Can Nebulised Heparin Reduce Time to Extubation in SARS CoV 2 The CHARTER Study Protocol

IntroductionCOVID-19 is associated with the development of ARDS displaying the typical features of diffuse alveolar damage with extensive pulmonary coagulation activation resulting in fibrin deposition in the microvasculature and formation of hyaline membranes in the air sacs. The anti-coagulant actions of nebulised heparin limit fibrin deposition and progression of lung injury. Serendipitously, unfractionated heparin also inactivates the SARS-CoV-2 virus and prevents its entry into mammalian cells. Nebulisation of heparin may therefore limit both fibrin-mediated lung injury and inhibit pulmonary infection by SARS-CoV-2. For these reasons we have initiated a multi-centre international trial of nebulised heparin in patients with COVID-19. Methods and interventionMechanically ventilated patients with confirmed or strongly suspected SARS-CoV-2 infection, hypoxaemia and an acute pulmonary opacity in at least one lung quadrant on chest X-ray, will be randomised to nebulised heparin 25,000 Units every 6 hours or standard care for up to 10 days while mechanically ventilated. The primary outcome is the time to separation from invasive ventilation to day 28, where non-survivors to day 28 are treated as though not separated from invasive ventilation. Ethics and disseminationThe study protocol has been submitted to the human research and ethics committee of St Vincents Hospital, Melbourne, Australia. Submission is pending in other jurisdictions. Results of this study will be published in scientific journals and presented at scientific meetings. Trial RegistrationACTRN: 12620000517976

Glycosaminoglycans induce conformational change in the SARS-CoV-2 Spike S1 Receptor Binding Domain.

The glycosaminoglycan (GAG) class of polysaccharides are utilised by a plethora of microbial pathogens as receptors for adherence and invasion. The GAG heparin prevents infection by a range of viruses when added exogenously, including the S-associated coronavirus strain HSR1 and more recently we have demonstrated that heparin can block cellular invasion by SARS-CoV-2. Heparin has found widespread clinical use as anticoagulant drug and this molecule is routinely used as a proxy for the GAG, heparan sulphate (HS), a structural analogue located on the cell surface, which is a known receptor for viral invasion. Previous work has demonstrated that unfractionated heparin and low molecular weight heparins binds to the Spike (S1) protein receptor binding domain, inducing distinct conformational change and we have further explored the structural features of heparin with regard to these interactions. In this article, previous research is expanded to now include a broader range of GAG family members, including heparan sulphate. This research demonstrates that GAGs, other than those of heparin (or its derivatives), can also interact with the SARS-CoV-2 Spike S1 receptor binding domain and induce distinct conformational changes within this region. These findings pave the way for future research into next-generation, tailor-made, GAG-based antiviral agents, against SARS-CoV-2 and other members of the Coronaviridae.

SARS-CoV-2 Spike S1 Receptor Binding Domain undergoes Conformational Change upon Interaction with Low Molecular Weight Heparins.

The dependence of the host on the interaction of hundreds of extracellular proteins with the cell surface glycosaminoglycan heparan sulphate (HS) for the regulation of homeostasis is exploited by many microbial pathogens as a means of adherence and invasion. The closely related polysaccharide heparin, the widely used anticoagulant drug, which is structurally similar to HS and is a common experimental proxy, can be expected to mimic the properties of HS. Heparin prevents infection by a range of viruses when added exogenously, including S-associated coronavirus strain HSR1 and inhibits cellular invasion by SARS-CoV-2. We have previously demonstrated that unfractionated heparin binds to the Spike (S1) protein receptor binding domain, induces a conformational change and have reported the structural features of heparin on which this interaction depends. Furthermore, we have demonstrated that enoxaparin, a low molecular weight clinical anticoagulant, also binds the S1 RBD protein and induces conformational change. Here we expand upon these studies, to a wide range of low molecular weight heparins and demonstrate that they induce a variety of conformational changes in the SARS-CoV-2 RBD. These findings may have further implications for the rapid development of a first-line therapeutic by repurposing low molecular weight heparins, as well as for next-generation, tailor-made, GAG-based antiviral agents, against SARS-CoV-2 and other members of the Coronaviridae.

Heparin inhibits cellular invasion by SARS-CoV-2: structural dependence of the interaction of the surface protein (spike) S1 receptor binding domain with heparin.

The dependence of the host on the interaction of hundreds of extracellular proteins with the cell surface glycosaminoglycan heparan sulphate (HS) for the regulation of homeostasis is exploited by many microbial pathogens as a means of adherence and invasion. The closely related polysaccharide heparin, the widely used anticoagulant drug, which is structurally similar to HS and is a common experimental proxy, can be expected to mimic the properties of HS. Heparin prevents infection by a range of viruses if added exogenously, including S-associated coronavirus strain HSR1. Heparin prevents infection by a range of viruses if added exogenously, including S-associated coronavirus strain HSR1. Here, we show that the addition of heparin to Vero cells between 6.25 - 200 g.ml-1, which spans the concentration of heparin in therapeutic use, and inhibits invasion by SARS-CoV-2 at between 44 and 80%. We also demonstrate that heparin binds to the Spike (S1) protein receptor binding domain and induces a conformational change, illustrated by surface plasmon resonance and circular dichroism spectroscopy studies. The structural features of heparin on which this interaction depends were investigated using a library of heparin derivatives and size-defined fragments. Binding is more strongly dependent on the presence of 2-O or 6-O sulphation, and the consequent conformational consequences in the heparin structure, than on N-sulphation. A hexasaccharide is required for conformational changes to be induced in the secondary structure that are comparable to those that arise from heparin binding. Enoxaparin, a low molecular weight clinical anticoagulant, also binds the S1 RBD protein and induces conformational change. These findings have implications for the rapid development of a first-line therapeutic by repurposing heparin as well as for next-generation, tailor-made, GAG-based antiviral agents against SARS-CoV-2 and other members of the Coronaviridae.