Analysis of the IGF Axis in Preneoplastic Hepatic Foci and Hepatocellular Neoplasms Developing after Low-Number Pancreatic Islet Transplantation into the Livers of Streptozotocin Diabetic Rats

Abstract

SUMMARY:Preneoplastic hepatic foci have been demonstrated in liver acini, which drain the blood from intraportally transplanted pancreatic islets in streptozotocin-induced diabetic rats with mild persisting diabetes. In long-term studies of this animal model, hepatocellular adenomas and carcinomas (HCC) developed after a sequence of characteristic preneoplastic hepatic foci. In this experimental model, the local hyperinsulinism is thought to have a causative role. Because insulin and the insulin-like growth factor (IGF) axis are closely linked, an altered gene expression of the IGF axis components is likely. Therefore, preneoplastic hepatic foci and HCC were studied for the expression of IGF axis components. Glycogen-storing "early" preneoplastic hepatic foci were detectable several days after pancreatic islet transplantation. Northern blot analysis, in-situ hybridization, and immunohistochemical studies of these "early" lesions demonstrated increased expressions of IGF-I and IGF binding protein-4 (IGFBP-4) in altered parenchymal cells, and a decreased expression of IGFBP-1. IGF-II was not detected in these preneoplastic foci. HCC arising in this model had decreased expressions of IGF-I and IGFBP-4 but IGFBP-1 expression was not significantly altered. Some HCC showed a more than 100-fold overexpression of IGF-II, whereas other tumors were completely negative for IGF-II expression. Low IGF-I receptor expression was detected in preneoplastic foci and adjacent nonaltered liver tissue. However, HCC tissue consistently showed an increased IGF-I receptor expression, rendering these tissues susceptible to the mitogenic effects of IGF. The altered gene expression in glycogen-storing preneoplastic hepatic foci, especially the up-regulation of IGF-I and IGFBP-4 with the down-regulation of IGFBP-1, resemble the insulin-dependent regulation of these components in normal rat hepatocytes. These data agree with previous studies demonstrating a correspondence of the focal character, morphology, and enzyme pattern of preneoplastic hepatic foci with insulin effects on hepatocytes. The development from preneoplastic foci to HCC may be driven by insulin itself and/or an altered IGF axis component or yet unidentified factors. (Lab Invest 2000, 80:1399-1411.

Overexpression of fatty acid synthase in chemically and hormonally induced hepatocarcinogenesis of the rat

“…This confirms the results of a previous study that investigated the gene expression of the IGF axis components in detail and that, apart from an overexpression of IGF-1 and IGFBP-4, demonstrated downregulation of IGFBP-1 in this model. 6 The most intriguing result of the array analysis was the discovery of FAS overexpression in the FAH, confirmed by RT-PCR. FAS gene expression in rat hepatocytes is regulated by both insulin and glucose.…”

“…At this stage, insulin effects manifested in several aspects, that is, an increase in glycogen storage and proliferative activity, lipid accumulation, and altered expression of several insulinrelated proteins, including IGF-I and its binding proteins, such as IGFBP-1 and IGFBP-4. 1,4,6 Moreover, we recently demonstrated increased insulin signalling within the FAH, reflected in a translocation of the insulin receptor and overexpression of several insulin signal transduction proteins, such as insulin receptor substrate-1, Raf-1 and Mek-1. 7 The carbohydrate metabolism in FAH has also been thoroughly investigated and was altered in an insulin-typical manner, 5 showing downregulation of glucose-6-phosphatase or upregulation of hexokinase and glucose-6-phosphate dehydrogenase among other altered enzyme activities.…”

“…4 Previous results indicate that insulin is the primary trigger for the development of FAH and hepatocarcinogenesis in this model. 1,[4][5][6][7] In the beginning of the carcinogenic process, however, these FAH can be regarded as purely adaptative in nature. At this stage, insulin effects manifested in several aspects, that is, an increase in glycogen storage and proliferative activity, lipid accumulation, and altered expression of several insulinrelated proteins, including IGF-I and its binding proteins, such as IGFBP-1 and IGFBP-4.…”

Hepatocellular neoplasms induced by low-number pancreatic islet transplants in autoimmune diabetic BB/Pfd rats

“…These include an up-regulation of enzymes of glycolysis (hexokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase), de novo lipid synthesis ( fatty acid synthase), and the pentose phosphate pathway (glucose-6-phosphate dehydrogenase), whereas key enzymes of gluconeogenesis (glucose-6-phosphatase), glycogenolysis (glycogen phosphorylase), and adenylate cyclase activity were down-regulated (20,23). Insulin effects in the CCF also manifested in an overexpression of apolipoprotein A-IV (25) and in an altered expression of proteins of the insulin-like growth factor (IGF) pathway in the CCF, including IGF-I and its binding proteins, such as IGF binding protein (IGFBP)-1 and IGFBP-4 (22). Moreover, we have recently shown strongly increased insulin signaling in CCF after islet transplantation, reflected in a translocation of the insulin receptor and in an overexpression of several insulin signal transduction proteins of the Ras-Raf-mitogenactivated protein kinase (MAPK) pathway, such as insulin receptor substrate-1 (IRS-1), Raf-1, and Mek-1 (24).…”

“…A possible explanation for the relationship of diabetes mellitus and liver cancer is provided by our previous studies in an animal model of hormonally induced hepatocarcinogenesis in which intrahepatic low number (i.e., 350-450 islets) pancreatic islet transplantation in streptozotocin-diabetic Lewis rats seemed to be the primary trigger for carcinogenesis (19)(20)(21)(22)(23)(24)(25)(26). Sole high number (i.e., 1,000-2,000 islets) transplantation in streptozotocin-diabetic Lewis rats, in which the h-cells of the grafts are not maximally stimulated to secrete insulin and the resulting local hyperinsulinemia is relatively slight, does not suffice to induce the carcinogenic process (19,21).…”