Germacrone ameliorates acute lung injury induced by intestinal ischemia-reperfusion by regulating macrophage M1 polarization and mitochondrial defects

Abstract

Intestinal ischemia-reperfusion (I/R) injury severely affects the lungs. Germacrone (Ger) possesses anti-inflammatory and antioxidant properties. However, it is unclear whether it protects the lungs from I/R injury. In this study, we elucidate the mechanisms by which Ger protects lungs from I/R injury. C57BLKS/J male mice are subjected to I/R injury via complete clamping of the superior mesenteric artery. Ger is administered before intestinal I/R. Mitochondrial morphology is observed via electron microscopy. The histopathology of the lung tissues is monitored via hematoxylin-eosin and immunofluorescence staining. The mitochondrial oxygen consumption rate is measured via an XF96 extracellular flux analyzer. In the I/R mouse model, lung specimens present significant lung damage accompanied by increases in the levels of collagen III, vimentin, and α-SMA in lung tissues. After treatment with Ger, lung impairment and fibrosis in I/R-induced acute lung injury (ALI) model mice are restored, suggesting that Ger improves I/R-ALI. In addition, Ger administration decreases the release of inflammatory factors such as IL-1β, IL-6, and COX2, as well as the expressions of M1 macrophage markers, facilitating cell survival in the I/R-ALI model. Additionally, Ger (EC50: 47.16 μM) ameliorates mitochondrial dysfunction by increasing I/R-ALI-induced apoptosis, increasing the expression of SIRT1, and reducing the levels of HIF1-α, Nrf2, and OGG1 in MLE-12 cells. Ger may affect macrophage polarization and improve subsequent mitochondrial defects through the SIRT1-HIF1α-Nrf2 signaling pathway in MLE-12 cells, which ultimately improves lung function and lung inflammation in the I/R-ALI model.

1. Introduction

Intestinal ischemia-reperfusion (I/R) injury is a common type of tissue and organ injury that plays an important role in the pathological evolution of severe infections, shock, cardiopulmonary insufficiency, and other diseases [1]. I/R not only causes local tissue damage in the digestive tract but also leads to damage to distant organs and even multiple system organ failure (MSOF), with acute respiratory distress syndrome (ARDS) caused by lung injury being the most prominent [2]. The intestine can tolerate hypoperfusion at 20% of maximal blood flow [3]. Research has shown that the delayed diagnosis of intestinal necrosis can lead to very high (60%–80%) mortality after acute mesenteric ischemia [4,5]. The signal transduction mechanism of intestinal I/R lung injury (I/R-ALI) is very complex [6]. Although extensive research has been conducted in recent years, the pathogenesis of this disease remains unclear [7]. Therefore, the signal regulatory mechanism of intestinal I/R lung injury remains a hotspot in respiratory research.

Several investigators have reported that damage to the intestinal mucosal barrier after I/R permits the entry of bacteria and endotoxins, resulting in a systemic inflammatory response [8]. Many inflammatory mediators are subsequently released from macrophages into the systemic circulation, which can lead to cell necrosis, tissue damage, and organ failure [9]. An increased neutrophil count in lung tissue can lead to increased vascular permeability, vascular and interstitial edema, and pulmonary edema [10]. I/R-induced lung injury is associated with increased neutrophils and related inflammatory mediators (including reactive oxygen species (ROS), cytokines, and bacterial endotoxins), impaired mitochondrial function, and pulmonary epithelial cells [11–13]. Resident alveolar macrophages, which typically exhibit an alternately activated phenotype (M2), transit to a classically activated phenotype (M1) and release various potent proinflammatory mediators during the acute phase of acute lung injury (ALI)/ARDS. At later stages, the M1 phenotype of activated resident and recruited macrophages shifts back to the M2 phenotype to eliminate apoptotic cells and participate in fibrosis [14]. Thus, the regulation of macrophage function may be a promising therapeutic strategy against I/R-ALI.