Nicorandil Attenuates High Glucose-Induced Insulin Resistance by Suppressing Oxidative Stress-Mediated Endoplasmic Reticulum Stress Protein Kinase RNA-Like Endoplasmic Reticulum Kinase Singling Pathway

Abstract

Background: Glucose- induced insulin resistance (IR) is a typical character of diabetes. Nicorandil is widely used in ischemic heart disease. Nicorandil shows protective effects against oxidative and endoplasmic reticulum (ER) stress which are involved in insulin resistance. Here we investigated mechanisms of nicorandil’s novel pharmacological activity on IR in diabetes. Methods: Nicorandil was administrated to diabetic animals and high-glucose exposed skeletal muscle cells. IR and glucose tolerance were evaluated. Molecular mechanisms concerning oxidative stress, ER stress and glucose uptake were assessed. Findings: Nicorandil attenuated high- glucose induced IR without affecting fasting blood glucose and glucose tolerance in whole body and skeletal muscle in diabetic rats. Nicorandil treatment suppressed protein kinase C(PKC)/ nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) system activities by reducing cytoplasmic free calcium level in skeletal muscle cells exposed to high glucose. As a result, the oxidative stress- mediated ER stress protein kinase RNA- like endoplasmic reticulum kinase (PERK)/ eukaryotic initiation factor (EIF) 2α/ activating transcription factor (ATF)4/CEBP homologous protein (CHOP)/tribbles homolog (TRB)3 signaling pathway activation was inhibited. Nicorandil down-regulated expression of TRB3 and thus facilitated Akt phosphorylation in response to insulin stimulation, leading to glucose transporter (GLUT)4 plasma membrane translocation which promoted glucose uptake capability of skeletal muscle cells. Interpretation: By reducing cytoplasmic calcium, nicorandil alleviated high-glucose induced IR by inhibiting oxidative stress- mediated ER stress PERK pathway. This study indicated nicorandil as a promising agent in treatment of patients with ischemic heart disease complicated with diabetes. Funding Statement: This study was supported by Innovative Talents Promotion Project of Shaanxi Province (2019KJXX-019); Fundamental Scientific Research Foundation of Xi’an Jiaotong University (xzy012019131); Health Scientific Foundation of Shaanxi Province (2018E11); Natural Science Basic Research Foundation of Shaanxi Province (2020JQ-941). Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The experimental protocols were reviewed and approved by Institutional Animal Care and Use Committee of Medical Research Institute of Northwestern Polytechnical University.