Pharmacological activation of endogenous protective pathways against oxidative stress under conditions of sepsis.

BACKGROUND: Mitochondrial oxidative stress has a role in sepsis-induced organ dysfunction. The endogenous mechanisms to initiate protective pathways are controlled by peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC1α) and nuclear factor erythroid 2-like 2 (NFE2L2). Activation of these pathways are potential therapeutic targets in sepsis. We used pharmacological activators to determine the effects on markers of mitochondrial damage and inflammation in human endothelial cells under conditions of sepsis. METHODS: Human endothelial cells were exposed to lipopolysaccharide plus peptidoglycan G to mimic a sepsis environment, with a range of concentrations of a selective synthetic agonist of silent information regulator-1 (SIRT-1) which activates PGC1α, or bis(2-hydroxy-benzylidene) acetone (2HBA) which activates NFE2L2, with and without inhibitors of these pathways. Cells were cultured for up to seven days and we measured mitochondrial membrane potential, metabolic activity, and density (as a marker of biogenesis), interkeukin-6 (to reflect inflammation) and glutathione (as a measure of antioxidant status). RESULTS: Under conditions mimicking sepsis, activation of the PGC1α and NFE2L2 pathways protected cells from LPS/PepG-induced loss of mitochondrial membrane potential (P=0.0002 and P=0.0009, respectively) and metabolic activity (P=0.05 and P<0.0001, respectively), and dampened interleukin-6 responses (P=0.003 and P=0.0001, respectively). Mitochondrial biogenesis (both P=0.0001) and glutathione (both P<0.0001) were also increased. These effects were blunted by the respective inhibitors. CONCLUSIONS: The development of organ dysfunction during human sepsis is linked to mitochondrial dysfunction, and so activation of PGC1α/NFE2L2 is likely to be beneficial. These pathways are attractive therapeutic targets for sepsis.

Low zinc and selenium concentrations in sepsis are associated with oxidative damage and inflammation.

BACKGROUND: Oxidative stress with dysregulated inflammation are hallmarks of sepsis. Zinc and selenium have important antioxidant functions, such that they could be important in patients with sepsis. We used an in vitro approach to assess the effect of zinc and selenium on oxidative stress, mitochondrial function, and inflammatory responses in conditions mimicking sepsis and related the findings to plasma concentrations and biomarkers in patients with and without sepsis. METHODS: Human endothelial cells were exposed to a range of zinc and selenium concentrations in conditions mimicking sepsis. Zinc, selenium, and a series of biomarkers of oxidative stress and inflammation were measured in plasma from critically ill patients with and without sepsis. RESULTS: Culturing cells with different concentrations of zinc caused altered zinc transporter protein expression and cellular zinc content, and selenium affected glutathione peroxidase 3 activity. Although zinc or selenium at physiological concentrations had no effect on interleukin-6 release in vitro, higher concentrations of the trace elements were associated with improved mitochondrial function. Plasma zinc and selenium concentrations were low in patients [zinc: median (range) 4.6 (2.1-6.5) µM in control patients without sepsis and 3.1 (1.5-5.4) µM in patients with sepsis, P=0.002; and selenium: 0.78 (0.19-1.32) µM in control patients and 0.42 (0.22-0.91) µM in sepsis patients, P=0.0009]. Plasma concentrations of interleukin-6, other biomarkers of inflammation, and markers of oxidative damage to proteins and lipids were elevated, particularly in patients with sepsis, and were inversely related to plasma zinc and selenium concentrations. CONCLUSIONS: Zinc and selenium concentrations were reduced in critically ill patients, with increased oxidative stress and inflammatory biomarkers, particularly in patients with sepsis. Oxidative stress as a result of suboptimal selenium and zinc concentrations might contribute to damage of key proteins. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov: registration number NCT01328509.

Antioxidants that protect mitochondria reduce interleukin-6 and oxidative stress, improve mitochondrial function, and reduce biochemical markers of organ dysfunction in a rat model of acute sepsis.

BACKGROUND: Sepsis-induced organ failure is the major cause of death in critical care units, and is characterized by a massive dysregulated inflammatory response and oxidative stress. We investigated the effects of treatment with antioxidants that protect mitochondria (MitoQ, MitoE, or melatonin) in a rat model of lipopolysaccharide (LPS) plus peptidoglycan (PepG)-induced acute sepsis, characterized by inflammation, mitochondrial dysfunction and early organ damage. METHODS: Anaesthetized and ventilated rats received an i.v. bolus of LPS and PepG followed by an i.v. infusion of MitoQ, MitoE, melatonin, or saline for 5 h. Organs and blood were then removed for determination of mitochondrial and organ function, oxidative stress, and key cytokines. RESULTS: MitoQ, MitoE, or melatonin had broadly similar protective effects with improved mitochondrial respiration (P<0.002), reduced oxidative stress (P<0.02), and decreased interleukin-6 levels (P=0.0001). Compared with control rats, antioxidant-treated rats had lower levels of biochemical markers of organ dysfunction, including plasma alanine amino-transferase activity (P=0.02) and creatinine concentrations (P<0.0001). CONCLUSIONS: Antioxidants that act preferentially in mitochondria reduce mitochondrial damage and organ dysfunction and decrease inflammatory responses in a rat model of acute sepsis.

Efficacy of dexmedetomidine compared with midazolam for sedation in adult intensive care patients: a systematic review.

Patients in Intensive Care Unit (ICU) often require sedatives which commonly include midazolam and the more recently developed α2-receptor agonist, dexmedetomidine. It was our aim to compare the sedative and clinical effectiveness of dexmedetomidine vs midazolam in adults admitted to ICU, using an objective appraisal of randomized control trials. Medline, Embase, SCOPUS, Web of Knowledge, Cinhal, the United States National Library of Medicine, and the Cochrane Database of Systematic Reviews were searched using keywords: 'dexmedetomidine', 'midazolam', and 'intensive care'. These were limited to human studies and adults (>18 yr old). Six randomized controlled trials were found and were critically appraised using a standardized appraisal method. Two papers described the time spent by each intervention group within a specified target sedation range and both found no statistically significant difference between midazolam and dexmedetomidine (P=0.18 and P=0.15). A third paper found no statistically significant difference in the length of time that patients were sedated within a target zone (P=0.445). Two additional pilot studies did not report P values as they were insufficiently statistically powered. A final paper found that, of the eight occasions measured, patients on dexmedetomidine were more often within the target sedation range than patients on midazolam. The sedative benefits of dexmedetomidine vs midazolam remain inconclusive. While some secondary outcomes showed clinical effectiveness of dexmedetomidine, more research is needed to validate the findings of these studies.

Role of microparticles in sepsis.

This review discusses the role of microparticles in inflammation, coagulation, vascular function, and most importantly, their physiological and pathological functions in sepsis. Microparticles are proinflammatory, procoagulant membrane vesicles released from various cell types. They are detectable in normal individuals and basal levels correlate with a balance between cell proliferation, stimulation, and destruction. Haemostatic imbalance leads to various pathological states of inflammation and thrombosis including cardiovascular disease and sepsis, where circulating microparticles display both an increase in number and phenotypic change. Microparticles, mainly of platelet origin enable both local and disseminated amplification of the haemostatic response to endothelial injury through exposure of phosphatidylserine, tissue factor, and coagulation factor binding sites. Surface expression of membrane antigens by microparticles facilitates cytoadhesion, chemotaxis, and cytokine secretion to drive a proinflammatory response. Microparticles behave as vectors in the transcellular exchange of biological information and are important regulators of endothelial function and angiogenesis. The extent to which circulating microparticles contribute to the pathogenesis of sepsis and disseminated intravascular coagulation is currently unknown. Microparticles may in fact be beneficial in early sepsis, given that activated protein C bound to endothelium-derived microparticles retains anticoagulant activity, and increased circulating microparticles are protective against vascular hyporeactivity. Elevated levels of microparticles in early sepsis may therefore compensate for the host's systemic inflammatory response. Importantly, in vivo, septic microparticles induce deleterious changes in the expression of enzyme systems related to inflammation and oxidative stress, thus they may represent important contributors to multi-organ failure in septic shock.

The influence of surgery on the onset of symptomatic coronary artery disease.

We speculated that asymptomatic patients undergoing routine surgery might be at higher risk of subsequent cardiac events. We studied 183,534 patients with no prior admission for heart disease, aged 50-75 years, admitted electively for one of five operations considered medium to low risk of peri-operative cardiac morbidity, between January 1997 and December 2005. Controls were generated from linked records. Within 3 years 3444 (1.9%) patients undergoing operations had subsequent myocardial infarction/acute coronary syndrome (MI/ACS) compared with 3708 (2.0%) controls (p < 0.001). Overall 8406 (4.6%) patients undergoing surgery had MI/ACS compared with 9306 (5.1%) controls (p < 0.001). Of patients undergoing surgery, 20.2% died compared with 25.7% of controls (p < 0.001). Patients undergoing certain surgical procedures did not have a higher incidence of readmission for cardiac events, but had a general survival benefit compared with other elective hospital admissions. Assessment for surgery may represent a health benefit beyond the original surgery.

Emerging modes of ventilation in the intensive care unit.

Potentially harmful effects of positive pressure mechanical ventilation have been recognized since its inception in the 1950s. Since then, the risk factors for and mechanisms of ventilator-induced lung injury (VILI) have been further characterized. Publication of the ARDSnet tidal volume trial in 2000 demonstrated that a ventilator strategy limiting tidal volumes and plateau pressure in patients with acute respiratory distress syndrome was associated with a 22% reduction in mortality. Since then, a variety of ventilator modes have emerged seeking to improve gas exchange, reduce injurious effects of ventilation, and improve weaning from the ventilator. We review here emerging ventilator modes in the intensive care unit (ICU). Airway pressure release ventilation seeks to optimize alveolar recruitment and maintain spontaneous ventilatory effort. It is associated with improved indices of respiratory and cardiovascular physiology, but data to support outcome benefit are lacking. High-frequency oscillatory ventilation is associated with improvements in gas exchange, but outcome data are conflicting. Extracorporeal modes of ventilation continue to evolve, and extra-corporeal CO(2) removal is a technique that could be used in non-specialist ICUs. Proportional-assist ventilation and neutrally adjusted ventilator assist are modes that vary level of assistance with patient ventilatory effort. They result in greater patient-ventilator synchrony, but at present there is no evidence of a reduction in the duration of mechanical ventilation or outcome benefit. Although the use of many of these modes is likely to increase in intensive care units, further evidence of a beneficial effect is desirable before they are recommended.

Melatonin and structurally similar compounds have differing effects on inflammation and mitochondrial function in endothelial cells under conditions mimicking sepsis.

BACKGROUND: Development of organ dysfunction associated with sepsis is due in part to oxidative damage to mitochondria. Melatonin regulates the sleep-wake cycle and also has potent antioxidant activity. The aim of this study was to determine the effects of melatonin and other structurally related compounds on mitochondrial function, endogenous glutathione (GSH), and control of cytokine expression under conditions mimicking sepsis. METHODS: Human endothelial cells were treated with lipopolysaccharide (LPS) plus peptidoglycan G (PepG) to simulate sepsis, in the presence of melatonin, 6-hydroxymelatonin, tryptamine, or indole-3-carboxylic acid. Nuclear factor κB (NFκB) activation, interleukin (IL)-6 and IL-8, total glutathione, mitochondrial membrane potential, and metabolic activity were measured. RESULTS: LPS and PepG treatment resulted in elevated IL-6 and IL-8 levels preceded by activation of NFκB (all P<0.0001). Treatment with all four compounds resulted in lower IL-6 and IL-8 levels, and lower NFκB activation (P<0.0001). Loss of mitochondrial membrane potential and endogenous glutathione was seen when cells were exposed to LPS/PepG, but these were maintained in cells co-treated with melatonin, tryptamine, or 6-hydroxymelatonin (P<0.05), but not indole-3-carboxylic acid. Metabolic activity decreased after exposure to LPS/PepG and was maintained by melatonin and 6-hydroxymelatonin at the highest concentrations only. CONCLUSIONS: We have shown that in addition to melatonin, other structurally related indoleamine compounds have effects on NFκB activation and cytokine expression, GSH, mitochondrial membrane potential, and metabolic activity in endothelial cells cultured under conditions mimicking sepsis. Further work is needed to determine whether these compounds represent therapeutic approaches for disrupting the oxidative stress-inflammatory response signalling pathway in sepsis.

Cytokines and the immunomodulatory function of the vagus nerve.

Cytokine synthesis and release is an essential component of the innate immune system, but inappropriate, excessive production results in a generalized systemic inflammatory response which damages distant organs. Recent research has identified an immunomodulatory function of the vagus nerve whereby activation of the efferent arm results in regulation of cytokine production. Termed the 'cholinergic anti-inflammatory pathway', this neuro-immune communication provides the host with a fast, discrete, and localized means of controlling the immune response and preventing excessive inflammation. Stimulation of the vagus nerve attenuates cytokine production and improves survival in experimental sepsis, haemorrhagic shock, ischaemia-reperfusion injury, and other conditions of cytokine excess and research is now underway in developing new and novel therapeutics aimed at stimulating the vagus nerve either directly or targeting specific components of the pathway.

Immunomodulation in the critically ill.

Immunotherapy in the critically ill is an appealing notion because of the apparent abnormal immune and inflammatory responses seen in so many patients. The administration of a medication that could alter immune responses and decrease mortality in patients with sepsis could represent a 'magic bullet'. Various approaches have been tried over the last 20 yr: steroids; anti-endotoxin or anti-cytokine antibodies; cytokine receptor antagonists; and other agents with immune-modulating side-effects. However, in some respects, research along these lines has been unsuccessful or disappointing at best. The current state of knowledge is summarized with particular reference to sepsis and the acute respiratory distress syndrome.

Regulation of pentraxin-3 by antioxidants.

BACKGROUND: Pentraxin-3 (PTX3) may be a useful biomarker in sepsis, but its regulatory mechanisms are still unclear. Oxidative stress is well defined in patients with sepsis and has a role in regulation of inflammatory pathways which may include PTX3. We undertook an in vitro study of the effect of antioxidants on regulation of PTX3 in endothelial cells combined with a prospective observational pilot study of PTX3 in relation to markers of antioxidant capacity and oxidative stress in patients with sepsis. METHODS: Human endothelial cells were cultured with lipopolysaccharide 2 microg ml(-1), peptidoglycan G 20 microg ml(-1), tumour necrosis factor (TNF) alpha 10 ng ml(-1), interleukin-1 (IL-1) beta 20 ng ml(-1), or killed Candida albicans yeast cells plus either N-acetylcysteine (NAC) 25 mM, trolox 100 mM, or idebenone 1 microM. Plasma samples were obtained from 15 patients with sepsis and 11 healthy volunteers. RESULTS: PTX3 levels in plasma were higher in patients with sepsis than in healthy people [26 (1-202) ng ml(-1) compared with 6 (1-12) ng ml(-1), P=0.01]. Antioxidant capacity was lower in patients with sepsis than healthy controls [0.99 (0.1-1.7) mM compared with 2.2 (1.3-3.3) mM, P=0.01]. In patients with sepsis, lipid hydroperoxide levels were 3.32 (0.3-10.6) nM and undetectable in controls. We found no relationship between PTX3 and antioxidant capacity or lipid hydroperoxides. Cell expression of PTX3 increased with all inflammatory stimulants but was highest in cells treated with TNFalpha plus IL-1beta. PTX3 concentrations were lower in cells co-treated with antioxidants (all P<0.05), associated with lower nuclear factor kappaB expression for NAC and trolox (P<0.05). CONCLUSIONS: PTX3 expression is down-regulated in vitro by antioxidants. Plasma levels of PTX3 are elevated in sepsis but seem to be unrelated to markers of oxidant stress or antioxidant capacity.