Marine Mammals as Out-of-the-Box Models for Diabetes and Insulin Resistance

Despite the ongoing diabetes pandemic, there is currently no single natural animal model for type 2 diabetes. It has been established that bottlenose dolphins (Tursiops truncatus) have a sustained postprandial hyperglycemia and have emerged as a novel model for both type 1 and type 2 diabetes. Unlike people, however, dolphins appear to be able to turn their diabetes-like metabolism on and off. Chronic diseases identified in dolphins that have been associated with insulin resistance (IR) in people include fatty liver disease, inflammation, iron overload (hemochromatosis), and urate nephrolithiasis. The hypothesized evolutionary driver of IR in dolphins is a high protein, low carbohydrate diet paired with a large brain's demand for glucose; this hypothesis was originally posed as the evolutionary origin of IR in humans by Miller and Colagiari, in which IR was advantageous during the Ice Age when our ancestors relied upon a high protein, low carbohydrate diet. Potential risk factors for metabolic perturbations in dolphins include the amount of protein ingested per meal or per day, duration of fasting, and time of day (circadian rhythm). In addition to dolphins, other marine mammals may have glucose metabolism adaptations, including a lack of ketosis in the face of long term fasting.

The aim of this Research Topic is to highlight marine mammals, especially dolphins, as unique and useful models for diabetes and insulin resistance. Biomarkers and genetic drivers glucose and lipid metabolism, diabetes, and insulin resistance in marine mammals will be investigated, especially as they relate to chronic diseases shared between dolphins and people with insulin resistance. The potential role of diet and feeding habits on dolphins' metabolic health will also be explored. Natural and non-pathologic states of long-term fasting in marine mammals, and how these adaptations may benefit human health, will be included. Original and review articles will be gathered from leading scientists in the field of marine mammal physiology, marine mammal anatomy, and diabetes.