ABSTRACT
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.
Subject(s)
Diet, High-Fat/adverse effects , Disease Models, Animal , Obesity/etiology , Animals , Anti-Obesity Agents/toxicity , Biomarkers/blood , Biomarkers/urine , Body Weight/physiology , Drug Evaluation, Preclinical , Estrous Cycle/physiology , Female , Male , Obesity/blood , Obesity/physiopathology , Obesity/urine , Organ Size/physiology , Organ Specificity/physiology , Proof of Concept Study , Rats, Sprague-DawleyABSTRACT
New insulin analogues with a longer duration of action and a 'peakless' pharmacokinetic profile have been developed to improve efficacy, safety and convenience for patients with diabetes. During non-clinical development, according to regulatory guidelines, these analogues are tested in healthy euglycaemic rats rendering them persistently hypoglycaemic. Little is known about the effect of persistent (24 hr/day) insulin-induced hypoglycaemia (IIH) in rats, complicating interpretation of results in pre-clinical studies with new longer-acting insulin analogues. In this study, we investigated the effects of persistent IIH and their reversibility in euglycaemic rats. Histopathological changes in insulin-infused animals included partly reversible axonal and reversible myofibre degeneration in peripheral nerve and skeletal muscle tissue, respectively, as well as reversible pancreatic islet atrophy and partly reversible increase in unilocular adipocytes in brown adipose tissue. Additionally, results suggested increased gluconeogenesis. The observed hyperphagia, the pancreatic, peripheral nerve and skeletal muscle changes were considered related to the hypoglycaemia. Cessation of insulin infusion resulted in transient hyperglycaemia, decreased food consumption and body-weight loss before returning to control levels. The implications for the interpretation of non-clinical studies with long-acting insulin analogues are discussed.
