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Aims Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds to angiotensin converting enzyme 2 (ACE2) enabling entrance of the virus into cells and causing the infection termed coronavirus disease of 2019 (COVID-19). Here, we investigate associations between plasma ACE2 and outcome of COVID-19. Methods and results This analysis used data from a large longitudinal study of 306 COVID-19 positive patients and 78 COVID-19 negative patients (MGH Emergency Department COVID-19 Cohort). Comprehensive clinical data were collected on this cohort, including 28-day outcomes. The samples were run on the Olink® Explore 1536 platform which includes measurement of the ACE2 protein. High admission plasma ACE2 in COVID-19 patients was associated with increased maximal illness severity within 28 days with OR = 1.8, 95%-CI: 1.4–2.3 (P < 0.0001). Plasma ACE2 was significantly higher in COVID-19 patients with hypertension compared with patients without hypertension (P = 0.0045). Circulating ACE2 was also significantly higher in COVID-19 patients with pre-existing heart conditions and kidney disease compared with patients without these pre-existing conditions (P = 0.0363 and P = 0.0303, respectively). Conclusion This study suggests that measuring plasma ACE2 is potentially valuable in predicting COVID-19 outcomes. Further, ACE2 could be a link between COVID-19 illness severity and its established risk factors hypertension, pre-existing heart disease and pre-existing kidney disease.

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds to angiotensin converting enzyme 2 (ACE2) enabling entrance of the virus into cells and causing the infection termed coronavirus disease of 2019 (COVID-19). COVID-19 is a disease with a very broad spectrum of clinical manifestations, ranging from asymptomatic and subclinical infection to severe hyperinflammatory syndrome and death. Methods This study used data from a large longitudinal study of 306 COVID-19 positive patients and 78 COVID-19 negative patients (MGH Emergency Department COVID-19 Cohort with Olink Proteomics). Comprehensive clinical data were collected on this cohort, including 28-day outcomes classified according to the World Health Organization (WHO) COVID-19 outcomes scale. The samples were run on the Olink® Explore 1536 platform which includes measurement of the ACE2 protein. Findings High baseline levels of ACE2 in plasma from COVID-19 patients were associated with worse WHOmax category at 28 days with OR=0.56, 95%-CI: 0.44-0.71 (P < 0.0001). This association was significant in regression models with correction for baseline characteristics, pre-existing medical conditions, and laboratory test results. High levels of ACE2 in plasma from COVID-19 patients were also significantly associated with worse WHO category at the time of blood sampling at both day 0, day 3, and day 7 (P = 0.0004, P < 0.0001, and P < 0.0001, respectively). The levels of ACE2 in plasma from COVID-19 patients with hypertension were significantly higher compared to patients without hypertension (P = 0.0045). The plasma ACE2 levels were also significantly higher in COVID-19 patients with pre-existing heart conditions and kidney disease compared with patients without these pre-existing conditions (P = 0.0363 and P = 0.0303, respectively). There was no difference in plasma ACE2 levels comparing patients with or without pre-existing lung disease, diabetes, or immunosuppressive conditions (P = 0.953, P = 0.291, and P = 0.237, respectively). The associations between high plasma levels of ACE2 and worse WHOmax category during 28 days were more pronounced in COVID-19 positive patients compared with COVID-19 negative patients but the difference was not significant in the two-way ANOVA analysis. Interpretation This study suggests that measuring ACE2 is potentially valuable in predicting COVID-19 outcomes. Further, ACE2 levels could be a link between severe COVID-19 disease and its risk factors, namely hypertension, pre-existing heart disease and pre-existing kidney disease. The design of the data analysis using the Olink platform does not allow assessment of quantitative differences. However, previous studies have described a positive correlation between plasma ACE2 and ACE1 activity. This is interesting because ACE1 (serum ACE) analysis is a standardized test in most hospital laboratories. Therefore, our study encourages quantitative investigations of both plasma ACE 1 and 2 in COVID-19. Key Points Question Can plasma levels of the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), angiotensin converting enzyme 2 (ACE2), predict outcome of coronavirus disease of 2019 (COVID-19). Findings In this study of 306 COVID-19 positive patients, high baseline levels of ACE2 in plasma from COVID-19 patients were associated with worse outcome measured by the World Health Organization (WHO) COVID-19 outcomes scale. Meaning Measuring ACE2 is potentially valuable in predicting COVID-19 outcomes and link COVID-19 disease and the risk factors hypertension, pre-existing heart disease and pre-existing kidney disease.