Renoprotective Effects of Nobiletin on High Glucose-Induced Loss of Proximal Tubular Microvilli

Abstract

Abstract Objectives Kidney proximal tubular epithelium has microvillar brush borders, which is critical to renal reabsorption. Hyperglycemia induce change the loss of brush border and cellular polarity, tight junction disruption. Nobiletin is a polymethoxyflavone present in citrus fruit and peels, and has anti-inflammatory effects. This study investigated the renoprotective effects of nobiletin on proximal tubule microvillar ultrastructure and reabsorption under diabetic condition. Methods Human renal proximal tubular epithelial cells (RPTEC) were incubated in a media exposed to 33 mM glucose in the absence and presence of 1–20 μM nobiletin up to 6 days. Antibodies F-actin, villin, cubulin, megalin, SGLT2 and GLUT2 were used for Western blot analysis. The in vivo animal model employed db/db mice orally administrated with 10 mg/kg of nobiletin. Extracts of tissues were subjected to Western blotting or immunohistochemical staining. Results High glucose declined expression of F-actin and villin required for the assembly of proximal tubule microvilli. In addition, the expression of glucose uptake proteins of GLUT2 and SGLT2 was prompted in hyperglycemia. However, nontoxic nobiletin enhanced the expression of F-actin reduced by high glucose, while the elevated expression of the GLUT2 and SGLT2 was attenuated by nobiletin. In the in vivo study, oral administration of 10 mg/kg nobiletin inhibited loss of tubular microvilli through restoring expression of F-actin and villin in diabetic kidneys. Furthermore, nobiletin reduced expressions of GLUT2 and the albumin uptake receptors of cubulin and megalin in db/db mouse kidneys. Conclusions These results demonstrated that nobiletin curtailed loss of the proximal tubular microvillar proteins responsible for tubular reabsorption. Nobiletin may be a potent renoprotective agent counteracting diabetes-associated proximal tubular dysfunctions leading to kidney failure. Funding Sources This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (2017R1A6A3A04011473).