Lipoproteins and apolipoprotein patterns in rat plasma after liver injury induced by D-galactosamine

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)

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.

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

The effect of an acute liver injury induced by thioacetamide (TAA) on hepatic and serum lipoprotein metabolism in rats was studied using biochemical and ultrastructural methods. A single dose of 100 mg TAA/kg body weight caused within 48 h a decrease of hepatic triglyceride (TG) output into the serum by about 50% in comparison to the controls. The steady state of serum TG concentration from 24 to 96 h after TAA treatment implies that the clearance of TG from serum must be diminished to the same extent as the hepatic TG output was found to decrease. Moreover, the TAA treatment caused changes in the electrophoretic mobility as well as in the concentration and composition of circulating serum-lipoproteins. The electrophoresis revealed a decrease in the alpha-band, which can be explained by the decrease in the high density lipoproteins (HDL) total lipid concentration. The pre-beta-migrating band disappeared, whereas a broad beta-mobility band appeared, which most likely consists of a mixture of very low density lipoproteins (VLDL) and low density lipoproteins (LDL) as can be concluded from the changes in concentration and composition of lipids in both fractions. For a better visualization of the VLDL-forming capability in perilobular and centrolobular liver parenchymal cells of the TAA-treated animals the VLDL secretion blocking agent colchicine was used. It was shown that in comparison with colchicine-treated controls the VLDL secretory products are accumulated at a considerably lower rate manifested in a diminution of VLDL clusters, secretory vesicle size and the number of intravesicular VLDL particles.(ABSTRACT TRUNCATED AT 250 WORDS)

On the mechanism of lactate dehydrogenase leakage from normal and D-galactosamine-treated hepatocytes in monolayer culture

Synthesis, degradation and leakage of lactate dehydrogenase and of total protein was measured using D-galactosamine-treated rat hepatocytes in monolayer culture. The kinetics of [3H]leucine incorporation into trichloroacetic acid-precipitable material and into isolated lactate dehydrogenase of cells and of the extra-cellular space revealed a similar extent of inhibition of both synthesis and leakage following exposure to D-galactosamine. Hepatocyte cultures that had been labeled before D-galactosamine treatment lost intracellular protein-associated radioactivity almost as rapidly as control cells up to the time of measurable enzyme leakage; thereafter, the rate of 3H-loss increased in the treated cells. Lactate dehydrogenase present in the medium is degraded less rapidly than the enzyme in the intracellular space. This explains the apparent increase of total lactate dehydrogenase activity in D-galactosamine-treated as compared to control cultures. Following [3H]leucine addition to D-galactosamine-treated cultures, the specific radioactivity of the leaked lactate dehydrogenase in the medium was never greater than that of the enzyme in the cytosolic compartment. The data rule out a direct excretion of newly synthesized enzyme as a result of D-galactosamine action.

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.

Decreased carbohydrate content of rat plasma apolipoproteins in galactosamine hepatitis

The total carbohydrate content and the monosaccharide composition of plasma apolipoproteins isolated from normal and D-galactosamine-treated rats were investigated. In the lipoprotein classes VLDL, LDL and HDL of control animals, the carbohydrate content was 5,5%, 3,4% and 2,9% of dry weight apolipoprotein, respectively. 24 h after galactosamine treatment, these values dropped to 1.8%, 1.6% and 2.3%. The reduction of the carbohydrate content in VLDL and LDL was mainly due to a decrease of the following monosaccharides: Mannose, galactose, N-acetylglucosamine and sialic acid. Minor changes were observed in the fucose, glucose and N-acetylgalactosamine content. Particularly, the mannose/galactose ratio in the LDL fraction fell from 2.3 in control animals to 1.0 in the galactosamine-treated animals. In another series of experiments, the time course of these carbohydrate alterations in the LDL apolipoprotein was studied. As early as 3 h after galactosamine application, we found a reduction of the mannose, galactose and N-acetylglucosamine levels, with the absolute minimum at 24 h, and later on a normalization at 48 and 72 h.