Characterization of nitric oxide dependent changes in carbohydrate hepatic metabolism during septic shock

Angiotensin II or epinephrine hemodynamic and metabolic responses in the liver of L-NAME induced hypertension and spontaneous hypertensive rats

AIM

To study hepatic vasoconstriction and glucose release induced by angiotensin (Ang)II or Epi in rats with pharmacological hypertension and spontaneously hypertensive rat (SHR).

METHODS

Isolated liver perfusion was performed following portal vein and vena cava cannulation; AngII or epinephrine (Epi) was injected in bolus and portal pressure monitored; glucose release was measured in perfusate aliquots.

RESULTS

The portal hypertensive response (PHR) and the glucose release induced by AngII of L-NAME were similar to normal rats (WIS). On the other hand, the PHR induced by Epi in L-NAME was higher whereas the glucose release was lower compared to WIS. Despite the similar glycogen content, glucose release induced by AngII was lower in SHR compared to Wistar-Kyoto rats although both PHR and glucose release induced by Epi in were similar.

CONCLUSION

AngII and Epi responses are altered in different ways in these hypertension models. Our results suggest that inhibition of NO production seems to be involved in the hepatic effects induced by Epi but not by AngII; the diminished glucose release induced by AngII in SHR is not related to glycogen content.

Hepatic morphological alterations, glycogen content and cytochrome P450 activities in rats treated chronically with N(omega)-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.

EFFECT OF NITRIC OXIDE ON THE HYPOGLYCAEMIC PHASE OF ENDOTOXAEMIA

BACKGROUND

Depletion of liver glycogen stores and subsequent hypoglycaemia is one of the unresolved features in endotoxaemia. The aim of this study was to elucidate the effect of L-arginine treatment on the glucose requirement and impending liver damage during the hypoglycaemic period of endotoxaemia.

METHODS

Sixty-three of 98 male Wistar rats were assigned equally to one of three groups and received saline as control, L-arginine as selective nitric oxide donor or N(G)-nitro-L-arginine methyl ester for non-selective inhibition of nitric oxide production 1 h before endotoxin injection. At 2, 4 and 6 h following endotoxin, blood and liver samples were collected. Plasma nitrite plus nitrate, glucose, insulin and glucagon concentrations and total liver-reduced glutathione were measured. Hepatocellular glycogen content and liver damage were assessed simultaneously by histological quantification. An additional seven rats were allocated to each group and subjected to i.v. glucose tolerance test during the hypoglycaemic period.

RESULTS

Increased levels of endogenousglutathione (P = 0.003) and excess nitric oxide (P = 0.002) apparently protected the liver from endotoxin-induced injury by preserving the optimum glucose consumption rate, insulin/glucagon ratio and liver glycogen in L-arginine-plus-endotoxin-treated group. Furthermore, expected hypoglycaemic period was not observed in these animals.

CONCLUSION

Exogenous L-arginine prevented the excessive liver glycogen release without inhibiting glucose consumption while decreasing hepatic injury during the expected hypoglycaemic phase of endotoxaemia.

Adjuvant-induced improvement of glucose intolerance in type 2 diabetic KK-Ay mice through interleukin-1 and tumor necrosis factor-alpha

We reported that administration of complete Freund's adjuvant (CFA) improved glucose tolerance test (GTT) results in obese diabetic KK-Ay mice. In this study, we investigated its mechanism. An injection with CFA remarkably improved GTT for more than a week in KK-Ay mice, although insulin response was not changed compared with saline controls. The hypoglycemic effect of insulin was significantly, but partially, potentiated in the CFA-treated mice compared with the controls, suggesting that CFA stimulated insulin-mediated and non-insulin-mediated glucose disposal. Improvement in the GTT with CFA was partially transferable to nontreated mice by peritoneal exudative cells, but not spleen or lymph node cells. Pretreatment with anti-interleukin (IL)-1 alpha and -1 beta antibodies or anti-tumor necrosis factor (TNF)-alpha antibody significantly abrogated the improvement in the GTT with CFA. The results indicate that CFA-induced improvement in glucose intolerance in KK-Ay mice was mediated at least by IL-1 and TNF-alpha.

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.

Effect of chronic bile duct obstruction and LPS upon targeting of naproxen to the liver using naproxen-albumin conjugate

Naproxen covalently linked to human serum albumin (NAP-HSA) is efficiently targeted to endothelial and Kupffer cells of the liver and may offer a new therapeutic approach in the treatment of liver disease associated with inflammatory processes. In the present investigation we explored the pharmacokinetic behaviour of targeted and non-targeted naproxen as well as the pharmacokinetic properties of the active metabolite, Naproxen lysine (Nap lysine), in rats rendered fibrotic by bile duct ligation (BDL) for 4 weeks. Furthermore, we studied the effect of endotoxemia, experimentally induced by intravenous injection of 800 microg/kg lipopolysaccaride (LPS) upon the pharmacokinetics of these agents in order to investigate the feasibility of targeting naproxen to non-parenchymal cells in the inflamed and fibrotic liver. Our studies demonstrate that liver disease altered the pharmacokinetic behaviour of the different naproxen compounds. Thus, initial plasma concentrations of NAP HSA and naproxen were markedly lower in BDL rats accompanied by an increase of the volume of distribution during the terminal elimination phase (Vd(beta) BDL vs control 114 +/- 63 vs 50 +/- 7 and 202 +/- 24 vs 115 +/- 11 ml/kg for naproxen and NAP-HSA, respectively). After injection of LPS, no significant change in the pharmacokinetics of NAP-HSA was found whereas the naproxen treated control animals showed an increase in the terminal volume of distribution (176 +/- 34 vs 115 +/- 11 ml/kg) as well as an elevation of the plasma half-life (171 +/- 27 vs 116 +/- 14 min). The feasibility of targeting naproxen to the chronically diseased liver could be clearly demonstrated: 15 min after administration of the conjugate 46% and 55% of the administered dose was found in the liver of CTR and BDL rats, whereas after injection of free naproxen only 5% and 12% of the dose was detected in liver tissue, respectively. We conclude that targeting albumin-linked naproxen to non-parenchymal cells in the liver is still feasible under the pathological conditions induced in the present study. Liver fibrosis induced significant alterations in the pharmacokinetic behaviour of the studied compounds.

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.

Effects of inhibitors of nitric oxide synthase on isolated uteri of fasting rats

The effects of inhibitors of nitric oxide synthase on the glucose metabolism of uteri isolated from 4-day underfed rats were studied. In control rats receiving normal feeding, the addition of indomethacin (5 x 10(-6) M); acetyl salicylic acid (10(-4) M); 400 microM of N(G)methyl-L-arginine, (L-NMMA) or 400 microM of sodium nitroprusside (SNP), does not modify the production of 14CO2 from U14C-glucose. On the contrary, in fasted rat uteri, indomethacin increases glucose oxidation significantly, while acetyl salicylic acid does not alter it. Also, the addition of L-NMMA has no effect. In another group of experiments, in the preparations containing indomethacin of uteri isolated from underfed rats, the addition of L-NMMA significantly changes the effect of indomethacin. Another inhibitor of nitric oxide synthase, N(omega)nitro-L-arginine methyl ester (L-NAME), or hemoglobin (2 microg ml(-1)) a nitric oxide scavenger have the same effects while N(omega)nitro arginine-D-methyl ester (D-NAME) does not. However (SNP), a nitric oxide donor, does not alter the production of 14CO2 in uteri isolated from fasted rats. These results show that in underfed rats, indomethacin increases glucose oxidation independently from its inhibiting effect on cyclooxygenase. Specific inhibitors of nitric oxide synthase can reverse this effect.

Increased nitric oxide production in the liver in the perioperative period of partial hepatectomy with Pringle's maneuver

BACKGROUND/AIMS

There is no evidence that nitric oxide is produced in the liver during ischemia/reperfusion injury. This study examined the production of nitric oxide and inducible nitric oxide synthase in patients undergoing partial hepatectomy.

METHODS

Twenty patients undergoing partial hepatectomy with only Pringle's maneuver were included. Peripheral blood was taken 1 day before the operation, during the operation (just after laparotomy and the first and last Pringle's maneuver) and 1 and 3 days after the operation, for measurement of plasma nitrate/nitrite, endotoxin and cytokine levels. Blood was also sampled from hepatic veins after Pringle's maneuver. Two liver specimens were taken from each patient, one before ischemia and one after partial hepatectomy, for the detection of inducible nitric oxide synthase.

RESULTS

Average nitrate reached a maximum (33.5+/-3.4 micromol/l) after the final clamp (hepatic venous level). The increase in nitrate level during the operation correlated with the total duration of clamping. Endotoxin and interleukin-6 levels increased in a similar manner to nitrate levels, but tumor necrosis factor-alpha and interleukin-1 beta levels did not. In liver specimens taken after partial hepatectomy from patients, inducible nitric oxide synthase mRNA and protein were detected.

CONCLUSIONS

Nitric oxide was produced in livers during ischemia/reperfusion injury and inducible nitric oxide synthase was involved in nitric oxide production.

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.

Beneficial effects of dantrolene on lipopolysaccharide-induced haemodynamic alterations in rats and mortality in mice

We investigated the effect of dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum, on the induction of nitric oxide (NO) synthase II by bacterial endotoxin (lipopolysaccharide) in the anaesthetised rat and on survival in a murine model of severe endotoxaemia. Injection of lipopolysaccharide (i) induced biphasic changes of rectal temperature and blood glucose: an initial increased phase (< 180 min after injection of lipopolysaccharide) followed by a decreased phase (at 240-360 min), (ii) caused a fall in mean arterial blood pressure from 115 +/- 3 mmHg (time 0) to 83 +/- 6 mmHg at 360 min, (iii) resulted in a substantial hyporeactivity to noradrenaline (1 microg/kg i.v.), (iv) raised plasma nitrate (an indicator of NO formation) in a time-dependent manner, (v) elicited a significant increase in NO synthase II activity in the lung and (vi) caused a 80% lethality (in mice). Pretreatment of animals with dantrolene not only attenuated the delayed circulatory failure, but also prevented the overproduction of NO and the induction of NO synthase II caused by lipopolysaccharide in the rat, and improved survival in a murine model of severe endotoxaemia. Thus, dantrolene has beneficial haemodynamic effects in animals with endotoxin shock. We propose that a decrease of free cytosolic Ca2+ levels plays an important role in the prevention of NO synthase II induction.

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.

Insoluble glycogen, a metabolizable internal adsorbent, decreases the lethality of endotoxin shock in rats

Insoluble glycogen is an enzymatically modified form of naturally occurring soluble glycogen with a great adsorbing capacity. It can be metabolized by phagocytes to glucose. In this study we used insoluble glycogen intravenously in the experimental endotoxin shock of rats. Wistar male rats were sensitized to endotoxin by Pb acetate. The survival of rats were compared in groups of animals endotoxin shock treated and non-treated with insoluble glycogen. Furthermore, we have determined in vitro the binding capacity of insoluble glycogen for endotoxin, tumour necrosis factor alpha, interleukin-1 and secretable phospholipase A₂. Use of 10 mg/kg dose of insoluble glycogen could completely prevent the lethality of shock induced by LD₅₀ quantity of endotoxin in rats. All animals treated survived. Insoluble glycogen is a form of ‘metabolizable internal adsorbents’. It can potentially be used for treatment of septic shock.