ABSTRACT
OBJECTIVES: Angiotensin-converting enzyme 2 (ACE2) represents the primary receptor for SARS-CoV-2 to enter endothelial cells. Here we investigated circulating ACE2 activity to predict the severity and mortality of COVID-19. METHODS: Serum ACE2 activity was measured in COVID-19 (110 critically ill and 66 severely ill subjects at hospital admission and 106 follow-up samples) and in 32 non-COVID-19 severe sepsis patients. Associations between ACE2, inflammation-dependent biomarkers, pre-existing comorbidities, and clinical outcomes were studied. RESULTS: Initial ACE2 activity was significantly higher in critically ill COVID-19 patients (54.4 [36.7-90.8] mU/L) than in severe COVID-19 (34.5 [25.2-48.7] mU/L; P<0.0001) and non-COVID-19 sepsis patients (40.9 [21.4-65.7] mU/L; P=0.0260) regardless of comorbidities. Circulating ACE2 activity correlated with inflammatory biomarkers and was further elevated during the hospital stay in critically ill patients. Based on ROC-curve analysis and logistic regression test, baseline ACE2 independently indicated the severity of COVID-19 with an AUC value of 0.701 (95% CI [0.621-0.781], P<0.0001). Furthermore, non-survivors showed higher serum ACE2 activity vs. survivors at hospital admission (P<0.0001). Finally, high ACE2 activity (≥45.4 mU/L) predicted a higher risk (65 vs. 37%) for 30-day mortality (Log-Rank P<0.0001). CONCLUSIONS: Serum ACE2 activity correlates with COVID-19 severity and predicts mortality.