Characterization of Enlarged Kidneys and Their Potential for Inducing Diabetes in DEK Rats

SIMPLE SUMMARY: The worldwide prevalence of diabetes mellitus (DM) in 2020 has been estimated at 463 million patients. About 90% of patients with diabetes have type 2 diabetes mellitus (T2D), caused primarily by insulin resistance and insufficiency. However, the specific etiology of T2D remains unknown. Sodium glucose cotransporter 2 (SGLT2) inhibitors are a novel class of anti-diabetic drugs that act independently of insulin and reduce blood glucose concentrations by inhibiting the reabsorption of glucose at renal proximal tubules. SGLT2 inhibitors have highlighted the role of the kidneys in glycemic control in diabetes. The kidneys have multiple roles in systemic glucose metabolism, such as glucose reabsorption, gluconeogenesis, and insulin degradation. Therefore, putative renal hyperfunction might contribute to the development of T2D. The present study characterized rats from a strain of novel type 2 diabetes model with enlarged kidneys (DEK). Their kidneys have increased parenchyma (nephrons and tubules), and uninephrectomy immediately after the onset inhibited the development of T2D for a significant period in DEK rats. These results highlight the contribution of kidney to the development of T2D, and indicate that the kidneys are therapeutic targets to prevent T2D. ABSTRACT: The kidneys participate in the regulation of systemic glucose metabolism via gluconeogenesis, insulin degradation, and the tubular reabsorption of glucose. The present study characterized rats from a strain of a novel type 2 diabetes model with enlarged kidneys (DEK). Histological and biochemical analyses of DEK rats were performed to assess the relationships between their kidneys and hyperglycemia. The kidney weight of diabetic DEK (DEK-DM) gradually increased over time from the onset of diabetes, with the glomerular number being higher in DEK-DM than in normal DEK (DEK-cont). A positive correlation between blood glucose level and kidney weight was observed in DEK-DM. The similar glomerular size and single glomerular creatinine clearance in DEK-cont and DEK-DM indicated that glomerular hypertrophy and hyperfiltration were not involved in the renal enlargement. Uninephrectomy (1/2Nx) in DEK-DM resulted in a reduction in blood glucose level at 7–28 post-operation days, with this concentration remaining lower than in Sham group until 84 days post-operation. 1/2Nx also improved systemic conditions, including reduced body weight gain, polyuria, polydipsia, and hyperphagia. Plasma concentrations of Na, total cholesterol, albumin, and total protein were higher, and urinary excretion of glucose, urea nitrogen, and proteins were lower, in the 1/2Nx than in the Sham group. Remnant kidney weight was two-fold higher in the 1/2Nx than in the Sham group 84 days later. In addition, 1/2Nx resulted in renal tubular dilatation but not in the progression of fibrosis or glomerular lesions. Taken together, these findings indicate that enlarged kidneys were associated with the onset of diabetes and with the resistance to diabetic nephropathy in DEK-DM.