6-Mercaptopurine reverses experimental vasospasm and alleviates the production of endothelins in NO-independent mechanism—a laboratory study

Introduction Increased endothelin-1 (ET-1) production and diminished nitric oxide synthase (NOS) bioavailability has been observed in aneurysmal subarachnoid hemorrhage (SAH). The authors previously found that 6-mercaptopurine (6-mp) is effective in preventing and reversing arterial narrowing in a rodent SAH model. This present study is of interest to examine the effect of 6-mp on ET-1/endothelial nitric oxide synthase (eNOS) in this animal model. Methods A rodent double hemorrhage SAH model was employed. Animals were randomly assigned to six groups (sham, SAH only, vehicle, 0.5, 1.0 and 2 mgkg.1day.1 6-mp treatment). Monoclonal CD45 immunostaining was utilized to evaluate monocytes and microglia. The level of pro-inflammatory cytokines, such as IL-1, IL-6 and TNF- ƒ؟(RT-PCR), and ET-1 (ELISA) was measured. The basilar arteries (BAs) were harvested and sliced, and their crosssectional areas were determined. Radiolabeled NOS assay kit was applied to detect eNOS. Results Morphologically, convolution of internal elastic lamina, endothelial cells distortion, and necrotic smooth muscle were prevalently present in the basilar artery of SAH groups, which was absent in the 1 and 2 mgkg.1day.1 6-mp plus SAH group or the healthy controls. Significant vasospasm was noted in the vehicle group (lumen patency, 54.6%, p.0.01 compared with the sham group), but it was less prominent in the 2 mgkg.1day.1 6-mp treatment group (lumen patency, 87.6%, p<0.05). In addition, administration with 2 mgkg.1day.1 6-mp reduced cytokine levels by 11%, 47%, and 34% for IL-1, IL-6, and TNF-ƒ؟, respectively, and increased ET-1 levels were found in all the animals subject to SAH (SAH only, SAH plus vehicle, SAH plus 0.5 and 1.0 mgkg.1day.1 6-mp) except in the 2 mgkg.1day.1 6-mp SAH group, when compared with the healthy controls (no SAH). Meanwhile, treatment with 6-mp did not induce the levels of expressed eNOS in BAs in the 6-mp groups (0.5, 1.0, and 2 mgkg.1day.1 6-mp plus SAH) when compared with that in the SAH groups (p>0.1). Conclusion In summary, treatment with 6-mp decreased the release of pro-inflammatory cytokines and diminished experimental vasospasm. This study offered first evidence that 6-mp dose-dependently reduces the level of ET-1 in a NO-independent mechanism, which corresponds to its antivasospastic effect in the condition of chronic vasospasm.