Hyperinsulinism in endotoxin shock dogs

Invited review: The influence of immune activation on transition cow health and performance-A critical evaluation of traditional dogmas

The progression from gestation into lactation represents the transition period, and it is accompanied by marked physiological, metabolic, and inflammatory adjustments. The entire lactation and a cow's opportunity to have an additional lactation are heavily dependent on how successfully she adapts during the periparturient period. Additionally, a disproportionate amount of health care and culling occurs early following parturition. Thus, lactation maladaptation has been a heavily researched area of dairy science for more than 50 yr. It was traditionally thought that excessive adipose tissue mobilization in large part dictated transition period success. Further, the magnitude of hypocalcemia has also been assumed to partly control whether a cow effectively navigates the first few months of lactation. The canon became that adipose tissue released nonesterified fatty acids (NEFA) and the resulting hepatic-derived ketones coupled with hypocalcemia lead to immune suppression, which is responsible for transition disorders (e.g., mastitis, metritis, retained placenta, poor fertility). In other words, the dogma evolved that these metabolites and hypocalcemia were causal to transition cow problems and that large efforts should be enlisted to prevent increased NEFA, hyperketonemia, and subclinical hypocalcemia. However, despite intensive academic and industry focus, the periparturient period remains a large hurdle to animal welfare, farm profitability, and dairy sustainability. Thus, it stands to reason that there are alternative explanations to periparturient failures. Recently, it has become firmly established that immune activation and the ipso facto inflammatory response are a normal component of transition cow biology. The origin of immune activation likely stems from the mammary gland, tissue trauma during parturition, and the gastrointestinal tract. If inflammation becomes pathological, it reduces feed intake and causes hypocalcemia. Our tenet is that immune system utilization of glucose and its induction of hypophagia are responsible for the extensive increase in NEFA and ketones, and this explains why they (and the severity of hypocalcemia) are correlated with poor health, production, and reproduction outcomes. In this review, we argue that changes in circulating NEFA, ketones, and calcium are simply reflective of either (1) normal homeorhetic adjustments that healthy, high-producing cows use to prioritize milk synthesis or (2) the consequence of immune activation and its sequelae.

Glucose-dependent insulinotropic peptide secretion is induced by inflammatory stimuli in an interleukin-1-dependent manner in mice

Recently, glucagon-like peptide-1 (GLP-1) levels have been found to be increased in response to inflammatory stimuli, leading to insulin secretion and prevention of hyperglycaemia during endotoxemia in mice. In the present study, we assess the relevance of the other incretin hormone, glucose-dependent insulinotropic peptide (GIP), as a regulator of glucose metabolism under inflammatory conditions. We found that lipopolysaccharide (LPS) increased GIP secretion in a time- and dose-dependent manner in C57BL/6J mice. To elucidate the underlying mechanisms, mice were injected with inflammatory cytokines known to be released by LPS. Circulating GIP levels significantly increased in response to interleukin (IL)-1β but not IL-6 or tumour necrosis factor (TNF)-α administration. Using respective knockout mice we found that LPS-mediated GIP secretion was selectively dependent on IL-1 signalling. To evaluate the functional relevance of inflammatory GIP secretion we pretreated mice with the GIP-receptor antagonist (Pro3)GIP. This blunted LPS-induced TNF-α and IL-6 secretion but did not affect LPS-induced insulin secretion or blood glucose-lowering. In conclusion, GIP provides a novel link between the immune system and the gut, with proinflammatory-immune modulatory function but minor glucose regulatory relevance in the context of acute endotoxemia.

GLP-1 secretion is increased by inflammatory stimuli in an IL-6-dependent manner, leading to hyperinsulinemia and blood glucose lowering

Hypoglycemia and hyperglycemia are both predictors for adverse outcome in critically ill patients. Hyperinsulinemia is induced by inflammatory stimuli as a relevant mechanism for glucose lowering in the critically ill. The incretine hormone GLP-1 was currently found to be induced by endotoxin, leading to insulin secretion and glucose lowering under inflammatory conditions in mice. Here, we describe GLP-1 secretion to be increased by a variety of inflammatory stimuli, including endotoxin, interleukin-1β (IL-1β), and IL-6. Although abrogation of IL-1 signaling proved insufficient to prevent endotoxin-dependent GLP-1 induction, this was abolished in the absence of IL-6 in respective knockout animals. Hence, we found endotoxin-dependent GLP-1 secretion to be mediated by an inflammatory cascade, with IL-6 being necessary and sufficient for GLP-1 induction. Functionally, augmentation of the GLP-1 system by pharmacological inhibition of DPP-4 caused hyperinsulinemia, suppression of glucagon release, and glucose lowering under endotoxic conditions, whereas inhibition of the GLP-1 receptor led to the opposite effect. Furthermore, total GLP-1 plasma levels were profoundly increased in 155 critically ill patients presenting to the intensive care unit (ICU) in comparison with 134 healthy control subjects. In the ICU cohort, GLP-1 plasma levels correlated with markers of inflammation and disease severity. Consequently, GLP-1 provides a novel link between the immune system and the gut with strong relevance for metabolic regulation in context of inflammation.

Lipopolysaccharides-mediated increase in glucose-stimulated insulin secretion: involvement of the GLP-1 pathway

Lipopolysaccharides (LPS) of the cell wall of gram-negative bacteria trigger inflammation, which is associated with marked changes in glucose metabolism. Hyperglycemia is frequently observed during bacterial infection and it is a marker of a poor clinical outcome in critically ill patients. The aim of the current study was to investigate the effect of an acute injection or continuous infusion of LPS on experimentally induced hyperglycemia in wild-type and genetically engineered mice. The acute injection of a single dose of LPS produced an increase in glucose disposal and glucose-stimulated insulin secretion (GSIS). Continuous infusion of LPS through mini-osmotic pumps was also associated with increased GSIS. Finally, manipulation of LPS detoxification by knocking out the plasma phospholipid transfer protein (PLTP) led to increased glucose disposal and GSIS. Overall, glucose tolerance and GSIS tests supported the hypothesis that mice treated with LPS develop glucose-induced hyperinsulinemia. The effects of LPS on glucose metabolism were significantly altered as a result of either the accumulation or antagonism of glucagon-like peptide 1 (GLP-1). Complementary studies in wild-type and GLP-1 receptor knockout mice further implicated the GLP-1 receptor-dependent pathway in mediating the LPS-mediated changes in glucose metabolism. Hence, enhanced GLP-1 secretion and action underlies the development of glucose-mediated hyperinsulinemia associated with endotoxemia.

Pancreatic beta-cell function and interleukin-1 beta in plasma during the acute phase response in patients with major burn injuries

Animal experiments demonstrate that interleukin-1 beta (IL-1 beta) is beta-cell cytotoxic in vitro and inhibits insulin secretion in vivo. However, it is unknown if IL-1 beta affects beta-cell function in man. Since IL-1 beta and other cytokines are main mediators of the acute phase response, the objectives of the present study were to examine beta-cell function in patients with major burn injuries, and to test if changes in beta-cell function correlated to systemic levels of IL-1 beta and tumour necrosis factor alpha (TNF alpha). We established and validated an IL-1 beta assay measuring free and protein bound IL-1 beta; protein bound IL-1 beta was detached from the IL-1 beta specific binding protein by acidification, rendering it accessible for the employed antibody. The IL-1 beta specific binding protein (43-60 kDa) was found in serum and plasma from all tested patients and normal subjects. Survivors of burn injuries had a stimulated beta-cell function, whereas non-survivors had an impaired beta-cell function as indicated by an increased plasma concentration of proinsulin, and an increased proinsulin/insulin ratio. In addition, non-survivors had significantly increased plasma levels of IL-1 beta. However, we could not demonstrate any correlation between C-peptide, proinsulin, insulin or proinsulin/insulin ratio and plasma concentration of IL-1 beta. In conclusion, beta-cell function abnormalities are evident in patients with major burn injuries, and a high plasma level of IL-1 beta correlates with a fatal outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of insulin in the blunted glucose metabolic response of septic rats to epinephrine

Epinephrine produces smaller incremental increases in plasma glucose concentration and rate of glucose appearance (Ra) in septic rats compared with nonseptic animals. In the present study, we investigated the role of insulin in the diminished response of septic rats to epinephrine-induced increases in glucose turnover. Glucose kinetics were assessed by the infusion of [6-3H]-glucose in conscious catheterized rats made septic by subcutaneous injections of live Escherichia coli. Epinephrine was infused at 1 micrograms/min/kg for 2 hours in the presence and absence of somatostatin and mannoheptulose (SRIF + MH). In comparison to nonseptic control animals, epinephrine-induced increases in plasma glucose concentration and glucose Ra were blunted by more than 50% in the septic rats. Infusion of SRIF + MH with epinephrine restored the blunted response to normal. During the infusion of epinephrine alone, the plasma insulin concentration in the septic rats was 2.8-fold higher than the nonseptic controls. SRIF + MH lowered the plasma insulin concentrations in both the nonseptic and septic rats to less than 10 microU/mL. SRIF + MH reversed the sepsis-induced hyperglucagonemia, but did not prevent a slight increase in glucagon levels during the epinephrine infusion in the nonseptic rats. In a second study, septic rats infused with SRIF + MH and replacement insulin showed a smaller increase in glucose concentration and glucose production in response to epinephrine than did septic animals administered SRIF + MH and no insulin. These results indicate that insulin plays an important role in the diminished response of septic rats to epinephrine.

Activation of phospholipases A1 and A2 in heart, liver, and blood during endotoxin shock

The effects of endotoxin shock on the activities of phospholipases A1 and A2 were studied in canine heart sarcolemma, liver plasma membrane, and blood serum. Results obtained from control dogs indicate that phospholipases A1 and A2 were equally active in cardiac sarcolemma. In liver plasma membrane the activity of phospholipase A1 was twice that of phospholipase A2, while in blood serum phospholipase A1 activity was only half that of phospholipase A2. Results obtained 4 hr after endotoxin administration (0.5 mg/kg, iv) demonstrate that phospholipase A1 activities were activated by 117% in cardiac sarcolemma, 188% in liver plasma membrane, and 150% in blood serum, while phospholipases A2 activities were stimulated by 71% in cardiac sarcolemma, 175% in liver plasma membrane, and 31% in blood serum. The in vitro incubation of all three enzyme preparations from control dogs with endotoxin (5-15 micrograms/0.5 ml) stimulated both phospholipase A1 and A2 activities and the stimulation was concentration dependent. These data suggest that endotoxin may have a direct stimulatory effect on phospholipases A1 and A2 activities in the cell membranes of heart and liver, and also in blood serum. Since phospholipases A play an important role in the regulation of membrane structure and function, the observed activation of phospholipases A1 and A2 may have a physiological significance in the pathogenesis of cellular dysfunction in endotoxin shock.

Down-regulation of insulin receptors in Propionibacterium acnes-activated macrophages in the mouse

Intraperitoneal administration of Propionibacterium acnes in CD-1 mice was associated with the reduction in number of insulin receptors in peritoneal macrophages (M phi), and with elevated levels of insulin in plasma and the peritoneal cavity. When insulin levels returned to normal, insulin receptors in P. acnes-M phi were still reduced. Insulin appears to contribute significantly to the down-regulation of the M phi-insulin receptors during the early stage of activation. Other biologically active substances released during M phi activation might assume greater influence on insulin resistance in activated M phi at a later stage. The induction of transient hyperinsulinemia in P. acnes-treated mice might be attributed to the effect of concurrently elevated interleukin-1 (IL-1) released in the early course of M phi activation.

Liver glycogen metabolism in endotoxin shock. I. Endotoxin administration decreases glycogen synthase activities in dog livers

The effects of E. coli endotoxin administration on hepatic glycogen content and glycogen synthase activities in dogs were studied. Liver glycogen content was decreased by 80% 2 hr after endotoxin injection. When enzyme preparations were preincubated at 25 degrees C for 3 hr prior to their assays, 75% of total glycogen synthase was in I form in control dogs. Under such conditions, endotoxin administration decreased the percentage I activity from 75 to 37%; decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 62.2 and 35.3%, respectively; decreased the Vmax and Km for UDP-glucose for glycogen synthase I by 75.6 and 15.6%, respectively; increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 126% at high (10 mM) and by 18-fold at low (1 mM) UDP-glucose concentration; increased the percentage D activity from 24 to 72%; decreased the I50 for ATP for the inhibition of total glycogen synthase by 49.7%; decreased the I50 for ATP for the inhibition of glycogen synthase I by 26.4%; and decreased the percentage I activity from 78 to 33% at ATP concentrations below 6 mM. When enzyme preparations were not preincubated prior to their assays, 90% of total glycogen synthase was in D form in control dogs. Under such conditions, endotoxin administration decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 47.1 and 33.3%, respectively, and increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 24.2% at high (10 mM) and by 106% at low (1 mM) UDP-glucose concentration. From these results, it is clear that endotoxin administration greatly impaired hepatic glycogenesis by decreasing the activity of glycogen synthase; this impairment is at least in part responsible for the depletion of liver glycogen content in endotoxin shock. Kinetic analyses revealed that the decrease in the activity of glycogen synthase in endotoxic shock is a result of a decrease in the interconversion of this enzyme from inactive to active form and an increase in the interconversion from active to inactive form.

The roles of glucagon, insulin and glucocorticoid hormones in the effects of sublethal doses of endotoxin on glucose homeostasis in rats

The effects of sub-lethal doses of endotoxin on plasma glucose, glucagon, insulin, glucocorticoids and non-esterified fatty acids (NEFA) were determined in rats. Endotoxin did not change the plasma concentration of glucocorticoids, but blocked the effects of elevated glucocorticoid hormone concentrations on both plasma glucose and hepatic tryptophan dioxygenase activity. Endotoxin increased the plasma concentrations of glucose, glucagon and insulin in rats with basal glucocorticoid concentrations, and changed the observed relationships between glucose, glucagon and insulin in a manner consistent with an increased sensitivity of glucagon secretion to lowered glucose concentrations. At the highest dose of endotoxin used, 20 mg/kg over 6 hr, a substantial decrease (greater than 7-fold) in the insulin/glucagon ratio provides evidence for changes in basal (as opposed to hormone-stimulated) glucose production and/or utilisation in vivo.

The effect of major thermal injury and carbohydrate-free intake on serum triglycerides, insulin, and 3-methylhistidine excretion

The severely burned patient responds differently to starvation ketosis in the early stage of injury as compared to the normal individual. A similar response has been observed in the patient after skeletal trauma and sepsis. In order to determine the extent of muscle protein contribution and the mechanism(s) involved, 11 burn patients with 35% to 80% BSA burn were resuscitated using carbohydrate-free solutions for 3 days followed by unrestricted intake. Blood was drawn daily and 24-hour urinary nitrogens were determined. Controls consisted of 10 preoperative elective surgical patients and two normal volunteers. The burned patients lost a mean +/- SEM of 17.1 +/- 1.72 g nitrogen per day on the third day. The mean +/- SEM ketone body response on the third day for burned patients was 385 +/- 77 mumol/l compared to 727 +/- 81 mumol/l for control patients. The mean +/- SEM 3-methylhistidine loss for burned patients on the third day was 9.83 +/- 0.82 mumol/kg compared to 3.6 mol/kg for control patients. Insulin levels on the third day of fast were three times the normal group. This insulin increase may be the modulating factor that suppresses excessive fat mobilization. This metabolic response causes a lower plasma ketone level, which may then necessitate the need for continued protein catabolism for glucose production for certain tissues. The protein contribution to the hypercatabolic response as assessed by increased urinary nitrogen losses is in part supported by an increased muscle protein breakdown as indicated by increased 3-methylhistidine excretion.

Biphasic effect of pertussis vaccine on serum insulin in mice

Administration of pertussis vaccine, consisting of whole, killed Bordetella pertussis organisms, causes hyperinsulinemia and enhanced secretion of insulin in response to a variety of secretagogues in rats and mice. In examining the time course and properties of this phenomenon, we discovered two distinct and separate effects of the bacteria on glucose and insulin levels in mice. First, a heat-stable (80 degrees C for 30 min) component causes a brief hyperinsulinemia which is +measureable by 1 h, maximal at 8 h, and ends in less than 48 h. This effect appears to be due to B. pertussis endotoxin, is mimicked by Escherichia coli endotoxin, and is associated with a transient, mild hypoglycemia. Second, there is a heat-labile component of the B. pertussis organism which induces a sustained (greater than 14 days), dose-dependent hyperinsulinemia which reaches a maximum at 5 to 7 days and has no associated hypoglycemia. The two effects are further distinguishable in that the early, endotoxin-induced hyperinsulinemia exhibits the normal suppressibility by exogenous epinephrine, whereas epinephrine markedly enhances the hyperinsulinemia occurring at 7 days. These two effects of B. pertussis appear to be mediated by different mechanisms and may be important in the well-recognized reactogenicity of pertussis vaccine in humans.

Role of the liver in endotoxin-induced hyperinsulinemia and hyperglucagonemia in rats

The intravenous administration of bacterial endotoxin to fasted rats elicited basal portal and systemic venous hyperinsulinemia and hyperglucagonemia. Enhanced pancreatic secretion of insulin and glucagon was implied by the elevated portal venous hormonal levels. Elevated insulin and glucagon levels were present at 4 hr after a 33 micrograms/100 gm intravenous endotoxin dose despite no fluctuation of the plasma glucose concentration. The role of the liver in the pancreatic hormonal response to endotoxin was investigated by infusing lipopolysaccharide slowly into the portal vein or systemic inferior vena cava. At doses of 33 and 100 micrograms per 100 gm, endotoxin administered via the systemic route stimulated significantly greater insulin and glucagon responses than did portal administration. Furthermore, rats with acute liver injury induced by partial (67%) hepatectomy, which depressed Kupffer cell phagocytosis, did respond to the 33 micrograms per 100 gm intraportal endotoxin dose with significantly greater hyperinsulinemia and hyperglucagonemia. These data suggest that hepatic Kupffer cells normally function to remove lipopolysaccharide from the portal venous blood and that at least at low pharmacological doses the pancreatic hormonal response to endotoxin is mediated by an unknown systemic mechanism.

Alterations in carbohydrate and lipid metabolism following administration of endotoxin

Endotoxin-induced alterations in blood flow, carbohydrate and lipid metabolism in various organs of the body are outlined. Peripheral utilization of carbohydrates and lipids does not appear to be adversely affected by the administration of mild to moderate doses of endotoxin (in fact, glucose turnover is even elevated). On the other hand, the supply of free fatty acids from adipose tissue is diminished, at least in part, due to severe hemodynamic changes that occur in this tissue following endotoxin. Hepatic gluconeogenesis is elevated, but does not match the increased demand for glucose by the periphery. The experimental conditions discussed in this brief review elicit changes that are reversible. However, during more severe endotoxemia, the metabolic alterations lead to irreversibility.

Glucose and lactate kinetics after endotoxin administration in dogs

We studied the effects of E. coli endotoxin on the glucose and lactate kinetics in dogs by means of the primed constant infusion of [6(-3)H] glucose and Na-L-(+)-[U-14C] lactate. The infusion of endotoxin induced a transient hyperglycemic level, followed by a steady fall in plasma glucose to hypoglycemic levels. The rate of appearance (Ra) and the rate of disappearance (Rd) of glucose were both significantly elevated (P less than .05) for 150 min after endotoxin, after which neither differed from the preinfusion value. The metabolic clearance rate of glucose was significantly elevated at all times 30 min postendotoxin. By 30 min postendotoxin, Ra and Rd of lactate, plasma lactate concentration, and the percent of glucose turnover originating from lactate were significantly elevated and remained so for the duration of the experiment. We concluded that after endotoxin hypoglycemia developed because of an enhanced peripheral uptake of glucose and a failure of the liver to maintain an increased Ra of glucose. We also concluded that lactate became an important precursor for gluconeogenesis and an important metabolic substrate.