Empagliflozin Lowers Mitochondrial Respiration and Skeletal Muscle Sphingolipid Content in Female Mice Fed Western Diet

Abstract

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a frontline treatment for type 2 diabetes due to their ability to attenuate hyperglycemia (via glucosuria). Mounting evidence indicates SGLT2 inhibitors can also alter mitochondrial metabolism, enhance reliance upon fat oxidation and attenuate fat accumulation in a growing list of tissues. Nevertheless, the impact of SGLT2 inhibition on skeletal muscle remains largely unexplored. The objective of this study was to test the hypothesis that SGLT2 inhibition would promote enhanced mitochondrial capacity for fat oxidation and lower accumulation of harmful lipids in skeletal muscle of diet-induced obese mice. Female C57BL/6J mice, aged 26 weeks, were provided ad libitum access to either low-fat diet (LFD, n=9) or western diet (WD) for 8-weeks. WD mice were then randomized to 4-weeks of diet supplemented with 10mg/kg (0.01%) empagliflozin (WD+Emp, n=10) or untreated control (WD, n = 10). Dual-energy x-ray absorptiometry and glucose tolerance tests were performed in all groups pre- and post-empagliflozin treatment. At week 12, mitochondria were isolated from quadriceps muscle and measured by high-resolution respirometry using octanoyl-carnitine+malate (OCM) and other non-lipid substrates. Intramyocellular lipids were assessed using liquid chromatography, tandem mass spectrometry. As expected, WD mice had greater body weight and fat mass, as well as impaired glucose tolerance, when compared with LFD mice (all P<0.05). Four weeks of empagliflozin treatment improved glucose tolerance in WD+Emp mice (P<0.01 for week 12 vs. 8), despite no differences in body weight or fat mass compared with pre-treatment (both P>0.05 for week 12 vs. 8). Lipid-supported mitochondrial respiration and overall lipid content (e.g., triacylglycerols, select sphingolipids and ceramides) were greater in skeletal muscle from WD compared with LFD mice (all comparisons P<0.05). Such effects of WD on muscle lipid metabolism were largely reversed with empagliflozin treatment. There was overall main effect of lower mitochondrial respiration in WD+Emp compared with WD (P<0.001), and a tendency for lower concentration of numerous sphingolipid and ceramide species (mean difference = 9-34%). We interpret this as preliminary evidence that empagliflozin can reverse some WD-induced adaptations to skeletal muscle lipid metabolism, which may contribute to the improvement in glucose control.