The quest for solutions to COVID's thrombosis pandemic: endothelial (glycocalyx) dysfunction and mitochondrial dysfunction are starting points

This is message is part of the "COVID-19 Thrombosis Collection", starting from April 2020. I have been actively reporting on the prominence of thrombosis and hypercoagulability as the main features 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.  

In this message, I will shed light on the starting point of thrombosis in COVID-19. Timing is a crucial aspect and it will become increasingly clear that the early stages of SARS-CoV-2 infection determine the development of (multi-organ) microthrombosis. Endothelial and epithelial integrity are a big driving force in maintaining healthy blood circulation. Previously, I have reported that the glycocalyx (a gel-like barrier of the endothelium) should be protected and restored in order to prevent catastrophic thrombosis. In 2018, restoration of the glycocalyx was proposed as a promising therapeutic target to accelerate lung injury recovery in sepsis-induced injuries like ARDS (The Pulmonary Endothelial Glycocalyx in ARDS: A Critical Role for Heparan Sulfate, Current Topics in Membranes Vol. 28, 2018, P33-52).

Note that endothelial damage, mitochondrial damage, cytotoxicity of the virus, recruitment of adhesive molecules, leukocytes and macrophages (inflammation), thrombus generation, platelet aggregation, imbalance of the Renin-Angiotensin and Kallikrein System (RAS/KKS), complement activation and release of coagulation factors each contribute to COVID severity and that each of these mechanisms offers therapeutic targets. Some therapeutic options are directed at protection of the glycocalyx, prevention of cytokine cascades ("cytokine storms", which is not specific), complement C5b-9 (MAC) inhibition, platelet inhibition and induction of thrombolysis and fibrinolysis.

Previous messages:
1. A stubborn complication: the quest for solutions to COVID's thrombosis pandemic, 30 November 2020;
2. COVID-19 Hypercoagulation, thrombosis, embolism and urokinase pathways: an up-to-date research collection, 20 October 2020;
3. A remaining challenge: hypercoagulability characterizing COVID-19, despite anticoagulation practices, 5 October 2020;
4. Pathways towards deterioration in SARS-CoV-2 IV: the complement system, 29 August 2020;
Pathways to deterioration in SARS-CoV-2 II: coagulation disorders (haemostatic imbalance): mechanisms driving thromboinflammation and pulmonary fibrosis, 6 May 2020;
5. Pathways towards deterioration in SARS-CoV-2 I: Is enhancement of ACE2 in the RAAS system (Renin-Angiotensin-Aldosterone/Kallikrein) key?, 18 April 2020;

This message covers:
1.   The endothelium and epithelium as starting points;
2.   Platelets and megakaryocytes: bordering between apoptosis (loss) and overcompensation;
2.1 SARS-CoV-2 interacts with platelets through primer TMPRSS2 and the ACE2 receptor;
3.   Endothelial health and intrinsic pathways;
3.1 Mitochondrial oxidative stress, sialic acid, oxidative phosphorylation and antioxidant Nrf2;
3.2 Naked megakaryocytes indicative of immunothrombosis in COVID-19

1. The endothelium and epithelium as starting points
The reason behind thrombosis is the attempt of the body to restore damaged tissue through prothrombotic and fibrotic factors. When the site of injury is restored, thrombi (blood clots) and fibrin clots are cleared by fibrinolysis and thrombolysis. In COVID-19 and other thrombotic diseases, the system fails to remove the clots. Mechanisms driving thromboinflammation and thromboembolism in COVID-19 are intertwined at the interaction of endotheliopathy, coagulability and thrombocytopathy. If one or more of these mechanisms fail to maintain the balance between pro-thrombotic and antithrombotic activity, the risk of catastrophic thrombosis increases.

COVID-19 patients show a hypercoagulable state (enhanced thrombin) and impaired fibrinolysis, but othen than a "common" Disseminated Intravascular Coagulopathy (DIC), depletion of antithrombin and alpha-2 antiplasmin is not observed in COVID-19 coagulopathy. This is why COVID-coagulopathy is often diagnosed as "CAC". The state of CAC strengthens the view that endothelial damage is the determinant in COVID thrombosis. In cases of delayed catastrophic thrombosis in young and asymptomatic post-COVID-19 patients without underlying thrombotic risks, persistent mural thrombosis, low-grade thrombosis, viral inclusion bodies, hypercoagulability and elevated VWF are suggestive of ongoing endotheliopathy as a main cause (Delayed catastrophic thrombotic events in young and asymptomatic post COVID-19 patients, Journal of Thrombosis and Thrombolysis 2020, 7 November 2020).

It is proposed that schistocytes are adequate markers of endotheliopathy; fragments of red blood cells are result of damage to erythrocytes, indicative of diffuse endothelial damage with formation of microthrombi in the peripheral circulation (Evidence of systemic endothelial injury and microthrombosis in hospitalized COVID-19 patients at different stages of the disease, Journal of Thrombosis and Thrombolysis 2020, 6 November 2020).

The development of CAC 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. 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 (Thrombocytopathy and endotheliopathy: crucial contributors to COVID-19 thromboinflammation, Nature Reviews Cardiology 2020 Nov 19: 1-16).

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)).

2. Platelets and megakaryocytes: bordering between apoptosis (loss) and overcompensation
Thrombocytopenia is progressive in COVID-19, which is reconcilable with the observation of early platelet aggregation. Platelet apoptosis (death of platelets) shifts platelet activation towards hyperactivation of remaining platelets. Hypoxia and endothelial damage further increase platelet activation and apoptosis. This was already observed in SARS-CoV-1 (2003)Thrombocytopenia in patients with SARS, Immune Hematology, April 2005; 10(2). Activated platelets express P-selectin and recruit alpha-granules, CCL2, CCL3, CCL7, IL-1beta, IL-7 and IL-8. IL-1beta is known to increase
endothelial permeability.

Hypoxia and C5a complement activation induces hyperactivation of platelets, antiphospholipid antibodies induce destruction
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. Release of the complement factor C5a further induces hyperactivation of platelets.

2.1 SARS-CoV-2 interacts with platelets through primer TMPRSS2 and dysregulation of ACE2
SARS-CoV-2 RNA was found to interact with platelets, which means that virus is able to contribute to platelet hyperactivation (Circulation Research Vol. 127, Issue 11, November 6, 2020). This is compatible with the previous finding that platelets express the primer for SARS-coronavirus entry, TMPRSS2 and the ACE2-receptor (SARS-CoV-2 binds platelet ACE2 to enhance thrombosis in COVID-19, Journal of Hematology & Oncology 13, Article no. 120(2020). In severe COVID cases, formations of lung megakaryocytes and platelets were seen to obstruct the cardiopulmonary microvasculature. 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).

In response to interferon signaling, ACE2 is upregulated in the epithelium. This potentiates cellular uptake of SARS-CoV-2. 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 prostaglandins (Coronavirus-19 (SARS-CoV-2) induces acute severe lung inflammation via IL-1 causing cytokine storm in COVID-19: a promising inhibitory strategy, Journal of Biological Regulators and Homeostatic Agents 2020 Oct 5;34(6)).

3. Endothelial health and intrinsic pathways
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. Nitic Oxide suppresses cytokines, adhesion molecules such as VCAM and chemoattractants in order to prevent blood vessel permeability. NO further 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. HDL are proposed to downregulate TNF-alpha, which is a known major factor driving hyperinflammation (Endothelial Protection by High-Density Lipoproteins: From Bench to Bedside, Arteriosclerosis, Thrombosis and Vascular Biology Vol. 23, Issue 10, October 2003).

3.1 Mitochondrial oxidative stress, sialic acid, oxidative phosphorylation and antioxidant Nrf2
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. In addition, CD68+ and CD163+ macrophages fill the pulmonary space, while CD16+ monocytes bind endothelial cells (Vascular Disease and Thrombosis in SARS-CoV-2 Infected Rhesus Macaques, Cell 2020; 183(5)). 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. Impairment of the intrinsic antioxidant NRF2 increases inflammation and endothelial cell apoptosis. In addition, removal of sialic acid from the endothelial glycocalyx impairs the antioxidant properties of Nrf2 exerted on mitochondria and reduced Nitric Oxide (eNOS) phosphorylation (OXPHOS) required to downregulate mitochondrial Oxidative Stress (Glycocalyx sialic acids regulate Nrf2-mediated signaling by fluid shear stress in human endothelial cells, Redox Biology 2021 Jan; 38: 101816 (published online Nov 28 2020).

Pro-thrombotic and pro-fibrotic activity is the natural way to restore the endothelium following injury. Upon loss of integrity, 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. Endothelial cells release tissue plasminogen activator (tPA) as a means of fibrinolysis. Endothelial dysfunction impairs fibrinolysis and thrombolysis (Fibrinolytic abnormalities in ARDS and versatility of thrombolytic drugs to treat COVID-19, Journal of Thrombosis and Haemostasis Vol 18, Issue 7, July 2020).

3.2 Naked megakaryocytes indicative of immunothrombosis in COVID-19
Megakaryocytopoiesis is the development of megakaryocytes, out of which blood platelets are eventually formed. 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, instigated by 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; further evidence of ongoing inflammation is indicated by high serum ferritin and ferritinemia markers in bone marrow biopsy specimens (A proof of evidence supporting abnormal immunothrombosis in severe COVID-19: naked megakaryocyte nuclei increase in the bone marrow and lungs of critically ill patients, Platelets Vol. 31, Issue 8, 2020).

Next feature
Next feature will cover an extensive view of mechanisms involved in COVID-19 thrombosis, along the lines of key factors inflammation, coagulopathy, endotheliopathy and thrombosis. The very starting point of focus in COVID-19 is endothelial damage. It is safe to assume that adequate treatment of COVID-19 should include endothelial restoration therapeutics, anti-inflammatory drugs and antithrombotic therapeutics.

Long COVID Awareness #1 (Long COVID Syndrome/ Post-COVID-19 long haulers)

Overview
1. What is long COVID?
2. What do reports on patients with post-COVID-19 syndrome point out?
3. What is MIS-A?
4. Inflammation of the heart caused by COVID-19: refer patients for examination;
5. What else should be paid attention to?
6. Is it a new phenomenon? About the consequences of the first SARS coronavirus, 2003;
7. Can lung capacity be improved?
8. How should post-COVID / long COVID be treated?
9. To be investigated further: hyperferritinaemia (iron overload), fat metabolism, EGFR and mitochondrial health

1. What is long COVID?
Long COVID was introduced by people who have had COVID-19 and are still dealing with health problems after weeks or months. These may include fatigue, exhaustion with moderate exertion, decrease in lung capacity, a persistent cough, chest pain, recurrent fever, and other symptoms. The official term is "Post acute COVID-19" or "Post-COVID-19 syndrome". The Long Alliance Netherlands uses the term "COVID-19 Associated Syndrome", CAS. Long COVID is not specific. In some cases, persistent symptoms may be the result of pneumonia (Persistent Symptoms in Patients After Acute COVID-19, JAMA 2020; 324 (6): 603-605).

COVID-19 poses all grades of the disease (mild to severe) at risk of damage to the heart, lungs, kidneys and brain. Because COVID is a microthrombotic disease, small "clumps" can form in the fine vessels. Psychological and motor problems that arise during and after COVID-19 can be the result of neurological damage from the virus. Strokes, epilepsy and Guillain-Barré syndrome (a neurological disease) can also occur in young people. COVID-19 increases the risk of developing Parkinson's and Alzheimer's in the long term (COVID-19 (coronavirus): Long-term effects, Mayo Clinic, November 17, 2020).

Long COVID is used as a collective term for systemic diseases, immune disorders and inflammatory reactions resulting from COVID-19. Long COVID also includes post-IC syndrome and post-viral syndrome. An specific example of an inflammatory disease that can result from COVID is MIS-A (Multisystem Inflammatory Syndrome in Adults).

2. What do reports on patients with Post-COVID-19 syndrome point out?
In a follow-up study in 150 people who have had non-critical COVID-19, 30% report respiratory difficulties (dyspnoea) on day 60 after the first symptoms; 40% report general weakness (asthenia) on day 60. Half of this patient group works in the medical sector and half of this study population has at least one underlying disease (Follow-up of adults with noncritical COVID-19 two months after symptom onset, Clinical Microbiology and Infection, October 5, 2020).

A similar picture is painted in an evaluation of patients hospitalized in 2020 for COVID-19 (IC and non-IC patients). The disadvantage of these and other recent evaluations is that the details are lacking, that patients themselves report, that no control takes place, and that no control group is involved in the study for comparison. The comorbidities in this group are high blood pressure (46.7%), high BMI (47.5%) and diabetes (21.7%) (Post-discharge persistent symptoms and health-related quality of life after hospitalization for COVID -19, Journal of Infection Vol. 81, Issue 6, December 1, 2020). In a group of 143 patients previously admitted for COVID, 35% of whom have high blood pressure, 18% thyroid disease, 11% immune disease, 9% COPD, and 7% diabetes, fatigue (53%), breathing problems (43%) and joint pain (arthralgia, 27%) have been reported. Also in this study, the necessary details are lacking, the study itself reports that the pneumonia resulting from COVID-19 can cause the persistent symptoms (Persistent Symptoms in Patients After Acute COVID-19, JAMA 2020; 324 (6): 603 -605).

More specific is a follow-up of 384 former COVID between day 47 and day 59 after hospital discharge. 7.3% of 247 patients have a persistently low level of white blood cells, 30.1% of 229 patients have an elevated D-dimer value (D-dimer elevation indicates the breakdown of blood clots in the body) and 9.5% of 190 patients have an increase in the C-reactive protein (CRP, a protein produced by the liver in inflammation). Of 244 patients who received a chest X-ray during the evaluation, 9% had deteriorated lung tissue and 14.8% needed further investigation (Long-COVID: a cross-sectional study of persisting symptoms, biomarker and imaging abnormalities following hospitalization for COVID-19, Thorax, November 10, 2020).

3. What is MIS-A?
MIS-A stands for Multi Inflammatory Syndrome in Adults. Until recently it was known that children can develop this systemic syndrome after infectious diseases, in children it is called "MIS-Children". It means that the body remains in a state where it is trying to clear up an infection. This inflammatory response is different from inflammation and organ dysfunction due to hypoxia. A variety of symptoms are reported in the sparse literature on MIS-A.

Patients may present with persistent sore throat, fever, weakness, general malaise, stiffness, diarrhea, rash, shock, kidney failure, eating problems, pressure, palpitations of the heart ("fluttering"), ringing in the ears, haemophilia, a weak pulse, low blood pressure, nausea, very dark urine, pain when swallowing and burning when urinating. To determine if it is MIS-A, an RT-PCR and antigen test must be performed, supplemented with a measurement of the inflammatory and thrombotic markers CRP (C-reactive protein), ferritin, D-dimer, alanine aminotransferase (liver function), absolute lymphocyte count (ALC) and troponin (heart function). The examination is complemented by CT scans to assess the organs, a chest X-ray to detect any frosted glass spots on the lungs, an ultrasound scan of the heart (TTE), ECG of the heart and ejection fraction examination of the heart.

In the reported cases of MIS-A, inflammatory markers were markedly elevated and resulted in endothelial damage or coagulopathy from SARS-CoV-2 infection. In one case, particles of the complement system were found in the blood vessels. Treatment with corticosteroids, heparin, phenylephrine, dobutamine, Remdesivir, tocilizumab, midodrine, norepinephrine and vasopressin, among others, improved (Case Series of MIS-A Associated with SARS-CoV-2 Infection-- United Kingdom and United States, March-August 2020 , Morbidity and Mortality Weekly Report CDC, Oct 9, 2020; 69 (40): 1450-1456).

 

4. Inflammation of the heart caused by COVID-19: refer patients for examination
Inflammation of the heart muscle may develop in recovered COVID patients. An MRI study of 100 patients recovered from COVID showed that 78% had heart problems and 60% had persistent inflammation of the heart. In the patient group, the presence of LGE (Late Gadolinium Enhancement, a marker for fibrosis and edema due to inflammation of the pericardium) and a marked increase in troponin (Outcomes of Cardiovascular MRI in Patients Recently Recovered from COVID-19, JAMA Cardiology 2020; 5 ( 11): 1265-1273).

Practitioners are advised to include COVID-19 suspicion in new cardiological complaints are reported (Myocardial injury and COVID-19: Possible mechanisms, Life Sciences 2020, July 15, 2020; 253). In a study among competitive and endurance athletes, 15% showed abnormalities on the Cardio-MR, which indicate myocarditis, while LGE is present in 30.8%. Also in this group, fibrosis and edema due to inflammation of the heart tissue as a result of COVID (Cardiovascular Magnetic Resonance Findings in Competitive Athletes Recovering from COVID-19 Infection, JAMA Cardiology, September 11, 2020). There is currently no guideline regulating a return to competitive and endurance sports after COVID-19. The collection of troponin, ECG and ultrasound is recommended in all cases (from asymptomatic COVID-19 to COVID with severe complaints).

At least 2 weeks of rest after infection is recommended. In case of myocarditis (inflammation of the heart muscle), 3 to 6 months rest may be recommended. If there has been "mild" COVID-19 infection, exercise can be resumed according to the "50/30/20/10 principle": in the first week, the normal intensity and duration are halved, until the fourth week. only 10% of the intensity and duration of sports activities is reduced (Considerations for Return to Exercise Following Mild-to-Moderate COVID-19 in the Recreational Athlete, Muscoskeletal Journal of Hospital for Special Surgery 2020 Nov; 16 (Suppl 1): 102 -107).

5. What else should be paid attention to?
Muscle pain occurs in 15% of COVID patients. In most cases this will pass. If the muscle pain persists due to inflammatory mechanisms after COVID, heat, ice cooling, optional topical non-steroidal anti-inflammatory drugs (NSAIDs) and stretching exercises are applied. Because COVID-19 is a disease with an increased risk of thromboembolic disease, physicians should be alert to athletes reporting fibula pain and consider investigating VTE (venous thromboembolism) (Considerations for Return to Exercise Following Mild -to-Moderate COVID-19 in the Recreational Athlete, Muscoskeletal Journal of Hospital for Special Surgery 2020 Nov; 16 (Suppl 1): 102-107).

Persistent fatigue could be due to Autoimmune Hemolytic Anemia (AIHA) (Autoimmune haemolytic anemia associated with COVID-19 infection, British Journal of Haematology Vol. 190, Issue 1, July 2020, p. 29-31). Hemoglobin must be checked to rule out anemia.

6. Is it a new phenomenon? About the consequences of the first SARS coronavirus, 2003
No, long term effects of coronavirus disease are not new. The virus that causes COVID-19 (Coronavirus Disease-2019) is SARS-CoV-2, a relative of SARS-CoV-1. In 2003 Asia and Canada were badly hit by the SARS-1 epidemic. In 2006 and 2010, international studies were conducted among people who had recovered from SARS-1. A 2005 evaluation reports that a decline in gas transmission in the lungs was observed in 15.5% of SARS survivors (Impact of SARS on pulmonary function, functional capacity and quality of life in survivors, Thorax May 2005; 60 (5 ): 401-409).

In a group of 37 patients, stability of deterioration was reported in 20-30% of cases 3 years after SARS-CoV-1 infection (the functions FVC, VC and especially FEF showed no improvement after 3 years), ( Changes in pulmonary function in SARS patients during the three-year convalescent period, Zhongguo Wei Zhong, September 2007; 19 (9): 536-8). This means that, while pulmonary performance had deteriorated, the clinical picture had not become worse.

In a 2010 study, 52% of SARS survivors found a deterioration in the diffusion capacity of the lungs (DLCO). In ARDS, 76% of patients have a limitation in DLCO after 5 years. On the CT scans, ground glass opacities, ground glass spots between the lungs and disruption of the pressure in the lungs (air trapping) were seen (Pulmonary sequelae in convalescent patients after SARS: evaluation with thin-section CT, Radiology , September 1, 2005). Epithelial tissue damage and pulmonary fibrosis explain these persistent limitations in lung capacity, while lack of fitness training aggravates the condition. Average performance on the 6-minute walk test (6MWT) remains below par (The long-term impact of SARS on pulmonary function, exercise and health status, Respirology April 2010; 15 (3): 543-550).

A 15-year review was published in February 2020, covering former SARS patients treated between 2003 and 2005. Lung function (total lung capacity, TLC and carbon monoxide diffusion, DCLO) has not significantly improved over the past 15 years in SARS patients with pulmonary fibrosis. Direct treatment of pneumonia can prevent the lung function of SARS / COVID survivors from deteriorating. In 15 of the 71 patients evaluated, hip necrosis (femoral head necrosis) has occurred on a bump course of corticosteroids, but remarkably (favorably) this hip necrosis may be reduced. With controlled dosing of corticosteroids, this risk can be reduced (Long-term bone and lung consequences associated with hospital-acquired SARS: a 15-year follow-up from a prospective cohort study. Bone Research 2020; 8: 8).

 
7. Can lung capacity be improved?
Patients that have been mechanically ventilated for any disease may present with post-IC syndrome. Post-IC syndrome (PICS) may also occur in patients admitted to the ICU for COVID-19. It is recommended that a special rehabilitation center be set up to see patients after discharge from the ICU. Ventilated patients should be examined for barotrauma and lactic acid deposition from respiratory exhaustion.

It is a common view that COVID patients discharged from the ICU score below average on the 6-minute walk test (6MWT). Rehabilitation specialists should monitor for neuropathy, myopathy (inflammation of the muscles), cognitive and neurological functions, respiration, heart function, and musculoskeletal functions. Neuromotor exercises should be performed to prevent disease and deterioration of body functions due to inactivity (Early Rehabilitation in post-acute COVID-19 patients: data from an Italian COVID-19 Rehabilitation Unit and proposal of a treatment protocol, Edizioni Minerva Medica 2020 October; 56 (6): 633-41).

A recent evaluation of 145 COVID-19 patients after 100 days concluded that the cardiopulmonary damage (damage to lungs and heart) has decreased and is no longer an obstacle. Although the CT scans seem to indicate no pulmonary fibrosis, it is difficult to distinguish between inflammation in the lung tissue and incipient pulmonary fibrosis (Cardiopulmonary recovery after COVID-19 - an observational prospective multi-center trial, European Respiratory Journal. 2020 December 10).

 
8. How should post-COVID / long COVID be treated?
Patients who have had "mild" or no COVID complaints have usually not had an examination. Fibrosis, thrombotic activity and any neurological consequences can be overlooked.

To avoid misdiagnoses, investigations for inflammation markers (inflammatory markers), thrombotic activity / pulmonary thromboembolism (D-dimer and C-reactive protein), neurological examination and imaging (CT / MRI) of lungs can be conclusive. If the symptoms persist 3 weeks after the first COVID-19 symptoms, the blood can be checked for the total picture, electrolytes, liver and kidney function, troponin, D-dimer, brain natriuretic peptides (BNP), CRP and ferritin to reduce inflammation and assess thrombosis activity. In addition, chest X-rays, urinalysis and an EKG can be performed, as well as tests of thyroid function. Patients should not be excluded from referral on the grounds that an RT-PCR gives a negative result (National Institute for Health and Care Excellence, COVID-19 Guideline: Managing the long-term effects of COVID-19, NICE Guideline 188).

The Royal College of General Practitioners (RCGP), has a clear module for general practitioners and referrers (Course: Long COVID-19). The BMJ has also issued an advisory report for management of post-acute COVID-19 (Management of post-acute COVID-19 in primary care, BMJ 2020; 370). Immune-related disruption of the autonomic system should be considered when orthostatic intolerance (orthostatic hypotension, a drop in blood pressure), fainting and tachycardia occur (Autonomic dysfunction in 'long COVID': rationale, physiology and management strategies, Clinical Medicine Journal, November 28, 2020 ). If the patient has swallowing and speech problems due to COVID-19, it is suggested that a referral is made to the speech therapist. Physiotherapy is recommended for condition building under supervision (monitoring heart / lung function), twice a week (A proposal for multidisciplinary tele-rehabilitation in the assessment and rehabilitation of COVID-19 survivors, International Journal of Environmental Research and Public Health, July 2020; 17 (13): 4890).

9. To be investigated further: hyperferritinaemia (iron overload), fat metabolism, EGFR and mitochondrial health

Hyperferritinaemia and CoVILD (Interstitial Lung Disease)
Hyperferritinaemia can occur during and after infections, such as coronavirus infection. It means that there is an excess of iron in certain parts of the body. Hyperferritin, iron overload, is associated with persistent inflammation and persistent lung disease after infectious diseases (The Hyperferritenemic Syndrome: macrophage activation syndrome, Still's disease, septic shock and catastrophic antiphospholipid syndrome, BMC Medicine 2013; 11: 185). It is not yet entirely clear whether hyperferritin is a result of inflammation, or whether it has an inflammatory effect; hyperferritin is believed to contribute to the "cytokine storm" that occurs in severe COVID-19 (Severe COVID-19, Another Piece in the Puzzle of the Hyperferritinemic Syndrome. An Immunomodulatory Perspective to Alleviate the Storm, Frontiers in Immunology 2020; 11; 1130).

The influence of a SARS-CoV-2 disrupted iron balance on persistent lung problems / lung fibrosis is currently being investigated (Persisting alterations of iron homeostasis in COVID-19 are associated with non-resolving lung pathologies and poor patients' performance: a prospective cohort study , Respiratory Research 2020; 21: 276). The study is registered under the "Development of Interstitial Lung Disease (ILD) in Patients with Severe SARS-CoV-2 Infection (COVID-19) (CovILD)" trial.

Lipid metabolism
In patients who survived the first SARS coronavirus (2003), impaired lipid metabolism is observed 12 years after infection. Long-term treatment of SARS patients with Methylprednisolone is associated with changes in fat metabolism (Altered Lipid Metabolism in SARS Patients Twelve Years after Infection, Scientific Reports 2017; 7: 9110).

Fibrosis due to over-activation of the epidermal growth factor receptor
A 2017 study found that over-activation of the epidermal growth factor receptor (EGFR) after infection with the SARS coronavirus causes fibrosis. Modulating EGFR activity is a potential treatment option to prevent / mitigate COVID-19 fibrosis (Overactive Epidermal Growth Factor Receptor Signaling Leads to Increased Fibrosis after SARS Coronavirus Infection, Journal of Virology 2017 Jun 15; 91 (12 )).

Mitochondrial dysfunction and oxidative stress
Finally, it is clear that the health of mitochondria during and after COVID-19 is an important factor in the disease process and recovery. Mitochondria regulate the energy of the cell and are involved in immunity and inflammatory responses. The cells' waste product is oxidative stress or, more specifically, Reactive Oxygen Species (ROS). If the functioning of mitochondria is disrupted by an invader, such as the coronavirus, oxidative stress increases and mitochondria can die.

By disrupting the normal functioning of the mitochondria, these energy regulators are less able to fight the cells against inflammation and infections. Physical activity, the absorption of antioxidants, including melatonin, Vitamin C, the steroid Vitamin D3 and phenols are important for the maintenance of healthy mitochondria. The exact role of mitochondria in long COVID is under investigation.

Colchicine, an anti-inflammatory agent
The reappraisal of colchicine for the treatment of inflammation deserves mention. This medicine could be given to treat pericarditis and myocarditis (inflammation of the pericardium or inflammation of the heart muscle).