Mitochondrial function in shock

Melatonin: an ancient molecule that makes oxygen metabolically tolerable

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, anti-inflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5-3.2 billion years ago, was as an antioxidant. The evolution of melatonin as an antioxidant by this organism was necessary as photosynthesis is associated with the generation of toxic-free radicals. The other secondary functions of melatonin came about much later in evolution. We also surmise that mitochondria and chloroplasts may be primary sites of melatonin synthesis in all eukaryotic cells that possess these organelles. This prediction is made on the basis that mitochondria and chloroplasts of eukaryotes developed from purple nonsulfur bacteria (which also produce melatonin) and cyanobacteria when they were engulfed by early eukaryotes. Thus, we speculate that the melatonin-synthesizing actions of the engulfed bacteria were retained when these organelles became mitochondria and chloroplasts, respectively. That mitochondria are likely sites of melatonin formation is supported by the observation that this organelle contains high levels of melatonin that are not impacted by blood melatonin concentrations. Melatonin has a remarkable array of means by which it thwarts oxidative damage. It, as well as its metabolites, is differentially effective in scavenging a variety of reactive oxygen and reactive nitrogen species. Moreover, melatonin and its metabolites modulate a large number of antioxidative and pro-oxidative enzymes, leading to a reduction in oxidative damage. The actions of melatonin on radical metabolizing/producing enzymes may be mediated by the Keap1-Nrf2-ARE pathway. Beyond its direct free radical scavenging and indirect antioxidant effects, melatonin has a variety of physiological and metabolic advantages that may enhance its ability to limit oxidative stress.

The contribution of the immune system to parturition

The immune system plays a central role before and during parturition, including the main physiological processes of parturition: uterine contractions and cervical ripening. The immune system comprises white blood cells and their secretions. Polymorphonuclear cells and macrophages invade the cervical tissue and release compounds, such as oxygen radicals and enzymes, which break down the cervical matrix to allow softening and dilatation. During this inflammatory process, white blood cells undergo chemotaxis, adherence to endothelial cells, diapedesis, migration and activation. Factors that regulate white blood cell invasion and secretion include cytokines such as tumour necrosis factor and interleukins. Glucocorticoids, sex hormones and prostaglandins, affect cytokine synthesis. They also modulate the target cells, resulting in altered responses to cytokines. On the other hand, the immune system has profound effects on the hormonal system and prostaglandin synthesis. In animals, nitric oxide has marked effects on uterine quiescence during gestation. At the same time, it plays an important role in regulating the vascular tone of uterine arteries and has anti-adhesive effects on leukocytes. Cytokines are found in amniotic fluid, and in maternal and foetal serum at term and preterm. Several intrauterine cells have been shown to produce these cytoldnes. Since neither white blood cells, cytokines nor nitric oxide seem to be the ultimate intermediate for human parturition, the immune system is an additional but obligatory and underestimated component in the physiology of delivery. Scientists, obstetricians and anaesthesiologists must thus be aware of these processes.

Effects of dichloroacetate and ubiquinone infusions on glycolysis activity and thermal sensitivity during sepsis

Energy-metabolism disturbances during sepsis are characterized by enhanced glycolytic fluxes and reduced mitochondrial respiration. However, it is not known whether these abnormalities are the result of a specific mitochondrial alteration, decreased pyruvate dehydrogenase (PDH) complex activity, depletion of ubiquinone (CoQ(10); electron donor for the mitochondrial complex III), or all 3. In this study we sought to specify metabolism disturbances in a murine model of sepsis, using either a PDH-activator infusion (dichloroacetate, DCA) or CoQ(10) supplementation. After anesthesia, Sprague-Dawley rats received intravenous saline solution (control; n = 5), DCA (n = 5; 20 mg/100 g), or CoQ(10) (n = 5; 1 mg/100 g), before the induction of sepsis. Increased plasma lactate levels and increased muscle glucose content were observed after 4 hours in the control group. In the DCA group, a decrease in the muscle content of lactate (P <.05) and an increase in muscle glucose content (P <.05) were observed at 4 hours, but no lactatemia variation was noted. In the CoQ(10) group, only increased plasma lactate levels were observed. Increased muscle glycolysis fluxes were observed after 4 hours in the control group, but to a slighter degree in both the DCA and CoQ(10) groups. Only DCA restored a normal temperature sensitivity in the hyperthermia range, but we noted no differences in survival time. In conclusion, only DCA infusion restores normal glycolysis function.

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.

Cerebral circulation and metabolism in patients with septic encephalopathy

Cerebral circulation and metabolism in septic encephalopathy have not been well documented. The authors measured cerebral blood flow (CBF) and metabolic rate for oxygen (CMRO2) in six patients with septic encephalopathy associated with multiple organ failure (three to five organs). They found that CBF and CMRO2 were significantly lower than awake control values of 46 +/- 2 to 28 +/- 3 mL/100g/min (mean +/- SEM) and 3.1 +/- 0.2 to 1.2 +/- 0.2 mL/100g/min, respectively. Cerebral vascular resistance (CVR) and cerebral circulatory index (CCI:CBF/CMRO2) were significantly higher than the control values of 2.0 +/- 0.1 to 3.0 +/- 0.4 mm Hg/mL/100g/min and 15.1 +/- 0.8 to 24.2 +/- 3.3, respectively. At the time of cerebral circulatory and metabolic measurements, their consciousness varied between 4 and 10 as evaluated by the Glasgow coma scale. The electroencephalogram showed diffuse slow wave activity and the latency of the auditory brain stem evoked response was prolonged in four of six patients. Computed brain tomography showed either no abnormality or mild atrophy. It is concluded that CBF and CMRO2 are disproportionally decreased during septic encephalopathy in association with dysfunction of the CNS and decreased electrical activity.

Current perspectives on septic shock

Although septic shock may be initiated by invading microbes, it is the metabolic and immunologic host responses that determine the true pathophysiology of this common critical care illness. Currently, septic shock therapeutics emphasize empiric and symptomatic treatment. Biochemical elucidation of the septic process will ultimately result in specific interventions for this ominous intensive care syndrome.