The Neuroprotective Effects of SGLT2 or Nox1/Nox4 Selective Inhibitors on Alzheimer’s-Like Symptoms Development in Diabetic Mice

Abstract

Background: Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive loss of memory and cognitive function along with molecular alterations involving the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs). Epidemiological evidence has shown that type II diabetes mellitus (T2DM) is a major risk factor for the development of AD. Among the shared pathological features of both diseases are impaired insulin signaling and oxidative stress. However, the exact mechanism of how peripheral insulin resistance in diabetes may contribute to AD pathology remains largely unknown. Aim: The aim of the present study is to determine the role of impaired insulin signaling along with reactive oxygen species (ROS) overproduction in the onset of AD-like pathology in an animal model of T2DM. We also investigate the potential ameliorative properties of dapagliflozin (SGLT2 inhibitor) and GKT137833 (dual Nox1/Nox4 inhibitor) on the Alzheimer’s-like symptoms developed in T2DM. Methods: Female C57BL/6J mice were used to conduct this study. T2DM was induced using a combination of high-fat diet and low doses of streptozotocin injections. Treatment groups were administered with either dapagliflozin (2mg/kg) or GKT (40mg/kg) over a period of 9 weeks. Cognitive function of the studied mice was assessed using the novel object recognition test and the spontaneous T-Maze alternation test. To test for sensory dysfunction associated with diabetes, mechanical and heat hyperalgesia were assessed using Hargreave’s test and the electronic von Frey. The raised beam walking test was also conducted to detect any motor dysfunction. At the molecular level, western blots were used to assess the expression of NADPH oxidase-4 (Nox4), insulin receptor substrate-1 (IRS-1) and Tau phosphorylated at Ser404 in the hippocampus and prefrontal cortex. RT-PCR was also conducted to study the mRNA levels of Nox1, IRS-1 and IRS-2. Immunohistochemical staining was performed to detect the deposition of amyloid-beta plaques and tauS404 and S396 hyperphosphorylation in the brain. Results: Compared to the control group, type 2 diabetic mice showed sensory, cognitive and motor dysfunction. Treatment with dapagliflozin and GKT reversed spatial and recognition memory loss, as well as sensory and motor dysfunction in mice. These observations were paralleled by the reestablishment of the insulin signaling activity and the inhibition of NADPHdependent ROS overproduction. Conclusion: This study reveals a potential neuroprotective role of SGLT2 inhibition as well as Nox1/Nox4 inhibition and highlights the involvement of insulin resistance and oxidative stress in the progression of Alzheimer’s-like symptoms associated with T2DM. These findings put forward a potential novel therapeutic strategy for the treatment of AD.