Inhibition of Kidney Proximal Tubular Glucose Reabsorption Does Not Prevent against Diabetic Nephropathy in Type 1 Diabetic eNOS Knockout Mice

Abstract

Background and ObjectiveSodium glucose cotransporter 2 (SGLT2) is the main luminal glucose transporter in the kidney. SGLT2 inhibition results in glycosuria and improved glycaemic control. Drugs inhibiting this transporter have recently been approved for clinical use and have been suggested to have potential renoprotective benefits by limiting glycotoxicity in the proximal tubule. We aimed to determine the renoprotective benefits of empagliflozin, an SGLT2 inhibitor, independent of its glucose lowering effect.Research Design and MethodsWe induced diabetes using a low dose streptozotocin protocol in 7–8 week old endothelial nitric oxide (eNOS) synthase knockout mice. We measured fasting blood glucose on a monthly basis, terminal urinary albumin/creatinine ratio. Renal histology was assessed for inflammatory and fibrotic changes. Renal cortical mRNA transcription of inflammatory and profibrotic cytokines, glucose transporters and protein expression of SGLT2 and GLUT1 were determined. Outcomes were compared to diabetic animals receiving the angiotensin receptor blocker telmisartan (current best practice).ResultsDiabetic mice had high matched blood glucose levels. Empagliflozin did not attenuate diabetes-induced albuminuria, unlike telmisartan. Empagliflozin did not improve glomerulosclerosis, tubular atrophy, tubulointerstitial inflammation or fibrosis, while telmisartan attenuated these. Empagliflozin did not modify tubular toll-like receptor-2 expression in diabetic mice. Empagliflozin did not reduce the upregulation of macrophage chemoattractant protein-1 (MCP-1), transforming growth factor β1 and fibronectin mRNA observed in the diabetic animals, while telmisartan decreased transcription of MCP-1 and fibronectin. Empagliflozin increased GLUT1 mRNA expression and telmisartan increased SGLT2 mRNA expression in comparison to untreated diabetic mice. However no significant difference was found in protein expression of GLUT1 or SGLT2 among the different groups.ConclusionHence SGLT2 inhibition does not have renoprotective benefits independent of glucose lowering.

Renal effects of canagliflozin in type 2 diabetes mellitus

“…Phlorizin prevented increases in total kidney weight and proteinuria in diabetic rats 31 Empagliflozin attenuated increases in kidney weight, albuminuria, markers of kidney growth and markers of inflammation in diabetic mice 29,34 SGLT2 inhibitors, including luseogliflozin, empagliflozin and tofogliflozin, have shown improved markers of diabetic nephropathy in diabetic rats 32,33 Decreased proteinuria has been observed with SGLT2 inhibition in diabetic rodents 31,35 Canagliflozin provided reductions in ACR 14,16,18,19 Indirect effects SGLT2 inhibitors have been shown to improve parameters associated with reductions in measures of diabetic nephropathy, including hyperglycemia, blood pressure and weight in diabetic rats 7,28,29 SGLT2 inhibitors have been shown to improve parameters associated with reductions in measures of diabetic nephropathy, including hyperglycemia, blood pressure, weight and uric acid levels in diabetes (e.g., hyperkalemia, AEs related to volume depletion, bone fractures, cardiovascular safety). This manuscript summarizes renal data from the pooled, placebo-controlled population, including patients with normal renal function from four placebo-controlled studies of canagliflozin 9,11-13 ; active-controlled studies of canagliflozin as add-on to metformin versus glimepiride and sitagliptin 11,14,18 and as add-on to metformin plus sulfonylurea versus sitagliptin 15 ; and a placebo-controlled study in older adults 17,20 ( Table 2).…”

“…Evidence from preclinical and clinical studies has shown that treatment with SGLT2 inhibitors may lead to improvements in markers of diabetic nephropathy, thereby suggesting a potential renoprotective role for this class in patients with diabetes (Table 1) [27][28][29][30][31][32][33][34][35][36][37][38][39][40] . Specifically, SGLT2 inhibitors may confer renoprotection through direct action on glucose lowering, activation of tubuloglomerular feedback and/or potentially weight loss, through volume normalization, reduced intraglomerular pressure and improved BP control [27][28][29][30][31][32][33][34][35][36][37][38][39][40] . Although lowering of ANP is another mechanism that could mitigate the progression of kidney damage in diabetes, the relationship between ANP and SGLT2 inhibition has not been described to date.…”

SGLT2 Inhibitors and the Diabetic Kidney

“…As outlined above, data in animal models often differ depending upon the model used. Thus, when streptozotocin-induced diabetic endothelial nitric oxide synthase knockout mice were treated with empagliflozin there was no attenuation of albuminuria (44) or improvement in renal lesions or inflammatory markers (44). In contrast, the beneficial effects of empagliflozin on DN lesions were recently described in normotensive BTBR ob/ob mice, where reductions in glomerular hypertrophy, mesangial matrix expansion, albuminuria, and markers of inflammation were observed (45).…”

Sodium glucose cotransporter 2 inhibition in the diabetic kidney

“…SGLT2 inhibition also reduced blood glucose from 400 to 200 mg/dl in T2DM ob/ob mice; again this was associated with a decrease in renal hypertrophy, albuminuria, and markers of inflammation and mesangial matrix expansion [15]. Furthermore, in T1DM eNOS knockout mice with matched high blood glucose levels across all groups, those with SGLT2 inhibition showed no benefit on glomerulosclerosis, tubular atrophy, or tubulointerstitial fibrosis, whereas those treated with an angiotensin II AT1 receptor antagonist did [44]. Together these studies are consistent with the notion that SGLT2 inhibition can lower early kidney growth and inflammation in the diabetic kidney primarily by lowering blood glucose (Figure 1).…”