Decreased serum ACE2 levels in patients with connective tissue diseases.

OBJECTIVE: To evaluate serum concentration and activity of angiotensin-converting enzyme 2 (ACE2) in patients with connective tissue diseases (CTDs). METHODS: Serum samples from healthy subjects and patients with SLE, systemic sclerosis (SSc), primary Sjogren's syndrome (SS) and RA were collected. The concentration and activity of ACE2 were measured by ELISA and fluorometric method, respectively, and analysed for associations with clinical features and concurrent medications. RESULTS: In total, 66 SLE, 55 SSc, 31 SS and 31 RA patients were involved. ACE2 concentration was significantly decreased in patients with either of the four CTDs compared with healthy subjects. The concentration was not linked to special clinical features expect that it was slightly lower in patients with lupus nephritis than those without. In SLE patients, ACE2 concentration elevated with the increase of glucocorticoids, and was not associated with other treatments. Different from the concentration, ACE2 activity was increased in CTD patients. A weak correlation of ACE2 activity with SLE disease activity index score was also observed. CONCLUSION: The clinical significance of ACE2 concentration and activity looks quite different among CTD patients. Preliminary data suggest ACE2 levels are not affected by most of the treatments.