Introduction: Infection by SARS-CoV-2 and subsequent COVID-19 can cause viral sepsis. We investigated plasma protease activity patterns in COVID-19-induced sepsis with bacterial superinfection, as well as plasma proteomics and peptidomics in order to assess the possible implications of enhanced proteolysis on major protein systems (e.g., coagulation).Methods: Patients (=4) admitted to the intensive care units (ICUs) at the University of California, San Diego (UCSD) Medical Center with confirmed positive test for COVID-19 by real-time reverse transcription polymerase chain reaction (RT-PCR) were enrolled in a study approved by the UCSD Institutional Review Board (IRB# 190699, Protocol #20-0006). Informed consent was obtained for the collection of blood samples and de-identified use of the data. Blood samples were collected at multiple time points and analyzed to quantify a) the circulating proteome and peptidome by mass spectrometry; b) the aminopeptidase activity in plasma; and c) the endopeptidase activity in plasma using fluorogenic substrates that are cleaved by trypsin-like endopeptidases, specific clotting factors and plasmin. The one patient who died was diagnosed with bacterial superinfection on day 7 after beginning of the study.Results: Spikes in protease activity (factor VII, trypsin-like activity), and corresponding increases in the intensity of peptides derived by hydrolysis of plasma proteins, especially of fibrinogen degradation products and downregulation of endogenous protease inhibitors were detected on day 7 for the patient who died. The activity of the analyzed proteases was stable in survivors.Discussion: The combination of multiomics and enzymatic activity quantification enabled to i) hypothesize that elevated proteolysis occurs in COVID-19-induced septic shock with bacterial superinfection, and ii) provide additional insight into malfunctioning protease-mediated systems, such as hemostasis.

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Infection by SARS-CoV-2 and subsequent COVID-19 can cause viral sepsis and septic shock. Several complications have been observed in patients admitted to the intensive care unit (ICU) with COVID-19, one of those being bacterial superinfection. Based on prior evidence that dysregulated systemwide proteolysis is associated with death in bacterial septic shock, we investigated whether protease activity and proteolysis could be elevated in COVID-19-induced sepsis with bacterial superinfection. In particular, we sought to assess the possible implications on the regulation of protein systems, such as for instance the proteins and enzymes involved in the clotting cascade.Blood samples collected at multiple time points during the ICU stay of four COVID-19 patients were analyzed to quantify: a) the circulating proteome and peptidome by mass spectrometry; b) plasma enzymatic activity of trypsin-like substrates and five clotting factors (plasmin, thrombin, factor VII, factor IX, factor X) by a fluorogenic assay.Of the four patients, one was diagnosed with bacterial superinfection on day 7 after beginning of the study and later died. The other three patients all survived (ICU length-of-stay 11.25±6.55 days, hospital stay of 15.25±7.18 days). Spikes in protease activity (factor VII, trypsin-like activity) were detected on day 7 for the patient who died. Corresponding increases in the total intensity of peptides derived by hydrolysis of plasma proteins, especially of fibrinogen degradation products, and a general reduction of coagulation proteins, were measured as well. A downregulation of endogenous enzymatic inhibitors, in particular trypsin inhibitors, characterized the non-surviving patient throughout her ICU stay. Enzymatic activity was stable in the patients who survived.Our study highlights the potential of multiomics approaches, combined with quantitative analysis of enzymatic activity, to i) shed light on proteolysis as a possible pathological mechanism in sepsis and septic shock, including COVID-19-induced sepsis; ii) provide additional insight into malfunctioning protease-mediated systems, such as the coagulation cascade; and iii) describe the progression of COVID-19 with bacterial superinfection.