Rationale and design of a trial evaluating the effects of losartan vs. nebivolol vs. the association of both on the progression of aortic root dilation in Marfan syndrome with FBN1 gene mutations

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BackgroundThe major clinical problem of Marfan syndrome (MFS) is the aortic root aneurysm, with risk of dissection when the root diameter approximates 5 cm. In MFS, a key molecule, transforming growth factor-β (TGF-β), normally bound to the extracellular matrix, is free and activated. In an experimental setting, TGF-β blockade prevents the aortic root structural damage and dilatation. The angiotensin receptor 1 blockers (sartanics) exert an anti-TGF-β effect; trials are now ongoing for evaluating the effect of losartan compared with atenolol in MFS. β-Adrenergic blockers are the drugs most commonly used in MFS. The third-generation β-adrenergic blocker nebivolol retains the β-adrenergic blocker effects on heart rate and further exerts antistiffness effects, typically increased in MFS.MethodsThe open-label phase III study will include 291 patients with MFS and proven FBN1 gene mutations, with aortic root dilation (z-score ≥2.5). The patients will be randomized to nebivolol, losartan and the combination of the two drugs. The primary end point is the comparative evaluation of the effects of losartan, nebivolol and the association of both on the progression of aortic root growth rate. Secondary end points include the pharmacokinetics of the two drugs, comparative evaluation of serum levels of total and active TGF-β, quantitative assessment of the expression of the mutated gene (FBN1, both 5′ and 3′), pharmacogenetic bases of drug responsiveness. The quality of life evaluation in the three groups will be assessed. Statistical evaluation includes an interim analysis at month 24 and conclusive analyses at month 48.ConclusionThe present study will add information about pharmacological therapy in MFS, supporting the new application of angiotensin receptor 1 blockers and finding β-adrenergic blockers that may give more specific effects. Moreover, the study will further deepen understanding of the pathogenetic mechanisms that are active in Marfan syndrome through the pharmacogenomic and transcriptomic mechanisms that may explain MFS phenotype variability.

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