ISSN 1535-3702 Experimental Biology and Medicine 2023; 248: 309–316 Copyright © 2023 by the Society for Experimental Biology and Medicine Introduction COVID-19 is a disease that primarily affects the respiratory tract caused by the SARS-CoV-2 virus which in severe cases can evolve to an acute respiratory distress syndrome associ- ated with a systemic inflammatory response. This inflamma- tory response involves several host defense systems such as hemostasis, angiogenesis, and complement. 1,2 Comorbidities such as diabetes, hypertension, and obesity, as well as advanced age are associated with higher mortality. 3 Heme-oxygenase 1 (HO-1) is an enzyme with well-known cytoprotective properties, mainly expressed in the liver, whose main role is to metabolize heme, catabolizing it into biliverdin, carbon monoxide, and iron. The circulat- ing protein hemopexin (HPX) is responsible to bind free extracellular heme and to deliver it to cells in which HO-1 Association of heme-oxygenase 1, hemopexin, and heme levels with markers of disease severity in COVID-19 Franciele de Lima 1 , Carla Roberta Peachazepi Moraes 1 , Mayck Silva Barbosa 1 , Bruna Bombassaro 2 , André C Palma 1 , Sergio San Juan Dertkigil 1 , Maria Luiza Moretti 1 , Fernanda Andrade Orsi 1 , Joyce M Annichino-Bizzacchi 1,3 , Eli Mansour 1 , Licio A Velloso 1,2 and Erich Vinicius De Paula 1,3 1 School of Medical Sciences, University of Campinas, Campinas 13083-887, Brazil; 2 Obesity and Comorbidities Research Center, University of Campinas, Campinas 13083-864, Brazil; 3 Hematology and Hemotherapy Center, University of Campinas, Campinas 13083-878, Brazil Corresponding author: Franciele de Lima. Email: franciele_lima@yahoo.com Abstract Heme-oxygenase 1 (HO-1) is an enzyme with well-known anti-infammatory and antioxidant properties, whose levels have been previously associated with disease severity in the context of sterile and infectious diseases. Moreover, the heme/HO-1 pathway has been associated with prothrombotic changes in other diseases. Accordingly, the potential of modulating HO-1 levels for the treatment of COVID-19 was extensively speculated during the COVID-19 pandemic, but very few actual data were generated. The aim of our study was to explore the association of HO-1, heme, and hemopexin (HPX) levels with COVID-19 severity and with markers of infammation and coagulation activation. The study was conducted in 30 consecutive patients with COVID-19 admitted due to hypoxemia, and 30 healthy volunteers matched by sex, age, and geographic region. HO-1 and HPX levels were measured by enzyme immunoassay (ELISA) and heme levels were measured by a colorimetric method. A comprehensive panel of coagulation and fbrinolysis activation was also used. Patients with COVID-19 presented increased levels of HO-1 when compared to controls (5741 ± 2696 vs 1953 ± 612 pg/mL, respectively, P < 0.0001), as well as a trend toward increased levels of HPX (3.724 ± 0.880 vs 3.254 ± 1.022 mg/mL, respectively; P = 0.06). In addition, HO-1 and HPX levels reduced from admission to day + 4. HO-1 levels were associated with duration of intensive care unit stay and with several markers of coagulation activation. In conclusion, modulation of HO-1 could be associated with the prothrombotic state observed in COVID-19, and HO-1 could also represent a relevant biomarker for COVID-19. New independent studies are warranted to explore and expand these fndings. Keywords: Heme-oxygenase 1, hemopexin, heme, COVID-19, infammation, coagulation 1139185EBM Experimental Biology and Medicinede Lima et al. Brief Communication Highlight article Impact statement Several authors have speculated about the poten- tial of heme-oxygenase 1 (HO-1) modulation in COVID-19, based on the anti-infammatory effects of this enzyme in other infectious and infammatory diseases. However, very little actual data have been produced to support these speculations. Here, we provide data about the behavior of important media- tors involved in HO-1 pathway, namely, total heme levels and hemopexin, in the course of COVID-19. Using a well-characterized population of patients from a clinical trial, we demonstrate that HO-1 levels are increased in COVID-19, and consist- ently associated with coagulation activation. The importance of these results lies on the fact that they represent a demonstration that circulating levels of HO-1 are increased in COVID-19, and that pro- thrombotic markers are associated with HO-1, pav- ing the way for future studies exploring the role of HO-1 as a biomarker for or mediator of COVID-19. Experimental Biology and Medicine 2023; 248: 309–316. DOI: 10.1177/15353702221139185