To investigate the effect and mechanism of celastrol (Cela) on secondary injury after traumatic brain injury (TBI).

A total of 120 healthy male C57BL/6J mice were randomly divided into Sham group (n=36), TBI group (n=42), and TBI+Cela group (n=42). The Sham group was only treated with open bone window. In TBI group and TBI+Cela group, a microprocessor controlled pneumatic impact device was used to establish the TBI model after opening the bone window. Mice in the TBI+Cela group were intraperitoneally injected with Cela (1 mg/kg body weight), while mice in the TBI group were intraperitoneally injected with the same amount of physiological saline solution. Twenty-four hours after modeling, Nissl staining was used to determine the brain injury volume after TBI. Brain water content was measured by dry-wet weight method. The degree of brain function injury after TBI was determined by modified neurological severity score (mNSS), turn Angle test and seton test. DHE staining was used to measure the level of reactive oxygen species (ROS) in brain tissue after TBI. The contents of malondialdehyde (MDA), adenosine triphosphate and the activity of mitochondrial respiratory chain complex Ⅰ-Ⅳ were measured by enzyme-linked immunosorbent assay. Transmission electron microscopy was used to observe and calculate the ultrastructural changes of mitochondria after TBI. Western blotting was used to determine the expression of SIRT3 protein after TBI.

Twenty-four hours after TBI, the brain injury volume and brain water content in the TBI+Cela group were significantly reduced than those of the TBI group, and the differences were statistically significant (P<0.05). The neurological function of mice was significantly impaired after TBI, the mNSS score of the TBI+Cela group was significantly lower than that of the TBI group, the latency to fall was significantly higher than that of the TBI group, and the proportion of left turning was significantly reduced than that of the TBI group, and the differences were statistically significant (P<0.05). The levels of ROS and MDA in mouse brain tissue were significantly increased after TBI, while the ROS and MDA levels in the TBI+Cela group were significantly lower than those in the TBI group, with statistical significance (P<0.05). The mitochondrial morphology and function were significantly impaired after TBI, and the degree of mitochondrial morphology and function damage of the TBI+Cela group were significantly improved than those of the TBI group, with statistical significance (P<0.05). The expression of SIRT3 was significantly reduced after TBI, while the expression level of SIRT3 was significantly increased in the TBI+Cela group, with statistical significance (P<0.05).

Cela can significantly reduce TBI induced brain parenchymal and functional damage, oxidative stress intensity, and mitochondrial morphological and functional damage, possibly by positively regulating SIRT3 to protect mitochondria, thereby reducing oxidative stress intensity after TBI, and ultimately alleviating secondary brain injury after TBI.