Skeletal muscle dysfunction is associated with derangements in mitochondrial bioenergetics (but not UCP3) in a rodent model of sepsis.

Muscle dysfunction is a common feature of severe sepsis and multiorgan failure. Recent evidence implicates bioenergetic dysfunction and oxidative damage as important underlying pathophysiological mechanisms. Increased abundance of uncoupling protein-3 (UCP3) in sepsis suggests increased mitochondrial proton leak, which may reduce mitochondrial coupling efficiency but limit reactive oxygen species (ROS) production. Using a murine model, we examined metabolic, cardiovascular, and skeletal muscle contractile changes following induction of peritoneal sepsis in wild-type and Ucp3(-/-) mice. Mitochondrial membrane potential (Δψm) was measured using two-photon microscopy in living diaphragm, and contractile function was measured in diaphragm muscle strips. The kinetic relationship between membrane potential and oxygen consumption was determined using a modular kinetic approach in isolated mitochondria. Sepsis was associated with significant whole body metabolic suppression, hypothermia, and cardiovascular dysfunction. Maximal force generation was reduced and fatigue accelerated in ex vivo diaphragm muscle strips from septic mice. Δψm was lower in the isolated diaphragm from septic mice despite normal substrate oxidation kinetics and proton leak in skeletal muscle mitochondria. Even though wild-type mice exhibited an absolute 26 ± 6% higher UCP3 protein abundance at 24 h, no differences were seen in whole animal or diaphragm physiology, nor in survival rates, between wild-type and Ucp3(-/-) mice. In conclusion, this murine sepsis model shows a hypometabolic phenotype with evidence of significant cardiovascular and muscle dysfunction. This was associated with lower Δψm and alterations in mitochondrial ATP turnover and the phosphorylation pathway. However, UCP3 does not play an important functional role, despite its upregulation.

The metabolic phenotype of rodent sepsis: cause for concern?

PURPOSE: Rodent models of sepsis are frequently used to investigate pathophysiological mechanisms and to evaluate putative therapeutic strategies. However, preclinical efficacy in these models has failed to translate to the clinical setting. We thus questioned the representativeness of such models and herein report a detailed comparison of the metabolic and cardiovascular phenotypes of long-term faecal peritonitis in fluid-resuscitated rats and mice with similar mortality profiles. METHODS: We conducted prospective laboratory-controlled studies in adult male Wistar rats and C57 black mice. Animals were made septic by intraperitoneal injection of faecal slurry. Rats received continuous intravenous fluid resuscitation, whereas mice received intermittent fluid boluses subcutaneously. Sham-treated animals served as controls. Survival was assessed over 72 h. In separate studies, whole body metabolism (O2 consumption, CO2 production) was measured over 24 h with echocardiography performed at early (6 h) and established (24 h) phases of sepsis. Blood gas analysis was performed at 6 h (rats) and 24 h (rats, mice). RESULTS: Similar survival curves were seen in both rodent models with approximately 75% mortality at 72 h. In mice, sepsis caused severity-dependent falls in core temperature and global metabolism. Oxygen consumption in severely septic mice fell by 38% within 2 h, and 80% at 22 h compared with baseline values. This was only partially restored by external warming. By contrast, septic rats maintained core temperature; only severely affected animals showed a pre-mortem decline in oxygen consumption. Significant myocardial dysfunction was seen in mice during early and established sepsis, whereas peak velocity and other hemodynamic variables in rats were similar at 6 h and significantly worse by 24 h in severely septic animals only. CONCLUSIONS: Markedly differing metabolic and cardiovascular profiles were seen in long-term fluid-resuscitated rat and mouse models of bacterial sepsis despite similar mortality. The mouse model, in particular, does not represent the human condition. We urge caution in applying findings in murine models to septic patients, both with regard to our understanding of pathophysiology and the failure to translate preclinical efficacy into successful clinical trials.

The tracheal tube: gateway to ventilator-associated pneumonia.

Ventilator-associated pneumonia (VAP) is a major healthcare-associated complication with considerable attributable morbidity, mortality and cost. Inherent design flaws in the standard high-volume low-pressure cuffed tracheal tubes form a major part of the pathogenic mechanism causing VAP. The formation of folds in the inflated cuff leads to microaspiration of pooled oropharyngeal secretions into the trachea, and biofilm formation on the inner surface of the tracheal tube helps to maintain bacterial colonization of the lower airways. Improved design of tracheal tubes with new cuff material and shape have reduced the size and number of these folds, which together with the addition of suction ports above the cuff to drain pooled subglottic secretions leads to reduced aspiration of oropharyngeal secretions. Furthermore, coating tracheal tubes with antibacterial agents reduces biofilm formation and the incidence of VAP. In this Viewpoint article we explore the published data supporting the new tracheal tubes and their potential contribution to VAP prevention strategies. We also propose that it may now be against good medical practice to continue to use a 'standard cuffed tube' given what is already known, and the weight of evidence supporting the use of newer tube designs.

In vivo killing of Staphylococcus aureus using a light-activated antimicrobial agent.

BACKGROUND: The widespread problem of antibiotic resistance in pathogens such as Staphylococcus aureus has prompted the search for new antimicrobial approaches. In this study we report for the first time the use of a light-activated antimicrobial agent, methylene blue, to kill an epidemic methicillin-resistant Staphylococcus aureus (EMRSA-16) strain in two mouse wound models. RESULTS: Following irradiation of wounds with 360 J/cm(2) of laser light (670 nm) in the presence of 100 microg/ml of methylene blue, a 25-fold reduction in the number of viable EMRSA was seen. This was independent of the increase in temperature of the wounds associated with the treatment. Histological examination of the wounds revealed no difference between the photodynamic therapy (PDT)-treated wounds and the untreated wounds, all of which showed the same degree of inflammatory infiltration at 24 hours. CONCLUSION: The results of this study demonstrate that PDT is effective at reducing the total number of viable EMRSA in a wound. This approach has promise as a means of treating wound infections caused by antibiotic-resistant microbes as well as for the elimination of such organisms from carriage sites.