The regulatory role of nitric oxide in apoptosis

Clozapine induces oxidative stress and proapoptotic gene expression in neutrophils of schizophrenic patients

The present study examined cellular effects of the atypical antipsychotic drug clozapine on blood cells of treated patients with and without clozapine-induced agranulocytosis (CA). Blood from one patient who commenced clozapine treatment was examined at weekly intervals for 128 days. Olanzapine-treated (n = 5) and polymedicated (n = 14) schizophrenic patients, as well as healthy subjects (n = 19) and septic shock patients (n = 8), were studied for comparison. We observed dramatically increased numbers of native neutrophils stained for superoxide anion production (P < or = 0.005, n = 10) and significantly elevated expression levels of the proapoptotic genes p53 (P < or = 0.020), bax alpha (P < or = 0.001), and bik (P < or = 0.002) in all tested non-CA patients (n = 19) and CA patients (n = 4). In non-CA patients, the expression of these genes did not correlate to the percentage of apoptotic neutrophils (2.0% +/- 1.3%), but in CA patients about 37% of the neutrophils show morphologic signs of apoptosis (P < or = 0.001). Under G-CSF therapy of CA, the number of apoptotic neutrophils and the expression of the proapoptotic genes decreased significantly. In conclusion, high production of reactive oxygen species in neutrophils of clozapine-treated patients, together with increased expression of proapoptotic genes, suggests that neutrophils are predisposed to apoptosis in schizophrenic patients under clozapine therapy. The correlation between drug and proapoptotic markers was highest for clozapine and bax alpha as well as superoxide anion radicals. This indicates oxidative mitochondrial stress in neutrophils of clozapine-treated patients which probably contributes to the induction of apoptosis and sudden loss of neutrophils and their precursors in CA patients.

Effect of staurosporine-induced apoptosis on endothelial nitric oxide synthase in transfected COS-7 cells and primary endothelial cells

Nitric oxide (NO) may block apoptosis by inhibiting caspases via S-nitrosylation of cysteines. Here, we investigated whether effector caspases might cleave and thereby inhibit endothelial nitric oxide synthase (eNOS). Exposure of eNOS-transfected COS-7 cells and bovine aortic endothelial cells to staurosporine resulted in significant loss of 135-kDa eNOS protein and activity, and appearance of a 60-kDa eNOS fragment; effects were inhibited by the general caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp[OMe]-fluoromethyl ketone (zVAD-fmk). In eNOS-transfected COS-7 cells, staurosporine-induced activation of caspase-3 and poly(ADP-ribose) polymerase (PARP) cleavage coincided with increased eNOS degradation and decreased activity. Loss of eNOS activity was greater than the degree of proteolysis. Incubation of immunoprecipitated eNOS with caspase-3, caspase-6 or caspase-7 resulted in eNOS cleavage. Staurosporine, a general protein kinase inhibitor, also reduced phosphorylation and decreased calmodulin binding, an effect that may explain the reduction in activity. eNOS, therefore, is both an inhibitor of apoptosis and a target of apoptosis-associated proteolysis.

Regulation of lipopolysaccharide-induced inflammatory response by glutathione S-transferase P1 in RAW264.7 cells

Glutathione S-transferase P1(GSTP1) plays an important role in the detoxification and xenobiotics metabolism. Here, we show that GSTP1 is also involved in LPS (lipopolysaccharide)-induced inflammatory response. GSTP1 expression, determined at the transcription and translation levels, were upregulated by the LPS stimulation in RAW264.7 macrophage-like cells. GSTP1 inhibited LPS-induced mitogen-activated protein kinases MAPKs including ERK, JNK and p38 as well as NF-kappaB activation dose- and time-dependently in transient transfected and stable transfected cells. Moreover this inhibition of the signaling pathways resulted in the decrease of tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO) synthesis. These data suggest that the GSTP1 prevents LPS-induced excessive production of pro-inflammatory factors and plays an anti-inflammatory role in response to LPS.

Actinodaphnine induces apoptosis through increased nitric oxide, reactive oxygen species and down-regulation of NF-kappaB signaling in human hepatoma Mahlavu cells

Actinodaphnine, extracted from Cinnamomum insularimontanum (Lauraceae), possesses cytotoxicity in some cancers, but the mechanism by which actinodaphnine induces apoptosis in human hepatoma cells remains poorly understood. In this study, we investigated the mechanisms of apoptosis induced by actinodaphnine in human hepatoma Mahlavu cells. Treatment with actinodaphnine dose-dependently induced apoptosis in Mahlavu cells that correlated with increased intracellular nitric oxide (NO) and reactive oxygen species (ROS), disruptive mitochondrial transmembrane potential (DeltaPsi(m)), and activation of caspase 3/7. Our data also demonstrated that actinodaphnine down-regulated activity of nuclear factor kappaB (NF-kappaB). The apoptotic response to actinodaphnine was markedly decreased in Mahlavu cells pretreated with dexsamethasone, a NO inhibitor, N-acetylcysteine (NAC), an antioxidant, and Boc-Asp(OMe)-fmk, a broad caspases inhibitor. These results suggested that actinodaphnine-induced apoptosis is initially mediated through the NO and/or ROS increase and caspases-dependent pathway. In conclusion, our results indicate that an increase of ROS and/or NO is the initial essential event that results in the decrease of DeltaPsi(m) and the activation of caspases that commits the cells to the apoptotic pathway in actinodaphnine-treated hepatoma Mahlavu cells.

Glutathione depletion renders rat hepatocytes sensitive to nitric oxide donor-mediated toxicity

Nitric oxide (NO) can be either cytoprotective or cytotoxic in hepatocytes, depending on conditions within the cell. We hypothesized that redox status is a determinant of NO effects on cell viability. To cause the disturbance of redox homeostasis in the hepatocytes, cells were treated with the following glutathione (GSH) depleting agents: (1) chronic depletion by 18 hours pretreatment with buthionine sulfoximine (BSO), which depletes GSH by blocking its biosynthesis; and (2) acute depletion by 1 hour pretreatment with diethyl maleate (DEM), which conjugates GSH by the GSH-S-transferase catalyzed reaction. S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a NO donor, was added after removal of GSH-depleting agents. Individual treatment with either SNAP or GSH depletion did not appreciably affect viability. A significant increase of cytotoxicity in hepatocytes was observed with the combination of a concentration and time course regimen of SNAP and GSH depletion. SNAP treatment of GSH-depleted hepatocytes led to an increase in LDH release and oxidative stress, disruption of mitochondrial membrane potential, the presence of nitrotyrosine (an indicator of peroxynitrite (ONOO-) generation), and a decrease in adenosine triphosphate (ATP) content. The interference of mitochondrial respiratory enzymes, especially with the combination treatments, indicated different levels of disturbance of electron transfer, superoxide generation, and ATP production. Other commonly used NO donors were found to exhibit lower and slower toxicity in the setting of GSH depletion than that evident with SNAP. In conclusion, the disruption of cellular redox homeostasis by GSH depletion leads hepatocytes to be more susceptible to NO (especially S-nitrosothiols) and subsequent necrotic cell death.

Sensitivity to ALA-PDT of cell lines with different nitric oxide production and resistance to NO cytotoxicity

In this work, we studied the in vitro interactions between aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) and nitric oxide (NO), as well as the interactions between ALA, porphyrins and some NO donors and precursors. We employed three murine adenocarcinoma cell lines: LM2, which does not produce NO; LM3, which produces NO, and LM3-SNP, a variant of LM3 resistant to NO producing the same amount of NO as the parental. We did not find cross-resistance between NO-induced cytotoxicity and ALA-PDT. In spite of the lower porphyrin synthesis, LM2 cells show the highest sensitivity to ALA-PDT. However, we hypothesised that this is not related to the lack of endogenous NO production, because modulation of NO levels did not modify the response to PDT in any of the cell lines. Two unexpected results were found: the enhancement of NO production from the donor sodium nitroprusside (SNP) induced by ALA in both cells and medium, and the inhibition by ALA of NO production from arginine. We also found that SNP strongly protected the cells from ALA-PDT by impairing porphyrin biosynthesis as a consequence of an inhibition of the enzyme ALA dehydratase. We were not able to evaluate the action of NO derived from SNP because of the unexpected porphyrin impairment. On the other hand, impairment of NO from Arginine driven by ALA, although not modulating in vitro the ALA-PDT response, by increasing in vivo blood flow, may be contributing to the mechanism of tumour cures.

No cross-resistance between ALA-mediated photodynamic therapy and nitric oxide

Photodynamic therapy (PDT) interactions with nitric oxide (NO) are not well understood. In this work, we attempted to elucidate whether NO cytotoxicity and PDT from aminolevulinic acid (ALA) have independent cell damage mechanisms. We employed the murine mammary adenocarcinoma cell line LM3 and its NO-resistant variant LM3-SNP obtained after successive exposures to sodium nitroprusside (SNP). No cross-resistance was found between NO cytotoxicity and ALA-PDT; LM3-SNP cells were not more resistant to ALA-PDT than the parental line, instead they were more sensitive. We also induced resistance to ALA-PDT in LM3-SNP cells after multiple cycles of photodynamic treatment. We isolated two clones, identified as Clon 1 and Clon 3, which were 9.2 and 12.5 times more resistant to ALA-PDT than the parental lines, showing that resistance to NO did not interfere in the development of PDT resistance. In addition, the sensitivity to NO decreased in Clon 1 and increased in Clon 3, but they did not show any modifications in NO production. All the cell lines have similar GSH content and GSH transferases activities. However, GSSG content is markedly lower in LM3-SNP, Clon 1, and Clon 3 compared to parental LM3 line and consequently GSH/GSSG ratios are also higher. Our results suggest that different degrees of NO resistance of tumours would not correlate with resistance to PDT.

Nitric oxide as a modulator of apoptosis

Unphysiologically high levels of nitric oxide (NO*) are mutagenic and may contribute to carcinogenesis. Proapoptotic and anitiapoptotic functions of NO* have been reported in various in vivo and in vitro experimental models. The complexity of biological responses induced is a consequence of the multiple chemical pathways through which NO* causes damage to critical cellular macromolecules. The extent and kinetics of apoptotic and other responses are highly dependent on steady-state NO* levels, cumulative total dose and cell type. Steady-state and total dose thresholds have been defined, both of which must be exceeded for the induction of apoptosis and other responses in human lymphoblastoid cells. DNA damage, protein modifications, p53 activation and mitochondrial respiratory inhibition contribute to NO*-mediated apoptosis via mitochondrial and Fas receptor pathways. Multifaceted cellular defense systems including glutathione, antioxidant enzymes and Nrf2-Keap1 signaling participate in protective responses to mitigate damage by toxic levels of NO*.

The nitric oxide prodrug, V-PYRRO/NO, protects against cadmium toxicity and apoptosis at the cellular level

The liver is an important target tissue of cadmium. The compound O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2 diolate (V-PYRRO/NO) is a liver-selective nitric oxide (NO) prodrug that is metabolized by hepatic P450 enzymes to release NO in hepatocytes. In vivo, V-PYRRO/NO can protect against the toxicity of various hepatotoxicants, including cadmium. Since NO is an effective vasodilator, whether this protective effect against cadmium toxicity is at the level of the hepatic vascular system or actually within the liver cells has not been defined. Thus, we studied the effects of V-PYRRO/NO pretreatment on cadmium-induced toxicity and apoptosis in cultured rat liver epithelial (TRL 1215) cells. Cells were pretreated with V-PYRRO/NO at 500 or 1000 microM for up to 24 h, then exposed to cadmium (as CdCl2) for additional 24 h and cytotoxicity was measured. Cadmium was significantly less cytotoxic in V-PYRRO/NO (1000 microM) pretreated cells (LC50=6.1+/-0.6 microM) compared to control cells (LC50=3.5+/-0.4 microM). TRL 1215 cells acted upon the prodrug to release NO, producing nitrite levels in the extracellular media after 24 h of exposure to 500 or 1000 microM V-PYRRO/NO measured at 87.0+/-4.2 and 324+/-14.8 microM, respectively, compared to basal levels of 7.70+/-0.46 microM. V-PYRRO/NO alone produced small increases in metallothionein (MT), a metal-binding protein associated with cadmium tolerance. However, V-PYRRO/NO pretreatment greatly enhanced cadmium induction of MT. V-PYRRO/NO pretreatment also markedly reduced apoptotic cell death induced by cadmium (5 microM), apparently by blocking cadmium-induced activation of the c-Jun N-terminal kinase (JNK) pathway. Thus, the prodrug, V-PYRRO/NO, protects against the adverse effects of cadmium directly within rat liver cells apparently through generation of NO and, at least in part, by facilitation of cadmium-induced MT synthesis.

Ookinete-induced midgut peroxidases detonate the time bomb in anopheline mosquitoes

Previous analysis of the temporal-spatial relationship between ookinete migration and the cellular localization of genes mediating midgut immune defense responses suggested that, in order to survive, parasites must complete invasion before toxic chemicals ("a bomb") are generated by the invaded cell. Recent studies indicate that ookinete invasion induces tyrosine nitration as a two-step reaction, in which NOS induction is followed by a localized increase in peroxidase activity. Peroxidases utilize nitrite and hydrogen peroxide as substrates, and detonate the time bomb by generating reactive nitrogen intermediates, such as nitrogen dioxide, which mediate nitration. There is evidence that peroxidases also mediate antimicrobial responses to bacteria, fungi and parasites in a broad range of biological systems including humans and plants. Defense reactions that generate toxic chemicals are also potentially harmful to the host mounting the response and often results in apoptosis. The two-step nitration pathway is probably an ancient response, as it has also been described in vertebrate leukocytes and probably evolved as a mechanism to circumscribe the toxic products generated during defense responses involving protein nitration.

Lymphocytes of dogs immunised with purified excreted-secreted antigens of Leishmania infantum co-incubated with Leishmania infected macrophages produce IFN gamma resulting in nitric oxide-mediated amastigote apoptosis

The role of nitric oxide (NO) in the anti-leishmanial activity has been confirmed both in vitro and in vivo. Recently, we demonstrated that NO-mediated apoptosis-like amastigote death pathway is an important and highly regulated mechanism used for the clearance of Leishmania within infected murine macrophages stimulated to produce NO endogenously. To further characterize these important effector mechanisms in dog, a natural host-reservoir of L. infantum/L. chagasi, we have developed an ex vivo infection model of canine macrophages. Exposure of L. infantum-infected macrophages to autologous peripheral lymphocytes derived from dogs immunised with purified excreted-secreted antigens of L. infantum promastigotes (LiESAp) formulated with muramyl dipeptide (MDP) as adjuvant resulted in a significant leishmanicidal effect due to interferon (IFN)-gamma dependent macrophage activation. Concomitant accumulation of NO(3)(-)/NO(2)(-) in supernatants of co-cultured cells and in situ staining of parasites with terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling (TUNEL) and YOPRO-1 showed that NO-mediated apoptosis of intracellular L. infantum amastigotes is occurring in canine macrophages as previously observed in mouse models. Monitoring these parameters in dogs after immunisation and before experimental challenge can represent a useful and easy way to rapidly evaluate vaccine candidates against canine visceral leishmaniasis.

Liriodenine inhibits the proliferation of human hepatoma cell lines by blocking cell cycle progression and nitric oxide-mediated activation of p53 expression

Liriodenine was isolated from the leaves of Michelia compressa. This study was designed to assess cell cycle arrest, the production of nitric oxide (NO) and p53 expression in liriodenine-treated human hepatoma cell lines, including wild-type p53 (Hep G2 and SK-Hep-1). As evidenced by flowcytometric studies, liriodenine induced cell cycle G(1) arrest and inhibited DNA synthesis in Hep G2 and SK-Hep-1 cell lines. The p53, iNOS expression and intracellular NO level were markedly increased in Hep G2 cells after liriodenine treatment. A NO inhibitor, carboxy-PTIO inhibited the p53 expression induced by liriodenine. In addition, liriodenine could not induce obvious cytotoxicity in normal human IMR-90 cell line. These results demonstrate that NO production and p53 expression are critical factors in liriodenine-induced growth inhibition in human wild-type p53 hepatoma cells.

Elevated expression of iNOS mRNA and protein in coeliac disease

BACKGROUND

The role of nitric oxide synthase (NOS) in the pathophysiology of coeliac disease (CD) was investigated.

METHODS

We examined mRNA (reverse transcription multiplex polymerase chain reaction) and protein expression (Western blotting) of i,e and nNOS in enterocytes isolated from the duodenum of patients with untreated CD (n=22) and iron deficiency anaemia (IDA, n=22). Expression of IL1beta and TNFalpha, two pivotal "NOS-controlling" cytokines, was also studied.

RESULTS

Enterocytes from both patient groups were negative for eNOS and TNF(alpha) message but positive for n and iNOS. nNOS gene expression was not statistically different between groups (158.38+/-29.11% vs. 114.95+/-24.17%, IDA vs. CD, p=0.07, Mann-Whitney U). iNOS expression was higher in patients with CD when compared to patients with IDA (96.95+/-17.82% vs. 48.76+/-8.07%, p<0.006). Low levels of IL1beta mRNA (15.66+/-3.70%) were detected in nine samples-all of these samples were isolated from patients with CD representing a positive result in 40% of coeliac patients. In support of these observations, patients with CD expressed more iNOS protein than those with IDA (159.7+/-14.9% vs. 69.8+/-20%, p<0.05).

CONCLUSION

These results suggest that iNOS could be an important mediator in coeliac disease. Expression of this regulatory protein may be under the control of IL1beta.

Thiamethoxam Induced Mouse Liver Tumors and Their Relevance to Humans

Thiamethoxam, a neonicotinoid insecticide, which is not mutagenic either in vitro or in vivo, caused an increased incidence of liver tumors in mice when fed in the diet for 18 months at concentrations in the range 500 to 2500 ppm. A number of dietary studies of up to 50 weeks duration have been conducted in order to identify the mode of action for the development of the liver tumors seen at the end of the cancer bioassay. Both thiamethoxam and its major metabolites have been tested in these studies. Over the duration of a 50-week thiamethoxam dietary feeding study in mice, the earliest change, within one week, is a marked reduction (by up to 40%) in plasma cholesterol. This was followed 10 weeks later by evidence of liver toxicity including single cell necrosis and an increase in apoptosis. After 20 weeks there was a significant increase in hepatic cell replication rates. All of these changes persisted from the time they were first observed until the end of the study at 50 weeks. They occurred in a dose-dependent manner and were only observed at doses (500, 1250, 2500 ppm) where liver tumors were increased in the cancer bioassay. There was a clear no-effect level of 200 ppm. The changes seen in this study are consistent with the development of liver cancer in mice and form the basis of the mode of action. When the major metabolites of thiamethoxam, CGA322704, CGA265307, and CGA330050 were tested in dietary feeding studies of up to 20 weeks duration, only metabolite CGA330050 induced the same changes as those seen in the liver in the thiamethoxam feeding study. It was concluded that thiamethoxam is hepatotoxic and hepatocarcinogenic as a result of its metabolism to CGA330050. Metabolite CGA265307 was also shown to be an inhibitor of inducible nitric oxide synthase and to increase the hepatotoxicity of carbon tetrachloride. It is proposed that CGA265307, through its effects on nitric oxide synthase, exacerbates the toxicity of CGA330050 in thiamethoxam treated mice.

In vitro and in vivo evaluation of NCX 4040 cytotoxic activity in human colon cancer cell lines

BACKGROUND: Nitric oxide-releasing nonsteroidal antiinflammatory drugs (NO-NSAIDs) are reported to be safer than NSAIDs because of their lower gastric toxicity. We compared the effect of a novel NO-releasing derivate, NCX 4040, with that of aspirin and its denitrated analog, NCX 4042, in in vitro and in vivo human colon cancer models and investigated the mechanisms of action underlying its antitumor activity. METHODS: In vitro cytotoxicity was evaluated on a panel of colon cancer lines (LoVo, LoVo Dx, WiDr and LRWZ) by sulforhodamine B assay. Cell cycle perturbations and apoptosis were evaluated by flow cytometry. Protein expression was detected by Western blot. In the in vivo experiments, tumor-bearing mice were treated with NCX 4040, five times a week, for six consecutive weeks. RESULTS: In the in vitro studies, aspirin and NCX 4042 did not induce an effect on any of the cell lines, whereas NCX 4040 produced a marked cytostatic dose-related effect, indicating a pivotal role of the -NO2 group. Furthermore, in LoVo and LRWZ cell lines, we observed caspase-9 and -3-mediated apoptosis, whereas no apoptotic effect was observed after drug exposure in WiDr or LoVo Dx cell lines. In in vivo studies, both NCX 4040 and its parental compound were administered per os. NCX 4040 induced a 40% reduction in tumor weight. Conversely, aspirin did not influence tumor growth at all. CONCLUSIONS: NCX 4040, but not its parental compound, aspirin, showed an in vitro and in vivo antiproliferative activity, indicating its potential usefulness to treat colon cancer.

Effects of microcystin-LR on patterns of iNOS and cytokine mRNA expression in macrophages in vitro

The presence of cyanobacterial toxins in drinking and recreational waters represent a potential health hazard to the public. Microcystin-LR (MC-LR) is the most commonly encountered toxin and is a potent cyclic heptapeptide hepatotoxin produced by cyanobacteria. In this study, the immunomodulation by MC-LR of BALB/c mice peritoneal macrophages was investigated in vitro on mRNA levels of induced nitric oxide synthase and multiple cytokines by reverse-transcription polymerase chain reaction (RT-PCR). Lavaged peritoneal macrophages were incubated for 6 h with lipopolysaccharide (LPS) at a concentration of 100 microg/L and MC-LR at doses of 1, 10, 100, and 1000 nmol/L. Total RNA was extracted from the incubated macrophages, and then the levels of mRNA for induced nitric oxide synthase (iNOS), IL-1beta, TNF-alpha, GM-CSF, and IFN-gamma were detected. The results showed that expression of mRNA for iNOS, IL-1beta, TNF-alpha, GM-CSF, and IFN-gamma decreased significantly compared to the positive control (LPS only). These results have led us to propose the need for the establishment of a survey of the immunotoxicity of microcystins.

Immunological mechanisms elicited at the tumour site by lymphocyte activation gene-3 (LAG-3) versus IL-12: sharing a common Th1 anti-tumour immune pathway

The experimentally induced TS/A murine mammary carcinoma is poorly immunogenic and mainly infiltrated by antigen-presenting cells (APCs), namely macrophages and immature dendritic cells (DCs). Human (h) and mouse (m) lymphocyte activation gene-3 (LAG-3 or CD233) is a physiological MHC class II ligand and powerful APC activator. A gene transfer approach has revealed its anti-tumour activity in this model: hLAG-3 was more effective than mLAG-3. To obtain a clearer picture of the immunoregulatory mechanisms associated with the rejection dynamics of h- and m-LAG-3 transfectants, immunohistochemistry and confocal microscopy analyses of TS/A-hLAG-3, TS/A-mLAG-3, and control TS/A-pc tumours were performed. The immune events elicited by mLAG-3 and m-interleukin (IL)-12 were also compared, since their rejection kinetics were quite similar, and LAG-3 enables IL-12 production by macrophages and DCs. Both the TS/A-h- and, to a lesser extent, the m-LAG-3 rejection areas were characterized by an impressive recruitment of APCs, granulocytes, NK cells, CD4+ T lymphocytes and CD8+ IFNgamma-expressing cells. In both cases, infiltration by APCs was accompanied by strong CD80 and CD86 expression and macrophage nitric oxide (NO) synthase up-regulation. Distinct expression of IL-12 and CXCL9 was also found, especially in the draining lymph nodes. T lymphocytes and CD86-expressing APCs were significantly prevalent in both the TS/A-h- and the m-LAG-3 compared with the TS/A-mIL-12 rejection area. Production of IFNgamma, TNFalpha and IL1beta, and chemokines, namely CXCL5, CXCL9, CXCL10, CXCL11, CCL5, and CCL2, by infiltrating leukocytes and signs of defective neovascularization were detected in tumours expressing h-LAG-3-, m-LAG-3-, and m-IL-12. However, IFNgamma, CCL2, and CCL5 production prevailed in the TS/A-hLAG-3 rejection area. Taken together, these results indicate that LAG-3 expression by engineered tumour cells efficiently promotes intra-tumoural recruitment, activation, and Th1 commitment of APCs, and leads to a wide intra-tumoural influx of non-specific and specific reactive cells, and the release of immunoregulatory and cytotoxic mediators. Many of LAG-3's anti-tumour activities are shared with IL-12.

Low doses of reactive oxygen species protect endothelial cells from apoptosis by increasing thioredoxin-1 expression

The redox regulator thioredoxin-1 (Trx-1) is required for the redox potential of the cell and exerts important functions in cell growth and apoptosis. Severe oxidative stress has been implicated in the oxidation of proteins and cell death. However, the role of low doses of reactive oxygen species (ROS) is poorly understood. Here, we show that 10 and 50 microM H2O2 and short-term exposure to shear stress significantly increased Trx-1 mRNA and protein levels in endothelial cells. Since it is known that Trx-1 exerts anti-apoptotic functions, we next investigated whether low doses of ROS can inhibit basal and serum-depletion induced endothelial cell apoptosis. Indeed, treatment of endothelial cells with 10 and 50 microM H2O2 significantly reduced apoptosis induction. Reduction of Trx-1 expression using an antisense oligonucleotide approach resulted in the induction of apoptosis and abolished the inhibitory effect of low doses of H2O2. Taken together, our results demonstrate that low doses of ROS act as signaling molecules and exert anti-apoptotic functions in endothelial cells via upregulation of the redox-regulator Trx-1.

Inducible Peroxidases Mediate Nitration of Anopheles Midgut Cells Undergoing Apoptosis in Response to Plasmodium Invasion

Plasmodium berghei invasion of Anopheles stephensi midgut cells causes severe damage, induces expression of nitric-oxide synthase, and leads to apoptosis. The present study indicates that invasion results in tyrosine nitration, catalyzed as a two-step reaction in which nitric-oxide synthase induction is followed by increased peroxidase activity. Ookinete invasion induced localized expression of peroxidase enzymes, which catalyzed protein nitration in vitro in the presence of nitrite and H(2)O(2). Histochemical stainings revealed that when a parasite migrates laterally and invades more than one cell, the pattern of induced peroxidase activity is similar to that observed for tyrosine nitration. In Anopheles gambiae, ookinete invasion elicited similar responses; it induced expression of 5 of the 16 peroxidase genes predicted by the genome sequence and decreased mRNA levels of one of them. One of these inducible peroxidases has a C-terminal oxidase domain homologous to the catalytic moiety of phagocyte NADPH oxidase and could provide high local levels of superoxide anion (O(2)), that when dismutated would generate the local increase in H(2)O(2) required for nitration. Chemically induced apoptosis of midgut cells also activated expression of four ookinete-induced peroxidase genes, suggesting their involvement in general apoptotic responses. The two-step nitration reaction provides a mechanism to precisely localize and circumscribe the toxic products generated by defense reactions involving nitration. The present study furthers our understanding of the biochemistry of midgut defense reactions to parasite invasion and how these may influence the efficiency of malaria transmission by anopheline mosquitoes.

Cholecystokinin-8-Induced Hypoplasia of the Rat Pancreas: Influence of Nitric Oxide on Cell Proliferation and Programmed Cell Death

The background of cholecystokinin-8 (CCK-8)-induced hypoplasia in the pancreas is not known. In order to increase our understanding we studied the roles of nitric oxide and NF-kappaB in rats. CCK-8 was injected for 4 days, in a mode known to cause hypoplasia, and the nitric oxide formation was either decreased by means of N(omega)-nitro-L-arginine (L-NNA) or increased by S-nitroso-N-acetylpencillamine (SNAP). The activation of NF-kappaB was quantified by ELISA detection, apoptosis with caspase-3 and histone-associated DNA-fragmentation and mitotic activity in the acinar, centroacinar and ductal cells were visualized by the incorporation of [(3)H]-thymidine. Pancreatic histology and weight as well as protein- and DNA contents were also studied. Intermittent CCK injections reduced pancreatic weight, protein and DNA contents and increased apoptosis, acinar cell proliferation and nuclear factor kappaB (NF-kappaB) activation. It also caused vacuolisation of acinar cells. The inhibition of endogenous nitric oxide formation by L-NNA further increased apoptosis and NF-kappaB activation but blocked the increased proliferation and vacuolisation of acinar cells. The DNA content was not further reduced. SNAP given together with CCK-8 increased apoptosis and other pathways of cell death, raised proliferation of acinar cells and strongly reduced the DNA content in the pancreas. Histological examination showed no inflammation in any group. We conclude that during CCK-8-induced pancreatic hypoplasia, endogenously formed nitric oxide suppresses apoptosis but increases cell death along non-apoptotic pathways and stimulates regeneration of acinar cells. Exogenous nitric oxide enhances the acinar cell turnover by increasing both apoptotic and non-apoptotic cell death and cell renewal. In this situation NF-kappaB activation seems not to inhibit apoptosis nor promote cell proliferation.

Hepatitis C virus infection activates the immunologic (type II) isoform of nitric oxide synthase and thereby enhances DNA damage and mutations of cellular genes

Hepatitis C virus (HCV) infection causes hepatitis, hepatocellular carcinoma, and B-cell lymphomas in a significant number of patients. Previously we have shown that HCV infection causes double-stranded DNA breaks and enhances the mutation frequency of cellular genes, including proto-oncogenes and immunoglobulin genes. To determine the mechanisms, we studied in vitro HCV infection of cell culture. Here we report that HCV infection activated the immunologic (type II) isoform of nitric oxide (NO) synthase (NOS), i.e., inducible NOS (iNOS), thereby inducing NO, which in turn induced DNA breaks and enhanced the mutation frequencies of cellular genes. Treatment of HCV-infected cells with NOS inhibitors or small interfering RNA specific for iNOS abolished most of these effects. Expression of the core protein or nonstructural protein 3 (NS3), but not the other viral proteins, in B cells or hepatocytes induced iNOS and DNA breaks, which could be blocked by NOS inhibitors. The core protein also enhanced the mutation frequency of cellular genes in hepatocytes derived from HCV core transgenic mice compared with that in control mice. The iNOS promoter was activated more than fivefold in HCV-infected cells, as revealed by a luciferase reporter assay driven by the iNOS promoter. Similarly, the core and NS3 proteins also induced the same effects. Therefore, we conclude that HCV infection can stimulate the production of NO through activation of the gene for iNOS by the viral core and NS3 proteins. NO causes DNA breaks and enhances DNA mutation. This sequence of events provides a mechanism for HCV pathogenesis and oncogenesis.

Gene expression profiles of apoptotic neurons

The multigenic program underlying neuronal apoptosis is mostly unknown. To study the program, we used genome-scale screening by oligonucleotide microarrays during serum and potassium deprivation-induced apoptosis of cerebellar granule neurons. From the 8740 genes interrogated by the arrays, 423 genes were found to be regulated at both the transcriptional and the posttranscriptional level and segregated into distinct clusters. Semantic clustering based on gene ontologies showed coordinated expression of genes with common biological functions and metabolic pathways. Among the genes implicated in apoptotic cerebellar granule neurons, 70 were in common with those differentially expressed in cortical neurons exposed to amyloid beta-protein, indicating the existence of common mechanisms responsible for neuronal cell death. Our results offer a genomic view of the changes that accompany neuronal apoptosis and yield new insights into the underlying molecular basis.

Position in cell cycle controls the sensitivity of colon cancer cells to nitric oxide-dependent programmed cell death

Mounting evidence suggests that the position in the cell cycle of cells exposed to an oxidative stress could determine their survival or apoptotic cell death. This study aimed at determining whether nitric oxide (NO)-induced cell death in colon cancer cells might depend on their position in the cell cycle, based on a clone of the cancer cell line HT29 exposed to an NO donor, in combination with the manipulation of the cell entry into the cell cycle. We show that PAPA NONOate (pNO), from 10(-4) m to 10(-3) m, exerted early and reversible cytostatic effects through ribonucleotide reductase inhibition, followed by late resumption of cell growth at 5 x 10(-4) m pNO. In contrast, 10(-3) m pNO led to late programmed cell death that was accounted for by the progression of cells into the cell cycle as shown by (a) the accumulation of apoptotic cells in the G(2)-M phase at 10(-3) m pNO treatment; and (b) the prevention of cell death by inhibiting the entry of cells into the cell cycle. The entry of pNO-treated cells into the G(2)-M phase was associated with actin depolymerization and its S-glutathionylation in the same way as in control cells. However, the pNO treatment interfered with the build-up of a high reducing power, associated in control cells with a dramatic increase in reduced glutathione biosynthesis in the G(2)-M phase. This oxidative stress prevented the exit from the G(2)-M phase, which requires a high reducing power for actin deglutathionylation and its repolymerization. Finally, our demonstration that programmed cell death occurred through a caspase-independent pathway is in line with the context of a nitrosative/oxidative stress. In conclusion, this work, which deciphers the connection between the position of colonic cancer cells in the cell cycle and their sensitivity to NO-induced stress and their programmed cell death, could help optimize anticancer protocols based on NO-donating compounds.

Nitric oxide induces BNIP3 expression that causes cell death in macrophages

Nitric oxide (NO) is involved in many physiological processes and also causes pathological effects by inducing apoptosis. It can enhance or suppress apoptosis depending on its concentration and the cell type involved. In this report, we used cDNA microarray analysis to show that SNAP, an NO donor, strongly induces Bcl-2/adenovirus E1B 19kDa-interacting protein 3 (BNIP3) in macrophages. BNIP3 is a mitochondrial pro-apoptotic protein that contains a Bcl-2 homology 3 domain and a COOH-terminal transmembrane (TM) domain. Macrophages activated by LPS/IFN-gamma produce nitric oxide synthase 2 (NOS2) and release endogenous NO. Expression of BNIP3 was also induced in macrophages by LPS/IFN-gamma, and the induction was blocked by a NOS2 inhibitor, S-methyl-isothiourea. Peritoneal macrophages from NOS2-null mice failed to produce BNIP3 in response to LPS/IFN-gamma. We conclude that BNIP3 expression in macrophages is controlled by the intracellular level of nitric oxide. Overexpression of BNIP3 but not of BNIP3 deltaTM, a BNIP3 mutant without the TM domain and C-terminal tail, led to apoptosis of the cells. Promoter analysis showed that the region between -281 and -1 of the 5'-upstream enhancer region of murine BNIP3 was sufficient for NO-dependent expression of BNIP3.

Stromal cell-derived factor-1 production by spleen cells is affected by nitric oxide in protective immunity against blood-stage Plasmodium chabaudi CR in C57BL/6j mice

Malaria, a major endemic tropical disease, is caused by the infection of blood cells by Plasmodium protozoa. Most patients control their parasitemia by a not fully understood spleen-dependent mechanism. SDF-1alpha is a chemokine produced by stromal cells such as reticular spleen cells. Nitric oxide (NO) has several immune functions, including killing of intracellular pathogens and its function in malaria is debated. We have previously shown that SDF-1alpha production peaks during the ascending parasitemia in Plasmodium chabaudi infection and its supplementation in lethal models could reduce the parasitemia. In the present study, we analyzed SDF-1 production by spleen cells as related to NO metabolism in the P. chabaudi rodent malaria model using IFN-gamma; TNFR and iNOS-knockout mice or iNOS-blocked, L-NAME- or aminoguanidine-treated mice. Parasitemia and production of SDF-1alpha and SDF-1beta were determined by RT-PCR. In vitro NO production by spleen adherent cells was also tested. The data showed that parasitemia was less intense in both iNOS(-/-) or NO-inhibited mice than in controls, with increased and long-lasting production of SDF-1alpha mRNA. In the absence of cytokines involved in the final regulation of NO production by effector cells, as is the case for TNFR(-/-) and GKO mice, the infection progressed in an uncontrolled manner regardless of SDF-1alpha production, suggesting that these cytokines must be involved in the control of parasitemia after the SDF-1alpha dependent process. The SDF-1beta isoform was constitutive in all experiments, with elevated levels only clearly seen in TNFR(-/-) mice. We conclude that SDF-1 is involved in the promotion of parasitemia control in malaria, and excessive NO could affect its production.

Apoptotic signaling pathways induced by nitric oxide in human lymphoblastoid cells expressing wild-type or mutant p53

Loss of p53 function by inactivating mutations results in abrogation of NO*induced apoptosis in human lymphoblastoid cells. Here we report characterization of apoptotic signaling pathways activated by NO* in these cells by cDNA microarray expression and immunoblotting. A p53-mediated transcriptional response to NO* was observed in p53-wild-type TK6, but not in closely related p53-mutant WTK1, cells. Several previously characterized p53 target genes were up-regulated transcriptionally in TK6 cells, including phosphatase PPM1D (WIP1), oxidoreductase homolog PIG3, death receptor TNFRSF6 (Fas/CD95), and BH3-only proteins BBC3 (PUMA) and PMAIP1 (NOXA). NO* also modulated levels of several gene products in the mitochondria-dependent and death-receptor-mediated apoptotic pathways. Inhibitors of apoptosis proteins X-chromosome-linked inhibitor of apoptosis, cellular inhibitor of apoptosis protein-1, and survivin were significantly down-regulated in TK6 cells, but not in WTK1 cells. Smac release from mitochondria was induced in both cell types, but release of apoptosis-inducing factor and endonuclease G was detected only in TK6 cells. Fas/CD95 was increased, and levels of the antiapoptotic proteins Bcl-2 and Bcl-x/L were reduced in TK6 cells. Activation of procaspases 3, 8, 9, and 10, as well as Bid and poly(ADP-ribose) polymerase cleavage, were observed only in TK6 cells. NO* treatment did not alter levels of death receptors 4 and 5, Fas-associated death domain or proapoptotic Bax and Bak proteins in either cell line. Collectively, these data show that NO* exposure activated a complex network of responses leading to p53-dependent apoptosis via both mitochondrial and Fas receptor pathways, which were abrogated in the presence of mutant p53.

Analysis of immunomodulating nitric oxide, iNOS and cytokines mRNA in mouse macrophages induced by microcystin-LR

Microcystins (MCs) are the toxic molecules produced by common cyanobacterium in freshwater blooms. Their toxicities have brought severe health issues to livestock and human being. Microcystin-LR (MC-LR) is one of the most toxic MCs. This paper presents the profile of the immunomodulation of MC-LR to BALB/c mice peritoneal macrophages. Macrophages were stimulated with 100microg/l lipopolysaccharide (LPS) and MC-LR at dose of 1, 10, 100, 1000nmol/l, respectively, for 24h. Nitric oxide (NO) production in cell culture supernatants was quantified by using Griess reagent method. Total RNA was extracted from incubated macrophages then the mRNA abundance of induced nitric oxide synthase (iNOS), IL-1beta, TNF-alpha, GM-CSF, IFN-gamma was monitored by using reverse-transcriptional polymerase chain reaction (RT-PCR). The results demonstrated that NO production, mRNA levels of iNOS, IL-1beta, TNF-alpha were down regulated by MC-LR dose-dependently and mRNA levels of GM-CSF and IFN-gamma were also decreased but in dose-independent manner. Our results illustrated the involvement of NO production, iNOS and some cytokines in mice immune system in microcystin shock.

Redox and oxidant-mediated regulation of apoptosis signaling pathways: immuno-pharmaco-redox conception of oxidative siege versus cell death commitment

The mechanisms controlling apoptosis remain largely obscure. Because apoptosis is an integral part of the developmental program and is frequently the end-result of a temporal course of cellular events, it is referred to as programmed cell death. While there is considerable variation in the signals and requisite cellular metabolic events necessary to induce apoptosis in diverse cell types, the morphological features associated with apoptosis are highly conserved. Free radicals, particularly reactive oxygen species (ROS), have been proposed as common mediators for apoptosis. Many agents that induce apoptosis are either oxidants or stimulators of cellular oxidative metabolism. Conversely, many inhibitors of apoptosis have antioxidant activities or enhance cellular antioxidant defenses. Mammalian cells, therefore, exist in a state of oxidative siege in which survival requires an optimum balance of oxidants and antioxidants. The respiratory tract is subjected to a variety of environmental stresses, including oxidizing agents, particulates and airborne microorganisms that, together, may injure structural and functional lung components and thereby jeopardize the primary lung function of gas exchange. To cope with this challenge, the lung has developed elaborate defense mechanisms that include inflammatory-immune pathways as well as efficient antioxidant defense systems. In the absence of adequate antioxidant defenses, the damage produced is detected by the cell leading to the activation of genes responsible for the regulation of apoptosis, conceivably through stress-responsive transcription factors. Oxidative stress, in addition, may cause a shift in cellular redox state, which thereby modifies the nature of the stimulatory signal and which results in cell death as opposed to proliferation. ROS/redox modifications, therefore, may disrupt signal transduction pathways, can be perceived as abnormal and, under some conditions, may trigger apoptosis.

Reactive nitrogen species in the chemical biology of inflammation

The preponderance of epidemiological evidence now points to a strong association between chronic inflammation and cancers of several organs, including the gastrointestinal tract, liver, and lungs. The strongest evidence for a mechanistic link here involves the generation of reactive oxygen and nitrogen species by macrophages and neutrophils that respond to cytokines and other signaling processes arising at sites of inflammation. These reactive species cause oxidation, nitration, halogenation, and deamination of biomolecules of all types, including lipids, proteins, carbohydrates, and nucleic acids, with the formation of toxic and mutagenic products. This review, in honor of Bruce Ames, will focus on recent advances in our understanding of the protein and DNA damage caused by reactive nitrogen species produced by macrophages and neutrophils, with emphasis on nitric oxide, nitrous anhydride, peroxynitrite, and nitrogen dioxide radical.

IRF-1 expression induces apoptosis and inhibits tumor growth in mouse mammary cancer cells in vitro and in vivo

Interferon regulatory factor-1 (IRF-1) is a nuclear transcription factor that mediates interferon and other cytokine effects and appears to have antitumor activity in vitro and in vivo in cancer cells. We have constructed a recombinant adenoviral vector (Ad-IRF-1) that infects mammary cells with high efficiency and results in high levels of functional IRF-1 protein in transfected cells. Overexpression of IRF-1 in two mouse breast cancer cell lines, C3-L5 and TS/A, resulted in apoptosis in these cell lines as assessed by Annexin V staining. The involvement of caspases was confirmed by significant inhibition of apoptosis by a caspase inhibitor, and by demonstration of caspase-3 activity, cleavage of caspase-3, and PARP cleavage. Interestingly, the growth of nonmalignant breast cell lines C127I and NMuMG did not appear to be inhibited by IRF-1 overexpression. Suppression of growth for breast cancer cell lines in vivo was demonstrated by both preinfection of breast cancer cells ex vivo and by intratumoral injection of Ad-IRF-1 into established tumors in their natural hosts. The mechanism of apoptosis may involve the transcriptional upregulation of bak, caspase-8, and caspase-7 expression. These data support the antitumor potential of IRF-1 and the use of agents that increase IRF-1 in breast cancer.

Therapeutic interventions targeting the nitric oxide system: current and potential uses in obstetrics, bone disease and erectile dysfunction

Nitric oxide is involved in a countless number of physiological processes and is known to have cytoprotective as well as cytotoxic effects. Increased knowledge about the multifaceted role of nitric oxide in a variety of disease states has led to the design of multiple treatment strategies involving the nitric oxide system. The current review focuses on recent research advances in the fields of obstetrics, bone disease and erectile dysfunction that have led to current or potential future therapies involving nitric oxide.

Nitric oxide and pro-inflammatory cytokines in acute hepatitis B

Background: Experimental studies demonstrate that hepatitis B virus may induce nitric oxide (NO) production in infected hepatocytes. Its presence in acute hepatitis B patients has not been studied. Methods: Serum levels of nitric oxide and its regulatory pro-inflammatory cytokines were detected in 15 patients with uncomplicated acute hepatitis B, 19 blood donors and 15 chronic hepatitis B patients. Cytokines were determined with an immunoassay. Nitric oxide was measured as the serum metabolic products of nitrates and nitrites using a modification of the Griess reaction. Results: All detected cytokines were increased in acute hepatitis B patients compared to healthy controls (p<0.001 for TNF-alpha, p<0.05 for IL-6, p<0.001 for IL1-beta and p<0.001 for IFN-gamma). High serum levels of nitric oxide were found in acute hepatitis B patients (156.96+/-9.76 micromol/l) compared to healthy controls (51+/-6.2 micromol/l, p<0.001) and chronic hepatitis B patients (63.97+/-3.78 micromol/l, p<0.001). No significant correlations were found between NO, cytokine levels and transaminases. Conclusions: High levels of nitric oxide and its regulatory cytokines were found in a group of patients with uncomplicated acute hepatitis B. The exact role of NO in the disease pathogenesis and outcome needs to be studied further.

Coronary revascularization in ischemic cardiomyopathy

This article first discusses coronary artery disease, including left-ventricular dysfunction, hibernating myocardium, the relationship between stunning, hibernation, and heart failure, and molecular mechanisms underlying myocardial hibernation. Left ventricular function and the prognosis and pathophysiology of left-ventricular dysfunction are then examined. Selection of patients for revascularization is discussed, to include which coronary patients should be investigated for myocardial viability, and other surgical considerations are outlined. The outcome following revascularization in the heart failure patient, the results of revascularization, and the time course of functional recovery after coronary artery bypass graft are also covered.

From molecules to mammals: what's NOS got to do with it?

Nitric oxide synthases (NOSs) generate nitric oxide (NO) and the by-product l-citrulline, via the catalytic combination of l-arginine and molecular oxygen. In mammals, there are three NOS genes: nNOS (NOS1), iNOS (NOS2) and eNOS (NOS3). The molecular structure, enzymology and pharmacology of these enzymes have been well defined, and reveal critical roles for the NOS system in a variety of important processes. The studies of NOS enzymes using knockout and transgenic mouse models have provided an invaluable contribution, highlighting critical roles in neuronal, renal, pulmonary, gastro-intestinal, skeletal muscle, reproductive and cardiovascular biology. This review will outline the data gleaned from complementary knockout and transgenic over-expression models in mice, and focus on the interactions between NOS enzymes and pathophysiology of the vascular system. These studies are a paradigm for the near future, which will involve the translation of an enormous amount of genomic data into physiological insights that penetrate the realms of both health care and biology.

Til cell death do us part: nitric oxide and mechanisms of hepatotoxicity

Like many juggernauts in biology, the elusive nature of nitric oxide (NO) sprints through the fields, sometimes the savior, at other times the scimitar. In the liver, which is the metabolic center of the organism, hepatocytes and immune cells trade blows using the reactive diatomic molecule NO to induce cellular damage under toxic conditions. In response, hepatocytes can utilize several mechanisms of NO to their protective advantage by prohibiting the activation of programmed cell death, a.k.a. apoptosis. The balance of these effects in this reactive milieu set the stage for the homeostatic response to cellular injury that determines whether hepatocytes will live, die, or regenerate. Insights that we and others have gained from the liver under pathologic conditions of stress can be applied to the understanding of cellular death mechanisms in other organs and tissues.

Depletion of Endogenous Nitric Oxide Enhances Cisplatin-induced Apoptosis in a p53-dependent Manner in Melanoma Cell Lines

The expression of inducible nitric-oxide synthase in melanoma tumor cells was recently shown to correlate strongly with poor patient survival after combination biochemotherapy (p<0.001). Furthermore, evidence suggests that nitric oxide, a reaction product of nitric oxide synthase, exhibits antiapoptotic activity in melanoma cells. We therefore hypothesized that nitric oxide antagonizes chemotherapy-induced apoptosis. Whether nitric oxide is capable of regulating cell growth and apoptotic responses to cisplatin treatment in melanoma cell lines was evaluated. We demonstrate herein that depletion of endogenously produced nitric oxide can inhibit melanoma proliferation and promote apoptosis. Moreover, our data indicate that the depletion of nitric oxide leads to changes in cell cycle regulation and enhances cisplatin-induced apoptosis in melanoma cells. Strikingly, we observed that the depletion of nitric oxide inhibits cisplatin-induced wild type p53 accumulation and p21(Waf1/Cip1/Sdi1) expression in melanoma cells. When cisplatin-induced p53 binding to the p21(Waf1/Cip1/Sdi1) promoter was examined, it was found that nitric oxide depletion significantly reduced the presence of p53-DNA complexes after cisplatin treatment. Furthermore, dominant negative inhibition of p53 activity enhanced cisplatin-induced apoptosis. Together, these data strongly suggest that endogenously produced nitric oxide is required for cisplatin-induced p53 activation and p21(Waf1/Cip1/Sdi1) expression, which can regulate melanoma sensitivity to cisplatin.

Biphasic modulation by nitric oxide of caspase activation due to malonate injection in rat striatum

The present study examined caspase activation and its modulation by nitric oxide (NO) in a model of oxidative stress induced by injection of malonate (3 micromol), a mitochondrial toxin, into rat striatum. Caspase-3-like enzymatic activity was maximal 6 h after malonate while NO production evaluated by its metabolites nitrites and nitrates was increased at 3 h. The neuronal NO-synthase inhibitor 7-nitroindazole reduced malonate induced-NO production by 50% at 25 mg/kg and enhanced by 32% caspase activation. This result suggests that a moderate production of NO potentiates caspase activation, an effect counterbalanced by NO itself at higher concentrations. Accordingly, complete inhibition of NO production by 7-nitroindazole at 50 mg/kg did not modify malonate-induced caspase activity. Thus NO production by the neuronal isoform of NO-synthase is not the major event leading to caspase activation due to malonate. However, NO seems to have pro- and anti-caspase effects that neutralize each other.

S-Nitrosation regulates the activation of endogenous procaspase-9 in HT-29 human colon carcinoma cells

Nitric oxide-mediated signals have been suggested to regulate the activity of caspases negatively, yet literature has provided little direct evidence. We show in this paper that cytokines and nitric-oxide synthase (NOS) inhibitors regulate S-nitrosation of an initiator caspase, procaspase-9, in a human colon adenocarcinoma cell line, HT-29. A NOS inhibitor, N(G)-methyl-l-arginine, enhanced the tumor necrosis factor-alpha (TNF-alpha)-induced cleavage of procaspase-9, procaspase-3, and poly-(ADP-ribose) polymerase, as well as the level of apoptosis. N(G)-Methyl-l-arginine, however, did not affect the cleavage of procaspase-8. These results suggest that nitric oxide regulates the cleavage of procaspase-9 and its downstream proteins and, subsequently, apoptosis in HT-29 cells. Labeling S-nitrosated cysteines with a biotin tag enabled us to reveal S-nitrosation of endogenous procaspase-9 that was immunoprecipitated from the HT-29 cell extracts. Furthermore, the treatment with TNF-alpha, as well as NOS inhibitors, decreased interferon-gamma-induced S-nitrosation in procaspase-9. Our results show that S-nitrosation of endogenous procaspase-9 occurs in the HT-29 cells under normal conditions and that denitrosation of procaspase-9 enhances its cleavage and consequent apoptosis. We, therefore, suggest that S-nitrosation regulates activation of endogenous procaspase-9 in HT-29 cells.

Phytoglobins and nitric oxide: new partners in an old signalling system in plants

The recent review summarizes the major achievements in discovery of role of phytoglobins in mediation of nitric oxide generated cellular functions in higher plants. Genes encoding non-symbiotic hemoglobins have been cloned from several plant species. The expression pattern of these genes show tissue-specificity that is also under the control of stress factors like hypoxia. The nitric oxide has pivotal role in signalling pathway specifically in hypersensitive reactions and programmed cell death. Production of transgenic tobacco plants overexpressing the alfalfa hemoglobin showed altered necrotic symptoms after treatment with nitric oxide generating compounds or infection by necrotic pathogens. The present review helps to outline the similar relation between hemoglobin and nitric oxide in plants as it was found in animal cells.

Mice lacking inducible nitric oxide synthase demonstrate impaired killing of Porphyromonas gingivalis

Porphyromonas gingivalis is a primary etiological agent of generalized severe periodontitis, and emerging data suggest the importance of reactive oxygen and nitrogen species in periodontal tissue damage, as well as in microbial killing. Since nitric oxide (NO) released from inducible NO synthase (iNOS) has been shown to possess immunomodulatory, cytotoxic, and antibacterial effects in experimental models, we challenged iNOS-deficient (iNOS(-/-)) mice with P. gingivalis by using a subcutaneous chamber model to study the specific contribution of NO to host defense during P. gingivalis infection. iNOS(-/-) mice inoculated with P. gingivalis developed skin lesions and chamber rejection with higher frequency and to a greater degree than similarly challenged C57BL/6 wild-type (WT) mice. Chamber fluid from iNOS(-/-) mice possessed significantly more P. gingivalis than that of WT mice. The immunoglobulin G responses to P. gingivalis in serum was similar in WT and iNOS(-/-) mice, and the inductions of tumor necrosis factor alpha, interleukin-1 beta and interleukin-6, and prostaglandin E(2) were comparable between the two mouse strains. Although no differences in total leukocyte counts in chamber fluids were observed between iNOS(-/-) and WT mice, the percentage of dead polymorphonuclear leukocytes (PMNs) was significantly greater in iNOS(-/-) mouse chamber fluids than that of WT samples. Interestingly, casein-elicited PMNs from iNOS(-/-) mice released more superoxide than did WT PMNs when stimulated with P. gingivalis. These results indicate that modulation of superoxide levels is a mechanism by which NO influences PMN function and that NO is an important element of the host defense against P. gingivalis.

Expression of nitric oxide, peroxynitrite, and apoptosis in loose total hip replacements

Nitric oxide (NO) is an effector molecule associated with inflammation, immune function, bone metabolism, and the induction of apoptosis. This study examined the role of NO, peroxynitrite (ONOO(-)), and apoptosis in cases of revision total hip replacements (THRs). We hypothesized that apoptosis and excess production of NO contribute to the inflammatory reaction to orthopedic biomaterial wear debris that is associated with loosening and osteolysis. Periprosthetic membranous specimens were collected from revised cemented acetabular components with simple loosening and ballooning osteolysis. Synovial samples from patients undergoing primary THR were used as controls. The presence of macrophages (CD68(+)) and levels of inducible nitric oxide synthase (INOS), endothelial nitric oxide synthase (EcNOS), ONOO(-) (Nitro, assayed by the amount of nitrated tyrosine residues), and apoptosis (TUNEL staining) were examined using immunohistochemistry. Increased expression for INOS, EcNOS, and ONOO(-) in both the loose/osteolytic and the loose/non-osteolytic groups was observed when compared to the synovium group. There were no significant differences between the loose/osteolytic group and loose/non-osteolytic group for these biologic markers. TUNEL staining showed a significant increase in apoptosis in the loose/osteolytic group compared to the loose/non-osteolytic group and synovial tissues. These findings suggest that NO and NO-derived molecules, such as ONOO(-), may be involved in sustaining the foreign-body reaction to wear debris. NO and ONOO(-) may prove to be useful markers of prosthetic loosening whereas apoptosis may be a marker distinguishing ballooning from simple osteolysis.

Expression of a stress-induced hemoglobin affects NO levels produced by alfalfa root cultures under hypoxic stress

Transgenic alfalfa root cultures expressing sense and antisense barley hemoglobin transcripts were examined under varying levels of atmospheric oxygen. Root cultures overexpressing the hemoglobin gene (Hb+) maintained root growth when placed under 3% oxygen, whereas control cultures or cultures underexpressing hemoglobin (Hb-) experienced 30-70% declines in growth under the same conditions. ATP levels and ATP/ADP ratios for Hb+ lines did not significantly differ in 40 and 3% oxygen, whereas the ATP levels and ATP/ADP ratios in control and Hb- lines were significantly lower under 3% oxygen. Large increases in the production of nitric oxide (NO) were measured in root cultures grown under hypoxic conditions compared to aerobic conditions. The amount of NO accumulated in an Hb- line was 2.5-fold higher than that in the Hb+ line. Treatment of transgenic root lines under 40% oxygen with NO resulted in significant declines in the ATP levels and ATP/ADP ratio of an Hb- line and the control line, with no significant change in an Hb+ line. The root cell structure of an Hb- line showed evidence of cell breakdown under hypoxic growth, whereas an Hb+ line had no evidence of cell breakdown under similar growth conditions. These results lead us to hypothesize that NO is involved in the response of plants to hypoxia and that hemoglobin modulates the levels of NO in the hypoxic cell.

Nitric oxide induces polarization of actin in encephalitogenic T cells and inhibits their in vitro trans-endothelial migration in a p70S6 kinase-independent manner

Nitric oxide (NO) inhibits both actively induced and transferred autoimmune encephalomyelitis. To explore potential mechanisms, we examined the ability of NO to inhibit migration of T lymphoblasts through both collagen matrices and monolayers of rat brain endothelial cells. The NO donor 1-hydroxy-2-oxo-3, 3-bis (2-aminoethyl)-1-triazene (HOBAT) inhibited migration in a concentration-dependent manner. NO pretreatment of T cells inhibited migration through untreated endothelial cells, but NO pretreatment of endothelial cells had no inhibitory effect on untreated T cells. Therefore NO's migration inhibitory action was mediated through its effect on T cells and not endothelial cells. HOBAT did not inhibit migration by inducing T-cell death but rather by polarizing the T cells, resulting in a morphology suggestive of migrating cells. P70S6 kinase, shown to have a role in NO-induced migration inhibition in fibroblasts, had no role in the inhibitory effect of NO on T-cell migration. Thus, HOBAT did not alter p70S6K activity nor did rapamycin, a specific inhibitor of p70S6K, inhibit HOBAT-induced T-cell morphological changes or T-cell migration. We suggest that NO-induced morphological changes result in T cells with predefined migratory directionality, thus limiting the ability of these cells to respond to other migratory signals.

Transient intrauterine hypotension causes apoptosis in fetal rat brain and affects learning

Hypotensive episodes are frequent during pregnancy, and their functional effect on fetal brain has not been studied. We produced systemic hypotension for 30 min during mid-gestation in pregnant rats and examined their offspring on postnatal days 1 and 28. When compared with sham controls, the brain of the hypotensive group contained more TUNEL-positive cells in the hippocampal and periventricular regions on both time points. Spatial learning assessed by water milk maze test was impaired in 28-day-old pups of the hypotensive mothers. According to these results, transient maternal hypotension can induce apoptotic cell death in fetal brain and affect learning. Similar mechanisms may be considered and investigated in the pathogenesis of human learning disorders.

Influence of nitric oxide on the secretory function of the bovine corpus luteum: dependence on cell composition and cell-to-cell communication

The objective of the present study was to investigate the role of cell-to-cell contact in the influence of nitric oxide (NO) on the secretory function of the bovine corpus luteum (CL). In Experiment 1, separate small luteal cells (SLC) or large (LLC) luteal cells were perfused with 100 micro M spermineNONOate, a NO donor, or with 100 micro M Nomega-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor; in Experiment 2, a mixture of LLC and SLC and endothelial cells was cultured and incubated with spermineNONOate or L-NAME; in Experiment 3, spermineNONOate was perfused into the CL (100 mg/4 hr) by a microdialysis system in vivo. Perfusion of isolated SLC and LLC with the NO donor or NOS inhibitor (Experiment 1) did not affect (P > 0.05) secretion of progesterone (P(4)) or oxytocin (OT). L-NAME perfusion increased (P < 0.05) leukotriene C(4) (LTC(4)) secretion by both SLC and LLC cells. Treatment of mixtures of luteal cells with an NO donor (Experiment 2) significantly decreased (P < 0.001) secretion of P(4) and OT and increased (P < 0.001) production of prostaglandin F(2alpha) (PGF(2alpha)) and LTC(4). L-NAME stimulated (P < 0.001) P(4) secretion, but did not influence (P > 0.05) OT, PGF(2alpha) or LTC(4) production. Intraluteal administration (Experiment 3) of spermineNONOate increased (P < 0.001) LTC(4) and PGF(2alpha), decreased OT, but did not change P(4) levels in perfusate samples. These data indicate that cell-to-cell contact and cell composition play important roles in the response of bovine CL to treatment with NO donors or NOS inhibitors, and that paracrine mechanisms are required for the full secretory response of the CL in NO action. Endothelial cells appear to be required for the full secretory response of the CL to NO.

Different capacities of carp leukocytes to encounter nitric oxide-mediated stress: a role for the intracellular reduced glutathione pool

Carp head kidney (HK) phagocytes can be stimulated by lipopolysaccharide (LPS) to produce nitric oxide (NO). High production of NO can suppress the carp immune system. Carp peripheral blood leukocytes (PBL) are highly susceptible but HK phagocytes are relatively resistant to the immunosuppressive effects of NO. This study demonstrates that the antioxidant glutathione plays an important role in the protection against nitrosative stress. Carp HK phagocytes, especially the neutrophilic granulocytes, contain higher levels of glutathione than PBL. Moreover, freshly isolated carp neutrophilic granulocytes have higher mRNA levels than PBL of glucose-6-phosphate dehydrogenase (G6PD), manganese superoxide dismutase (MnSOD) and gamma-glutamylcysteine synthetase (gamma-GCS). Since these molecules are part of the glutathione redox cycle, neutrophilic granulocytes have a higher capacity than PBL to maintain glutathione in a reduced state following nitrosative stress. When stimulated with LPS, neutrophilic granulocytes upregulate the expression of G6PD, MnSOD and gamma-GCS.

Nitric oxide regulation of maspin expression in normal mammary epithelial and breast cancer cells

In this study, we examined the unique relationship of maspin, a serine protease inhibitor (serpin), that plays a critical role in mammary gland development and is silenced during breast cancer progression, and nitric oxide (NO), a multifaceted water and lipid soluble free radical. The hypothesis tested was that there is a correlation between endothelial nitric oxide synthase and maspin in MCF-7 cells and that NO is capable of regulating maspin expression. An experimental system was developed in which cellular levels of NO in normal human mammary epithelial cells and the breast cancer cell line MCF-7 could be altered using NO modulators. The effect(s) of NO modulators on maspin was measured using reverse transcriptase-polymerase chain reaction and Western blot analysis of subcellular fractions of both cell types. The data revealed that NO induced maspin expression in MCF-7 cells, and the induced maspin resulted in diminished cell motility and invasion, concomitant with an increase in the apoptotic index. This novel finding provides new information regarding the molecular role of maspin in regulating mammary epithelial growth, remodeling, tumor progression, and the metastatic process. More significantly, these findings could have a potential impact on future therapeutic intervention strategies for breast cancer. Targeted delivery of NO within the tumor microenvironment could provide a feasible noninvasive approach for effective treatment.