The nongenomic neuroprotective effects of estrogen, E2-BSA, and G1 following traumatic brain injury: PI3K/Akt and histopathological study.

Objectives: Studies suggest that both genomic and nongenomic pathways are involved in mediating the salutary effects of steroids following traumatic brain injury (TBI). This study investigated the nongenomic effects of 17β-estradiol (E2) mediated by the PI3K/p-Akt pathway after TBI.

Methods: Ovariectomized rats were apportioned to E2, E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicles were injected before the induction of TBI and injection of drugs. Diffuse TBI was induced by the Marmarou model. Evans blue (EBC, 5 h), brain water contents (BWC), histopathological changes, and brain PI3K and p-Akt protein expressions were measured 24 h after TBI. The veterinary comma scale (VCS) was assessed before and at different times after TBI.

Results: The results showed a reduction in BWC and EBC and increased VCS in the E2, E2-BSA, and G1 groups. Also, E2, E2-BSA, and G1 reduced brain edema, inflammation, and apoptosis. The ICI and G15 inhibited the beneficial effects of E2, E2-BSA, and G1 on these parameters. All drugs, following TBI, prevented the reduction of brain PI3K/p-Akt expression. The individual or combined use of ICI and G15 eliminated the beneficial effects of E2, E2-BSA, and G1 on PI3K/p-Akt expressions.

Conclusions: These findings indicated that PI3K/p-Akt pathway plays a critical role in mediating the salutary effects of estradiol on histopathological changes and neurological outcomes following TBI, suggesting that GPER and classic ERs are involved in regulating the expression of PI3K/p-Akt.