Atrial fibrillation and its arrhythmogenesis associated with insulin resistance

(2019) 18:125 Chan et al. Cardiovasc Diabetol https://doi.org/10.1186/s12933-019-0928-8 ORIGINAL INVESTIGATION Cardiovascular Diabetology Open Access Atrial fibrillation and its arrhythmogenesis associated with insulin resistance Yi‑Hsin Chan1,2,3, Gwo‑Jyh Chang5, Ying‑Ju Lai7, Wei‑Jan Chen1,2, Shang‑Hung Chang1,2,4, Li‑Man Hung6, Chi‑Tai Kuo1,2*† and Yung‑Hsin Yeh1,2*† Abstract Background: Insulin resistance (IR) is considered as a risk factor for atrial fibrillation (AF) even before diabetes devel‑ ops. The pathophysiology and underlying mechanism are largely unclear. Methods: We investigated the corresponding mechanism in two IR models of rats fed 15-week high-fat (HFa) and high-fructose/cholesterol (HFr) diets. AF was evaluated and induced by burst atrial pacing. Isolated atrial myocytes were used for whole-cell patch clamp and calcium assessment. Ex vivo whole heart was used for optical mapping. Western blot and immunofluorescence were used for quantitative protein evaluation. Results: Both HFa and HFr rat atria were vulnerable to AF evaluated by burst atrial pacing. Isolated atrial myocytes from HFa and HFr rats revealed significantly increased sarcoplasmic reticulum calcium content and diastolic calcium sparks. Whole-heart mapping showed prolonged calcium transient duration, conduction velocity reduction, and repetitive ectopic focal discharge in HFa and HFr atria. Protein analysis revealed increased TGF-β1 and collagen expres‑ sion; increased superoxide production; abnormal upregulation of calcium-homeostasis-related proteins, including oxidized CaMKIIδ, phosphorylated-phospholamban, phosphorylated-RyR-2, and sodium-calcium exchanger; and increased Rac1 activity in both HFa and HFr atria. We observed that inhibition of CaMKII suppressed AF in both HF and HFr diet-fed rats. In vitro palmitate-induced IR neonatal cardiomyocytes and atrial fibroblasts expressed significantly more TGF-β1 than did controls, suggesting paracrine and autocrine effects on both myocytes and fibroblasts. Conclusions: IR engenders both atrial structural remodeling and abnormal intracellular calcium homeostasis, con‑ tributing to increased AF susceptibility. The inhibition of CaMKII may be a potential therapeutic target for AF in insulin resistance. Keywords: Atrial fibrillation, Insulin resistance, CaMKII, TGF-β Background Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical settings, affecting ~ 2% of patients worldwide and carrying a significantly increased risk of ischemic stroke and mortality [1]. Diabetes is one of the major risk factors for AF. A large meta-analysis indicated that patients with diabetes have a nearly 40% greater risk of AF than do patients without diabetes [2]. People with *Correspondence: ; † Chi-Tai Kuo and Yung-Hsin Yeh contributed equally to this article 1 Cardiovascular Department, Chang-Gung Memorial Hospital, Linkou, Taoyuan, Taiwan Full list of author information is available at the end of the article diabetes may have diabetic cardiomyopathy and progress to heart failure independent of coronary artery disease or hypertension, which was attributed to various pathological conditions, including hyperglycemia, obesity, and insulin resistance (IR) [3, 4]. IR is a pathological condition in which cells or tissues fail to respond normally to insulin, and it is characterized by a set of signs comprising obesity, increased blood sugar, dyslipidemia, and elevated blood pressure. IR is the common denominator of metabolic syndrome, prediabetes, and diabetes. People who develop type 2 diabetes usually pass through earlier stages of prediabetes and IR, although these stages are often undiagnosed. Metabolic syndrome and IR have been suggested as risk factors for incident AF, but they © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Chan et al. Cardiovasc Diabetol (2019) 18:125 have not been supported by all clinical observations [5–9]. Previous studies have demonstrated the pathological mechanisms of overt hyperglycemia-related atrial remodeling and arrhythmogenesis in animal models of diabetes [10, 11]. The characteristics of IR atria and their arrhythmogenesis have not been completely clarified [12, 13]. Food containing high fat, high sugar, and high cholesterol causes the development of IR and significantly increases the susceptibility to diabetes and the risk for cardiovascular disease. Previously, we established two IR rat models by feeding them high-fat (HFa) and highfructose/high-cholesterol (HFr) diets [14]. In the present study, we used these models to investigate IR-related atrial remodeling and AF vulnerability. We demonstrated significant remodeling in HFa and Hfr rat atria, including changes in the expression of calcium handling–related proteins, increased interstitial fibrosis, and increased oxidative stress and expression of transforming growth factor (TGF)-β1. Furthermore, we showed that oxidized calcium/calmodulin-dependent protein kinase II (CaMKII) may mediate the AF arrhythmogenesis in rats fed HFa and HFr diets. Methods Animals and diets Male Sprague–Dawley rats weighing 150–170 g were assigned to three groups fed one of the following three diets for 15 weeks as previously described: [14] (1) a regular standard diet (5.1% fat, 23.5% protein, and 50.3% carbohydrate; Laboratory Autoclavable Rodent Diet 5010; LabDiet, St. Louis, MO, USA) (control; n = 30), (2) an HFr diet (4% cholesterol, 10.1% fat, 17% protein, and 51.6% carbohydrate, TD03468; Harlan Teklad, Indianapolis, IN, USA) with 10% fructose in drinking water (n = 30), or (3) an HFa diet (45% fat, 20% protein and 35% carbohydrate, D12451; Research Diets, New Brunswick, NJ, USA) (n = 30). For sacrifices, all the experimental rats were under deep anesthesia with 3–4% Isoflurane inhalation. Further, euthanasia was taken place by exsanguinations via massive blood-collection from inferior vena cava. The whole heart was taken out immediately for further examination. This study protocol was approved by the Institutional Animal Care and Use Committee of ChangGung Memorial Hospital (approval No. 2015032302) and conformed to the Guide for the Care and Use of Laboratory Animals published by the United States National Institutes of Health. Whole‑heart Langendorff preparation The heart was harvested immediately and cannulated through the aorta after the rats were killed. Blood was flushed out by injection of a 30-mL cardioplegic soluti (...truncated)