Electroacupuncture improves ischemic myocardial injury by activating Nrf2/HO-1 signaling pathway to inhibit ferroptosis in rats

Abstract

To explore the role of nuclear factor E2 related factor 2 (Nrf2) / heme oxygenase (HO-1) signal pathway in electroacupuncture (EA) induced improvement of acute myocardial ischemia (AMI) and its relationship with ferroptosis in rats. Male SD rats were randomly and equally divided into sham operation, model, EA and EA+ML385 (inhibitor of Nrf2) groups (n=8). The rat model of AMI was established by ligating the descending anterior branch of the left coronary artery. EA (2 Hz/100 Hz) was applied to bilateral "Shenmen"(HT7) and "Tongli"(HT5) for 20 min, once daily for 7 days. The electrocardiogram (ECG) of standard Ⅱ (ECG ST) lead and heart rate (HR) in each group was recorded and analyzed before and after modeling and after treatment by using PowerLab physiological recorder system. Histopathological changes of myocardial tissue were observed by H.E. staining, and the ultrastructure of myocardiocytes of cardiac apical tissue was observed under transmission electron microscope. The contents of Fe2+ and glutathione (GSH) in the myocardial tissue were measured by chromato-metry. The protein expression levels of Nrf2, HO-1, glutathione peroxidase 4 (GPX4), ferritin heavy chain polypeptide 1 (FTH1) and long chain acyl CoA synthase 4 (ACSL4) in the myocardial tissue were detected by Western blot. Compared with the sham operation group, the HR, ECG ST, Fe2+ content, expression levels of Nrf2, HO-1, FTH1 and ACSL4 proteins in myocardial tissues were significantly increased (P<0.01), while GSH content and GPX4 protein expression considerably decreased (P<0.01) in the model group. Compared with the model group, both EA and EA+ML385 groups had an obvious decrease in HR, Fe2+ content, and ACSL4 levels (P<0.01), and an increase in the expression levels of GPX4 and FTH1 proteins (P<0.01), EA (rather than EA+ML385) effectively down-regulated ECG ST, and up-regulated GSH, Nrf2 and HO-1 (P<0.01), whereas EA+ML385 apparently down-regulated expression levels of Nrf2 and HO-1 (P<0.01). It shows that ML385 pronouncedly weaken the effects of EA in slowing down ECG ST and HR, down-regulating Fe2+ content and ACSL4 expression (P<0.01), up-regulating GSH content, Nrf2, HO-1, GPX4 and FTH1 expressions (P<0.01). H.E. staining showed disordered arrangement and hyperplasia of myocardiocytes, enlarged myocardial fiber gap, agglomerated and deeply stained myoplasma, and some broken myocardial fibers with irregular mass and local tissue fibrosis in the model group, which was relatively milder in both EA and EA+ML385 groups. Compared with the sham operation group, the model group showed decreased mitochondrial atrophy, increased membrane density, and disappearance or reduction of cristae in myocardial cells，which was improved in the EA group. EA of HT7 and HT5 has a protective effect on ischemic myocardium in rats, which may be related to its effects in reducing oxidative stress by regulating Nrf2/HO-1 signaling pathway, and inhibiting "iron death" of myocardial cells.