Sodium glucose co-transporter 2 inhibition reduces succinate levels in diabetic mice

Type 1 diabetes (T1D) is associated with major chronic microvascular complications which contribute significantly to diabetes associated morbidity. The protein primarily responsible for glucose reabsorption in the kidney is sodium glucose co-transporter 2 (SGLT2). Presently, SGLT2 inhibitors are widely used in diabetic patients to improve blood glucose levels and prevent cardiovascular and renal complications. Given the broad therapeutic application of SGLT2 inhibitors, we hypothesised that SGLT2 inhibition may exert its protective effects via alterations of the gut microbiome and tested this in a type 1 diabetic mouse model of diabetic retinopathy.

To determine whether the treatment with two independent SGLT2 inhibitors affects gut health in a type 1 diabetic mouse model.

The SGLT2 inhibitors empagliflozin or dapagliflozin (25 mg/kg/d) or vehicle dimethylsulfoxide (DMSO) were administered to C57BL/6J, Akita, Kimba and Akimba mice at 10 wk of age for 8 wk via their drinking water. Serum samples were collected and the concentration of succinate and the short chain fatty acid (SCFA) butyric acid was measured using gas chromatography-mass spectrometry. Enzyme-linked immunosorbent assay (ELISA) was performed to determine the concentration of insulin and leptin. Furthermore, the norepinephrine content in kidney tissue was determined using ELISA. Pancreatic tissue was collected and stained with haematoxylin and eosin and analysed using brightfield microscopy.

Due to the presence of the Akita allele, both Akita and Akimba mice showed a reduction in insulin production compared to C57BL/6J and Kimba mice. Furthermore, Akita mice also showed the presence of apoptotic bodies within the pancreatic islets. The acinar cells of Akita and Akimba mice showed swelling which is indicative of acute injury or pancreatitis. After 8 wk of SGLT2 inhibition with dapagliflozin, the intermediate metabolite of gut metabolism known as succinate was significantly reduced in Akimba mice when compared to DMSO treated mice. In addition, empagliflozin resulted in suppression of succinate levels in Akimba mice. The beneficial SCFA known as butyric acid was significantly increased in Akita mice after treatment with dapagliflozin when compared to vehicle treated mice. The norepinephrine content in the kidney was significantly reduced with both dapagliflozin and empagliflozin therapy in Akita mice and was significantly reduced in Akimba mice treated with empagliflozin. In non-diabetic C57BL/6J and Kimba mice, serum leptin levels were significantly reduced after dapagliflozin therapy.

The inhibition of SGLT2 reduces the intermediate metabolite succinate, increases SCFA butyric acid levels and reduces norepinephrine content in mouse models of T1D. Collectively, these improvements may represent an important mechanism underlying the potential benefits of SGLT2 inhibition in T1D and its complications.