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Query: UNIPROT:P43026 (lipopolysaccharide)
 62,215 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Bacterial lipopolysaccharide (LPS) and a diverse array of other immunostimulants and cytokines suppress the metabolism of endogenous and exogenous substances by reducing activity of the hepatic cytochrome P450 mixed-function oxidase system. Although this effect of immunostimulants was first described almost 40 yr ago, the mechanism is obscure. Immunostimulants are now known to cause NO overproduction by cells via induction of nitric oxide synthase. We have investigated whether NO overproduction is involved in suppressing hepatic metabolism by LPS. In vitro treatment of hepatic microsomes with NO, produced by chemical decomposition of 3-morpholinosydnonimine or by nitric oxide synthase, substantially suppressed cytochrome P450-dependent oxygenation reactions. This effect of NO was seen with hepatic microsomes prepared from two species (rat and chicken) and after exposure to chemicals that induce distinct molecular isoforms of cytochromes P450 (beta-naphthoflavone, 3-methylcholanthrene, and phenobarbital). Spectral studies indicate that NO reacts in vitro with both Fe(2+)- and Fe(3+)-hemes in microsomal cytochromes P450. In vivo, LPS diminished the phenobarbital-induced dealkylation of 7-pentoxyresorufin by rat liver microsomes and reduced the apparent P450 content as measured by CO binding. These LPS effects were associated with induction of NO synthesis; LPS-induced NO synthesis showed a strong positive correlation with the severity of cytochrome P450 inhibition. The decrease in both hepatic microsomal P450 activity and CO binding caused by LPS was largely prevented by the selective NO synthase inhibitor N omega-nitro-L-arginine methyl ester. Our findings implicate NO over-production as a major factor mediating the suppression of hepatic metabolism by immunostimulants such as LPS.
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PMID:Nitric oxide is a mediator of the decrease in cytochrome P450-dependent metabolism caused by immunostimulants. 750 96

Nitric oxide (NO) may mediate the hypotension of septic shock, but the effect of endotoxin on inducible NO synthase (iNOS) mRNA expression remains unclear. We studied the effects of lipopolysaccharide (LPS) treatment in vivo on iNOS mRNA expression using reverse transcription and polymerase chain reaction. The iNOS mRNA was absent or negligible in any tissue studied from control rats, but was markedly increased in lung, liver, spleen, skeletal muscle and kidney from LPS-treated rats. The LPS-induced increase in iNOS mRNA was prevented by dexamethasone. Our results indicate that LPS treatment in vivo induces the expression of an iNOS mRNA via a dexamethasone-sensitive mechanism, and thus provide direct molecular evidence for the involvement of NO in septic shock.
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PMID:Lipopolysaccharide treatment in vivo induces widespread tissue expression of inducible nitric oxide synthase mRNA. 750 69

Biosynthesis of nitric oxide (NO) from L-arginine modulates activity of iron-dependent enzymes, including mitochondrial acontiase, an [Fe-S] protein. We examined the effect of NO on the activity of iron regulatory factor (IRF), a cytoplasmic protein which modulates both ferritin mRNA translation and transferrin receptor mRNA stability by binding to specific mRNA sequences called iron responsive elements (IREs). Murine macrophages were activated with interferon-gamma and lipopolysaccharide to induce NO synthase activity and cultured in the presence or absence of NG-substituted analogues of L-arginine which served as selective inhibitors of NO synthesis. Measurement of the nitrite concentration in the culture medium was taken as an index of NO production. Mitochondria-free cytosols were then prepared and aconitase activity as well as IRE binding activity and induction of IRE binding activity were correlated and depended on NO synthesis after IFN-gamma and/or LPS stimulation. Authentic NO gas as well as the NO-generating compound 3-morpholinosydnonimine (SIN-1) also conversely modulated aconitase and IRE binding activities of purified recombinant IRF. These results provide evidence that endogenously produced NO may modulate the post-transcriptional regulation of genes involved in iron homeostasis and support the hypothesis that the [Fe-S] cluster of IRF mediates iron-dependent regulation.
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PMID:Biosynthesis of nitric oxide activates iron regulatory factor in macrophages. 750 26

We have examined the induction of nitric oxide synthase (NOS) activity in the rat astrocyte-derived C6 glioma cell line. In contrast to the previous results with primary astrocyte cultures, incubation of C6 cells with bacterial endotoxin lipopolysaccharide (LPS; 1 microgram/ml for 24 h) did not stimulate NO2 production. However, addition of either tumor necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma), cytokines that by themselves had no effect on NOS activity, imparted LPS responsiveness onto these cells in a dose-dependent manner (EC50 values of 39 ng/ml of TNF-alpha and 9.4 U/ml of IFN-gamma), and the effect of TNF-alpha could be further potentiated (twofold) by the presence of interleukin-1 beta. The simultaneous presence of TNF-alpha and IFN-gamma yielded a greater response than either cytokine alone; however, the respective EC50 values were not affected. A cytoplasmic extract from induced C6 cells catalyzed the Ca(2+)-independent conversion of L-arginine to L-citrulline, with an apparent Km of 51.2 microM, and this activity could be blocked by L-arginine analogues in the potency order amino > methyl > nitroarginine. Immunoblot analysis revealed an apparent molecular mass of 125 kDa for the NOS protein induced in C6 cells. These results indicate that the combination of LPS plus cytokines can induce NOS activity in C6 glioma cells with properties similar to those of the enzyme expressed in primary astrocyte cultures.
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PMID:Induction of nitric oxide synthase in rat C6 glioma cells. 750 14

NO synthase (NOS) is a unique P-450-type enzyme containing both a reductase and a heme domain on a single polypeptide. We show that ebselen [Ebs, 2-phenyl-1,2-benzisoselenazol-3-(2H) one], a nontoxic selenoorganic compound known to break a cysteine thiolate/Fe bond of some of P-450 enzymes, is a relatively selective inhibitor of endothelial isoform of NOS. In rings of rabbit aorta, Ebs irreversibly blocked both the basal as well as acetylcholine- or calcium ionophore A23187-stimulated release of nitric oxide with an IC50 of 6 microM. In homogenates of bovine aortic endothelial cells, Ebs inhibited the activity of NOS, assayed by monitoring conversion of L-[2,3-3H]arginine to L-[2,3-3H]citrulline, with an IC50 of 8.5 microM. The inhibitory action of Ebs was prevented by glutathione, N-acetyl-L-cysteine or dithiothreitol (30-500 microM). The prevention by thiols of Ebs-induced inhibition of NOS suggests that these are competing with a thiol group of NOS that is essential for the catalytic activity of the enzyme. The consequence of the presence of thiols is the "trapping" of Ebs in the form of inactive selenyl sulfides. Consistent with the proposed mechanism of action of Ebs is lack of activity of diselenide of Ebs, which also demonstrates that the action of Ebs is independent of its glutathione peroxidase-like activity. In comparison to endothelial preparations, IC50 values of Ebs for inhibition of soluble isoforms of NOS present in homogenates of porcine cerebellum and of spleens obtained from lipopolysaccharide-treated rats were more than 30-fold higher.
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PMID:Inhibition of endothelial nitric oxide synthase by ebselen. Prevention by thiols suggests the inactivation by ebselen of a critical thiol essential for the catalytic activity of nitric oxide synthase. 750 26

Recent demonstration of cytokine-inducible production of nitric oxide (NO) in vascular smooth muscle cells (VSMC) from rat aorta has implicated VSMC-derived NO as a key mediator of hypotension in septic shock. Our studies to determine whether an inducible NO pathway exists in human VSMC have revealed a novel cytokine-inducible, NO-independent pathway of guanylate cyclase activation in VSMC from human saphenous vein (HSVSMC). Interleukin 1 (IL-1), tumor necrosis factor (TNF), interferon gamma (IFN-gamma) and Escherichia coli lipopolysaccharide (LPS) increased cGMP at 24 h, whereas IL-2 and IL-6 were ineffective. The effect of IL-1 on cyclic guanosine 3',5'-monophosphate (cGMP) was delayed, occurring after 6 h of exposure, and was maximal after 10 h. Methylene blue and LY83583 reversed the IL-1-induced increase in cGMP, suggesting that it was mediated by activation of soluble guanylate cyclase. However, IL-1-induced cGMP in HSVSMC was not inhibited by extracellular hemoglobin. Also, the effect of IL-1 on cGMP was not reversed by nitro- or methyl-substituted L-arginine analogs, aminoguanidine, or diphenyleneiodonium, all of which inhibit IL-1-induced NO synthase in rat aortic VSMC (RAVSMC). IL-1-induced cGMP in HSVSMC was also independent of tetrahydrobiopterin and extracellular L-arginine, as it was not affected by 2,4-diamino-6-hydroxyprytimidine, an inhibitor of tetrahydrobiopterin biosynthesis, and was similar in L-arginine-free and L-arginine-containing media. Analysis of NO synthase mRNA with the use of polymerase chain reaction indicates that levels of mRNA for inducible NO synthase are several orders of magnitude lower in IL-1-treated human HSVSMC than in IL-1-treated RAVSMC. IL-1-induced cGMP was also NO independent in human umbilical artery VSMC, and NO dependent in rat vena cava VSMC. Together these results indicate that IL-1 activates a novel NO-independent pathway of soluble guanylate cyclase activation in human VSMC.
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PMID:Interleukin 1 activates soluble guanylate cyclase in human vascular smooth muscle cells through a novel nitric oxide-independent pathway. 750 3

The effect of cloricromene, a coumarin derivative, was investigated on the lipopolysaccharide-stimulated nitric oxide (NO) synthase induction in intact aortas from endotoxin shocked rats and in the murine macrophage cell line J774. Rings of thoracic aortas from lipopolysaccharide (4 mg/kg, i.v.)-shocked rats, contracted with phenylephrine, showed a progressive decrease in tone, that was of a greater magnitude than that of aortas from naive rats. Moreover, a decreased response to the constrictor effect of phenylephrine was observed in aortas from shocked rats. In vivo treatment with cloricromene (2 mg/kg, i.v.) 30 min before lipopolysaccharide administration partially prevented the loss in tone of aortic rings and improved their reactivity to phenylephrine. Murine J774 macrophages activated with lipopolysaccharide (100 ng/ml) produced significant amounts of nitrites (NO2-; 28.2 +/- 3.5 nmol/10(6) cells per 24 h). Cloricromene (2, 20 or 200 microM) added to the cells concomitantly with lipopolysaccharide inhibited NO2- production in a concentration-dependent manner. Maximum inhibition (84.0 +/- 8.0%) was observed when cloricromene (200 microM) was added to the cells 6 h before lipopolysaccharide, whereas it was ineffective when given 6 h after endotoxin. These results demonstrate that cloricromene inhibits the expression but not the activity of the inducible NO synthase.
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PMID:Cloricromene inhibits the induction of nitric oxide synthase. 750 14

An enhanced formation of nitric oxide (NO) due to induction of a calcium-independent (inducible) NO synthase (iNOS) contributes importantly to the cardiovascular failure caused by bacterial endotoxin. Repeated challenges with small doses of endotoxin result in tolerance to both peripheral vascular failure and death caused by subsequent injection of a higher dose of endotoxin. Here we investigate whether tolerance to endotoxin is associated with a lack of induction of iNOS in vivo and whether endogenous glucocorticoids play a role in the development of endotoxin tolerance. In anesthetized rats, i.v. administration of Escherichia coli endotoxin [lipopolysaccharide (LPS); 2 mg.kg-1] resulted in a prolonged decrease in mean arterial blood pressure (MAP) and hyporeactivity to the contractile responses elicited by norepinephrine (NE; 10 nM) in aortic rings ex vivo. Hyporeactivity to NE was partially reversed by NG-nitro-L-arginine methyl ester (0.3 mM) in vitro, suggesting that an enhanced formation of NO contributes to this hyporeactivity. There was a substantial increase in the activity of iNOS in the lung 3 h after i.v. injection of LPS (0.2 +/- 0.1 to 6.6 +/- 0.6 pmol.mg-1.min-1; n = 5; P < 0.01). Rats injected i.p. with LPS (0.5 mg.kg-1) for 4 consecutive days became tolerant to an i.v. injection of LPS (2 mg.kg-1) in that both hypotension and vascular hyporeactivity to NE were significantly attenuated. Moreover, in these endotoxin-tolerant rats, the induction of iNOS by LPS in the lung was attenuated by 63% +/- 6%. Injection of LPS caused a 9-fold increase in plasma corticosterone (CCS) levels within 2 h and CCS levels remained significantly elevated 6 and 24 h after LPS. Animals rendered tolerant to endotoxin by administration of a low dose of LPS (0.5 mg.kg-1, i.p.) for 4 days still had a 6-fold increase in plasma CCS levels 24 h after the last injection of LPS. When endotoxin-tolerant rats were treated with the glucocorticoid receptor antagonist RU 486 (50 mg.kg-1, p.o. 3 h prior to LPS), there was a restoration of the effects of LPS (2 mg.kg-1, i.v.) in causing hypotension, vascular hyporeactivity to NE, and iNOS induction in the lung. However, in control rats RU 486 enhanced neither the decrease in MAP nor the induction of iNOS in response to LPS (2 mg.kg-1, i.v.). Thus, cardiovascular tolerance to endotoxin is accompanied and explained by reduced induction of iNOS in vivo due to the elevation of endogenous glucocorticoid levels.
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PMID:Attenuation of the induction of nitric oxide synthase by endogenous glucocorticoids accounts for endotoxin tolerance in vivo. 750 16

Nitric oxide (NO) is a potent mediator involved in many biological functions including inflammation and non-specific immunity. Murine macrophages possess the prototype of high-output NO synthase which is not constitutively expressed but induced within a few hours by immunological stimuli. In this study, we explored the possibility of controlling the activity of the inducible NO synthase by interfering with the transduction signal which triggers its induction, in the RAW 264.7 macrophage cell line. We found that nicotinamide, an inhibitor of ADP-ribosylation, prevented NO synthase induction in RAW 264.7 cells after stimulation with interferon gamma (IFN-gamma) and lipopolysaccharide (LPS). Furthermore, the level of NO synthase mRNA was measured by Northern-blot analysis and we found that nicotinamide prevents expression of NO synthase mRNA in IFN-gamma- and LPS-stimulated cells. Nicotinamide was also found to inhibit other macrophage functions expressed in response to IFN-gamma, i.e. tumour necrosis factor secretion and the expression of the Ia antigen of the major histocompatibility complex. Analysis of the pattern of ADP-ribosylated proteins revealed that nicotinamide as well as cholera toxin prevented the ADP-ribosylation of a 107-117 kDa protein found constitutively ADP-ribosylated in stimulated and non-stimulated macrophage extracts. Together, our results indicate ADP-ribosylation as a crucial point of the signalling pathway which leads to NO synthase mRNA induction.
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PMID:Nicotinamide inhibits nitric oxide synthase mRNA induction in activated macrophages. 750 33

In macrophages and other cell types, bacterial lipopolysaccharide and certain cytokines stimulate nitric oxide (NO) production via expression of the inducible isoform of nitric oxide synthase (NOS). Citrulline, which is the coproduct of NOS-catalyzed metabolism of arginine, can be recycled to arginine by the action of argininosuccinate synthetase and argininosuccinate lyase, which are present at high levels in hepatocytes and renal tubular cells but normally at very low levels in other cell types such as macrophages. The present study demonstrates that lipopolysaccharide and interferon-gamma, which induce NOS in the murine macrophage cell line RAW 264.7, also coinduce activity and mRNA for argininosuccinate synthetase, which is limiting for arginine synthesis. Argininosuccinate lyase activity and mRNA abundance are unaffected. Induction of argininosuccinate synthetase is not blocked by NG-monomethyl-L-arginine, a potent inhibitor of NOS, indicating that argininosuccinate synthetase induction is not the consequence of depleting cellular arginine levels by NOS. Because plasma levels of arginine are limiting for NO synthesis, enhanced cellular capacity to regenerate arginine from citrulline could play a significant role in regulating NO production, especially under conditions where the inducible isoform of NOS is expressed.
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PMID:Coinduction of nitric oxide synthase and argininosuccinate synthetase in a murine macrophage cell line. Implications for regulation of nitric oxide production. 750 6


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