Unraveling the Interplay between Cytochromes P450 and Insulin Signaling in the Pathogenesis of Type 2 Diabetes and Alzheimer’s Disease (Type 3 Diabetes)

Abstract

Background: Diabetes mellitus is a persistent metabolic condition marked by elevated blood glucose levels due to inadequate insulin production or inefficient insulin utilization. The underlying metabolic disruption is fraught with complications affecting multiple organs. Type 3 Diabetes (T3D) is one of the diabetic complications affecting the brain, and it is characterized by the ‘sporadic’ onset of neurodegeneration that is like that of Alzheimer’s disease (AD). Overtime, memory, cognition, and plasticity of the brain deteriorate as insulin/insulin-like growth factor receptor binding is reduced, culminating in deficient insulin responsiveness. Emerging evidence points to the key role of impaired insulin signaling and oxidative stress in mediating diabetic complications, as well as AD. In fact, patients with AD show a susceptibility to insulin resistance (IR). Meanwhile, patients with diabetes are increasingly shown to develop cognitive impairments. In this study, we aim to better understand the relationship between AD and Type 2 diabetes (T2D). Cytochrome P450 (CYPs) enzymes have been reported to be a prominent and emerging contributor to IR, cognitive impairment, and oxidative stress in a multitude of diabetic complications including diabetic neuropathy. More importantly, CYP-derived metabolites, 20-HETE and EET, have been described to play central roles in nervous system health. However, to our knowledge, no study investigates CYP contribution to T3D or AD. Aim: This work aims to investigate the role of CYP-metabolites 20-HETE and EET in mediating AD or diabetes-induced brain injury. We further aim to assess the possible effect of central insulin resistance on the 20-HETE/EETs levels and oxidative stress on the pathogenesis of AD. Methods: A battery of tests assessing multiple cognitive modalities correlating a spectrum of AD-like symptoms in our animal model were done. We utilized the Novel Object Recognition test, Y-maze, Sociability and Social Novelty test, and Morris Water Maze for the assessment of aspects of memory processing. Animals were subjected to behavioral cognitive testing after treatment with CYP-modulators HET0016 and AUDA to assess their therapeutic potential. Our investigation was followed by molecular testing on brain tissue with focus on the prefrontal cortex and the hippocampus in which we screened for CYP protein expression, 20-HETE and EET metabolites levels in circulation and in the brain, reactive oxygen species production, and key pathological markers of AD such as beta-amyloid accumulation and tau hyperphosphorylation in both mice models. We further screened for specific markers of IR and neurodegeneration using a variety of techniques including western blotting and immunohistology to identify alterations in our target proteins. Results: Our results showed an alteration at the molecular level in the expression of CYP450 enzymes as well as a disruption in myelin protein MBP. These were correlated with the deposition of β-amyloid in the cortical regions of T2DM and AD mice, which were further associated with an alteration of IRS-1 phosphorylation and 20-HETE and EETs levels, along with an increased ROS production. Administering either AUDA or HET0016 mitigated the effects of diabetes on mice brains. Conclusion: The results obtained highlight a prominent mechanistic axis involving CYPs alteration and 20-HETE/EET imbalance in mediating oxidative brain injury in diabetes and AD. Moreover, we show that CYP-modulation with pharmacological targets may hold therapeutic value, however these mechanisms necessitate further experimentation.