Role of nitric oxide in the circulatory failure and organ injury in a rodent model of gram-positive shock

The selective guanylate cyclase inhibitor ODQ reduces multiple organ injury in rodent models of Gram-positive and Gram-negative shock

OBJECTIVE

An enhanced formation of endogenous nitric oxide contributes to the circulatory failure caused by endotoxin (lipopolysaccharide). Many of the biological actions of nitric oxide are mediated by the guanylate cyclase/cyclic guanosine 3prime;,5'-monophosphate system. We recently discovered that two cell wall components, namely lipoteichoic acid and peptidoglycan of the Gram-positive bacterium Staphylococcus aureus, synergize to cause shock and multiple organ dysfunction syndrome in the rat. Here we investigate the effects of a selective guanylate cyclase inhibitor, 1H-(1,2,4)oxadiazole(4,3-alpha)quinoxaline-1-one (ODQ), on the circulatory failure and multiple organ dysfunction syndrome (kidney, liver, lung) caused by a) coadministration of lipoteichoic acid and peptidoglycan (Gram-positive shock) or b) lipopolysaccharide (Gram-negative shock) in the anesthetized rat. Furthermore, we investigated whether ODQ scavenges superoxide anions and/or hydroxyl radicals.

DESIGN

The in vivo portion of the study was a prospective, randomized, controlled animal study. The in vitro portion included a) cultured ventricular myoblasts of the rat, H9c2(2-1) cells, and b) a cell free superoxide anion assay system.

SETTING

University-based research laboratory.

SUBJECTS

Seventy-five anesthetized, male Wistar rats were used for the in vivo study.

INTERVENTIONS

For the in vivo portion of the study, after surgical preparation, anesthetized rats were observed for 6 hrs. All rats were pretreated and received an intravenous infusion of saline (1.5 mL.kg-1.hr-1), which was maintained throughout the experiment. The rats were assigned to nine groups. Group 1 contained control rats (sham) subjected to 2 mL/kg saline intraperitoneally, 2 hrs before the experiment (n = 7). Group 2 contained control rats (sham) that received 2 mg/kg ODQ intraperitoneally, 2 hrs before the experiment (n = 9). Group 3 contained control rats (sham) that received 2 mL/kg dimethyl sulfoxide, 30% v/v in saline intraperitoneally, as a vehicle for ODQ, 2 hrs before the experiment (n = 6). In group 4 rats, Gram-positive shock was induced by coadministration of lipoteichoic acid (3 mg/kg intravenously) and peptidoglycan (10 mg/kg intravenously) (n = 10). In group 5, rats were pretreated with ODQ (as described previously) before lipoteichoic acid/peptidoglycan (n = 9). In group 6, rats were pretreated with dimethyl sulfoxide (as described previously) before lipoteichoic acid/peptidoglycan (n = 7). In group 7, Gram-negative shock was induced by lipopolysaccharide (6 mg/kg intravenously) (n = 11). In group 8, rats were pretreated with ODQ (as described previously) before lipopolysaccharide (n = 8). In group 9, rats were pretreated with dimethyl sulfoxide (as described previously) before lipopolysaccharide (n = 8). For the in vitro portion of the study, rat cells were preincubated with vehicle (saline and/or dimethyl sulfoxide) and ODQ (0.1 microM to 1 mM) for 2 hrs. The cells then were exposed to H2O2 (1 mM) for 4 hrs at 37 degrees C, after which time cell viability was determined by measuring the mitochondrial-dependent reduction of 3-(4,5-di-methyliazol-2-yl)-2,5-diphenyltetrazolium bromide to blue formazan. Next, an aqueous solution was incubated with ODQ (as described previously), and superoxide anions were produced by using a hypoxanthine/xanthine-oxidase assay. The chemiluminescence assay was used to evaluate any potential antioxidative effects of ODQ.

MEASUREMENTS AND MAIN RESULTS

In vivo, administration of lipoteichoic acid/peptidoglycan or lipopolysaccharide resulted within 6 hrs in hypotension, acute renal dysfunction, hepatocellular injury, and lung injury. Pretreatment of rats with ODQ attenuated the renal dysfunction, lung injury, and hepatocellular injury caused by lipoteichoic acid/peptidoglycan or lipopolysaccharide. In vitro, administration of H2O2 (for 4 hrs) to rat cardiomyoblasts decreased mitochondrial respiration attributable to generation of hydroxyl radicals. Pretreatment of cells with ODQ did not abolish this cell injury. In addition, ODQ did not scavenge superoxide anions.

CONCLUSIONS

These results imply that ODQ, an inhibitor of guanylate cyclase, reduces the multiple organ injury and dysfunction caused by wall fragments of Gram-positive or Gram-negative bacteria in the anesthetized rat. The observed protective effects of ODQ are not attributable to the ability of ODQ to reduce the formation or the effects of superoxide anions or hydroxyl radicals.

Erythrocyte deformability is a nitric oxide-mediated factor in decreased capillary density during sepsis

Erythrocyte deformability has been recognized as a determinant of microvascular perfusion. Because nitric oxide (NO) is implicated in the modulation of red blood cell (RBC) deformability and NO levels increase during sepsis, we tested the hypothesis that a NO-mediated decrease in RBC deformability contributes to decreased functional capillary density (CD) in remote organs. With the use of a peritonitis model of sepsis in the rat [cecal ligation and perforation (CLP)] and aminoguanidine (AG) to prevent increases in NO, we measured CD in skeletal muscle (intravital microscopy), mean erythrocyte membrane deformability (; micropipette aspiration), systemic NO production [plasma nitrite/nitrate (NO(x)) chemiluminescence], and NO accumulation in RBC [NO bound to hemoglobin (HbNO) detected by electron paramagnetic resonance spectroscopy]. In untreated CLP animals relative to sham, NO(x) increased 254% (P < 0.05), stopped flow capillaries increased 149% (P < 0.05), and decreased 12.7% (P < 0.05), with a subpopulation (5%) of RBC with deformabilities below the normal range. AG prevented increases in NO(x), accumulation of HbNO, and decreases in both and functional CD. We found no evidence of leukocyte plugging postcapillary venules. Our findings suggest that decreased functional CD during sepsis resulted from a NO-mediated decrease in erythrocyte deformability.

Characterization of a monoclonal antibody that binds to an epitope on soluble bacterial peptidoglycan fragments

We employed an inhibition-type enzyme-linked immunosorbent assay (ELISA) to characterize a murine immunoglobulin M monoclonal antibody (MAb) that bound soluble macromolecular peptidoglycan (PG). With this ELISA, the MAb was capable of detecting soluble PG concentrations of less than 10 ng/ml. Enzymatic digestion of PG reduced binding by more than 100-fold, implying that the epitope recognized by this antibody depended on repeating subunits within the glycan backbone. Additionally, the MAb bound to epitopes on both O-acetylated and non-O-acetylated PG fragments from gram-negative bacteria, as well as PG fragments from Staphylococcus aureus and PG fragments released into the medium by a number of gram-positive and gram-negative bacteria.

The influence of phosphodiesterase inhibitor, rolipram, on hemodynamics in lipopolysaccharide-treated rats

Administration of bacterial endotoxin (lipopolysaccharide, LPS) intravenously has been noted to produce a shock state, which is characterized by hypotension and multi-organ system failure. The aim of the present investigation was to (a) examine the influence of rolipram on hemodynamics, plasma levels of tumor necrosis factor-alpha (TNF-alpha) levels, and production of inducible nitric oxide synthase (iNOS) in the lungs, ex vivo, in LPS-treated rats, and (b) determine the cardiovascular effects of a selective alpha1-adrenoceptor agonist, methoxamine, in the absence or presence of rolipram in rats treated with LPS. Blood pressure, cardiac index, heart rate and arterial resistance were assessed in Long-Evans rats anesthetized with thiobutabarbital. Administration of LPS to animals resulted in a significant reduction in cardiac index over time. The administration of LPS to rats resulted in a substantial rise in the plasma levels of TNF-alpha. Furthermore, the injection of LPS resulted in a significant increase in the iNOS activity in the lungs. Pre-treatment with rolipram prevented the decline in cardiac index in animals that received LPS. Infusion of methoxamine into animals injected with rolipram and pre-treated with LPS did not result in significant changes in cardiac index. Pre-treatment with rolipram or dexamethasone in animals injected with LPS significantly prevented the rise in TNF-alpha when compared to the respective values in vehicle-treated animals. Our present observations support the view that the cardiac index can be maintained in animals treated with LPS independent of iNOS inhibition.

Prevention of early islet graft failure by selective inducible nitric oxide synthase inhibitors after pig to nude rat intraportal islet transplantation

BACKGROUND

Clinical and experimental data indicate that early failure of intraportally grafted islets is caused by inflammation including secretion of cytokines and nitric oxide. Direct inducible nitric oxide synthase suppression may avoid detrimental effects associated with steroid administration. We compared the efficiency of selective and unselective inducible nitric oxide synthase inhibitors with dexamethasone to suppress nitric oxide generation after intraportal islet xenotransplantation into nude rats.

METHODS

Nonfasting serum glucose levels were daily evaluated after intraportal transplantation of 4000 freshly isolated pig islets into diabetic nude rats (85 mg/kg streptozotocin) either sham-treated with saline (n=21) or continuously infused for 7 days with L-NG-monomethyl-arginine (n=7), S-methyl-isothiourea (n=15), or S-(2-aminoethyl)-isothiourea (n=19) in a dosage of 240, 100, or 50 mg/kg/day, respectively. Dexamethasone was injected i.p. twice as a daily bolus of 20 mg/kg (n=10) starting 1 day pretransplant. The nitrate/nitrite serum level was quantified colorimetrically 0, 24, and 48 hr posttransplant.

RESULTS

Saline treatment partially resulted in graft function (4/21) throughout the observation period (21 days). L-NG-monomethyl-arginine-treated rats showed sustained hyperglycemia (0/7) not different from diabetic controls. Normoglycemia was observed after treatment with dexamethasone (6/10, P<0.05 versus saline and L-NG-monomethyl-arginine), S-methyl-isothiourea (10/15, P<0.01), or S-(2-aminoethyl)-isothiourea (15/19, P<0.001). Graft function was associated with complete suppression of nitric oxide generation after S-methyl-isothiourea and S-(2-aminoethyl)-isothiourea treatment (P<0.001 versus saline) and partial suppression after dexamethasone treatment (P<0.05).

CONCLUSIONS

Our observation of long-term function of xenogeneic islets in an inflammatory environment without interference of reactive T cells revealed the potency of highly selective isothioureas to completely suppress inducible nitric oxide synthase making reduction of islet-toxic immunosuppression feasible.

Nitric oxide: a review for veterinary surgeons

Nitric oxide (NO) is an endogenous gas that serves as a biologic messenger in many physiologic processes including neurotransmission, blood-pressure control, the immune system's ability to kill tumor cells, and wound healing. NO is produced after oxidation of L-arginine by a family of nitric oxide synthase (NOS) enzymes. Two of the NOS enzymes are present continuously and are thereby termed constitutive NOS. One of the enzymes, inducible NOS, is not typically expressed in resting cells and is induced by various substances including endotoxin, some cytokines, and microbial products. Thus, NO often has paradoxical activities. When NO is over- or underproduced, it can result in potentiation of disease states with disastrous results. This review discusses the biochemistry of NO, its functions in normal and disease states, and therapy for modulating NO production in disease states.

Nitric oxide as a mediator of nucleus pulposus-induced effects on spinal nerve roots

Nerve root dysfunction and sciatic pain in disc herniation are considered to be caused by mechanical compression and related to the presence of nucleus pulposus in the epidural space. Autologous nucleus pulposus has been shown to induce endoneural edema and to decrease nerve-conduction velocity in spinal nerve roots in experimental disc herniation models, and inflammatory mediators have been suggested to be involved in these mechanisms. Nitric oxide, a potent inflammatory mediator, is implicated in vasoregulation, neurotransmission, and neuropathic pain. Nitric oxide synthesis can be induced by different cytokines, e.g., tumor necrosis factor-alpha, which recently was shown to be of pathophysiological importance in experimental disc herniation. The enzyme nitric oxide synthase mediates the production of nitric oxide. Three series of experiments were performed in rat and pig disc herniation models to (a) investigate nitric oxide synthase activity in spinal nerve roots after exposure to autologous nucleus pulposus and (b) evaluate the effects of systemic treatment with aminoguanidine, a nitric oxide synthase inhibitor, on vascular permeability and nerve-conduction velocity. In a disc herniation model in the rat, calcium-independent nitric oxide synthase activity was measured in nerve roots exposed to nucleus pulposus; however, no nitric oxide synthase activity was detected in nerve roots from animals that underwent a sham operation, reflecting increased inducible nitric oxide synthase activity. In nucleus pulposus-exposed spinal nerve roots in the pig, the edema was less severe after systemic aminoguanidine administration than without aminoguanidine treatment. Aminoguanidine treatment also significantly reduced the negative effect of nucleus pulposus on nerve-conduction velocity in spinal nerve roots in the pig. These results demonstrate that nucleus pulposus increases inducible nitric oxide synthase activity in spinal nerve roots and that nitric oxide synthase inhibition reduces nucleus pulposus-induced edema and prevents reduction of nerve-conduction velocity. Furthermore, the results suggest that nitric oxide is involved in the pathophysiological effects of nucleus pulposus in disc herniation.

Antiplatelet activity of Staphylococcus aureus lipoteichoic acid is mediated through a cyclic AMP pathway

In this study, Gram-positive Staphylococcus aureus lipoteichoic acid (LTA) dose dependently (0.1-1.0 microg/mL) and time dependently (10-60 min) inhibited platelet aggregation in human platelets stimulated by agonists (i.e., thrombin and collagen). LTA also dose dependently inhibited intracellular Ca(2+) mobilization in human platelets stimulated by collagen. In addition, LTA (0.5 and 1.0 microg/mL) dose dependently increased the formation of cyclic AMP but not cyclic GMP in platelets. LTA (0.5 and 1.0 microg/mL) did not significantly increase the production of nitrate within a 10-min incubation period. Rapid phosphorylation of a platelet protein of M(r) 47,000, a marker of protein kinase C activation, was triggered by PDBu (0.03 microM). This phosphorylation was dose dependently inhibited by LTA (0.5 and 1.0 microg/mL) within a 10-min incubation period. Furthermore, LTA (0.5 and 1.0 microg/mL) also inhibited platelet aggregation induced by PDBu (0.03 microM) in human platelets. These results indicate that the antiplatelet activity of LTA may be involved in the increase of cyclic AMP, leading to inhibition of intracellular Ca(2+) mobilization and protein kinase C activity. Therefore, LTA-mediated alteration of platelet function may contribute to bleeding diathesis in septicemic and endotoxemic patients.

Aminoguanidine attenuates endotoxin-induced mesenteric vascular hyporeactivity

BACKGROUND

The aim of this study was to investigate the effects of inducible nitric oxide synthase inhibition by aminoguanidine on endotoxin-induced reduction in mesenteric blood flow.

METHODS

Twenty Sprague-Dawley rats (180-230 g) allocated into four groups were administered either Escherichia coli endotoxin 1 mg/kg intraperitoneally or its solvent saline and were pretreated with either aminoguanidine (15 mg/kg intraperitoneally 20 min before and 2 h after endotoxin injection) or saline. Some 4 h after endotoxin injection, animals were anaesthetized, arterial blood pressure and mesenteric blood flow were measured and the resistance in the mesenteric vascular beds was then calculated. The effect of phenylephrine (1-30 microg/kg intravenously) on these parameters was also investigated.

RESULTS

Endotoxin did not significantly modify the mean arterial blood pressure but decreased mesenteric blood flow by increasing the vascular resistance (mean(s.e.m.) 7.8(1.0) versus 13.7(1.2) mmHg per min per ml for control versus endotoxin groups; n = 5, P = 0.0099). Aminoguanidine alone had no effect on either the mean arterial blood pressure or mesenteric blood flow, but it completely blocked the effects of endotoxin. On the other hand, endotoxin significantly attenuated the responsiveness to phenylephrine which was restored by aminoguanidine.

CONCLUSION

The present results indicate that endotoxin decreases the mesenteric vascular blood flow by increasing vascular resistance and decreases responsiveness to phenylephrine. The effects of endotoxin were inhibited by aminoguanidine. The mesenteric vasoconstriction in response to endotoxin might not be explained by the overproduction of nitric oxide; other actions of aminoguanidine may explain its inhibitory effect. Presented in part to the 10th Annual Meeting of the Surgical Infection Society - Europe, Istanbul, Turkey, May 1997

Allosteric inhibitors of inducible nitric oxide synthase dimerization discovered via combinatorial chemistry

Potent and selective inhibitors of inducible nitric oxide synthase (iNOS) (EC ) were identified in an encoded combinatorial chemical library that blocked human iNOS dimerization, and thereby NO production. In a cell-based iNOS assay (A-172 astrocytoma cells) the inhibitors had low-nanomolar IC(50) values and thus were >1,000-fold more potent than the substrate-based direct iNOS inhibitors 1400W and N-methyl-l-arginine. Biochemical studies confirmed that inhibitors caused accumulation of iNOS monomers in mouse macrophage RAW 264.7 cells. High affinity (K(d) approximately 3 nM) of inhibitors for isolated iNOS monomers was confirmed by using a radioligand binding assay. Inhibitors were >1,000-fold selective for iNOS versus endothelial NOS dimerization in a cell-based assay. The crystal structure of inhibitor bound to the monomeric iNOS oxygenase domain revealed inhibitor-heme coordination and substantial perturbation of the substrate binding site and the dimerization interface, indicating that this small molecule acts by allosterically disrupting protein-protein interactions at the dimer interface. These results provide a mechanism-based approach to highly selective iNOS inhibition. Inhibitors were active in vivo, with ED(50) values of <2 mg/kg in a rat model of endotoxin-induced systemic iNOS induction. Thus, this class of dimerization inhibitors has broad therapeutic potential in iNOS-mediated pathologies.

Immunomodulation of pneumococcal pulmonary infection with N(G)-monomethyl-L-arginine

It has recently become apparent that inflammatory reactions including nitric oxide (NO) release contribute to the outcome of pulmonary infections. To investigate the effect of N(G)-monomethyl-L-arginine (L-NMMA), a NO synthase inhibitor, on the pathogenesis of pneumococcal pneumonia, we inoculated CD(1) Swiss mice with 10(7) CFU of Streptococcus pneumoniae. Treatment with two daily subcutaneous injections of 3 mg of L-NMMA per kg of body weight (over a 5-day period) reproducibly delayed mortality, as the number of surviving mice 72, 84, and 96 h after infection was increased by 16.8% (P < 0.05), 25.0% (P < 0.005), and 11.5% (P < 0. 05), respectively. In fact, the following chronology of events was noted in L-NMMA-treated infected animals, compared to the untreated infected controls. (i) At 12 to 24 h after infection, larger amounts of leukotriene B(4) in bronchoalveolar lavage (BAL) fluid associated with greater neutrophilia in lung tissue and alveolar spaces and more persistent release of tumor necrosis factor alpha, interleukin-1 alpha (IL-1alpha), and IL-6 were observed. (ii) At 24 to 72 h, there was better preservation of lung ultrastructure, including reduction of edema in the interstitium and protection of alveolar spaces, despite identical bacterial growth in lungs, in L-NMMA-treated infected animals than in untreated animals. (iii) At 72 to 96 h, the death rate was delayed, despite the absence of antibiotic therapy. In our experiment, partial blockade of NO release was achieved. These data indicate that NO plays an important role in the induction of tissue injury and death during pneumococcal pneumonia and that L-NMMA is helpful for host protection.

Pacing-induced delayed protection against arrhythmias is attenuated by aminoguanidine, an inhibitor of nitric oxide synthase

1. Cardiac pacing, in anaesthetized dogs, protects against ischaemia and reperfusion-induced ventricular arrhythmias when this is initiated 24 h after the pacing stimulus. Now we have examined whether this delayed cardioprotection afforded by cardiac pacing is mediated through nitric oxide. 2. Twenty-two dogs were paced (4 x 5 min periods at 220 beats min(-1)) by way of the right ventricle, 24 h prior to a 25 min period of coronary artery occlusion. Nine of these dogs were given the inhibitor of induced nitric oxide synthase, aminoguanidine (50 mg kg(-1) i.v.), 0.5 h prior to coronary artery occlusion. Sham-operated non-paced dogs with and without aminoguanidine treatment served as controls. 3. Pacing markedly (P<0. 05) reduced arrhythmia severity (ventricular fibrillation, VF, during occlusion 15%; survival from the combined ischaemia-reperfusion insult 62%) compared to control, sham-operated, unpaced dogs (VF during occlusion 58%; survival 17%). This protection was attenuated by the administration of aminoguanidine prior to coronary artery occlusion (survival from the combined ischaemia-reperfusion insult 11%, which was significantly (P<0.05) less than in the paced dogs not given aminoguanidine and similar to the controls). Aminoguanidine had no significant effects on coronary artery occlusion when given to dogs that had not been paced. In the dose used aminoguanadine transiently elevated systemic arterial pressure by a mean of 20 mmHg and reduced heart rate by a mean of 22 beats min(-1). 4. These results suggest that nitric oxide, probably derived from induced nitric oxide synthase, contributes significantly to the delayed cardioprotection afforded by cardiac pacing.

Clinical gram-positive sepsis: does it fundamentally differ from gram-negative bacterial sepsis?

OBJECTIVE

To review the basic differences between gram-positive and gram-negative sepsis and to assess the effect of these differences on current and future therapeutic strategies for sepsis.

DESIGN

Literature review of the past 30 yrs of laboratory and clinical reports that analyze the microbial aspects of sepsis and the immunologic response to systemic infection.

RESULTS

The increasing prevalence of sepsis from gram-positive bacterial pathogens necessitates reevaluation of many of the basic assumptions about the molecular pathogenesis of septic shock. It has been assumed that the initiation of the systemic inflammatory response with activation of the proinflammatory cytokine networks and other mediators results in a similar pathophysiologic process, regardless of the causative microbic pathogen. Yet, there is increasing experimental evidence that fundamental differences exist in the host response to gram-positive bacterial pathogens compared with the host response to gram-negative organisms. Systemic immune activation during sepsis may promote the clearance of the microbic pathogen; however, generalized inflammation also contributes to the pathogenesis of septic shock. The balance between these beneficial and deleterious effects may differ between gram-positive and gram-negative pathogens.

CONCLUSIONS

Results of antimediator therapies in clinical trials in septic shock are inconclusive but suggest that the response may differ, depending on the type of microbic pathogen. The immune-mediated pathophysiologic mechanisms that underlie gram-positive sepsis and the potential interactions between the infecting microorganism and efficacy of anticytokine therapies require further investigation. Treatment strategies that explain the causative organism may be necessary for optimal use of immunoadjuvants in the future.

Inhibition of nitric oxide synthase as a potential therapeutic target

Nitric oxide (NO) regulates numerous physiological processes, including neurotransmission, smooth muscle contractility, platelet reactivity, and the cytotoxic activity of immune cells. Because of the ubiquitous nature of NO, inappropriate release of this mediator has been linked to the pathogenesis of a number of disease states. This provides the rationale for the design of therapies that modulate NO concentrations selectively. A well-characterized family of compounds are the inhibitors of NO synthase, the enzyme responsible for the generation of NO; such agents are potentially beneficial in the treatment of conditions associated with an overproduction of NO, including septic shock, neurodegenerative disorders, and inflammation. This article provides an overview of NO synthase inhibitors, focusing on agents that prevent binding of substrate L-arginine.

An enhancement of nitric oxide production regulates energy metabolism in rat hepatocytes after a partial hepatectomy

BACKGROUND/AIMS

Infection after a liver resection often results in hepatic failure. Nitric oxide is one of the candidates which has been suspected to cause cellular dysfunction during infection in the liver. We have previously reported that the inflammatory cytokine interleukin-1beta (IL-1beta) induced the expression of the inducible nitric oxide synthase gene in primary cultured rat hepatocytes. We hypothesized that an enhancement of nitric oxide production after the resection was implicated in a change in liver energy metabolism, thus resulting in liver dysfunction.

METHODS

In this study, we performed a 70% hepatectomy or a sham operation in rats, and then isolated hepatocytes from the remnant liver by collagenase perfusion. The cultured hepatocytes were treated with cytokines including IL-1beta. The effects on nitric oxide induction, the ATP content and ketone body ratio (acetoacetate/beta-hydroxybutyrate) were then compared between the partial hepatectomized (PH) and sham-operated (control) rats.

RESULTS

IL-1beta augmented the induction of nitric oxide production two-fold in hepatocytes from the PH rats as compared to the control rats. IL-1beta markedly decreased the ATP content in the PH rats, although IL-1beta also decreased the ATP content in the control rats, but to a lesser extent. IL-1beta also decreased the ketone body ratio in both groups. The addition of L-arginine further stimulated the inhibition of the ATP levels and the ketone body ratio concomitantly with increased nitric oxide production in the PH rats. N(G)-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, abolished the effects of IL-1beta on the ATP levels and ketone body ratio, as well as on the nitric oxide production.

CONCLUSIONS

These results demonstrate that the decreased ATP content observed in PH rats resulted from an increase in nitric oxide production. The decrease in ketone body ratio indicates that nitric oxide-induced mitochondrial dysfunction contributes significantly to ATP attenuation in hepatocytes. Therefore, the regulation of nitric oxide induction may be crucial for preventing liver failure after a hepatic resection.

Nitrosation of uric acid by peroxynitrite. Formation of a vasoactive nitric oxide donor

Peroxynitrite (ONOO-), formed by the reaction between nitric oxide (. NO) and superoxide, has been implicated in the etiology of numerous disease processes. Low molecular weight antioxidants, including uric acid, may minimize ONOO---mediated damage to tissues. The tissue-sparing effects of uric acid are typically attributed to oxidant scavenging; however, little attention has been paid to the biology of the reaction products. In this study, a previously unidentified uric acid derivative was detected in ONOO--treated human plasma. The product of the uric acid/ONOO- reaction resulted in endothelium-independent vasorelaxation of rat thoracic aorta, with an EC50 value in the range of 0.03-0.3 microM. Oxyhemoglobin, a .NO scavenger, completely attenuated detectable .NO release and vascular relaxation. Uric acid plus decomposed ONOO- neither released .NO nor altered vascular reactivity. Electrochemical quantification of .NO confirmed that the uric acid/ONOO- reaction resulted in spontaneous (thiol-independent) and protracted (t1/2 approximately 125 min) release of .NO. Mass spectroscopic analysis indicated that the product was a nitrated uric acid derivative. The uric acid nitration/nitrosation product may play a pivotal role in human pathophysiology by releasing .NO, which could decrease vascular tone, increase tissue blood flow, and thereby constitute a role for uric acid not previously described.

Evidence that aminoguanidine inhibits endotoxin-induced bacterial translocation

BACKGROUND

The role of inducible nitric oxide synthase (iNOS) in endotoxin-induced bacterial translocation was investigated by using its specific blocker aminoguanidine in 46 albino mice (25-35 g) allocated into four groups.

METHODS

The first group received intraperitoneal saline (control; 0.9 per cent w v(-1) sodium chloride 1 ml kg(-1); n=6), the second group intraperitoneal endotoxin (Escherichia coli lipopolysaccharide 055:B5 20 mg kg(-1); n=19), the third group intraperitoneal aminoguanidine (20 mg kg(-1), 20 min before and 12 h after saline; n=6) and the fourth group both endotoxin and aminoguanidine intraperitoneally (n=15). Some 24 h later, the animals were anaesthetized with ether and blood samples were collected by cardiac puncture together with mesenteric lymph node (MLN), spleen and liver specimens under aseptic conditions. Specimens were then cultured to determine the presence of colony-forming units as an index of bacterial translocation.

RESULTS

No bacterial growth was detected in samples from the first and third groups. Colony-forming bacteria were found in ten of 14 MLN samples, eight of 14 spleens, four of 14 livers and three of 14 peripheral blood samples in the second group, with E. coli being the predominant pathogen. In contrast, in the fourth group, colony-forming bacteria were found in only three of 14 MLN samples (P=0.02 versus the second group), three of 14 spleens and one of 14 liver specimens. None of the values in the fourth group was significantly different from those in the saline control group.

CONCLUSION

The inhibition of iNOS during endotoxaemia by its specific blocker aminoguanidine attenuates the incidence of bacterial translocation in mice. These results may be exploited clinically for the prophylaxis and treatment of septic states.

Mechanism of gram-positive shock: identification of peptidoglycan and lipoteichoic acid moieties essential in the induction of nitric oxide synthase, shock, and multiple organ failure

The incidence of septic shock caused by gram-positive bacteria has risen markedly in the last few years. It is largely unclear how gram-positive bacteria (which do not contain endotoxin) cause shock and multiple organ failure. We have discovered recently that two cell wall fragments of the pathogenic gram-positive bacterium Staphylococcus aureus, lipoteichoic acid (LTA) and peptidoglycan (PepG), synergize to cause the induction of nitric oxide (NO) formation, shock, and organ injury in the rat. We report here that a specific fragment of PepG, N-acetylglucosamine-beta-[1--> 4]-N-acetylmuramyl-L-alanine-D-isoglutamine, is the moiety within the PepG polymer responsible for the synergism with LTA (or the cytokine interferon gamma) to induce NO formation in the murine macrophage cell line J774.2. However, this moiety is also present in the PepG of the nonpathogenic bacterium Bacillus subtilis. We have discovered subsequently that S. aureus LTA synergizes with PepG from either bacterium to cause enhanced NO formation, shock, and organ injury in the rat, whereas the LTA from B. subtilis does not synergize with PepG of either bacterium. Thus, we propose that the structure of LTA determines the ability of a particular bacterium to cause shock and multiple organ failure (pathogenicity), while PepG acts to amplify any response induced by LTA.

Neurotransmitter and amino acid analysis and ultrastructural observations of fetal brain cortex transplantation to adult rat brain under the effect of dexamethasone

OBJECTIVE

To conduct an investigation of fetal cortical tissue graft survival using transmission electron microscopy and analyzing neurotransmitters and amino acids and their function, with special reference to the effect of dexamethasone.

METHODS

Transplantation of fetal cortical brain tissue to 100 adult Wistar albino rats weighing 170 to 220 g was performed. The rats were divided into three groups. Only transplantation of fetal cortical brain tissue was performed in the first group (n=36). In the second group (n=48), dexamethasone was administered in addition to fetal cortical tissue transplantation. The third group (n=16) was used as the surgical control group. The rats were allowed to live for 6 weeks and were then decapitated. The grafts were examined by electron microscopy. Additionally, quantitative analyses of the neurotransmitters and amino acids of the grafts were conducted using high-pressure liquid chromatography.

RESULTS

Electron microscopic observations revealed that the grafts were still surviving at the end of the 6th week in both groups. However, in the group that received dexamethasone, neurons and their organelles were better developed than in the group that did not receive dexamethasone. Concommitantly, results of quantitative analysis in the dexamethasone group revealed statistically extremely significant higher amino acid values for glutamic acid, aspartic acid, beta-alanine, and lysine and significantly higher values for gamma-aminobutyric acid, glutamine, glycine, and serine when compared to the nondexamethasone group.

CONCLUSION

Dexamethasone is effective in increasing the survival and in developing the ultrastructural and functional outcome of transplanted neurons in fetal grafts.

Intrarenal haemodynamics and renal dysfunction in endotoxaemia: effects of nitric oxide synthase inhibition

1. This study investigated the effects of low dose endotoxin (lipopolysaccharide, LPS) on (i) systemic haemodynamics, (ii) renal blood flow (RBF), (iii) renal cortical and medullary perfusion and (iv) renal function in the anaesthetized rat. We have also investigated the effects of nitric oxide (NO) synthase (NOS) inhibition with NG-methyl-L-arginine (L-NMMA) on the alterations in systemic and renal haemodynamics and renal function caused by endotoxin. 2. Infusion of low dose LPS (1 mg kg-1 over 30 min, n = 6) caused a late fall in mean arterial blood pressure (MAP, at 5 and 6 h after LPS), but did not cause an early (at 1-4 h after LPS) hypotension. The pressor effect of noradrenaline (NA, 1 microgram kg-1, i.v.) was significantly reduced at 1 to 6 h after LPS (vascular hyporeactivity). Infusion of L-NMMA (50 micrograms kg-1 min-1 commencing 60 min before LPS and continued throughout the experiment, n = 7) abolished the delayed hypotension and significantly attenuated the vascular hyporeactivity to NA (at 2-6 h). 3. Infusion of LPS (1 mg kg-1 over 30 min, n = 6) caused a rapid (within 2 h) decline in renal function (measured by inulin clearance) in the absence of a significant fall in MAP or renal blood flow (RBF). L-NMMA (n = 7) attenuated the impairment in renal function caused by LPS so that the inulin clearance in LPS-rats treated with L-NMMA was significantly greater than in LPS-rats treated with vehicle (control) at 3-6 h after infusion of LPS. 4. Endotoxaemia also caused a significant reduction in renal cortical, but not medullary perfusion (measured as Laser Doppler flux). Infusion of L-NMMA caused a significant further fall in cortical perfusion and a significant fall in medullary perfusion in the absence of changes in RBF. 5. Infusion of LPS resulted in a progressive increase in the plasma levels of nitrite/nitrate (an indicator of the formation of NO), so that the plasma concentration of nitrite/nitrate was significantly higher than baseline at 150 to 330 min after LPS. Infusion of L-NMMA attenuated the rise in the plasma concentration of nitrite/nitrate (at 270 and 330 min, P < 0.05) caused by LPS. 6. Thus, the renal dysfunction caused by injection of low dose of endotoxin in the rat occurs in the absence of significant falls in blood pressure or total renal blood flow. Inhibition of NOS activity with L-NMMA attenuates the renal dysfunction caused by endotoxin (without improving intrarenal haemodynamics), suggesting that an overproduction of NO may contribute to the development of renal injury and dysfunction by causing direct cytotoxic effects.