Inhibition of hepatic gluconeogenesis by nitric oxide: a comparison with endotoxic shock

Anti-obesity and anti-diabetic effects of L-citrulline are sex-dependent

AIMS

Anti-diabetic and anti-obesity effects of L-citrulline (Cit) have been reported in male rats. This study determined sex differences in response to Cit in Wistar rats.

MAIN METHODS

Type 2 diabetes (T2D) was induced using a high-fat diet followed by low-dose of streptozotocin (30 mg/kg) injection. Male and female Wistar rats were divided into 4 groups (n = 6/group): Control, control+Cit, T2D, and T2D + Cit. Cit (4 g/L in drinking water) was administered for 8 weeks. Obesity indices were recorded, serum fasting glucose and lipid profile were measured, and glucose and pyruvate tolerance tests were performed during the Cit intervention. White (WAT) and brown (BAT) adipose tissues were weighted, and the adiposity index was calculated at the end of the study.

KEY FINDINGS

Cit was more effective in decreasing fasting glucose (18 % vs. 11 %, P = 0.0100), triglyceride (20 % vs. 14 %, P = 0.0173), and total cholesterol (16 % vs. 11 %, P = 0.0200) as well as decreasing gluconeogenesis and improving glucose tolerance, in females compared to male rats with T2D. Following Cit administration, decreases in WAT weight (16 % vs. 14 % for gonadal, 21 % vs. 16 % for inguinal, and 18 % vs. 13 % for retroperitoneal weight, all P < 0.0001) and increases in BAT weight (58 % vs. 19 %, for interscapular and 10 % vs. 7 % for axillary, all P < 0.0001) were higher in females than male rats with T2D. The decrease in adiposity index was also higher (11 % vs. 9 %, P = 0.0007) in females.

SIGNIFICANCE

The anti-obesity and anti-diabetic effects of Cit in rats are sex-dependent, with Cit being more effective in female than male rats.

Enhancing Muscle Intracellular Ca2+ Homeostasis and Glucose Uptake: Passive Pulsatile Shear Stress Treatment in Type 2 Diabetes

Type 2 diabetes mellitus (T2D) is a significant global public health problem that has seen a substantial increase in the number of affected individuals in recent decades. In a murine model of T2D (db/db), we found several abnormalities, including aberrant intracellular calcium concentration ([Ca2+]i), decreased glucose transport, increased production of reactive oxygen species (ROS), elevated levels of pro-inflammatory interleukins and creatine phosphokinase (CK), and muscle weakness. Previously, we demonstrated that passive pulsatile shear stress, generated by sinusoidal (headward-forward) motion, using a motion platform that provides periodic acceleration of the whole body in the Z plane (pGz), induces the synthesis of nitric oxide (NO) mediated by constitutive nitric oxide synthase (eNOS and nNOS). We investigated the effect of pGz on db/db a rodent model of T2D. The treatment of db/db mice with pGz resulted in several beneficial effects. It reduced [Ca2+]i overload; enhanced muscle glucose transport; and decreased ROS levels, interleukins, and CK. Furthermore, pGz treatment increased the expression of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), and neuronal nitric oxide synthase (nNOS); reduced inducible nitric oxide synthase (iNOS); and improved muscle strength. The cytoprotective effects of pGz appear to be mediated by NO, since pretreatment with L-NAME, a nonspecific NOS inhibitor, abolished the effects of pGz on [Ca2+]i and ROS production. Our findings suggest that a non-pharmacological strategy such as pGz has therapeutic potential as an adjunct treatment to T2D.

Nitric oxide regulation of cellular metabolism: Adaptive tuning of cellular energy

Nitric oxide can interact with a wide range of proteins including many that are involved in metabolism. In this review we have summarized the effects of NO on glycolysis, fatty acid metabolism, the TCA cycle, and oxidative phosphorylation with reference to skeletal muscle. Low to moderate NO concentrations upregulate glucose and fatty acid oxidation, while higher NO concentrations shift cellular reliance toward a fully glycolytic phenotype. Moderate NO production directly inhibits pyruvate dehydrogenase activity, reducing glucose-derived carbon entry into the TCA cycle and subsequently increasing anaploretic reactions. NO directly inhibits aconitase activity, increasing reliance on glutamine for continued energy production. At higher or prolonged NO exposure, citrate accumulation can inhibit multiple ATP-producing pathways. Reduced TCA flux slows NADH/FADH entry into the ETC. NO can also inhibit the ETC directly, further limiting oxidative phosphorylation. Moderate NO production improves mitochondrial efficiency while improving O2 utilization increasing whole-body energy production. Long-term bioenergetic capacity may be increased because of NO-derived ROS, which participate in adaptive cellular redox signaling through AMPK, PCG1-α, HIF-1, and NF-κB. However, prolonged exposure or high concentrations of NO can result in membrane depolarization and opening of the MPT. In this way NO may serve as a biochemical rheostat matching energy supply with demand for optimal respiratory function.

Regulation of hepatic oxidative stress by voltage-gated proton channels (Hv1/VSOP) in Kupffer cells and its potential relationship with glucose metabolism

Voltage-gated proton channels (Hv1/VSOP), encoded by Hvcn1, are important regulator of reactive oxygen species (ROS) production in many types of immune cells. While in vitro studies indicate that Hv1/VSOP regulates ROS production by maintaining pH homeostasis, there are few studies investigating the functional importance of Hv1/VSOP in vivo. In the present study, we first show that Hv1/VSOP is functionally expressed in liver resident macrophage, Kupffer cells, regulating the hepatic oxidative stress in vivo. Our immunocytochemistry and electrophysiology data showed that Hvcn1 is specifically expressed in Kupffer cells, but not in hepatocytes. Furthermore, Hvcn1-deficiency drastically altered the hepatic oxidative stress. The Hvcn1-deficient mice showed high blood glucose and serum insulin but normal insulin sensitivity, indicating that these phenotypes were not linked to insulin resistance. Transcriptome analysis indicated that the gene expression of glycogen phosphorylase (Pygl) and Glucose-6-phosphatase, catalytic subunit (G6pc) were upregulated in Hvcn1-deficient liver tissues, and quantitative PCR confirmed the result for Pygl. Furthermore, we observed higher amount of glucose-6-phosphate, a key sugar intermediate for glucose in Hvcn1-deficient liver than WT, suggesting that glucose production in liver is accelerated in Hvcn1-deficient mice. The present study sheds light on the functional importance of Kupffer cells in hepatic oxidative stress and its potential relationship with glucose metabolism.

Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism

Nitric oxide (NO) contributes to carbohydrate metabolism and decreased NO bioavailability is involved in the development of type 2 diabetes mellitus (T2DM). NO donors may improve insulin signaling and glucose homeostasis in T2DM and insulin resistance (IR), suggesting the potential clinical importance of NO-based interventions. In this review, site-specific roles of the NO synthase (NOS)-NO pathway in carbohydrate metabolism are discussed. In addition, the metabolic effects of physiological low levels of NO produced by constitutive NOS (cNOS) versus pathological high levels of NO produced by inducible NOS (iNOS) in pancreatic β-cells, adipocytes, hepatocytes, and skeletal muscle cells are summarized. A better understanding of the NOS-NO system in the regulation of glucose homeostasis can hopefully facilitate the development of new treatments for T2DM.

iNOS as a metabolic enzyme under stress conditions

Nitric oxide (NO) is a free radical acting as a cellular signaling molecule in many different biochemical processes. NO is synthesized from l-arginine through the action of the nitric oxide synthase (NOS) family of enzymes, which includes three isoforms: endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS). iNOS-derived NO has been associated with the pathogenesis and progression of several diseases, including liver diseases, insulin resistance, obesity and diseases of the cardiovascular system. However, transient NO production can modulate metabolism to survive and cope with stress conditions. Accumulating evidence strongly imply that iNOS-derived NO plays a central role in the regulation of several biochemical pathways and energy metabolism including glucose and lipid metabolism during inflammatory conditions. This review summarizes current evidence for the regulation of glucose and lipid metabolism by iNOS during inflammation, and argues for the role of iNOS as a metabolic enzyme in immune and non-immune cells.

Lipopolysaccharide inhibits hepatic gluconeogenesis in rats: The role of immune cells

AIMS/INTRODUCTION

Bacterial septicemia has diverse clinical symptoms including severe hypoglycemia. However, sepsis-induced hypoglycemia has not yet been examined in detail. The aim of the present study was to investigate the mechanisms underlying hypoglycemia in sepsis.

MATERIALS AND METHODS

We induced endotoxin shock in rats using lipopolysaccharide (LPS). After an intraperitoneal injection of LPS, we measured gluconeogenesis using the pyruvate tolerance test. The effects of LPS on glucose metabolism were investigated in perfused livers and isolated hepatocytes. Furthermore, its effects on the production of inflammatory cytokines were examined in isolated splenocytes. The interaction between splenocytes and hepatocytes in response to LPS was investigated in vitro using a co-culture of splenocytes and hepatocytes.

RESULTS

In the pyruvate tolerance test, the pretreatment with LPS decreased gluconeogenesis. The in vivo pretreatment of rats with LPS did not inhibit glucose production in perfused livers. The in vitro treatment of isolated hepatocytes with LPS did not decrease hepatic gluconeogenesis. Although LPS increased the production of inflammatory cytokines (tumor necrosis factor-α, interferon-γ, interleukin-1β, interleukin-6 and interleukin-10) and nitric oxide in isolated splenocytes, only nitric oxide significantly inhibited gluconeogenesis in isolated hepatocytes. When splenocytes and hepatocytes were co-cultured in medium containing LPS, the messenger ribonucleic acid expression of glucose-6-phosphatase in hepatocytes was suppressed.

CONCLUSIONS

LPS reduced hepatic gluconeogenesis, at least in part, by stimulating the production of nitric oxide in splenocytes. This effect could contribute to the mechanisms responsible for septicemia-induced hypoglycemia.

Disclosing caffeine action on insulin sensitivity: effects on rat skeletal muscle

Caffeine, a non-selective adenosine antagonist, has distinct effects on insulin sensitivity when applied acutely or chronically. Herein, we investigated the involvement of adenosine receptors on insulin resistance induced by single-dose caffeine administration. Additionally, the mechanism behind adenosine receptor-mediated caffeine effects in skeletal muscle was assessed. The effect of the administration of caffeine, 8-cycle-1,3-dipropylxanthine (DPCPX, A1 antagonist), 2-(2-Furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261, A2A antagonist) and 8-(4-{[(4-cyanophenyl)carbamoylmethyl]-oxy}phenyl)-1,3-di(n-propyl)xanthine (MRS1754, A2B antagonist) on whole-body insulin sensitivity was tested. Skeletal muscle Glut4,5'-AMP activated protein kinase (AMPK) and adenosine receptor protein expression were also assessed. The effect of A1 and A2B adenosine agonists on skeletal muscle glucose uptake was evaluated in vitro. Sodium nitroprussiate (SNP, 10nM), a nitric oxide (NO) donor, was used to evaluate the effect of NO on insulin resistance induced by adenosine antagonists. Acute caffeine decreased insulin sensitivity in a concentration dependent manner (Emax=55.54±5.37%, IC50=11.61nM), an effect that was mediated by A1 and A2B adenosine receptors. Additionally, acute caffeine administration significantly decreased Glut4, but not AMPK expression, in skeletal muscle. We found that A1, but not A2B agonists increased glucose uptake in skeletal muscle. SNP partially reversed DPCPX and MRS1754 induced-insulin resistance. Our results suggest that insulin resistance induced by acute caffeine administration is mediated by A1 and A2B adenosine receptors. Both Glut4 and NO seem to be downstream effectors involved in insulin resistance induced by acute caffeine.

Lipoprotein in the cell wall of Staphylococcus aureus is a major inducer of nitric oxide production in murine macrophages

Staphylococcus aureus is a Gram-positive bacterium that causes inflammation at infection sites by inducing various inflammatory mediators such as nitric oxide (NO). To identify the staphylococcal virulence factors contributing to NO production, we compared the ability of ethanol-killed wild-type S. aureus and mutant strains lacking lipoteichoic acid (ΔltaS), lipoproteins (Δlgt), or d-alanine (ΔdltA) to stimulate NO production in a murine macrophage cell line, RAW 264.7, and the primary macrophages derived from C57BL/6 mice. Wild-type, ΔltaS, and ΔdltA strains induced NO production in a dose-dependent manner but this response was not observed when the cells were stimulated with the Δlgt strain. Moreover, purified lipoproteins triggered NO production in macrophages. Coincident with NO induction, the wild-type, ΔltaS, and ΔdltA strains induced expression of inducible NO synthase (iNOS) at both mRNA and protein levels whereas Δlgt failed to induce iNOS protein or mRNA. Transient transfection followed by a reporter gene assay and Western blotting experiments demonstrated that wild-type, ΔltaS, and ΔdltA strains, but not the Δlgt strain, induced substantial activation of NF-κB and STAT1 phosphorylation, both of which are known to be crucial for iNOS expression. Moreover, wild-type, ΔltaS, and ΔdltA strains increased Toll-like receptor 2 (TLR2) activation, which is known to mediate S. aureus-induced innate immunity, whereas the Δlgt strain did not. Collectively, these results suggest that lipoproteins in the cell wall of S. aureus play a major role in the induction of NO production in murine macrophages through activation of the TLR2 receptor.

Adiponectin signaling in the liver

High glucose production contributes to fed and fasted hyperglycemia in Type 1 Diabetes (T1D) and Type 2 Diabetes (T2D). The breakdown of the adiponectin signaling pathway in T1D and the reduction of circulating adiponectin in T2D contribute to this abnormal increase in glucose production. Sufficient amounts of insulin could compensate for the loss of adiponectin signaling in T1D and T2D and reduce hyperglycemia. However, the combination of low adiponectin signaling and high insulin resembles an insulin resistance state associated with cardiovascular disease, fatty liver disease and decreased life expectancy. The future development of "adiponectin sensitizers", medications that correct the deficiency in adiponectin signaling, could restore the metabolic balance in T1D and T2D and reduce the need for insulin. This article reviews the adiponectin signaling pathway in the liver through T-cadherin, AdipoR1, AdipoR2, AMPK, ceramidase activity, APPL1 and the recently discovered Suppressor Of Glucose from Autophagy (SOGA).

CNS control of glucose metabolism: response to environmental challenges

Over the last 15 years, considerable work has accumulated to support the role of the CNS in regulating postprandial glucose levels. As discussed in the first section of this review, the CNS receives and integrates information from afferent neurons, circulating hormones, and postprandially generated nutrients to subsequently direct changes in glucose output by the liver and glucose uptake by peripheral tissues. The second major component of this review focuses on the effects of external pressures, including high fat diet and changes to the light:dark cycle on CNS-regulating glucose homeostasis. We also discuss the interaction between these different pressures and how they contribute to the multifaceted mechanisms that we hypothesize contribute to the dysregulation of glucose in type 2 diabetes mellitus (T2DM). We argue that while current peripheral therapies serve to delay the progression of T2DM, generating combined obesity and T2DM therapies targeted at the CNS, the primary site of dysfunction for both diseases, would lead to a more profound impact on the progression of both diseases.

The effect of nitric oxide inhibitors and Snitroso-Nacetylpenicillamine on glucose concentration in an animal model

BACKGROUND

Nitric oxide (NO) is becoming an increasingly important signaling molecule implicated in a growing number of physiological and pathophysiological processes. Research on the effect of NO donors on glucose metabolism in peripheral tissues have grown rapidly in the last decade. This study examined the effects of N(G)methyl-L-arginine acetate (L-NMMA) and N(G)methyl-L-arginine ester (L-NAME) on fasting and postprandial blood glucose concentrations. The study also investigated if L-NMMA and L-NAME decrease the hyperglycemic effect caused by the NO donor S-nitrosoN-acetylpenicillamine (SNAP) in normoglycemic rats.

RESULTS

L-NAME and L-NMMA significantly lowered the postprandial blood glucose concentrations. Mean postprandial blood glucose concentrations in rats treated with L-NAME were 5.04 ± 0.07 mmol/L at 120 min, 4.62 ± 0.19 mmol/L at 150 min and 4.36 ± 0.17 mmol/L at 180 min time points compared with 5.46 ± 0.14 (P = 0.029), 5.20 ± 0.17 mmol/L (P = 0.036), and 4.89 ± 0.14 mmol/L (P = 0.015) at the same time points respectively for saline control. Mean blood glucose concentrations in rats treated with L-NMMA were 4.35 ± 0.23 mmol/L (P = 0.0018) at 120 min, 4.60 ± 0.14 mmol/L (P = 0.090) at 150 min and 3.88 ± 0.16 mmol/L (P 0.001) at 180 min. There were significant differences in mean postprandial blood glucose concentrations in rats treated with SNAP, compared with those treated with L-NAME and SNAP at 90 min (P = 0.012), 180 min (P = 0.013) and 210 min (P < 0.0001). In addition, there were significant differences in mean postprandial blood glucose concentrations in rats treated with SNAP compared with those treated with L-NMMA and SNAP at 90 min (P = 0.0011), 180 min (P = 0.015) and 210 min (P = 0.0077).

CONCLUSION

The nitric oxide synthase [NOS] inhibitors were effective in reducing postprandial blood glucose concentration in rats treated with SNAP. This suggests that although SNAP is an effective antihypertensive agent it decreases glucose tolerance which can be improved by the use of NOS inhibitors such as L-NMMA or L-NAME. These drugs could be beneficial in controlling blood glucose tolerance in rats administered with SNAP, and possibly in humans.

Hepatic muscarinic acetylcholine receptors are not critically involved in maintaining glucose homeostasis in mice

OBJECTIVE

An increase in the rate of hepatic glucose production is the major determinant of fasting hyperglycemia in type 2 diabetes. A better understanding of the signaling pathways and molecules that regulate hepatic glucose metabolism is therefore of great clinical importance. Recent studies suggest that an increase in vagal outflow to the liver leads to decreased hepatic glucose production and reduced blood glucose levels. Since acetylcholine (ACh) is the major neurotransmitter of the vagus nerve and exerts its parasympathetic actions via activation of muscarinic ACh receptors (mAChRs), we examined the potential metabolic relevance of hepatocyte mAChRs.

RESEARCH DESIGN AND METHODS

We initially demonstrated that the M(3) mAChR is the only mAChR subtype expressed by mouse liver/hepatocytes. To assess the physiological role of this receptor subtype in regulating hepatic glucose fluxes and glucose homeostasis in vivo, we used gene targeting and transgenic techniques to generate mutant mice lacking or overexpressing M(3) receptors in hepatocytes only.

RESULTS

Strikingly, detailed in vivo phenotyping studies failed to reveal any significant metabolic differences between the M(3) receptor mutant mice and their control littermates, independent of whether the mice were fed regular or a high-fat diet. Moreover, the expression levels of genes for various key transcription factors, signaling molecules, and enzymes regulating hepatic glucose fluxes were not significantly altered in the M(3) receptor mutant mice.

CONCLUSIONS

This rather surprising finding suggests that the pronounced metabolic effects mediated by activation of hepatic vagal nerves are mediated by noncholinergic signaling pathways.

Free radicals and antioxidants in inflammatory processes and ischemia-reperfusion injury

This article discusses the current understanding of the role of free radicals and antioxidants in inflammatory processes and in ischemia reperfusion injury. It begins by describing the manifestations of acute inflammation and outlining the cellular events that occur during inflammation. It then describes the biochemical mediators of inflammation with special attention to nitric oxide. It details the process of hypoxia reperfusion injury, the enzymes involved, its treatment, and studies involving specific hypoxia reperfusion injuries in various animal species.

Effects of the nitric oxide donor SIN-1 on net hepatic glucose uptake in the conscious dog

To determine the role of nitric oxide in regulating net hepatic glucose uptake (NHGU) in vivo, studies were performed on three groups of 42-h-fasted conscious dogs using a nitric oxide donor [3-morpholinosydnonimine (SIN-1)]. The experimental period was divided into period 1 (0-90 min) and period 2 (P2; 90-240 min). At 0 min, somatostatin was infused peripherally, and insulin (4-fold basal) and glucagon (basal) were given intraportally. Glucose was delivered intraportally (22.2 mumol.kg(-1).min(-1)) and peripherally (as needed) to increase the hepatic glucose load twofold basal. At 90 min, an infusion of SIN-1 (4 mug.kg(-1).min(-1)) was started in a peripheral vein (PeSin-1, n = 10) or the portal vein (PoSin-1, n = 12) while the control group received saline (SAL, n = 8). Both peripheral and portal infusion of SIN-1, unlike saline, significantly reduced systolic and diastolic blood pressure. Heart rate rose in PeSin-1 and PoSin-1 (96 +/- 5 to 120 +/- 10 and 88 +/- 6 to 107 +/- 5 beats/min, respectively, P < 0.05) but did not change in response to saline. NHGU during P2 was 31.0 +/- 2.4 and 29.9 +/- 2.0 mumol.kg(-1).min(-1) in SAL and PeSin-1, respectively but was 23.7 +/- 1.7 in PoSin-1 (P < 0.05). Net hepatic carbon retention during P2 was significantly lower in PoSin-1 than SAL or PeSin-1 (21.4 +/- 1.2 vs. 27.1 +/- 1.5 and 26.1 +/- 1.0 mumol.kg(-1).min(-1)). Nonhepatic glucose uptake did not change in response to saline or SIN-1 infusion. In conclusion, portal but not peripheral infusion of the nitric oxide donor SIN-1 inhibited NHGU.

Glucose metabolism and catecholamines

Until now, catecholamines were the drugs of choice to treat hypotension during shock states. Catecholamines, however, also have marked metabolic effects, particularly on glucose metabolism, and the degree of this metabolic response is directly related to the beta2-adrenoceptor activity of the individual compound used. Under physiologic conditions, infusing catecholamine is associated with enhanced rates of aerobic glycolysis (resulting in adenosine triphosphate production), glucose release (both from glycogenolysis and gluconeogenesis), and inhibition of insulin-mediated glycogenesis. Consequently, hyperglycemia and hyperlactatemia are the hallmarks of this metabolic response. Under pathophysiologic conditions, the metabolic effects of catecholamines are less predictable because of changes in receptor affinity and density and in drug kinetics and the metabolic capacity of the major gluconeogenic organs, both resulting from the disease per se and the ongoing treatment. It is also well-established that shock states are characterized by a hypermetabolic condition with insulin resistance and increased oxygen demands, which coincide with both compromised tissue microcirculatory perfusion and mitochondrial dysfunction. This, in turn, causes impaired glucose utilization and may lead to inadequate glucose supply and, ultimately, metabolic failure. Based on the landmark studies on intensive insulin use, a crucial role is currently attributed to glucose homeostasis. This article reviews the effects of the various catecholamines on glucose utilization, both under physiologic conditions, as well as during shock states. Because, to date (to our knowledge), no patient data are available, results from relevant animal experiments are discussed. In addition, potential strategies are outlined to influence the catecholamine-induced effects on glucose homeostasis.

The control of hepatic glycogen metabolism in an in vitro model of sepsis

Culturing hepatocytes with a combination of LPS, TNF-alpha, IL-1beta and IFN-gamma resulted in an inhibition of glucose output from glycogen and prevented the repletion of glycogen in freshly cultured cells. The reduced glycogen mobilisation correlated with the lower cell glycogen content and reduced rate of glycogen synthesis from [U-(14)C]glucose rather than alterations in either total phosphorylase or phosphorylase a activity. There was no change in the percentage of glycogen exported as glucose nor the production of lactate plus pyruvate indicating that redistribution of the Gluc-6-P cannot explain the failure of the liver to export glucose. Although changes in glycogen mobilisation correlated with NO production, inhibition of NO synthase by inclusion of L-NMMA in the culture medium failed to prevent the inhibition of either glycogen accumulation or mobilisation by the proinflammatory cytokines, precluding the involvement of NO in this response. LPS plus cytokine treatment had no effect on total glycogen synthase activity although the activity ratio was lowered, indicative of increased phosphorylation. The inhibition of glycogen synthesis correlated with a fall in the intracellular concentrations of Gluc-6-P and UDP-glucose and in the absence of measured changes in kinase activity, it is suggested that the fall in Gluc-6-P reduces both substrate supply and glycogen synthase phosphatase activity. The fall in Gluc-6-P coincided with a reduction in total glucokinase and hexokinase activity within the cells, but no significant change in either the translocation of glucokinase or glucose-6-phosphatase activity. This demonstrates direct cytokine effects on glycogen metabolism independent of changes in glucoregulatory hormones.

The effect of iNOS deletion on hepatic gluconeogenesis in hyperdynamic murine septic shock

OBJECTIVE

To investigate the role of the inducible nitric oxide synthase activation-induced excess nitric oxide formation on the rate of hepatic glucose production during fully resuscitated murine septic shock.

DESIGN

Prospective, controlled, randomized animal study.

SETTING

University animal research laboratory.

SUBJECTS

Male C57Bl/6 and B6.129P2-Nos2(tm1Lau)/J (iNOS-/-) mice.

INTERVENTIONS

Fifteen hours after cecal ligation and puncture, anesthetized, mechanically ventilated and instrumented mice (wild-type controls, n = 13; iNOS-/-, n = 12; wild-type mice receiving 5 mg.kg(-1) i.p. of the selective iNOS inhibitor GW274150 immediately after cecal ligation and puncture, n =8) received continuous i.v. hydroxyethylstarch and norepinephrine to achieve normotensive and hyperdynamic hemodynamics.

MEASUREMENTS AND RESULTS

Measurements were recorded 18, 21 and 24 h after cecal ligation and puncture. Liver microcirculatory perfusion and capillary hemoglobin O2 saturation (laser Doppler flowmetry and remission spectrophotometry) were well maintained in all groups. Despite significantly lower norepinephrine doses required to achieve the hemodynamic targets, the rate of hepatic glucose production (gas chromatography--mass spectrometry measurements of tissue isotope enrichment during continuous i.v. 1,2,3,4,5,6-13C6-glucose infusion) at 24 h after cecal ligation and puncture was significantly higher in both iNOS-/- and GW274150-treated mice, which was concomitant with a significantly higher hepatic phosphoenolpyruvate carboxykinase activity (spectrophotometry) in these animals.

CONCLUSIONS

In normotensive, hyperdynamic septic shock, both pharmacologic and genetic deletion of the inducible nitric oxide synthase allowed maintenance of hepatic glucose production, most likely due to maintained activity of the key regulatory enzyme of gluconeogenesis, phosphoenolpyruvate carboxykinase.

Effect of acute swimming exercise on lactate levels and its relation with zinc in pinealectomized rats

It is argued that melatonin secreted from the pineal gland regulates the levels of zinc, which is an important trace element. Decreases in zinc levels of pinealectomized rats supports this relationship. There is an increasing amount of evidence suggesting that the pineal gland can have important effects on physical activity. The objective of the present study was to explore the changes in serum lactate levels in pinealectomized rats subjected to acute swimming exercise and its relation with zinc. Forty adult male rats of Spraque Dawley strain were equally allocated to four groups. Group 1: General Control Group. Group 2: Pinealectomized Control Group. Group 3: Swimming Control Group. Group 4: Pinealectomized Swimming Group. Serum zinc, melatonin and lactate levels were determined in the blood samples collected from the animals by a decapitation method. Zinc and melatonin levels were higher in Group 1 than in Groups 2, 3 and 4 (p < 0.01), higher in Group 3 than in Groups 2 and 4 (p < 0.01) and higher in Group 2 than in Group 4 (p < 0.01). The highest lactate levels were found in Group 4 (p < 0.01). Lactate levels in Group 3 were higher than those in Groups 1 and 2 (p < 0.01), while the levels in Groups 1 and 2 did not differ. Pinealectomy results in a significant increase in lactate levels in rats subjected to an acute swimming exercise. This increase in lactate levels may be associated with the decrease observed in zinc levels after pinealectomy.

Regulatory role for the arginine–nitric oxide pathway in metabolism of energy substrates

Nitric oxide (NO) is synthesized from L-arginine by NO synthase in virtually all cell types. Emerging evidence shows that NO regulates the metabolism of glucose, fatty acids and amino acids in mammals. As an oxidant, pathological levels of NO inhibit nearly all enzyme-catalyzed reactions through protein oxidation. However, as a signaling molecule, physiological levels of NO stimulate glucose uptake as well as glucose and fatty acid oxidation in skeletal muscle, heart, liver and adipose tissue; inhibit the synthesis of glucose, glycogen, and fat in target tissues (e.g., liver and adipose); and enhance lipolysis in adipocytes. Thus, an inhibition of NO synthesis causes hyperlipidemia and fat accretion in rats, whereas dietary arginine supplementation reduces fat mass in diabetic fatty rats. The putative underlying mechanisms may involve multiple cyclic guanosine-3',5'-monophosphate-dependent pathways. First, NO stimulates the phosphorylation of adenosine-3',5'-monophosphate-activated protein kinase, resulting in (1) a decreased level of malonyl-CoA via inhibition of acetyl-CoA carboxylase and activation of malonyl-CoA decarboxylase and (2) a decreased expression of genes related to lipogenesis and gluconeogenesis (glycerol-3-phosphate acyltransferase, sterol regulatory element binding protein-1c and phosphoenolpyruvate carboxykinase). Second, NO increases the phosphorylation of hormone-sensitive lipase and perilipins, leading to the translocation of the lipase to the neutral lipid droplets and, hence, the stimulation of lipolysis. Third, NO activates expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha, thereby enhancing mitochondrial biogenesis and oxidative phosphorylation. Fourth, NO increases blood flow to insulin-sensitive tissues, promoting substrate uptake and product removal via the circulation. Modulation of the arginine-NO pathway through dietary supplementation with L-arginine or L-citrulline may aid in the prevention and treatment of the metabolic syndrome in obese humans and companion animals, and in reducing unfavorable fat mass in animals of agricultural importance.

Altered response to inflammatory cytokines in hepatic energy metabolism in inducible nitric oxide synthase knockout mice

BACKGROUND/AIMS

Production of nitric oxide (NO) in the liver is believed to be a critical factor for carbohydrate and energy metabolism in endotoxin shock. The present study focuses on the involvement of NO produced by inducible nitric oxide synthase (iNOS) in glycogen synthesis and energy metabolism stimulated by insulin.

METHODS

Primary hepatocytes prepared from wild-type and iNOS knockout (iNOS(-/-)) mice were employed.

RESULTS

Incubation of wild-type hepatocytes with a combination of cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) and lipopolysaccharide (cytokines/LPS) inhibited insulin-stimulated glycogen synthesis and adenosine triphosphate (ATP) increase, and decreased the ketone body ratio (KBR) at 8-12 h, concomitant with expression of iNOS protein and NO production. While the glycogen synthesis was suppressed by cytokines/LPS, reduction of the ATP increase and a decrease in KBR by cytokines/LPS were not observed in iNOS(-/-) hepatocytes. Further, N(G)-monomethyl-L-arginine, a NOS inhibitor, reversed the inhibition of ATP increase and decrease in KBR by cytokines/LPS, but not the inhibition of glycogen synthesis. Conversely, addition of S-nitroso-N-acetylpenicillamine, a NO donor, inhibited the insulin-stimulated ATP increase synthesis in iNOS(-/-) hepatocytes, but not the insulin-stimulated glycogen synthesis.

CONCLUSIONS

These results demonstrate that NO mediates the suppression of insulin-stimulated energy metabolism, but not glycogen synthesis, in cytokines/LPS-treated hepatocytes.

Glucose deprivation decreases nitric oxide production via NADPH depletion in immunostimulated rat primary astrocytes

We have previously reported that the production of nitric oxide (NO) in immunostimulated astrocytes was markedly decreased under glucose-deprived conditions. The present study was undertaken to find the contributing factor(s) for the decreased NO production in glucose-deprived immunostimulated astrocytes. NO production in rat primary astrocytes was stimulated for 24-48 h by cotreatment with lipopolysaccharides (1 microg/ml) and interferon-gamma (100 U/ml). Decreased NO production in immunostimulated astrocytes by glucose deprivation was mimicked by the glycolytic inhibitor 2-deoxyglucose and reversed by addition of pyruvate and lactate. Glucose deprivation did not alter the expression of inducible nitric oxide synthase (iNOS) in immunostimulated astrocytes. Addition of beta-NADPH, but not tetrahydrobiopterine, both of which are essential cofactors for NOS function, completely restored the NO production that was decreased in glucose-deprived immunostimulated astrocytes. Glucose deprivation and immunostimulation synergistically reduced intracellular NADPH level in astrocytes. The results indicate that glucose deprivation decreases NO production in immunostimulated astrocytes by depleting intracellular NADPH, a cofactor of iNOS.

Cytokine-mediated inhibition of ketogenesis is unrelated to nitric oxide or protein synthesis

Cytokines play an important role in the lipid disturbances commonly associated with sepsis. Ketogenesis is inhibited during sepsis, and tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) have been suggested to mediate this impairment, irrespective of the ketogenic substrate (fatty acid or branched chain ketoacid). However, the underlying mechanism of cytokine action is still unknown. First we investigated the possible role of the induction of nitric oxide (NO) synthesis, using rat hepatocyte monolayers. Hepatocytes were incubated for 6 h, with either alpha -ketoisocaproate (KIC) (1 mM) or oleic acid (0.5 mM) in the presence or absence of TNF alpha (25 microg/L) and IL-6 (15 microg/L). In some experiments, cells were incubated with NO synthase (NOS) inhibitors. The ketone body (beta -hydroxybutyrate and acetoacetate) production and nitrite production were measured in the incubation medium. Our results indicated no involvement of nitric oxide in the inhibitory action of cytokines on ketogenesis. Secondly, we showed that cycloheximide (10(-4)M) did not counteract the cytokine-mediated ketogenesis decrease; hence, the effects of cytokines on ketogenesis are not protein synthesis-dependent. The cytokine-mediated inhibition of ketogenesis is therefore unrelated to either NO production or protein synthesis.

Role of nitric oxide in the regulation of glucose kinetics in response to endotoxin in dogs

The purpose of the present in vivo study was to determine the role of nitric oxide (NO) in the regulation of glucose metabolism in response to endotoxin by blocking NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA). In five dogs, the appearance and disappearance rates of glucose (by infusion of [6,6-(2)H(2)]glucose), plasma glucose concentration, and plasma hormone concentrations were measured on five different occasions: saline infusion, endotoxin alone (E coli, 1.0 microg/kg i.v.), and endotoxin administration plus three different doses of primed, continuous infusion of L-NMMA. Endotoxin increased rate of appearance of glucose from 13.7 +/- 1.6 to 23.6 +/- 3.3 micromol x kg(-1) x min(-1) (P < 0.05), rate of disappearance of glucose from 13.9 +/- 1.1 to 24.8 +/- 3.1 micromol x kg(-1) x min(-1) (P < 0.001), plasma lactate from 0.5 +/- 0.1 to 1.7 +/- 0.1 mmol/l (P < 0.01), and counterregulatory hormone concentrations. L-NMMA did not affect the rise in rate of appearance and disappearance of glucose, plasma lactate, or the counterregulatory hormone response to endoxin. Plasma glucose levels were not affected by endotoxin with or without L-NMMA. In conclusion, in vivo inhibition of NO synthesis by high doses of L-NMMA does not affect glucose metabolism in response to endotoxin, indicating that NO is not a major mediator of glucose metabolism during endotoxemia in dogs.

Combined intraportal infusion of acetylcholine and adrenergic blockers augments net hepatic glucose uptake

Portal glucose delivery in the conscious dog augments net hepatic glucose uptake (NHGU). To investigate the possible role of altered autonomic nervous activity in the effect of portal glucose delivery, the effects of adrenergic blockade and acetylcholine (ACh) on hepatic glucose metabolism were examined in 42-h-fasted conscious dogs. Each study consisted of an equilibration (-120 to -20 min), a control (-20 to 0 min), and a hyperglycemic-hyperinsulinemic period (0 to 300 min). During the last period, somatostatin (0.8 microg. kg(-1). min(-1)) was infused along with intraportal insulin (1.2 mU. kg(-1). min(-1)) and glucagon (0.5 ng. kg(-1). min(-1)). Hepatic sinusoidal insulin was four times basal (73 +/- 7 microU/ml) and glucagon was basal (55 +/- 7 pg/ml). Glucose was infused peripherally (0-300 min) to create hyperglycemia (220 mg/dl). In test protocol, phentolamine and propranolol were infused intraportally at 0.2 microg and 0.1 microg. kg(-1). min(-1) from 120 min on. ACh was infused intraportally at 3 microg. kg(-1). min(-1) from 210 min on. In control protocol, saline was given in place of the blockers and ACh. Hyperglycemia-hyperinsulinemia switched the net hepatic glucose balance (mg. kg(-1). min(-1)) from output (2.1 +/- 0.3 and 1.1 +/- 0.2) to uptake (2.8 +/- 0.9 and 2.6 +/- 0.6) and lactate balance (micromol. kg(-1). min(-1)) from uptake (7.5 +/- 2.2 and 6.7 +/- 1.6) to output (3.7 +/- 2.6 and 3.9 +/- 1.6) by 120 min in the control and test protocols, respectively. Thereafter, in the control protocol, NHGU tended to increase slightly (3.0 +/- 0.6 mg. kg(-1). min(-1) by 300 min). In the test protocol, adrenergic blockade did not alter NHGU, but ACh infusion increased it to 4.4 +/- 0.6 and 4.6 +/- 0.6 mg. kg(-1). min(-1) by 220 and 300 min, respectively. These data are consistent with the hypothesis that alterations in nerve activity contribute to the increase in NHGU seen after portal glucose delivery.

Melatonin increases muscle and liver glycogen content in nonexercised and exercised rats

The effects of melatonin on several parameters of carbohydrate and lipid metabolism were investigated in exercised and nonexercised rats. Animals were run to exhaustion on a rodent treadmill at 24 m/min and a 12% slope. Exercise resulted in a significant hypoglycemia and increased plasma levels of lactate and beta-hydroxybutyrate, together with a significant reduction of glycogen in muscle and liver. Muscle and liver glycogen content was elevated and plasma free fatty acid decreased in nonexercised animals receiving melatonin (0.5 or 2.0 mg/kg i.p). Melatonin at 2.0 mg/kg reduced plasma lactate and increased lactate concentration in liver. When compared to untreated exercised animals glycemia and muscle and liver glycogen content were significantly higher in melatonin-treated exercised animals, while plasma and liver lactate and plasma beta-hydroxybutyrate were significantly reduced. Our data indicate that melatonin preserves glycogen stores in exercised rats through changes in carbohydrate and lipid utilization.

Inhibition of nitric oxide synthesis in primary cultured mouse hepatocytes by alpha-lipoic acid

Recent work shows that septic or endotoxic shock is associated with lipopolysaccharide and cytokine mixture-induced nitric oxide (NO) synthesis in liver. Here we found that DL-alpha-lipoic acid inhibited but other thiol-containing antioxidants such as glutathione and N-acetylcysteine enhanced lipopolysaccharide and cytokine mixture (referred as LPS/CM)-induced NO synthesis in hepatocytes. The inhibitory action of alpha-lipoic acid on hepatocyte NO synthesis was as potent as that of NG-monomethyl-L-arginine without obvious cytotoxicity. Deletion by diethylmaleate or inhibition by buthionine sulfoximine of intracellular glutathione caused a significant decrease in hepatocyte NO synthesis, implying that increased intracellular reduced glutathione levels could not be the reason for alpha-lipoic acid inhibited NO synthesis. alpha-Lipoic acid inhibition of NO synthesis seems to be from alpha-lipoic acid improved carbohydrate metabolism in hepatocytes. Since alpha-lipoic acid is an essential compound existing naturally in physiological systems, it may serve as both a research and therapeutic agent for sepsis.

Nitric oxide inhibits neonatal hepatocyte oxidative metabolism

BACKGROUND/PURPOSE

Liver function is frequently impaired in neonates with sepsis. Nitric oxide (NO) is thought to be a mediator of organ dysfunction and liver oxidative metabolism during sepsis. The authors developed an in vitro model to investigate the effect of NO and the combined effect of NO plus H2O2 on neonatal hepatocyte oxidative metabolism.

METHODS

Hepatocytes were isolated from neonatal rats. Oxygen consumption was measured polarographically. In Study A, cells were exposed to S-Nitroso-N-acetylpenicillamine (SNAP), an NO donor, at various concentrations. In study B, myxothiazol and oligomycin, inhibitors of mitochondrial respiration, were added to investigate the site of action of NO. In study C, hepatocytes were incubated in the presence of both SNAP (300 micromol/L) and H2O2 (1.5 mmol/L). In study D, morphological alterations induced by NO and NO plus H2O2 were investigated by hepatocyte electron microscopy.

RESULTS

In study A, SNAP caused a dose-dependent decrease in oxygen consumption. A significant inhibition was reached at 300 micromol/L SNAP. In study B, the lack of further inhibition when SNAP was given together with myxothiazol indicates that NO acts intramitochondrially. Similarly, no further inhibition occurred when the NO donor was given together with oligomycin, suggesting that the effect of NO is mainly at the level of ATP synthase. In study C, concomitant addition of 300 micromol/L SNAP and 1.5 mmol/L H2O2 to hepatocytes caused further inhibition of oxygen consumption compared with either SNAP or H2O2 alone. In study D, mild alterations in hepatocyte morphology were noted in the presence of SNAP or SNAP plus H2O2.

CONCLUSIONS

In neonatal hepatocytes, NO significantly inhibits mitochondrial oxygen consumption, possibly at the level of ATP synthase. The effect of NO is additive to that of H2O2. Morphological findings were consistent with these biochemical effects and suggest that NO and H2O2 are important mediators of liver damage during sepsis.

Nitric oxide inhibits norepinephrine-induced hepatic vascular responses but potentiates hepatic glucose output

We previously reported that sympathetic nerve-induced vasoconstriction in the intestine resulted in shear stress induced release of nitric oxide (NO) that led to presynaptic inhibition of transmitter release. In contrast, studies in the liver suggested a postsynaptic inhibition of vascular responses, thus leading to the hypothesis tested here that maintained catecholamine release in the liver would result in maintained metabolic catecholamine action in the face of inhibition of vascular responses. In rats, norepinephrine (NE) induced elevations in arterial glucose content were inhibited by NO synthase antagonism (Nω-nitro-L-arginine methyl ester (L-NAME), 10 mg/kg, intraportal) but potentiated by NO donor administration (3-morpholinosydnonimine (SIN-1), 0.2 mg/kg, intraportal). The potentiated effect of SIN-1 was abolished by indomethacin (7.5 mg/kg, intraportal). To confirm the hepatic site of metabolic effect, cats were used so that blood flow and hepatic glucose balance could be determined. SIN-1 potentiated NE-induced glucose output from the liver from 5.0 ± 0.4 to 7.2 ± 0.6 mg·min-1·kg-1. The potentiation was blocked by methylene blue, a guanylate cyclase inhibitor. Contrary to the glucose response, L-NAME potentiated but SIN-1 attenuated NE-induced portal vasoconstriction. Thus NO is shown to produce differential modulation of vascular and metabolic effects of NE. Vasoconstriction of the hepatic vasculature is inhibited by NO, whereas the glycogenolytic response to NE is potentiated, responses that are probably mediated by prostaglandin.Key words: prostaglandin, glucose, portal vasculature, Nω-nitro-L-arginine methyl ester, 3-morpholinosydnonimine.

Experimental evaluation of the effects of the intraportal administration of cyclic guanosine monophosphate on ischemia/reperfusion in the porcine liver

This study was done to examine the protective effects of cyclic guanosine monophosphate (cGMP), a second messenger of nitric oxide, for ischemia/reperfusion injury of the liver, since it is known to induce vasodilatation and to inhibit platelet aggregation. Using an experimental model of porcine liver ischemia, 8-bromoguanosine 3',5' monophosphate, a cGMP analog, was continuously administered into the portal vein before ischemia and after reperfusion 30 min for each in the cGMP group (n = 6). Saline water was administered in the same way in the control group (n = 6). The cardiac output (CO), mean arterial blood pressure (MAP), portal venous flow (PVF), hepatic arterial flow (HAF), hepatic tissue blood flow (HTBF), and hepatic tissue cGMP level were determined. Hepatic enzymes and the bile discharge were also assessed as indicators of hepatic function. The hepatic tissue cGMP level was significantly higher, and PVF, HTBF, and the bile discharge were significantly greater in the cGMP group, while there were no remarkable differences between the groups with CO, MAP, HAF, and hepatic enzymes. In conclusion, the continuous supplementation of cGMP into the portal vein was found to be beneficial for preserving both the hepatic circulation and, consequently, the hepatic function after warm ischemia of porcine liver.

Norepinephrine and nomega-monomethyl-L-arginine in porcine septic shock: effects on hepatic O2 exchange and energy balance

We compared the effects of norepinephrine (NOR; n = 11) and the nonselective nitric oxide synthase inhibitor Nomega-monomethyl-L-arginine (L-NMMA; n = 11) on hepatic blood flow (Q liv), O2 exchange, and energy metabolism over 24 h of hyperdynamic, normotensive porcine endotoxic shock. Endotoxin (ETX; n = 8) caused a continuous fall in mean arterial pressure (MAP) despite a sustained 50% increase in cardiac output (Q) achieved by adequate fluid resuscitation. NOR maintained MAP at preshock levels owing to a further rise in Q, while the comparable hemodynamic stabilization during L-NMMA infusion resulted from systemic vasoconstriction, increasing the systemic vascular resistance (SVR) about 30% from shock level after 6 h of treatment concomitant with a reduction in Q to preshock values. Whereas NOR also increased Q liv and, hence, hepatic O2 delivery (hDO2), but did not affect hepatic O2 uptake (hVO2), L-NMMA influenced neither Q liv nor hDO2 and hVO2. Mean capillary hemoglobin O2 saturation (HbScO2) on the liver surface as well as HbScO2 frequency distributions, which mirror microcirculatory O2 availability, remained unchanged as well. Neither treatment influenced the ETX-induced derangements of cellular energy metabolism reflected by the progressive decrease in hepatic lactate uptake rate and increased hepatic venous lactate/pyruvate ratios. ETX nearly doubled the endogenous glucose production (EGP) rate, which was further increased with NOR, whereas L-NMMA nearly restored EGP to preshock levels. Nevertheless, despite the different mechanisms in maintaining blood pressure neither treatment influenced ETX-induced liver dysfunction.

Nitric oxide in septic shock

Septic shock is a major cause of death following trauma and is a persistent problem in surgical patients throughout the world. It is characterised by hypotension and vascular collapse, with a failure of the major organs within the body. The role of excessive nitric oxide (NO) production, following the cytokine-dependent induction of the inducible nitric oxide synthase (iNOS), in the development of septic shock is discussed. Emphasis is placed upon the signal-transduction process by which iNOS is induced and the role of NO in cellular energy dysfunction and the abnormal function of the cardiovascular system and liver during septic shock.

Endogenous nitric oxide is responsible for the early loss of P450 in cultured rat hepatocytes

Loss of P450 during the early hours of monolayer formation is known to be the more serious limitation of primary cultured hepatocytes as an adequate model for the study of drug metabolism, toxicity and P450 induction. This study reports that endogenous nitric oxide (NO) formation is activated shortly after isolation by the classical collagenase-based liver perfusion methods. Both rapid P450 loss and aerobic mitochondrial energy metabolism impairment -- with subsequent changes on glucose metabolism -- are directly related to the high local generation of the radical at this stage. These effects can be reverted by the sole addition of NO biosynthesis inhibitors during liver perfusion and early culture hours, which allows catalytically active P450 to be preserved at levels close to those of the intact liver.

Nitric oxide inhibits glycogen synthesis in isolated rat hepatocytes

There is increasing evidence for the existence of intrahepatic regulation of glucose metabolism by Kupffer cell products. Nitric oxide (NO) is known to inhibit gluconeogenic flux through pyruvate carboxylase and phosphoenolpyruvate carboxykinase. However, NO may also influence glucose metabolism at other levels. Using hepatocytes from fasted rats incubated with the NO-donor S-nitroso-N-acetylpenicillamine, we have now found that the synthesis of glycogen from glucose is even more sensitive to inhibition by NO than gluconeogenesis. Inhibition of glycogen production by NO was accompanied by a rise in intracellular glucose 6-phosphate and UDPglucose. Activity of glycogen synthase, as measured in extracts of hepatocytes after the cells had been exposed to NO, was decreased. Experiments with gel-filtered liver extracts revealed that inhibition of glycogen synthase was caused by an inhibitory effect of NO on the conversion of glycogen synthase b into glycogen synthase a.

Indomethacin stimulates glucose production in adults with uncomplicated falciparum malaria

In healthy subjects, basal hepatic glucose production is (partly) regulated by paracrine intrahepatic factors. It is unknown if these paracrine factors also influence basal glucose production in infectious diseases with increased glucose production. We compared the effects of 150 mg indomethacin (n = 9), a nonendocrine stimulator of glucose production in healthy adults, and placebo (n = 7) on hepatic glucose production in Vietnamese adults with uncomplicated falciparum malaria. Glucose production was measured by primed, continuous infusion of [6,6-2H2]glucose. After indomethacin, the plasma glucose concentration and glucose production increased in all subjects from 5.3 +/- 0.1 mmol/L to a maximum of 7.1 +/- 0.3 mmol/L (P < .05) and from 17.6 +/- 0.8 micromol x kg(-1) x min(-1) to a maximum of 26.2 +/- 2.5 micromol x kg(-1) x min(-1) (P < .05), respectively. In the control group, the plasma glucose concentration and glucose production declined gradually during 4 hours from 5.4 +/- 0.2 mmol/L to 5.1 +/- 0.1 mmol/L (P < .05) and from 17.1 +/- 0.8 micromol x kg(-1) x min(-1) to 15.1 +/- 1.0 micromol x kg(-1) x min(-1) (P < .05), respectively. There were no differences in plasma concentrations of insulin, counterregulatory hormones, or cytokines between the groups. We conclude that indomethacin administration results in a transient increase in glucose production in patients with uncomplicated falciparum malaria in the absence of changes in plasma concentrations of glucoregulatory hormones or cytokines. Thus, this study indicates that in uncomplicated falciparum malaria, the rate of basal hepatic glucose production is also regulated by paracrine intrahepatic factors.

The importance of nitric oxide in the cytokine-induced inhibition of glucose formation by cultured hepatocytes incubated with insulin, dexamethasone, and glucagon

Culturing hepatocytes with a combination of tumor necrosis factor alpha, interferon gamma, and interleukin 1 beta plus lipopolysaccharide resulted in an induction of nitric oxide synthase and concomitant inhibition of both hepatic gluconeogenesis and glycogenolysis. The inhibition of gluconeogenesis was evident both under basal conditions and in cells stimulated acutely with glucagon. The stimulation of glycogen mobilization by glucagon was largely prevented by the presence of the cytokines. Chronic 24-h treatment of the cells with glucagon attenuated the cytokine response on both glucose output and NO formation in the dexamethasone-treated cells. This effect was antagonized by insulin. Inclusion of 1 mM NG-nitro-L-arginine methyl ester or 0.5 mM NG-monomethyl-L-arginine in the incubation abolished the increase in NO2- plus NO3- induced by the cytokine mixture and partially reversed the inhibitory effects on glucose mobilization in the presence of either insulin or glucagon, confirming the involvement of NO. In contrast the NO synthase inhibitors had little effect on either gluconeogenesis or glycogenolysis in the presence of dexamethasone alone, indicating that NO is only partially responsible for the inhibitory action of the cytokines, and the extent of its involvement depends upon the influence of other hormonal factors on the pathways. The antioxidant trolox also suppressed the inhibition of glucose release by the cytokines under conditions where nitric oxide synthase inhibitors were ineffective, suggesting that both reactive oxygen intermediates and NO may act as mediators, the relative importance of each depending upon the metabolic status of the cell.

Nitric oxide donor NOR 3 inhibits ketogenesis from oleate in isolated rat hepatocytes by a cyclic GMP-independent mechanism

Studies were conducted to clarify the effects of nitric oxide donors NOR 3 ((+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide, FK409), SIN-1 (3-morpholinosydnonimine) and SNAP (S-nitroso-N-acetylpenicillamine) on the accumulation of cGMP and cAMP and Ca2+ mobilization as well as ketogenesis from oleate in isolated rat hepatocytes. NOR 3 caused inhibition of ketogenesis from oleate along with stimulation of cGMP accumulation in rat hepatocytes, whereas SIN-1 and SNAP exerted no effect on ketogenesis despite their marked stimulation of cGMP accumulation. Although the nitric oxide trapping agent, carboxy-PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), antagonized the stimulation by NOR 3 of cGMP accumulation, it failed to modulate the anti-ketogenic action of NOR 3. Furthermore, neither 8-bromoguanosine-3',5'-cyclic monophosphate nor N2,2'-O-dibutyrylguanosine-3',5'-cyclic monophosphate mimicked the anti-ketogenic action of NOR 3. It is concluded in the present study that NOR 3-induced inhibition of ketogenesis in rat hepatocytes is not mediated by cGMP. The present study revealed that the remaining structure of NOR 3 from which nitric oxide had been spontaneously released had no anti-ketogenic action. We first and clearly demonstrated that nitrite production was dramatically enhanced when NOR 3 was incubated in the presence of rat hepatocytes. The mechanism whereby NOR 3 inhibits ketogenesis in rat hepatocytes will be discussed.

Origin of endotoxemia influences the metabolic response to endotoxin in dogs

Different routes of endotoxin administration have been used to mimic inflammatory and metabolic responses observed during sepsis. Because the origin of endotoxemia may affect the reactions to endotoxin, we compared the induction of tumor necrosis factor (TNF), interleukin-6 (IL-6), hormones, and glucose production after endotoxin (1.0 microg/kg Escherichia coli 0111:B4) administration into a peripheral (n = 8) versus the portal (n = 8) vein in anesthetized dogs. Prior to endotoxin, a laparotomy was performed for cannulation of hepatic vessels. To evaluate the effects of surgery and anesthesia, we also studied the effects of peripheral endotoxin administration in six awake dogs. The rate of appearance of glucose was measured by primed continuous infusion of [6,6-2H2]glucose. In anesthetized dogs, arterial concentrations of TNF and IL-6 increased after endotoxin administration (P < 0.01 vs basal; NS between groups). Net hepatic TNF production was increased after endotoxin administration (peripheral vs portal endotoxin administration: 533 +/- 177 vs 2135 +/- 1127 ng/min, both P < 0.05 vs basal; NS between groups). Net hepatic IL-6 production was stimulated only after portal endotoxin delivery (from 86 +/- 129 to 4740 +/- 1899 ng/min, P < 0.05; NS between groups). Although there were no differences in neuroendocrine activation, portal endotoxin administration resulted in decreased glucose production compared with peripheral administration (13.6 +/- 0.9 vs 16.8 +/- 1.2 micromol/kg.min, P < 0. 05). In contrast to anesthetized dogs, endotoxin increased glucose production considerably in awake dogs from 13.8 +/- 1.2 to 24.2 +/- 3.2 micromol/kg.min (P < 0.05; P < 0.05 vs anesthetized dogs). The contribution of anesthesia and surgery increased the endotoxin-induced IL-6 response by approximately 350% compared with the effect of endotoxin in awake dogs (P < 0.01). In conclusion, there are no major differences in the responses to endotoxin between peripherally treated and portally treated dogs, except for differences in glucose production. Portal delivery compared with systemic delivery of endotoxin alters hepatic metabolism through nonendocrine mechanisms, reflected in decreased glucose production. The inflammatory, endocrine, and metabolic effects of endotoxin are altered by the combination of surgery and anesthesia.

Role of metabolic intermediates in lipopolysaccharide/cytokine-mediated production of nitric oxide in isolated mouse hepatocytes

Induction of nitric oxide synthase by bacterial endotoxin in vivo can be mimicked by treating cultured hepatocytes with a combination of lipopolysaccharide and cytokines (LPS/cytokines), but the role of LPS/cytokine-induced nitric oxide in hepatocyte glucose metabolism is ambiguous. In this study, intermediary metabolite effects on LPS/cytokine-induced hepatocyte nitric oxide synthesis were examined. Pyruvate, lactate, oxaloacetate, and fumarate all showed some inhibitory effects on hepatocyte nitric oxide synthesis. However, these metabolic intermediates could not improve the mitochondrial respiration of LPS/cytokine-treated hepatocytes. Phosphoenolpyruvate carboxykinase activity (or flux) relating factors, glucocorticoids and cAMP, also blocked LPS/cytokine-induced nitric oxide synthesis. Insulin was much less potent than cAMP and glucocorticoids, and phorbol ester did not show any effect on hepatocyte nitric oxide synthesis. These results suggest that LPS/cytokine-induced nitric oxide synthesis is related, at least partly, to phosphoenolpyruvate carboxykinase activity (or flux) in hepatocytes.

Inhibition of glycerol metabolism in hepatocytes isolated from endotoxic rats

Sepsis or endotoxaemia inhibits gluconeogenesis from various substrates, the main effect being related to a change in the phosphoenolpyruvate carboxykinase transcription rate. In addition, sepsis has been reported to affect the oxidative phosphorylation pathway. We have studied glycerol metabolism in hepatocytes isolated from rats fasted and injected 16 h previously with lipopolysaccharide from Escherichia coli. Endotoxin inhibited glycerol metabolism and led to a very large accumulation of glycerol 3-phosphate; the cytosolic reducing state was increased. Furthermore glycerol kinase activity was increased by 33% (P<<0.01). The respiratory rate of intact cells was significantly decreased by sepsis, with glycerol or octanoate as exogenous substrates, whereas oxidative phosphorylation (ATP-to-O ratio or respirations in state 4, state 3 and the oligomycin-insensitive state as well as the uncoupled state) was unchanged in permeabilized hepatocytes. Hence the effect on energy metabolism seems to be present only in intact hepatocytes. An additional important feature was the observation of a significant increase in cellular volume in cells from endotoxic animals, which might account for the alterations induced by sepsis.

Effects of carboxy-PTIO on systemic hemodynamics, liver energetics, and concentration of liver metabolites during endotoxic shock in rabbits: a 31P and 1H magnetic resonance spectroscopic study

OBJECTIVE

To investigate the effects of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), a nitric oxide scavenger, on the lipopolysaccharide-induced hypotension, hepatocellular dysfunction, and liver damage in endotoxic rabbits.

DESIGN

Experimental, comparative study.

SETTING

Laboratory of a university hospital.

SUBJECTS

Eighteen Japanese white rabbits (3.0 to 3.2 kg body weight) anesthetized with ketamine-xylazine were studied.

INTERVENTIONS

We randomly divided the rabbits into three groups: saline controls (group 1, n = 5); animals receiving lipopolysaccharide (400 micrograms/kg) alone (group 2, n = 8); and animals receiving lipopolysaccharide plus carboxy-PTIO at a rate of 0.17 mg/kg/min for 3 hrs (group 3, n = 5). Blood gases and mean arterial pressure (MAP) were monitored. In vivo phosphorus-31 magnetic resonance spectra were continuously obtained every 30 mins. In addition, the livers were sampled and underwent fractionation at 7 hrs after lipopolysaccharide administration. The hydrophilic and hydrophobic extracts from the livers were analyzed by in vitro hydrogen-1 and phosphorus-31 magnetic resonance spectroscopy.

MEASUREMENTS AND MAIN RESULTS

After the administration of lipopolysaccharide, the first phase of decrease in MAP within 30 mins was followed by partial recovery within the next 30 mins. In group 2, MAP started to decrease progressively within 180 mins after lipopolysaccharide administration (second phase) and decreased by 33% from the baseline value to 49 +/- 9 mm Hg at 420 mins. In contrast, the infusion of carboxy-PTIO significantly attenuated the second decrease in MAP (68 +/- 10 mm Hg, at 420 mins). In group 2, a slow and progressive decrease in adenosine triphosphate (ATP) and increase in inorganic phosphate concentrations occurred from 120 mins after lipopolysaccharide administration, and continued throughout the observation period. These changes were accompanied by a progressive decrease in intracellular pH. On the other hand, in group 3, there were no significant changes in ATP and inorganic phosphate concentrations compared with the controls from 120 to 360 mins after lipopolysaccharide administration. Moreover, restorations of both arterial and hepatocellular acidosis were observed in group 3. The differences of the degree of liver damage--as determined by the total amount of phospholipid, free fatty acids concentration, and membrane fluidity--were not significant among the three groups. Three of eight rabbits in group 2 died within 7 hrs, but no animal in the other two groups died during the study.

CONCLUSIONS

The results of this study indicate that the infusion of carboxy-PTIO: a) prevented the delayed hypotension associated with endotoxic shock in rabbits; b) returned the hepatocellular ATP concentrations nearly to the level of the controls and alleviated hepatocellular acidosis; c) normalized various hydrophilic metabolites, such as lactate and alanine in the liver; and d) did not exacerbate liver injury after the administration of lipopolysaccharide. These findings indicate that carboxy-PTIO, a nitric oxide scavenger, may have a positive vasopressor effect during hypodynamic septic shock without exacerbating liver injury.

Effects of reducing reagents and temperature on conversion of nitrite and nitrate to nitric oxide and detection of NO by chemiluminescence

To measure the concentration of nitrites and nitrates by chemiluminescence, we examined the efficiency of five reducing agents [V(III), Mo(VI) + Fe(II), NaI, Ti(III), and Cr(III)] to reduce nitrite (NO2−) and (or) nitrate (NO3−) to nitric oxide (NO). The effect of each reducing agent on the conversion of different amounts of NO2− and (or) NO3−(100–500 pmol, representing concentrations of 0.4 to 2 μmolar) to NO was determined at 20 °C for NO2− and at 80 °C for NO3−. The effect of temperature from 20 to 90 °C on the conversion of a fixed amount of NO2− or NO3− (400 pmol or 1.6 μmolar) to NO was also determined. These five reducing agents are similarly efficient for the conversion of NO2− to NO at 20 °C. V(III) and Mo(VI) + Fe(II) can completely reduce NO3− to NO at 80 °C. NaI and Cr(III) were unable to convert NO3− to NO. Increased temperature facilitated the conversion of NO3− to NO, rather than that of NO2− to NO. We evaluated the recovery of NO2− and NO3− from plasmas of pig and of dog. Recovery from plasma of both animals was reproducible and near quantitative.

Regulation of rat liver S-adenosylmethionine synthetase during septic shock: role of nitric oxide

We investigated the modulation of rat liver S-adenosylmethionine (SAM) synthetase in a model of acute sepsis. Our results show that animals treated with bacterial lipopolysaccharide experience a marked decrease in liver SAM synthetase activity. No changes were detected in the hepatic levels of SAM synthetase protein, suggesting that inactivation of the existing enzyme was the cause of the observed activity loss. Lipopolysaccharide treatment resulted in the expression of calcium-independent/cytokine-inducible nitric oxide (NO) synthase in liver and the accumulation in plasma of the NO-derived species nitrite and nitrate. NO implication in the in vivo regulation of SAM synthetase was evaluated in animals treated with the NO donor molecule 3-morpholinosydnonimine. The analysis of liver enzymatic activity, along with protein and messenger RNA levels yielded results similar to those obtained with lipopolysaccharide treatment. To assess directly the sensitivity of SAM synthetase to NO, the rat liver-purified high- and low-molecular weight forms of the enzyme were exposed to various doses of 3-morpholinosydnonimine and other NO donors such as S-nitroso-N-acetylpenicillamine, resulting in a dose-dependent inhibition of enzymatic activity. This effect was reversed by addition of the reducing agents beta-mercaptoethanol and glutathione. Finally, cysteine 121 was identified as the site of molecular interaction between NO and rat liver SAM synthetase that is responsible for the inhibition of the enzyme. To reach this conclusion, the 10 cysteine residues of the enzyme were changed to serine by site-directed mutagenesis, and the effect of NO on the various recombinant enzymes was measured.

3':5'-cyclic guanosine monophosphate (cGMP) potentiates the inositol 1,4,5-trisphosphate-evoked Ca2+ release in guinea-pig hepatocytes

The effect of cGMP on noradrenaline-induced intracellular Ca2+ mobilization was investigated in whole-cell voltage-clamped guinea-pig hepatocytes. Treatment of the cells with 8-Br-cGMP (1-500 microM) resulted in an increase in the sensitivity of the cells to noradrenaline and to inositol 1,4,5-trisphosphate (InsP3) photo-released from caged InsP3. The positive effect of 8-Br-cGMP on the Ca2+ release evoked by Ca(2+)-mobilizing agonists or InsP3 was blocked by a protein kinase G (PKG; cGMP-dependent protein kinase) inhibitor, the RP-8-(4-chlorophenylthio)guanosine 3':5'-monophosphorothioate. 8-Br-cGMP affected neither the basal InsP3 concentration nor the noradrenaline-induced production of InsP3. In permeabilized hepatocytes, the dose-response curve for InsP3-induced Ca2+ release was shifted to the left in the presence of 8-Br-cGMP. Furthermore, the treatment with 8-Br-cGMP did not affect the Ca2+ content of the InsP3-sensitive Ca2+ stores. These results indicate that intracellular cGMP potentiates the noradrenaline-induced Ca2+ response by enhancing Ca2+ release from the intracellular Ca2+ stores. We suggest that cGMP increases the apparent affinity of InsP3 receptors for InsP3 in guinea-pig hepatocytes probably by phosphorylation via the activation of PKG.

Effect of multiple cytokines plus bacterial endotoxin on glucose and nitric oxide production by cultured hepatocytes

Treatment of cultured hepatocytes with a combination of cytokines, including tumour necrosis factor-alpha, interferon-gamma and interleukin-1 beta, plus lipopolysaccharide resulted in a time-dependent induction of nitric oxide (NO) synthase (as measured by NO2- (+) NO3- production) and inhibition of hepatic gluconeogenesis and glycogen breakdown. The inhibition of glucose release was comparable with the observed following treatment of rats with lipopolysaccharide or treatment of isolated hepatocytes with artificial NO donors. In addition, this effect was also evident with all substrates tested that enter the gluconeogenic pathway below the level of phosphoenolpyruvate carboxykinase, suggesting that this combination of cytokines may underlie the inhibition of gluconeogenesis observed in endotoxic shock. The maximal inhibition of glucose output required the presence of all the cytokines plus lipopolysaccharide, whereas the induction of NO synthase was independent of the lipopolysaccharide when the cytokines were employed. Inclusion of interferon-gamma was essential to obtain a maximal response for either parameter. Inclusion of 1 mM N(G)-monomethyl-L-arginine in the incubation abolished the increase in NO2- (+) NO3- observed with the complete cytokine mixture and various combinations; however, it failed to prevent the inhibition in glucose output, indicating that mechanisms other than NO underlie the cytokine-induced inhibition of glucose release.