SGLT2 is not expressed in pancreatic α- and β-cells, and its inhibition does not directly affect glucagon and insulin secretion in rodents and humans

Abstract

Objective Sodium-glucose cotransporter 2 (SGLT2) inhibitors (SGLT2i), or gliflozins, are anti-diabetic drugs that lower glycemia by promoting glucosuria, but they also stimulate endogenous glucose and ketone body production. The likely causes of these metabolic responses are increased blood glucagon levels, and decreased blood insulin levels, but the mechanisms involved are hotly debated. This study verified whether or not SGLT2i affect glucagon and insulin secretion by a direct action on islet cells in three species, using multiple approaches. Methods We tested the in vivo effects of two selective SGLT2i (dapagliflozin, empagliflozin) and a SGLT1/2i (sotagliflozin) on various biological parameters (glucosuria, glycemia, glucagonemia, insulinemia) in mice. mRNA expression of SGLT2 and other glucose transporters was assessed in rat, mouse, and human FACS-purified α- and β-cells, and by analysis of two human islet cell transcriptomic datasets. Immunodetection of SGLT2 in pancreatic tissues was performed with a validated antibody. The effects of dapagliflozin, empagliflozin, and sotagliflozin on glucagon and insulin secretion were assessed using isolated rat, mouse and human islets and the in situ perfused mouse pancreas. Finally, we tested the long-term effect of SGLT2i on glucagon gene expression. Results SGLT2 inhibition in mice increased the plasma glucagon/insulin ratio in the fasted state, an effect correlated with a decline in glycemia. Gene expression analyses and immunodetections showed no SGLT2 mRNA or protein expression in rodent and human islet cells, but moderate SGLT1 mRNA expression in human α-cells. However, functional experiments on rat, mouse, and human (29 donors) islets and the in situ perfused mouse pancreas did not identify any direct effect of dapagliflozin, empagliflozin or sotagliflozin on glucagon and insulin secretion. SGLT2i did not affect glucagon gene expression in rat and human islets. Conclusions The data indicate that the SGLT2i-induced increase of the plasma glucagon/insulin ratio in vivo does not result from a direct action of the gliflozins on islet cells.

Do sodium‐glucose co‐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?

“…However, very little has been reported regarding alpha‐cell secretion in studies of the potential effects of SGLT2is on the beta and delta cells 49 . We and others have found minimal or undetectable Slc5a2 expression in whole mouse islets (Table 1) and in mouse, rat and human beta and delta cells, 29–31,37,49 and, in our hands, dapagliflozin affected neither insulin nor somatostatin secretion 49 . However, another recent study concluded that insulin‐mediated inhibition of glucagon secretion was indirectly mediated by stimulation of delta‐cell SGLT2 activity and increased somatostatin secretion 32 .…”

“…However, whether this effect resulted from a direct action on the alpha cell was unclear because it occurred much later than the maximum effects on urinary glucose excretion. Furthermore, as already mentioned, a recent study on perifused human islets using the dual SGLT1/2 inhibitor, sotagliflozin, did not indicate effects of islet SGLT1 inhibition on glucagon output 37 . While we await publication of further studies on the significance of alpha‐cell SLGT1 and SGLT2 activity for glucagon secretion, any potential role would raise a new conundrum, namely why, from a mechanistic point of view, would it be sensible to have glucose transportation into the alpha cell regulated by transporters that efficiently transport glucose against its concentration gradient?…”

“…Moreover, and more relevant for the scope of this review, it also remains to be clarified whether these differences in SGLT2 selectivity translate into potential differences in inhibition of alpha‐cell SGLT1 activity and, if so, whether this has any effect on glucagon secretion. As mentioned, the findings from animal and ex vivo and in vitro models are conflicting, with one study indicating an important role of alpha‐cell SGLT1 activity for glucagon secretion, 29 whereas others did not find any effect of SGLT1 inhibition on glucagon secretion from isolated perfused rat pancreases or perifused mouse or human islets by use of dual SGLT1/2 inhibitors (phloridzin or sotagliflozin) 37,49 . In summary, the reported data, therefore, show that the SLGT2 selectivity of SGLT2is do not support that off‐target SGLT1 inhibition occurs at therapeutic dosing and, even if so, animal and ex vivo studies (using concentrations that should cross‐inhibit SGLT1 activity) do not support that SGLT1 inhibition affects glucagon secretion.…”

“…Different methodologies have been used for both the assessment of expression and for the functional studies, making comparison of data somewhat challenging. Regarding SLC5A2 expression (Table 1), most, but not all, 30,31 studies find minimal or undetectable expression in mouse, rat and human islets and in mouse and human alpha cells, 29,37,48,49 and the single study showing detectable islet/alpha‐cell expression 30 also revealed considerable interindividual heterogeneity. On the other hand, robust expression of SLC5A1 (the gene encoding SGLT1) was detected in those studies, where this was also investigated 29,37,48,49 .…”

A Low-Carbohydrate Diet Improves Glucose Metabolism in Lean Insulinopenic Akita Mice Along With Sodium-Glucose Cotransporter 2 Inhibitor

“…Others indicated that alpha-cells expressed SGLT1 but not SGLT2 (21,22). However, a recent report indicated that SGLT2 was not expressed in both rodent and human pancreatic alpha-and beta-cells and concluded that SGLT2i did not directly modulate insulin and glucagon secretion (23). Our previous reports indicated that the improvement of the beta/alpha cell area ratio was crossly related to recovery from chronic hyperglycemia (12,13).…”