Electroacupuncture Attenuates Limb Ischemia-Reperfusion-Induced Lung Injury Via p38 Mitogen-Activated Protein Kinase-Nuclear Factor Erythroid-2-Related Factor-2/Heme Oxygenase Pathway

Abstract

Background

Electroacupuncture has been reported to protect the body from organ damages, but its mechanisms remain to be explored. This research was designed to investigate the function of electroacupuncture in lung injury resulted from hind limb ischemia–reperfusion (LIR) and whether p38 mitogen-activated protein kinase (p38 MAPK)–mediated nuclear factor erythroid-2–related factor-2 (Nrf2)/heme oxygenase (HO)-1 pathway contributes to the protective effect of electroacupuncture on LIR-originated lung damage.

Materials and methods

Rabbits were subjected to occluding femoral artery for 2 h. Then they received reperfusion for 4 h to establish lung injury model. Electroacupuncture stimulation was performed bilaterally at Feishu and Zusanli acupoints for 15 min once a day for 5 d before the experiment and throughout the hind LIR model performing in the experimental day. Blood samples and lung tissues were collected to examine the role of electroacupuncture treatment in inflammatory response, oxidative stress, and lung injury. Both the protein expression and the messenger RNA level of Nrf2 and HO-1 were detected.

Results

The results showed that electroacupuncture treatment remarkably alleviated lung injury, decreased inflammatory cytokines secretion, attenuated lung oxidative stress, increased the amount of Nrf2 and HO-1, and increased the ratio of phospho-p38 MAPK to p38 MAPK after LIR. However, the protective effects exerted by electroacupuncture were reversed to some extent by the preconditioning with SB203580, a p38 MAPK–specific inhibitor.

Conclusions

These results suggested that electroacupuncture could attenuate lung injury in rabbits subjected to LIR by inhibition of proinflammatory cytokine response and oxidative stress through activating p38 MAPK-mediated Nrf2/HO-1 pathway.

Introduction

Limb ischemia–reperfusion (LIR) is a common pathologic process in clinical practice, such as critical crush injury, artery embolism, and some surgical operation.1, 2, 3 Reperfusion of the ischemic limb not only results in further severe limb vital injury but also causes systemic inflammation response and functional and structural damage of multiple organs. The lung is the most vulnerable organ to insult after ischemia–reperfusion.4, 5 It was proved that excessive inflammatory response and oxidative stress contributed to the pathologic process of lung injury induced by LIR.6, 7, 8 However, in the progress of organ injury after LIR, some endogenous adaptive cascade reactions can be activated to exert beneficial effects on damaged organs.9, 10 Noticeably, activating the nuclear factor erythroid 2–related factor-2 (Nrf2) is the main method to the protection of organs.¹¹

Nrf2 has the function of antioxidant response by regulating transcription of antioxidant and cytoprotective genes, such as glutathione peroxidase (GPx), catalase (CAT), heme oxygenase (HO-1).12, 13 In this regard, HO-1, the main target of Nrf2, exerts antioxidant, anti-inflammatory, and antiapoptosis functions through catalyzing the chemical reaction of heme into biologically active products such as bilirubin.14, 15 Our previous studies elucidated that upregulation of Nrf2 expression followed by increasing HO-1 protein could mitigate lung injury and renal injury.16, 17, 18 A previous study showed that HO-1 activation may be beneficial to relieve the lung damage after LIR.¹⁹ Moreover, it was reported that p38 MAPK signal pathway regulated the activation of Nrf2.20, 21 However, it still remains unclear what regulated Nrf2 and HO-1 levels in lung injury.

Acupuncture, a nonpharmacologic therapy, has been proved to be helpful to relieve many clinical disorders, such as pain,22, 23 chronic inflammation,24, 25 female stress urinary incontinence,²⁶ menopausal symptoms,²⁷ persistent depression,²⁸ nausea and vomiting,²⁹ cancer-related fatigue, and hot flashes.30, 31 In particular, electroacupuncture in specific acupoints has exhibited certain protective effects on organ injury, including increasing the activities of antioxidant enzymes and suppressing systemic inflammatory responses.32, 33 A report suggested that electroacupuncture relieved proinflammatory responses and myocardial injury via the vagal nerve in ischemia–reperfusion cardiomyocytes.³⁴ A clinical study showed that electroacupuncture could lessen the lung injury in patients with severe acute pancreatitis.³⁵ Another preliminary study confirmed that electroacupuncture stimulation at Feishu (BL13) and Zusanli (ST36) had anti-inflammatory or antioxidant effects against lipopolysaccharide (LPS)-induced acute lung damage.³⁶ However, whether electroacupuncture can protect the lung from the damage caused by LIR and the potential regulatory mechanisms are still unclear. In the present study, we hypothesized that electroacupuncture treatment at BL13 and ST36 acupoints could exert a protective role against lung injury following LIR in rabbits via the activation of Nrf2/HO-1 axis through modulating p38 MAPK pathway.