Cytochrome-P450 Implications in the Mechanisms of Central and Peripheral Nerve Injury

Abstract

Diabetes mellitus (DM) is a chronic metabolic disorder that targets a multitude of organs. Among the common complications of diabetes is Diabetic Neuropathy (DN), characterized by a range of clinical syndromes resulting from damage to the nervous system. Abnormalities in glucose metabolism can result in neural dysfunction and a variety of acute and chronic nervous system disorders, In the periphery, Diabetic Peripheral Neuropathy (DPN) is the most common and intractable microvascular complication of diabetes, affecting somatic sensory and motor nerves. In the central nervous system, type 2 diabetes (T2D) is a robust predictor of cognitive impairment and decline mimicking Alzheimer’s Disease (AD). This is currently recognized as type 3 diabetes (T3D). Research has shown insulin signaling deficits, increased oxidative stress and accumulation of neurotoxic proteins to be a common pathogenic mechanism to both AD and diabetes. To date, no therapies are available beyond symptomatic relief for both pathologies. Thus, the importance of this work is to find biomarkers for the early detection and novel mechanistic targets that may be of promise for intervention. To be able to do that, we aimed to investigate common mechanisms of injury to both pathologies. Aims: Our study focuses on the role of Cytochrome P450 (CYP450) as a major source of ROS production while exploring the concomitant occurrence of peripheral nerve injuries and central cognitive decline like Alzheimer’s Disease dementia, and the implication of the CYP450 metabolites of arachidonic acid metabolism, 20-HETE and EET imbalance in both pathologies. To that end, we hypothesize that hyperglycemia because of chronic diabetes progression triggers alterations in the CYP450 pathway and a pathophysiological imbalance in 20-HETE and EETs levels. Altogether, a state of oxidative stress ensues culminating in behavioral and molecular changes in the diabetic brain and sciatic nerve tissue. We further hypothesize that the pharmacological intervention with 20-HETE synthase or sEH enzyme inhibitors may alleviate cognitive deficits and peripheral nerve damage. Methods: The following study investigates CYP mechanisms using pharmacological agents, HET0016 and AUDA in vivo in an experimental model of T2D, the MKR murine model. Animals were subjected to peripheral and central nerve assessments using the Beam Walking Test, Grip Strength test, Thermal Algesia Test, Novel Object Recognition, and Y-maze. In parallel, markers of nerve injury as well as oxidative stress were assessed using a variety of techniques such as western blot, HPLC and NADPH oxidase assay. We pay particular attention to the markers of myelination MPZ and PMP22, EET-degrading enzyme, the soluble epoxide hydrolase, and the 20-HETE synthase CYP4A as well as EET-synthase CYP2C. We also investigated the beta amyloid expression in the hippocampus to screen for brain injury. Results: Behavioral data showed hyperglycemia induced damage in the central and peripheral nervous system in our mice model. Treatments with AUDA or HET0016 revealed a restoration in the peripheral and cognitive behavior. On the molecular level, sciatic nerves of the diabetic mice exhibited changes in the myelin protein profiles and CytochromeP450 enzymes. In the brain, hippocampal lysates demonstrated accumulations of beta amyloid proteins in the diabetic group. NADPH dependent ROS production presented increased ROS in the sciatic nerve and brain of diabetic group revealing a significant rise oxidative stress. We also observed fluctuations in the levels of EETs and 20-HETE in sciatic nerves of our animal models. HET0016 or AUDA administration were shown to restore diabetes-induced 20-HETE/EET imbalance as well as ROS overproduction. Conclusion: In conclusion, we provide evidence for the concomitant occurrence of both DPN and cognitive decline in diabetic animals with emphasis on the role of CYP450 20-HETE/EET imbalance as a mechanism of injury common to diabetes-induced nerve injury in both the CNS and PNS.