Lipoprotein lipase in rats sensitized to endotoxin by surgical trauma

A non-lethal traumatic/hemorrhagic insult strongly modulates the compartment-specific PAI-1 response in the subsequent polymicrobial sepsis

Introduction

Plasminogen activator inhibitor 1 (PAI-1) is a key factor in trauma- and sepsis-induced coagulopathy. We examined how trauma-hemorrhage (TH) modulates PAI-1 responses in subsequent cecal ligation and puncture (CLP)-induced sepsis, and the association of PAI-1 with septic outcomes.

Methods

Mice underwent TH and CLP 48 h later in three separate experiments. In experiment 1, mice were sacrificed pre- and post-CLP to characterize the trajectory of PAI-1 in plasma (protein) and tissues (mRNA). Post-CLP dynamics in TH-CLP (this study) and CLP-Only mice (prior study) were then compared for modulatory effects of TH. In experiment 2, to relate PAI-1 changes to outcome, mice underwent TH-CLP and were sampled daily and followed for 14 days to compare non-survivors (DEAD) and survivors (SUR). In experiment 3, plasma and tissue PAI-1 expression were compared between mice predicted to die (P-DIE) and to live (P-LIVE).

Results

In experiment 1, an early post-TH rise of circulating PAI-1 was contrasted by a delayed (post-TH) decrease of PAI-1 mRNA in organs. In the post-CLP phase, profiles of circulating PAI-1 were similar between TH-CLP and CLP-Only mice. Conversely, PAI-1 mRNA declined in the liver and heart of TH-CLP mice versus CLP-Only. In experiment 2, there were no DEAD/SUR differences in circulating PAI-1 prior to CLP. Post-CLP, circulating PAI-1 in DEAD was 2–4-fold higher than in SUR. PAI-1 increase heralded septic deaths up to 48 h prior but DEAD/SUR thrombomodulin (endothelial injury marker) levels were identical. In experiment 3, levels of circulating PAI-1 and its hepatic gene expression were higher in P-DIE versus P-LIVE mice and those increases closely correlated with liver dysfunction.

Conclusions

Trauma modulated septic PAI-1 responses in a compartment-specific fashion. Only post-CLP increases in circulating PAI-1 predicted septic outcomes. In posttraumatic sepsis, pre-lethal release of PAI-1 was mostly of hepatic origin and was independent of endothelial injury.

TNF-alpha impairs heart and skeletal muscle protein synthesis by altering translation initiation

This study examined potential mechanisms contributing to the inhibition of protein synthesis in skeletal muscle and heart after administration of tumor necrosis factor (TNF)-alpha. Rats had vascular catheters implanted, and TNF-alpha was infused continuously for 24 h. TNF-alpha decreased in vivo-determined rates of global protein synthesis in gastrocnemius (39%) and heart (25%). The TNF-alpha-induced decrease in protein synthesis in the gastrocnemius involved a reduction in the synthesis of both myofibrillar and sarcoplasmic proteins. To identify potential mechanisms responsible for regulating mRNA translation, we examined several eukaryotic initiation factors (eIFs) and elongation factors (eEFs). TNF-alpha decreased the activity of eIF-2B in muscle (39%) but not in heart. This diminished activity was not caused by a reduction in the content of eIF-2B epsilon or the content and phosphorylation state of eIF-2 alpha. Skeletal muscle and heart from TNF-alpha-treated rats demonstrated 1) an increased binding of the translation repressor 4E-binding protein-1 (4E-BP1) with eIF-4E, 2) a decreased amount of eIF-4E associated with eIF-4G, and 3) a decreased content of the hyperphosphorylated gamma-form of 4E-BP1. In contrast, the infusion of TNF-alpha did not alter the content of eEF-1 alpha or eEF-2, or the phosphorylation state of eEF-2. In summary, these data suggest that TNF-alpha impairs skeletal muscle and heart protein synthesis, at least in part, by decreasing mRNA translational efficiency resulting from an impairment in translation initiation associated with alterations in eIF-4E availability.

Effect of combined treatment of anti-inflammatory drug and mannoheptulose on the production of tumour necrosis factor and endotoxin shock in mice

The endotoxin shock induced in mice by injection of viable Listeria monocytogenes and challenged with endotoxin can be alleviated by combined administration of mannoheptulose with acetylsalicylate or sulindac. The ability of animals to secrete tumour necrosis factor into the blood was, however, not affected. The significance of these observations are discussed.

Perturbation of glycerolipid content and biosynthesis in hepatocytes of rats continuously infused with Escherichia coli endotoxin

The effect of chronic, nonlethal endotoxemia on the endogenous content and de novo biosynthesis of glycerolipids was investigated in rat hepatocytes. Continuous E. coli endotoxin (ET) infusion for 30 hours through a subcutaneously implanted mini-pump greatly altered the composition of membrane phospholipids. Sphingomyelin (SPH) and phosphatidylserine (PS) content increased by 56% and 29%, respectively, while the content of phosphatidylcholine (PC) decreased slightly (6%) as compared with saline-infused rats. These effects contrasted with those observed in pair-fed rats (whose food intake was matched to that voluntarily consumed by ET-infused animals). Food restriction induced a great depletion of phospholipid content, mainly phosphatidylethanolamine (PE), PC, phosphatidylinositol (PI), and PS, with no changes at the level of SPH as compared with control (fed ad libitum) rats. Triacylglycerol (TG) content was greatly decreased (66%) in ET-infused rats and the magnitude of the change and the fatty acid composition followed a pattern similar to that observed in pair-fed rats. The kinetics of [2-3H]-glycerol incorporation reflected efficient utilization of the precursor for de novo biosynthesis of glycerolipids. Labeling of the intermediate metabolite phosphatidic acid (PA) peaked at an earlier time (1 min) in ET-infused, and in pair-fed rats, as compared with saline-infused and control rats (3 min) respectively, and was followed by a later peak in diacylglycerol (DG) labeling. The metabolic flux thereafter in endotoxemia reflected a redirection toward the synthesis of TG and PI, while in pair-fed animals the label went mainly to PC, concomitantly with a great reduction in the uptake of label into PI.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin shock and tumour necrosis factor release in mannoheptulose-treated mice

Administration of mannoheptulose partially protected mice infected with Listeria monocytogenes against the lethal effect of a subsequent endotoxin challenge. The ability of these animals to produce tumour necrosis factor was however unaffected. Mannoheptulose was observed to reverse the hypoglycaemic effect of endotoxin, possibly through inhibition of insulin secretion. The therapeutic significance of these observations is discussed.

Effect of sepsis on VLDL kinetics: responses in basal state and during glucose infusion

The effect of gram-negative sepsis on the kinetics and oxidation of very low-density lipoprotein (VLDL) fatty acids was assessed in conscious dogs in the normal state and 24 h after infusion of live Escherichia coli. VLDL, labeled with [2-3H]glycerol and [1-14C]palmitic acid, was used to trace VLDL kinetics and oxidation, and [1-13C]palmitic acid bound to albumin was infused simultaneously to quantify kinetics and oxidation of free fatty acid (FFA) in plasma. Sepsis caused a fivefold increase in the rate of VLDL production (RaVLDL). In the control dogs, the direct oxidation of VLDL-fatty acids was not an important contributor to their overall energy metabolism, but in dogs with sepsis, 17% of the total rate of CO2 production could be accounted for by VLDL-fatty acid oxidation. When glucose was infused into dogs with insulin and glucagon levels clamped at basal levels (by means of infusion of somatostatin and replacement of the hormones), RaVLDL increased significantly in the control dogs, but it did not increase further in dogs with sepsis. We conclude that the increase in triglyceride concentration in fasting dogs with gram-negative sepsis is the result of an increase in VLDL production and that the fatty acids in VLDL can serve as an important source of energy in sepsis.

Hypertriglyceridemia and its relation to tissue lipoprotein lipase activity in endotoxemic, Escherichia coli bacteremic, and polymicrobial septic rats

Hypertriglyceridemia, commonly observed in septic patients, may result from a decreased ability of tissues to remove plasma triacylglycerol due to depressed lipoprotein lipase activity. While endotoxin administration results in substantial decreases in muscle lipoprotein lipase activity, enzyme activity is increased in animals subjected to other forms of stress and trauma. The present study was initiated to compare changes in plasma triacylglycerol concentrations and tissue lipoprotein lipase activities in rats challenged with endotoxin or live Escherichia coli (iv or ip) or rats subjected to polymicrobial peritoneal sepsis. Sixteen hours post-treatment plasma triacylglycerol levels were increased 200 to 300% in endotoxin- and E. coli-treated rats but did not differ from control animals subjected to peritoneal sepsis. At the same time, endotoxin administration resulted in significant decreases in heart (71-80%), soleus muscle (52-74%), and adipose tissue (21-32%) lipoprotein lipase activity regardless of the route injected. Intravenous E. coli also lead to a decrease in the three tissues examined while ip administration of E. coli reduced muscle and adipose tissue but not heart lipoprotein lipase activity. In contrast to endotoxemic and E. coli bacteremic rats, polymicrobial peritonitis resulted in significant increases in heart (46-89%) and skeletal muscle (18-39%) lipoprotein lipase activity. Thus, hypertriglyceridemia is not necessarily a consequence of sepsis but occurred in endotoxemic and bacteremic states when muscle and adipose tissue lipoprotein lipase activities were reduced. These findings support the postulate that sepsis-induced hypertriglyceridemia is likely to be associated with a decreased ability of lipoprotein lipase-containing tissues to clear circulating triacylglycerol.

Glucose and lactate kinetics in septic rats

Glucose turnover was measured in rats subjected to experimental peritonitis. Fifteen hours following cecal ligation and puncture or sham surgery, rats were anesthetized with pentobarbital and glucose metabolism was estimated by constant infusion tracer techniques. Septic rats demonstrated significantly elevated rates of glucose appearance without any elevation of plasma glucose concentration. There was also significant hyperlactacidemia in the cecally ligated rats. The elevated plasma lactate was not accompanied by a lowering of blood pH. Arterial blood pressure were not different between groups, however the blood pressure of septic rats did fall during the infusion experiment. Septic rats demonstrated significantly elevated initial heart rates and blood hematocrit. The turnover of lactate was also elevated in the septic rats. By calculation of the relative percentage of glucose production from labeled lactate, it is obvious that septic rats had elevated rates of gluconeogenesis. Determination of plasma immunoreactive insulin indicated that septic rats were not insulin resistant.