Induced hypothermia is associated with reduced circulating subunits of mitochondrial DNA in cardiac arrest patients.

Induced hypothermia may protect from ischemia reperfusion injury. The mechanism of protection is not fully understood and may include an effect on mitochondria. Here we describe the effect of hypothermia on circulating mitochondrial (mt) DNA in a substudy of a multicenter randomized trial (the Target Temperature Management trial). Circulating levels of mtDNA were elevated in patients with cardiac arrest at all-time points compared to healthy controls. After 24 h of temperature management, patients kept at 33 °C had significantly lower levels of COX3, NADH1 and NADH2 compared to baseline, in contrast to those kept at 36 °C. After regain of temperature, cytochrome - B was significantly reduced in patients kept at 33 °C with cardiac arrest. Cardiac arrest results in circulating mtDNA levels, which reduced during a temperature management protocol in patients with a target temperature of 33 °C.

Prolonged helium postconditioning protocols during early reperfusion do not induce cardioprotection in the rat heart in vivo: role of inflammatory cytokines.

Postconditioning of myocardial tissue employs short cycles of ischemia or pharmacologic agents during early reperfusion. Effects of helium postconditioning protocols on infarct size and the ischemia/reperfusion-induced immune response were investigated by measurement of protein and mRNA levels of proinflammatory cytokines. Rats were anesthetized with S-ketamine (150 mg/kg) and diazepam (1.5 mg/kg). Regional myocardial ischemia/reperfusion was induced; additional groups inhaled 15, 30, or 60 min of 70% helium during reperfusion. Fifteen minutes of helium reduced infarct size from 43% in control to 21%, whereas 30 and 60 minutes of helium inhalation led to an infarct size of 47% and 39%, respectively. Increased protein levels of cytokine-induced neutrophil chemoattractant (CINC-3) and interleukin-1 beta (IL-1ß) were found after 30 or 60 min of helium inhalation, in comparison to control. 30 min of helium increased mRNA levels of CINC-3, IL-1ß, interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α) in myocardial tissue not directly subjected to ischemia/reperfusion. These results suggest that the effectiveness of the helium postconditioning protocol is very sensitive to duration of noble gas application. Additionally, helium was associated with higher levels of inflammatory cytokines; however, it is not clear whether this is causative of nature or part of an epiphenomenon.

The receptor for advanced glycation end products in ventilator-induced lung injury.

BACKGROUND: Mechanical ventilation (MV) can cause ventilator-induced lung injury (VILI). The innate immune response mediates this iatrogenic inflammatory condition. The receptor for advanced glycation end products (RAGE) is a multiligand receptor that can amplify immune and inflammatory responses. We hypothesized that RAGE signaling contributes to the pro-inflammatory state induced by MV. METHODS: RAGE expression was analyzed in lung brush and lavage cells obtained from ventilated patients and lung tissue of ventilated mice. Healthy wild-type (WT) and RAGE knockout (KO) mice were ventilated with relatively low (approximately 7.5 ml/kg) or high (approximately 15 ml/kg) tidal volume. Positive end-expiratory pressure was set at 2 cm H2O during both MV strategies. Also, WT and RAGE KO mice with lipopolysaccharide (LPS)-induced lung injury were ventilated with the above described ventilation strategies. In separate experiments, the contribution of soluble RAGE, a RAGE isoform that may function as a decoy receptor, in ventilated RAGE KO mice was investigated. Lung wet-to-dry ratio, cell and neutrophil influx, cytokine and chemokine concentrations, total protein levels, soluble RAGE, and high-mobility group box 1 (HMGB1) presence in lung lavage fluid were analyzed. RESULTS: MV was associated with increased RAGE mRNA levels in both human lung brush samples and lung tissue of healthy mice. In healthy high tidal volume-ventilated mice, RAGE deficiency limited inflammatory cell influx. Other VILI parameters were not affected. In our second set of experiments where we compared RAGE KO and WT mice in a 2-hit model, we observed higher pulmonary cytokine and chemokine levels in RAGE KO mice undergoing LPS/high tidal volume MV as compared to WT mice. Third, in WT mice undergoing the LPS/high tidal volume MV, we observed HMGB1 presence in lung lavage fluid. Moreover, MV increased levels of soluble RAGE in lung lavage fluid, with the highest levels found in LPS/high tidal volume-ventilated mice. Administration of soluble RAGE to LPS/high tidal volume-ventilated RAGE KO mice attenuated the production of inflammatory mediators. CONCLUSIONS: RAGE was not a crucial contributor to the pro-inflammatory state induced by MV. However, the presence of sRAGE limited the production of pro-inflammatory mediators in our 2-hit model of LPS and high tidal volume MV.

Mechanical ventilation with heliox in an animal model of acute respiratory distress syndrome.

BACKGROUND: Heliox has a lower density and higher diffusion capacity compared to oxygen-in-air. We hypothesized that heliox ventilation allows for a reduction in minute volume ventilation and inspiratory pressures needed for adequate gas exchange in an animal model of an acute lung injury. METHODS: After intratracheal instillation of lipopolysaccharide (10 mg/kg), adult rats were randomized to ventilation with either a gas mixture of helium/oxygen (50:50%) or oxygen/air (50:50%). They were mechanically ventilated according to the ARDSnet recommendations with tidal volumes of 6 ml/kg and monitored with a pneumotachometer. Bronchoalveolar lavage fluid was analyzed for markers of lung injury, and embedded lung sections were histologically scored for lung injury. RESULTS: Heliox limited the increase in driving pressures needed to achieve preset tidal volumes, with a concomitant decrease in loss of compliance. Heliox did neither allow for reduced minute volume ventilation in this model nor improve gas exchange. Also, heliox did not reduce lung injury. CONCLUSIONS: Heliox modestly improved respiratory mechanics but did not improve lung injury in this rat model of acute respiratory distress syndrome.

Heliox allows for lower minute volume ventilation in an animal model of ventilator-induced lung injury.

BACKGROUND: Helium is a noble gas with a low density, allowing for lower driving pressures and increased carbon dioxide (CO2) diffusion. Since application of protective ventilation can be limited by the development of hypoxemia or acidosis, we hypothesized that therefore heliox facilitates ventilation in an animal model of ventilator-induced lung injury. METHODS: Sprague-Dawley rats (N=8 per group) were mechanically ventilated with heliox (50% oxygen; 50% helium). Controls received a standard gas mixture (50% oxygen; 50% air). VILI was induced by application of tidal volumes of 15 mL kg(-1); lung protective ventilated animals were ventilated with 6 mL kg(-1). Respiratory parameters were monitored with a pneumotach system. Respiratory rate was adjusted to maintain arterial pCO2 within 4.5-5.5 kPa, according to hourly drawn arterial blood gases. After 4 hours, bronchoalveolar lavage fluid (BALF) was obtained. Data are mean (SD). RESULTS: VILI resulted in an increase in BALF protein compared to low tidal ventilation (629 (324) vs. 290 (181) µg mL(-1); p<0.05) and IL-6 levels (640 (8.7) vs. 206 (8.7) pg mL(-1); p<0.05), whereas cell counts did not differ between groups after this short course of mechanical ventilation. Ventilation with heliox resulted in a decrease in mean respiratory minute volume ventilation compared to control (123 ± 0.6 vs. 146 ± 8.9 mL min(-1), P<0.001), due to a decrease in respiratory rate (22 (0.4) vs. 25 (2.1) breaths per minute; p<0.05), while pCO2 levels and tidal volumes remained unchanged, according to protocol. There was no effect of heliox on inspiratory pressure, while compliance was reduced. In this mild lung injury model, heliox did not exert anti-inflammatory effects. CONCLUSIONS: Heliox allowed for a reduction in respiratory rate and respiratory minute volume during VILI, while maintaining normal acid-base balance. Use of heliox may be a useful approach when protective tidal volume ventilation is limited by the development of severe acidosis.

Traumatic brain injury in rats induces lung injury and systemic immune suppression.

Traumatic brain injury (TBI) is frequently complicated by acute lung injury, which is predictive for poor outcome. However, it is unclear whether lung injury develops independently or as a result of mechanical ventilation after TBI. Further, TBI is strongly associated with the development of pneumonia, suggesting a specific vulnerability for the development of nosocomial infections in the lung after TBI. In this study, we evaluated whether indeed pulmonary injury and immune suppression develop spontaneously in an animal model of mild TBI (mTBI). TBI was induced in male PVG rats by closed-head trauma using a weight-drop device. Subsequently, we evaluated the effects of this on the lungs as well as on the excitability of the systemic immune system. Finally, we performed an experiment in which TBI was followed by induction of pneumonitis and evaluated whether TBI affects the severity of subsequent pneumonitis induced by intratracheal instillation of heat-killed Staphylococcus aureus. mTBI resulted in significant lung injury, as evidenced by pulmonary edema, protein leakage to the alveolar compartment, and increased concentrations of interleukin-1 and -6 in broncho alveolar lavage fluid (all p<0.05 vs. sham-treated animals). Further, after TBI, the release of tumor necrosis factor alpha was decreased when whole blood was stimulated ex vivo (p<0.05 TBI vs. sham), indicating systemic immune suppression. When TBI was followed by pneumonitis, the severity of subsequent pneumonitis was not different in rats previously subjected to TBI or sham treatment (p>0.05), suggesting that systemic immune suppression is not translated toward the pulmonary compartment in this specific model. We here show that during mild experimental TBI, acute pulmonary injury, as well as a decrease in the excitability of the systemic immune system, can be observed.

High levels of S100A8/A9 proteins aggravate ventilator-induced lung injury via TLR4 signaling.

BACKGROUND: Bacterial products add to mechanical ventilation in enhancing lung injury. The role of endogenous triggers of innate immunity herein is less well understood. S100A8/A9 proteins are released by phagocytes during inflammation. The present study investigates the role of S100A8/A9 proteins in ventilator-induced lung injury. METHODS: Pulmonary S100A8/A9 levels were measured in samples obtained from patients with and without lung injury. Furthermore, wild-type and S100A9 knock-out mice, naive and with lipopolysaccharide-induced injured lungs, were randomized to 5 hours of spontaneously breathing or mechanical ventilation with low or high tidal volume (VT). In addition, healthy spontaneously breathing and high VT ventilated mice received S100A8/A9, S100A8 or vehicle intratracheal. Furthermore, the role of Toll-like receptor 4 herein was investigated. RESULTS: S100A8/A9 protein levels were elevated in patients and mice with lung injury. S100A8/A9 levels synergistically increased upon the lipopolysaccharide/high VT MV double hit. Markers of alveolar barrier dysfunction, cytokine and chemokine levels, and histology scores were attenuated in S100A9 knockout mice undergoing the double-hit. Exogenous S100A8/A9 and S100A8 induced neutrophil influx in spontaneously breathing mice. In ventilated mice, these proteins clearly amplified inflammation: neutrophil influx, cytokine, and chemokine levels were increased compared to ventilated vehicle-treated mice. In contrast, administration of S100A8/A9 to ventilated Toll-like receptor 4 mutant mice did not augment inflammation. CONCLUSION: S100A8/A9 proteins increase during lung injury and contribute to inflammation induced by HVT MV combined with lipopolysaccharide. In the absence of lipopolysaccharide, high levels of extracellular S100A8/A9 still amplify ventilator-induced lung injury via Toll-like receptor 4.

Hydrogen sulfide donor NaHS reduces organ injury in a rat model of pneumococcal pneumosepsis, associated with improved bio-energetic status.

Sepsis is characterized by a generalized inflammatory response and organ failure, associated with mitochondrial dysfunction. Hydrogen sulfide donor NaHS has anti-inflammatory properties, is able to reduce metabolism and can preserve mitochondrial morphology and function. Rats were challenged with live Streptococcus pneumonia or saline and infused with NaHS (36 µmol/kg/h) or vehicle. Lung and kidney injury markers were measured as well as mitochondrial function, viability and biogenesis. Infusion of NaHS reduced heart rate and body temperature, indicative of a hypo-metabolic state. NaHS infusion reduced sepsis-related lung and kidney injury, while host defense remained intact, as reflected by unchanged bacterial outgrowth. The reduction in organ injury was associated with a reversal of a fall in active oxidative phosphorylation with a concomitant decrease in ATP levels and ATP/ADP ratio. Preservation of mitochondrial respiration was associated with increased mitochondrial expression of α-tubulin and protein kinase C-ε, which acts as regulators of respiration. Mitochondrial damage was decreased by NaHS, as suggested by a reduction in mitochondrial DNA leakage in the lung. Also, NaHS treatment was associated with upregulation of peroxisome proliferator-activated receptor-γ coactivator 1α, with a subsequent increase in transcription of mitochondrial respiratory subunits. These findings indicate that NaHS reduces organ injury in pneumosepsis, possibly via preservation of oxidative phosphorylation and thereby ATP synthesis as well as by promoting mitochondrial biogenesis. Further studies on the involvement of mitochondria in sepsis are required.

Nebulized fibrinolytic agents improve pulmonary fibrinolysis but not inflammation in rat models of direct and indirect acute lung injury.

BACKGROUND: Critically ill patients frequently develop acute lung injury (ALI). Disturbed alveolar fibrin turnover, a characteristic feature of ALI, is the result of both activation of coagulation and inhibition of fibrinolysis. Nebulized fibrinolytic agents could exert lung-protective effects, via promotion of fibrinolysis as well as anti-inflammation. METHODS: Rats were challenged intratracheally with Pseudomonas aeruginosa, resulting in pneumonia as a model for direct ALI, or received an intravenous bolus infusion of lipopolysaccharide, as a model for indirect ALI. Rats were randomized to nebulization of normal saline (placebo), recombinant tissue plasminogen activator (rtPA), or monoclonal antibodies against plasminogen activator inhibitor-type 1 (anti-PAI-1). RESULTS: Nebulized rtPA or anti-PA1-1 enhanced the bronchoalveolar fibrinolytic system, as reflected by a significant reduction of PAI-1 activity levels in bronchoalveolar lavage fluid, and a consequent increase in plasminogen activator activity (PAA) levels to supranormal values. Both treatments also significantly affected systemic fibrinolysis as reflected by a significant increase in PAA levels in plasma to supranormal levels. Neither nebulized rtPA nor anti-PA1-1 affected pulmonary inflammation. Neither treatment affected bacterial clearance of P. aeruginosa from the lungs in case of pneumonia. CONCLUSIONS: Local treatment with rtPA or anti-PA1-1 affects pulmonary fibrinolysis but not inflammation in models of direct or indirect ALI in rats.

A short course of infusion of a hydrogen sulfide-donor attenuates endotoxemia induced organ injury via stimulation of anti-inflammatory pathways, with no additional protection from prolonged infusion.

Organ failure is associated with increased mortality and morbidity in patients with systemic inflammatory response syndrome. Previously, we showed that a short course of infusion of a hydrogen sulfide (H(2)S) donor reduced metabolism with concurrent reduction of lung injury. Here, we hypothesize that prolonged H(2)S infusion is more protective than a short course in endotoxemia with organ failure. Also, as H(2)S has both pro- and anti-inflammatory effects, we explored the effect of H(2)S on interleukin production. Endotoxemia was induced by an intravenous bolus injection of LPS (7.5mg/kg) in mechanically ventilated rats. H(2)S donor NaHS (2mg/kg) or vehicle (saline) was infused and organ injury was determined after either 4 or 8h. A short course of H(2)S infusion was associated with reduction of lung and kidney injury. Prolonged infusion did not enhance protection. Systemically, infusion of H(2)S increased both the pro-inflammatory response during endotoxemia, as demonstrated by increased TNF-α levels, as well as the anti-inflammatory response, as demonstrated by increased IL-10 levels. In LPS-stimulated whole blood of healthy volunteers, co-incubation with H(2)S had solely anti-inflammatory effects, resulting in decreased TNF-α levels and increased IL-10 levels. Co-incubation with a neutralizing IL-10 antibody partly abrogated the decrease in TNF-α levels. In conclusion, a short course of H(2)S infusion reduced organ injury during endotoxemia, at least in part via upregulation of IL-10.

Pre-treatment with allopurinol or uricase attenuates barrier dysfunction but not inflammation during murine ventilator-induced lung injury.

INTRODUCTION: Uric acid released from injured tissue is considered a major endogenous danger signal and local instillation of uric acid crystals induces acute lung inflammation via activation of the NLRP3 inflammasome. Ventilator-induced lung injury (VILI) is mediated by the NLRP3 inflammasome and increased uric acid levels in lung lavage fluid are reported. We studied levels in human lung injury and the contribution of uric acid in experimental VILI. METHODS: Uric acid levels in lung lavage fluid of patients with acute lung injury (ALI) were determined. In a different cohort of cardiac surgery patients, uric acid levels were correlated with pulmonary leakage index. In a mouse model of VILI the effect of allopurinol (inhibits uric acid synthesis) and uricase (degrades uric acid) pre-treatment on neutrophil influx, up-regulation of adhesion molecules, pulmonary and systemic cytokine levels, lung pathology, and regulation of receptors involved in the recognition of uric acid was studied. In addition, total protein and immunoglobulin M in lung lavage fluid and pulmonary wet/dry ratios were measured as markers of alveolar barrier dysfunction. RESULTS: Uric acid levels increased in ALI patients. In cardiac surgery patients, elevated levels correlated significantly with the pulmonary leakage index. Allopurinol or uricase treatment did not reduce ventilator-induced inflammation, IκB-α degradation, or up-regulation of NLRP3, Toll-like receptor 2, and Toll-like receptor 4 gene expression in mice. Alveolar barrier dysfunction was attenuated which was most pronounced in mice pre-treated with allopurinol: both treatment strategies reduced wet/dry ratio, allopurinol also lowered total protein and immunoglobulin M levels. CONCLUSIONS: Local uric acid levels increase in patients with ALI. In mice, allopurinol and uricase attenuate ventilator-induced alveolar barrier dysfunction.

Ventilator-induced lung injury is mediated by the NLRP3 inflammasome.

BACKGROUND: The innate immune response is important in ventilator-induced lung injury (VILI) but the exact pathways involved are not elucidated. The authors studied the role of the intracellular danger sensor NLRP3 inflammasome. METHODS: NLRP3 inflammasome gene expression was analyzed in respiratory epithelial cells and alveolar macrophages obtained from ventilated patients (n = 40). In addition, wild-type and NLRP3 inflammasome deficient mice were randomized to low tidal volume (approximately 7.5 ml/kg) and high tidal volume (approximately 15 ml/kg) ventilation. The presence of uric acid in lung lavage, activation of caspase-1, and NLRP3 inflammasome gene expression in lung tissue were investigated. Moreover, mice were pretreated with interleukin-1 receptor antagonist, glibenclamide, or vehicle before start of mechanical ventilation. VILI endpoints were relative lung weights, total protein in lavage fluid, neutrophil influx, and pulmonary and systemic cytokine and chemokine concentrations. Data represent mean ± SD. RESULTS: Mechanical ventilation up-regulated messenger RNA expression levels of NLRP3 in alveolar macrophages (1.0 ± 0 vs. 1.70 ± 1.65, P less than 0.05). In mice, mechanical ventilation increased both NLRP3 and apoptosis-associated speck-like protein messenger RNA levels, respectively (1.08 ± 0.55 vs. 3.98 ± 2.89; P less than 0.001 and 0.95 ± 0.53 vs. 6.0 ± 3.55; P less than 0.001), activated caspase-1, and increased uric acid levels (6.36 ± 1.85 vs. 41.9 ± 32.0, P less than 0.001). NLRP3 inflammasome deficient mice displayed less VILI due to high tidal volume mechanical ventilation compared with wild-type mice. Furthermore, treatment with interleukin-1 receptor antagonist or glibenclamide reduced VILI. CONCLUSIONS: Mechanical ventilation induced a NLRP3 inflammasome dependent pulmonary inflammatory response. NLRP3 inflammasome deficiency partially protected mice from VILI.

Mild hypothermia reduces ventilator-induced lung injury, irrespective of reducing respiratory rate.

In the era of lung-protective mechanical ventilation using limited tidal volumes, higher respiratory rates are applied to maintain adequate minute volume ventilation. However, higher respiratory rates may contribute to ventilator-induced lung injury (VILI). Induced hypothermia reduces carbon dioxide production and might allow for lower respiratory rates during mechanical ventilation. We hypothesized that hypothermia protects from VILI and investigated whether reducing respiratory rates enhance lung protection in an in vivo model of VILI. During 4 h of mechanical ventilation, VILI was induced by tidal volumes of 18 mL/kg in rats, with respiratory rates set at 15 or 10 breaths/min in combination with hypothermia (32°C) or normothermia (37°C). Hypothermia was induced by external cooling. A physiologic model was established. VILI was characterized by increased pulmonary neutrophil influx, protein leak, wet weights, histopathology score, and cytokine levels compared with lung protective mechanical ventilation. Hypothermia decreased neutrophil influx, pulmonary levels, systemic interleukin-6 levels, and histopathology score, and it tended to decrease the pulmonary protein leak. Reducing the respiratory rate in combination with hypothermia did not reduce the parameters of the lung injury. In conclusion, hypothermia protected from lung injury in a physiologic VILI model by reducing inflammation. Decreasing the respiratory rate mildly did not enhance protection.

Induced hypothermia is protective in a rat model of pneumococcal pneumonia associated with increased adenosine triphosphate availability and turnover*.

OBJECTIVE: To determine the effect of induced hypothermia on bacterial growth, lung injury, and mitochondrial function in a rat model of pneumococcal pneumosepsis. DESIGN: Animal study. SETTING: University research laboratory. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: Subjects were inoculated intratracheally with Streptococcus pneumoniae and controls received saline. After the development of pneumonia, mechanical ventilation was started with or without induced mild hypothermia (32 °C). Bacterial growth and inflammatory markers were determined in bronchoalveolar lavage fluid, blood, and organs. Oxidative phosphorylation and adenosine triphosphate contents were measured in mitochondria isolated from the liver and soleus muscle. MEASUREMENTS AND MAIN RESULTS: Inoculation with S. pneumoniae resulted in severe pneumonia with bacterial dissemination, distal organ injury, and blunted peripheral oxygen consumption on mechanical ventilation. Hypothermia did not affect bacterial growth in bronchoalveolar lavage fluid and in homogenized lungs compared with normothermic controls but was associated with reduced bacterial dissemination to the spleen with a trend toward reduced bacterial load in blood and liver. Hypothermia reduced lung injury, exemplified by reductions in pulmonary cell influx and bronchoalveolar lavage fluid protein levels compared with controls. Hypothermia reduced bronchoalveolar lavage fluid levels of interleukin-1ß, tended to reduce bronchoalveolar lavage fluid CINC-3 levels, but no effect was observed on bronchoalveolar lavage fluid tumor necrosis factor-α and interleukin-6 levels. Induced hypothermia restored the fall in oxygen consumption and adenosine triphosphate levels in the liver, whereas adenosine triphosphate/adenosine diphosphate ratios remained low. In muscle, induced hypothermia also reversed low oxygen consumption as a result of pneumonia, but with an increase in adenosine triphosphate levels, whereas adenosine triphosphate/adenosine diphosphate ratios were low. CONCLUSION: Hypothermia did not adversely affect bacterial growth, but rather reduced bacterial dissemination in a rat model of pneumococcal pneumosepsis. Furthermore, hypothermia reduced lung injury associated with restored adenosine triphosphate availability and turnover. These findings suggest that hypothermia may reduce organ injury by preventing sepsis-related mitochondrial dysfunction.

The effect of induced hypothermia on respiratory parameters in mechanically ventilated patients.

AIM: Mild hypothermia is increasingly applied in the intensive care unit. Knowledge on the effects of hypothermia on respiratory parameters during mechanical ventilation is limited. In this retrospective study, we describe the effect of hypothermia on gas exchange in patients cooled for 24 h after a cardiac arrest. METHODS: Respiratory parameters were derived from electronic patient files from 65 patients at the start and end of the hypothermic phase and at every centigrade increase in body temperature until normo-temperature, including tidal volume, positive end expiratory pressure (PEEP), plateau pressure, respiratory rate, exhaled CO(2) concentrations (etCO(2)) and FIO(2). Static compliance was calculated as V(T)/P(plateau)-PEEP. Dead space ventilation was calculated as (PaCO(2)-etCO(2))/PaCO(2). RESULTS: During hypothermia, PaCO(2) decreased, at unchanged PaCO(2)-etCO(2) gap and minute ventilation. During rewarming, PaCO(2) did not change, while etCO(2) increased at unchanged minute ventilation. Dead space ventilation did not change during hypothermia, but lowered during rewarming. During hypothermia, PaO(2)/FIO(2) ratio increased at unchanged PEEP levels. Respiratory static compliance did not change during hypothermia, nor during rewarming. CONCLUSION: Hypothermia possibly improves oxygenation and ventilation in mechanically ventilated patients. Results may accord with the hypothesis that reducing metabolism with applied hypothermia may be beneficial in patients with acute lung injury, in whom low minute ventilation results in severe hypercapnia.

Suspended animation inducer hydrogen sulfide is protective in an in vivo model of ventilator-induced lung injury.

PURPOSE: Acute lung injury is characterized by an exaggerated inflammatory response and a high metabolic demand. Mechanical ventilation can contribute to lung injury, resulting in ventilator-induced lung injury (VILI). A suspended-animation-like state induced by hydrogen sulfide (H2S) protects against hypoxia-induced organ injury. We hypothesized that suspended animation is protective in VILI by reducing metabolism and thereby CO2 production, allowing for a lower respiratory rate while maintaining adequate gas exchange. Alternatively, H2S may reduce inflammation in VILI. METHODS: In mechanically ventilated rats, VILI was created by application of 25 cmH2O positive inspiratory pressure (PIP) and zero positive end-expiratory pressure (PEEP). Controls were lung-protective mechanically ventilated (13 cmH2O PIP, 5 cmH2O PEEP). H(2)S donor NaHS was infused continuously; controls received saline. In separate control groups, hypothermia was induced to reproduce the H2S-induced fall in temperature. In VILI groups, respiratory rate was adjusted to maintain normo-pH. RESULTS: NaHS dose-dependently and reversibly reduced body temperature, heart rate, and exhaled amount of CO2. In VILI, NaHS reduced markers of pulmonary inflammation and improved oxygenation, an effect which was not observed after induction of deep hypothermia that paralleled the NaHS-induced fall in temperature. Both NaHS and hypothermia allowed for lower respiratory rates while maintaining gas exchange. CONCLUSIONS: NaHS reversibly induced a hypometabolic state in anesthetized rats and protected from VILI by reducing pulmonary inflammation, an effect that was in part independent of body temperature.

Potential applications of hydrogen sulfide-induced suspended animation.

A suspended animation-like state has been induced in rodents with the use of hydrogen sulfide, resulting in hypothermia with a concomitant reduction in metabolic rate. Also oxygen demand was reduced, thereby protecting against hypoxia. Several therapeutic applications of induction of a hibernation-like state have been suggested, including ischemia-reperfusion injury. More recently, hydrogen sulfide has been found to be protective in states of exaggerated inflammatory responses, such as acute lung injury. Possible mechanisms of this protective effect may include reduction of metabolism, as well as reduction of inflammation. In this manuscript, the methods of inducing a suspended animation-like state in experimental models using hydrogen sulfide are described. We discuss the effects of hydrogen sulfide-induced hypo-metabolism on hemodynamic, metabolic and inflammatory changes in animal models of various hypoxic and inflammatory diseases. In addition, potential therapeutic possibilities of hydrogen sulfide-induced hibernation are outlined.

Medical-grade honey kills antibiotic-resistant bacteria in vitro and eradicates skin colonization.

BACKGROUND: Antibiotic resistance among microbes urgently necessitates the development of novel antimicrobial agents. Since ancient times, honey has been used successfully for treatment of infected wounds, because of its antibacterial activity. However, large variations in the in vitro antibacterial activity of various honeys have been reported and hamper its acceptance in modern medicine. METHODS: We assessed the in vitro bactericidal activity of Revamil (Bfactory), a medical-grade honey produced under controlled conditions, and assessed its efficacy for reduction of forearm skin colonization in healthy volunteers in a within-subject-controlled trial. RESULTS: With Bacillus subtilis as a test strain, we demonstrated that the variation in bactericidal activity of 11 batches of medical-grade honey was <2-fold. Antibiotic-susceptible and -resistant isolates of Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, Enterobacter cloacae, and Klebsiella oxytoca were killed within 24 h by 10%-40% (vol/vol) honey. After 2 days of application of honey, the extent of forearm skin colonization in healthy volunteers was reduced 100-fold (P < .001), and the numbers of positive skin cultures were reduced by 76% (P < .001). CONCLUSIONS: Revamil is a promising topical antimicrobial agent for prevention or treatment of infections, including those caused by multidrug-resistant bacteria.