Do sodium-glucose transporter-2 inhibitors increase plasma glucagon by direct actions on the alpha-cell? - and does the increase matter for the associated increase in endogenous glucose production?

Sodium-glucose transporter-2 inhibitors (SGLT2i) lower blood glucose and are used for treatment of type-2-diabetes. However, SGLT2i have been associated with increases in endogenous glucose production (EGP) by mechanisms that have been proposed to result from SGLT2i-mediated increases in circulating glucagon concentrations, but the relative importance of this effect is debated, and mechanisms possibly coupling SGLT2i to increased plasma glucagon are unclear. A direct effect on alpha-cell activity has been proposed, but data on alpha-cell SGLT2 expression are inconsistent, and studies investigating direct effects of SGLT2 inhibition on glucagon secretion are conflicting. In contrast, alpha-cell SGLT1 expression has been found more consistently and seems to be more prominent, pointing to an underappreciated role for this transporter. Nevertheless, the selectivity of most SGLT2i does not support interference with SGLT1 during therapy. Paracrine effects mediated by secretion of glucagonotropic/-static molecules from beta- and/or delta-cells have also been suggested to be involved in SGLT2i-induced increase in plasma glucagon, but studies are few and arrive at different conclusions. It is also possible that the effect on glucagon is secondary to drug-induced increases in urinary glucose excretion and lowering of blood glucose, as demonstrated in experiments with glucose clamping where SGLT2i-associated increases in plasma glucagon is are prevented. However, regardless of the mechanisms involved, the current balance of evidence does, not support that SGLT2 plays a crucial role for alpha-cell physiology or that SGLT2i-induced glucagon secretion is important for the associated increased EGP, particularly since the increase in EGP occurs before any rise in plasma glucagon. This article is protected by copyright. All rights reserved.