Inducible nitric oxide synthase in human diseases

iNOS expression in rat aorta is increased after spinal cord transection: a possible cause of orthostatic hypotension in man

Orthostatic hypotension commonly occurs in persons with spinal cord injury (SCI), limiting rehabilitation and independence. Findings of increased production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) after exposure to simulated microgravity suggest that increased iNOS expression contributes to OH in persons with SCI. To test this possibility, male Wistar rats underwent surgical transection of the spinal cord (T10) or sham-SCI surgery followed by euthanasia 3, 7 or 14 days later. Expression in thoracic aortic of inducible (iNOS), endothelial (eNOS) and neuronal (nNOS) NOS was then determined. In SCI rats, expression of iNOS mRNA was decreased at 3 days, had returned to normal levels of expression at 7 days and was increased at 14 days post-SCI (1.8-fold). In contrast, levels of eNOS mRNA were increased at 3 days (1.4-fold), then declined over time reaching levels by day 14 that were reduced compared to sham-SCI (0.23-fold). There were no significant effects of SCI on nNOS expression. These findings suggest a possible role for increased iNOS expression in the pathogenesis of OH in persons with SCI.

Reactive oxygen species (ROS), but not nitric oxide (NO), contribute to strain differences in the susceptibility to experimental arthritis in rats

There is extensive evidence for the critical role of reactive oxygen species (ROS) and nitric oxide (NO) produced by phagocytes in development of inflammatory processes and pathogenesis of numerous diseases, including rheumatoid arthritis (RA). Apart from their function as mediators of inflammation and tissue damage, recent research supports their role as signaling and regulatory molecules. In the present study we have investigated the production of ROS and NO over the course of adjuvant arthritis (AA) and oil-induced arthritis (OIA), by resident peritoneal macrophages of two rat strains: Dark Agouti (DA), susceptible, and Albino Oxford (AO), resistant to induction of AA and OIA. We have compared levels of ROS and NO produced by susceptible vs. resistant rat strain, and investigated their relevancy for arthritis development and severity. In addition, we have stimulated macrophages in vitro with Mycobacterium bovis BCG, and two heat shock proteins (HSP): endogenous HSP47 and mycobacterial HSP71 (mHSP71). Our results suggest a possible contribution of increased ROS production to arthritis resistance of AO rats. The ROS production in AO rats is potentiated by endogenous HSP47, but not with mycobacterial cell and mHSP71, suggesting HSP47 participates in AA control. We have found no fundamental relationship between the magnitude of NO production and AA and OIA susceptibility and severity, suggesting that NO has no effector role in AA and OIA. Our results advocate a regulatory type action of NO molecule might be more significant in arthritis development.

An inhaled inducible nitric oxide synthase inhibitor reduces damage of Candida-induced acute lung injury

Excessive nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS) aggravates acute lung injury (ALI) by producing peroxynitrite. We previously showed by immunostaining that the expression of iNOS was suppressed by inhalation of N(G)-nitro-L-arginine methyl ester in mice with Candida-induced ALI. This study tested the hypothesis that a novel iNOS inhibitor suppresses not only iNOS expression, but also iNOS messenger RNA (mRNA) production by interrupting a positive feedback loop at the time of NO production in Candida-induced ALI. Mice were pretreated by inhalation of saline or ONO-1714, a selective iNOS inhibitor, and were given an intravenous injection of Candida albicans to induce ALI. After inhalation of 1 mM aerosolized ONO-1714, the nitrite-nitrate concentration in bronchoalveolar lavage fluid (BALF) at 24 h was significantly lower than that after inhalation of saline. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) levels and neutrophils in BALF were decreased by inhalation of ONO-1714. Inhalation of ONO-1714 markedly suppressed nitrotyrosine production and inhibited the expression of iNOS mRNA as well as proteins in the lung. Survival was prolonged by inhalation of ONO-1714. We conclude that pretreatment with inhaled ONO-1714 suppresses the production of peroxinitrite and decreases oxidative stress associated with peroxinitrite in Candida-induced ALI.

Correlation between Flavonoid Content and the NO Production Inhibitory Activity of Peel Extracts from Various Citrus Fruits

We investigated the correlation between the flavonoid content and NO production inhibitory activity of fruit peel extracts using 20 citrus plants. The contents of seven flavonoids (naringin, naringenin, hesperidin, hesperetin, rutin, nobiletin, and tangeretin) were determined by HPLC analysis. Each citrus peel extract varied in flavonoid content, but the contents of nobiletin and tangeretin, which were contained in all 20 fruit peels, showed a positive and significant correlation with each other (r=0.879, p<0.0005 for immature fruit peels; r=0.858, p<0.0005 for mature fruit peels). All citrus peel extracts dose-dependently inhibited LPS-induced NO production in RAW 264.7 cells. This inhibitory effect was significantly and positively correlated with the content of nobiletin and tangeretin. Nobiletin showed a more potent NO production inhibitory activity (IC50=26.5 microM) compared to tangeretin (IC50=136.6 microM). This result supports the premise that nobiletin-rich citrus may provide protection against disease resulting from excessive NO production.

Normalization of supine blood pressure after nitric oxide synthase inhibition in persons with tetraplegia

BACKGROUND/OBJECTIVE

Orthostatic hypotension is a well-defined clinical consequence of spinal cord injury (SCI), particularly in those with tetraplegia. The etiology of orthostatic hypotension is thought to be loss of sympathetic vasomotor control, although other factors may play a role. There is evidence of up-regulation of nitric oxide synthase (NOS) activity after hind-limb suspension in rats, a condition of antigravity that may have similar vascular effects as shown in persons with tetraplegia caused by paralysis. The study objective was to determine the effect of a NOS inhibitor (nitro-L-arginine methyl ester [L-NAME]) on supine mean arterial pressure in persons with chronic tetraplegia compared with non-SCI controls.

METHODS

Fourteen individuals participated (7 with tetraplegia and 7 controls). Subjects visited the laboratory twice for placebo on day 1 and L-NAME (1 mg/kg) on day 2; both were infused intravenously over 60 minutes. Blood pressure was monitored for 3 hours after infusion at the brachial artery using a standard manual cuff.

RESULTS

Mean arterial pressure (MAP) was lower at baseline (P < 0.05) and after placebo administration (P < 0.0001) in the tetraplegia group compared with the control group. L-NAME increased MAP in both groups; however, the relative increase was greater in the tetraplegia group compared with the control group, such that group differences for MAP were eliminated. Supine MAP was normalized with L-NAME, and there was an increased sensitivity to NOS inhibition in the group with tetraplegia.

CONCLUSIONS

These findings indicate that blood pressure dysregulation in persons with tetraplegia may reflect increased vascular NO and suggest a novel treatment of hypotension using NOS inhibition in this population.

Nitric oxide increases toxicity of hydrogen peroxide against rat liver endothelial cells and hepatocytes by inhibition of hydrogen peroxide degradation

Nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) show cooperativity in their cytotoxic action. The present study was performed to decipher the mechanisms underlying this phenomenon. In cultured liver endothelial cells and in cultured, glutathione-depleted hepatocytes, the combined exposure to NO (released by spermine NONOate, 1 mM) and H(2)O(2) (released by glucose oxidase) induced cell injury that was far higher than the injury elicited by NO or H(2)O(2) alone. In both cell types, the addition of the NO donor increased H(2)O(2) steady-state levels, although with different kinetics: in hepatocytes, the increase in H(2)O(2) levels was already evident at early time points while in liver endothelial cells it became evident after > or =2 h of incubation. NO exposure inhibited H(2)O(2) degradation, assessed after addition of 50 microM, 200 microM, or 4 mM authentic H(2)O(2), significantly in both cell types. However, again, early and delayed inhibition was observed. The late inhibition of H(2)O(2) degradation in endothelial cells was paralleled by a decrease in glutathione peroxidase activity. Glutathione peroxidase inactivation was prevented by hypoxia or by ascorbate, suggesting inactivation by reactive nitrogen oxide species (NO(x)). Early inhibition of H(2)O(2) degradation by NO, in contrast, could be mimicked by the catalase inhibitor azide. Together, these results suggest that the cooperative effect of NO and H(2)O(2) is due to inhibition of H(2)O(2) degradation by NO, namely to inhibition of catalase by NO itself (predominant in hepatocytes) and/or to inhibition of glutathione peroxidase by NO(x) (prevailing in endothelial cells).

Identification of a classic cytokine‐induced enhancer upstream in the human iNOS promoter

The human inducible NOS (iNOS) promoter transcriptionally regulated by 5' flanking region extending 16 kb upstream that contains cytokine-responsive DNA motifs. In this study, we further identified a classic inducible enhancer located between -5 and -6 kb in the hiNOS upstream promoter. This 1 kb promoter sequence functions as a cytokine-inducible enhancer in an orientation- and position-independent manner in human lung A549 and liver AKN1 cells. This DNA enhancer also confers cytokine inducibility to the heterologous thymidine kinase (TK) promoter. Chromatin immunoprecipitation (ChIP) analysis was applied, and confirmed cytokine-inducible in vivo DNA-protein interactions within this enhancer region. In vivo functional binding of both NF-kappaB (p65/p50) and Stat-1alpha at the -5.8 kb human iNOS promoter site was significantly increased in A549 cells after cytokine stimulation, while only Stat-1alpha bound at the -5.2 kb site. These results identify the -5 to -6 kb promoter region as a classic transcriptional enhancer for the human iNOS gene and provide definitive in vivo evidence of specific NF-kappaB and Stat-1 nuclear protein binding that mediates transcription of the hiNOS gene under cytokine stimulation.

NOS2A and the modulating effect of cigarette smoking in Parkinson's disease

OBJECTIVE

Inducible nitric oxide synthase, a protein product of NOS2A, generates nitric oxide as a defense mechanism, but excessive levels threaten cellular survival. NOS2A is a candidate gene for Parkinson's disease (PD) that potentially interacts with cigarette smoking. We examined NOS2A for association with PD risk and age at onset (AAO) and for interaction with smoking.

METHODS

We genotyped 13 NOS2A single nucleotide polymorphisms (SNPs) in 466 singleton families and in a validation set of 286 multiplex families. We tested allelic and haplotypic association using the association in the presence of linkage test, genotypic associations using the genotype pedigree disequilibrium test, AAO effects using the quantitative transmission disequilibrium test, and interactions using generalized estimating equations.

RESULTS

Among the pooled earliest onset families, rs2255929 and rs1060826 generated significant allelic (p = 0.000059 and 0.0062, respectively) and genotypic (p = 0.0039 and 0.0014, respectively) associations with risk and AAO (p = 0.00070 and 0.0073, respectively); the two-SNP haplotype generated even stronger association with PD (p = 0.000013). Significant interactions with smoking (p = 0.0015 for rs 2255929 and p < 0.0001 for rs 1060826) were detected in a subset of the families; smoking was inversely associated with PD among risk allele noncarriers, but significance diminished among carriers.

INTERPRETATION

Our findings support NOS2A as a genetic risk factor in PD, potentially by influencing AAO and by modifying the inverse association between PD and smoking.

Identification of a regulatory cis-element within the 3'-untranslated region of the murine inducible nitric oxide synthase (iNOS) mRNA; interaction with heterogeneous nuclear ribonucleoproteins I and L and role in the iNOS gene expression

The aim of this study was to investigate the role of heterogeneous nuclear ribonucleoprotein I (hnRNPI) and hnRNPL in the regulation of the murine inducible nitric oxide synthase (iNOS) gene during inflammation. Treatment of mice with lipopolysaccharide (LPS)/D-galactosamine, or of RAW 264.7 cells with LPS/interferon-gamma (IFN-gamma), strongly increased iNOS expression while reducing hnRNPI levels and complex formation between hnRNPI/hnRNPL and the 3'-untranslated region (3'-UTR) of iNOS mRNA. Introduction of the iNOS 3'-UTR to a luciferase reporter gene reduced its expression in RAW 264.7 cells. However, when hnRNPI and hnRNPL binding sites were deleted, luciferase expression was recovered. LPS/IFN-gamma increased the luciferase activity of the full-length 3'-UTR construct compared to control, while its effects on the deletion constructs were modest. The results indicate that LPS/IFN-gamma induce iNOS through a mechanism involving hnRNPI and hnRNPL binding to iNOS 3'-UTR. Our data suggest that iNOS mRNA degradation is promoted upon binding of hnRNPI and hnRNPL to a destabilizing region within its 3'-UTR, while inflammatory stimuli causing dissociation of the mRNA-protein complex, yield a more stable transcript. This appears to be particularly significant during extended inflammatory stimuli, resulting in sustained nitric oxide production. The critical event launching this process appears to be the degradation of hnRNPI.

Effects of inducible nitric oxide synthase inhibitors on asthma depending on administration schedule

The effectiveness of two inducible nitric oxide synthase (iNOS) inhibitors on allergic airway inflammation was investigated under different administration schedules. Rats sensitized to ovalbumin (OVA) were exposed to OVA for 3 consecutive days. Both iNOS inhibitors showed markedly different effects between two pretreatment schedules: pretreatment before each of three OVA exposures S1 and before the third exposure alone S2. S1 pretreatment resulted in higher pulmonary resistance than triple OVA alone. This potentiation was associated with increased eosinophil infiltration and malondialdehyde levels in the lungs, which were suppressed by superoxide dismutases (SODs) but not by methylprednisolone. However, the S2 administration of both iNOS inhibitors completely suppressed the airway response. Administration by schedule S1 completely suppressed plasma nitrite and nitrate levels, but that by S2 caused only a slight suppression. The triple OVA exposures resulted in the upregulation of iNOS in alveolar macrophages and arginase activity, Mn- and Cu/Zn-SOD expression, and nitrotyrosine and lipid peroxide deposition in the airway. However, inhibitors administered by schedule S1 suppressed this upregulation, but further potentiated nitrotyrosine, which in turn was inhibited by SOD. Although iNOS inhibitors may be beneficial for asthma, repeated administration may be detrimental because of extensive reduction of NO and downregulation of SOD.

Differential effects of TNF-alpha and IFN-gamma on gene transcription mediated by NF-kappaB-Stat1 interactions

Regulation of gene transcription by the cytokines tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) involves complex interactions between NF-kappaB and Stat families of transcription factors. The purpose of this study was to identify the spatial promoter requirements that govern cytokine synergy for gene transcription regulated by NF-kappaB and Stat factors. Using a set of transcription reporter-luciferase constructs, we show that the relative orientation of juxtaposed NF-kappaB-Stat (SIE) cis-elements determines the ability of TNF-alpha and IFN- gamma to induce gene transcription. Further, NF-kappaB and Stat1 proteins directly regulate transcription by interacting cooperatively on NF-kappaB-SIE DNA binding in response to TNF-alpha plus IFN-gamma. Coimmunoprecipitation provides evidence for a direct NF-kappaB/Stat1 protein-protein interaction. In contrast, IFN-gamma inhibits TNF-alpha-induced transcription of an NF-kappaB reporter gene in a Stat1-dependent mechanism in 2fTGH fibroblasts. Similarly, Stat1 is inhibitory to NF-kappaB overexpression-induced transcription. IFN-gamma and Stat1-dependent inhibition of NF-kappaB transcription occurs independent of TNF-alpha-induced NF-kappaB DNA binding. Interestingly, IFN-gamma pretreatment of 2fTGH fibroblasts potentiates TNF-alpha induction of Stat1 DNA binding. Further, ChIP analysis was applied to detect cytokine-induced in vivo binding and transcriptional regulation of the human inducible nitric oxide synthase (iNOS) gene by NF-kappaB and Stat1. These data demonstrate complex transcriptional regulatory mechanisms elicited by TNF-alpha and IFN-gamma and have potentially important implications for other genes differentially controlled by cytokines.

Src-mediated phosphorylation regulates subcellular distribution and activity of human inducible nitric oxide synthase

Inducible nitric oxide synthase (iNOS) expression is regulated at both the transcriptional and post-transcriptional level in epithelial cells. The aim of this study was to characterize the effects of tyrosine phosphorylation on iNOS activity. In a human intestinal epithelial cell line stimulated with cytokines, tyrosine phosphorylation of human iNOS protein was observed after 30 min exposure to pervanadate (PV), an inhibitor of protein tyrosine phosphatases. 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, a specific inhibitor of Src tyrosine kinases, abolished the PV-induced iNOS tyrosine phosphorylation. Cotransfection of Src with iNOS cDNA in human embryonic kidney (HEK) 293 cells resulted in a threefold (P<0.001) increase of iNOS protein levels and tyrosine phosphorylation of iNOS. In the presence of Src, 76% of wild-type (wt) iNOS was redistributed to detergent-insoluble domains and iNOS activity was decreased by 28% (P<0.05) despite increased iNOS protein levels. Analysis of iNOS tyrosine mutants revealed decreased Src-induced effects in Y151F iNOS mutant. Using a GST-fusion protein containing a domain encompassing Y151, we show that Y151 is a direct substrate for active Src in vitro. These findings indicate a role for iNOS tyrosine phosphorylation in the regulation of iNOS activity and the implication of Src tyrosine kinases in this pathway.

Estrogen up-regulates inducible nitric oxide synthase, nitric oxide, and cyclooxygenase-2 in splenocytes activated with T cell stimulants: role of interferon-gamma

Estrogen is implicated in many autoimmune diseases and is a robust immunomodulator. For example, it regulates interferon (IFN)-gamma, a cytokine believed to up-regulate inducible nitric oxide synthase (iNOS). A notable gap in the literature is a lack of information on the regulation of nitric oxide in immune tissues by estrogen. We now show that activation of splenocytes with T cell stimulants [concanavalin-A (Con-A) or anti-CD3 antibodies] results in copious release of nitric oxide in splenocyte cultures from estrogen-treated but not placebo-treated mice. Moreover, even a low dose of T cell stimulants induced nitric oxide in splenocytes from estrogen-treated, but not placebo-treated, mice. Con-A-activated splenocytes from estrogen-treated mice also have up-regulated iNOS mRNA, iNOS protein, and cyclooxygenase-2 (a nitric oxide-regulated downstream proinflammatory protein) when compared with controls. Our studies suggest that the induction of nitric oxide by activated splenocytes from estrogen-treated mice is mediated in part by IFNgamma. First, blocking costimulatory signals mediated through interactions of CD28 and B7 molecules by CTLA-4Ig markedly decreased not only IFNgamma but also nitric oxide. Second, estrogen treatment of IFNgamma-knockout (IFNgamma(-)/(-)) mice did not induce iNOS protein or nitric oxide. Finally, in vitro addition of recombinant IFNgamma to Con-A-activated splenocytes from IFNgamma((-)/(-)) mice induced iNOS protein primarily in estrogen-treated mice. Overall, this is the first report to show that estrogen treatment up-regulates IFNgamma-inducible-iNOS gene expression, iNOS protein, nitric oxide, and cyclooxygenase-2 as an indirect consequence of activation of T cells. These findings may have wide implications to immunity and inflammatory disorders including female-predominant autoimmune diseases.

Induction of MCP1, CCR2, and iNOS expression in THP-1 macrophages by serum of children late after Kawasaki disease

Evidence of premature atherosclerosis late after Kawasaki disease (KD) is accumulating. Given the potential roles of monocyte chemoattractant protein-1 (MCP-1), chemokine receptor CCR-2, and inducible nitric oxide synthase (iNOS) in atherogenesis, we sought to determine whether serum obtained from children late after KD would induce expression of these genes in macrophages in vitro. A total of 79 subjects were studied, which comprised 57 KD patients, 33 of whom had coronary aneurysms, and 22 age-matched controls. Expression of MCP-1, CCR2, and iNOS mRNA in THP-1 macrophages in the presence of patient and control serum was quantified as a ratio to beta-actin mRNA and expressed as a percentage of control. MCP-1 expression was significantly increased in the presence of serum from patients with coronary aneurysms. Expression of CCR2 and iNOS was significantly increased when THP-1 macrophages were incubated with serum from patients with and without coronary aneurysms. The magnitude of induction of MCP-1, CCR2, and iNOS or in combinations correlated positively with serum high-sensitivity C-reactive protein (hs-CRP), and low-density lipoprotein (LDL) cholesterol levels and negatively with high-density lipoprotein (HDL) cholesterol level. In conclusion, the serum of patients with a history of KD induces expression of MCP-1, CCR2, and iNOS in THP-1 macrophages in vitro. Induction of these genes in vivo may be related to chronic inflammation and may have important implications for premature atherosclerosis.

The effects of l-arginine and l-NAME supplementation on redox-regulation and thermogenesis in interscapular brown adipose tissue

Changes in inducible nitric oxide synthase (iNOS) protein levels and its relationship with the hyperplasia and uncoupling protein 1 (UCP1) levels were examined in interscapular brown adipose tissue (IBAT) of adult rat males receiving l-arginine (l-Arg; 2.25%) or N-nitro-l-arginine methyl ester (l-NAME; 0.01%)as a drinking liquid and maintained at low (4±1°C) or room(22±1°C) temperature for 45 days.

Cold generally diminished both iNOS immunopositivity and protein level in IBAT, as well as the rate of apoptosis. Among groups acclimated to cold,higher iNOS immunopositivity and protein levels were detected only in the l-Arg-treated group. Furthermore, chronic l-Arg treatment increased IBAT mass and UCP1 protein content, while l-NAME had an opposite effect, decreasing both IBAT mass and UCP1 protein level, as compared to the control maintained at 4±1°C.

These data suggest that nitric oxide (NO) produced by iNOS could also contribute to overall NO-associated regulation of thermogenesis in IBAT. Namely, that iNOS, i.e. NO, in correlation with enhanced thermogenesis,additionally induced IBAT hyperplasia and UCP1 level compared to that induced by low temperature. Cooperative action of decreased apoptosis accompanied by increased tissue hyperplasia and UCP1 level, observed in IBAT of cold-acclimated rats, would be a way of meeting the metabolic requirements for increased thermogenesis.

What sense lies in antisense inhibition of inducible nitric oxide synthase expression?

The impact of nitric oxide (NO) synthesized after activation by proinflammatory cytokines and/or bacterial products by an inducible NO synthase (iNOS) is still contradictory. Expression of iNOS in inflammatory reactions is often found predominantly in cells of epithelial origin, and in these cases NO may serve as a protective agent limiting pathogen spreading, downregulating local inflammatory reactions by inducing production of Th2-like responses in a classical feedback circle, or limiting tissue damage during stress conditions. However, an abundant amount of data on chronic human disorders with predominant proinflammatory Th1-like reactions points to a destructive role of iNOS activity calling for a specific inhibition. Various methods to inhibit iNOS have been established to elucidate a protective versus a destructive role of NO during various stresses. In this review, we focus on antisense (AS)-mediated gene knock-down as a relatively new method to inhibit NO production and summarize the techniques applied and their successes. At least in theory, it provides a specific, rapid, and potentially high-throughput method for inhibiting gene expression and function. We here discuss the opportunities of iNOS-directed AS-ODN, and extensively deal with limitations and experimental problems.

Inhibitory effects of a fermented ginseng extract, BST204, on the expression of inducible nitric oxide synthase and nitric oxide production in lipopolysaccharide-activated murine macrophages

In this study, the effects of BST204, a fermented ginseng extract, on the expression of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production are looked into. Crude ginseng extract was incubated with ginsenoside-beta-glucosidase to prepare BST204. BST204, unlike lipopolysaccharide (LPS) and crude ginseng extract, did not affect the level of iNOS protein and NO production in unstimulated RAW 264.7 cells. However, it suppressed the level of iNOS protein and NO production in LPS-stimulated RAW 264.7 cells but did not manifest the same effect on the iNOS mRNA level. An investigation of the activating phosphorylation of p70 S6 kinase and 4E-BP1, which are important for translation, was conducted to investigate the suppressive mechanism of iNOS protein. LPS increased the phosphorylation of p70 S6 kinase, but not 4E-BP1, in a time-dependent manner, and BST204 inhibited it in a dose-dependent manner. The expression of iNOS protein, however, was partially suppressed by rapamycin, an upstream inhibitor of p70 S6 kinase. Therefore, this paper suggests that the suppression of iNOS protein by BST204 was partially correlated with the inhibition of p70 S6 kinase activation.

Comparison of effects of nitric oxide synthase (NOS) inhibitors on plasma nitrite/nitrate levels and tissue NOS activity in septic organs

An excessive production of nitric oxide (NO) by NO synthase (NOS) is considered to contribute to circulatory disturbance, tissue damage, and refractory hypotention, which are often observed in septic disorders. It is anticipated that a selective inducible NOS (iNOS) inhibitor with excellent pharmacokinetics may be potentially effective as a novel and potent therapeutic intervention in sepsis. We examined whether or not a selective iNOS inhibitor shows iNOS selectivity at the tissue level, when administered systemically. The effects of four NOS inhibitors on plasma nitrite/nitrate (NOx) and tissue NOS levels were compared in major organs (lungs, liver, heart, kidneys, and brain) 6 hr after the injection of E. coli lipopolysaccharide (LPS) into male Wistar-King rats. The rats treated with the three iNOS inhibitors (N-(3-(aminomethyl)benzyl)acetamidine (1400W), (1 S, 5 S, 6 R, 7 R )-2-aza-7-chloro-3-imino-5-methylbicyclo [4.1.0] heptane hydrochloride (ONO-1714), and aminoguanidine) administered 1 hr after LPS injection, showed dose-dependent decreases in plasma NOx levels and NOS activity in the lungs. The non-selective NOS inhibitor (N(G)-methyl-L-arginine (L-NMMA)) had an effect only at the maximum dose. The differences in in vitro iNOS selectivity among these drugs did not correlate with iNOS selectivity at the tissue level. The relationship between plasma NOx levels and NOS activity in the lungs showed a linear relationship with or without the NOS inhibitors. In conclusion, the iNOS selectivity of these drugs does not seem to differ at the tissue level. Plasma NOx levels may be a useful indicator of lung NOS activity.

Involvement of KSRP in the post-transcriptional regulation of human iNOS expression-complex interplay of KSRP with TTP and HuR

We purified the KH-type splicing regulatory protein (KSRP) as a protein interacting with the 3′-untranslated region (3′-UTR) of the human inducible nitric oxide (iNOS) mRNA. Immunodepletion of KSRP enhanced iNOS 3′-UTR RNA stability in in vitro-degradation assays. In DLD-1 cells overexpressing KSRP cytokine-induced iNOS expression was markedly reduced. In accordance, downregulation of KSRP expression increases iNOS expression by stabilizing iNOS mRNA. Co-immunoprecipitations showed interaction of KSRP with the exosome and tristetraprolin (TTP). To analyze the role of KSRP binding to the 3′-UTR we studied iNOS expression in DLD-1 cells overexpressing a non-binding mutant of KSRP. In these cells, iNOS expression was increased. Mapping of the binding site revealed KSRP interacting with the most 3′-located AU-rich element (ARE) of the human iNOS mRNA. This sequence is also the target for HuR, an iNOS mRNA stabilizing protein. We were able to demonstrate that KSRP and HuR compete for this binding site, and that intracellular binding to the iNOS mRNA was reduced for KSRP and enhanced for HuR after cytokine treatment. Finally, a complex interplay of KSRP with TTP and HuR seems to be essential for iNOS mRNA stabilization after cytokine stimulation.

Flavonoids differentially modulate nitric oxide production pathways in lipopolysaccharide-activated RAW264.7 cells

Naturally occurring flavonoids are known to modulate various inflammatory and immune processes. Based on structural property, in this study, molecular mechanism of flavonoids in modulating nitric oxide (NO) production and its signaling pathway were investigated using lipopolysaccharide (LPS)-activated RAW264.7 cells. Although flavonol-typed flavonoids (kaempferol and quercetin) more potently scavenged reactivity of nitric oxide (*NO) as well as peroxynitrite (ONOO-) than isoflavones (genistein and genistin), kaempferol, quercetin and genistein showed a little difference in inhibition of both inducible NO synthase expression and NO production, with IC50 values of 13.9, 20.1 and 26.8 microM. However, there was a striking pattern related to structural feature in modulation of LPS-mediated signaling pathways. Thus, flavonols only inhibited transcription factor AP-1 activation, whereas isoflavones suppressed the DNA binding activation of NF-kappaB and C/EBPbeta. Therefore, these data suggest that structural feature may be linked to decide drugs target molecule in LPS-mediated signaling pathways, rather than its potency.

Regulation of the expression of inducible nitric oxide synthase

The role of nitric oxide (NO) generated by the inducible isoform of nitric oxide synthase (iNOS) is very complex. Induction of iNOS expression and hence NO production has been described to have beneficial antiviral, antiparasital, microbicidal, immunomodulatory, and antitumoral effects. However, induced at the wrong place or at the wrong time, iNOS has detrimental consequences and seems to be involved in the pathophysiology of different human diseases. The pathways regulating iNOS expression seem to vary in different cells or different species. In general, activation of the transcription factors nuclear factor (NF)-kappaB and signal transducer and activator of transcription (STAT)-1alpha and thereby activation of the iNOS promoter seems to be an essential step in the regulation of iNOS expression in most cells. Also, post-transcriptional mechanisms are critically involved in the regulation of iNOS expression.

Green tea modulation of inducible nitric oxide synthase in hypoxic/reoxygenated cardiomyocytes

Hypoxia/reoxygenation (H/R) is one of the causes of the increased expression of inducible nitric oxide synthase (iNOS) in cardiomyocytes. Since an aberrant NOS induction has detrimental consequences, we evaluated the effect of a green tea extract (GTE) on the NOS induction and activity in H/R-cardiomyocytes to define a nutritional strategy. Cultured rat cardiomyocytes were exposed to H/R in the presence of two concentrations of a green tea extract (GTE), which is reported to inhibit NOS expression and activity in different cells. In cultured cardiomyocytes two NOS isoforms were constitutively expressed, but only iNOS was induced by H/R. GTE supplementation at the lowest concentration, comparable to that in human plasma after dietary consumption, was ineffective, while the highest, comparable to that achievable by dietary supplements, counteracted the effect of H/R on iNOS induction and activity. It is necessary to verify in humans the relationship between the modulation of NO production and green tea dietary consumption.

High levels of endogenous nitric oxide produced after burn injury in rats arrest activated T lymphocytes in the first G1 phase of the cell cycle and then induce their apoptosis

Major physical traumas provoke a systemic inflammatory response and immune dysfunction. In a model of thermal injury in rats, we previously showed that an overproduction of nitric oxide (NO) was responsible for the collapse of lymphoproliferative responses. In the present work, we performed a time-course analysis of cell proliferation and cell death parameters in order to establish the sequence of events triggered by the high NO output in Wistar/Han rat splenocytes activated with Con A, 10 days after burn injury. We demonstrate that activated T cells from burned rats never divided whereas normal T cells underwent four division cycles. However, T cells from both burned and normal rat entered the G1 phase as shown by increase of cell size, mitochondria hyperpolarization, and expression of cyclin D1. Burned rat T cells progressed to the late G1 phase as shown by expression of the nuclear Ki-67 antigen, but they never entered the S phase. They underwent apoptosis as shown by morphological parameters, disruption of transmembrane mitochondrial potential, and DNA fragmentation. Persistent accumulation of the p53 protein accompanied these phenomena. NO synthase inhibitors antagonize alterations of cell proliferation and cell death parameters in burned rat T cells and accelerated p53 turnover.

Selective inducible nitric oxide synthase inhibition attenuates organ dysfunction and elevated endothelin levels in LPS-induced DIC model rats

We examined the role of nitric oxide (NO) produced by an inducible isoform of NO synthase (iNOS) using N[6]-(iminoethyl)-lysine (L-NIL), a selective iNOS inhibitor, in the rat model of lipopolysaccharide (LPS)-induced disseminated intravascular coagulation (DIC) and investigated changes in organ function, plasma levels of NOX (metabolites of NO) and endothelin. We induced experimental DIC by the sustained infusion of 30 mg kg(-1) LPS for 4 h via the tail vein. We then investigated the effect of L-NIL (6 mg kg(-1), from - 0.5 to 4 h) on LPS-induced DIC. Blood was withdrawn at 4 and 8 h, and all four groups (LPS with or without L-NIL at 4 and 8 h) consisted of eight rats. Three of the animals in the 8-h LPS group died, and we examined blood samples from five rats in this group. None of the other rats died. The LPS-induced elevation of creatinine, alanine aminotransferase, glomerular fibrin deposition and plasminogen activator inhibitor was significantly suppressed by L-NIL coadministration, although L-NIL did not affect the platelet count, fibrinogen concentration or the level of thrombin-antithrombin complex. Moreover, plasma levels of the D-dimer that reflect the lysis of cross-linked fibrin were significantly increased by L-NIL coadministration in the LPS-induced DIC model. Plasma levels of NOX and endothelin were obviously increased by LPS infusion. However, both levels were significantly suppressed in the LPS + L-NIL group, when compared with the LPS group. Although mean arterial pressure (MAP) was significantly decreased between 2 and 8 h compared with the control in the LPS group, this depression was significantly attenuated in the LPS + L-NIL group. Our results suggest that NO induced by iNOS contributes to hypotension (depressed MAP), the progression of hepatic and renal dysfunction, microthrombus deposition and elevated endothelin levels in the rat model of LPS-induced DIC.

Suppression of lipopolysaccharide-induced expression of inducible nitric oxide synthase by brazilin in RAW 264.7 macrophage cells

Brazilin (7,11b-dihydrobenz[b]indeno[1,2-d]pyran-3,6a,9,10 (6H)-tetrol) isolated from Caesalpinia sappan has been known as a natural red pigment. Many studies suggest that inducible isoform of nitric oxide synthase (NOS) plays an important role in inflammation and carcinogenesis. On this line, we evaluated the inhibitory effect of brazilin on nitric oxide (NO) production and investigated its mechanism of action. As a result, brazilin exhibited the inhibitory effect on lipopolysaccharide (LPS)-stimulated NO production in a dose-dependent manner (IC50=24.3 microM). In addition, brazilin suppressed LPS-induced iNOS protein and mRNA expression in RAW 264.7 macrophage cells, indicating that the inhibitory activity of brazilin possibly involved in the regulation of iNOS expression. To further investigate the mechanism responsible for the suppression of iNOS gene expression by brazilin, the effect of brazilin on LPS-induced transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) activation was examined. The DNA binding activity of NF-kappaB and AP-1 stimulated LPS was inhibited by treatment of brazilin in a dose-dependent manner, suggesting that brazilin-mediated inhibition of NO production might be associated with the regulation of transcription factors NF-kappaB and AP-1. Taken together, these findings suggest that the suppressive effect of iNOS gene expression by brazilin might provide one possible mechanism for its anti-inflammatory and cancer chemopreventive activity.

Polarized distribution of inducible nitric oxide synthase regulates activity in intestinal epithelial cells

Inducible nitric oxide synthase (iNOS) functions as a homodimer. In cell extracts, iNOS molecules partition both in cytosolic and particulate fractions, indicating that iNOS exists as soluble and membrane associated forms. In this study, iNOS features were investigated in human intestinal epithelial cells stimulated with cytokines and in duodenum from mice exposed to flagellin. Our experiments indicate that iNOS is mainly associated with the particulate fraction of cell extracts. Confocal microscopy showed a preferential localization of iNOS at the apical pole of intestinal epithelial cells. In particulate fractions, iNOS dimers were more abundant than in the cytosolic fraction. Similar observations were seen in mouse duodenum samples. These results suggest that, in epithelial cells, iNOS activity is regulated by localization-dependent processes.

Myeloperoxidase: friend and foe

Neutrophilic polymorphonuclear leukocytes (neutrophils) are highly specialized for their primary function, the phagocytosis and destruction of microorganisms. When coated with opsonins (generally complement and/or antibody), microorganisms bind to specific receptors on the surface of the phagocyte and invagination of the cell membrane occurs with the incorporation of the microorganism into an intracellular phagosome. There follows a burst of oxygen consumption, and much, if not all, of the extra oxygen consumed is converted to highly reactive oxygen species. In addition, the cytoplasmic granules discharge their contents into the phagosome, and death of the ingested microorganism soon follows. Among the antimicrobial systems formed in the phagosome is one consisting of myeloperoxidase (MPO), released into the phagosome during the degranulation process, hydrogen peroxide (H2O2), formed by the respiratory burst and a halide, particularly chloride. The initial product of the MPO-H2O2-chloride system is hypochlorous acid, and subsequent formation of chlorine, chloramines, hydroxyl radicals, singlet oxygen, and ozone has been proposed. These same toxic agents can be released to the outside of the cell, where they may attack normal tissue and thus contribute to the pathogenesis of disease. This review will consider the potential sources of H2O2 for the MPO-H2O2-halide system; the toxic products of the MPO system; the evidence for MPO involvement in the microbicidal activity of neutrophils; the involvement of MPO-independent antimicrobial systems; and the role of the MPO system in tissue injury. It is concluded that the MPO system plays an important role in the microbicidal activity of phagocytes.

Reactive nitrogen intermediates in experimental trichomoniasis induced with isolates from symptomatic and asymptomatic women

Trichomoniasis is the interplay between the infecting parasite, Trichomonas vaginalis, and the host, on which the clinical presentation of the disease depends. Although the clinical spectrum varies from an asymptomatic state to mild, moderate or severe symptoms, the exact virulence markers of T. vaginalis have not been well elucidated. Free radical generation during the disease process and its role in pathogenesis has been reported in various microbial diseases. In the present study, an attempt has been made to study reactive nitrogen intermediate (RNI) concentrations in experimental animals infected with T. vaginalis isolates from symptomatic and asymptomatic women. A significant increase in polymorphs, vaginal epithelial cells and RNI levels was observed in mice infected with isolates from symptomatic and asymptomatic subjects as compared to uninfected controls. The mean concentration of RNI in the vaginal tissue of mice infected with isolates from symptomatic women (75.5+/-7.7) was significantly higher than that of the vaginal tissue of mice infected with isolates from asymptomatic women (47.9+/-7.8), while it was less in the vaginal washes and plasma of mice infected with isolates from symptomatic women (18.7+/-3.6 and 17.1+/-3.3, respectively) compared to those infected with isolates from asymptomatic women (28.9+/-7.3 and 26.7+/-4.4, respectively), which may be due to different macrophage populations with different functional capabilities. Our study indicates that RNI production may play a role in establishing the infection.

Vascular effects of the Mangifera indica L. extract (Vimang)

The effects of the Mangiferia indica L. (Vimang) extract, and mangiferin (a C-glucosylxanthone of Vimang) on the inducible isoforms of cyclooxygenase (cyclooxygenase-2) and nitric oxide synthase (iNOS) expression and on vasoconstrictor responses were investigated in vascular smooth muscle cells and mesenteric resistance arteries, respectively, from Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Vimang (0.5-0.1 mg/ml) and mangiferin (0.025 mg/ml) inhibited the interleukin-1beta (1 ng/ml)-induced iNOS expression more in SHR than in WKY, and cyclooxygenase-2 expression more in WKY than in SHR. Vimang (0.25-1 mg/ml) reduced noradrenaline (0.1-30 microM)- and U46619 (1 nM-30 microM)- but not KCl (15-70 mM)-induced contractions. Mangiferin (0.05 mg/ml) did not affect noradrenaline-induced contraction. In conclusion, the antiinflammatory action of Vimang would be related with the inhibition of iNOS and cyclooxygenase-2 expression, but not with its effect on vasoconstrictor responses. Alterations in the regulation of both enzymes in hypertension would explain the differences observed in the Vimang effect.

Suppressive effect of inducible nitric oxide synthase (iNOS) expression by the methanol extract of Actinodaphne lancifolia

Nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) has played a crucial role in various pathophysiological processes including inflammation and carcinogenesis. Therefore, the inhibitors of NO synthesis or iNOS gene expression have been considered as potential anti-inflammatory and cancer chemopreventive agents. In our continuous search for iNOS inhibitors from natural products we have evaluated indigenous Korean plant extracts using an assay for inhibition of nitric oxide formation on lipopolysaccharide (LPS)-activated mouse macrophage RAW 264.7 cells. As a result, the methanolic stem extract of Actinodaphne lancifolia showed an inhibitory activity of NO production in a dose-dependent manner (IC50 = 2.5 microg/ml). Additional study demonstrated that the extract of Actinodaphne lancifolia significantly suppressed the iNOS protein and gene expression in a dose-dependent manner. These results suggest that Actinodaphne lancifolia could be a potential candidate for developing an iNOS inhibitor from natural products. Further elucidation of active principles for development of new cancer chemopreventive and/or anti-inflammatory agents could be warranted.

Influence of post-mortem delay and storage temperature on the immunohistochemical detection of antigens in the CNS of mice

The aim of this work was to compare the results of histochemical and immunohistochemical methods using mouse brains which were fixed with various post-mortem delays and storage temperatures (at a constant 4 degrees C or 22 degrees C, or at gradually decreasing post-mortem temperatures, mimicking conditions of human corpse). We studied the effects of post-mortem delay on glial fibrillary acidic protein, extracellular matrix components to which Wisteria floribunda agglutinin binds, non-phosphorylated neurofilament H, synaptophysin, calbindin and nitric oxide synthase isoenzymes. At the light microscopic level first signs of post-mortem changes were detectable after 6 h. Glial fibrillary acidic protein was most affected by post-mortem delay since its immunoreactivity increased dramatically with increasing post-mortem delay. N-acetylgalactosamines-beta1 labeled lectin binding sites, calbindin and intraneuronal non-phosphorylated neurofilament H seemed to be stable up to 12 h post-mortem. Storage temperature influenced the NADPH-d activity and the content of synaptophysin immunoreactivity to higher degree than all of the other parameters. We found only marginal differences of alterations comparing neocortex, hippocampus and corpus callosum. Our results indicate that different antigens are affected differently by the ongoing catabolic processes during post-mortem delay.

Nitric oxide signaling in colon cancer chemoprevention

Nitric oxide (NO) is a pleiotrophic regulator, pivotal to numerous biological processes, including vasodilation, neurotransmission, and macrophage-mediated immunity. The highly reactive free radicals, produced by NO synthases (NOS) have been implicated in the modulation of carcinogenesis. Over-expression of inducible NOS (iNOS), a common phenomenon during chronic inflammatory conditions, generates sustainable amounts of NO, that its reactive intermediates are mutagenic, causing DNA damage or impairment of DNA repair, has been well established in carcinogenesis. Recent studies also implicate NO as having a key signaling molecule that regulates processes of tumorigenesis. Increased expression of iNOS has been observed in tumors of the colon, lung, oropharynx, reproductive organs, breast, and central nervous system besides its occurrence in chronic inflammatory diseases. Progression of a large majority of human and experimental colon tumors appears to progress by NO resulting from stimulation of proinflammatory cytokines, and inactivation (nitrosylation) of p53 mediated caspase activities in the tumors, whereas in some cases it associated with induction of apoptosis and tumor regression. This dichotomy is largely explained by the complexity of signaling pathways in tumor cells, that respond to NO very differently depending on its concentration. p53 mutation, functional loss, activation, and inactivation of apoptotic proteins all have been linked with NO resistance and dependence. Evidence from both in vitro and in vivo experiments support that NO and its reactive metabolite peroxynitrite stimulate COX-2 activity leading generation of tumor growth enhancing prostaglandins. Thus, NO mediated signaling can augment the tumor growth and metastasis by promoting invasive and angiogenic properties of tumor cells, which includes triggering and activation of COX-2. Thus, developing selective inhibitors of iNOS and NO-releasing agents may lead to important strategies for chemoprevention of colon cancer. Chemoprevention studies at preclinical level with several selective inhibitors of iNOS in both chemically and transgenic models of colon cancer are encouraging.

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.

Nitric oxide is synthesized in acute leukemia cells after exposure to phenolic antioxidants and initially protects against mitochondrial membrane depolarization

We investigated the early events involved in loss of mitochondrial membrane potential (DeltaPsi(mt)) leading to apoptosis in cells derived from patients with acute lymphocytic leukemia after exposure to phenolic antioxidants. Using the nitric oxide binding dye diaminofluorescein-FM diacetate, we found that intracellular nitric oxide (NO) levels increased significantly within 4h after exposure to the antioxidants curcumin, carnosol, and quercetin. Inhibition of nitric oxide synthetase (NOS) activity with mercaptoethylguanidine increased the percentage of leukemia cells with depolarized mitochondria membranes after antioxidant treatment. These data suggest that NO production in the leukemia-derived cells may be a protective response to maintain DeltaPsi(mt) after antioxidant exposure and inhibition of NOS increases the disruption of mitochondrial homeostasis induced by the antioxidants.

Gastrointestinal nitric oxide generation in germ-free and conventional rats

Nitric oxide (NO) is a central mediator of various physiological events in the gastrointestinal tract. The influence of the intestinal microflora for NO production in the gut is unknown. Bacteria could contribute to this production either by stimulating the mucosa to produce NO, or they could generate NO themselves. Using germ-free and conventional rats, we measured gaseous NO directly in the gastrointestinal tract and from the luminal contents using a chemiluminescence technique. Mucosal NO production was studied by using an NO synthase (NOS) inhibitor, and to evaluate microbial contribution to the NO generation, nitrate was given to the animals. In conventional rats, luminal NO differed profoundly along the gastrointestinal tract with the greatest concentrations in the stomach [>4,000 parts per billion (ppb)] and cecum (approximately 200 ppb) and lower concentrations in the small intestine and colon (< or =20 ppb). Cecal NO correlated with the levels in incubated luminal contents. NOS inhibition lowered NO levels in the colon, without affecting NO in the stomach and in the cecum. Gastric NO increased greatly after a nitrate load, proving it to be a substrate for NO generation. In germ-free rats, NO was low (< or =30 ppb) throughout the gastrointestinal tract and absent in the incubated luminal contents. NO also remained low after a nitrate load. Our results demonstrate a pivotal role of the intestinal microflora in gastrointestinal NO generation. Distinctly compartmentalized qualitative and quantitative NO levels in conventional and germ-free rats reflect complex host microbial cross talks, possibly making NO a regulator of the intestinal eco system.

Suppressive effects of nitric oxide production and inducible nitric oxide synthase (iNOS) gene expression by Calystegia soldanella methanol extract on lipopolysaccharide-activated RAW 264.7 cells

Since nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) has been found to be involved in various pathophysiological processes, including inflammation and carcinogenesis, the modulators of NO synthesis or expression have been considered as potential anti-inflammatory and cancer chemopreventive agents. In this study, to procure the iNOS inhibitors from natural products, we evaluated 57 methanol extracts of natural products including Korean indigenous plants for the inhibition of NO formation on lipopolysaccharide (LPS)-activated mouse macrophage-like RAW 264.7 cells. As a result, several extracts including those from Actinodaphne lancifolia, Calystegia soldanella, Caryratia japonica, Citrus dachibana, Dystaenia takeshimana, Erysimum aurantiacum, Hovenia undulata, Stewartia koreana and Viburnum awabuki showed potent inhibitory activities of NO production (>70% inhibition at the test concentration of 40 microg/ml). In particular, the extract of Calystegia soldanella showed a potential inhibition of NO production in a dose-dependent manner (IC50=4.3 microg/ml). Subsequent study also exhibited that the extract of Calystegia soldanella significantly suppressed iNOS protein and gene expression in a dose-dependent manner. These results suggest that Calystegia soldanella might be a new potential candidate for developing an iNOS inhibitor from natural products and also could be warranted for further elucidation of active principles for the development of new anti-inflammatory and/or cancer chemopreventive agents.

Vasoactive mediators (VEGF and TNF-alpha) in patients with malignant and tuberculous pleural effusions

OBJECTIVE

Vascular endothelial growth factor (VEGF) is a potent endothelial cell-specific mitogen that promotes angiogenesis, vascular hyperpermeability, and vasodilatation by autocrine mechanisms involving nitric oxide (NO). This study was undertaken to determine the potential role of VEGF in the pathogenesis of pleural effusions, and its relationship with tumour necrosis factor (TNF)-alpha and NO in the pleural fluid and serum of patients with tuberculous and malignant pleural effusions.

METHODOLOGY

Pleural fluid and serum (SE) VEGF, TNF-alpha and NO levels were measured in 30 patients with exudative pleural effusion (15 with malignancies and 15 with tuberculosis). Control pleural fluid was obtained from 10 patients with transudative pleural effusion due to congestive heart failure and control serum samples were obtained from 10 healthy individuals. VEGF and TNF-alpha were measured by enzyme-linked immunosorbent assay and NO by a colorimetric method. Pleural biopsy, cytology or microbiological methods were used to make the final diagnosis.

RESULTS

In patients with exudative pleural effusions, the mean pleural fluid and serum VEGF levels and their ratios (P < 0.0001 for all) and TNF-alpha levels (P < 0.01, P < 0.0001 and P < 0.05) were significantly elevated compared to those with transudative pleural effusion. In malignant effusions, pleural fluid and serum VEGF levels were significantly elevated (P < 0.001 and P < 0.0001) while pleural fluid, and serum levels and their ratios of TNF-alpha (P < 0.001, P < 0.01 and P < 0.05) were significantly lower than those in tuberculosis. NO levels did not distinguish between tuberculous and malignant effusions.

CONCLUSIONS

In patients with malignant pleural effusions, levels of VEGF were significantly higher, while levels of TNF-alpha were significantly lower, than in patients with tuberculous effusions. In malignant pleural effusions, the elevated pleural fluid levels of VEGF and TNF-alpha are noteworthy. Our data support the hypothesis that blockade of VEGF, might benefit cancer patients with recurrent ascites or pleural fluid accumulation.

iNOS-mediated nitric oxide production and its regulation

This review focuses on the production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) and its regulation under physiological and pathophysiological conditions. NO is an important biological mediator in the living organism that is synthesized from L-arginine using NADPH and molecular oxygen. However, the overproduction of NO which is catalyzed by iNOS, a soluble enzyme and active in its dimeric form, is cytotoxic. Immunostimulating cytokines or bacterial pathogens activate iNOS and generate high concentrations of NO through the activation of inducible nuclear factors, including NFkB. iNOS activation is regulated mainly at the transcriptional level, but also at posttranscriptional, translational and postranslational levels through effects on protein stability, dimerization, phosphorylation, cofactor binding and availability of oxygen and L-arginine as substrates. The prevention of the overproduction of NO in the living organism through control of regulatory pathways may assist in the treatment of high NO-mediated disorders without changing physiological levels of NO.

Enhanced iNOS expression in leukocytes and circulating endothelial cells is associated with the progression of coronary artery lesions in acute Kawasaki disease

Nitric oxide (NO) serves many vasoprotective roles, but the massive release of NO causes arterial wall degeneration. We investigated whether enhanced nitric oxide synthase (iNOS) expression in peripheral blood leukocytes and circulating endothelial cells mirrors the progression of coronary arterial lesions in 55 children with acute Kawasaki disease (KD), including 24 with and 31 without coronary artery lesions (CAL). Patients were treated with i.v. gamma-globulin at the time of diagnosis and blood samples were collected before and after treatment. The cellular origin of NO synthesis was determined by flow cytometric analysis of iNOS expression in peripheral blood, and by immunohistochemical analysis of circulating endothelial cells and coronary arteries. iNOS expression in neutrophils peaked at the time of diagnosis, but did not peak in monocytes until 2 wk post onset of disease. Levels were significantly higher in both cell types in patients with CAL (p = 0.001 and p = 0.035, respectively). In addition, the number of circulating endothelial cells and levels of iNOS expression were higher in patients with CAL (p = 0.011 and p = 0.012, respectively). Immunohistochemical analysis of the coronary arteries from three patients with acute KD revealed iNOS immunoreactivity in endothelial cells, as well as infiltrating monocytes/macrophages in the aneurysms. We conclude that the expression of iNOS in peripheral blood leukocytes, as well as circulating endothelial cells, correlates with the severity of coronary arterial wall injury and the progression of CAL in patients with acute KD.

The Novel HMG-CoA Reductase Inhibitor, Pitavastatin, Induces a Protective Action in Vascular Endothelial Cells through the Production of Nitric Oxide (NO)

This study sought to induce the effect of nitric oxide (NO) production in vascular endothelial cells by Pitavastatin, which is a novel HMG-CoA reductase inhibitor (statin). The growth capacity of vascular endothelial cells significantly (p < 0.01) declined when stimulated with TNF-alpha (10 ng/ml). The growth capacity of the TNF-alpha treated cells recovered, when the TNF-alpha stimulation was performed after Pitavastatin (100 nM) pretreatment. The recovery of the growth capacity of the cells was suppressed by the presence of the NO synthase inhibitor, L-NAME. Pitavastatin increased NO production by the vascular endothelial cells in a dose and time dependent manner. The NO production was suppressed by the presence of mevalonic acid and geranylgeranyl pyrophosphate. In addition, the expression of endothelial nitric oxide synthase was strongly induced by Pitavastatin, and was suppressed by mevalonic acid and geranylgeranyl pyrophosphate by Western blot analysis. Our results show that Pitavastatin induces NO production by vascular endothelial cells, and protects vascular endothelial cells from injury due to the inflammatory reaction induced by TNF-alpha.

Green tea inhibits human inducible nitric-oxide synthase expression by down-regulating signal transducer and activator of transcription-1alpha activation

Green tea has been reported to show anti-inflammatory properties because of its inhibitory effects on the expression of several pro-inflammatory genes. Because the inducible nitricoxide synthase (iNOS) plays an important role in chronic inflammatory diseases, we have focused our attention on the regulation of iNOS expression by green tea in two different human epithelial cell lines, alveolar A549/8 and colon DLD-1 cells. With the use of electrophoretic mobility shift assays, we found a green tea-mediated down-regulation of the DNA binding activity of the transcription factor signal transducer and activator of transcription-1alpha (STAT-1alpha), but not of nuclear factor-kappaB. This down-regulation of the STAT-1alpha DNA binding was shown to result from reduced tyrosine phosphorylation of the STAT-1alpha protein and not from antioxidative effects of the green tea extract. Green tea extract inhibited human iNOS expression in a concentration-dependent manner, quantified in terms of iNOS mRNA, iNOS protein, and nitric oxide production in both cell lines. This inhibitory effect of green tea resulted from transcriptional inhibition as shown in reporter gene experiments. These data suggest that green tea extracts may be promising at least as an auxiliary anti-inflammatory principle in chronic inflammatory diseases.

Mutations in the extracellular loop of alpha-rENaC alter sensitivity to amiloride and reactive species

We studied the effects of two mutations of the extracellular loop of the alpha-subunit of the (ENaC) on amiloride-sensitive current in Xenopus laevis oocytes and the inhibition of this current by 3-morpholinosydnonimine (SIN-1). Injection of oocytes with wild-type (wt) alpha-,beta-,gamma-rENaC cRNA (8.3 ng/subunit) resulted 48-72 h later in inward Na(+) currents (-5.5 +/- 0.8 microA; means +/- SE at -100 mV; n = 21), which were completely inhibited by amiloride. Oocytes injected with either alpha(Y279A)- or alpha(Y283A)- and beta-,gamma-rENaC cRNAs had significantly lower Na(+) currents. Furthermore, alpha(Y279A)-,beta-,gamma-rENaC-injected oocytes had a higher K(i) for amiloride (0.54 +/- 0.97 vs. 0.10 +/- 0.04 microM; P < 0.01). Exposure of oocytes to SIN-1 (1 mM) for 5 min decreased both total Na(+) and amiloride-sensitive currents across wt and alpha(Y279A)- but not alpha(Y283A)-,beta-,gamma-rENaC. Furthermore, exposure to SIN-1 increased the K(i) for amiloride across wt but not alpha(Y279A)-,beta-,gamma-rENaC-injected oocytes. These data indicate that both tyrosines are important for proper ENaC function and their oxidative modifications contribute to altered ENaC function.

Effect of Inhaled N G -Nitro-L-Arginine Methyl Ester on Candida-Induced Acute Lung Injury

STUDY OBJECTIVES

Nitric oxide (NO) and peroxynitrite play a crucial role in acute lung injury (ALI). Whether NO synthase (NOS) inhibition is beneficial in the treatment of lung injury remains controversial. The objective of this study was to test the hypothesis that local inhibition of NOS in the lung reduces lung injury.

DESIGN

We developed a model of Candida-induced ALI in the mouse by IV injection of Candida albicans. To evaluate the effect of NOS inhibitor, mice were pretreated by inhalation of saline solution or N(G)-nitro-L-arginine methyl ester (L-NAME) before induction of Candida-induced ALI.

MEASUREMENTS AND RESULTS

After inhalation of 1 mM aerosolized L-NAME, nitrite-nitrate concentrations in BAL fluid (BALF) were significantly lower at 24 h and 48 h than those in mice treated with C albicans alone. Tumor necrosis factor-alpha, interleukin-1beta, and macrophage inflammatory protein-2 concentrations in lung homogenates, measured by enzyme-linked immunosorbent assay, and neutrophil counts in BALF were decreased by inhalation of L-NAME (n = 6 per group). Immunohistochemical analysis of inducible NOS (iNOS) and nitrotyrosine, a major product of protein nitration by peroxynitrite, revealed that alveolar macrophages and alveolar epithelial cells were positive for both substances in Candida-induced ALI. Inhalation of L-NAME markedly suppressed iNOS protein expression and nitrotyrosine production. Histologic evidence of lung injury decreased and survival improved after inhalation of L-NAME.

CONCLUSIONS

We conclude that NO might play a crucial role in the pathogenesis of Candida-induced ALI, and such injury might be reduced by local inhibition of NOS. Our findings suggest that inhalation of L-NAME is beneficial in the treatment of Candida-induced ALI.

Regulation of zinc homeostasis by inducible NO synthase-derived NO: nuclear metallothionein translocation and intranuclear Zn2+ release

Zn2+ is critical for the functional and structural integrity of cells and contributes to a number of important processes including gene expression. It has been shown that NO exogenously applied via NO donors resulting in nitrosative stress leads to cytoplasmic Zn2+ release from the zinc storing protein metallothionein (MT) and probably other proteins that complex Zn2+ via cysteine thiols. We show here that, in cytokine-activated murine aortic endothelial cells, NO derived from the inducible NO synthase (iNOS) induces a transient nuclear release of Zn2+. This nuclear Zn2+ release depends on the presence of MT as shown by the lack of this effect in activated endothelial cells from MT-deficient mice and temporally correlates with nuclear MT translocation. Data also show that NO is an essential but not sufficient signal for MT-mediated Zn2+ trafficking from the cytoplasm into the nucleus. In addition, we found that, endogenously via iNOS, synthesized NO increases the constitutive mRNA expression of both MT-1 and MT-2 genes and that nitrosative stress exogenously applied via an NO donor increases constitutive MT mRNA expression via intracellular Zn2+ release. In conclusion, we here provide evidence for a signaling mechanism based on iNOS-derived NO through the regulation of intracellular Zn2+ trafficking and homeostasis.

iNOS activity is essential for endothelial stress gene expression protecting against oxidative damage

In endothelial cells, the expression of the inducible nitric oxide synthase (iNOS) and the resulting high-output nitric oxide synthesis have often been assumed as detrimental to endothelial function, but recent publications have demonstrated a protective role resulting from iNOS espression and activity. To address this question, we used antisense-mediated iNOS knockdown during proinflammatory cytokine challenge in primary endothelial cell cultures and studied endothelial function by monitoring the expression of stress defense genes. Using antisense oligonucleotides, we achieved a block of iNOS protein formation, accompanied by a strong decrease in the expression of the protective stress response genes bcl-2, vascular endothelial growth factor, and heme oxygenase-1 (HO-1). Additionally, cells were also maintained in the presence of limited exogenous substrate concentrations during cytokine challenge, thereby mimicking a situation of low serum arginine level during inflammation. Under these conditions, cytokine addition results in full iNOS protein expression with minimal nitric oxide formation, concomitant with a significant reduction in stress response gene expression and susceptibility to cell death induced by reactive oxygen species. Taken together, our data suggest that cytokine-induced endogenous iNOS expression and activity have key functions in increasing endothelial survival and maintaining function. Thus suppression of iNOS expression or limited substrate supply, as has been reported to occur in atherosclerosis patients, appears to significantly contribute to endothelial dysfunction and death during oxidative stress.

Protective effect of flavonoids against aging- and lipopolysaccharide-induced cognitive impairment in mice

Flavonoids, naturally occurring polyphenolic compounds, are known to inhibit both lipopolysaccharide (LPS) stimulated tumor necrosis factor alpha and interleukin 6 release which modulate the proinflammatory molecules that have been reported in many progressive neurodegenerative disorders, including Alzheimer's disease (AD), viral and bacterial meningitis, AIDS dementia complex, and stroke. The present experiments were performed to study the possible effects of exogenously administered flavonoids (apigenin-7-glucoside and quercetin) on the cognitive performance in aged and LPS-treated mice (an animal model for AD) using passive avoidance and elevated plus-maze tasks. Aged and LPS-treated mice showed poor retention of memory in step-through passive avoidance and in plus-maze tasks. Chronic administration of the flavonoids apigenin-7-glucoside (5-20 mg/kg i.p.) and quercetin (25-100 mg/kg i.p.) dose dependently reversed the age-induced and LPS-induced retention deficits in both test paradigms. However, flavonoids after chronic administration in young mice did not show any improvement of memory retention in both paradigms. Apigenin-7-glucoside showed more efficacy as compared with quercetin in both models that may be probably due to its greater efficacy to inhibit cyclooxygenase-2 and inducible nitric oxide synthase. Chronic treatment with flavonoids did not alter the locomotor activity in both young and aged mice; however, aged mice showed improvement of performance on Rota-Rod test. The results showed that chronic treatment with flavonoids reverses cognitive deficits in aged and LPS-intoxicated mice which suggests that modulation of cyclooxygenase-2 and inducible nitric synthase by flavonoids may be important in the prevention of memory deficits, one of the symptoms related to AD.

Anti-inflammatory actions of St. John's wort: inhibition of human inducible nitric-oxide synthase expression by down-regulating signal transducer and activator of transcription-1alpha (STAT-1alpha) activation

St. John's wort (SJW) has been described to show anti-inflammatory properties due to its inhibitory effects on the expression of pro-inflammatory genes like cyclooxygenase-2, interleukin-6, and inducible nitric-oxide synthase (iNOS). Since iNOS plays a critical role in chronic inflammatory diseases, we have focused our attention on the regulation of iNOS expression by SJW in two different human epithelial cell lines, alveolar A549/8 and colon DLD-1 cells. SJW extract concentration dependently inhibited human iNOS expression evaluated by measuring the amounts of iNOS mRNA, iNOS protein, and NO production in both cell lines. This inhibitory effect resulted from transcriptional inhibition as shown in reporter gene experiments. With electrophoretic mobility shift experiments, we found a SJW-mediated down-regulation of the DNA binding activity of the transcription factor signal transducer and activator of transcription-1alpha (STAT-1alpha), but not of nuclear factor-kappaB. This down-regulation of the STAT-1alpha DNA binding was shown to result from reduced tyrosine phosphorylation of the STAT-1alpha protein. The diminished STAT-1alpha tyrosine phosphorylation resulted from SJW-mediated reduction of Janus kinase 2 activity. These data suggest that extracts from SJW may be a promising anti-inflammatory principle in chronic inflammatory diseases.

A critical role for C/EBPbeta binding to the AABS promoter response element in the human iNOS gene

The human iNOS (hiNOS) gene is expressed in a tissue-specific manner, but the molecular basis for this regulation has not been elucidated. Here, we show that liver cell-specific hiNOS gene activation involves protein-DNA binding to an A-activator binding site (AABS) located at -192 nucleotides in the hiNOS promoter region. Mutation of this site in the -7.2 kb hiNOS promoter construct inhibited basal hiNOS promoter activity in primary rat hepatocytes (77%), and two human liver cell lines, AKN-1 (63%) and HepG2 (60%), but had no significant effect on basal hiNOS activity in three non-hepatic human cell types. Interestingly, mutation of AABS significantly abrogated cytokine-induced promoter activity in all cell types. C/EBPbeta transcription factor bound to AABS by gel shift assay. Overexpression of C/EBPbeta active form (LAP) increased hiNOS basal promoter activity approximately sixfold in liver cells, but had minimal effect in non-hepatic cells. In contrast, overexpression of the transcriptional inhibitor (LIP) strongly suppressed both basal and cytokine-inducible promoter activity. These data show that the cis-acting AABS DNA element mediates liver-specific basal hiNOS promoter activity through binding of the trans-acting C/EBPbeta factor. Further, C/EBPbeta binding to AABS functions as a "switchpoint" that is necessary for cytokine-inducible hiNOS gene expression in all cell types examined.

The pathophysiology of falciparum malaria

Falciparum malaria is a complex disease with no simple explanation, affecting organs where the parasite is rare as well as those organs where it is more common. We continue to argue that it can best be understood in terms of excessive stimulation of normally useful pathways mediated by inflammatory cytokines, the prototype being tumor necrosis factor (TNF). These pathways involve downstream mediators, such as nitric oxide (NO) that the host normally uses to control parasites, but which, when uncontrolled, have bioenergetic failure of patient tissues as their predictable end point. Falciparum malaria is no different from many other infectious diseases that are clinically confused with it. The sequestration of parasitized red blood cells, prominent in some tissues but absent in others with equal functional loss, exacerbates, but does not change, these overriding principles. Recent opportunities to stain a wide range of tissues from African pediatric cases of falciparum malaria and sepsis for the inducible NO synthase (iNOS) and migration inhibitory factor (MIF) have strengthened these arguments considerably. The recent demonstration of bioenergetic failure in tissue removed from sepsis patients being able to predict a fatal outcome fulfils a prediction of these principles, and it is plausible that this will be demonstrable in severe falciparum malaria. Understanding the disease caused by falciparum malaria at a molecular level requires an appreciation of the universality of poly(ADP-ribose) polymerase-1 (PARP-1) and Na(+)/K(+)-ATPase and the protean effects of activation by inflammation of the former that include inactivation of the latter.