Respiratory muscle dysfunction in sepsis

Role of Protein Carbonylation in Skeletal Muscle Mass Loss Associated with Chronic Conditions

Muscle dysfunction, characterized by a reductive remodeling of muscle fibers, is a common systemic manifestation in highly prevalent conditions such as chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), cancer cachexia, and critically ill patients. Skeletal muscle dysfunction and impaired muscle mass may predict morbidity and mortality in patients with chronic diseases, regardless of the underlying condition. High levels of oxidants may alter function and structure of key cellular molecules such as proteins, DNA, and lipids, leading to cellular injury and death. Protein oxidation including protein carbonylation was demonstrated to modify enzyme activity and DNA binding of transcription factors, while also rendering proteins more prone to proteolytic degradation. Given the relevance of protein oxidation in the pathophysiology of many chronic conditions and their comorbidities, the current review focuses on the analysis of different studies in which the biological and clinical significance of the modifications induced by reactive carbonyls on proteins have been explored so far in skeletal muscles of patients and animal models of chronic conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and physiological aging. Future research will elucidate the specific impact and sites of reactive carbonyls on muscle protein content and function in human conditions.

Influence of mechanical ventilation and sepsis on redox balance in diaphragm, myocardium, limb muscles, and lungs

Mechanical ventilation (MV), using high tidal volumes (V(T)), causes lung (ventilator-induced lung injury [VILI]) and distant organ injury. Additionally, sepsis is characterized by increased oxidative stress. We tested whether MV is associated with enhanced oxidative stress in sepsis, the commonest underlying condition in clinical acute lung injury. Protein carbonylation and nitration, antioxidants, and inflammation (immunoblotting) were evaluated in diaphragm, gastrocnemius, soleus, myocardium, and lungs of nonseptic and septic (cecal ligation and puncture 24 hours before MV) rats undergoing MV (n = 7 per group) for 150 minutes using 3 different strategies (low V(T) [V(T) = 9 mL/kg], moderate V(T) [V(T) = 15 mL/kg], and high V(T) [V(T) = 25 mL/kg]) and in nonventilated control animals. Compared with nonventilated control animals, in septic and nonseptic rodents (1) diaphragms, limb muscles, and myocardium of high-V(T) rats exhibited a decrease in protein oxidation and nitration levels, (2) antioxidant levels followed a specific fiber-type distribution in slow- and fast-twitch muscles, (3) tumor necrosis factor α (TNF-α) levels were higher in respiratory and limb muscles, whereas no differences were observed in myocardium, and (4) in lungs, protein oxidation was increased, antioxidants were rather decreased, and TNF-α remained unmodified. In this model of VILI, oxidative stress does not occur in distant organs or skeletal muscles of rodents after several hours of MV with moderate-to-high V(T), whereas protein oxidation levels were increased in the lungs of the animals. Inflammatory events were moderately expressed in skeletal muscles and lungs of the MV rats. Concomitant sepsis did not strongly affect the MV-induced effects on muscles, myocardium, or lungs in the rodents.

Protein carbonylation and muscle function in COPD and other conditions

Skeletal muscle, the most abundant tissue in mammals, is essential for any activity in life. Muscle dysfunction is a common systemic manifestation in highly prevalent conditions such as chronic obstructive pulmonary disease (COPD), cancer cachexia, and sepsis. It has a significant impact on exercise tolerance, thus worsening the patients' quality of life and survival. Among several factors, oxidative stress is a major player in the etiology of skeletal muscle dysfunction associated with those conditions. Whereas low levels of oxidants are absolutely required for normal cell adaptation, high levels of reactive oxygen species (ROS) alter the function and structure of molecules such as proteins, DNA, and lipids. Specifically, protein carbonylation, a common variety of protein oxidation, was shown to alter the function of key enzymes and structural proteins involved in muscle contractile performance. Moreover, increased levels of ROS may also activate proteolytic systems, thus leading to enhanced protein breakdown in several models. In the current review, the specific modifications induced by carbonylation in protein structure and function in muscles have been described. Furthermore, the potential role of ROS in the activation of proteolytic systems in skeletal muscles is also discussed. The review summarizes the effects of protein carbonylation on muscles in several models and conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and aging. Future research should focus on the elucidation of the specific protein sites modified by ROS in these muscles using redox proteomics analyses and on the assessment of the consequent alterations in protein function and stability.

Delivery of recombinant adeno-associated virus vectors to rat diaphragm muscle via direct intramuscular injection

The diaphragm is the most important inspiratory muscle in all mammals, and ventilatory insufficiency caused by diaphragm dysfunction is the leading cause of morbidity and mortality in many genetic and acquired diseases affecting skeletal muscle. Currently, pharmacological inhibitors, genetically modified animals, and invasive procedures are used to study disorders affecting the diaphragm. However, these methodologies can be problematic because of off-target drug effects and the possible nonphysiological consequences of lifelong genetic alterations. Therefore, alternative methods to study this important respiratory muscle are needed. To resolve this, we have developed a methodology to deliver recombinant adeno-associated virus (rAAV) vectors to the rat diaphragm via direct intramuscular injection. We hypothesized that by direct injection of rAAV into the muscle we can selectively target the diaphragm and establish a novel experimental method for studying signaling pathways and also provide a strategy for effectively using rAAV to protect the diaphragm against disease. This report describes the methods and evidence to support the use of rAAV as a therapeutic intervention to study rat diaphragm biology during conditions that promote diaphragm dysfunction.

[Inflammation and oxidative stress in respiratory and limb muscles of patients with severe sepsis]

BACKGROUND AND OBJECTIVE

Oxidative stress and inflammation contribute to the diaphragm contractile dysfunction observed in animal models of sepsis and endotoxemia. In septic patients, molecular events have never been explored in their respiratory muscles. Levels of oxidative stress and inflammation were evaluated in a respiratory muscle, the external intercostal, and a limb muscle, the vastus lateralis, of patients with sepsis.

PATIENTS AND METHODS

Levels of oxidized and nitrated proteins, protein adducts of malondialdehyde and hydroxinonenal, antioxidant enzymes catalase and Mn-superoxide dismutase, tumor necrosis factor (TNF)-α, TNF-α receptors i and ii, interleukin (IL)-1 and IL-6, the panleukocyte marker CD18, and fiber type composition were explored using immunoblotting, real time-polymerase chain reaction, and immunohistochemistry in the external intercostal and vastus lateralis of patients with severe sepsis and/or septic shock.

RESULTS

Compared to the controls, in septic patients, levels of oxidized and nitrated proteins were increased in the vastus lateralis, but not in the external intercostal, while those of the antioxidant enzymes did not differ, and the proportions and sizes of the muscle fibers were not significantly different in any muscle between patients and controls.

CONCLUSIONS

Differences in activity between the respiratory and limb muscles may account for the differential pattern of oxidative stress and inflammation observed among patients with severe sepsis. These findings may have relevant implications for the clinical and therapeutic management of these patients.

Turning up the heat: immune brinksmanship in the acute-phase response

The acutephase response (APR) is a systemic response to severe trauma, infection, and cancer, although many of the numerous cytokine-mediated components of the APR are incompletely understood. Some of these components, such as fever, reduced availability of iron and zinc, and nutritional restriction due to anorexia, appear to be stressors capable of causing harm to both the pathogen and the host. We review how the host benefits from differences in susceptibility to stress between pathogens and the host. Pathogens, infected host cells, and neoplastic cells are generally more stressed or vulnerable to additional stress than the host because: (a) targeted local inflammation works in synergy with APR stressors; (b) proliferation/growth increases vulnerability to stress; (c) altered pathogen physiology results in pathogen stress or vulnerability; and (d) protective heat shock responses are partially abrogated in pathogens since their responses are utilized by the host to enhance immune responses. Therefore, the host utilizes a coordinated system of endogenous stressors to provide additional levels of defense against pathogens. This model of immune brinksmanship can explain the evolutionary basis for the mutually stressful components of the APR.

NF-κB activation and polyubiquitin conjugation are required for pulmonary inflammation-induced diaphragm atrophy

Loss of diaphragm muscle strength in inflammatory lung disease contributes to mortality and is associated with diaphragm fiber atrophy. Ubiquitin (Ub) 26S-proteasome system (UPS)-dependent protein breakdown, which mediates muscle atrophy in a number of physiological and pathological conditions, is elevated in diaphragm muscle of patients with chronic obstructive pulmonary disease. Nuclear factor kappa B (NF-κB), an essential regulator of many inflammatory processes, has been implicated in the regulation of poly-Ub conjugation of muscle proteins targeted for proteolysis by the UPS. Here, we test if NF-κB activation in diaphragm muscle and subsequent protein degradation by the UPS are required for pulmonary inflammation-induced diaphragm atrophy. Acute pulmonary inflammation was induced in mice by intratracheal lipopolysaccharide instillation. Fiber cross-sectional area, ex vivo tyrosine release, protein poly-Ub conjugation, and inflammatory signaling were determined in diaphragm muscle. The contribution of NF-κB or the UPS to diaphragm atrophy was assessed in mice with intact or genetically repressed NF-κB signaling or attenuated poly-Ub conjugation, respectively. Acute pulmonary inflammation resulted in diaphragm atrophy measured by reduced muscle fiber cross-sectional area. This was accompanied by diaphragm NF-κB activation, and proteolysis, measured by tyrosine release from the diaphragm. Poly-Ub conjugation was increased in diaphragm, as was the expression of muscle-specific E3 Ub ligases. Genetic suppression of poly-Ub conjugation prevented inflammation-induced diaphragm muscle atrophy, as did muscle-specific inhibition of NF-κB signaling. In conclusion, the present study is the first to demonstrate that diaphragm muscle atrophy, resulting from acute pulmonary inflammation, requires NF-κB activation and UPS-mediated protein degradation.

Systemic inflammation impairs respiratory chemoreflexes and plasticity

Many lung and central nervous system disorders require robust and appropriate physiological responses to assure adequate breathing. Factors undermining the efficacy of ventilatory control will diminish the ability to compensate for pathology, threatening life itself. Although most of these same disorders are associated with systemic and/or neuroinflammation, and inflammation affects neural function, we are only beginning to understand interactions between inflammation and any aspect of ventilatory control (e.g. sensory receptors, rhythm generation, chemoreflexes, plasticity). Here we review available evidence, and present limited new data suggesting that systemic (or neural) inflammation impairs two key elements of ventilatory control: chemoreflexes and respiratory motor (versus sensory) plasticity. Achieving an understanding of mechanisms whereby inflammation undermines ventilatory control is fundamental since inflammation may diminish the capacity for natural, compensatory responses during pathological states, and the ability to harness respiratory plasticity as a therapeutic strategy in the treatment of devastating breathing disorders, such as during cervical spinal injury or motor neuron disease.

Protein nitration is associated with increased proteolysis in skeletal muscle of bile duct ligation-induced cirrhotic rats

Cirrhosis is characterized by skeletal muscle wasting. In this study, the effects of nitric oxide production on skeletal muscle protein nitration and degradation in cirrhosis were investigated. Cirrhosis was induced by bile duct ligation (BDL) in Sprague-Dawley rats for 4 weeks. The BDL-induced cirrhotic rats and sham-operated rats were then injected daily with either saline or N(G)-l-nitro-arginine methyl ester (l-NAME) for 7 days from week 4 to week 5, after which nitrite/nitrate, glutathione reduction, as well as protein nitration, ubiquitination, and degradation were assessed in skeletal muscle. Elevated muscular nitrite/nitrate concentrations, protein nitration, total ubiquitin conjugates, and degradation fragments of myosin heavy chain as well as diminished glutathione reduction levels were observed in BDL-induced cirrhotic rats as compared with controls. Administration of l-NAME for 1 week led to reduction of nitrite/nitrate levels; protein nitration was also decreased in the skeletal muscle. In addition, ubiquitination of muscular proteins and degradation of myosin heavy chain were significantly diminished after treatment of l-NAME. In conclusion, nitrosative stress occurred in the skeletal muscle of BDL-induced cirrhotic rats and may lead to increased proteolysis of muscle-specific structural proteins.

Intensive care unit-acquired weakness: risk factors and prevention

Intensive care unit-acquired weakness, the main clinical sign of critical illness neuromyopathy, is an increasingly recognized cause of prolonged mechanical ventilation and delayed return to physical self-sufficiency. Identifying risk factors and developing preventive measures are therefore important goals. Several studies on risk factors for critical illness neuromyopathy including prospective observational studies with a multivariate analysis of potential risk factors were conducted over the last decade. A large body of data is also available from two large prospective randomized trials comparing the effect of strict vs. conventional blood-glucose control on intensive care unit mortality and on secondary outcomes including the occurrence of critical illness neuromyopathy. Five central risk factors and their related potential measures to prevent intensive care unit-acquired weakness can be identified including multiple organ failure, muscle inactivity, hyperglycemia, and use of corticosteroids and neuromuscular blockers. Although strong evidence regarding the efficacy of preventive measures is still lacking, the results of available studies are promising and cast doubt on the widespread belief that the treatment of intensive care unit-acquired weakness is essentially supportive. Early identifying and treating conditions leading to multiple organ failure, especially severe sepsis and septic shock, avoiding unnecessary deep sedation and excessive blood glucose levels, promoting early mobilization, and carefully weighing the risks and benefits of corticosteroids might contribute to reduce the incidence and severity of intensive care unit-acquired weakness.

Impairment of diaphragm muscle force and neuromuscular transmission after normothermic cardiopulmonary bypass: effect of low-dose inhaled CO

Cardiopulmonary bypass (CPB) is associated with significant postoperative morbidity, but its effects on the neuromuscular system are unclear. Recent studies indicate that even relatively short periods of mechanical ventilation result in significant neuromuscular effects. Carbon monoxide (CO) has gained recent attention as therapy to reduce the deleterious effects of CPB. We hypothesized that 1) CPB results in impaired neuromuscular transmission and reduced diaphragm force generation; and 2) CO treatment during CPB will mitigate these effects. In adult male Sprague-Dawley rats, diaphragm muscle-specific force and neuromuscular transmission properties were measured 90 min after weaning from normothermic CPB (1 h). During CPB, either low-dose inhaled CO (250 ppm) or air was administered. The short period of mechanical ventilation used in the present study ( approximately 3 h) did not adversely affect diaphragm muscle contractile properties or neuromuscular transmission. CPB elicited a significant decrease in isometric diaphragm muscle-specific force compared with time-matched, mechanically ventilated rats ( approximately 25% decline in both twitch and tetanic force). Diaphragm muscle fatigability to 40-Hz repetitive stimulation did not change significantly. Neuromuscular transmission failure during repetitive activation was 60 +/- 2% in CPB animals compared with 76 +/- 4% in mechanically ventilated rats (P < 0.05). CO treatment during CPB abrogated the neuromuscular effects of CPB, such that diaphragm isometric twitch force and neuromuscular transmission were no longer significantly different from mechanically ventilated rats. Thus, CPB has important detrimental effects on diaphragm muscle contractility and neuromuscular transmission that are largely mitigated by CO treatment. Further studies are needed to ascertain the underlying mechanisms of CPB-induced neuromuscular dysfunction and to establish the potential role of CO therapy.

Skeletal muscle contractile properties and proinflammatory cytokine gene expression in human endotoxaemia

Background

Muscle dysfunction associated with sepsis contributes to morbidity and mortality but the underlying mechanisms are unclear. This study examined whether muscle weakness relates to an intrinsic defect in contraction, or to central mechanisms associated with acute illness, and whether systemic endotoxaemia induces changes in gene expression for proinflammatory cytokines within human muscle in vivo.

Methods

In this experimental study, 12 healthy men received intravenous Escherichia coli lipopolysaccharide (LPS, 4 ng/kg) or saline (control). Voluntary and electrically stimulated quadriceps contraction, and tumour necrosis factor (TNF) α mRNA expression in quadriceps muscle biopsies were studied before and after the infusion.

Results

Endotoxaemia induced transient weakness of voluntary quadriceps contraction, equivalent to a 7·8 (95 per cent confidence interval 2·1 to 13·5) per cent reduction in contractile force at 180 min (P = 0·027) and a 9·0 (5·2 to 12·8) per cent reduction at 300 min (P = 0·008). Electrically stimulated contraction was unaffected. LPS administration resulted in an apparent fibre-specific induction of TNF-α mRNA.

Conclusion

Endotoxaemia results in a reduction in voluntary muscle contractile force without an apparent defect in stimulated muscle contraction. Loss of volition may be a more important factor than intrinsic dysfunction in acute sepsis-associated human muscle weakness.

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.

Infection decreases fatty acid oxidation and nuclear hormone receptors in the diaphragm

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARalpha and beta/delta, RXRalpha, beta, and gamma, thyroid hormone receptor alpha and beta, and estrogen related receptor alpha (ERRalpha) and their coactivators PGC-1alpha, PGC-1beta, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARalpha deficient mice, baseline CPT-1beta and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARalpha signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis.

Bench-to-bedside review: ventilatory abnormalities in sepsis

In septic patients increased central drive and increased metabolic demands combine to increase energy demands on the ventilatory muscles. This occurs at a time when energy supplies are limited and energy production hindered, and it leads to an energy supply-demand imbalance and often ventilatory failure. Problems related to contractile function of the ventilatory muscles also contribute, especially when the clinical course is prolonged. The increased ventilatory activity increases interactions between the ventilatory and cardiovascular systems, and when ventilatory muscles fail and mechanical ventilatory support is required a new set of problems emerges. In this review I discuss factors related to ventilatory muscle failure, giving emphasis to mechanical and supply demand aspects. I also review the implications of changes in ventilatory patterns for heart-lung interactions.

The alteration of autonomic function in multiple organ dysfunction syndrome

Autonomic dysfunction is associated with the severity of illness and mortality in patients with multiple organ dysfunction syndrome (MODS) and may contribute significantly to the pathogenesis of this syndrome. Several treatment approaches may possibly restore autonomic function in MODS and thus cause the survival benefit.

[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.

Respiratory weakness is associated with limb weakness and delayed weaning in critical illness

OBJECTIVE

Although critical illness neuromyopathy might interfere with weaning from mechanical ventilation, its respiratory component has not been investigated. We designed a study to assess the level of respiratory muscle weakness emerging during the intensive care unit stay in mechanically ventilated patients and to examine the correlation between respiratory and limb muscle strength and the specific contribution of respiratory weakness to delayed weaning.

DESIGN

Prospective observational study.

SETTING

Two medical, one surgical, and one medicosurgical intensive care units in two university hospitals and one university- affiliated hospital.

PATIENTS

A total of 116 consecutive patients were enrolled after >or=7 days of mechanical ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Maximal inspiratory and expiratory pressures and vital capacity were measured via the tracheal tube on the first day of return to normal consciousness. Muscle strength was measured using the Medical Research Council score. After standardized weaning, successful extubation was defined as the day from which mechanical ventilatory support was no longer required within the next 15 days. The median value (interquartile range) of maximal inspiratory pressure was 30 (20-40) cm H2O, maximal expiratory pressure was 30 (20-50) cm H2O, and vital capacity was 11.1 (6.3-19.8) mL/kg. Maximal inspiratory pressure, maximal expiratory pressure, and vital capacity were significantly correlated with the Medical Research Council score. The median time (interquartile range) from awakening to successful extubation was 6 (1-17) days. Low maximal inspiratory pressure (hazard ratio, 1.86; 95% confidence interval, 1.07-3.23), maximal expiratory pressure (hazard ratio, 2.18; 95% confidence interval, 1.44-3.84), and Medical Research Council score (hazard ratio, 1.96; 95% confidence interval, 1.27-3.02) were independent predictors of delayed extubation. Septic shock before awakening was significantly associated with respiratory weakness (odds ratio, 3.17; 95% confidence interval, 1.17-8.58).

CONCLUSIONS

Respiratory and limb muscle strength are both altered after 1 wk of mechanical ventilation. Respiratory muscle weakness is associated with delayed extubation and prolonged ventilation. In our study, septic shock is a contributor to respiratory weakness.

Ventilatory response to hypoxia during endotoxemia in young rats: role of nitric oxide

Administration of Escherichia coli endotoxin attenuates the ventilatory response to hypoxia (VRH) in newborn piglets, but the mechanisms responsible for this depression are not clearly understood. Nitric oxide (NO) production increases during sepsis and elevated NO levels can inhibit carotid body function. The role of endothelial NO on the VRH during endotoxemia was evaluated in 26 young rats. Minute ventilation (VE) and oxygen consumption (VO2) were measured in room air (RA) and during 30 min of hypoxia (10% O2) before and after E. coli endotoxin administration. During endotoxemia, animals received placebo (PL, n = 8); a nonselective nitric oxide synthase (NOS) inhibitor (NG-nitro-L-arginine methyl ester, L-NAME, n = 9), or a neuronal NOS (nNOS) inhibitor (7-nitroindazole, 7-NI, n = 9). During endotoxemia, a larger increase in VE was observed only during the first min of hypoxia in the L-NAME group when compared with PL or 7-NI (p < 0.001). VRH was similar in the PL and 7-NI groups. A larger decrease in VO2 at 30 min of hypoxia was observed in L-NAME and 7-NI groups when compared with PL (p < 0.03). These data demonstrate that the attenuation of the early VRH during endotoxemia is in part mediated by an inhibitory effect of endothelial NO on the respiratory control mechanisms.

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.

Critical illness neuromuscular syndromes

Critical illness neuromyopathy (CINM) is the most common peripheral neuromuscular disorder encountered in the ICU. Bilateral diffuse weakness predominant in the proximal part of the limbs after improvement of the acute phase of the critical illness is highly suggestive of CINM. Although muscle and peripheral nerve are often involved in combination, muscle involvement alone is increasingly identified on electrophysiologic investigation, including direct muscle stimulation. Respiratory weakness results in delayed weaning and prolonged mechanical ventilation. Besides muscle immobilization and prolonged sepsis-induced multiorgan failure, which are risk factors for CINM, hyperglycemia and use of corticosteroids might have a deleterious effect on the neuromuscular system in critically ill patients.

Critical Illness Neuromuscular Syndromes

Critical illness neuromyopathy (CINM) is the most common peripheral neuromuscular disorder encountered in the ICU. Bilateral diffuse weakness predominant in the proximal part of the limbs after improvement of the acute phase of the critical illness is highly suggestive of CINM. Although muscle and peripheral nerve often are involved in combination, muscle involvement alone increasingly is identified on electrophysiological investigation, including direct muscle stimulation. Respiratory muscles also are involved, and CINM may cause delayed weaning and prolonged MV. Besides muscle immobilization and prolonged sepsis-induced multiple organ failure, which are both strong contributors to CINM, hyperglycemia and use of corticosteroids also might have a deleterious effect on the neuromuscular system in critically ill patients.

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.

A selective beta2-adrenergic agonist, terbutaline, improves sepsis-induced diaphragmatic dysfunction in the rat

BACKGROUND

Sepsis causes diaphragmatic dysfunction, which can lead to the development of respiratory failure. We previously reported that isoproterenol, non-selective beta-adrenergic agonist, improved contractility of the diaphragm in a septic rat model. Since beta(2)-adrenoceptor agonists are widely used in the treatment of chronic respiratory disease, we investigated the effect of terbutaline, a selective beta(2)-adrenergic agonist, on contractility of the septic rat diaphragm and the contribution of intracellular Ca(2+) to the effect of terbutaline in vitro.

METHODS

Forty-eight rats were divided into a sham group (in which sham laparotomy was performed) and a CLP group (in which peritonitis was induced by cecal ligation and perforation). The left hemidiaphragm was removed at 16 h after the operation. The effect of terbutaline (10(-)(6) M) on contractility of the diaphragm was assessed by twitch characteristics (twitch tension, contraction time and contraction velocity) and force-frequency relationship. In addition, to investigate the role of calcium ions in the effect of terbutaline on contractility of the diaphragm, contractility of the diaphragm was assessed after the pre-incubation of the diaphragm with methoxy-verapamil (10(-)(5) M), Ca(2+)-free Krebs-Ringer's solution buffered with 2 mM of ethylene glycol tetra-acetic acid (EGTA), and ryanodine (10(-)(6) M).

RESULTS

Terbutaline significantly improved twitch characteristics and force-frequency relationship of the diaphragm in the CLP group (P<0.01). Incubation with methoxy-verapamil or calcium-free solution with EGTA did not show any changes in the inotropic effect of terbutaline in the CLP group. However, incubation with ryanodine completely abolished the inotropic effect of terbutaline in the CLP group.

CONCLUSIONS

The present study demonstrated that terbutaline increased contractility of the diaphragm in the septic rats. Since this inotropic effect was abolished by ryanodine administration, calcium release from the sarcoplasmic reticulum may contribute to the terbutaline-induced improvement in dysfunction of the septic diaphragm.

Critical illness myopathy: what is happening?

PURPOSE OF REVIEW

The current review focuses on recent studies, both clinical and from basic sciences, which approach possible pathomechanisms of critical illness myopathy in order to better derive potential clinical strategies for a preventive or curative clinical setting. Trends and concepts of clinical diagnosis and handling will be evaluated and their implications for muscle physiology and nutritional/metabolic intervention discussed.

RECENT FINDINGS

Conventional electrophysiology was combined with direct muscle stimulation to better differentiate critical illness myopathy from other neuromuscular disorders in critical illness. Muscle weakness was the result of impaired excitation-contraction-coupling at the level of the sarcolemma and the sarcoplasmic reticulum membrane. Critical illness may alter sodium and ryanodine receptor calcium-release channels. Also, increased muscle proteolysis contributes to weakness in critical illness myopathy. Myosin loss is due to the risk factors systemic inflammatory response syndrome/sepsis, steroids and neuromuscular blocking agents. Steroids can also induce necrosis and apoptosis in muscle. Inflammatory mediators aggravated muscle metabolic failure in critical illness myopathy. Ubiquitin-proteasome pathways, cyclooxygenase activation, altered glucose transporter expression, MyoD suppression, impaired respiratory chain enzymes, ATP depletion, glucose toxicity and insulin resistance can all contribute to the critical illness myopathy pathomechanism.

SUMMARY

The search for pathomechanisms is an important task for both clinical and basic sciences. Targets for treatment or prevention of critical illness myopathy include systemic inflammatory response, increased proteolysis and reduced antioxidative capacitance in critically ill patients.

Melatonin counteracts inducible mitochondrial nitric oxide synthase-dependent mitochondrial dysfunction in skeletal muscle of septic mice

Mitochondrial nitric oxide synthase (mtNOS) produces nitric oxide (NO) to modulate mitochondrial respiration. Besides a constitutive mtNOS isoform it was recently suggested that mitochondria express an inducible isoform of the enzyme during sepsis. Thus, the mitochondrial respiratory inhibition and energy failure underlying skeletal muscle contractility failure observed in sepsis may reflect the high levels of NO produced by inducible mtNOS. The fact that mtNOS is induced during sepsis suggests its relation to inducible nitric oxide synthase (iNOS). Thus, we examined the changes in mtNOS activity and mitochondrial function in skeletal muscle of wild-type (iNOS(+/+)) and iNOS knockout (iNOS(-/-)) mice after sepsis. We also studied the effects of melatonin administration on mitochondrial damage in this experimental paradigm. After sepsis, iNOS(+/+) but no iNOS(-/-) mice showed an increase in mtNOS activity and NO production and a reduction in electron transport chain activity. These changes were accompanied by a pronounced oxidative stress reflected in changes in lipid peroxidation levels, oxidized glutathione/reduced glutathione ratio, and glutathione peroxidase and reductase activities. Melatonin treatment counteracted both the changes in mtNOS activity and rises in oxidative stress; the indole also restored mitochondrial respiratory chain in septic iNOS(+/+) mice. Mitochondria from iNOS(-/-) mice were unaffected by either sepsis or melatonin treatment. The data suggest that inducible mtNOS, which is coded by the same gene as that for iNOS, is responsible for mitochondrial dysfunction during sepsis. The results also suggest the use of melatonin for the protection against mtNOS-mediated mitochondrial failure.

Protein Carbonyl Formation in the Diaphragm

Although protein carbonyl formation is an index of oxidative stress in skeletal muscles, the exact proteins, which undergo oxidation in these muscles, remain unknown. We used 2D electrophoresis, immunoblotting, and mass spectrometry to identify carbonylated proteins in the diaphragm in septic animals. Rats were injected with saline (control) or Escherichia coli lipopolysaccharides (LPS) and killed after various intervals. Diaphragm protein carbonylation increased significantly and peaked 12 h after LPS injection, and it was localized both inside muscle fibers and in blood vessels supplying muscle fibers. Aldolase A, glyceraldehyde 3-phosphate dehydrogenase, enolase 3beta, mitochondrial and cytosolic creatine kinases, alpha-actin, carbonic anyhdrase III, and ubiquinol-cytochrome c reductase were all carbonylated in septic rat diaphragms. In addition, we found significant negative correlations between the intensity of carbonylation and creatine kinase and aldolase activities. We conclude that glycolysis, ATP production, CO2 hydration, and contractile proteins are targeted by oxygen radicals inside the diaphragm during sepsis.

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.

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.

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.

The effect of Escherichia coli endotoxin infusion on the ventilatory response to hypoxia in unanesthetized newborn piglets

To determine the effects of endotoxemia on the neonatal ventilatory response to hypoxia, 17 chronically instrumented and unanesthetized newborn piglets (</=7 d) were studied before and 30 min after the administration of Escherichia coli O55:B5 endotoxin (n = 8) or normal saline (n = 9). Minute ventilation, oxygen consumption, heart rate, arterial blood pressure, and blood gases were measured during normoxia and 10 min of hypoxia (fraction of inspired oxygen, 0.10). Basal ventilation was not modified by E. coli endotoxin infusion (mean +/- SE, 516 +/- 49 versus 539 +/- 56 mL/min/kg), but the ventilatory response to hypoxia was markedly attenuated at 1 min (955 +/- 57 versus 718 +/- 97 mL/min/kg, p < 0.002, saline versus endotoxin) and at 10 min (788 +/- 51 versus 624 +/- 66 mL/min/kg, p < 0.002). A larger decrease in oxygen consumption was observed during hypoxia and endotoxemia (6.3 +/- 2.8 versus 18.3 +/- 2.7%, p < 0.03, pre- versus post-endotoxin). A significant correlation was demonstrated between the changes in minute ventilation and oxygen consumption with hypoxia during endotoxemia (r = 0.9, p < 0.002). The ventilatory response to hypoxia was not modified by the saline infusion. These data show a significant attenuation in the ventilatory response to hypoxia during E. coli endotoxemia. This decrease in ventilation was associated with a significant decrease in the metabolic rate during hypoxia and endotoxemia.

Respiratory muscle fatigue

The contribution of respiratory muscle fatigue to the development of ventilatory failure has been the subject of considerable interest and has stimulated much research. Experimental studies in dogs have shown respiratory muscle fatigue to be a cause of ventilatory failure in both cardiogenic and septic shock models. In clinical conditions resulting in acute or chronic hypercapnia, respiratory muscle fatigue is believed to occur; however, the specific role of fatigue has been difficult to prove.

Upregulation of alpha-synuclein by lipopolysaccharide and interleukin-1 in human macrophages

Alpha-synuclein was originally identified as the presynaptic nerve terminal protein. Recently, we reported that alpha-synuclein is also expressed in cultured human astrocytes and that its levels are increased by stimulation with interleukin-1beta, suggesting that it may be involved in inflammatory processes. We therefore investigated the effect of inflammatory stimuli on alpha-synuclein expression in human macrophages. Alpha-synuclein mRNA and protein were detected in cultured human macrophages and levels of alpha-synuclein protein were increased by stimulation with lipopolysaccharide and interleukin-1beta in a time- and concentration-dependent manner. Immunofluorescent staining showed that alpha-synuclein protein was expressed within the cytoplasm and nucleus. Furthermore, alpha-synuclein immunoreactivity was present in alveolar macrophages from human lung tissues. These findings suggest that the function of alpha-synuclein is not exclusive to the nervous system and that alpha-synuclein may play a role in inflammatory processes and immune responses.

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.

Specificity of antioxidant enzyme inhibition in skeletal muscle to reactive nitrogen species donors

Nitric oxide (*NO) and its by-products modulate many physiological functions of skeletal muscle including blood flow, metabolism, glucose uptake, and contractile function. However, growing evidence suggests that an overproduction of nitric oxide contributes to muscle wasting in a number of pathologies including chronic heart failure, sepsis, COPD, muscular dystrophy, and extreme disuse. Limited data point to the potential of inhibition various enzymes by reactive nitrogen species (RNS), including (.)NO and its downstream products such as peroxynitrite, primarily in purified systems. We hypothesized that exposure of skeletal muscle to RNS donors would reduce or downregulate activities of the crucial antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). Diaphragm muscle fiber bundles were extracted from 4-month-old Fischer-344 rats and, in a series of experiments, exposed to either (a) 0 (control), 1, or 5 mM diethylamine NONOate (DEANO: *NO donor); (b) 0, 100, 500 microM, or 1 mM sodium nitroprusside (SNP: *NO donor); (c) 0 or 2 mM S-nitroso-acetylpenicillamine (SNAP: *NO donor); or (d) 0 or 500 microM SIN-1 (peroxynitrite donor) for 60 min. DEANO resulted in a 50% reduction in CAT, GPX, and a dose-dependent inhibition of Cu, Zn-SOD. SNP resulted in significantly lower activities for total SOD, Mn-SOD isoform, Cu, Zn-SOD isoform, CAT, and GPX in a dose-dependent fashion. Two millimolar SNAP and 500 microM SIN-1 also resulted in a large and significant inhibition of total SOD and CAT. These data indicate that reactive nitrogen species impair antioxidant enzyme function in an RNS donor-specific and dose-dependent manner and are consistent with the hypothesis that excess RNS production contributes to skeletal muscle oxidative stress and muscle dysfunction.

Altered diaphragm contractile properties with controlled mechanical ventilation

This study shows that, over time, diaphragm inactivity with controlled mechanical ventilation (CMV) decreases diaphragm force and produces myofibril damage contributing to the reduced force. We measured in vivo and in vitro diaphragm contractile and morphological properties in 30 sedated rabbits grouped (n = 6) as follows: 1 or 3 days of CMV, 1 or 3 days of 0 cmH(2)O continuous positive airway pressure, and control. The CMV rate was set sufficient to suppress diaphragm electrical activity. Compared with the control group, phrenic-stimulated maximum transdiaphragmatic pressure did not decrease with continuous positive airway pressure but decreased to 63% after 1 day of CMV and to 49% after 3 days of CMV. The in vitro tetanic force decreased to 86% after 1 day of CMV and to 44% after 3 days of CMV. After 3 days of CMV, significant myofibril damage occurred in the diaphragm but not in the soleus. The decrease in tetanic force correlated with the volume density of abnormal myofibrils. We conclude that CMV had a detrimental effect on diaphragm contractile properties.