Abstract 3129: Endothelin-1 Antagonism And Nitric oxide Augmentation Prevents CyA Induced Vasomotor Impairment
BACKGROUND: We previously demonstrated that Cyclosporine (CyA) impairs endothelial function as a result of alterations in NO and ET regulation. Bosentan (BOS), an endothelin-1 (ET) antagonist, and tetrahydrobiopterin (BH4), a NO synthase cofactor, may reduce endothelial dysfunction by limiting ET injury and improving NO production. Our study examined the effects of BOS and BH4 exposure on CyA induced dysfunction.
METHODS: Lewis rats were injected with CyA, BOS, BH4, BOS+BH4, BOS+CyA, BH4+CyA, BOS+BH4+CyA or saline (Control (Con)) IP daily for 2 weeks. Thoracic aortic (TAo) segments were assessed for endothelial-dependent(Edep) and independent(Eind) relaxation following exposure to acetylcholine and sodium nitroprusside by deriving the %maximum relaxation (Emax). Vessel sensitivity to ET induced vasospasm was assessed. Protein expression of eNOS, ETA and ETB receptors in the TAo were determined. Oxidative injury (OI) was assessed by changes in 8-isoprostane levels.
RESULTS: CyA resulted in impaired Edep vasorelaxation compared to Con while BOS and BH4 treatment preserved Edep vasorelaxation (Emax: Con: 52±8%, CyA: 23±7%, BOS: 54±4%, BOS+BH4: 61±15%, BOS+CyA: 53±4%, BOS+BH4+CyA: 63±3%, p=0.001). No significant differences in Eind vasorelaxation were seen. Compared to Con, CyA and BH4 exposure demonstrated increased sensitivity to ET vasospasm, p < 0.05. BOS therapy abrogated both CyA and BH4 induced sensitivity to vasospasm, p < 0.05. CyA reduced eNOS and increased ETA receptor expression compared to control, p < 0.01. BOS and BH4 therapy prevented CyA induced eNOS downregulation and ETA receptor overexpression (p < 0.01). ETB receptor expression was increased by BH4 treatment compared to CyA and Con (p < 0.01), however, BOS therapy blocked BH4 induced upregulation. CyA treatment resulted in higher 8-isoprostane levels compared to Con, p = 0.02. BOS and BH4 abrogated CyA induced OI.
CONCLUSIONS: CyA vascular dysfunction is characterized by impaired NO and ET homeostasis. Our study suggests potential therapeutic benefits of BOS and BH4 in preventing endothelial dysfunction associated with CyA. Since BH4 results in increased vasospasm, BOS supplementation is required for optimize treatment strategies for reducing CyA induced vascular injury.