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Introduction
Acute lung injury (ALI) is characterized by rapid onset lung and capillary endothelial cell damage caused by a series of factors (1), which may consequently result in pulmonary edema and hypoxic respiratory insufficiency. The clinical manifestations include progressive hypoxemia and respiratory distress. Severe ALI is termed acute respiratory distress syndrome (ARDS).
According to the literature (2), the mortality rate of ALI is 35–40%. Studies investigating the mechanism of ALI have revealed that its etiology involves imbalances between inflammatory and anti-inflammatory factors, as well as oxidant and antioxidant capacity (3–5), indicating that oxidative stress and excessive inflammatory factor release are critical factors that should be targeted in the treatment of lung injury.
When the body is confronted by a series of external stimuli, the oxidant and antioxidant system become imbalanced, which may lead to reactive oxygen species (ROS) accumulation, resulting in oxidative damage to tissues and organs. This phenomenon is termed oxidative stress (6). It has been demonstrated that the nuclear factor erythroid 2-like 2 (Nrf2)-kelch-like ECH-associated protein 1 (Keap1)-antioxidant response element (ARE) signaling pathway is a major regulator of the antioxidant response (7).
Under normal physiological conditions, Nrf2 molecules bind to the Keap1 protein molecules in the cytoplasm and are in an inactive state, and are therefore unable to translocate to the nucleus to activate transcription. When oxidative stress occurs, Nrf2 and Keap1 uncouple, Nrf2 is phosphorylated and translocates to the nucleus to bind ARE, and the transcription of downstream detoxification enzymes and antioxidant genes is initiated, in order to increase the antioxidant ability of the cell (8).
Mesenchymal stem cells (MSCs) originate from the early developmental mesoderm and are multipotent cells; they have been recognized as an ideal seed for tissue repair due to their strong multilineage differentiation potential and immunoregulatory ability (9). Shalaby et al (10) confirmed that MSCs alleviate lung injury and improve the activity of antioxidant enzymes in serum, by injecting MSCs into the caudal vein of a rat model. In addition, the use of MSCs in the treatment of lung disease is not limited to laboratory and animal models, but has also been partially developed as a clinical treatment. Wilson et al (11) used MSCs for the clinical treatment of ARDS, and achieved successful results. Furthermore, it has...