Carnosic acid attenuates ventilator-induced diaphragmatic dysfunction via activation of the Nrf2/HO-1 pathway

Prolonged or inappropriate mechanical ventilation (MV) can cause ventilator-induced diaphragmatic dysfunction (VIDD), characterized by progressive diaphragmatic atrophy, reduced contractile force and diminished endurance, leading to difficult weaning and increased mortality. The core pathophysiological mechanisms involve mitochondrial dysfunction and aberrant apoptotic pathway activation in diaphragmatic myocytes. Therefore, exploring effective prevention and treatment strategies is crucial. Carnosic acid (CA), a natural compound with significant antioxidant, anti-inflammatory and cytoprotective effects has recently gained interest. However, CA's role in VIDD remains unclear. This study investigates CA's protective effects and potential mechanisms against VIDD, highlighting its promise as a novel therapeutic agent.

VIDD models in vivo and muscle atrophy models in vitro were established. Mice and C2C12 myotubes were administered CA. Ultrasound, muscle contractility tests, histological examinations, immunofluorescence, western blotting, and biochemical assays were employed to assess oxidative stress levels, atrophy-related proteins alterations and apoptosis levels in the diaphragm following MV. Cell viability assays, flow cytometry and EdU assays were used to measure cell proliferation and apoptosis. JC-1 staining and transmission electron microscopy (TEM) were applied to evaluate mitochondrial morphology and function.

CA effectively protected muscle cells both in vivo and in vitro, alleviating MV- and dexamethasone (DXMS)-induced oxidative stress, atrophy, and apoptosis in myocytes. Compared with the model group, CA intervention significantly increased the expression levels of NRf2, p-Nrf2 and HO-1 in both the diaphragms of MV mice and DXMS-treated C2C12 cells. We observed improved mitochondrial morphology and function with decreased expression of ROS, MDA and atrophy-related proteins (MuRF-1/Atrogin-1). Furthermore, CA intervention significantly ameliorated the mitochondrial membrane potential in cardiomyocytes, reduced the expression levels of the pro-apoptotic molecules Bax and the Cleaved-Caspase-3/Caspase-3 and Cleaved-Caspase-9/Caspase-9 ratios, while upregulating the expression level of the anti-apoptotic molecule Bcl-2.

CA can activate the Nrf2/HO-1 pathway both in vivo and in vitro, mitigate mitochondrial damage and apoptosis in myocytes, attenuate muscle atrophy, and maintain normal physiological function. It can be considered as a potential novel therapeutic agent for the prevention and treatment of VIDD.