No abstract

Glucagon is classically described as a counterregulatory hormone that plays an essential role in the protection against hypoglycemia. In addition to its role in the regulation of glucose metabolism, glucagon has been described to promote ketosis in the fasted state. Sodium–glucose cotransporter 2 inhibitors (SGLT2i) are a new class of glucose-lowering drugs that act primarily in the kidney, but some reports have described direct effects of SGLT2i on α-cells to stimulate glucagon secretion. Interestingly, SGLT2 inhibition also results in increased endogenous glucose production and ketone production, features common to glucagon action. Here, we directly test the ketogenic role of glucagon in mice, demonstrating that neither fasting- nor SGLT2i-induced ketosis is altered by interruption of glucagon signaling. Moreover, any effect of glucagon to stimulate ketogenesis is severely limited by its insulinotropic actions. Collectively, our data suggest that fasting-associated ketosis and the ketogenic effects of SGLT2 inhibitors occur almost entirely independent of glucagon.

The current consensus mechanism for hepatic ketogenesis posits a key role for islet hormones, with insulin inhibiting and glucagon stimulating formation of ketone bodies. In this model the action of glucagon in the presence of low portal insulin concentrations causes ketosis. Sodium-glucose co-transporter 2 inhibitors (SGLT2i) are effective for lowering glucose in diabetic patients, and cause a relative insulinopenia. These agents have been described to increase ketone production, and have been associated with cases of diabetic ketoacidosis. SGLT2i have been recently reported to stimulate islet α-cells, suggesting the hypothesis that SGLT2i-induced glucagon secretion drives ketogenesis. To test this hypothesis, mice were given the SGLT2i dapagliflozin (dapa) in the presence or absence of glucagon signaling. Fasting-induced ketosis was used as a positive control. In both dapa-treated mice and 16 hour fasted mice, blood glucose decreased to the 4-5 mM range, β-OHB increased 2-3 fold, and NEFA rose 30-50%. Fasting had minimal effects on plasma glucagon, but dapa increased glucagon concentrations, albeit at a delayed rate compared to changes in glycemia, β-OHB, or NEFAs. Interruption of glucagon signaling with either: 1) a glucagon receptor antagonist (GRA); or 2) mice with a deletion of the proGlucagon gene had no effect on the development of ketosis in response to dapa or fasting, indicating that glucagon is not necessary for ketosis in these conditions. To test its sufficiency, glucagon (20µg/kg) was given to fed mice, 16 hour fasted mice, dapa-treated mice, and mice with insulin receptor blockade (IRB). Fasting, dapa and IRB all increased β-OHB significantly but glucagon did not add to this. In contrast, epinephrine significantly elevated ketone levels under these conditions. These findings indicate that the current model of the regulation of ketogenesis needs to be reconsidered, and that in mice glucagon does not have a significant role in this process. Disclosure M. Capozzi: None. R. Coch: None. J.B. Wait: None. J.J. Koech: None. J. Campbell: Research Support; Self; Eli Lilly and Company. Speaker's Bureau; Self; Merck Sharp & Dohme Corp. D.A. D'Alessio: Advisory Panel; Self; Eli Lilly and Company. Research Support; Self; Eli Lilly and Company, Merck & Co., Inc. Funding National Institutes of Health (F32-DK116542)