Comparison of the effects of aminoguanidine and N omega-nitro-L-arginine methyl ester on the multiple organ dysfunction caused by endotoxaemia in the rat

The dual role of immune response in acetaminophen hepatotoxicity: Implication for immune pharmacological targets

Acetaminophen (APAP), one of the most widely used antipyretic and analgesic drugs, principally contributes to drug-induced liver injury when taken at a high dose. APAP-induced liver injury (AILI) results in extensive necrosis of hepatocytes along with the occurrence of multiple intracellular events such as metabolic activation, cell injury, and signaling pathway activation. However, the specific role of the immune response in AILI remains controversial for its complicated regulatory mechanisms. A variety of inflammasomes, immune cells, inflammatory mediators, and signaling transduction pathways are activated in AILI. These immune components play antagonistic roles in aggravating the liver injury or promoting regeneration. Recent experimental studies indicated that natural products showed remarkable therapeutic effects against APAP hepatotoxicity due to their favorable efficacy. Therefore, this study aimed to review the present understanding of the immune response in AILI and attempted to establish ties among a series of inflammatory cascade reactions. Also, the immune molecular mechanisms of natural products in the treatment of AILI were extensively reviewed, thus providing a fundamental basis for exploring the potential pharmacological targets associated with immune interventions.

Mapping the Multi-Organ miRNA-mRNA Regulatory Network in LPS-Mediated Endotoxemic Mice: Exploring the Shared Underlying Key Genes and Mechanisms

Background

To this day, the molecular mechanism of endotoxin-induced multi-organ failure has not been completely clarified. This study aimed to construct an miRNA-mRNA regulatory network and identify main pathways and key genes in multi-organ of LPS-mediated endotoxemic mice.

Methods

Public datasets from six mRNA and three miRNA microarray datasets were downloaded from the GEO website to screen final differentially expressed genes (FDEGs) and hub genes in the heart, lung, liver, and kidney of LPS-mediated endotoxemic mice. Functional and pathway enrichment analysis of FDEGs was used to identify the main pathways in multi-organ damage of LPS-treated mice. Finally, hub genes of each organ were intersected to obtain the key genes of multi-organ.

Results

Firstly, 158, 358, 299, and 91 FDEGs were identified in the heart, lung, liver, and kidney, respectively. The pathway enrichment analysis of the FDEGs then showed that the TNF signaling pathway, Toll-like receptor signaling pathway, and some viral-infection-related pathways (influenza A, measles, and herpes simplex) were the main pathways in multi-organ damage of LPS-mediated endotoxemic mice. Moreover, miRNA-mRNA or PPI regulatory networks were constructed based on FDEGs. According to these networks, 31, 34, 34, and 31 hub genes were identified in the heart, lung, liver, and kidney, respectively. Among them, nine key genes (Cd274, Cxcl1, Cxcl9, Icam1, Ifit2, Isg15, Stat1, Tlr2, and Usp18) were enriched in Toll-like receptor signaling pathway and chemokine signaling pathway. Finally, seven potential drugs were predicted based on these key genes.

Conclusion

The shared underlying molecular pathways in endotoxin-induced multi-organ damage that have been identified include Toll-like receptor signaling pathway and TNF signaling pathway. Besides, nine key genes (Cd274, Cxcl1, Cxcl9, Icam1, Ifit2, Isg15, Stat1, Tlr2, and Usp18) and seven potential drugs were identified. Our data provide a new sight and potential target for future therapy in endotoxemia-induced multi-organ failure.

Inducible and endothelial nitric oxide synthase distribution and expression with hind limb per-conditioning of the rat kidney

INTRODUCTION

We recently reported that a series of brief hind limb ischemia and reperfusion (IR) at the beginning of renal ischemia (remote per-conditioning - RPEC) significantly attenuated the ischemia/reperfusion-induced acute kidney injury. In the present study, we investigated whether the nitric oxide synthase (NOS) pathway is involved in the RPEC protection of the rat ischemic kidneys.

MATERIAL AND METHODS

Male rats were subjected to right nephrectomy and randomized as: (1) sham, no additional intervention; (2) IR, 45 min of renal ischemia followed by 24 h reperfusion; (3) RPEC, four 5 min cycles of lower limb IR administered at the beginning of renal ischemia; (4) RPEC+L-NAME (a non-specific NOS inhibitor, 10 mg/kg, i.p.) (5) RPEC + 1400W (a specific iNOS inhibitor, 1 mg/kg, i.p.). After 24 h, blood, urine and tissue samples were collected.

RESULTS

The protective effect of RPEC on renal function, oxidative stress indices, pro-inflammatory marker expression and histopathological changes of kidneys subjected to 45 min ischemia were completely inhibited by pretreatment with L-NAME or 1400W. It was accompanied by increased iNOS and eNOS expression in the RPEC group compared with the IR group.

CONCLUSIONS

These findings suggest that the protective effects of RPEC on renal IR injury are closely dependent on the nitric oxide production after the reperfusion and both eNOS and iNOS are involved in this protection.

The poly-γ-d-glutamic acid capsule surrogate of the Bacillus anthracis capsule induces nitric oxide production via the platelet activating factor receptor signaling pathway

The poly-γ-d-glutamic acid (PGA) capsule, a major virulence factor of Bacillus anthracis, confers protection of the bacillus from phagocytosis and allows its unimpeded growth in the host. PGA capsules released from B. anthracis are associated with lethal toxin in the blood of experimentally infected animals and enhance the cytotoxic effect of lethal toxin on macrophages. In addition, PGA capsule itself activates macrophages and dendritic cells to produce proinflammatory cytokine such as IL-1β, indicating multiple roles of PGA capsule in anthrax pathogenesis. Here we report that PGA capsule of Bacillus licheniformis, a surrogate of B. anthracis capsule, induces production of nitric oxide (NO) in RAW264.7 cells and bone marrow-derived macrophages. NO production was induced by PGA in a dose-dependent manner and was markedly reduced by inhibitors of inducible NO synthase (iNOS), suggesting iNOS-dependent production of NO. Induction of NO production by PGA was not observed in macrophages from TLR2-deficient mice and was also substantially inhibited in RAW264.7 cells by pretreatment of TLR2 blocking antibody. Subsequently, the downstream signaling events such as ERK, JNK and p38 of MAPK pathways as well as NF-κB activation were required for PGA-induced NO production. In addition, the induced NO production was significantly suppressed by treatment with antagonists of platelet activating factor receptor (PAFR) or PAFR siRNA, and mediated through PAFR/Jak2/STAT-1 signaling pathway. These findings suggest that PGA capsule induces NO production in macrophages by triggering both TLR2 and PAFR signaling pathways which lead to activation of NF-kB and STAT-1, respectively.

Arginine Supplementation Induces Arginase Activity and Inhibits TNF-α Synthesis in Mice Spleen Macrophages After Intestinal Obstruction

BACKGROUND

The purpose of this study was to assess the effect of arginine supplementation on arginase activity, tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) synthesis in cultured splenic macrophages from a murine model of intestinal obstruction (IO). The effects of nitric oxide synthase (iNOS) inhibition were also studied using iNOS knockout animals.

MATERIAL AND METHODS

Male C57BL6/J wild-type (WT) and iNOS knockout (iNOS-/-) mice were randomized into 6 groups: Sham and Sham-/- (standard chow), IO and IO-/- (standard chow + IO), and Arg and Arg-/- (standard chow supplemented with arginine + IO). After 7 days of treatment with standard or supplemented chow, IO was induced. Arginase activity as well as TNF-α and IL-10 levels were analyzed in splenic macrophage cultures.

RESULTS

Arginine supplementation and the absence of iNOS increased arginase activity in splenic macrophages (Arg, IO-/-, and Arg-/- groups vs the Sham group; P < .05). Arginine was also related to a decrease in TNF-α levels (Arg vs IO group, P < .05) and maintenance of IL-10 levels (Arg vs other groups, P > .05). The inhibition of iNOS did not result in effects on the concentration of cytokines (Sham-/-, IO-/-, and Arg-/- vs other, P < .05).

CONCLUSIONS

Arginine supplementation and iNOS inhibition led to increased arginase activity. Arginine availability decreased plasma TNF-α levels, which may be directly related to nitric oxide derived from arginine.

Role of peroxynitrite in sepsis-induced acute kidney injury in an experimental model of sepsis in rats

The mechanisms involved in sepsis-induced acute kidney injury (AKI) are unknown. We investigated the role of nitrosative stress in sepsis-induced AKI by studying the effects of manganese (III) tetrakis-(1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP), a peroxynitrite decomposition catalyst, and aminoguanidine (AG), a selective nitric oxide synthase 2 (NOS2) inhibitor and peroxynitrite scavenger, on kidney function of rats subjected to cecal ligation and puncture (CLP). Sprague-Dawley rats (weighing 350 [SD, 50] g) were treated with MnTMPyP (6 mg/kg i.p.) or AG (50 mg/kg i.p.) at t = 12 and 24 h after CLP or sham procedure. At t = 36 h, mean arterial pressure and aortic blood flow were measured, and blood and urine samples were obtained for biochemical determinations, including creatinine clearance, fractional excretion of sodium, and neutrophil gelatinase-associated lipocalin concentration in the urine. Kidney tissue samples were obtained for (i) light microscopy, (ii) immunofluorescence and Western blot for 3-nitrotyrosine and NOS2, (iii) gene expression (quantitative real-time polymerase chain reaction) studies (NOS1, NOS2, NOS3, and superoxide dismutase 1), and (iv) matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Mean arterial pressure was unchanged and aortic blood flow decreased 25% in CLP animals. The sepsis-induced (i) decreased urine output and creatinine clearance and increased fractional excretion of sodium and urinary neutrophil gelatinase-associated lipocalin concentration, (ii) increased protein nitration and NOS2 protein, and (iii) NOS1 and NOS2 upregulation were all significantly attenuated by treatment with MnTMPyP or AG. Nitrated proteins in renal tissue from CLP animals (matrix-assisted laser desorption ionization time-of-flight mass spectrometry) were glutamate dehydrogenase, methylmalonate-semialdehyde dehydrogenase, and aldehyde dehydrogenase, mitochondrial proteins involved in energy metabolism or antioxidant defense. Nitro-oxidative stress is involved in sepsis-induced AKI, and protein nitration seems to be one mechanism involved.

Plasma nitrate/nitrite concentrations in dogs with naturally developing sepsis and non-infectious forms of the systemic inflammatory response syndrome

The aim of this prospective observational study was to evaluate the differences in plasma nitrate/nitrite concentrations between dogs with sepsis and those with non-infectious forms of the systemic inflammatory response syndrome (SIRS). Eighteen dogs with sepsis, 20 dogs with SIRS and 29 healthy control dogs were enrolled. Blood samples were obtained from the dogs within 12 hours of admission to the University of Missouri Veterinary Medical Teaching Hospital (MU VMTH) Intensive Care Unit (ICU) in lithium heparin blood tubes. Plasma nitrate/nitrite concentrations were measured using the Greiss reaction. Plasma nitrate/nitrite concentrations at presentation, clinical parameters, organ dysfunction and in-hospital mortality were compared between groups. Plasma total nitrate/nitrite was significantly greater in the sepsis group compared with the control group (P=0.005) and SIRS group (P=0.037). There was no statistical difference in plasma nitrate/nitrite concentration between the SIRS and control groups (P=0.489). The sensitivity was 66.7 per cent (95 per cent CI, 41 to 87 per cent) and the specificity was 75.5 per cent (95 per cent CI, 61 to 87 per cent) for differentiating dogs with sepsis from dogs without sepsis.

The role of cytokines and inducible nitric oxide synthase in endotoxemia-induced endothelial dysfunction

Sepsis is characterized by a blunted vascular responses due to impairment of endothelial function. The aim of our study was to assess endothelial function and the role of cytokines and nitric oxide (NO). Endotoxin tolerance was induced in 14 healthy volunteers by intravenous injection of 2 ng.kg.d lipopolysaccharide on 5 consecutive days. Forearm blood flow (FBF) was measured by strain-gauge plethysmography during dose-response curves of endothelium-dependent vasodilator acetylcholine and endothelium-independent vasodilator sodium nitroprusside before and 4 hours after LPS administration on days 1 and 5. In another study, 7 healthy volunteers were given selective inducible NO synthase inhibitor aminoguanidine intravenous continuously from 1 hour after a single LPS administration until 5 hours. FBF showed an attenuation of ACh-induced vasodilatory response with 67% (45%-72%) 4 hours after the first LPS administration (P = 0.01) with an unchanged dose-response curve to sodium nitroprusside. This attenuation to ACh infusion did not occur in the presence of aminoguanidine (P = 0.21) and also did not occur when tolerance was present on day 5 (P = 0.45). Our data demonstrate that endothelial dysfunction caused by endotoxemia does not occur when endotoxin tolerance develops, indicated by the absence of cytokine production and during administration of selective inducible NO synthase inhibitor aminoguanidine in vivo.

Selective iNOS inhibition for the treatment of sepsis-induced acute kidney injury

The incidence and mortality of sepsis and the associated development of acute kidney injury (AKI) remain high, despite intense research into potential treatments. Targeting the inflammatory response and/or sepsis-induced alterations in the (micro)circulation are two therapeutic strategies. Another approach could involve modulating the downstream mechanisms that are responsible for organ system dysfunction. Activation of inducible nitric oxide (NO) synthase (iNOS) during sepsis leads to elevated NO levels that influence renal hemodynamics and cause peroxynitrite-related tubular injury through the local generation of reactive nitrogen species. In many organs iNOS is not constitutively expressed; however, it is constitutively expressed in the kidney and, in humans, a relationship between the upregulation of renal iNOS and proximal tubular injury during systemic inflammation has been demonstrated. For these reasons, the selective inhibition of renal iNOS might have important implications for the treatment of sepsis-induced AKI. Various animal studies have demonstrated that selective iNOS inhibition-in contrast to nonselective NOS inhibition-attenuates sepsis-induced renal dysfunction and improves survival, a finding that warrants investigation in clinical trials. In this Review, the selective inhibition of iNOS as a potential novel treatment for sepsis-induced AKI is discussed.

Nitric oxide synthase inhibition enhances the tumor vascular-damaging effects of combretastatin a-4 3-o-phosphate at clinically relevant doses

PURPOSE

The therapeutic potential of combining the prototype tumor vascular-disrupting agent combretastatin A-4 3-O-phosphate (CA-4-P) with systemic nitric oxide synthase (NOS) inhibition was investigated preclinically.

EXPERIMENTAL DESIGN

Vascular response (uptake of (125)I-labeled iodoantipyrine; laser Doppler flowmetry) and tumor response (histologic necrosis; cytotoxicity and growth delay) were determined.

RESULTS

Inducible NOS selective inhibitors had no effect on blood flow in the P22 rat sarcoma. In contrast, the non-isoform-specific NOS inhibitor N(omega)-nitro- l-arginine (l-NNA; 1 and 10 mg/kg i.v. or chronic 0.1 or 0.3 mg/mL in drinking water) decreased the P22 blood flow rate selectively down to 36% of control at 1 hour but did not induce tumor necrosis at 24 hours. CA-4-P, at clinically relevant doses, decreased the P22 blood flow rate down to 6% of control at 1 hour for 3 mg/kg but with no necrosis induction. However, l-NNA administration enhanced both CA-4-P-induced tumor vascular resistance at 1 hour (chronic l-NNA administration) and necrosis at 24 hours, with 45% or 80% necrosis for 3 and 10 mg/kg CA-4-P, respectively. Bolus l-NNA given 3 hours after CA-4-P was the most effective cytotoxic schedule in the CaNT mouse mammary carcinoma, implicating a particular enhancement by l-NNA of the downstream consequences of CA-4-P treatment. Repeated dosing of l-NNA with CA-4-P produced enhanced growth delay over either treatment alone in P22, CaNT, and spontaneous T138 mouse mammary tumors, which represented a true therapeutic enhancement.

CONCLUSIONS

The combination of NOS inhibition with CA-4-P is a promising approach for targeting tumor vasculature, with relevance for similar vascular-disrupting agents in development.

Role of nitric oxide produced by constitutive and inducible nitric oxide synthases in the mouse gastric fundus

In the present study, the role of nitric oxide (NO) produced by constitutive and inducible nitric oxide synthases (cNOS and iNOS, resepctively) on the contraction and relaxation of fundus in normal and lipopolysaccharide (LPS)-treated mice was examined. A whole fundic ring isolated from mice pretreated with reserpine was mounted in an organ bath containing Krebs' solution with 0.001 mmol/L atropine. Rings were contracted initially by 5-hydroxytryptamine (5-HT; 0.03 mmol/L) before relaxation was induced using ATP (0.03 mmol/L), ADP (0.03 mmol/L), pentoxifylline (0.002 mmol/L), electrical field stimulation (EFS; 50 V, 1 msec, 50 Hz, 3 min) and L-arginine (0.05 mmol/L). All drugs and EFS induced significant relaxation of isolated rings. The relaxations induced were significantly inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 1.0 mmol/L). However, the iNOS inhibitors L-N(6)-(1-iminoethyl) lysine hydrochloride (L-NIL; 1.0 mmol/L) and amino guanidine (AMG; 1.0 mmol/L) had no significant effect on tissue relaxation. Then, the relaxant effects of 0.03 mmol/L ATP were tested on precontracted isolated fundic rings taken from 10 mg/kg LPS-treated animals. The non-selective NOS inhibitor L-NAME (10 mg/kg), the iNOS inhibitors L-NIL (3 mg/kg) and AMG (20 mg/kg) and betamethasone (0.1 mg/kg) were used to examine the role of NO produced by iNOS in the relaxation responses. It was found that the level of contraction induced by 0.03 mmol/L 5-HT in rings isolated from LPS-treated animals was significantly (P < 0.5) less than that in rings from untreated mice. However, precontracted tissues from LPS-treated mice were significantly relaxed by ATP and the relaxation response to ATP was significantly inhibited by L-NIL, ANG and betamethasone, but not by L-NAME. We suggest that, in LPS-treated mice, the production of NO from iNOS produces a reduction in the contractile response, as well as a decrease in NO formation by cNOS, resulting in changes to smooth muscle cell function.

Protective effect of baicalein against endotoxic shock in rats in vivo and in vitro

Dried roots of Scutellaria baicalensis Georgi (Huang qin) are widely used in traditional Chinese medicine. Baicalein is a major bioactive flavonoid component of H. qin that shows a wide range of biological activities, including antioxidant and anti-inflammatory actions. We evaluated therapeutic effects and possible mechanisms of action of baicalein on circulatory failure and vascular dysfunction during sepsis induced by lipopolysaccharide (LPS; 10 mg/kg, i.v.) in anesthetized rats. Treatment of the rats with baicalein (20 mg/kg, i.v.) significantly attenuated the deleterious hemodynamic changes of hypotension and tachycardia caused by LPS and significantly inhibited the elevation of plasma tumor necrosis factor alpha (TNF-alpha). Baicalein also decreased levels of inducible nitric oxide synthase (iNOS) and the overproduction of NO and superoxide anions caused by LPS. It also increased the survival rate of ICR mice (25-30 g) challenged by LPS (60 mg/kg). Moreover, infiltration of neutrophils into the liver and lungs of rats 6h after treatment with LPS was also reduced by baicalein. To investigate the mechanism of action of baicalein on sepsis, RAW 264.7 cells were used as a model. Baicalein inhibited iNOS protein production, and suppressed LPS-induced degradation of IkappaBalpha, the formation of a nuclear factor kappa B (NF-kappaB)-DNA complex and NF-kappaB-dependent reporter gene expression. Thus, the therapeutic effects of baicalein were associated with reductions in TNF-alpha and superoxide anion levels during sepsis. The inhibitory effects of baicalein on iNOS production may be mediated by inhibition of the activation of NF-kappaB. Baicalein may thus prove a potential agent against endotoxemia.

Lipoproteins in inflammation and sepsis. I. Basic science

BACKGROUND

High-density lipoproteins (HDL) have been shown to bind and neutralize lipopolysaccharide (LPS) and are regarded as possible therapeutic agents for sepsis and conditions associated with local or systemic inflammation. However, in recent years, a multitude of possible immunomodulatory properties other than LPS neutralization have become evident.

DISCUSSION

This review highlights the advances in the understanding of how HDL is protective in both in vitro and in vivo inflammatory settings, including the ability of HDL to modulate adhesion molecule expression, upregulate endothelial nitric oxide synthase and counteract oxidative stress. Also, the active components of HDL and the recent discovery of novel lipid modulators of inflammation are discussed.

Beneficial effects of LK-4, an analog of dextromethorphan on lipopolysaccharide-induced sepsis in rats

Dextromethorphan (DM), an anti-tussive agent, has been claimed to have anti-inflammatory and immunomodulatory effects in vitro. In our preliminary screening test, LK-4, an analog of DM, can afford more protection against circulatory failure induced by LPS than that of DM. Thus, the aim of this study was to evaluate the effects of LK-4 on sepsis induced by intravenous (i.v.) administration of lipopolysaccharide (LPS; 10 mg/kg) in anesthetized Wistar rats and survival rate by intraperitoneal administration of LPS (70 mg/kg) in conscious ICR mice. Results demonstrated that posttreatment with LK-4 (3 and 5 mg/kg, i.v.) significantly attenuated the deleterious hemodynamic changes (e.g., hypotension and tachycardia) in rats treated with LPS. Meanwhile, LK-4 (3 mg/kg) significantly inhibited the elevation of plasma tumor necrosis factor-alpha, as well as values of GOT and GPT, and BUN and creatinine caused by LPS. The induction of inducible NO synthase and the overproduction of NO and superoxide anions by LPS were also reduced by LK-4. Moreover, infiltration of neutrophils into the lungs and liver of rats 8 h after treatment with LPS was also reduced by LK-4. Furthermore, LK-4 increased the survival rate of mice insulted by toxic dose of LPS. In conclusion, the beneficial effects of LK-4 on LPS-induced sepsis result from its anti-inflammatory and anti-oxidant effects. Thus, LK-4 can be potentially used as a therapeutic agent for sepsis in the future.

Sepsis: emerging role of nitric oxide and selectins

Sepsis--a state of systemic bacterial infection--often leads to multiorgan failure and is associated with high mortality despite the recent advances achieved in intensive care treatment. Many of the ill effects of sepsis are attributed to an abnormally enhanced host inflammatory response that leads to neutrophil recruitment and activation involving selectins, a class of adhesion molecules, in the initial stages. Nitric oxide and its various isoforms have also been implicated in various vascular alterations and directly participate in the cellular toxicity in sepsis. This review briefly describes the role of selectins and nitric oxide in experimental and clinical sepsis as well as the therapeutic outcomes of blocking therapies.

Endotoxin Releases a Substance from the Aorta that Dilates an Isolated Arteriole by Up-Regulating INOS

BACKGROUND

Loss of vascular tone in resistance arterioles has been implicated as the cause of hypotension in septic shock. It is believed that the overproduction of nitric oxide (NO) by the inducible isoform of nitric oxide synthase (iNOS) results in the vasodilatation seen in septic shock. However, we have shown that endotoxin has no effect on vascular tone of an isolated resistance vessel unless the endotoxin flows over a segment of aorta or vena cava upstream in the superfusion line. The aim of this study was to determine if the subsequent vasodilation was due to the release of a direct vasodilator or production of NO in the arteriole and if its source was iNOS by using its selective inhibitor, aminoguanidine.

MATERIALS AND METHODS

First-order rat cremaster arterioles (n = 36) were isolated and cannulated onto micropipettes, superfused with physiological buffer at 34 degrees C, pressurized to 70 mm Hg, and allowed to gain spontaneous tone over 90 min. A segment of abdominal aorta was then placed in series with the arteriole so that the superfusate passed over the aorta and then into the tissue bath containing the isolated arteriole. The vessels were allowed to equilibrate over 60 min. During this interval, the arteriole was exposed to l-NAME (100 mum), aminoguanidine (100 mum), or buffer. The aorta and arteriole were then superfused with endotoxin (Salmonella enteritidis 2.5 mug/ml). Internal diameters of cannulated arterioles were measured and recorded with videomicroscopy and videocalipers at a resolution of +/-1 mum every 15 min for 1 h. Six groups were created with n = 6 for each group: Group 1, endotoxin; Group 2, control; Group 3, l-NAME and endotoxin; Group 4, l-NAME; Group 5, aminoguanidine and endotoxin; and Group 6, aminoguanidine.

RESULTS

After the 60-min equilibration period, there was no significant difference in resting tone among the six groups. At t = 120, the percentage of tone in the control group was 42.7 +/- 0.4% (mean +/- SEM) and this was not changed by treatment with aminoguanidine (42.2 +/- 0.7%). However, exposure to l-NAME alone resulted in vasoconstriction with a gain in tone to 49.5 +/- 1.6% (P > 0.05). Endotoxin alone caused arteriolar tone to fall to 33.5 +/- 1.2% (P < 0.05). Arterioles treated with aminoguanidine did not lose tone (42.6 +/- 1.7%) when exposed to endotoxin and arterioles treated with l-NAME retained their elevated tone (46.0 +/- 2.2%) after treatment with endotoxin.

CONCLUSIONS

This study demonstrates that the aorta exposed to endotoxin releases a substance that vasodilates resistance arterioles through the up-regulation of iNOS. Aminoguanidine prevented the fall in tone following exposure to endotoxin, while use of the nonselective NOS inhibitor, l-NAME, not only blocked the fall due to endotoxin but increased basal tone by blocking the constitutively active eNOS.

Dextromethorphan prevents circulatory failure in rats with endotoxemia

Dextromethorphan (DM), an antitussive agent, has been claimed to have anti-inflammatory and immunomodulatory effects in vitro. Thus, the aim of this study was to evaluate the effects of DM on sepsis induced by intravenous (i.v.) administration of lipopolysaccharide (LPS) in anesthetized Wistar rats and by intraperitoneal administration in conscious ICR mice. Results demonstrated that pretreatment with DM (1, 5 and 10 mg/kg, i.v.) significantly attenuated the deleterious hemodynamic changes (e.g., hypotension and tachycardia) in rats treated with LPS. Meanwhile, DM (5 mg/kg) significantly inhibited the elevation of plasma tumor necrosis factor-alpha and interleukin-10 levels, as well as values of GOT and GPT (as an index of liver function), and BUN and creatinine (as an index of renal function) caused by LPS. The induction of inducible NO synthase and the overproduction of NO and superoxide anions by LPS were also reduced by DM. Moreover, infiltration of neutrophils into the lungs and liver of rats 6 h after treatment with LPS was also reduced by DM. In conclusion, the beneficial effects of DM on LPS-induced sepsis result from its anti-inflammatory and antioxidant effects. Thus, DM can possibly be used as a prophylactic agent for sepsis in the future.

The effects of selective nitric oxide synthase blocker on survival, mesenteric blood flow and multiple organ failure induced by zymosan1

BACKGROUND

Circulatory failure in multiple organ dysfunction syndromes (MODS) is characterized with systemic vasodilation, diminished blood flow to various vascular beds. The aim of this study was to investigate the effects of selective inhibition of nitric oxide on the mesenteric arterial blood flow (MABF), survival and organ injury of the liver, kidney, lung and spleen in zymosan-induced MODS.

MATERIALS AND METHODS

Forty Swiss albino mice (20-40 g), 7 to 9 weeks old, were obtained. Animals were randomly divided into four groups. The first group were treated intraperitoneally (i.p) with vehicle (saline) and served as a sham group for aminoguanidine (AG) (n=10). The second group was treated with zymosan (500 mg/kg, suspended in saline solution, i.p). The mice in the third and fourth group received AG (15 mg/kg) 1 h and 6 h after zymosan or saline administration, respectively. Eighteen hours after the administration of zymosan, animals were assessed for MODS described subsequently. The signals from the flowmeter were also recorded on mesenteric arterial blood flow values.

RESULTS

In zymosan-treated animals, the MABF was significantly lower than that of solvent (saline)-treated controls (ml min(-1), controls: 4.6 +/- 0.6; zymosan: 1.6 +/- 0.9, P <0.05). When animals were treated with AG, there were no significant differences in MABF values between AG group and solvent (saline)-treated control group. However AG prevented zymosan-induced mesenteric MABF decrease. Treatment with aminoguanidine also decreased mortality.

CONCLUSION

AG is capable of inhibiting both the induction and the activity of the already iNOS; it remains a potential therapeutic agent in patients with MODS.

Simvastatin Decreases Nitric Oxide Overproduction and Reverts the Impaired Vascular Responsiveness Induced by Endotoxic Shock in Rats

Lipopolysaccharides (LPS) can be used to induce experimental endotoxic shock, which is characterized by a significant decrease in mean arterial pressure (MAP) and a decreased vasoconstrictor response that have been attributed to excessive nitric oxide production. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), in addition to lowering serum cholesterol levels, exert many pleiotropic effects, including anti-inflammatory action. In the present study, we investigated the effect of simvastatin, an HMG-CoA reductase inhibitor, on the production of nitric oxide and the cardiovascular response to LPS. Male Wistar rats were pretreated with different doses of simvastatin (10, 20, 40, and 80 mg/kg, i.p.) or saline 20 min before i.v. injection of LPS (1.5 mg/kg) or saline (control). MAP was continuously recorded and nitrate plasma concentration was determined during the 6-h experimental session at 1-h intervals. The pressor response to phenylephrine (1 microg/kg) was evaluated before and 6 h after LPS administration. In the LPS-treated group, there was a time-dependent increase in nitrate plasma concentration (P<0.001), and this response was decreased in simvastatin pretreated rats (P<0.001). We also observed that LPS decreased the pressor response to phenylephrine (P<0.001), an effect that was reverted by simvastatin pretreatment (P<0.05). However, simvastatin did not modify the decrease of MAP induced by LPS. We concluded that simvastatin decreases nitrate plasma concentration in response to LPS and recovers vascular responsiveness during an experimental endotoxic shock. These data suggest the potential use of HMG-CoA reductase inhibitors as a coadjuvant in the treatment of septic shock.

ONO-1714, a nitric oxide synthase inhibitor, attenuates endotoxin-induced acute lung injury in rabbits

Overproduction of nitric oxide by inducible nitric oxide synthase (iNOS) expressed in the lung is thought to play a crucial role in the pathogenesis of endotoxin-induced acute lung injury (ALI). In this two-part study, we determined whether ONO-1714, a new selective iNOS inhibitor, attenuates endotoxin-induced ALI in rabbits. For Part I of the study, a control group received IV saline and ALI was induced by IV infusion of endotoxin 5 mg/kg over 30 min in 4 groups. Three groups received either 0.1, 0.03, or 0.01 mg/kg of ONO-1714 10 min before the start of endotoxin and the fourth group received saline. For Part II of the study, ALI was induced by endotoxin infusion in all 6 groups. One group was treated with saline. The other 5 groups received ONO-1714 0.1 mg/kg at various timings (10 min before or 1, 2, 3, or 4 h after ALI induction). The lungs were mechanically ventilated with 40% oxygen for 6 h after induction of ALI. In Part I, pretreatment with 0.1 mg/kg ONO-1714 mitigated endotoxin-induced ALI. In Part II, early posttreatment (within 2 h after the insult) with ONO-1714 was as effective as pretreatment in improving oxygenation, lung mechanics, lung leukosequestration, pulmonary edema, and histological change. However, lung damage was not improved in rabbits receiving the drug 3 or 4 h after endotoxin. These data suggest that the current study is a basis for future clinical trials to elucidate whether ONO-1714 can be a promising therapeutic approach in patients with acute respiratory distress syndrome induced by endotoxin/sepsis.

IMPLICATIONS

An excess of nitric oxide is thought to play a crucial role in the pathogenesis of acute organ injury in endotoxemia. Early posttreatment with ONO-1714, a nitric oxide synthase inhibitor, attenuated physiological, biochemical, and pathological changes in endotoxin-induced acute lung injury in rabbits.

In vivo vascular effects of genistein on a rat model of septic shock induced by lipopolysaccharide

The aim of this study was to investigate the effects of in vivo administration of genistein on rat cardiovascular abnormalities induced by lipopolysaccharide (LPS). Four hours after injection, LPS (10 mg/kg) caused a stable fall in mean arterial pressure (13%) accompanied by ex vivo vascular hyporeactivity to noradrenaline (NA) and relaxation to l-arginine (L-arg), which were inhibited by previous incubation with l-NAME. Endotoxin also caused impairment of aortic relaxant response to acetylcholine, increase nitrite and malonaldehyde plasma levels by 8.6-fold and 2-fold, respectively, and induced aortic expression of inducible nitric-oxide synthase (iNOS) and nitrotyrosine protein. Genistein (1 mg/kg) and daidzein (1 mg/kg) reduced contractile response to NA in vascular tissue, but only genistein was able to inhibit hyporesponsiveness to NA, relaxation to l-arg, increase in nitrite plasma levels, and iNOS expression produced by endotoxin. Moreover, genistein restored impaired aortic relaxation to acetylcholine, lipid peroxidation, and suppressed long-term hypotension. In conclusion, genistein administrated in vivo prevents hypotension and vascular alterations induced by LPS. These protective effects are mediated by both its antioxidant properties and the inhibition of nitric oxide overproduction from de novo synthesis of iNOS due to its tyrosine kinase inhibitor effect.

Cardiac response to nitric oxide synthase inhibition using aminoguanidine in a rat model of endotoxemia

This study evaluates the effect of aminoguanidine, a preferential inhibitor of inducible nitric oxide synthase (iNOS), on the prevention of cardiac depression in acute endotoxemia. Cardiac performance was evaluated after 4 h of exposure to endotoxin. Rats (n = 5) were selected randomly to receive, by intraperitoneal injection, one of four treatments: saline, LPS (lipopolysaccharide, E. coli, 4 mg/kg, AG (aminoguanidine 100 mg/kg), and LPS + AG at various times. AG and saline treatments were administered 30 min before LPS and at 1 and 3 h after LPS injection. Hearts were perfused using the Langendorff isolated perfusion system and a balloon-tipped catheter was placed into the left ventricle to measure left ventricular developed pressure (LVDP). Myocyte contractile function was assessed with electrical field stimulation and video microscopy. Tissue was immunostained for the expression of iNOS and for nitrotyrosine, a byproduct of protein nitration by peroxynitrite. Perfused hearts from LPS-treated rats exhibited a 57% decrease (P < 0.05) in LVDP compared to saline-treated animals. No improvement in ventricular function was observed with the administration of AG. Similarly, cardiac myocytes prepared from LPS-treated animals demonstrated a significant (P < 0.05) reduction in percent and velocity of shortening and this effect was unaltered with the same dose of AG. AG administration significantly reduced serum nitrite/nitrate levels (P < 0.05) in endotoxemic rats to control levels. Localized expression of iNOS in the myocardium was lessened with AG treatment and was not associated with peroxynitrite formation in this model of endotoxemia. The results indicate that AG given in vivo before and after endotoxin (at a concentration sufficient to decrease NO production) did not reduce cardiac depression. We conclude that selective inhibition of iNOS and the reduction of NO production do not prevent cardiac dysfunction at an early stage in an acute model of endotoxemia.

Clinical trials of immunomodulatory therapies in severe sepsis and septic shock

Sepsis remains one of the leading causes of mortality in critically ill patients. Increased insight into the complexities of this disease process has resulted in the targeting of various aspects of the inflammatory response as offering potential therapeutic benefits. There have been encouraging results in the past few years. Some of the tested agents have been shown to improve mortality rates in large randomized controlled trials involving patients with severe sepsis. In this article, we discuss the positive and negative results of trials in this field; some of the possible reasons for the negative results are examined, and directions for the future are suggested.

Differential involvement of guanylate cyclase and potassium channels in nitric oxide-induced hyporesponsiveness to phenylephrine in endotoxemic rats

This study evaluated the involvement of nitric oxide (NO), guanylate cyclase, and potassium channels in the long-lasting vascular hyporesponsiveness to phenylephrine induced by Escherichia coli lipopolysaccharide (LPS) in vitro and in vivo. Experiments in rat aorta rings with endothelium incubated with LPS (10 microg/mL) for 12 h showed that the hyporesponsiveness depends on guanylate cyclase activity and tetraethylammonium-sensitive, but not voltage- or ATP-dependent, potassium channels. Pressor responses to phenylephrine were reduced by 50% in rats injected 8 and 24 h before with LPS (10 mg/kg, intraperitoneally). Pretreatment with NO synthase inhibitors (iNOS; Nomega-nitro-L-arginine methyl ester [L-NAME], 55 micromol/kg or aminoguanidine, 244 micromol/kg, intraperitoneally) fully prevented LPS-induced hyporesponsiveness. When administered just before phenylephrine, L-NAME (11 micromol/kg, intravenously) reversed the hyporesponsiveness in rats injected 8 h, but not in those injected 24 h before with LPS, whereas 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1 (ODQ, 11 micromol/kg, intravenously) reversed the hyporesponsiveness in animals injected 24 h, but not in those injected 8 h before with LPS. Tetraethylammonium (360 micromol/kg, intravenously) reestablished normal responses to phenylephrine in rats injected 8 and 24 h before with LPS. Again, neither voltage- nor ATP-dependent potassium channels appears to be involved. Western blot showed that iNOS expression peaked at 8 h, decreasing to low levels 24 h after LPS injection. Therefore, NO is important in initiating LPS-induced hyporesponsiveness to vasoconstrictors, but not in maintaining it for long periods. Once NO has exerted its effects and even when iNOS expression is minimal, the long-lasting hyporesponsiveness appears to depend on a complex interplay between guanylate cyclase and potassium channel activation.

Effective inhibition of nitric oxide production by aminoguanidine does not reverse hypotension in endotoxaemic rats

BACKGROUND

Excess production of nitric oxide (NO) by the inducible NO synthase (iNOS) has been implicated in the pathophysiology of septic shock. Using methaemoglobin (metHb) and the stable NO metabolite nitrate as markers of NO formation, we assessed the effect of iNOS blockade by aminoguanidine (AG) on hypotension and NO formation in endotoxaemic rats.

METHODS

In 32 male Wistar rats under chloralose anaesthesia, MetHb (at 15 and 330 min, respectively) and plasma nitrate (at 330 min) were determined. Mean arterial pressure, heart rate and haematocrit were monitored. The LPS group (n=8) received bacterial endotoxin (LPS), 3 mg kg(-1) i.v. and was subsequently monitored for 5 h. At 2 h after LPS, the LPS+AG20 group (n=8) received AG, 5 mg kg(-1), and 5 mg kg(-1) h(-1) for the remaining 3 h. The LPS+AG100 group (n=8) instead received 25 mg kg(-1), followed by 25 mg kg(-1) h(-1). The NaCl group (n=8) was given corresponding volumes of isotonic saline.

RESULTS

AG decreased the LPS-induced rise in plasma nitrate by about 50% in the LPS+AG20 group. MetHb levels, however, were not appreciably reduced by this dose. Both NO metabolites reached control levels after the higher dose of AG. LPS caused a progressive decrease in haematocrit. AG did not influence the LPS-induced hypotension, tachycardia or haemodilution.

CONCLUSION

AG inhibited NO formation in a dose-dependent way. Yet, AG had no haemodynamic effects, suggesting a minor cardiovascular influence of iNOS in this endotoxin model, in parallel to what has been found in microbial sepsis.

Nitric oxide: does it play a role in the heart of the critically ill?

Nitric oxide regulates many aspects of myocardial function, not only in the normal heart but also in ischemic and nonischemic heart failure, septic cardiomyopathy, cardiac allograft rejection, and myocarditis. Accumulating evidence implicates the endogenous production of nitric oxide in the regulation of myocardial contractility, distensibility, heart rate, coronary vasodilation, myocardial oxygen consumption, mitochondrial respiration, and apoptosis. The effects of nitric oxide promote left ventricular mechanical efficiency, ie, appropriate matching between cardiac work and myocardial oxygen consumption. Most of these beneficial effects are attributed to the low physiologic concentrations generated by the constitutive endothelial or neuronal nitric oxide synthase. By contrast, inducible nitric oxide synthase generates larger concentrations of nitric oxide over longer periods of time, leading to mostly detrimental effects. In addition, the recently identified beta3-adrenoceptor mediates a negative inotropic effect through coupling to endothelial nitric oxide synthase and is overexpressed in heart failure. An imbalance between beta 1 and beta2-adrenoceptor and beta3-adrenoceptor, with a prevailing influence of beta3-adrenoceptor, may play a causal role in the pathogenesis of cardiac diseases such as terminal heart failure. Likewise, changes in the expression of endothelial nitric oxide synthase or inducible nitric oxide synthase within the myocardium may alter the delicate balance between the effects of nitric oxide produced by either of these isoforms. New treatments such as selective inducible nitric oxide synthase blockade, endothelial nitric oxide synthase promoting therapies, and selective beta3-adrenoceptor modulators may offer promising new therapeutic approaches to optimize the care of critically ill patients according to their stage and specific underlying disease process.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Aminoguanidine does not influence tissue extravasation of albumin in endotoxaemic rats

BACKGROUND

It is generally maintained that protein and fluid are lost from the circulation under septic conditions. The role played by an increased production of nitric oxide, by the inducible nitric oxide synthase (iNOS), in this process is unclear.

METHODS

Chloralose anaesthetised male Wistar rats received E. coli lipopolysaccharide (LPS), 3 mg kg(-1) i.v., and were studied for 5 h. Mean arterial pressure (MAP) and heart rate (HR) were monitored and haematocrit (Hct) was determined intermittently. Tissue plasma volume and tissue clearances of radiolabelled albumin over the last 2 h of the experiment were determined by a double-isotope method. In 8 rats, 2 h after LPS, aminoguanidine, an iNOS selective blocker, was given i.v. at a dose of 5 mg kg(-1). This was followed by a continuous infusion for the duration of the experiment; altogether 20 mg kg(-1) was administered. In the control group (n=8), a corresponding volume of saline was infused.

RESULTS

Aminoguanidine did not significantly influence Hct, MAP and HR, as evidenced by inter-group comparisons (Mann-Whitney test). Tissue plasma clearances of albumin and tissue plasma volume were similar in both groups.

CONCLUSION

Aminoguanidine at 20 mg kg(-1) did not reverse the haemodynamic changes induced by LPS. Neither did the drug affect the tissue plasma clearance of albumin or the tissue plasma volume.

Effects of nitric oxide in septic shock

Nitric oxide (NO) is believed to play a key role in the pathogenesis of septic shock, although many aspects of NO's involvement remain poorly defined. Recent years have seen advances in our understanding of the production and effects of NO, but much of the work has been done in animal models and may not be directly relevant to the clinical situation. Differences between species and models can account for many of the apparently conflicting results obtained. Nevertheless, NO-directed strategies have been developed and tested clinically. However, NO can have both beneficial and detrimental effects on many organ systems in sepsis and attempts to nonselectively block all its actions may therefore not yield positive results on outcome. Further exploration and precision of the role of NO and development of techniques to assess the NO balance in individual patients is necessary before further progress can be made in this field.

Effect of endotoxin on opossum oesophageal motor function

Endotoxin induces nitric oxide (NO*) synthase and alters gastrointestinal functions. We explored the effect of lipopolysaccharide (LPS) on oesophageal motor function at 6, 12, 24, and 48 h. The effects of inhibiting inducible NO* synthase (iNOS) were studied 12 h after administration of LPS with/without aminoguanidine (AG). Oesophageal manometry was performed and tissue bath studies were performed with muscle strips from the oesophagus and lower oesophageal sphincter (LOS). Plasma nitrite/nitrate concentrations were determined. The amplitudes of peristaltic pressure waves, resting LOS pressure and the percentage LOS relaxations were diminished by LPS. AG attenuated the decrease in amplitude of oesophageal pressure waves, LOS pressure, and percentage relaxation of LOS brought about by LPS. LPS decreased electrical field stimulation (EFS)-induced relaxation of LOS muscle. AG attenuated this decrease in LOS relaxation. The off-response of transverse oesophageal muscle strips was decreased, and AG antagonized this effect. Plasma concentrations of nitrite/nitrate were increased. The increase in plasma nitrite/nitrate was attenuated by AG. These studies support the hypothesis that endotoxin modulates oesophageal motor function by increasing NO production and suggest that this results from the induction of iNOS.

The effects of bosentan, aminoguanidine and L-canavanine on mesenteric blood flow, spleen and liver in endotoxaemic mice

The modulatory effects of a non-selective endothelin receptor antagonist, bosentan, were investigated together with those of relatively selective inducible nitric oxide synthase inhibitors, aminoguanidine and L-canavanine, on mesenteric blood flow decrease, liver and spleen injury elicited by endotoxaemia. Swiss albino mice (20-40 g) were administered intraperitoneally bosentan (3, 10 or 30 mg kg(-1)), aminoguanidine (15 mg kg(-1)) or L-canavanine (20 or 100 mg kg(-1)) 10 min before they received saline or Escherichia coli endotoxin (10 mg kg(-1)). After 4 h, the mice were anaesthetized, mesenteric blood flow values were measured, spleen and liver weight/body weight ratios were determined and the organs were examined histopathologically. Endotoxin decreased mesenteric blood flow (ml min(-1), saline: 3.0 +/- 0.2; endotoxin: 2.2 +/- 0.2: n = 10, P < 0.05), increased the weight of liver (g per kg body weight, saline: 47.5 +/- 2.0; endotoxin: 60.8 +/- 1.9: n = 10, P < 0.05) and spleen (g per kg body weight, saline: 3.9 +/- 0.5; endotoxin: 8.6 +/- 0.9; n = 10, P < 0.01) while it inflicted significant histopathological injury to both organs. Bosentan was ineffective at 3 mg kg(-1) but at 10 and 30 mg kg(-1) doses, it abolished all the deleterious effects of endotoxin without exception. Aminoguanidine blocked most of the effects of endotoxin except those on spleen. In contrast, L-canavanine blocked only the endotoxin-induced increase in liver weight but itself increased spleen weight and failed to block any other effects of endotoxin. Thus, it can be speculated that the beneficial effects of aminoguanidine are produced largely by mechanisms other than selective inducible nitric oxide synthase inhibition since L-canavanine was not fully effective. The beneficial effects of endothelin inhibition by using bosentan in endotoxaemia can be further exploited for the understanding and the therapy of sepsis-related syndromes.

Selective in vivo inhibition of inducible nitric oxide synthase in a rat model of sepsis

Elevated production of nitric oxide (NO) by the inducible NO synthase (type II, iNOS) may contribute to the vascular hyporesponsiveness and hemodynamic alterations associated with sepsis. Selective inhibition of this isoenzyme is a possible therapeutic intervention to correct these pathophysiological alterations. Aminoguanidine has been shown to be a selective iNOS inhibitor and to correct the endotoxin-mediated vascular hypocontractility in vitro. However, to date aminoguanidine has not been shown to selectively block iNOS activity in vivo. The in vivo effects of aminoguanidine were assessed in the cecal ligation and perforation model of sepsis in rats. Aminoguanidine (1.75-175 mg/kg) was administered to septic and sham-operated rats for 3 h before euthanasia and harvest of tissues. NOS activities were determined in the thoracic aorta and lung from these animals. Aminoguanidine (17.5 mg/kg) did not alter the mean arterial pressure; however, it did inhibit induced iNOS (but not constitutive NOS) activity in the lung and thoracic aorta from septic animals. Only the higher dose of aminoguanidine (175 mg/kg) was able to increase the mean arterial pressure in septic and sham-operated animals. Thus selective inhibition of iNOS in vivo with aminoguanidine is possible, but our data suggest that other mechanisms, in addition to iNOS induction, are responsible for the loss of vascular tone characteristic of sepsis.

Diet-induced protection against lipopolysaccharide includes increased hepatic NO production

The host response to Gram-negative infection includes the elaboration of numerous proinflammatory agents, including tumor necrosis factor alpha (TNFalpha) and nitric oxide (NO). A component of the hepatic response to infection is an elevation in serum lipids, the so-called "lipemia of sepsis," which results from the increased production of triglyceride (TG)-rich lipoproteins by the liver. We have postulated that these lipoproteins are components of a nonadaptive, innate immune response to endotoxin [lipopolysaccharide (LPS)] and have previously demonstrated the capacity of TG-rich lipoproteins to protect against endotoxicity in rodent models of sepsis. Herein we report the capacity of a high-fructose diet to protect against LPS, most likely by inducing high circulating levels of endogenous TG-rich lipoproteins. The protective phenotype included the increased production of NO by hepatic endothelial cells. Rats, made hypertriglyceridemic by fructose feeding, experienced decreased LPS-induced mortality (P < 0.03) and systemic TNFalpha levels (P < 0.05) as compared with normolipidemic (chow-fed) controls. The increased survival was associated with elevated levels of inducible NO synthase (NOS2) mRNA levels and NO production (82 +/- 26 vs 3 +/- 3 nmol nitrite/10(6) cells, P < 0.001) by hepatic endothelial cells. Nonselective NOS inhibitors reversed the protective phenotype in vivo and readily decreased NO production by cultured endothelial cells from hypertriglyceridemic rats in vitro. This study suggests that a high-fructose diet can protect against endotoxicity in part through induction of endogenous TG-rich lipoproteins and hepatic endothelial cell NO production. This is the first report of diet-induced hyperlipoproteinemia and subsequent protection against endotoxemia.

Enteral infusion of sodium 2-ketoisocaproate in endotoxic rats

OBJECTIVE

In view of our previous finding that the intravenous infusion of 2-ketoisocaproate (KIC) improved survival in septic rats, we endeavored to determine whether the enteral infusion of KIC improves survival in endotoxic rats, and, if so, the mechanism of this effect.

SUBJECTS

Eighty-five rats were given 15 mg/kg of Escherichia coli lipopolysaccharide (026:B6).

INTERVENTIONS

KIC, sodium pyruvate (PYR), or sodium bicarbonate (HCO3) was infused continuously intragastrically at 18.75 mmol/kg/day.

MEASUREMENTS AND MAIN RESULTS

KIC administration increased circulating concentrations of KIC and ketone bodies. Survival rates were: KIC 17/32; PYR 2/22; and HCO3 8/31. The significant improvement in survival with KIC, in contrast with HCO3 (p<.04) or PYR (p<.002), points to an effect specific to KIC rather than to ketoacids generally, and argues against an antioxidant mechanism to explain improved survival with enteral administration. To determine whether altered nitric oxide production was responsible, plasma nitrite plus nitrate concentrations were measured sequentially in rats given a lower dose of lipopolysaccharide plus continuous intragastric KIC, PYR, or HCO3. All rats exhibited pronounced increases in plasma nitrite plus nitrate concentrations, peaking at 8 hrs, but both KIC and PYR caused greater increases than HCO3. Thus, differences in nitric oxide production cannot account for the different effects of PYR and KIC on survival. However, KIC infusion for 8 hrs substantially increased ketone bodies in blood and liver, in comparison with the infusion of HCO3 or PYR.

CONCLUSION

Continuous enteral infusion of KIC improves survival in endotoxemia, probably by its conversion to ketone bodies, which serve as an alternative energy substrate.

Treatment of septic shock in rats with nitric oxide synthase inhibitors and inhaled nitric oxide

OBJECTIVE

To evaluate the effect of treatment with a combination of nitric oxide synthase inhibitors and inhaled nitric oxide on systemic hypotension during sepsis.

DESIGN

Prospective, randomized, controlled study on anesthetized animals.

SETTING

A cardiopulmonary research laboratory.

SUBJECTS

Forty-seven male adult Sprague-Dawley rats.

INTERVENTIONS

Animals were anesthetized, mechanically ventilated with room air, and randomized into six groups: a) the control group (C, n=6) received normal saline infusion; b) the endotoxin-treated group received 100 mg/kg i.v. of Escherichia coli lipopolysaccharide (LPS, n=9); c) the third group received LPS, and 1 hr later the animals were treated with 100 mg/kg i.v. Nw-nitro-L-arginine (LNA, n=9); d) the fourth group received LPS, and after 1 hr, the animals were treated with 100 mg/kg i.v. aminoguanidine (AG, n=9); e) the fifth group received LPS and 1 hr later was treated with LNA plus 1 ppm inhaled nitric oxide (LNA+NO, n=7); f) the sixth group received LPS and 1 hr later was treated with aminoguanidine plus inhaled NO (AG+NO, n=7). Inhaled NO was administered continuously until the end of the experiment.

MEASUREMENTS AND MAIN RESULTS

Systemic mean blood pressure (MAP) was monitored through a catheter in the carotid artery. Mean exhaled NO (ENO) was measured before LPS (T0) and every 30 mins thereafter for 5 hrs. Arterial blood gases and pH were measured every 30 mins for the first 2 hrs and then every hour. No attempt was made to regulate the animal body temperature. All the rats became equally hypothermic (28.9+/-1.2 degrees C [SEM]) at the end of the experiment. In the control group, blood pressure and pH remained stable for the duration of the experiment, however, ENO increased gradually from 1.3+/-0.7 to 17.6+/-3.1 ppb after 5 hrs (p< .05). In the LPS treated rats, MAP decreased in the first 30 mins and then remained stable for 5 hrs. The decrease in MAP was associated with a gradual increase in ENO, which was significant after 180 mins (58.9+/-16.6 ppb) and reached 95.3+/-27.5 ppb after 5 hrs (p< .05). LNA and AG prevented the increase in ENO after LPS to the level in the control group. AG caused a partial reversal of systemic hypotension, which lasted for the duration of the experiment. LNA reversed systemic hypotension almost completely but only transiently for 1 hr, and caused severe metabolic acidosis in all animals. The co-administration of NO with AG had no added benefits on MAP and pH. In contrast, NO inhalation increased the duration of the reversal in MAP after LNA, alleviated the degree of acidosis, and decreased the mortality rate (from 55% to 29%).

CONCLUSIONS

In this animal model, LPS-induced hypotension was alleviated slightly and durably after AG, but only transiently after LNA. Furthermore, co-administration of NO with AG had no added benefits but alleviated the severity of metabolic acidosis and mortality after LNA. We conclude that nitric oxide synthase (NOS) inhibitors, given as a single large bolus in the early phase of sepsis, can exhibit some beneficial effects. Administration of inhaled NO with NOS inhibitors provided more benefits in some conditions and therefore may be a useful therapeutic combination in sepsis. NO production in sepsis does not seem to be a primary cause of systemic hypotension. Other factors are likely to have a major role.

Intravenous endotoxin does not increase tissue extravasation of albumin in rats

BACKGROUND

It is unclear whether activation of the inducible nitric oxide synthase (iNOS) increases or decreases the extravasation of plasma.

METHODS

Chloralose anaesthetised male Wistar rats received E. coli lipopolysaccharide (LPS), 3 mg kg-1 i.v., or the corresponding volume of saline, 3 or 5 h before the end of the experiment. Mean arterial pressure (MAP) and heart rate (HR) were recorded. Tissue clearance of radio-labelled albumin, during the last 2 h of each experiment, was determined by a double-isotope method. In separate animals, the serum concentration of nitrite and nitrate was determined, 5 h after LPS or the solvent.

MAIN RESULTS

LPS initially decreased MAP and lastingly increased HR. In the 3-h LPS animals (n = 8), tissue plasma clearance was lower in the heart and calf muscle and increased only in diaphragm, compared to corresponding control animals (n = 8). In the 5-h LPS rats, clearance was lowered (n = 8) in the entire gastrointestinal tract and in testes, compared to controls (n = 8). The serum nitrite/nitrate concentration was higher in animals given LPS (n = 6) than in controls (n = 6).

CONCLUSION

After LPS, tissue clearance of albumin was not increased in any major tissue, in spite of increased serum levels of NO end products. Apparently, after activation of iNOS, the augmented release of NO is not necessarily associated with increased albumin extravasation.

Effect of L-NAME, an inhibitor of nitric oxide synthesis, on cardiopulmonary function in human septic shock

STUDY OBJECTIVES

We tested the effects of continuous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, on cardiovascular performance and pulmonary gas exchange in patients with hyperdynamic septic shock.

DESIGN

Prospective clinical study.

SETTING

ICU of a university hospital.

PATIENTS

Eleven critically ill patients with severe refractory septic shock.

INTERVENTIONS

Standard hemodynamic measurements were made and blood samples taken before, during, and after 12 h of continuous infusion of 1 mg/kg/h of L-NAME.

MEASUREMENTS AND RESULTS

Continuous infusion of L-NAME increased mean arterial pressure (MAP) from 65+/-3 (SEM) to 93+/-4 mm Hg and systemic vascular resistance (SVR) from 962+/-121 to 1,563+/-173 dyne x s x cm(-5)/m2. Parallel to this, cardiac index (CI) decreased from 4.8+/-0.4 to 3.9+/-0.4 L/min/m2 and myocardial stroke volume (SV) was reduced from 43+/-3 to 34+/-3 mL/m2. Left ventricular stroke work was increased in the first hour of L-NAME infusion from 31+/-3 to 43+/-4 g x m/m2 (all p<0.01 compared with baseline). Heart rate, cardiac filling pressures, and right ventricular stroke work did not change significantly (p>0.05). L-NAME increased the ratio of arterial PO2 to the fraction of inspired O2 from 167+/-23 to 212+/-27 mm Hg (p<0.05). Venous admixture (QVA/QT) was reduced from 19.4+/-2.6% to 14.2+/-2.1% (p<0.05) and oxygen extraction ratio increased from 21.1+/-2.4% to 25.3+/-2.7% (p<0.05). Oxygen delivery (DO2) was reduced following L-NAME, whereas oxygen uptake and arterial lactate and pH were unchanged.

CONCLUSIONS

Prolonged inhibition of NO synthesis with L-NAME can restore MAP and SVR in patients with severe septic shock. Myocardial SV and CI decrease, probably as a result of increased afterload, since heart rate and stroke work were not reduced. L-NAME can improve pulmonary gas exchange with a concomitant reduction in QVA/QT. L-NAME did not promote anaerobe metabolism despite a reduction in DO2.

Aminoguanidine attenuates endotoxin-induced acute lung injury in rabbits

OBJECTIVE

To assess the effect of aminoguanidine, a selective inducible nitric oxide synthase inhibitor, on endotoxin-induced acute lung injury in rabbits.

DESIGN

Prospective, blinded, controlled laboratory study.

SETTING

University research laboratory.

SUBJECTS

Twenty-eight male rabbits.

INTERVENTIONS

The animals were randomly assigned to receive one of four treatments (n = 7 for each group): infusion of saline only (S-S group), infusion of saline and aminoguanidine (S-AG group), infusion of Escherichia coli endotoxin (5 mg/kg over 60 mins) (E-S group), and infusion of endotoxin and aminoguanidine (E-AG group). Fifteen minutes before infusion of endotoxin (E-S and E-AG groups) or saline (S-S and S-AG groups), the animals received an intravenous injection of 1 mg/kg of aminoguanidine (S-AG and E-AG groups) or saline (S-S and E-S groups). The same dose of aminoguanidine or saline was given 1 hr after the end of endotoxin or saline infusion. The lungs of the rabbits were ventilated with 40% oxygen.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, peripheral leukocyte counts, and PaO2 were recorded during the ventilation period (6 hrs). After these observations were made, lung mechanics, cell fraction of bronchoalveolar lavage fluid, and concentrations of thromboxane A2 and prostacyclin metabolites in bronchoalveolar lavage fluid were determined. The wet weight/dry weight ratio of the lung and albumin concentrations in bronchoalveolar lavage fluid were analyzed as indices of pulmonary edema. Endotoxin decreased the lung compliance and PaO2 and increased the wet weight/dry weight ratio, neutrophil counts, and albumin concentrations in bronchoalveolar lavage fluid. The bronchoalveolar lavage fluid concentrations of thromboxane B2 in bronchoalveolar lavage fluid were increased by infusion of endotoxin. Aminoguanidine attenuated these changes. Endotoxin caused extensive morphologic lung damage, which was lessened by aminoguanidine.

CONCLUSIONS

Aminoguanidine given intravenously before and after endotoxin attenuated endotoxin-induced lung injury in rabbits. These findings suggest that inducible nitric oxide synthase inhibition may be useful in the treatment of endotoxin-induced lung injury. However, further studies are required to determine the optimal dosage of aminoguanidine, when the inhibitor is given alone as therapy after lung injury.

Role of nitric oxide in acetaminophen-induced hepatotoxicity in the rat

Acetaminophen is a mild analgesic and antipyretic agent known to cause centrilobular hepatic necrosis at toxic doses. Although this may be due to a direct interaction of reactive acetaminophen metabolites with hepatocyte proteins, recent studies have suggested that cytotoxic mediators produced by parenchymal and nonparenchymal cells also contribute to the pathophysiological process. Nitric oxide is a highly reactive oxidant produced in the liver in response to inflammatory mediators. In the present studies we evaluated the role of nitric oxide in the pathophysiology of acetaminophen-induced liver injury. Treatment of male Long Evans Hooded rats with acetaminophen (1 g/kg) resulted in damage to centrilobular regions of the liver and increases in serum transaminase levels, which were evident within 6 hours of treatment of the animals and reached a maximum at 24 hours. This was correlated with expression of inducible nitric oxide synthase (iNOS) protein in these regions. Hepatocytes isolated from both control and acetaminophen-treated rats were found to readily synthesize nitric oxide in response to inflammatory stimuli. Cells isolated from acetaminophen-treated rats produced more nitric oxide than cells from control animals. Production of nitric oxide by cells from both control and acetaminophen-treated rats was blocked by aminoguanidine, a relatively specific inhibitor of iNOS. Arginine uptake and metabolism studies revealed that the inhibitory effects of aminoguanidine were due predominantly to inhibition of iNOS enzyme activity. Pretreatment of rats with aminoguanidine was found to prevent acetaminophen-induced hepatic necrosis and increases in serum transaminase levels. This was associated with reduced nitric oxide production by hepatocytes. Inhibition of toxicity was not due to alterations in acetaminophen metabolism since aminoguanidine had no effect on hepatocyte cytochrome P4502E1 protein expression or N-acetyl-p-benzoquinone-imine formation. Taken together, these data demonstrate that nitric oxide is an important mediator of acetaminophen-induced hepatotoxicity.

Effect of L-lysine on nitric oxide overproduction in endotoxic shock

1. An enhanced production of nitric oxide (NO) from L-arginine, related to the diffuse expression of an inducible NO synthase (iNOS), contributes to the pathogenesis of endotoxic shock. Since iNOS activity depends on extracellular L-arginine, we hypothesized that limiting cellular L-arginine uptake would reduce NO production in endotoxic shock. We investigated the effects of L-lysine, an inhibitor of L-arginine uptake through system y+, on NO production, multiple organ dysfunction and lactate levels, in normal and endotoxaemic rats. 2. Anaesthetized rats challenged with intravenous lipopolysaccharide (LPS, 10 mg kg[-1]) received a 5 h infusion of either L-lysine (500 micromol kg(-1) h(-1), n = 12) or isotonic saline (2 ml kg(-1) h(-1), n = 11). In rats treated with saline, LPS produced a large increase in plasma nitrate and L-citrulline concentrations at 5 h, both markers of enhanced NO production. LPS also caused severe hypotension, low cardiac output and marked hyperlactataemia. All these changes were significantly reduced by L-lysine administration. 3. Endotoxaemia also caused a significant rise in the plasma levels of alanine aminotransferase (ALAT), lipase, urea and creatinine, and hence, liver, pancreatic and renal dysfunction. These changes tended to be less pronounced in rats treated with L-lysine, although the differences did not reach statistical significance. 4. Similar experiments were conducted in 10 rats challenged with LPS vehicle in place of LPS and then treated with L-lysine (500 micromol kg(-1) h(-1), n = 5) or saline (2 ml kg(-1) h(-1), n = 5) for 5 h. In these animals, all the haemodynamic and metabolic variables remained stable and not statistically different between both treatment groups, except for a slight rise in ALAT, which was comparable in L-lysine and saline-treated rats. 5. In conclusion, L-lysine, an inhibitor of cellular L-arginine uptake, reduces NO production and exerts beneficial haemodynamic effects in endotoxaemic rats. L-lysine also reduces hyperlactataemia and tends to blunt the development of organ injury in these animals. Contrastingly, L-lysine has no effects in the absence of endotoxin and thus appears to act as a selective modulator of iNOS activity.

Nitric oxide and septic shock

1. Nitric oxide (NO) is generated by three different isoforms of NO synthase, two of which are expressed constitutively (in endothelium: eNOS, brain: nNOS), while one is induced by endotoxin (LPS) or cytokines (iNOS). 2. Expression of iNOS in many organs or tissues in septic shock (caused by Gram-negative or Gram-positive bacteria) results in an enhanced formation of NO that contribute to hypotension, vascular hyporeactivity to vasoconstrictors, organ injury, and dysfunction as well as host defense. 3. Inhibition of either the expression of iNOS protein (e.g., with dexamethasone) or of NOS activity (e.g., with selective inhibitors of iNOS activity) exerts beneficial effects in animal models of shock. In contrast, inhibition of eNOS activity may lead to excessive vasoconstriction (adverse effects). 4. There is limited evidence regarding the degree of iNOS induction in human cells or tissues with septic shock. Preliminary data from ongoing clinical trials indicate that nonselective inhibitors of NOS activity (e.g., NG-methyl-L-arginine [L-NMMA]) exert beneficial hemodynamic effects.

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.

Beneficial effects of dantrolene on lipopolysaccharide-induced haemodynamic alterations in rats and mortality in mice

We investigated the effect of dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum, on the induction of nitric oxide (NO) synthase II by bacterial endotoxin (lipopolysaccharide) in the anaesthetised rat and on survival in a murine model of severe endotoxaemia. Injection of lipopolysaccharide (i) induced biphasic changes of rectal temperature and blood glucose: an initial increased phase (< 180 min after injection of lipopolysaccharide) followed by a decreased phase (at 240-360 min), (ii) caused a fall in mean arterial blood pressure from 115 +/- 3 mmHg (time 0) to 83 +/- 6 mmHg at 360 min, (iii) resulted in a substantial hyporeactivity to noradrenaline (1 microg/kg i.v.), (iv) raised plasma nitrate (an indicator of NO formation) in a time-dependent manner, (v) elicited a significant increase in NO synthase II activity in the lung and (vi) caused a 80% lethality (in mice). Pretreatment of animals with dantrolene not only attenuated the delayed circulatory failure, but also prevented the overproduction of NO and the induction of NO synthase II caused by lipopolysaccharide in the rat, and improved survival in a murine model of severe endotoxaemia. Thus, dantrolene has beneficial haemodynamic effects in animals with endotoxin shock. We propose that a decrease of free cytosolic Ca2+ levels plays an important role in the prevention of NO synthase II induction.

Effect of adrenergic and nitrergic blockade on experimental ileus in rats

1. In a rat model of experimental ileus, the effect of blockade of adrenergic and nitrergic neurotransmission was studied on the intestinal transit of Evans blue. 2. Ether anaesthesia and skin incision had no influence on the transit. Laparotomy significantly inhibited the transit of Evans blue. This inhibition was even more pronounced when the small intestine was manipulated. 3. Reserpine (5 mg kg-1), a drug that blocks adrenergic neurotransmission, completely reversed the inhibition of the transit induced by laparotomy but only partially reversed that induced by laparotomy with manipulation of the small intestine. 4. N omega-nitro-L-arginine (L-NOARG, 5 mg kg-1), a nitric oxide synthase inhibitor, completely reversed the reserpine-resistant inhibition induced by laparotomy with manipulation of the small intestine. The effect of L-NOARG was prevented by concomitant administration of L-arginine. L-Arginine itself slightly, but significantly enhanced the inhibition. S-methylisothiourea and aminoguanidine, selective inhibitors of the inducible NO synthase, had no effect on the transit after the three operations. 5. Treatment of the rats with reserpine plus L-NOARG had no additional effect on the transit after laparotomy as compared to reserpine alone. However, reserpine plus L-NNA completely reversed the inhibition of the transit induced by laparotomy with manipulation of the small intestine. 6. These findings support the involvement of adrenergic pathways in the pathogenesis of ileus and suggest that the additional inhibitory effect of mechanical stimulation results from an enhanced release of NO by the constitutive NO synthase.