The dual role of S-nitrosoglutathione (GSNO) during thymocyte apoptosis

Comparison of S-nitrosoglutathione- and staurosporine-induced apoptosis in human neural cells

S-nitrosoglutathione (GSNO) is an endogenously produced S-nitrosylating compound that controls the function of various proteins. While a number of rodent cell lines have been used to study GSNO-induced apoptosis, the mechanisms of action remain to be evaluated in human cells and in parallel with other common apoptosis-inducing agents. In this study, we compared the pro-apoptotic effects of GSNO and staurosporine (STS) on human neural progenitors (NT2, hNP1) and neuroblasts (SH-SY5Y). We show that these cells exhibit comparable levels of susceptibility to GSNO- and STS-induced apoptotic cell death, as demonstrated by condensed nuclei and CASP3 activation. Mechanistic differences in apoptotic responses were observed as differential patterns of DNA fragmentation and levels of BAX, BCL-XL, CASP8, and p-ERK in response to GSNO and STS treatment. Mitochondrial membrane potential analysis revealed that NT2 and hNP1 cells, but not SH-SY5Y cells, undergo mitochondrial hyperpolarization in response to short-term exposure to STS prior to undergoing subsequent depolarization. This is the first study to report differences in apoptotic responses to GSNO and STS in 3 complementary human neural cell lines. Furthermore, these cells represent useful tools in cell pharmacological paradigms in which susceptibility to apoptosis-inducing agents needs to be assessed at different stages of neural cell fate commitment and differentiation.

SNO spectral counting (SNOSC), a label-free proteomic method for quantification of changes in levels of protein S-nitrosation

S-Nitrosation plays an important role in regulation of protein function and signal transduction. Discovering S-nitrosated targets is a prerequisite for further functional study. However, current proteomic methods used to quantify S-nitrosation are limited in their applicability to certain types of samples, or by the need for special reagents and complex procedures to obtain the results. Here we devised a label-free proteomic method for quantification of changes in the level of protein S-nitrosation on the basis of a spectral counting strategy, called S-nitrosothiol (SNO) spectral counting (SNOSC). With this method, samples can be from any source (cells, tissues); there is no need for labelling reagents or procedures, and the results yield quantitative information. Moreover, as it is based on the irreversible biotinylation procedure (IBP) for S-nitrosation protein enrichment, false positive targets caused by the interference of intermolecular disulphide bonds are ruled out. Using SNOSC we studied S-nitrosation in the cell line RAW264.7 induced exogenously with S-nitrosoglutathione (GSNO), or induced endogenously by lipopolysaccharides/interferon-gamma (LPS/IFN-γ). We detected a significant increase in S-nitrosation of 50 proteins after exogenous induction and 17 proteins after endogenous induction. We thus demonstrate that SNOSC is a widely applicable proteomic method for fast screening of SNO proteins.

Effects of nitric oxide on the survival and neuritogenesis of cerebellar Purkinje neurons

Nitric oxide has been investigated widely both during neurodevelopment and in neurological diseases. However, whilst it has been established that nitric oxide-producing enzymes of nitric oxide synthase family are expressed in cerebellar Purkinje neurons, the effects of nitric oxide on the viability and morphology of these neurons remain unknown. Here, we have demonstrated that the activity of neuronal nitric oxide synthase, but not the inducible or endothelial forms of this enzyme, is required to support the survival of a proportion of cerebellar Purkinje neurons in vitro. We discovered that donation of high concentrations of exogenous nitric oxide reduces Purkinje neuron survival in culture and that peroxynitrite is also toxic to these cells. Finally, we demonstrated that exogenous nitric oxide and peroxynitrite reduce both the magnitude and the complexity of the neurite arbour extended by cerebellar Purkinje neurons. Taken together, these findings reveal that whilst a low level of endogenous nitric oxide, released by the activity of neuronal nitric oxide synthase, is beneficial to cerebellar Purkinje neurons in vitro, high levels of exogenous nitric oxide and peroxynitrite are detrimental to both the survival of these neurons and to their ability to extend processes and form functional neural networks.

Quantitative analysis of intracellular calcium and mitochondrial kinetic fluorescence changes in GSNO-induced thymocyte early apoptosis

A fluorescence microscopy imaging technique was applied to observe the single-cell kinetic changes of intracellular Ca(2+) concentration ([Ca(2+)](i)) and mitochondrial membrane potential (ΔΨ(m)) during the early stage of S-nitrosoglutathione (GSNO)-induced thymocytes apoptosis. The kinetic features of [Ca(2+)](i) and ΔΨ(m) were quantitatively analyzed and compared by fitting the fluorescence intensity data. The mathematical parameter, inflection point which indicated the time point when [Ca(2+)](i) or ΔΨ(m) changed the most rapidly, was proposed to analyze the fitting curve. The results revealed that the inflection point of [Ca(2+)](i) always appeared prior to that of ΔΨ(m) during apoptosis induced by a certain GSNO concentration. Both the [Ca(2+)](i) and ΔΨ(m) changed in a GSNO concentration-dependent manner. Another parameter, half-max effect point was also employed and displayed the similar results. Such quantitative analyses of real-time observations at the single-cell level are useful for interpreting the sequence of the biological events operating in GSNO-induced thymocyte apoptosis.

The nitric oxide donor S-nitrosoglutathione reduces apoptotic primary liver cell loss in a three-dimensional perfusion bioreactor culture model developed for liver support

INTRODUCTION

Artificial extracorporeal support for hepatic failure has met with limited clinical success. In hepatocytes, nitric oxide (NO) functions as an antiapoptotic modulator in response to a variety of stresses. We hypothesized that NO administration would yield improved viability and hepatocellular restructuring in a four-compartment, hollow fiber-based bioreactor with integral oxygenation for dynamic three-dimensional perfusion of hepatic cells in bioartificial liver support systems.

METHODS

Isolated adult rat liver cells were placed in culture medium alone (control) or medium supplemented with various concentrations of an NO donor (S-nitrosoglutathione [GSNO]) in the bioreactors. Media samples were obtained from the cell perfusion circuit to monitor cellular response. After 24 and 72 h, histology biopsies were taken to investigate spontaneous restructuring of the cells. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was performed to quantify apoptotic nuclei.

RESULTS

Control bioreactors exhibited 47.9 +/- 2.9% (mean +/- standard error of the mean) apoptotic nuclei. In contrast, NO-treated bioreactors exhibited a biphasic response. Fewer apoptotic nuclei were seen in the 200 and 500 microM GSNO groups (14.4 +/- 0.4%). No effect was observed in the 10 microM GSNO group (47.3%), and increased TUNEL staining was observed in the 1000 microM GSNO group (82.6%). Media lactate dehydrogenase levels were lower in bioreactor groups treated with 200 or 500 microM GSNO (310 +/- 38 IU/L) compared with the control group (919 +/- 188 IU/L; p < 0.05). Protein synthesis was not affected, as measured by albumin levels in the media (115 +/- 19 microg/day/cell inoculum in GSNO-treated bioreactors at 24 h vs. 110 +/- 13 in controls; p = 0.851). Histologically, all of the bioreactor groups exhibited liver cell aggregates with some attached to the bioreactor capillaries. Increased numbers of cells in the aggregates and superior spontaneous restructuring of the cells were seen at 24 and 72 h in the bioreactor groups treated with either 200 or 500 microM GSNO compared with the control groups.

CONCLUSION

Addition of an NO donor reduces adult rat liver cell apoptosis during the initial 24 h after cell inoculation within a three-dimensional perfusion bioreactor system for liver support and promotes liver cell aggregation and spontaneous restructuring of the cells at 24 and 72 h. GSNO-treated bioreactors remain metabolically active and show significantly lower levels of cellular injury as compared with controls. Further studies will be required to evaluate the impact of NO treatment of liver support bioreactors for clinical studies.

ESNOQ, proteomic quantification of endogenous S-nitrosation

S-nitrosation is a post-translational protein modification and is one of the most important mechanisms of NO signaling. Endogenous S-nitrosothiol (SNO) quantification is a challenge for detailed functional studies. Here we developed an ESNOQ (Endogenous SNO Quantification) method which combines the stable isotope labeling by amino acids in cell culture (SILAC) technique with the detergent-free biotin-switch assay and LC-MS/MS. After confirming the accuracy of quantification in this method, we obtained an endogenous S-nitrosation proteome for LPS/IFN-gamma induced RAW264.7 cells. 27 S-nitrosated protein targets were confirmed and using our method we were able to obtain quantitative information on the level of S-nitrosation on each modified Cys. With this quantitative information, over 15 more S-nitrosated targets were identified than in previous studies. Based on the quantification results, we found that the S-nitrosation levels of different cysteines varied within one protein, providing direct evidence for differences in the sensitivity of cysteine residues to reactive nitrosative stress and that S-nitrosation is a site-specific modification. Gene ontology clustering shows that S-nitrosation targets in the LPS/IFN-gamma induced RAW264.7 cell model were functionally enriched in protein translation and glycolysis, suggesting that S-nitrosation may function by regulating multiple pathways. The ESNOQ method described here thus provides a solution for quantification of multiple endogenous S-nitrosation events, and makes it possible to elucidate the network of relationships between endogenous S-nitrosation targets involved in different cellular processes.

Detergent-free biotin switch combined with liquid chromatography/tandem mass spectrometry in the analysis of S-nitrosylated proteins

High-throughput proteomic analysis based on a biotin switch combined with liquid chromatography/tandem mass spectrometry (LC/MS/MS) enables simultaneous identification of S-nitrosylated sites and their cognate proteins in complex biological mixtures, which is a great help in elucidating the functions and mechanisms of this redox-based post-translational modification. However, detergents such as sodium dodecyl sulfate (SDS) and Triton X-100 adopted in these systems, which are hard to fully remove in the subsequent MS-based analyses, can suppress the peptide signals and influence the SNO-Cys site identification and the reproducibility of the experiments. Here we developed a detergent-free biotin-switch method, which applied urea to replace detergents, and successfully combined it with LC/MS/MS in the analysis of S-nitrosylated proteins. With this approach, 44 SNO-Cys sites were specified on 35 distinct proteins in S-nitrosoglutathione (GSNO)-treated HeLa cell extracts of proteins with good reproducibility. The LC/MS performance was greatly improved as analyzed with Pep3D and the amount of samples for analysis reduced from 40 mg used in the literature to 3-5 mg. For S-nitrosylated targets detected both in the control sample and in the GSNO-treated sample, extracted ion chromatography (XIC) was employed to estimate the quantitative change of S-nitrosylation (S-nitrosation), which facilitates the judgment on 'accept or reject' of the identified targets.

On-gel fluorescent visualization and the site identification of S-nitrosylated proteins

Mounting evidence indicates that S-nitrosylation of critical cysteine residues in a protein represents a common feature of protein function regulation and cell signaling. However, the progress in studying the exact role of S-nitrosylation has been hampered by a lack of rapid and accurate methods for the detection of these S-nitrosylated proteins and the exact modification sites. In this article, we report a fluorescence-based method in which the S-nitrosylated cysteines are converted into 7-amino-4-methylcoumarin-3-acetic acid (AMCA) fluorophore-labeled cysteines-termed the AMCA switch method. The labeled proteins are then analyzed by nonreducing SDS-PAGE, and the S-nitrosylated proteins can be readily detected as brilliant blue bands after the activation of ultraviolet light. Furthermore, the sites of modification can be determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after in-gel tryptic digestion of the fluorescent band, and the recognizable AMCA tag in the MS spectra ensures the accurate site identification of the nitrosocysteines. Therefore, our method offers some apparent advantages by direct visualization of on-gel image of S-nitrosylated proteins, shorter experiment time by skipping the anti-biotin immunoblotting step, and elimination of the potential interference of endogenous biotinylated proteins. Based on this method, we detected the S-nitrosylation and the modified site in bovine serum albumin and gankyrin after in vitro S-nitrosylation. Overall, our results indicate that the AMCA switch method is a fast and accurate method to identify the S-nitrosylated protein and the modification sites.

Real-time imaging of viable-apoptotic switch in GSNO-induced mouse thymocyte apoptosis

Many scientists are focusing on the apoptotic-necrotic or the necrotic-apoptotic switch and its mechanism, but little attention has been paid to the viable-apoptotic switch. Most of the techniques and methods used for detecting apoptosis are performed on fixed samples, yielding static information of specific time points. We have studied the viable-apoptotic switch in S-nitrosoglutathione (GSNO)-induced mouse thymocyte apoptosis in real-time by means of a novel technique, intensified charge coupled device (ICCD)-based real-time fluorescence micro-imaging, coupled with Annexin V-FITC labeling for phosphatidylserine (PS) translocation in cell membrane. We have successfully recorded the initiating time points (mostly at 2 h) of the viable-apoptotic switch in GSNO-initiated apoptosis, as well as shown the real-time differences between living and apoptotic thymocytes. These findings suggest that NO is also a switch molecule for the conversion from viable to apoptotic cell. Thymocytes cotreated by N-G-monomethyl-L-arginine acetate salt (L-NMMA) provide further evidence for this suggestion, as well as for the suggestion that L-NMMA prolongs the early stage of thymocyte apoptosis rather than strongly blocks it.

Magnetic Fields Protect from Apoptosis via Redox Alteration

Magnetic fields (MFs) are receiving much attention in basic research due to their emerging ability to alter intracellular signaling. We show here that static MFs with intensity of 6 mT significantly alter the intracellular redox balance of U937 cells. A strong increase of reactive oxygen species (ROS) and a decrease of glutathione (GSH) intracellular levels were found after 2 h of MF exposure and maintained thereafter. We found that also other types of MFs, such as extremely-low-frequency (ELF) MFs affect intracellular GSH starting from a threshold at 0.09 mT. We previously reported that static MFs in the intensity range of 0.3-60 mT reduce apoptosis induced by damaging agents (Fanelli et al., 1998). Here, we show that ELF-MFs are also able to protect U937 from apoptosis. Interestingly, this ability is limited to the ELF intensities able to alter redox equilibrium, indicating a link between MF's antiapoptotic effect and the MF alteration of intracellular redox balance. This suggests that MF-produced redox alterations may be part of the signaling pathway leading to apoptosis antagonism. Thus, we tested whether MFs may still exert an antiapoptotic action in cells where the redox state was artificially altered in both directions, that is, by creating an oxidative (via GSH depletion with BSO) or a reducing (with DTT) cellular environment. In both instances, MFs fail to affect apoptosis. Thus, a correct intracellular redox state is required in order for MFs to exert their antiapoptotic effect.

Dual effect of nitric oxide in immortalized and malignant human oral keratinocytes: induction of apoptosis and differentiation

BACKGROUND

Nitric oxide (NO) is known to act cytostatically on several tumor cell when functioning as an effector molecule of activated macrophages, but the differential effects of NO on immortalized and malignant oral keratinocytes have not been examined.

METHODS

We investigated the influence of NO on the proliferation, cell cycle, apoptosis, and differentiation of immortalized human oral keratinocytes (IHOK) and primary oral cancer cells (HN4) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, sulforhodamine B (SRB) assay, flow cytometry, nuclear DNA staining, and Western blotting.

RESULTS

The MTT and SRB assays indicated inhibited growth of IHOK and HN4 cells that were treated with sodium nitroprusside (SNP) at concentrations higher than 1 mM but not at lower SNP concentrations. The higher concentrations of SNP up-regulated the apoptosis-related protein expression, which is consistent with the analyses of sub-G(1) phase arrest, annexin V-FITC (fluorescein isothiocynate) staining, nuclear staining, and DNA fragmentation. On the other hand, the lower concentrations of SNP enhanced the expression of keratinocyte differentiation markers in IHOK and HN4 cells.

CONCLUSIONS

These data suggest that high concentrations of NO can inhibit the growth of IHOK and HN4 cells through the induction of apoptosis, while low concentrations of NO can induce cytodifferentiation. The dual effects of NO, namely, the induction of apoptosis or cytodifferentiation, have important implications for the possible anti-oral cancer treatment.

Nitric oxide regulates synthesis of gene products involved in keratinocyte differentiation and ceramide metabolism

During terminal differentiation of keratinocytes the expression of various proteins, which are required for the formation of the epidermal water barrier in the skin of land dwelling animals, is upregulated. Using a cell culture model for the differentiation of human keratinocytes and real-time PCR, we quantified the mRNA levels of several proteins involved in differentiation and ceramide metabolism. A calcium shift (1.1 mM CaCl2, 10 microM linoleic acid) for 8 days triggered an increase in mRNA levels of keratin 10 (75-fold), profilaggrin (55-fold), glucosylceramide synthase (40-fold), beta-glucocerebrosidase (30-fold), prosaposin (15-fold), acid sphingomyelinase (5-fold), and serine palmitoyltransferase (SPTLC2, 4-fold). However, mRNA levels of keratin 14 and acid ceramidase did not change significantly. On the other hand nitric oxide added at concentrations lower than 0.25mM stimulates proliferation of keratinocytes (Krischel et al., J. Invest. Dermatol. 111, 286-291, 1998). Accordingly, the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 0.2 mM) had no effect on the morphology of cultured keratinocytes, whereas in cultured human fibroblasts apoptosis was induced. The expression patterns obtained suggest that keratinocytes remain in a basal proliferative state, with a 3-fold increase in keratin 14 expression, a marked decrease in mRNA levels of differentiation markers and of most ceramide-metabolizing enzymes to negligible levels. The inhibitor of the NO synthase, N(G)-nitro-L-arginine-methyl ester (L-NAME, 10 mM), induced a transient increase in ceramide formation, followed by apoptosis in keratinocytes but not in fibroblasts. Both, SNAP and L-NAME, decreased the mRNA levels of all proteins involved in ceramide metabolism.

The endoplasmic reticulum-related events in S-nitrosoglutathione-induced neurotoxicity in cerebellar granule cells

Nitric oxide (NO)-induced neurotoxicities are involved in the pathogenesis of several neurodegenerative disorders featured by misfolded proteins. However, the details remain to be investigated. In the present work, we focus on the study of some endoplasmic reticulum-related events in S-nitrosoglutathione (GSNO)-induced neurotoxicity in cerebellar granule cells (CGCs) and we demonstrated that: (1) GSNO caused sustained elevation of intracellular calcium; (2) This calcium elevation resulted partially from the depletion of endoplasmic reticulum (ER) calcium stores; (3) There was ER stress which was indicated by the incomplete splicing of X-box binding protein (XBP-1) mRNA by 8-polysialyltransferase (Pst1); (4) GSNO upregulated the expression of the proapoptotic growth arrest and DNA damage-inducible gene (Gadd153) and caused the depletion of intracellular glutathione (GSH) pools. At the same time, GSNO downregulated the expression of the antiapoptotic gene Sarco/endoplasmic reticulum calcium-ATPase (SERCA2b) in parallel with the downregulation of the antiapoptotic ER chaperones-glucose-regulated protein genes (Grp78 and Grp94). These effects indicate that ER is one of the NO targets in GSNO-induced neurotoxicity in cerebellar granule cells besides mitochondria.

Effect of nitric oxide on cytotoxicity of Taxol: enhanced Taxol transcellular permeability

The present studies were aimed at testing the hypothesis that nitric oxide (NO) may enhance Taxol-induced cytotoxicity in carcinoma cells by increasing influx of Taxol into intracellular compartments. Prostate carcinoma cells (PC-3, LNCaP) and neuroblastoma cells (SKNDZ, CHP212) were used to investigate both transmembrane permeability and cytotoxicity of Taxol in the presence and absence of S-nitrosocaptopril (CapNO), a nitric oxide donating compound. The order of permeability rate of Taxol across the four cell lines was SKNDZ>LNCaP>PC-3>CHP212. Pretreatment of the cell lines with CapNO (100 microM) enhanced permeability of Taxol across prostate PC-3 and LNCaP cells, but not neuroblastoma SKNDZ and CHP212 cells. Taxol inhibited cell growth at nanomolar levels with IC(50)s of 0.21, 17.4, 96.4 and 842.9 nM corresponding to SKNDZ, PC-3, LNCaP and CHP212 cells, respectively. However, CapNO inhibited proliferation of the four cell lines at millimolar levels with IC(50)s ranging from 0.3 to 1.1 mM. Enhancing effect of CapNO (100 microM) on Taxol cytotoxicity were found in PC-3 and LNCaP cells, but not in SKNDZ and CHP212. The findings suggest that the cytotoxic potency of Taxol is mainly dependent upon the cell membrane permeabilization to Taxol, and the enhancing effect of CapNO on Taxol-induced cytotoxicity is primarily mediated via the increased influx of Taxol by NO into intracellular compartments, while NO-induced cytotoxicity cannot be excluded.

Nitric oxide at a low concentration protects murine macrophage RAW264 cells against nitric oxide-induced death via cGMP signaling pathway

1. We investigated the cytoprotective effect of low-dose nitric oxide (NO) on NO-induced cell death in mouse macrophage-like cell line RAW264. 2. Sodium nitroprusside (SNP), an NO donor, at a high concentration (4 mM) released cytochrome c from mitochondria and induced death in RAW264 cells. Acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspart-1-al (Ac-DEVD-CHO, 100-200 microM), a caspase-3 inhibitor, attenuated the SNP-induced cell death in a concentration-dependent manner. 3. Pretreatment with 100 microM SNP for 24 h, which had no effect on cell viability, attenuated the cell death and reduced cytochrome c release from mitochondria to the cytosol induced by 4 mM SNP. 4. LY83583 (1-3 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 30-100 microM), soluble guanylate cyclase inhibitors, negated the protective effect of the 100 microM SNP pretreatment. 5. Pretreatment with 1 mM dibutylyl guanosine-3',5'-cyclic monophosphate (DBcGMP), a cell-permeable guanosine-3',5'-cyclic monophosphate (cGMP) analogue, for 24 h inhibited both cytochrome c release and cell death induced by SNP. 6. Protein kinase G inhibitor KT5823 (10 microM) significantly reduced the cytoprotective effects of low-dose SNP and DBcGMP. 7. These results indicate that low-dose NO protects RAW264 cells from NO-induced apoptosis through cGMP production and activation of protein kinase G.

S-Nitrosoglutathione-induced mouse thymocyte apoptosis studied by fluorescence near-field scanning optical microscopy

This study is an attempt to deeply understand the mechanisms ensuring self-tolerance of T cells via clonal deletion of thymocytes and exploring T lymophocyte homeostasis by observing the apoptosis of single mouse thymocyte induced by S-nitrosoglutathione (GSNO, a nitric oxide donor) using fluorescence near-field scanning optical microscopy (NSOM) in illumination mode. The GSNO-induced thymocytes were stained with propidium iodide containing 0.01% Triton X-100 and excited with light of 488 nm and the emitting fluorescence at 525 nm. According to the NSOM fluorescence image and the simultaneously obtained topography image, the feature of mouse thymocyte apoptosis was characterized by scattering pattern of the fluorescence spots with the size 0.2-2.1 micro m at the full width at half-maximum of fluorescence intensity 78-80 kHz in the GSNO-treated thymocyte nucleus. Whereas there is no fluorescence from the untreated thymocyte. The intensity of the fluorescence from the dexamethasone-treated thymocyte was much stronger than that from GSNO-induced thymocytes. Furthermore, the fluorescence distribution in the latter were concentrated in the nucleus. Those results also demonstrate the advantages of NSOM such as high spatial resolution and the topography of biology samples.

Metabolism of S-nitrosoglutathione by endothelial cells

S-nitrosoglutathione (GSNO) is an inhibitor of platelet aggregation and has also been shown to protect the ischemic heart from reperfusion-mediated injury. Although GSNO is often used in cell culture as a source of nitric oxide, the mechanisms of GSNO metabolism are not well established. We show here that GSNO decomposition by bovine aortic endothelial cells has an absolute dependence on the presence of cystine in the cell culture medium. In addition, GSNO decay is inhibited by diethyl maleate, an intracellular glutathione scavenger, but not by buthionine sulfoximine, a glutathione synthesis inhibitor. This indicates that thiols in general, rather than specifically glutathione, are the major factors that influence GSNO decay. Only 40% of the nitroso group of GSNO could be recovered as nitrite/nitrate, suggesting that the primary route of GSNO decay is reductive and that nitric oxide is only a minor product of GSNO decay. We conclude that the intracellular thiol pool causes the reduction of extracellular disulfides to thiols, which then directly reduce GSNO.

S-nitrosoglutathione breakdown prevents airway smooth muscle relaxation in the guinea pig

Airway levels of the endogenous bronchodilator S-nitrosoglutathione (GSNO) are low in children with near-fatal asthma. We hypothesized that GSNO could be broken down in the lung and that this catabolism could inhibit airway smooth muscle relaxation. In our experiments, GSNO was broken down by guinea pig lung homogenates, particularly after ovalbumin sensitization (OS). Two lung protein fractions had catabolic activity. One was NADPH dependent and was more active after OS. The other was NADPH independent and was partially inhibited by aurothioglucose. Guinea pig lung tissue protein fractions with GSNO catabolic activity inhibited GSNO-mediated guinea pig tracheal ring relaxation. The relaxant effect of GSNO was partially restored by aurothioglucose. These observations suggest that catabolism of GSNO in the guinea pig 1) is mediated by lung proteins, 2) is partially upregulated after OS, and 3) may contribute to increased airway smooth muscle tone. We speculate that enzymatic breakdown of GSNO in the lung could contribute to asthma pathophysiology by inhibiting the beneficial effects of GSNO, including its effect on airway smooth muscle tone.

Decreased levels of nitrosothiols in the lower airways of patients with cystic fibrosis and normal pulmonary function

Airway S-nitrosothiols (SNOs) are naturally occurring bronchodilators. SNOs, nitrate, and nitrite were measured in bronchoalveolar lavage fluid of 23 patients with cystic fibrosis (CF) and mild pulmonary disease (aged 6-16 years) and 13 healthy children (aged 8-15 years). Concentrations of SNOs were decreased in the lower airways of patients with CF and mild pulmonary disease (median, range: 0, 0-320 nmol/L vs 80, 0-970 nmol/L) despite normal levels of the inert nitric oxide metabolites nitrate and nitrite (mean +/- SEM: 3.7 +/- 0.5 micromol/L vs 4.8 +/- 0.9 micromol/L). S-nitrosolation- mediated bioreactivities may be impaired by depletion of the CF airway SNO reservoir.

Nitric oxide down-regulates Epstein-Barr virus reactivation in epithelial cell lines

Nitric oxide (NO), a mediator of biological functions, has an antimicrobial activity against a variety of pathogens including viruses. In this study, we found that a constitutive, low level of inducible NO synthase (iNOS) mRNA was expressed in the EBV-infected gastric tissue-derived GT38 and GT39 cell lines, by analysis with the reverse transcription-polymerase chain reaction (RT-PCR) and Southern blotting. Treatment of these cells with a specific NOS inhibitor, NG-monomethyl-L-arginine (L-NMMA), induced the immediate-early, EBV transactivator gene BZLF1 protein ZEBRA, suggesting a significant increase in EBV reactivation by L-NMMA. Northern blotting demonstrated that BZLF1 and BRLF1 transcripts were also induced by 12-O-tetradecanoylphorbol-13 acetate (TPA). Meanwhile, constitutive expression of iNOS mRNA was inhibited by TPA. L-NMMA also enhanced TPA-induced expression of the BZLF1 gene. On the other hand, a NO donor, S-nitroso-N-acetylpenicillamine (SNAP), which releases NO in an aqueous solution, inhibited the TPA-induced BZLF1 gene expression in a dose-dependent manner at both mRNA and protein levels. These results demonstrated that NO is a regulatory factor in maintaining virus latency via inhibiting EBV reactivation in the infected epithelial cells.

Nitric oxide and apoptosis

Apoptosis occurs during normal development of an organism but also plays an important role under pathophysiological conditions. Nitric oxide (NO) exhibits a double-edged role in apoptosis induction. Both pro- and antiapoptotic effects of NO have been demonstrated. The proapoptotic effects appear to be linked to pathophysiological conditions, where high concentrations of NO are produced by the inducible nitric oxide synthase, especially in macrophages. In contrast, NO also prevents apoptosis induction by various stimuli. The antiapoptotic effects thereby were mainly mediated by low amounts of NO or stimulation of the constitutive, endothelial nitric oxide synthase. The present review characterizes the apoptotic cell death program and aims to give a detailed insight into the function of NO in affecting apoptotic processes in biological systems, with special regards to the immune and cardiovascular systems.

Nitric oxide and thiol groups

S-Nitroso(sy)lation reactions have recently been appreciated to regulate protein function and mediate 'nitrosative' stress. S-Nitrosothiols (SNOs) have been identified in a variety of tissues, and represent a novel class of signaling molecules which may act independently of homolytic cleavage to NO - and, indeed, in a stereoselective fashion - or be metabolized to other bioactive nitrogen oxides. It is now appreciated that sulfur-NO interactions have critical physiological relevance to mammalian neurotransmission, ion channel function, intracellular signaling and antimicrobial defense. These reactions are promising targets for the development of new medical therapies.

Nitric oxide stimulates chronic ceramide formation in glomerular endothelial cells

Exposure of glomerular endothelial cells for 24 h to compounds releasing NO, including spermine-NO, MAHMA-NO, and S-nitroso-glutathione, results in a dose-dependent and delayed (after 24 h) increase in the lipid signaling molecule ceramide. This NO-induced stimulation occurs in a cGMP-independent fashion since the membrane-permeant cGMP analogue dibutyryl cGMP has no effect on chronic ceramide production. Short-term incubation of endothelial cells for 20 min reveals that NO and dibutyryl cGMP fail to stimulate an acute ceramide increase, whereas TNF-alpha, a well-known activator of sphingomyelinases, is able to acutely increase ceramide formation. Interestingly, N-oleoylethanolamine, an acidic ceramidase inhibitor, potentiates NO-induced chronic ceramide production, indicating that ceramide generation rather than ceramide metabolism is modulated by NO. Furthermore, NO-induced delayed ceramide formation is partially inhibited by the thiol-specific inhibitor iodoacetamide and the radical scavenger alpha-tocopherol, suggesting a regulatory role of thiol-containing enzymes and the involvement of a redox-sensitive mechanism. In addition, NO causes an increased DNA fragmentation in glomerular endothelial cells which is further enhanced by N-oleoylethanolamine and can be mimicked by exogenous ceramide. In summary, these results imply that ceramide represents an important mediator of NO-triggered chronic cell responses like apoptosis. Inhibition of ceramide synthesis may provide a new therapeutic approach to the treatment of pathological conditions involving increased NO formation.

Nitric oxide donors induce stress signaling via ceramide formation in rat renal mesangial cells

Exogenous NO is able to trigger apoptosis of renal mesangial cells, and thus may contribute to acute lytic phases as well as to resolution of glomerulonephritis. However, the mechanism involved in these events is still unclear. We report here that chronic exposure of renal mesangial cells for 24 h to compounds releasing NO, including spermine-NO, (Z)-1-{N-methyl-N-[6-(N-methylammoniohexyl)amino]}diazen-1-ium-1, 2-diolate (MAHMA-NO), S-nitrosoglutathione (GS-NO), and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) results in a potent and dose-dependent increase in the lipid signaling molecule ceramide. Time courses reveal that significant effects occur after 2-4 h of stimulation with NO donors and reach maximal levels after 24 h of stimulation. No acute (within minutes) ceramide production can be detected. When cells were stimulated with NO donors in the presence of phorbol ester, a direct activator of protein kinase C, both ceramide production and DNA fragmentation are completely abolished. Furthermore, addition of exogenous ceramide partially reversed the inhibitory effect of phorbol ester on apoptosis, thus suggesting a negative regulation of protein kinase C on ceramide formation and apoptosis. In contrast to exogenous NO, tumor necrosis factor (TNF)-alpha stimulates a very rapid and transient increase in ceramide levels within minutes but fails to induce the late-phase ceramide formation. Moreover, TNF fails to induce apoptosis in mesangial cells. Interestingly, NO and TNFalpha cause a chronic activation of acidic and neutral sphingomyelinases, the ceramide-generating enzymes, whereas acidic and neutral ceramidases, the ceramide-metabolizing enzymes, are inhibited by NO, but potently stimulated by TNFalpha. Furthermore, in the presence of an acidic ceramidase inhibitor, N-oleoylethanolamine, TNFalpha leads to a sustained accumulation of ceramide and in parallel induces DNA fragmentation. In summary, our data demonstrate that exogenous NO causes a chronic up-regulation of ceramide levels in mesangial cells by activating sphingomyelinases and concomitantly inhibiting ceramidases, and that particularly the late-phase of ceramide generation may be responsible for the further processing of a proapoptotic signal.

NF-kappaB and AP-1 activation by nitric oxide attenuated apoptotic cell death in RAW 264.7 macrophages

A toxic dose of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO; 1 mM) promoted apoptotic cell death of RAW 264.7 macrophages, which was attenuated by cellular preactivation with a nontoxic dose of GSNO (200 microM) or with lipopolysaccharide, interferon-gamma, and NG-monomethyl-L-arginine (LPS/IFN-gamma/NMMA) for 15 h. Protection from apoptosis was achieved by expression of cyclooxygenase-2 (Cox-2). Here we investigated the underlying mechanisms leading to Cox-2 expression. LPS/IFN-gamma/NMMA prestimulation activated nuclear factor (NF)-kappaB and promoted Cox-2 expression. Cox-2 induction by low-dose GSNO demanded activation of both NF-kappaB and activator protein-1 (AP-1). NF-kappaB supershift analysis implied an active p50/p65 heterodimer, and a luciferase reporter construct, containing four copies of the NF-kappaB site derived from the murine Cox-2 promoter, confirmed NF-kappaB activation after NO addition. An NF-kappaB decoy approach abrogated not only Cox-2 expression after low-dose NO or after LPS/IFN-gamma/NMMA but also inducible protection. The importance of AP-1 for Cox-2 expression and cell protection by low-level NO was substantiated by using the extracellular signal-regulated kinase inhibitor PD98059, blocking NO-elicited Cox-2 expression, but leaving the cytokine signal unaltered. Transient transfection of a dominant-negative c-Jun mutant further attenuated Cox-2 expression by low-level NO. Whereas cytokine-mediated Cox-2 induction relies on NF-kappaB activation, a low-level NO-elicited Cox-2 response required activation of both NF-kappaB and AP-1.

Calcium-dependent nitric oxide synthase activity in rat thymocytes

We examined the conversion of L-[3H]arginine to L-[3H]citrulline in lysate from rat thymocytes, which was dependent on Ca2+ and cofactors (FAD, BH4, NADPH). Removal of Ca2+ of the medium, reduced the total L-[3H]citrulline formation by about 97%. The L-[3H]citrulline formation was completely inhibited by the NO synthase inhibitors, NG-nitro-L-arginine and NG-monomethyl-L-arginine, with values for IC50 of 1.2 microM and 19.4 microM, respectively. In intact thymocytes, the L-[3H]citrulline formation was dependent on the intracellular Ca2+ ([Ca2+]i) concentration. Increasing the extracellular free-Ca2+ concentration up to 1.5 mM, was accompanied by an increase in [Ca2+]i inside the thymocytes and there was a parallel increase in the intracellular L-[3H]citrulline formation, which reached a maximal value of 371.2 nM of [Ca2+]i. Addition of NG-nitro-L-arginine to the medium, completely inhibited the formation of L-[3H]citrulline. The immunolabeling study revealed that 15% of the thymocytes isolated from rat thymus constitutively expressed the endothelial isoform of NO synthase.

Nitric oxide and its role in apoptosis

Nitric oxide (NO.), a potentially toxic molecule, has been implicated in a wide range of diverse (patho)physiological processes. It is appreciated that the production of NO. from L-arginine is important for nonspecific host defense, helping to kill tumors and intracellular pathogens. Cytotoxicity as a result of a massive NO.-formation is now established to initiate apoptosis. Apoptotic cell death in RAW 264.7 macrophages and several other systems as a result of inducible NO-synthase activation comprises upregulation of the tumor suppressor p53, activation of caspases, chromatin condensation, and DNA fragmentation. The involvement of NO was established by blocking adverse effects by NO-synthase inhibition. Overexpression of the antiapoptotic protein Bcl-2 rescued cells from apoptosis by blocking signal propagation downstream of p53 and upstream of caspase activation. As the wide variety of NO.-effects is achieved through its interactions with targets via redox and additive chemistry, the biological milieu, as a result of internal and external stimuli, may modulate toxicity. Therefore, transducing pathways of NO. are not only adopted to cytotoxicity but also refer to cell protection. NO.-signaling during protection from apoptosis is in part understood by the requirement of gene transcription and protein synthesis. NO.-formation causes upregulation of protective proteins such as heat shock proteins, cyclooxygenase-2, or heme oxygenase-1 which in a cell specific way may attenuate apoptotic cell death. Alternatively, protection may result as a consequence of a diffusion controlled NO./O2- (superoxide) interaction. The NO./O2--interaction redirects the apoptotic initiating activity of either NO. or O2- towards protection as long as reduced glutathione compensates the resultant oxidative stress. Protective principles may further arise from cyclic GMP formation or thiol modification. NO shares with other toxic molecules such as tumor necrosis factor-alpha the unique ability to initiate and to block apoptosis, depending on multiple variables that are being elucidated. The crosstalk between cell destructive and protective signaling pathways, their activation or inhibition under the modulatory influence of NO. will determine the role of NO in apoptotic cell death.

Enzyme inactivation through sulfhydryl oxidation by physiologic NO-carriers

Nitric oxide (NO) is a pluripotent regulatory molecule, yet the molecular mechanisms by which it exerts its effects are largely unknown. Few physiologic target molecules of NO have been identified, and even for these, the modifications caused by NO remain uncharacterized. Human glutathione reductase (hGR), a central enzyme of cellular antioxidant defense, is inhibited by S-nitrosoglutathione (GSNO) and by diglutathionyl-dinitroso-iron (DNIC-[GSH]2), two in vivo transport forms of NO. Here, crystal structures of hGR inactivated by GSNO and DNIC-[GSH]2 at 1.7 A resolution provide the first picture of enzyme inactivation by NO-carriers: in GSNO-modified hGR, the active site residue Cys 63 is oxidized to an unusually stable cysteine sulfenic acid (R-SOH), whereas modification with DNIC-[GSH]2 oxidizes Cys 63 to a cysteine sulfinic acid (R-SO2H). Our results illustrate that various forms of NO can mediate distinct chemistry, and that sulfhydryl oxidation must be considered as a major mechanism of NO action.

Nitrosative and oxidative stress induced heme oxygenase-1 accumulation in rat mesangial cells

The formation of nitric oxide (NO.) and superoxide (O2-) promotes rat mesangial cell death. Apoptotic death is characterized by DNA fragmentation, caspase-3 activation and concomitant poly(ADPribose) polymerase cleavage, as well as accumulation of the tumor suppressor protein p53. In close association with apoptotic parameters we noticed upregulation of heme oxygenase by the NO donor S-nitrosoglutathione (GSNO) and the redox cycler 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) in a time- and concentration-dependent manner. In response to the NO. donor, heme oxygenase-1 expression was more easily obtained than initiation of apoptosis. Radical (NO./O2-) cogeneration abrogated DNA fragmentation, suppressed caspase activation and lowered p53 accumulation, thereby promoting cell survival of mesangial cells. In contrast, heme oxygenase-1 expression remained elevated under conditions of GSNO/DMNQ coadministration. Conclusively, heme oxygenase-1 is a stress marker for both nitrosative and oxidative stress. Accumulation of heme oxygenase-1 is found under conditions of both, apoptotic cell death and cell survival, thereby questioning a specific cytoprotective role of heme oxygenase-1 under conditions of NO. and/or O2- formation in rat mesangial cells.

U937 apoptotic cell death by nitric oxide: Bcl-2 downregulation and caspase activation

Upon treatment with NO-releasing compounds such as S-nitrosoglutathione or spermine NO, human myeloid leukemia U937 cells undergo apoptosis. Early NO-mediated signals comprise activation of a Z-A-DCB (benzoyloxycarbonyl-Asp-CH2OC(O)-2,6-dichlorobenzene)-sensit ive, caspase-3 like cysteine protease that cleaved poly (ADP-ribose) polymerase (PARP), U1 small nuclear ribonucleoprotein (U1 snRNP), and the fluorogenic substrate N-acetyl-Asp-Glu-Val-Asp-7-amido-4-methylcoumarin. In association with these early apoptotic alterations p21 (WAF1/Cip1) is upregulated, but NO affected cell proliferation and apoptosis at a similar dose. At later time points the classical antiapoptotic protein Bcl-2 is downregulated, indicating that decreased Bcl-2 expression is secondary and not a prerequisite for initiation of apoptosis. N-Acetylcysteine (1 mM) interfered with NO-mediated apoptotic signaling, blocking DNA fragmentation as well as PARP and U1 snRNP cleavage. In contrast Z-A-DCB suppressed DNA fragmentation and U1 snRNP cleavage, while PARP breakdown proceeded unaltered. Observing proteolytic PARP digestion without apoptotic alterations questions PARP cleavage as an apoptotic parameter. These results suggest that a Z-A-DCB-sensitive caspase that is distinct from the PARP-cleaving enzyme is activated during NO exposure. NO-mediated apoptotic signaling in U937 cells activates caspases, some of which are dispensable for propagating the death signal.

Nitric oxide and superoxide induced p53 and Bax accumulation during mesangial cell apoptosis

During proliferative glomerulonephritis, the early phase of mesangiolysis is linked to increased nitric oxide (NO) production. NO. as well as superoxide (O2-) are inflammatory mediators that are generated by mesangial cells (MC) after cytokine stimulation. Added individually, both radicals induce MC apoptosis. However, the co-existence of a defined NO./O2- ratio is cross-protective. Apoptosis is characterized by specific features such as chromatin condensation, DNA strand breaks, and the occurrence of apoptotic regulating proteins. The tumor suppressor p53 and Bax (Bcl-2 associated protein x) are considered to be classical death promotors, which accumulate after toxic insults. To study p53 and Bax protein accumulation in NO. and/or O2(-)-induced apoptosis, we used the NO-donor S-nitrosoglutathione (GSNO) and the redox cycler 2,3-dimethoxy-1,4-naphtoquione (DMNQ). Both agonists initiated DNA fragmentation in a concentration dependent manner associated with transient p53 and Bax up-regulation. Co-generation of NO./O2- resulted not only in reduced DNA fragmentation, but also in decreased Bax accumulation. Comparable to the NO./O2- co-generation, cytokines failed to induce apoptosis. In contrast, cytokines in combination with pyrrolidine dithiocarbamate, which blocks endogenous superoxide dismutase, allowed p53 and Bax accumulation as well as DNA fragmentation. Our results demonstrate p53 and Bax as early components in NO. and O2(-)-induced rat MC apoptosis and point to the NO./O2- interaction as a naturally occurring cell defense mechanism.

Nitric oxide donors induce apoptosis in glomerular mesangial cells, epithelial cells and endothelial cells

Renal mesangial cells exposed to inflammatory cytokines produce high concentrations of nitric oxide (NO) which may exert cytotoxic actions. We report here that glomerular mesangial cells, endothelial cells and epithelial cells in culture are themselves targets for NO and undergo apoptotic cell death upon exposure to high concentrations of NO. NO generated from different NO-releasing compounds as well as NO-saturated solution induce apoptosis in all three cell types as demonstrated by internucleosomal DNA fragmentation, an enrichment of cytosolic DNA/histone complexes, an increasing number of cellular 3'-OH-fragmented DNA ends and typical nuclear chromatin condensation. Induction of apoptosis was found to be dependent on protein synthesis and is preceded by expression of the tumour suppressor gene product p53 in mesangial cells. Induction of inducible NO synthase in mesangial cells by interleukin-1 beta leads to excessive formation of NO by the cells as measured by nitrite production. However, there was no evidence for apoptotic changes in mesangial cells triggered by endogenously produced NO. Co-cultures of glomerular endothelial or epithelial cells with interleukin-1 beta-activated mesangial cells expressing inducible NO synthase do not show apoptotic alterations in endothelial or epithelial cells. Moreover, preincubation of mesangial cells with interleukin-1 beta protects the cells from apoptosis induced by subsequent addition of exogenous NO thus suggesting that interleukin-1 beta not only triggers the expression of inducible NO synthase and massive NO formation but simultaneously stimulates a protecting principle in the cells. In summary, these results suggest that exogenous NO can induce apoptosis in all three types of intrinsic glomerular cells. However, whether endogenously produced NO can fulfil this function critically depends on a balance between a yet to be defined protective mechanism and inducible NO synthase expression in mesangial cells in response to interleukin-1 beta and eventually other inflammatory cytokines.

Nitric oxide stimulates stress-activated protein kinases in glomerular endothelial and mesangial cells

Exposure of rat glomerular mesangial cells and primary cultures of bovine glomerular endothelial cells to compounds releasing nitric oxide (NO), including MAHMA-NONOate, S-nitrosoglutathione, and spermine-NO, results in a time- and concentration-dependent activation of stress-activated protein kinases (SAPK) as measured by the phosphorylation of c-Jun in a solid phase kinase assay. Dibutyryl cGMP had no effect on SAPK activity. Pretreatment of the cells with the tyrosine kinase inhibitor genistein strongly attenuated NO-induced c-Jun phosphorylation. Furthermore, N-acetylcysteine markedly reduced the activation of SAPK in response to NO. These studies identify SAPK as a target for NO which may be critical for the NO-induced apoptosis of glomerular mesangial and endothelial cells.