Comparative effects of epidermal growth factor, an insulin-glucagon combination, and a hepatocyte growth factor preparation on epidermal growth factor receptors

Gefitinib, an EGFR inhibitor, prevents hepatocellular carcinoma development in the rat liver with cirrhosis

Epidermal growth factor receptor (EGFR) binds transforming growth factor alpha (TGF-alpha) which is mitogenic for hepatocytes. Diverse lines of evidence suggest that activation of the TGF-alpha /EGFR pathway contributes to hepatocellular carcinoma (HCC) formation. Herein, we developed an experimental model of cirrhosis giving rise to HCC and tested the antitumoral effect of gefitinib, a selective EGFR tyrosine kinase inhibitor, in this model. Rats received weekly intraperitoneal injections of diethylnitrosamine (DEN) followed by a 2-week wash-out period that caused cirrhosis in 14 weeks and multifocal HCC in 18 weeks. Hepatocyte proliferation was increased in diseased tissue at 14 weeks compared with control liver and at even higher levels in HCC nodules compared with surrounding diseased tissues at 18 weeks. Increased proliferation was paralleled by upregulation of TGF-alpha messenger RNA expression. A group of DEN-treated rats received daily intraperitoneal injections of gefitinib between weeks 12 and 18. In rats treated with gefitinib, the number of HCC nodules was significantly lower than in untreated rats (18.1 +/- 2.4 vs. 3.7 +/- 0.45; P < .05), while EGFR was activated to a lesser extent in the diseased and tumoral tissues of these animals compared with untreated rats. HCC nodules from both untreated and gefitinib-treated animals displayed insulin-like growth factor 2 overexpression that contributed to tumor formation in treated animals. In conclusion, the blockade of EGFR activity by gefitinib has an antitumoral effect on the development of HCC in DEN-exposed rats, suggesting that it may provide benefit for the chemoprevention of HCC.

Induction of cholestasis in the perfused rat liver by 2-aminoethyl diphenylborate, an inhibitor of the hepatocyte plasma membrane Ca2+ channels

BACKGROUND AND AIMS

An increase in the cytoplasmic free Ca2+ concentration in hepatocytes as a result of the release of Ca2+ from intracellular stores and Ca2+ inflow from the extracellular space is a necessary part of the mechanism by which bile acids are moved along the bile cannaliculus by contraction of the cannaliculus. 2-Aminoethyl diphenylborate (2-APB) is a recently discovered inhibitor of store-operated plasma membrane Ca2+ channels in hepatocytes. The aim of the present study was to test the ability of 2-APB to inhibit bile flow.

METHODS

Bile flow was measured in the isolated perfused rat liver using cannulation of the common bile duct. Measurements were carried out in the presence or absence of 2-APB in either the presence of taurocholic acid (to enhance basal bile flow) or in the absence of taurocholic acid and in the presence of the hormones vasopressin and glucagon, which are known to stimulate bile flow.

RESULTS

In livers perfused in the presence of taurocholic acid, 2-APB reversibly inhibited bile flow with a slow time of onset. The time of onset of inhibition was reduced by prior addition of the endoplasmic reticulum (Ca(2+) + Mg2+)adenosine triphosphatase inhibitor, 2,5-di-t-butylhydroquinone. In livers perfused in the absence of taurocholate, 2-APB had little effect on the basal rate of bile flow, but inhibited the ability of vasopressin and glucagon to stimulate bile flow.

CONCLUSIONS

It is concluded that an inhibitor of hepatocyte plasma membrane Ca2+ channels can induce cholestasis. The results provide evidence that suggests that, over a period of time, the normal function of hepatocyte store-operated Ca2+ channels is required to maintain bile flow. Future strategies directed at the regulation of bile flow might include pharmacological or other interventions that modulate Ca2+ inflow to hepatocytes.

Butyrate inhibits and Escherichia coli-derived mitogen(s) stimulate DNA synthesis in human hepatocytes in vitro

Bacterial constituents and products of the bacterial metabolism pass from the gut lumen to the portal vein and may influence the homeostasis of the liver. Our aim is to examine whether DNA synthesis of human hepatocyte cell lines is affected by constituents of Escherichia coli species as well as by intracolonic products of bacterial fermentation that reach the liver via the portal vein. Supernatant solutions and bacterial cell fractions (containing either whole dead bacteria, cell walls, cytosol or non-soluble intracellular components) of E. coli K12 and of E. coli species from rat fecal flora were separated by multi-step centrifugation, French press, and microfiltration. The supernatant solution and the cell fractions were incubated with a human hepatoma cell line (Hep-G2) and with a cell line derived from non-malignant human liver cells (Chang cells) for 24 h. The cells were labeled with tritiated thymidine before processing to autoradiography. DNA synthesis was estimated by the labeling index (LI%). DNA synthesis was also estimated following incubation of Hep-G2 cells with short chain fatty acids (acetic, propionic, butyric and succinic acid), acetaldehyde, and ammonium chloride. Epidermal growth factor and a water extract of Helicobacter pylori were used as references. The fractions of E. coli from rat fecal flora containing cytosol and non-soluble intracellular components significantly increased the labeling index in both Hep-G2 and Chang cells (p < 0.05). In addition, the supernatant solution significantly increased the LI in Chang cells (p < 0.05). Epidermal growth factor increased the LI of Hep-G2 cells dose-dependently (p < 0.05). Butyric acid reduced DNA synthesis at 10(-4) M (p < 0.05). The highest doses of acetaldehyde were cytotoxic and reduced the LI. Escherichia coli species contain mitogenic factors to human hepatocytes. The mitogen(s) are present in the supernatant solution, in the cytosol and in non-soluble intracellular components. Butyrate, which is a product of bacterial fermentation of colonic substrates inhibit DNA synthesis in the hepatocyte cell lines. Our findings suggest that soluble mitogen(s) that diffuse from the microorganism to the outer environment, intracellular bacterial constituents, and products of the bacterial metabolism that reach the liver via the portal vein may influence the cell kinetic steady-state of hepatic cells.

Down regulation of epidermal growth factor receptors in rat hepatocytes treated with clofibric acid

The effect of clofibric acid (CA), a peroxisome proliferator and a non-genotoxic hepatocarcinogen was investigated on epidermal growth factor (EGF) receptors in hepatocytes of female Sprague-Dawley rats treated at a dose of 9000 ppm in a diet for up to 13 weeks. Hepatocyte plasma membranes were isolated in Weeks 1 and 13, and assayed with [125I]EGF. The binding of EGF to the hepatocyte plasma membranes was reduced in Week 1 as a result of decreased number of low-affinity receptors. The fall of binding capacity was further evident in Week 13, which was associated with decreased numbers of both high- and low-affinity receptors. The equilibrium dissociation constant remained unchanged either in Week 1 or 13. These results were in agreement with previous observations of a decreased hepatocyte response to mitogens after prolonged treatment with CA. This suggested that the CA-associated liver tumor promoting effect is related to its ability to decrease the number of EGF receptors and the resultant aberrant growth environment.

EGF causes hyperproliferation and apoptosis in T51B cells: involvement of high and low affinity EGFR binding sites

We have recently described an in vitro model for liver homeostasis which involves growing T51B rat liver epithelial cells with 1 nM epidermal growth factor (EGF). There is an initial period of hyperplasia, lasting about 3 days, which is followed by an increase in apoptosis. The cell density returns to around the confluent control level 5 days after EGF addition. The dose response of T51B cells to EGF shows three distinct growth patterns. We have carried out EGF binding studies that suggest that the occupancy of the low affinity binding site of the EGF receptor, is responsible for the hyperproliferation seen when the cells are grown with high doses of EGF. These studies also suggest that the apoptosis could be triggered by down-regulation of the receptor, in a manner analogous to the removal of a trophic hormone in other systems.