The effects of 17 beta-estradiol on blood brain barrier integrity in the absence of the estrogen receptor alpha; an in-vitro model

Abstract

The blood-brain barrier (BBB), which saves the brain from toxic substances, is formed by endothelial cells. It is mainly composed of tight junction (TJ) proteins existing between endothelial cells. Estrogen is an important regulatory hormone of BBB permeability. It protects the BBB before menopause, but may increase BBB permeability with aging. In addition, nitric oxide modulates BBB permeability. Alcohol impairs the integrity of the BBB with oxidants and inflammatory mediators such as iNOS. We investigated the effects of estrogen on BBB integrity in an in vitro BBB model created with ER alpha-free HUVEC (human umbilical vein endothelial-like cells) to mimics the menopausal period. In vitro BBB model is created with HUVEC/C6 (rat glioma cells) co-culture. The effect of 17 beta-estradiol on ethanol-induced BBB disruption and change/or increase of iNOS activity, which modulate BBB integrity, were evaluated. Inducibility and functionality of BBB were investigated using transendothelial electrical resistance (TEER) and the expression of proteins TJ proteins (occludin and claudin-1) and iNOS activity by immunostaining. Our results revealed that 17 beta-estradiol treatment before and after ethanol decrease expression of occludin and claudin-1 and value of TEER which are BBB disrupt indicators. In addition, ethanol and 17 beta-estradiol separately and pre-and post-ethanol 17 beta-estradiol treatment increased iNOS expression. Thus our study suggests caution in the use of 17 beta-estradiol after menopause because 17 beta-estradiol at this time may both increase the inflammatory process as well as damage the BBB. We think that beneficial effects of 17 beta-estradiol may be through ER alpha but it needs further studies.