Delayed Intracranial Delivery of a Nitric Oxide Donor from a Controlled-release Polymer Prevents Experimental Cerebral Vasospasm in Rabbits

Abstract

Decreased local availability of nitric oxide (NO) may mediate chronic vasospasm after aneurysmal subarachnoid hemorrhage (SAH). Previous reports have shown that early treatment with NO prevents vasospasm in animals. We evaluated the efficacy of controlled-release polymers that contain the NO donor diethylenetriamine (DETA-NO) for the delayed treatment of vasospasm in a rabbit model of SAH. DETA-NO 20% (wt/wt) was incorporated into ethylene-vinyl acetate (EVAc) polymers. Animals (n = 52) were randomized to two experimental groups. In the first group (n = 32), animals received SAH and implantation of either 20% DETA-NO/EVAc polymer at a dose of 0.5 mg/kg of DETA-NO (n = 16) or empty EVAc polymer (n = 16). Polymers were implanted 24 (n = 16) or 48 hours (n = 16) after SAH. In the second group (n = 20), animals received SAH and implantation of either 20% DETA-NO/EVAc polymer at a dose of 1.3 mg/kg (n = 10) or empty EVAc (n = 10). Polymers were implanted 24 (n = 10) or 48 hours (n = 10) after SAH. An additional group (n = 16) underwent either sham operation (n = 6) or SAH only (n = 10). Animals were killed 3 days after hemorrhage, and the basilar arteries were processed for morphometric measurements. Results were analyzed using Student's t test. Treatment with 20% DETA-NO/EVAc polymers at a dose of 1.3 mg/kg significantly increased basilar artery lumen patency when administered at 24 (97 +/- 6% versus 73 +/- 10%; P = 0.0396) or 48 hours (94 +/- 6% versus 71 +/- 9%; P = 0.03) after SAH. Treatment with 20% DETA-NO/EVAc polymers at a dose of 0.5 mg/kg administered 48 hours after SAH significantly increased lumen patency (82 +/- 8% versus 68 +/- 12%; P = 0.03); a dose of 0.5 mg/kg, 24 hours after SAH, did not reach statistical significance (74 +/- 7% versus 65 +/- 9%; P = 0.16). The SAH-only group had a lumen patency of 67 +/- 12%. Delayed treatment of SAH with controlled-release DETA-NO polymers prevented experimental posthemorrhagic vasospasm in the rabbit. This inhibition was dose-dependent. This further confirms the role of NO in the pathogenesis of vasospasm.