Role of periductal and ductular epithelial cells of the adult rat pancreas in pancreatic hepatocyte lineage. A change in the differentiation commitment

Development of pancreatic hepatocytes in adult rats maintained on copper deficient diet containing 0.6% trien (CuDT) has been reported recently. To elucidate the histogenesis of hepatocytes a sequential study was undertaken using morphologic, histochemical, immunochemical, in situ hybridization, and Northern blot analysis. Male F-344 rats weighing 80 to 90 g were fed CuDT for 8 weeks and returned to normal rat chow. Beginning from 4 weeks of copper depletion, there was a progressive loss of acinar cells and by 8 weeks more than 90% of the acinar tissue was lost. During this period, there was an increase in the number of adipocytes in the interstitium, and in the number of interstitial and ductular cells. Morphologic observations were confirmed by immunoblot and Northern blot analysis, in which the amount of pancreatic proteins and their mRNAs decreased between 5 and 8 weeks. During this period, a progressive increase in the level of albumin mRNA was observed. In situ hybridization, performed at 7 weeks of copper deficiency, showed localization of albumin mRNA over interstitial and ductular cells. Pancreatic hepatocytes were identified immediately after the rats were returned to a normal diet and gradually increased in number. The hepatocytes occupied almost 60% of the pancreatic volume by 8 weeks. During the early recovery phase, hepatocytes were identified in ductules as well as in the interstitium. Based on these studies, it is concluded that both the ductular cells and interstitial cells, which resemble oval cells of liver, are capable of transforming into pancreatic hepatocytes and these cells may be considered stem-cell equivalent.

gamma-Glutamyltranspeptidase-negative phenotypic property of preneoplastic and neoplastic liver lesions induced by ciprofibrate does not change following 2-acetylaminofluorene administration

Preneoplastic and neoplastic lesions induced by peroxisome proliferators in the livers of rats and mice do not express gamma-glutamyltranspeptidase (GGT). Previous studies have shown that the absence of GGT is not due to the toxic effect of peroxisome proliferators or due to the presence of inactive enzyme. The present experiment was designed to examine whether the GGT-negative property of these lesions is stable and irreversible or whether these lesions can be modulated to express GGT by 2-acetylaminofluorene (AAF). Hepatic lesions were induced in F-344 rats by feeding ciprofibrate (0.025%) in diet for 60 or 84 weeks. These rats were then administered AAF in diet (0.02%) for 5 weeks and the altered areas (AAs), neoplastic nodules (NNs) and hepatocellular carcinomas were analyzed for the expression of GGT. Ninety per cent of carcinomas, 90-100% of NNs and greater than 60% AAs were negative for GGT following AAF treatment. These results are very similar to the phenotypic features observed in the livers of rats treated with ciprofibrate alone. The results of this study suggest that the GGT-negative property of ciprofibrate-induced lesions is stable and not modulatable by AAF.

Pancreatic acinar cell regeneration following copper deficiency-induced pancreatic necrosis

Rats maintained on a diet deficient in copper for up to 8-10 weeks exhibit marked necrosis and depletion of acinar cells in the pancreas. When these animals are subsequently fed a copper-supplemented diet, foci of hepatocyte differentiation emerge by about 12 weeks. The present study deals with pancreatic changes during copper depletion and determines the extent of regenerative capacity of the pancreas during the early phases of copper supplementation. During the period of copper depletion, the pancreas gradually decreased in size, and by eight weeks of deficiency weighed approx. 30% as much as the control pancreas. Light-microscopic examination showed focal necrosis of acinar cells at 4 weeks, loss of lobular architecture by six weeks and loss of 85-90% of acinar tissue by eight weeks. Regeneration of the pancreas was initiated by feeding copper-supplemented diet at the end of eight weeks of copper deficiency. The wet weight of the pancreas increased gradually, and by 17 days it weighed 50% more than on the first day of regeneration. Mitotic activity was observed mainly in the acinar cells, beginning at 24 h and reaching a maximum of 19 +/- 1/1000 acinar cells at 72 h, and decreasing steadily thereafter. [3H]Thymidine autoradiography showed a labeling index of 51 +/- 1.7/1000 acinar cell nuclei at 24 h, reaching a peak value of 261 +/- 5.5/1000 acinar cells at 96 h. By 17 days, pancreatic regeneration was only partially complete; however, the proliferative activity was still persistent, albeit at a slower pace. Morphometric analysis of the pancreas on the 17th day of regeneration showed that acinar tissue occupied only 37% of the volume, as compared to 84% in the normal pancreas. These studies clearly demonstrate that acinar tissue of the pancreas following copper deficiency is capable of regeneration, but that the recovery of the pancreas is only partial. Additional studies are necessary to establish the role of this early acinar cell regeneration in pancreatic hepatocyte differentiation.