Biochemical and substructural studies on hepatic and serum lipoprotein metabolism after acute liver injury induced by thioacetamide in rats

Hepatic injury due to combined choline-deprivation and thioacetamide administration: an experimental approach to liver diseases

BACKGROUND

The induction of prolonged choline-deprivation (CD) in rats receiving thioacetamide (TAA) is an experimental approach of mild hepatotoxicity that could resemble commonly presented cases in clinical practice (in which states of malnutrition and/or alcoholism are complicated by the development of other liver-associated diseases).

AIM

The present study aimed to investigate the time-dependent effects of a 30-, a 60- and a 90-day dietary CD and/or TAA administration on the adult rat liver histopathology and the serum markers of hepatic functional integrity.

METHODS

Rats were divided into four main groups: (a) control, (b) CD, (c) TAA and (d) CD + TAA. Dietary CD was provoked through the administration of choline-deficient diet, while TAA administration was performed ad libitum through the drinking water (300 mg/l of drinking water).

RESULTS

Histological examination of the CD + TAA liver sections revealed micro- and macro-vesicular steatosis with degeneration and primary fibrosis at day 30, to extensive steatosis and fibrosis at day 90. Steatosis was mostly of the macrovesicular type, involving all zones of the lobule, while inflammatory infiltrate consisted of foci of acute and chronic inflammatory cells randomly distributed in the lobule. These changes were accompanied by gradually increasing mitotic activity, as well as by a constantly high alpha-smooth muscle actin immunohistochemical staining. The determination of hepatocellular injury markers such as the serum enzyme levels' of alanine aminotransferase and aspartate aminotransferase demonstrated a decrease at day 30 (they returned to control levels at days 60 and 90). However, the determination of those serum enzymes used for the assessment of cholestatic liver injury (gamma-glutamyltransferase, alkaline phosphatase) revealed a constant (time-independent) statistically-significant increase versus control values.

CONCLUSIONS

Long-term combined dietary CD and TAA administration could be a more realistic experimental approach to human liver diseases involving severe steatosis, fibrosis, stellate cell activation and significant regenerative hepatocellular response.

Boron ameliorates fulminant hepatic failure by counteracting the changes associated with the oxidative stress

Boron has well-defined biological effects and may be of therapeutic benefit. In the current paper, the effect of boron in the form of borax was tested in experimental animal model of fulminant hepatic failure (FHF). The syndrome was induced in female Wistar rats by three consecutive daily intraperitoneal injections of thioacetamide (400 mg/kg). In the treatment groups, rats received borax (4.0 mg/kg) orally for three consecutive days followed by thioacetamide. The group administered with thioacetamide plus vehicle, and the borax alone treated rats served as controls. In all groups, rats were terminated 4 h after administering the last dose of thioacetamide, and the tissue/serum was used to measure hepatic levels of thiobarbituric acid reactive substances, reduced glutathione, and various enzymes associated with oxidative stress including peroxide metabolizing enzymes and xanthine oxidase. In thioacetamide treated group, many fold increase in the activity level of serum marker enzymes suggesting FHF was observed that could be brought down significantly in rats receiving boron. Modulation and a correlation in the activity level of oxidant generating enzyme and lipid peroxidation as well as hepatic glutathione level was also observed in rats receiving thioacetamide. In the group receiving boron followed by thioacetamide, these changes could be minimized moderately. The activity level of the peroxide metabolizing enzymes and the tripeptide glutathione, which decreased following thioacetamide treatment were moderately elevated in the group receiving boron followed by thioacetamide. The data clearly shows that borax partly normalizes the liver and offsets the deleterious effects observed in FHF by modulating the oxidative stress parameters.

Serum amino acid changes in rats with thioacetamide-induced liver cirrhosis

To date, no attempt has been made to study alterations occurring in the amino acid profile in chronic models of thioacetamide-induced liver cirrhosis. In this work, changes in serum amino acids and proteins in rats with thioacetamide-induced liver cirrhosis are reported, together with changes in enzyme activities in the liver and serum. Seventeen female Wistar rats were used. Eight rats were given 300 mg thioacetamide/l in drinking water for 4 months and nine rats were given water ad libitum during the same time-period. Significant increases in glycine, alanine, serine, methionine, glutamate, ornithine, phenylalanine, tyrosine, histidine and proline were observed in rats with the resulting experimental liver cirrhosis. Threonine, taurine, glutamine, lysine and citrulline tended to increase while isoleucine, leucine, aspartate, arginine and tryptophan tended to decrease. Total and nonessential amino acids increased significantly in cirrhotic animals. Total essential and aromatic amino acids tended to increase in the thioacetamide-treated group, whereas branched chain amino acids tended to decrease in the same group. Regarding serum proteins, a decrease in albumin concentration in the thioacetamide-treated animals was the only change detected. The liver enzyme activities under observation (aspartate and alanine aminotransferases, glutamate dehydrogenase and threonine deaminase) were lower in the thioacetamide group. Decreases were significant for both transaminases and threonine deaminase. Results for serum activities showed that transaminases did not change in thioacetamide-treated rats in comparison with controls. In contrast, alkaline phosphatase rose dramatically in cirrhotic rats. We conclude that the serum amino acid pattern in this chronic model of liver cirrhosis resembles in part that of the corresponding human disease.

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)

Substructural alterations of liver parenchymal cells induced by xenobiotics

Xenobiotic-induced basic ultrastructural reactions of liver parenchymal cells as visualized with the basic method in ultrastructural research, the transmission electron microscopy, are described. There exists no "average hepatocyte", but even the normal liver is composed of a heterogeneous population of parenchymal cells revealing distinct ultrastructural and functional differences according to the intra-acinar location, circadian rhythms or metabolic and physiologic conditions. This liver cell heterogeneity is, as a rule, very much increased after acute or chronic exposure of the liver to any xenobiotic compound. Although most electron microscopic techniques are laborious and time consuming, electron microscopic research will play a growing role in analysing the response of the hepatocytes to drugs or other newly developed chemicals. There is no doubt that new methods and instrumental improvements will enable us to visualize more and more the primary site of action of any xenobiotic and the underlying molecular mechanisms in the hepatocytes followed by a sequence of events which lead to the manifestation of a complex reaction pattern composed of adaptation, injury, degeneration and reparation of the liver.

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.

Studies on lipid and lipoprotein metabolism in rat liver cirrhosis induced by different regimens of thioacetamide administration

In female Wistar rats the animal model of TAA-induced liver cirrhosis has been tested for reliability and usefulness for studies on lipid and lipoprotein metabolism in cirrhosis. From our results we draw the following conclusions: Application of 300 mg TAA/l drinking water from the 4th to the 6th month of life leads in all treated rats to liver cirrhosis which is rather uniformly of micronodular surface morphology. Under this treatment the survival rate is about 90 percent. Increasing the administered dose (450 and 600 mg/l) and/or extension of TAA administration time (4 or more months) leads to decreasing survival rates, and to a shift from micronodular towards macronodular cirrhosis. To produce macronodular cirrhosis it is suggested to extent the application time rather than to increase the dose since in the latter case the survival rate is very low. The alterations of lipid and lipoprotein metabolism observed in this animal model, i.e. decrease of pre-beta-lipoproteins, increase of beta-lipoproteins, decrease of serum triglyceride concentration and decrease of hepatic VLDL-TG output into the serum are in good agreement with those observed in human cirrhosis. Thus, the TAA-induced chronic liver injury proved to be a reliable and useful model for studies on lipid and lipoprotein metabolism in liver cirrhosis.

Changes in intra- and extrahepatic VLDL in the rat following acute injury by thioacetamide. A morphometric and biochemical study

The effect of a single dose of TAA (100 mg/kg body weight) on intra- and extrahepatic lipoproteins of the very low density (VLDL) type was studied in rats by morphometric and biochemical methods. For a better quantification of VLDL in the periportal (zone 1) and centrilobular (zone 3) hepatocytes of control and TAA-intoxicated livers, colchicine was used as an inhibitor of hepatic lipoprotein secretion. Generally, there exists a great functional heterogeneity between the hepatocytes of zone 1 and 3 in the colchicine-treated controls manifested in a significantly different accumulation rate of VLDL particles. The mean number of VLDL particles per vesicle, the mean secretory vesicle size and the volume density of the electron-lucent secretory vesicles are two times larger in hepatocytes of zone 1 than zone 3. The volume of the VLDL particles amounts to 7.3 X 10(-5) microns3 and 22 X 10(-5) microns3 in the peri- and centrilobular regions. On the other hand, there is no significant lobular-zonal difference in the number of light and dark secretory vesicles. Within 48 h TAA treatment causes a reduction in the number of VLDL particles/100 microns 2 in zone 1 and 3 by 66% and 61%, whereas the number of light secretory vesicles is decreased by 31% and 58%, respectively. The volume density of the latter is significantly diminished only in zone 1. Moreover, the VLDL particle volume is reduced to nearly 50% in each lobular zone examined. The data obtained after TAA treatment from the electron-dense secretory vesicles do not differ significantly from those of the colchicine-treated controls. Acute TAA intoxication lowers the hepatic VLDL-TG output by about 50% in comparison with controls. The steady state of the serum TG concentration after TAA application implies that the clearance of TG from the serum must be diminished to the same extent as the hepatic TG output is found to decrease due to acute liver injury. The results presented here support our view that acute TAA intoxication lowers the hepatic VLDL output by inhibiting the intracellular formation of VLDL. The intrahepatic degradation of the newly synthesized VLDL seems to be unaffected. Despite the fact that the substructure of the hepatocytes in zone 3 is much more changed than in zone 1 after TAA treatment the quantitative data on the VLDL secretory products provide evidence that the process of lipoprotein formation is disturbed to nearly the same extent by TAA both in zone 1 and 3.