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

Hydrocortisone decreases lethality and inflammatory cytokine and nitric oxide production in rats challenged with B. anthracis cell wall peptidoglycan

Background

Lethal B. anthracis infection produces high proinflammatory peptidoglycan (PGN) burdens in hosts. We investigated whether the lethality and inflammation anthrax PGN can produce are related.

Methods

At 6 h before and the start of 24 h anthrax PGN infusions, rats (n = 198) were treated with diluent (controls) or one of three IV-doses of either hydrocortisone (125, 12.5 or 1.25 mg/kg) or TNF-soluble receptor (TNFsr; 2000, 1000 or 333 μg/kg), non-selective and selective anti-inflammatory agents, respectively.

Results

Compared to controls, hydrocortisone 125 and 12.5 mg/kg each decreased 7-day lethality (p ≤ 0.004). Hydrocortisone 125 mg/kg decreased IL-1β, IL-6, TNFα, MCP, MIP-1α, MIP-2, RANTES and nitric oxide (NO) blood levels at 4 and 24 h after starting PGN (except MCP at 24 h). Each decrease was significant at 4 h (except MIP-1α that was significant at 24 h) (p ≤ 0.05). Similarly, hydrocortisone 12.5 mg/kg decreased each measure at 4, 24 and 48 h (except TNFα at 24 h and MIP-1α at 24 and 48 h and NO at 48 h). Decreases were significant for IL-6 and NO at 4 h and RANTES at 48 h (p ≤ 0.05). Hydrocortisone 1.25 mg/kg had non-significant effects. Each TNFsr dose decreased lethality but non-significantly. However, when doses were analyzed together, TNFsr decreased lethality in a potential trend (p = 0.16) and IL-6 and NO significantly at 4 h (p = 0.05).

Conclusions

Peptidoglycan-stimulated host inflammation may contribute to B. anthracis lethality.

Emerging roles of allosteric modulators in the regulation of protein-protein interactions (PPIs): A new paradigm for PPI drug discovery

Protein-protein interactions (PPIs) are closely implicated in various types of cellular activities and are thus pivotal to health and disease states. Given their fundamental roles in a wide range of biological processes, the modulation of PPIs has enormous potential in drug discovery. However, owing to the general properties of large, flat, and featureless interfaces of PPIs, previous attempts have demonstrated that the generation of therapeutic agents targeting PPI interfaces is challenging, rendering them almost "undruggable" for decades. To date, rapid progress in chemical and structural biology techniques has promoted the exploitation of allostery as a novel approach in drug discovery. By attaching to allosteric sites that are topologically and spatially distinct from PPI interfaces, allosteric modulators can achieve improved physiochemical properties. Thus, allosteric modulators may represent an alternative strategy to target intractable PPIs and have attracted intense pharmaceutical interest. In this review, we first briefly introduce the characteristics of PPIs and then present different approaches for investigating PPIs, as well as the latest methods for modulating PPIs. Importantly, we comprehensively review the recent progress in the development of allosteric modulators to inhibit or stabilize PPIs. Finally, we conclude with future perspectives on the discovery of allosteric PPI modulators, especially the application of computational methods to aid in allosteric PPI drug discovery.

Emodin Attenuates Lipopolysaccharide-Induced Acute Liver Injury via Inhibiting the TLR4 Signaling Pathway in vitro and in vivo

Aims: Emodin is an anthraquinone with potential anti-inflammatory properties. However, the possible molecular mechanisms and protective effects of emodin are not clear. The objective of this study was to investigate the possible molecular mechanisms and protective effects of emodin on lipopolysaccharide (LPS)-induced acute liver injury (ALI) via the Toll-like receptor 4 (TLR4) signaling pathway in the Raw264.7 cell line and in Balb/c mice. Methods: This study established an inflammatory cellular model and induced an ALI animal model. TLR4 was overexpressed by lentivirus and downregulated by small interfering RNA (siRNA) technology. The mRNA and protein levels of TLR4 and downstream molecules were detected in cells and liver tissue. The tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 levels in supernatant and serum were determined by ELISA. The distribution and expression of mannose receptor C type 1 (CD206) and arginase 1 (ARG1) in the liver were tested by immunofluorescence. Mouse liver function and histopathological observations were assessed. Results: Administration of emodin reduced the protein and/or mRNA levels of TLR4 and its downstream molecules following LPS challenge in Raw264.7 cells and in an animal model. Additionally, emodin suppressed the expression of TNF-α and IL-6 in cell culture supernatant and serum. The inhibitory effect of emodin was also confirmed in RAW264.7 cells, in which TLR4 was overexpressed or knocked down. Additionally, ARG1 and CD206 were elevated in the emodin groups. Emodin also decreased serum ALT and AST levels and alleviated the liver histopathological damage induced by LPS. Conclusion: Emodin showed excellent hepatoprotective effects against LPS-induced ALI, possibly by inhibiting TLR4 signaling pathways.

Combined Hemorrhagic Shock and Unilateral Common Carotid Occlusion Induces Neurological Injury in Adult Male Rats

Background: Clinical assessment reveals that patients after surgery of cardiopulmonary bypass or coronary bypass experience postoperative cognitive dysfunction. This study aimed to investigate whether resuscitation after a hemorrhagic shock (HS) and/or mild cerebral ischemia caused by a unilateral common carotid artery occlusion (UCCAO) can cause brain injury and concomitant neurological dysfunction, and explore the potential mechanisms. Methods: Blood withdrawal (6 mL/100 g body weight) for 60 min through the right jugular vein catheter-induced an HS. Immediately after the termination of HS, we reinfused the initially shed blood volumes to restore and maintain the mean arterial blood pressure (MABP) to the original value during the 30-min resuscitation. A cooling water blanket used to induce whole body cooling for 30 min after the end of resuscitation. Results: An UCCAO caused a slight cerebral ischemia (cerebral blood flow [CBF] 70%) without hypotension (MABP 85 mmHg), systemic inflammation, multiple organs injuries, or neurological injury. An HS caused a moderate cerebral ischemia (52% of the original CBF levels), a moderate hypotension (MABP downed to 22 mmHg), systemic inflammation, and peripheral organs injuries. However, combined an UCCAO and an HS caused a severe cerebral ischemia (18% of the original CBF levels), a moderate hypotension (MABP downed to 17 mmHg), systemic inflammation, peripheral organs damage, and neurological injury, which can be attenuated by whole body cooling. Conclusions: When combined with an HS, an UCCAO is associated with ischemic neuronal injury in the ipsilateral hemisphere of adult rat brain, which can be attenuated by therapeutic hypothermia. A resuscitation from an HS regards as a reperfusion insult which may induce neurological injury in patients with an UCCAO disease.

The hepatocyte as a microbial product-responsive cell

Much research has focused on the responses to microbial products of immune cells such as monocytes, macrophages, and neutrophils. Although the liver is a primary response organ in various infections, relatively little is known about the antimicrobial responses of its major cell type, the hepatocyte. It is now known that the recognition of bacteria occurs via cell-surface proteins that are members of the Toll-like receptor (TLR) family. In addition, lipopolysaccharide (LPS) is bound by circulating LPS-binding protein (LBP) and presented to cell-surface CD14, which in turn interacts with TLR and transduces an intracellular signal. We investigated the CD14 and TLR2 responses of whole liver and isolated hepatocytes, and demonstrated that these cells can be induced to express the molecules necessary for responses to both Gram-positive and Gram-negative bacteria. Our findings may have clinical implications for pathological states such as sepsis.

Endothelial nitric oxide synthase deficient mice are protected from lipopolysaccharide induced acute lung injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.

Lipoprotein in the cell wall of Staphylococcus aureus is a major inducer of nitric oxide production in murine macrophages

Staphylococcus aureus is a Gram-positive bacterium that causes inflammation at infection sites by inducing various inflammatory mediators such as nitric oxide (NO). To identify the staphylococcal virulence factors contributing to NO production, we compared the ability of ethanol-killed wild-type S. aureus and mutant strains lacking lipoteichoic acid (ΔltaS), lipoproteins (Δlgt), or d-alanine (ΔdltA) to stimulate NO production in a murine macrophage cell line, RAW 264.7, and the primary macrophages derived from C57BL/6 mice. Wild-type, ΔltaS, and ΔdltA strains induced NO production in a dose-dependent manner but this response was not observed when the cells were stimulated with the Δlgt strain. Moreover, purified lipoproteins triggered NO production in macrophages. Coincident with NO induction, the wild-type, ΔltaS, and ΔdltA strains induced expression of inducible NO synthase (iNOS) at both mRNA and protein levels whereas Δlgt failed to induce iNOS protein or mRNA. Transient transfection followed by a reporter gene assay and Western blotting experiments demonstrated that wild-type, ΔltaS, and ΔdltA strains, but not the Δlgt strain, induced substantial activation of NF-κB and STAT1 phosphorylation, both of which are known to be crucial for iNOS expression. Moreover, wild-type, ΔltaS, and ΔdltA strains increased Toll-like receptor 2 (TLR2) activation, which is known to mediate S. aureus-induced innate immunity, whereas the Δlgt strain did not. Collectively, these results suggest that lipoproteins in the cell wall of S. aureus play a major role in the induction of NO production in murine macrophages through activation of the TLR2 receptor.

Vasoplegia in septic shock: do we really fight the right enemy?

Vasoplegia is a key factor for the death of patients with septic shock in intensive care unit owing to persistent and irreversible hypotension. Impairment of vascular reactivity has been attributed to a combination of endothelial injury, arginine-vasopressin system dysfunction, release of other vasodilatory inflammatory mediators, and muscle hyperpolarizaton. Nitric oxide induced by a Ca(+2) independent isoform of nitric oxide synthase has been suggested to play an important role in sepsis-induced vasoplegia. However, inhibition of nitric oxide synthase only partially restores the endotoxin-induced vascular hyporeactivity. The aim of this review is to discuss in detail the recent suggested alternative mechanisms of vasoplegia and to briefly outline the current therapeutic strategies and the novel therapeutic options based on those mechanisms.

Inhibition of IκB kinase reduces the multiple organ dysfunction caused by sepsis in the mouse

Nuclear factor κB (NF-κB) plays a pivotal role in sepsis. Activation of NF-κB is initiated by the signal-induced ubiquitylation and subsequent degradation of inhibitors of kappa B (IκBs) primarily via activation of the IκB kinase (IKK). This study was designed to investigate the effects of IKK inhibition on sepsis-associated multiple organ dysfunction and/or injury (MOD) and to elucidate underlying signaling mechanisms in two different in vivo models: male C57BL/6 mice were subjected to either bacterial cell wall components [lipopolysaccharide and peptidoglycan (LPS/PepG)] or underwent cecal ligation and puncture (CLP) to induce sepsis-associated MOD. At 1 hour after LPS/PepG or CLP, mice were treated with the IKK inhibitor IKK 16 (1 mg/kg body weight). At 24 hours, parameters of organ dysfunction and/or injury were assessed in both models. Mice developed a significant impairment in systolic contractility (echocardiography), and significant increases in serum creatinine, serum alanine aminotransferase and lung myeloperoxidase activity, thus indicating cardiac dysfunction, renal dysfunction, hepatocellular injury and lung inflammation, respectively. Treatment with IKK 16 attenuated the impairment in systolic contractility, renal dysfunction, hepatocellular injury and lung inflammation in LPS/PepG-induced MOD and in polymicrobial sepsis. Compared with mice that were injected with LPS/PepG or underwent CLP, immunoblot analyses of heart and liver tissues from mice that were injected with LPS/PepG or underwent CLP and were also treated with IKK 16 revealed: (1) significant attenuation of the increased phosphorylation of IκBα; (2) significant attenuation of the increased nuclear translocation of the NF-κB subunit p65; (3) significant attenuation of the increase in inducible nitric oxide synthase (iNOS) expression; and (4) a significant increase in the phosphorylation of Akt and endothelial nitric oxide synthase (eNOS). Here, we report for the first time that delayed IKK inhibition reduces MOD in experimental sepsis. We suggest that this protective effect is (at least in part) attributable to inhibition of inflammation through NF-κB, the subsequent decrease in iNOS expression and the activation of the Akt-eNOS survival pathway.

An integrated approach to assessing nitroso-redox balance in systemic inflammation

Most studies examining the metabolic fate of NO during systemic inflammation have focused on measuring the quantitatively predominating, stable anions nitrite and nitrate within the circulation. However, these are not necessarily the NO-related products that govern NO metabolism and signaling in tissues. We assessed all major NO derivatives temporally in blood and vital organs during inflammation and explored their relationship to insult severity and redox status. Male rats receiving intraperitoneal endotoxin or vehicle were sacrificed for organ and blood sampling between 0 and 24 h. Endotoxin induced transient and organ-specific changes in a variety of NO metabolites. Nitrite and nitrate increased, peaking at 8 and 12 h, respectively. S- and N-nitrosation and heme-nitrosylation products also peaked at 8 h; these posttranslational protein modifications were associated with decreased myocardial function (echocardiography). Evidence of oxidative stress and systemic inflammation was also obtained. The rise in most NO derivatives was proportional to insult severity. All metabolite levels normalized within 24 h, despite evidence of persisting myocardial dysfunction and clinical unwellness. Our findings point to a complex interplay between NO production, antioxidant defense, and redox status. Although the precise (patho)physiologic roles of specific NO derivatives and their diagnostic/prognostic utility await further investigation, nitroso species in erythrocytes are the most sensitive markers of NO in systemic inflammation, detectable before clinical symptoms manifest.

Mediators of systemic inflammatory response syndrome and the role of recombinant activated protein C in sepsis syndrome

The systemic inflammatory response syndrome, the host's response to infection involves a series of cascading events that mobilize a series of mediators involving the immune system, complement, and the coagulation cascade. Although the initial focus of mediators is to limit infection, this cascade may run amok and cause the development of hypotension, vascular instability, and disseminated intravascular coagulation, leading to morbidity and mortality in the host. Several therapeutic trials have focused on the modulation of these mediators, but use of recombinant human activated protein C in patients with severe sepsis is the only one that has shown a benefit in clinical trials.

Staphylococcus aureus induces microglial inflammation via a glycogen synthase kinase 3beta-regulated pathway

A proinflammatory role for glycogen synthase kinase 3beta (GSK-3beta) has been demonstrated. Here, we addressed its roles on heat-inactivated Staphylococcus aureus-induced microglial inflammation. Heat-inactivated S. aureus induced tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO) production, at least in part, via a Toll-like receptor 2-regulated pathway. Neutralization of TNF-alpha largely blocked heat-inactivated S. aureus-induced NO. Heat-inactivated S. aureus activated GSK-3beta, and inhibiting GSK-3beta reduced TNF-alpha production as well as inducible NO synthase (iNOS)/NO biosynthesis. While activation of NF-kappaB was essential for heat-inactivated S. aureus-induced TNF-alpha and NO, inhibiting GSK-3beta blocked heat-inactivated S. aureus-induced NF-kappaB p65 nuclear translocation. Additionally, inhibiting GSK-3beta enhanced heat-inactivated S. aureus-induced interleukin-10 (IL-10) production (IL-10 is an anti-inflammatory cytokine which inhibits TNF-alpha production). Neutralization of IL-10 reduced TNF-alpha downregulation caused by GSK-3beta inhibition. These results suggest that GSK-3beta regulates heat-inactivated S. aureus-induced TNF-alpha and NO production in microglia mainly by activating NF-kappaB and probably by inhibiting IL-10.

Effect of Nitric Oxide Synthase Inhibition and Saline Administration on Blood Pressure and Renal Sodium Handling During Experimental Sepsis in Rats

Much effort has been made in recent years to clarify metabolic and renal function changes in sepsis. A number of studies performed in different models of sepsis have been described. One such model that is frequently used is cecal ligation and puncture (CLP) in rats. This model resembles human sepsis in several important aspects, such as an early phase of hyperdynamic, hypermetabolic sepsis followed by a late hypodynamic, hypometabolic phase. The present study evaluated the blood pressure (n = 5) and renal function changes during development of CLP renal failure and to determine the effects of NOS inhibition (L-NAME) and 0.15 M NaCl administration on tail blood pressure and renal function in randomly assigned five groups (n = 10 each): (1) Sham-operated, (2) Sham-operated L-NAME-treated, (3) CLP rats, (4) CLP L-NAME-treated, and (5) CLP 0.15 M NaCl-treated rats. The basal tail blood pressure was not significantly different among the four groups. One week later, arterial pressure was significantly increased in sham-operated L-NAME-treated rats (159 +/- 12 mmHg) compare with the other groups (118 +/- 9.0 mmHg in nontreated rats, p < 0.05). Blood pressure shows a slightly and not significant decrease up to 12h in L-NAME and 0.15 M NaCl treated rats, which in turn was followed by a significant reduced arterial pressure 18h after CLP in both groups (L-NAME: 96.0 +/- 3.6 mmHg, p < 0.05) and NaCl: 82.3 +/- 2.4 mmHg, p < 0.05) compared to sham-operated groups. The glomerular filtration rate estimated by CCr decreases significantly in the CLP untreated group (p < 0.001) and did not significantly differ from the sham-operated and L-NAME-treated groups (p = 0.4) during the studies of renal tubule sodium handling. On the other hand, subcutaneous 0.15 M NaCl administration prevented CCr decreases in CLP rats (p = 0.25). CLP increased the FENa in the sham-operated from: 857.2 +/- 85.1 delta%min(-1) to CLP: 1197.8 +/- 119.0 delta%min(-1). The high FENa to CLP was blunted and significantly reduced by previous systemic treatment of animals with L-NAME from sham-operated+L-NAME: 1368.0 +/- 72.0 delta%min(-1) to CLP+L-NAME: 1148.0 +/- 60.4 delta%min(-1) (p < 0.01). The enhanced FENa in the CLP group were accompanied by a significant increase in proximal sodium reabsorption rejection. The salient findings of the present study suggest that a decrease in the blood pressure and creatinine clearance caused by CLP may benefit from L-NAM and fluid resuscitation during initial bacteremia (first 12 h) by promoting an additional increase of tubule sodium reabsorption in the post-proximal segments of nephrons, but these therapies could not prevent acute renal failure after established endotoxemia.

Nitric oxide administration restores the hepatic artery buffer response during porcine endotoxemia

The hepatic artery buffer response, which is lost during endotoxemia, plays a central role in the autoregulation of liver perfusion. A temporarily decreased synthesis of nitric oxide during early endotoxemia might be responsible for this dysfunction; hence exogenous administration of nitric oxide could reestablish the autoregulation of hepatic blood flow and help prevent hepatic damage later in septic shock. Fifteen pigs were treated with lipopolysaccharide +/- the nitric oxide donor nitroprusside-sodium via the portal vein. Hemodynamics were measured, and serum chemistry and liver biopsies for nitric oxide synthase expression were obtained. Lipopolysaccharide decreased arterial liver perfusion after 5 hours by 38% (p = .012), which was reversed by addition of nitroprusside (8%). Administration of nitroprusside preserved an increase of 28% in hepatic arterial upon portal vein flow reduction (p < .001). Nitroprusside maintained mRNA levels of constitutive nitric oxide synthase in liver tissue which were decreased by lipopolysaccharide (p = .026 vs. p = .114) and tempered the burst in inducible nitric oxide synthase expression at t = 3 hours. The early administration of the nitric oxide donor sodium nitroprusside during endotoxemia is able to reestablish the autoregulatory response of the hepatic artery following reduction of hepatic blood flow. This beneficial effect might help to prevent subsequent hepatic damage in the course of abdominal sepsis.

The immunology of sepsis

Sepsis, the systemic inflammatory response to infection, is considered the major cause of death among critically ill patients in the developed world. While there is a general view that this reflects contributions from both the pathogen and the host with respect to an inappropriate inflammatory response, there is a lack of agreement as to the key immune mechanisms. This has been reflected in the diverse range of immunotherapies tested in clinical trials, often with rather marginal effects. The case has been made for a pathogenic role of excessive immunity, the so-called 'cytokine storm', and for a role of too little immunity through immune paralysis. Apoptosis is implicated as a key mechanism in both this immune paralysis and the multi-organ failure that is a feature of severe sepsis. A number of polymorphisms have been implicated in susceptibility to sepsis, including cytokine genes, HLA class II and caspase-12. In this review we focus in particular on the role of group A streptococci in severe sepsis. Here the effect of bacterial superantigens appears to be a correlate of inflammatory activation, although the precise evolutionary role of the superantigens remains unclear.

Hyperbaric oxygenation reduces overexpression of c-Fos and oxidative stress in the brain stem of experimental endotoxemic rats

OBJECTIVE

Septic encephalopathy is associated with an increased mortality rate in septic patients. We have previously shown that a peripheral lipopolysaccharide (LPS) injection induces neuronal activation in the brain-stem nuclei of rats. Nitric oxide (NO) and superoxide are involved in LPS-induced brain damage. Hyperbaric oxygenation (HBO) provides protective effects against systemic oxidative stress and mortality in animals with septic shock. We examined the effects of HBO on neuronal activation and oxidative stress in the brain-stem nuclei of LPS-treated rats.

DESIGN AND INTERVENTIONS

Wistar rats were randomly distributed into six groups for the following treatments:(a) normal saline injection (NS); (b) HBO; (c) LPS; (d) LPS-HBO; (e) LPS-aminoguanidine (AG, an inhibitor of inducible nitric oxide synthase); or (f) hydralazine (HYD, a direct vasodilator). The HYD induces prolonged hypotension and was used as a comparison for LPS stimulation. The AG was used as a comparison for HBO treatment. Two HBO sessions were administered, 1 and 4[Symbol: see text]h after LPS.

RESULTS

HBO and AG significantly reversed the overproduction of c-Fos induced by LPS in the brain stems of rats, with greater reversal in the nucleus tractus solitarii (NTS) by HBO. Although AG did not reduce the superoxide level, HBO significantly abolished superoxide production and NADPH diaphorase expression in the brain stems of LPS-treated rats. The HYD induced much lower c-Fos expression in the brain-stem nuclei than that in LPS-treated animals and caused no significant increase in NADPH diaphorase expression or superoxide formation.

CONCLUSION

HBO protects against endotoxin-related neuronal activation and oxidative stress in the brain-stem nuclei of rats.

Cardiovascular and pulmonary effects of NOS inhibition in endotoxemic conscious rats subjected to swimming training

Sepsis is characterized by systemic hypotension, hyporeactiveness to vasoconstrictors, impaired tissue perfusion, and multiple organ failure. During exercise training (ET), dynamic cardiovascular adjustments take place to maintain proper blood pressure and adjust blood supply to different vascular beds. The aim of this study was to investigate whether ET protects against the cardiovascular abnormalities induced by LPS, a model of experimental endotoxemia, and to evaluate the role of nitric oxide (NO) in pulmonary edema. Wistar rats were subjected to swimming training (up to 1 h/day, 5 days/week for 4 weeks) after which their femoral artery and vein were catheterized. LPS (5 mg/kg, i.v.), injected in control (C) and trained animals (ET), promoted 3 distinct phases in mean arterial pressure (MAP) and heart rate (HR). After ET the alterations in MAP were attenuated. The ET animals showed a lower pulmonary edema index (PEI) after LPS (C=0.65+/-0.01; ET=0.60+/-0.02), which was attenuated after treatment with aminoguanidine in both groups (C=0.53+/-0.02; ET=0.53+/-0.02, p<0.05). After l-NAME, PEI was enhanced numerically in the C and was statistically higher in the ET group (C=0.73+/-0.05; ET=1.30+/-0.3, p<0.05). 7-nitroindazole did not promote any alteration in either group. The adaptations promoted by ET seem to be beneficial, counteracting the cardiovascular abnormalities and pulmonary edema seen in septicemia induced by LPS. The results suggest that iNOS aggravates and cNOS protects against this pulmonary edema.

Roles of calcium and IP3 in impaired colon contractility of rats following multiple organ dysfunction syndrome

The purpose of the present study was to explore changes in rat colon motility, and determine the roles of calcium and inositol (1,4,5)-triphosphate (IP3) in colon dysmotility induced by multiple organ dysfunction syndrome (MODS) caused by bacteria peritonitis. The number of stools, the contractility of the muscle strips and the length of smooth muscle cells (SMC) in the colon, the concentration of calcium and IP3 in SMC, and serum nitric oxide were measured. Number of stools, fecal weight, IP3 concentration in SMC and serum nitric oxide concentration were 0.77 +/- 0.52 pellets, 2.51 +/- 0.39 g, 4.14 +/- 2.07 pmol/tube, and 113.95 +/- 37.89 micromol/L, respectively, for the MODS group (N = 11) vs 1.54 +/- 0.64 pellets, 4.32 +/- 0.57 g, 8.19 +/- 3.11 pmol/tube, and 37.42 +/- 19.56 micromol/L for the control group (N = 20; P < 0.05). After treatment with 0.1 mM acetylcholine and 0.1 M potassium chloride, the maximum contraction stress of smooth muscle strips, the length of SMC and the changes of calcium concentration were 593 +/- 81 and 458 +/- 69 g/cm(3), 48.1 +/- 11.8 and 69.2 +/- 15.7 microM, 250 +/- 70 and 167 +/- 48%, respectively, for the control group vs 321 +/- 53 and 284 +/- 56 g/cm(3), 65.1 +/- 18.5 and 87.2 +/- 23.7 microM, 127 +/- 35 and 112 +/- 35% for the MODS group (P < 0.05). Thus, colon contractility was decreased in MODS, a result possibly related to reduced calcium concentration and IP3 in SMC.

Acupuncture stimulation of ST36 (Zusanli) attenuates acute renal but not hepatic injury in lipopolysaccharide-stimulated rats

BACKGROUND

We sought to determine the effects of ST36 acupuncture on sepsis-induced kidney and liver injuries.

METHODS

A total of 120 rats were randomized into 10 groups: 1) lipopolysaccharide (LPS), 2) normal saline (N/S), 3) LPS + ST36, 4) ST36, 5) LPS + P-ST36, 6) P-ST36, 7) LPS + Sham, 8) Sham, 9) LPS + P-Sham, and 10) P-Sham groups. Rats in the LPS + ST36, ST36, LPS +Sham, and Sham groups received ST36 (designated as "ST36") or a nonacupoint (designated as "Sham") acupuncture for 30 min followed by LPS or N/S injection. Rats in the LPS + P-ST36, P-ST36, LPS + P-Sham, and P-Sham groups received LPS or N/S injection for 3 h followed by a 30 min of ST36 or a "nonacupoint" acupuncture. Rats were killed at 6 h after LPS injection.

RESULTS

LPS caused prominent kidney and liver injuries. The renal and hepatic nitric oxide (NO) concentrations and inducible NO synthase (iNOS) expression were also increased by LPS. ST36 acupuncture pretreatment significantly attenuated the LPS-induced kidney injury and the increases in renal NO concentration and iNOS expression. However, ST36 acupuncture pretreatment did not affect the LPS-induced liver injury and increases in hepatic NO concentration or iNOS expression. Furthermore, ST36 acupuncture performed after LPS did not affect the LPS-induced organ injuries or increases in NO concentration and iNOS expression.

CONCLUSIONS

ST36 acupuncture pretreatment significantly attenuated sepsis-induced kidney, but not liver, injury in rats, whereas ST36 acupuncture performed after sepsis induction had no protective effects against sepsis-induced organ injuries.

HO-1 Mediates the Effects of HBO Pretreatment Against Sepsis

BACKGROUND

We have recently shown that attenuation of sepsis-induced lung injury by hyperbaric oxygen (HBO) pretreatment involves expression regulation of inducible nitric oxide synthase (iNOS) and heme oxygenase (HO)-1. This study was performed to determine the effects of HBO pretreatment on acute kidney and liver injuries in septic rats and the roles of iNOS and HO-1.

MATERIALS AND METHODS

One group of adult male rats (n = 48) were pretreated with HBO. The other group of rats (n = 48) breathed air at normal atmospheric pressure instead. Rats in each group were randomly allocated to receive injection of lipopolysaccharide (LPS), normal saline (N/S), LPS plus hemin (a HO-1 inducer), hemin, LPS plus SnPP (a HO-1 inhibitor), SnPP, LPS plus hemin plus SnPP, or hemin plus SnPP. Hemin and SnPP were injected at 1 h before HBO or air pretreatment. Rats were maintained for 6 h before sacrifice.

RESULTS

LPS caused prominent kidney and liver injuries as well as iNOS and HO-1 expression in stimulated rats. HBO pretreatment significantly attenuated LPS-induced kidney but not liver injury. However, in conjunction with hemin (a HO-1 inducer), HBO pretreatment did attenuate LPS-induced liver injury. In addition, the inhibition of iNOS expression by HBO pretreatment was associated with "super-induction" (i.e., further enhancement) of LPS-induced HO-1 expression. Furthermore, the therapeutic effect of HBO could be counteracted by SnPP (a HO-1 inhibitor).

CONCLUSIONS

HBO pretreatment significantly attenuates LPS-induced acute organ injuries in septic rats. The beneficial effect of HBO pretreatment against sepsis is mediated, at least in part, by "super-induction" of HO-1.

Platelet-activating factor-acetylhydrolase can monodeacylate and inactivate lipoteichoic acid

Bacterial lipoteichoic acid (LTA) shares a structural motif with platelet-activating factor (PAF). Both molecules are strong inflammatory agents and have a glycerol backbone with two lipid chains at the sn-1 and sn-2 positions. PAF is normally inactivated by PAF-acetylhydrolase (PAF-AH), a phospholipase A2 (PLA2), which removes a short acyl group at the sn-2 position. To investigate whether PAF-AH can similarly degrade LTA, we studied the effects of porcine PLA2, bee venom PLA2, and recombinant human PAF-AH on pneumococcal LTA (PnLTA) and staphylococcal LTA (StLTA). After incubation with a porcine or bee venom PLA2, a large fraction of PnLTA lost 264 Da, which corresponds to the mass of the oleic acid group at the sn-2 position. After incubation with recombinant human PAF-AH, PnLTA lost 264 Da; the reduction did not occur when PAF-AH was exposed to Pefabloc SC, an irreversible inhibitor of the PAF-AH active site. Following PAF-AH treatment, PnLTA and StLTA were not able to stimulate mouse RAW 264.7 cells to produce tumor necrosis factor alpha but could stimulate CHO cells expressing human TLR2. This stimulation pattern has been observed with monoacyl PnLTA prepared by mild alkali hydrolysis (22). Taking these data together, we conclude that PAF-AH can remove one acyl chain at the sn-2 position of LTA and produce a monoacyl-LTA that is inactive against mouse cells.

DTPA Fe(III) decreases cytokines and hypotension but worsens survival with Escherichia coli sepsis in rats

OBJECTIVE

Nonselective inhibition of nitric oxide (NO) with NO synthase antagonists decreases hypotension but worsens outcome clinically. We investigated whether iron (III) complex of diethylenetriaminepentaacetic acid [DTPA Fe(III)], a scavenger of NO as well as other oxidant mediators, has similar divergent effects in E. coli challenged rats.

METHODS

Animals with venous and arterial catheters and challenged with intrabronchial or intravenous E. coli were randomized to treatment with DTPA Fe(III) in doses from 3 to 800 mg/kg or placebo. Mean blood pressure (MBP) was measured in all animals and plasma NO, cytokines, and blood and lung leukocyte and bacteria counts in animals administered intrabronchial E. coli and DTPA Fe(III) 50 mg/kg or placebo. Animals received antibiotics and were observed 168 h.

RESULTS

Independent of drug regimen or infection site, compared to placebo, DTPA Fe(III) increased MBP although this was greater with high vs. lower doses. Despite increased MBP, DTPA Fe(III) worsened the hazards ratio of survival . At 6 and 24 h DTPA Fe(III) decreased NO but not significantly and decreased four cytokines (tumor necrosis factor-alpha, interleukins 1 and 10, and macrophage inflammatory protein 3alpha) and lung lavage neutrophils. From 6 to 24 h DTPA Fe(III) increased blood bacteria.

CONCLUSIONS

DTPA Fe(III) while increasing blood pressure has the potential to worsen outcome in sepsis. Further preclinical testing is required before this agent is applied clinically.

Propofol exerts protective effects on the acute lung injury induced by endotoxin in rats

Acute lung injury (ALI) is a major culprit of mortality in endotoxemia. Propofol has been commonly used in critical ill patients for sedation. This experiment attempted to elucidate the effects and possible mechanisms of propofol on the ALI induced by endotoxin. Experimentations were carried out using anesthetized, ventilated rats and isolated perfused rat lungs. Endotoxemia was induced by intravenous lipopolysaccharide (LPS, 10 mg kg(-1)). Various groups of rats received infusion of physiological saline solution (PSS) and LPS. Five min after LPS, propofol at low dose (5 mg kg(-1)h(-1)) or high dose (10 mg kg(-1)h(-1)) was infused for 6h. In isolated perfused rat lungs, PSS, LPS, and propofol (30 or 60 mg kg(-1)) were added into the perfusion circuit. During or after 6h observation, we determined the lung weight (LW)/body weight ratio, LW gain, exhaled nitric oxide (NO) and protein concentration in broncheoalveolar lavage. Lung pathology was evaluated to quantify the lung injury score. Plasma nitrate/nitrite, methyl guanidine (MG), tumor necrosis factor(alpha), and interleukin-1(beta) were examined. Blood leukocytes were counted. Capillary filtration coefficient (K(fc)) was obtained in isolated perfused lungs. Posttreatment of propofol at low or high dose attenuated or prevented the extent of ALI. It also reduced the plasma nitrate/nitrite, MG, and pro-inflammatory cytokines including tumor necrosis factor(alpha) (TNF(alpha)) and interleukin-1(beta) (IL-1(beta)). In the isolated perfused rat lungs, propofol significantly reduced the LPS-induced increase in K(fc). This agent did not affect the leukocytopenia caused by LPS. Accordingly, the effects of propofol on the ALI were not related to leukocyte activation or sequestration. Our results suggest that propofol exerts protective effect on the endotoxin-induced ALI. The mechanisms of actions may be mediated through inhibition on the release of pro-inflammatory cytokines, free radicals and NO. In addition, propofol abrogates the microvascular leakage of water and protein in the lungs. The results imply that the use of propofol in critically ill is not only for sedation, but also useful for the prevention of inflammatory progression and lung damage.

Effects of post-treatment with low-dose propofol on inflammatory responses to lipopolysaccharide-induced shock in conscious rats

1. In the present study, we used a low dose of propofol (5 mg/kg per h) to investigate its effects on the pro-inflammatory cytokines (tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-10) and changes in nitric oxide (NO) following lipopolysaccharide (LPS) for a period of 12 h in conscious rats. 2. Experiments were designed to induce endotoxin shock by intravenous injection of Klebsiella pneumoniae LPS (10 mg/kg) in conscious rats. Arterial pressure (AP) and heart rate (HR) were monitored continuously for 12 h after LPS administration. Tumour necrosis factor-alpha, IL-1beta, IL-10 and plasma nitrates/nitrites were determined before and 0.5, 1, 3, 6, 9 and 12 h after LPS administration. A low dose of intravenous propofol (5 mg/kg per h) was administered to investigate the effects on cytokine responses and changes in NO in endotoxin shock. 3. Lipopolysaccharide significantly increased TNF-alpha, IL-1beta, IL-10, nitrites/nitrates and HR, whereas mean AP was decreased. Post-treatment with propofol suppressed the release of TNF-alpha, IL-1beta, IL-10 and NO production after endotoxin shock. 4. Lipopolysaccharide also caused a decrease in the white blood cell count and haematocrit. 5. Post-treatment with propofol slightly, but not significantly, affected the LPS-induced systemic hypotension, tachycardia, leukocytopenia and anaemia. 6. These findings suggest that low-dose propofol may be beneficial to the inflammatory change in sepsis.

Inducible Nitric Oxide Synthase Inhibition Potentiates Multiple Organ Dysfunction Induced by Endotoxin in Conscious Rats

This study was designed to investigate the effects of inducible nitric oxide synthase (iNOS) inhibition with S-methylisothiourea (SMT) and L-N-(1-iminoethyl)-lysine (L-Nil) on the endotoxemia induced by intravenous lipopolysaccharide (LPS, 10 mg/kg) in conscious rats. Arterial pressure (AP), heart rate (HR), WBC, platelets, plasma nitrite/nitrate, tumor necrosis factor alpha (TNF alpha), and biochemical factors were measured for 24 hours after LPS with or without iNOS inhibitors. RT-PCR was employed to determine the iNOS and endothelial NOS (eNOS) mRNA. Pathologic examinations of the liver and heart were performed. SMT and L-Nil improved the systemic hypotension and increased the HR after LPS. These agents attenuated the LPS-induced leukocytopenia and thrombocytopenia and the increase in nitrite/nitrate. However, iNOS inhibition aggravated the LPS-induced changes in TNF alpha, all biochemical factors, and the hepatic and cardiac tissue damage. The iNOS mRNA, but not the eNOS, was reduced. Our results in conscious rats indicate that iNOS inhibition enhances the organ dysfunction and tissue damage in sepsis. The discrepancy may be attributed to the method for evaluating the sepsis and the effects of anesthesia. Further investigation is required to ensure the effects of iNOS inhibition on sepsis before iNOS inhibitors can be applied in clinical cases with sepsis.

Reductions in levels of bacterial superantigens/cannabinoids by plasma exchange in a patient with severe toxic shock syndrome

Toxic shock syndrome is a rare but potentially fatal toxin-mediated febrile illness. We report a case of toxic shock syndrome complicated by life-threatening organ dysfunction with high toxin-1 and staphylococcus enterotoxin type A levels that were successfully reduced by early introduction of plasma exchanges. The report shows the time course of the concentrations of anandamide and 2-arachidonyl glyceride and confirms that early introduction of plasma exchange can result in a rapid reduction of circulating toxins and mediators in the treatment of life-threatening multiple organ dysfunction.

NF-kappaB inhibitors stabilize the mRNA of high-affinity type-2 cationic amino acid transporter in LPS-stimulated rat liver

BACKGROUND

Induction of inducible nitric oxide synthase (iNOS) results in nitric oxide (NO) overproduction during endotoxemia. Cellular uptake of L-arginine, modulated by the isozymes of type-2 cationic amino acid transporters (CAT), including CAT-2, CAT-2A and CAT-2B, has been reported to be a crucial factor in the regulation of iNOS activity. We sought to elucidate the expression of CAT-2 isozymes and the role of nuclear factor-kappaB (NF-kappaB) in this expression in lipopolysaccharide (LPS)-treated rat liver.

METHODS

Adult male Sprague-Dawley rats were randomly given intravenous (i.v.) injections of normal saline (N/S), LPS, LPS preceded by an NF-kappaB inhibitor (PDTC, dexamethasone or salicylate) or an NF-kappaB inhibitor alone. After injection, rats were sacrificed at different times and enzyme expression and liver injury were examined. Hepatic and systemic NO production were also measured.

RESULTS

CAT-2, CAT-2A and CAT-2B were constitutively expressed in un-stimulated rat liver. LPS stimulation not only significantly increased iNOS mRNA and NO concentrations but also decreased the mRNA concentrations of CAT-2 and CAT-2B, but not CAT-2A, in a time-dependent manner. LPS-induced hepatic and systemic NO overproduction was associated with hepatocellular injury. Pre-treatment with NF-kappaB inhibitors significantly attenuated LPS-induced iNOS induction as well as CAT-2/CAT-2B mRNA destabilization, which was associated with significant inhibition of NO biosynthesis and less liver injury.

CONCLUSION

NF-kappaB inhibitors stabilize CAT-2 and CAT-2B mRNA in LPS-stimulated rat liver. The hepatic CAT-2/CAT-2B pathway may be a constitutive part of cytoprotective mechanisms against sepsis.

Monoacyl lipoteichoic acid from pneumococci stimulates human cells but not mouse cells

We have developed a method for obtaining pneumococcal lipoteichoic acid (LTA) with none, one, or two acyl chains. Anion-exchange chromatography at pH 9.5 yields pneumococcal LTA (labeled LTA-9.5) that has a mass spectrum identical to that of pre-ion-exchange LTA and loses 500 mass units after deacylation by alkali hydrolysis. Anion exchange at pH 10.5 produces LTA (labeled LTA-10.5) with mass peaks that are 264 mass units lower than those of pre-ion-exchange LTA, and deacylation of LTA-10.5 by alkali hydrolysis reduces the mass by only 239 mass units. This result indicates that LTA-10.5 has lost one of the two acyl chains, whereas LTA-9.5 has both acyl chains. When the biological properties of LTA-9.5 and LTA-10.5 are examined with mouse cells, only LTA-9.5 (and not LTA-10.5) is able to stimulate mouse cells to produce tumor necrosis factor alpha, interleukin-1beta, and nitric oxide. In contrast, both LTA-9.5 and LTA-10.5 can stimulate human cells. LTA became inactive when both acyl chains were removed. Thus, acyl chains are critical for LTA function, and small variations in acyl chains can alter biological properties of LTA.

Bradykinin-Induced Pulmonary Vasoconstriction Is Time and Inducible Nitric Oxide Synthase Dependent in a Peritonitis Sepsis Model

In an isolated perfused lung model, bradykinin induced pulmonary vasoconstriction in rats made septic by the injection of lipopolysaccharide (LPS). To mimic the pathophysiology of sepsis in humans more closely, we investigated pulmonary endothelial injury in a peritonitis model (cecal ligation and perforation; CLP). Male Sprague-Dawley rats were randomly divided into nine groups (n = 6-8). LPS and CLP rats were compared after 6 h with and without treatment with a selective inhibitor of inducible nitric oxide synthase (iNOS), L-N(6)-(1-iminoethyl)-lysine. Time dependency was investigated in CLP-treated rats at 24 h. The pulmonary circulation was isolated and perfused with a constant flow after the rats' tracheas were intubated and ventilated. Bradykinin (1, 3, and 6 microg) was injected, and changes in perfusion pressure were measured. Lungs were harvested for Western blot analysis to determine the role of iNOS in pulmonary endothelial dysfunction. In contrast to CLP 24 h rats, dose-dependent bradykinin-induced pulmonary vasoconstriction was observed in LPS and CLP 6 h rats. Concomitant administration of L-N(6)-(1-iminoethyl)-lysine significantly attenuated this vasoconstriction in both groups. The iNOS protein was expressed in lung homogenates from LPS 6 h and CLP 6 h but not from CLP 24 h rats. Both sepsis models caused bradykinin-induced pulmonary vasoconstriction, with the CLP groups demonstrating a time dependency of this effect. In conjunction with the time-dependent decrease in iNOS protein, the attenuated bradykinin-induced vasoconstriction due to selective iNOS inhibition suggests an important role for iNOS in pulmonary endothelial injury for both sepsis models.

Biology and chemistry of the inhibition of nitric oxide synthases by pteridine-derivatives as therapeutic agents

Inhibitors of the family of nitric oxide synthases (NOS-I-III; EC 1.14.13.39) are of interest as pharmacological agents to modulate pathologically high nitric oxide (NO) levels in inflammation, sepsis, and stroke. In this article, we discuss the approach for targeting the unique (6R)-5,6,7,8-tetrahydro-L-biopterin (H4Bip) binding site of NOS by appropriate inhibitors. This binding site maximally increases enzyme activity and NO production from the substrate L-arginine upon cofactor binding. The first generation of H4Bip-based NOS inhibitors was based on 4-amino H4Bip derivatives in analogy to anti-folates such as methotrexate. In addition, we discuss the structure-activity relationship of a related series of 4-oxo-pteridine derivatives. Furthermore, molecular modeling studies provide an understanding of pterin antagonism on a structural level based on favorable and unfavorable interactions between protein binding site and ligands. These techniques include 3D-QSAR (CoMFA, CoMSIA) to understand ligand affinity and GRID/consensus principal component analysis (CPCA) to learn about selectivity requirements. Collectively these approaches, in combination with the presented SAR and structural data, provide useful information for the design of novel NOS inhibitors with increased isoform selectivity.

Pneumococcal lipoteichoic acid (LTA) is not as potent as staphylococcal LTA in stimulating Toll-like receptor 2

Streptococcus pneumoniae is a leading cause of gram-positive sepsis, and lipoteichoic acid (LTA) may be important in causing gram-positive bacterial septic shock. Even though pneumococcal LTA is structurally distinct from the LTA of other gram-positive bacteria, the immunological properties of pneumococcal LTA have not been well characterized. We have investigated the ability of LTAs to stimulate human monocytes by using highly pure and structurally intact preparations of pneumococcal LTA and its two structural variants. The variants were pneumococcal LTA with only one acyl chain (LTA-1) and completely deacylated LTA (LTA-0). The target cells used in the study were peripheral blood mononuclear cells (PBMCs) and two model cell lines (CHO/CD14/TLR2 and CHO/CD14/TLR4) that express human CD25 protein in response to Toll-like receptor 2 (TLR2) and TLR4 stimulation, respectively. Intact pneumococcal LTA and LTA-1 stimulated PBMC and CHO/CD14/TLR2 cells in a dose-dependent manner but did not stimulate CHO/CD14/TLR4 cells. Pneumococcal LTA was about 100-fold less potent than Staphylococcus aureus LTA in stimulating the CHO/CD14/TLR2 cells and PBMCs. LTA-0 (or pneumococcal teichoic acid) stimulated neither CHO/CD14/TLR2 nor CHO/CD14/TLR4 cells even at high concentrations. Excess teichoic acid, LTA-0, antibodies to phosphocholine, or antibodies to TLR4 did not inhibit the LTA-induced TLR2 stimulation. However, antibodies to CD14, TLR1, or TLR2 suppressed tumor necrosis factor alpha (TNF-alpha) production by PBMCs in response to LTA or LTA-1. These results suggest that pneumococcal LTA with one or both acyl chains stimulates PBMCs primarily via TLR2 with the help of CD14 and TLR1.

Nitric oxide, human diseases and the herbal products that affect the nitric oxide signalling pathway

1. Nitric oxide (NO) is formed enzymatically from l-arginine in the presence of nitric oxide synthase (NOS). Nitric oxide is generated constitutively in endothelial cells via sheer stress and blood-borne substances. Nitric oxide is also generated constitutively in neuronal cells and serves as a neurotransmitter and neuromodulator in non-adrenergic, non-cholinergic nerve endings. Furthermore, NO can also be formed via enzyme induction in many tissues in the presence of cytokines. 2. The ubiquitous presence of NO in the living body suggests that NO plays an important role in the maintenance of health. Being a free radical with vasodilatory properties, NO exerts dual effects on tissues and cells in various biological systems. At low concentrations, NO can dilate the blood vessels and improve the circulation, but at high concentrations it can cause circulatory shock and induce cell death. Thus, diseases can arise in the presence of the extreme ends of the physiological concentrations of NO. 3. The NO signalling pathway has, in recent years, become a target for new drug development. The high level of flavonoids, catechins, tannins and other polyphenolic compounds present in vegetables, fruits, soy, tea and even red wine (from grapes) is believed to contribute to their beneficial health effects. Some of these compounds induce NO formation from the endothelial cells to improve circulation and some suppress the induction of inducible NOS in inflammation and infection. 4. Many botanical medicinal herbs and drugs derived from these herbs have been shown to have effects on the NO signalling pathway. For example, the saponins from ginseng, ginsenosides, have been shown to relax blood vessels (probably contributing to the antifatigue and blood pressure-lowering effects of ginseng) and corpus cavernosum (thus, for the treatment of men suffering from erectile dysfunction; however, the legendary aphrodisiac effect of ginseng may be an overstatement). Many plant extracts or purified drugs derived from Chinese medicinal herbs with proposed actions on NO pathways are also reviewed.

Teichoic acids are not required for Streptococcus pneumoniae and Staphylococcus aureus cell walls to trigger the release of tumor necrosis factor by peripheral blood monocytes

In gram-negative bacteria, the outer membrane lipopolysaccharide is the main component triggering cytokine release from peripheral blood mononuclear cells (PBMCs). In gram-positive bacteria, purified walls also induce cytokine release, but stimulation requires 100 times more material. Gram-positive walls are complex megamolecules reassembling distinct structures. Only some of them might be inflammatory, whereas others are not. Teichoic acids (TA) are an important portion (> or =50%) of gram-positive walls. TA directly interact with C3b of complement and the cellular receptor for platelet-activating factor. However, their contribution to wall-induced cytokine-release by PBMCs has not been studied in much detail. In contrast, their membrane-bound lipoteichoic acids (LTA) counterparts were shown to trigger inflammation and synergize with peptidoglycan (PGN) for releasing nitric oxide (NO). This raised the question as to whether TA are also inflammatory. We determined the release of tumor necrosis factor (TNF) by PBMCs exposed to a variety of TA-rich and TA-free wall fragments from Streptococcus pneumoniae and Staphylococcus aureus. TA-rich walls from both organisms induced measurable TNF release at concentrations of 1 microg/ml. Removal of wall-attached TA did not alter this activity. Moreover, purified pneumococcal and staphylococcal TA did not trigger TNF release at concentrations as high as > or =100 microg/ml. In contrast, purified LTA triggered TNF release at 1 microg/ml. PGN-stem peptide oligomers lacking TA or amino-sugars were highly active and triggered TNF release at concentrations as low as 0.01 microg/ml (P. A. Majcherczyk, H. Langen, et al., J. Biol. Chem. 274:12537-12543,1999). Thus, although TA is an important part of gram-positive walls, it did not participate to the TNF-releasing activity of PGN.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Beneficial effect of hyperbaric oxygen pretreatment on lipopolysaccharide-induced shock in rats

1. We investigated the effect of hyperbaric oxygenation (HBO2) pretreatment on the production of exhaled nitric oxide (ENO) and the expression of lung inducible nitric oxide synthase (iNOS) by Escherichia coli lipopolysaccharide (LPS)-induced shock in an experimental rat model. 2. Rats were randomized into four groups, anaesthetized, mechanically ventilated with room air and infused with normal saline (2 mL/h) through the jugular vein for 5 h. Group 1 (NS) received only normal saline. Group 2 (HBO2-NS) was pretreated with HBO2 at 2.8 absolute atmospheres for 2 h and then received normal saline. Group 3 (LPS) received LPS, 20 mg/kg, i.v., bolus. Group 4 (HBO2-LPS) was pretreated with HBO2 for 2 h, followed by LPS. 3. Arterial blood gases, blood pressure, blood pH and ENO production were measured every 30 min. Plasma nitrite/nitrate (NOx) concentrations were assessed at the beginning (baseline) and at the end of the study. Lung myeloperoxidase (MPO) activity, iNOS expression and histological scores were measured for the evaluation of lung injury. 4. Administration of LPS was associated with decreased blood pressure and pH, increased ENO production, plasma NOx concentrations, lung iNOS expression and MPO activity. 5. Pretreatment with HBO2 significantly alleviated the LPS-induced hypotension, acidosis and decreased ENO production, plasma NOx concentrations, lung MPO activity and expression of iNOS. Hyperbaric O2 had no effect on control rats. 6. Our data show that HBO2 pretreatment has beneficial haemodynamic effects in rats with endotoxin shock. The beneficial effects of HBO2 may be partially mediated by decreased ENO production via reduced LPS-induced lung iNOS expression.

Endogenous versus exogenous glucocorticoid responses to experimental bacterial sepsis

Although lack of adrenals dramatically reduces resistance against sepsis generally, the value of glucocorticoid levels above those normally produced by stress remains controversial. An early and long-held concept is that glucocorticoid protection against lipopolysaccharides in animal models is important. Supporting this concept, C3H/HeJ mice, lacking Toll-like receptor-4 (TLR-4), and consequently, endotoxin hyporesponsive, have recently been shown to be resistant to glucocorticoid protection against live Escherichia coli. Effective antibiotic intervention, as an additional parameter and with concomitant administration of glucocorticoid, not only allows for expected antibiotic protection but also for glucocorticoid protection against E. coli or Staphylococcus aureus of mice sensitized to tumor necrosis factor alpha, regardless of the status of the TLR-4 receptor. TLRs, including but not limited to TLR-2, may be involved in glucocorticoid protective efficacy against Gram-positive and Gram-negative sepsis. Overlapping and possibly endotoxin-independent signaling may become important considerations.

Inducible nitric oxide synthase mediates bone loss in ovariectomized mice

Several clinical studies have shown that bone loss may be attributed to osteoclast recruitment induced by mediators of inflammation. In different experimental paradigms we have recently demonstrated that estrogen exhibits antiinflammatory activity by preventing the induction of inducible nitric oxide synthase (iNOS) and other components of the inflammatory reaction. To verify whether this could explain the estrogen-dependent blockade of osteoporosis, we investigated the effect of ovariectomy in mice in which iNOS activity had been blunted by genetic or pharmacological manipulation. The consequences of iNOS blockade were evaluated initially on bone formation and resorption by histomorphometric analysis. The proximal tibiae of mice with iNOS genotypes revealed that 32 d after ovariectomy bone volume and bone formation rate were significantly decreased, and osteoclast surface was increased. Conversely, in iNOS knockout (iNOSKO) and wild-type (WT) mice treated with a specific inhibitor of iNOS, N-iminoethyl-L-lysine, ovariectomy did not result in bone depletion. In WT mice, ovariectomy also affected bone formation, as shown by a decreased mineral apposition rate. Also in this case, iNOS inactivation prevented the effect of ovariectomy. Immunocytochemical analysis showed that after ovariectomy iNOS protein accumulates in chondrocytes, and a significant increase in nitrotyrosine and poly(ADP-ribose) synthetase staining was observed in the femur metaphyses. The increase in nitrotyrosine and poly(ADP-ribose) synthetase formation induced by ovariectomy was significantly reduced in sections from iNOSKO mice. These data indicate that in WT mice the observed induction of iNOS has functional relevance, because it leads to overproduction of nitric oxide and accumulation of highly reactive molecules, triggering a local inflammatory reaction. These inflammatory foci attract cytokines, well known actors in the mechanism of osteoclastogenesis. In iNOSKO mice the measurements of IL-1 beta, IL-6, and TNFalpha plasma levels showed that ovariectomy fails to elicit the increase observed in WT animals and suggests that iNOS plays a primary role in the protective effects of estrogens. To further support this hypothesis, we show that estradiol-dependent activation of estrogen receptor-alpha blocks phorbol 12-acetate 13-myristate-induced transcription of iNOS promoter in transfected cells, thus demonstrating that the promoter of iNOS is under estrogen negative control. Our findings point to a key role of iNOS in mediating the negative effects of estrogen depletion on bones and provide a novel mechanistic explanation for the effects of menopause in osteoporosis and possibly also in other diseases in which the inflammatory component is elevated.

Bench-to-bedside review: microvascular dysfunction in sepsis--hemodynamics, oxygen transport, and nitric oxide

The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.

Hypothermia attenuates iNOS, CAT-1, CAT-2, and nitric oxide expression in lungs of endotoxemic rats

Endotoxemia stimulates endogenous nitric oxide formation, induces transcription of arginine transporters, and causes lung injury. Hypothermia inhibits nitric oxide formation and is used as a means of organ preservation. We hypothesized that hypothermia inhibits endotoxin-induced intrapulmonary nitric oxide formation and that this inhibition is associated with attenuated transcription of enzymes that regulate nitric oxide formation, such as inducible nitric oxide synthase (iNOS) and the cationic amino acid transporters 1 (CAT-1) and 2 (CAT-2). Rats were anesthetized and randomized to treatment with hypothermia (18-24 degrees C) or normothermia (36-38 degrees C). Endotoxin was administered intravascularly. Concentrations of iNOS, CAT-1, CAT-2 mRNA, iNOS protein, and nitrosylated proteins were measured in lung tissue homogenates. We found that hypothermia abrogated the endotoxin-induced increase in exhaled nitric oxide and lung tissue nitrotyrosine concentrations. Western blot analyses revealed that hypothermia inhibited iNOS, but not endothelial nitric oxide synthase, protein expression in lung tissues. CAT-1, CAT-2, and iNOS mRNA concentrations were lower in the lungs of hypothermic animals. These findings suggest that hypothermia protects against intrapulmonary nitric oxide overproduction and nitric oxide-mediated lung injury by inhibiting transcription of iNOS, CAT-1, and CAT-2.

Interactions between lipoteichoic acid and peptidoglycan from Staphylococcus aureus: a structural and functional analysis

The cell wall of Gram-positive bacteria contains lipoteichoic acid (LTA) and peptidoglycan (PepG), which synergise to cause shock and organ failure in animals, and to activate human blood to release proinflammatory cytokines. The structural elements within LTA and PepG that are essential for the observed synergism are discussed.

Hypotension during septic shock does not correlate with exhaled nitric oxide in anesthetized rat

Sepsis is characterized by hypotension, acidosis, and increased nitric oxide (NO) production. The role of NO in the development of sepsis-related hypotension is still unclear. The relationship among exhaled nitric oxide (ENO), arterial blood pressure (BP), and pH after administration of lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFalpha) was investigated in anesthetized rats. Forty-three adult male Sprague-Dawley rats were randomized into five groups: group 1 (C, n = 8) received normal saline; group 2 (LPS-I, n = 8) received Escherichia coli (LPS) 10 mg/kg intravenously (i.v.); group 3 (LPS-h, n = 10) received 100 mg/kg LPS i.v.; group 4 (n = 9) was treated with 100 mg/kg i.v. aminoguanidine (AG) 1 h after receiving 100 mg/kg i.v. LPS; group 5 (TNFalpha, n = 8) received 1 microg recombinant rat TNFalpha i.v.. ENO, BP, and pH were measured every 30 min for 4 h whereas arterial blood gases and pH were measured every hour. LPS administration induced a dose-related increase in ENO and a dose-related decrease in BP and pH. AG blocked the increase in ENO after LPS but had minimal effect on BP and pH. TNFalpha administration increased ENO without changing BP and pH. In LPS-treated rats, no significant correlation was found between ENO and BP (r2 = 0.13, P= ns). However, there was a significant correlation between pH and BP (r2 = 0.7, P < 0.01). Our results suggest that, in this animal model, ENO may not be a key mediator in the development of systemic hypotension during sepsis, while acidosis may significantly contribute to it.

Migration inhibitory factor in the cerebral and systemic endothelium in sepsis and malaria

OBJECTIVE

We have included migration inhibitory factor (MIF) in an ongoing immunohistochemical study comparing the site and intensity of the generation of inflammatory mediators in falciparum malaria, sepsis, and other causes of pediatric death in Africa. We wanted to determine whether it could account for our observation that inducible nitric oxide synthase is less strongly induced in the cerebral, compared with the systemic, vasculature.

DATA SOURCES

Comparisons of tissue samples taken from blood vessel walls from the brain and the axillary space in a series of sepsis and falciparum malaria autopsies of African children.

DATA SUMMARY

Intense staining for MIF has been detected in endothelial cells of axillary region vessels of all sepsis cases and most of the malaria cases examined. This parallels our findings with inducible nitric oxide synthase staining. African and Western control tissues from noninfectious causes of death stained lightly or not at all. In contrast, MIF could not be detected in vascular endothelial cells within the brain, where inducible nitric oxide synthase staining was much less intense. Detection of both MIF and inducible nitric oxide synthase in ependymal and glial cells in the same brains served as an internal positive staining control.

CONCLUSION

These outcomes add weight to the proposal that endothelial cells are a site of intense inflammatory mediator activity in sepsis and malaria. They also suggest that suppression of anti-inflammatory glucocorticoids by MIF may be lower in the brain than elsewhere in the body. The lack of MIF in cerebral vasculature endothelial cells may be linked to the absence of thrombomodulin in these cells. The systemic cellular distribution and intensity of MIF in human systemic inflammatory states has not been described.

Role of lipoteichoic acid in infection and inflammation

Lipoteichoic acid (LTA) is a surface-associated adhesion amphiphile from Gram-positive bacteria and regulator of autolytic wall enzymes (muramidases). It is released from the bacterial cells mainly after bacteriolysis induced by lysozyme, cationic peptides from leucocytes, or beta-lactam antibiotics. It binds to target cells either non-specifically, to membrane phospholipids, or specifically, to CD14 and to Toll-like receptors. LTA bound to targets can interact with circulating antibodies and activate the complement cascade to induce a passive immune kill phenomenon. It also triggers the release from neutrophils and macrophages of reactive oxygen and nitrogen species, acid hydrolases, highly cationic proteinases, bactericidal cationic peptides, growth factors, and cytotoxic cytokines, which may act in synergy to amplify cell damage. Thus, LTA shares with endotoxin (lipopolysaccharide) many of its pathogenetic properties. In animal studies, LTA has induced arthritis, nephritis, uveitis, encephalomyelitis, meningeal inflammation, and periodontal lesions, and also triggered cascades resulting in septic shock and multiorgan failure. Binding of LTA to targets can be inhibited by antibodies, phospholipids, and specific antibodies to CD14 and Toll, and in vitro its release can be inhibited by non-bacteriolytic antibiotics and by polysulphates such as heparin, which probably interfere with the activation of autolysis. From all this evidence, LTA can be considered a virulence factor that has an important role in infections and in postinfectious sequelae caused by Gram-positive bacteria. The future development of effective antibacteriolitic drugs and multidrug strategies to attenuate LTA-induced secretion of proinflammatory agonists is of great importance to combat septic shock and multiorgan failure caused by Gram-positive bacteria.

Elevation of plasma peptidoglycan and peripheral blood neutrophil activation during hemorrhagic shock: plasma peptidoglycan reflects bacterial translocation and may affect neutrophil activation

OBJECTIVE

To investigate the relations among bacterial transloation, plasma peptidoglycan elevation, and peripheral blood neutrophil activation during hemorrhagic shock.

DESIGN

Prospective, randomized, unblinded animal study.

SETTING

Surgical research laboratories of Shiga University of Medical Science.

SUBJECTS

Male, specific pathogen-free Sprague-Dawley rats.

INTERVENTIONS

The rats were randomly divided into three groups: a conventional group with normal intestinal flora (NF), an antibiotic (streptomycin and penicillin G) decontaminated group (AD), and a sham shock group with normal intestinal flora. The NF and AD groups were subjected to hemorrhagic shock (mean arterial pressure 30 mm Hg, for 30 to 90 mins). Rats were killed at 30, 60, and 90 mins after shock induction. Systemic blood and mesenteric lymph nodes (MLNs) were cultured for the determination of bacterial translocation (BT). Systemic plasma peptidoglycan and endotoxin concentrations were measured. To evaluate peripheral blood neutrophil activation, phagocytosis and hydrogen peroxide generation were assayed by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

In the NF group, BT to MLNs was significantly increased from 30 mins after shock induction. Blood culture and plasma endotoxin were positive at 90 mins but there were no significant differences. Assayed plasma peptidoglycan was significantly increased at 90 mins. Phagocytosis and hydrogen peroxide generation were significantly increased. Assayed plasma peptidoglycan concentrations showed significant positive correlations with the magnitude of BT to MLNs (r2 = .54) and hydrogen peroxide generation (r2 = .22) in individual animals. Furthermore, BT and these parameters were significantly suppressed in the AD group.

CONCLUSIONS

First, we concluded that assayed plasma peptidoglycan reflects BT induced by hemorrhage because the increase in assayed plasma peptidoglycan was suppressed, as was BT, by antibiotic decontamination. Second, peripheral blood neutrophil activation was also suppressed when BT was prevented. We concluded BT to be involved in neutrophil activation. Our findings suggest hydrogen peroxide generation by neutrophils to be involved in plasma peptidoglycan elevation.

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.