Inhibitory effects of rat alpha2 macroferoprotein (alphaMFP), an acute phase globulin, on galactosamine hepatitis

Connective tissue growth factor reacts as an IL-6/STAT3-regulated hepatic negative acute phase protein

AIM

To investigate the mechanisms involved in a possible modulator role of interleukin (IL)-6 signalling on CYR61-CTGF-NOV (CCN) 2/connective tissue growth factor (CTGF) expression in hepatocytes (PC) and to look for a relation between serum concentrations of these two parameters in patients with acute inflammation.

METHODS

Expression of CCN2/CTGF, p-STAT3, p-Smad3/1 and p-Smad2 was examined in primary freshly isolated rat or cryo-preserved human PC exposed to various stimuli by Western blotting, electrophoretic mobility shift assay (EMSA), reporter-gene-assays and reverse-transcriptase polymerase chain reaction.

RESULTS

IL-6 strongly down-regulated CCN2/CTGF protein and mRNA expression in PC, enhanceable by extracellular presence of the soluble IL-6 receptor gp80, and supported by an inverse relation between IL-6 and CCN2/CTGF concentrations in patients' sera. The inhibition of TGFβ1 driven CCN2/CTGF expression by IL-6 did not involve a modulation of Smad2 (and Smad1/3) signalling. However, the STAT3 SH2 domain binding peptide, a selective inhibitor of STAT3 DNA binding activity, counteracted the inhibitory effect of IL-6 on CCN2/CTGF expression much more pronounced than pyrrolidine-dithiocarbamate, an inhibitor primarily of STAT3 phosphorylation. An EMSA confirmed STAT3 binding to the proposed proximal STAT binding site in the CCN2/CTGF promoter.

CONCLUSION

CCN2/CTGF is identified as a hepatocellular negative acute phase protein which is down-regulated by IL-6 via the STAT3 pathway through interaction on the DNA binding level.

Susceptibility to Plasmodium berghei infection in rats is modulated by the acute phase response

Brown Norway (BN) and Sprague Dawley (SD) rats are known to differ in their susceptibility to infection with sporozoites of Plasmodium berghei, as measured by the density of liver schizonts. Because of the known inhibitory effect of non-specific immunomodulators on schizont development, we compared some aspects of the acute phase response in these two rat strains. LPS induced IL-6 production was measured in supernatants of spleen cells and peritoneal macrophages of both strains. SD rats, which are the least susceptible to P. berghei sporozoites, showed significantly higher IL-6 production by macrophages from both sources. When LPS was administered in vivo, SD rats also had a significantly higher IL-6 response. Hepatocytes from both strains were cultured in the presence of IL-6. After three days of culture, alpha 2-Macroglobulin concentrations in the supernatants of SD hepatocytes were much higher than those from BN rats. Kupffer cell depletion in both BN and SD rats was correlated with a significant increase in liver schizont density, but did not abrogate the difference in susceptibility. From these results we conclude that the higher cytokine production capacity of SD rats compared to BN rats, may contribute to the difference in susceptibility to P. berghei sporozoites between these strains, but that other yet unknown factors are also involved.

Experimental colitis in rats induces low-grade endotoxinemia without hepatobiliary abnormalities

In three experimental models in rats, surgical construction of a self-filling blind loop (SFBL), trinitrobenzene sulfonic acid (TNB) -induced colitis, and the combination of SFBL and TNB, the hypothesis was studied that intestine-derived endotoxins play a role in the pathogenesis of hepatobiliary disorders in chronic inflammatory bowel disease (CIBD). After eight weeks of treatment, a mild increase in portal and systemic endotoxin levels and interleukin-6 concentrations was observed and the serum levels of alkaline phosphatase, bilirubin, and ALAT were only mildly increased in SFBL plus TNB rats. Histopathological examination of the liver showed hardly any abnormalities in all three rat models. These results show that low-grade portal and systemic endotoxinemia in rats, induced by bacterial overgrowth and/or chemical colitis, is not able to induce hepatobiliary alterations. To exclude definitively a possible role for portal endotoxinemia in the pathogenesis of CIBD-associated hepatobiliary abnormalities, however, an adequate animal model for CIBD is urgently needed.

Pretreatment with alpha 2-macroglobulin leads to recovery of rats exposed to a lethal scald

The effect of alpha 2-macroglobulin (alpha 2M) administration on the survival rate of lethally injured rats and molecular mechanisms regulating its hepatic expression after sublethal and lethal scalding were examined. Transcriptional activity of nuclei for the alpha 2M gene increased after a sublethal 20 per cent TBSA scald reaching a maximal three-fold increase by 12 h, whereas concentrations of the corresponding mRNA and protein attained the maximal nine- and 18-fold enhancements by 24 h, respectively. After the second, lethal scald, the plasma alpha 2M level increased during the first few hours, then dropped rapidly below the control value although the abundance of its mRNA was several fold enhanced. This anomaly was ascribed to inhibition of the alpha 2M mRNA translation caused by the second scald-induced disturbance of the haemodynamic equilibria. Eighty per cent of rats receiving alpha 2M prior to rescalding survived the second injury. Their recovery proceeded in parallel with normalization of the plasma volume and reactivation of the process of acute phase protein synthesis in the liver. A functional link between these events is discussed.

Effect of acute phase proteins, especially alpha 2-macroglobulin, on granuloma formation around Schistosoma mansoni eggs in the rat

A new model for the study of granuloma formation in the liver is described. Rats received an injection of 20,000 Schistosoma mansoni eggs in the portal vein and granuloma formation was evaluated at 3, 5 and 7 weeks post-injection. Liver collagen was estimated at the same time and serum procollagen III peptide, a marker of collagenesis, weekly. With this model, wherein the number of S. mansoni eggs and the time of injury are standardized, the effect of high levels of acute phase proteins especially alpha 2-macroglobulin on granuloma formation was studied. It appeared that in rats with high levels of alpha 2-macroglobulin the mean size of granulomas was significantly greater at 3 and 5 weeks compared with controls. In both groups an increase in liver collagen was observed during this period, reaching a peak at 5 weeks in the acute phase group. This model facilitates the study of the effects of S. mansoni eggs on granuloma formation.

Relation between acute-phase proteins and enhanced bleomycin-induced pulmonary fibrosis in the rat

Intratracheal application of Bleomycin (Bleo) in rats induces interstitial pneumonitis followed by progressive fibrosis. As the presence of high levels of acute-phase proteins (= reactants = APR), especially alpha 2-macroglobulin of the rat (alpha 2M), enhances liver fibrosis, we investigated whether this phenomenon also occurs in rats with Bleo-induced lung fibrosis. The experiments showed that this is the case; lung fibrosis assessed by measuring hydroxyproline, hexosamine, and prolyl-4-hydroxylase was enhanced when just before Bleo application an acute-phase reaction was induced. This effect can be explained by the inhibitory effect of alpha 2M on collagenase. The experiments showed a significant positive correlation between alpha 2M and parameters of fibrosis. This is especially the case in the third week after Bleo application. Bleo itself does not induce a strong acute-phase reaction, notwithstanding the pneumonitis during the first weeks. The increased fibrosis is accompanied by progressive ventilatory disturbances demonstrated by high arterial pCO2 and low pO2. In patients undergoing Bleo treatment, varying levels of APR can be expected, and this could explain the rapid development of fibrosis in individual cases.

Copper protects against galactosamine-induced hepatitis

Although copper is believed to be hepatotoxic in Wilson's disease and Indian Childhood Cirrhosis (ICC), the rat shows only minimal hepatic damage on copper-loading. To investigate the possibility that copper deposition may potentiate the effects of a superimposed hepatitis, D-galactosamine (GalN) was given to copper-loaded and control rats. In the non-copper-dosed rats, GalN 0.85 g/kg i.p. produced elevated serum AST (3731 +/- 545 IU/l; normal 64.8 +/- 2.1), ALT (2090 +/- 190 IU/l; normal 18.0 +/- 0.7), and OCT (16.7 +/- 2.6 mmol/min/ml; normal 0.12 +/- 0), and liver cell necrosis with portal infiltration. In rats whose liver copper was elevated to 1298 +/- 169 micrograms/g (control 18.7 +/- 1.7) by oral copper supplementation, GalN produced much smaller increases in AST (825 +/- 122 IU/l), ALT (103 +/- 15 IU/l) and OCT (0.27 +/- 0.02 mmol/min/ml) and minimal histological damage. Viable bacterial cell counts from faecal homogenates showed that the anaerobically cultured bacteria were reduced on copper-dosing of rats. Therefore the protective effect of copper may be due to a decrease in gut-derived endotoxin acting on the liver, or to an impaired prostaglandin synthesis or perhaps to synthesis of acute phase reactants.

Mechanisms by which acute phase proteins enhance development of liver fibrosis: effects on collagenase and prolyl-4-hydroxylase activity in the rat liver

Previous experiments showed that the presence of high levels of acute phase reactants (APR) enhance CCl4-induced liver fibrosis in the rat. A high correlation was found between the degree of fibrosis and alpha 2-macroglobulin of the rat (alpha 2-macrofetoprotein, alpha M-FP) used for monitoring the acute phase response. This acute phase reaction was provoked by epinephrine just before CCl4 treatment was started. In the present study we analyzed the effect of APR by repeating these experiments and estimating liver neutral collagenase with a synthetic substrate and endogenous collagen as a substrate, and liver prolyl-4-hydroxylase. A strong depression of liver collagenase activity was found in rats with a preceding acute phase reaction contrary to the rats that underwent CCl4 treatment only. A high level of alpha M-FP correlated negatively with collagenase activity. Also in vitro alpha M-FP proved to inhibit collagenase activity. Prolyl-4-hydroxylase was increased in the rats during acute phase reaction and correlated highly and positively with alpha M-FP, haptoglobin, and ceruloplasmin. Thus high levels of APR promote development of CCl4-induced fibrosis, partly by anticollagenase activity and partly because of enhancement of prolyl-4-hydroxylase activity. The latter phenomenon can also be explained by the presence of APR, but this has to be proved.

Acute phase reactants enhance CCl4 induced liver cirrhosis in the rat

High levels of acute phase proteins (acute phase reactants, APR) suppress acute inflammatory reactions in the rat. As many APR have antiprotease properties, including an anticollagenase activity, the effect of APR on the development of CCl4-induced liver fibrosis was investigated in rats. APR were provoked by repeated injections of epinephrine, inducing a broad spectrum of APR. This reaction can be monitored measuring alpha 2-macroglobulin levels in the rat (alpha 2-macrofetoprotein, alpha M FP). This protein was found to inhibit both acute galactosamine hepatitis and acute CCl4-induced liver toxicity. The animals with high levels of APR at the start of CCl4 treatment developed a more severe degree of fibrosis and cirrhosis than the control group in which no acute phase reaction was induced. Epinephrine alone had no such effects. Additionally, the APR positive group showed an initially lower degree of hepatocellular damage when compared to control animals. This uncoupling of liver cell damage and subsequent fibrosis may demonstrate that higher levels of APR might be important as to the development of cirrhosis, possibly based on the anticollagenase activity of these proteins.

Toxicity of D-galactosamine for rat hepatocytes in monolayer culture

Hepatocellular injury was induced by exposure of primary cultures of rat hepatocytes to 4 mM D-galactosamine. The cell damage was very similar to that seen in vivo and in the isolated perfused rat liver, both in biochemical and in structural terms. The severity of the lesions caused by D-galactosamine was dependent on the age of the culture being treated. Less severe damage was found with older cultures. Since the primary metabolic effects of D-galactosamine were age-independent, the reduction in cell damage seems to be due to progressive cell dedifferentiation. Dexamethasone (1 microM) suppressed the full development of the injury, while 1 microM triiodo-L-thyronine enhanced it. A protection of hepatocytes by alpha 2-macroglobulin against the effects of D-galactosamine could be observed neither in vivo nor in vitro. Direct cytotoxic effects of endotoxin from Salmonella minnesota R 595 could be demonstrated only on hepatocytes in the early phases of primary culture using rather high doses of the purified lipopolysaccharide. It is unlikely that they play a major role in the hepatocellular injury seen following endotoxinemia in vivo. Lowering of extracellular Ca2+ concentration and additions of calcium/calmodulin inhibitors did not prevent cell injury after treatment with D-galactosamine. The results suggest that cell death is not due to an increased influx of Ca2+ into the cells.

Distribution of alpha 2-macroglobulin in normal, inflammatory, and tumor tissues in rats

Distribution of uptake and catabolism of intravenously administered 125I-labeled rat alpha 2-macroglobulin(125I-alpha 2MG) were examined in normal, inflammatory, and tumor tissues of rats. Clearance of intravenously administered [125I]alpha 2MG from the circulation was rapid. Accumulation of this compound into inflammatory tissue was 2-3 times more extensive than in normal tissues. The accumulation into sarcoma tissue was much less. Radioactivity in TCA-PTA precipitates remained fairly constant for the first 12 h in inflammatory tissue and for the first 24 h in sarcoma. These patterns of accumulation were never observed in the normal tissues. As the kidney preferentially accumulated large amounts of [125I]alpha 2MG in the nondegraded form and its degradation products, the tissue may play a special role in the metabolism of alpha 2MG. Rapid clearance from the circulation and relatively small amounts of accumulation in tissues suggest that alpha 2MG may function as a protease inhibitor, mainly in the circulation rather than in the tissues.

Glucocorticoids and catecholamines as mediators of acute-phase proteins, especially rat alpha-macrofoetoprotein

Adrenal hormones were studied as possible triggering substances of the synthesis of acute-phase reactants in rats. alpha-Macrofoetoprotein, which rises sharply in concentration during inflammation, was used to monitor the acute-phase reaction. In normal rats glucocorticoids and catecholamines induce alpha-macrofoetoprotein synthesis; glucocorticoids only increase alpha-macrofoetoprotein to moderate levels in plasma, but catecholamines enhance alpha-macrofoetoprotein synthesis to very high levels, comparable with those observed in the post-injury phase. However, catecholamines in vivo also activate the adrenal cortex, suggesting a synergistic effect of both kinds of adrenal hormones. Our study showed that in adrenalectomized rats, the effect of catecholamines on alpha-macrofoetoprotein synthesis is greatly diminished, whereas the moderate effect of glucocorticoids remains. Combination of glucocorticoids and catecholamines induces extremely high alpha-macrofoetoprotein levels in both adrenalectomized and normal rats. With crossed immunoelectrophoresis it was shown that other acute-phase reactants, such as haptoglobin and alpha 1-major acute-phase protein, are affected differently by the hormones. Contrary to glucocorticoids, catecholamines give a pattern comparable with that found after surgical injury.

Profiles of acute-phase reactants and clinical significance of alpha 2-macroglobulin in acute hepatitis B

Acute-phase proteins (APRs), albumin, and alpha 2-macroglobulin (alpha 2M), were studied in 14 patients with acute hepatitis B. No acute-phase reaction in this disease was observed, contrary to other viral infections. Peak SGPT correlated negatively with prealbumin, but no other relations with APR, albumin, or alpha 2M were found. As many APRs have antiinflammatory properties, the relation of these proteins at the start and the subsequent course of hepatitis, measured by "SGPT area" and duration of the illness, was calculated. The serum level of APR and albumin at the start of the disease is not significantly related to the subsequent course. However alpha 2M, not being an APR, and prealbumin are negatively correlated to these parameters: high levels of alpha 2M and prealbumin point to a less severe course than low levels. The clinical significance of the depressed acute-phase reaction during hepatitis and the effect of alpha 2M are discussed.

Galactosamine hepatitis, endotoxemia, and lactulose

Studies by Liehr et al. suggest that endotoxins are important in the pathogenesis of galactosamine hepatitis (Gal-N hepatitis) in rats. Lactulose (9.1 gm per kg per day) prevents hepatic lesions induced by Gal-N; an antiendotoxin effect of lactulose is postulated. However, commercial preparations of lactulose are contaminated with galactose, which shows a competitive action to Gal-N. To analyze the effect of galactose, male Wistar rats were pretreated with lactulose (Duphalac, 9.1 gm per kg per day) and given Gal-N (375 mg per kg i.p.). After 24 hr, serum was analyzed for glutamic pyruvate transaminase, glutamate dehydrogenase, and sorbitol dehydrogenase activities. Pretreatment with Duphalac, even 1 hr before Gal-N, abolished toxicity. Duphalac contains 10 gm galactose per 100 ml. Galactose was given in a similar concentration and similar inhibition occurred. Pretreatment with purified lactulose (9.1 gm per kg for 5 days) diminished the effects of Gal-N but did not normalize enzyme concentrations. Because small doses of galactose (80 and 300 mg per kg) showed similar inhibitory effects, we conclude that the protective effect of commercial lactulose preparations is mainly due to galactose contamination and not to an antiendotoxin effect.

Influence of D-galactosamine upon the NAD-metabolism in rat liver

After application of D-galactosamine a hepatitis develops in the rat liver. This can be prevented by different agents, including tryptophan. Yet it has not been possible to give definitive conclusions about the mechanism of galactosamine hepatitis. In this paper we report about the influence of galactosamine on the NAD metabolism. D-galactosamine inhibits the NAD synthesis initiated by nicotinamide in normal and adrenalectomized animals. The NAD synthesis from tryptophan is prevented in normal animals, in adrenalectomized ones however there is an increase of NAD in the presence of D-galactosamine reduces the activity of the ADPR transferase. Inhibitors of the ADPR transferase prevent the galactosamine hepatitis. From the results presented we conclude that the ADPR transferase plays an important role in the development of the galactosamine hepatitis.

Inhibition of polymorphonuclear leukocyte chemotaxis by alpha-macrofetoprotein, an acute-phase reactant of the rat

alpha-Macrofetoprotein (alpha M FP) is a normal fetal plasma constituent in the rat, with very low plasma levels in the adult phase but rising sharply after injury. This fetal acute-phase protein is a strong inhibitor of inflammatory edema. Fetal inflammatory reactions show diminished exudation, but also impaired emigration of polymorph nuclear cells (PMNs). Therefore we studied the effect of alpha M FP on chemotaxis of PMN in vitro and in vivo. In vitro experiments showed a strong inhibitory effect on casein-induced leukotaxis (Boyden technique) with a clear dose-effect relationship. In vivo with glycogen-induced pleurisy and peritonitis, high alpha M FP levels are accompanied by diminished PMN emigration and vice versa. The significance of these findings is discussed in relation to fetal pathology and also as a model showing the modulating effects of acute-phase proteins on the inflammatory reaction induced by tissue injury.

Modification of galactosamine-induced liver injury in rats by reticuloendothelial system stimulation or depression

The reticuloendothelial system has been implicated in galactosamine-induced liver injury because of a correlation between phagocytic alterations induced by colloidal carbon or endotoxin, and development of liver necrosis. To evaluate this concept, the influence of galactosamine on liver function and histology was determined in rats in which the reticuloendothelial system was normal, stimulated, or depressed. Methyl palmitate was used as a reticuloendothelial system suppressant, and glucan was used as a reticuloendothelial system activating agent. Administration of galactosamine to control rats resulted in hypoglycemia and increased serum bilirubin concentration, elevated serum glutamic oxalacetic transaminase, lactic dehydrogenase and glutamic pyruvic transaminase activities, and retention of sodium sulfobromophthalein. Histological studies revealed hepatic necrosis, and a polymorphonuclear and lymphocytic cellular infiltrate in galactosamine-treated rats. Pretreatment of rats with methyl palmitate inhibited galactosamine-induced alterations in serum glucose concentration, glutamic oxalacetic transaminase and lactic dehydrogenase activities, and sodium sulfobromophthalein retention. Liver necrosis and inflammatory reactions were also reduced in methyl palmitate-treated galactosamine-injected animals. In contrast, activation of the reticuloendothelial system by glucan increased galactosamine-induced alterations in serum bilirubin, glucose and cholesterol concentrations, glutamic oxalacetic transaminase, glutamic pyruvic transaminase and lactic dehydrogenase activities, and sodium sulfobromophthalein retention. Liver necrosis and inflammation were also increased. These findings suggest that the degree of galactosamine-induced liver injury is directly correlated with macrophage function when specific macrophage-modifying agents are used.

A histochemical study about changes in rat liver plasma membrane enzyme activities after galactosamine administration

In rats changes in plasma membrane enzyme activities due to Gal-N intoxication were studied by enzymehistochemical methods. The bile canalicular 5'-nucleotidase and nucleoside polyphosphatase activities decreased; the sinusoidal 5'-nucleotidase remained unchanged. The bile canalicular leucyl-beta-naphthyl-amidase showed an increase in activity; the alkaline phosphatase activity remained unchanged. In contrast to the spotty necrosis, changes in plasma membrane enzyme activities were seen in all liver cells, suggesting that changes of these activities, occurring after Gal-N treatment, do not correlate with cell death. The conclusion was drawn that the deviations of the enzyme activities might be due to changes in the lipid environment of the enzyme proteins in the membrane. With the exception of alkaline phosphatase, partial hepatectomy caused the same changes in enzyme activities as did Gal-N intoxication. Nevertheless Gal-N administration to partial hepatectomized rats did not lead to hepatic necrosis. Galactose given simultaneously or within two hours after Gal-N prevented both changes in plasma membrane enzyme activities and hepatocellular damage. This suggests an important role of galactolipids and galactoproteins in the plasma membrane alterations.