Studies on experimental diabetes in the Wellesley hybrid mouse. IV. Morphologic changes in islet tissue

Acute and chronic animal models for the evaluation of anti-diabetic agents

Diabetes mellitus is a potentially morbid condition with high prevalence worldwide thus being a major medical concern. Experimental induction of diabetes mellitus in animal models is essential for the advancement of our knowledge and understanding of the various aspects of its pathogenesis and ultimately finding new therapies and cure. Experimental diabetes mellitus is generally induced in laboratory animals by several methods that include: chemical, surgical and genetic (immunological) manipulations. Most of the experiments in diabetes are carried out in rodents, although some studies are still performed in larger animals. The present review highlights the various methods of inducing diabetes in experimental animals in order to test the newer drugs for their anti-diabetic potential.

Deconstructing and reconstructing obesity-induced diabetes (diabesity) in mice

Obesity-driven type 2 diabetes (diabesity) involves complex genetic and environmental interactions to trigger disease. Here, we combine variable numbers of known quantitative trait loci (QTL) for obesity and diabetes contributed by New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/Lt) strains in the form of 10 interval-directed recombinant congenic strains (RCS), with NON/Lt as the background strain, to dissect the genetic interactions involved. All 10 RCS gain significantly more weight than the NON parental strain, but none are as obese as the parental, diabetes-prone NZO. Diabetes development in these RCS at F12 ranges between 0 and 100%, depending on genetic constitution. RCS-2, -1, and -10 represent a step-wise increase in numbers of specific diabetogenic QTL, resulting in a step-wise increase in diabetes incidence. RCS-10 recreates the 100% incidence seen in (NZOxNON)F1 males, but with less weight gain. Similarly, RCS-6, -7, -8, and -9 represent diabetes-prone strains with different combinations of diabetogenic QTL. RCS-3, -4, and -5 represent obese strains that do not transit to diabetes. Because these obesity and diabetes syndromes reflect different collections of QTL, rather than null mutations in the leptin or leptin receptor genes, they are extremely relevant as models for the polygenic obesity/diabesity syndromes in humans.

Paternal-maternal effects on phenotypic characteristics in spontaneously diabetic Nagoya-Shibata-Yasuda mice

The Nagoya-Shibata-Yasuda (NSY) mouse is an inbred strain with spontaneous development of type 2 (non-insulin-dependent) diabetes mellitus. The purpose of this study was to determine the mode of inheritance of various phenotypes related to diabetes in this strain. Two reciprocal outcrosses, female C3H/He x male NSY F1 (C3NF1) and female NSY x male C3H/He F1 (NC3F1) mice, were performed. The phenotypic characteristics in both F1 mice were investigated. The cumulative incidence of diabetes was 100% (25 of 25) in male C3NF1 mice and 97% (29 of 30) in male NC3F1 mice at 48 weeks of age, indicating that diabetes in NSY mice was transmitted to male F1 hybrids in an autosomal dominant manner. Fatty liver also showed an autosomal dominant mode of inheritance. In contrast, epididymal fat accumulation and impaired insulin secretion showed an autosomal recessive mode of inheritance. The body mass index (BMI) showed a codominant mode of inheritance. Paternal-maternal effects associated with the severity of diabetes were observed. Insulin resistance was much more severe in male F1 mice than in the parental NSY strain. These data indicate different modes of inheritance among phenotypes related to type 2 diabetes. The presence of more severe insulin resistance in F1 mice versus the parental strains suggests the interaction of both parental genomes in the development of insulin resistance. The F1 mouse is expected to be useful for studies of the pathogenesis and genetic synergism of the insulin resistance syndrome.

Control of spontaneous glucose intolerance, hyperinsulinemia, and islet hyperplasia in nonobese C3H.SW male mice by Y-linked locus and adrenal gland

An inbred strain predisposition to maturity-onset impairment of glucose tolerance was discovered in C3H.SW/SnJ inbred male mice. Males were group-caged from weaning and subjected to repetitive handling stress; deterioration of glucose tolerance developed between 5 and 8 months of age in association with extreme hyperinsulinemia. Some males developed transient chemical diabetes in which plasma glucose concentrations were inappropriately high in relation to the high levels of plasma insulin. By 12 months of age, males previously glucose intolerant had regained a normal glucose tolerance. At death, a massive hypertrophy and hyperplasia of the islet beta-cells was documented in these mice. The impaired glucose tolerance could be circumvented by adrenalectomy at weaning. Although these finding suggested the presence of an obesity gene, the C3H.SW group-caged males were not obese when compared with C3HeB/FeJ males which, although moderately hyperinsulinemic, did not develop the glucose intolerance syndrome. Transfer of the Y chromosome from the C3HeB/FeChp background into the C3H.SW inbred background led to a reduction in the hyperinsulinemic and hyperglycemic stress on the pancreatic islets. Thus the extrinsic environment (caging and handling stress), mediated in part via the adrenal gland, could interact with sex-linked genetic susceptibility modifiers to stimulate hyperplasia of the pancreatic islets and produce a transient insulin resistant state of impaired glucose tolerance in the absence of obesity.

Islet organ, blood glucose and glucose tolerance of lean and obese Mongolian gerbils. A quantitative study

Gerbils were divided, on the basis of body weight, into obese (greater than 80 gms) and lean (less than 80 gms) groups. Fasting blood glucose estimations on all 31 gerbils, and glucose tolerance tests on 9 lean and 6 obese animals, were carried out. All lean and some obese gerbils were normoglycaemic and other obese were hyperglycaemic. All obese gerbils exhibited glucose intolerance. General morphological studies were undertaken as follows: (i) assessment of mesenteric fat deposits, (ii) measurement of anterior abdominal wall thickness, (iii) ratio of animal length to width at specified loci (index of shape). The degree of obesity was less than previously reported in this species though blood glucose abnormality was comparable. The index of animal shape showed a strong correlation with body weight. The following kinds of histological observation were made on pancreases from 4 lean and 4 obese gerbils: (i) % islet representation, (ii) islet size distribution, (iii) beta-cell granularity, (iv) islet vascularity, (v) islet/duct association, (vi) proportions of alpha- and D-cells, (vii) glycogen deposition in islet and duct cells. The pancreases of obese gerbils contained a higher proportion of islet tissue than those of lean due to generally larger islets: this hyperplasia was mainly attributable to beta-cell proliferation. Many obese gerbil islets exhibited hyperaemia and beta-cell degranulation. There was no evidence of glycogen deposition.

Stereological study of B-cell mitochondria in alloxan-treated mice

Using stereological techniques, including semi-automatic image analysis, the B-cell mitochondria were studied in the pancreatic islets from one group of control mice and two groups of mice killed 10 min and 60 min, respectively, after alloxan administration. Ten min following alloxan the mitochondrial volume and envelope surface densities, the mean mitochondrial volume and surface area, and the area of mitochondrial profiles were significantly increased, whereas the mitochondrial numerical density was not significantly altered. At the 60 min observation time the mitochondrial volume density, the mean mitochondrial volume and surface areas, and the area of mitochondrial profiles were significantly decreased, whereas the mitochondrial envelope surface was not significantly altered. The findings indicate a rapid swelling, followed by disintegration of the mitochondria in the B-cells of alloxan-treated mice, thereby supporting our view that mitochondrial lesions play a primary role in the development of alloxan diabetes. These lesions are believed to be due to ionic alterations in the B-cells ("Pi-pH hypothesis").

Effect of 1.25-dihydroxycholecalciferol administration on blood glucose and pancreatic islet morphology in mice

1.25-dihydroxycholecalciferol (DHCC) administration to fed and starved mice had no effect on the blood-glucose concentration or the light-microscopic appearance of the endocrine or exocrine pancreas. Electron microscopy, however, disclosed changes which appeared early after the injection and were more marked in starved than in fed animals. The B-cells exhibited mitochondrial hypertrophy, studied both by qualitative and quantitative methods, invagination and vacuolation of mitochondrial membranes, increased occurrence of light secretory granules, multiple rough endoplasmic cisternae, multi-lamellar bodies, and a rather rich Ca2+-containing pyroantimonate precipitation mainly localized to nuclei and mitochondria. A tendency to mitochondrial hypertrophy was observed also in some D-cells. The A-cells were unaffected. The findings indicate that the endocrine pancreas (or at least the B-cells) is affected in some way, directly or indirectly, by DHCC.

Pancreatic islets subjected to different concentrations of glucose in vitro. A study with special regard to mitochondrial changes

Isolated pancreatic islets of mice and gerbils were cultured for 6 days at low (2mM) or high (20mM) concentrations of glucose after which they were studied using qualitative and quantitative electron microscopy, histo- and microchemistry, and X-ray microanalysis. Compared with the islets cultured at high glucose, those subjected to low glucose exhibited enhanced succinate dehydrogenase activity, a decreased content of adenosine triphosphate, and an increased volume of B-cell mitochondria which often were rounded or oval.

Mitotic division in pancreatic beta cells

Successful expansion of the islet cell mass occurs in genetically diabetic mice (C57 Bl/Ks-dbdb) following a period of dietary restriction, in the absence of a population of precursor cells. Differentiated cells that synthesize insulin retain the capability of undergoing mitotic division.