Inducible nitric oxide synthase in a human glioblastoma cell line

Roles of nitric oxide and polyamines in brain tumor growth

Nitric oxide (NO) and polyamines: putrescine, spermidine and spermine, are key arginine metabolites in mammalian tissues that play critical roles i.a. in regulation of vascular tone (NO), and cell cycle regulation (polyamines). In the brain, both classes of molecules additionally have neuromodulatory and neuroprotective potential, and NO also a neurotoxic potential. Here we review evidence that brain tumors use the NO- and polyamine-synthesizing machineries to the benefit of their differentiation and growth from healthy glia and neurons. With a few exceptions, brain tumors show increased activities of one or all of the three arginine (Arg) to NO-converting nitric oxide synthase (NOS) isoforms (iNOS, eNOS, nNOS), but also elevated activities of polyamines-generating and modifying enzymes: arginase I/II, ornithine decarboxylase and spermidine/spermine N¹-acetyltransferase. The degree of stimulation of NO- and polyamine synthesis often correlates with brain tumor malignancy. Excess NO, but also spermine, spermidine and their N¹-acetylated forms, are tumor- and context-dependently involved in angiogenesis, tumor initiation and growth, and resistance to chemo- or radiotherapy. Hypothetically, increased demand for NO and/or polyamines is likely to contribute to Arg auxotrophy of malignant brain tumors, albeit the causal nexus awaits experimental verification.

Immunohistochemical and ultrastructural evidence for the pathogenesis of white matter degeneration in patients with panencephalopathic-type Creutzfeldt-Jakob disease: Inducible nitric oxide synthase overexpression in bizarre astrocytes

Excessive production of nitric oxide (NO) due to the overinduction of inducible nitric oxide synthase (iNOS) has a severe cytotoxic effect, which may relate to the pathogenesis of neurodegenerative disorders. In this study, we report the novel finding that iNOS is overinduced in a large number of bizarre astrocytes in the white matter of patients with panencephalopathic (PE)-type Creutzfeldt-Jakob disease (CJD). This study was carried out on brain tissue from seven patients with PE-type CJD. As controls, 12 normal individuals and nine patients with cerebral infarction were examined. We identified a large number of bizarre astrocytes in the degenerative cerebral white matter in PE-type CJD. Using immunohistochemistry, only bizarre astrocytes in PE-type CJD showed strong immunoreactivity for both iNOS and superoxide dismutase 1 (SOD1). Ultrastructural examination demonstrated that these bizarre astrocytes contained many free polyribosome-like granules. No significant iNOS immunoreactivity was observed in either the astrocytes of patients with cerebral infarcts or in the normal controls. This study suggests that the iNOS-overexpressing astrocytes, especially iNOS-overexpressing bizarre astrocytes, could play an important role in the development of white matter lesions in PE-type CJD. Our data also suggest that the bizarre astrocytes could be protecting themselves from the cytotoxicity of NO by producing SOD1. These immunohistochemical findings are supported by the ultrastructural observation of numerous polyribosome granules restricted to the cytoplasm of these bizarre astrocytes.

NOS Expression and NO Function in Glioma and Implications for Patient Therapies

SIGNIFICANCE

Gliomas are central nervous system tumors that primarily occur in the brain and arise from glial cells. Gliomas include the most common malignant brain tumor in adults known as grade IV astrocytoma, or glioblastoma (GBM). GBM is a deadly disease for which the most significant advances in treatment offer an improvement in survival of only ∼2 months.

CRITICAL ISSUES

To develop novel treatments and improve patient outcomes, we and others have sought to determine the role of molecular signals in gliomas. Recent Advances: One signaling molecule that mediates important biologies in glioma is the free radical nitric oxide (NO). In glioma cells and the tumor microenvironment, NO is produced by three isoforms of nitric oxide synthase (NOS), NOS1, NOS2, and NOS3. NO and NOS affect glioma growth, invasion, angiogenesis, immunosuppression, differentiation state, and therapeutic resistance.

FUTURE DIRECTIONS

These multifaceted effects of NO and NOS on gliomas both in vitro and in vivo suggest the potential of modulating the pathway for antiglioma patient therapies. Antioxid. Redox Signal. 26, 986-999.

A multi-targeted approach to suppress tumor-promoting inflammation

Cancers harbor significant genetic heterogeneity and patterns of relapse following many therapies are due to evolved resistance to treatment. While efforts have been made to combine targeted therapies, significant levels of toxicity have stymied efforts to effectively treat cancer with multi-drug combinations using currently approved therapeutics. We discuss the relationship between tumor-promoting inflammation and cancer as part of a larger effort to develop a broad-spectrum therapeutic approach aimed at a wide range of targets to address this heterogeneity. Specifically, macrophage migration inhibitory factor, cyclooxygenase-2, transcription factor nuclear factor-κB, tumor necrosis factor alpha, inducible nitric oxide synthase, protein kinase B, and CXC chemokines are reviewed as important antiinflammatory targets while curcumin, resveratrol, epigallocatechin gallate, genistein, lycopene, and anthocyanins are reviewed as low-cost, low toxicity means by which these targets might all be reached simultaneously. Future translational work will need to assess the resulting synergies of rationally designed antiinflammatory mixtures (employing low-toxicity constituents), and then combine this with similar approaches targeting the most important pathways across the range of cancer hallmark phenotypes.

Bee venom suppresses LPS-mediated NO/iNOS induction through inhibition of PKC-alpha expression

ETHNOPHARMACOLOGICAL RELEVANCE

Bee venom (BV) is a traditional Korean medicine that has been widely used with satisfactory results in the treatment of some immune-related diseases, especially rheumatoid arthritis.

AIM OF THE STUDY

The purpose of this study is to elucidate the molecular mechanism underlying the anti-inflammatory effects of BV, which is used in the treatment of various inflammatory diseases in traditional Korean medicine. We evaluated the anti-inflammatory effect of BV on NO generation and iNOS expression by LPS in rat C6 glioma cells.

MATERIAL AND METHODS

BV was obtained from the National Institute of Agricultural Science and Technology (NIAST) of Korea. Nitrite measurement, Immuno blot analysis, Reverse transcriptase-PCR and Electrophoretic mobility shift assay (EMSA) were used for assessment.

RESULTS

BV suppressed the LPS-induced NO generation and iNOS expression, and it also inhibited the expressions of LPS-induced pro-inflammatory molecules including Cox-2 and IL-1 beta in rat C6 glioma cells. Then, BV inhibited LPS-induced expression of PKC-alpha and MEK/ERK, not p38 and JNK. Moreover, inhibition of LPS-induced iNOS expression by BV was dependent on transcriptional activities of AP-1/NF-kappaB through MEK/ERK pathway.

CONCLUSION

These results indicate that BV suppresses LPS-induced iNOS activation through regulation of PKC-alpha. Accordingly, BV exerts a potent suppressive effect on pro-inflammatory responses in rat C6 glioma cells.

S-nitrosoglutathione and hypoxia-inducible factor-1 confer chemoresistance against carbamoylating cytotoxicity of BCNU in rat C6 glioma cells

BCNU (1,3-bis[2-chloroethyl]-1-nitrosourea) is the mainstay in glioblastoma multiform chemotherapy with only minimal effects. BCNU may kill tumor cells via carbamoylating cytotoxicity, which irreversibly inhibits glutathione reductase with resultant accumulation of oxidized form of glutathione causing oxidative stress. S-nitrosoglutathione (GSNO) is a product of glutathione and nitric oxide interaction. We report that GSNO formation may underlie carbamoylating chemoresistance mediated by activation of inducible nitric oxide synthase. Transactivation of hypoxia-inducible factor-1 (HIF-1)-responsive genes reduces oxidative stress caused by glutathione depletion. We also noted that preconditioning of C6 glioma cells to induce HIF-1 and its downstream genes confers chemoresistance against carbamoylating cytotoxicity of BCNU.

Development, characterization, and epitope mapping of a panel of twenty-four monoclonal antibodies specific for human inducible nitric oxide synthase

A panel of monoclonal antibodies (MAbs) to human inducible nitric oxide synthase (hiNOS) has been developed. By isotype analysis of the MAbs cloned from the 24 different positive hybridomas, 13 were determined to be mouse IgG1, two were mouse IgG2a, two were mouse IgG2b, and the seven others were mouse IgM antibodies: all contained kappa light chains. The anti-hiNOS MAbs were initially characterized by ELISA, RIA, Western blot, and immunocytochemistry, and then they were epitope mapped using synthetic peptides and a three-step mapping procedure. In the first step, each of the 24 MAbs was tested by indirect ELISA for binding to 96 overlapping 18-amino acid-long peptides that span the entire 1153-amino acid length of hiNOS. Eight IgG class anti-hiNOS MAbs were found to bind to one of five different peptides. In the second step, a series of amino terminal and carboxyl terminal truncated peptides were synthesized for each of the five peptides to which one or more of the MAbs bound. Each of the eight anti-hiNOS MAbs was found to bind to the truncated peptides with a unique specificity that identified the amino acid segment involved in binding. The third step in the epitope mapping process utilized three series of overlapping 5-, 6-, 7-, 8-, and 9-amino acid-long peptides for each of these segments and identified the exact amino acids of hiNOS involved in antibody binding. Anti-hiNOS MAbs 2A1-F8, 2D2-B2, 21C10-1D10, and 24B10-2C7 were found to be especially useful in different immunoassays.

Differential effects of interferon-γ on the expression of cyclooxygenase-2 in high-grade human gliomas versus primary astrocytes

We compared effects of interferon-gamma (IFNgamma) on cyclooxygenase-2 (COX-2) expression in malignant human glioma cell lines and cultured primary human astrocytes. While IFNgamma inhibited interleukin-1beta (IL1beta)-induced expression of COX-2 in the glioma cells, it enhanced expression in primary astrocytes. This differential effect correlated with the observed modulation of NFkappaB and AP-1 DNA binding activity; reduced in the glioma cells, increased in primary astrocytes. Furthermore, IFNgamma had a significantly greater anti-proliferative effect on the glioma cells than COX inhibitors. This inhibitory effect of IFNgamma on expression of COX-2 in human glioma cells may have relevance for immunotherapies directed against high-grade gliomas.

Protein kinase C-eta (PKC-eta) is required for the development of inducible nitric oxide synthase (iNOS) positive phenotype in human monocytic cells

Several murine and human monocytic cell lines and monocyte-derived macrophages (MDM) from healthy volunteers were studied to compare their production of nitric oxide (NO) and induction of iNOS following endotoxin treatment. Although the human cells were sensitive to endotoxin and responded well by producing TNF-alpha and matrix metalloproteases (MMP), there was no induction of iNOS expression or NO production by any of these cells. Murine cells, however, produced large amounts of NO and expressed iNOS following similar endotoxin stimulation. We investigated the expression of PKC isotypes in all human and murine cell lines as well as in MDM, and found that the human cells lacked PKC-eta while the murine counterparts lacked PKC-beta1. Subsequently, human cells that were transfected with PKC-eta were found to make large quantities of NO following endotoxin exposure, an observation not seen in untransfected cells. We propose that PKC-eta is essential for the development of the iNOS positive phenotype in human monocytic cells, and may be responsible for the development of a number of inflammatory related conditions. As such it may be a suitable target for therapeutic intervention.

Nitric oxide and BCNU chemoresistance in C6 glioma cells: role of S-nitrosoglutathione

Inducible nitric oxide synthase (iNOS or NOS2) is expressed in malignant glioma. Previously we noted that C6 glioma cells overexpressing NOS2 displayed chemoresistance against 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and other chloroethylnitrosourea derivatives with carbamoylating action. Herein we report experimental evidence supporting the contention that this NOS2 effect is mediated, at least in part, by S-nitrosoglutathione (GSNO), a potent antioxidant derived from interaction of NO and glutathione. Out of three NO donors tested, only GSNO was effective in protecting glioma cells against BCNU cytotoxicity. Furthermore, the protective effect of GSNO, similar to that of NOS2, was confined to carbamoylating, but not alkylating action. Experimental manipulations that were expected to increase or decrease cellular GSNO stores, as confirmed by immunocytochemical staining using a GSNO-specific antibody and HPLC analysis of GSNO contents in culture medium, led respectively to enhanced or reduced chemoresistance against carbamoylating cytotoxicity. Finally, neocuproine, a selective cuprous ion chelator known to neutralize GSNO actions, abolished NOS2-mediated chemoresistance against carbamoylating agents. Our results reveal a novel action of NOS2/GSNO that may potentially contribute to the development of chemoresistance against BCNU, which remains a mainstay in chemotherapy for glioblastoma multiforme.

Roles of inducible nitric oxide synthase in the development and healing of experimentally induced gastric ulcers

The roles of inducible nitric oxide synthase (iNOS) in the development and healing of gastric ulcers have not been fully characterized. We characterized iNOS expression in experimentally induced ulcers in rat and mouse stomachs and investigated the roles of iNOS using iNOS gene-deficient (iNOS-/-) mice and wildtype mice. Gastric ulcers were induced in rats and mice by the application of acetic acid and cryoinjury, respectively. iNOS expression was detected on days 1-7 and peaked 3 days after ulcer induction in the rat. iNOS-positive cells were distributed mainly among the infiltrating cells and fibroblasts in the ulcer bed. The almost similar courses of healing and iNOS expression were observed in the ulcers of mice. During the course of healing, the iNOS gene status did not affect cell proliferation in the healing zone or vessel formation in the ulcer bed. iNOS deficiency, however, caused larger ulcers and severer inflammation during ulcer healing; the clearance of inflammatory cells in the ulcer bed by apoptosis was also delayed when the ulcer was re-epithelialized in the iNOS-deficient mice. These results indicate that iNOS is expressed in the ulcer bed and that iNOS activity may play beneficial roles in the ulcer repair process, possibly by regulating inflammation.

Role of nitric oxide in tumor angiogenesis

Nitric oxide (NO) is an important signalling molecule that acts in many tissues to regulate different physiological and pathological processes. We have contributed to demonstrate that NO stimulates angiogenesis and mediates the effect of different angiogenic molecules. In human tumors NOS expression and activity correlate with tumor growth and aggressiveness, through angiogenesis stimulation and regulation of angiogenic factor expression. Drugs affecting the NOS pathway appear promising antitumor strategies by reducing edema, inhibiting angiogenesis and facilitating the delivery of chemotherapeutical agents.

Inducible nitric oxide synthase activity induced by sodium chloride solution prolongs luminal pH elevation in rat and mouse stomachs

BACKGROUND

Sodium chloride (NaCl) is a strong promoter of gastric cancer. We hypothesized that inducible nitric oxide synthase (iNOS) induced by NaCl may be involved in its promoting effects. We investigated iNOS expression by hypertonic NaCl solutions and its pathophysiological roles in the gastric mucosa of rats and mice.

METHODS

iNOS mRNA and protein expressions were examined in the rat and mouse gastric mucosa after intragastric administration of NaCl solution by northern blot, reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. The effect on luminal pH by iNOS activity was assessed using aminoguanidine, a potent iNOS inhibitor, and iNOS gene deficient (iNOS-/-) mice.

RESULTS

iNOS expression was detected at concentrations higher than 1.7 M, mainly in the cells infiltrating the damaged mucosa of rats. Administration of a higher than 3.4 M NaCl solution elevated luminal pH of the rat stomach remarkably, enabling bacterial overgrowth and dramatically increasing iNOS expression (n = 5 per concentration). Pretreatment with ampicillin (p.o), an antibiotic, attenuated the iNOS expression in duplicate experiments. Co-treatment with aminoguanidine (s.q) accelerated recovery of elevated luminal pH at 8 h and 16 h or 24 h after administration of 3.4 M (n = 8) and 5.2 M NaCl solution (n = 5), respectively. iNOS expression and luminal pH elevation were also observed in mice stomachs after administration of 3.4 M NaCl solution. The elevated luminal pH of iNOS-/- mice stomachs after the administration of NaCl solution was significantly lower at 6 h (n = 7) and at 9 h (n = 11), compared to that of wild type mice (n = 9 and 10, respectively).

CONCLUSIONS

Hypertonic NaCl solutions induced iNOS expression in the gastric mucosa. iNOS activity prolonged the elevation of the luminal pH, potentially leading to bacterial overgrowth, which in turn enhanced iNOS expression. This vicious cycle might be related to the promoting effect of NaCl.

Mitochondria, oxidative damage, and inflammation in Parkinson's disease

The pathogenesis of Parkinson's disease (PD) remains obscure, but there is increasing evidence that impairment of mitochondrial function, oxidative damage, and inflammation are contributing factors. The present paper reviews the experimental and clinical evidence implicating these processes in PD. There is substantial evidence that there is a deficiency of complex I activity of the mitochondrial electron transport chain in PD. There is also evidence for increased numbers of activated microglia in both PD postmortem tissue as well as in animal models of PD. Impaired mitochondrial function and activated microglia may both contribute to oxidative damage in PD. A number of therapies targeting inflammation and mitochondrial dysfunction are efficacious in the MPTP model of PD. Of these, coenzyme Q(10) appears to be particularly promising based on the results of a recent phase 2 clinical trial in which it significantly slowed the progression of PD.

Immunohistochemical expression of inducible nitric oxide synthase (iNOS) in human brain tumors: relationships of iNOS to superoxide dismutase (SOD) proteins (SOD1 and SOD2), Ki-67 antigen (MIB-1) and p53 protein

In this study, inducible nitric oxide synthase (iNOS) expression in a series of 158 human primary brain tumors was analyzed. To gain some insight into the biological significance of iNOS expression in tumor cells, comparative immunohistochemical analyses were employed to characterize the expression of iNOS, superoxide dismutase (SOD) proteins (SOD1 and SOD2), Ki-67 antigen (MIB-1) and p53 protein in these cells. Sixteen (39.0%) of the 41 glioblastoma multiforme (GBM) specimens showed iNOS immunoreactivity. Positive immunoreactions with iNOS were also detected in 2/8 anaplastic astrocytomas, 1/17 astrocytomas, 1/14 medulloblastomas and 1/11 primitive neuroectodermal tumors, but no positive reactions were observed in oligodendrogliomas (0/11), ependymomas (0/5), schwannomas (0/21), meningiomas (0/23) or pituitary adenomas (0/7). The MIB-1 labeling index of GBMs that expressed iNOS was significantly higher than that of GBMs that did not (0.025< P <0.05, Wilcoxon rank-sum test). Unlike iNOS-negative tumors, all iNOS-positive tumors coexpressed SOD1 or SOD2. In particular, there was a significant correlation between iNOS induction and SOD1 expression (P =1.65x10(-10), Fisher's exact test) in GBM specimens. There was no significant relationship between iNOS and p53 protein in any type of primary brain tumor (P >0.05, Fisher's exact test). No significant immunohistochemical reactions with iNOS, MIB-1 or p53 protein were observed in normal brain tissue sections. We conclude that primary brain tumors express iNOS, and that iNOS expression in brain tumor cells may depend, in part, on cellular proliferation potential. Based on the fact that SOD1 scavenges oxidative-stress species originating from large amounts of nitric oxide (NO) produced by iNOS, iNOS-expressing brain tumor cells may protect themselves against NO cytotoxicity by overinducing SOD1.

Induction of matrix metalloproteinase gene transcription by nitric oxide and mechanisms of MMP-1 gene induction in human melanoma cell lines

Expression of 12 matrix metalloproteinases (MMPs) after exposure of human melanoma cell lines C32TG and Mewo to nitric oxide (NO) was investigated by the reverse transcription-polymerase chain reaction. Expression of the mRNA of MMP-1, -3, -10 and -13 in C32TG cells was transcriptionally enhanced in a dose-dependent manner by exposure to an NO donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP) and mRNA expression of MMP-1 and -10 was similarly enhanced in Mewo cells. Exposure of C32TG cells to NO increased the MMP-1 protein concentration in the culture medium. Testing with the luciferase gene fused to the 1.5 Kbp 5'-flanking region of the human MMP-1 gene showed that exposure to NO upregulated MMP-1 promoter activity in C32TG cells. Endogenous NO production after introduction of inducible NO synthase cDNA also enhanced MMP-1 promoter activity in C32TG cells. Deletion and mutational analysis identified a critical AP-1 binding site required for NO regulation of MMP-1. A neighboring Ets motif from the AP-1 site in the promoter region acted as an accessory to enhance MMP-1 expression. Electromobility shift analysis using the AP-1 binding site showed that NO enhanced the AP-1 binding ability of nuclear factors in C32TG cells. PD98059, a selective MEK inhibitor and SB202190, a p38 MAPK inhibitor, attenuated the MMP-1 mRNA expression enhanced by NO. Thus, MMP-1 was transcriptionally enhanced by NO via MAPK (ERK and p38) pathways. The results of our study suggest that the increased expression of MMPs in response to NO may be associated with tumor progression under inflammation.

NO-mediated chemoresistance in C6 glioma cells

Expression of inducible nitric oxide synthase (iNOS) in malignant glioma and other tumors has been extensively documented. Massive production of NO by iNOS has been shown to exert tumoricidal effects. However, NO may enhance vasodilation and promote neovascularization, thereby facilitating tumor growth. Compared to the effects of NO on tumor cell death and survival, correlation between NO and cytotoxicity of chemotherapeutic reagents in glioma have been less well characterized. Another gene product often linked to tumor malignancy is hypoxia-inducible factor-1 (HIF-1). HIF-1 is a transcription factor that renders malignant tumors adaptive to hypoxic stress during massive vascularization and tumor invasion. Interestingly, HIF-1 also contributes to iNOS induction under hypoxia. We have characterized the interrelationship between iNOS, HIF-1 and chemoresistance. We note that increased NO synthesis by cytokine exposure or iNOS overexpression neutralized the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), but not cisplatin, in rat C6 glioma cells. Both BCNU and CCNU are chloroethylnitrosoureas that kill tumor cells via carbamoylating and alkylating actions. Further studies indicated that iNOS only neutralized carbamoylating action of chloroethylnitrosoureas. Expression of iNOS may inhibit HIF-1 activity under hypoxia in C6 glioma cells transfected with a VEGF promoter-driven luciferase gene. Pretreatment of C6 cells with N-acetyl-l-cysteine (NAC), an antioxidant, nullified the inhibitory effect of iNOS on HIF-1 binding. That NO generated by iNOS expression inhibits HIF-1 activity in hypoxic C6 cells reveals a negative feedback loop in the HIF-1 --> iNOS cascade. Together these results suggest a complicated role of NO in malignant tumor growth, survival and invasion.

Elevated expression of inducible nitric oxide synthase and inflammatory cytokines in the alveolar macrophages after esophagectomy

OBJECTIVE

To evaluate the role of inducible nitric oxide (NO) synthase (iNOS) and inflammatory cytokines in alveolar macrophages (AMs) after esophagectomy in the pathogenesis of acute lung injury.

DESIGN

Prospective, exploratory, open-labeled clinical study.

SETTING

Intensive care unit and operating room in a university hospital.

PATIENTS

Thirteen patients receiving esophagectomy with carcinoma of the esophagus (postesophagectomy group), ten patients just before the surgery (preoperation group), and seven patents receiving surgery less invasive than esophagectomy (other surgery group) were selected.

INTERVENTIONS

Bronchoalveolar lavage fluid (BALF) and blood samples were obtained from study groups.

MEASUREMENTS AND MAIN RESULTS

The AMs in the BALF collected from each group were stained immunohistochemically with antibodies against iNOS, interleukin (IL)-6, and IL-8. The intensities of these expressions were determined by semiquantitative cytofluorometric system. NOx (NO2- + NO3-), IL-6, and IL-8 levels in the BALF and plasma were measured concurrently. The expressional intensities of iNOS, IL-6, and IL-8 in AMs obtained from the postesophagectomy group were maximal 24 hrs after the skin incision and significantly more evident than those from other groups. The IL-6, IL-8, and NOx levels in BALF and IL-6 and IL-8 levels in plasma in the postesophagectomy patients were also elevated. The intensities of iNOS and inflammatory cytokines expressions in AMs were closely related to postoperative respiratory failure.

CONCLUSIONS

The activation of topical alveolar macrophages may be involved in the pathogenesis of pulmonary complications in the postoperative period after esophagectomy.

Cell cycle regulation via p53 phosphorylation by a 5'-AMP activated protein kinase activator, 5-aminoimidazole- 4-carboxamide-1-beta-D-ribofuranoside, in a human hepatocellular carcinoma cell line

5-Aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) is an activator of AMP activated protein kinase (AMPK) and a regulator of de novo purine synthesis. There are several earlier reports indicating that AICAR treatment suppresses cell growth via regulation of AMPK or de novo purine synthesis. We found cell growth to be suppressed by AICAR treatment in HepG2 because of p53 accumulation, which was associated with p53-Ser15 phosphorylation. Moreover, a motif very similar to the consensus motif of AMPK phosphorylation was found around p53-Ser15, and Ser15 phosphorylation was detected in AICAR treated HepG2 as was in vitro phosphorylation by AMPK. Our results suggest that AICAR may regulate cell growth via p53 phosphorylation, and also indicate the possibility of p53 phosphorylation.

Inducible nitric oxide synthase expression

This unit contains three protocols that can be used to determine iNOS expression in mouse macrophage-like cells, RAW 264.7, by measuring end product, protein, and mRNA. A bacterial product, lipopolysaccharide (LPS), stimulates iNOS expression in RAW 264.7 cells.

iNOS expression inhibits hypoxia-inducible factor-1 activity

Hypoxia-inducible factor-1 (HIF-1) activates genes important in vascular function such as vascular endothelial growth factor (VEGF), erythropoietin (EPO), and inducible nitric oxide synthase (iNOS). iNOS catalyzes the synthesis of nitric oxide (NO), a free radical gas that mediates a number of cellular processes, including regulation of gene expression, vasodilatation, and neurotransmission. Here we demonstrate that iNOS expression inhibits HIF-1 activity under hypoxia in C6 glioma cells transfected with an iNOS gene and a VEGF promoter-driven luciferase gene. HIF-1 induction of VEGF-luciferase activity in C6 cell is also inhibited by sodium nitroprusside (SNP). Furthermore, pretreatment of C6 cells with N-acetyl-l-cysteine (NAC), an antioxidant, nullified the inhibitory effect of iNOS on HIF-1 binding. These results demonstrate that NO generated by iNOS expression inhibits HIF-1 activity in hypoxic C6 cells and suggest a negative feedback loop in the HIF-1 --> iNOS cascade.

Nitric oxide and angiogenesis

The steps required for new vessel growth are biologically complex and require coordinate regulation of contributing components, including modifications of cell--cell interactions, proliferation and migration of endothelial cells and matrix degradation. The observation that in vivo angiogenesis is accompanied by vasodilation, that many angiogenesis effectors possess vasodilating properties and that tumor vasculature is in a persistent state of vasodilation, support the existence of a molecular/biochemical link between vasodilation and angiogenesis. Several pieces of evidence converge in the indication of a role for nitric oxide (NO), the factor responsible for vasodilation, in physiological and pathological angiogenesis. Data originated in different labs indicate that NO can act both as an 'actor' of angiogenesis and as a 'director of angiogenesis', both functions being equally expressed during physiological and pathological processes. NO significantly contributes to the prosurvival/proangiogenic program of capillary endothelium by triggering and transducing cell growth and differentiation via endothelial-constitutive NO synthase (ec-NOS) activation, cyclic GMP (cGMP) elevation, mitogen activated kinase (MAPK) activation and fibroblast growth factor-2 (FGF-2) expression. Re-establishment of a balanced NO production in the central nervous system results in a reduction of cell damage during inflammatory and vascular diseases. Elevation of NOS activity in correlation with angiogenesis and tumor progression has been extensively reported in experimental and human tumors. In the brain, tumor expansion and edema formation are sensitive to NOS inhibition. On this basis, the nitric oxide pathway appears to be a promising target for consideration in pro- and anti-angiogenic therapeutic strategies. The use of NOS inhibitors seems appropriate to reduce edema, block angiogenesis and facilitate antitumor drug delivery.

Inhibitory and stimulatory effects of lactacystin on expression of nitric oxide synthase type 2 in brain glial cells. The role of Ikappa B-beta

Expression of inflammatory nitric oxide synthase (NOS2) is mediated by transcription factor NFkappaB. By using the specific proteasome inhibitor lactacystin to examine IkappaB degradation, we observed a paradoxical increase in lipopolysaccharide- and cytokine-dependent NOS2 expression at low concentrations or when lactacystin was added subsequent to cytokines. Lactacystin reduced the initial accumulation of NOS2 mRNA but reduced its subsequent decrease. Lactacystin increased NOS2 promoter activation after 24 h, but not after 4 h, and similarly prevented initial NFkappaB activation and at later times caused NFkappaB reactivation. Lactacystin reduced initial degradation of IkappaB-alpha and IkappaB-beta, however, at later times selectively increased IkappaB-beta, which was predominantly non-phosphorylated. Expression of full-length rat IkappaB-beta, but not a carboxyl-terminal truncated form, inhibited NOS2 induction and potentiation by lactacystin. Lactacystin increased IkappaB-beta expression in the absence of NOS2 inducers, as well as expression of heat shock protein 70, and the heat shock response due to hyperthermia increased IkappaB-beta expression. These results suggest that IkappaB-beta contributes to persistent NFkappaB activation and NOS2 expression in glial cells, that IkappaB-beta is a stress protein inducible by hyperthermia or proteasome inhibitors, and that delayed addition of proteasome inhibitors can have stimulatory rather than inhibitory actions.

Modification of vascular tone using iNOS under the control of a radiation-inducible promoter

It may be therapeutically advantageous to alter tumour blood supply specifically. Nitric oxide is a potent vasodilator which is produced in many tissues by the enzyme nitric oxide synthase (NOS). We have transfected cDNA for the inducible isoform of this enzyme (iNOS), under the control of the radiation-inducible promoter WAF1. The activity of the promoter was initially assessed using green fluorescent protein (GFP) in both endothelial cells and rat tail artery segments. Induction of protein expression by 9.5- and 4.5-fold respectively, was observed after a radiation dose of 4 Gy. Artery sections were then transfected with the WAF1/iNOS construct; this gave five-fold induction of iNOS protein after a dose of 4 Gy. The transfected artery was also tested functionally for relaxation, indicative of NO production. One hour after exposure to 4 Gy there was a significant (65%) relaxation of artery segments that had been preconstricted with phenylephrine. This could be partially reversed by the NOS inhibitor nitro-L-arginine. This study demonstrates that we can regulate vascular tone using an X-ray inducible promoter.

Human Immunodeficiency Virus-1–Infected Macrophages Induce Inducible Nitric Oxide Synthase and Nitric Oxide (NO) Production in Astrocytes: Astrocytic NO as a Possible Mediator of Neural Damage in Acquired Immunodeficiency Syndrome

Nitric oxide (NO) plays an important role in normal neural cell function. Dysregulated or overexpression of NO contributes to neurologic damage associated with various pathologies, including human immunodeficiency virus (HIV)-associated neurological disease. Previous studies suggest that HIV-infected monocyte-derived macrophages (MDM) produce low levels of NO in vitro and that inducible nitric oxide synthase (iNOS) is expressed in the brain of patients with neurologic disease. However, the levels of NO could not account for the degree of neural toxicity observed. In this study, we found that induction of iNOS with concomitant production of NO occurred in primary human astrocytes, but not in MDM, when astrocytes were cocultured with HIV-1–infected MDM. This coincided with decreased HIV replication in infected MDM. Supernatants from cocultures of infected MDM and astrocytes also stimulated iNOS/NO expression in astrocytes, but cytokines known to induce iNOS expression (interferon-γ, interleukin-1β, and tumor necrosis factor-) were not detected. In addition, the recombinant HIV-1 envelope protein gp41, but not rgp120, induced iNOS in cocultures of uninfected MDM and astrocytes. This suggests that astrocytes may be an important source of NO production due to dysregulated iNOS expression and may constitute one arm of the host response resulting in suppression of HIV-1 replication in the brain. It also leads us to speculate that neurologic damage observed in HIV disease may ensue from prolonged, high level production of NO.

Nitric oxide synthase activity in fresh cells from ovarian tumour tissue: relationship of enzyme activity with clinical parameters of patients with ovarian cancer

Recent studies suggest a dual role for nitric oxide (NO) in tumour biology. High concentrations of NO can mediate tumouricidal activity, whereas lower concentrations have been shown to promote tumour growth. In this study, NO synthase (NOS) activity was investigated in cells that were prepared from tissue from primary and metastatic sites and from malignant effusions in 41 cases of suspected ovarian cancer. NO biosynthesis, determined by nitrite + nitrate (NOx) accumulation in medium from cultured cells prepared from disaggregated tumours or effusions and indicative of the inducible NO synthase isoform, was detected in 37% of the cases investigated (range 10.2-114 microM). There was a significant relationship between NOx and tumour differentiation (P = 0.014), with NOx being significantly higher for the more differentiated tumours. NOS activity, determined by the conversion of radiolabelled L-arginine to citrulline by tissue or cell extracts, was detected in 29% of cases (range 0.9-6.9 pmol/min per mg of protein), with all samples tested being moderately or poorly differentiated. Seventy percent of this activity was calcium dependent, indicative of constitutive NOS isoforms. Morphological and immunohistochemical assessment of tumour samples indicated a significant relationship between high macrophage content and NOS activity (as NOx biosynthesis) (rs = 0.726, N = 16, P < 0.01). The relationship between NOS expression, immune response, and disease progression is complex and not simply dependent on the differentiation status of ovarian cancer.

Enhanced expression of inducible nitric oxide synthase in chronic gastritis with intestinal metaplasia

Nitric oxide produced by inducible nitric oxide synthase (iNOS) has been claimed to be involved in gastritis; however, its characteristics are largely unknown. We assessed (1) iNOS expression in the human gastric mucosa in chronic gastritis and (2) the cytokines associated with iNOS expression. Gastric biopsy specimens were obtained from patients with chronic gastritis. Total RNA was isolated and reverse transcription-polymerase chain reaction (PCR) was performed semiquantitatively using specific primer sets for iNOS, interleukin (IL)-1beta, IL-8, IL-6, interferon-y, tumor necrosis factor-alpha (TNF-alpha), TNF receptors, IL-6 receptors, and sucrase, respectively. Helicobacter pylori infection was examined by the PCR assay. Reverse transcription-PCR analysis showed that expression of iNOS was detected in 10 of 23 samples. Expression of iNOS mRNA was closely correlated with expression of TNF-alpha and was observed frequently in subjects with intestinal metaplasia. The Helicobacter pylori gene was detected by PCR assay in all iNOS-positive cases. These results indicate that iNOS is predominantly expressed in the gastric mucosa with intestinal metaplasia and H. pylori infection. TNF-alpha is thought to be an important cytokine associated with iNOS expression.

Expression and localization of inducible nitric oxide synthase in the rat ovary: a possible involvement of nitric oxide in the follicular development

In the present study, using Northern blot analysis, we demonstrated that the level of iNOS mRNA in the ovary of immature rats decreased after 6 h of pregnant mare serum gonadotropin administration and recovered gradually up to the untreated level 48 h after the administration. Both in situ hybridization and immunohistochemistry revealed that iNOS mRNA and protein was predominantly localized in granulosa cells in most of immature follicles, but not in mature follicles with an antrum, which was a consistent finding regardless of gonadotropin treatment. Furthermore, we found that cultured granulosa cells had the ability to express iNOS mRNA in the presence of cytokines such as tumor necrosis factor-alpha, interleukin-1 beta and interferon-gamma, which are inherently detectable in the ovary. These results raise the possibility that locally produced NO synthesized by iNOS may be involved in the developmental status of ovarian follicles in concert with gonadotropin.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

Ovarian nitric oxide synthase (NOS) gene expression during peripubertal development

Nitric oxide (NO) is generated from L-arginine by different isoforms of the enzyme nitric oxide synthase (NOS) and is known to be involved in mediating several biological functions, some of which are associated with reproduction. In this study, we examined the ability of the prepubertal ovary to express the inducible (i), as well as the neuronal-type constitutive (c) form of NOS and also, investigated whether either isoform undergoes changes in the ovary during peripubertal development. Results indicate that both forms of NOS were expressed in the ovary and that the iNOS mRNA transcripts were expressed without being exogenously induced. When compared with juvenile levels, iNOS, but not cNOS, mRNA increased (p<0.01) during the early proestrous phase of development. By the late proestrous phase, the levels of iNOS mRNA declined markedly (p<0.001) and remained low throughout both the first estrous and diestrous phases. Western blot analysis revealed both iNOS and cNOS protein expression in each phase of puberty with only iNOS showing a significant change during the peripubertal period. Specifically, there was an initial increase in the expression of iNOS protein during the late proestrous phase (p<0.05) which was accompanied by preovulatory increases in serum estradiol (p<0.01) and LH (p<0.001). The iNOS protein levels then dramatically increased to peak on the morning of first estrus (p<0.001), an event associated with declining (p<0.05) serum levels of estradiol. These data demonstrate developmental changes in the expression of ovarian iNOS mRNA and protein both before and after first ovulation; hence, suggesting a role for NO in the ovary during pubertal maturation and furthermore, providing compelling evidence at the gene level supporting the hypothesis that the NO/NOS system plays a physiological role in ovarian function.

TNF-alpha mediates inducible nitric oxide synthase expression in human neuroblastoma cell line by cisplatin

The human neuroblastoma cell line NB-39-nu expressed inducible nitric oxide synthase (iNOS) mRNA following treatment with a combination of interferon-gamma (IFN-gamma) and cis-diamminedichloroplatinum(II) (cisplatin). The level of iNOS mRNA peaked at 48 hr after treatment, and dexamethasone inhibited the induction of iNOS mRNA expression. Cisplatin induced tumor necrosis factor-alpha (TNF-alpha) mRNA expression, and an anti-TNF-alpha neutralizing antibody inhibited the induction of iNOS expression by a combination of cisplatin and IFN-gamma in NB-39-nu cells. Thus, iNOS expression in NB-39-nu cells by a combination of cisplatin and IFN-gamma involves in the TNF-alpha-mediated signal transduction mechanism.

Inducible nitric-oxide synthase and nitric oxide production in human fetal astrocytes and microglia. A kinetic analysis

The understanding of the induction and regulation of inducible nitric-oxide synthase (iNOS) in human cells may be important in developing therapeutic interventions for inflammatory diseases. In the present study, we not only demonstrated that human fetal mixed glial cultures, as well as enriched microglial cultures, synthesize iNOS and nitric oxide (NO) in response to cytokine stimulation, but also assessed the kinetics of iNOS and NO synthesis in human fetal mixed glial cultures. The iNOS mRNA was expressed within 2 h after stimulation and decreased to base line by 2 days. Significant levels of iNOS protein appeared within 24 h after stimulation and remained elevated during the culture period. A dramatic increase in NO production and NO-mediated events, such as the induction of cyclic guanosine monophosphate (cGMP), NADPH diaphorase activity, and nitrotyrosine occurred 3 days after stimulation, a delay of 48 h from the time of the first expression of iNOS enzyme. This delay of NO production was altered by the addition of tetrahydrobiopterin, but not by the addition of L-arginine, heme, flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), or NADPH. These findings suggest that a post-translational regulatory event might be involved in iNOS-mediated NO production in human glia.

In vivo induction of inducible nitric oxide synthase by microinjection with interferon-gamma and lipopolysaccharide in rat hippocampus

To clarify whether the inducible nitric oxide synthase (iNOS) protein can be induced in in vivo brain, we examined the influence of direct intrahippocampal injection with interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS) in the rat. In the area surrounding the microinjection site, NOS activity (NO2- accumulation) was enhanced 24 h after injection with IFN-gamma plus LPS. Although the level of 160-kDa nNOS protein was not changed, the 130-kDa iNOS protein was induced 12 h after the injection. On the other hand, iNOS mRNA could be detected at 6 and 12 h but not at 24 h. iNOS immunoreactivity was observed in CD11b-immunopositive microglia in close proximity to the injection site, but the immunoreactivity was not colocalized with glial fibrillary acidic protein-immunopositive astrocytes. Although CD11b-immunopositive microglia were of the ramified type even after injection with vehicle after 24 h, injection with IFN-gamma plus LPS caused numerous microglia to change to the ameboid type and to express major histocompatibility complex (MHC) class II antigens. In some of these ameboidal microglia, iNOS immunoreactivity was observed. These results suggest that intrahippocampal injection with IFN-gamma plus LPS induced iNOS mRNA after 6 h and iNOS protein after 12 h in some of the ameboidal microglia that expressed MHC class II antigens in in vivo rat brain.

Inductions of Cu/Zn superoxide dismutase- and nitric oxide synthase-like immunoreactivities in rabbit spinal cord after transient ischemia

The distributions and inductions of Cu/Zn superoxide dismutase (SOD), neuronal and endothelial nitric oxide (NO) synthase (nNOS and eNOS), and nitrotyrosine (NT) were immunohistochemically examined in rabbit spinal cords after 5 and 15 min of transient ischemia. The neurons in the anterior horns (AH) were selectively lost 7 days after 15-min ischemia as compared with those of sham-operated controls. In the normal spinal cords, a number of neurons in the AHs were positive for the nNOS, and only slightly positive for the Cu/Zn SOD and the eNOS. Immunoreactivities for the proteins were induced at 8-24 h both after 5- and 15-min ischemia. In contrast, NT-like immunoreactivity was negative both in the normal and postischemic spinal cords. These results suggest that Cu/Zn SOD- and nNOS-, and eNOS-like immunoreactivities are induced, but that, even though an interaction of Cu/Zn SOD with NO could be present, NT was not detected in the motor neurons in the rabbit spinal cords after transient ischemia. Other factors could be required for NT formation found in degenerative motor neuron death in humans.

Regulation of the mouse inducible-type nitric oxide synthase gene promoter by interferon-gamma, bacterial lipopolysaccharide and NG-monomethyl-L-arginine

Cytokines and bacterial lipopolysaccharides (LPSs) stimulate nitric oxide production in macrophages by inducing transcription of the gene coding for the inducible isoform of nitric oxide synthase (iNOS). We have cloned the mouse iNOS gene promoter and analysed its structural features and its response to interferon-gamma (IFN-gamma) and Escherichia coli LPS in RAW 264.7 mouse macrophage-like cells. Transcription of a recombinant reporter gene including the promoter and 4 kb of its 5'-flanking DNA, linked to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene, is stimulated by IFN-gamma and, more efficiently, by LPS upon transient transfection in RAW 264.7 cells. Two upstream DNA regions are required for maximal promoter activation of LPS: the first maps between positions -1541 and -775 and the other between -420 and -47, with respect to the major transcriptional start site of the iNOS gene. The upstream-most region also mediates promoter trans-activation by IFN-gamma. As reported earlier for transcription of the endogenous iNOS gene, combined stimulation of RAW 264.7 cells with IFN-gamma and LPS results in lower activation of the transfected promoter, when compared with LPS alone. NG-Monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthase activity, enhances iNOS gene mRNA induction and promoter activation by IFN-gamma and LPS, indicating that nitric oxide can influence negatively the reponsiveness of this gene to inducers. These results suggest the possibility of a negative regulatory feedback exerted by iNOS on the transcriptional activation of its own gene.