Oral hypoglycemic signaling pathways : unveiling novel therapeutic targets in diabetic nephropathy

Abstract

Background: Diabetic nephropathy (DN) is a major chronic diabetic complication that arises from persistent hyperglycemia. It is characterised by a gradual loss of glomerular filtration surface area and capillary volume as well as expansion of mesangial matrix due to the excessive production and deposition of extracellular matrix. One unifying mechanism that is shown through extensive research to mediate DN injury is oxidative stress. However, the mechanisms have yet to be elucidated. Previous work in our lab has implicated the NADPH-oxidase (NOX) enzymes in the pathologies of DN. However, to our knowledge, no studies have examined the role of NOXs on autophagy. Aim: The following study aimed to investigate the impact of selected Type 2 diabetes pharmacological drugs on Type 1-induced DN, as well as to dissect novel mechanisms associated with NADPH-induced oxidative stress on autophagy in DN. Methods: Sprague-Dawley male rats were used for this study. RT-PCR was used to assess mRNA levels of PPAR-γ, Fibronectin, COL IV, Nephrin, DUOX1, DUOX2, AMPK, mTOR, and autophagy markers, LC3A, and LC3B. NOX activity was assessed using the NADPH Oxidase Activity Assay. High Performance Liquid Chromatography (HPLC) was used to assess oxidative status and ROS production in kidney tissue. Blood samples were also harvested for creatinine level analysis. Finally, histological studies were performed to illustrate pathological changes using Periodic Acid Schiff and Masson Trichrome staining. Results: Both monotherapy and combination therapy showed no effect on the blood glucose levels. However, a restoration of excreted urinary albumin levels, glomerulosclerosis and tubulointerstitial fibrosis were demonstrated. Diabetes-induced oxidative stress was reflected via HPLC concomitant with increased NADPH oxidase activity. The administration of the drugs or their combinations were shown to reverse NOX-induced ROS production. The expression of PPARγ, Fibronectin, COL IV, Nephrin, DUOX1, DUOX2, AMPK, mTOR, and autophagy