Two low molecular weight heparins (LMWH) were introduced to RT4 cells that were pre-treated with anti-ACE2 antibodies: dalteparin and enoxaparin.  They were reported to have IC50 values, a measurement of the potency of an inhibitor, of 0.558 and 0.072U/ml.  Both were found to be partial inhibitors and less potent than unfractionated heparin.  

Low Molecular Weight Heparins are Partial Inhibitors of SARS-CoV-2 S Protein

RT4 cells that were pre-treated with anti-ACE2 antibodies were introduced to unfractionated heparin (UFH).  At a 10U/ml dose, 80% of 330nM S1S2 interaction with cells was inhibited (data not shown).  A significant reduction in S1S2 protein binding was observed compared to the control (p<0.01).  

Unfractionated Heparin Inhibits SARS-CoV-2 S Protein Binding in RT4 Cells

- unfractionated Heparin Inhibits SARS-CoV-2 S Protein Binding in RT4 Cells
- low Molecular Weight Heparins are Partial Inhibitors of SARS-CoV-2 S Protein

Michigan State University

Anticoagulants like heparin may improve outcomes in COVID-19 patients. Many patients exhibit unusual clotting patterns that may be alleviated by use of anticoagulants.  Heparin has been shown to directly bind to the S1 subunit of SARS-CoV-2 S protein which may interfere with its ability to infect cells.

Heparin as a treatment for COVID-19

RT4 cells were treated with 15µg/ml anti-ACE-2 antibody (alpha-ACE2).  A significant, 54.25% increase in S protein (S1 and S2 subunits) interaction with the cells was observed (p=0.0025).  The antibodies bound to ACE2 may cause the receptors to cluster together, and this may make them an easier target for SARS-CoV-2 S protein.  

Anti-ACE2 Antibody Treatment Increases S1S2 Binding

Overall, heparin use did not improve outcomes. However, in severe COVID-19 cases with a sepsis-induced coagulopathy (SIC)  score of 4 or higher and patients with D-dimer levels above 6 times normal levels, heparin treatment reduced 28-day mortality rates.

- results for heparin vs. no anticoagulants by SIC score
- results for heparin vs. no anticoagulants by D-dimer level
- results for univariate analysis for other clotting factors
- patient characteristics
- SIC score
- methods
- discussion

Findings supporting heparin use in COVID-19 patients for patients at high risk of coagulopathy from retrospective study in Wuhan, China

Heparin Studies Using RT4 Cells Pre-Treated with Anti-ACE2 Antibodies

- Prophylactic concentration: 0.1-0.4U/ml
- Therapeutic concentration: 0.3-0.7U/ml

IU: international units (arbitrary amount)

Prophylactic and Therapeutic Serum Concentrations of Unfractionated Heparin (UFH)

LMWHs include drugs such as dalteparin and enoxparin.

- Prophylactic concentration:  0.2-0.5IU/ml
- Therapeutic concentration: 0.5-1.2IU/ml 

IU: international units (arbitrary amount)

Prophylactic and Therapeutic Serum Concentrations of Low Molecular Weight Heparins (LMWH)

Partridge et al. have observed multiple heparin binding sites on the SARS-CoV-2 S protein, including:

- one at the furin cleavage site between the S1 and S2 subunits
- others in the S2 domain 
- others in the receptor binding domain (RBD)

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