Hepatic stimulator substance activity in animal model of fulminant hepatic failure and encephalopathy

Hepatic stimulator substance (HSS) is a known liver-specific but species-nonspecific growth factor. In the present study we examined the activity of the endogenously produced HSS in an established experimental model of fulminant hepatic failure (FHF) and encephalopathy, induced by repeated injections of thioacetamide (TAA). FHF was induced by three consecutive intraperitoneal injections of TAA (400 mg/kg body weight) in rats, at time intervals of 24 hr. The animals were killed at 0, 6, 12, or 18 hr following the last injection of TAA. The rate of tritiated thymidine incorporation into hepatic DNA, the enzymatic activity of liver thymidine kinase (EC 2.7.1.21), and the assessment of mitotic index in hepatocytes were used to estimate liver regeneration. HSS extract obtained from the livers of TAA-treated rats, sacrificed at the above-mentioned time points was tested for its activity. Increased HSS activity was noted in all TAA-treated animals, presenting a peak at 12 hr following the third TAA dose, suggesting active participation of this growth factor in hepatocyte replication in this animal model of FHF and encephalopathy. It may also be suggested that up-regulation of HSS activity could be used in future as a therapeutic approach in FHF.

Immunohistochemical studies on the expression pattern of molecular chaperones HSC70 and HSP25 and cell cycle-related proteins cyclin D1 and PCNA in rat liver after thioacetamide intoxication

Intoxication of rats with thioacetamide (TAA) is a model system to investigate mechanisms involved in liver cell death and tissue reconstitution. Our study was undertaken to determine by immunohistochemistry the expression pattern of the cytoprotective chaperone proteins HSC70 and HSP25 and proliferation markers cyclin D1 and PCNA in livers of Wistar rats intraperitoneally injected with TAA at a single dose of 50 mg/kg. For each protein studied we observed distinct dynamic changes in appearance and localization in liver lobules. During 24-36 h after TAA injection the HSC70 cytoplasmic immunoreaction gradually disappeared from hepatocytes localized around central veins and a shift of immunostaining to cell nuclei took place. Then, 36-48 h after TAA injection the HSC70 cytoplasmic immunoreaction reappeared with the highest intensity in hepatocytes surrounding the areas of inflammatory cells. HSP25, undetectable in control hepatocytes began to appear at approximately 36 h after TAA injection and HSP25-immunopositive cells formed a characteristic ring around areas of inflammation. Of the proteins studied, the most rapid reaction to TAA was observed for cyclin D1. As early as 15 min after TAA administration cyclin D1-positive hepatocytes appeared in intermediate and periportal areas of liver lobules and a subsequent shift of staining to centrilobular hepatocytes took place at 36 and 48 h. There was no correlation of cyclin D1 localization either with PCNA-positive cells or mitotic cells. Our observations suggest that in TAA-treated livers HSP25 and HSC70 proteins can play an anti-inflammatory role, and the early and distinct cyclin D1 expression is not related to proliferation of hepatocytes.

Tetramethylpyrazine protects mice against thioacetamide-induced acute hepatotoxicity

In this study, the intraperitoneal administration of 1 mg/kg thioacetamide (TAA) produced hepatotoxicity in mice. The increase in serum SGOT and SGPT produced at 24 h by this regimen was decreased in a dose-dependent manner by coadministration of tetramethylpyrazine (TMP; 10, 25 and 50 mg/kg). A rise in serum interleukin-2 was similarly prevented. Increased concentrations of malondialdehyde (MDA) generated in vitro in liver homogenates prepared from TAA-treated mice were decreased by TMP treatments. The increase in MDA produced by TAA was also prevented by in vitro addition of TMP to liver homogenates. These results suggest that part of the hepatocellular injury induced by TAA is mediated by oxidative stress caused by the action of cytokines through lipid peroxidation. TMP appears to act by preventing lipid peroxidation.

Thioacetamide impairs retinol storage and dolichol content in rat liver cells in vivo

The aim of this paper was to ascertain whether chronic pretreatment with thioacetamide (TAA) might alter the uptake of a load of retinol and dolichol distribution in hepatocytes (HC), hepatic stellate cells (HSC) (Ito-1 and Ito-2 subfractions), Kupffer (KC) and sinusoidal endothelial cells (SEC). The reason why retinol and dolichol content was studied is that their metabolism and transport might be interrelated and that the two isoprenoids might exert different functions in the cells of the hepatic sinusoid. Rats were treated for 2 and 4 months with TAA, a known fibrogenic hepatotoxin, at a low dosage, to produce an early stage of damage. Three days before sacrifice, the rats were given a load of vitamin A, and cells were isolated to investigate its uptake. In HC, the load of retinol was taken up and accumulated, while a decrease in dolichol preceded retinol increase. In HSC, much less of the retinol load was stored than in controls, and dolichol content also decreased. Various minor modifications were seen in KC and SEC.Collectively, the results show that the distribution of these two isoprenoids, which play important roles in cellular differentiation and proliferation, is differently altered in the multiple cell types that line the hepatic sinusoid, and that both isoprenoids seem to participate in the first steps of liver damage.

Dolichol content in isolated sinusoidal liver cells after in vivo chronic treatment with thioacetamide

The content of dolichol, an isoprenoid present in all biological membranes, was determined in isolated sinusoidal liver cells after treatment of rats for 2 and 4 months with a low dosage of the hepatotoxin thioacetamide. The significant decrease in dolichol observed in hepatocytes after 2 months might be explained by peroxidation of the isoprenoid. At the same time point, retinol was retained, and decreased only after 4 months of treatment. After 4 months of treatment therefore both lipids decreased. In a subfraction of hepatic stellate cells, Ito-1 cells, the main storage site of vitamin A, dolichol decreased significantly only after 4 months. A remarkable difference from hepatocytes is that in Ito-1 cells retinol content significantly decreased after 2 months of treatment. In another subfraction, Ito-2 cells, the content of the two isoprenoids decreased in parallel. This heterogeneous subfraction might represent those transitional hepatic stellate cells that, while losing retinol, are in the process of differentiating into myofibroblasts secreting extracellular matrix components. In Kupffer cells and sinusoidal endothelial cells, impairment of dolichol might be observed later, only after 4 months of treatment, while retinol decreases uniformly over time. Starting after two months of treatment, the decrease of dolichol and the increase of retinol in hepatocytes, at the same time as retinol decreases in hepatic stellate cells, might be taken as an early index of incipient liver injury due to thioacetamide. This hypothesis is discussed with regard to a role of dolichol in the modulation of membrane fluidity for intracellular and intercellular retinol transport.

Alpha-glutathione S-transferase in the assessment of hepatotoxicity--its diagnostic utility in comparison with other recognized markers in the Wistar Han rat

The diagnostic utility of alpha-glutathione S-transferase (alphaGST) in the assessment of acute hepatotoxicity was compared with a range of markers including alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Rats were given a single oral dose of either alpha-naphthylisothiocynate (AN IT), bromobenzene (BrB). or thioacetamide (TAM) at concentrations previously shown to induce marked hepatotoxicity. The progression of each hepatic lesion was monitored by the measurement of a battery of markers, including alphaGST, in plasma collected at time points ranging from 3 h to 7 days after dosing. alphaGST was seen to increase significantly at 24 h (ANIT/BrB) and 3 h (TAM) postdosing, corresponding with histopathological findings. For each compound, when the degree of insult was most severe, fold increases in alphaGST were greater than those seen with ALT and AST, yet lower than those seen with glutamate dehydrogenase (BrB and ANIT). sorbitol dehydrogenase (TAM), or total bilirubin and bile acids (ANIT). Elevations in alphaGST were also detected no earlier than any other marker. AlphaGST in the rat was shown to be a valid marker of hepatotoxicity; however, its measurement offered no additional information in detecting either the time of onset/recovery or the severity of each type of hepatic injury induced.

Level of superoxide dismutase, glutathione peroxidase and uric acid in thioacetamide-induced cirrhotic rats

Levels of superoxide dismutase and glutathione peroxidase were determined in blood and hepatic tissues of thioacetamide-induced cirrhotic rats and compared to levels in age-matched control animals. The plasma level of uric acid was also determined in these animals. A general decrease was noticed in the level of all the antioxidants examined as compared to the control. This decrease was statistically significant in the level of all the antioxidants studied, except for the level of superoxide dismutase in blood. A decrease in the antioxidant level may indicate an increase in free radical level and thereby an increase in cellular damage in cirrhotic rats. The changes in the level of antioxidants showed a direct correlation with the changes in the level of trace elements observed in our previous studies. These studies suggest that antioxidants alone or in combination with trace elements may have beneficial effects in treating liver cirrhosis.

Failure of liver cirrhosis induction by thioacetamide in Nagase analbuminaemic rats

Repeated administration of thioacetamide (TA), either intraperitoneally or in drinking water, produced liver cirrhosis in normal Sprague-Dawley rats (SDR) with significant histological alterations similar to those observed in human cirrhosis. In the present study, we evaluated the ability of TA to induce liver cirrhosis in mutant Nagase analbuminaemic SDR. Thioacetamide was administered either intraperitoneally up to 4 months or in drinking water up to 6 months to normal and to Nagase analbuminaemic SDR. Nagase analbuminaemic rats (NAR) were also administered TA in drinking water up to 10 months. Liver cirrhosis development was determined by macroscopic and microscopic analysis. In contrast to normal SDR, no histological characteristics of cirrhosis could be observed in NAR submitted to a 4 or 6 months treatment with TA. Such failure to induce cirrhosis in Nagase rats was confirmed even after prolonged TA administration in drinking water for up to 10 months. In contrast, fibrosis and cholangiolar proliferation occurred in the 10-month TA-treated analbuminaemic rats, suggesting that the mechanisms involved in cirrhosis induction are different from those involved in fibrosis development and carcinogenesis. It is unlikely that the protective effect against TA-induced cirrhosis observed in analbuminaemic rats is related to the absence of albumin in this rat strain, since a co-administration of TA with albumin in analbuminaemic rats did not restore the potential for TA to induce cirrhosis in this rat strain. In conclusion, the fact that induction of cirrhosis by TA is prevented in the inherently hyperlipidaemic and hypercholesterolaemic analbuminaemic rats could be considered for potential application in the treatment of clinical cirrhosis.

Dietary nucleotide supplementation reduces thioacetamide-induced liver fibrosis in rats

Dietary nucleotides reportedly promote functionality and repair in fibrotic liver. Liver fibrosis is characterized by an excessive accumulation of extracellular matrix components, which lead to the impairment of the hepatic function. The aim of this work was to evaluate the influence of dietary nucleotides on liver fibrosis induced by thioacetamide and to elucidate the mechanism by which nucleotides exert their protective effects. Rats consumed ad libitum 300 mg/L thioacetamide in drinking water and were pair-fed diets with (group TN) or without nucleotides (group TS) for 4 mo. Liver histology and extracellular matrix components, liver collagenase and prolyl 4-hydroxylase activities, and tissue inhibitor of metalloproteinases-1 were assessed. The degree of fibrosis was lower in group TN than in group TS. Group TN had lower hepatic concentration of hydroxyproline (P < 0.05), collagen type I (P = 0.12) and type III (P = 0.20), fibronectin (P = 0.05), laminin (P = 0.11) and desmin (P = 0.07), higher collagenolytic activity (P < 0.05), lower prolyl 4-hydroxylase activity (P < 0.05) and lower prolyl 4-hydroxylase (P = 0.10) and tissue inhibitor of metalloproteinase-1 (P = 0.06) expression than group TS. Moreover, expression of tissue inhibitor of the metalloproteinases-1 gene was lower in group TN than in group TS (P < 0.05). These data indicate that the reduction of liver fibrosis in nucleotide-supplemented rats may rely on the enhancement of collagenase activity and the reduction of collagen content and maturation.

Evaluation of hepatoprotective potential of jigrine post-treatment against thioacetamide induced hepatic damage

Jigrine a polypharmaceutical herbal formulation containing aqueous extracts of 14 medicinal plants developed on the principles of unani system of medicine is used for liver ailments. The hepatoprotective potential of jigrine post-treatment at the dose of 0.5 ml/kg per day p.o. for 21 days was evaluated against thiocetamide induced liver damage in rats. Biochemical parameters like AST, ALT in serum and TBARS and glutathione in tissues were estimated to assess liver function. Data on the biochemical parameters revealed hepatoprotective potential of jigrine post-treatment against thioacetamide induced hepatotoxicity in rats. Silymarin used as reference standard also exhibited significant hepatoprotective activity on post-treatment against thioacetamide-induced hepatotoxity in rats. The biochemical observations were supplemented with histopathological examination of rat liver sections.

Aggresome formation in liver cells in response to different toxic mechanisms: role of the ubiquitin-proteasome pathway and the frameshift mutant of ubiquitin

Aggresomes form in cells when intracellular proteins undergo conformational changes, as in so-called conformational diseases. This phenomenon has been observed in the liver and brain and in cell culture in response to abnormal protein formation, such as mutant proteins. In the case of the brain the frameshift mutant ubiquitin (UBB+1) is involved. Mallory body formation in the liver is one example of this phenomenon in vivo. Mallory body formation is common in a variety of liver diseases of diverse pathogenesis. The study of the Mallory body forming model indicated that drug-conditioned hepatocytes form Mallory bodies when mice are given colchicine, ethanol, okadaic acid, or exposure to heat shock. These findings suggest that aggresome formation is a common pathway of liver injury due to diverse mechanisms. To further characterize the role of this common pathway, drug-primed mice were exposed to different types of liver injury, i.e., using such drugs as thioacetamide, galactosamine, tautomycin, and the proteasome inhibitor PS341. Mallory body formation was induced by treatment with all the toxins tested, giving credence to the proposal that aggresome formation in the liver is a common pathway in response to different primary mechanisms of liver injury. The frameshift mutant UBB+1 was invariably found to colocalize with ubiquitin in the Mallory body, indicating its essential involvement in the mechanism of MB formation.

Cytochrome P4502E1 induction increases thioacetamide liver injury in diet-restricted rats

Earlier studies have shown highly exaggerated mechanism-based liver injury of thioacetamide (TA) in rats following moderate diet restriction (DR) and in diabetes. The objective of the present study was to investigate the mechanism of higher liver injury of TA in DR rats. Since both DR and diabetes induce CYP2E1, we hypothesized that hepatic CYP2E1 plays a major role in the bioactivation-based liver injury of TA. When male Sprague-Dawley rats (250-275 g) were maintained on diet restriction (DR, 35% of ad libitum fed rats, 21 days) the total hepatic microsomal cytochrome P450 (CYP450) was increased 2-fold along with a 4.6-fold increase in CYP2E1 protein, which corresponded with a 3-fold increase in CYP2E1 activity as measured by chlorzoxazone hydroxylation. To further test the involvement of CYP2E1, 24 and 18 h after pretreatment with pyridine (PYR) and isoniazid (INZ), specific inducers of CYP2E1, male Sprague-Dawley rats received a single administration of 50 mg of TA/kg (i.p.). TA liver injury was >2.5- and >3-fold higher at 24 h in PYR + TA and INZ + TA groups, respectively, compared with the rats receiving TA alone. Pyridine pretreatment resulted in significantly increased total CYP450 content accompanied by a 2.2-fold increase in CYP2E1 protein and 2-fold increase in enzyme activity concordant with increased liver injury of TA, suggesting mechanism-based bioactivation of TA by CYP2E1. Hepatic injury of TA in DR rats pretreated with diallyl sulfide (DAS), a well known irreversible in vivo inhibitor of CYP2E1, was significantly decreased (60%) at 24 h. CCl(4) (4 ml/kg i.p.), a known substrate of CYP2E1, caused lower liver injury and higher animal survival confirming inhibition of CYP2E1 by DAS pretreatment. The role of flavin-containing monooxygenase (FMO) in TA bioactivation implicated by previous in vitro studies, and consequent increased TA-induced liver injury in DR rats was tested in vivo with a relatively selective inhibitor of FMO, indole-3-carbinol, and then treated with 50 mg of TA/kg. FMO activity and alanine aminotransferase levels measured at different time points revealed that TA liver injury was not decreased although FMO activity was significantly decreased, suggesting that hepatic FMO is unlikely to bioactivate TA. These findings suggest induction of CYP2E1 as the primary mechanism of increased bioactivation-based liver injury of TA in DR rats.

Diallyl sulfide inhibition of CYP2E1 does not rescue diabetic rats from thioacetamide-induced mortality

Previously we have shown that hepatotoxicity of thioacetamide (TA) was increased in streptozotocin (STZ)-induced diabetic (DB) rats due to combined effects of enhanced bioactivation-based liver injury of TA and compromised liver tissue repair response. We have also shown that TA is primarily bioactivated by hepatic CYP2E1. The present study was done to further investigate the importance of liver tissue repair in determining the final outcome of hepatotoxicity. STZ-induced DB rats were pretreated with a CYP2E1 inhibitor, diallyl sulfide (DAS), to decrease the bioactivation-based liver injury of TA. The treatments were as follows: DB/DAS/TA, DB/corn oil/TA, and DB/DAS/saline. Nondiabetic (non-DB) rats received the same treatments as controls. A dose of TA (300 mg/kg ip), which was nonlethal in non-DB rats, caused 92 and 90% mortality in DB/DAS/TA and DB/corn oil/TA groups, respectively. At various times (0--60 h) after treatment, liver injury was assessed by plasma alanine aminotransferase and histopathology. Cell proliferation was evaluated by [(3)H]thymidine incorporation and immunohistochemical staining of proliferating cell nuclear antigen (PCNA). In the DB/DAS/TA rats, DAS pretreatment markedly reduced the CYP2E1-dependent liver injury of TA compared to that in DB/corn oil/TA rats. However, subsequent hepatic DNA synthesis in both DB groups was inhibited approximately 50%. PCNA analysis showed a corresponding decrease in cell-cycle progression. This compromised tissue repair response in DB rats was insufficient to compensate for cell loss, resulting in progression of liver injury and culminating in high mortality in both DB groups. Furthermore, non-DB rats were pretreated with a CYP2E1 inducer, isoniazid, to increase the bioactivation-based TA liver injury equal to the liver injury observed in DB/DAS/TA rats. Despite equal injury up to 36 h following TA treatment, the tissue repair response in the non-DB rats was highly stimulated to compensate for liver injury and led to 70% survival in this group. These studies underscore the importance of adequate and timely tissue repair in compensating for liver injury and protecting from lethality.

Hepatic encephalopathy in rats with thioacetamide-induced fulminant hepatic failure: role of endotoxin and tumor necrosis factor-alpha

BACKGROUND

Hepatic encephalopathy, a complex neuropsychiatric syndrome secondary to acute liver failure, chronic parenchymal liver disease or portal-systemic shunting, may possibly develop through mediators of endotoxin and tumor necrosis factor-alpha (TNF-alpha). However, there are no published data concerning the relationships between the severity of encephalopathy and the plasma levels of endotoxin and TNF-alpha.

METHODS

Male Sprague-Dawley rats weighing about 300-350 g were used. Fulminant hepatic failure was induced by intraperitoneal injection ofthioacetamide (350 mg/kg/day) for 3 consecutive days. Severity of encephalopathy was assessed by measuring motor counts using an Opto-Varimex animal activity meter. Plasma levels of endotoxin and TNF-alpha were determined by chromogenic Limulus assay and ELISA method, respectively.

RESULTS

Our study revealed that higher plasma levels of endotoxin (> 5.9 pg/ml) and TNF-alpha (> 18.8 pg/ml) were significantly associated with more blunted motor activities in rats with fulminant hepatic failure (p < 0.05). A significant correlation was observed between plasma concentrations of endotoxin and TNF-alpha (r = 0.59, p < 0.001). Plasma levels of endotoxin were weakly correlated with the total movements in an open field (r = -0.34, p = 0.032) and the counts of ambulatory (r = -0.38, p = 0.014) and vertical movements (r = -0.40, p = 0.010). There were no correlations between the motor counts and plasma levels of TNF-alpha (p > 0.05).

CONCLUSIONS

In addition to endotoxin and TNF-alpha, other factors may participate in the pathogenesis of hepatic encephalopathy in rats with thioacetamide-induced fulminant hepatic failure.

Reversible decrease of dopamine D2 receptor density in the striatum of rats with acute hepatic failure

The binding of a D2 receptor ligand, [3H]spiperone, was measured in striatal membranes derived from rats in which acute hepatic failure induced with thioacetamide (TAA) was associated with symptoms of hepatic encephalopathy (HE), and during recovery from HE. A 28% decrease of Bmax for the binding was measured in a symptomatic stage of HE, 1 day after TAA administration. The B(max) for [3H]spiperone binding was no longer different from control 7 days after TAA administration, when blood and brain biochemical correlates of HE were already absent. At 21 days after TAA administration, the B(max) was increased by 31% above the control level, consistent with other aspects of metabolic activation of the brain characteristic of the late recovery period from acute HE.

Preclinical models of hepatic encephalopathy

Hepatic encephalopathy is a multifactorial neuropsychiatric syndrome accompanying acute or chronic liver failure. Techniques for developing animal models of hepatic encephalopathy associated with acute or chronic liver failure, or vascular shunting are illustrated. In addition, the behavioral and biochemical characteristics of these models are described.

Xanthine oxidase-derived reactive oxygen metabolites contribute to liver necrosis: protection by 4-hydroxypyrazolo[3,4-d]pyrimidine

Xanthine oxidase (XO) generates reactive oxygen metabolites (ROM) as a by-product while catalyzing their reaction. The present study implicates these ROM in the pathogenesis of liver necrosis produced in rats by the intraperitoneal administration of thioacetamide (TAA; 400 mg/kg b.wt.). After 16 h of TAA administration, the activity of rat liver XO increased significantly compared to that of the control group. At the same time, the level of serum marker enzymes of liver necrosis (aminotransferases and alkaline phosphatase) and tissue malondialdehyde content also increased in TAA treated rats. Tissue malondialdehyde concentration is an indicator of lipid peroxidation and acts as a useful marker of oxidative damage. Pretreatment of rats with XO inhibitor (4-hydroxypyrazolo[3,4-d]pyrimidine; allopurinol (AP)) followed by TAA could lower the hepatotoxin-mediated rise in malondialdehyde level as well as the level of marker enzymes associated with liver necrosis. The survival rate also increased in rats given AP followed by the lethal dose of TAA. In either case, the effect of AP was dose-dependent. Results presented in the paper indicate that increased production of XO-derived ROM contributes to liver necrosis, which can be protected by AP.

Reassessment of monoethylglycinexylidide as preoperative liver function test in a rat model of liver cirrhosis and man

It is known that lidocaine is rapidly metabolized by the hepatic cytochrome P-450 system to form monoethylglycinexylidide (MEGX), its primary metabolite. We analyzed serum MEGX levels experimentally and clinically by fluorescent polarization immunoassay to reassess preoperative liver microsome functions.

EXPERIMENTAL STUDY

Liver cirrhosis was produced in rats by intra-abdominal injection of thioacetamide. MEGX, indocyanine green test (ICG), and liver biochemical variables were measured periodically. Then, survival rates were assessed after the rats received a 70% hepatectomy.

CLINICAL STUDY

MEGX levels were measured in various human patients with chronic hepatitis or liver cirrhosis who underwent hepatectomy. Serum MEGX levels significantly dropped and ICG levels significantly rose with macroscopic and histologic progression of liver cirrhosis in rats. The MEGX levels correlated closely with albumin levels and ICG. Preoperative MEGX and ICG levels of the mortal group of rats differed significantly from those of the survival group with 70% hepatectomy. Furthermore, 100% of the rats with MEGX levels above 40 ng/ml and ICG levels below 1.0%. In the clinical study, MEGX levels were significantly lower in patients with chronic hepatitis or liver cirrhosis than in healthy volunteers and correlated significantly with liver function tests such as albumin, Fischer's ratio, prothrombin time, hepaplastin and ICG. A significant difference was found in MEGX levels between patients receiving lobectomy and those receiving subsegmentectomy or partial hepatectomy. All patients tolerated their operations. Our data indicate that the MEGX test combined with ICG test and Child-Pugh classification is a better predictor of residual liver reserve capacity, and the analysis of hepatic MEGX formation might prove useful for rapid and reliable assessment liver function and choice of surgical treatment.

Endotoxin clearance and its relation to hepatic and renal disturbances in rats with liver cirrhosis

BACKGROUND/AIMS

Little is known about endotoxin clearance and secretion of cytokines from macrophages in liver cirrhosis. The aims of this study were to investigate the relationship of endotoxin clearance and release of tumor necrosis factor alpha by various macrophages to hepatic and renal disturbances in liver cirrhosis.

METHODS

Male Sprague-Dawley rats were given 0.04% thioacetamide orally for 6 or 12 months. The organ distribution of infused [3H]-endotoxin (10 microg/kg b.w.) was analyzed at 30 min or at 24 h. Uptake of [3H]-endotoxin and secretion of tumor necrosis factor alpha by Kupffer cells, splenic macrophages and peripheral blood monocytes (1 x 10(4) cells/ml) from cirrhotic and control rats were determined.

RESULTS

In cirrhotic rats, more endotoxin was left in the body and more endotoxin accumulated in the spleen and kidney, and thus was related to elevation of serum total bilirubin, aspartate aminotransferase, alanine aminotransferase, blood urea nitrogen, creatinine and tumor necrosis factor alpha. Endotoxin uptake and tumor necrosis factor alpha release by the Kupffer cells were decreased and those by the splenic macrophages and peripheral blood monocytes were increased in cirrhotic rats.

CONCLUSIONS

In liver cirrhosis, impaired clearance of endotoxin together with increased secretion of tumor necrosis factor alpha by extrahepatic macrophages may play an important role in the progression of hepatic and renal disturbances.

Transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats: effects of different cytotoxins on cytochrome P450 mediated monooxygenase functions and on oxidative state

Syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fisher 344 inbred rats. Four months after surgery, transplant recipients and age matched control rats were treated with different cytotoxins (allyl alcohol [AAL], bromobenzene [BBZ], carbon tetrachloride [CCl4], or thioacetamide [TAA]) or the respective solvents 24 or 48 hours before sacrifice. Effects of the cytotoxins on P450 mediated monooxygenase functions in liver and spleen 9,000 g supernatants were assessed by measuring the model reactions ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD), pentoxyresorufin O-depentylation (PROD), and ethylmorphine N-demethylation (EMND). Additionally, the influence on the oxidative state was investigated by assessing the liver and spleen tissue content of lipid peroxidation (LPO) products and of reduced and oxidized glutathione (GSH;GSSG). The livers of both solvent treated transplant recipients and control rats displayed regular EROD, ECOD, PROD and EMND activities. After AAL treatment EROD and EMND activities within the livers were not affected, but ECOD and PROD activities were increased. BBZ administration caused a decrease in EROD and EMND activities, ECOD activity remained unaffected, and PROD activity was even increased. CCl4 and TAA administration caused a strong reduction in the activity of all four model reactions. Spleens of control rats displayed almost no P450 mediated monooxygenase functions, independent whether the rats had been treated with the cytotoxins or not. In the transplant containing spleens, however, significant EROD and ECOD, but hardly any PROD or EMND activities were seen. After AAL administration EROD activity was not affected in the transplant containing spleens, but ECOD activity was increased. BBZ treatment led to a decrease in EROD and an elevation in ECOD activity. CCl4 and TAA strongly reduced the activity of both of these model reactions. The tissue content of LPO products within livers and transplant containing spleens was significantly increased after BBZ and CCl4 treatment. An elevation in LPO products was also seen in the spleens of the control rats due to CCl4 administration. Tissue GSH and GSSG content in both livers and transplant containing spleens were strongly reduced after BBZ treatment. After CCl4 administration only a significant decrease in liver GSSG contents was seen. TAA treatment caused a reduction in the GSH and GSSG content in the spleens of both transplant recipients and control rats, but not in the livers. From these results it can be concluded, that the effects of cytotoxins like AAL, BBZ, CCl4 or TAA on P450 dependent monooxygenase functions and on oxidative state are exerted in the ectopic intrasplenic liver cell transplants in a similar way as in normal orthotopic liver.

Restitutive response of Mini rat liver to injury induced by a single oral administration of thioacetamide

Mini rats are a transgenic rat strain carrying antisense gene for rat growth hormone (GH), resulting in retarded growth and a lower blood GH level (136 +/- 42.0 ng/mL) compared with that of age-matched parental strain Wistar rats (329 +/- 337 ng/mL). Mini rats have been used by several investigators as a GH deficiency model. In this work, we gave a single oral administration of thioacetamide (TAA), a hepatotoxicant, to both Mini rats and Wistar rats to ascertain the influence of GH deficiency on liver response to chemically induced injury and subsequent regeneration. TAA administration caused liver injury in both strains, with a greater extent of injury in Mini rats. Proliferation of bile epithelial cells and so-called oval cells was prominent at Day 3 in Mini rats only, and this change correlated well with serum total bilirubin concentrations. Antibody against Ki-67 antigen revealed that cellular proliferation after TAA-induced liver injury was suppressed but prolonged in the Mini rat liver. Although hepatic stellate cells and Kupffer cells/macrophages were more abundant in the livers of TAA-treated Mini rats, the hepatic expression patterns of hepatocyte growth factor and transforming growth factor beta 1 were comparable to those of Wistar rats. Insulin-like growth factor-I gene expression was significantly reduced in the Mini rat liver. Our results imply that a lower GH level may exacerbate chemically induced liver injury, enhance infiltration/proliferation of non-parenchymal cells, suppress regeneration of hepatocytes, and induce proliferation of bile epithelial cells and oval cells when the liver is injured by TAA.

Altered remodeling of nucleolar machineries in cultured hepatocytes treated with thioacetamide

Thioacetamide (TA) is converted into a hyperacetylating agent which causes hepatic necrosis, regeneration, cirrhosis and cancerous transformation. One of the most characteristic toxicities of TA in rat is observed with a 50 mg/kg per day which induces nucleolar enlargement different from that in regenerating liver. From TA-treated liver, the nucleoli were isolated and characterized for an altered nucleolar signal transduction system. Immunochemistry revealed that the poisoned nucleoli had increased levels of both nucleolus specific proteins (nucleophosmin and nucleolin) and various signal molecules (CK2, Erk1/2, p38, protein kinases A and C, and cyclin A). Using flow cytometry, the nucleoli were found to be in G2-arrested nuclei. Manifestation of the nucleolar enlargement could be readily observed using an ex vivo hepatocyte culture. There were two types of nucleolar enlargement. One was observed in normal hepatocytes with light density of enlarged nucleoli. The other was in TA-treated hepatocytes with dense and compact density of enlarged nucleoli, which contained a 3 to 5-fold higher nudeophosmin content than the control. In vitro induction of nucleolar enlargement with TA was possible. As soon as the hepatocytes anchored on a collagen coat, exogeneous TA (higher than 1 microg/mL) could induce dense and compact nucleoli. However, when an exogeneous drug was added after monolayer formation (1 day), no drug-induced nucleolar enlargement was observed.

The protective effect of taurine against thioacetamide hepatotoxicity of rats

Thioacetamide (TAA) administration (three consecutive intraperitoneal injections of 400 mg/kg at 24-h interval) to rats resulted in hepatic injury as assessed by the measurement of serum transaminase activities and histopathological findings. This treatment caused an increase in the levels of malondialdehyde (MDA), diene conjugates (DCs) and glutathione (GSH) and the activity of superoxide dismutase SOD ), and a decrease in the levels of vitamins E and C and the activity of glutathione peroxidase (GSH-Px) in the liver of rats. Taurine administration (400 mg/kg, i.p., every 12 h and started 24 h prior to the first TAA injection) was found to decrease serum transaminase activities and hepatic lipid peroxidation without any significant change in hepatic antioxidant system. Histopathological findings also suggested that taurine has ameliorated effect on TAA-induced hepatic necrosis. These results indicate that taurine treatment, together with TAA administration, diminished the severity of the liver injury by decreasing oxidative stress due to its possible scavenger effect.

Extracellular concentrations of taurine, glutamate, and aspartate in the cerebral cortex of rats at the asymptomatic stage of thioacetamide-induced hepatic failure: modulation by ketamine anesthesia

Subclinical hepatic encephalopathy (SHE) was produced in rats by two intraperitoneal injections of TAA at 24 h intervals and the animals were examined 21 days later. Concentrations of the neuroactive amino acids taurine (Tau), glutamate (Glu) and aspartate (Asp), were measured in the cerebral cortical microdialysates of thioacetamide (TAA)-treated and untreated control rats. During microdialysis some animals were awake while others were anesthetized with ketamine plus xylazine. There was no difference in the water content of cerebral cortical slices isolated from control and SHE rats, indicating a recovery from cerebral cortical edema that accompanies the acute, clinical phase of hepatic encephalopathy in this model. When microdialysis was carried out in awake rats, dialysate concentrations of all the three amino acids were 30% to 50% higher in SHE rats than in control rats. Ketamine anesthesia caused a 2.2% increase of water content of cerebral cortical slices and increased Asp, Glu, and Tau concentration in microdialysates of control rats. In SHE rats, ketamine anesthesia produced a similar degree of cerebral edema, however, it did not alter Asp and Glu concentrations in the microdialysates. These data may reflect on one hand a neuropathological process of excitotoxic neuronal damage related to increased Glu and Asp, on the other hand neuroprotection from neuronal swelling indicated by Tau redistribution in the cerebral cortex. The reduction of the effects of SHE on Glu and Asp content in ketamine-anesthesized rats is likely to be due to interference of ketamine with the NMDA receptor-mediated component of the SHE-evoked excitatory neurotransmitter efflux and/or reuptake of the two amino acids. By contrast, the SHE-related increase of Tau content was not affected by ketamine anesthesia, indicating that the mechanism(s) underlying SHE-evoked accumulation of Tau must be different from the mechanism causing release of excitatory amino acids. The results with ketamine advocate caution when using this anesthetic in studies employing the cerebral microdialysis technique for measurement of extracellular amino acids.