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

Abstract

It has been shown that combined high local hyperinsulinism and hyperglycemia after low-number islet transplantation into the livers of streptozotocin-diabetic rats lead to the development of hepatocellular neoplasms but a substantial cocarcinogenic effect of genotoxic streptozotocin could not be ruled out completely. Thus, we herein investigated this model in BB/Pfd rats (n = 805; nine experimental groups), which develop spontaneous autoimmune diabetes similar to human type 1 diabetes. After low-number islet transplantation (n = 450), the liver acini downstream of the islets show insulin-induced alterations: massive glycogen and/or fat accumulation, translocation of the insulin receptor, decrease in glucose-6-phosphatase activity, increase in expression of insulin-like growth factor (IGF)-I, IGF-II/mannose-6-phosphate receptor, insulin receptor substrate-1, Raf-1, and Mek-1, corresponding to clear cell preneoplastic foci of altered hepatocytes known from chemical hepatocarcinogenesis and identical to that in streptozotocin-diabetic Lewis rats. After 6 months, many altered liver acini progressed to other types of preneoplasias often accompanied by an overexpression of the glutathione-S transferase (placental form), IGF-I receptor, and transforming growth factor (TGF)-A. After 12 to 15 and 15 to 18 months, 52% and 100% of the animals showed one or multiple hepatocellular adenomas or hepatocellular carcinomas (HCCs), respectively. Conclusively, this study identifies combined hyperinsulinism and hyperglycemia as a carcinogenic mechanism for the development of HCCs in diabetic rats. Hepatocarcinogenesis is independent from additional genotoxic compounds (i.e., streptozotocin), but is primarily triggered by increased intracellular insulin signaling via pathways associated with cell growth and proliferation, such as the Ras-Raf-mitogen-activated protein kinase pathway and the IGF system, and secondarily involves other growth factors, such as TGF-A. (Cancer Res 2006; 66(3): 1833-43)

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

“…Details of animal treatment and transplantation procedures have been described . 14,16,20 Briefly, in the insulin model, Lewis rats (3 months old; body weight: 250-300 g) were made diabetic by injection of a single subcutaneous dose of streptozotocin (65 mg/kg body weight). Hormone deficiency in the T3 model was reached by thyroidectomy.…”

“…This is a decisive prerequisite for the models to function and was carefully monitored by determining glucose and hormone blood levels as described. 14,16,20 If the systemic hormonal deficiency is secured, each transplanted endocrine tissue piece is permanently stimulated to maximally synthesize and secrete the respective hormone into the portal/sinusoidal blood. In this study we used animals between 1 and 12 weeks after transplantation, because at this time interval, the altered liver morphology was dependent only on primary effects of the grafts as previously shown 14,20 and was thus optimal for the purposes of this experiment.…”

“…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.…”

Metformin and Hepatic Carcinogenesis

“…It is intriguing, however, that separate research has shown that experimental hepatitis C infection is associated with downregulation of AMPK activity, and that restoring AMPK activation by metformininduced energy stress reduces viral infection and some of its consequences (16). Another example of interesting research in this context is evidence that insulin (which reaches the liver in high concentrations in the hyperinsulinemic phase of type II diabetes) is sufficient to induce liver cancer (17,18); thus, information concerning insulin levels and signaling downstream of the insulin receptor in the presence and absence of metformin in the model of Bhalla and colleagues (2) would be of interest. Another unanswered question is the relevance of the recently described metformin-induced inhibition of mitochondrial ROS production in vitro to step-wise carcinogenesis in vivo (4).…”