Central role of interleukin-6 in burn induced stimulation of hepatic amino acid transport.
ABSTRACT Burn injury produces a marked and prolonged hypermetabolic state, which is characterized by accelerated hepatic amino acid metabolism and negative nitrogen balance. The effect of burn injury on hepatocyte transport of glutamine, a key substrate in gluconeogenesis and ureagenesis, was examined following the administration of a full thickness 20% total body surface scald injury. The burn injury was induced in wild-type mice, as well as two types of knockout mice: a CD-14 knockout and an interleukin-6 (IL-6) knockout. In both the wild-type and CD-14 knockout mice a latent and profound 2-fold increase in hepatocyte glutamine transport was seen. In contrast, hepatocytes isolated from IL-6 knockout mice failed to show an induction of glutamine transport after burn injury. Hepatocytes isolated from burned wild-type and CD-14 knockout mice produced significantly higher levels of IL-6 as compared to hepatocytes isolated from sham burned mice. Histologic analysis of skin isolated from wild-type mice showed a robust inflammatory response whereas skin from IL-6 deficient mice showed minimal inflammation and decreased granulation tissue. The results of this study suggest that IL-6 may play a key role in the stimulation of hepatic glutamine transport following burn injury.
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ABSTRACT: Glutamine is the most abundant amino acid in the human body and can be synthesized by almost all tissues by the glutamine synthetase (GS)-catalyzed amidation of glutamate. Hepatocytes have access to extracellular glutamine by the concentrative uptake via members of the sodium-dependent neutral amino acid transport systems N and A. Hepatic glutamine metabolism in connection with urea synthesis is importantly involved in systemic ammonia detoxication and pH regulation due to the unique regulatory properties of the liver-type glutaminase, the acinar compartimentation of urea and glutamine synthesis, and a cycling of glutamine between periportal and perivenous hepatocytes. Upregulation of GS expression in hepatocellular carcinoma is related to growth advantage and an enhanced metastatic potential. Glutamine is a potent activator of signal transduction. Recent progress concerns the understanding of glutamine-induced hepatocyte swelling and the downstream activation of integrins, Src, and MAP-kinases in the regulation of autophagic proteolysis, canalicular bile acid excretion, glycogen and fatty acid synthesis, insulin signaling, and protection from apoptosis. Most recently the first primary GS defect leading to inherited glutamine deficiency with fatal outcome was described in human. This review summarizes recent progress in the understanding of glutamine metabolism and signal transduction, which provides further rationale for the use of glutamine as a therapeutic tool.Frontiers in Bioscience 02/2007; 12:371-91. · 3.29 Impact Factor
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ABSTRACT: Hyperglycemia, glucose intolerance and elevated insulin levels frequently occur in burned patients; however, the mechanism(s) for this insulin resistance has not been fully elucidated. One possible mechanism could involve alterations in the phosphorylation of serine 307 of the insulin receptor substrate-1 (IRS-1) via activation of stress kinase enzymes, including SAPK/JNK. In the present study we examined the time course of the effect of burn injury to mice on: levels of IRS-1 protein, phosphorylation of serine 307 of IRS-1, SAPK/JNK kinase levels and activity and Akt kinase activity in hind limb skeletal muscle. Burn injury produced a reduction in hind limb muscle mass 24 h after injury, and, which persisted for 168 h. At 24 h after injury, there was a dramatic ( approximately 9-fold) increase in phosphorylation of IRS-1 serine 307 followed by a more moderate elevation thereafter. Total IRS-1 protein was slightly elevated at 24 h after injury and decreased to levels below sham treated animals at the later times. Burn injury did not appear to change total SAPK/JNK protein content, however, enzyme activity was increased for 7 days after injury. Akt kinase activity was decreased in skeletal muscle following burn injury; providing a biochemical basis for burn-induced insulin resistance. These findings are consistent with the hypothesis that burn-induced insulin resistance may be related, at least in part, to alterations in the phosphorylation of key proteins in the insulin signaling cascade, including IRS-1, and that changes in stress kinases, such as SAPK/JNK produced by burn injury, may be responsible for these changes in phosphorylation.Life Sciences 11/2005; 77(24):3068-77. · 2.56 Impact Factor
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ABSTRACT: OBJECTIVE:: We aimed to determine whether the severity of inhalation injury evokes an immune response measurable at the systemic level and to further characterize the balance of systemic pro- and anti-inflammation early after burn and inhalation injury. BACKGROUND:: Previously, we reported that the pulmonary inflammatory response is enhanced with worse grades of inhalation injury and that those who die of injuries have a blunted pulmonary immune profile compared with survivors. METHODS:: From August 2007 to June 2011, bronchoscopy was performed on 80 patients admitted to the burn intensive care unit when smoke inhalation was suspected. Of these, inhalation injury was graded into 1 of 5 categories (0, 1, 2, 3, and 4), with grade 0 being the absence of visible injury and grade 4 corresponding to massive injury. Plasma was collected at the time of bronchoscopy and analyzed for 28 immunomodulating proteins via multiplex bead array or enzyme-linked immunosorbent assay. RESULTS:: The concentrations of several plasma immune mediators were increased with worse inhalation injury severity, even after adjusting for age and % total body surface area (TBSA) burn. These included interleukin (IL)-1RA (P = 0.002), IL-6 (P = 0.002), IL-8 (P = 0.026), granulocyte colony-stimulating factor (P = 0.002), and monocyte chemotactic protein 1 (P = 0.007). Differences in plasma immune mediator concentrations in surviving and deceased patients were also identified. Briefly, plasma concentrations of IL-1RA, IL-6, IL-8, IL-15, eotaxin, and monocyte chemotactic protein 1 were higher in deceased patients than in survivors (P < 0.05 for all), whereas IL-4 and IL-7 were lower (P < 0.05). After adjusting for the effects of age, % TBSA burn, and inhalation injury grade, plasma IL-1RA remained significantly associated with mortality (odds ratio, 3.12; 95% confidence interval, 1.03-9.44). Plasma IL-1RA also correlated with % TBSA burn, inhalation injury grade, fluid resuscitation, Baux score, revised Baux score, Denver score, and the Sequential Organ Failure Assessment score. CONCLUSIONS:: The severity of smoke inhalation injury has systemically reaching effects, which argue in favor of treating inhalation injury in a graded manner. In addition, several plasma immune mediators measured early after injury were associated with mortality. Of these, IL-1RA seemed to have the strongest correlation with injury severity and outcomes measures, which may explain the blunted pulmonary immune response we previously found in nonsurvivors.Annals of surgery 11/2012; · 7.90 Impact Factor