Association between synthesis and release of cGMP and nitric oxide biosynthesis by hepatocytes

Pro-opiomelanocortin-derived peptides, cytokines, and nitric oxide in immune responses and stress: an evolutionary approach

In vertebrates, including man, the study of stress has contributed substantially to unravelling the complex relationship between immune-neuroendocrine interactions and the systems involved. On the basis of data on the presence and distribution of the main actors (POMC products, cytokines, biogenic amines, and steroid hormones) in different species and taxa from invertebrates to vertebrates, we argue that these responses have been deeply connected and interrelated since the beginning of life. Moreover, the study of nitric oxide suggests that the inflammatory reaction is located precisely between the immune and stress responses, sharing the same fundamental evolutionary roots. The major argument in favor of this hypothesis is that the immune, stress, and inflammation responses appear to be mediated by a common pool of molecules that have been conserved throughout evolution and that from a network of adaptive mechanisms. One cell type, the macrophage, appears to emerge as that most capable of supporting this network critical for survival; it was probably a major target of selective pressure. All these data fit the unitarian hypothesis we propose, by which evolution favors what has been conserved, rather than what has changed, as far as both molecules and functions are concerned.

Glutathione regulates nitric oxide synthase in cultured hepatocytes

OBJECTIVE

The authors determine the relationship between glutathione and nitric oxide (NO) synthesis in cultured hepatocytes.

SUMMARY BACKGROUND DATA

Glutathione is a cofactor for a number of enzymes, and its presence is essential for maximal enzyme activity by the inducible macrophage nitric oxide synthase (iNOS), which produces the reactive nitric oxide radical. Hepatocytes contain substantial quantities of glutathione, and this important tripeptide is decreased in hepatocytes stressed by ischemia/reperfusion or endotoxemia. Endotoxemia also induces the synthesis of inflammatory cytokines that result in the production of nitric oxide from hepatocytes by iNOS, suggesting that hepatocytes may be attempting to synthesize nitric oxide at times when intracellular glutathione is reduced.

METHODS

Hepatocytes were cultured with buthionine sulfoximine and 1,3-bis(chloroethyl)-1-nitrosourea (BCNU) to inhibit glutathione. After exposure to cytokines, NO synthesis was assessed by supernatant nitrite levels, cytosolic iNOS enzyme activity, and iNOS mRNA levels.

RESULTS

Inhibition of glutathione synthesis with buthionine sulfoximine or inhibition of glutathione reductase activity with BCNU inhibited nitrite synthesis. Both buthionine sulfoximine and BCNU inhibited the induction of iNOS mRNA, as detected by Northern blot analysis. Exogenous glutathione increased cytokine-stimulated iNOS induction, overcame the inhibitory effects of BCNU, and increased nitrite production by intact hepatocytes, induced hepatocyte cytosol, and partially purified hepatocyte iNOS.

CONCLUSIONS

In cultured hepatocytes, adequate glutathione levels are required for optimal nitric oxide synthesis. This finding is predominantly due to an effect on iNOS mRNA levels, although glutathione also participates in the regulation of iNOS enzyme activity.

Nitric oxide synthase induction with renal transplant rejection or infection

Nitric oxide (NO) is readily oxidized to nitrate and nitrite and NO activates guanylyl cyclase, increasing cyclic GMP levels. To determine if nitric oxide synthase (NOS) is present in urine collected daily from patients following renal transplantation, we evaluated NOS activity in the leukocyte-rich particulate fraction and measured nitrate, nitrite, and cyclic GMP levels in the supernatant fraction of the urine. Reverse transcriptase-PCR and cDNA sequencing confirmed the presence of inducible NOS (iNOS) in cells obtained from the urine of renal transplant patients with rejection. NOS activity was elevated significantly in renal transplant patients with rejection (6.40 +/- 1.47 pmol citrulline/min/mg protein) or with urinary tract infection (29.56 +/- 11.00 pmol citrulline/min/mg protein), when compared to post-renal transplantation patients without rejection or urinary tract infection (0.51 +/- 0.21 pmol citrulline/min/mg protein). Nitrate levels increased in renal transplant patients with rejection and nitrite levels increased in renal transplant patients with urinary tract infection (UTI). Cyclic GMP levels increased with both rejection and UTI. This study demonstrates the presence of NOS activity and inducible NOS-mRNA in cells isolated from the urine of patients undergoing renal allograft rejection.

3':5'-cyclic guanosine monophosphate (cGMP) potentiates the inositol 1,4,5-trisphosphate-evoked Ca2+ release in guinea-pig hepatocytes

The effect of cGMP on noradrenaline-induced intracellular Ca2+ mobilization was investigated in whole-cell voltage-clamped guinea-pig hepatocytes. Treatment of the cells with 8-Br-cGMP (1-500 microM) resulted in an increase in the sensitivity of the cells to noradrenaline and to inositol 1,4,5-trisphosphate (InsP3) photo-released from caged InsP3. The positive effect of 8-Br-cGMP on the Ca2+ release evoked by Ca(2+)-mobilizing agonists or InsP3 was blocked by a protein kinase G (PKG; cGMP-dependent protein kinase) inhibitor, the RP-8-(4-chlorophenylthio)guanosine 3':5'-monophosphorothioate. 8-Br-cGMP affected neither the basal InsP3 concentration nor the noradrenaline-induced production of InsP3. In permeabilized hepatocytes, the dose-response curve for InsP3-induced Ca2+ release was shifted to the left in the presence of 8-Br-cGMP. Furthermore, the treatment with 8-Br-cGMP did not affect the Ca2+ content of the InsP3-sensitive Ca2+ stores. These results indicate that intracellular cGMP potentiates the noradrenaline-induced Ca2+ response by enhancing Ca2+ release from the intracellular Ca2+ stores. We suggest that cGMP increases the apparent affinity of InsP3 receptors for InsP3 in guinea-pig hepatocytes probably by phosphorylation via the activation of PKG.

Cyclic GMP induces oscillatory calcium signals in rat hepatocytes

The ability of guanosine-3',5'-cyclic monophosphate (cGMP) to induce increases in the intracellular free calcium ion concentration ([Ca2+]i) was studied at the single cell level in fura-2-loaded rat hepatocytes. Both 8-bromo-cGMP (Br-cGMP) and dibutyryl cGMP (db-cGMP) produced oscillatory [Ca2+]i increases in hepatocytes. In addition, Br-cGMP increased the frequency of agonist-induced spiking or converted [Ca2+]i oscillations into sustained nonoscillatory [Ca2+]i responses. Addition of the nitric oxide donor sodium nitroprusside also produced oscillatory [Ca2+]i increases similar to those generated by cGMP analogues. In the absence of extracellular Ca2+, cGMP-induced [Ca2+]i responses were significantly reduced and mainly appeared as single transient [Ca2+]i increases. The effects of cGMP analogues do not appear to be mediated by a secondary increase in cAMP or activation of cAMP-dependent protein kinase (PKA), since [Ca2+]i responses to cGMP analogues were inhibited by the G-kinase inhibitor 8-bromoguanosine-3',5'-cyclic monophosphorothioate (Rp-Br-cGMP[S]). Both Br-cGMP and db-cGMP also increased [Ca2+]i in the presence of the PKA inhibitor 8-bromoadenosine-3',5'-cyclic monophosphorothioate (Rp-Br-cAMP[S]) and when the cGMP-inhibitable cAMP phosphodiesterase activity was inhibited by pretreatment with siguazodan. Br-cGMP stimulated the Mn2+-induced quench of compartmentalized fura-2 in intact hepatocytes, indicating a site of action at the level of the Ca2+ stores. This locus was further supported by the finding that pretreatment of hepatocytes with Br-cGMP potentiated submaximal inositol 1,4,5-trisphosphate (InsP3)-induced Mn2+ quench in subsequently permeabilized hepatocytes. db-cGMP also decreased PKA-mediated back phosphorylation of the hepatic type-1 InsP3 receptor, indicating that G-kinase phosphorylates the InsP3 receptor at sites targeted by PKA. These data indicate that phosphorylation of the hepatic InsP3 receptor by G-kinase increases the sensitivity to InsP3 for [Ca2+]i release and is associated with the production of [Ca2+]i oscillations in single rat hepatocytes.

Export of guanosine 3',5'-cyclic monophosphate (cGMP) from human erythrocytes characterized by inside-out membrane vesicles

The present study was undertaken to characterize the export of cGMP from human erythrocytes at 37 degrees C. Inside-out membrane vesicles were exposed to cGMP and [3H]-cGMP in the presence and absence of 2 mmol l-1 ATP. In the absence of ATP, an equilibrium was reached within 15 min for the lowest tested concentration (0.65 mumol l-1), and the amount of cGMP in the vesicles was linearly correlated to the cGMP concentrations in the incubate. These observations suggest that the ATP-independent process represents passive diffusion or non-saturated binding to membrane components. In the presence of ATP, cGMP accumulated linearly during the test period (up to 120 min) and the transport into the inside-out vesicles was dependent on both low- and high-Km transport. The kinetic parameters for the low-Km process were determined after 5 and 120 min, the Km values being 4.6 (SD 1.9) and 4.7 (SD 1.1) mumol l-1 (n = 3), respectively. The corresponding Vmax values were 400 (SD 50) and 440 (SD 70) fmol mg-1 min-1. The high-Km process was characterized by Km = 170 (SD 50) mumol-1 and Vmax = 1610 (SD 280) fmol mg-1 min-1 (n = 5). The present data demonstrate an ATP-requiring saturable transport system for cGMP in human erythrocytes.

Inhibition of biotransformation by nitric oxide (NO) overproduction and toxic consequences

Hepatic nitric oxide (NO) biosynthesis is induced by local or systemic inflammation. The highly reactive NO radical binds to prosthetic iron groups such as heme or iron-sulfur clusters leading to either activation or inhibition of enzymes such as guanylate cyclase, cyclooxygenase and aconitase. It has been known for years that NO also binds to the heme moiety of cytochrome P450s (CYP) with high affinity. However, it was demonstrated recently that binding of NO to CYPs also inhibits their enzymatic activity. This is true for exogenously applied as well as for endogenously synthesized NO. Suppression of CYP-dependent metabolism, which is a major problem of inflammatory liver diseases, can be significantly reversed by inhibition of NO synthesis in vivo under experimental conditions. We investigated whether these findings are applicable as a novel therapeutic principle in severe inflammatory liver dysfunction.

Potential genotoxicity of chronically elevated nitric oxide: a review

Several human cancers are associated with chronic bacterial, viral and parasitic infections. Nitric oxide, which is a short-lived free radical produced by many types of cells for a number of important physiological functions, is elevated in these infections. Long-term exposure to elevated NO. in cells could have potential genotoxic effects on hosts. There are at least three mechanisms by which intracellular elevated NO. could exert genotoxic affects after reacting with O2. These include formation of carcinogenic N-nitroso compounds, direct deamination of DNA bases, and oxidation of DNA after formation of peroxynitrite and/or hydroxyl radicals. One or more of these mechanisms could, theoretically, explain why chronic infection increases the risk of certain cancers.

Does nitric oxide play a role in liver function?

Nitric oxide (NO) is becoming increasingly recognised as a signalling molecule in many organs, although its role in the liver remains to be fully elucidated. There is no doubt that liver cells can produce NO in response to a variety of stimuli including Corynebacterium parvum-infection, lipopolysaccharide (LPS) and a variety of cytokines. Within the liver, NO modulates some fundamental intracellular functions such as protein synthesis, mitochondrial electron transport and components of the citric acid cycle. Intercellular roles for NO in the liver may include drug metabolism and blood storage. Also, NO acts to protect the liver from immunological damage in models of hepatic inflammation. Understanding the role of NO in the liver may provide insight into the functioning of this organ in health and disease.

Cyclic nucleotides and vasoactive intestinal peptide production in a rabbit model of Escherichia coli septicemia

Nitric oxide and vasoactive intestinal peptide (VIP) are potent vasodilators and postulated as inducers of hypotension. These mediators activate guanylate cyclase and adenylate cyclase, respectively, with subsequent biosynthesis of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) producing vascular smooth muscle relaxation and vasodilatation. Cyclic nucleotides and VIP were evaluated during Escherichia coli septicemia in two groups of rabbits; 1) sepsis alone and 2) sepsis and a competitive inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine. Arterial blood was obtained for determination of bacteremia, lactic acidemia, nucleotides, nitrites, and VIP levels. Significant bacteremia, endotoxemia, tachycardia, lactic acidosis, and hypotension occurred in all animals (P < 0.005). Circulating blood levels of cGMP, nitrites, cAMP, and VIP (P < 0.005) increased with development of shock. The NG-monomethyl-L-arginine treated animals had less cGMP, nitrites, cAMP, and VIP produced (P < 0.01). Plasma cGMP levels remained stable, suggesting that stimulated phagocytes in whole blood were responsible for increased cGMP levels. Infusion of VIP produced profound hypotension and lactic acidemia. Results of these experiments provide definitive evidence that nitric oxide and VIP are mediators during septic shock and their messengers are cGMP and cAMP, respectively. In addition, phagocytic stimulation with increased production of cGMP may initiate shock, with these mediators acting synergistically to prolong hypotension.

Nitric oxide up-regulates the release of inflammatory mediators by mouse macrophages

Nitric oxide (NO) plays a key role in mediating macrophage cytotoxicity towards different targets, including tumoral cells and intracellular pathogens. However, its role in macrophage immunoregulation is less well defined. In this study, we have investigated the effect of altering NO levels on the production by mouse macrophages of cytokines, and reactive oxygen intermediates as measured by luminol-dependent chemiluminescence. Our results demonstrate that NO can enhance the release of both tumor necrosis factor-alpha and interleukin-1 alpha, and chemiluminescence. Thus, in addition to acting as a powerful effector molecule in mediating cytotoxic activities of mouse macrophages, NO can play a role in enhancing the production of a variety of other inflammatory mediators, and thus can contribute both directly and indirectly to the immunopathology of macrophage-dependent inflammation.

Tumor necrosis factor alpha: a major contributor to the hyperdynamic circulation in prehepatic portal-hypertensive rats

BACKGROUND/AIMS

Portal hypertension is often accompanied by a hyperdynamic circulatory syndrome. Tumor necrosis factor (TNF) alpha causes vasodilatation and a hyperdynamic state in mammals by activating nitric oxide synthesis. The aim of this study was to investigate whether TNF-alpha plays a role in developing the hyperdynamic syndrome in portal hypertension.

METHODS

Portal-hypertensive rats, induced by partial ligation of the portal vein (PVL), were used. In experiment 1, rats that underwent PVL were treated with polyclonal anti-mouse TNF-alpha or placebo intravenously the same day of the PVL operation and 24 hours before hemodynamic studies. Hemodynamic studies were performed 5 days after PVL. In experiment 2, rats that underwent PVL received anti-TNF-alpha or placebo intravenously 3 days and 24 hours before hemodynamics as in experiment 1. Hemodynamics were performed 14 days after the PVL operation. TNF-alpha blood levels were measured using a bioassay.

RESULTS

Anti-TNF-alpha treatment induced a significant increase in mean arterial pressure, heart rate, and systemic vascular resistance and a significant decrease in cardiac index, portal pressure, and TNF-alpha levels in comparison with placebo animals. No significant effects were observed in sham rats.

CONCLUSIONS

Anti-TNF-alpha treatment in rats that underwent PVL significantly blunts the development of the hyperdynamic circulation and reduces portal pressure. TNF-alpha may play a role in the hemodynamic abnormalities of portal hypertension.

Nitric oxide blocks bile canalicular contraction by inhibiting inositol trisphosphate-dependent calcium mobilization

BACKGROUND/AIMS

The biochemical mechanism of bile canalicular contraction is similar to that of smooth muscle contraction. Contraction follows inositol-1,4,5-trisphosphate (InsP3)-dependent Ca2+ release, which activates actin-myosin interactions. Nitric oxide is a myorelaxant through the actions of 5'-cyclic guanosine monophosphate (cGMP) and is produced in hepatocytes exposed to endotoxin and cytokines. The aim of this study was to investigate the effect of nitric oxide on canalicular contraction and to determine the mechanism by which cGMP interferes with the contractile signal.

METHODS

The canalicular motility in rat hepatocyte doublets was measured by microscopic image analysis, and intracellular Ca2+ was measured by fluorescence microscopy. cGMP and InsP3 were determined by radio-immunoassay and high-pressure liquid chromatography. Ca2+ release from liver homogenate was measured by filtration and superfusion assays.

RESULTS

Compounds that release nitric oxide stimulated hepatocellular production of cGMP and prevented agonist-induced contraction by inhibiting the increase in intracellular Ca2+. The cGMP analogue bromo-cGMP prevented contraction and the increase in Ca2+. Bromo-cGMP marginally decreased InsP3 production. cGMP blocked InsP3-dependent Ca2+ release from internal stores.

CONCLUSIONS

These findings suggest that nitric oxide interferes with Ca2+ signals by cGMP-mediated inhibition of the InsP3 receptor/Ca2+ channel and that hepatocellular production of nitric oxide may be cholestatic by impairing canalicular motility.

Nitric oxide induces necrotic but not apoptotic cell death in oligodendrocytes

We have investigated the mechanism of nitric oxide-induced damage in glial cells. Genomic DNA isolated from astrocytes and microglia, treated for 18 h with varying concentrations of a nitric oxide donor, was analysed by electrophoresis. No DNA damage was evident. Oligodendrocytes, treated with 2 mM nitric oxide for 3-48 h, showed single stranded breaks at 48 h but no laddering of nucleosomic fragments of DNA. When analysed by electron microscopy, ultrastructural changes in oligodendrocytes treated with 1 mM nitric oxide for 24 h showed intact nuclei but alterations in membranes and organelles characteristic of necrosis, including disrupted mitochondria with dissolution of their christae. Astrocytes, a glial cell type that we have previously shown to be much less sensitive to nitric oxide-induced damage, did not show ultrastructural changes. DNA analysis by flow cytometry of glial cells treated with nitric oxide supported the apparent necrotic-type death in oligodendrocytes. Double staining of oligodendrocytes, using Hoechst 33342 and propidium iodide for the simultaneous assessment of both apoptotic and necrotic cells, demonstrated that, while the proportion of dead cells increased with time and increasing concentrations of nitric oxide, the death was due to necrosis and not apoptosis. In this study, we demonstrate that direct exposure to soluble nitric oxide, produced in vitro from a nitric oxide donor chemical, ultimately kills oligodendrocytes by necrosis. Microglia and astrocytes maintain DNA and organelle integrity when exposed to exogenous nitric oxide.

Sequential induction of nitric oxide synthase by Corynebacterium parvum in different organs of the mouse

1. The ability of Corynebacterium parvum (C. parvum) to induce nitric oxide (NO) synthase in the macrophage, spleen, liver, aorta, heart and brain, and to elevate plasma NO2-/NO3- in the mouse was investigated. In addition, the relationship between NO synthase activity and blood pressure was studied. 2. C. parvum (100 mg kg-1, i.p.) induced a time-dependent expression of a Ca(2+)-independent NO synthase in the macrophage, spleen, liver, aorta and heart. The time course of induction of the NO synthase varied such that the maximum enzyme activity was at day 8 in the macrophage and liver, day 12 in the spleen and heart and day 16 in the aorta. 3. There was no significant induction of a Ca(2+)-independent NO synthase in the brain, nor was there any change in the Ca(2+)-dependent enzyme in this organ, during the study period. 4. C. parvum produced a gradual decrease in blood pressure, with a maximum fall at day 16 (from 108 +/- 1 mmHg to 79 +/- 3 mmHg), which recovered gradually by day 28. 5. Plasma NO2-/NO3- was significantly elevated between days 8 and 24, with a maximum increase at day 12. 6. These results show that C. parvum induces a Ca(2+)-independent NO synthase in a number of tissues and that this induction occurs initially in macrophages and the liver. This suggests that induction of the NO synthase in the other tissues is secondary and probably the result of activation of macrophages and some cells of the liver. 7. Furthermore, the decrease in blood pressure induced by C. parvum is associated with the induction of NO synthase in the vasculature, whereas the increased concentration of plasma NO2-/NO3- seems to result from the generation of NO by a number of tissues.

Detection of endothelial cell-derived nitric oxide: current trends and future directions

The vascular endothelium is a significant site of NO release that inhibits cellular adhesion and maintains a non-thrombogenic surface. Use of newly described technology suggests for the first time that the maximal release of NO induced by cNOS and iNOS activation may be quite similar, implying that it is the duration of NO release and not the concentration of NO produced from stimulated endothelial cells that accounts for the different biological activities of the enzymes. The respective roles of cNOS and iNOS must be carefully evaluated since both enzymes may have potent biological effects at local sites of production.

Nitric oxide in the liver: physiopathological roles

Many of the known roles of arginine (e.g. in immune function, wound healing, and protection against ammonia intoxication) are mediated by a metabolic pathway synthesising nitric oxide (NO) in the liver. Contrary to some of the current views, liver-produced NO may be basically beneficial, as it exerts both protective actions against tissue injury and cytotoxic effects on invading microorganisms, parasites, or tumor cells. An ongoing equilibrium between NO and other NO-reactive compounds (e.g. O2 and non-heme iron-sulphur-containing moieties) appears to be important in this respect, even under critical conditions. Thus, NO may prevent liver tissue harm from oxidant stress. Only when this putative counterbalance is upset by an uncontrolled, prolonged and/or massive production of NO, liver tissue damage may occur leading to hepatic inflammation or even tumor development. Moreover, the currently available data support the working hypothesis that hepatocytes partake not only to immunoregulatory processes, but even to immune defence mechanisms. Thus, the liver constitutes an excellent model for investigations into the crosstalks regulating the production of NO which take place among not only the various networks operating inside a single hepatic cell, but even the individual types of liver cells.

Genetic regulation of leishmanial and mycobacterial infections: the Lsh/Ity/Bcg gene story continues

A common basis to genetic regulation of leishmanial and mycobacterial infections is provided by the action of the murine Lsh/Ity/Bcg gene in controlling the priming/activation of macrophages for antimicrobial activity. This relies on the TNF-alpha-dependent sustained expression of the inducible nitric oxide synthase (iNOS) gene responsible for the generation of large amounts of toxic nitric oxide (NO). The Lsh/Ity/Bcg gene has many pleiotropic effects, including differential expression of the early response gene KC following stimulation of macrophages with bacterial lipopolysaccharide (LPS) and mycobacterial lipoarabinomannan (LAM). The major signal transduction pathway involved in KC induction requires the generation of low levels of NO via constitutive nitric oxide synthase (cNOS) activity, leading to activation of guanylate cyclase and the cGMP-dependent kinase pathway. NO therefore appears to provide a common link between the early influence of Lsh in regulating the expression of genes which mediate many pleiotropic effects, and the later production of NO as the final effector mechanism for kill. The recently cloned candidate for Lsh/Ity/Bcg, designated Nramp for Natural resistance associated macrophage protein, encodes a polytopic integral membrane protein that has structural features common to prokaryotic and eukaryotic transporters and includes a conserved binding-protein-dependent transport motif which may be involved in interaction with peripheral ATP-binding subunits. The N-terminal sequence also carries a proline/serine rich putative SH3 binding domain, consistent with a role for tyrosine kinases in regulating Nramp function. (ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of cAMP and cGMP in the mode of action of molt-inhibiting hormone (MIH) a neuropeptide which inhibits steroidogenesis in a crab

In crustaceans, production of molting hormones (or ecdysteroids) by the molting glands (Y-organs; YO), is under negative control exerted by a neuropeptide, the molt-inhibiting hormone (MIH). MIH of the crab Carcinus maenas inhibits in vitro steroidogenesis of basal (intermolt crab) or activated (premolt crab) YO. MIH inhibits secretion of the two ecdysteroids synthesized by crab YO, ecdysone (E) secreted throughout the molting cycle, and 25-deoxyecdysone (25dE), secreted during the premolt period. At a MIH concentration of 10(-8) M, E is reduced about 50% and 25dE 94%. Regardless of the molting stage, this inhibition of steroidogenesis is reversible, dose dependent and measurable after 5 min. On intermolt YO, MIH induced cGMP increase and 8BrcGMP mimics the effect of MIH: at this stage cGMP seems to be involved with MIH inhibition of steroidogenesis. On premolt YO MIH induced a transient increase of cAMP (2-fold) and a long-lasting enhancement of cGMP (60-fold). On active YO, we demonstrated that a low concentration (10(-5) M) of dbcAMP, 8BrcAMP, 8BrcGMP, or agents increasing intracellular cAMP, mimic MIH effects and inhibit steroidogenesis. From these observations it is concluded that both cyclic nucleotides are involved in the mode of action of MIH on activated YO. At this premolt period, MIH/cAMP may act cooperatively with MIH/cGMP in the inhibitory control of steroidogenesis by crab YO.

Involvement of cyclic AMP and nitric oxide in immunoglobulin E-dependent activation of Fc epsilon RII/CD23+ normal human keratinocytes

Epidermal keratinocytes (EK) are exposed to multiple inflammatory stimuli and paracrine factors secreted by various dermal cells (lymphocytes, mast cells, macrophages, fibroblasts) during wounding, cutaneous allergy, and infections. We have previously demonstrated that after stimulation with interleukin 4 or interferon-gamma, human EK express the low-affinity receptor for IgE (Fc epsilon RII/CD23) on their surface. In the present study, we showed that the ligation of CD23 by IgE/anti-IgE immune complexes or specific monoclonal antibody induces a dose-dependent release of interleukin 6 and tumor necrosis factor-alpha from EK. CD23-ligation activates the nitric oxide-dependent pathway, as demonstrated by the high levels of nitrites released in cell supernatants, and the accumulation of intracellular cyclic nucleotides in EK. These second messengers are required for IgE-dependent stimulation of cytokine production by these cells, inasmuch as this is completely abolished by the use of cAMP or nitric oxide synthase antagonists. Human epithelial keratinocytes may thus participate in IgE-mediated immune responses, through their ability to express functional CD23 antigen.

Induction of early-response genes KC and JE by mycobacterial lipoarabinomannans: regulation of KC expression in murine macrophages by Lsh/Ity/Bcg (candidate Nramp)

The murine chromosome 1 gene Lsh/Ity/Bcg (candidate Nramp) regulates macrophage activation for antimicrobial activity against Salmonella typhimurium, Leishmania donovani, and Mycobacterium spp. To determine early events in the activation pathway, the ability of mycobacterial lipoarabinomannan (LAM) to induce early gene (KC and JE) expression in macrophages from susceptible (S) C57BL/10ScSn (Lshs) and congenic resistant (R) B10.L-Lshr mice was investigated. Stimulation with 1.8 microgram of arabinofuranosyl-terminated LAM (AraLAM) per ml resulted in similar kinetics for KC or JE expression in S and R macrophages. However, whereas JE/glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA ratios remained equivalent, R macrophages consistently showed enhanced KC/GAPDH ratios within 30 to 40 min of stimulation compared with S macrophages. Significant differences in KC/GAPDH ratios were observed throughout the peak period (0.5 to 6 h) of the KC response and with doses of AraLAM ranging from 0.01 to 2.5 micrograms/ml. Heavily mannosylated LAM from virulent Mycobacterium tuberculosis Erdman, in doses of up to 2.5 micrograms/ml, failed to stimulate KC or JE in S or R macrophages. Gamma interferon alone (25 U/ml) stimulated equivalent JE expression in S and R macrophages and synergized with AraLAM to enhance JE in both. In contrast, AraLAM-induced KC expression was inhibited in the presence of gamma interferon. Agonist/inhibitor studies were undertaken to determine the signal transduction pathways mediating KC expression. The protein kinase C (PKC) inhibitor Calphostin C (200 nM) inhibited AraLAM-induced KC by 34% +/- 4% in S macrophages and 43% +/- 5% in R macrophages; the cyclic AMP-dependent PKA inhibitor KT5720 (2 microM) inhibited AraLAM-induced KC by 33% +/- 4% (S) and 25% +/- 5% (R). A role for Ca2+ was indicated because ionophore alone stimulated KC expression and synergized with AraLAM to give a dramatically enhanced response. Induction of KC was also inhibited by (i) blocking constitutive nitric oxide (NO) production by preincubation of macrophages with NG-monomethyl-L-arginine (400 microM) (48% +/- 8% [S] and 40% +/- 11% [R]) and (ii) incubation of macrophages with the cyclic GMP-dependent kinase inhibitor KT5823 (4 microM) (65% +/- 4% [S] and 72% +/- 6% [R]). The manner in which these PKC-, PKA-, and Ca(2+)-dependent, NO-mediated cyclic GMP-dependent kinase signal transduction pathways may relate to function of the candidate Lsh/Ity/Bcg gene Nramp is discussed.

Endotoxin-induced nitric oxide synthesis in the perfused rat liver: effects of L-arginine and ammonium chloride

We used the single-pass-perfused rat liver model to study short-term regulation of endotoxin-inducible nitric oxide synthesis by following the release of nitrite and nitrate, the oxidation products of nitric oxide, into the effluent perfusate. In endotoxin-pretreated livers, the basal nitrite+nitrate release was 5.3 +/- 1.2 nmol.gm liver-1.min-1. Nitrite and nitrate release was stimulated by L-arginine in a dose-dependent and saturable fashion. Maximal nitrite+nitrate release with 1 mmol/L L-arginine infused to the influent perfusate was 10.2 +/- 1.1 nmol.gm liver-1.min-1, with a half-maximal effect at 53 mumol/L L-arginine. In the absence of molecular oxygen, nitric oxide synthesis was inhibited. Ammonium chloride infusion also stimulated nitrite and nitrate release to a maximal rate of 9.2 +/- 0.8 nmol.gm liver-1.min-1 with half-maximal effects at 60 mumol/L ammonium chloride. Ammonium chloride-stimulated nitrite and nitrate release was abolished when urea synthesis was inhibited by bicarbonate-free liver perfusion. Citrulline and ornithine (200 mumol/L each) were without effect on nitrite and nitrate release. L-Nitroarginine methyl ester inhibited both, L-arginine-and ammonium chloride-induced nitrite and nitrate release. Stimulation of nitric oxide synthesis by L-arginine and ammonium chloride addition (1 mmol/L each) was accompanied by a threefold-to-fourfold increase of cyclic GMP release into the effluent perfusate. In livers of endotoxin-pretreated rats the urea production from L-arginine was higher than that in untreated livers, suggesting induction of an L-arginine transport system in hepatocytes by endotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of inducible nitric oxide synthase by fibroblast growth factors and transforming growth factor beta in bovine retinal pigmented epithelial cells: inverse correlation with cellular proliferation

Bovine retinal pigmented epithelial (RPE) cells express, after activation with interferon gamma (IFN-gamma) and lipopolysaccharide (LPS), an inducible nitric oxide synthase (NOS). Experiments were done to investigate the effects of the transforming growth factor beta 1, epidermal growth factor, and fibroblast growth factors (FGFs), which are abundant in the retina, on NOS activity. Transforming growth factor beta 1 slightly increases the production of nitrite, an oxidation product of NO, induced by LPS plus IFN-gamma, whereas acidic and basic FGFs markedly inhibit the nitrite release due to LPS/IFN-gamma in a concentration-dependent manner, and epidermal growth factor did not modify LPS/IFN-gamma-induced NOS activity. The growth factors alone did not stimulate nitrite release. We have attempted to elucidate the mechanism of FGF inhibition. Results with heparin, suramin, and tyrphostin suggest involvement of the high-affinity receptor for FGF in its inhibition of LPS/IFN-gamma-stimulated NOS activity. Continued stimulation of RPE cells with LPS/IFN-gamma was essential for the induction of NO synthesis, and maximal inhibition was obtained when FGF was present during stimulation with LPS/IFN-gamma, suggesting that FGF inhibits NOS induction. Furthermore, an antiproliferative action of NO was demonstrated by an inverse correlation between the amounts of nitrite or citrulline produced in response to different stimuli (LPS/IFN-gamma or LPS/IFN-gamma with growth factors) and the level of cellular proliferation. Similar inhibition of growth was obtained when RPE cells were incubated with an NO donor, sydnonimide. Because NO acts as a cytotoxic compound in the retina, FGF, by inhibiting the induction of NOS in RPE cells, may have beneficial effects in protecting the retina from cytokine and endotoxin-mediated tissue damage.

Phorbol esters induce nitric oxide synthase and increase arginine influx in cultured peritoneal macrophages

Incubation of peritoneal macrophages with beta-phorbol 12,13-dibutyrate promotes a time-dependent release of NO to the incubation medium. This effect was antagonized by LPS, a well known inducer of nitric oxide synthase (NOS) expression in macrophages, and was inhibited by NG-methyl-L-arginine and N omega-nitro-L-arginine. An increase in intracellular cGMP and NOS activity was observed in parallel with NO release. The induction of NOS was accompanied by a stimulation of arginine influx within the cell. These results suggest that activation of protein kinase C by phorbol esters is sufficient to promote NOS induction in macrophages.

Cytokines, endotoxin, and glucocorticoids regulate the expression of inducible nitric oxide synthase in hepatocytes

Nitric oxide (NO.) is a short-lived mediator which can be induced in a variety of cell types and produces many physiologic and metabolic changes in target cells. The inducible or high-output NO. synthase (NOS) pathway was first characterized in macrophages activated by lipopolysaccharide (LPS) and interferon gamma (IFN-gamma). Hepatocytes also express an inducible NOS following exposure to the combination of endotoxin (LPS) and tumor necrosis factor (TNF), interleukin 1 (IL-1), and IFN-gamma. In this study, to identify which of these cytokines, if any, was acting to induce the gene expression for hepatocyte NOS, we measured the levels of rat hepatocyte NOS mRNA by Northern blot analysis after stimulation by various combinations of endotoxin and cytokines in vitro. We found the mRNA for hepatocyte NOS to be a single band at approximately 4.5 kilobases which was maximally up-regulated (approximately 70-fold) by the combination of TNF, IL-1, IFN-gamma, and LPS. Abundance of NOS mRNA peaked 6-8 hr after stimulation and then declined by 25% at 24 hr. Unstimulated hepatocytes in vitro showed only a trace mRNA band after prolonged autoradiographic exposure. As single agents, TNF and IL-1 were the most effective inducers of hepatocyte NOS mRNA. Combinations of two or three stimuli revealed strong synergy between TNF, IL-1, and IFN-gamma. The increased mRNA levels correlated with elevated nitrogen oxide release and cGMP levels in the culture supernatants. Dexamethasone and cycloheximide inhibited induction of mRNA for hepatocyte NOS in a dose-dependent fashion. The addition of NG-monomethyl-L-arginine had no effect on mRNA levels but effectively blocked NO. formation. The inducible hepatocyte NOS mRNA was also detected in rat hepatocytes following chronic hepatic inflammation triggered by Corynebacterium parvum injection in vivo. These data demonstrate that the inducible NOS is functional in rat hepatocytes both in vitro and in vivo and that this pathway is under complex control. Endotoxin and inflammatory cytokines act synergistically to up-regulate gene expression for hepatocyte NOS, whereas glucocorticoids down-regulate the mRNA.

Oxidation of nitric oxide by oxygen in biological systems monitored by porphyrinic sensor

A porphyrinic sensor was used to monitor the reaction of nitric oxide (NO) with oxygen. In the absence of biological material, the reaction rate is independent of the initial concentration of NO (zero order) and depends only on O2 concentration (first order). At physiologic concentration of NO and O2, the half-life of nitric oxide is in order of minutes and decreased to seconds only in the presence of biological material (intact cells).