[Show abstract][Hide abstract] ABSTRACT: Background:
In clinical practice, global oxygen delivery (DO2) is often considered as a whole; however pathological and adaptive responses after a decrease in individual constituents of the DO2 equation (cardiac output, haemoglobin, oxyhaemoglobin saturation) are likely to be diverse. We hypothesized that an equivalent decrease in DO2 after reductions in each separate component of the equation would result in different haemodynamic, tissue oxygenation, and stress hormonal responses.
Anaesthetized, fluid-resuscitated male Wistar rats were subjected to circulatory, anaemic, or hypoxic hypoxia (by haemorrhage, isovolaemic haemodilution, and breathing a hypoxic gas mix, respectively), produced either rapidly over 5 min or graded over 30 min, to a targeted 50% decrease in global oxygen delivery. Sham-operated animals acted as controls. Measurements were made of haemodynamics, skeletal muscle tissue oxygen tension, blood gas analysis, and circulating stress hormone levels.
Whereas haemorrhage generated the largest decrease in cardiac output, and the greatest stress hormone response, haemodilution had the most marked effect on arterial pressure. In contrast, rapid hypoxaemia produced a minor impact on global haemodynamics yet induced the greatest decrease in regional oxygenation. A greater degree of hyperlactataemia was observed with graded insults compared with those administered rapidly.
Decreasing global oxygen delivery, achieved by targeted reductions in its separate components, induces varying circulatory, tissue oxygen tension, and stress hormone responses. We conclude that not all oxygen delivery is the same; this disparity should be emphasized in classical teaching and re-evaluated in patient management.
BJA British Journal of Anaesthesia 05/2014; 113(4). DOI:10.1093/bja/aeu089 · 4.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background:
Hepatic dysfunction and jaundice are traditionally viewed as late features of sepsis and portend poor outcomes. We hypothesized that changes in liver function occur early in the onset of sepsis, yet pass undetected by standard laboratory tests.
Methods and findings:
In a long-term rat model of faecal peritonitis, biotransformation and hepatobiliary transport were impaired, depending on subsequent disease severity, as early as 6 h after peritoneal contamination. Phosphatidylinositol-3-kinase (PI3K) signalling was simultaneously induced at this time point. At 15 h there was hepatocellular accumulation of bilirubin, bile acids, and xenobiotics, with disturbed bile acid conjugation and drug metabolism. Cholestasis was preceded by disruption of the bile acid and organic anion transport machinery at the canalicular pole. Inhibitors of PI3K partially prevented cytokine-induced loss of villi in cultured HepG2 cells. Notably, mice lacking the PI3Kγ gene were protected against cholestasis and impaired bile acid conjugation. This was partially confirmed by an increase in plasma bile acids (e.g., chenodeoxycholic acid [CDCA] and taurodeoxycholic acid [TDCA]) observed in 48 patients on the day severe sepsis was diagnosed; unlike bilirubin (area under the receiver-operating curve: 0.59), these bile acids predicted 28-d mortality with high sensitivity and specificity (area under the receiver-operating curve: CDCA: 0.77; TDCA: 0.72; CDCA+TDCA: 0.87).
Liver dysfunction is an early and commonplace event in the rat model of sepsis studied here; PI3K signalling seems to play a crucial role. All aspects of hepatic biotransformation are affected, with severity relating to subsequent prognosis. Detected changes significantly precede conventional markers and are reflected by early alterations in plasma bile acids. These observations carry important implications for the diagnosis of liver dysfunction and pharmacotherapy in the critically ill. Further clinical work is necessary to extend these concepts into clinical practice. Please see later in the article for the Editors' Summary.
PLoS Medicine 11/2012; 9(11):e1001338. DOI:10.1371/journal.pmed.1001338 · 14.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Myocardial function is depressed in sepsis and is an important prognosticator in the human condition. Using echocardiography in a long-term, fluid-resuscitated Wistar rat model of fecal peritonitis we investigated whether depressed myocardial function could be detected at an early stage of sepsis and, if so, whether the degree of depression could predict eventual outcome. At 6 hours' post-insult, a stroke volume <0.17ml prognosticated 3-day mortality with positive and negative predictive values of 93% and 80%, respectively. Subsequent fluid loading studies demonstrated intrinsic myocardial depression with poor prognosis animals tolerating less fluid than either good prognosis or sham-operated animals. Cardiac gene expression analysis at 6 hours detected 527 transcripts significantly up- or down-regulated by the septic process, including genes related to inflammatory and cell cycle pathways. Predicted mortality was associated with significant differences in transcripts of genes expressing proteins related to the TLR-2/MyD88 and JAK-STAT inflammatory pathways, b-adrenergic signaling and intracellular calcium cycling. Our findings highlight the presence of myocardial depression in early sepsis and its prognostic significance. Transcriptomic analysis in heart tissue identified changes in signaling pathways that correlated with clinical dysfunction. These pathways merit further study to both better understand and potentially modify the disease process.
[Show abstract][Hide abstract] ABSTRACT: Hydrogen peroxide (H(2)O(2)) is central to mitochondrial oxidative damage and redox signaling, but its roles are poorly understood due to the difficulty of measuring mitochondrial H(2)O(2) in vivo. Here we report a ratiometric mass spectrometry probe approach to assess mitochondrial matrix H(2)O(2) levels in vivo. The probe, MitoB, comprises a triphenylphosphonium (TPP) cation driving its accumulation within mitochondria, conjugated to an arylboronic acid that reacts with H(2)O(2) to form a phenol, MitoP. Quantifying the MitoP/MitoB ratio by liquid chromatography-tandem mass spectrometry enabled measurement of a weighted average of mitochondrial H(2)O(2) that predominantly reports on thoracic muscle mitochondria within living flies. There was an increase in mitochondrial H(2)O(2) with age in flies, which was not coordinately altered by interventions that modulated life span. Our findings provide approaches to investigate mitochondrial ROS in vivo and suggest that while an increase in overall mitochondrial H(2)O(2) correlates with aging, it may not be causative.
[Show abstract][Hide abstract] ABSTRACT: Plant alternative oxidase (AOX) activity in isolated mitochondria is regulated by carboxylic acids, but reaction and regulatory mechanisms remain unclear. We show that activity of AOX protein purified from thermogenic Arum maculatum spadices is sensitive to pyruvate and glyoxylate but not succinate. Rapid, irreversible AOX inactivation occurs in the absence of pyruvate, whether or not duroquinol oxidation has been initiated, and is insensitive to duroquinone. Our data indicate that pyruvate stabilises an active conformation of AOX, increasing the population of active protein in a manner independent of reducing substrate and product, and are thus consistent with an exclusive effect of pyruvate on the enzyme's apparent V(max).
[Show abstract][Hide abstract] ABSTRACT: We previously reported outcome-associated decreases in muscle energetic status and mitochondrial dysfunction in septic patients with multiorgan failure. We postulate that survivors have a greater ability to maintain or recover normal mitochondrial functionality.
To determine whether mitochondrial biogenesis, the process promoting mitochondrial capacity, is affected in critically ill patients.
Muscle biopsies were taken from 16 critically ill patients recently admitted to intensive care (average 1-2 d) and from 10 healthy, age-matched patients undergoing elective hip surgery.
Survival, mitochondrial morphology, mitochondrial protein content and enzyme activity, mitochondrial biogenesis factor mRNA, microarray analysis, and phosphorylated (energy) metabolites were determined. Ten of 16 critically ill patients survived intensive care. Mitochondrial size increased with worsening outcome, suggestive of swelling. Respiratory protein subunits and transcripts were depleted in critically ill patients and to a greater extent in nonsurvivors. The mRNA content of peroxisome proliferator-activated receptor γ coactivator 1-α (transcriptional coactivator of mitochondrial biogenesis) was only elevated in survivors, as was the mitochondrial oxidative stress protein manganese superoxide dismutase. Eventual survivors demonstrated elevated muscle ATP and a decreased phosphocreatine/ATP ratio.
Eventual survivors responded early to critical illness with mitochondrial biogenesis and antioxidant defense responses. These responses may partially counteract mitochondrial protein depletion, helping to maintain functionality and energetic status. Impaired responses, as suggested in nonsurvivors, could increase susceptibility to mitochondrial damage and cellular energetic failure or impede the ability to recover normal function. Clinical trial registered with clinical trials.gov (NCT00187824).
American Journal of Respiratory and Critical Care Medicine 09/2010; 182(6):745-51. DOI:10.1164/rccm.201003-0326OC · 13.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sepsis is a complex pathophysiological disorder arising from a systemic inflammatory response to infection. Patients are clinically classified according to the presence of signs of inflammation alone, multiple organ failure (MOF), or organ failure plus hypotension (septic shock). The organ damage that occurs in MOF is not a direct effect of the pathogen itself, but rather of the dysregulated inflammatory response of the patient. Although mechanisms underlying MOF are not completely understood, a disruption in cellular energetic metabolism is increasingly implicated. In this review, we describe how various factors affecting cellular ATP supply and demand appear to be altered in sepsis, and how these vary through the timecourse. We will emphasise the need for an integrated systems approach to determine the relative importance of these factors in both the failure and recovery of different organs. A modular framework is proposed that can be used to assess the control hierarchy of cellular energetics in this complex pathophysiological condition.
[Show abstract][Hide abstract] ABSTRACT: The alternative oxidase is a respiratory chain protein found in plants, fungi and some parasites that still remains physically uncharacterised. In this report we present EPR evidence from parallel mode experiments which reveal signals at approximately g=16 in both purified alternative oxidase protein (g=16.9), isolated mitochondrial membranes (g=16.1), and in trypanosomal AOX expressed in Escherichia coli membranes (g=16.4). Such signals are indicative of a dicarboxylate diiron centre at the active site of the enzyme. To our knowledge these data represent the first EPR signals from AOX present in its native environment.
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial dysfunction, particularly affecting complex I of the respiratory chain, could play a fundamental role in the development of multiple organ failure during sepsis. Increasing electron flow through complex II by addition of succinate may improve mitochondrial oxygen utilization and thus adenosine triphosphate production.
Ex vivo animal study.
University research laboratory.
Male adult Wistar rats.
Fecal peritonitis was induced in conscious, fluid-resuscitated, hemodynamically-monitored rats. Sham-operation and naïve animals acted as controls. At 48 hrs, clinical severity was graded. Soleus muscle was taken for measurement of mitochondrial complex activities and oxygen consumption. The effect of glutamate plus malate (complex I substrates) and succinate (complex II substrate) on mitochondrial respiration was assessed.
In the presence of glutamate plus malate, mitochondrial oxygen consumption was abnormally low in skeletal muscle tissue from moderately-to-severely septic animals as compared with naïve and sham-operation controls (both p < .01). On addition of succinate, mitochondrial respiration was augmented in all groups, particularly in moderately-to-severely septic animals (39% +/- 6% increase) as compared with naïve (11% +/- 5%; p < .01) and sham-operation controls (10% +/- 5%; p < .01). In the presence of succinate, mitochondrial oxygen consumption was similar between the groups.
Succinate increases mitochondrial oxygen consumption in ex vivo skeletal muscle taken from septic animals, bypassing the predominant inhibition occurring at complex I. This warrants further exploration in vivo as a putative therapeutic modality.
Critical Care Medicine 10/2007; 35(9):2150-5. DOI:10.1097/01.ccm.0000281448.00095.4d · 6.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Over the last ten years or so, a role of NO in sepsis and MOF has been established. A number of studies have been performed
in animals and in patients in which the generation of NO in sepsis has been pharmacologically manipulated. While improvements
in hemodynamics have generally been reported, to date none of these investigations has clearly demonstrated improved organ
function or outcomes in human sepsis.
It is becoming increasingly clear that NO mediates both cytoprotective and cytopathic roles in sepsis. However, much remains
to be elucidated in terms of how NO mediates these effects and also whether the consequences of NO are causative or reactive
to organ dysfunction. Future therapies, better targeted towards selectively inhibiting iNOS, will no doubt help to clarify
this question. In addition, it is possible that targeting downstream effects of NO, such as mitochondrial dysfunction or promoting
mitochondrial biogenesis, may emerge as possible approaches to the management of this complex and widespread condition.
[Show abstract][Hide abstract] ABSTRACT: Activity of the plant mitochondrial alternative oxidase (AOX) can be regulated by organic acids, notably pyruvate. To date, only two well-conserved cysteine residues have been implicated in this process. We report the functional expression of two AOX isozymes (Sauromatum guttatum Sg-AOX and Arabidopsis thaliana At-AOX1a) in Schizosaccharomyces pombe. Comparison of the response of these two isozymes to pyruvate in isolated yeast mitochondria and disrupted mitochondrial membranes reveals that in contrast to At-AOX1a, Sg-AOX activity is insensitive to pyruvate and appears to be in a constitutively active state. As both of these isozymes conserve the two cysteines, we propose that such contrasting behaviour must be a direct result of differences in their amino acid sequence and have subsequently identified novel candidate residues.