Assessment of the labelling index of cohorts of the pancreatic islet cell population in phenobarbitone-treated male rats using a double immunohistochemical technique for 5-bromo-2'-deoxyuridine and pancreatic hormones

Islets of Langerhans from prohormone convertase-2 knockout mice show α-cell hyperplasia and tumorigenesis with elevated α-cell neogenesis

Antagonism of the effects of glucagon as an adjunct therapy with other glucose-lowering drugs in the chronic treatment of diabetes has been suggested to aggressively control blood glucose levels. Antagonism of glucagon effects, by targeting glucagon secretion or disabling the glucagon receptor, is associated with α-cell hyperplasia. We evaluated the influence of total glucagon withdrawal on islets of Langerhans using prohormone convertase-2 knockout mice (PC2-ko), in which α-cell hyperplasia is present from a young age and persists throughout life, in order to understand whether or not sustained glucagon deficit would lead to islet tumorigenesis. PC2-ko and wild-type (WT) mice were maintained drug-free, and cohorts of these groups sampled at 3, 12 and 18 months for plasma biochemical and morphological (histological, immunohistochemical, electron microscopical and image analytical) assessments. WT mice showed no islet tumours up to termination of the study, but PC2-ko animals displayed marked changes in islet morphology from α-cell hypertrophy/hyperplasia/atypical hyperplasia, to adenomas and carcinomas, these latter being first encountered at 6-8 months. Islet hyperplasias and tumours primarily consisted of α-cells associated to varying degrees with other islet endocrine cell types. In addition to substantial increases in islet neoplasia, increased α-cell neogenesis associated primarily with pancreatic duct(ule)s was present. We conclude that absolute blockade of the glucagon signal results in tumorigenesis and that the PC2-ko mouse represents a valuable model for investigation of islet tumours and pancreatic ductal neogenesis.

Lobule-dependent zonal measurement (LZM) method for the determination of cell proliferation in the liver

Using the conventional method of measurement (randomly distributed fields) there is a risk of overlooking a biologically relevant effect due to the different zonal expression of cell proliferation. Therefore a lobule-dependent zonal measurement (LZM) method was developed that guaranteed the independent evaluation of the hepatic zones in lobules of a comparable size. With this method, applied in a 3-month-study, a statistically significant increase in cell proliferation after one week (71%) and a distinct increase after six weeks (49%) and thirteen weeks (32%) of exposure could be proved, whereas the conventional method revealed after one week only a slight increase (22%), after six weeks a distinct but not statistically significant increase (56%) and after thirteen weeks even a decrease of 24%. In comparison, the LZM-method revealed a panlobular increase of cell proliferation after one week of administration, that shifted to the periportal region after six and thirteen weeks representing the target zone as it was shown by electronmicroscopy later on. Since the test substance evoked an increased tumor incidence in both sexes in a lif-span study, the enhanced cell proliferation, in our case especially in the periportal area, seems to be a key mechanism in tumor development. These data confirm that the, LZM-method represents a very sensitive and stable method in the evaluation of cell proliferation in the liver.