Blood-Based Indicators of Insulin Resistance and Metabolic Syndrome in Bottlenose Dolphins (Tursiops truncatus)

Abstract

Similar to people with metabolic syndrome, bottlenose dolphins (Tursiops truncatus) can have a sustained postprandial hyperglycemia and hyperinsulinemia, dyslipidemia, and fatty liver disease. A panel of potential postprandial blood-based indicators of insulin resistance and metabolic syndrome were compared among 34 managed collection dolphins in San Diego Bay, CA, USA (Group A) and 16 wild, free-ranging dolphins in Sarasota Bay, FL, USA (Group B). Compared to Group B, Group A had higher insulin (2.1 ± 2.5 and 13 ± 13 μIU/ml), glucose (87 ± 19 and 108 ± 12 mg/dl), and triglycerides (75 ± 28 and 128 ± 45 mg/dl) as well as higher cholesterol (total, high-density lipoprotein cholesterol, and very low density lipoprotein cholesterol), iron, transferrin saturation, gamma-glutamyl transpeptidase (GGT), alanine transaminase, and uric acid. Group A had higher percent unmodified adiponectin. While Group A dolphins were older, the same blood-based differences remained when controlling for age. There were no differences in body mass index (BMI) between the groups, and comparisons between Group B and Group A dolphins have consistently demonstrated lower stress hormones levels in Group A. Group A dolphins with high insulin (greater than 14 μIU/ml) had higher glucose, iron, GGT, and BMI compared to Group A dolphins with lower insulin. These findings support that some dolphin groups may be more susceptible to insulin resistance compared to others, and primary risk factors are not likely age, BMI, or stress. Lower high-molecular weight adiponectin has been identified as an independent risk factor for type 2 diabetes in humans and may be a target for preventing insulin resistance in dolphins. Future investigations with these two dolphin populations, including dietary and feeding differences, may provide valuable insight for preventing and treating insulin resistance in humans.

Molecular Footprints of Aquatic Adaptation Including Bone Mass Changes in Cetaceans

“…Because overexpression of OGT has been associated with insulin resistance and dyslipidemia in mice (Yang et al. 2008), expansion of OGT (11 copies) in the bottlenose dolphin genome may be underlying the unusual response of this species to insulin (Venn-Watson et al. 2013).…”

“…Other features reported in cetaceans include extreme longevity (>200 years in the case of the bowhead whale, Balaena mysticetus ; George et al. 1999; George and Bockstoce 2008), reduced cancer incidence (e.g., in the blue whale, Balaenoptera musculus ; Caulin and Maley 2011), and resistance to insulin (bottlenose dolphin, Tursiops truncatus ; Venn-Watson et al. 2013).…”

Adiponectin, Leptin, and Fatty Acids in the Maintenance of Metabolic Homeostasis through Adipose Tissue Crosstalk

“…The insulin sensitizing action of adiponectin is impressively conserved among mammals, extending from mice and humans (Turer and Scherer, 2012) to the yellow-bellied marmot and dolphin (Florant et al, 2004; Venn-Watson et al, 2013). While the insulin sensitizing effects are a combination of the vast metabolic effects exerted on multiple tissues, adiponectin also acts locally on the adipocyte to increase glucose uptake, contributing to euglycemia and promotion of adipose tissue expansion.…”

Preliminary Investigation of Bottlenose Dolphins (Tursiops truncatus) forhfeGene–related Hemochromatosis

“…Serum ferritin levels, hepatic function, age, sex, alcohol consumption, and hepatitis C can all affect the development of the clinical syndrome (Rochette et al 2010). Managed-collection bottlenose dolphins have significantly higher iron levels than free-ranging dolphins, indicating that environmental, dietary, and metabolic factors likely play significant roles in disease development (Mazzaro et al 2012;Venn-Watson et al 2013).…”

“…Bottlenose dolphins have a diabetes-like metabolism, including a sustained postprandial hyperglycemia (Venn-Watson et al 2007). Subsequent studies have demonstrated an association between elevated insulin levels and elevated serum iron and hemochromatosis in dolphins (Venn-Watson et al 2011, 2013. Further studies are needed to assess potential parallels between insulin resistance-associated hemochromatosis in dolphins and humans.…”