Abstract
78 This study tested the hypothesis that adenovirus expressing heme oxygenase-1 (HO-1), the enzyme that metabolises hemoglobin, would reduce contractions of cerebral arteries to hemoglobin and decrease vasospasm after subarachnoid hemorrhage (SAH). Rats underwent injection of vehicle or replication defective adenovirus expressing HO-1 (Ad5HO-1) or β-galactosidase (Ad-βGal) into the cisterna magna. Transgene expression was assessed by reverse transcriptase polymerase chain reaction for messenger ribonucleic acid (mRNA) levels, immunoblotting for protein levels, immunohistochemistry, response of the basilar artery to pure, ferrous hemoglobin and carboxyhemoglobin production 1 day after virus injection. Effects of Ad5HO-1 and Ad-βGal on vasospasm were assessed in a rat double hemorrhage model. Injection of Ad5HO-1 significantly increased HO-1 mRNA, protein and activity in basilar artery compared to Ad-βGal and vehicle. Injection of Ad-βGal result in low level expression and activity of HO-1 but this was significantly less than after injection of Ad5HO-1. HO-1 immunoreactivity was present in the basilar artery adventitia after injection of Ad5HO-1 and Ad-βGal. Injection of Ad5HO-1 and Ad-βGal increased basilar artery diameter and brainstem blood flow compared to control (P < 0.001, ANOVA). Ad5HO-1, however, significantly and selectively prevented contraction of the basilar artery and reduction in brainstem cerebral blood flow due to hemoglobin and significantly increased carboxyhemoglobin concentration compared to Ad-βGal and vehicle. Basilar artery diameter 7 days after SAH was significantly greater after injection of Ad5HO-1 (380 ± 36 μm) compared to Ad-βGal (282 ± 44 μm) and vehicle (287 ± 31μm, P < 0.001, ANOVA). In conclusion, injection of Ad5HO-1 into the cisterna magna of rats results in expression of functional HO-1 in the adventitia of the basilar artery. This is associated with an increase in basilar artery diameter. HO-1 expression with Ad5HO-1 inhibits arterial contractions to hemoglobin and after SAH.
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