Prolonged insulin-induced hypoglycaemia reduces ß-cell activity rather than number in pancreatic islets in non-diabetic rats.

Pancreatic ß-cells have an extraordinary ability to adapt to acute fluctuations in glucose levels by rapid changing insulin production to meet metabolic needs. Although acute changes have been characterised, effects of prolonged metabolic stress on ß-cell dynamics are still unclear. Here, the aim was to investigate pancreatic ß-cell dynamics and function during and after prolonged hypoglycaemia. Hypoglycaemia was induced in male and female rats by infusion of human insulin for 8 weeks, followed by a 4-week infusion-free recovery period. Animals were euthanized after 4 or 8 weeks of infusion, and either 2 days and 4 weeks after infusion-stop. Total volumes of pancreatic islets and ß-cell nuclei, islet insulin and glucagon content, and plasma c-peptide levels were quantified. Prolonged hypoglycaemia reduced c-peptide levels, islet volume and almost depleted islet insulin. Relative ß-cell nuclei: total pancreas volume decreased, while being unchanged relative to islet volume. Glucagon: total pancreas volume decreased during hypoglycaemia, whereas glucagon: islet volume increased. Within two days after infusion-stop, plasma glucose and c-peptide levels normalised and all remaining parameters were fully reversed after 4 weeks. In conclusion, our findings indicate that prolonged hypoglycaemia inactivates ß-cells, which can rapidly be reactivated when needed, demonstrating the high plasticity of ß-cells even following prolonged suppression.

Placental nutrient transporters adapt during persistent maternal hypoglycaemia in rats.

Maternal malnutrition is associated with decreased nutrient transfer to the foetus, which may lead to foetal growth restriction, predisposing children to a variety of diseases. However, regulation of placental nutrient transfer during decreased nutrient availability is not fully understood. In the present study, the aim was to investigate changes in levels of placental nutrient transporters accompanying maternal hypoglycaemia following different durations and stages of gestation in rats. Maternal hypoglycaemia was induced by insulin-infusion throughout gestation until gestation day (GD)20 or until end of organogenesis (GD17), with sacrifice on GD17 or GD20. Protein levels of placental glucose transporters GLUT1 (45/55 kDa isotypes) and GLUT3, amino acid transporters SNAT1 and SNAT2, and insulin receptor (InsR) were assessed. On GD17, GLUT1-45, GLUT3, and SNAT1 levels were increased and InsR levels decreased versus controls. On GD20, following hypoglycaemia throughout gestation, GLUT3 levels were increased, GLUT1-55 showed the same trend. After cessation of hypoglycaemia at end of organogenesis, GLUT1-55, GLUT3, and InsR levels were increased versus controls, whereas SNAT1 levels were decreased. The increases in levels of placental nutrient transporters seen during maternal hypoglycaemia and hyperinsulinemia likely reflect an adaptive response to optimise foetal nutrient supply and development during limited availability of glucose.

Evaluation of Cell Proliferation in Rat Mammary Glands Is Not Predictive of the Carcinogenic Potential of Insulin In Vivo.

For nonclinical safety-assessment of insulin analogues in vivo, mitogenic effects are compared to that of human insulin. Besides histopathologic evaluation, this usually includes assessment of cell proliferation (CP) in mammary glands. Insulin analogue X10 is recommended as positive control, due to its known carcinogenic effect in rat mammary glands. Here, we discuss the mitogenic effect of insulin in vivo and use of X10 as positive control. We present results from 4 nonclinical rat studies evaluating effects of repeated dosing with insulin detemir (≤26 weeks) or degludec (52 weeks) in mammary glands. Studies included human insulin-dosed groups as comparators, CP, and histopathologic evaluation. One study included an X10-dosed group (26 weeks), another ≤3 weeks of dosing with X10 or human insulin evaluating effects of these comparators. Neither human insulin, insulin detemir, degludec, nor X10 induced mammary tumors or increased CP in the studies. The CP marker proliferating cell nuclear antigen varied within/between studies and was not correlated with the remaining markers or CP fluctuations during estrous cycle, whereas the other CP markers, Ki-67 and 5-bromo-2'-deoxyuridine (BrdU), correlated with estrous cycle changes and each other. In conclusion, we propose that the mitogenic effect of insulin in rat mammary glands is weak in vivo. Cell proliferation evaluation in nonclinical safety assessment studies is not predictive of the carcinogenic potential of insulin, thus, the value of including this end point is debatable. Moreover, X10 is not recommended as positive control, due to lack of proliferative effects. Typical CP markers vary greatly in quality, BrdU seemingly most reliable.

Inner histopathologic changes and disproportionate zone volumes in foetal growth plates following gestational hypoglycaemia in rats.

Maternal hypoglycaemia throughout gestation until gestation day (GD)20 delays foetal growth and skeletal development. While partially prevented by return to normoglycaemia after completed organogenesis (GD17), underlying mechanisms are not fully understood. Here, we investigated the pathogenesis of these changes and significance of maternal hypoglycaemia extending beyond organogenesis in non-diabetic rats. Pregnant rats received insulin-infusion until GD20 or GD17, with sacrifice on GD20. Hypoglycaemia throughout gestation increased maternal corticosterone levels, which correlated with foetal levels. Growth plates displayed central histopathologic changes comprising disrupted cellular organisation, hypertrophic chondrocytes, and decreased cellular density; expression of pro-angiogenic factors, HIF-1α and VEGF-A increased in surrounding areas. Disproportionately decreased growth plate zone volumes and lower expression of the structural protein MATN-3 were seen, while bone ossification parameters were normal. Ending maternal/foetal hypoglycaemia on GD17 reduced incidence and severity of histopathologic changes and with normal growth plate volume. Compromised foetal skeletal development following maternal hypoglycaemia throughout gestation is hypothesised to result from corticosterone-induced hypoxia in growth plates, where hypoxia disrupts chondrocyte maturation and growth plate structure and volume, decreasing long bone growth. Maternal/foetal hypoglycaemia lasting only until GD17 attenuated these changes, suggesting a pivotal role of glucose in growth plate development.

Lipid Embolism in Obese Göttingen Minipigs.

Pigs are used as a model of human obesity, both for metabolic characterization and for evaluation of pharmacological interventions. Over a period of 7 years, acute death or clinical signs requiring immediate euthanasia were observed in 12 obese Göttingen minipigs (GMs) included in different pharmacological studies. The GM were fed ad libitum on normal chow-diet and the unscheduled deaths occurred in animals treated with drug candidates as well as in untreated animals. The most prominent clinical signs requiring euthanasia included varying degrees of respiratory distress; and on histopathological examination, thickening of the alveolar septa due to vacuolation was observed throughout the lung in 10 of the 12 animals. Furthermore, vacuolation in glomeruli of the kidney was detected in 9 of the 10 animals. Oil red O staining of cryosections demonstrated that the vacuoles both in lung and kidney contained lipid, and immunohistochemistry with anti-von Willebrand factor and transmission electron microscopy revealed that the lipid was localized in the lumen of blood vessels establishing the occurrence of fatal pulmonary lipid embolism. Additionally, lipogranulomatous inflammation in the abdominal adipose tissue was observed in all the GMs with lipid emboli.

The Effect of Diet-induced Obesity on Toxicological Parameters in the Polygenic Sprague-Dawley Rat Model.

The obese rodent serves as an indispensable tool for proof-of-concept efficacy and mode-of-action pharmacology studies. Yet the utility of this disease model as an adjunct to the conventional healthy animal in the nonclinical safety evaluation of anti-obesity pharmacotherapies has not been elucidated. Regulatory authorities have recommended employing disease models in toxicology studies when necessary. Our study investigated standard and exploratory toxicology parameters in the high-fat diet (HFD)-induced obese, polygenic Sprague-Dawley rat model in comparison to chow diet (CD)-fed controls. We sought to establish feasibility of the model for safety testing and relevance to human obesity pathophysiology. We report that both sexes fed a 45% kcal HFD for 29 weeks developed obesity and metabolic derangements that mimics to a certain extent, common human obesity. Minor clinical pathologies were observed in both sexes and considered related to CD versus HFD differences. Histopathologically, both sexes exhibited mild obesity-associated findings in brown and subcutaneous white fat, bone, kidneys, liver, lung, pancreas, salivary parotid glands, and skeletal muscle. We conclude that chronic HFD feeding in both sexes led to the development of an obese but otherwise healthy rat. Therefore, the diet-induced obese Sprague-Dawley rat may serve as a suitable model for evaluating toxicity findings encountered with anti-obesity compounds.

Proximal Neuropathy and Associated Skeletal Muscle Changes Resembling Denervation Atrophy in Hindlimbs of Chronic Hypoglycaemic Rats.

Peripheral neuropathy is one of the most common complications of diabetic hyperglycaemia. Insulin-induced hypoglycaemia (IIH) might potentially exacerbate or contribute to neuropathy as hypoglycaemia also causes peripheral neuropathy. In rats, IIH induces neuropathy associated with skeletal muscle changes. Aims of this study were to investigate the progression and sequence of histopathologic changes caused by chronic IIH in rat peripheral nerves and skeletal muscle, and whether such changes were reversible. Chronic IIH was induced by infusion of human insulin, followed by an infusion-free recovery period in some of the animals. Sciatic, plantar nerves and thigh muscle were examined histopathologically after four or eight weeks of infusion and after the recovery period. IIH resulted in high incidence of axonal degeneration in sciatic nerves and low incidence in plantar nerves indicating proximo-distal progression of the neuropathy. The neuropathy progressed in severity (sciatic nerve) and incidence (sciatic and plantar nerve) with the duration of IIH. The myopathy consisted of groups of angular atrophic myofibres which resembled histopathologic changes classically seen after denervation of skeletal muscle, and severity of the myofibre atrophy correlated with severity of axonal degeneration in sciatic nerve. Both neuropathy and myopathy were still present after four weeks of recovery, although the neuropathy was less severe. In conclusion, the results suggest that peripheral neuropathy induced by IIH progresses proximo-distally, that severity and incidence increase with duration of the hypoglycaemia and that these changes are partially reversible within four weeks. Furthermore, IIH-induced myopathy is most likely secondary to the neuropathy.

Long-Term Safety of PEGylated Coagulation Factor VIII in the Immune-Deficient Rowett Nude Rat.

Turoctocog alfa pegol (N8-GP) is a glycoPEGylated human recombinant factor VIII for the treatment of hemophilia A. The safety profile of rFVIII, and polyethylene glycols (PEG) technology, is well-established. Conducting long-term toxicity studies in animals using human proteins can be complicated by anti-drug antibody (ADA) development. To evaluate long-term safety of N8-GP, 26- and 52-week toxicity studies were conducted in immune-deficient rats dosed intravenously every fourth day with 0, 50, 150, 500, or 1200 IU/kg N8-GP. Observations included clinical observations, body weight, ophthalmoscopy, hematology, chemistry, coagulation, urinalysis, toxicokinetics, antibody analysis, and macroscopic/microscopic organ examination. Immunohistochemical staining examined the distribution of PEG in the brain. No adverse test item-related findings were seen and PEG was not detected in the brain. Exposure was confirmed for ~75% of the animals dosed with 500 and 1200 IU/kg N8-GP; the high lower limit of quantification of the bioanalysis assay prevented confirmation of exposure in the lower doses. A small number of animals developed ADAs, and the proportion of animals surviving until scheduled termination was >80%. N8-GP was well tolerated, and the immune-deficient rat proved suitable for testing long-term toxicity of human proteins that are immunogenic in animals.

Evaluation of Nonacog Beta Pegol Long-term Safety in the Immune-deficient Rowett Nude Rat (Crl:NIH-Foxn1rnu).

Nonacog beta pegol is a 40-kDa polyethylene glycosylated (PEGylated) human recombinant coagulation factor IX, intended for the treatment of hemophilia B. Human coagulation factors are immunogenic in animals; therefore, to evaluate the long-term toxicity of nonacog beta pegol, an immune-deficient, athymic rat (Rowett nude; Crl:NIH-Foxn1(rnu)) was used. Rats (n = 216) were given intravenous nonacog beta pegol 0, 40, 150, 600, or 1,200 IU/kg every 5th day for 26 weeks. To avoid infections, the animals were housed in a full-barrier environment with sterilized food and bedding. Standard toxicity end points were unaffected by treatment. All treated animals were exposed to nonacog beta pegol throughout the study, and no animals developed antidrug antibodies. Immunohistochemical staining revealed PEG in choroid plexus epithelial cells in a dose-dependent manner. Transmission electron microscopy showed that PEG was distributed in cytoplasmic vesicles of these cells, with no apparent effect on cellular organelle structures. Fourteen (6.5%) animals were euthanized or died prematurely due to nontreatment-related infections in the urogenital system and skin. In conclusion, the athymic rat is a suitable model for testing chronic toxicity of human proteins that are immunogenic in animals. Nonacog beta pegol was generally well tolerated, with no adverse effect of PEG on choroid plexus epithelial cells.

Stimulatory adrenocortical effects of a selective estrogen receptor modulator in ovariectomized female macaques.

Here, we report the effects of estrogen and the selective estrogen receptor modulator (SERM) levormeloxifene on adrenocortical measures in ovariectomized female cynomolgus monkeys (Macaca fascicularis). Animals were randomized into one of five treatment groups, each containing 23 to 26 animals: (1) placebo, (2) 0.016 mg/kg 17ß-estradiol (E(2)), (3) 0.5 mg/kg levormeloxifene (L(1)), (4) 1.0 mg/kg levormeloxifene (L(2)), and (5) 5.0 mg/kg levormeloxifene (L(3)). Treatments were administered orally each day for 18 mo. All doses of levormeloxifene resulted in adrenal weights at least 50% greater than placebo (p < .0001 for all). The target dose of levormeloxifene (L(2)) resulted in higher serum concentrations of cortisol (+63%), dehydroepiandrosterone-sulfate (+73%), and androstenedione (+37%) compared with the placebo group (p < .05 for all). In contrast, E(2) resulted in no significant differences in adrenal weight or adrenocortical steroids. Oral E(2) and all SERM doses resulted in similar reductions in serum gonadotropins and at least threefold greater uterine weight versus placebo (p < .0001 for all). Results indicate that the SERM levormeloxifene, in contrast to E(2), may have robust stimulatory effects on adrenocortical hormones in a postmenopausal model. These findings warrant further investigation into long-term SERM effects on adrenocortical function.

Glucagon-like Peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation.

Liraglutide is a glucagon-like peptide-1 (GLP-1) analog developed for type 2 diabetes. Long-term liraglutide exposure in rodents was associated with thyroid C-cell hyperplasia and tumors. Here, we report data supporting a GLP-1 receptor-mediated mechanism for these changes in rodents. The GLP-1 receptor was localized to rodent C-cells. GLP-1 receptor agonists stimulated calcitonin release, up-regulation of calcitonin gene expression, and subsequently C-cell hyperplasia in rats and, to a lesser extent, in mice. In contrast, humans and/or cynomolgus monkeys had low GLP-1 receptor expression in thyroid C-cells, and GLP-1 receptor agonists did not activate adenylate cyclase or generate calcitonin release in primates. Moreover, 20 months of liraglutide treatment (at >60 times human exposure levels) did not lead to C-cell hyperplasia in monkeys. Mean calcitonin levels in patients exposed to liraglutide for 2 yr remained at the lower end of the normal range, and there was no difference in the proportion of patients with calcitonin levels increasing above the clinically relevant cutoff level of 20 pg/ml. Our findings delineate important species-specific differences in GLP-1 receptor expression and action in the thyroid. Nevertheless, the long-term consequences of sustained GLP-1 receptor activation in the human thyroid remain unknown and merit further investigation.

Abnormal bone collagen morphology and decreased bone strength in growth hormone-deficient rats.

Patients with growth hormone deficiency (GHD) have an increased risk of bone fractures. In these patients, the well-described decrease in bone mineral density (BMD) and content (BMC) may, however, not alone explain the increase in fracture rate. Accordingly, the aim of this study was to evaluate collagen morphology and bone mineralisation in cortical bone as well as bone strength in GHD rats to try to clarify the explanation for the increased fracture rate. The Dw-4 rat was used as a model for GHD. This strain of rats has an autosomal recessive disorder, reducing GH synthesis to approximately 10% and growth rate to approximately 40-50% when compared to normal control rats. Five male Dw-4 rats were examined at age 12 weeks and five healthy Lewis rats served as age-matched controls. The animals were examined for (1) bone mineral status by dual energy X-ray absorptometry (DXA) and ash weight/bone volume, (2) biomechanical properties, (3) serum insulin-like growth factor I (IGF-I) and IGF binding protein 3 (IGFBP-3), and (4) collagen morphology of cortical bone from the right femurs was examined by scanning and transmission electron microscopy. A significant decrease was found in serum IGF-I, IGFBP-3 and biomechanical properties in GHD rats compared to controls (P < 0.009). While DXA-derived BMD was decreased, no significant difference was found in ash weight/bone volume. Electron microscopy showed a significant decrease in the number and a significant increase in the diameter of collagen microfibrils in GHD rats as compared to their controls (P < 0.009). In conclusion, we report for the first time that collagen morphology in bone is markedly altered in rats with isolated GHD. Whether similar conditions are present in GHD patients need further investigations. The changes described, however, may provide a co-explanation for the increased fracture rate in GHD.