Alterations in the functional expression of receptors on cirrhotic rat hepatocytes

Treatment of cirrhotic rats with epidermal growth factor and insulin accelerates liver DNA synthesis after partial hepatectomy

Prevention of postoperative hepatic failure is important after hepatic resection. In patients with cirrhosis, impaired liver function and regenerative capacity after major hepatic resection are associated with increased morbidity and mortality. In this study, a combination of epidermal growth factor (EGF) and insulin were used as hepatotrophic factors in an attempt to stimulate DNA synthesis after 70% hepatectomy (HTX). Regenerative capacity was evaluated in normal and cirrhotic rat liver by measuring DNA synthesis in vivo. Micronodular liver cirrhosis was established by the simultaneous oral administration of CCl4 and phenobarbital. Epidermal growth factor plus insulin was injected subcutaneously immediately after and 12 h after HTX or sham operation was performed. Rats were killed 24 h after the operation and liver regeneration was estimated by [3H]-thymidine incorporation into DNA as well as an autoradiographic nuclear labelling index. Hepatectomy increased [3H]-thymidine incorporation significantly in both normal and cirrhotic rats. In cirrhotic rats, [3H]-thymidine incorporation after HTX was significantly lower than in normal rats and administration of a combination of EGF and insulin after HTX enhanced [3H]-thymidine incorporation. In conclusion, DNA synthesis 24 h after HTX is decreased in cirrhotic rats compared with normal rats and EGF supplementation with insulin accelerates DNA synthesis in hepatectomized cirrhotic rats. The data suggest that administration of combinations of exogenous hepatotrophic factors may play a useful role in the treatment of cirrhotic patients undergoing major hepatic resection.

Differential effect of micronodular and biliary cirrhosis on epidermal growth factor receptor expression in the rat

Cirrhosis is characterized by fibrogenesis, hepatocyte necrosis and the formation of regenerative nodules. Modulation of the epidermal growth factor receptor is an early event during regeneration. We have recently demonstrated alterations in the epidermal growth factor receptor during the development of biliary cirrhosis. The aim of the present study was to compare epidermal growth factor receptor distribution, expression and binding in biliary cirrhosis to that occurring in micronodular cirrhosis induced by phenobarbital/CCl4 exposition. Biliary cirrhosis and micronodular cirrhosis had similar functional impairment as assessed by the aminopyrine breath test. Epidermal growth factor receptor binding capacity was reduced in both models (control vs micronodular cirrhosis vs biliary cirrhosis: (mean +/- 1 SD) 60 +/- 22 vs 16 +/- 12 vs 27 +/- 9 fmol/mg protein, p < 0.05), while the binding constant was increased in biliary cirrhosis only. The receptor mass in plasma membrane, determined by Western blotting, was not changed. Distribution of epidermal growth factor receptor was assessed immunohistochemically on tissue sections. In both models, cytoplasmic staining was decreased and basolateral plasma membrane labeling was maintained. Nuclear localization was found in biliary cirrhosis only. In conclusion, in both models, cirrhosis induces an alteration in the binding properties, but not in the number of epidermal growth factor receptors in the plasma membrane. The loss of cytoplasmic epidermal growth factor receptor could reflect alterations in expression and/or in intracellular trafficking. This is supported by the reduced mRNA steady state levels for epidermal growth factor receptor which were found in both models, presumably representing down-regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Chylomicron metabolism in experimental cirrhosis and cholestasis

Recently it has been demonstrated that artificial emulsions made of lecithin, cholesterol, cholesteryl-oleate and triolein simulate the metabolism of the natural chylomicra. Artificial-chylomicron delipidation and remnant disappearance from plasma were investigated in rats with carbon tetrachloride-induced hepatic cirrhosis or with cholestasis due to bile-duct ligation. Artificial chylomicra were labelled simultaneously with glyceryl tri [9, 10 (N)-3H] oleate and cholesteryl [1-14C] oleate and injected intra-arterially. Simultaneous chylomicron delipidation and remnant removal by the liver were calculated from the plasma radioactivity decay curves: that of glyceryl tri [9, 10 (N)-3H] oleate signifying the combined delipidation and particle-removal processes, whereas that of cholesteryl [1-14C] oleate representing the particle disappearance rate from plasma. Particle delipidation was increased in cirrhosis and decreased in cholestasis, implying faster and slower lipolysis rates respectively. On the other hand, the remnant removal rate by the liver slowed down in both experimental pathologies.

Transforming growth factor-alpha (TGF-alpha) improves hepatic DNA synthesis after hepatectomy in cirrhotic rats

Impaired liver regeneration in cirrhosis complicates the surgical treatment of liver tumors which arise in this setting. We developed a rat model to investigate the regenerative response of cirrhotic liver after hepatectomy and studied the effect of exogenous transforming growth factor-alpha (TGF-alpha), a potent liver mitogen. Micronodular cirrhosis was established by the simultaneous administration of CCl4 and phenobarbital. Hepatic DNA synthesis ([3H]thymidine incorporation into DNA) 24 hr after partial hepatectomy in cirrhotic rats was 15.6 +/- 3.4 cpm/micrograms DNA (means +/- SEM), which was significantly lower than in normal rats (37.3 +/- 3.4 cpm/micrograms DNA, P less than 0.05). Exogenous TGF-alpha (30 nmol/kg, sc every 12 hr) significantly improved [3H]thymidine incorporation (35.6 +/- 8.2 cpm/micrograms DNA, P less than 0.05). An autoradiographic nuclear labeling index also confirmed increased DNA synthesis (6.7% vs 13.4%). TGF-alpha had no effect on normal regenerating liver (42.5 +/- 8.8 cpm/micrograms DNA, NS). Although the significance of TGF-alpha-enhanced liver regeneration in cirrhosis has yet to be assessed, this model may be useful for the study of mechanisms which control hepatic proliferation.

Mechanism of insulin resistance in CCl4-induced cirrhosis of rats

Insulin action was studied in rats with CCl4/phenobarbital-induced cirrhosis of the liver using the euglycemic hyperinsulinemic clamp technique coupled with isotopic measurement of individual tissue glucose uptake, glycogen formation, and lipogenesis. In cirrhotic rats, dose response curves showed a reduction of insulin-stimulated total body glucose disposal of about 30%. Insulin action on tissue glucose uptake and initial phosphorylation (assessed with [3H]2-deoxyglucose) were unchanged; however, incorporation of [14C]glucose into lipids and particularly into glycogen was reduced substantially (being most pronounced in skeletal muscle and diaphragm) at maximally as well as half-maximally effective serum insulin concentrations during euglycemic clamping. At identical IV insulin infusion rates, steady-state serum insulin concentrations were elevated up to fourfold in cirrhotic animals. Antilipolytic action of insulin was unaltered. These data suggest that the principal metabolic pathway affected in insulin resistance of rats with experimental cirrhosis appeared to be insulin-stimulated glycogen formation in muscle tissues.

Asialoglycoprotein receptor in human isolated hepatocytes from normal liver and its apparent increase in liver with histological alterations

We have characterized a binding site for galactosyl terminal glycoproteins in hepatocytes isolated from human biopsies. The binding of asialoorosomucoid on hepatocytes previously treated by Triton X-100 was saturable, calcium-dependent and highly affine (Ka = 1.11 +/- 0.87.10(9) M-1) thus corresponding to a ligand-receptor binding. The total number of receptors in the normal human liver was 140,000 +/- 65,000 sites per cell. This corresponded to the value obtained in the human hepatoma cell line HepG2, but was significantly lower than for isolated rat hepatocytes. Furthermore, in hepatocytes isolated from livers with histological features of either fibrosis, cirrhosis, hepatocarcinoma with cirrhosis or nodular regenerative hyperplasia, the number of asialoglycoprotein receptors per cell was increased, while the binding affinity was unchanged.

The role of capillarization in hepatic failure: studies in carbon tetrachloride-induced cirrhosis

During the cirrhotic process, the hepatic microvascular phenotype is transformed from sinusoids (discontinuous capillaries) into continuous capillaries. This transformation has been termed capillarization. Many hepatic functions depend on the rapid, bidirectional exchange of macromolecules between plasma and hepatocytes. To determine whether capillarization contributes to hepatic failure in cirrhosis, we decided to study the plasma clearance (125I) and hepatocyte uptake (electron microscopy) of three tracers in normal and cirrhotic rats. The tracers chosen were a hemeundecapeptide with peroxidatic activity (fluid-phase pinocytosis), asialofetuin (receptor-mediated endocytosis of a medium size protein) and ferritin (receptor-mediated endocytosis of a large size protein). The results demonstrate a decreased hepatocyte uptake of hemeundecapeptide; a significant delay in plasma clearance of asialofetuin; and a minor delay in plasma clearance of ferritin, but a striking trapping of ferritin in the cirrhotic capillary basement membrane. The delayed plasma clearance in cirrhosis cannot be ascribed to a decreased number of surface receptors because, in isolated hepatocytes, the number of molecules bound per cell was equivalent in normal and cirrhotic livers. These findings support the concept of capillarization, with the formation of continuous diffusion and filtration barriers between plasma and hepatocytes, representing a significant hindrance to the bidirectional macromolecular exchange normally taking place between these two compartments. Furthermore, at least in the case of ferritin, the capillary basement membrane of cirrhotic livers seems to be the major filtration barrier. This hindrance to hepatocyte uptake, and presumably also to secretion, may be the cause (or at least a major determinant) of the hepatic failure characteristic of cirrhosis.

Growth factors, endocrine aspects and hormonal treatment in hepatocellular carcinoma--an overview

Several clinical observations suggest that hepatocellular carcinoma (HCC or "hepatoma") may be a hormone-dependent tumour; the apparent relation to anabolic steroids and oral contraceptive preparations, and the striking male predominance particularly among patients with cirrhosis. In many animal models thyroid hormones, prolactin and testosterone stimulate tumour growth, and the latter may enhance the progression of chemically-induced hyperplastic nodules to frank malignancy. In animals and humans, both oestrogen and androgen receptors have been reported in normal and malignant liver tissue though some of the evidence is conflicting and the amounts detected vary widely. From a therapeutic standpoint, we failed to show any advantage from the addition of tamoxifen to adriamycin, in a controlled trial although other workers have, more recently, reported prolonged survival using tamoxifen alone. About 20% of HCC patients receiving the antiandrogen cyproterone acetate showed a clinical response.

Mitochondrial structure and function in CCl4-induced cirrhosis in the rat

To investigate whether the impairment of mitochondrial function in cirrhosis is due to a reduction in liver cell mass or whether mitochondrial function is altered specifically, we analyzed mitochondrial volume and surface density of mitochondrial membranes in control and cirrhotic rats by stereological means. Cirrhosis was induced by long-term exposure to phenobarbital and CCl4. Hepatocellular and mitochondrial volumes were reduced to a similar extent, by 39% and 40%, respectively, in cirrhotic animals (p less than 0.01). Thus the fraction of hepatocytes occupied by mitochondria did not differ between the two groups. Both total outer (31 +/- 3 vs. 19 +/- 6 m2; p less than 0.01) and inner (87 +/- 24 vs. 45 +/- 12 m2; p less than 0.01) mitochondrial membranes were significantly reduced. Membrane surface was normal per unit of mitochondrial volume, however, suggesting intact mitochondrial structure. Matrix and outer membrane enzyme activities expressed per compartment did not differ between control and cirrhotic animals. Inner membrane, in contrast, had an increased enzyme content per unit area both for cytochrome oxidase (10.3 +/- 2.9 vs. 13.0 +/- 1.6; p less than 0.05) and ATPase (13.7 +/- 1.4 vs. 21.2 +/- 2.9; p less than 0.01). Basal oxygen consumption measured in the perfused liver in situ was significantly reduced in cirrhotic livers (1.6 +/- 0.1 vs. 1.1 +/- 0.4 mumol/min-1/gm-1) but was unchanged when expressed per square meter of inner membrane. Our results demonstrate that impaired mitochondrial function is mainly due to loss of hepatocellular mass. Increased enzyme activity per unit surface area of inner mitochondrial membrane may be important to maintain mitochondrial function of the cirrhotic liver.

Age-related DNA modifications (I-compounds): modulation by physiological and pathological processes

I-compounds are covalent DNA modifications that can be detected and measured by 32P-postlabeling assay because of their DNA-adduct like properties. They accumulate in an age-dependent, highly reproducible manner in tissue DNA of untreated animals in the absence of exogenous carcinogens and, therefore, appear to arise via the interaction of DNA with endogenous reactants formed in the course of normal metabolism. Chromatographically, they exhibit a wide range of polarities, indicative of structural diversity. In addition to age-dependent increases, I-compound profiles exhibit prominent species-, sex-, tissue- and diet-dependent qualitative and quantitative differences. Natural-ingredient (chow) diets produce qualitative differences as well as substantially higher I-compound levels in rat liver and kidney, when compared with purified diets. Modified purified diets containing high carbohydrate, protein, or fat concentrations further modulate I-compound profiles. During liver regeneration, I-compounds behave like DNA adducts rather than m5 C in that their levels are not quickly restored. Treatment of rats with the hepatocarcinogens 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), CCl4, and peroxisome proliferators as well as with a choline-devoid hepatocarcinogenic diet depressed the age-related increases of I-compound levels in liver, the target organ. Additional 32P-labeled derivatives were observed only with the peroxisome proliferators and presumably represent DNA adducts of exogenous origin. No I-compounds were detected in a series of Morris hepatomas with different degrees of differentiation. Thus, loss of I-compounds may be associated with altered gene expression/dedifferentiation. On the other hand, the age-dependent accumulation of I-compounds and their adduct-like character suggest potential relations to aging-associated dysdifferentiation and initiation of cancer. Structural complexity indicates different biological roles of I-compounds.