Effect of Bosentan on Skin Fibrosis in Patients With Systemic Sclerosis

• Measurable reduction of skin thickening using 20 MHz-ultrasound and the Rodnan Skin Score after treatment with study medication over 24 weeks in patients with systemic sclerosis.
  

• Effect of bosentan on hand functionality measured by SHAQ, UK-functional score, and fist closure as well as on nitrosylated serum protein levels in the plasma of patients with systemic scleroderma.
  

Systemic sclerosis (SSc) is a polymorphic disorder with an unknown cause characterized by fibrosis of the skin, blood vessels, and visceral organs. The degree of skin involvement is a very important outcome measure in patients with this disease. The pathogenesis of SSc involves immunologic mechanisms, vascular damage, and excessive accumulation of extracellular matrix component in the skin. One reason for these changes is meant to be an increased release of endothelin-1, a peptide which has vasoconstrictor effects and possesses mitogenic activity on cultured vascular smooth muscle cells and fibroblasts, cell types that are involved in SSc pathogenesis. Interestingly, endothelin-1 levels are raised in patients with SSc and Raynaud´s disease, particularly, in the subset of patients with diffuse cutaneous SSc who have widespread dermal sclerosis. However, skin fibrosis in SSc is a poorly studied, rare condition for which there are no approved therapies. Bosentan is a dual endothelin receptor antagonist, that competes with the binding of endothelin-1 to both receptors (ET-A and AT-B). It was recently shown to be effective in the treatment of idiopathic as well as pulmonary arterial hypertension (PAH) in SSc, but it has also been proved in two multicenter randomized prospective placebo-controlled double-blind studies in Europe and the US (RAPIDS-1 and RAPIDS-2) that there is a beneficial effect of bosentan in preventing digital ulcers in these patients. Furthermore,it has been suggested that bosentan has also a positive effect on skin fibrosis. In this study, skin fibrosis will be measured using 20-MHz-ultrasound, the Rodnan Skin Score, and investigation of the fist closure of each patient during treatment with bosentan over 24 weeks.