The SGLT2 inhibitor dapagliflozin promotes systemic FFA mobilization,enhances hepatic β-oxidation,and induces ketosis

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have been shown to increase ketone bodies in patients with type 2 diabetes; however, the underlying mechanisms have not been fully elucidated. Here we examined the effect of the SGLT2 inhibitor dapagliflozin (1 mg/kg/day, formulated in a water, PEG400, ethanol, propylene glycol solution, 4 weeks) on lipid metabolism in obese Zucker rats. Fasting FFA metabolism was assessed in the anesthetized state using a 9,10-³H(N)]-palmitic acid tracer by estimating rates of plasma FFA appearance (R_a), whole-body FFA oxidation (R_ox), and nonoxidative disposal (R_st). In the liver, clearance (K_β-ox) and flux (R_β-ox) of FFA into β-oxidation were estimated using 9,10-³H]-(R)-bromopalmitate/U-¹⁴C]palmitate tracers. As expected, dapagliflozin induced glycosuria and a robust antidiabetic effect; treatment reduced fasting plasma glucose and insulin, lowered glycated hemoglobin, and increased pancreatic insulin content compared with vehicle controls. Dapagliflozin also increased plasma FFA, R_a, R_ox, and R_st with enhanced channeling toward oxidation versus storage. In the liver, there was also enhanced channeling of FFA to β-oxidation, with increased K_β-ox, R_β-ox and tissue acetyl-CoA, compared with controls. Finally, dapagliflozin increased hepatic HMG-CoA and plasma β-hydroxybutyrate, consistent with a specific enhancement of ketogenesis. Since ketogenesis has not been directly measured, we cannot exclude an additional contribution of impaired ketone body clearance to the ketosis. In conclusion, this study provides evidence that the dapagliflozin-induced increase in plasma ketone bodies is driven by the combined action of FFA mobilization from adipose tissue and diversion of hepatic FFA toward β-oxidation.Supplementary key words: β-oxidation, diabetes, drug therapy, fatty acids, metabolism, tracer kinetics, SGLT2, HMG-CoA, ketone bodies

SGLT2 inhibitors, including dapagliflozin, are established treatments for patients with type 2 diabetes leading to improved glucose control as well as decreased risk of cardiovascular events and development of kidney disease (1, 2, 3, 4, 5, 6, 7). The improved cardiovascular and renal outcome data for this class of drugs have resulted in a change in standard of care recommendations, placing SGLT2 inhibitors after lifestyle interventions and metformin treatment for patients with combined diabetes and heart failure or chronic kidney disease (8).A consistent effect of SGLT2 inhibitors in patients is an increase in plasma ketone body levels (9, 10, 11), which is presumed to be caused by increased ketogenesis. Enhanced ketogenesis may play a role in the organ protective action of SGLT2 inhibitors (12, 13, 14); therefore, understanding the nature of this phenomenon is important. The increased ketone body levels might result from a systemic increase in FFA mobilization driven by the established treatment-induced reductions in plasma glucose and insulin. Although involvement of enhanced FFA mobilization seems likely, data directly assessing this mechanism is currently lacking in the literature.In patients with type 2 diabetes, empagliflozin (25 mg/day for 4 weeks) increased fasting ketone bodies and plasma FFA levels (15). However, the rate of appearance of glycerol, a measure of whole-body lipolysis, was not markedly altered. As described by Wolfe et al. (16), general changes in FFA mobilization can result not only from changes in lipolysis, but also from alterations in intra-adipocyte re-esterification of fatty acids. This could occur, for example, if reduced circulating glucose and insulin levels lower the intra-adipocyte formation of glycerol-3-phosphate leading to reduced capture of FFA released by the action of ongoing lipolysis.An alternative explanation for the enhanced ketogenesis could be a liver-specific effect of SGLT2 inhibitors. Thus, the major site of ketone body production in the body is the liver (17), and the rate controlling enzyme for ketogenesis, at least in rodents, appears to be carnitine palmitoyl transferase 1 (CPT1) (18). The most important regulator of the activity of CPT1 is cytosolic malonyl-CoA, which is a potent CPT1 inhibitor (19). Glucose excess in the hepatocyte would tend to increase the formation and level of cytosolic malonyl-CoA, resulting in inhibition of ketogenesis. By contrast, unloading glucose from the hepatocyte would reduce malonyl-CoA removing the brake on ketogenesis.The aim of this study was to elucidate the mechanism behind the increased ketone body levels seen following SGLT2 inhibition by measuring whole-body and tissue-specific FFA metabolism and liver co-enzyme A intermediates. Obese Zucker rats were treated with the SGLT2 inhibitor, dapagliflozin (1 mg/kg, 4 weeks), or vehicle before performing dedicated tracer studies using either 9,10-³H(N)]-Palmitic Acid or 9,10-³H]-(R)-bromopalmitate/U-¹⁴C]palmitate. This study provides evidence that the dapagliflozin-induced increase in plasma ketone bodies is driven by the combined action of FFA mobilization from adipose tissue and diversion of hepatic FFA toward β-oxidation.