Practical Considerations when Using Mouse Models of Diabetes

Matching model with mechanism: Appropriate rodent models for studying various aspects of diabetes pathophysiology

Many rodent models are available for preclinical diabetes research making it a challenge for researchers to choose the most appropriate one for their experimental question. To aid in this, models have classically been categorized according to which type of diabetes they represent, and further into whether the model is induced, spontaneous or the result of genetic manipulation. This fails to capture the complexity of pathogenesis seen in diabetes in humans. This includes pathogenesis specifically involving the beta cell, which is no longer considered to be innocuous in the development and progression of diabetes. In this chapter we explore rodent models that incorporate the initiating factors believed to be involved in type 1 diabetes (autoimmunity) and type 2 diabetes (insulin resistance), before further discussing rodents that can be used to model specific mechanisms involved in a failure of functional beta cell mass (impaired beta cell function and beta cell apoptosis). We segregate models of beta cell pathogenesis based on the beta cell stressor predominantly associated with phenotype, but it is important to consider that most rodent models will exhibit more than one beta cell stressor. Similarly, many models exhibit more than one pathogenic mechanism, for example the same model may show insulin resistance, impaired beta cell function as well as beta cell loss. This can complicate interpretation of results and should be considered, and the model thoroughly researched, during the experimental planning stage.

Differences in glucose homeostasis and islet injury among diverse mice strains post acute pancreatitis

Diverse animal models have been used to study postpancreatitis diabetes mellitus (PPDM) development; however, no study has yet conducted a comparative analysis of the specific differences in glucose homeostasis and islet injury between these models. Therefore, we investigated the differences in pancreatic islet injury and glucose homeostasis among diverse strains in a cerulein-induced acute pancreatitis (AP) model to determine the appropriate animal model for PPDM. BALB/cJ, C57BL/6J, C57BL/6 N, and FVB/NJ mice were administered cerulein to induce AP. Serum amylase levels, pancreatic acinar injury, blood glucose homeostasis, islet function, and islet injury were measured and analyzed. All strains exhibited elevated amylase secretion post pancreatitis, and BALB/cJ, C57BL/6J, and C57BL/6 N mice exhibited sex-related differences. All strains exhibited pancreatic acinar injury post pancreatitis but mostly recovered within 15 days. Overall, glucose homeostasis remained balanced post pancreatitis in all strains compared to that in the control groups, except in FVB/NJ male and female mice, which exhibited an imbalance in glucose homeostasis on day 7 post pancreatitis. All the strains, except BALB/cJ mice, exhibited a decline in Homeostasis model assessment-β(HOMA-β) values post pancreatitis, with significant decrease in C57BL/6J females and FVB/NJ males. Islet size decreased post pancreatitis in all strains, except BALB/cJ mice. Pancreatic islet insulin secretion levels significantly decreased in male FVB/NJ mice post pancreatitis onset and did not recover within 15 days. Therefore, FVB/NJ male mice are a useful model for studying PPDM.

Abscisic Acid Improves Insulin Action on Glycemia in Insulin-Deficient Mouse Models of Type 1 Diabetes

Abscisic acid (ABA), a plant hormone, has recently been shown to play a role in glycemia regulation in mammals, by stimulating insulin-independent glucose uptake and metabolism in skeletal muscle. The aim of this study was to test whether ABA could improve glycemic control in a murine model of type 1 diabetes (T1D). Mice were rendered diabetic with streptozotocin and the effect of ABA administration, alone or with insulin, was tested on glycemia. Diabetic mice treated with a single oral dose of ABA and low-dose subcutaneous insulin showed a significantly reduced glycemia profile compared with controls treated with insulin alone. In diabetic mice treated for four weeks with ABA, the effect of low-dose insulin on the glycemia profile after glucose load was significantly improved, and transcription both of the insulin receptor, and of glycolytic enzymes in muscle, was increased. Moreover, a significantly increased transcription and protein expression of AMPK, PGC1-α, and GLUT4 was observed in the skeletal muscle from diabetic mice treated with ABA, compared with untreated controls. ABA supplementation in conjunction with insulin holds the promise of reducing the dose of insulin required in T1D, reducing the risk of hypoglycemia, and improving muscle insulin sensitivity and glucose consumption.

The use of mice in diabetes research: The impact of physiological characteristics, choice of model and husbandry practices

Diabetes mellitus is characterised by hyperglycaemia, which results from an absolute or relative lack of insulin. Chronic and acute hyperglycaemia are associated with a range of health complications and an overall increased risk of mortality. Mouse models are vital in understanding the pathogenesis of this disease and its complications, as well as for developing new diabetes therapeutics. However, for experimental questions to be suitably tested, it is critical that factors inherent to the animal model are considered, as these can have profound impacts on experimental outcome, data reproducibility and robustness. In this review, we discuss key considerations relating to model choice, physiological characteristics (such as age, sex and genetic background) and husbandry practices and explore the impact of these on common experimental readouts used in preclinical diabetes research.

The use of mice in diabetes research: The impact of experimental protocols

Mice are used extensively in preclinical diabetes research to model various aspects of blood glucose homeostasis. Careful experimental design is vital for maximising welfare and improving reproducibility of data. Alongside decisions regarding physiological characteristics of the animal cohort (e.g., sex, strain and age), experimental protocols must also be carefully considered. This includes choosing relevant end points of interest and understanding what information they can provide and what their limitations are. Details of experimental protocols must, therefore, be carefully planned during the experimental design stage, especially considering the impact of researcher interventions on preclinical end points. Indeed, in line with the 3Rs of animal research, experiments should be refined where possible to maximise welfare. The role of welfare may be particularly pertinent in preclinical diabetes research as blood glucose concentrations are directly altered by physiological stress responses. Despite the potential impact of variations in experimental protocols, there is distinct lack of standardisation and consistency throughout the literature with regards to several experimental procedures including fasting, cage changing and glucose tolerance test protocol. This review firstly highlights practical considerations with regard to the choice of end points in preclinical diabetes research and the potential for novel technologies such as continuous glucose monitoring and glucose clamping techniques to improve data resolution. The potential influence of differing experimental protocols and in vivo procedures on both welfare and experimental outcomes is then discussed with focus on standardisation, consistency and full disclosure of methods.