Effect of peritonitis on mitochondrial respiration

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.

Cytopathic hypoxia. Mitochondrial dysfunction as mechanism contributing to organ dysfunction in sepsis

Several lines of evidence support the notion that cellular energetics are deranged in sepsis, not on the basis of inadequate tissue perfusion, but rather on the basis of impaired mitochondrial respiration and/or coupling; that is, organ dysfunction in sepsis may occur on the basis of cytopathic hypoxia. If this concept is correct, then the therapeutic implications are enormous. Efforts to improve outcome in patients with sepsis by monitoring and manipulating cardiac output, systemic Do2, and regional blood flow are doomed to failure. Instead, the focus should be on developing pharmacologic strategies to restore normal mitochondrial function and cellular energetics.

Oxidative metabolism in sepsis and sepsis syndrome

The high mortality associated with sepsis syndrome and multiple organ dysfunction syndrome has persisted despite extraordinary research efforts in the laboratory and the intensive care unit. These syndromes produce systemic tissue damage that is likely to result from widespread inflammation and subsequent endothelial injury. This article reviews the oxidative metabolic effects and responses to sepsis syndrome at several levels: the oxygen transport system, the cell, and the mitochondrion. Specifically, aerobic metabolism of carbon substrates and oxygen is altered in sepsis. As a result of systemic inflammation and nonmetabolic oxygen use, oxidative stress may occur both outside and inside the cell. The consequences of these oxidative processes during sepsis may be ongoing cell damage mediated by reactive oxygen and nitrogen oxide species that culminates in multisystem organ failure.

Rat liver peroxisomal and mitochondrial fatty acid oxidation in sepsis

Time course changes in hepatic mitochondrial and peroxisomal fatty acid oxidative capacities, as well as changes in the related enzyme activities, were investigated in rats with sepsis induced by cecal ligation and puncture. Palmitoyl-L-carnitine oxidation was not altered, but carnitine palmitoyl-transferase (CPT) dependent palmitoyl-CoA (plus L-carnitine) oxidation was slightly increased in the liver mitochondria of the septic rats. Hepatic CPT activity, being the rate-limiting step of mitochondrial beta-oxidation, was also enhanced by sepsis. In contrast, cyanide-insensitive peroxisomal beta-oxidation and the carnitine acetyltransferase and catalase activities associated with the peroxisomal-enriched fraction were markedly reduced by abdominal sepsis. Cyanide-insensitive beta-oxidation in control livers showed optimal specificity for lauroyl- and myristoyl-CoA and this pattern remained unchanged by sepsis. However, oxidation rates were reduced for all acyl-CoA esters tested, being more pronounced with longer carbon chain length acyl-CoA substrates. These results indicate that in early sepsis, hepatic mitochondrial fatty acid oxidative capacity was increased, probably due to enhanced CPT activity, whereas peroxisomal beta-oxidation was seriously disturbed along with reduced catalase activity.

Multiple Organ Failure Syndrome—Part I: Epidemiology, Prognosis, and Pathophysiology

The multiple organ failure syndrome (MOFS) is the leading cause of death in intensive care units. Although sepsis is an important cause of MOFS, it is clear that MOFS can occur in the absence of infection. The pathophysiology of MOFS is complex and multifactorial and includes derangements in oxygen delivery and consumption, the release of inflammatory and vasoactive mediators capable of inflicting tissue damage, and alterations in the barrier function of the intestinal mucosa. Although advances have been made in our understanding of MOFS, treatment remains nonspecific and largely supportive. Early and aggressive restoration of tissue perfusion, adequate treatment of infection, timely nutritional support, and support of individual failed organs remain the mainstay of therapy. Therapeutic agents directed against the various mediators associated with the pathophysiology of MOFS may prove useful in the future.

An in vivo examination of rat brain during sepsis with 31P-NMR spectroscopy

Neurological symptoms including lethargy, obtundation, and confusion are early and common findings in patients with sepsis. The etiology of the mental status changes that occur during severe infection is not known. We investigated the effects of sepsis on the levels of high-energy phosphates to determine whether decreased energy metabolism was a factor in the depressed neurological state. The time course of changes in brain pH and brain high-energy phosphate metabolites during an Escherichia coli infusion was determined from sequential phosphorus-31 nuclear magnetic resonance (31P-NMR) spectra of ketamine-xylazine-anesthetized rats. A second group of rats received 0.9% saline infusion and served as a control group. Despite severe obtundation and near loss of righting reflex, the rats in the septic group had no significant differences in the brain pH, the ratio of phosphocreatine (PCr) to beta-adenosine 5'-triphosphate (beta-ATP), or in the ratio of PCr to Pi. The only significant decrease in brain high-energy phosphates or pH occurred terminally in the septic rat group and corresponded with a rapidly falling arterial blood pressure. We conclude that the severe neurological depression that is characteristic of sepsis is not due to decreased levels of brain high-energy phosphates or brain acidosis.

Alterations in metabolite levels in carbohydrate and energy metabolism of rat in hemorrhagic shock and sepsis

For comparison of the extent of metabolite content alteration caused by etiologically different types of shock, septic peritonitis and hemorrhagic shock (mean arterial blood pressure at 40 mm Hg for 1 h or 2 h) were produced in rats. Contents of metabolites were determined in the liver and the muscle. Characteristic differences were found in the alteration modes of hepatic lactate level, muscle adenine nucleotide concentrations, and muscle protein content between these shock models. Rapid and significant alterations were observed in the levels of adenine nucleotides, glucose-6-phosphate and lactate in the liver in both types of shock. Hepatic energy charge and contents of glycogen and protein also significantly decreased. On the other hand, noticeable changes in the muscles were elevation of lactate level and the decrease of phosphocreatine and protein concentrations. Another distinct change was the decrease of total adenine nucleotide content in the muscle of septic rats, whereas it remained unchanged in the muscle of hemorrhagic shock rats. Thus, the changes of metabolite levels did not occur simultaneously in different tissues, and their rate and magnitude varied between different types of shock. The difference in adaptive response of metabolism may result in pathophysiologic diversity in shock.

Alterations of hepatic mitochondrial function in a model of peritonitis in immature rats

Severe intra-abdominal infection results in significant metabolic dysfunction, multiple systems failure, and mortality. Although the course of peritonitis is particularly rapid and severe in neonates and small children, its physiologic consequences have been poorly studied in these age groups. In order to assess hepatic mitochondrial integrity in a model of fulminant peritonitis in immature animals, the following study was undertaken. Thirty-three immature Sprague-Dawley rats (21 to 28 days of age) and 32 mature rats (weight greater than 250 g) were anesthetized and laparotomies performed. The animals received either cecal ligation and gross perforation (CLP) or cecal manipulation alone (sham). Animals were killed at 2 and 4 hours and livers removed. Mitochondria were isolated by differential centrifugation. Mitochondrial respirations were studied polarographically with glutamate and succinate as substrates in the presence (state 3) and absence (state 4) of adenosine diphosphate (ADP). The Respiratory Control Index (RCI) is the ratio of state 3 to state 4 respiration and is a sensitive indicator of mitochondrial coupling. Results revealed that in mature animals, peritonitis produced a significant increase in RCI with glutamate as substrate (5.2 +/- 0.2) by 4 hours duration as compared with sham operated rats (4.3 +/- 0.1, P less than 0.01). Succinate as substrate revealed no significant alteration in mitochondrial coupling in mature rat hepatic mitochondria in animals subjected to peritonitis. By contrast, peritonitis in immature animals produced a significantly decreased RCI (3.6 +/- 0.2) with glutamate as substrate as compared with sham operated animals (4.8 +/- 0.2, P less than 0.01) by two hours duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitochondrial death in sepsis: a failed concept

The concept of early selective mitochondrial injury has been proposed to explain the global metabolic dysfunction observed in the septic state. A two phase study was undertaken to test the validity of this hypothesis. In the initial phase, an endotoxin shock model was employed in the rat to delineate the function of skeletal muscle mitochondria. Mitochondrial function was determined polarimetrically, comparing state three and state four rates, respiratory control index (RCI) and ADP:O ratios. No significant alteration in these parameters was observed in the endotoxic state. Phase II of the study was designed to investigate mitochondrial function in a bacterial peritonitis rat model. Both liver and skeletal muscle mitochondrial function were determined to control for possible alterations in liver metabolism. Neither muscle nor liver mitochondria exhibited functional impairment during sepsis. We conclude from this study that neither endotoxemia nor peritonitis selectively "kills" mitochondria as previously suggested.

Alterations of mitochondrial metabolism and protein concentrations in subacute septicemia

Male Sprague-Dawley rats were made septic by cecal ligation for a period of 6 days. Sham-operated rats were used as control animals. Septic rats developed gram-negative bacteremia within 18 to 24 h. Blood cultures were positive for Escherichia coli, Proteus spp., and Klebsiella spp. in all cases. Significant loss of body weight was observed in septic rats during the 6-day period, whereas control rats exhibited a steady gain in body weight after the second postoperative day. Liver and muscle mitochondria were isolated and analyzed 6 days after the operation in control and septic rats. Liver mitochondrial cytochrome a(a3), b, and c concentrations were normal in septic rats. Oxygen utilization rates in state 3 (during ATP synthesis) were also within the normal range. State 4 respiratory rates, however, were increased with glutamate and pyruvate as substrates, resulting in low respiratory control ratios in septic rats. Muscle mitochondria from septic rats exhibited several abnormalities: the yield of cytochromes b, c, and a(a3) per gram of tissue was 34% below normal in septic rats. ATP synthesis rates declined significantly with pyruvate as substrate. Respiratory control ratios were below normal with all substrates studied except glutamate. These data are in agreement with previous reports on loss of muscle proteins and abnormalities in energy fuel utilization in septic patients.

Intraperitoneal oxygen and carbon dioxide tensions in experimental adhesion disease and peritonitis

Intraperitoneal oxygen and carbon dioxide tensions were studied in rats during silica-induced adhesion formation or fecal peritonitis. Measurements of PO2 and PCO2 in the abdominal cavity were performed by means of an implanted Silastic tonometer. During active adhesion formation one to three weeks after administration of silica, the intra-abdominal PO2 decreased by 50 per cent from normal whereas the intra-abdominal PCO2 and the rate of oxygen consumption in the peritoneum were elevated. Progressing peritonitis also resulted in decreased intraperitoneal PO2 and increased accumulation of carbon dioxide in the peritoneal cavity. In rats with peritonitis the rate of oxygen consumption in the peritoneal exudate clearly exceeded that in the peritoneal membrane.