This study investigated the potential beneficial effects of natural products and their major component on redistribution of ZO-1 and FoxO3a-mediated degradation of claudin-5 during ischemia/hypoxia using the mouse middle cerebral artery occlusion (MCAO) model and hypoxia model. The possible underlying mechanisms are also investigated, especially those linked to the oxidative stresses.
Onion extract (OE) and its major component, quercetin (Quer), as well as yuzu extract (YE) and hesperidin (HSP) prevented brain ischemia-induced brain edema in dose-dependent manners. Evans blue extravasation in the ischemic hemisphere of the mouse brain was also significantly reduced by treatment with the four materials. In addition, they inhibited the immunoreactivity of tight junction proteins (TJs; ZO-1 (Zonula occludens-1) and claudin-5).
In in vitro model, pre-treatment of OE, Quer, YE, and HSP significantly attenuated hypoxia-induced Blood-Brain Barrier (BBB) hyperpermeability. The four materials also inhibited hypoxia-induced redistribution of ZO-1, degradation of claudin-5, increase of matrix metalloproteinase (MMP)-3/9 mRNA levels, and translocation of Forkhead box O 3a (FoxO3a) into nucleus. The effects of antioxidant, trolox, and N-acetyl-cysteine (NAC) as well as siFoxO3a transfection also mimicked those effects of OE, Quer, YE, and HSP. However, transfection of siFoxO3a did not inhibit transcription of MMP-9 and redistribution of ZO-1 induced by hypoxia. In addition, OE, Quer, YE, and HSP attenuated the generation of oxidative stress induced by hypoxia, indicating that they may have antioxidant effects against hypoxia induced-dysfunction of BBB.
The results from this study demonstrate that OE, Quer, YE, and HSP prevent BBB hyperpermeability and tight junction proteins (TJs) disruption in MCAO and hypoxia model. In addition, these findings suggest that BBB protection by the four materials involves reduction of MMPs transcription, the inhibition of ZO-1 redistribution, and FoxO3a inhibition-mediated suppression of claudin-5 degradation, possibly through its antioxidant effects in hypoxia model.