Changes in rat liver mRNA for alpha-1-acid-glycoprotein, apolipoprotein E, apolipoprotein B and beta-actin after mouse recombinant tumor necrosis factor injection

The immunology of sickness metabolism

Everyone knows that an infection can make you feel sick. Although we perceive infection-induced changes in metabolism as a pathology, they are a part of a carefully regulated process that depends on tissue-specific interactions between the immune system and organs involved in the regulation of systemic homeostasis. Immune-mediated changes in homeostatic parameters lead to altered production and uptake of nutrients in circulation, which modifies the metabolic rate of key organs. This is what we experience as being sick. The purpose of sickness metabolism is to generate a metabolic environment in which the body is optimally able to fight infection while denying vital nutrients for the replication of pathogens. Sickness metabolism depends on tissue-specific immune cells, which mediate responses tailored to the nature and magnitude of the threat. As an infection increases in severity, so do the number and type of immune cells involved and the level to which organs are affected, which dictates the degree to which we feel sick. Interestingly, many alterations associated with metabolic disease appear to overlap with immune-mediated changes observed following infection. Targeting processes involving tissue-specific interactions between activated immune cells and metabolic organs therefore holds great potential for treating both people with severe infection and those with metabolic disease. In this review, we will discuss how the immune system communicates in situ with organs involved in the regulation of homeostasis and how this communication is impacted by infection.

IL-1beta and IL-6 modulate apolipoprotein E gene expression in rat hepatocyte primary culture

Incubation of rat hepatocytes in primary culture with IL-1β at a concentration of 2.5 units/ml resulted in an increase (+80%) in the amount of apoE mRNA without any effect upon apoE synthesis. IL-6 at a low concentration (10 units/ml) induced a decrease (−35%) in the amount of apoE mRNA, but increased apoE synthesis (+28%). No effect was observed with higher concentrations of IL-1β (10 units/ml) or IL-6 (100 units/ml). These results suggest that inflammatory cytokines IL-1β and IL-6 modulate the expression of apoE gene in cultured rat hepatocytes, at a concentration that does not induce the acute phase response.

Escherichia coli sepsis increases hepatic apolipoprotein B secretion by inhibiting degradation

Sepsis leads to hypertriglyceridemia in both humans and animals. Previously, we reported that plasma very low density lipoprotein apolipoprotein (apo) B and hepatic production of apoB increased during Escherichia coli sepsis. The present experiments were undertaken to determine whether the altered hepatic secretion of apoB was associated with an increase in synthesis or a decrease in degradation rate. Sepsis was induced in male, Lewis rats (225-275 g) by intravenous injection of 3.8 x 10(8) live E. coli colonies/100 g body. Twenty-four hours later rats were sacrificed, and primary hepatocytes were prepared and incubated overnight with 35S-methionine. Hepatocytes from E. coli-treated rats secreted twice as much apoB-48 and total apoB than the hepatocytes from control rats. Escherichia coil sepsis increased cellular triglyceride mass by 86%, which was due to a stimulation in triglyceride synthesis from newly synthesized fatty acids, measured by 3H2O incorporation into triglycerides. The apoB synthesis rate, apoB mRNA levels, and apoB mRNA editing were not altered during E. coil sepsis. The pulse-chase experiments showed that the rate of apoB degradation decreased in E. coli-treated rats. These findings demonstrate that the secretion of apoB is regulated posttranslationally during E. coli sepsis by decreasing the degradation of newly synthesized apoB, which contributes to the development of hypertriglyceridemia.

Differential expression of inducible nitric oxide synthase messenger RNA along the longitudinal and crypt-villus axes of the intestine in endotoxemic rats

OBJECTIVES

To characterize the mechanisms leading to excessive production of nitric oxide within the gut as a consequence of endotoxemia. We sought to: a) determine the time course of inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) expression in the intestine after challenging rats with lipopolysaccharide (LPS); and b) investigate whether there is differential expression of iNOS in enterocytes along the longitudinal or crypt-villus axes of the intestine in rats after LPS administration.

DESIGN

Prospective, randomized, unblinded study.

SETTING

Research laboratories at a large university-affiliated medical center.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

At T = 0 hr, rats were injected with O111:B4 Escherichia coli LPS (5 mg/kg) or a similar volume of the saline vehicle. At various time points thereafter, samples of duodenum, jejunum, ileum, colon, and liver were harvested for subsequent extraction of RNA. In some cases, populations of enterocytes enriched in either crypt or villus cells were harvested from the ileum. In some studies, rats were injected with cycloheximide (25 mg i.p.) 15 mins before being challenged with LPS or dexamethasone (2 mg i.p.) 30 mins before being injected with LPS.

MEASUREMENTS AND MAIN RESULTS

iNOS mRNA was undetectable in ileal tissue from rats under basal conditions, but was evident by T = 1 hr and was maximal at T = 2 hrs after injection of LPS. Thereafter, ileal iNOS mRNA concentrations decreased and were undetectable again at T = 24 hrs. At T = 2 hrs after LPS injection, there was marked expression of iNOS mRNA in the ileum, whereas much lower concentrations of iNOS mRNA were detected in the jejunum and colon, and no iNOS mRNA was detected in the duodenum. At T = 3 hrs after LPS injection, expression of iNOS mRNA was up-regulated in both villus and crypt cells, although LPS-induced iNOS mRNA was more prominent in the former than the latter cell type. Pretreatment of rats with dexamethasone virtually abrogated the expression of iNOS mRNA in ileal samples obtained 3 hrs after the injection of LPS. Prior treatment of rats with the protein synthesis inhibitor, cycloheximide, also blunted LPS-induced iNOS mRNA expression.

CONCLUSIONS

LPS-induced iNOS expression is differentially regulated along both the longitudinal and crypt villus axes of the intestinal mucosa, being most prominent in the villus cells of the ileum. LPS-induced iNOS expression is blunted by pretreating rats with dexamethasone or cycloheximide. The latter finding suggests that LPS-induced expression of iNOS mRNA in the gut requires new protein synthesis. Differential regulation of nitric oxide production along the longitudinal and crypt-villus axes of the gut may be a determinant of the pattern of sepsis-induced intestinal damage.

LPS and cytokines regulate extra hepatic mRNA levels of apolipoproteins during the acute phase response in Syrian hamsters

Altered hepatic expression of apolipoproteins occurs during the acute phase response. Here we examined whether the acute phase response alters extra hepatic expression of apolipoproteins. Syrian hamsters were injected with endotoxin (LPS), tumor necrosis factor (TNF), interleukin (IL)-1, or the combination of TNF + IL-1 and mRNAs for serum amyloid A (apoSAA), apolipoprotein (apo) J, apo E. apo A-I, and apo D, were analyzed. LPS increased mRNA levels for apoSAA in all tissues examined. LPS and TNF + IL-1 increased mRNA levels for apo J in kidney, heart, stomach, intestine, and muscle. Individually, TNF and IL-1 were less potent than the combination of the two cytokines. LPS decreased mRNA levels for apo E in all tissues, except for mid and distal intestine. TNF and IL-1 were less effective than LPS. LPS, TNF + IL-1 and TNF decreased mRNA levels for apo A-I in duodenum. mRNA for apo D decreased in heart, were unchanged in brain and increased in muscle, following LPS. The widespread extra hepatic regulation of the apolipoproteins during the acute phase response may be important for the alterations in lipid metabolism that occur during infection and inflammation as well as the immune response.

Effect of acute phase response on phenytoin metabolism in neurotrauma patients

The purpose of this prospective study was to correlate measures of the acute phase response, associated therapeutic interventions, and other clinical variables with the process of altered drug metabolism previously observed in patients with severe neurotrauma. Nine patients with severe head injury (Glasgow Coma Scale < or = 8) requiring intravenous phenytoin were included in the study. A loading dose of phenytoin was followed by daily maintenance doses. Serial blood samples were taken after the loading dose and every even-numbered study day for 10 to 14 days for measurement of total and unbound concentrations of phenytoin, interleukin-1 beta, interleukin-6 (IL-6), tumor necrosis factor alpha, alpha 1-acid-glycoprotein, C-reactive protein, and albumin. Time-invariant and time-variant Michaelis-Menten models were fit to the phenytoin concentration-time data. Protein intake was closely monitored. The mean (+/- SEM) unbound fraction of phenytoin increased from 0.17 +/- 0.02 on day 1 to 0.24 +/- 0.04 on day 10 (P < 0.05). The time-variant model was superior in describing the concentration-time data of unbound phenytoin in eight of nine patients. Mean (+/- SEM) pharmacokinetic parameter estimates for unbound phenytoin were: Vmax delta = 605 +/- 92 mg/day, VmaxB = 149 +/- 26.3 mg/day, K(ind) = 0.013 +/- 0.004 hr-1. Interleukin-6 was the only cytokine with significant concentration changes over time; it was inversely correlated with Vmax,t. Peak concentrations of interleukin-6 also proved to be inversely correlated with VmaxB. The daily amount of protein administered was significantly correlated with Vmax,t. Significant alterations in the metabolism of phenytoin occur after severe neurotrauma. The etiology of these changes is probably multifaceted. These results suggest that low initial phenytoin Vmax may be explained by the presence of interleukin-6. An increase in oxidative metabolism that correlated with nutritional protein administration was observed later in these patients.

The rat, a useful animal model for pharmacological studies on apolipoprotein E

Apolipoprotein E is a major protein component of lipoproteins and plays an important role in cholesterol transport. The structure of the gene and the polymorphism of apolipoprotein E have been studied in human and rat, which show similar structures of apolipoprotein E. The wide tissue distribution of this apolipoprotein suggests diverse functions like cholesterol distribution between cells, intracellular cholesterol trafficking and tissue reparation. Nevertheless, the presence of apolipoprotein E in atherosclerotic plaques and amyloid deposits in brains of Alzheimer's disease patients also indicate pathologic functions staying misunderstood. The aim of this paper is to review the present knowledge on the distribution of apolipoprotein E between the different organs with the related functions and to make an overview of the implications of this apolipoprotein is physiological events and pathological states in the rat. The rat is widely used for drug metabolism studies. Its serum levels are 5-10 times higher than in human and thus this animal provides an useful pharmacological model to elucidate the functions of apo E.

Upregulation of low density lipoprotein receptor activity by tumor necrosis factor, a process independent of tumor necrosis factor-induced lipid synthesis and secretion

It has been shown that tumor necrosis factor (TNF) rapidly upregulates expression of the low density lipoprotein (LDL) receptors on Hep G2 cells and acutely stimulates hepatic lipid synthesis and secretion in vivo. It may thus be possible that TNF-induced expression of LDL receptors is secondary to a decrease in cellular cholesterol content caused by TNF-stimulated lipid secretion. In order to know whether TNF upregulates LDL receptors by depletion of the cellular cholesterol content, the present experiments were designed to study the temporal relationship between TNF-stimulated expression of LDL receptor activity and TNF-induced changes in lipid synthesis and secretion in an in vitro setting by using Hep G2 cells (a highly differentiated human hepatoma cell line) as a hepatocyte model. Hep G2 cells were incubated with TNF (usually 2.5 nmol/L) for certain periods, and LDL receptor activity was evaluated by measuring [125I]LDL binding at 4 degrees C; lipid synthesis and secretion were assayed by measuring [3H]glycerol incorporation into triglycerides and phospholipids as well as [14C]acetate incorporation into cholesterol. We found that a 30-h exposure of the cells to TNF was needed for the effect of TNF to be seen on lipid synthesis and secretion as measured by incorporation of [3H]glycerol into triglycerides and phospholipids, whereas TNF rapidly (in several hours) upregulated LDL receptor activity. TNF stimulated triglyceride synthesis, but did not stimulate phospholipid synthesis. On the other hand, TNF stimulated phospholipid secretion, but did not stimulate triglyceride secretion. Exposure of the cells to TNF for 16 or 24 h neither decreased cholesterol synthesis nor stimulated cholesterol secretion as measured by [14C]acetate incorporation into cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin and cytokines increase hepatic messenger RNA levels and serum concentrations of apolipoprotein J (clusterin) in Syrian hamsters

Infection and inflammation induce alterations in hepatic synthesis and plasma concentrations of the acute phase proteins. Our results show that apolipoprotein (apo) J is a positive acute phase protein. Endotoxin (LPS), tumor necrosis factor (TNF), and interleukin (IL)-1 increased hepatic mRNA and serum protein levels of apo J in Syrian hamsters. Hepatic apo J mRNA levels increased 10- to 15-fold with doses of LPS from 0.1 to 100 micrograms/100 g body weight within 4 h and were elevated for > or = 24 h. Serum apo J concentrations were significantly increased by 16 h and further elevated to 3.3 times that of control, 24 h after LPS administration. Serum apo J was associated with high density lipoprotein and increased fivefold in this fraction, after LPS administration. Hepatic apo J mRNA levels increased 3.5- and 4.6-fold, with TNF and IL-1, respectively, and 8.2-fold with a combination of TNF and IL-1. Serum apo J concentrations were increased 2.3-fold by TNF, 79% by IL-1, and 2.9-fold with a combination of TNF and IL-1. These results demonstrate that apo J is a positive acute phase protein.

Extent of the acute phase response in fulminant hepatic failure

The extent of the acute phase response and the relation between acute phase proteins and cytokines in plasma was investigated in 50 patients with fulminant hepatic failure. On admission, C reactive protein was significantly higher in fulminant hepatic failure (median: 12.4 micrograms/ml, range:0.2-112 micrograms/ml) than in 20 controls (median: 0.8 microgram/ml, range: 0.3-2.9 micrograms/ml, p < 0.001). Serial measurements showed that plasma C reactive protein increased daily after admission until day 5, the end of the study period. alpha 1-Antitrypsin (AAT) (median: 69.1%, range: 27.5-124%) and fibrinogen (median: 1.10 g/l, range: 0-2.82 g/l) were significantly lower in fulminant hepatic failure on admission than in controls (AAT: median: 126%, range: 75.4-149%; fibrinogen: median 2.48 g/l, range: 1.82-3.39 g/l, p < 0.001) and did not change subsequently. Both AAT and fibrinogen were maintained at significantly higher concentrations in survivors than in those who did not. Bacterial infection occurred in 23 patients during the course of fulminant hepatic failure, but did not influence the concentrations of these three proteins. Interleukin 6 was significantly higher in fulminant hepatic failure (median: 21.2 pg/ml, range: 0-871 pg/ml) than in controls (median: 2.4 pg/ml, range: 1.5-8.2 pg/ml, p < 0.001). There was a significant correlation between interleukin 6 and the C reactive protein concentrations in patients with viral hepatitis on admission and in all patients 48 hours later, consistent with other evidence that interleukin 6 stimulates synthesis of this acute phase protein.

Cytokines decrease apolipoprotein accumulation in medium from Hep G2 cells

Cytokines, important biochemical mediators of inflammation, cause a rapid fall in the plasma concentration of cholesterol in vivo. One mechanism by which cytokines may cause acquired hypocholesterolemia is by decreasing the hepatic synthesis and secretion of apolipoproteins. To test this hypothesis, we incubated Hep G2 cells with human recombinant tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6. Each of the cytokines resulted in a dose-related reduction in the concentrations of apolipoprotein (apo) A-I, apoB, and lecithin:cholesterol acyltransferase (LCAT) activity in the medium after 24 hours of incubation. The effect of cytokines on apolipoprotein accumulation was not affected by preincubation of Hep G2 cells with fatty acids. Cytokines decreased the concentration of cellular apoA-I mRNA in a dose-related fashion but did not affect cellular concentrations of apoB mRNA. The concentrations of triglyceride and cholesterol were also reduced in the medium of cells incubated with cytokines. Total cell sterol synthesis rates were calculated by [14C]acetate incorporation. Cells incubated with interleukin-6 had a 31% increase in sterol synthesis rate but a 41% decrease in sterol secretion. These data suggest that these cytokines can decrease the hepatic synthesis and/or secretion of apolipoproteins and that this may explain, in part, the acquired hypocholesterolemia seen during acute and chronic inflammation.

TNF-alpha induces endothelial cell F-actin depolymerization, new actin synthesis, and barrier dysfunction

Tumor necrosis factor-alpha (TNF-alpha) influences pulmonary vascular endothelial barrier function in vitro. We studied whether recombinant TNF-alpha (rTNF-alpha) regulates endothelial barrier function through actin reorganization. Postconfluent bovine pulmonary artery endothelial cell monolayers were exposed to human rTNF-alpha (1,000 U/ml) and evaluated for 1) transendothelial [14C]albumin flux, 2) F-actin organization with fluorescence microscopy, 3) F-actin quantitation by spectrofluorometry, and 4) monomeric G-actin levels by the deoxyribonuclease I inhibition assay. rTNF-alpha induced increments in [14C]albumin flux (P < 0.04) and intercellular gap formation at > or = 2-6 h. During this same time, the endothelial F-actin pool decreased (P = 0.0064), with reciprocal increases in the G-actin pool (P < 0.0001). Prior F-actin stabilization with phallicidin protected against the rTNF-alpha-induced increments in G-actin (P < 0.002) as well as changes in barrier function (P < 0.01). Prior protein synthesis inhibition enhanced the rTNF-alpha-induced decrement in F-actin (P < 0.0001), blunted the G-actin increment (P < 0.002), and increased rTNF-alpha-induced changes in endothelial barrier function (P < 0.003). Therefore, rTNF-alpha induces pulmonary vascular endothelial F-actin depolymerization, intercellular gap formation, and barrier dysfunction. rTNF-alpha also increased total actin (P < 0.02) and new actin synthesis (P < 0.002), which may be a compensatory endothelial cell response to rTNF-alpha-induced F-actin depolymerization.

Lipid synthesis and apolipoprotein gene expression in hepatocytes in primary culture from (puromycin-induced) nephrotic rats

Primary culture of hepatocytes from puromycin aminonucleoside-induced nephrotic rats were used to discriminate between the hepatic and extra-hepatic contribution to the hyperlipidemia occurring in the nephrotic syndrome. De novo lipogenesis and utilization of exogenous fatty acids were not modified in nephrotic hepatocytes as compared to controls. In contrast 2.2 and 5.3-fold more triacylglycerol and phospholipids were secreted respectively by nephrotic hepatocytes than by controls. Triacylglycerol overproduction was not associated with an increase either in apo B mRNA level or in apo B synthesis or secretion measured by [35S]-methionine incorporation and immunoprecipitation. We also observed a significant increase in apo AI and apo E synthesis and secretion by nephrotic hepatocytes. This increase was correlated with a greater amount of apo AI and apo E mRNA than in controls. The overproduction of apo AI and apo E by nephrotic hepatocytes might intervene in the clearance of plasma lipoproteins and the redistribution of plasma cholesterol.

Recombinant human interleukin 1 beta and tumor necrosis factor affect glycosylation of serum alpha 1-acid glycoprotein in rats

Serum concentration and glycosylation of rat alpha 1-acid glycoprotein (alpha 1-AGP) were evaluated after the in vivo administration of recombinant human interleukin-1 beta (rhIL-1 beta) and tumor necrosis factor alpha (rhTNF-alpha), alone or associated. The effect of LPS and turpentine was also studied. In all models, serum alpha 1-AGP concentrations were increased and glycosylation was altered. The alpha 1-AGP levels reached 1.8 g/liter with cytokines alone, 2.1 g/liter with cytokines associated or LPS, and 3.4 g/liter with turpentine. Analysis by concanavalin A (Con A) affinoimmunoelectrophoresis (CAIE) revealed that the relative proportion of Con A unreactive form always decreased whatever the inducing agent. On the other hand, the resulting effect on the concentrations of Con A unreactive alpha 1-AGP concentrations was an increase with cytokines alone or LPS and a decrease with cytokines associated or turpentine. These results suggest a dissociation between the alteration in the level of alpha 1-AGP synthesis and in the pattern of its glycosylation in the various inflammatory models.

Modifications of hepatic alpha-1-acid glycoprotein and albumin gene expression in rats treated with phenobarbital

The serum level of alpha 1-acid glycoprotein (alpha 1-AGP) is significantly increased in various animal species by treatment with cytokines, glucocorticoids and phenobarbital. The mechanisms responsible for the cytokine-induced and glucocorticoid-induced increases are now well documented, but not so in the case of phenobarbital. The main purpose of this study was to assess whether phenobarbital acts on alpha 1-AGP synthesis in the liver at the transcriptional or translational level. Male Dark Agouti rats received 70 mg phenobarbital/kg daily for 7 days. The analysis of total hepatic RNA showed that a single injection of phenobarbital induced an 11-fold increase in phenobarbital-dependent cytochrome P450IIB mRNA, whereas seven injections of phenobarbital were required to induce a maximum 5.5-fold increase in alpha 1-AGP mRNA. Concurrently, the transcription rate of the alpha 1-AGP gene rose 3.5-fold. Hepatocytes isolated after the seventh injection of phenobarbital showed a threefold increased capacity to secrete alpha 1-AGP, corresponding to a 3.2-fold increased alpha 1-AGP mRNA content in the liver. In conditions in which its effect on the induction of alpha 1-AGP synthesis was maximum, phenobarbital caused a 30% reduction in liver albumin mRNA and in albumin secretion by isolated hepatocytes, resulting from a 60-70% reduction in the rate of transcription of the albumin gene measured in isolated nuclei. We conclude that the effect of phenobarbital on alpha 1-AGP and albumin gene expression occurs at the transcriptional rather than the translational level.

Effects of cytokines on the liver

Cytokines are essential for the communication not only between the liver and extrahepatic sites but also within the liver itself. Cytokines regulate the intermediary metabolism of amino acids, proteins, carbohydrates, lipids and minerals. Cytokines partially interact with classical hormones such as glucocorticoids, resulting in a complex network of mutual control. Since many cytokines exert growth factor-like activities in addition to their specific proinflammatory effects, the distinction between cytokines and growth factors is somewhat artificial. The liver is an important site of synthesis and the major clearance organ for several cytokines. In liver disease, cytokines are involved in the onset of intrahepatic immune responses (e.g., during viral hepatitis), in liver regeneration (e.g., after partial hepatectomy) and in the fibrotic and cirrhotic transformation of the liver such as chronic chemical injury or viral infection. Further studies of cytokine actions may lead to a better understanding of liver diseases and to the development of new immunomodulating therapeutic options.