Elektronen- und lichtmikroskopische Untersuchungen am Cytoplasma der Leberzellen nach akuter und chronischer Thioacetamid-Vergiftung

Evaluation of different models of experimentally induced liver cirrhosis for MRI research with correlation to histopathologic findings

RATIONALE AND OBJECTIVES

Three models of experimentally induced liver cirrhosis were evaluated for MRI research on chronic liver disease. The influence of different histopathologic changes in liver fibrosis and cirrhosis on relaxation times and signal intensities was studied in vitro and in vivo.

METHODS

Liver fibrosis and cirrhosis in rats was induced by oral or subcutaneous administration of carbon tetrachloride (CCl4) or by thioacetamide (TAA) in drinking water. On histology, the degree of liver fibrosis and cirrhosis, fatty infiltration, iron accumulation, and inflammatory changes were measured semiquantitatively. The amount of connective tissue was quantitatively determined by morphometry. The results were correlated with T1 and T2 relaxation times and signal intensities of the liver studied in vitro by relaxometry and in vivo by MRI.

RESULTS

In both groups with CCl4 administration, histology revealed different degrees of liver fibrosis and cirrhosis. Subcutaneous injection of CCl4 also resulted in increased fatty infiltration. On the contrary, TAA produced complete liver cirrhosis in all animals. Overall, there was a good correlation between the liver T2 relaxation time and the amount of connective tissue in liver fibrosis and cirrhosis. However, the degree of liver fibrosis and cirrhosis was also strongly correlated with the degree of inflammatory changes. In the group with CCl4 administration, there was a good correlation between the fatty infiltration and the T1 relaxation time, as well as with the liver signal intensity on the T1-weighted gradient echo sequence. An increased iron accumulation was also correlated with the degree of liver fibrosis/cirrhosis; however, there was no significant influence of the iron on relaxation times or signal intensities.

CONCLUSIONS

The TAA model is easier to perform and more reliable in liver cirrhosis induction than the CCl4 models. Although there is a positive correlation between the T2 relaxation times and the degree of liver fibrosis/cirrhosis, this probably results from the associated inflammatory changes and is not caused by the increased amount of connective tissue.

Zonal differences in lipoprotein formation in the thioacetamide-induced micronodular-cirrhotic rat liver

The aim of the studies was to answer the question to what extent thioacetamide-induced structural alterations of hepatic architecture leading to fibrosis and micronodular pseudolobuli affect the formation of very low density lipoproteins and the zonation of lipoprotein metabolism observed in normal and acutely injured livers. Therefore, the number of the VLDL particles/Golgi complex and the relative specific volume of Golgi complexes as well as the number and relative specific volume of VLDL-filled vesicles was determined in lobular and nodular zones of normal and the micronodular-cirrhotic livers, respectively. The perinodular and centrinodular regions were morphometrically analysed in nodules with diameters between 0.3 and 0.5 mm. -Generally, in thioacetamide-induced micronodular liver cirrhosis a zonality was observed with respect to the amount of VLDL particles as well as the number and volume of organelles involved in the formation and secretion of hepatic lipoproteins. However, the number of VLDL particles/Golgi complex was significantly reduced to 52% in the centrinodular and to 71% in the perinodular region of cirrhotic livers when compared with the corresponding periportal and perivenous area, respectively. Furthermore, the relative specific volume of the Golgi complexes markedly increased in the perinodular region, thus abolishing the zonal difference observed in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Early liver cell lesions in rats induced by thioacetamide. An ultrastructural, cytophotometric and autoradiographic study

A morphological, cytophotometrical and autoradiographical study was carried out on the early liver cell lesions present after one month of thioacetamide (TAA) exposure. We wanted to determine the extent of cell damage in the hepatocytes in relation to the later occurring cholangiocarcinoma. Cytoplasmic and nuclear alterations were present in the hepatocytes. They were mainly due to the toxic influence of the metabolites of TAA. No Feulgen-DNA changes have been observed in the hepatocytes in any of the studied zones. The increased TdR H3+ uptake and mitotic activity in the periportal and midzonal areas represented regenerative activity. In addition to these hepatocytic changes, the centrolobular area was infiltrated by oval cells. These cells appeared at first singly, later on they formed clusters. The electron microscopy of these cells revealed phenotypic characteristics, which were different from the hepatocytes. When separately, these cells resembled undifferentiated cells with cytoplasmic extensions and absent basement membrane. When arranged in clusters, a definite canalicular arrangement was present with characteristics of bile canalicular cells with microvillous extensions at the apical border of the cytoplasm and the presence of a basement membrane. A transition from the first oval cell type to the second oval cell type was suggested. This transition might represent a differentiation process of cells, which are regarded as the target cell and the precursor cell in the development of the cholangiocarcinoma. This is the first study reporting oval cell proliferation in the centrolobular area in a multistep model of livercarcinogenesis in rats.

Relation between renal and hepatic excretion of drugs: VII. Hepatic and renal excretion of phenol red in thioacetamide-induced acute and chronic liver damage

Acute and chronic liver damage was induced in rats by thioacetamide (TAA). Centrilobular liver cell damage associated with an accumulation of lipid droplets was produced by a single high dose (10 mg TAA/100 g b.m.). Liver fibrosis, micronodular and macronodular liver cirrhosis were induced by chronic TAA treatment (300 ml/l drinking water for 1.5, 3 or 6 months). Acute administration of TAA caused a significant decrease of hepatic phenol red excretion but no compensatory increase of its urinary excretion. In contrast, 24 h after bile duct ligation renal excretion of the dye increased by about 50%. After chronic exposure to TAA for three months hepatic phenol red excretion remained reduced and renal excretion raised significantly. This compensatory increase of urinary excreted phenol red amounts did not occur after 6 months of TAA treatment, probably as a result of additional nephrotoxicity of TAA. Two weeks after cessation of TAA exposure for 3 months, hepatic and renal phenol red excretion returned to normal. Bile flow per animal increased significantly after 3 months of TAA exposure. Apparently this is due to a reduced intrahepatic reabsorption of canalicular bile in TAA-damaged liver.

Locoregional application of 5-fluorouracil to the liver: alteration of pharmacokinetics and bone marrow toxicity in rats with thioacetamide-induced cirrhosis

Pharmacokinetics and toxicity of 5-fluorouracil (5-FU) applied intra-arterially into the liver were studied in control and cirrhotic rats. Cirrhosis was induced by administering thioacetamide (4.5 mg/rat X day) over 6 months. 5-FU was administered into the hepatic artery at 30 mg/kg b.w. by bolus injection followed by infusion of 0.63 mg/kg X min for 40 min. Pharmacokinetics of 5-FU in plasma was studied by HPLC analysis. 5-FU induced toxicity was examined in a second group of control and cirrhotic rats at 48 and 168 hours after treatment with 5-FU (31.4 mg/kg b.w.) infused into the liver artery for 1 h. Analysis of toxicity was carried out by determining liver enzymes in plasma, bone marrow cellularity and colony forming units in vitro (CFU-C) and in vivo (CFU-S). The results indicate that during the period investigated (85 min) 5-FU was not eliminated from the plasma of cirrhotic rats in contrast to controls. The constant level of 5-FU in the plasma of cirrhotic rats induced a considerably higher myelosuppression in these animals, than the short-lived 5-FU peak in controls.

Functional impairment of mitochondria from rat livers acutely injured by thioacetamide

Thioacetamide, when administered in a dose of 100 mg/kg body weight to adult female rats, leads to functional disturbances in mitochondria isolated from livers 24 h after its application. The RCI is significantly reduced due to an increase in state 4 respiration and a lowered state 3 activity. Maximum respiratory activity of the mitochondria is also depressed. The mitochondrial Ca2+-content is significantly increased to 185%. In accordance with the uncoupling effect the Ca2+-transport behaviour of the hepatic mitochondria from thioacetamide-injured rats is altered. The results are indicative of structural alterations of the inner mitochondrial membranes.

Histogenesis of cholangiomas and cholangiocarcinomas in thioacetamide fed rats

A sequential, histologic analysis of the livers of male albino rats chronically fed the hepatocarcinogen thioacetamide (TAA) is performed after one, two, three, four, eight and twelve months of treatment. Liver cell alterations present after one, two and three months consist of centrolobular liver cell degeneration and oval cell proliferation. After 8 months of TAA treatment, a variety of benign tumors (cystadenomas, angiomas, cholangiomas) is observed. From the 12th month all experimental animals develop cholangiocarcinomas. Pulmonary metastases are discovered after 15 months. The role of the oval cells in relation to the later appearing cholangiocarcinoma is discussed. A review of literature is given.

Qualitative and quantitative changes in hepatic lipoprotein particles following acute injury of the rat liver induced by thioacetamide

Acute intoxication of the rat liver with a single dose of 100 mg thioacetamide (TAA)/kg body weight causes within 48 h a fatty liver and a heterogeneous reaction in the hepatocytes. This affects principally the centrilobular liver parenchymal cells (zone 3) and to a lesser extent the periportal ones (zone 1). Ultrastructural analysis was performed to determine to what extent the formation of lipid-carrying particles of the very low density type (VLDL) is changed in affected hepatocytes in zones 1 and 3. Being morphologically the most conspicuous site of VLDL processing, the Golgi complex was chosen for quantitation by measuring its volume, VLDL content and particle size. The concentration and composition of the liver lipids were determined, biochemically. After TAA treatment of the liver the number of Golgi-VLDL particles is significantly reduced to about 50% in both the lobular zones examined. In addition, distinct classes of size-modified Golgi-VLDL particles appear which show an abnormally wide size distribution pattern. In periportal hepatocytes the size distribution of Golgi-VLDL particles shows a clear shift towards smaller particles homogeneous in size (mean diameter 39 nm). In contrast, centrilobular hepatocytes contain particles of very heterogeneous size, the mean diameter of which is nearly doubled (77 nm). The decrease in VLDL particle number and their size modification induced by TAA is not accompanied by significant changes in the volume of the Golgi complex. Biochemical analysis showed that the accumulation of lipids in the TAA-treated liver, mainly evident morphologically as drop-like deposits in the central area of the liver lobules, is due to an increase in triglycerides (TG) by 23 mumol/g liver wet weight, which represents nearly 95% of the accumulated lipids. Despite the striking elevation of the absolute cholesterol ester (CHOL-E) content (2 mumol/g liver wet weight), this corresponds to only 5% of the newly accumulated lipids. Our electron optical and biochemical results support the suggestion that, in spite of the markedly different intralobular reaction of TAA-intoxicated hepatocytes, the formation of triglyceride-carrying particles is altered significantly in both lobular zones examined.

The pattern of D-galactosamine-induced hepatocellular injury modified by simultaneous application of D (--)-fructose

As shown by light and electron microscopy, and by biochemical investigation, D-galactosamine-induced hepatocellular injury in the rat can be prevented by giving fructose simultaneously. However, when injected 3 h after D-galactosamine, fructose has no protective effect. It is suggested that rapid fructose phosphorylation, with the consequent marked depression of the hepatocellular ATP pool, inhibits the more prolonged D-galactosamine phosphorylation and with it the injurious effects of D-galactosamine metabolism.

Metabolic zonation in thioacetamide-induced liver cirrhosis

After TAA administration to rats a central part may be distinguished histochemically from a marginal part in most of the cirrhotic nodules. The centre is characterized by a high glycogen content and by high activity of phosphorylase, G6Pase and SDH; the maxima of which are situated around the larger blood vessels. The vasculatory periphery, however, shows moderate G6PDH-activity. The marginal parts of the nodules are poor in glycogen and possess only weak G6Pase and phosphorylase activity, whereas high SDH- and G6PDH-activity can be demonstrated here. This distribution pattern leads to the conclusion that the larger blood vessels in the centre of the nodules are themselves the terminal afferent vessels. Thus the centre of the nodule corresponds to periportal zone 1, while G6PDH-activity marks the area corresponding to zone 3. The fact that the marginal parts of the nodules are marked by high SDH- but weak G6Pase-activity is interpreted as the result of a preferential arterial supply to this parenchymal part. The high G6PDH-activity of the marginal part is seen in context with the regeneration processes. In all animals single nodules could be found with a high glycogen content and extremely high G6PDH-activity. This loss of heterogeneity is interpreted as a first step in the direction of malignancy.

Hemodynamic parameters and blood gas analyses in the normal and the cirrhotic rat

Thioacetamide-fed rats developed cirrhosis with portal hypertension (P portal=23.0 +/- 5.2 cm H2O, controls: 14.4 +/- 1.0 cm H2O). The PO2 of liver tissue was markedly reduced in cirrhosis (PO2=7.6 +/- 3.4 torr, controls 22.3 +/- 5.8 torr), and the aortal pH was significantly lower as well. No correlation was found between portal hypertension, development of large--nodular cirrhosis, and ascites.

Elimination of vasopressin by the normal and the damaged liver. Experiments on unanaesthetized normal and thiocetamide treated rats with a note on the influence of ethanol

Arginine vasopressin was infused into the V. portae and into the V. cava of unanesthetized rats in water diuresis. The differential antidiuretic response of the same animal to these infusions was used to calculate extraction fraction of ADH by the liver. In the normal rat no extraction was detected. The liver of rats hydrated with 5% ethanol extracted 10% and that of rats treated with thioacetamide extracted 60% of the ADH infused into the portal vein. It is postulated that disturbances of liver cell function by narcotics and substances causing liver damage may liberate ADH-destroying ferments into the blood.

Effects of clofibrate (alpha-p-chlorophenoxyisobutyryl-ethyl-ester) on male rat liver

In male rats, fed 0.5% clofibrate in their diet for 8 days and 21 days, the ultrastructural morphometric alterations of the hepatocytes were evaluated and compared with the biochemical data. The morphologic alterations of the microbodies were particularly related to the changes of the catalase activity of the liver homogenates. The results showd a marked hypertrophy of the liver and an increase in the volume of the individual hepatocyte. The numerical density and, even more pronounced, the volume density of the microbodies increased excessively during the treatment. The numerical density of the mitochondria decreased markedly after 21 days of administration. The surface of the rough endoplasmic reticulum showed a significant decrease, whereas the surface of the smooth endoplasmic reticulum showed a hypertrophy. The catalase activity of the liver homogenates increased 2-fold after 8 days and remained at this new steady-state after 21 days of treatment. The results suggest that the enzyme content of the microbodies changed after treatment with clofibrate, and support the suggestion that clofibrate may induce the synthesis of a yet unidentified peroxisomal protein.

Octabromobiphemyl-induced ultrastructural changes in rat liver

Single oral administration of octabromobiphenyls at 1,000 mg/kg, or two consecutive doses of 3,000 mg/kg, to rats produced liver enlargement. Light microscopic examination revealed hepatocellular hyperplasia, margination of basophillic cytoplasm, and foamy cytoplasmic alteration on the third day posttreatment. Laminated cytoplasmic inclusions developed seven days after treatment and subsequently disappeared about one week later. Under electron microscopy, the cytoplasmic margination corresponded to peripherally displaced granular reticulum and the foamy cytoplasm was recognizable as proliferating agranular reticulum with depletion of particualte glycogen. The cytoplasmic inclusions were identified as myelin configurations enclosing lipid bodies, membrane-bound vacuoles with whorled figures, and vesicular agranular reticulum. In the early developmental stages, the myelin figures were studded with ribosomes and associated with the granular reticulum.