A possible association between glucagon-like peptide-1 (GLP-1) analogs and incidences of pancreatitis has been suggested based on clinical studies. In male and female diabetic Zucker diabetic fatty (ZDF) rats, we investigated the effects of continuous administration of liraglutide and exenatide on biochemical [lipase, pancreatic amylase (P-amylase)] and histopathological markers of pancreatitis. Male and female ZDF rats were dosed for 13 wk with liraglutide (0.4 or 1.0 mg·kg(-1)·day(-1) sc once daily) or exenatide (0.25 mg·kg(-1)·day(-1) sc, Alzet osmotic minipumps). P-amylase and lipase plasma activity were measured, and an extended histopathological and stereological (specific cell mass and proliferation rate) evaluation of the exocrine and the endocrine pancreas was performed. Expectedly, liraglutide and exenatide lowered blood glucose and Hb A(1c) in male and female ZDF rats, whereas β-cell mass and proliferation rate were increased with greatly improved blood glucose control. Whereas neither analog affected lipase activity, small increases in P-amylase activity were observed in animals treated with liraglutide and exenatide. However, concurrent or permanent increases in lipase and P-amylase activity were never observed. Triglycerides were lowered by both GLP-1 analogs. The qualitative histopathological findings did not reveal adverse effects of liraglutide. The findings were mainly minimal in severity and focal in distribution. Similarly, the quantitative stereological analyses revealed no effects of liraglutide or exenatide on overall pancreas weight or exocrine and duct cell mass or proliferation. The present study demonstrates that, in overtly diabetic male and female ZDF rats, prolonged exposure to GLP-1 receptor agonists does not affect biochemical or histopathological markers of pancreatitis, and whereas both exenatide and liraglutide increase β-cell mass, they have no effect on the exocrine pancreas. However, clinical outcome studies and studies using primate tissues and/or studies in nonhuman primates are needed to further assess human risk.

New insulin analogues with a longer duration of action and a flatter pharmacodynamic profile are developed to improve convenience and safety for diabetic patients. During the nonclinical development of such analogues, safety studies must be conducted in nondiabetic rats, which consequently are rendered chronically hypoglycemic. A rat comparator model using human insulin would be valuable, as it would enable differentiation between effects related to either persistent insulin-induced hypoglycemia (IIH) or a new analogue per se. Such a model could alleviate the need for an in-study-comparator and thereby reduce the number of animals used during development. Thus, the aims of the present study were i) to develop a preclinical animal model of persistent hypoglycemia in rats using human insulin infusion for four weeks and ii) to investigate histopathological changes in sciatic nerves and quadriceps femoris muscle tissue, as little is known about the response to persistent hypoglycemia in these tissues. Histopathologic changes in insulin-infused animals included axonal degeneration and myofibre degeneration. To our knowledge, this is the first study to show that persistent IIH provokes peripheral nerve and skeletal myofiber degeneration within the same animals. This suggests that the model can serve as a nonclinical comparator model during development of long-acting insulin analogues.

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.

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.

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