Circulating endothelin-1 levels in systemic sclerosis subsets--a marker of fibrosis or vascular dysfunction?
OBJECTIVE: To investigate the circulating levels of endothelin-1 (ET-1) in serum (sET-1) in patients with pulmonary disease [pulmonary fibrosis (PF) and pulmonary hypertension (PHT)], and renal involvement [hypertensive renal crisis (HRC)] in the 2 major subsets of systemic sclerosis (SSc) in order to determine the significance of sET-1 levels in relation to specific organ involvement or to the underlying pathogenic mechanisms of vascular damage and fibrosis. METHODS: In addition to the measurement of ET-1 in serum using a competitive radioimmunoassay, the circulating levels of angiotensin converting enzyme (ACE) and plasma von Willebrand factor (vWF) were measured as markers of endothelial damage in the various disease groups. RESULTS: Levels of sET-1 were significantly increased in 64 patients with diffuse systemic sclerosis (dSSc) and 17 patients with primary Raynaud's phenomenon (RP) compared with 22 healthy individuals. sET-1 levels were equally elevated in diffuse cutaneous disease (dcSSc) with only fibrotic dermal or lung pathology compared with patients with additional PHT or HRC crisis. These observations were in marked contrast to the sET-1 levels seen in patients with the limited cutaneous form of SSc (lcSSc) where only patients with lcSSc with hypertensive lung or renal disease had significantly higher levels of sET-1 than comparable lcSSc patients with only fibrotic dermal and lung disease. sET-1 levels were additionally found to correlate with plasma vWF, skin fibrosis (skin score) and duration of disease in patients with SSc. CONCLUSION: The presence of significantly raised sET-1 levels in patients with dcSSc with widespread fibrosis and patients with lcSSc with hypertensive disease and the relationship seen between sET-1 levels and markers of fibrosis and vascular damage suggest that ET-1 may be important in the pathogenesis of both the fibrotic and vascular manifestations in SSc.