Quantitative effects of thermal injury and insulin on the metabolism of the skeletal muscle using the perfused rat hindquarter preparation

Abstract

Injury from a severe burn or trauma can propel the body into a hypermetabolic state that can lead to the significant erosion of lean muscle mass. Investigations describing this process have been somewhat limited due to the lack of adequate experimental models. Here we report the use of a perfused rat hindquarter preparation to study the consequences of a moderate burn injury (approximately 20% total body surface area), with or without the addition of exogenous insulin (12.5 mU/mL), on the fluxes of major metabolites across the isolated skeletal muscle. The metabolic flux data was further analyzed using metabolic flux analysis (MFA), which allows for the estimation of the impact of these conditions on the intracellular muscle metabolism. Results indicate that this model is able to capture the increased rate of proteolysis, glutamine formation, and the negative nitrogen balance associated with the burn-induced hypermetabolic state. The inclusion of exogenous insulin resulted in significant changes in several fluxes, including an increase in the metabolism of glucose and the flux through the pentose phosphate pathway, as well as a reduction in the metabolism of glutamine, alanine, and leucine. However, insulin administration did not affect the nitrogen balance or the rate of proteolysis in the muscle, as has been suggested using other techniques. The use of the perfused hindquarter model coupled with MFA is a physiologically relevant and experimentally flexible platform for the exploration of skeletal muscle metabolism under catabolic conditions, and it will be useful in quantifying the specific metabolic consequences of other therapeutic advances.

Effects of Dehydroepiandrosterone Administration on Rat Hepatic Metabolism Following Thermal Injury

“…The role of these factors could be investigated by changing substrate and hormone levels in the perfusate from the physiological to the pathological range. By coupling the biochemical measurements with MFA, we were able to gain a more comprehensive view of the metabolic state of the organ, as we have done previously in both liver [35,43,45] and skeletal muscle [48].…”

Contribution of gene expression to metabolic fluxes in hypermetabolic livers induced through burn injury and cecal ligation and puncture in rats

“…CLP has also been shown to reduce the hepatic energy charge due to decreased function of mitochondria (Chen et al, 2004;Hampton et al, 1987;Hsieh et al, 2004). Since many transport mechanisms indirectly derive their energy Prior studies have also suggested that in a hypermetabolic state, a large flux of amino acids is generated from the catabolism of the skeletal muscle (Banta et al, 2004;Demling and Seigne, 2000). Both Sham-CLP and Burn-CLP treatment induced delayed gain and even loss of weight (Fig.…”

“…Prior studies using isolated perfused organs have identified differences in metabolic fluxes within liver Lee et al, 2000;Yamaguchi et al, 1997) and muscle (Banta et al, 2004) after burn injury that were not dependent upon the continual presence of elevated stress hormones and substrate loads, which suggests that intrinsic changes in the metabolism of these tissues had occurred. Such differences might be explained by changes in gene expression and enzyme protein levels; for example, sepsisinduced inhibition of gluconeogenesis has been attributed to decreased transcription of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase (Deutschman et al, 1995;Maitra et al, 2000).…”

“…This is especially true when characterizing hypermetabolic and catabolic states that involve many interorgan and intraorgan metabolic fluxes (Herndon and Tompkins, 2004;Tredget and Yu, 1992). Metabolomicsbased studies, more specifically metabolic flux analysis (MFA) with or without isotopic tracers, have been used to characterize carbon and nitrogen metabolism in vivo (Hellerstein and Murphy, 2004;Yang and Brunengraber, 2000), in individual organs and tissues in isolated perfusion systems (Banta et al, 2004Chatziioannou et al, 2003;Des Rosiers et al, 2004;Jin et al, 2004;Lee et al, 2000;Lee et al, 2003;Yokoyama et al, 2005), and isolated and cultured mammalian cells (Chan et al, 2003a,b;Marin et al, 2004;Zupke et al, 1995). Techniques to characterize systemwide changes in protein levels and gene expression include proteomic (Aulak et al, 2001;Duan et al, 2004) and DNA microarray analysis (Chinnaiyan et al, 2001;Dasu et al, 2004;Vemula et al, 2004).…”

Integrated Energy and Flux Balance Based Multiobjective Framework for Large-Scale Metabolic Networks

“…1,[5][6][7][8][11][12][13][14]24,25 Flux balance analysis (FBA) uses stoichiometric and mass balance constraints to compute the intracellular fluxes. Recently, energy balance analysis (EBA) was developed to ensure the thermodynamic feasibility of the computed fluxes.…”