Electron paramagnetic resonance investigations of nitrosyl complex formation during endotoxin tolerance

Effect of acute endotoxin tolerance on NO production by isolated hepatic parenchymal and nonparenchymal cells and alveolar macrophages in rats

The changes in NO production induced by endotoxin (LPS) tolerance are controversial. The aim of this study was to explore modulation of NO production by LPS tolerance in different liver cell types and alveolar macrophages. Such cells were studied in three groups of male Sprague Dawley rats: non-tolerant rats (sal-LPS) received saline or no treatment 48 h before a 3 mg/kg LPS injection, tolerant rats received low dose LPS (0.5 mg/kg) 48 h before a second injection of saline (LPS-sal) or LPS 3 mg/kg (LPS-LPS). All injections were delivered i.v. Animals were studied 1 and 6 h after the second injection. NO production (assessed by nitrite release) by hepatocytes, Kupffer cells, endothelial cells and alveolar macrophages was simultaneously determined after 20 h of culture in the presence or in the absence of LPS, interferon-y (IFN) or both. Basal NO production by hepatocytes of tolerant and nontolerant LPS injected rats was high 1 h after the second injection, and was dramatically reduced 6 h after the second injection. Hepatocytes of tolerized LPSinjected (LPS-LPS) rats were significantly less sensitive to in vitro stimulation by LPS and IFN at 1 h than hepatocytes of tolerized saline-injected rats and this difference disappeared by 6 h. In Kupffer cells of tolerant rats 6 h after the second LPS injection, basal NO generation was significantly less than in nontolerant rats. In both cell types of tolerant LPS-LPS rats, in vitro stimulated NO production was moderately upregulated at 1 h and then highly upregulated at 6 h, whereas in nontolerant (sal-LPS) animals, stimulated NO production was only slightly upregulated or not at all. Sensitivity to LPS and IFN stimulation of Kupper cells of LPS-LPS rats was not different from Kupffer cells of LPS-sal rats at 1 h, but became significantly higher at 6 h relative to both LPS-sal and sal-LPS animals. In endothelial cells of tolerant saline-injected (LPS-sal) rats, basal NO production was significantly less than in the sal-LPS group both at 1 and 6 h after the second injection. In endothelial cells of tolerant LPS-LPS animals, a significant upregulation of stimulated NO production higher than in the other groups was observed only at 1 h. No difference was evident in basal or stimulated NO production by alveolar macrophages of the different treatment groups, except for a significant increase in basal NO production in tolerant rats (LPS-LPS) at 6 h relative to 1 h after the second LPS injection.

Recent advances in the identification of a 1- and a 2-adrenoceptor subtypes: therapeutic implications

The cloning of multiple subtypes of both alpha1- and alpha2-adrenoceptors has renewed interest in the therapeutic application of agents interacting with these receptors. Effort has primarily been directed towards the design of uroselective alpha1-adrenoceptor antagonists for the treatment of benign prostatic hyperplasia (BPH). Evidence is accumulating for the involvement of a novel alpha1-adrenoceptor, designated as alpha1L-adrenoceptor, in alpha1-adrenoceptor-mediated smooth muscle contraction in prostatic and other urogenital tissues. While several antagonists showing a high degree of uroselectivity in animal models have been identified, their clinical superiority over the currently available alpha1-adrenoceptor antagonists has not yet been demonstrated. It is possible that the interaction with alpha1-adrenoceptors, as yet uncharacterised subtypes, at non-prostatic sites contributes to the therapeutic activity of this drug class in BPH. The alpha1-adrenoceptor subtypes involved in the control of vascular tone are currently being evaluated, and the profile of interaction with the various alpha1-adrenoceptor subtypes may play a key role in the efficacy of cardiovascular drugs such as carvedilol. Alpha2-adrenoceptor agonists are now being employed for a variety of therapeutic applications, most involving actions on receptors within the central nervous system (CNS). These agents are useful in the treatment of hypertension, glaucoma, opiate withdrawal and attention deficit hyperactivity disorder (ADHD), and as analgesics and adjuncts to general anaesthesia. While subtype selectivity has not yet been applied to the design of new alpha2-adrenoceptor agonists for these applications, recent gene mutation/knock-out experiments have identified the alpha2-subtypes involved in some of these actions, and optimisation of a therapeutic profile may be possible. Furthermore, the design of agents combining affinities for multiple adrenoceptor subtypes, or the combination of a specific adrenoceptor affinity profile with another pharmacological action, may offer advantages over molecules selective for an individual adrenoceptor subtype.

Selective delivery of nitric oxide to a cellular target: a pseudosubstrate-coupled dinitrosyl-iron complex inhibits the enteroviral protease 2A

Nitric oxide (NO) regulates multiple biological processes. To use NO as a potential therapeutic substance, a more selective modulation of individual NO targets is desirable. Here, we tested whether peptide conjugation of the dinitrosyl-iron complex (DNIC), a potent NO donor, confers targeted NO delivery. As target, we used the protease 2A of Coxsackie-B-viruses (2A(pro)), which can cause dilated cardiomyopathy. Through S-nitrosylation, NO inhibits this protease, which is essential for viral replication. The tetrapeptide Leu-Ser-Thr-Cys (LSTC) (based on the 2A(pro) substrate recognition motif) and DNIC generated LSTC-DNIC in vitro by S-nitrosylation as evidenced by reverse-phase chromatography. In vitro, LSTC-DNIC (IC(50) 510 nM) dose-dependently inhibited purified 2A(pro) 4.7-fold more effectively than DNIC (IC(50) 2.4 microM), whereas LSTC alone had no effect. In intact cells, expression of Coxsackievirus protease 2A by transient transfection led to eIF4G-I-cleavage. LSTC-DNIC (IC(50) 23 microM) dose-dependently inhibited eIF4G cleavage in 2A(pro)-transfected cells 3.8-fold more effectively than DNIC (IC(50) 88 microM). To test the specificity of the DNIC-conjugated LSTC peptide part, we investigated its influence on Caspase-3, a known target for S-nitrosylation. LSTC-DNIC and DNIC inhibited purified Caspase-3 in vitro (IC(50) 3.7 microM) and in intact cells similarly. LSTC conjugation of DNIC enhances its fidelity for inhibition of 2A(pro) in vitro and intracellularly. Peptide-DNIC may be useful to selectively modulate cellular processes by NO, i.e., to enhance its antiviral properties.

Lipopolysaccharide tolerance and ethanol modulate hepatic nitric oxide production in a gender-dependent manner

This study was directed at the role of tolerance to endotoxin (lipopolysaccharide, LPS) and ethanol (EtOH) intoxication in modulating hepatic nitric oxide (NO) production, and the demonstration of gender differences. Previous studies demonstrated that tolerance to either LPS or EtOH was associated with reduced hepatic production of superoxide anions. We now tested the hypothesis that the reduced hepatic production of superoxide anions during tolerance to LPS and the altered response to EtOH are accompanied by increased sensitivity of hepatic NO release to stimulation. Age-matched male and female Sprague-Dawley rats were made tolerant to LPS by an i.v. injection of LPS (0.5 or 0.45 mg/kg) 2 days prior to an in vivo EtOH infusion for 3 h (LPS-EtOH group). Control groups were saline-pretreated, saline-infused; saline-pretreated, EtOH-infused; and LPS-pretreated, saline-infused. At the end of the infusion, isolated hepatocytes, Kupffer, and sinusoidal endothelial cells were cultured for 20 h for subsequent measurement of basal (spontaneous) and in vitro-stimulated nitrite release. LPS-tolerance resulted in significantly enhanced stimulated NO production by hepatocytes and Kupffer cells in both male and female rats. EtOH abolished this priming effect in hepatocytes from male, but not from female rats. The priming effect was markedly diminished by EtOH in Kupffer cells of female rats only. LPS-tolerance increased NO production by stimulated endothelial cells of males, and decreased NO production by cells of females. EtOH infusion did not influence NO production by endothelial cells from male rats and it reversed the LPS-tolerance-induced inhibition in females. These data demonstrate that modulation by LPS-tolerance of hepatic NO release in EtOH-treated rats leads to enhanced stimulated NO production, while hepatic superoxide anion release was previously shown to be reduced within the same time frame. Since NO is able to scavenge superoxide, the LPS-tolerance-induced alterations in the EtOH effects on NO production may have a potential significance in modulating - in a time-dependent manner - oxidative injury associated with LPS and acute EtOH intake.

Transfer of nitric oxide from the liver to erythrocytes--an ESR study using nitroglycerin-treated mice

Nitric oxide (NO) formation in the liver and blood of the mouse following intraperitoneal treatment with nitroglycerin (glycerol trinitrate, GTN) was determined using electron spin resonance (ESR) spectroscopy. ESR signals of heme-NO complexes were detected at maximum levels within 5 min in the liver, but increased to a maximum level about 15-30 min later in the blood. GTN is not metabolized to release NO in vitro in the blood of the mouse. The hepatic microsomes which showed the heme-NO complexes ESR signals were incubated with mouse erythrocytes, with the result that a hemoglobin-NO signal was obtained from the erythrocytes. The activities of microsomal cytochrome P-450, the hepatic level of glutathione, and the reduction rate of nitroxide radicals in the in vivo liver, measured using L-band ESR spectroscopy, were temporarily decreased following GTN administration. In conclusion, NO in the liver could be scavenged by circulating erythrocytes, which might minimize NO-induced liver damage.

Detection of nitrosyl-iron complexes by proton-electron-double-resonance imaging

The nitrogen monoxide radical (NO*) forms paramagnetic mono- and dinitrosyl-iron complexes in biologic tissues. To establish a noninvasive technique for in vivo NO* imaging, we evaluated the suitability of these complexes as magnetic resonance (MR) contrast agents, making use of the ability of the unpaired electrons of the complexes to enter into dynamic nuclear polarization with water protons and hence produce enhancement on images generated by the technique of proton-electron-double-resonance imaging (PEDRI). Phantom solutions of synthetic nitrosyl-iron complexes (NICs) altered the signal intensity of PEDRI images. The dinitrosyl-iron complex (DNIC) with serum albumin induced a significantly larger signal alteration than the mononitrosyl-iron complex (MNIC) with dithiocarbamate. Exposure of rat liver to sodium nitroprusside (SNP) by ex vivo and in situ perfusion induced a composite X-band electron spin resonance (ESR) spectrum of the isolated liver characteristic of a MNIC and DNIC. On storage of the tissue, the MNIC signal disappeared and the DNIC signal intensity increased. Correspondingly, in cross-sectional PEDRI images taken at room temperature, the SNP-exposed livers initially exhibited a weak signal that strongly increased with time. In conclusion, NICs can be detected using PEDRI and could be exploited for in vivo NO* imaging.

Continuous monitoring of in vivo nitric oxide formation using EPR analysis in biliary flow

A method to continuously monitor the nitric oxide (NO) level in anesthetized rats, using an in vivo trapping reaction of NO by iron-dithiocarbamate complex, is reported. Previously, we developed a method of monitoring NO in bile samples containing an NO complex excreted from the liver (Anal. Biochem. 243, 8-14, 1996). In the present study, we modified the method so that the bile flows directly through the EPR sample cell. Rats were injected with low doses of lipopolysaccharide (LPS) to induce NO formation and were later anesthetized. After cannulation, the bile duct was connected to the inlet of the EPR sample cell and the trapping agent iron complex of D-N-methylglucamine dithiocarbamate (MGD-Fe) was administered. The EPR signal level from NO complex of MGD-Fe in the flowing bile was continuously monitored. Using this method, immediate changes in in vivo NO level in rats were observed following administration of drugs that can affect NO formation. In addition, a continuous intravenous saline containing MGD-Fe made the EPR signal level stable and improved animal condition as well as survival time. Therefore, this method has two merits; (1) one can continuously monitor NO formation until it reaches the maximum level; (2) a rapid change in NO level after intervention can be followed. Using this method, we tested the effect of the substrate L-arginine and inhibitors for NO synthase activity and NO synthase induction. The sensitivity of the present method was tested by monitoring NO formation in rats after exposure to ionizing radiation.

Hyperdynamic circulation in patients with cirrhosis: direct measurement of nitric oxide levels in hepatic and portal veins

BACKGROUND/AIMS

Peripheral vasodilation represents the main vascular dysfunction associated with the hyperdynamic circulation of liver cirrhosis. This study was intended to measure directly regional and systemic levels of nitric oxide, a potent vasorelaxing mediator, in order to assess its role in the development of hemodynamic changes of cirrhosis.

METHODS

We compared nitric oxide levels in the splanchinic and systemic circulation of 25 patients with cirrhosis undergoing transjugular intrahepatic portosystemic stent shunt and in the hepatic vein and peripheral blood of 10 patients without cirrhosis submitted to venous catheterization. Nitric oxide levels were measured through electron paramagnetic resonance spectroscopy as nitrosylhemoglobin complexes.

RESULTS

Significantly higher nitric oxide levels were calculated in patients with cirrhosis with respect to controls, both in the peripheral and hepatic veins. In patients with cirrhosis, nitric oxide levels in the portal vein (3.44 +/- 2.17, expressed in arbitrary units) were higher than in the systemic circulation (1.89 +/- 1.15), but lower than in the hepatic vein (4.75 +/- 2.53; p < 0.001 by variance analysis).

CONCLUSIONS

These data suggest that nitric oxide synthetic pathway activity as well as nitric oxide release are enhanced at the level of splanchnic vasculature and, more important, in the hepatic tissue, confirming evidence of the predominant role of nitric oxide in the pathogenesis of hemodynamic changes in patients with cirrhosis with portal hypertension.

Tolerance to lipopolysaccharide-induced increase in vascular permeability in mouse skin

We investigated whether tolerance develops to the lipopolysaccharide-induced increase in vascular permeability of mouse skin on pretreatment with Salmonella typhimurium lipopolysaccharide. Lipopolysaccharide-induced plasma extravasation was assessed by determining Pontamine sky blue dye accumulation in the skin where lipopolysaccharide was injected s.c. 2 h previously. When mice were pretreated with lipopolysaccharide (0.15 mg/kg i.p.), the dye leakage induced by s.c. challenge with lipopolysaccharide (400 micrograms/site) was significantly, inhibited for 2-24 h after pretreatment, indicating the development of lipopolysaccharide tolerance. At 4 h after lipopolysaccharide (0.15 mg/kg i.p.), the dose-response curve of dye leakage against the challenge dose of lipopolysaccharide shifted about 2-fold to the higher dose. The dye leakage induced by lipopolysaccharide was inhibited by pretreatment with lipopolysaccharide in a dose-dependent manner (0.05-0.15 mg/kg i.p.). Lipopolysaccharide tolerance was not seen in adrenalectomized mice. When mice were pretreated with lipopolysaccharide and NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, at the same time, the hyporesponsiveness to lipopolysaccharide challenge disappeared. However, L-NAME was ineffective to inhibit the development of lipopolysaccharide tolerance when administered 24 h after lipopolysaccharide pretreatment or just before the lipopolysaccharide challenge. Tumor necrosis factor-alpha and interleukin-1 alpha but not interleukin-6 induced a similar hyporesponsiveness to lipopolysaccharide. These results suggest that tolerance develops to the lipopolysaccharide-induced increase in vascular permeability in mouse skin after a single lipopolysaccharide administration and that endogenous glucocorticoids and NO are necessary for induction of lipopolysaccharide tolerance. Hyporesponsiveness induced by lipopolysaccharide pretreatment may be mediated by production of some cytokines such as tumor necrosis factor-alpha or interleukin-1 alpha.