Catecholamines: important factors in the increase of oxidative phosphorylation coupling in rat-liver mitochondria during the early phase of burn injury

The role of hormones in sepsis: an integrated overview with a focus on mitochondrial and immune cell dysfunction

Sepsis is a dysregulated host response to infection that results in life-threatening organ dysfunction. Virtually every body system can be affected by this syndrome to greater or lesser extents. Gene transcription and downstream pathways are either up- or downregulated, albeit with considerable fluctuation over the course of the patient's illness. This multi-system complexity contributes to a pathophysiology that remains to be fully elucidated. Consequentially, little progress has been made to date in developing new outcome-improving therapeutics. Endocrine alterations are well characterised in sepsis with variations in circulating blood levels and/or receptor resistance. However, little attention has been paid to an integrated view of how these hormonal changes impact upon the development of organ dysfunction and recovery. Here, we present a narrative review describing the impact of the altered endocrine system on mitochondrial dysfunction and immune suppression, two interlinked and key aspects of sepsis pathophysiology.

Differential acute and chronic effects of burn trauma on murine skeletal muscle bioenergetics

Altered skeletal muscle mitochondrial function contributes to the pathophysiological stress response to burns. However, the acute and chronic impact of burn trauma on skeletal muscle bioenergetics remains poorly understood. Here, we determined the temporal relationship between burn trauma and mitochondrial function in murine skeletal muscle local to and distal from burn wounds. Male BALB/c mice (8-10 weeks old) were burned by submersion of the dorsum in water (∼ 95 °C) to create a full thickness burn on ∼ 30% of the body. Skeletal muscle was harvested spinotrapezius underneath burn wounds (local) and the quadriceps (distal) of sham and burn treated mice at 3h, 24h, 4d and 10d post-injury. Mitochondrial respiration was determined in permeabilized myofiber bundles by high-resolution respirometry. Caspase 9 and caspase 3 protein concentration were determined by western blot. In muscle local to burn wounds, respiration coupled to ATP production was significantly diminished at 3h and 24h post-injury (P<0.001), as was mitochondrial coupling control (P<0.001). There was a 5- (P<0.05) and 8-fold (P<0.001) increase in respiration in response to cytochrome at 3h and 24h post burn, respectively, indicating damage to the outer mitochondrial membranes. Moreover, we also observed greater active caspase 9 and caspase 3 in muscle local to burn wounds, indicating the induction of apoptosis. Distal muscle mitochondrial function was unaltered by burn trauma until 10d post burn, where both respiratory capacity (P<0.05) and coupling control (P<0.05) were significantly lower than sham. These data highlight a differential response in muscle mitochondrial function to burn trauma, where the timing, degree and mode of dysfunction are dependent on whether the muscle is local or distal to the burn wound.

Lactate kinetics and mitochondrial respiration in skeletal muscle of healthy humans under influence of adrenaline

Plasma lactate is widely used as a biomarker in critical illness. The aims of the present study were to elucidate the usefulness of a three-compartment model for muscle lactate kinetics in humans and to characterize the response to an exogenous adrenaline challenge. Repeated blood samples from artery and femoral vein together with blood flow measurements and muscle biopsies were obtained from healthy male volunteers (n=8) at baseline and during an adrenaline infusion. Concentrations of lactate and enrichment of [13C]lactate were measured and kinetics calculated. Mitochondrial activity, glycogen concentration, oxygen uptake and CO2 release were assessed. The adrenaline challenge increased plasma lactate 4-fold as a result of a greater increase in the rate of appearance (R(a)) than the increase in the rate of disappearance (R(d)). Leg muscle net release of lactate increased 3.5-fold, whereas intramuscular production had a high variation but did not change. Mitochondrial state 3 respiration increased by 30%. Glycogen concentration, oxygen uptake and CO2 production remained unchanged. In conclusion a three-compartment model gives additional information to the two-compartment model but, due to its larger variation and invasive muscle biopsy, it is less likely to become a regularly used tool in clinical research. Hyperlactataemia in response to adrenergic stimuli was driven by an elevated lactate release from skeletal muscle most probably due to a redirection of a high intramuscular turnover rather than an increased production.

Temporal changes in cellular energy following burn injury

Availability of ADP is a predominant influence on respiratory control. Associated with severe burn injury is an increase in energy expenditure. The purpose of this study was to determine the temporal changes in ATP, ADP, NAD, and NADH following severe burn and thereby assess any related alterations in respiratory control and energy deficit. During isoflurane anesthesia and following intraperitoneal injection of saline, 32 mice were flame burned at 40% body surface area. Twelve mice served as controls. At 12, 24, 72, and 168 h post-burn, groups of mice underwent celiotomy with determination of hepatic surface blood flow using laser Doppler and oxygen saturation using pulse oximetry. Biopsies of liver were then frozen in liquid nitrogen for subsequent quantification of ATP, ADP, AMP, NAD, and NADH by HPLC. Mortality was 12.5% at 72 h post-burn and 25% at 1 week. Oxygen saturation and hepatic surface blood flow remained similar to control values throughout the week after burn. ATP, ADP, and energy charge decreased progressively following burn reaching a significant decrease from unburned controls at 72 h. Availability of NADH remained statistically similar to unburned controls throughout the week after burn. These results demonstrate that despite maintenance of baseline oxygen delivery, there was a nadir in ATP and ADP availability and energy charge in the liver at 72 h after burn. This finding supports the concept of a limitation in phosphorylation after injury. Availability of NADH remained at or above pre-burn concentrations suggesting that the rate of fuel oxidation was not a limiting factor for ongoing oxidative phosphorylation for energy.

Multiorgan failure is an adaptive, endocrine-mediated, metabolic response to overwhelming systemic inflammation

Sepsis and other critical illnesses produce a biphasic inflammatory, immune, hormonal, and metabolic response. The acute phase is marked by an abrupt rise in the secretion of so-called stress hormones with an associated increase in mitochondrial and metabolic activity. The combination of severe inflammation and secondary changes in endocrine profile diminish energy production, metabolic rate, and normal cellular processes, leading to multiple organ dysfunction. This perceived failure of organs might instead be a potentially protective mechanism, because reduced cellular metabolism could increase the chances of survival of cells, and thus organs, in the face of an overwhelming insult. We propose that, first, multiple organ failure induced by critical illness is primarily a functional, rather than structural, abnormality. Indeed, it may not be failure as such, but a potentially protective, reactive mechanism. Second, the decline in organ function is triggered by a decrease in mitochondrial activity and oxidative phosphorylation, leading to reduced cellular metabolism. Third, this effect on mitochondria might be the consequence of acute-phase changes in hormones and inflammatory mediators.

The effect of hypermetabolism induced by burn trauma on the ethanol-oxidizing capacity of the liver

OBJECTIVE

To study the rate of elimination of ethanol after a major burn trauma.

DESIGN

Prospective, controlled study.

SETTING

National burns unit in a Swedish university hospital.

PATIENTS AND SUBJECTS

Eight consecutive patients suffering from 18%-72% total burned surface area and nine healthy male control subjects.

INTERVENTIONS

The patients received ethanol, 0.35-0.60 g/kg body weight intravenously, during 1 hr. This was repeated daily during the first week postburn. The control subjects received the same amount of ethanol once.

MEASUREMENTS AND MAIN RESULTS

Blood samples were drawn at 20- to 30-min intervals during 5 hrs after the start of the infusion. Serum ethanol was determined by headspace gas chromatography. The rate of elimination of ethanol was calculated from the concentration time profile. In the control subjects, the median elimination rate was 0.074 g/kg/hr (range, 0.059-0.083 g/kg/hr). In the patients, it was already 0.138 g/kg/hr (range, 0.111-0.201 g/kg/hr) on the first day; this increased even further over the following 6 days, reaching 0.183 g/kg/hr (range, 0.150-0.218 g/kg/hr) on the seventh day.

CONCLUSIONS

Ethanol elimination is augmented postburn. A more effective reoxidation of reduced nicotinamide adenine dinucleotide seems the most likely explanation for the increased rate of ethanol elimination in these hypermetabolic trauma patients. This finding suggests that the oxidative capacity of the liver may be assessed by studying the rate of ethanol elimination in burn victims.