Roles of tyrosine kinases in the regulation of nitric oxide synthesis in murine liver cells: modulation of NF-kappa B activity by tyrosine kinases

L-Arginine increases AMPK phosphorylation and the oxidation of energy substrates in hepatocytes, skeletal muscle cells, and adipocytes

Previous work has shown that dietary L-arginine (Arg) supplementation reduced white fat mass in obese rats. The present study was conducted with cell models to define direct effects of Arg on energy-substrate oxidation in hepatocytes, skeletal muscle cells, and adipocytes. BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes, and 3T3-L1 mouse adipocytes were treated with different extracellular concentrations of Arg (0, 15, 50, 100 and 400 µM) or 400 µM Arg + 0.5 mM N^G-nitro-L-arginine methyl ester (L-NAME; an NOS inhibitor) for 48 h. Increasing Arg concentrations in culture medium dose-dependently enhanced (P < 0.05) the oxidation of glucose and oleic acid to CO₂ in all three cell types, lactate release from C2C12 cells, and the incorporation of oleic acid into esterified lipids in BNL CL.2 and 3T3-L1 cells. Arg at 400 µM also stimulated (P < 0.05) the phosphorylation of AMP-activated protein kinase (AMPK) in all three cell types and increased (P < 0.05) NO production in C2C12 and BNL CL.2 cells. The inhibition of NOS by L-NAME moderately reduced (P < 0.05) glucose and oleic acid oxidation, lactate release, and the phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) in BNL CL.2 cells, but had no effect (P > 0.05) on these variables in C2C12 or 3T3-L1 cells. Collectively, these results indicate that Arg increased AMPK activity and energy-substrate oxidation in BNL CL.2, C2C12, and 3T3-L1 cells through both NO-dependent and NO-independent mechanisms.

Allergen-Removed Rhus verniciflua Extract Induces Ovarian Cancer Cell Death via JNK Activation

Nuclear factor-[Formula: see text]B (NF-[Formula: see text]B)/Rel transcription factors are best known for their central roles in promoting cell survival in cancer. NF-[Formula: see text]B antagonizes tumor necrosis factor (TNF)-[Formula: see text]-induced apoptosis through a process involving attenuation of the c-Jun-N-terminal kinase (JNK). However, the role of JNK activation in apoptosis induced by negative regulation of NF-[Formula: see text]B is not completely understood. We found that allergen-removed Rhus verniciflua Stokes (aRVS) extract-mediated NF-[Formula: see text]B inhibition induces apoptosis in SKOV-3 ovarian cancer cells via the serial activation of caspases and SKOV-3 cells are most specifically suppressed by aRVS. Here, we show that in addition to activating caspases, aRVS extract negatively modulates the TNF-[Formula: see text]-mediated I[Formula: see text]B/NF-[Formula: see text]B pathway to promote JNK activation, which results in apoptosis. When the cytokine TNF-[Formula: see text] binds to the TNF receptor, I[Formula: see text]B dissociates from NF-[Formula: see text]B. As a result, the active NF-[Formula: see text]B translocates to the nucleus. aRVS extract (0.5[Formula: see text]mg/ml) clearly prevented NF-[Formula: see text]B from mobilizing to the nucleus, resulting in the upregulation of JNK phosphorylation. This subsequently increased Bax activation, leading to marked aRVS-induced apoptosis, whereas the JNK inhibitor SP600125 in aRVS extract treated SKOV-3 cells strongly inhibited Bax. Bax subfamily proteins induced apoptosis through caspase-3. Thus, these results indicate that aRVS extract contains components that inhibit NF-[Formula: see text]B signaling to upregulate JNK activation in ovarian cancer cells and support the potential of aRVS as a therapeutic agent for ovarian cancer.

Exchange of cytosolic content between T cells and tumor cells activates CD4 T cells and impedes cancer growth

BACKGROUND

T cells are known to participate in the response to tumor cells and react with cytotoxicity and cytokine release. At the same time tumors established versatile mechanisms for silencing the immune responses. The interplay is far from being completely understood. In this study we show contacts between tumor cells and lymphocytes revealing novel characteristics in the interaction of T cells and cancer cells in a way not previously described.

METHODS/ FINDINGS

Experiments are based on the usage of a hydrophilic fluorescent dye that occurs free in the cytosol and thus transfer of fluorescent cytosol from one cell to the other can be observed using flow cytometry. Tumor cells from cell lines of different origin or primary hepatocellular carcinoma (HCC) cells were incubated with lymphocytes from human and mice. This exposure provoked a contact dependent uptake of tumor derived cytosol by lymphocytes--even in CD4⁺ T cells and murine B cells--which could not be detected after incubation of lymphocytes with healthy cells. The interaction was a direct one, not requiring the presence of accessory cells, but independent of cytotoxicity and TCR engagement. Electron microscopy disclosed 100-200 nm large gaps in the cell membranes of connected cells which separated viable and revealed astonishing outcome. While the lymphocytes were induced to proliferate in a long term fashion, the tumor cells underwent a temporary break in cell division. The in vitro results were confirmed in vivo using a murine acute lymphoblastic leukemia (ALL) model. The arrest of tumor proliferation resulted in a significant prolonged survival of challenged mice.

CONCLUSIONS

The reported cell-cell contacts reveal new characteristics i.e. the enabling of cytosol flow between the cells including biological active proteins that influence the cell cycle and biological behaviour of the recipient cells. This adds a completely new aspect in tumor induced immunology.

Novel role of IL-6/SIL-6R signaling in the expression of inducible nitric oxide synthase (iNOS) in murine B16, metastatic melanoma clone F10.9, cells

Inducible nitric oxide synthase (iNOS) has been shown to be frequently expressed in melanomas; up-regulation of this enzyme is though to be associated with tumor progression. In this study, we investigated whether diverse cytokines such as: IL-6, TNF-alpha, IL-1beta, IFN-gamma and IL6RIL6 (a highly active fusion protein of the soluble form of the IL-6R (sIL-6R) and IL-6) enhance the iNOS gene expression in B16/F10.9 murine metastatic melanoma cells. An increase at iNOS expression and NO production was observed with the co-treatment of IL6RIL6 plus TNF-alpha. Gel shift and reporter gene analyses revealed that IL6RIL6 selectively activated AP-1; while TNF-alpha increased the activities of both NF-kappaB and AP-1. Persistent activation of AP-1 was also seen in cells treated with IL6RIL6 plus TNF-alpha. Stimulation of cells with IL6RIL6/TNF-alpha resulted in the activation of mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK) and p38, and the abrogation by pretreatment with JNK or p38 MAPK inhibitor. IL6RIL6 or IL6RIL6/TNFalpha-inducible AP-1 binding increase was supershifted by anti-c-Jun or c-Fos antibodies, and the activation of c-Jun and c-Fos was dependent on JNK and p38, respectively. These results suggest that IL-6/sIL-6R/gp130 complex signaling has an unexpected positive effect on iNOS gene expression through JNK/p38 MAPK mediated-AP-1 activation in melanoma cells.

The tyrosine kinase inhibitor tyrphostin AG126 reduces renal ischemia/reperfusion injury in the rat

BACKGROUND

We investigate the effects of tyrphostin AG126, an inhibitor of tyrosine kinase activity, on the renal dysfunction and injury caused by ischemia/reperfusion (I/R) of the kidney.

METHODS

Tyrphostin AG126 (5 mg/kg intraperitoneally) was administered to male Wistar rats 30 minutes prior to bilateral renal ischemia for 45 minutes followed by reperfusion for up to 48 hours. Biochemical markers of renal dysfunction and injury were measured and renal sections assessed for renal injury. Expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and formation of nitrotyrosine and poly (ADP) ribose (PAR) were assessed using immunohistochemistry. Rat proximal tubular cells (PTCs) were incubated with interferon-gamma (100 IU/mL), bacterial lipopolysaccharide (10 microg/mL), and with increasing concentrations of tyrphostin AG126 (0.0001-1 mmol/L) for 24 hours. Nitric oxide production was measured in both plasma from rats subjected to I/R and in incubation medium from PTCs.

RESULTS

After 6 hours of reperfusion, tyrphostin AG126 significantly reduced the increase in serum and urinary indicators of renal dysfunction and injury caused by I/R and reduced histologic evidence of renal injury. Tyrphostin AG126 also improved renal function (after 24 and 48 hours of reperfusion) and reduced the histologic signs of renal injury (after 48 hours of reperfusion). Tyrphostin AG126 reduced the expression of iNOS and nitric oxide levels in both rat plasma and in PTC cultures, as well as expression of COX-2. Tyrphostin AG126 also reduced nitrotyrosine and PAR formation, suggesting reduction of nitrosative stress and poly (ADP-ribose) polymerase (PARP) activation, respectively.

CONCLUSION

Taken together, these results show that tyrphostin AG126 significantly reduces the renal dysfunction and injury caused by I/R of the kidney. We propose that inhibition of tyrosine kinase activity may be useful against renal I/R injury.

Role of mitogen-activated protein kinases and tyrosine kinases on IL-1-Induced NF-kappaB activation and iNOS expression in bovine articular chondrocytes

Nitric oxide (NO), produced by the inducible isoform of the NO synthase (iNOS), plays an important role in the pathophysiology of arthritic diseases. This work aimed at elucidating the role of the mitogen-activated protein kinases (MAPK), p38MAPK and p42/44MAPK, and of protein tyrosine kinases (PTK) on interleukin-1beta (IL-1)-induced iNOS expression in bovine articular chondrocytes. The specific inhibitor of the p38MAPK, SB 203580, effectively inhibited IL-1-induced iNOS mRNA and protein synthesis, as well as NO production, while the specific inhibitor of the p42/44MAPK, PD 98059, had no effect. These responses to IL-1 were also inhibited by treatment of the cells with the tyrosine kinase inhibitors, genistein and tyrphostin B42, which also prevented IL-1-induced NF-kappaB activation. The p38MAPK inhibitor, SB 203580, had no effect on IL-1-induced NF-kappaB activation. Finally, the p42/44MAPK inhibitor, PD 98059, prevented IL-1-induced AP-1 activation in a concentration that did not inhibit iNOS expression. In conclusion, this study shows that (1) PTK are part of the signaling pathway that leads to IL-1-induced NF-kappaB activation and iNOS expression; (2) the p38MAPK cascade is required for IL-1-induced iNOS expression; (3) the p42/44MAPK and AP-1 are not involved in IL-1-induced iNOS expression; and (4) NF-kappaB and the p38MAPK lie on two distinct pathways that seem to be independently required for IL-1-induced iNOS expression. Hence, inhibition of any of these two signaling cascades is sufficient to prevent iNOS expression and the subsequent production of NO in articular chondrocytes.

Cytokine-activated Jak-2 is involved in inducible nitric oxide synthase expression independent from NF-kappaB activation in vascular smooth muscle cells

Inflammatory cytokines, such as interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha, activate nuclear factor-kappa B (NF-kappaB) which transactivates inducible nitric oxide synthase (iNOS) gene in vascular smooth muscle cells (VSMCs). However, it remains obscure whether cytokine-mediated iNOS expression in VSMCs requires signaling pathway(s) other than NF-kappaB activation. The present study was designed to elucidate whether protein tyrosine kinases (PTKs) are involved in the cytokine-induced NF-kappaB activation and iNOS expression in cultured rat VSMCs. Both IL-1beta and TNF-alpha stimulated NF-kappaB activity, iNOS mRNA and protein expression with massive nitrite/nitrate (NOx) production in rat VSMCs. PTK inhibitors (genistein, herbimycin A) dose-dependently inhibited the cytokine-stimulated NOx production and iNOS mRNA expression. However, neither genistein nor herbimycin A affected the cytokine-stimulated phosphorylation and degradation of IkappaB-alpha, or NF-kappaB activation, whereas they completely blocked the cytokine-stimulated iNOS transcriptional activity. Tyrphostin B42 (AG490), a Jak-2 tyrosine kinase inhibitor, similarly blocked the cytokine-induced NOx production, iNOS expression and its promoter activity without affecting NF-kappaB-dependent transcription. Transfection of a dominant-negative Jak-2 mutant antagonized the cytokine-induced NOx production and iNOS expression, while wild-type Jak-2 expressing construct was without effect. These data indicate that the cytokine-induced iNOS expression involves activation of Jak-2 signaling pathway independent from NF-kappaB activation in rat VSMCs.

Differential activation pattern of redox-sensitive transcription factors and stress-inducible dilator systems heme oxygenase-1 and inducible nitric oxide synthase in hemorrhagic and endotoxic shock

OBJECTIVE

To investigate the role of redox-sensitive transcription factors nuclear factor kappa-B (NF-kappaB) or activator protein-1 (AP-1) for hepatic gene expression of heme oxygenase (HO)-1 and inducible nitric oxide synthase (iNOS) in models of hemorrhagic or endotoxic shock.

DESIGN

Prospective controlled laboratory study.

SETTING

Animal research laboratory at a university hospital.

SUBJECTS

Male Sprague-Dawley rats (250-350 g).

INTERVENTIONS

After anesthesia, animals were assigned to hemorrhagic shock (mean arterial pressure 35-40 mm Hg for 60 mins), sham operation, or endotoxemia (1 mg/kg intraperitoneally). To assess the role of reactive oxygen species for activation of NF-kappaB or AP-1, animals were treated with the antioxidant trolox (6 mg/kg body weight). In additional experiments, animals were pretreated with dexamethasone (10 mg/kg body weight), an inhibitor of the transactivating function of DNA-bound AP-1 or with actinomycin-D (2 mg/kg body weight), an inhibitor of DNA-directed RNA synthesis. Activation of NF-kappaB or AP-1 was assessed by electrophoretic mobility shift assay. HO-1 and iNOS gene expression were assessed by Northern and Western blot.

MEASUREMENTS AND MAIN RESULTS

Hemorrhage and resuscitation induced hepatic HO-1 transcripts 12-fold. Induction was abolished by actinomycin-D and was attenuated by dexamethasone and the antioxidant trolox. Activation of AP-1 was observed after hemorrhagic but not after endotoxic shock. AP-1 activation was inhibitable by trolox and correlated with accumulation of HO-1 transcripts. In contrast, a weak activation of NF-kappaB was observed after hemorrhage that was not affected by trolox. A profound activation of NF-kappaB after endotoxic shock correlated with induction of iNOS but failed to induce HO-1 transcripts.

CONCLUSIONS

These data suggest that AP-1 but not NF-kappaB activation is dependent on reactive oxygen intermediates in vivo and contributes to HO-1 gene expression. Thus, AP-1-dependent HO-1 induction under oxidative stress conditions may subserve a similar function as a stress-inducible vasodilator system as does NF-kappaB-dependent iNOS expression in liver inflammation.

Serum after partial hepatectomy stimulates iNOS gene transcription via downstream NF-kappa B site

It has been known that the expression of inducible nitric oxide synthase (iNOS) is up-regulated during hepatic regeneration. The present study characterized the molecular mechanisms involved in the transcriptional activation of iNOS gene by using the serum after partial hepatectomy (post-PH serum) in vitro. The post-PH serum rapidly induced iNOS mRNA expression, which was blocked by anti-tumor necrosis factor-alpha (TNF-alpha) antibody in BNL CL.2 cells, murine embryonic liver cell line. In addition, EMSAs using a NF-kappa B-specific oligomer showed that the up-regulated iNOS mRNA expression in cells treated with post-PH serum correlated with transient activation of NF-kappa B complex (p50/p65 heterodimer). Transient transfection of BNL CL.2 cells with iNOS promoter linked to a CAT reporter gene showed the transcriptional activation of iNOS promoter by post-PH serum. Furthermore, site-directed mutational analysis of the two NF-kappa B sites individually or in combination revealed that iNOS expression by post-PH serum is regulated by the downstream NF-kappa B site, but not by upstream NF-kappa B site. Taken together, these results suggest that the downstream NF-kappa B site acts as an essential component for the iNOS expression by post-PH serum during hepatic regeneration.

Brief hypoxic stress suppresses postbacteremic NF-kappaB activation and TNF-alpha bioactivity in perfused liver

Reductions in hepatic O(2) delivery are common early after gram-negative bacteremic sepsis owing to cardiopulmonary dysfunction and derangements in sinusoidal perfusion. Although gram-negative endotoxin and cellular hypoxia independently enhance activation of nuclear factor-kappaB (NF-kappaB) via generation of reactive O(2) species (ROS), the combination of these stimuli downregulates hepatic TNF-alpha gene expression. Here we tested the hypothesis that hypoxic suppression of postbacteremic TNF-alpha gene expression is transcriptionally mediated by reduced activation of NF-kappaB. Buffer-perfused rat livers (n = 52) were studied over 180 min after intraportal infection at t = 0 with 10(9) live Escherichia coli (EC), serotype O55:B5, or 0.9% NaCl controls under normoxic conditions, compared with 0.5 h of constant-flow hypoxia (PO(2) approximately 41 +/- 7 Torr) beginning at t = 30 min, followed by 120 min of reoxygenation. In parallel studies, tissue was obtained at peak hypoxia (t = 60 min). To determine the role of xanthine oxidase (XO)-induced ROS in modulating NF-kappaB activity after hypoxia/reoxygenation (H/R), livers were pretreated with the XO inhibitor allopurinol, with results confirmed in organs of tungstate-fed animals. Electrophoretic mobility shift assays were performed on nuclear extracts of whole liver lysates using (32)P-labeled oligonucleotides specific for NF-kappaB. Compared with normoxic EC controls, hypoxia reduced postbacteremic NF-kappaB nuclear translocation and TNF-alpha bioactivity, independent of reoxygenation, tissue levels of reduced glutathione, or posthypoxic O(2) consumption. XO inhibition reversed the hypoxic suppression of NF-kappaB nuclear translocation and ameliorated decreases in cell-associated TNF-alpha. Thus decreases in hepatic O(2) delivery reduce postbacteremic nuclear translocation of NF-kappaB and hepatic TNF-alpha biosynthesis by signaling mechanisms involving low-level generation of XO-mediated ROS.

NO increases permeability of cultured human cervical epithelia by cGMP-mediated increase in G-actin

Human cervical epithelial cells express mRNA for the nitric oxide (NO) synthase (NOS) isoforms ecNOS, bNOS, and iNOS and release NO into the extracellular medium. N(G)-nitro-L-arginine methyl ester (L-NAME), an NOS inhibitor, and Hb, an NO scavenger, decreased paracellular permeability; in contrast, the NO donors sodium nitroprusside (SNP) and N-(ethoxycarbonyl)-3-(4-morpholinyl)sydnonimine increased paracellular permeability across cultured human cervical epithelia on filters, suggesting that NO increases cervical paracellular permeability. The objective of the study was to understand the mechanisms of NO action on cervical paracellular permeability. 8-Bromo-cGMP (8-BrcGMP) also increased permeability, and the effect was blocked by KT-5823 (a blocker of cGMP-dependent protein kinase), but not by LY-83583 (a blocker of guanylate cyclase). In contrast, LY-83583 and KT-5823 blocked the SNP-induced increase in permeability. Treatment with SNP increased cellular cGMP, and the effect was blocked by Hb and LY-83583, but not by KT-5823. Neither SNP nor 8-BrcGMP had modulated cervical cation selectivity. In contrast, both agents increased fluorescence from fura 2-loaded cells in the Ca(2+)-insensitive wavelengths, indicating that SNP and 8-BrcGMP stimulate a decrease in cell size and in the resistance of the lateral intercellular space. Neither SNP nor 8-BrcGMP had an effect on total cellular actin, but both agents increased the fraction of G-actin. Hb blocked the SNP-induced increase in G-actin, and KT-5823 blocked the 8-BrcGMP-induced increase in G-actin. On the basis of these results, it is suggested that NO acts on guanylate cyclase and stimulates an increase in cGMP; cGMP, acting via cGMP-dependent protein kinase, shifts actin steady-state toward G-actin; this fragments the cytoskeleton and renders cells more sensitive to decreases in cell size and resistance of the lateral intercellular space and, hence, to increases in permeability. These results may be important for understanding NO regulation of transcervical paracellular permeability and secretion of cervical mucus in the woman.

Regulation of nitric oxide synthesis in the liver

Nitric oxide signalling during the past two decades has been one of the most rapidly growing areas in biology. This simple free radical gas can regulate an ever-growing list of biological processes. Here the regulation of NO synthesis in the liver is reviewed. The biogenesis of nitric oxide (NO) is catalysed by nitric oxide synthases (NOS). These enzymes catalyse the oxidation of one of the guanidino nitrogens of l-arginine by molecular oxygen to form NO and citrulline. Three NOS have been identified: two constitutive (cNOS: type 1 or neuronal and type 3 or endothelial) and one inducible (iNOS: type 2). As to the liver, cNOS activity is normally detectable in Kupffer cells, whereas no cNOS is ever encoded in hepatocytes. However, hepatocytes, Kupffer and stellate cells (the three main types of liver cells) are prompted to express an intense iNOS activity once exposed to effective stimuli such as bacterial lipopolysaccharide and cytokines. This review is focused mainly on two aspects: regulation of NOS activity and expression by endogenous and exogenous compounds. Because NO production has beneficial and detrimental effects, understanding the molecular mechanisms that govern NOS is critical to developing strategies to manipulate NO production in liver diseases.

Ionizing radiation potentiates the induction of nitric oxide synthase by interferon-gamma (Ifn-gamma) or Ifn-gamma and lipopolysaccharide in bnl cl.2 murine embryonic liver cells: role of hydrogen peroxide

The effects of ionizing irradiation on the nitric oxide (NO) production in murine embryonic liver cell line, BNL CL.2 cells, were investigated. Various doses (5-40 Gy) of radiation made BNL CL.2 cells responsive to interferon-gamma alone for the production of NO in a dose-dependent manner. Small amounts of lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) synergized with IFN-gamma in the production of NO from irradiated BNL CL.2 cells, even though LPS or TNF-alpha alone did not induce NO production from the same cells. Immunoblots showed parallel induction of inducible nitric oxide synthase (iNOS). NO production in irradiated BNL CL.2 cells by IFN-gamma or IFN-gamma plus LPS was decreased by the addition of catalase, suggesting that H(2)O(2) produced by ionizing irradiation primed the cells to trigger NO production in response to IFN-gamma or IFN-gamma plus LPS. Furthermore, the treatment of nongamma-irradiated BNL CL.2 cells with H(2)O(2) made the cells responsive to IFN-gamma or IFN-gamma plus LPS for the production of NO. This study shows that ionizing irradiation has the ability to induce iNOS gene expression in responsive to IFN-gamma via the formation of H(2)O(2) in BNL CL.2 murine embryonic liver cells.

Elevated, sustained peroxynitrite levels as the cause of chronic fatigue syndrome

The etiology of chronic fatigue syndrome (CFS) has been both obscure and highly contentious, leading to substantial barriers to both clear diagnosis and effective treatment. I propose here a novel hypothesis of CFS in which either viral or bacterial infection induces one or more cytokines, IL-1beta IL-6, TNF-alpha and IFN-gamma. These induce nitric oxide synthase (iNOS), leading to increased nitric oxide levels. Nitric oxide, in turn, reacts with superoxide radical to generate the potent oxidant peroxynitrite. Multiple amplification and positive feedback mechanisms are proposed by which once peroxynitrite levels are elevated, they tend to be sustained at a high level. This proposed mechanism may lower the HPA axis activity and be maintained by consequent lowered glucocorticoid levels. Similarities are discussed among CFS and autoimmune and other diseases previously shown to be associated with elevated peroxynitrite. Multiple pharmacological approaches to the treatment of CFS are suggested by this hypothesis.

Hepatic ischemia/reperfusion in rats induces iNOS gene transcription by activation of NF-kappaB

It has been known that many immediately early genes are expressed during ischemia/reperfusion (I/R) injury. Here, employing a model of hepatic I/R, we show that inducible nitric oxide synthase (iNOS) is induced via the activation of nuclear factor kappaB (NF-kappaB) after I/R in rat liver. When liver was subjected to ischemia followed by reperfusion, but not ischemia alone, an NF-kappaB complex composed of p50/p65 heterodimer and p50 homodimer was rapidly activated within 1 h and remained elevated for up to 3 h, and then tended to decline after 5 h of reperfusion. Also, the expression of iNOS mRNA was initiated after 1 h and continued to increase after 5 h of reperfusion during the time course studied. This upregulated iNOS mRNA expression coincides with increased iNOS enzyme activity and NF-kappaB binding activity after hepatic I/R. Administration of N-acetylcysteine (NAC, 20 mg/kg i.v. 10 min before reperfusion), an antioxidant, not only significantly inhibited the expression of iNOS mRNA but also blocked upregulated NF-kappaB binding activity after reperfused liver. These results suggest that NF-kappaB is activated by oxidative stress during hepatic I/R and may play a significant role in the induction of the iNOS gene.

Inducible nitric oxide synthase can be induced in the absence of active nuclear factor-kappaB in rat mesangial cells: involvement of the Janus kinase 2 signaling pathway

The contribution of nuclear factor-kappaB (NF-kappaB) and interferon-gamma (IFN-gamma) signaling to nitric oxide generation is not completely understood. The effect of NF-kappaB release and its inhibition on nitrite production and the involvement of Janus kinase 2 (JAK2) in inducible nitric oxide synthase (iNOS) induction were investigated. The following assays were performed. (1) Nitrite produced by rat mesangial cells in primary culture was measured in incubations with tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS), with or without IFN-gamma. Cells were stimulated with TNF-alpha or LPS plus IFN-gamma in the presence of NF-kappaB inhibitors, herbimycin A (HerA), or the more specific JAK2 inhibitor AG490. (2) Immunoblotting was performed against the p65 and p50 subunits of NF-kappaB and iNOS. (3) Electrophoretic mobility shift assays were performed against NF-kappaB in the presence of NF-kappaB inhibitors or AG490. (4) iNOS promoter activity was measured in the presence of AG490 or JAK2 antisense oligonucleotides. TNF-alpha or LPS alone did not induce nitrite production, but with IFN-gamma these compounds did induce nitrite production. Pyrrolidine dithiocarbamate (PDTC), N-acetyl-L-cysteine, dexamethasone (Dex), HerA, and AG490 partially inhibited LPS/ IFN-gamma- or TNF-alpha/IFN-gamma-induced nitrite production. p65 was inhibited by the three NF-kappaB inhibitors described above, whereas p50 was not. PDTC and Dex completely inhibited the p65/p50 heterodimer, but HerA and AG490 had little effect on p65/p50. AG490 and JAK2 antisense oligonucleotides suppressed iNOS promoter activity. It can be concluded that (1) iNOS can be induced without active NF-kappaB; (2) Dex, acetylsalicylic acid, and PDTC inhibit only p65; and (3) JAK2 is involved in iNOS induction, and the contribution of JAK2 to nitrite production is greater than that of NF-kappaB.

Interferon-gamma alone triggers the production of nitric oxide from serum-starved BNL CL.2, murine embryonic liver cells

A previous study has demonstrated that both interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) were needed to induce the production of nitric oxide (NO) in BNL CL.2 cells, murine embryonic liver cells. We here demonstrate that when BNL CL.2 cells were cultured with serum-free medium, they were induced to produce NO by the stimulation of IFN-gamma alone. BNL CL.2 cells were cultured with serum-free or serum-containing medium for 1-3 days and then stimulated to synthesize NO by IFN-gamma. Surprisingly, only serum-starved cells showed significant amount of nitrite accumulation and iNOS protein expression in response to IFN-gamma in dose- and time-dependent manners, but serum-supplied cells did not. When the cells were stimulated with IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), or LPS in combinations, only the combination of IFN-gamma and LPS produced more NO than that produced by IFN-gamma alone. The production of NO by the cells stimulated with IFN-gamma or IFN-gamma plus LPS was blocked by the addition of N(G)-monomethyl-L-arginine (N(G)MMA), a NO synthesis inhibitor. To address the intracellular signal pathway responsible for the production of NO by the cells stimulated with IFN-gamma aloneor IFN-gamma plus LPS, we examined the effects of several protein kinase inhibitors on the production of NO from the cells. The production of NO was significantly inhibited by protein tyrosine kinase (PTK) inhibitors, genistein and herbimycin A, but not by protein kinase A or C inhibitors. These results suggest that the deprivation of serum from BNL CL.2 cell culture medium might prime the cells to induce NO synthesis when the cells are triggered by IFN-gamma and the involvement of PTK signal transduction pathway in the expression of inducible NO synthase gene in murine hepatoma cells.

Estrogen modulates paracellular permeability of human endothelial cells by eNOS- and iNOS-related mechanisms

Estradiol had a biphasic effect on permeability across cultures of human umbilical vein endothelial cells (HUVEC): at nanomolar concentrations it decreased the HUVEC culture permeability, but at micromolar concentrations it increased the permeability. The objective of the present study was to test the hypothesis that the changes in permeability were mediated by nitric oxide (NO)-related mechanisms. The results revealed dual modulation of endothelial paracellular permeability by estrogen. 1) An endothelial NO synthase (eNOS)-, NO-, and cGMP-related, Ca2+-dependent decrease in permeability was activated by nanomolar concentrations of estradiol, resulting in enhanced Cl- influx, increased cell size, and increases in the resistance of the lateral intercellular space (RLIS) and in the resistance of the tight junctions (RTJ); these effects appeared to be limited by the ability of cells to generate cGMP in response to NO. 2) An inducible NO synthase (iNOS)- and NO-related, Ca2+-independent increase in permeability was activated by micromolar concentrations of estradiol, resulting in enhanced Cl- efflux, decreased cell size, and decreased RLIS and RTJ. We conclude that the net effect on transendothelial permeability across HUVEC depends on the relative contributions of each of these two systems to the total paracellular resistance.

Pharmacological evidence that inducible nitric oxide synthase is a mediator of delayed preconditioning

Brief periods of myocardial ischaemia preceding a subsequent more prolonged ischaemic period 24-72 h later confer protection against myocardial infarction ('delayed preconditioning' or the 'second window' of preconditioning). In the present study, we examined the effects of pharmacological modifiers of inducible nitric oxide synthase (iNOS) induction and activity on delayed protection conferred by ischaemic preconditioning 48 h later in an anaesthetized rabbit model of myocardial infarction. Rabbits underwent a myocardial preconditioning protocol (four 5 min coronary artery occlusions) or were sham-operated. Forty-eight hours later they were subjected to a sustained 30 min coronary occlusion and 120 min reperfusion. Infarct size was determined with triphenyltetrazolium staining. In rabbits receiving no pharmacological intervention, the percentage of myocardium infarcted within the risk zone was 43.9+5.0% in sham-operated animals and this was significantly reduced 48 h after ischaemic preconditioning with four 5 min coronary occlusions to 18.5+5.6% (P<0.01). Administration of the iNOS expression inhibitor dexamethasone (4 mg kg(-1) i.v) 60 min before ischaemic preconditioning completely blocked the infarct-limiting effect of ischaemic preconditioning (infarct size 48.6+/-6.1%). Furthermore, administration of aminoguanidine (300 mg kg(-1), s.c.), a relatively selective inhibitor of iNOS activity, 60 min before sustained ischaemia also abolished the delayed protection afforded by ischaemic preconditioning (infarct size 40.0+/-6.0%). Neither aminoguanidine nor dexamethasone per se had significant effect on myocardial infarct size. Myocardial risk zone volume during coronary ligation, a primary determinant of infarct size in this non-collateralized species, was not significantly different between intervention groups. There were no differences in systolic blood pressure, heart rate, arterial blood pH or rectal temperature between groups throughout the experimental period. These data provide pharmacological evidence that the induction of iNOS, following brief periods of coronary occlusion, is associated with increased myocardial tolerance to infarction 48 h later.

Extracellular signal-regulated kinase and p38 subgroups of mitogen-activated protein kinases regulate inducible nitric oxide synthase and tumor necrosis factor-alpha gene expression in endotoxin-stimulated primary glial cultures

Tumor necrosis factor-alpha (TNFalpha) and nitric oxide (NO), the product of inducible NO synthase (iNOS), mediate inflammatory and immune responses in the CNS under a variety of neuropathological situations. They are produced mainly by "activated" astrocytes and microglia, the two immune regulatory cells of the CNS. In this study we have examined the regulation of TNFalpha and iNOS gene expression in endotoxin-stimulated primary glial cultures, focusing on the role of mitogen-activated protein (MAP) kinase cascades. The bacterial lipopolysaccharide (LPS) was able to activate extracellular signal-regulated kinase (ERK) and p38 kinase subgroups of MAP kinases in microglia and astrocytes. ERK activation was sensitive to PD98059, the kinase inhibitor that is specific for ERK kinase. The activity of p38 kinase was inhibited by SB203580, a member of the novel class of cytokine suppressive anti-inflammatory drugs (CSAIDs), as revealed by blocked activation of the downstream kinase, MAP kinase-activated protein kinase-2. The treatment of glial cells with either LPS alone (microglia) or a combination of LPS and interferon-gamma (astrocytes) resulted in an induced production of NO and TNFalpha. The two kinase inhibitors, at micromolar concentrations, individually suppressed and, in combination, almost completely blocked glial production of NO and the expression of iNOS and TNFalpha, as determined by Western blot analysis. Reverse transcriptase-PCR analysis showed changes in iNOS mRNA levels that paralleled iNOS protein and NO while indicating a lack of effect of either of the kinase inhibitors on TNFalpha mRNA expression. The results demonstrate key roles for ERK and p38 MAP kinase cascades in the transcriptional and post-transcriptional regulation of iNOS and TNFalpha gene expression in endotoxin-activated glial cells.