Nitric oxide production in rheumatoid arthritis

Nitric oxide (NO), originally found as endothelium-derived relaxing factor (EDRF), is a free radical synthesized by NO synthases (NOS). Two isoforms exist in NOS,i.e. constitutive NOS (cNOS) and inducible NOS (iNOS). Inflammatory cytokines such as interleukin-1, interferon-γ, tumor necrosis factor-α induce iNOS expression in various cells including macrophages. Enhanced NO production is observed in arthritic conditions both in rodent models and human. The onset of arthritis in rodent models is significantly inhibited by the NOS inhibitor,N ^G-monomethyl-l-arginine. These data suggest a possible involvement of NO in the induction and/or maintenance of rheumatoid arthritis.     

Geranylgeranylacetone stimulates mucin synthesis in cultured guinea pig gastric pit cells by inducing a neuronal nitric oxide synthase

Nitric oxide (NO) has been considered to play an important role in the regulation of blood flow, mucosal integrity, and mucus production in the stomach. We investigated the stimulatory actions of epidermal growth factor (EGF) and a cytoprotective compound, geranylgeranylacetone (GGA), on mucin synthesis in guinea pig gastric pre-pit cells, maintained in a serum-free culture system. GGA increased [³H]glucosamine uptake and the accumulation of mucus granules positive for galactose oxidase-Schiff reaction in the cells. This stimulatory action of GGA was equivalent to that of EGF, but GGA did not stimulate the cell growth. Both EGF and GGA increased the release of NO degeneration products, NO₂ ⁻ and NO₃ ⁻. The [³H]glucosamine uptake was completely inhibited by the non-selective NO synthase (NOS) inhibitors, N ^G -nitro-l-arginine and N ^G -monomethyl-l-arginine, and it was only partially inhibited by a more selective inhibitor for inducible NOS isoform (iNOS), aminoguanidine. Northern blotting with a cDNA probe for rat iNOS, and Western blotting with a polyclonal antibody against iNOS, demonstrated that GGA did not up-regulate the iNOS mRNA expression nor induce its protein. In contrast, GGA and EGF induced neuronal NOS, but not endothelial NOS, which was confirmed by immunoblot analyses with antibodies against these constitutive NOS isoforms. Thus, the present experiments suggests that GGA, as well as EGF, stimulates mucin synthesis at least in part through an NO-dependent pathway, leading to an increase in the integrity of the gastric mucosa. Received: September 7, 1999 / Accepted: March 24, 2000     

Intestinal nitric oxide synthase activity changes during experimental colon obstruction

Objective. The experiments in this study were designed to follow the time course of nitric oxide (NO) synthesis in the large bowel during acute mechanical ileus. Material and methods. Occlusion of the mid-transverse colon was maintained for 420 min in anesthetized dogs. Strain-gauge transducers were used to analyze motility changes on the hepatic and lienal flexures, respectively. Constitutive NO synthase (cNOS) and inducible NOS (iNOS) activities were determined in tissue biopsies, and plasma nitrite/nitrate (NO_x) level was measured in the portal blood. Following completion of the baseline studies, the animals were treated with either 7-nitroindazole (7-NI, selective neuronal NOS inhibitor), or N-nitro-L-arginine (NNA, non-selective NOS inhibitor). Results. In the sham-operated group the cNOS activities differed significantly in the oral and aboral tissue samples (oral: 102.9; versus aboral: 62.1 fmol/mg protein/min). The obstruction elicited a significant increase in portal NO_x and elevated tissue inducible NO synthase (iNOS) activity. NNA treatment decreased the motility index in both intestinal segments for 60 min, but 120 min later the motility index was significantly elevated (2.5-fold increase in the oral part, and 1.8-fold enhancement in the aboral segment, respectively). Treatment with 7-NI decreased the cNOS activity in the oral and aboral parts by approximately 40% and 70%, respectively, and suppressed the motility increase in the aboral colon segment. Conclusions. The motility of the colon was either significantly increased or decreased, depending on the type and selectivity of the NOS inhibitor compounds applied. NO of neuronal origin is a transmitter that stimulates peristaltic activity; but an increased iNOS/nNOS ratio significantly moderates the obstruction-induced motility increase.     

The role of NOS in heart failure: lessons from murine genetic models

Nitric Oxide Synthases (NOSs) are a group of related proteins that produce nitric oxide (NO). In mammals, there are three known members of this gene family: nNOS (NOS1), iNOS (NOS2) and eNOS (NOS3). Each has been disrupted by targeted gene ablation in mice and the corresponding phenotypes examined. These mice have allowed an examination of the contribution of each NOS in a variety of experimental models and continue to provided insights into the patho-physiological role of NOS and NO. With increasing sophistication, murine transgenic approaches continue to offer a wealth of information, and invaluable tools to further study the NOS system. The focus of this review will be an examination of the tools available, and the insights gained from studies done on murine NOS genetic models in the context of heart failure.     

Endothelial,but not the inducible,nitric oxide synthase is detectable in normal and portal hypertensive rats

Abstract: Background: Chronic portal hypertension is accompanied by a nitric oxide (NO) dependent vasodilation. Three isoforms of NO producing synthases (NOS) are characterized: neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS). Sources of increased NO levels in chronic hypertension is disputed. Methods: To determine eNOS and iNOS expression in different organs of portal hypertensive and control rats, we divided Sprague-Dawley rats in 6 groups: (1) Partial portal vein ligated rats, (2) Bile duct ligated rats, (3) Carbon tetrachloride treated rats, (4) Sham operated rats, (5) Untreated control rats, and (6) LPS treated rats. Immunohistochemistry (IHC) and immunoblotting (IB) using antibodies against eNOS or iNOS were carried out on samples from thymus, aorta, heart, lung, oesophagus, liver, spleen, kidney, pancreas, small and large intestine. Results: IHC revealed an even eNOS expression in all groups. Expression of iNOS was restricted to macrophages in organs of LPS treated and the thymus of rats. IB mirrored these results. Conclusion: In chronic portal hypertension, the main source for NO production depends on eNOS activity.     

Dynamic involvement of the inducible type of nitric oxide synthase in acid-induced duodenal mucosal alkaline secretion in the rat

It has previously been shown that mucosal nitric oxide synthase (NOS) is involved in acid-induced duodenal mucosal alkaline secretion. The primary aim of the present study was to elucidate which isoform of NOS is responsible in rats. Immunohistochemistry showed that inducible NOS (iNOS) was constitutively expressed in villous epithelial cells. Exposing the duodenal mucosa to 10 mM HCl resulted in an increased duodenal mucosal alkaline secretion. This response was totally inhibited by intraluminal administration of a selective inhibitor of iNOS (l-N ⁶-1-iminoethyl-lysine). One hour after the acid exposure, western blot technique showed a marked increase in mucosal iNOS expression. A second acid exposure resulted in a further stimulation of alkaline secretion. These data suggest that exposure of the duodenal mucosa to HCl initiates an increased mucosal alkaline secretion, via NO synthesis mediated by iNOS located in the epithelial cells of the villi. In addition, luminal acid stimulates expression of iNOS.     

Pathogenic Role of Endothelial Nitric Oxide Synthase (eNOS/NOS-III) in Cerulein-Induced Rat Acute Pancreatitis

Nitric oxide (NO) is a potent pancreatic vasodilator, yet the pathogenic role of NO in acute pancreatitis remains controversial. NO is generated from L-arginine by NO synthase (NOS), classified into three isozymes: neuronal (nNOS), inducible (iNOS), and endothelial NOS (eNOS). The purpose of the present study was to investigate the role of NO/NOS isozymes in the pathogenesis of cerulein-induced acute pancreatitis in rats. Acute pancreatitis was induced in male Wistar rats by two subcutaneous injections of cerulein (20 μg/kg). N ^G-Nitro-L-arginine methyl ester (L-NAME: a nonselective NOS inhibitor) or aminoguanidine (a relatively selective iNOS inhibitor) was given orally, while tetrahydrobiopterin (BH₄), a critical cofactor for NOS, was administered intraperitoneally 30 min before the first cerulein injection. Cerulein given repeatedly twice produced acute pancreatitis, with concomitant increases in the serum amylase level, pancreas weight, myeloperoxidase activity, lipid peroxidation and microvascular permeability. Prior administration of L-NAME, but not aminoguanidine, significantly prevented these changes, in a dose-dependent manner, and this effect was antagonized by the coadministration of L-arginine, a precursor of NO. The expression of dimetric eNOS in the pancreas was markedly suppressed by cerulein injections, together with a decrease in NO production, but the response was partially but significantly reversed by the prior administration of BH₄. The increases in the serum amylase level and pancreas weight, as well as the lipid peroxidation induced by cerulein, were significantly attenuated by the administration of BH₄. L-NAME had no effect on pancreatic secretion induced by cerulein. These results suggest that the uncoupled eNOS, probably caused by the decrease in endogenous BH₄ availability, plays a deleterious role in the pathogenesis of cerulein-induced acute pancreatitis.     

Nitric oxide production during adjuvant-induced and collagen-induced arthritis

Objective. To investigate the role of nitric oxide (NO) production and NO synthase (NOS) induction during adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) in Dark Agouti rats. Methods. Urinary nitrate excretion and immune NOS (iNOS) messenger RNA (mRNA) expression were measured in the joint, lymph node, spleen, and liver tissues following the induction of either AIA or CIA. Results. Urinary nitrate excretion and iNOS mRNA expression increased substantially during joint inflammation in both models of arthritis. However, the increases in urinary nitrate excretion and iNOS mRNA expression observed in the joint, liver, and spleen tissues during AIA were greater than those observed during CIA, although iNOS induction in the lymph nodes was similar for both models. A prior injection with Mycobacterium bovis heat-shock protein resulted in suppression of arthritis and NO production in AIA, but not in CIA. Conclusion. Differences in NO production during AIA versus CIA are a reflection of the fundamental pathophysiologic differences between these 2 models of arthritis. Thus, NO production in these 2 models could not be merely a nonspecific reaction to the adjuvant injection, nor simply a byproduct of local inflammation in the joint.     

The role of nitric oxide in tissue destruction

Nitric oxide (NO) is synthesized via the oxidation of arginine by a family of nitric oxide synthases (NOS), which are either constitutive (ie. endothelial (ec)NOS and neuronal (nc)NOS) or inducible (iNOS). The production of nitric oxide plays a vital role in the regulation of physiological processes, host defence, inflammation and immunity. Pro-inflammatory effects include vasodilation, oedema, cytotoxicity and the mediation of cytokine-dependent processes that can lead to tissue destruction. Nitric oxide-dependent tissue injury has been implicated in a variety of rheumatic diseases, including systemic lupus erythematosus (SLE), rheumatoid arthritis and osteoarthritis. Conversely, the production of NO by endothelial cell NOS may serve a protective, or anti-inflammatory, function by preventing the adhesion and release of oxidants by activated neutrophils in the microvasculature. In this chapter we describe the multifaceted role of nitric oxide in inflammation and address the potential therapeutic implications of NOS inhibition.     

High red blood cell nitric oxide synthase activation is not associated with improved vascular function and red blood cell deformability in sickle cell anaemia

Human red blood cells (RBC) express an active and functional endothelial‐like nitric oxide (NO) synthase (RBC‐NOS). We report studies on RBC‐NOS activity in sickle cell anaemia (SCA), a genetic disease characterized by decreased RBC deformability and vascular dysfunction. Total RBC‐NOS content was not significantly different in SCA patients compared to healthy controls; however, using phosphorylated RBC‐NOS‐Ser¹¹⁷⁷ as a marker, RBC‐NOS activation was higher in SCA patients as a consequence of the greater activation of Akt (phosphorylated Akt‐Ser⁴⁷³). The higher RBC‐NOS activation in SCA led to higher levels of S‐nitrosylated α‐ and β‐spectrins, and greater RBC nitrite and nitrotyrosine levels compared to healthy controls. Plasma nitrite content was not different between the two groups. Laser Doppler flowmetric experiments demonstrated blunted microcirculatory NO‐dependent response under hyperthermia in SCA patients. RBC deformability, measured by ektacytometry, was reduced in SCA in contrast to healthy individuals, and pre‐shearing RBC in vitro did not improve deformability despite an increase of RBC‐NOS activation. RBC‐NOS activation is high in freshly drawn blood from SCA patients, resulting in high amounts of NO produced by RBC. However, this does not result in improved RBC deformability and vascular function: higher RBC‐NO is not sufficient to counterbalance the enhanced oxidative stress in SCA.     

Inducible nitric oxide synthase controls experimental Strongyloides infection

Infection with Strongyloides sp. induces a host immune response, predominantly the Th2 type, that is able to eliminate the parasite. However, little is known about the role of the nitric oxide (NO) mediator, induced by the enzyme nitric oxide synthase (NOS), in strongyloidiasis. Therefore, in this study, we investigated the immune response of mice genetically deficient in the enzyme inducible nitric oxide synthase (iNOS^?/?), infected with Strongyloides venezuelensis. C57BL/6 wild‐type (WT) and iNOS^?/? mice were individually inoculated by subcutaneous injection of 3000 S. venezuelensis L3 larvae. In the absence of iNOS, mice were more susceptible to the infection than WT animals, in which the parasite was completely eliminated. The overall production of cytokines and specific IgG, IgG1 or IgE antibodies against the parasite was significantly lowered in infected iNOS^?/? mice. The expression of iNOS was observed in the intestine of WT hosts but mainly in the wall of the parasite, despite the presence of iNOS in mice. Altogether, we concluded that iNOS expression may play an important role in the control of S. venezuelensis infection.     

Nitric oxide modulates hepatocyte growth factor/scatter factor-induced angiogenesis

Objective: There is limited knowledge about potential therapeutic targets in Hepatocyte growth factor/scatter factor (HGF)-induced pathophysiological angiogenesis. Recent candidates have included phosphatidylinositol-3-kinase, which is an upstream activator for endothelial nitric oxide (NO) synthase (NOS III). The current study is the first to evaluate the possible involvement of NOS-NO cascade in HGF-induced angiogenesis. Methods and results: NOS III inhibitors blocked the HGF-induced functional neovascularization in vivo, as quantified using vessel counts, ¹³³Xe-clearance, and immunohistology. This was reversed by L-arginine. Western blot analysis of HGF-treated cells also revealed a temporal increase in HGF-induced phosphorylation. In a deconstructional approach, HGF induced the proliferation and chemokinesis of human endothelial cells. These phenotypic effects were inhibited by NOS inhibitors, L-NAME and L-NIO, and the NO scavenger, carboxy PTIO, but unaltered by 1400W, a NOS II inhibitor. This inhibition was reversed by spermine NONOate, a NO donor, which independently exerted a biphasic effect on endothelial cell proliferation. The modulation of NO did not alter HGF-induced chemoinvasion of endothelial cells, while spermine-NONOate destabilized HGF-induced tubulogenesis, suggesting that a single assay is not sufficient for predicting the final phenotypic outcome on angiogenesis. Conclusions: The study is the first to demonstrate that the NOS III nitric oxide is a key signal cascade in HGF-induced angiogenesis, and represents a promising target for the clinical management of pathological conditions characterized by overt HGF signaling.     

Guidelines for the proper use of etanercept in Japan

Abstract

Nitric oxide (NO) is produced by many cell types in the joint, and its expression is delicately regulated. Depending on its concentration and cellular origin, NO appears to have both pro- and anti-inflammatory potential in the joint. Constitutively expressed nitric oxide synthase (NOS) produces small amounts of NO, which is essential for normal physiological homeostasis. However, inflammatory stimuli such as endotoxins, cytokines, and growth factors promote inducible NOS (iNOS) expression, initially as an anti-inflammatory response, and catalyse a high output of NO. Excessive NO can amplify inflammatory pathways and contribute to the development and maintenance of arthritis. Consequently, proper regulation of NO synthesis can lead to a novel therapeutic approach for inflammatory joint diseases. Further careful study will be necessary to develop new drugs to regulate the NO pathway and to determine the dosage, timing of administration, and duration of treatment in order to avoid both undesirable immunostimulatory effects and immunosuppressive effects.     

Enhanced Cardioprotection Against Ischemia-Reperfusion Injury with Combining Sildenafil with Low-Dose Atorvastatin

Summary Purpose: Both ATV and SL reduce myocardial infarct size (IS) by enhancing expression and activity of NOS isoforms. We investigated whether atorvastatin (ATV) and sildenafil (SL) have synergistic effects on myocardial infarct size (IS) reduction and enhancing nitric oxide synthase (NOS) expression. Method: Rats were randomized to nine groups: ATV-1 (1 mg/kg/d); ATV-10 (10 mg/kg/d); SL-0.7 (0.7 mg/kg); SL-1 (1 mg/kg); ATV-1 + SL-0.7; water alone (controls); 1400W (iNOS inhibitor; 1 mg/kg); ATV-10 + 1400W; and ATV-1 + SL-0.7 + 1400W. ATV was administered orally for 3 days. SL was administered intraperitoneally 18 h before surgery and 1400W intravenously 15 min before surgery. Rats either underwent 30 min ischemia-4 h reperfusion or the hearts were explanted for immunoblotting and enzyme activity tests without being exposed to ischemia. Results: IS (% risk area, mean ± SEM) was smaller in the ATV-10 (13 ± 1%), SL-1 (11 ± 2%), SL-0.7 (18 ± 2%) and ATV-1 + SL-0.7 (9 ± 1%) groups as compared with controls (34 ± 3%; P < 0.001), whereas ATV-1 had no effect (29 ± 2%). ATV-1 + SL-0.7 (9 ± 1%) reduced IS more than SL-0.7 alone (p = 0.012). 1400W abrogated the protective effect of ATV-10 (35 ± 3%) and ATV-1 + SL-0.7 (34 ± 1%). SL-0.7 and ATV-10 increased phosphorylated endothelial (P-eNOS; 210 ± 2.5% and 220 ± 8%) and inducible (iNOS; 151 ± 1% and 154 ± 1%) NOS expression, whereas ATV-1 did not. These changes were significantly enhanced by ATV-1 + SL-0.7 (P-eNOS, 256 ± 2%, iNOS 195 ± 1%). SL-1 increased P-eNOS (311 ± 22%) and iNOS (185 ± 1%) concentrations. Conclusions: Combining low-dose ATV with SL augments the IS limiting effects through enhanced P-eNOS and iNOS expression.     

Mechanisms Involved in Protection Afforded by l-Arginine in Ibuprofen-Induced Gastric Damage: Role of Nitric Oxide and Prostaglandins

l-Arginine (l-arg) exhibits multiple biological properties and plays an important role in the regulation of different functions in pathological conditions. Many of these effects could be achieved on this amino acid serving as a substrate for the enzyme nitric oxide synthase (NOS). At the gastrointestinal level, recent reports revealed its protective activities involving a hyperemic response increasing the gastric blood flow. The aim of this study was to characterize the relationship between NOS activity/expression and prostaglandin changes (PGs) in rats gastric mucosa, with l-arg associated resistance to the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen (IBP). The protective effect of oral l-arg (100 mg/kg body wt), administerred together with IBP (100 mg/kg body wt, per os), was evident enough 90 min after drug administration, although a significant protection persisted for more than 6 hr. Pretreatment with N^G-nitro-l-arginine (l-NNA) (40 mg/kg body wt, intraperitoneally), a competitive inhibitor of constitutive NOS, partly altered the protection afforded by the amino acid. In contrast, no changes could be observed after inducible NOS inhibition [aminoguanidine (AG) 50 mg/Kg body wt, intraperitoneally). l-arg, plus IBP, produced a significant increase of the cyclic GMP (cGMP) response in tissue samples from rat stomach, 90 min and 6 h after drug administration. iNOS activity and mRNA expression were higher in IBP-treated rats, and no differences were observed in inducible responses in the l-arg plus IBP group. No variations in the cNOS activity and expression were found among the different groups of animals assayed. The measurement of mucosal PGE₂ content confirmed that biosynthesis of the eicosanoid is maintained by l-arg for over 90 min after IBP, while a total inhibition was observed 6 hr later. The mechanisms of the l-arg protective effect on the damaged induced by IBP could be explained by the different period after drug administration. The early phase is mediated by cyclooxygenase/prostaglandins pathway (COX/PGs) although NO liberated by cNOS and the guanylate cyclase/cGMP pathway could be also relevant. The later phase implicates inhibition of the iNOS/NO response.     

Conservation of whole body nitric oxide metabolism in human alcoholic liver disease: Implications for nitric oxide production

Objective. Patients with advanced liver diseases tend to develop a hyperdynamic circulation which complicates cirrhosis. Impairment of nitric oxide (NO) metabolism has been implicated in the pathogenesis of portal hypertension. The aim of this study was to determine nitric oxide synthase (NOS)-dependent whole body NO production in patients with decompensated liver cirrhosis and portal hypertension. Material and methods. Ten patients with decompensated alcoholic liver disease and portal hypertension (Child-Pugh Classifications B and C with no signs of infection) and 10 age- and gender-matched control subjects received an intravenous infusion of L-[¹⁵N]₂-arginine (50 µmol/min for 30 min). Urine and serum nitrite and nitrate concentrations were determined using ion chromatography-mass spectrometry. Results. NOS-dependent whole body NO synthesis was estimated by the conversion of [¹⁵N]guanidino nitrogen of arginine to urine ¹⁵N-nitrite and ¹⁵N-nitrate. The amount of ¹⁵N-nitrite and ¹⁵N-nitrate in the urine of patients and control subjects was significantly correlated with the amount of urine nitrite and nitrate over 36 h (r=0.91 and 0.77, respectively, p<0.0001). However, neither a median of 12 h ¹⁵N-nitrite and ¹⁵N-nitrate nor nitrite and nitrate excretion in the urine was different between patients and control subjects, 46.4 (9.4–152.2) versus 98.7 (29.9–146.5) nmol/mmol creatinine and 20.6 (2.1–69.0) versus 40.0 (27.0–70.1) µmol/mmol creatinine, respectively. No differences were found in serum nitrite and nitrate concentrations and glomerular filtration rates between patients and control subjects, 111.4 (73.2–158.8) versus 109.3 (83.5–176.4) µmol/l. Conclusion. Our results contraindicate a greater basal NOS-dependent whole body NO production in patients with decompensated liver disease and portal hypertension.     

Human vascular smooth muscle cells express a constitutive nitric oxide synthase that insulin rapidly activates, thus increasing guanosine 3′ : 5′-cyclic monophosphate and adenosine 3′ : 5′-cyclic monophosphate concentrations

Aims/hypothesis. Insulin incubation of human vascular smooth muscle cells (hVSMC) for 120 min increases both guanosine 3′ : 5′-cyclic monophosphate (cGMP) and adenosine 3′ : 5′-cyclic monophosphate (cAMP) and these effects are blocked by inhibiting nitric oxide synthase (NOS). These data suggest that insulin activates a constitutive Ca²⁺-dependent NOS (cNOS), not described at yet in hVSMC. To test this hypothesis, we evaluated in hVSMC: i) the kinetics of the insulin-induced enhancement of the two cyclic nucleotides; ii) the ability of nitric oxide (NO) to increase both cyclic nucleotides; iii) NO involvement in the short-term influence of insulin on both cyclic nucleotides; iv) the ability of insulin to increase NO production in a few minutes; v) the presence of a cNOS activity; vi) the expression of mRNA for cNOS. Methods. In hVSMC incubated with insulin, NO donors and the Ca²⁺ ionophore ionomycin, we measured cAMP and cGMP (RIA); in hVSMC incubated with insulin and ionomycin we measured NO, evaluated as l-(³H)-citrulline production from l-(³H)-arginine; by northern blot hybridization, we measured the expression of cNOS mRNA. Results. i) By incubating hVSMC with 2 nmol/l insulin for 0–240 min, we observed an increase of both cGMP and cAMP (ANOVA: p = 0.0001). Cyclic GMP rose from 0.74 ± 0.01 to 2.62 ± 0.10 pmol/10⁶ cells at 30 min (p = 0.0001); cAMP rose from 0.9 ± 0.09 to 11.65 ± 0.74 pmol/10⁶ cells at 15 min (p = 0.0001). ii) Sodium nitroprusside (100 μmol/l) and glyceryltrinitrate (100 μmol/l) increased both cGMP and cAMP (p = 0.0001). iii) The effects of insulin on cyclic nucleotides were blocked by NOS inhibition. iv) An increase of NO was observed by incubating hVSMC for 5 min with 2 nmol/l insulin (p = 0.0001). v) Ionomycin (1 μmol/l) enhanced NO production (p = 0.0001) and increased both cyclic nucleotides (p = 0.0001). vi) hVSMC expressed mRNA of cNOS. Conclusion/interpretation. Human VSMC express cNOS, which is rapidly activated by insulin with a consequent increase of both cGMP and cAMP, suggesting that insulin-induced vasodilation in vivo is not entirely endothelium-mediated. [Diabetologia (1999) 42: 831–839] Received: 30 November 1998 and in revised form: 25 January 1999     

Norfloxacin reduces aortic NO synthases and proinflammatory cytokine up-regulation in cirrhotic rats: role of Akt signaling

BACKGROUND & AIMS: Arterial vasodilation plays a role in the pathogenesis of the complications of cirrhosis. This vasodilation is caused by the overproduction of arterial nitric oxide (NO). Bacterial translocation may be involved in NO synthase (NOS) up-regulation by activating both endothelial NOS (eNOS) and inducible NOS (iNOS). The prevention of intestinal gram-negative translocation by norfloxacin administration corrects systemic circulatory changes by decreasing NO production in cirrhosis. However, the signaling mechanisms for NO overproduction from bacterial translocation are unknown. In this study, we investigated the signal transduction pathway of bacterial translocation-induced aortic NOS up-regulation in cirrhotic rats. METHODS: Proinflammatory cytokine levels, Akt and NOS activities, eNOS phosphorylation, and NOS expressions were assessed in aorta from norfloxacin-treated and untreated cirrhotic rats. Norfloxacin was administered to reduce intestinal bacterial translocation. RESULTS: Aortic eNOS and iNOS protein expressions, Akt activity, and eNOS phosphorylation by Akt at serine 1177 were up-regulated in cirrhotic rats. Norfloxacin administration significantly decreased the incidence of gram-negative translocation and proinflammatory cytokine (tumor necrosis factor-alpha, interferon-gamma, and interleukin-6) levels; norfloxacin also decreased aortic Akt activity, eNOS phosphorylation, and NOS expressions and activities. The decrease in aortic Akt activity and NOS expressions also was obtained after colistin or anti-tumor necrosis factor-alpha antibody administration to cirrhotic rats. CONCLUSIONS: This study identifies a signaling pathway in which bacterial translocation induces aortic NOS up-regulation and thus NO overproduction in cirrhotic rats. These results strongly suggest that bacterial translocation and proinflammatory cytokines play a role in systemic NO overproduction in cirrhosis by the Akt pathway.