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.

Wat is een goede strafrechtadvocaat?

De proceshouding van de advocaat komt voor rekening van de verdachte
Een strafrechtadvocaat treedt in de rechten van de verdachte. De handelingen en uitspraken die worden verricht en gedaan door de advocaat, kunnen de verdachte worden aangerekend als zou de verdachte zelf het woord voeren. Beide "procesdeelnemers" kunnen als geheel worden beschouwd, namelijk als de verdediging tegenover de openbaar aanklager.

Wat maakt een goede strafrechtadvocaat? De meningen over hoe vér een advocaat kan gaan in de verdediging van zijn cliënt zijn verdeeld, maar de juridische grenzen zijn duidelijk. Liegen, het onmogelijke suggereren en de procesgang verstoren door overduidelijk onzinnige handelingen voor te stellen (bijvoorbeeld onderzoek laten doen naar aanvallen door wilde dieren die in Nederland niet voorkomen), vallen niet onder een behoorlijke verdediging. Door inconsistente verklaringen kan een advocaat zijn cliënt ook nog eens benadelen. De proceshouding van de advocaat zal later in het proces voor rekening van de cliënt komen. 

Een goede strafrechtadvocaat is er om de procesgang te bewaken, om te waken voor suggestief bewijs, om de processtukken in te dienen en zo nodig het woord te voeren namens zijn cliënt. Als de enige mogelijke weerlegging van hetgeen de openbaar aanklager aanvoert een valse verklaring is, dan is de grens bereikt. Het gaat niet alleen om een morele grens, maar ook om een juridische (art. 10a Advocatenwet): integriteit en onafhankelijkheid ten opzichte van de cliënt zijn formele, wettelijke vereisten die worden gesteld in het kader van de goede rechtsbedeling. 

Zwijgrecht of verklaringsrecht?
Het zwijgrecht houdt in dat een verdachte niet gehouden is om zichzelf met een verklaring te belasten, omdat het aan de openbaar aanklager is om het bewijsmateriaal te leveren en vervolgens aan de rechter om het ten laste gelegde te bewijzen (de rechter is de deelnemer die bewijst, "bewijzen als activiteit"). Het zwijgrecht wordt niet zodanig uitgelegd, dat de rechtbank de zwijgende verdachte nooit zal kunnen veroordelen. In plaats van een spreekplicht is er sprake van een verdedigingsrecht of een verklaringsrecht van de verdachte, dat inhoudt dat de verdachte een aannemelijk scenario dient te schetsen om het bewijs te weerspreken.

Doet hij dat niet, dan riskeert hij dat de rechter op basis van het bewijsmateriaal aanneemt "wat de rechter wettig en overtuigend bewezen acht". Een volhardend beroep op het zwijgrecht werkt ten nadele van de verdachte als het bewijsmateriaal om een verklaring vraagt. Daarom is het goed om te benadrukken dat verklaren een recht is, zoals dat ook is beoogd in het strafproces op tegenspraak. Zwijgt de verdachte en komen er later in het proces onsamenhangende verklaringen, dan zal deze procesopstelling de verdachte worden aangerekend. Het moet de advocaat dan ook duidelijk zijn dat "het zich in allerlei bochten wringen" en het proces vertragen door onderzoekshandelingen voor te stellen die eerder gedaan hadden kunnen worden of evident niets op kunnen leveren, alleen maar in het nadeel van zowel zijn cliënt als het gehele strafproces werken.

Feiten fingeren, bewijsmateriaal verdraaien en valse suggesties? Een advocaat die zich daarvan bedient, weet dat hij een verloren zaak op zich heeft genomen.

The cookbook edition

In the "Nutrition series", I discuss the biochemical mechanisms underlying immunomodulatory, anti-inflammatory, cardiovasculoprotective and antithrombotic activities of nutrients. Metabolism of nutrients needs further investigation. The uptake and metabolism (after processing in the liver, kidneys and intestines) of some nutrients is seemingly poor (but not proven yet).  The point is to not believe in a prodigy nutrient or to rely on an unbalanced diet consisting of what people think are "super foods".

I will share some examples of foods that are abundant in antioxidants and that likely exert anti-inflammatory as well as immunomodulatory properties.

Antioxidants and quercetin: bell peppers, red cabbage, garlic, red and white onions, tomatoes and grapes

Citrus fruits, onions and cauliflower are sources of quercetin. Apple peels are a source of Ursolic Acid

 

Antioxidants naturally appear in colored legumes and fruits and color compounds protect vegetables against UV-radiation. Use it, don't overdo it. A varied diet is key

Cyanidin is a dominant flavylium in red cabbage, blueberries, red onion and blue grapes. Cyanidin exerts antioxidant and neuroprotective properties

Recipes for color-rich food

Home-made noodles with bell peppers and mushrooms
- 1,5 kg red (and/or white) onions;
- Red, green and orange bell peppers;
- 2 bulbs of garlic;
- 2 or 3 chili peppers;
- 2-3 trays of mushrooms;
- 1,5 inch of ginger;
- Season: curry, cumin, turmeric, pepper powder, cumin seed;
- Bean sprouts;
- Optional: chicken meat;
- Optional: linguine;
- Butter

Cut the onions and bell peppers in small pieces. It will take less time to extract water out of the vegetables. Peel 1 to 2 bulbs of garlic and cut them in very small slices or use a grater. Don't be afraid of the garlic: even these amounts will blend into your season and vegetable mix without getting too intense. Use latex gloves or a fork and a knive to part 2 chili peppers and cut them into small rings. The "pungent" part of a chili peppers is its skin, which contains capsaicin. Fatty substances absorb capsaicin. Adding butter during cooking will make the mix less pungent. Peel 1,5 inch or more of ginger root with the edge of a grapefruit spoon. The peel will come off surprisingly easy. You can grate the ginger root or julienne them. Some ginger roots can be very 'thready' when trying to julienne. This is when it's easier to use a handheld grater with small holes.

Make a season consisting of curry, cumin, turmeric, pepper powder and cumin seed. Slice the mushrooms. You can use a cast iron pan or a casserole. The benefit of a cast iron pan is that your legumes will not easily stick to the bottom. Stew the mushroom slices in a small amount of vegetable oil (1 spoon) until all the water has evaporated. Take the mushrooms out and store them on a heat-resistant plate. Stew the vegetables in one spoon of oil. Add the season during the process. If you opt to use a high temperature, keep stirring the mix with a ladle! If the water has evaporated, add the mushrooms to the legumes. Turn the lid on the pan and lower or minimize the temperature.

Take the chicken out of the fridge. Pat it dry with thick paper towel. Use a separate, heat-resistant plate for processing raw chicken meat; rinse the plate with boiling water immediately after storing raw chicken on it. Fry the chicken in a frying pan. Use sunflower oil or another vegetable oil. Chicken meat should always be well-done to avoid contamination with salmonella bacteria! Is the chicken well-done? Cut the meat into smaller pieces on a clean plate. Add the chicken to the vegetables. Lastly, add the bean sprouts. Never eat raw bean sprouts, as these might contain E.coli and salmonella, due to contamination of its sources.

You can now opt to add spaghettini, linguine, spaghetti or ramen noodles, depending on the favorable thickness.

Red cabbage salad
- 1/2 red cabbage (optional: a quarter white cabbage and a quarter red cabbage);
- Raisins;
- Mayonnaise or tartar sauce;
- Lemon;
- 1 yellow onion;
- 1 inch of grated ginger (optional)

Take off the outer layer of the cabbage and part the cabbage with a knife. Use a grater with medium holes to grate the cabbage. Peel the onion and grate. Add a few spoons of mayonnaise or tartar sauce. Add raisins to Squeeze half a lemon and pour the lemon juice over the mix. You can opt to add 1 inch of grated ginger, but do not overdo this combination, as ginger and lemon juice might taste like "dish water".

White/pointed cabbage curry
- 1 pointed cabbage or white cabbage;
- 3 leeks;
- 3 yellow or red onions;
- 2 chili peppers;
- 1 1/2 inch of ginger;
- 1 bulb of garlic;
- 1 teaspoon 5 spice mix;
- fennel seed;
- cayenne pepper, ground;
- cumin ground;
- cinnamon ground;
- optional: chicken, bacon or without meat

A biochemical perspective on nutrition (2): immunomodulatory, cardioprotective and antithrombotic properties of Vitamin D (= steroid hormone)- and the importance of Vit D-Vitamin K cooperation

Amidst the COVID pandemic, there has been a revival of the "Vitamin D hype", following previous Vitamin C, Resveratrol and Vitamin B hypes. First, let me say that no nutrition hype will prove to be effective to curb the pandemic. Expectations should not be elevated to unrealistic heights: no dietary nor supplementary intake of any nutrient will prevent diseases from occurring. Too many factors are involved, there is no such "one-size-fits-all"-solution as simple as "this supplement is a prodigy drug". It is not a complete novelty: the Hope-Simpson doctrine, established in 1981, reads that a seasonal stimulus related to UV-radiation is explanatory for the occurrence of seasonal epidemics (Epidemic influenza and vitamin D, Epidemiology & Infection 2006 Sep, 134).

Nevertheless, dietary habits are relevant with regards to inflammation and immunity-related diseases. Vitamin D is a notable regulator of immunomodulation and, as such, has been associated with modulation of inflammatory pathways in systemic and infectious diseases. Other well-documented immunomodulatory nutrients are zinc, selenium and vitamin A. In this message, I will discuss the immunomodulatory mechanisms of Vitamin D as well as presumed cardioprotective and antithrombotic properties of Vitamin D. Note that the modulatory effect on the Renin-Angiotensin Aldosterone System-Kallikrein System (RAS/KKS) remains controversial for the lack of human in vivo studies addressing questions of causality. One should always be cautious with regards to "promiscious" papers that do not actually address causality questions!

Another main topic is the bioavailability as well as the bioaccessibility of nutritients. It is inaccurate to say that nutrition is a minor topic according to scientists and medical professionals. To discriminate between natural sources and synthetic sources (pharmacological compound) makes no sense, as either compound exerts its molecular properties. What does actually make a difference, is that every nutrient has to meet the threshold of bioavailability and bioaccessibility: the nutrient must be able to be absorbed and remain available for use or storage. To date, no formula exists to ascertain the availability and accessibility of Vitamin D and other nutrients upon being transferred into the human digestive tract and blood serum.

1.    Vitamin D;
1.1. Vitamin D metabolism;
1.2. The immune landscape of Vitamin D: innate and adaptive immunity;
2.    Relationship between Vitamin D, the cardiovascular system and (deep venous) thrombosis;
2.1. Association of low serum 25-Hydroxyvitamin D with Venous Thrombosis and Embolism;
2.2. Low Vitamin D at presentation of ischemic stroke is associated with elevated risk of Venous Thromboembolism and neurological deterioration;
2.3. Platelet aggregation disorders and anti-platelet aggregation properties of VitD;
2.4. Genetic indications for anticoagulatory properties of Vitamin D;
2.5. Endothelial function and antioxidative properties of Vitamin D;
2.6  A role for vitamin K2 (menaquinone);
3.    Autoimmune diseases and Vitamin D deficiency;
3.1. Antiphospholipid (Antibody) Syndrome, thrombosis and Vitamin D;
4.    The RAS and ROCK hypothesis;
5.    Inhibitory and immunomodulatory properties of Vitamin D metabolites

1. Vitamin D

1.1 Vitamin D metabolism
Vitamin D is a noun for a group of steroid hormone compounds. Vitamin D is a lipophilic (fat-soluble) steroid. Vitamin D2 (ergocalciferol) is formed after ultraviolet-B (UVB) irradiation of plant ergosterol and Vitamin D3 (cholecalciferol) is generated in the skin from interaction of 7-dehydrocholesterol with UV radiation. Calcitriol (1,25-dihydroxycholecalciferol or 1,25(OH)2D3 (= 1,25 dihydroxyvitamin D3)) is the active form of Vitamin D following 25-hydroxyvitamin D3 (25(OH)D3) conversion in the kidneys and liver. While D2, ergocalciferol is mostly found in supplements, D3, cholecalciferol is regarded the most potential pharmacological agent (PubChem: Cholecalciferol compound summary).

1.2 The immune landscape of Vitamin D: innate and adaptive immunity
While the endocrine sites for calcitriol are the tubule cells of the kidneys, the paracrine and autocrine sites are macrophages, monocytes and dendrites of the innate immune system. The Vitamin D Receptor (VDR) regulates inflammatory genes such as CD14 and cathelicidin anti-microbial peptide (CAMP). Vitamin D is a key regulator of maturation, differentiation and stimulatory capacity of dendrites, derived from monocytes. Vitamin D antagonizes pro-inflammatory activity of Nuclear Factor activated T cells (NF-AT) and NF-kB in T cells (Vitamin D Signaling in the Context of Innate Immunity: Focus on Human Monocytes, Frontiers in Immunology 2019; 10: 2211). Humans with a genetic modification of the Vitamin D receptor, the C genotype (ACG instead of ATG) in which the VDR allele is shortened, show higher expression of NF-kB, NFAT and a higher IL-2 expression in dendrites and monocytes, thus a different immune profile (Vitamin D: Effect on Haematopoiesis and Immune System and Clinical Applications, International Journal of Molecular Sciences 2018 Sep; 19(9): 2663).

A 2013 study, focused on inflammation during pregnancy, offers some points as to how Vitamin D is involved in the regulation of innate immunity. Following stimulation of human myometrial cells with Lipopolysaccharides (LPS) and administration of 100nmol/L Vitamin D3, Vitamin D was shown to downregulate inflammatory cytokines IL-2, IL-9, IL-13 and TNF-α, chemokines MCP-1, CXCL-10 and CXCL-11, IL-1β, connexin 43, COX-2, Toll-like Receptor-4 and -5 (TLR-4 and TLR-5, see Toll-Like Receptors in Antiviral Innate Immunity, Journal of Molecular Biology 2014 Mar 20; 426(6): 1246-1264) and the prostaglandin receptor. Vitamin D3 increased anti-inflammatory IL-10 and upregulated anti-inflammatory activity through TLR-10 (Vitamin D Elicits Anti-Inflammatory Response, Inhibits Contractile-Associated Proteins and Modulates Toll-like Receptors in Human Myometrial Cells, Reproductive Sciences 2013 Apr;20(4): 463-475).

While correlation does not address causality questions, serum TNF-α concentrations were found to be negatively correlated with serum 25(OH)D concentrations in healthy females, indicating that Vitamin D decreases the highly inflammatory TNF-α (Serum tumor necrosis factor-alpha concentrations are negatively correlated with serum 25(OH)D concentrations in healthy women, Journal of Inflammation 2008;5:10). Vitamin D is intrinsically linked to autophagy: TLR-8 activation in macrophages induces the expression of CAMP and the Vitamin D receptor, while TLR-8 agonists inhibit HIV through Vitamin D and CAMP autophagy (Toll-Like Receptor 8 Ligands Activate a Vitamin D Mediated Autophagic Response that Inhibits Human Immunodeficiency Virus Type 1, PLoS Pathogens 2012;8).

The innate immunity is a first line host defence against pathogens, comprising vascular endothelial cells, enzymes expressed by epithelial cells and phagocytes, cathelicidins (CAMP), complement factors, Toll-Like Receptor, mast cells, macrophages, dendrites, neutrophils and Natural Killer Cells. Interaction of TLR2/1 with Vitamin D 25(OH)2D3 stimulates expression of cathelecidin. 25(OH)2D3 upregulates CAMP and defensing β2. Vitamin 1,25(OH)2D3 modulates the physical epithelial barrier. Vitamin D decreases permeability of the intestines and cornea, thus protecting tissue integrity against migration of inflammatory cytokines. The adaptive immunity consists of T and B cells, constituting immunological memory (recognition of pathogens and adjusting an adequate response).

With regards to the adaptive immune system, the role of Vitamin D in suppressing Th1, Th17, subsequent blocking of Nuclear Factor Activated T Cells (NFAT) and induction of FOXP3 and Treg cells cannot consecutively proved by in vivo studies (Vitamin D: Nutrient, Hormone and Immunomodulator, Nutrients 2018 Nov; 10(11): 1656). An explanation might be that in vitro studies and animal profiles differ greatly from human in vivo Vitamin D interaction with T cells, Tregs (T regulators) and T-helper cells.

2. Relationship between Vitamin D, the cardiovascular system and (deep venous) thrombosis

2.1 Association of low serum 25-Hydroxyvitamin D with Venous Thrombosis and Embolism
Vitamin D is speculated to have anticoagulant properties. Due to inconsecutive research papers, conclusions upon the role of Vitamin D in preventing thrombotic events cannot be drawn. One main objective is that the role of Vitamin D suppletion has been focused on markers of coagulation instead of causative factors. One study found that a low 25(OH)D level was not a risk for Venous Thromboembolism (VTE), while reviews suggest that a low 25(OH)D level might modestly increase VTE risk in white people (Serum 25(OH)D and risk of Venous Thromboembolism: The Atherosclerosis Risk in Communities (ARIC) Study, Journal of Thrombosis and Haemostasis Vol. 12, Issue 9, September 2014). A cohort study involving 18791 participants proves a correlation (not causality!) between decreasing levels of 25(OH)D and incidence of Venous Thromboembolism (25-Hydroxyvitamin D concentrations and risk of venous thromboembolism in the general population with 18791 participants, Journal of Thrombosis and Haemostasis Vol. 11, Issue 3, March 2013).

While one study found that normal serum levels of 25(OH)D were not associated with future risk of Venous Thromboembolism (VTE), a major limitation of said study is that subjects with Vitamin D deficiency were not included (Serum levels of Vitamin D are not associated with the future risk of venous thromboembolism. The Tromso Study, Thrombosis and Haemostasis 2013 May;109(5)). On the other hand, a large cohort study and meta-analysis of 18 studies, comprising 29 years of clinical follow-ups, observed increasing risk of ischemic heart disease, myocardial infarction and early death with decreasing plasma 25-hydroxyvitamin D levels. The probable mechanisms of Vit D deficiency increasing the risk of ischemic heart disease and infarction are elevated parathyroid hormone release levels, inflammation, thrombogenicity, dyslipidemia and progression of Extracellular Matrix Remodeling as well as increased renin gene transcription, subsequent hypertension, atherosclerosis and ischaemia (25-Hydroxyvitamin D Levels and Risk of Ischemic Heart Disease, Myocardial Infarction and Early Death, Arteriosclerosis, Thrombosis and Vascular Biology Vol. 31, Issue 11, November 2012).

Anti-thrombotic actions carried out by vitamin D are reported to be a strengthening of the anticoagulant effect of warfarin following 3 months of vitamin D supplementation as compared to the placebo group. In another study, cholecalciferol supplementation resulted in reduced levels of E-selectin, VCAM and ICAM-1, indicating improvement of endothelial function. While inactive, cholecalciferol might contribute to endothelial stabilization through vitamin D-receptor (VDR) indepedent mechanisms (Emerging Role of Vitamin D and its Associated Molecules in Pathways Related to Pathogenesis of Thrombosis, Biomolecules 2019 Nov;9(11):649)

2.2  Low Vitamin D at presentation of ischemic stroke is associated with elevated risk of Venous Thromboembolism and neurological deterioration
Likewise, a 2018 report found associations between low serum Vitamin D levels and the development of Venous Thromboembolism (VTE) in patients presenting with ischemic stroke during an inpatient rehabilitation stay (Low Vitamin D Levels Are Associated With the Development of Deep Venous Thromboembolic Events in Patients with Ischemic Stroke, Clinical and Applied Thrombosis/Hemostasis 2018 Dec;24(9 Supplement)).

It is hypothesized that decreasing serum 25(OH)D is associated with Early Neurological Deterioration (END) following acute ischemic stroke (Decreasing serum 25-hydroxyvitamin D levels and risk of early neurological deterioration in patients with ischemic stroke, Brain and Behavior Vol. 9, Issue 3, March 2019).

2.3 Platelet aggregation disorders and anti-platelet aggregation properties of VitD
Notably, platelet aggregation disorders, loss of vascular wall integrity (endothelial dysfunction) and low Vitamin D serum concentration are associated with the Vascular Wall-type Ehlers-Danlos Syndrome (Vascular type Ehlers-Danlos syndrome is associated with platelet dysfunction and low Vitamin D serum concentration, Orphanet Journal of Rare Diseases 2016; 11: 111).

Note that there is a distinction between clots in thrombus formation as well as the location of thrombus formation (underlying thrombosis): thrombi can consist of  "white clots" (= platelet-rich clots, which are found in arteries) or "red clots" (= red blood cells and fibrin accumulation, found in veins) (Thrombosis and platelets: an update, European Heart Journal Vol. 38, Issue 11, 14 March 2017). This, however, does not mean that venous and arterial thrombosis are entirely distinct.

The presence of Vitamin D Receptors (VDR) on platelets has been discovered only recently. Mean platelet volume (MPV) and platelet distribution width (PDW) are reportedly elevated and increased in vitamin D deficient and insufficient patients with stable coronary artery disease (Mean platelet volume is associated with serum 25-hydroxyvitamin D concentrations in patients with stable coronary artery disease, Heart and Vessels 2018; 33(11): 1275-1281). In 2020, it has been confirmed that platelet aggregation amounting to an increased risk of cardiovascular events is associated with vitamin D deficiency. Platelet activation and megakaryocytopoiesis are calcium-dependent mechanisms modulated by VDR. Of relevance is the finding that uric acid and estrogens are associated with platelet activation and reactivity (Hydroxyvitamin D Serum Levels are Negatively Associated with Platelet Number in a Cohort of Subjects Affected by Overweight and Obesity, Nutrients 2020 Feb; 12(2): 474).

In 2017, a cohort study found that calcitriol, a vitamin D analogue, diminished platelet aggregation in Diabetes Mellitus type 2 patients. Glycemic control was inversely associated with high platelet aggregation and low vitamin D25 levels. This effect of calcitriol was hypothesized to be of benefit to treat vascular complications related to diabetes (Vitamin D diminishes the high platelet aggregation of type 2 diabetes mellitus patients, Platelets Journal Vol. 30, Issue 1, 2019).

2.4 Genetic indications for anticoagulatory properties of Vitamin D
Tissue Factor (TF) and Thrombomodulin (TM) are contributors to thrombosis. Tissue Factor Pathway Inhibitor (TFPI) and antithrombin (AT) are antithrombotic factors. While human in vivo studies addressing causality questions on the role of vitamin D on thrombosis are lacking, there is biological evidence suggesting a thrombomodulatory role of vitamin D (Emerging Role of Vitamin D and its Associated Molecules in Pathways Related to Pathogenesis of Thrombosis, Biomolecules 2019 Nov;9(11):649). The regulation of the Antithrombin (AT) gene by vitamin D is documented (Identification of Regulatory Mutations in SERPINC Affecting Vitamin D Response Elements Associated with Antithrombin Deficiency, PLoS One 2016; 11(3)). Mutations affecting the vitamin D response are associated with a higher risk of thrombotic activity.

2.5 Endothelial function and antioxidative properties of Vitamin D
Like polyphenols, quercetin, kaempferol, flavonoids and other nutrients that will be discussed in the following features, vitamin D exerts antioxidative mechanisms to protect the integrity of endothelial cells. Vitamin D increases the vasodilator Nitric Oxide (NO) and decreases Reactive Oxygen Species(ROS)/Oxidative Stress. NO is required to maintain integrity of endothelial cells. Calcitriol Vitamin D analogues inhibit the expression of highly inflammatory IL-6 and IL-8, as well as adhesion molecules ICAM-1, PECAM-1 (Platelet-endothelial cell adhesion molecule), E-selectin and VCAM-1 (Vascular cell adhesion molecule). In addition, vitamin D reduces prostaglandin by repressing COX-2 (cyclo-oxygenase-2) (The Role of Toll-Like Receptors and Vitamin D in Cardiovascular Diseases- A Review, International Journal of Molecular Sciences 2017 Nov;18(11): 2252).

2.6 A role for vitamin K2 (menaquinone)
The role of vitamin K2 in preventing cardiovascular diseases, as well as the interplay of vitamin K2 with vitamin D needs further investigation. Animal studies proved that K2 suppresses the expression of Toll-like receptors TLR-2 and TLR-4 and inhibits calcification of the aorta and smooth muscle cells. In vitro menaquinone treatment of human macrophages and stimulation with TLR-agonists resulted in reduction of inflammatory cytokine production (The Role of Toll-Like Receptors and Vitamin D in Cardiovascular Diseases- A Review, International Journal of Molecular Sciences 2017 Nov;18(11): 2252). Furtermore, vitamin K2 in the form of MK-7 regulates osteoporosis, atherosclerosis, cancer and cardiovascular diseases without risk of overdosing. MK-7 modulates expression of TNF-α, IL-1α and IL-1β. Both K1 and K2 are involved in maintaining healthy hemostasis and coagulation (coagulants Factor II, VII, IX, X and anticoagulants protein C, protein S and protein Z). Vitamin K-hydroquinone (KH2) exerts anti-oxidative activity.

Vitamin K1 is found in cabbage, Brussel sprouts, green grapes, kiwi fruit and avocado; K2 is found in fermented soy beans, cheese, chicken meat, pork and salmon. The highest levels of K1 are found in leaf vegetables, while K2 is highest in fermented soy. Moderate levels of K1 are found in green asparagus, sprouts and cabbage, while moderate K2 is found in cheese, chicken, beef and zuurkool (Vitamin K: Double Bonds beyond Coagulation, Insights into Differences between K1 and K2 in Health and Disease, International Journal of Molecular Sciences 2019 Feb;20(4): 896).

3. (Auto)immune diseases and Vitamin D deficiency

3.1 Antiphosholipid (Antibody) Syndrome, thrombosis and vitamin D
Antiphospholipid Syndrome (APS) is an autoimmune disorder, characterized by thrombosis and the presence of antiphospholipid antibodies (APS, in: The Autoimmune Diseases, Fifth Edition, 2014). Catastrophic ADS is known as a manifestation of Disseminated Thrombosis in large and small vessels, resulting in Multiple Organ Failure (MOF) (L.R. Wolgast MD, "Antiphospholipid Syndrome", in: Transfusion Medicine and Hemostasis, Third Edition 2019).

A retrospective cohort study reports a significant frequency of vitamin D deficiency among patients with APS (Vitamin D and antiphospholipid syndrome: A retrospective cohort study and meta-analysis, Seminars in Arthritis and Rheumatism Vol. 47, Issue 6, June 2018, P877-882). With regards to lupus, patients were shown to have a higher prevalence of vitamin D deficiency even without classic risk factors (The anti-thrombotic effects of vitamin D and their possible relationship with antiphospholipid syndrome, Lupus Vol. 27, Issue 14, 2018). In vitro studies show the inhibition of Tissue Factor (TF) expression induced by anti-β2GPI-(antiphospholipid) antibodies (Vitamin D: an instrumental factor in the anti-phospholipid syndrome by inhibition of tissue factor expression, Annals of the Rheumatic Diseases Vol 70, Issue 1, 2011).

A 2009 study reports suppression of antirenal autoimmunity through inhibitory effects of calcitriol (vitamin D) on the Th17 effector response. Calcitriol inhibits the priming of Th17 cells by splenic dendritic cells in vivo, the ability of CD4+ T cells to commit to Th17 activity and the ability of Th17 to produce IL-17 (Calcitriol Suppresses Antirenal Autoimmunity through inhibitory effects on the Th17 effector response, Journal of Immunology 2009 Apr 15; 182(8): 4624-4632). IL-17 and IL-23 play an important role in some autoimmune diseases (Either a Th17 or a Th1 effector response can drive autoimmunity: conditions of disease induction affect dominant effector category, Journal of Experimental Medicine 2008 Apr. 14;205(4): 799-810). A low vitamin D level, elevated markers of Th1 response, increased levels of C-reactive protein (CRP), elevated sCD14, Interferon-γ (IFNγ) are  associated with Immune Reconstitution Inflammatory Syndrome (IRIS) (Vitamin D, d-dimer, Interferon γ and sCD14 levels are independently associated with Immune Reconstitution Inflammatory Syndrome: A prospective, International Study, EBioMedicine 2016 Feb; 4: 115-123). Low 25 Hydroxyvitamin D levels are also independently associated with autoimmune inlammation of the thyroid gland in healthy obese people (Low 25 Hydroxyvitamin D Levels are Independently Associated with Autoimmune Thyroiditis in a Cohort of Apparently healthy Overweight and Obese Subjects, Endocrine, metabolic and immune disorders drug targets 2018; 18(6):646-652). 

4. The RAS and ROCK hypothesis *Renin-Angiotensin Aldosterone (RAS/RAAS)

To date, no human in vivo trial has shown the actual role of vitamin D on regulation of the Renin-Angiotensin-Aldosterone System. In vitro, calcitriol has been shown to impair the effect of Lipopolysaccharides (LPS) on the expression of ACE and ACE2. LPS is a proinflammatory molecule attached to the outer membrane of pathogens, known for its induction of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) through damage of endothelial pulmonary microvascular cells. Its actions increasing the permeability of the capillary membrane result in edema and hypoxia. LPS proved to induce ACE expression and to suppress ACE2, in order to induce ALI. The AT1R receptor induces ACE expression, while Ang II regulates the ACE/AT1R Receptor axis. Renin induces conversion of Ang I and Ang II, contributing to Lung Injury.

Vitamin D inhibits renin, ACE and Ang II and induces ACE2 in LPS-induced Lung Injury. While Ang II promotes ALI, Ang 1-7 decreases severity of ALI and inflammation. ACE2 is known to convert Ang II to Ang 1-7. The protective properties of vitamin D might be the induction of Ang 1-7 and ACE2, inhibition of renin and the ACE/Ang II/AT1R axis (Vitamin D alleviates lipopolysaccharide-induced acute lung injury via regulation of the renin-angiotensin system, Molecular Medicine Reports Vol. 16, Issue 5, November 2017). Thus: the ACE2/Ang 1-7-axis has vasodilatory and anti-inflammatory effects, while the ACE/Ang II axis is vasoconstricting and pro-inflammatory, of which the latter contributes to Acute Lung Injury and hyperinflammatory states.

In addition to the ACE/Ang II axis, the RhoA/Rho Kinase (ROCK) pathway is vasoconstrictive, pro-inflammatory and pro-oxidative. A remarkable report reads that of 100 patients with Bartter's and Gitelman's tubulopathies, living in a COVID-19 hotspot, none was infected with SARS-CoV-2 (Rho kinase inhibitors for SARS-CoV-2 induced acute respiratory distress syndrome: Support from Bartter's and Gitelman's syndrome patients, Pharmacological Research 2020 Aug; 158: 104903). Barrter's and Gitelman's patients have increased levels of ACE2 and Ang 1-7 and reduced ROCK activity. In addition to Angiotensin Receptor (AT1R/AT2R) blockers and/or ROCK inhibitors, vitamin D supplementation might be of benefit (Letter: ACE2, Rho kinase inhibitors and the potential role of Vitamin D against COVID-19, Alimentary Pharmacology & Therapeutics 2020 Aug; 52(3):577-578).

A randomized trial found no benefit of correcting vitamin D (25(OH)D) deficiency in obese without hypertension. Neither RAS activity nor blood pressure was corrected by the increase of serum vitamin D 25(OH)D. Participants were given ergocalciferol, the least potent vitamin D analogue. The conclusion of this placebo-control trial is that vitamin D is not a modifiable factor in RAS activity. However, participants were not hypertensive nor severly vitamin D deficient and levels of bioactive vitamin D were not measured, leaving open the possibility that participants were not actually vitamin D deficient (The Effect of Vitamin D on Renin-Angiotensin-System (RAS) Activation and Blood Pressure- A Randomized Control Trial, Journal of Hypertension 2017 Apr; 35(4): 822-829).

5. Inhibitory and immunomodulatory properties of Vitamin D metabolites: confusion follows contradiction?

Calcitriol, the active metabolite (1,25(OH)2D) was reported to have direct effect on T-cells, independent of Dendritic Cell activity. Through inhibition of Interferon-gamma, production of IL-2, TNF-alpha, IL-17 and IL-21 is inhibited. Calcitriol inhibits T-helper-1 (Th1-)priming cytokines in favor of Th2, increasing production of IL-4, IL-5 and IL-10 (Vitamin D and 1,25(OH)2D Regulation of T cells, Nutrients 2015 Apr;12(4): 988). While IL-10 is an anti-inflammatory cytokine, IL-4 is a pro-inflammatory cytokine with profibrotic properties. On the other hand, calcitriol was found to reduce Th2 response in CD4+ T-cells. Inhibition of Th1 cytokines might be detrimental for the immune response to pathogens (Modulation of the Immune Response to Respiratory Viruses by Vitamin D, Nutrients 2015 Jun;7(6)). The effect of vitamin D on Th1 and Th2 as well as on cytokine secretion, is differentiation. From what has been regarded "contradictory studies" can be gathered that vitamin D does not either favor Th1 or Th2, but its mechanism is characterized by differentiation of the immune response dependent on the immunological context (for example, the pathogen involved).

A 2017 meta-analysis concerning 11321 participants concludes benefit for patients with severe vitamin D deficiency not receiving a bolus dose of vitamin D (Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of indivual participant data, BMJ 2017; 356). The trials assessed in this analysis are too inconsistent to draw conclusions with regards to the preventive effect of vitamin D supplementation on respiratory infections, however: data relating to adherence were not available for all participants, no distinction is drawn with regards to the pathogenic nature of respiratory infections and confirmation was only obtained in a minority of cases. Actually, the main question "Does vitamin D supplementation prevent respiratory tract infections?", does not seem to be addressed. In other words, the net effect of vitamin D supplementation on prevention of respiratory viruses remains unclear, while this analysis is referred to as "evidence" for the benefits of vitamin D.

Calcitriol did not show direct effect on Rhinovirus replication, but was shown to potentiate secretion of CXCL8 and CXCL10 (Effects of Vitamin D on Airway Epithelial Cell Morphology and Rhinovirus Replication, PLoS One 2014; 9(1)). CXCL10 exerts both pro-fibrotic and anti-fibrotic properties. Like vitamin D, CXCL10 is able to exert a differentiation of effector responses, depending on immunological context.

Caution

A 2017 paper noted that many interventional studies in inflammatory and immune diseases with Vit D supplementation have proven to be inconclusive, possibly for measuring the 25-hydroxyVitaminD instead of calcitriol (Modulation of inflammatory and immune responses by Vitamin D, Journal of Autoimmunity Vol. 85, December 2017). The main factor for the amount of contradictory and confusing studies might be that Vitamin D metabolites differ with regards to endocrine systems and diseases. There is no general base-level to decide whether Vitamin D insufficiency contributes to a certain disease: the serum level is, in other words, tissue-dependent and disease-dependent (Does Vitamin D Sufficiency Equate to a Single Serum 25-Hydroxyvitamin D Level or are Different Levels Required for Non-Skeletal Diseases?, Nutrients 2013 Dec;5(12)). Some diseases, such as chronic inflammation, are correlated with slightly decreased serum levels of 25(OH)D.

Toxicity
Increasing VitD intake through supplementation is contraindicated in some specific situations. A 2017 study found that Vitamin D3 supplementation reduced the risk of advanced adenomas in individuals of the rs7968585 AA Vitamin D receptor gene who recently had colorectal adenomas by 64%, while D3 supplementation increases the risk of advanced colorectal adenomas in individuals with 1 or 2 G alleles by 41% (Vitamin D Receptor Genotype, Vitamin D3 supplementation and Risk of Colorectal Adenomas, JAMA Oncology 2017;3(5):628-635).

Hypercalcemia
Increasing vitamin D intake promotes serum calcium and phosphorus levels, which can result in hypercalcemia and hyperphosphatemia, posing a risk for the development of cardiovascular calcification. Using newer vitamin D analogs other than calcitriol, such as paricalcitol, might reduce this risk (The influence of selective vitamin D receptor activator paricalcitol on cardiovascular system and cardiorenal protection, Clinical Interventions in Aging 2013; 8: 149-156). The concentration associated with hyperphosphatemia and hypercalcemia is > 150 ng/mL (Optimal Vitamin D Supplementation Doses that Minimize the Risk for Both Low and High Serum 25-Hydroxyvitamin D Concentrations in the General Population, Nutrients 2015 Dec;7(12)).

Broccoli, cauliflower, green Granny Smith apples are a source of Vit K

Freaky leaves: Vitamin K, an essential amino acid that cooperates with Vitamin D, is found in green leaves, cabbage, sprouts, kiwi fruit and other green legumes

Metabolism of forming menaquinone (K2) out of K1 (phylloquinone) in broccoli

Food illustration by Mercedes Bouter

Member of the brassica family

Pathogenesis and structure of SARS-CoV-2 and therapeutic options for COVID-19: a research collection

Coagulopathy characterizing COVID-19
The unique characteristics of COVID-19 coagulopathy, Critical Care 2020; 24: 360;

IL-6 and central cytokine storms are not characteristic for COVID-19
Severe COVID-19 Infections- Knowledge gained and remaining questions, JAMA Internal Medicine, 18 September 2020;

Immune profile
Doctors may have found a new way to predict and treat severe coronavirus cases (IL-7 to treat severe COVID-19), BGR Science, May 31, 2020;

Pathogenesis and viral tropism of SARS-Coronaviruses
Role of SARS-CoV Viroporins E, 3a and 8a in Replication and Pathogenesis, mBio 2018 May-Jun; 9(3);
Secondary structure of the SARS-CoV-2 5'-UTR, RNA Biology 2020:1-10;
SARS-CoV-2 uses a second doorway into cells: Neuropilin-1 facilitates SARS-CoV-2 cell entry and infectivity, Science 20 October 2020;
The SARS-coronavirus papain-like protease: Structure, function and inhibition by designed antiviral compounds, Antiviral Research 2015 Mar;115:21-38;
Molecular epidemiology, evolution and phylogeny of SARS-coronavirus, Infection, Genetics and Evolution 2019 Jul;71:21-30;
SARS-CoV-2 ORF3b is a Potent Interferon Antagonist whose activity is increased by a naturally occurring elongation variant, Cell Reports 2020 Sep 22;32(12);
Cardiovascular Implications of Fatal Outcomes of Patients with COVID-19, JAMA Cardiology 2020 Jul; 5(7): 1-8;
Outcomes of Cardiovascular MRI in Patients Recently discovered from COVID-19, JAMA Cardiology 2020, 27 July 2020;
Patient-derived SARS-CoV-2 mutations impact viral replication dynamics and infectivity in vitro and with clinical implications in vivo, Cell discovery 2020;6:76;
Lung tissue in fatal COVID-19 shows broad cell tropism and extensive damage, News Medical Life Sciences, September 30, 2020;
The Natural History, Pathobiology and Clinical Manifestations of SARS-CoV-2 Infections, Journal of Neuroimmune Pharmacology 2020 Jul 21: 1-28;
The PDZ-Binding Motif of SARS-Coronavirus envelope protein is a determinant of viral pathogenesis, PLoS Pathogens 2014 Aug; 10(8);
In silico identification of Tretinoin as a SARS-CoV-2 envelope (E) protein ion channel inhibitor, Computers in Biology and Medicine 2020 Dec; 127: 104063;
SARS-CoV-2 strategically mimics proteolytic activation of human ENaC, eLife Sciences 2020;9;
Dying with SARS-CoV-2 infection-- an autopsy study of the first consecutive 80 cases in Hamburg, Germany, International Journal of Legal Medicine 2020 Jun 4: 1-10;

Possible treatment options for COVID-19
Kallikrein-kinin blockade in patients with COVID-19 to prevent Acute Respiratory Syndrome, eLife 2020; 9;
Mechanisms of Protective Effects of SGLT2 Inhibitors in Cardiovascular Disease and Renal Dysfunction, Current topics in medicinal chemistry 2019;19(20): 1818-1849;
Outcomes Associated with use of a Kinin B2 Receptor Antagonist among patients with COVID-19, JAMA Infectious Diseases 2020;3(8);
Abelson Kinase Inhibitors Are Potent Inhibitors of SARS-CoV and MERS-CoV Fusion, Journal of Virology 2016 Oct 1; 90(19):8924-8933;
Salvia miltiorrhiza Injection alleviates LPS-induced Acute Lung Injury by adjusting the balance of MMPs/TIMPs ratio, Evidence Based Complement Alternative Medicine 2020;2020;
Sonic Hedgehog Signaling: Evidence for its Protective Role in Endotoxin Induced ALI in mouse model, PLoS One 2015; 10(11);
Extracorporeal membrane oxygenation for SARS associated with COVID-19: a retrospective cohort study, Lancet Respiratory Medicine Vol. 8, Issue 11, November 01, 2020;
Novel hybrid antiviral VTRRT-13V2.1 against SARS-CoV-2 main protease: retro-combinatorial synthesis and molecular dynamics analysis, Heliyon Vol. 6, Issue 10, October 2020;
A perspective on Erythropoietin as a potential adjuvant therapy for ALI/ARDS in patients with COVID-19, Archives of Medical Research 2020 Aug 11;
Association between chronic ACE receptor inhibitor exposure and decreased odds of severe disease in patients with COVID-19, Anatolian Journal of Cardiology 2020; 24(1): 21-29;
Vorolanib and everolimus: Lenvatinib and everolimus part deux, or something new?, EBioMedicine Vol. 56, June 2020;
MMP-8 Inactivates Macrophage Inflammatory Protein-1alpha to Reduce Acute Lung Inflammation and Injury in Mice, Journal of Immunology 2010 Feb 1;184(3): 1575-1588;
Sofosbuvir for COVID-19 infection: a potential candidate, Indian Journal of Pharmacology 2020 May-Jun; 52(3): 232-233;
Broad spectrum coronavirus antiviral drug discovery, Expert Opin Drug Discovery 2019; 14(4): 397-412;
Apirin Use is Associated with Decreased Mechanical Ventilation, ICU Admission, and In-Hospital Mortality in Hospitalized Patients with COVID-19, Anesthesia & Analgesia: October 21, 2020;
Is Acetylsalicylic Acid a Safe and Potentially Useful Choice for Adult Patients with COVID-19?, Drugs 80, 1383-1396(2020);
Ac2-26 mimetic peptide of annexin A1 to treat severe COVID-19: A hyptothesis, Medical Hypotheses 2020 Dec; 145: 110352;
Umbilical cord: an allogenic tissue for potential treatment of COVID-19,
Ebselen, Disulfirum, Carmofur, PX-12, Tideglusib and Shikonin are nonspecific promiscious SARS-CoV-2 main protease inhibitors, ACS Pharmacological Translational Sciences 2020 Oct 9;

Preprints (warning: never draw conclusions based on MedRxiv and BioRxiv research papers: preprints from the Rxiv server still have to undergo peer review, conclusions are preliminary and might turn out to be invalid)
Ethacridine inhibits SARS-CoV-2 by inactivating viral particles in cellular models, October 28, 2020;
A neutrophil activation signature predicts critical illness and mortality in COVID-19, September 02, 2020;