ABSTRACT
COVID-19-related severe respiratory failure (SRF) leads to mechanical ventilation increasing the in-hospital mortality substantially. Abundancy of lung fibroblasts (LFs) in injured lung tissue has been associated with the progression of respiratory failure in COVID-19. Aiming to reduce mortality in patients with SRF (PaO2/FiO2<100 mmHg) and considering the multi-mechanistic nature of severe COVID-19 pathogenesis, we applied a combined rescue treatment (COMBI) on top of standard-of-care (SOC: dexamethasone and heparin) comprised inhaled DNase to dissolve thrombogenic neutrophil extracellular traps, plus agents against cytokine-mediated hyperinflammation, such as anti-IL-6 receptor tocilizumab and selective JAK1/2 inhibitor baricitinib. COMBI (n=22) was compared with SOC (n= 26), and with two previously and consecutively used therapeutic approaches, including either IL-1 receptor antagonist anakinra (ANA, n=19), or tocilizumab (TOCI, n=11), on top of SOC. In parallel, evaluation of immunothrombosis was assessed in vitro in human LFs, treated with the applied therapeutic agents upon stimulation with COVID-19 plasma. COMBI was associated with lower in-hospital mortality (p=0.014) and intubation rate (p=0.013), shorter duration of hospitalization (p=0.019), and prolonged overall survival after a median follow-up of 110{+/-}4 days (p=0.003). In vitro, COVID-19 plasma markedly induced tissue factor/thrombin pathway in LFs, while this effect was inhibited by the immunomodulatory agents of COMBI providing a mechanistic explanation for the clinical observations. These results suggest the design of randomized trials using combined immunomodulatory therapies in COVID-19-associated SRF targeting multiple interconnected pathways of immunothrombosis.
ABSTRACT
Emerging data indicate that complement and neutrophils are involved in the maladaptive host immune response that fuels hyper-inflammation and thrombotic microangiopathy increasing the mortality rate in coronavirus disease 2019 (COVID-19). Here, we investigated the interaction between complement and the platelet/neutrophil extracellular traps (NETs)/thrombin axis, using COVID-19 clinical samples, cell-based inhibition studies and NETs/human aortic endothelial cell (HAEC) co-cultures. Increased plasma levels of NETs, TF activity and sC5b-9 were detected in patients. Neutrophils yielded high tissue factor (TF) expression and released NETs carrying functionally active TF. Confirming our ex vivo findings, treatment of control neutrophils with COVID-19 platelet-rich plasma generated TF-bearing NETs that induced thrombotic activity of HAEC. Thrombin or NETosis inhibition or C5aR1 blockade attenuated platelet-mediated NET-driven thrombogenicity. Serum isolated from COVID-19 patients induces complement activation in vitro, which is consistent with high complement activity in clinical samples. Complement inhibition at the level of C3 with compstatin Cp40 disrupted TF expression in neutrophils. In conclusion, we provide a mechanistic basis that reveals the pivotal role of complement and NETs in COVID-19 immmunothrombosis. This study supports emerging strategies against SARS-CoV-2 infection that exploit complement therapeutics or NETosis inhibition.
