Background— Marfan syndrome (MFS) is caused by mutations in the fibrillin-1 gene and dysregulation of transforming growth factor-β (TGF-β). Recent evidence suggests that losartan, an angiotensin II type 1 blocker that blunts TGF-β activation, may be an effective treatment for MFS. We hypothesized that dysregulation of TGF-β might be mirrored in circulating TGF-β concentrations.

Methods and Results— Serum obtained from MFS mutant mice (Fbn1^C1039G/+) treated with losartan was analyzed for circulating TGF-β1 concentrations and compared with those from placebo-treated and wild-type mice. Aortic root size was measured by echocardiography. Data were validated in patients with MFS and healthy individuals. In mice, circulating total TGF-β1 concentrations increased with age and were elevated in older untreated Fbn1^C1039G/+ mice compared with wild-type mice (P=0.01; n=16; mean±SEM, 115±8 ng/mL versus n=17; mean±SEM, 92±4 ng/mL). Losartan-treated Fbn1^C1039G/+ mice had lower total TGF-β1 concentrations compared with age-matched Fbn1^C1039G/+ mice treated with placebo (P=0.01; n=18; 90±5 ng/mL), and circulating total TGF-β1 levels were indistinguishable from those of age-matched wild-type mice (P=0.8). Correlation was observed between circulating TGF-β1 levels and aortic root diameters in Fbn1^C1039G/+ and wild-type mice (P=0.002). In humans, circulating total TGF-β1 concentrations were elevated in patients with MFS compared with control individuals (P<0.0001; n=53; 15±1.7 ng/mL versus n=74; 2.5±0.4 ng/mL). MFS patients treated with losartan (n=55) or β-blocker (n=80) showed significantly lower total TGF-β1 concentrations compared with untreated MFS patients (P≤0.05).

Conclusions— Circulating TGF-β1 concentrations are elevated in MFS and decrease after administration of losartan, β-blocker therapy, or both and therefore might serve as a prognostic and therapeutic marker in MFS.