Effect of free radical scavengers on diaphragmatic contractility in septic peritonitis

Medicinal evaluation and molecular docking study of osajin as an anti-inflammatory, antioxidant, and antiapoptotic agent against sepsis-associated acute kidney injury in rats

Despite efforts to find effective drugs for sepsis-associated acute kidney injury (SA-AKI), mortality rates in patients with SA-AKI have not decreased. Our study evaluated the protective effects of isoflavone osajin (OSJ) on SA-AKI in rats by targeting inflammation, oxidative stress, and apoptosis, which represent the cornerstones in the pathophysiological mechanism of SA-AKI. Polymicrobial sepsis was induced in rats via the cecal ligation and puncture (CLP) technique. Markers of oxidative stress were evaluated in kidney tissues using biochemical methods. The expression of interleukin-33 (IL-33), 8-hydroxydeoxyguanosine (8-OHdG), caspase-3, and kidney injury molecule-1 (KIM-1) was evaluated as indicators of inflammation, DNA damage, apoptosis, and SA-AKI respectively in the kidney tissues using immunohistochemical and immunofluorescent detection methods. The CLP technique significantly (p < 0.001) increased lipid peroxidation (LPO) levels and significantly (p < 0.001) decreased the activities of superoxide dismutase and catalase in kidney tissues. In the renal tissues, strong expression of IL-33, 8-OHdG, caspase-3, and KIM-1 was observed with severe degeneration and necrosis in the tubular epithelium and intense interstitial nephritis. In contrast, the administration of OSJ significantly (p < 0.001) reduced the level of LPO, markedly improved biomarkers of antioxidant status, decreased the levels of serum creatinine and urea, lowered the expression of IL-33, 8-OHdG, caspase-3, and KIM-1 and alleviated changes in renal histopathology. A promising binding score was found via a molecular docking investigation of the OSJ-binding mode with mouse IL-33 (PDB Code: 5VI4). Therefore, OSJ protects against SA-AKI by suppressing the IL-33/LPO/8-OHdG/caspase-3 pathway and improving the antioxidant system.

Mechanical ventilation preserves diaphragm mitochondrial function in a rat sepsis model

BACKGROUND

To describe the effect of mechanical ventilation on diaphragm mitochondrial oxygen consumption, ATP production, reactive oxygen species (ROS) generation, and cytochrome c oxidase activity and content, and their relationship to diaphragm strength in an experimental model of sepsis.

METHODS

A cecal ligation and puncture (CLP) protocol was performed in 12 rats while 12 controls underwent sham operation. Half of the rats in each group were paralyzed and mechanically ventilated. We performed blood gas analysis and lactic acid assays 6 h after surgery. Afterwards, we measured diaphragm strength and mitochondrial oxygen consumption, ATP and ROS generation, and cytochrome c oxidase activity. We also measured malondialdehyde (MDA) content as an index of lipid peroxidation, and mRNA expression of the proinflammatory interleukin-1β (IL-1β) in diaphragms.

RESULTS

CLP rats showed severe hypotension, metabolic acidosis, and upregulation of diaphragm IL-1β mRNA expression. Compared to sham controls, spontaneously breathing CLP rats showed lower diaphragm force and increased susceptibility to fatigue, along with depressed mitochondrial oxygen consumption and ATP production and cytochrome c oxidase activity. These rats also showed increased mitochondrial ROS generation and MDA content. Mechanical ventilation markedly restored mitochondrial oxygen consumption and ATP production in CLP rats; lowered mitochondrial ROS production by the complex 3; and preserved cytochrome c oxidase activity.

CONCLUSION

In an experimental model of sepsis, early initiation of mechanical ventilation restores diaphragm mitochondrial function.

Thymopentin improves the survival of septic mice by promoting the production of 15-deoxy-prostaglandin J2 and activating the PPARγ signaling pathway

Sepsis, a systemic inflammatory response syndrome (SIRS) caused by infection, is a major public health concern with limited therapeutic options. Infection disturbs the homeostasis of host, resulting in excessive inflammation and immune suppression. This has prompted the clinical use of immunomodulators to balance host response as an alternative therapeutic strategy. Here, we report that Thymopentin (TP5), a synthetic immunomodulator pentapeptide (Arg-Lys-Asp-Val-Tyr) with an excellent safety profile in the clinic, protects mice against cecal ligation and puncture (CLP)-induced sepsis, as shown by improved survival rate, decreased level of pro-inflammatory cytokines and reduced ratios of macrophages and neutrophils in spleen and peritoneum. Regarding mechanism, TP5 changed the characteristics of LPS-stimulated macrophages by increasing the production of 15-deoxy-Δ^12,14 -prostaglandin J2 (15-d-PGJ2). In addition, the improved effect of TP5 on survival rates was abolished by the peroxisome proliferator-activated receptor γ (PPARγ) antagonist GW9662. Our results uncover the mechanism of the TP5 protective effects on CLP-induced sepsis and shed light on the development of TP5 as a therapeutic strategy for lethal systemic inflammatory disorders.

Hydrogen Sulfide Attenuates Hydrogen Peroxide-Induced Injury in Human Lung Epithelial A549 Cells

Lung tissues are frequently exposed to a hyperoxia environment, which leads to oxidative stress injuries. Hydrogen sulfide (H₂S) is widely implicated in physiological and pathological processes and its antioxidant effect has attracted much attention. Therefore, in this study, we used hydrogen peroxide (H₂O₂) as an oxidative damage model to investigate the protective mechanism of H₂S in lung injury. Cell death induced by H₂O₂ treatment could be significantly attenuated by the pre-treatment of H₂S, resulting in a decrease in the Bax/Bcl-2 ratio and the inhibition of caspase-3 activity in human lung epithelial cell line A549 cells. Additionally, the results showed that H₂S decreased reactive oxygen species (ROS), as well as neutralized the damaging effects of H₂O₂ in mitochondria energy-producing and cell metabolism. Pre-treatment of H₂S also decreased H₂O₂-induced suppression of endogenous H₂S production enzymes, cystathionine-beta-synthase (CBS), cystathionine-gamma-lyase (CSE), and 3-mercapto-pyruvate sulfurtransferase (MPST). Furthermore, the administration of H₂S attenuated [Ca²⁺] overload and endoplasmic reticulum (ER) stress through the mitogen-activated protein kinase (MAPK) signaling pathway. Therefore, H₂S might be a potential therapeutic agent for reducing ROS and ER stress-associated apoptosis against H₂O₂-induced lung injury.

Diaphragm Weakness in the Critically Ill: Basic Mechanisms Reveal Therapeutic Opportunities

The diaphragm is the primary muscle of inspiration. Its capacity to respond to the load imposed by pulmonary disease is a major determining factor both in the onset of ventilatory failure and in the ability to successfully separate patients from ventilator support. It has recently been established that a very large proportion of critically ill patients exhibit major weakness of the diaphragm, which is associated with poor clinical outcomes. The two greatest risk factors for the development of diaphragm weakness in critical illness are the use of mechanical ventilation and the presence of sepsis. Loss of force production by the diaphragm under these conditions is caused by a combination of defective contractility and reduced diaphragm muscle mass. Importantly, many of the same molecular mechanisms are implicated in the diaphragm dysfunction associated with both mechanical ventilation and sepsis. This review outlines the primary cellular mechanisms identified thus far at the nexus of diaphragm dysfunction associated with mechanical ventilation and/or sepsis, and explores the potential for treatment or prevention of diaphragm weakness in critically ill patients through therapeutic manipulation of these final common pathway targets.

Effect of maturity and infection on the rate of relaxation of the respiratory muscles in ventilated, newborn infants

AIM

To assess the respiratory muscle time constant of relaxation (τ), an index of respiratory muscle function in ventilated newborns.

METHODS

Sixty-two infants (42 born prematurely) with a median gestational age of 29 [interquartile range (IQR) 26-37] weeks were prospectively studied. Measurement of τ was taken during spontaneous breathing on endotracheal continuous positive airway pressure prior to extubation, and τ was calculated from the reciprocal of the slope of the airway pressure decline versus time. Infants were classified as having had systemic or respiratory infection (positive microbiology) if they had any positive bacterial blood or respiratory culture prior to measurement.

RESULTS

Measurement of τ was taken at a median post-natal age of 6 (IQR 3-29) days. The median τ was higher in premature infants [17.4 (IQR 7.7-28.3) sec/cmH₂ O] compared to term infants [6.8 (IQR 4.4-8.7) sec/cmH₂ O, p < 0.001]. The median τ was higher in infants who had had positive microbiology [17.6 (IQR 9.9-29.1) sec/cmH₂ O] compared to infants with negative microbiology [8.0 (IQR 6.3-17.9) sec/cmH₂ O, p = 0.034]. τ was related to gestational age (r = -0.265, p = 0.003) and weight at measurement (r = -0.269, p = 0.002).

CONCLUSION

Respiratory muscle function in ventilated newborns is negatively affected by prematurity and previous systemic or respiratory infection.

Nitrite administration improves sepsis-induced myocardial and mitochondrial dysfunction by modulating stress signal responses

PURPOSE

A specific therapeutic strategy in sepsis-induced myocardial dysfunction remains to be determined. Nitrite may have cardioprotective effects against sepsis-induced myocardial dysfunction. This study investigated the cardioprotective effects of nitrite on myocardial function, mitochondrial bioenergetics, and its underlying molecular mechanisms in severe septic rats.

METHODS

Sepsis was induced in male Wistar rats by cecal ligation and puncture (CLP). After CLP, we administered normal saline (NS group) or nitrite (nitrite group) subcutaneously. We administered nitrite at different doses (0.1-10 mg/kg) to ascertain the most effective dose and examined cardiac function in an isolated heart experiment 8 h after CLP. We investigated mitochondrial bioenergetics and molecular mechanisms underlying the administration of nitrite in vitro.

RESULTS

In isolated heart experiments, the left ventricular developed pressure (96 ± 5 mmHg) at a moderate nitrite dose (1.0 mg/kg) was significantly higher than that in the NS group (75 ± 4 mmHg, P < 0.05). Mitochondrial oxidative phosphorylation in the nitrite group was significantly higher than that in the NS group (P < 0.01). Immunoblotting revealed that nitrite significantly increased the phosphorylation of Akt (P < 0.05) and reduced the nuclear translocation of NF-κB (P < 0.05) compared with the NS group. Nitrite was also shown to improve the rate of survival in severe septic rats (P < 0.001).

CONCLUSIONS

Our results showed that a moderate nitrite dose improved septic myocardial dysfunction at organ, cellular, and molecular levels via modulation of stress signal responses, which resulted in an improvement in survival.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Montelukast attenuates lipopolysaccharide-induced cardiac injury in rats

This study investigates the possible protective effects of montelukast (MNT) against lipopolysaccharide (LPS)-induced cardiac injury, in comparison to dexamethasone (DEX), a standard anti-inflammatory. Male Sprague Dawley rats (160–180 g) were assigned to five groups ( n = 8/group): (1) control; (2) LPS (10 mg/kg, intraperitoneal (i.p.)); (3) LPS + MNT (10 mg/kg, per os (p.o.)); (4) LPS + MNT (20 mg/kg, p.o.); and (5) LPS + DEX (1 mg/kg, i.p.). Twenty-four hours after LPS injection, heart/body weight (BW) ratio and percent survival of rats were determined. Serum total protein, creatine kinase muscle/brain (CK-MB), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) activities were measured. Heart samples were taken for histological assessment and for determination of malondialdehyde (MDA) and glutathione (GSH) contents. Cardiac tumor necrosis factor α (TNF-α) expression was evaluated immunohistochemically. LPS significantly increased heart/BW ratio, serum CK-MB, ALP, and LDH activities and decreased percent survival and serum total protein levels. MDA content increased in heart tissues with a concomitant reduction in GSH content. Immunohistochemical staining of heart specimens from LPS-treated rats revealed high expression of TNF-α. MNT significantly reduced percent mortality and suppressed the release of inflammatory and oxidative stress markers when compared with LPS group. Additionally, MNT effectively preserved tissue morphology as evidenced by histological evaluation. MNT (20 mg/kg) was more effective in alleviating LPS-induced heart injury when compared with both MNT (10 mg/kg) and DEX (1 mg/kg), as evidenced by decrease in positive staining by TNF-α immunohistochemically, decrease MDA, and increase GSH content in heart tissue. This study demonstrates that MNT might have cardioprotective effects against the inflammatory process during endotoxemia. This effect can be attributed to its antioxidant and/or anti-inflammatory properties.

Montelukast reduces sepsis-induced lung and renal injury in rats

This study was undertaken to examine the effects of montelukast (MNT) on lung and kidney injury in lipopolysaccharide (LPS) induced systemic inflammatory response. Rats were randomized into 5 groups (n = 8 rats/group): (i) Control; (ii) LPS treated (10 mg/kg body mass, by intraperitoneal (i.p.) injection); (iii) LPS + MNT (10 mg/kg, per oral (p.o.)); (iv) LPS + MNT (20 mg/kg, p.o); (v) LPS + dexamethasone (DEX; 1 mg/kg, i.p.). Twenty-four hours after sepsis was induced, the lung or kidney:body mass ratio and percent survival of rats were determined. Creatinine, blood urea nitrogen (BUN), albumin, total protein, and LDH activity were measured. Lung and kidney samples were taken for histological assessment and for determination of their malondialdehyde (MDA) and glutathione (GSH) contents. The expression of tumour necrosis factor α (TNF-α) in tissue was evaluated immunohistochemically. LPS significantly increased the organ:body mass ratio, serum creatinine, BUN, and LDH, and decreased serum albumin and total protein levels. MDA levels increased in lung and kidney tissues after treatment with LPS, and there was a concomitant reduction in GSH levels. Immunohistochemical staining of lung and kidney specimens from LPS-treated rats revealed high expression levels of TNF-α. MNT suppresses the release of inflammatory and oxidative stress markers. Additionally, MNT effectively preserved tissue morphology as evidenced by histological evaluation. These results demonstrate that MNT could have lung and renoprotective effects against the inflammatory process during endotoxemia. This effect can be attributed to its antioxidant and (or) anti-inflammatory properties.

Investigation into the role of Cu/Zn-SOD delivery system on its antioxidant and antiinflammatory activity in rat model of peritonitis

BACKGROUND

The current study evaluated the role of delivery system (solution, conventional liposomes and PEG-ylated liposomes) on superoxide dismutase (SOD) antioxidant and antiinflammatory properties in a rat model of lipopolysaccharide (LPS)-induced peritonitis.

METHODS

Fifty male albino rats (Wistar-Bratislava) were divided into five groups (n=10). Control group received saline and the other four groups received intraperitoneal injections of LPS (5mg/kg). Among the LPS-injected groups, one was LPS control group and the other three groups received the endotoxin injection 30min after receiving the same dose of SOD (500U/kg, ip) in different delivery systems: saline solution (SOD-S), conventional liposomes (SOD-L) or PEG-ylated liposomes (SOD-PL). The animals were euthanized 6h after LPS injection, blood samples were collected and acute phase response (total and differential leukocytes count; tumor necrosis factor α), antioxidants (total antioxidants; reduced glutathione), oxidative stress (total oxidants; lipid peroxidation) and nitrosative stress (nitric oxide metabolites; nitrotyrosine) were evaluated.

RESULTS

Intraperitoneal administration of LPS to rats induced a marked inflammatory and oxidative response in plasma. On the other hand, all SOD formulations had protective effect against endotoxin-induced inflammation and oxidative/nitrosative stress, but PEG-ylated liposomes had the most significant activity. Thus, SOD-PL administration significantly reduced the effects of LPS on bone marrow acute phase response, the oxidative status and production of nitric oxide metabolites, while increasing the markers of antioxidant response in a significant manner.

CONCLUSION

SOD supplementation interferes both with inflammatory and oxidative pathways involved in LPS-induced acute inflammation, PEG-ylated liposomal formulation being of choice among the tested delivery systems.

Reactive oxygen species mediated diaphragm fatigue in a rat model of chronic intermittent hypoxia

Respiratory muscle dysfunction documented in sleep apnoea patients is perhaps due to oxidative stress secondary to chronic intermittent hypoxia (CIH). We sought to explore the effects of different CIH protocols on respiratory muscle form and function in a rodent model. Adult male Wistar rats were exposed to CIH (n = 32) consisting of 90 s normoxia-90 s hypoxia (either 10 or 5% oxygen at the nadir; arterial O2 saturation ∼ 90 or 80%, respectively] for 8 h per day or to sham treatment (air-air, n = 32) for 1 or 2 weeks. Three additional groups of CIH-treated rats (5% O2 for 2 weeks) had free access to water containing N-acetyl cysteine (1% NAC, n = 8), tempol (1 mM, n = 8) or apocynin (2 mM, n = 8). Functional properties of the diaphragm muscle were examined ex vivo at 35 °C. The myosin heavy chain and sarco(endo)plasmic reticulum Ca(2+)-ATPase isoform distribution, succinate dehydrogenase and glyercol phosphate dehydrogenase enzyme activities, Na(+)-K(+)-ATPase pump content, concentration of thiobarbituric acid reactive substances, DNA oxidation and antioxidant capacity were determined. Chronic intermittent hypoxia (5% oxygen at the nadir; 2 weeks) decreased diaphragm muscle force and endurance. All three drugs reversed the deleterious effects of CIH on diaphragm endurance, but only NAC prevented CIH-induced diaphragm weakness. Chronic intermittent hypoxia increased diaphragm muscle myosin heavy chain 2B areal density and oxidized glutathione/reduced glutathione (GSSG/GSH) ratio. We conclude that CIH-induced diaphragm dysfunction is reactive oxygen species dependent. N-Acetyl cysteine was most effective in reversing CIH-induced effects on diaphragm. Our results suggest that respiratory muscle dysfunction in sleep apnoea may be the result of oxidative stress and, as such, antioxidant treatment could prove a useful adjunctive therapy for the disorder.

Hydrogen peroxide alters sternohyoid muscle function

Upper airway (UA) dilator muscles are critical for the maintenance of airway patency. Injury or fatigue to this group of muscles, as observed in patients with obstructive sleep apnoea (OSA) and animal models of OSA, may leave the UA susceptible to collapse. Although the mechanisms underlying respiratory muscle dysfunction are not completely understood, there is strong evidence suggesting a link between increased production of reactive oxygen species and altered muscle function. The aim of this study was to examine the effects of H2O2 on rat sternohyoid muscle function in vitro. Sternohyoid contractile and endurance properties were examined at 35 °C under control or hypoxic conditions. Studies were conducted in the presence of varying concentrations of H2O2 (0, 0.01, 0.1 and 1 mM). Muscle function was also examined in the presence of antioxidants [desferoxamine (DFX), catalase] and the reducing agent dithiothreitol (DTT). H2O2 decreased muscle endurance in a concentration-dependent manner. This was partially reversed by catalase, DFX and DTT. Our results suggest that oxidants may contribute to UA respiratory muscle dysfunction with implications for the control of UA patency in vivo.

Critical diaphragm failure in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the leading cause of death in infants between the ages of 1 and 12 months in developed countries. SIDS is by definition a diagnosis of exclusion, and its mechanism of action is unknown. The SIDS-Critical Diaphragm Failure (CDF) hypothesis postulates that the cause of death in SIDS is respiratory failure caused by CDF. Four principal risk factors contribute to CDF in young infants: undeveloped respiratory muscles, non-lethal infections, prone resting position, and REM sleep. Even relatively minor infections can cause an acute and significant reduction in diaphragm force generation capacity that in conjunction with other risk factors can precipitate CDF. CDF-induced acute muscle weakness leaves few, if any pathological marks on the affected tissue.Understanding the underlying mechanism of SIDS may help in formulating new approaches to child care that can help to further reduce the incidence of SIDS.

Double-stranded RNA-dependent protein kinase activation modulates endotoxin-induced diaphragm weakness

Diaphragm caspase-8 activation plays a key role in modulating sepsis-induced respiratory muscle dysfunction. It is also known that double-stranded RNA-dependent protein kinase (PKR) is a regulator of caspase-8 activation in neural tissue. We tested the hypothesis that the PKR pathway modulates sepsis-induced diaphragmatic caspase-8 activation. We first evaluated the time course of diaphragm PKR activation following endotoxin administration in mice. We then determined whether administration of a PKR inhibitor (2-aminopurine) prevents endotoxin-induced diaphragm caspase-8 activation and contractile dysfunction in mice. Finally, we investigated if inhibition of PKR (using either 2-aminopurine or transfection with dominant-negative PKR) blocks caspase-8 activation in cytokine treated C₂C₁₂ cells. Endotoxin markedly activated diaphragm PKR (with increases in both active phospho-PKR protein levels, P < 0.03, and directly measured PKR activity, P < 0.01) and increased active caspase-8 levels (P < 0.01). Inhibition of PKR with 2-aminopurine prevented endotoxin-induced diaphragm caspase-8 activation (P < 0.01) and diaphragm weakness (P < 0.001). Inhibition of PKR with either 2-aminopurine or transfection with dominant-negative PKR blocked caspase-8 activation in isolated cytokine-treated C₂C₁₂ cells. These data implicate PKR activation as a major factor mediating cytokine-induced skeletal muscle caspase-8 activation and weakness.

Sphingomyelinase stimulates oxidant signaling to weaken skeletal muscle and promote fatigue

Sphingomyelinase (SMase) hydrolyzes membrane sphingomyelin into ceramide, which increases oxidants in nonmuscle cells. Serum SMase activity is elevated in sepsis and heart failure, conditions where muscle oxidants are increased, maximal muscle force is diminished, and fatigue is accelerated. We tested the hypotheses that exogenous SMase and accumulation of ceramide in muscle increases oxidants in muscle cells, depresses specific force of unfatigued muscle, and accelerates the fatigue process. We also anticipated that the antioxidant N-acetylcysteine (NAC) would prevent SMase effects on muscle function. We studied the responses of C2C12 myotubes and mouse diaphragm to SMase treatment in vitro. We observed that SMase caused a 2.8-fold increase in total ceramide levels in myotubes. Exogenous ceramide and SMase elevated oxidant activity in C2C12 myotubes by 15-35% (P < 0.05) and in diaphragm muscle fiber bundles by 58-120% (P < 0.05). The SMase-induced increase in diaphragm oxidant activity was prevented by NAC. Exogenous ceramide depressed diaphragm force by 55% (P < 0.05), while SMase depressed maximal force by 30% (P < 0.05) and accelerated fatigue--effects opposed by treatment with NAC. In conclusion, our findings suggest that SMase stimulates a ceramide-oxidant signaling pathway that results in muscle weakness and fatigue.

Eicosapentaenoic acid preserves diaphragm force generation following endotoxin administration

Introduction

Infections produce severe respiratory muscle weakness, which contributes to the development of respiratory failure. An effective, safe therapy to prevent respiratory muscle dysfunction in infected patients has not been defined. This study examined the effect of eicosapentaenoic acid (EPA), an immunomodulator that can be safely administered to patients, on diaphragm force generation following endotoxin administration.

Methods

Rats were administered the following (n = 5/group): (a) saline, (b) endotoxin, 12 mg/kg IP, (c) endotoxin + EPA (1.0 g/kg/d), and (d) EPA alone. Diaphragms were removed and measurements made of the diaphragm force-frequency curve, calpain activation, caspase activation, and protein carbonyl levels.

Results

Endotoxin elicited large reductions in diaphragm specific force generation (P < 0.001), and increased diaphragm caspase activation (P < 0.01), calpain activation (P < 0.001) and protein carbonyl levels (P < 0.01). EPA administration attenuated endotoxin-induced reductions in diaphragm specific force, with maximum specific force levels of 27 ± 1, 14 ± 1, 23 ± 1, and 24 ± 1 N/cm², respectively, for control, endotoxin, endotoxin + EPA, and EPA treated groups (P < 0.001). EPA did not prevent endotoxin induced caspase activation or protein carbonyl formation but significantly reduced calpain activation (P < 0.02).

Conclusions

These data indicate that endotoxin-induced reductions in diaphragm specific force generation can be partially prevented by administration of EPA, a nontoxic biopharmaceutical that can be safely given to patients. We speculate that it may be possible to reduce infection-induced skeletal muscle weakness in critically ill patients by administration of EPA.

Sepsis-induced myopathy

Sepsis is a major cause of morbidity and mortality in critically ill patients, and despite advances in management, mortality remains high. In survivors, sepsis increases the risk for the development of persistent acquired weakness syndromes affecting both the respiratory muscles and the limb muscles. This acquired weakness results in prolonged duration of mechanical ventilation, difficulty weaning, functional impairment, exercise limitation, and poor health-related quality of life. Abundant evidence indicates that sepsis induces a myopathy characterized by reductions in muscle force-generating capacity, atrophy (loss of muscle mass), and altered bioenergetics. Sepsis elicits derangements at multiple subcellular sites involved in excitation contraction coupling, such as decreasing membrane excitability, injuring sarcolemmal membranes, altering calcium homeostasis due to effects on the sarcoplasmic reticulum, and disrupting contractile protein interactions. Muscle wasting occurs later and results from increased proteolytic degradation as well as decreased protein synthesis. In addition, sepsis produces marked abnormalities in muscle mitochondrial functional capacity and when severe, these alterations correlate with increased death. The mechanisms leading to sepsis-induced changes in skeletal muscle are linked to excessive localized elaboration of proinflammatory cytokines, marked increases in free-radical generation, and activation of proteolytic pathways that are upstream of the proteasome including caspase and calpain. Emerging data suggest that targeted inhibition of these pathways may alter the evolution and progression of sepsis-induced myopathy and potentially reduce the occurrence of sepsis-mediated acquired weakness syndromes.

Glutamine preserves skeletal muscle force during an inflammatory insult

The purpose of this study was to test the hypothesis that acute glutamine (GLN) supplementation can counteract skeletal muscle contractile dysfunction occurring in response to inflammation by elevating muscle heat shock protein (Hsp) expression and reducing inflammatory cytokines. Mice received 5 mg/kg lipopolysaccharide (LPS) concurrently with 1 g/kg GLN or vehicle treatments. Plantarflexor isometric force production was measured at 2 hours post-injection. Blood and gastrocnemius muscles were collected, and serum and muscle tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) and muscle Hsp70 and Hsp25 were quantified. Saline/LPS treatment was associated with a 33% reduction in maximal force and elevated serum TNF-alpha and IL-6. GLN completely prevented this force decrement with LPS. GLN was found to reduce muscle Hsp70 and IL-6, but only in the presence of LPS. GLN supplementation provides an effective, novel, clinically applicable means of preserving muscle force during acute inflammation. These data indicate that force preservation is not dependent on reductions in serum cytokines or muscle TNF-alpha, or elevated Hsp levels.

Neutralization of receptor for advanced glycation end-products and high mobility group box-1 attenuates septic diaphragm dysfunction in rats with peritonitis

OBJECTIVES

: To determine the relationship between intra-abdominal sepsis-induced high mobility group-box 1 and diaphragm contractile performance and to determine the inhibitory effects of antibodies for high mobility group-box 1 and receptor for advanced glycation end-products on septic peritonitis-induced diaphragmatic dysfunction, lipid peroxidation, and intracellular signal transduction in the rat diaphragm. In animal models of sepsis, production of reactive oxygen species has been shown to elicit diaphragmatic dysfunction. Extracellularly released high mobility group-box 1 can bind to cell surface receptors, such as receptor for advanced glycation end-products, eliciting inflammatory responses that lead to the development of sepsis.

DESIGN

: Prospective laboratory study.

SETTING

: University laboratory.

SUBJECTS

: Wistar rats (n = 186).

INTERVENTIONS

: Intra-abdominal sepsis was induced, using cecal ligation and perforation. In experiment 1, serum and diaphragm homogenates were obtained from sham-operated rats and from cecal ligation and perforation rats at 4-hr intervals postoperatively. In experiment 2, anti-high mobility group-box 1 and anti-receptor for advanced glycation end-products antibodies were administered 4 hrs and 8 hrs after cecal ligation and perforation to determine their effects on cecal ligation and perforation-induced diaphragm dysfunction, reactive oxygen species-related variables, and intracellular signal transduction.

MEASUREMENTS AND MAIN RESULTS

: In experiment 1, cecal ligation and perforation induced serum and diaphragmatic high mobility group-box 1 within 8 hrs postoperatively with a decline in diaphragmatic force generation at 12 hrs after cecal ligation and perforation. In experiment 2, anti-receptor for advanced glycation end-products and anti-high mobility group-box 1 antibodies significantly attenuated cecal ligation and perforation-induced diaphragmatic dysfunction in a dose-related manner. Diaphragmatic malondialdehyde concentration and phosphorylation level of extracellular signal-regulated kinase 1/2 in the groups treated with these antibodies were significantly lower than those in the nontreated group. Anti-receptor for advanced glycation end-products antibody downregulated high mobility group-box 1 expression in the diaphragm during sepsis.

CONCLUSIONS

: Cecal ligation and perforation induces high mobility group-box 1 in the diaphragm and increases serum high mobility group-box 1 level as a late-phase mediator, decreasing contractile performance by high mobility group-box 1 receptor for advanced glycation end-products interaction-mediated reactive oxygen species production. These findings suggested an important role of receptor for advanced glycation end-products-high mobility group-box 1 interaction in diaphragmatic dysfunction induced by lipid peroxidation in rats with intra-abdominal sepsis.

p38 Mitogen-activated protein kinase modulates endotoxin-induced diaphragm caspase activation

We postulated that the p38 pathway is activated in the diaphragm during sepsis and contributes to sepsis-induced diaphragm caspase activation and contractile dysfunction. This study determined whether: (1) endotoxin administration elicits p38 activation in the diaphragm; (2) cytokines activate p38 in isolated muscle cells; (3) activation of p38 is accompanied by caspase 8 activation; (4) inhibition of p38 prevents caspase 8 activation and; (5) inhibition of p38 prevents diaphragm dysfunction in endotoxin-treated animals. We first evaluated the time course of diaphragm p38 activation after endotoxin in mice. We then determined if p38 inhibitor administration could prevent caspase 8 activation in endotoxin-treated mice. We also assessed p38 and caspase 8 activation in C2C12 muscle cells treated with control media or a cytokine mixture, with or without concomitant chemical inhibition of p38 (using SB203580, 25 muM) or loss of p38 function due to cell transfection with a dominant negative p38 genetic construct. Endotoxin administration activated diaphragm p38 (P < 0.001), and cytokines activated p38 in C2C12 cells (P < 0.05). In both the diaphragm and cells, p38 activation was accompanied by increases in active caspase 8 (P < 0.01). Inhibition of p38 with either SB203580 or with a dominant negative p38 construct prevented caspase activation (P < 0.001). p38 inhibitors also prevented endotoxin-induced diaphragm weakness (P < 0.001). p38 modulates cytokine-induced skeletal muscle caspase activation.

Caspase and calpain activation both contribute to sepsis-induced diaphragmatic weakness

The cecal ligation perforation (CLP) model of sepsis is known to induce severe diaphragm dysfunction, but the cellular mechanisms by which this occurs remain unknown. We hypothesized that CLP induces diaphragm caspase-3 and calpain activation, and that these two enzymes act at the level of the contractile proteins to reduce muscle force generation. Rats (n = 4/group) were subjected to 1) sham surgery plus saline (intraperitoneal); 2) CLP; 3) CLP plus administration of calpain inhibitor peptide III (12 mg/kg ip); or 4) CLP plus administration of a caspase inhibitor, zVAD-fmk (3 mg/kg). At 24 h, diaphragms were removed, and the following were determined: 1) calpain and caspase-3 activities by fluorogenic assay; 2) caspase-3 and calpain I protein levels; 3) the intact diaphragm force-frequency relationship; and 4) the force generated by contractile proteins of single, permeabilized diaphragm fibers in response to exogenous calcium. CLP significantly increased diaphragm calpain activity (P < 0.02), caspase-3 activity (P < 0.02), active calpain I protein levels (P < 0.02), and active caspase-3 protein (P < 0.02). CLP also reduced the force generated by intact diaphragm muscle (P < 0.001) and the force generated by single-fiber contractile proteins (P < 0.001). Administration of either calpain inhibitor III or zVAD-fmk markedly improved force generation of both intact diaphragm muscle (P < 0.01) and single-fiber contractile proteins (P < 0.001). CLP induces significant reductions in diaphragm contractile protein force-generating capacity. This force reduction is mediated by the combined effects of activated caspase and calpain. Inhibition of these pathways may prevent diaphragm weakness in infected patients.

The JNK MAP kinase pathway contributes to the development of endotoxin-induced diaphragm caspase activation

We previously demonstrated that endotoxin-induced sepsis results in caspase 8-mediated diaphragmatic dysfunction. The upstream signaling pathways modulating diaphragm caspase 8 activation in response to endotoxin administration are, however, unknown. The purpose of the present study was to test the hypothesis that the JNK (Jun N-terminal Kinase) pathway is activated in the diaphragm during sepsis and contributes to sepsis-induced diaphragm caspase 8 activation. Endotoxin was administered to intact animals to model the effects of sepsis. We first assessed the time course of JNK activation after endotoxin (12 mg/kg i.p.) administration to mice. We then determined whether JNK inhibitor administration (30 microm/kg i.p. SP600125) could prevent caspase 8 activation and diaphragm weakness in endotoxin-treated mice. Experiments were then repeated comparing the effects of endotoxin on control and transgenic JNK knockout mice. We finally determined whether cytomix (LPS, TNFalpha, IL1beta, and IFN-gamma) exposure activated caspase 8 in C2C12 muscle cells and whether caspase 8 activation was attenuated by either chemical inhibition of JNK (30 microM SP600125) or transfection with a dominant negative JNK construct. We found that endotoxin activated diaphragm JNK (P < 0.001) and increased active caspase 8 (P < 0.01). Inhibition of JNK with SP600125 or by use of JNK-deficient animals prevented diaphragm caspase 8 activation (P < 0.01) and prevented diaphragm weakness (P < 0.05). JNK inhibition also prevented caspase 8 activation in cytokine-treated muscle cells (P < 0.001). These data implicate JNK activation as a major factor mediating inflammation-induced skeletal muscle caspase 8 activation and weakness.

Apoptotic-Related Protein Expression in the Diaphragm and the Effect of Dopamine During Inspiratory Resistance Loading

Dopamine (DA) is a free radical scavenger that attenuates apoptosis. We studied the effects of normal saline (NS) and DA on diaphragm apoptotic protein expression following 60 min of inspiratory resistance loading in rats. We tested for 27 apoptotic-related proteins and found 12 in the diaphragm. Of the 12 proteins, superoxide dismutase copper zinc (SOD [CuZn]) and proprioceptive event related potential (PERP) were significantly higher in the DA group than in the NS and sham groups ( p = .002, p = .007). DA group diaphragms had significantly greater expression of SOD (CuZn) than the NS ( p = .005) and sham group diaphragms ( p = .003). Likewise, the DA group had significantly greater expression of PERP than the NS group ( p = .008). These results suggest that DA decreases diaphragm apoptosis through elevated expression of SOD (CuZn). The identification of 12 apoptotic-related proteins will assist investigators as they study diaphragm apoptosis.

Antioxidant treatment reverses mitochondrial dysfunction in a sepsis animal model

Evidence from the literature has demonstrated that reactive oxygen species (ROS) play an important role in the development of multiple organ failure and septic shock. In addition, mitochondrial dysfunction has been implicated in the pathogenesis of multiple organ dysfunction syndrome (MODS). The hypothesis of cytopathic hypoxia postulates that impairment in mitochondrial oxidative phosphorylation reduces aerobic adenosine triphosphate (ATP) production and potentially induces MODS. In this work, our aim was to evaluate the effects of antioxidants on oxidative damage and energy metabolism parameters in liver of rats submitted to a cecal ligation puncture (CLP) model of sepsis. We speculate that CLP induces a sequence of events that culminate with liver cells death. We propose that mitochondrial superoxide production induces mitochondrial oxidative damage, leading to mitochondrial dysfunction, swelling and release of cytochrome c. These events occur in early sepsis development, as reported in the present work. Liver cells necrosis only occurs 24 h after CLP, but all other events occur earlier (6-12 h). Moreover, we showed that antioxidants may prevent oxidative damage and mitochondrial dysfunction in liver of rats after CLP. In another set of experiments, we verified that L-NAME administration did not reverse increase of superoxide anion production, TBARS formation, protein carbonylation, mitochondrial swelling, increased serum AST or inhibition on complex IV activity caused by CLP. Considering that this drug inhibits nitric oxide synthase and that no parameter was reversed by its administration, we suggest that all the events reported in this study are not mediated by nitric oxide. In conclusion, although it is difficult to extrapolate our findings to human, it is tempting to speculate that antioxidants may be used in the future in the treatment of this disease.

[Salbutamol improves diaphragm force generation in experimental sepsis]

OBJECTIVE

In a high percentage of cases, severe sepsis is accompanied by acute respiratory failure, in which weakness of the respiratory muscles plays an important role. Weakened respiratory muscles that are subjected to an increased mechanical load may develop muscle fatigue, with exacerbation of the respiratory failure. Because beta2-adrenergic drugs increase muscle contraction force, they may play a role in preventing and managing respiratory failure in septic patients. Our aim was to study the effects of salbutamol on diaphragm function in an animal model of peritoneal sepsis.

MATERIAL AND METHODS

The study included 3 groups of animals: a) a control group (n=7), in which the animals underwent a median laparotomy without visceral manipulation; b) a septic group (n=10), in which peritoneal sepsis was induced by cecal ligation and puncture (CLP); and c) a salbutamol group (n=7), in which peritoneal sepsis (CLP) was treated with salbutamol. Hemodynamic parameters and blood gases were measured in vivo. Diaphragm function was evaluated in vitro.

RESULTS

Salbutamol increased aortic blood flow and heart rate while it reduced mean arterial pressure in the animals with peritoneal sepsis (P< .05). Sepsis produced a significant drop in diaphragmatic force both before and after the application of a muscle-fatigue protocol. Treatment with salbutamol improved muscle contraction force before and after application of the protocol (P< .05).

CONCLUSIONS

The use of beta2-adrenergic drugs such as salbutamol improves diaphragm function in experimental sepsis. The mechanisms that produce this improvement require further study.

Direct inotropic effect of the beta-2 receptor agonist terbutaline on impaired diaphragmatic contractility in septic rats

The purpose of this study was to determine which beta-adrenoceptor agonist (1 or 2) is responsible for the direct inotropic effects on diaphragmatic contractility during sepsis. Rats were divided into two groups: a cecal ligation and perforation (CLP) group and a sham group. The hemidiaphragm was removed at 16 hours after the operation. Dobutamine (a beta-1 agonist) or terbutaline (a beta-2 agonist) was administered to an organ bath containing diaphragmatic tissues, and muscle contractility was assessed. Muscle contractility was diminished in the CLP group. Terbutaline increased peak twitch tension, caused an upward shift in the force-frequency curves, and improved contractility of the fatigued diaphragm in the CLP group. Dobutamine did not have any effect on these parameters in the CLP group. We conclude that activation of beta-2 adrenoceptors might be responsible for the direct inotropic effects on the diaphragm in an intra-abdominal septic model.

Free radical-mediated skeletal muscle dysfunction in inflammatory conditions

Loss of functional capacity of skeletal muscle is a major cause of morbidity in patients with a number of acute and chronic clinical disorders, including sepsis, chronic obstructive pulmonary disease, heart failure, uremia, and cancer. Weakness in these patients can manifest as either severe limb muscle weakness (even to the point of virtual paralysis), respiratory muscle weakness requiring mechanical ventilatory support, and/or some combination of these phenomena. While factors such as nutritional deficiency and disuse may contribute to the development of muscle weakness in these conditions, systemic inflammation may be the major factor producing skeletal muscle dysfunction in these disorders. Importantly, studies conducted over the past 15 years indicate that free radical species (superoxide, hydroxyl radicals, nitric oxide, peroxynitrite, and the free radical-derived product hydrogen peroxide) play an key role in modulating inflammation and/or infection-induced alterations in skeletal muscle function. Substantial evidence exists indicating that several free radical species can directly alter contractile protein function, and evidence suggests that free radicals also have important effects on sarcoplasmic reticulum function, on mitochondrial function, and on sarcolemmal integrity. Free radicals also modulate activation of several proteolytic pathways, including proteosomally mediated protein degradation and, at least theoretically, may also influence pathways of protein synthesis. As a result, free radicals appear to play an important role in regulating a number of downstream processes that collectively act to impair muscle function and lead to reductions in muscle strength and mass in inflammatory conditions.

Preferable inotropic action of procaterol, a potent bronchodilator, on impaired diaphragmatic contractility in an intraabdominal septic model

Intraabdominal sepsis can lead to acute respiratory failure, and concomitant diaphragmatic dysfunction may be aggravated by sepsis-induced airway hyperreactivity. We previously reported that isoproterenol, a nonselective beta-adrenoceptor agonist, increased diaphragmatic contractility and accelerated recovery from fatigue during sepsis. The purpose of this study was to demonstrate the direct inotropic effect of a potent bronchodilator and beta(2)-selective adrenoceptor agonist, procaterol, on fatigued diaphragmatic contractility in an intraabdominal septic model. Rats were divided into two groups: a cecal ligation and perforation (CLP) group and a sham group. CLP was performed in the CLP group whereas laparotomy alone was performed in the sham group. The left hemidiaphragm was removed at 16 h after the operation. The diaphragmatic tissues were exposed to procaterol (10(-8)-10(-6) M), and muscle contractility was assessed. Intracellular cyclic AMP levels were also measured in the CLP model. Procaterol caused an upward shift in the force-frequency curves in the CLP group whereas it had no effect on the curves in the sham group. Procaterol significantly increased cyclic AMP levels in the CLP model. We conclude that the potent bronchodilator procaterol had a direct and positive inotropic effect on the diaphragm in an intraabdominal septic model.

Low-level laser therapy can reduce lipopolysaccharide-induced contractile force dysfunction and TNF-alpha levels in rat diaphragm muscle

Our objective was to investigate if low-level laser therapy (LLLT) could improve respiratory function and inhibit tumor necrosis factor (TNF-alpha) release into the diaphragm muscle of rats after an intravenous injection of lipopolysaccharide (LPS) (5 mg/kg). We randomly divided Wistar rats in a control group without LPS injection, and LPS groups receiving either (a) no therapy, (b) four sessions in 24 h with diode Ga-AsI-Al laser of 650 nm and a total dose of 5.2 J/cm2, or (c) an intravenous injection (1.25 mg/kg) of the TNF-alpha inhibitor chlorpromazine (CPZ). LPS injection reduced maximal force by electrical stimulation of diaphragm muscle from 24.15+/-0.87 N in controls, but the addition of LLLT partly inhibited this reduction (LPS only: 15.01+/-1.1 N vs LPS+LLLT: 18.84+/-0.73 N, P<0.05). In addition, this dose of LLLT and CPZ significantly (P<0.05 and P<0.01, respectively) reduced TNF-alpha concentrations in diaphragm muscle when compared to the untreated control group.

Effect of dopamine on rat diaphragm apoptosis and muscle performance

The purpose of this study was to determine whether dopamine (DA) decreases diaphragm apoptosis and attenuates the decline in diaphragmatic contractile performance associated with repetitive isometric contraction using an in vitro diaphragm preparation. Strenuous diaphragm contractions produce free radicals and muscle apoptosis. Dopamine is a free radical scavenger and, at higher concentrations, increases muscle contractility by simulating beta2-adrenoreceptors. A total of 47 male Sprague-Dawley rats weighing 330-450 g were used in a prospective, randomized, controlled in vitro study. Following animal anaesthetization, diaphragms were excised, and muscle strips prepared and placed in a temperature-controlled isolated tissue bath containing Krebs-Ringer solution (KR) or KR plus 100 microm DA. The solutions were equilibrated with oxygen (O2) at 10, 21 or 95% and 5% carbon dioxide, with the balance being nitrogen. Diaphragm isometric twitch and subtetanic contractions were measured intermittently over 65 min. The diaphragms were then removed and, using a nuclear differential dye uptake method, the percentages of normal, apoptotic and necrotic nuclei were determined using fluorescent microscopy. There were significantly fewer apoptotic nuclei in the DA group diaphragms than in the KR-only group diaphragms in 10 and 21% O2 following either twitch or subtetanic contractions. Dopamine at 100 microm produced only modest increases in muscle performance in both 10 and 21% O2. The attenuation of apoptosis by DA was markedly greater than the effect of DA on muscle performance. Dopamine decreased diaphragmatic apoptosis, perhaps by preventing the activation of intricate apoptotic pathways, stimulating antiapoptotic mechanisms and/or scavenging free radicals.

N-ACETYLCYSTEINE PROTECTS THE RATS AGAINST PHRENIC NERVE DYSFUNCTION IN SEPSIS

This study investigates the association of oxidative stress with the function of the phrenic nerve and inquires whether N-acetylcysteine (NAC) may counteract the possible detrimental effects. Thirty rats were divided into three groups: sham, cecal ligation and puncture (CLP), and CLP plus NAC treatment. Sepsis was produced by the CLP procedure. NAC was administered at 70 mg/day for 7 days. Electrophysiology was evaluated by the needle electromyography of the diaphragm and phrenic nerve conduction study. Oxidative stress was evaluated by malondialdehyde (MDA), nitrite/nitrate (NN), and reduced-glutathione (ReGSH) levels and myeloperoxidase (MPO) and catalase (CAT) activities in the phrenic nerve. In the CLP group, ReGSH and CAT were decreased (P = 0.0001, P = 0.07, respectively); and MDA, MPO, and NN were increased (P = 0.02, P = 0.0001, P = 0.043, respectively), compared with the sham group. NAC administration increased the ReGSH (P = 0.036) and decreased the MDA, MPO, and NN (P = 0.008, P = 0.01, P = 0.032, respectively), compared with the CLP group. In the CLP group, electrophysiology revealed reductions in the number of motor unit action potentials (P = 0.0001) and prolongations in the latency of the compound nerve action potential (P = 0.0001), indicating phrenic nerve neuropathy. NAC administration significantly ameliorated these electrophysiological alterations (P = 0.011, P = 0.0001, respectively), compared with the CLP group. The present results showed that intraabdominal sepsis is closely associated with phrenic nerve neuropathy. In addition, NAC administration protects the rats against the detrimental events of sepsis.

Role of oxidative stress in the pathogenesis of septic ileus in mice

We investigated the role of oxidative stress in the pathogenesis of septic ileus. Sepsis was induced by intraperitoneal (i.p.) injection of lipopolysaccharides (LPS, 20 mg kg(-1)) in mice. The effect of two i.p. injections of superoxide dismutase [polyethylene glycol (PEG)-SOD, 4000 U kg(-1)] and catalase (PEG-CAT, 15,000 U kg(-1)) was investigated on gastric emptying, intestinal transit and total nitrite plasma concentrations. We also performed immunohistochemical experiments on gastric and ileal tissue. LPS significantly delayed gastric emptying and intestinal transit while plasma nitrite levels increased. Polyethylene glycol (PEG)-SOD reversed the endotoxin-induced delay in gastric emptying and improved the delay in intestinal transit without effect on plasma nitrite levels. PEG-CAT slightly improved the delay in gastric emptying without effect on intestinal transit. Immunohistochemistry showed the presence of nitrotyrosine (NT) and 4-hydroxy-2-nonenal (HNE) in the gastric and ileal mucosa of LPS-treated mice. Treatment with PEG-SOD or PEG-CAT of LPS mice diminished the presence of NT or HNE in both tissues. In addition, LPS induced a significant increase in inducible nitric oxide synthase (iNOS)-positive residential macrophages in the external musculature of stomach and ileum, which significantly decreased after PEG-SOD or PEG-CAT treatment. The present results support a role for oxidative and nitrosative stress in the pathogenesis of septic ileus in mice.

Sepsis Stage Dependently and Differentially Attenuates the Effects of Nondepolarizing Neuromuscular Blockers on the Rat Diaphragm In Vitro

We investigated the effects of early and late sepsis on the actions of nondepolarizing neuromuscular blockers by using a rat sepsis model induced by cecal ligation and puncture. Isometric twitch tensions of nerve-hemidiaphragm preparations elicited by indirect (phrenic nerve) supramaximal stimulation at 0.1 Hz were evaluated. Rocuronium, pancuronium, and d-tubocurarine dose-dependently decreased the twitch tensions of the nonseptic, early septic, and late septic diaphragms (P < 0.01 each by analysis of variance [ANOVA]). Late sepsis shifted the concentration-twitch tension curves rightward from those of nonsepsis to larger degrees than did early sepsis, as indicated by increases in 50% inhibitory concentration (IC(50)) values (P < 0.01 each by ANOVA and P < 0.01 or 0.05 by the Scheffe F test). The standardized rightward shifts in early and late sepsis were largest for pancuronium, second largest for rocuronium, and smallest for d-tubocurarine (5.741, 2.979, and 1.660 times in late sepsis, respectively; P < 0.01 each by ANOVA and the Scheffe F test). Sepsis-induced increases in IC(50) values did not accompany the decreases in slopes. The results indicate that sepsis induces hyposensitivities to nondepolarizing neuromuscular blockers, the degree of which depends on the stage of sepsis and on the kind of neuromuscular blocker.

Correlation of plasma and tissue oxidative stresses in intra-abdominal sepsis

BACKGROUND

The aim of this study was to investigate the correlation between plasma and tissue oxidative stress and the antioxidative response, by measuring malon dialdehyde (MDA) and glutathione (GSH) in late sepsis induced by cecal ligation and perforation.

MATERIALS AND METHODS

A prospective, randomized, controlled experimental study in rats was done. Forty rats, weighing 200-250 g, were randomly divided into two groups (n = 20). In group 1, laparotomy was performed under aseptic conditions, and the cecum ligated and perforated. The abdomen was closed. In group 2, sham control, there was only laparotomy. Twenty-four hours later, blood samples were taken by cardiac puncture for plasma MDA and GSH, followed by harvesting of samples from lung, liver, kidney, and heart in both groups.

RESULTS

In the liver, lung, plasma, heart, and kidney, MDA concentrations were increased in the sepsis group after 24 h (P < 0.001 for all organ samples). In the same organs, GSH concentrations were decreased by sepsis (P < 0.001 for all organ samples). In both groups, plasma MDA was positively correlated to MDA in heart (r = 0.82, P < 0.001), liver (r = 0.76, P < 0.001), lung (r = 0.78, P < 0.001), and kidney (r = 0.73, P < 0.001). Similarly, plasma GSH was positively correlated to GSH in liver (r = 0.93, P < 0.001), heart (r = 0.86, P < 0.001), lung (r = 0.91, P < 0.001), and kidney (r = 0.79, P < 0.001).

CONCLUSIONS

Plasma MDA and GSH were positively correlated with tissue MDA and GSH in intra-abdominal sepsis in a rat model.

Septic diaphragmatic dysfunction is prevented by Mn(III)porphyrin therapy and inducible nitric oxide synthase inhibition

OBJECTIVE

Decreased diaphragmatic contractility and organ failure observed during sepsis is mediated by an overproduction of nitric oxide ((.)NO)-derived species, mitochondria being a major target of oxidative and nitrative stress. We tested the potential protective effects of (a) a novel synthetic antioxidant, the manganese(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl) porphyrin (MnTE-2-PyP(5+)) and (b) the inducible (.)NO synthase inhibitor aminoguanidine (AG) on a rat model of sepsis.

SETTING

University research laboratories.

SUBJECTS AND INTERVENTIONS

Sepsis was induced by cecal ligation and perforation in rats.

MEASUREMENTS AND RESULTS

Systemic hemodynamics, pulmonary gas exchange, in vitro diaphragmatic function and mitochondrial respiration were evaluated. Moreover, plasma and mitochondrial oxidative and nitrative stress parameters were investigated. Sepsis determined diaphragmatic dysfunction and a significant decrease in mitochondrial coupling and respiration. Oxidative stress was evidenced by decreased plasma antioxidants and increased lipid oxidation. Tyrosine nitration was increased in the plasma and mitochondria of the septic animals. These alterations were ameliorated or prevented by either MnTE-2-PyP(5+) or AG.

CONCLUSIONS

Our results demonstrate that overproduction of (.)NO and (.)NO-derived reactive species play a critical role in mitochondrial impairment and diaphragmatic function during sepsis. More importantly, AG but mainly the novel metalloporphyrin MnTE-2-PyP(5+) were able to ameliorate diaphragmatic and mitochondrial dysfunction and could contribute to preventing organ failure during severe sepsis.

Olprinone improves diaphragmatic contractility and fatigability during abdominal sepsis in a rat model

BACKGROUND

Respiratory failure with diaphragmatic fatigability is common in patients suffering sepsis or septic shock. However, the development and progress of diaphragmatic fatigability remains poorly understood, and no method has been established to treat fatigability. In this study, we hypothesize that neutrophil activation contributes to the development of diaphragmatic fatigability. We also sought to investigate whether a phosphodiesterase inhibitor, olprinone, improves diaphragmatic fatigability associated with abdominal sepsis and inhibits an increase in myeloperoxidase activity in diaphragmatic muscle.

METHODS

Male Wistar rats were randomly assigned to a sham group, coecal legation perforation group (CLP), and a phosphodiesterase inhibitor (PDE) pretreated group. At 16 h after surgical procedure, the left hemidiaphragm was removed for the measurement of diaphragmatic contractility and fatigability. In addition, for the measurement of serial changes in myeloperoxidase activity, the right hemidiaphragm was also removed at 4, 8 or 16 h after the surgical procedure in each group.

RESULTS

In a septic model involving rats, we observed that diaphragmatic muscles were fatigable and myeloperoxidase activity increased. We also demonstrated that intraperitoneal administration of olprinone improves diaphragmatic fatigability and inhibits an increase in myeloperoxidase activity induced by abdominal sepsis.

CONCLUSION

Olprinone represents a potential therapy for cases of respiratory failure with diaphragmatic fatigability resulting from inhibition of neutrophil activation.

Treatment with N-acetylcysteine plus deferoxamine protects rats against oxidative stress and improves survival in sepsis*

OBJECTIVE

Oxidative stress plays an important role in the development of multiple organ failure and septic shock. Here we have evaluated the effects of a combination of antioxidants (N-acetylcysteine plus deferoxamine) in a murine model of polymicrobial sepsis induced by cecal ligation and puncture (CLP).

DESIGN

Prospective, randomized, controlled experiment.

SETTING

Animal basic science laboratory.

SUBJECTS

Male Wistar rats, weighing 300-350 g.

INTERVENTIONS

Rats subjected to CLP were treated with either N-acetylcysteine (20 mg/kg, 3 hrs, 6 hrs, 12 hrs, 18 hrs, and 24 hrs after CLP, subcutaneously) plus deferoxamine (20 mg/kg, 3 hrs and 24 hrs after CLP, subcutaneously) or vehicle with or without "basic support" (saline at 50 mL/kg immediately and 12 hrs after CLP plus ceftriaxone at 30 mg/kg and clindamycin 25 mg/kg every 6 hrs).

MEASUREMENTS AND MAIN RESULTS

After 12 hrs, tissue myeloperoxidase (indicator of neutrophil infiltration), thiobarbituric acid reactive species (as a marker of oxidative stress), catalase and superoxide dismutase activities (antioxidant enzymes), and mitochondrial superoxide production (index of uncoupling of electron transfer chain) were measured in major organs involved in septic response. Rats treated with antioxidants had significantly lower myeloperoxidase activity and thiobarbituric acid reactive species formation in all organs studied. Mitochondrial superoxide production was significantly reduced by antioxidant treatment. Furthermore, antioxidants significantly improved the balance between catalase and superoxide dismutase activities. Survival in untreated septic rats was 10%. Survival increased to 40% with fluids and antibiotics. In rats treated only with N-acetylcysteine plus deferoxamine, survival was also significantly improved (47%) in a manner similar to basic support. Survival increased to 66% with basic support with N-acetylcysteine plus deferoxamine.

CONCLUSIONS

Our data provide the first experimental demonstration that N-acetylcysteine plus deferoxamine reduces the consequences of septic shock induced by CLP in the rat, by decreasing oxidative stress and limiting neutrophil infiltration and mitochondrial dysfunction, thereby improving survival.

Geranylgeranylacetone attenuates septic diaphragm dysfunction by induction of heat shock protein 70*

OBJECTIVE

The purposes of the present study were to evaluate the induction of heat shock protein (HSP) 70 expression in the diaphragm by geranylgeranylacetone (GGA) administration and to determine the effect of HSP70 induction on diaphragm contractility measured in vitro and the production of oxygen-derived free radicals during experimental septic peritonitis.

DESIGN

Prospective laboratory study.

SETTING

University laboratory.

SUBJECTS

One-hundred sixty male Wistar rats.

INTERVENTIONS

In experiment 1, rats received GGA intragastrically, and time-dependent induction of HSP70 expression in the diaphragm was determined at 0, 12, 24, and 36 hrs after GGA administration. To evaluate dose-dependent inhibition of GGA-induced HSP70 expression by quercetin, rats were pretreated with progressive doses of quercetin before GGA administration. In experiment 2, rats received gum arabic solution (vehicle), 100, 200, or 400 mg/kg of GGA. In experiment 3, rats were pretreated with quercetin or glycerol before GGA or vehicle administration. Intra-abdominal sepsis was induced by cecal ligation and perforation (CLP) under inhalation anesthesia after GGA or vehicle administration in experiments 2 and 3.

MEASUREMENTS AND MAIN RESULTS

Western blot analysis using diaphragm homogenates obtained from normal rats showed that HSP70 expression peaked at 24 or 36 hrs after GGA administration and that pretreatment with >10 mg/kg of quercetin blocked the induction of HSP70 expression by GGA. CLP induced diaphragmatic dysfunction and increased diaphragmatic malondialdehyde concentrations and superoxide dismutase and glutathione peroxidase activities. GGA attenuated CLP-induced diaphragm dysfunction and increased malondialdehyde concentrations in a dose-dependent manner but did not affect superoxide dismutase and glutathione peroxidase activities after CLP. Diaphragm dysfunction and increased diaphragmatic malondialdehyde concentrations after CLP were maintained on quercetin pretreatment despite GGA administration.

CONCLUSIONS

GGA induces HSP70 expression in the diaphragm, and this induction attenuates septic diaphragm impairment by inhibiting the production of oxygen-derived free radicals.

Oxidative parameters and mortality in sepsis induced by cecal ligation and perforation

OBJECTIVE

This study assessed parameters of free radical damage to biomolecules, mitochondrial superoxide production, superoxide dismutase, and catalase activities and their relationship to sepsis mortality.

DESIGN AND SETTING

Prospective animal study in a university laboratory for experimental.

SUBJECTS

140 male Wistar rats.

INTERVENTIONS

The animals were randomly divided into three groups: sham-operated (n=20), cecal ligation and perforation resuscitated with normal saline (n=40), and cecal ligation and perforation with normal saline plus antibiotics (n=40).

MEASUREMENTS AND RESULTS

Blood samples were collected from all animals 3, 12, and 24 h after CLP through a jugular catheter inserted before CLP. Rats were evaluated during 5 days after the intervention. Nonsurvivor animals were grouped according to the duration between sepsis induction and death, and oxidative parameters were compared to survivors and sham-operated. Lipid peroxidation, protein carbonyls, and superoxide dismutase were significantly increased in nonsurvivor septic rats and were predictive of mortality. We demonstrated that there is a different modulation of superoxide dismutase and catalase in nonsurvivors during the course of septic response. There was a marked increase in superoxide dismutase activity without a proportional increase in catalase activity in nonsurvivors.

CONCLUSIONS

This is the first report of plasma superoxide dismutase as an earlier marker of mortality. Ours results might help to clarify an important aspect of oxidative response to sepsis, i.e., an increase in superoxide dismutase activity without a proportional increase in catalase activity

Disorders of the respiratory muscles

The act of breathing depends on coordinated activity of the respiratory muscles to generate subatmospheric pressure. This action is compromised by disease states affecting anatomical sites ranging from the cerebral cortex to the alveolar sac. Weakness of the respiratory muscles can dominate the clinical manifestations in the later stages of several primary neurologic and neuromuscular disorders in a manner unique to each disease state. Structural abnormalities of the thoracic cage, such as scoliosis or flail chest, interfere with the action of the respiratory muscles-again in a manner unique to each disease state. The hyperinflation that accompanies diseases of the airways interferes with the ability of the respiratory muscles to generate subatmospheric pressure and it increases the load on the respiratory muscles. Impaired respiratory muscle function is the most severe consequence of several newly described syndromes affecting critically ill patients. Research on the respiratory muscles embraces techniques of molecular biology, integrative physiology, and controlled clinical trials. A detailed understanding of disease states affecting the respiratory muscles is necessary for every physician who practices pulmonary medicine or critical care medicine.

Respiratory and limb muscle weakness induced by tumor necrosis factor-alpha: involvement of muscle myofilaments

The respiratory and limb skeletal muscles become weakened in sepsis, congestive heart failure, and other inflammatory diseases. A potential mediator of muscle weakness is tumor necrosis factor (TNF)-alpha, a cytokine that can stimulate muscle wasting and also can induce contractile dysfunction without overt catabolism. This study addressed the latter process. Murine diaphragm and limb muscle (flexor digitorum brevis [FDB]) preparations were used to determine the relative sensitivities of these muscles to TNF-alpha. Intact muscle fibers were isolated from FDB and microinjected with indo-1 to measure changes in sarcoplasmic calcium regulation. We found that TNF-alpha depressed tetanic force of the diaphragm and FDB to comparable degrees across a range of stimulus frequencies. In isolated muscle fibers, TNF-alpha decreased tetanic force without altering tetanic calcium transients or resting calcium levels. We conclude that (1) TNF-alpha compromises contractile function of diaphragm and limb muscle similarly, and (2) TNF-alpha decreases force by blunting the response of muscle myofilaments to calcium activation.