta power, suggesting ChBF cells are important for mediating NO homeostatic effects. Finally, SD-induced iNOS was mostly expressed in ChBF cells, and the intensity of iNOS induction correlated with the increase in low-theta activity. Together, our data indicate ChBF cells are important in regulating the biochemical and EEG mechanisms that contribute to HSP.

Free radical generation from an aniline derivative in HepG2 cells: a possible captodative effect

Xenobiotic metabolism can induce the generation of protein radicals, which are believed to play an important role in the toxicity of chemicals and drugs. It is therefore important to identify chemical structures capable of inducing macromolecular free radical formation in living cells. In this study, we evaluated the ability of four structurally related environmental chemicals, aniline, nitrosobenzene, N,N-dimethylaniline, and N,N-dimethyl-4-nitrosoaniline (DMNA), to induce free radicals and cellular damage in the hepatoma cell line HepG2. Cytotoxicity was assessed using lactate dehydrogenase assays, and morphological changes were observed using phase contrast microscopy. Protein free radicals were detected by immuno-spin trapping using in-cell western experiments and confocal microscopy to determine the subcellular locale of free radical generation. DMNA induced free radical generation, lactate dehydrogenase release, and morphological changes in HepG2 cells, whereas aniline, nitrosobenzene, N,N-dimethylaniline did not. Confocal microscopy showed that DMNA induced free radical generation mainly in the cytosol. Preincubation of HepG2 cells with N-acetylcysteine and 2,2'-dipyridyl significantly prevented free radical generation on subsequent incubation with DMNA, whereas preincubation with apocynin and dimethyl sulfoxide had no effect. These results suggest that DMNA is metabolized to reactive free radicals capable of generating protein radicals which may play a critical role in DMNA toxicity. We propose that the captodative effect, the combined action of the electron-releasing dimethylamine substituent, and the electron-withdrawing nitroso substituent, leads to a thermodynamically stabilized radical, facilitating enhanced protein radical formation by DMNA.

An exogenous source of nitric oxide modulates zinc nutritional status in wheat plants

The effect of addition of the nitric oxide donor S-nitrosoglutathione (GSNO) on the Zn nutritional status was evaluated in hydroponically-cultured wheat plants (Triticum aestivum cv. Chinese Spring). Addition of GSNO in Zn-deprived plants did not modify biomass accumulation but accelerated leaf senescence in a mode concomitant with accelerated decrease of Zn allocation to shoots. In well-supplied plants, Zn concentration in both roots and shoots declined due to long term exposure to GSNO. A further evaluation of net Zn uptake rate (ZnNUR) during the recovery of long-term Zn-deprivation unveiled that enhanced Zn-accumulation was partially blocked when GSNO was present in the uptake medium. This effect on uptake was mainly associated with a change of Zn translocation to shoots. Our results suggest a role for GSNO in the modulation of Zn uptake and in root-to-shoot translocation during the transition from deficient to sufficient levels of Zn-supply.

Involvement of nitric oxide with activation of Toll-like receptor 4 signaling in mice with dextran sodium sulfate-induced colitis

Ulcerative colitis is an inflammatory bowel disease characterized by acute inflammation, ulceration, and bleeding of the colonic mucosa. Its cause remains unknown. Increases in adhesion molecules in vascular endothelium, and activated neutrophils releasing injurious molecules such as reactive oxygen species, are reportedly associated with the pathogenesis of dextran sodium sulfate (DSS)-induced colitis. Nitric oxide (NO) production derived from inducible NO synthase (iNOS) via activation of nuclear factor κB (NF-κB) has been reported. It is also reported that stimulation of Toll-like receptor 4 (TLR4) by lipopolysaccharide can activate NF-κB. In this study, we investigated the involvement of NO production in activation of the TLR4/NF-κB signaling pathway in mice with DSS-induced colitis. The addition of 5% DSS to the drinking water of male ICR mice resulted in increases in TLR4 protein in colon tissue and NF-κB p65 subunit in the nuclear fraction on day 3, increases in colonic tumor necrosis factor-α on day 4, and increases in P-selectin, intercellular adhesion molecule-1, NO2(-)/NO3(-), and nitrotyrosine in colonic mucosa on day 5. These activated inflammatory mediators and pathology of colitis were completely suppressed by treatment with a NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, as well as an iNOS inhibitor, aminoguanidine. Conversely, a NO-releasing compound, NOC-18, increased TLR4 levels and nuclear translocation of NF-κB p65 and exacerbated mucosal damage induced by DSS challenge. These data suggest that increases in TLR4 expression induced by drinking DSS-treated water might be directly or indirectly associated with NO overproduction.

Soluble guanylyl cyclase activators increase the expression of tolerance to morphine analgesic effect

OBJECTIVES

It is aimed to investigate the effects of guanylyl cyclase activation and inhibition on acute morphine antinociception and the development of tolerance to its effect.

BACKGROUND

Nitric oxide-soluble guanylyl cyclase signal transduction cascade suggested to play an important role in the development of tolerance to antinociceptive effects of morphine.

METHODS

Nociception was evaluated by tail flick and hot plate tests in male Wistar rats. The analgesic effects of intraperitoneal protoporphyrin IX (PPIX; an activator of soluble guanylyl cyclase), 3-morpholinosydnonimine hydrochloride (SIN-1; NO donor and activator of guanylyl cyclase), S-Nitroso-N-acetylpenicillamine (SNAP; an activator of guanylyl cyclase), 3,3-Bis (amino ethyl)-1-hydroxy-2-oxo-1-triazene (NOC-18; NO donor activating guanylyl cyclase) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; an inhibitor of guanylyl cyclase) alone or in combination with subcutaneous morphine injection were evaluated. Their effects on morphine tolerance development were evaluated by giving these agents 20 minutes prior to twice daily morphine injection during tolerance development for 5 days. On day 6, the expression of morphine tolerance was determined.

RESULTS

PPIX, SIN-1, SNAP and NOC-18 significantly increased expression of morphine tolerance while ODQ decreased.

CONCLUSION

These data suggested that sGC activators have a significant role in tolerance to the analgesic effect of morphine (Tab. 1, Fig. 4, Ref. 29).

Induction of a feed forward pro-apoptotic mechanistic loop by nitric oxide in a human breast cancer model

We have previously demonstrated that relatively high concentrations of NO [Nitric Oxide] as produced by activated macrophages induced apoptosis in the human breast cancer cell line, MDA-MB-468. More recently, we also demonstrated the importance of endogenous H₂O₂ in the regulation of growth in human breast cancer cells. In the present study we assessed the interplay between exogenously administered NO and the endogenously produced reactive oxygen species [ROS] in human breast cancer cells and evaluated the mechanism[s] in the induction of apoptosis. To this end we identified a novel mechanism by which NO down regulated endogenous hydrogen peroxide [H₂O₂] formation via the down-regulation of superoxide [O₂^.−] and the activation of catalase. We further demonstrated the existence of a feed forward mechanistic loop involving protein phosphatase 2A [PP2A] and its downstream substrate FOXO1 in the induction of apoptosis and the synthesis of catalase. We utilized gene silencing of PP2A, FOXO1 and catalase to assess their relative importance and key roles in NO mediated apoptosis. This study provides the potential for a therapeutic approach in treating breast cancer by targeted delivery of NO where NO donors and activators of downstream players could initiate a self sustaining apoptotic cascade in breast cancer cells.

Yeast flavohemoglobin protects against nitrosative stress and controls ferric reductase activity

The role of Saccharomyces cerevisiae flavohemoglobin (Yhb1) is controversial and far from understood. This study compares the effects of nitrosative and oxidative challenge on the yeast mutant lacking the YHB1 gene. Growth of the mutant was impaired by nitrosoglutathione and peroxynitrite, whereas increased sensitivity to reactive oxygen species was not observed. Increased levels of intracellular NO(*) after incubation with NO(*) donors were found in the mutants cells as compared to the wild-type cells. Deletion of the YHB1 gene was found to augment the reduction of Fe(3+) by yeast cells which suggests that flavohemoglobin participates in regulation of the activity of plasma membrane ferric reductase(s).

Response of mitochondrial antioxidant system and respiratory pathways to reactive nitrogen species in pea leaves

Nitric oxide (NO) has emerged as an important signaling molecule in plants, but little is known about the effects of reactive nitrogen species in plant mitochondria. In this study, the effects of DETA-NONOate, a pure NO slow generator, and of SIN-1 (3-morpholinosydnonimine), a peroxynitrite producer, on the activities of respiratory pathways, enzymatic and non-enzymatic antioxidants have been investigated in isolated mitochondria from pea leaves. No significant changes in lipid peroxidation, protein oxidation or in ascorbate and glutathione redox state were observed after DETA-NONOate treatments whereas cytochrome pathway (CP) respiration was reversibly inhibited and alternative pathway (AP) respiration showed little inhibition. On the other hand, NO did not affect neither activities of Mn superoxide dismutase (Mn-SOD) nor enzymes involved in the ascorbate and glutathione regeneration in mitochondria except for ascorbate peroxidase (APX), which was reversely inhibited depending on ascorbate concentration. Finally, SIN-1 treatment of mitochondria produced a decrease in CP respiration, an increase in protein oxidation and strongly inhibited APX activity (90%), with glutathione reductase and dehydroascorbate reductase (DHAR) being moderately inhibited (30 and 20%, respectively). This treatment did not affect monodehydroascorbate reductase (MDHAR) and Mn-SOD activities. Results showed that mitochondrial nitrosative stress was not necessarily accompanied by oxidative stress. We suggest that NO-resistant AP and mitochondrial APX may be important components of the H(2) O(2) -signaling pathways under nitrosative stress induced by NO in this organelle. Also, MDHAR and DHAR, via ascorbate regeneration, could constitute an essential antioxidant defense together with Mn-SOD, against NO and ONOO(-) stress in plant mitochondria.

Stabilization of the skeletal muscle ryanodine receptor ion channel-FKBP12 complex by the 1,4-benzothiazepine derivative S107

Activation of the skeletal muscle ryanodine receptor (RyR1) complex results in the rapid release of Ca²⁺ from the sarcoplasmic reticulum and muscle contraction. Dissociation of the small FK506 binding protein 12 subunit (FKBP12) increases RyR1 activity and impairs muscle function. The 1,4-benzothiazepine derivative JTV519, and the more specific derivative S107 (2,3,4,5,-tetrahydro-7-methoxy-4-methyl-1,4-benzothiazepine), are thought to improve skeletal muscle function by stabilizing the RyR1-FKBP12 complex. Here, we report a high degree of nonspecific and specific low affinity [³H]S107 binding to SR vesicles. SR vesicles enriched in RyR1 bound ∼48 [³H]S107 per RyR1 tetramer with EC₅₀ ∼52 µM and Hillslope ∼2. The effects of S107 and FKBP12 on RyR1 were examined under conditions that altered the redox state of RyR1. S107 increased FKBP12 binding to RyR1 in SR vesicles in the presence of reduced glutathione and the NO-donor NOC12, with no effect in the presence of oxidized glutathione. Addition of 0.15 µM FKBP12 to SR vesicles prevented FKBP12 dissociation; however, in the presence of oxidized glutathione and NOC12, FKBP12 dissociation was observed in skeletal muscle homogenates that contained 0.43 µM myoplasmic FKBP12 and was attenuated by S107. In single channel measurements with FKBP12-depleted RyR1s, in the absence and presence of NOC12, S107 augmented the FKBP12-mediated decrease in channel activity. The data suggest that S107 can reverse the harmful effects of redox active species on SR Ca²⁺ release in skeletal muscle by binding to RyR1 low affinity sites.

Nitric oxide, can it be only good? Increasing the antioxidant properties of nitric oxide in hepatocytes by YC-1 compound

The aim of the study was to evaluate the effect of Nitric oxide (NO) on redox changes and fat accumulation in hepatocytes. AML-12 hepatocytes were exposed to the NO donor Diethylenetriamine-NONOate (DETA-NO). DETA-NO led to a dose- and time-dependent increase in lipid accumulation in the cells, measured by Nile red fluorescence. Exposure of the cells to 1mM DETA-NO for 24h increased reactive oxygen species production, mainly peroxides. At the same time, NO induced elevation of reduced glutathione (GSH) and a mild activation of the antioxidant transcription factors Hypoxia-inducible factor 1α (HIF1α) and NF-E2 related factor 2 (Nrf-2). We used 100 μM YC-1 to inhibit HIF1α activity and induce activation of soluble Guanylate Cyclase (sGC). YC-1 alone did not affect fat accumulation, and only moderately increased the expression of Nrf-2-targeted genes Heme oxygenase 1 (Hmox1), NAD(P)H dehydrogenase (quinone 1) (Nqo1) and Glutathione S-transferase α1 (Gstα1). However, YC-1 abolished the negative effect of NO on fat accumulation when administered together. Strikingly, YC-1 potentiated the effect of NO on Nrf-2 activation, thus increasing dramatically the antioxidant properties of NO. Moreover, YC-1 intensified the effect of NO on the expression of peroxisome-proliferator-activated receptor-gamma co-activator 1α (PGC1α) and mitochondrial biogenesis markers. This study suggests that YC-1 may shift the deleterious effects of NO into the beneficial ones, and may improve the antioxidant properties of NO.

CCK receptors-related signaling involved in nitric oxide production caused by gastrin 17 in porcine coronary endothelial cells

In anesthetized pigs gastrin-17 increased coronary blood flow through CCK1/CCK2 receptors and β(2)-adrenoceptors-related nitric oxide (NO) release. Since the intracellular pathway has not been investigated the purpose of this study was to examine in coronary endothelial cells the CCK1/CCK2 receptors-related signaling involved in the effects of gastrin-17 on NO release. Gastrin-17 caused a concentration-dependent increase of NO production (17.3-62.6%; p<0.05), which was augmented by CCK1/CCK2 receptors agonists (p<0.05). The effect of gastrin-17 was amplified by the adenylyl-cyclase activator and β(2)-adrenoceptors agonist (p<0.05), abolished by cAMP/PKA and β(2)-adrenoceptors and CCK1/CCK2 receptors blockers, and reduced by PLC/PKC inhibitor. Finally, Western-blot revealed the preferential involvement of PKA vs. PKC as downstream effectors of CCK1/CCK2 receptors activation leading to Akt, ERK, p38 and endothelial NOS (eNOS) phosphorylation. In conclusion, in coronary endothelial cells, gastrin-17 induced eNOS-dependent NO production through CCK1/CCK2 receptors- and β(2)-adrenoceptors-related pathway. The intracellular signaling involved a preferential PKA pathway over PKC.

Effects of type 5-phosphodiesterase inhibition on energy metabolism and mitochondrial biogenesis in human adipose tissue ex vivo

OBJECTIVE

An excess of adipose tissue (AT) in obese individuals is linked to increased cardiovascular risk and mitochondria have been shown to be defective in the muscle and AT of patients with metabolic disorders such as obesity and Type 2 diabetes. Nitric oxide (NO) generated by endothelial NO synthase (eNOS) plays a role in mitochondrial biogenesis through cyclic-GMP (cGMP). AT harbors the whole molecular signaling pathway of NO, together with type 5-phosphodiesterase (PDE- 5), the main cGMP catabolising enzyme.

AIM

Our aim was to evaluate the effect of the modulation of NO pathway, through PDE-5 inhibition, on energy metabolism and mitochondria biogenesis in human omental AT.

METHODS AND MEASUREMENTS

Cultured human omental AT was stimulated with PDE-5 inhibitor, vardenafil, at different concentration for 24 and 72 h. Analysis of the expression of both key-regulator genes of adipocyte metabolism and mitochondria-biogenesis markers was performed.

RESULTS

We found an increased gene expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), adiponectin, and proliferator- activated receptor gamma coactivator-1 α (PGC-1α) after a 24-h stimulation with vardenafil at the lowest concentration employed compared to controls (p<0.05). After 72 h of stimulation, a significant increase of mitochondrial DNA was found compared to control samples (p<0.05).

CONCLUSION

Our data suggest that PDE-5 inhibition could have an impact on mitochondrial content of human AT suggesting a positive effect on energy metabolism and adding new elements in the comprehension of AT pathophysiology.

Heterogeneity in relaxation of different sized porcine coronary arteries to nitrovasodilators: role of PKG and MYPT1

The present study was to determine the role of the type I isoform of cGMP-dependent protein kinase (PKG I) and its downstream effector myosin phosphatase target subunit 1 (MYPT1) in the responses of different sized coronary arteries to nitrovasodilators. Relaxations of isolated porcine coronary arteries were determined by isometric tension recording technique. Protein levels of PKG I and its effectors were analyzed by Western blotting. The activities of PKG I and MYPT1 were studied by analyzing phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and MYPT1, respectively. Nitroglycerin, DETA NONOate, and 8-Br-cGMP caused greater relaxations in large than in small coronary arteries. Relaxations were attenuated to a greater extent by Rp-8-Br-PET-cGMPS (a PKG inhibitor) in large vs. small arteries. The expressions of PKG I and MYPT1 in large arteries were more abundant than in small arteries. DETA NONOate stimulated phosphorylation of VASP at Ser239 and inhibited phosphorylation of MYPT1 at Thr853 to a greater extent in large than in small arteries. A suppressed phosphorylation of MYPT1 at Thr853 was caused by 8-Br-cGMP in large but not small arteries, which was inhibited by Rp-8-Br-PET-cGMPS. These results suggest that the greater responsiveness of large coronary arteries to nitrovasodilators result in part from greater activities of PKG I and MYPT1. Dysfunction in nitric oxide signaling is implicated in the vulnerability of large coronary arteries to certain disorders such as atherosclerosis and spasm. Augmentation of PKG I-MYPT1 signaling may be of therapeutic benefit for combating these events.

Shockwaves enhance the osteogenetic gene expression in marrow stromal cells from hips with osteonecrosis

BACKGROUND

This in vitro study investigated the angiogenesis and osteogenesis effects of shockwaves on bone marrow stromal cells (BMSCs) from hips with osteonecrosis.

METHODS

BMSCs were harvested from the bone marrow cavity of the proximal femur in six patients with osteonecrosis of the femoral head. The specimens were divided into four groups, the control, shockwave, shockwave plus nω-nitro- L-arginine methyl ester (L-NAME) and a nitric oxide (NO) donor (NOC18) groups. The control group received no shockwaves and was used as the baseline. The shockwave group received 250 shockwave impulses at 14 Kv (equivalent to 0.18 mJ/mm2 energy flux density). The shockwave plus LNAME group was pre-treated with L-NAME before receiving shockwaves. The NOC18 group received NOC18 after cell culture for 48 hours. The evaluations included cell proliferation (MTT) assay, alkaline phosphatase, real time reverse transcriptase-polymerase chain reaction analysis of vessel endothelial growth factor (VEGF), bone morphogenic protein (BMP)-2, RUNX2 and osteocalcin mRNA expression and von Kossa stain for mineralized nodules.

RESULTS

The shockwave group showed significant increases in MTT, VEGF, alkaline phosphatase, BMP2, RUNX2 and osteocalcin mRNA expression and more mature mineralized nodules compared with the control. Pre-treatment with L-NAME significantly reduced the angiogenic and osteogenic effects of extracorporeal shockwave therapy (ESWT) and the results were comparable with the control. Administration of NOC18 significantly enhanced the angiogenesis and osteogenesis effects compared with the control and the results were comparable with the shockwave group.

CONCLUSION

ESWT significantly enhanced the angiogenic and osteogenic effects of BMSCs mediated through the NO pathway in hips with osteonecrosis. These innovative findings, at least in part, explain some of the mechanism of shockwaves in osteonecrosis of the hip.

Part II. Initial molecular and cellular characterization of high nitric oxide-adapted human tongue squamous cell carcinoma cell lines

It is not understood why some head and neck squamous cell carcinomas, despite having identical morphology, demonstrate different tumor aggressiveness, including radioresistance. High levels of the free radical nitric oxide (NO) and increased expression of the NO-producing enzyme nitric oxide synthase (NOS) have been implicated in tumor progression. We previously adapted three human tongue cancer cell lines to high NO (HNO) levels by gradually exposing them to increasing concentrations of an NO donor; the HNO cells grew faster than their corresponding untreated ("parent") cells, despite being morphologically identical. Herein we initially characterize the HNO cells and compare the biological properties of the HNO and parent cells. HNO/parent cell line pairs were analyzed for cell cycle distribution, DNA damage, X-ray and ultraviolet radiation response, and expression of key cellular enzymes, including NOS, p53, glutathione S-transferase-pi (GST-pi), apurinic/apyrimidinic endonuclease-1 (APE1), and checkpoint kinases (Chk1, Chk2). While some of these properties were cell line-specific, the HNO cells typically exhibited properties associated with a more aggressive behavior profile than the parent cells (greater S-phase percentage, radioresistance, and elevated expression of GST-pi/APE1/Chk1/Chk2). To correlate these findings with conditions in primary tumors, we examined the NOS, GST-pi, and APE1 expression in human tongue squamous cell carcinomas. A majority of the clinical samples exhibited elevated expression levels of these enzymes. Together, the results herein suggest cancer cells exposed to HNO levels can develop resistance to free radicals by upregulating protective mechanisms, such as GST-pi and APE1. These upregulated defense mechanisms may contribute to their aggressive expression profile.

Linking in vitro and in vivo survival of clinical Leishmania donovani strains

BACKGROUND

Leishmania donovani is an intracellular protozoan parasite that causes a lethal systemic disease, visceral leishmaniasis (VL), and is transmitted between mammalian hosts by phlebotomine sandflies. Leishmania expertly survives in these 'hostile' environments with a unique redox system protecting against oxidative damage, and host manipulation skills suppressing oxidative outbursts of the mammalian host. Treating patients imposes an additional stress on the parasite and sodium stibogluconate (SSG) was used for over 70 years in the Indian subcontinent.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated whether the survival capacity of clinical L. donovani isolates varies significantly at different stages of their life cycle by comparing proliferation, oxidative stress tolerance and infection capacity of 3 Nepalese L. donovani strains in several in vitro and in vivo models. In general, the two strains that were resistant to SSG, a stress encountered in patients, attained stationary phase at a higher parasite density, contained a higher amount of metacyclic parasites and had a greater capacity to cause in vivo infection in mice compared to the SSG-sensitive strain.

CONCLUSIONS/SIGNIFICANCE

The 2 SSG-resistant strains had superior survival skills as promastigotes and as amastigotes compared to the SSG-sensitive strain. These results could indicate that Leishmania parasites adapting successfully to antimonial drug pressure acquire an overall increased fitness, which stands in contrast to what is found for other organisms, where drug resistance is usually linked to a fitness cost. Further validation experiments are under way to verify this hypothesis.

Flavohemoglobin and nitric oxide detoxification in the human protozoan parasite Giardia intestinalis

Flavohemoglobins (flavoHbs), commonly found in bacteria and fungi, afford protection from nitrosative stress by degrading nitric oxide (NO) to nitrate. Giardia intestinalis, a microaerophilic parasite causing one of the most common intestinal human infectious diseases worldwide, is the only pathogenic protozoon as yet identified coding for a flavoHb. By NO amperometry we show that, in the presence of NADH, the recombinant Giardia flavoHb metabolizes NO with high efficacy under aerobic conditions (TN=116+/-10s(-1) at 1microM NO, T=37 degrees C). The activity is [O(2)]-dependent and characterized by an apparent K(M,O2)=22+/-7microM. Immunoblotting analysis shows that the protein is expressed at low levels in the vegetative trophozoites of Giardia; accordingly, these cells aerobically metabolize NO with low efficacy. Interestingly, in response to nitrosative stress (24-h incubation with 5mM nitrite) flavoHb expression is enhanced and the trophozoites thereby become able to metabolize NO efficiently, the activity being sensitive to both cyanide and carbon monoxide. The NO-donors S-nitrosoglutathione (GSNO) and DETA-NONOate mimicked the effect of nitrite on flavoHb expression. We propose that physiologically flavoHb contributes to NO detoxification in G. intestinalis.

Long-term adaptation of breast tumor cell lines to high concentrations of nitric oxide

Nitric oxide (NO), a free radical, has been implicated in the biology of human cancers, including breast cancer, yet it is still unclear how NO affects tumor development and propagation. We herein gradually adapted four human breast adenocarcinoma cell lines (BT-20, Hs578T, T-47D, and MCF-7) to increasing concentrations of the NO donor DETA-NONOate up to 600 muM. The resulting model system consisted of a set of fully adapted high nitric oxide ("HNO") cell lines that are biologically different from the "parent" cell lines from which they originated. Although each of the four parent and HNO cell lines had identical morphologic appearance, the HNO cells grew faster than their corresponding parent cells and were resistant to both nitrogen- and oxygen-based free radicals. These cell lines serve as a novel tool to study the role of NO in breast cancer progression and potentially can be used to predict the therapeutic response leading to more efficient therapeutic regimens.

Nitric oxide-induced IL-8 expression is mediated by NF-kappaB and AP-1 in gastric epithelial AGS cells

Inducible nitric oxide synthase (iNOS) and interleukin-8 (IL-8) mediate gastric inflammation. Nitric oxide (NO) produced by iNOS may activate oxidant-sensitive transcription factors. There are the binding sites for NF-kappaB, AP-1, and C/EBP (CCAAT/enhancer binding protein) in the promoter regions of IL-8 gene. The present study aims to investigate whether NO donors, SIN-1 and NOC-18, activate oxidant-sensitive transcription factors NF-kappaB and AP-1 as well as C/EBP to induce IL-8 expression in gastric epithelial AGS cells. Gastric epithelial AGS cells were treated with NO donors, SIN-1 and NOC-18. mRNA expression and protein level of IL-8 in the medium were determined. Nitrite level in the medium and DNA binding activities of NF-kappaB, AP-1, and C/EBP were assessed. NO donors induced the increase in the levels of IL-8 and nitrite in the medium as well as mRNA expression of IL-8 in AGS cells time-dependently. The induction of IL-8 by NO donors was accompanied with the activation of NF-kappaB and AP-1 but not C/EBP in AGS cells.

CONCLUSION

Large amount of NO, which may be produced by iNOS, may induce the activation of NF-kappaB and AP-1 and the expression of IL-8 in gastric epithelial cells.

Nitric Oxide Inhibits Ultraviolet B-induced Murine Keratinocyte Apoptosis by Regulating Apoptotic Signaling Cascades

Cytotoxic effects of nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) are considered to be one of the major causes of inflammatory diseases. On the other hand, protective effects of NO on toxic insults-induced cellular damage/apoptosis have been demonstrated recently. Ultraviolet B (UVB)-induced apoptosis of epidermal keratinocytes leads to skin inflammation and photoageing. However, it has not been elucidated what kind of effects NO has on UVB-induced keratinocyte apoptosis. Thus, in the present study, we investigated the problem and demonstrated that NO from NO donor suppressed UVB-induced apoptosis of murine keratinocytes. In addition, NO significantly suppressed activities of caspase 3, caspase 8 and caspase 9 that had been upregulated by UVB radiation. NO also suppressed p53 expression that had been upregulated by UVB radiation and upregulated Bcl-2 expression that had been down-regulated by UVB radiation. These findings suggested that NO might suppress UVB-induced keratinocyte apoptosis by regulating apoptotic signaling cascades in p53, Bcl-2, caspase3, caspase 8 and caspase 9.

PTR1-dependent synthesis of tetrahydrobiopterin contributes to oxidant susceptibility in the trypanosomatid protozoan parasite Leishmania major

Leishmania must survive oxidative stress, but lack many classical antioxidant enzymes and rely heavily on trypanothione-dependent pathways. We used forward genetic screens to recover loci mediating oxidant resistance via overexpression in Leishmania major, which identified pteridine reductase 1 (PTR1). Comparisons of isogenic lines showed ptr1 (-) null mutants were 18-fold more sensitive to H(2)O(2) than PTR1-overproducing lines, and significant three- to fivefold differences were seen with a broad panel of oxidant-inducing agents. The toxicities of simple nitric oxide generators and other drug classes (except antifolates) were unaffected by PTR1 levels. H(2)O(2) susceptibility could be modulated by exogenous biopterin but not folate, in a PTR1- but not dihydrofolate reductase-dependent manner, implicating H(4)B metabolism specifically. Neither H(2)O(2) consumption nor the level of intracellular oxidative stress was affected by PTR1 levels. Coupled with the fact that reduced pteridines are at least 100-fold less abundant than cellular thiols, these data argue strongly that reduced pteridines act through a mechanism other than scavenging. The ability of unconjugated pteridines to counter oxidative stress has implications to infectivity and response to chemotherapy. Since the intracellular pteridine levels of Leishmania can be readily manipulated, these organisms offer a powerful setting for the dissection of pteridine-dependent oxidant susceptibility in higher eukaryotes.

Balancing role of nitric oxide in complement-mediated activation of platelets from mCd59a and mCd59b double-knockout mice

CD59 is a membrane protein inhibitor of the membrane attack complex (MAC) of complement. mCd59 knockout mice reportedly exhibit hemolytic anemia and platelet activation. This phenotype is comparable to the human hemolytic anemia known as paroxysmal nocturnal hemoglobinuria (PNH), in which platelet activation and thrombosis play a critical pathogenic role. It has long been suspected but not formally demonstrated that both complement and nitric oxide (NO) contribute to PNH thrombosis. Using mCd59a and mCd59b double knockout mice (mCd59ab(-/-) mice) in complement sufficient (C3(+/+)) and deficient (C3(-/-)) backgrounds, we document that mCd59ab(-/-) platelets are sensitive to complement-mediated activation and provide evidence for possible in vivo platelet activation in mCd59ab(-/-) mice. Using a combination of L-NAME (a NO-synthase inhibitor) and NOC-18 or SNAP (NO-donors), we further demonstrate that NO regulates complement-mediated activation of platelets. These results indicate that the thrombotic diathesis of PNH patients could be due to a combination of increased complement-mediated platelet activation and reduced NO-bioavailability as a consequence of hemolysis.

N-nitrosomelatonin: synthesis, chemical properties, potential prodrug

Melatonin is easily nitrosated via various mechanisms at the nitrogen atom of the indole ring to give N-nitrosomelatonin (NOMela). This mini-review provides a comprehensive view of this N-nitroso compound. With an improved procedure NOMela can now economically synthesized with low laboratory expenditure. The major chemical property of NOMela, i.e. the (formally) transfer of the NO+ function to its target nucleophile, is explained in detail and a variety of detection methods using this reaction are suggested. As the suspected carcinogenical potential of NOMela is clearly overruled it seems attractive to apply this nitroso compound for endogenous generation of S-nitrosothiols that act as nitric oxide donors in vivo.

Salt inactivates endothelial nitric oxide synthase in endothelial cells

There is a 1-4 mmol/L rise in plasma sodium concentrations in individuals with high salt intake and in patients with essential hypertension. In this study, we used 3 independent assays to determine whether such a small increase in sodium concentrations per se alters endothelial nitric oxide synthase (eNOS) function and contributes to hypertension. By directly measuring NOS activity in living bovine aortic endothelial cells, we demonstrated that a 5-mmol/L increase in salt concentration (from 137 to 142 mmol/L) caused a 25% decrease in NOS activity. Importantly, the decrease in NOS activity was in a salt concentration-dependent manner. The NOS activity was decreased by 25, 45, and 70%, with the increase of 5, 10, and 20 mmol/L of NaCl, respectively. Using Chinese hamster ovary cells stably expressing eNOS, we confirmed the inhibitory effects of salt on eNOS activity. The eNOS activity was unaffected in the presence of equal milliosmol of mannitol, which excludes an osmotic effect. Using an ex vivo aortic angiogenesis assay, we demonstrated that salt attenuated the nitric oxide (NO)-dependent proliferation of endothelial cells. By directly monitoring blood pressure changes in response to salt infusion, we found that in vivo infusion of salt induced an acute increase in blood pressure in a salt concentration-dependent manner. In conclusion, our findings demonstrated that eNOS is sensitive to changes in salt concentration. A 5-mmol/L rise in salt concentration, within the range observed in essential hypertension patients or in individuals with high salt intake, could significantly suppress eNOS activity. This salt-induced reduction in NO generation in endothelial cells may contribute to the development of hypertension.

Oxidative DNA damage in osteoarthritic porcine articular cartilage

Osteoarthritis (OA) is associated with increased levels of reactive oxygen species. This study investigated if increased oxidative DNA damage accumulates in OA articular cartilage compared with non-OA articular cartilage from pigs with spontaneous OA. Additionally, the ability of nitric oxide (NO) or peroxynitrite (ONOO(-)) induced DNA damage in non-OA chondrocytes to undergo endogenous repair was investigated. Porcine femoral condyles were graded for the stage of OA, macroscopically by the Collins Scale, and histologically by the modified Mankin Grade. Levels of DNA damage were determined in non-OA and OA cartilage, using the comet assay. For calibration, DNA damage was measured by exposing non-OA chondrocytes to 0-12 Gray (Gy) of X-ray irradiation. Non-OA articular chondrocytes were treated with 0-500 microM of NO donors (NOC-18 or SIN-1), and DNA damage assessed after treatment and 5 days recovery. A significant increase (P < 0.01) in oxidative DNA damage occurred in OA chondrocytes in joints with Mankin Grades 3 or greater, compared to non-OA chondrocytes. The percentage of nuclei containing DNA damage increased significantly (P < 0.001) from early to late grades of OA. An increase of approximately 0.65-1.7 breaks/1,000 kb of DNA occurred in OA, compared to non-OA nuclei. NOC-18 or SIN-1 caused significant DNA damage (P < 0.001) in non-OA chondrocytes that did not undergo full endogenous repair after 5 days (P < 0.05). Our data suggest significant levels of oxidative DNA damage occur in OA chondrocytes that accumulates with OA progression. Additionally, DNA damage induced by NO and ONOO(-) in non-OA chondrocytes does not undergo full endogenous repair.

The impact of N-nitrosomelatonin as nitric oxide donor in cell culture experiments

N-nitrosomelatonin (NOMela) is well-known for its capabilities of transnitrosating nucleophiles such as thiols and ascorbate, thereby generating nitric oxide (NO)-releasing compounds. It is unknown, however, whether NOMela can be successfully applied as a precursor of NO in a complex biological environment like a cell culture system. NO donors may be useful to induce the transcription factor hypoxia inducible factor 1 (HIF-1), which coordinates the protection of cells and tissues from the lack of oxygen (hypoxia). In this study, the effects of NOMela in an in vitro cell-free assay [NO-release, inhibition of prolylhydroxylase1 (PHD1)] and in living cells (upregulation of HIF-1, reduction of HIF-1 hydroxylation, upregulation of the HIF-1-target gene PHD2) were compared with those of the frequently applied NO donor S-nitrosoglutathione (GSNO) under normoxic and hypoxic conditions. In contrast to GSNO, NOMela released NO in a predictable manner and this release in vitro was found to be independent of the composition of the buffer system. The NOMela-mediated effects in oxygenated cells were in all cases comparable to the hypoxic response, whereas unphysiological strong effects were observed with GSNO. Probably, because of the antioxidative power of the NOMela-dependent formation of melatonin, cells were completely protected against the attack of reactive nitrogen oxygen species, which are generated by autoxidation of NO. In conclusion, NOMela had to be an excellent NO precursor for cells in culture and potentially tissues.

Nitric oxide enhances Oct-4 expression in bone marrow stem cells and promotes endothelial differentiation

This study was designed to investigate the role of nitric oxide (NO) in bone marrow stem cells and their differentiation into endothelial cells in vitro. Adult mouse bone marrow multipotent progenitor cells (MAPCs) were used as the source of stem cells. Oct-4 expression (both mRNA and protein) was significantly increased by up to 68.0% in MAPCs when incubated with NO donors DETA-NONOate or sodium nitroprusside (SNP) in a concentration-dependant manner (n=3, P<0.05). However, the cell proliferation was dramatically decreased by over 3-folds when treated with DETA-NONOate or SNP for 48 h (n=3, P<0.05). When MAPCs were exposed to DETA-NONOate (100 microM) for the first 48 h during differentiation, the expression (both mRNA and protein) of vWF was significantly increased at day 14 in the differentiating cells. The effects of DETA-NONOate or SNP on cell proliferation, Oct-4 expression and endothelial differentiation of MAPCs were not affected by the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one or cGMP analog 8-Br-cGMP. These data indicate that NO may regulate both the pluripotency and differentiation of MAPCs via a cGMP-independent mechanism.

N-nitrosomelatonin outcompetes S-nitrosocysteine in inhibiting glyceraldehyde 3-phosphate dehydrogenase: first evidence that N-nitrosomelatonin can modify protein function

Low-molecular-weight S-nitrosothiols (RSNOs) are well known for their capability to transnitrosate cysteine residues of enzymes thereby altering their catalytic activity. It is unknown, however, whether N-nitrosomelatonin (NOMela) which is highly effective in transnitrosating low-molecular-weight thiols (RSHs) can also alter protein function. In the present study, we report on such a capability with glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as a target enzyme. Reaction of NOMela with GAPDH resulted in an increase of RSNOs at the expense of RSHs. Somewhat surprisingly, NOMela was about 10-fold more effective than S-nitrosocysteine in inhibiting GAPDH. Vitamin C and glutathione increased the NOMela-dependent inhibition of the enzyme by accelerating the intermediacy of nitroxyl which is also highly effective in nitrosating RSHs. The occurrence of this intermediate during the NOMela-vitamin C reaction was verified by using Mn(III)-tetrakis(1-methyl-4-pyridyl)porphorin pentachloride as nitroxyl scavenger. The NOMela-dependent inactivation of GAPDH was so effective that this reaction can be used to quantify NOMela with high sensitivity.

[Quasi-adaptive response to alkylating agents in Escherichia coli and Ada-protein functions]

In 2005 we have described in exponentially growing E. coli cells a new fundamental genetic phenomenon,--quasi-adaptive response to alkylating compounds (quasi-Ada). Phenotypic expression of quasi-Ada is similar to the true Ada response. However, in contrast to the letter, it develops in the course of pretreatment of the cells by a sublethal dose of nonalkylating agent, an NO-containing dinitrosyl iron complex with glutathione (DNICglu). To reveal the mechanisms of quasi-adaptation and its association with the function of the Ada regulatory protein, here we used a unique property of dual gene expression regulation of aidB1 gene, a part of the Ada-regulon, namely its relative independence from Ada protein in anaerobic conditions. Based on the results of aidB1 gene expression analysis an EPR spectra of E. coli MV2176 cells (aidB1::lacZ) in aerobic and anaerobic conditions after the corresponding treatments, we conclude that the function and the spatial structure of meAda and [(Cys-)2Fe+(NO+)2]Ada are identical and thus the nitrosylated protein represents a regulator of the Ada regulon gene expression during quasi-adaptation development.

Low nitric oxide: a key factor underlying copper-deficiency teratogenicity

Copper (Cu)-deficiency-induced teratogenicity is characterized by major cardiac, brain, and vascular anomalies; however, the underlying mechanisms are poorly understood. Cu deficiency decreases superoxide dismutase activity and increases superoxide anions, which can interact with nitric oxide (NO), reducing the NO pool size. Given the role of NO as a developmental signaling molecule, we tested the hypothesis that low NO levels, secondary to Cu deficiency, represent a developmental challenge. Gestation day 8.5 embryos from Cu-adequate (Cu+) or Cu-deficient (Cu-) dams were cultured for 48 h in Cu+ or Cu- medium, respectively. We report that NO levels were low in conditioned medium from Cu-/Cu- embryos and yolk sacs, compared to Cu+/Cu+ controls under basal conditions and with NO synthase (NOS) agonists. The low NO production was associated with low endothelial NOS phosphorylation at serine 1177 and cyclic guanosine-3',5'-monophosphate (cGMP) concentrations in the Cu-/Cu- group. The altered NO levels in Cu-deficient embryos are functionally significant, as the administration of the NO donor DETA/NONOate increased cGMP and ameliorated embryo and yolk sac abnormalities. These data support the concept that Cu deficiency limits NO availability and alters NO-dependent signaling, which contributes to abnormal embryo and yolk sac development.

S-nitrosothiols signal hypoxia-mimetic vascular pathology

NO transfer reactions between protein and peptide cysteines have been proposed to represent regulated signaling processes. We used the pharmaceutical antioxidant N-acetylcysteine (NAC) as a bait reactant to measure NO transfer reactions in blood and to study the vascular effects of these reactions in vivo. NAC was converted to S-nitroso-N-acetylcysteine (SNOAC), decreasing erythrocytic S-nitrosothiol content, both during whole-blood deoxygenation ex vivo and during a 3-week protocol in which mice received high-dose NAC in vivo. Strikingly, the NAC-treated mice developed pulmonary arterial hypertension (PAH) that mimicked the effects of chronic hypoxia. Moreover, systemic SNOAC administration recapitulated effects of both NAC and hypoxia. eNOS-deficient mice were protected from the effects of NAC but not SNOAC, suggesting that conversion of NAC to SNOAC was necessary for the development of PAH. These data reveal an unanticipated adverse effect of chronic NAC administration and introduce a new animal model of PAH. Moreover, evidence that conversion of NAC to SNOAC during blood deoxygenation is necessary for the development of PAH in this model challenges conventional views of oxygen sensing and of NO signaling.