Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2020 Apr 27;9:e57555.
doi: 10.7554/eLife.57555.

Kallikrein-kinin Blockade in Patients With COVID-19 to Prevent Acute Respiratory Distress Syndrome

Free PMC article

Kallikrein-kinin Blockade in Patients With COVID-19 to Prevent Acute Respiratory Distress Syndrome

Frank L van de Veerdonk et al. Elife. .
Free PMC article


COVID-19 patients can present with pulmonary edema early in disease. We propose that this is due to a local vascular problem because of activation of bradykinin 1 receptor (B1R) and B2R on endothelial cells in the lungs. SARS-CoV-2 enters the cell via ACE2 that next to its role in RAAS is needed to inactivate des-Arg9 bradykinin, the potent ligand of the B1R. Without ACE2 acting as a guardian to inactivate the ligands of B1R, the lung environment is prone for local vascular leakage leading to angioedema. Here, we hypothesize that a kinin-dependent local lung angioedema via B1R and eventually B2R is an important feature of COVID-19. We propose that blocking the B2R and inhibiting plasma kallikrein activity might have an ameliorating effect on early disease caused by COVID-19 and might prevent acute respiratory distress syndrome (ARDS). In addition, this pathway might indirectly be responsive to anti-inflammatory agents.

Keywords: COVID-19; SARS; bradykinin; human biology; icatibant; immunology; inflammation; kinin; medicine; virus.

Plain Language Summary

The COVID-19 pandemic represents an unprecedented threat to global health. Millions of cases have been confirmed around the world, and hundreds of thousands of people have lost their lives. Common symptoms include a fever and persistent cough and COVID-19 patients also often experience an excess of fluid in the lungs, which makes it difficult to breathe. In some cases, this develops into a life-threatening condition whereby the lungs cannot provide the body's vital organs with enough oxygen. The SARS-CoV-2 virus, which causes COVID-19, enters the lining of the lungs via an enzyme called the ACE2 receptor, which is present on the outer surface of the lungs’ cells. The related coronavirus that was responsible for the SARS outbreak in the early 2000s also needs the ACE2 receptor to enter the cells of the lungs. In SARS, the levels of ACE2 in the lung decline during the infection. Studies with mice have previously revealed that a shortage of ACE2 leads to increased levels of a hormone called angiotensin II, which regulates blood pressure. As a result, much attention has turned to the potential link between this hormone system in relation to COVID-19. However, other mouse studies have shown that ACE2 protects against a build-up of fluid in the lungs caused by a different molecule made by the body. This molecule, which is actually a small fragment of a protein, lowers blood pressure and causes fluid to leak out of blood vessels. It belongs to a family of molecules known as kinins, and ACE2 is known to inactivate certain kinins. This led van de Veerdonk et al. to propose that the excess of fluid in the lungs seen in COVID-19 patients may be because kinins are not being neutralized due to the shortage of the ACE2 receptor. This had not been hypothesized before, even though the mechanism could be the same in SARS which has been researched for the past 17 years. If this hypothesis is correct, it would mean that directly inhibiting the receptor for the kinins (or the proteins that they come from) may be the only way to stop fluid leaking into the lungs of COVID-19 patients in the early stage of disease. This hypothesis is unproven, and more work is needed to see if it is clinically relevant. If that work provides a proof of concept, it means that existing treatments and registered drugs could potentially help patients with COVID-19, by preventing the need for mechanical ventilation and saving many lives.

Conflict of interest statement

Fv, MN, Mv, Qd, RB, Hv No competing interests declared, Jv Senior editor, eLife


Figure 1.
Figure 1.. The kinin-kallikrein system and ACE/ACE2.
The pathways of processing of low-molecular-weight kininogen (LMWK) and high-molecular-weight kallikrein (HMWK) leading to Bradykinin 1 (B1) receptor agonists and Bradykinin 2 (B2) receptor agonists. CPM = carboxypeptidaseM; CPN = carboxypeptidaseN.
Figure 2.
Figure 2.. Schematic view of treatment strategies in COVID-19.
Figure 3.
Figure 3.. Alveolus in normal setting and during moderate and severe COVID-19, (A) normal, (B) mild inflammation, (C) hyperinflammation.
ACE2 downregulation by the SARS-CoV-2 is followed by loss of neutralizing capacity of Lys-des-arg9-bradykinin (BK) in the lung leading to plasma leakage. Subsequently plasma leakage results in more B1R ligands (des-arg9-BK) and B2R ligands (bradykinin).

Similar articles

See all similar articles


    1. Batlle D, Wysocki J, Satchell K. Soluble angiotensin-converting enzyme 2: a potential approach for coronavirus infection therapy? Clinical Science. 2020;134:543–545. doi: 10.1042/CS20200163. - DOI - PubMed
    1. Bhoola KD, Figueroa CD, Worthy K. Bioregulation of kinins: kallikreins, Kininogens, and kininases. Pharmacological Reviews. 1992;44:1–80. - PubMed
    1. Ceravolo GS, Montezano AC, Jordão MT, Akamine EH, Costa TJ, Takano AP, Fernandes DC, Barreto-Chaves ML, Laurindo FR, Tostes RC, Fortes ZB, Chopard RP, Touyz RM, Carvalho MH. An interaction of renin-angiotensin and kallikrein-kinin systems contributes to vascular hypertrophy in angiotensin II-induced hypertension: in vivo and in vitro studies. PLOS ONE. 2014;9:e111117 doi: 10.1371/journal.pone.0111117. - DOI - PMC - PubMed
    1. European Medicines Agency . Assessment Report: Firazyr, INN-Icatibant. London, UK: European Medicines Agency; 2014.
    1. Fang L, Karakiulakis G, Roth M. Are patients with hypertension and diabetes mellitus at increased risk for COVID-19 infection? The Lancet Respiratory Medicine. 2020;8:e21 doi: 10.1016/S2213-2600(20)30116-8. - DOI - PMC - PubMed

MeSH terms

Supplementary concepts

Grant support

No external funding was received for this work.