The role of tumor necrosis factor-alpha in acute endotoxin-induced hepatotoxicity in ethanol-fed rats

An in vivo model of ethanol ingestion in rats was used to examine tumor necrosis factor-alpha production after intravenous injection with lipopolysaccharide or saline solution. Four groups of 125-gm male Sprague-Dawley rats were given one of the following four diets: liquid ethanol diet (ethanol, 36% of calories), liquid control diet, chow ad libitum or control liquid diet pair-fed to match calories consumed by ethanol-fed rats. After 6 wk of diet, all rats were injected with 1 mg/kg lipopolysaccharide or 0.9% saline. AST concentrations in the ethanol-lipopolysaccharide group (388 +/- 54 U/ml) were significantly increased compared with those in control-saline, ethanol-saline and control-lipopolysaccharide groups (166 +/- 23, 166 +/- 18, 219 +/- 47; p < 0.01). Serum tumor necrosis factor-alpha concentrations for the ethanol-LPS group (3,990 +/- 624 pg/ml) were increased compared with those in control-saline (87 +/- 18), ethanol-saline (68 +/- 24) and control-LPS (695 +/- 165) groups (p < 0.001). A strong correlation was seen between serum tumor necrosis factor-alpha and AST concentrations (r = 0.91, p < 0.001). Treatment with lipopolysaccharide also increased transcriptional levels of tumor necrosis factor-alpha-specific mRNA from hepatic Kupffer cells isolated from rats fed the long-term ethanol diet by a factor of 3 compared with control rats. From these data, we conclude that long-term ethanol administration sensitized hepatic Kupffer cells to secrete high levels of tumor necrosis factor-alpha after lipopolysaccharide injection. Increased serum tumor necrosis factor-alpha concentrations correlated directly with increased levels of serum transaminase, which may have reflected hepatic injury.

The lysosomal hydrolases in the rat pancreas after maximal or supramaximal stimulation with cerulein

The decompartmentation of lysosomal compartment in pancreatic acinar cells with consecutive activation of zymogens might play an important role as a "trigger mechanism" in acute pancreatitis. The admixture of lysosomal hydrolases to secretory enzymes in pancreatic juice was found, but their role in pancreatic secretion remains obscure. The aim of the present study was to assess the fragility of pancreatic lysosomal structure after maximal (optimal) or supramaximal stimulation of rats with cerulein during 3, 6, 12 h, and after recovery. In the mitochondrial-lysosomal (M-L) and in the supernatant (S) of pancreases free (F) total (T), and fractional free (%F/T) activities of beta-glucuronidase (beta G), acid phosphatase (AcP), cathepsins (Cs), and beta-N-acetyl-hexosaminidase (NAH) were estimated. In edematous pancreatitis following supramaximal stimulation with cerulein, a significant increase of %F/T of beta G in whole homogenate began at 6 h of hyperstimulation in comparison to the control (93 vs 42% p < 0.01). This increment persisted until 12 h of hyperstimulation and declined after 24 and 48 h of recovery to 67-69%. The changes of %F/T of beta G in M-L followed those in whole homogenate, and additionally the increase free activity in S after 6 h of hyperstimulation and after 24 h recovery occurred. The respective activities of other hydrolases showed a similar pattern of changes. It is of interest that fragility of lysosomal membranes increases significantly also after maximal stimulation when inflammatory changes were absent. Our results suggest that the increase of lysosomal fragility of the pancreas is most unlikely pathological in itself, but also occurs during stimulated pancreatic secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol administration alters the proteolytic activity of hepatic lysosomes

Protein accumulation in liver cells contributes to alcohol-induced hepatomegaly and is the result of an ethanol-elicited deceleration of protein catabolism (Alcohol Clin Exp Res 13:49, 1989). Because lysosomes are active in the degradation of most hepatic proteins, the present studies were conducted to determine whether ethanol administration altered the proteolytic activities of partially purified hepatic lysosomes. Rats were fed liquid diets containing either ethanol (36% of calories) or isocaloric maltodextrin for periods of 2-34 days. Prior to death, all animals were injected with [3H]leucine to label hepatic proteins. Rats subjected to even brief periods of ethanol feeding (2-8 days) exhibited significant hepatomegaly and hepatic protein accumulation compared with pair-fed control animals. Crude liver homogenates and isolated lysosomal-mitochondrial and cytosolic subfractions were incubated at 37 degrees C, and the acid-soluble radioactivity generated during incubation was measured as an index of proteolysis. At neutral pH, in vitro protein breakdown in incubated liver homogenates and subcellular fractions from control and ethanol-fed rats did not differ significantly. The extent of protein hydrolysis increased when samples were incubated at pH 5.5, which approximates the pH optimum for catalysis by lysosomal acid proteases. Under the latter conditions, partially purified lysosomes from control animals had 2-fold higher levels of proteolysis than corresponding fractions from ethanol-fed rats. The difference in proteolytic capacity appeared to be related to a lower latency and a higher degree of fragility of lysosomes from ethanol-fed rats at the acidic pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of platelet-activating factor and its 1O-acyl analogue by liver fat-storing cells

BACKGROUND/AIMS

Platelet-activating factor (PAF) is an important mediator of proinflammatory cell-to-cell interactions with powerful vasoactive properties. We evaluated the biosynthesis of PAF by cultured human fat-storing cells (FSC), liver-specific pericytes involved in the inflammatory and fibrogenic process of liver tissue.

METHODS

PAF synthesis was evaluated by measuring [3H]acetate incorporation under basal conditions and upon stimulation with A23187, thrombin, and lipopolysaccharide. Further analysis of PAF species synthesized by FSC was performed using gas chromatography/mass spectrometry.

RESULTS

All stimuli induced a significant increase of basal PAF synthesis by FSC. Further analysis showed that > 50% of the newly synthesized PAF species was secreted whereas the remaining fraction was cell-associated. PAF species produced by FSC were able to induce aggregation of rabbit washed platelets with an effectiveness correspondent to 10(-9) mol/L authentic PAF. Gas chromatography/mass spectrometry analysis revealed that a large percentage (74%) of PAF-like lipids synthesized by FSC consisted of 1O-acyl PAF. Finally, stimulation of FSC with PAF caused an increase in cytosolic free calcium, thus suggesting a possible involvement of this pericyte in the well-known effects of PAF on portal pressure.

CONCLUSIONS

These results expand the available knowledge concerning the role of PAF in conditions characterized by extensive activation and damage of the liver sinusoidal endothelium and decreased hepatic scavenger activity.

Eicosanoid profile and evidence for endotoxin tolerance in chronic ethanol-fed rats

The present study evaluated the role of endotoxin, prostaglandin E2 (PGE2), leukotriene B4 (LTB4) and thromboxane B2 in alcoholic liver injury. Animals (4-5 per group per time period) were fed ethanol and either saturated fat (SE group) or corn oil (CE group) and sacrificed at various time intervals: 1, 2, and 4 weeks. Non parenchymal cells (NPC) were isolated and the spontaneous and LPS-stimulated production of eicosanoids was evaluated. In addition, severity of pathology, plasma levels of endotoxin, TXB2, LTB4 and PGE2 were compared in the two groups. The severity of fatty, liver, necrosis and inflammation was significantly greater in the CE group compared to the SE group after 1 month. Plasma endotoxin levels were significantly higher in the CE group vs. SE group at all time periods studied. PGE2 levels in NPCS and plasma were in general higher in the SE group. LTB4 levels in NPCS declined with time in the SE group; in contrast the levels rose in the CE group. There was no difference in LTB4 levels in plasma between the two groups. TXB2 levels in plasma and NPCS were significantly higher in the CE group at all times. The pattern of LPS-stimulated eicosanoid production by NPC in the two groups (SE and CE) suggested the development of endotoxin tolerance in the CE group. However, an additional modulatory effect of ethanol was also suggested by our findings.

HBsAg retention sensitizes the hepatocyte to injury by physiological concentrations of interferon-gamma

The role that inflammatory cytokines may play in the life cycle of the hepatitis B virus and in the pathogenesis of its associated liver disease has not been carefully delineated. In this report, we demonstrate that bacterial lipopolysaccharide, a potent inducer of inflammatory cytokines in vivo, causes a severe acute liver disease in transgenic mice whose hepatocytes produce the hepatitis B virus large envelope polypeptide and retain HBsAg within the endoplasmic reticulum. In contrast, 100-fold higher doses of bacterial lipopolysaccharide do not induce liver cell injury in nontransgenic littermate controls or in transgenic mice whose hepatocytes secrete HBsAg rather than retain it. Coincident with the hepatocellular injury and the influx of inflammatory cells into the liver, a marked reduction occurs in the intrahepatic content of hepatitis B virus steady-state messenger RNA, thereby confirming the selectivity of this process for the HBsAg-positive hepatocyte. Bacterial lipopolysaccharide-induced hepatocellular injury appears to be principally mediated by interferon-gamma because it can be markedly reduced by the prior administration of neutralizing interferon-gamma-specific monoclonal antibodies and because recombinant interferon-gamma is also selectively cytotoxic for the HBsAg-positive transgenic hepatocyte in vivo. Tumor necrosis factor-alpha is also involved in this process because bacterial lipopolysaccharide-induced liver cell injury is significantly reduced by tumor necrosis factor-alpha specific monoclonal antibodies. The role of tumor necrosis factor-alpha in bacterial lipopolysaccharide-induced liver cell injury is less clear than interferon-gamma, however, because unlike interferon-gamma it is also toxic for nontransgenic hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of lipid peroxidation in enhancement of endotoxin hepatotoxicity

The present study was undertaken in the rats to examine whether endotoxin hepatotoxicity is enhanced by increased lipid peroxidation. The rats were given 10 ml of water, corn oil or heated and oxygenated corn oil per kg body weight by stomach tube twice a day for 14 days, and then they were injected physiological saline solution or endotoxin (2 or 2.5 mg per kg body weight) into the tail vein. In the rats pretreated with water or corn oil, the activity of serum glutamic pyruvic transaminase was within the normal limit, and there was no conspicuous morphological change in the liver, except for accumulation of fine fat droplets in few liver cells. On the other hand, in the rats pretreated with heated and oxygenated corn oil, containing a large amount of lipid peroxides, accumulation of small fat droplets in the liver cells and a slight elevation of serum transaminase activity were induced. The challenge with endotoxin (2.5 mg per kg body weight) caused focal hepatocellular coagulative necrosis and a marked elevation of serum transaminase activity, irrespective of the sorts of pretreatment, and there was no significant difference in the biochemical change and the histopathological damage between the rats pretreated with water, corn oil and heated and oxygenated corn oil. These results suggest that increased lipid peroxidation does not contribute to the enhancement of endotoxin hepatotoxicity, although it is thought that carbon tetrachloride and ethanol enhance endotoxin hepatotoxicity by synergism between endotoxin and the chemicals through lipid peroxidation.

Tumor necrosis factor in alcohol enhanced endotoxin liver injury

Endotoxin administration causes liver injury. Patients with alcoholic liver disease frequently have portal vein and systemic endotoxemia, and some investigators have suggested that endotoxin plays an etiologic role in alcoholic liver injury. Many of the metabolic effects of endotoxin are mediated by the cytokine tumor necrosis factor (TNF). It was the purpose of this study to determine whether TNF plays a role in ethanol-enhanced endotoxin liver injury. Rats were fed either a diet in which 36% of the calories were from ethanol or an isocaloric control diet. After 6 weeks, groups of 10 rats were intravenously injected with either saline, 1 mg/kg endotoxin, or 30 micrograms/kg of a prostaglandin E1 (PGE1) analogue + 1 mg/kg endotoxin 24 hr prior to sacrifice. Ethanol/endotoxin-treated rats had significantly higher liver enzyme levels (ALT: 1064 +/- 355 IU/liter, AST: 2024 +/- 515 IU/liter) compared with isocaloric/endotoxin controls (ALT: 237 +/- 54 IU/liter, AST: 602 +/- 80 IU/liter). Ethanol/endotoxin rats also had significantly higher peak serum TNF concentrations (992 +/- 200 units/ml) compared with isocaloric/endotoxin controls (344 +/- 96 units/ml). Pretreatment of ethanol/endotoxin rats with PGE1 caused significant attenuation of liver injury (ALT: 267 +/- 64 IU/liter, AST: 612 +/- 77 IU/liter) and a diminished serum TNF response. In contrast to chronic ethanol administration, acute gavage with 2 mg/kg ethanol (30% w/v) followed by intravenous injection of 2 mg/kg endotoxin produced significantly lower peak serum TNF concentrations (401 +/- 76 units/ml) than gavage with distilled water (1152 +/- 208 units/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Generation of chemotactic factor by hepatocytes isolated from chronically ethanol-fed rats

In an attempt to clarify a mechanism of polymorphonuclear cell and/or macrophage infiltration in alcoholic liver disease, we investigated a novel chemotactic and activating factor generated by rat hepatocytes isolated from the chronically ethanol-fed rats. Hepatocytes and hepatic macrophages were isolated from rat liver by perfusion and digestion with collagenase and subsequently by differential centrifugation on a metrizamide gradient. Rat polymorphonuclear cells were prepared from blood by the dextran sedimentation and Hypaque-Ficoll technique. Chemotactic activity was measured as migration of polymorphonuclear cells or hepatic macrophages using a chemotactic chamber. When hepatocytes isolated from the ethanol-fed rats were cultured in vitro, chemotactic activity for rat polymorphonuclear cells and hepatic macrophages was demonstrated in the culture supernatant. Inhibitors of transcription and protein synthesis reduced generation of chemotactic factor from these hepatocytes. Chemotactic activity of the conditioned medium was reduced after trypsin (0.25%, 37 degrees C, 30 min) or heat (56 degrees C, 30 min) treatment. The chemotactic activity was eluted at molecular weights of 20-25 kDa and 40-45 kDa following Sephadex G-150 chromatography. Superoxide anion production by polymorphonuclear cells and hepatic macrophages under the stimulation of phorbolmyristate acetate was enhanced in the presence of this chemotactic factor. This chemotactic factor may contribute to the pathogenesis of alcoholic liver disease.

Non-alcoholic steatohepatitis: impaired antipyrine metabolism and hypertriglyceridaemia may be clues to its pathogenesis

Non-alcoholic steatohepatitis resembles alcoholic liver disease in hepatic morphology but appears to have a different natural history. We sought to assess the nature of non-alcoholic steatohepatitis by a prospective study of its clinical progression and the relationship of biochemical abnormalities to changes in serum lipids among 15 patients with this disorder. In addition, antipyrine clearance (Cl-AP), which reflects hepatic microsomal oxidative capacity, was measured serially. Although initial liver histology included micronodular cirrhosis in five cases and bridging fibrosis in another three, only one patient developed a hepatic complication during 1-10 years (median: 3.7) of follow up. This confirms the relatively benign nature of non-alcoholic steatohepatitis. Moreover, Cl-AP, which was below the normal range in 13 patients, did not change significantly during 10-40 months of follow up. However, compared with other chronic liver diseases, the reduced Cl-AP was disproportionately low relative to the uniformly normal serum albumin concentration and other indices of hepatic metabolic function. This is consistent with selective impairment of endoplasmic reticular drug oxidizing enzymes. Hyperlipidaemia was present in 11 patients. In three of these, diet-induced correction of serum triglyceride elevation was associated with reduction of hepatocellular damage as indicated by serum enzyme levels. A hypothesis that unites these and earlier findings is that release of cytokines may occur in non-alcoholic steatohepatitis and produce accumulation of free fatty acids in the liver, leading to focal necro-inflammatory lesions and the destruction or down-regulation of cytochrome P450.

Endotoxin hepatotoxicity augmented by ethanol

To determine whether alcohol increases endotoxin hepatotoxicity, we administered ethanol (4.8 g/kg body wt in 4 ml of water) to rats through a gastric tube, then immediately injected endotoxin (2, 2.5, or 3 mg/kg body wt). In the rats pretreated with ethanol, the injection of 2 mg/kg body wt of endotoxin induced a slight rise of serum transaminase. However, when 2.5 mg/kg body wt of endotoxin was given, there were no significant histopathological or biochemical differences between the rats pretreated with ethanol and those pretreated with water. Moreover, there was no significant difference in mortality rates between the rats pretreated with ethanol and the controls when 3 mg/kg body wt (LD50) of endotoxin was injected. These results suggest that acute administration of alcohol enhances endotoxin hepatotoxicity when the dose of endotoxin is small, but that the effect of alcohol is masked when larger doses of endotoxin are given.

Increased endotoxin sensitivity following T-2 toxin treatment is associated with increased absorption of endotoxin

Oral exposure to T-2 Toxin (T-2) in experimental animals results in a syndrome similar to that observed in endotoxemia. Endotoxins are lipopolysaccharide, outer-membrane components of gram-negative bacteria which induce acute, inflammatory responses. In the present study, several aspects of endotoxin pathophysiology were investigated in mice following simultaneous exposure to T-2 and endotoxin, including mortality, hypothermia, tumor necrosis factor-alpha (TNF-alpha) and corticosterone production, and thymic weight. The disposition of endotoxin was also assessed, Acute, simultaneous exposure to T-2 (4 mg/kg, po) and endotoxin (3 micrograms/mouse, ip) resulted in increased mortality, hypothermia, TNF-alpha production, and thymic atrophy compared to treatment with either T-2 of endotoxin alone. Pretreatment of mice with endotoxin, a regime that renders the animals resistant to the effects of endotoxin, reduced many endotoxin effects in animals treated simultaneously with T-2 and endotoxin. Upon further investigation, it was observed that T-2 increased the absorption rate of endotoxin: as the peak height of serum endotoxin increased, the time-to-peak decreased, and the area under the curve was unchanged in animals treated simultaneously with T-2 and endotoxin. It was concluded that increased endotoxin absorption accounted for the increases in mortality, hypothermia, and TNF-alpha associated with T-2 exposure.

Hepatic fibrosis and iron accumulation due to endotoxin-induced haemorrhage in the gerbil

This study reports the findings of hepatic fibrosis and the accumulation of iron in the livers of 12 gerbils. The primary lesion was a haemorrhagic necrosis of the liver that was identical to that produced experimentally in the gerbil by administration of E. coli endotoxin lipopolysaccharide. The resulting extravasation of blood caused focal histiocytic reactions. The number of lesions increased with age, eventually resulting in a micronodular cirrhosis after 9 to 12 months owing to repeated episodes of endotoxin-induced haemorrhages in the liver. The accumulation of iron occurred in perisinusoidal cells, Kupffer cells and hepatocytes. The perisinusoidal cells were responsible for the subsequent hepatic fibrosis. The fibrosis associated with this condition appears to result from iron accumulation in the liver, following haemorrhage caused by endotoxin lipopolysaccharide. The gerbil is the first recorded rodent species to develop hepatic fibrosis in response to hepatic iron overload.

Excessive in vitro bacterial lipopolysaccharide-induced production of monokines in cirrhosis

The objective of this study was to analyze monokine production by peripheral blood mononuclear cells from patients with alcoholic cirrhosis. The capacity of peripheral blood mononuclear cells and purified monocytes from these patients to produce tumor necrosis factor alpha, interleukin 1 beta, and interleukin 6 was investigated. Spontaneous production of tumor necrosis factor alpha, interleukin 6 and interleukin 1 beta was similar in cirrhotic and healthy subjects, but serum levels of interleukin 6 (less than 2 U/ml vs. 9.5 +/- 3 U/ml) and tumor necrosis factor alpha (3.1 +/- 1.2 pg/ml vs. 12.0 +/- 1.2 pg/ml) were significantly higher in cirrhotic patients. However, peripheral blood mononuclear cells or purified monocytes from patients with alcoholic liver cirrhosis, stimulated in vitro with Escherichia coli lipopolysaccharide, displayed a marked increase of tumor necrosis factor alpha, interleukin 1 beta and interleukin 6 secretions compared with healthy controls. A striking feature of this overproduction was its reversibility as assessed by allowing cells to rest in vitro without lipopolysaccharide for 1 to 7 days before stimulation. In such conditions, tumor necrosis factor alpha and interleukin 6 secretions declined to levels present in healthy subjects in whom production remained stable, whereas interleukin 1 beta secretion markedly decreased in both groups to the point where no difference could be seen. This reversible oversecretion of cytokines after lipopolysaccharide stimulation, along with the lack of abnormality of spontaneous cytokine secretion, suggests that monocytes in these patients may have undergone an in vivo activation process analogous to a priming phenomenon. The in vitro activation with lipopolysaccharide may represent the correlate of in vivo endotoxemia observed during acute events such as sepsis.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Increased tumor necrosis factor production by monocytes in alcoholic hepatitis

Tumor necrosis factor is a cytokine that mediates many of the biologic actions of endotoxin. Recent studies have shown that tumor necrosis factor administration may cause liver injury and that tumor necrosis factor may mediate the lethality of the hepatotoxin galactosamine. One of the most potent inducers of tumor necrosis factor production is endotoxin. Because patients with alcoholic liver disease frequently have endotoxemia and because many of the clinical manifestations of alcoholic hepatitis are known biologic actions of tumor necrosis factor, we thought it would be important to evaluate tumor necrosis factor activity in patients with alcoholic hepatitis. Basal and lipopolysaccharide-stimulated tumor necrosis factor release from peripheral blood monocytes, a major source of tumor necrosis factor production, was determined in 16 patients with alcoholic hepatitis and 16 healthy volunteers. Eight of 16 alcoholic hepatitis patients and only two of 16 healthy volunteers had detectable spontaneous tumor necrosis factor activity (p less than 0.05). After lipopolysaccharide stimulation, mean monocyte tumor necrosis factor release from alcoholic hepatitis patients was significantly increased to over twice that of healthy controls (25.3 +/- 3.7 vs. 10.9 +/- 2.4 units per ml, p less than 0.005). We conclude that monocytes from alcoholic hepatitis patients have significantly increased spontaneous and lipopolysaccharide-stimulated tumor necrosis factor release compared to monocytes from healthy volunteers. We suggest that some of the metabolic abnormalities and possibly some of the liver injury of alcoholic hepatitis may be due to enhanced tumor necrosis factor production.