Hemoglobin-Induced Nitric Oxide Synthase Overexpression and Nitric Oxide Production Contribute to Blood–Brain Barrier Disruption in the Rat

Abstract

Hemoglobin (Hb) released from extravasated erythrocytes may have a critical role in the process of blood-brain barrier (BBB) disruption and subsequent edema formation after intracerebral hemorrhage (ICH). Excessive nitric oxide (NO) production synthesized by nitric oxide synthase (NOS) has been well documented to contribute to BBB disruption. However, considerably less attention has been focused on the role of NO in Hb-induced BBB disruption. This study was designed to examine the hypothesis that Hb-induced NOS overexpression and excessive NO production may contribute to the changes of tight junction (TJ) proteins and subsequent BBB dysfunction. Hemoglobin was infused with stereotactic guidance into the right caudate nucleus of male Sprague Dawley rats. Then, we investigated the effect of Hb on the BBB permeability, changes of TJ proteins (claudin-5, occludin, zonula occludens-1 (ZO-1), and junctional adhesion molecule-1 (JAM-1)), iron deposition, expression of inducible NOS (iNOS) and endothelial NOS (eNOS), as well as NO production. Hb injection caused a significant increase in BBB permeability. Significant reduction of claudin-5, ZO-1, and JAM-1 was observed after Hb injection as evidenced by PCR and immunofluorescence. After a decrease at early stage, occludin showed a fivefold increase in mRNA level at 7 days. Significant iron deposition was detectable from 48 h to 7 days in a time-dependent manner. The iNOS and eNOS levels dramatically increased after Hb injection concomitantly with large quantities of NO released. Furthermore, enhanced iNOS or eNOS immunoreactivity was co-localized with diffused or diminished claudin-5 staining. We concluded that overexpressed NOS and excessive NO production induced by Hb may contribute to BBB disruption, which may provide an important potential therapeutic target in the treatment of ICH.