Increased miR-155 and heme oxygenase-1 expression is involved in the protective effects of formononetin in traumatic brain injury in rats.

Oxidative stress has been considered a major contributing factor to traumatic brain injury (TBI). Formononetin, a phytoestrogen that belongs to the flavonoid family, is extracted from plants and herbs such as the red clover. Growing evidence demonstrates that formononetin has antioxidant properties. Therefore, formononetin has potential use in treating oxidative stress injuries in TBI. In this study, the neuroprotective and antioxidant effects of formononetin against TBI, as well as the related probable mechanisms, were investigated. The TBI model was produced in male Wistar rats through Feeney's weight-drop model. At 1 day after TBI, the neurological function score and brain water content were assessed. TUNEL assay was used to determine neuronal apoptosis. The expression levels of miR-155, HO-1, and BACH1 were measured by RT-PCR and western blotting. Consequently, our findings showed that formononetin pretreatment for 5 days significantly improved the neurological scores, reduced brain edema and inhibited neuronal apoptosis in rats after TBI. MiR-155 was substantially decreased and BACH1 expression was significantly increased in the TBI model, while pretreatment with formononetin dramatically up-regulated the expression levels of miR-155 and HO-1 and down-regulated the protein expression of BACH1 in rats after TBI. In summary, formononetin has been shown to have neuroprotective effects, and the mechanisms of this effect may be associated with its inhibition of oxidative stress and activation of Nrf2-dependent antioxidant pathways in TBI.