Endogenous peroxynitrite mediates mitochondrial dysfunction in rat diaphragm during endotoxemia

Focus on oliguria during renal replacement therapy

Oliguria is a clinical symptom characterized by decreased urine output, which can occur at any stage of acute kidney injury and also during renal replacement therapy. In some cases, oliguria may resolve with adjustment of blood purification dose or fluid management, while in others, it may suggest a need for further evaluation and intervention. It is important to determine the underlying cause of oliguria during renal replacement therapy and to develop an appropriate treatment plan. This review looks into the mechanisms of urine production to investigate the mechanism of oliguria during renal replacement therapy from two aspects: diminished glomerular filtration rate and tubular abnormalities. The above conditions all implying a renal oxygen supply-demand imbalance, which is the signal of worsening kidney injury. It also proposes a viable clinical pathway for the treatment and management of patients with acute kidney injury receiving renal replacement therapy.

SEPTIC SHOCK: LPS TOLERANCE PROTECTS MITOCHONDRIAL BIOGENESIS AND RESPIRATION

ABSTRACT

Mitochondrial dysfunction is a recognized feature of sepsis, characterized by ultrastructural damage, diminished oxidative phosphorylation, and depletion of mitochondrial antioxidant capacity observed in deceased septic patients. LPS tolerance induces a controlled response to sepsis. This study aimed to evaluate the function of tolerant mitochondria after cecal ligation and puncture (CLP)-induced sepsis. Mytochondrial oxygen consumption was determined using polarography. Extraction and quantification of RNA for the expression of Tfam, Nrf-1, and Ppargc-1α, and respiratory complex activity were measured. CLP-tolerant animals presented preserved respiratory rates of S3 and S4 and a ratio of respiratory control (RCR) compared to CLP-nontolerant animals with reduced oxidative phosphorylation and increased uncoupled respiration. Complex I Vmax was reduced in septic animals; however, CLP animals sustained normal Vmax. Mitochondrial biogenesis was preserved in CLP-tolerant animals compared to the CLP-nontolerant group, likely due to increased TFAM expression. LPS tolerance protected septic animals from mitochondrial dysfunction, favoring mitochondrial biogenesis and preserving mitochondrial respiration and respiratory complex I activity.

The Integral Role of Magnesium in Muscle Integrity and Aging: A Comprehensive Review

Aging is characterized by significant physiological changes, with the degree of decline varying significantly among individuals. The preservation of intrinsic capacity over the course of an individual's lifespan is fundamental for healthy aging. Locomotion, which entails the capacity for independent movement, is intricately connected with various dimensions of human life, including cognition, vitality, sensory perception, and psychological well-being. Notably, skeletal muscle functions as a pivotal nexus within this intricate framework. Any perturbation in its functionality can manifest as compromised physical performance and an elevated susceptibility to frailty. Magnesium is an essential mineral that plays a central role in approximately 800 biochemical reactions within the human body. Its distinctive physical and chemical attributes render it an indispensable stabilizing factor in the orchestration of diverse cellular reactions and organelle functions, thereby rendering it irreplaceable in processes directly impacting muscle health. This narrative review offers a comprehensive exploration of the pivotal role played by magnesium in maintaining skeletal muscle integrity, emphasizing the critical importance of maintaining optimal magnesium levels for promoting healthy aging.

Effect of starvation and refeeding on reactive oxygen species, autophagy and oxidative stress in Chinese perch (Siniperca chuatsi) muscle growth

In skeletal muscle, autophagy regulates the development and growth of muscle fibres and maintains the normal muscle metabolism. Under starvation and refeeding conditions, the effect of reactive oxygen species (ROS) levels on skeletal muscle autophagy is still unclear, although the excessive accumulation of ROS has been shown to increase autophagy in cells. The purpose of this study was to explore the effects of starvation and diet after starvation on the autophagy of adult Chinese perch muscle, and to determine the level of ROS in the muscle. We performed zero (Normal control), three and seven starvation treatments on adult Chinese perch, and returned to normal feeding for 3 days after starvation for 7 days. In the muscles of the adult Chinese perch muscle after 3 days of starvation, the autophagy marker protein LC3 and the number of autophagosomes remained basically the same as in the normal feeding situation. However, on starvation for 7 days, the mitochondrial autophagy was sensitive and the number of autophagosomes increased, but the antioxidant-related molecules (malondialdehyde, catalase, glutathione S-transferase, glutathione and anti-superoxide anion) decreased and the accumulation of ROS was obvious. In addition, the extended starvation time also increased the level of LC3 protein. However, by refeeding after starvation this nutritional stress resulted in a decrease in ROS levels and a partial restoration of antioxidant enzyme activity. Our data show that in the adult Chinese perch muscle, starvation could reduce the antioxidant activity through the accumulation of ROS, and that the number of autophagosomes continues to increase. Refeeding after starvation could effectively compensate for the level of ROS, and restore the mRNA abundance of antioxidant genes and the activity of antioxidant enzymes to reduce autophagy and improve feed efficiency. Further research should optimize starvation conditions to reduce autophagy in muscles and maintain normal muscle metabolism.

Regulation of Oxidative Phosphorylation of Liver Mitochondria in Sepsis

The link between liver dysfunction and decreased mitochondrial oxidative phosphorylation in sepsis has been clearly established in experimental models. Energy transduction is plastic: the efficiency of mitochondrial coupling collapses in the early stage of sepsis but is expected to increase during the recovery phases of sepsis. Among the mechanisms regulating the coupling efficiency of hepatic mitochondria, the slipping reactions at the cytochrome oxidase and ATP synthase seem to be a determining element, whereas other regulatory mechanisms such as those involving proton leakage across the mitochondrial membrane have not yet been formally proven in the context of sepsis. If the dysfunction of hepatic mitochondria is related to impaired cytochrome c oxidase and ATP synthase functions, we need to consider therapeutic avenues to restore their activities for recovery from sepsis. In this review, we discussed previous findings regarding the regulatory mechanism involved in changes in the oxidative phosphorylation of liver mitochondria in sepsis, and propose therapeutic avenues to improve the functions of cytochrome c oxidase and ATP synthase in sepsis.

Pathophysiology, mechanisms, and managements of tissue hypoxia

Oxygen is needed to generate aerobic adenosine triphosphate and energy that is required to support vital cellular functions. Oxygen delivery (DO₂) to the tissues is determined by convective and diffusive processes. The ability of the body to adjust oxygen extraction (ERO₂) in response to changes in DO₂ is crucial to maintain constant tissue oxygen consumption (VO₂). The capability to increase ERO₂ is the result of the regulation of the circulation and the effects of the simultaneous activation of both central and local factors. The endothelium plays a crucial role in matching tissue oxygen supply to demand in situations of acute drop in tissue oxygenation. Tissue oxygenation is adequate when tissue oxygen demand is met. When DO₂ is severely compromised, a critical DO₂ value is reached below which VO₂ falls and becomes dependent on DO₂, resulting in tissue hypoxia. The different mechanisms of tissue hypoxia are circulatory, anaemic, and hypoxic, characterised by a diminished DO₂ but preserved capacity of increasing ERO₂. Cytopathic hypoxia is another mechanism of tissue hypoxia that is due to impairment in mitochondrial respiration that can be observed in septic conditions with normal overall DO₂. Sepsis induces microcirculatory alterations with decreased functional capillary density, increased number of stopped-flow capillaries, and marked heterogeneity between the areas with large intercapillary distance, resulting in impairment of the tissue to extract oxygen and to satisfy the increased tissue oxygen demand, leading to the development of tissue hypoxia. Different therapeutic approaches exist to increase DO₂ and improve microcirculation, such as fluid therapy, transfusion, vasopressors, inotropes, and vasodilators. However, the effects of these agents on microcirculation are quite variable.

Mitoquinone mesylate (MitoQ) prevents sepsis-induced diaphragm dysfunction

Sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. There are no pharmacological treatments for this syndrome, but studies suggest that diaphragm weakness is linked to mitochondrial free radical generation. We hypothesized that administration of mitoquinone mesylate (MitoQ), a mitochondrially targeted free radical scavenger, would prevent sepsis-induced diaphragm dysfunction. We compared diaphragm function in 4 groups of male mice: 1) sham-operated controls treated with saline (0.3 mL ip), 2) sham-operated treated with MitoQ (3.5 mg/kg/day given intraperitoneally in saline), 3) cecal ligation puncture (CLP) mice treated with saline, and 4) CLP mice treated with MitoQ. Forty-eight hours after surgery, we assessed diaphragm force generation, myosin heavy chain content, state 3 mitochondrial oxygen consumption (OCR), and aconitase activity. We also determined effects of MitoQ in female mice with CLP sepsis and in mice with endotoxin-induced sepsis. CLP decreased diaphragm specific force generation and MitoQ prevented these decrements (e.g. maximal force averaged 30.2 ± 1.3, 28.0 ± 1.3, 12.8 ± 1.9, and 30.0 ± 1.0 N/cm² for sham, sham + MitoQ, CLP, and CLP + MitoQ groups, respectively, P < 0.001). CLP also reduced diaphragm mitochondrial OCR and aconitase activity; MitoQ blocked both effects. Similar responses were observed in female mice and in endotoxin-induced sepsis. Moreover, delayed MitoQ treatment (by 6 h) was as effective as immediate treatment. These data indicate that MitoQ prevents sepsis-induced diaphragm dysfunction, preserving force generation. MitoQ may be a useful therapeutic agent to preserve diaphragm function in critically ill patients with sepsis.NEW & NOTEWORTHY This is the first study to show that mitoquinone mesylate (MitoQ), a mitochondrially targeted antioxidant, treats sepsis-induced skeletal muscle dysfunction. This biopharmaceutical agent is without known side effects and is currently being used by healthy individuals and in clinical trials in patients with various diseases. When taken together, our results suggest that MitoQ has the potential to be immediately translated into treatment for sepsis-induced skeletal muscle dysfunction.

Mitochondrial Dysfunction Is a Common Denominator Linking Skeletal Muscle Wasting Due to Disease, Aging, and Prolonged Inactivity

Skeletal muscle is the most abundant tissue in the body and is required for numerous vital functions, including breathing and locomotion. Notably, deterioration of skeletal muscle mass is also highly correlated to mortality in patients suffering from chronic diseases (e.g., cancer). Numerous conditions can promote skeletal muscle wasting, including several chronic diseases, cancer chemotherapy, aging, and prolonged inactivity. Although the mechanisms responsible for this loss of muscle mass is multifactorial, mitochondrial dysfunction is predicted to be a major contributor to muscle wasting in various conditions. This systematic review will highlight the biochemical pathways that have been shown to link mitochondrial dysfunction to skeletal muscle wasting. Importantly, we will discuss the experimental evidence that connects mitochondrial dysfunction to muscle wasting in specific diseases (i.e., cancer and sepsis), aging, cancer chemotherapy, and prolonged muscle inactivity (e.g., limb immobilization). Finally, in hopes of stimulating future research, we conclude with a discussion of important future directions for research in the field of muscle wasting.

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.

The nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO), increases survival by attenuating hyperoxia-compromised innate immunity in bacterial clearance in a mouse model of ventilator-associated pneumonia

Mechanical ventilation (MV) with supraphysiological levels of oxygen (hyperoxia) is a life-saving therapy for the management of patients with respiratory distress. However, a significant number of patients on MV develop ventilator-associated pneumonia (VAP). Previously, we have reported that prolonged exposure to hyperoxia impairs the capacity of macrophages to phagocytize Pseudomonas aeruginosa (PA), which can contribute to the compromised innate immunity in VAP. In this study, we show that the high mortality rate in mice subjected to hyperoxia and PA infection was accompanied by a significant decrease in the airway levels of nitric oxide (NO). Decreased NO levels were found to be, in part, due to a significant reduction in NO release by macrophages upon exposure to PA lipopolysaccharide (LPS). Based on these findings, we postulated that NO supplementation should restore hyperoxia-compromised innate immunity and decrease mortality by increasing the clearance of PA under hyperoxic conditions. To test this hypothesis, cultured macrophages were exposed to hyperoxia (95% O₂) in the presence or absence of the NO donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO). Interestingly, D-NO (up to 37.5 µM) significantly attenuated hyperoxia-compromised macrophage migratory, phagocytic, and bactericidal function. To determine whether the administration of exogenous NO enhances the host defense in bacteria clearance, C57BL/6 mice were exposed to hyperoxia (99% O₂) and intranasally inoculated with PA in the presence or absence of D-NO. D-NO (300 µM-800 µM) significantly increased the survival of mice inoculated with PA under hyperoxic conditions, and significantly decreased bacterial loads in the lung and attenuated lung injury. These results suggest the NO donor, D-NO, can improve the clinical outcomes in VAP by augmenting the innate immunity in bacterial clearance. Thus, provided these results can be extrapolated to humans, NO supplementation may represent a potential therapeutic strategy for preventing and treating patients with VAP.

Demystifying Lactate in the Emergency Department

The role of lactic acid and its conjugate base, lactate, has evolved during the past decade in the care of patients in the emergency department (ED). A recent national sepsis quality measure has led to increased use of serum lactate in the ED, but many causes for hyperlactatemia exist outside of sepsis. We provide a review of the biology of lactate production and metabolism, the many causes of hyperlactatemia, and evidence on its use as a marker in prognosis and resuscitation. Additionally, we review the evolving role of lactate in sepsis care. We provide recommendations to aid lactate interpretation in the ED and highlight areas for future research.

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.

Prolonged mechanical ventilation worsens sepsis-induced diaphragmatic dysfunction in the rat

Background

Short-term mechanical ventilation (MV) protects against sepsis-induced diaphragmatic dysfunction. Prolonged MV induces diaphragmatic dysfunction in non-septic animals, but few reports describe the effects of prolonged MV in sepsis. We hypothesized that prolonged MV is not protective but worsens the diaphragmatic dysfunction induced by a mild sepsis, because MV and sepsis share key signaling mechanisms, such as cytokine upregulation.

Method

We studied the impact of prolonged MV (12 h) in four groups (n = 8) of male Wistar rats: 1) endotoxemia induced by intraperitoneal injection of Escherichia coli lipopolysaccharide, 2) MV without endotoxemia, 3) combination of endotoxemia and MV and 4) sham control. Diaphragm mechanical performance, pro-inflammatory cytokine concentrations (Tumor Necrosis Factor-α, Interleukin-1β, Interleukin-6) in plasma were measured.

Results

Prolonged MV and sepsis independtly reduced maximum diaphragm force (-27%, P = 0.003; -37%, P<0.001; respectively). MV and sepsis acted additively to further decrease diaphragm force (-62%, P<0.001). Similar results were observed for diaphragm kinetics (maximum lengthening velocity -47%, P<0.001). Sepsis and MV reduced diaphragm cross sectional area of type I and IIx fibers, which was further increased by the combination of sepsis and MV (all P<0.05). Sepsis and MV were individually associated with the presence of a robust perimysial inflammatory infiltrate, which was more marked when sepsis and MV were both present (all P<0.05). Sepsis and, to a lesser extent, MV increased proinflammatory cytokine production in plasma and diaphragm (all P<0.05); proinflammatory cytokine expression in plasma was increased further by the combination of sepsis and MV (all P<0.05). Maximum diaphragm force correlated negatively with plasma and diaphragmatic cytokine production (all p<0.05).

Conclusions

Prolonged (12 h) MV exacerbated sepsis-induced decrease in diaphragm performance. Systemic and diaphragmatic overproduction of pro-inflammatory cytokines may contribute to diaphragm weakness.

Renal Tubular Cell Mitochondrial Dysfunction Occurs Despite Preserved Renal Oxygen Delivery in Experimental Septic Acute Kidney Injury

OBJECTIVE

To explain the paradigm of significant renal functional impairment despite preserved hemodynamics and histology in sepsis-induced acute kidney injury.

DESIGN

Prospective observational animal study.

SETTING

University research laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTION

Using a fluid-resuscitated sublethal rat model of fecal peritonitis, changes in renal function were characterized in relation to global and renal hemodynamics, and histology at 6 and 24 hours (n = 6-10). Sham-operated animals were used as comparison (n = 8). Tubular cell mitochondrial function was assessed using multiphoton confocal imaging of live kidney slices incubated in septic serum.

MEASUREMENTS AND MAIN RESULTS

By 24 hours, serum creatinine was significantly elevated with a concurrent decrease in renal lactate clearance in septic animals compared with sham-operated and 6-hour septic animals. Renal uncoupling protein-2 was elevated in septic animals at 24 hours although tubular cell injury was minimal and mitochondrial ultrastructure in renal proximal tubular cells preserved. There was no significant change in global or renal hemodynamics and oxygen delivery/consumption between sham-operated and septic animals at both 6- and 24-hour timepoints. In the live kidney slice model, mitochondrial dysfunction was seen in proximal tubular epithelial cells incubated with septic serum with increased production of reactive oxygen species, and decreases in nicotinamide adenine dinucleotide and mitochondrial membrane potential. These effects were prevented by coincubation with the reactive oxygen species scavenger, 4-hydroxy-2,2,6,6-tetramethyl-piperidin-1-oxyl.

CONCLUSIONS

Renal dysfunction in sepsis occurs independently of hemodynamic instability or structural damage. Mitochondrial dysfunction mediated by circulating mediators that induce local oxidative stress may represent an important pathophysiologic mechanism.

Neuroprotective Efficacy of Mitochondrial Antioxidant MitoQ in Suppressing Peroxynitrite-Mediated Mitochondrial Dysfunction Inflicted by Lead Toxicity in the Rat Brain

Lead (Pb) is one of the most pollutant metals that accumulate in the brain mitochondria disrupting mitochondrial structure and function. Though oxidative stress mediated by reactive oxygen species remains the most accepted mechanism of Pb neurotoxicity, some reports suggest the involvement of nitric oxide (^•NO) and reactive nitrogen species in Pb-induced neurotoxicity. But the impact of Pb neurotoxicity on mitochondrial respiratory enzyme complexes remains unknown with no relevant report highlighting the involvement of peroxynitrite (ONOO^-) in it. Herein, we investigated these effects in in vivo rat model by oral application of MitoQ, a known mitochondria-specific antioxidant with ONOO^- scavenging activity. Interestingly, MitoQ efficiently alleviated ONOO^--mediated mitochondrial complexes II, III and IV inhibition, increased mitochondrial ATP production and restored mitochondrial membrane potential. MitoQ lowered enhanced caspases 3 and 9 activities upon Pb exposure and also suppressed synaptosomal lipid peroxidation and protein oxidation accompanied by diminution of nitrite production and protein-bound 3-nitrotyrosine. To ascertain our in vivo findings on mitochondrial dysfunction, we carried out similar experiments in the presence of different antioxidants and free radical scavengers in the in vitro SHSY5Y cell line model. MitoQ provided better protection compared to mercaptoethylguanidine, N-nitro-L-arginine methyl ester and superoxide dismutase suggesting the predominant involvement of ONOO^- compared to ^•NO and O₂^•-. However, dimethylsulphoxide and catalase failed to provide protection signifying the noninvolvement of ^•OH and H₂O₂ in the process. The better protection provided by MitoQ in SHSY5Y cells can be attributed to the fact that MitoQ targets mitochondria whereas mercaptoethylguanidine, N-nitro-L-arginine methyl ester and superoxide dismutase are known to target mainly cytoplasm and not mitochondria. Taken together the results from the present study clearly brings out the potential of MitoQ against ONOO^--induced toxicity upon Pb exposure indicating its therapeutic potential in metal toxicity.

Magnesium deficiency and oxidative stress: an update

Magnesium deficiency (MgD) has been shown to impact numerous biological processes at the cellular and molecular levels. In the present review, we discuss the relationship between MgD and oxidative stress (OS). MgD is accompanied by increased levels of OS markers such as lipid, protein and DNA oxidative modification products. Additionally, a relationship was detected between MgD and a weakened antioxidant defence. Different mechanisms associated with MgD are involved in the development and maintenance of OS. These mechanisms include systemic reactions such as inflammation and endothelial dysfunction, as well as changes at the cellular level, such as mitochondrial dysfunction and excessive fatty acid production.

Exercise training in chronic heart failure: correlation between reduced local inflammation and improved oxidative capacity in the skeletal muscle

Background Chronic heart failure (CHF) is accompanied by an inflammatory activation which occurs both systemically and in the skeletal muscle. Exercise training has been shown to reduce the local expression of cytokines and inducible nitric oxide synthase (iNOS) in muscle biopsies of CHF patients. INOS-derived NO can inhibit oxidative phosphorylation and contribute to skeletal muscle dysfunction in CHF.

Design To investigate the correlation between changes in local iNOS expression associated with regular exercise and changes in aerobic enzyme activities in the skeletal muscle of patients with CHF. Twenty male CHF patients [ejection fraction 25% (SE 2), age 54 (SE 2) years] were randomized to a training ( n = 10) or a control group (C, n = 10).

Methods At baseline and after 6 months skeletal muscle iNOS expression was measured by real-time polymerase chain reaction. INOS protein and protein nitrosylation were assessed by immunohistochemistry. Cytochrome c oxidase (COX) activity was quantified electrochemically using the Clark oxygen electrode.

Results Exercise training led to a 27% increase in cytochrome c oxidase activity [from 21.8 (SE 3.2) to 27.7 (SE 3.5) nmol O2/mg per min, P=0.02 versus baseline]. Changes in iNOS expression and iNOS protein content were inversely correlated with changes in COX-activity ( r= −0.60, P=0.01; r= −0.71, P<0.001).

Conclusions The inverse correlation between iNOS expression/iNOS protein content and COX-activity indicates that local anti-inflammatory effects may contribute to improved muscular oxidative metabolism.

Reactive oxygen/nitrogen species and contractile function in skeletal muscle during fatigue and recovery

The production of reactive oxygen/nitrogen species (ROS/RNS) is generally considered to increase during physical exercise. Nevertheless, direct measurements of ROS/RNS often show modest increases in ROS/RNS in muscle fibres even during intensive fatiguing stimulation, and the major source(s) of ROS/RNS during exercise is still being debated. In rested muscle fibres, mild and acute exposure to exogenous ROS/RNS generally increases myofibrillar submaximal force, whereas stronger or prolonged exposure has the opposite effect. Endogenous production of ROS/RNS seems to preferentially decrease submaximal force and positive effects of antioxidants are mainly observed during fatigue induced by submaximal contractions. Fatigued muscle fibres frequently enter a prolonged state of reduced submaximal force, which is caused by a ROS/RNS-dependent decrease in sarcoplasmic reticulum Ca(2+) release and/or myofibrillar Ca(2+) sensitivity. Increased ROS/RNS production during exercise can also be beneficial and recent human and animal studies show that antioxidant supplementation can hamper the beneficial effects of endurance training. In conclusion, increased ROS/RNS production have both beneficial and detrimental effects on skeletal muscle function and the outcome depends on a combination of factors: the type of ROS/RNS; the magnitude, duration and location of ROS/RNS production; and the defence systems, including both endogenous and exogenous antioxidants.

Dexmedetomidine May Produce Extra Protective Effects on Sepsis-induced Diaphragm Injury

OBJECTIVE

The objective was to evaluate the protective effects of dexmedetomidine (DEX), a selective agonist of α2-adrenergic receptor, on sepsis-induced diaphragm injury and the underlying molecular mechanisms.

DATA SOURCES

The data used in this review were mainly from PubMed articles published in English from 1990 to 2015.

STUDY SELECTION

Clinical or basic research articles were selected mainly according to their level of relevance to this topic.

RESULTS

Sepsis could induce severe diaphragm dysfunction and exacerbate respiratory weakness. The mechanism of sepsis-induced diaphragm injury includes the increased inflammatory cytokines and excessive oxidative stress and superfluous production of nitric oxide (NO). DEX can reduce inflammatory cytokines, inhibit nuclear factor-kappaB signaling pathways, suppress the activation of caspase-3, furthermore decrease oxidative stress and inhibit NO synthase. On the basis of these mechanisms, DEX may result in a shorter period of mechanical ventilation in septic patients in clinical practice.

CONCLUSIONS

Based on this current available evidence, DEX may produce extra protective effects on sepsis-induced diaphragm injury. Further direct evidence and more specific studies are still required to confirm these beneficial effects.

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.

Levosimendan affects oxidative and inflammatory pathways in the diaphragm of ventilated endotoxemic mice

INTRODUCTION

Controlled mechanical ventilation and endotoxemia are associated with diaphragm muscle atrophy and dysfunction. Oxidative stress and activation of inflammatory pathways are involved in the pathogenesis of diaphragmatic dysfunction. Levosimendan, a cardiac inotrope, has been reported to possess anti-oxidative and anti-inflammatory properties. The aim of the present study was to investigate the effects of levosimendan on markers for diaphragm nitrosative and oxidative stress, inflammation and proteolysis in a mouse model of endotoxemia and mechanical ventilation.

METHODS

Three groups were studied: (1) unventilated mice (CON, n =8), (2) mechanically ventilated endotoxemic mice (MV LPS, n =17) and (3) mechanically ventilated endotoxemic mice treated with levosimendan (MV LPS + L, n =17). Immediately after anesthesia (CON) or after 8 hours of mechanical ventilation, blood and diaphragm muscle were harvested for biochemical analysis.

RESULTS

Mechanical ventilation and endotoxemia increased expression of inducible nitric oxide synthase (iNOS) mRNA and cytokine levels of interleukin (IL)-1β, IL-6 and keratinocyte-derived chemokine, and decreased IL-10, in the diaphragm; however, they had no effect on protein nitrosylation and 4-hydroxy-2-nonenal protein concentrations. Levosimendan decreased nitrosylated proteins by 10% (P <0.05) and 4-hydroxy-2-nonenal protein concentrations by 13% (P <0.05), but it augmented the rise of iNOS mRNA by 47% (P <0.05). Levosimendan did not affect the inflammatory response in the diaphragm induced by mechanical ventilation and endotoxemia.

CONCLUSIONS

Mechanical ventilation in combination with endotoxemia results in systemic and diaphragmatic inflammation. Levosimendan partly decreased markers of nitrosative and oxidative stress, but did not affect the inflammatory response.

Effects of controlled mechanical ventilation on sepsis-induced diaphragm dysfunction in rats

OBJECTIVES

Diaphragm dysfunction develops during severe sepsis as a consequence of hemodynamic, metabolic, and intrinsic abnormalities. Similarly, 12 hours of controlled mechanical ventilation also promotes diaphragm dysfunction. Importantly, patients with sepsis are often treated with mechanical ventilation for several days. It is unknown if controlled mechanical ventilation exacerbates sepsis-induced diaphragm dysfunction, and this forms the basis for these experiments. We investigate the effects of 12-hour controlled mechanical ventilation on contractile function, fiber dimension, cytokine production, proteolysis, autophagy, and oxidative stress in the diaphragm of septic rats.

DESIGN

Randomized controlled experiment.

SETTING

Animal research laboratory.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

Treatment with a single intraperitoneal injection of either saline or Escherichia coli lipopolysaccharide (5 mg/kg). After 12 hours, the saline-treated animals (controlled mechanical ventilation) and half of the septic animals (lipopolysaccharide + controlled mechanical ventilation) were submitted to 12 hours of controlled mechanical ventilation while the remaining septic animals (lipopolysaccharide) were breathing spontaneously for 12 hours. They were compared to a control group. All animals were studied 24 hours after saline or lipopolysaccharide administration.

MEASUREMENTS AND MAIN RESULTS

Twenty-four hours after saline or lipopolysaccharide administration, diaphragm contractility was measured in vitro. We also measured diaphragm muscle fiber dimensions from stained cross sections, and inflammatory cytokines were determined by proteome array. Activities of calpain, caspase-3, and proteasome, expression of 20S-proteasome α subunits, E2 conjugases, E3 ligases, and autophagy were measured with immunoblotting and quantitative polymerase chain reaction. Lipopolysaccharide and/or controlled mechanical ventilation independently decreased diaphragm contractility and fiber dimensions and increased diaphragm interleukin-6 production, protein ubiquitination, expression of Atrogin-1 and Murf-1, calpain and caspase-3 activities, autophagy, and protein oxidation. Compared with lipopolysaccharide alone, lipopolysaccharide + controlled mechanical ventilation worsened diaphragm contractile dysfunction, augmented diaphragm interleukin-6 levels, autophagy, and protein oxidation, but exerted no exacerbating effects on diaphragm fiber dimensions, calpain, caspase-3, or proteasome activation.

CONCLUSIONS

Twelve hours of controlled mechanical ventilation potentiates sepsis-induced diaphragm dysfunction, possibly due to increased proinflammatory cytokine production and autophagy and worsening of oxidative stress.

Crosstalk between nitric oxide synthases and cyclooxygenase 2 in the adrenal cortex of rats under lipopolysaccharide treatment

The effect of lipopolysaccharide on the modulation of steroid production by adrenal cells has been recently acknowledged. The purpose of this study was to determine the in vivo effects of LPS on adrenal cyclooxygenase 2 (COX-2) expression, analyze its crosstalk with the nitric oxide synthase (NOS) system, and assess its involvement on the modulation of glucocorticoid production. Male Wistar rats were injected with LPS and with specific inhibitors for NOS and COX activities. PGE2 and corticosterone levels were determined by RIA. Protein levels were analyzed by immunoprecipitation and western blotting. Transfection assays were performed in murine adrenocortical Y1 cells. Results show that LPS treatment increases PGE2 production and COX-2 protein levels in the rat adrenal cortex. Systemic inhibition of COX-2 blunted the glucocorticoid response to ACTH, as well as the increase in NOS activity and the NOS-2 expression levels induced by LPS. Conversely, NOS inhibition prevented the LPS-dependent increase in PGE2 production, COX-2 protein levels, and the nitrotyrosine modification of COX-2 protein. Treatment of adrenocortical cells with a NO-donor significantly potentiated the LPS-dependent increase in NFκB activity and COX-2 expression levels. In conclusion, our results show a significant crosstalk between COX-2 and NOS in the adrenal cortex upon LPS stimulation, in which each activity has a positive impact on the other. In particular, as both the activities differently affect adrenal steroid production, we hypothesize that this kind of fine modulation enables the gland to adjust steroidogenesis to prevent either an excessive or an insufficient response to the endotoxin challenge.

Evidence of oxidative stress and mitochondrial respiratory chain dysfunction in an in vitro model of sepsis-induced kidney injury

To investigate the role of oxidative stress and/or mitochondrial impairment in the occurrence of acute kidney injury (AKI) during sepsis, we developed a sepsis-induced in vitro model using proximal tubular epithelial cells exposed to a bacterial endotoxin (lipopolysaccharide, LPS). This investigation has provided key features on the relationship between oxidative stress and mitochondrial respiratory chain activity defects. LPS treatment resulted in an increase in the expression of inducible nitric oxide synthase (iNOS) and NADPH oxidase 4 (NOX-4), suggesting the cytosolic overexpression of nitric oxide and superoxide anion, the primary reactive nitrogen species (RNS) and reactive oxygen species (ROS). This oxidant state seemed to interrupt mitochondrial oxidative phosphorylation by reducing cytochrome c oxidase activity. As a consequence, disruptions in the electron transport and the proton pumping across the mitochondrial inner membrane occurred, leading to a decrease of the mitochondrial membrane potential, a release of apoptotic-inducing factors and a depletion of adenosine triphosphate. Interestingly, after being targeted by RNS and ROS, mitochondria became in turn producer of ROS, thus contributing to increase the mitochondrial dysfunction. The role of oxidants in mitochondrial dysfunction was further confirmed by the use of iNOS inhibitors or antioxidants that preserve cytochrome c oxidase activity and prevent mitochondrial membrane potential dissipation. These results suggest that sepsis-induced AKI should not only be regarded as failure of energy status but also as an integrated response, including transcriptional events, ROS signaling, mitochondrial activity and metabolic orientation such as apoptosis.

Early septic shock induces loss of oxidative phosphorylation yield plasticity in liver mitochondria

We aimed to study the change in mitochondrial oxidative phosphorylation efficiency occurring at the early stage of septic shock in an experimental model. Thirty-six male Wistar rats were divided into two groups. In the first group, a cecal ligation and puncture (CLP) was carried out to induce septic shock for 5 h. The second group includes sham-operated rats and constitutes the control group. Blood gas analysis, alanine amino transferase, and lactic acid dosages were assayed 5 h after surgery. Liver mitochondria were isolated for in vitro functional characterization, including mitochondrial respiratory parameters, oxidative phosphorylation efficiency, oxi-radical production, membrane potential, and cytochrome c oxidase activity and content. Liver interleukin 1β (IL-1β) and tumor necrosis α mRNA levels were determined. Septic shock induced a severe hypotension occurring 180 min after CLP in association with a metabolic acidosis, an increase in plasma alanine amino transferase, liver IL-1β gene expression, and mitochondrial reactive oxygen species production. The rates of mitochondrial oxygen consumption and the activity and content of cytochrome c oxidase were significantly decreased while no alterations in the oxidative phosphorylation efficiency and inner membrane integrity were found. These results show that contrary to what was expected, liver mitochondria felt to adjust their oxidative phosphorylation efficiency in response to the decrease in the mitochondrial oxidative activity induced by CLP. This loss of mitochondrial bioenergetics plasticity might be related to mitochondrial oxidative stress and liver cytokines production.

Reactive oxygen species regulation of autophagy in skeletal muscles

OBJECTIVE

To evaluate the effects of physiological levels of mitochondrial-derived reactive oxygen species (ROS) on skeletal muscle autophagy, a proteolytic pathway designed to regulate contractile and myofilament homeostasis and to recycle long-lived proteins and damaged organelles.

RESULTS

Basal levels of autophagy and autophagy triggered by 1.5 to 4 h of acute nutrient deprivation, rapamycin treatment, or leucine deprivation were measured in differentiated C2C12 myotubes using long-lived protein degradation assays, LC3B lipidation, autophagy-related gene expression, and electron microscopy. Preincubation with the general antioxidants tempol (superoxide dismutase mimic) and N-acetyl cysteine (NAC) or the mitochondria-specific antioxidants mito-tempol and SS31 significantly decreased the rates of long-lived protein degradation and LC3B flux and blocked the induction of autophagy-related gene expression. Mitochondrial ROS levels significantly increased in response to acute nutrient deprivation and rapamycin treatment. Mito-tempol and tempol blocked this response. Antioxidants decreased AMP-activated protein kinase (AMPK) phosphorylation by 40% and significantly increased protein kinase B (AKT) phosphorylation, but exerted no effects on mTORC1-dependent ULK1 phosphorylation on Ser(555). NAC significantly decreased basal LC3B autophagic flux in skeletal muscles of mice.

INNOVATION

We report for the first time that endogenous ROS promote skeletal muscle autophagy at the basal level and in response to acute nutrient starvation and mTORC1 inhibition. We also report for the first time that mitochondrial-derived ROS promote skeletal muscle autophagy and that this effect is mediated, in part, through regulation of autophagosome initiation and AKT inhibition.

CONCLUSION

Mitochondrial-derived ROS promote skeletal muscle autophagy and this effect is mediated, in part, through activation of AMPK and inhibition of AKT.

The beneficial effects of melatonin against heart mitochondrial impairment during sepsis: inhibition of iNOS and preservation of nNOS

While it is accepted that the high production of nitric oxide (NO˙) by the inducible nitric oxide synthase (iNOS) impairs cardiac mitochondrial function during sepsis, the role of neuronal nitric oxide synthase (nNOS) may be protective. During sepsis, there is a significantly increase in the expression and activity of mitochondrial iNOS (i-mtNOS), which parallels the changes in cytosolic iNOS. The existence of a constitutive NOS form (c-mtNOS) in heart mitochondria has been also described, but its role in the heart failure during sepsis remains unclear. Herein, we analyzed the changes in mitochondrial oxidative stress and bioenergetics in wild-type and nNOS-deficient mice during sepsis, and the role of melatonin, a known antioxidant, in these changes. Sepsis was induced by cecal ligation and puncture, and heart mitochondria were analyzed for NOS expression and activity, nitrites, lipid peroxidation, glutathione and glutathione redox enzymes, oxidized proteins, and respiratory chain activity in vehicle- and melatonin-treated mice. Our data show that sepsis produced a similar induction of iNOS/i-mtNOS and comparable inhibition of the respiratory chain activity in wild-type and in nNOS-deficient mice. Sepsis also increased mitochondrial oxidative/nitrosative stress to a similar extent in both mice strains. Melatonin administration inhibited iNOS/i-mtNOS induction, restored mitochondrial homeostasis in septic mice, and preserved the activity of nNOS/c-mtNOS. The effects of melatonin were unrelated to the presence or the absence of nNOS. Our observations show a lack of effect of nNOS on heart bioenergetic impairment during sepsis and further support the beneficial actions of melatonin in sepsis.

Endothelial NO and O₂·⁻ production rates differentially regulate oxidative, nitroxidative, and nitrosative stress in the microcirculation

Endothelial dysfunction causes an imbalance in endothelial NO and O₂·⁻ production rates and increased peroxynitrite formation. Peroxynitrite and its decomposition products cause multiple deleterious effects including tyrosine nitration of proteins, superoxide dismutase (SOD) inactivation, and tissue damage. Studies have shown that peroxynitrite formation during endothelial dysfunction is strongly dependent on the NO and O₂·⁻ production rates. Previous experimental and modeling studies examining the role of NO and O₂·⁻ production imbalance on peroxynitrite formation showed different results in biological and synthetic systems. However, there is a lack of quantitative information about the formation and biological relevance of peroxynitrite under oxidative, nitroxidative, and nitrosative stress conditions in the microcirculation. We developed a computational biotransport model to examine the role of endothelial NO and O₂·⁻ production on the complex biochemical NO and O₂·⁻ interactions in the microcirculation. We also modeled the effect of variability in SOD expression and activity during oxidative stress. The results showed that peroxynitrite concentration increased with increase in either O₂·⁻ to NO or NO to O₂·⁻ production rate ratio (QO₂·⁻/QNO or QNO/QO₂·⁻, respectively). The peroxynitrite concentrations were similar for both production rate ratios, indicating that peroxynitrite-related nitroxidative and nitrosative stresses may be similar in endothelial dysfunction or inducible NO synthase (iNOS)-induced NO production. The endothelial peroxynitrite concentration increased with increase in both QO₂·⁻/QNO and QNO/QO₂·⁻ ratios at SOD concentrations of 0.1-100 μM. The absence of SOD may not mitigate the extent of peroxynitrite-mediated toxicity, as we predicted an insignificant increase in peroxynitrite levels beyond QO₂·⁻/QNO and QNO/QO₂·⁻ ratios of 1. The results support the experimental observations of biological systems and show that peroxynitrite formation increases with increase in either NO or O₂·⁻ production, and excess NO production from iNOS or from NO donors during oxidative stress conditions does not reduce the extent of peroxynitrite mediated toxicity.

Mitochondrial dysfunction and sarcopenia of aging: from signaling pathways to clinical trials

Sarcopenia, the age-related loss of muscle mass and function, imposes a dramatic burden on individuals and society. The development of preventive and therapeutic strategies against sarcopenia is therefore perceived as an urgent need by health professionals and has instigated intensive research on the pathophysiology of this syndrome. The pathogenesis of sarcopenia is multifaceted and encompasses lifestyle habits, systemic factors (e.g., chronic inflammation and hormonal alterations), local environment perturbations (e.g., vascular dysfunction), and intramuscular specific processes. In this scenario, derangements in skeletal myocyte mitochondrial function are recognized as major factors contributing to the age-dependent muscle degeneration. In this review, we summarize prominent findings and controversial issues on the contribution of specific mitochondrial processes - including oxidative stress, quality control mechanisms and apoptotic signaling - on the development of sarcopenia. Extramuscular alterations accompanying the aging process with a potential impact on myocyte mitochondrial function are also discussed. We conclude with presenting methodological and safety considerations for the design of clinical trials targeting mitochondrial dysfunction to treat sarcopenia. Special emphasis is placed on the importance of monitoring the effects of an intervention on muscle mitochondrial function and identifying the optimal target population for the trial. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Late brain alterations in sepsis-survivor rats

Central nervous system (CNS) dysfunction secondary to sepsis is characterized by long-term cognitive impairment. It was observed that oxidative damage, energetic metabolism impairment, and cytokine level alteration seen in early times in an animal model of sepsis may persist for up to 10 days and might be associated with cognitive damage. In order to understand these mechanisms, at least in part, we evaluated the effects of sepsis on cytokine levels in the cerebrospinal fluid (CSF), oxidative parameters, and energetic metabolism in the brain of rats at both 30 and 60 days after sepsis induction by cecal ligation and perforation (CLP). To this aim, male Wistar rats underwent CLP with "basic support" or were sham-operated. Both 30 and 60 days after surgery, the CSF was collected and the animals were killed by decapitation. Then, the prefrontal cortex, hippocampus, striatum, and cortex were collected. Thirty days after surgery, an increase of IL-6 level in the CSF; an increase in the thiobarbituric acid-reactive species (TBARS) in prefrontal cortex and a decrease in hippocampus, striatum, and cortex; a decrease of carbonyl protein formation only in prefrontal cortex and an increase in striatum; and an increase in the complex IV activity only in hippocampus were observed. Sixty days after sepsis, an increase of TNF-α level in the CSF; a decrease of TBARS only in hippocampus; an increase of carbonyl protein formation in striatum; and a decrease of complex I activity in prefrontal cortex, hippocampus, and striatum were observed. These findings may contribute to understanding the role of late cognitive impairment. Further studies may address how these findings interact during sepsis development and contribute to CNS dysfunction.

Mitochondrial function in sepsis

BACKGROUND

The relevance of mitochondrial dysfunction as to pathogenesis of multiple organ dysfunction and failure in sepsis is controversial. This focused review evaluates the evidence for impaired mitochondrial function in sepsis.

DESIGN

Review of original studies in experimental sepsis animal models and clinical studies on mitochondrial function in sepsis. In vitro studies solely on cells and tissues were excluded. PubMed was searched for articles published between 1964 and July 2012.

RESULTS

Data from animal experiments (rodents and pigs) and from clinical studies of septic critically ill patients and human volunteers were included. A clear pattern of sepsis-related changes in mitochondrial function is missing in all species. The wide range of sepsis models, length of experiments, presence or absence of fluid resuscitation and methods to measure mitochondrial function may contribute to the contradictory findings. A consistent finding was the high variability of mitochondrial function also in control conditions and between organs.

CONCLUSION

Mitochondrial function in sepsis is highly variable, organ specific and changes over the course of sepsis. Patients who will die from sepsis may be more affected than survivors. Nevertheless, the current data from mostly young and otherwise healthy animals does not support the view that mitochondrial dysfunction is the general denominator for multiple organ failure in severe sepsis and septic shock. Whether this is true if underlying comorbidities are present, especially in older patients, should be addressed in further studies.

ICU-acquired weakness: mechanisms of disability

PURPOSE OF REVIEW

ICU-acquired weakness (ICUAW) is now recognized as a major complication of critical illness. There is no doubt that ICUAW is prevalent - some might argue ubiquitous - after critical illness, but its true role, the interaction with preexisting nerve and muscle lesions as well as its contribution to long-term functional disability, remains to be elucidated.

RECENT FINDINGS

In this article, we review the current state-of-the-art of the basic pathophysiology of nerve and muscle weakness after critical illness and explore the current literature on ICUAW with a special emphasis on the most important mechanisms of weakness.

SUMMARY

Variable contributions of structural and functional changes likely contribute to both early and late myopathy and neuropathy, although the specifics of the temporality of both processes, and the influence patient comorbidities, age, and nature of the ICU insult have on them, remain to be determined.

[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.

Mathematical and computational models of oxidative and nitrosative stress

The importance of nitric oxide (NO), superoxide (O2-), and peroxynitrite (ONOO-), interactions in physiologic functions and pathophysiological conditions such as cardiovascular disease, hypertension, and diabetes have been established extensively in in vivo and in vitro studies. Despite intense investigation of NO, O2-, and ONOO- biochemical interactions, fundamental questions regarding the role of these molecules remain unanswered. Mathematical models based on fundamental principles of mass balance and reaction kinetics have provided significant results in the case of NO. However, the models that include interaction of NO, O2-, and ONOO- have been few because of the complexity of these interactions. Not only do these mathematical and computational models provided quantitative knowledge of distributions and concentrations of NO, O2-, and ONOO- under normal physiologic and pathophysiologic conditions, they also can help to answer specific hypotheses. The focus of this review article is on the models that involve more than one of the 3 molecules (NO, O2-, and ONOO-). Specifically, kinetic models of O2- dismutase and tyrosine nitration and biotransport models in the microcirculation are reviewed. In addition, integrated experimental and computational models of dynamics of NO/O2-/ONOO- in diverse systems are reviewed.

Nuclear factor-κB: a key regulator in health and disease of lungs

Rel/NF-κB transcription factors play a key role in modulating the response of immunoregulatory genes including cytokines and chemokines, cell adhesion molecules, acute phase proteins, and anti-microbial peptides. Furthermore, an array of genes important for angiogenesis, tumor invasion and metastasis is also regulated by nuclear factor-κB (NF-κB). Close association of NF-κB with inflammation and tumorigenesis makes it an attractive target for basic research as well as for pharmaceutical industries. Studies involving various animal and cellular models have revealed the importance of NF-κB in pathobiology of lung diseases. This review (a) describes structures, activities, and regulation of NF-κB family members; (b) provides information which implicates NF-κB in pathogenesis of pulmonary inflammation and cancer; and (c) discusses information about available synthetic and natural compounds which target NF-κB or specific components of NF-κB signal transduction pathway and which may provide the foundation for development of effective therapy for lung inflammation and bronchogenic carcinomas.

Nitrosative protein oxidation is modulated during early endotoxemia

Formation of nitric oxide and its derivative reactive nitrogen species during endotoxemia has been implicated in the pathogenesis of the associated cardiovascular dysfunction. This stress can promote nitrosative post-translational modifications of proteins that may alter their activity and contribute to dysregulation. We utilized the ascorbate-dependent biotin-switch method to assay protein S-nitrosylation and immunoblotted for tyrosine nitration to monitor changes in nitrosative protein oxidation during endotoxemia. Hearts from lipopolysaccharide (LPS)-treated rats showed no apparent variation in global protein S-nitrosylation, but this may be due to the poor sensitivity of the biotin-switch method. To sensitize our monitoring of protein S-nitrosylation we exposed isolated hearts to the efficient trans-nitrosylating agent nitrosocysteine (which generated a robust biotin-switch signal) and then identified a number of target proteins using mass spectrometry. We were then able to probe for these target proteins in affinity-capture preparations of S-nitrosylated proteins prepared from vehicle- or LPS-treated animals. Unexpectedly this showed a time-dependent loss in S-nitrosylation during sepsis, which we hypothesized, may be due to concomitant superoxide formation that may lower nitric oxide but simultaneously generate the tyrosine-nitrating agent peroxynitrite. Indeed, this was confirmed by immunoblotting for global tyrosine nitration, which increased time-dependently and temporally correlated with a decrease in mean arterial pressure. We assessed if tyrosine nitration was causative in lowering blood pressure using the putative peroxynitrite scavenger FeTPPS. However, FeTPPS was ineffective in reducing global protein nitration and actually exacerbated LPS-induced hypotension.

Effect of selective inhibitors of nitric oxide synthesis on the course of experimental hemorrhagic shock

Selective inhibitors of NO synthesis (derivatives of lysine, ornithine, and isothiourea) increased the efficiency of infusion therapy for experimental hemorrhagic shock in rats. These changes were related to improvement of cardiac function (increase in stroke volume, cardiac output, and left ventricular efficiency). Among the three inhibitors, N5-(1-iminoethyl)-L-ornithine dihydrochloride was most potent on this experimental model. This compound improved cardiac function and microcirculation and provided 100% survival of experimental animals.

Factors associated with noninvasive ventilation failure in postoperative acute respiratory insufficiency: an observational study

BACKGROUND AND OBJECTIVE

Few data are available on the efficacy of noninvasive ventilation (NIV) in postoperative patients with acute respiratory failure (ARF).

METHODS

Seventy-two patients coming from the surgical wards with postoperative ARF were retrospectively evaluated. The major characteristics of patients who were intubated were compared with the characteristics of those who were not after a trial of NIV. Predictive factors for failure of NIV were analysed.

RESULTS

Out of 72 patients with ARF after surgery who were treated with NIV, 42 avoided intubation (58%). On a univariate analysis, a decrease in the paO2/FiO2 ratio after 1 h of NIV (223 +/- 84 to 160 +/- 68 mmHg, P < 0.05) was associated with NIV failure and need for tracheal intubation because of nosocomial pneumonia and an increased simplified acute physiology score (SAPS) 2. In a multivariate analysis, nosocomial pneumonia [odds ratio (OR) 4.189; 95% confidence interval (CI) 1.383-12.687] and SAPS 2 higher than 35 (OR 4.969; 95% CI 1.627-15.172) were independent predictive factors of NIV failure. NIV success was associated with a reduced ICU stay (16.8 vs. 26.1 days, P < 0.001).

CONCLUSION

NIV could be considered in postoperative patients who presented with ARF. Nosocomial pneumonia is predictive of NIV failure.

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.

In situ and real time muscle chemiluminescence determines singlet oxygen involvement in oxidative damage during endotoxemia

Many studies have reported the occurrence of oxidative stress in different models of sepsis, but no measurements in real time and in non-invasive manner in an acute model of endotoxemia were done, being its mechanism still under debate. In the present work, we have used in situ surface chemiluminescence to evaluate the reactive oxygen species steady-state concentrations and to identify the main chemical species involved in this phenomenon. Experimental endotoxemia provoked a twofold increase in skeletal muscle chemiluminescence (control value: 31+/-4cps/cm(2)). The use of cutoff filters and D(2)O and biacetyl as specific enhancers, indicates that singlet oxygen is the main emitting species in this model. This result closely correlates with elevated TBARS levels, an index of oxidative damage to lipids. Increased NO production and NADPH oxidase activity may support the formation of ONOO(-), which in turn may originate HO, an initiator of the lipid oxidation chain. In summary, our data show for the first time that (1)O(2) is the main chemical and emitting species involved in the mechanism of oxidative stress present in an acute model of endotoxemia. This work provides new insights necessary to understand free radical mechanisms behind endotoxemic syndrome.

Alterations of mitochondrial function in sepsis and critical illness

PURPOSE OF REVIEW

Septic shock is the consequence of a conflict between a pathogenic agent and the immune system of the host. This conflict induces an immune-mediated cytokine storm, with a whole-body inflammatory response often leading to multiple organ failure. Although extensively studied, the pathophysiology of sepsis-associated multiorgan failure remains unknown. One postulated mechanism is changes in mitochondrial function with an inhibition of mitochondrial respiratory chain and a decrease of oxygen utilization.

RECENT FINDINGS

Mitochondrion is a key organelle in supplying energy to the cell according to its metabolic need. Hypoxia and a number of the mediators implicated in sepsis and in the associated systemic inflammatory response have been demonstrated to directly impair mitochondrial function. A large body of evidence supports a key role of the peroxynitrite, which can react with most of the components of the electron transport chain, in the mitochondrial dysfunction.

SUMMARY

A pivotal role is suggested for mitochondrial dysfunction during the occurrence of multiorgan failure. Understanding the precise effect of sepsis on the mitochondrial function and the involvement of mitochondria in the development of multiple organ failure is fundamental. More human studies are thus necessary to clarify the mitochondrial dysfunction in the various phases of sepsis (early and late phase) before testing therapeutic strategies targeting mitochondria.

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.

Genetic deficiency of NADPH oxidase does not diminish, but rather enhances, LPS-induced acute inflammatory responses in vivo

Reactive oxygen species (ROS) and oxidative stress are thought to play a central role in the etiology of cell dysfunction and tissue damage in sepsis. However, there is limited and controversial evidence from in vivo studies that ROS mediate cell signaling processes that elicit acute inflammatory responses during sepsis. Because NADPH oxidase is one of the main cellular sources of ROS, we investigated the role of this enzyme in lipopolysaccharide (LPS)-induced acute inflammation in vivo, utilizing mice deficient in the gp91(phox) or p47(phox) subunits of NADPH oxidase. Age-and body weight-matched C57BL/6J wild-type (WT) and gp91(phox-/-) and p47(phox-/-) mice were injected ip with 50 microg LPS or saline vehicle and sacrificed at various time points up to 24 h. We found that LPS-induced acute inflammatory responses in serum and tissues were not significantly diminished in gp91(phox-/-) and p47(phox-/-) mice compared to WT mice. Rather, genetic deficiency of NADPH oxidase was associated with enhanced gene expression of inflammatory mediators and increased neutrophil recruitment to lung and heart. Furthermore, no protection from LPS-induced septic death was observed in either knockout strain. Our findings suggest that NADPH oxidase-mediated ROS production and cellular redox signaling do not promote, but instead limit, LPS-induced acute inflammatory responses in vivo.