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

Abstract

Fatty acid synthase (FAS) is the key enzyme of de novo fatty acid synthesis and has been shown to be involved in carcinogenesis of numerous human malignancies, including breast, colorectal, and prostate carcinomas, often associated with a worse prognosis. Although FAS is mainly expressed in the liver, an implication of FAS in hepatocarcinogenesis, has not yet been investigated. FAS expression is stimulated by insulin and glucose, and insulin is also the primary trigger of hepatocarcinogenesis in an endocrine experimental model, which is induced by low-number transplantation of islets of Langerhans into the livers of diabetic rats. We therefore investigated, whether FAS is implicated in hepatocarcinogenesis in this model and in comparison to chemically induced hepatocarcinogenesis after N-nitrosomorpholine (NNM) treatment in diabetic and normoglycemic rats. Preneoplastic clear-cell foci of altered hepatocytes (FAH), harvested after laser-microdissection of kryostat sections, showed an overexpression of FAS messenger RNA in gene expression profiles, done by arrayhybridization, and in quantitative RT-PCR (Light-Cycler). Virtually, all (96-98%) of the subsequently investigated FAH and the glycogenotic hepatocellular adenomas and carcinomas showed an additional strong FAS protein overexpression. In the NNM-model, FAS protein was also overexpressed in the vast majority (87%) of glycogenotic FAH and neoplasms, in particular in the diabetic animals. Also two spontaneous glycogenotic FAH in control animals displayed strong FAS overexpression. Basophilic lesions and neoplasms, which occasionally develop out of the primary clear-cell FAH at later stages of carcinogenesis, however, lost FAS overexpression. In conclusion, FAS overexpression is an early phenonemon in spontaneous, hormonally and chemically induced rat hepatocarcinogenesis, demonstrable in early clear-cell (glycogenotic) FAH and hepatocellular neoplasms. Keywords: fatty acid synthase; glucose; hepatocarcinogenesis; insulin; islet transplantatation; N-nitrosomorpholine After low-number transplantation of islets of Langerhans into the livers of diabetic rats, the liver acini draining the blood from the islet grafts show cellular alterations, the foci of altered hepatocytes (FAH). 1 FAH resemble the glycogen-storing or clear-cell phenotype of preneoplastic foci known from experimental and human hepatocarcinogenesis. 2,3 In the transplantation model, these preneoplastic FAH may develop into hepatocellular adenomas (HCA) and carcinomas (HCC) within 6-24 months after islet transplantation. 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 a...

Hepatocellular Neoplasms Induced by Low-Number Pancreatic Islet Transplants in Autoimmune Diabetic BB/Pfd Rats

“…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).…”

“…These alterations are reflected in an increase in glycogen and lipid storage, in an increase in cell-turnover, (i.e., high proliferative activity and apoptotic elimination of preneoplastic hepatocytes), as well as in characteristic alterations in the activities of key enzymes, in particular of the carbohydrate and fatty acid metabolism (19-21, 23, 25). 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).…”

Revelation of simple and complex liver acini after portal transplantation of pancreatic islets or thyroid follicles in rats

“…One has not only to accept that there are no anatomical structures in the normal liver that would help to outline the borders of the acinus but also that the acinus outlines are not uniform but depend on several factors, such as the hepatocytes' size (Fig. 2), functional gene activation (e.g., fatty acid synthase, see Evert et al 23 ) or the anatomical location (Fig. 4).…”

“…These alterations are typical insulin effects that have been studied in detail earlier, and were shown to be the results of insulin-induced alterations of enzymes of the carbohydrate and lipid metabolism. [14][15][16][21][22][23] Thus, the altered liver acini sharply contrasted to the hormonally unaffected surrounding liver tissue not only histologically but also even on macroscopic evaluation of unstained liver slices (see below).…”

“…[6][7] Here, we report on our observations made by examining morphologically altered liver acini in animal models that were originally designed to study hormonally induced hepatocarcinogenesis. [14][15][16][17][18][19][20][21][22][23] The altered morphology of the liver acini was induced by local action of hormones [such as insulin and tri-iodothyronine (T3)] on the hepatocellular metabolism after transplantation of endocrine tissues into the rat liver, resulting in considerable changes of the hepatocellular phenotype of the downstream liver acini, such as an excess in glycogen and/or fat storage in the insulin model [14][15][16][17][18][21][22][23] or increased basophilia and loss of glycogen in the T3 model. 20 Therefore, we were able to depict the anatomy of a simple liver acinus for the first time, conclusively proving the correctness of Rappaport's acinus model.…”