Tumor-like features of gene expression and metabolic profiles in enlarged pancreatic islets are associated with impaired incretin-induced insulin secretion in obese diabetes: A study of Zucker fatty diabetes mellitus rat.

AIMS/INTRODUCTION: Pancreatic islets are heterogenous. To clarify the relationship between islet heterogeneity and incretin action in the islets, we studied gene expression and metabolic profiles of non-large and enlarged islets of the Zucker fatty diabetes mellitus rat, an obese diabetes model, as well as incretin-induced insulin secretion (IIIS) in these islets. MATERIALS AND METHODS: Pancreatic islets of control (fa/+) and fatty (fa/fa) rats at 8 and 12 weeks-of-age were isolated. The islets of fa/fa rats at 12 weeks-of-age were separated into non-large islets (≤200 µm in diameter) and enlarged islets (>300 µm in diameter). Morphological analyses, insulin secretion experiments, transcriptome analysis, metabolome analysis and oxygen consumption analysis were carried out on these islets. RESULTS: The number of enlarged islets was increased with age in fatty rats, and IIIS was significantly reduced in the enlarged islets. Markers for ß-cell differentiation were markedly decreased in the enlarged islets, but those for cell proliferation were increased. Glycolysis was enhanced in the enlarged islets, whereas the tricarboxylic acid cycle was suppressed. The oxygen consumption rate under glucose stimulation was reduced in the enlarged islets. Production of glutamate, a key signal for IIIS, was decreased in the enlarged islets. CONCLUSIONS: The enlarged islets of Zucker fatty diabetes mellitus rats, which are defective for IIIS, show tumor cell-like metabolic features, including a dedifferentiated state, accelerated aerobic glycolysis and impaired mitochondrial function. The age-dependent increase in such islets could contribute to the pathophysiology of obese diabetes.

GLP-1 analog liraglutide-induced cardiac dysfunction due to energetic starvation in heart failure with non-diabetic dilated cardiomyopathy.

BACKGROUND: Glucagon-like peptide-1 (GLP-1) reduces cardiovascular events in diabetic patients; however, its counter-protective effects have also been suggested in patients with heart failure and the clear explanation for its mechanisms have not yet been offered. METHODS: The effects of GLP-1 analog on cardiac function and energy metabolism, especially glycemic and lipid metabolisms were elucidated using non-diabetic J2N-k hamsters which showed spontaneous dilated cardiomyopathy. J2N-k hamsters were treated with PBS (HF group), low-dose (HF-L group) or high-dose liraglutide (HF-H group). RESULTS: In failing heart, GLP-1 analog exerted further deteriorated cardiac function (e.g. positive and negative dP/dt; p = 0.01 and p = 0.002, respectively) with overt fibrosis and cardiac enlargement (heart/body weight, 5.7 ± 0.2 in HF group versus 7.6 ± 0.2 in HF-H group; p = 0.02). The protein expression of cardiac muscles indicated the energy starvation status. Indirect calorimetry showed that failing hearts consumed higher energy and carbohydrate than normal hearts; moreover, this tendency was augmented by GLP-1 analog administration. Upon 10% glucose solution loading with GLP-1 analog administration (HF-H-G group) as complementary experiments, the cardiac function and fibrosis significantly ameliorated, whereas carbohydrate utilization augmented further and lipid utilization reduced more. The prognosis of HF-H-G group also significantly improved (p = 0.025). CONCLUSIONS: Glucagon-like peptide-1 analog caused the relative but desperate shortage of glycemic energy source for the failing cardiac muscles and it may restrict ATP synthesis, resulting in cardiac function deterioration. Therefore, appropriate energy supply and amount of carbohydrate intake should be carefully considered when administrating incretin-related drugs to patients with heart failure.