The COVID's thrombosis pandemic: A stubborn challenge. Is the endothelial glycocalyx overlooked?

The COVID's thrombosis pandemic: A stubborn challenge. Is the endothelial glycocalyx overlooked?
An insight into eGC damage, thrombosis and glycocalyx restoration (Nov 2020, update 2021)

An unrolled thread by: Мэрсэдэ́с Bouter LL.M
@Mercedes_Bouter

Part 1:
1.
COVID is characterized by ongoing thrombosis in spite of thromboprophylaxis and thrombolysis (= breaking down clots). When thrombolysis is applied, new clots will form due to ongoing endothelial damage + inflammation and other pro-thrombotic factors.

2.
Observations of an untreated COVID patient
In an untreated COVID patient, severe edema of the lungs, fibrin particles, hyaline membranes and pyroptosis of large alveolocytes were observed. Epithelial damage was accompanied by surfactant networks, macrophages and neutrophils in the alveoli.Seven autopsies found accumulation of fluid with surfactant, damaged epithelium, alveolar macrophages, neutrophils and pyroptosis in the alveoli (lung sacs). Hyaline membranes were found in the alveolar space, some alveolar septa were sclerotic. Capillaries were fibrotic.

3.
In the MYSTIC cohort study, COVID patients showed a 90% reduction in vascular density in the small capillaries. Loss of glycocalyx thickness of the endothelium is associated with severity (Microvascular dysfunction in COVID-19: the MYSTIC study, Angiogenesis 2021; 24(1): 145-157).

4. C
Angiopoeitin-2 : Tie2- ratio
The vascular leakage-increasing Angiopoietin-2 (Angpt-2) was significantly increased in mechanically ventilated COVID patients. A 2019 study reports the therapeutic potential of Tie2 activation to promote endothelial glycocalyx restoration in human sepsis.

This 2019 study/observation on Tie2 to treat patients to reduce Angiopoietin-2 in COVID might hold up well today: "Tie2 Activation promotes protection and reconstruction of the Endothelial Glycocalyx in Human Sepsis", Journal of Thrombosis and Haemostasis 2019 Nov;119(11).

5.
The vasodilator and permeability factor VEGF-A is found to correlate with severity of COVID. ADAMTS13 levels (ADAMTS13 is the protease that cuts Ultra Large Von Willebrand Factor Multimers to protect against thrombosis) were significantly decreased in severe COVID. Thrombomodulin (TM) and levels of shed ACE2 were markedly high. Plateletcrit (PCT = blood volume occupied by platelets) and Tumor Necrosis Factor-Alpha (TNF-α) were high in ventilated patients, while CRP, IL-6 and ferritin did not stand out as markers of severity.

6
What can be gathered from the MYSTIC study, is:
- markers such as TNF-alpha, and elevation of plateletcrit should be monitored to estimate the severity of COVID-19;
- the VWF/ADAMTS13 ratio is a marker for severity = increasing imbalance of VWF (elevation) to ADAMTS13 (loss);
- loss of glycocalyx is an outstanding marker for deterioration in COVID, associated with the loss of endothelial integrity;
- a therapeutic target to explore in COVID-19 is prevention of the heparanase-mediated loss of glycocalyx through a non-coagulant heparin fragment.

7.
Markers for unmatched perfusion due to loss of anticoagulant function in COVID

Inflammatory infiltration of the vascular wall consists of CD45 lymphocytes, CD68 macrophages, CD61 megakaryocytes, CD3-, CD4- and CD8+ T-cells and CD15 neutrophils. Thrombosis of pulmonary artery branches is observed less frequently than thrombosis of the microvasculature.
It is hypothesized that loss of anticoagulant function is key in unmatched perfusion. This is a plausible explanation: erratic pulmonary perfusion is consistent with persistence of thrombotic activity and failing thrombolytic therapies. A therapy targeting perfusion is proposed.

8.

Inflammatory markers

The cytokine cascade in COVID/Cytokine Release Syndrome (COVID-CRS)/hypercytokinemia follows a path similar to hemophagocytic lymphohistiocytosis (HLH) and Castleman. These hematologic syndromes share with COVID a tendency for thrombosis, hypercoagulation, hypotension and hypoxia

9.
What is known since 2003

Since SARS-CoV-1 (2003), it's known that epithelial cell proliferation and macrophage induction in the lungs mark inflammation that contributes to severity. An increased IL-6/IFN-γ ratio can be predictive of disease severity. Procalcitonin and CRP should be measured. Procalcitonin levels were observed to be significantly elevated in severe SARS-CoV-2. Severe cases can be marked by dyspnea, lymphopenia, hypoalbuminemia, elevated alanine aminotransferase (ALA), lactate dehydrogenase, higher levels of IL-2R, IL-6, IL-10 and TNF-alpha.

10.
Erythropoeitin (EPO)

Erythropoietin is known to regulate inflammatory cytokines and hepcidin, allowing iron absorption in the bone marrow. Iron redistribution could impair viral replication. As of April 2020, EPO has been shown to alleviate ARDS and to reduce damage through inhibition of NF-kB.  More on recombinant Erythropoietin (EPO) in COVID: "Does recombinant human EPO administration in critically ill COVID-19 have miraculous therapeutic effects?", Journal of Medical Virology Vol. 92, Issue 7, July 2020. EPO has a potential negative effect, nevertheless, as this agent increases the risk of thrombosis in COVID-patients who are already at risk of developing thrombosis.

11.
Why glycocalyx restoration and maintenance are treatment options in COVID

It has been well known for + 20 years that the endothelium is key in maintaining homeostasis in order to prevent sepsis and thrombosis. Thrombosis is an acknowledged complication of SARS-Coronaviruses (SARS-CoV-1, 2003 and SARS-CoV-2, 2019) and other highly thrombotic pathogens.

12.
Given the fact that endothelial damage marks the turnover to disease progression in COVID, glycocalyx integrity should be included in therapeutic treatment of COVID-19. Performing a search in PubMed, I used the keywords "Glycocalyx" an "EGx". The 2017 study "Therapeutic Restoration of Endothelial Glycocalyx in Sepsis, Journal of Pharmacology and Experimental Therapeutics 2017 Apr; 361(1): 115-121", proposes administration of Sulodexide (SDX), a heparin sulfate-like agent to restore endothelial integrity in sepsis.

Part II of the "Quest for solutions to COVID's thrombosis pandemic": Endothelial glycocalyx dysfunction and mitochondrial dysfunction are starting points.

13.
COVID coagulation depends on the interplay of endothelial cells, platelet-endothelium interaction and leukocytes. Elevated Von Willebrand Factor (VWF) levels, Plasmin activator inhibitor-1 (PAI-1 or SERPINE1) and angiopoietin 2 are markers of severity in COVID-19 coagulopathy.

14.
The interplay of megakaryocytes, platelets, endothelial cells and mitochondria in COVID
IL-6 and IL-beta correlate with fibrinogen upregulation. Platelets are involved in autophagy and programmed cell death. Platelets mediate between endothelial cells and leukocyte recruitment and release of inflammatory factors, contributing to thrombotic activity. Coronaviruses also have a propensity to bind acetylated sialic acid residues on megakaryocytes and endothelial cells (Diagnosis, Management and Pathophysiology of Arterial and Venous Thrombosis in COVID-19, JAMA 2020;324(24)).

15.
Thrombocytopenia in COVID: result of overcompensation (platelet aggregation, hyperactivation and exhaustion)

Thrombocytopenia occurs in COVID-19 and has a progressive tendency, which is reconcilable with the observation of early platelet aggregation followed by depletion. Platelet apoptosis (death of platelets) shifts platelet activation towards hyperactivation of remaining platelets. This means: while blood platelets are heavily recruited early on in COVID, this process will exhaust platelets eventually. This was already observed in SARS-CoV-1 (2003) (Thrombocytopenia in patients with SARS, Immune Hematology, April 2005; 10(2)).

16.

Why is platelet aggregation relevant for this discussion of endothelial glycocalyx health? Activated platelets express P-selectin and recruit alpha-granules, CCL2, CCL3, CCL7, IL-1beta, IL-7 and IL-8. IL-1beta ⬆️endothelial permeability, which makes the glycocalyx vulnerable.

17.
Platelet health, megakaryocytes and mitochondrial health: intertwined!
Platelet health depends on megakaryocyte health. The intrinsic pathways of BAK/BAX-mediated and FasL extrinsic apoptosis are downregulated in order to allow megakaryocytes to mature and to produce platelets from megakaryocytes. Bcl-xL mediates platelet survival. Platelet activation requires calcium through the mitochondrial cyclophilin D. Hypoxia and Reactive Oxygen Species/oxidative stress affect mitochondrial homeostasis. Hypoxia induces platelet hyperactivation, while antiphospholipid antibodies induce platelet destruction. Thus: platelets are derived from megakaryocytes, which are affected by SARS-Coronavirus infection directly and will stimulate hyperactivity of platelets ultimately. When the production of platelets becomes inapt, megakaryocytes will hyperactivate platelets (= overcompensation!).

18.
Hypoxia and (auto)antibodies complicate platelet activation

Hypoxia and antiphospholipid antibodies & anticardiolipin antibodies (antibodies mistakenly targeting one's own body) further complicate the platelet activation and eventual depletion process.

To make it worse, SARS-Coronavirus-2 RNA is found to interact with platelets, which means that virus is able to contribute to platelet hyperactivation. In severe COVID cases, lung megakaryocytes and platelet formations obstruct cardiopulmonary microvasculature.

19.

This is indicative of megakaryocytes hyperactivating surviving platelets to compensate for the loss of platelets (Apoptosis in megakaryocytes and platelets: the life and death of a lineage, Blood spotlight Vol. 131, Issue 6, February 8, 2018). Furthermore, SARS-CoV-2 is hypothesized to induce the release of IL-1 macrophages, acting on adhesion molecules and endothelial cells to provoke hypotension and septic shock through IL-6, TNF, arachidonic acid products thromboxane A2 and prostaglandin.

20.
How the endothelium should maintain its integrity

The endothelium sits in a 'gel-like' layer, the endothelial glycocalyx. Endothelial cells are protected by pericytes. The function of the endothelium is to maintain vascular homeostasis through release of relaxation factors and contractile factors.

Relaxation factors are Nitric Oxide (NO), Prostaglandin I2 (PGI2 or prostacyclin), contractile factors are endothelin, Reactive Oxygen Species (ROS), Angiotensin II (Ang II) and Thromboxane.

Anti-inflammatory and anti-thrombotic factors are thrombomodulin, tissue factor pathway inhibitor (TFPI), antithrombin and protein C. NO suppresses cytokines and adhesion molecules such as VCAM in order to prevent blood vessel permeability. NO also acts as an antiplatelet agent.

The endothelium is protected by tightly regulated High-Density Lipoproteins (HDL), which help maintain endothelial integrity by inhibition of blood cell adhesion to the vascular endothelium, reduction of platelet aggregation and coagulation and by promotion of fibrinolysis.

This 2003 study on HDL protection of the endothelium is of relevance today, amidst the COVID pandemic: "Endothelial Protection by High-Density Lipoproteins: From Bench to Bedside", Arteriosclerosis, Thrombosis and Vascular Biology Vol. 23, Issue 10, October 2003.

21.
Mitochondrial function

The one main point in life is protection of mitochondrial function. Mitochondria regulate metabolism of energy and Nitric Oxide, as well as in- and output of Reactive Oxygen Species (ROS) and Oxidative Stress. Oxidative Stress is needed to give off "signals" under circumstances.

But accumulation of ROS/Oxidative Stress and impairment of outflow and antioxidant, will harm cells and exert detrimental action on regeneration of cells. Also, impairment of healthy Nitric Oxide (NO) transmission will kill endothelial cells.

22.
Oxidative Stress

Note: homeostasis and metabolism require adaptation to constant changes in cell signaling. Every factor involved in the process following SARS-coronavirus infection need be conducted tightly. If one of these factors fail, others will try to (over)compensate.

During infection, accumulation of Reactive Oxygen Species (ROS) and mitochondrial oxidative stress enhances production of IL-1beta, IL-6 and Tumor Necrosis Factor, which contribute to the inflammatory state. The decrease of NO and prostacyclin induce endothelial cell death. Activation of Adenosine Diphosphate (ADP) through P2Y purinoreceptors contributes to platelet aggregation and subsequent thrombus formation.

23.
Impairment of Nrf2 antioxidant function
Impairment of the intrinsic antioxidant NRF2 increases inflammation.

Removal of sialic acid from the endothelial glycocalyx impairs the antioxidant properties of Nrf2. Nrf2 exerts antioxidant properties on mitochondria and Nitric Oxide (eNOS) phosphorylation (OXPHOS) required to downregulate mitochondrial Oxidative Stress.

When imbalances are detected, platelets and endothelial cells release vasoconstrictors thromboxane, ADP, PAI-1 and serotonin. Von Willebrand Factors (VWFs) and thrombin act pro-thrombotic. When restoration of the vasculature is done, fibrin and thrombi need to be cleared.

To aggregate platelets in response to SARS-Coronavirus infection, megakaryocytopoiesis is induced by thrombopoietin, erythropoietin, IL-6 and other cytokines.

The final step in the process, following platelet production, is to remove the naked nuclei of megakaryocytes (NK-MK) through phagocytosis in the bone marrow and periphery. Thus, naked megakaryocytes are result of exhaustion for platelet production following endothelial injury.

SARS-CoV-2 infection of alveolar cells type II causes pneumocyte deficiency and disruptive hyaline membranes responsible for hypoxemia (Diffuse Alveolar Damage). IL-6 excess is hypothesized to stimulate megakaryocytopoiesis and platelet production in COVID-19.

Everything might seem chaotic and the processes underlying COVID's thrombosis, endothelial dysfunction and mitochondrial impairment are indeed chaotic.

To make it look less chaotic, I've summarized the COVID processes in these slides:

A stubborn complication: the quest for solutions to COVID's thrombosis pandemic should highlight the endothelium and glycocalyx

If one thing is for sure, it is that thrombosis is a prominent characteristic of COVID-19. Thromboinflammation due to SARS-CoV-2 infection hits young and old, symptomatic and asymptomatic, the healthy and the immunocompromised. In young, "healthy", asymptomatic cases or cases with so-called "mild symptoms", this is even further complicated by the fact that thrombosis goes undetected as opposed to severe cases that are admitted to hospital. In order to assess whether people who have had "mild" SARS-CoV-2 infection will actually recover, imaging and screening is required. This topic should raise enough concern to be part of long-term cohort studies.

I have been actively reporting on the prominence of thrombosis as the main feature of COVID since April 2020. Amidst the quest for vaccines to prevent infection with SARS-CoV-2, the thrombosis question must still be addressed. Firstly, because it is highly undesirable to create a generation of long-term cardiovascular, pulmonary and multiple organ damage due to COVID. 

The one main question during this pandemic is: how should COVID's prominent thromboinflammation be treated or prevented?

1. COVID-19 is characterized by ongoing thrombotic events in spite of thromboprophylaxis and thrombolysis;
2. A close look at angiopathy in COVID-19: findings;
3. Loss of endothelial glycocalyx (eGC) thickness;
4. How COVID affects systemic systems and therefore poses a threat to the young and healthy as well as the immunocompromised;
5. Therapeutic restoration of the glycocalyx in COVID-19: an overlooked essential?

Some of the many mechanisms involved in COVID-19-thromboinflammation

1. COVID-19 is characterized by ongoing thrombotic events in spite of thromboprophylaxis and thrombolysis
Thrombosis is such a stubborn complication of COVID-19, as there is a low response to adequate anticoagulation (Low Molecular Weight Heparin, enoxaparin 40-60 mg twice a day prophylaxis; or 1 mg/kg body weight twice a day for therapeutic treatment) and thrombolytic therapies (tissue Plasminogen Activator (tPA)). Inflammatory and prothrombotic changes in the arterial wall with the lack of lung perfusion are thought to cause diffuse arterial thrombosis in the lungs.

Outstanding parameters for determining the severity of COVID-thrombosis are the increase of platelet count, D-dimer, ferritin and LDH levels. While prothrombin time and fibrinogen levels are not extremely prolongated nor elevated, increase of platelet count is markedly high in some of the most severe cases (Thrombosis of pulmonary vasculature despite anticoagulation and thrombolysis: The findings from seven autopsies, Thrombosis update 2020 Dec; 1).

2. A close look at angiopathy in COVID-19: findings
Thrombus formation in the lungs shows underlying inflammatory abnormalities that are caused by the virus itself (SARS-CoV-2) and immune cells. Disseminated Intravascular Coagulation (DIC) is considered to be one of the causes of COVID-thrombosis in pulmonary vessels, the liver, kidneys and pelvic veins. The pulmonary vasculature prevails over deep vein thrombosis in the lower limbs (DVT). Seven autopsies found accumulation of fluid with surfactant, damaged epithelium, alveolar macrophages and neutrophils in the alveolar sacs. Focal epithelial proliferation with fused cells were found, as well as enlarged epithelial cells with SARS particles and pyroptosis in the alveoli (lung sacs). Hyaline membranes and fibrin were found in the alveolar space, some alveolar septa were infiltrated sclerotic. Thrombi in the capillaries were predominantly fibrotic. 

Hypertrophy was found in the bronchi, while epithelium, mucus and macrophages were observed in the bronchial lumina. Dystrophy and necrosis were observed in the endothelium and muscle fibers, accompanied by fibrinoid necrosis, collagen particles and elastic fibers and infiltration of the vascular wall and perivascular space by plasma, neutrophils and lymphocytes.

In an untreated COVID patient, severe edema of the lungs, fibrin particles, hyaline membranes and pyroptosis of large alveolocytes were observed. Epithelial damage was accompanied by surfactant networks, macrophages and neutrophils in the alveoli. Advanced thrombosis was found in the pulmonary artery. Hemorrhages were observed in the brain (cerebral cortex, cerebellum and white matter of the hemispheres) and the lungs, stomach, colon, bladder and kidneys.

3. Loss of endothelial glycocalyx (eGC) thickness
In the MYSTIC cohort study, COVID patients showed a 90% reduction in vascular density in the small capillaries. Loss of glycocalyx thickness of the endothelium is associated with severity. Notably, a 2019 study found the glycocalyx to be a therapeutic target in sepsis (The glycocalyx: a novel diagnostic and therapeutic target in sepsis, Critical Care 2019; 23: 16). In mechanically ventilated COVID patients, the decrease in vascular density was greater than in non-mechanically ventilated COVID patients, but both groups showed loss of vascular density. Density of microvessels > 10 µm did not differ in mechanically ventilated or non-mechanically ventilated COVID patients, showing that the small capillaries are the main affected site. Plasma syndecan-1, a marker for glycocalyx shedding, was increasingly elevated in patients with higher need for mechanical ventilation.

The vascular leakage-increasing Angiopoietin-2 (Angpt-2) was significantly increased in mechanically ventilated COVID patients. A 2019 study reports the therapeutic potential of Tie2 activation to promote endothelial glycocalyx restoration in human sepsis (Tie2 Activation Promotes Protection and Reconstitution of the Endothelial Glycocalyx in Human Sepsis, Journal of Thrombosis and Haemostasis 2019 Nov;119(11):1827-1838). The vasodilator and permeability factor VEGF-A was found to correlate with severity. ADAMTS13 levels (ADAMTS13 is the protease that cuts Ultra Large Von Willebrand Factor Multimers to protect against thrombosis) were significantly decreased in severe COVID, while Thrombomodulin (TM) and levels of shed ACE2 were markedly high. Plateletcrit (PCT = blood volume occupied by platelets) and Tumor Necrosis Factor-Alpha (TNF-α) were high in ventilated patients, while CRP, IL-6 and ferritin did not stand out as markers of severity (Microvascular dysfunction in COVID-19: the MYSTIC Study, Angiogenesis 2020 Oct 14: 1-13).

What can be gathered from the MYSTIC study, is:
- markers such as TNF-alpha, and elevation of plateletcrit should be monitored to estimate the severity of COVID-19;
- the VWF/ADAMTS13 ratio is a marker for severity, as increasing imbalance of VWF (elevation) to ADAMTS13 (loss) is associated with deterioration and endothelial disease;
- loss of glycocalyx is an outstanding marker for deterioration in COVID, associated with the loss of endothelial integrity;
- a therapeutic target to explore in COVID-19 is prevention of the heparanase-mediated loss of glycocalyx through a non-coagulant heparin fragment. 

Immunopathological findings
Inflammatory infiltration of the vascular wall consists of CD45 lymphocytes, CD68 macrophages, CD61 megakaryocytes, CD3-, CD4- and CD8+ T-cells and CD15 neutrophils. Thrombosis of pulmonary artery branches is observed less frequently than thrombosis of the microvasculature. Therefore, it is essential to differentiate between pulmonary embolism and thrombosis in COVID.

Regardless of ARDS or the degree of viral pneumonia, the capillary is found to be destroyed, accompanied by fibrinoid necrosis. It is likely the loss of integrity of the vascular wall that initiates advanced thrombotic mechanisms in COVID. The virus itself damages the endothelium, followed by apoptosis which increases the loss of anticoagulation function. Cytotoxic upregulation of immune cells and endotheliocytes and activation of the complement system further endothelial damage.

Targeting the loss of pulmonary perfusion
It is hypothesized that loss of anticoagulant function is key in unmatched perfusion. This is a plausible explanation, as erratic pulmonary perfusion is consistent with persistence of thrombotic activity and failing thrombolytic therapies. Therefore, a therapy targeting pulmonary perfusion is proposed (Thrombosis of pulmonary vasculature despite anticoagulation and thrombolysis: The findings from seven autopsies, Thrombosis update 2020 Dec; 1).

4. How COVID affects systemic systems and therefore poses a threat to the young and healthy as well as the immunocompromised
From a hematologist's perspective, COVID is a systemic infection that encompasses cardiovascular, gastrointestinal, respiratory and hematopoietic systems. SARS-CoV-2 affects young individuals with no underlying disease and puts healthy young at risk for DIC (disseminated intravascular coagulopathy), myocarditis, venous thrombo-embolism (VTE) and lymphopenia.

Around 14 days after symptom onset, severe lymphopenia is reported in 83.2% of COVID cases, according to a cohort study involving 1099 patients. Progressive thrombocytopenia and leukopenia are  reported to make for 26.2% and 33.7% of cases, showing about two weeks after symptom onset. Prominent lymphoplasmacytoid-lymphocytes with eccentric nuclei and basophilic cytoplasm and neutrophils with abnormal pseudo-Pelger nuclei and unusually enlarged vacuolated platelets were observed in severe COVID cases. Inflammatory cytokines contribute to lymphopenia.

It is noted that the cytokine cascade in COVID, also called Cytokine Release Syndrome (COVID-CRS) or hypercytokinemia, follows a path similar to hemophagocytic lymphohistiocytosis (HLH) and Castleman. Interestingly, these hematologic syndromes share with COVID a tendency for thrombosis, hypercoagulation, hypotension and hypoxia (SARS-CoV-2 Infected Patient: from a Hematologist's Perspective, Mediterranean Journal of Hematology and Infectious Diseases 2020;12(1)). It can be confirmed that nasopharyngeal viral load (RNAaemia) correlates to levels of Interleukin-6 (IL-6) and disease severity. Serum levels of IL-6 relate to infection severity and viral load. Also, a significant positive correlation was found between viral load and IL-2R.

Patients at risk of vasculopathy are prone to endothelial damage due to COVID. Diabetes and hypertension are the main comorbities that increase the risk of severe disease, associated with endotheliopathy in COVID. Fasting blood sugar level (FPG) is a marker for severity and hypoxia risk. Endotheliopathy and platelet hyperactivation are marked by increased Von Willebrand Factor (VWF) antigen and thrombomodulin (TM) levels and low ADAMTS13 levels.

Inflammatory profile
The hematologist's perspective offers great insight into the inflammatory markers that should be monitored closely to predict COVID severity. Since SARS-CoV-1 (2003), it has been known that epithelial cell proliferation and macrophage induction in the lungs illustrate the inflammatory process that contributes to disease severity. An increased IL-6/IFN-γ ratio can be predictive of disease severity. Procalcitonin and C-reactive protein should be measured regularly. Procalcitonin levels were observed to be significantly elevated, from 4 to 8 times higher in severe SARS-CoV-2 infection. Severe cases can be further marked by dyspnea, lymphopenia, hypoalbuminemia, elevated alanine aminotransferase (ALA), lactate dehydrogenase, higher levels of IL-2R, IL-6, IL-10 and TNF-alpha.

From the hematologist's perspective, it is speculated that hyperferritinemia is not a common feature of COVID-19. However, iron availability favors viral replication in macrophages. Erythropoietin is known to regulate inflammatory cytokines and hepcidin, allowing iron absorption in the bone marrow. Iron redistribution could impair viral replication. Erythropoietin increases the red blood cell mass and has anti-apoptotic cytoprotective properties. As of April 2020, EPO has been shown to alleviate ARDS and to reduce damage through inhibition of  NF-kB (Does recombinant human erythropoietin administration in critically ill COVID-19 patients have miraculous therapeutic effects?, Journal of Medical Virology Vol. 92, Issue 7, July 2020, P915-918). EPO has a potential negative effect, nevertheless, as this agent increases the risk of thrombosis in COVID-patients who are already at risk of developing thrombosis. 

5. Therapeutic restoration of the glycocalyx in COVID-19: an overlooked essential?
It has been well known for 20 years or even more, that the endothelium is key in maintaining a healthy homeostasis in order to prevent sepsis and thrombosis. Thrombosis is an acknowledged complication of SARS-Coronaviruses (SARS-CoV-1, 2003 and SARS-CoV-2, 2019) and other highly thrombo-inflammatory pathogens. Sepsis is, in short, a toxic phase in which organs start to fail due to infection, inflammation, hypercoagulation and thrombosis. The glycocalyx exerts shear stress to maintain healthy blood flow. In COVID-19, microcirculation and shear stress are impaired. Sepsis, along with thrombosis, is a major contributor to deterioration in COVID.

Given the fact that endothelial damage marks the turnover to disease progression in COVID, glycocalyx integrity should be included in therapeutic treatment of COVID-19. Performing a search in PubMed, I used the keywords "Glycocalyx", "EGx" (Endothelial glycocalyx) and "restoration". The 2017 study "Therapeutic Restoration of Endothelial Glycocalyx in Sepsis, Journal of Pharmacology and Experimental Therapeutics 2017 Apr; 361(1): 115-121) proposes administration of Sulodexide (SDX), a heparin sulfate-like agent to restore endothelial integrity in sepsis.

A combination of antithrombotic therapy and endothelial glycocalyx restoration could offer new perspectives for an adequate treatment of COVID-19.