Tag: endothelial dysfunction

The occurrence of hyperactivated platelets and fibrinaloid microclots in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Abstract:

We have previously demonstrated that platelet poor plasma (PPP) obtained from patients with LongCovid/Post-Acute Sequelae of COVID-19 (PASC) is characterized by a hypercoagulable state reflected in hyperactivated platelets and the presence of considerable numbers of fibrin(ogen) amyloid microclots or fibrinaloid microclots. Due to substantial overlap in symptoms and aetiology between PASC and ME/CFS, we investigated whether coagulopathies, platelet hyperactivation and/or fibrin amyloid formation differed between individuals exhibiting ME/CFS and gender- and age-matched healthy controls.

ME/CFS patients were statistically far more hypercoagulable as judged by thromboelastography of both whole blood and platelet-poor plasma. The area of plasma images containing fibrinaloid microclots was commonly more than 10-fold greater in untreated platelet-poor plasma from individuals with ME/CFS than in that of healthy controls. A similar difference was found when the plasma samples were treated with thrombin. Using fluorescently labelled PAC-1, which recognizes glycoprotein IIb/IIIa, and CD62P, which binds P-selectin, we observed massive hyperactivation and spreading of platelets in samples from individuals with ME/CFS. Using a quantitative scoring system, this was found to have a score of 2.72 ± 1.24 vs 1.00 (activation with pseudopodia formation) for healthy controls.

We conclude that ME/CFS is accompanied by substantial and measurable changes in coagulability, platelet hyperactivation, and fibrinaloid microclot formation. However, fibrinaloid microclot load was not as prevalent as was previously noted in PASC. Fibrinaloid microclots, in particular can provide a ready explanation, via (temporary) blockage of microcapillaries and hence ischaemia, for many of the symptoms, such as fatigue, seen in patients with ME/CFS. The discovery of these biomarkers pointing to significant and systemic endothelial inflammation, represents an important development in ME/CFS research. It also points at novel treatment strategies using known drugs and/or nutraceuticals that target systemic vascular pathology and endothelial inflammation.

Source: Massimo Nunes, Arneaux Kruger, Amy Proal et al. The occurrence of hyperactivated platelets and fibrinaloid microclots in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), 08 June 2022, PREPRINT (Version 1) available at Research Square https://doi.org/10.21203/rs.3.rs-1727226/v1 (Full text)

Impaired exercise capacity in post-COVID syndrome: the role of VWF-ADAMTS13 axis

Abstract:

Post-COVID syndrome (PCS) or Long-COVID is an increasingly recognised complication of acute SARS-CoV-2 infection, characterised by persistent fatigue, reduced exercise tolerance chest pain, shortness of breath and cognitive slowing. Acute COVID-19 is strongly linked with increased risk of thrombosis; a prothrombotic state, quantified by elevated Von Willebrand Factor (VWF) Antigen (Ag):ADAMTS13 ratio, and is associated with severity of acute COVID-19 infection. We investigated if patients with PCS also had evidence of a pro-thrombotic state associating with symptom severity.

In a large cohort of patients referred to a dedicated post-COVID-19 clinic, thrombotic risk including VWF(Ag):ADAMTS13 ratio, was investigated. An elevated VWF(Ag):ADAMTS13 ratio (≥1.5) was raised in nearly one-third of the cohort and four times more likely in patients with impaired exercise capacity as evidenced by desaturation ≥3% and/or rise in lactate level more than 1 from baseline on 1-minute sit to stand test and/or 6-minute walk test (p<0.0001). 20% (56/276) had impaired exercise capacity, of which 55% (31/56) had a raised VWF(Ag):ADAMTS13 ratio ≥1.5 (p<0.0001). FVIII and VWF(Ag) were elevated in 26% and 18% respectively and support a hypercoagulable state in some patients with PCS.

These findings suggest possible ongoing microvascular/endothelial dysfunction in the pathogenesis of PCS and highlight a potential role for antithrombotic therapy in the management of these patients.

Source: Prasannan N, Heightman M, Hillman T, Wall E, Bell R, Kessler A, Neave L, Doyle AJ, Devaraj A, Singh D, Dehbi HM, Scully M. Impaired exercise capacity in post-COVID syndrome: the role of VWF-ADAMTS13 axis. Blood Adv. 2022 May 11:bloodadvances.2021006944. doi: 10.1182/bloodadvances.2021006944. Epub ahead of print. PMID: 35543533; PMCID: PMC9098525. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9098525/ (Full text)

Neurocognitive and psychiatric post-coronavirus disease 2019 conditions: pathogenic insights of brain dysfunction following severe acute respiratory syndrome coronavirus 2 infection

Abstract:

Purpose of review: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of coronavirus disease 2019 (COVID-19), can trigger a myriad of neuropsychiatric manifestations. As a 2-year-old disease (at the writing of this manuscript), its long-term cognitive and neuropsychiatric implications, known as post-COVID-19 conditions, are incompletely recognized and mechanistically obscure.

Recent findings: Fatigue, anxiety, depression, posttraumatic stress disorder, and cognitive dysfunction are reported more frequently in COVID-19 survivors than in matching, non-COVID-19 population. Risk factors are unclear, including comorbidities, age at COVID-19 onset, or disease severity; women, however, have been reported to be at increased risk than men. Although the frequency of these symptoms decreases over time, at least one in five will have persistent cognitive and neuropsychiatric manifestations one year after recovering from COVID-19.

Summary: Neurocognitive and psychiatric post-COVID-19 long-term conditions are frequent and complex multifactorial sequelae. Several acute and chronic factors such as hypoxemia, cerebral thrombotic and inflammatory endothelial damage, and disruption of the blood-brain barrier (leading to parenchymal translocation of pro-inflammatory molecules, cytokines, and cytotoxic T lymphocytes) are involved, leading to microglial activation and astrogliosis. As an evolving topic, evidence derived from prospective studies will expand our understanding of post-COVID-19 these long-term outcomes.

Source: García-Grimshaw M, Sankowski R, Valdés-Ferrer SI. Neurocognitive and psychiatric post-coronavirus disease 2019 conditions: pathogenic insights of brain dysfunction following severe acute respiratory syndrome coronavirus 2 infection. Curr Opin Neurol. 2022 Mar 11. doi: 10.1097/WCO.0000000000001046. Epub ahead of print. PMID: 35283463. https://pubmed.ncbi.nlm.nih.gov/35283463/

Endothelial dysfunction and altered endothelial biomarkers in patients with post-COVID-19 syndrome and chronic fatigue syndrome (ME/CFS)

Abstract:

Background: Fatigue, exertion intolerance and post-exertional malaise are among the most frequent symptoms of Post-COVID Syndrome (PCS), with a subset of patients fulfilling criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). As SARS-CoV-2 infects endothelial cells, causing endotheliitis and damaging the endothelium, we investigated endothelial dysfunction (ED) and endothelial biomarkers in patients with PCS.

Methods: We studied the endothelial function in 30 PCS patients with persistent fatigue and exertion intolerance as well as in 15 age- and sex matched seronegative healthy controls (HCs). 14 patients fulfilled the diagnostic criteria for ME/CFS. The other patients were considered to have PCS. Peripheral endothelial function was assessed by the reactive hyperaemia index (RHI) using peripheral arterial tonometry (PAT) in patients and HCs. In a larger cohort of patients and HCs, including post-COVID reconvalescents (PCHCs), Endothelin-1 (ET-1), Angiopoietin-2 (Ang-2), Endocan (ESM-1), IL-8, Angiotensin-Converting Enzyme (ACE) and ACE2 were analysed as endothelial biomarkers.

Results: Five of the 14 post-COVID ME/CFS patients and five of the 16 PCS patients showed ED defined by a diminished RHI (< 1.67), but none of HCs exhibited this finding. A paradoxical positive correlation of RHI with age, blood pressure and BMI was found in PCS but not ME/CFS patients. The ET-1 concentration was significantly elevated in both ME/CFS and PCS patients compared to HCs and PCHCs. The serum Ang-2 concentration was lower in both PCS patients and PCHCs compared to HCs.

Conclusion: A subset of PCS patients display evidence for ED shown by a diminished RHI and altered endothelial biomarkers. Different associations of the RHI with clinical parameters as well as varying biomarker profiles may suggest distinct pathomechanisms among patient subgroups.

Source: Haffke M, Freitag H, Rudolf G, Seifert M, Doehner W, Scherbakov N, Hanitsch L, Wittke K, Bauer S, Konietschke F, Paul F, Bellmann-Strobl J, Kedor C, Scheibenbogen C, Sotzny F. Endothelial dysfunction and altered endothelial biomarkers in patients with post-COVID-19 syndrome and chronic fatigue syndrome (ME/CFS). J Transl Med. 2022 Mar 22;20(1):138. doi: 10.1186/s12967-022-03346-2. PMID: 35317812. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-022-03346-2 (Full text)

Decreased NO production in endothelial cells exposed to plasma from ME/CFS patients

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease characterized by severe and persistent fatigue. Along with clinical studies showing endothelial dysfunction (ED) in a subset of ME/CFS patients, we have recently reported altered ED-related microRNAs in plasma from affected individuals. Inadequate nitric oxide (NO), mainly produced by the endothelial isoform of nitric oxide synthase (eNOS) in endothelial cells (ECs), is a major cause of ED. In this study, we hypothesized that plasma from that cohort of ME/CFS patients induces eNOS-related ED in vitro.

To test this, we cultured human umbilical vein endothelial cells (HUVECs) in the presence of either plasma from ME/CFS patients (ME/CFS-plasma, n = 11) or healthy controls (HC-plasma, n = 12). Then, we measured the NO production in the absence or presence of tyrosine kinase and G protein-coupled receptors agonists (TKRs and GPCRs, respectively), well-known to activate eNOS in ECs.

Our data show that HUVECs incubated with ME/CFS-plasma produced less NO either in the absence or presence of eNOS activators compared to ones in presence of HC-plasma. Also, the NO production elicited by bradykinin, histamine, and acetylcholine (GPCRs agonists) was more affected than the one triggered by insulin (TKR agonist). Finally, inhibitory eNOS phosphorylation at Thr495 was higher in HUVECs treated with ME/CFS-plasma compared to the same treatment with HC-plasma. In conclusion, this study in vitro shows a decreased NO production in HUVECs exposed to plasma from ME/CFS patients, suggesting an unreported role of eNOS in the pathophysiology of this disease

Source: Bertinat R, Villalobos-Labra R, Hofmann L, Blauensteiner J, Sepúlveda N, Westermeier F. Decreased NO production in endothelial cells exposed to plasma from ME/CFS patients. Vascul Pharmacol. 2022 Jan 21:106953. doi: 10.1016/j.vph.2022.106953. Epub ahead of print. PMID: 35074481. https://pubmed.ncbi.nlm.nih.gov/35074481/

Letter: Could endothelial dysfunction and vascular damage contribute to pain, inflammation and post-exertional malaise in individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)?

To the Editor,

In their hypothesis paper, Wirth, Scheibenbogen, and Paul describe how endothelial dysfunction could produce a wide range of neurological symptoms in people with ME/CFS [1]. As they and others work to refine their understanding of ME/CFS and the related Long COVID syndrome, I would encourage consideration of the possibility that endothelial dysfunction and vascular damage could also explain other symptoms, including widespread pain and inflammation and post-exertional malaise.

For the past four years, my wife and I have been caregivers for our teenage daughter, who has ME/CFS, hypermobile Ehlers-Danlos syndrome, craniocervical instability, Chiari malformation and several other comorbid conditions. Through observation and trial and error, I have developed a number of hypotheses on these matters that I offer here in the hope they might prompt formal research into how to effectively treat these conditions [2].

Widespread pain and inflammation

Discussion of endothelial dysfunction and vascular damage in ME/CFS and Long COVID generally focuses on how leakages from dysfunctional blood vessels lead to reduced blood flow, which has many consequences, including reduced oxygenation of muscles and reduced cerebral brain flow. As researchers study this phenomenon, I would encourage consideration of the additional possibility that the leaking fluid causes independent damage. Lipedema researchers have found that leakages from microangiopathic blood vessels cause an excess of interstitial fluid that stimulates the formation of subcutaneous adipose tissue [3], which generates hypoxic conditions and becomes fibrotic, contributing to pain and inflammation [4].

I hypothesize that a similar process happens when fluid leaks from faulty blood vessels in ME/CFS, possibly exacerbated by endothelial dysfunction in lymphatic vessels that inhibit the fluid’s removal, causing widespread pain and inflammation. This mechanism appears most pronounced among people with hypermobility or other connective tissue disorders, a common trait among people with both ME/CFS and lipedema.

My daughter experiences pain from fibrotic adipose tissue as well as what appears to be nerve compression from accumulated interstitial / lymphatic fluid. Manual lymphatic drainage, the squeezing of affected tissue, and the manual break-up of fibrotic adipose tissue have helped to ameliorate these symptoms.

In my daughter, I have also observed impaired drainage of fluid from the glymphatic system, both at the cribriform plate and down her spine. Could this be related to damaged lymphatic vessels or blockages from fibrotic adipose tissue?

Post-exertional malaise

Like many people with moderate or severe ME/CFS, my daughter struggles to recover from even small amounts of physical exertion. In addition to mitigating her pain, manual lymphatic drainage and the squeezing of affected tissue greatly accelerates this recovery process. We have observed a direct dose–response relationship: the more exercise, the more fluid is present in her tissues, and the more manual draining / squeezing is necessary for her to recover.

Based on this experience, I hypothesize that excess interstitial fluid resulting from dysfunctional blood and lymphatic vessels contributes to the experience of post-exertional malaise, with fluid literally drowning affected tissue, leading to hypoxic conditions and inflammation. Possible explanations for the increased interstitial fluid are increases in blood pressure during physical exertion, hypermobile joints going out of place, prompting localized increases in interstitial fluid, and increases in cortisol that generate an increase in fluid and blood volume. Increases in fluid leakage due to elevated cortisol levels may also explain why some people with ME/CFS feel worse when stressed or anxious. The role of cortisol (or another mediator with fluid retaining properties) may explain why cognitive exertion can also generate post-exertional malaise. When present, elevated estrogen levels may exacerbate leakage by increasing fluid volume.

I am not sure why there is typically a delay between physical exertion and the experience of the most acute symptoms of post-exertional malaise. One possibility is that it takes time for the tissue inundated with fluid to feel the full effects of the hypoxic conditions. Another possibility is that a biphasic reaction triggered during physical exertion leads to the release of a mediator that causes heightened endothelial dysfunction and fluid release.

Further research is needed into the causes of endothelial dysfunction and damage (in addition to initial infection and inflammatory overreaction, consider major “crashes,” mast cell activations, surgeries and microclots as additional contributors) and appropriate treatment.

References

1. Wirth KJ, Scheibenbogen C, Paul F. An attempt to explain the neurological symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. J Transl Med. 2021;19:471. https://doi.org/10.1186/s12967-021-03143-3.

Article PubMed PubMed Central Google Scholar

2. For background, see Lubell, J. To speed progress in treating chronic conditions, engage patients and caregivers as research partners. 2021 Sept.20 In: BMJ Opinion. https://blogs.bmj.com/bmj/2021/09/20/to-speed-progress-in-treating-chronic-conditions-engage-patients-and-caregivers-as-research-partners/

3. Allen M, Schwartz M, Herbst KL. Interstitial Fluid in Lipedema and Control Skin. Womens Health Rep (New Rochelle). 2020;1(1):480–7. https://doi.org/10.1089/whr.2020.0086.PMID:33786515;PMCID:PMC7784769.

Article Google Scholar

4. Herbst KL. Subcutaneous Adipose Tissue Diseases: Dercum Disease, Lipedema, Familial Multiple Lipomatosis, and Madelung Disease. [Updated 2019 Dec 14]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. South Dartmouth (MA).

Source: Lubell J. Letter: Could endothelial dysfunction and vascular damage contribute to pain, inflammation and post-exertional malaise in individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)? J Transl Med. 2022 Jan 24;20(1):40. doi: 10.1186/s12967-022-03244-7. PMID: 35073915. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-022-03244-7

Combined triple treatment of fibrin amyloid microclots and platelet pathology in individuals with Long COVID/ Post-Acute Sequelae of COVID-19 (PASC) can resolve their persistent symptoms

Abstract:

We recognise that fibrin(ogen) amyloid microclots and platelet hyperactivation, that we have previously observed in COVID-19 and Long COVID/Post-Acute Sequelae of COVID-19 (PASC) patients, might form a suitable set of foci for the clinical treatment of the symptoms of long COVID/PASC. We first report on the comorbidities and symptoms found in a cohort of 845 South African Long COVID/PASC patients who filled in the South African Long COVID/PASC registry, of which hypertension and high cholesterol levels (dyslipidaemia) were the most important comorbidities. The gender balance (70% female) and the most commonly reported Long COVID/PASC symptoms (fatigue, brain fog, loss of concentration and forgetfulness, shortness of breath, as well as joint and muscle pains) were comparable to those reported elsewhere. This suggests that our sample was not at all atypical. Using a previously published scoring system for fibrin amyloid microclots and platelet pathology, we analysed blood samples from 70 patients, and report the presence of significant fibrin amyloid microclots and platelet pathology in all cases; these were associated with Long COVID/PASC symptoms that persisted after the recovery from acute COVID-19.

A subset of 24 patients was treated with one month of dual antiplatelet therapy (DAPT) (Clopidogrel 75mg/Aspirin 75mg) once a day, as well as a direct oral anticoagulant (DOAC) (Apixiban) 5 mg twice a day. A proton pump inhibitor (PPI) pantoprazole 40 mg/day was also prescribed for gastric protection. Such a regime must only be followed under strict and qualified medical guidance to obviate any dangers, especially haemorrhagic bleeding, and of the therapy as a whole. Thromboelastography (TEG®) was used to assist in determining their clotting status.

Each of the 24 treated cases reported that their main symptoms were resolved and fatigue as the main symptom was relieved, and this was also reflected in a decrease of both the fibrin amyloid microclots and platelet pathology scores. Nine patients were genotyped for genetic variation in homocysteine metabolism implicated in hypertension, a common COVID-19 co-morbidity reported in both patients found to be homozygous for the risk-associated MTHFR 677 T-allele. Fibrin amyloid microclots that block capillaries and inhibit the transport of O2 to tissues, accompanied by platelet hyperactivation, provide a ready explanation for the symptoms of Long COVID/PASC. The removal and reversal of these underlying endotheliopathies provide an important treatment option that seems to be highly efficacious, and warrants controlled clinical studies.

Source: Pretorius, Etheresia & Venter, Chantelle & Laubscher, Gert & Kotze, Maritha & Moremi, Kelebogile & Oladejo, Sunday & Watson, Liam & Rajaratnam, Kanshu & Watson, Bruce & Kell, Douglas. Combined triple treatment of fibrin amyloid microclots and platelet pathology in individuals with Long COVID/ Post-Acute Sequelae of COVID-19 (PASC) can resolve their persistent symptoms. Preprint from Research Square, 28 Dec 2021 https://assets.researchsquare.com/files/rs-1205453/v1_covered.pdf?c=1640805028 (Full text)

Sulodexide in the treatment of patients with long COVID 19 symptoms and endothelial dysfunction: The results of TUN-EndCOV study

Abstract:

Background: Endothelial dysfunction is probably one of the mechanisms of long COVID-19 symptoms. Sulodexide has pleiotropic properties within the vascular endothelium that can prove beneficial in the long COVID-19 symptoms.

Purpose: We aimed to evaluate the effect of sulodexide when used in patients with endothelial dysfunction and long COVID-19 symptoms.

Methods: We conducted a prospective multicenter longitudinal case-control study. Endothelial function was evaluated with DTM “E4-Diagnose” Polymath based on the Endothelium Quality Index (EQI). A group of patients with endothelial dysfunction (EQI < 2.0) received sulodexide. All the patients were followed-up 21 days after inclusion. Primary outcomes were defined as endothelial function amelioration (delta EQI) and long COVID-19 symptoms evolution during the follow-up.

Results: A total of 410 patients were included in this study. Patients were included at an average time of 1.89 ± 1.2 month after COVID-19 infection. At inclusion, 210 (51.2%) patients had an EQI < 2. The median age was 49 ± 13.8 (18–80) years. Among the patients with endothelial dysfunction, only 79 patients received sulodexide. Patients in sulodexide group had lower EQI than the non-medical intervention group (0.94 ± 0.6 vs. 1.52 ± 0.4; P < 10−3). They were more diabetic, hypertensive, had more coronary artery disease and received more long-term medications (aspirin, Bblockers and statins) than the others (P = 0.01, 0.002, 0.01, 0.009, 0.001 and 0.01, respectively). At the 21-days follow-up, patients in sulodexide group presented lower long COVID symptoms especially chest pain, palpitations, fatigue and neuro-cognitive difficulties associated to a significant amelioration of endothelial function (delta EQI 1.26 ± 1.07 vs. 0.22 ± 0.7; P < 10−3).

Conclusion: Sulodexide in patients with long COVID-19 may be a good intervention to ameliorate chest pain, palpitations, fatigue and neuro-cognitive difficulties associated to endothelial dysfunction.

Source: S. Charfeddine, H. Ibn Hadjamor, S. Torjmen, S. Kraiem, R. Hammami, A. Bahloul, N. Kallel, N. Moussa, I. Touil, J. Jdidi, S. Abdesselem, L. Abid. Sulodexide in the treatment of patients with long COVID 19 symptoms and endothelial dysfunction: The results of TUN-EndCOV study,
Archives of Cardiovascular Diseases Supplements. Volume 14, Issue 1, 2022, Page 127, ISSN 1878-6480,
https://doi.org/10.1016/j.acvdsp.2021.10.007. (https://www.sciencedirect.com/science/article/pii/S1878648021006455)

Endothelial dysfunction is the key of long COVID-19 symptoms: The results of TUN-EndCOV study

Abstract:

Background: The COVID-19 disease is a multisystem disease due to in part to the vascular endothelium injury. Lasting effects and long-term sequalae could persist after the infection and may be due to persistent endothelial dysfunction.

Purpose: Our study focused on the study of endothelial function measurement by digital thermal monitoring (DTM) of endothelial quality index with E4 diagnosis Polymath in a large cohort of long COVID-19 patients to determine whether long COVID-19 symptoms are due to endothelial dysfunction.

Methods: This is a prospective multicenter longitudinal observational cohort study. Endothelial function was evaluated with “E4-Diagnose” Polymath Tunisia based on the Endothelium Quality Index (EQI). A complete echocardiographic evaluation analysis was performed. Primary outcomes were defined as the occurrence of long COVID-19 symptoms in patients with endothelial dysfunction measured by EQI.

Results: A total of 798 patients were included in this study. Patients were included at an average time of 68.93 ± 43.1 days. The mean EQI was 2.02 ± 0.99 [0–5]. A total of 397 (49.7%) patients had poor or very poor EQI and 211 (26.4%) patients had very poor EQI. The median age was 49.94 ± 14.2 (18–80) years. A total of 618 patients (77.4%) had long COVID-19 symptoms. Patients with long COVID-19 symptoms had a reduced EQI (1.99 ± 0.97 vs. 2.09 ± 1.05, P = 0.24). Among long COVID-19 symptoms, fatigue was the most common symptom reported in 42.2%. Fatigue and chest pain were significantly associated to the endothelial dysfunction (P = 0.04 and 0.001 respectively). Patients with chest pain had significantly lower EQI (1.74 ± 1.0 vs. 2.09 ± 0.9, P ≤ 10−3) and LVGLS (−16.35 ± 3.0 vs. −17.16 ± 2.5, P = 0.04).

Conclusion: Long COVID-19 symptoms specifically chest pain and fatigue are due to persistent poor endothelial quality index. These findings allow a better care of patients with long COVID-19 symptoms.

Source: S. Charfeddine, H. Ibnhadjamor, S. Torjmen, S. Kraiem, R. Hammami, A. Bahloul, N. Kallel, N. Moussa, I. Touil, S. Milouchi, J. Elghoul, Z. Meddeb, Y. Thabet, J. Jdidi, K. Bouslema, S. Abdesselem, L. Abid. Endothelial dysfunction is the key of long COVID-19 symptoms: The results of TUN-EndCOV study. Archives of Cardiovascular Diseases Supplements, Volume 14, Issue 1, 2022, Page 126, ISSN 1878-6480, https://doi.org/10.1016/j.acvdsp.2021.10.004. (https://www.sciencedirect.com/science/article/pii/S187864802100642X)