Sulforaphane administration alleviates diffuse axonal injury (DAI) via regulation signaling pathway of NRF2 and HO-1

Background Nuclear factor erythroid 2-related factor 2 (Nrf2) can alleviate diffuse axonal injury (DAI)-induced apoptosis by regulating expression of heme oxygenase-1 (HO-1), while sulforaphane (SFN) was shown to reduce oxidative stress by increasing the expression of Nrf2. Therefore, we aimed to investigate therapeutic effect of SFN in the treatment of DAI and the ability of SFN to reduce oxidative stress. Methods The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was used to observe the effects of H2O2 and SFN on cell viability. Fluorometric assay, Western blot analysis, and flow cytometry were conducted to validate the protective role of SFN in an animal model of DAI. In addition, the levels of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were measured in DAI rats treated by SFN, while Western blot, immunohistochemistry assay, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were carried out to verify the effect of SFN in different animal groups. Results Cell viability was reduced by H2O2 in a dose-dependent manner, while the treatment by SFN significantly promoted cell growth. Meanwhile the administration of SFN effectively reduced the levels of caspase-3/poly(ADP-ribose) polymerase (PARP) activity increased by the H2O2 treatment, indicating that the protective effect of SFN could be mediated by its ability to suppress caspase-3 activation and PARP cleavage. In addition, the SFN treatment reduced the intracellular reactive oxygen species (ROS) generation induced by H2O2. Moreover, the MDA levels of SOD/GPx activity in various rat groups showed the protective effects of SFN in DAI rats. It is suspected that the protective effect of SFN was exerted via the activation of the Nrf2/HO-1 signaling pathway. In this study, DAI and DAI + phosphate-buffered saline (PBS) groups also showed the presence of more TUNEL-positive cells compared with the sham-operated group, while the SFN treatment reduced the extent of neuronal apoptosis. Conclusions By activating the Nrf2/HO-1 signaling pathway and reducing the activity of caspase-3, SFN reduces the apoptosis of neurons in brain trauma-induced DAI.