COVID-19’s immuno-pathology and cardiovascular diseases

Abstract

The pandemic of COVID-19 in worldwide causes recent millions of morbidity and mortality in all countries and is the most important challenge in the world in recent years. Coronavirus is a single-stranded RNA virus and infection with COVID-19 leads to acute respiratory distress syndrome, lung inflammation, cytokine storm, and death. The other complications include endothelial dysfunction, activation of coagulation, thromboembolic events, and vascular disease. Cardiovascular complications such as myocardial and stroke ischemia, pulmonary thromboembolism, systemic arterial, and deep vein thrombosis were reported. In this review, we presented immuno-pathological mechanisms and the effects of COVID-19 on the cardiovascular system, heart, vessels, coagulation system, and molecular glance of immuno-inflammation to the COVID-19’s pathology on the cardiovascular system.

• The COVID-19 has strong effect on cardiovascular system.

• Endothelial dysfunction, myocardial ischemia, and arterial and vein thromboembolism are the side effects of SARS-CoV-2.

• In COVID-19, the inflammation dysregulates cardiac ion channels which results in arrhythmia.

• These downstream effects of COVID-19 result in cardiac valvular disease.

Introduction

COVID-19, a recently discovered disease, is circulated rapidly worldwide and this pandemic involved more than several hundred million cases that were diagnosed and confirmed; also, these numbers have continued to increase. Clinically, the COVID-19 is markedly heterogeneous and has range from asymptomatic form to severe viral pneumonia and may progress to cytokine storm (CS), acute respiratory distress syndrome (ARDS), and death.^1,2

SARS-CoV-2 is an enveloped novel strain in the coronavirus family, singled-stranded positive-sense RNA viruses. Additional other members of this family are SARS-CoV-1 and MERS-CoV. The rapid spread of COVID-19, caused by SARS-CoV-2, leads to ARDS in patients. Recent studies indicate that in SARS-CoV-2, CS and hyper-inflammation contribute to disease severity and COVID-19 mortality.^1,3,4 The rapid transmission and divergent presentation of the SARS-CoV-2 strengthened the COVID-19’s status as a major public health threat.^5,6 The hyper-inflammatory syndrome in COVID-19 results from a dysregulated innate immune response of the patients. The potential therapeutic approaches to the immune system modulation and abrogate lung injury in COVID-19 are necessary.^1,7

Although the COVID-19 in the world has been substantial, concerns have arisen about the direct and indirect effects of the pandemic on higher-risk patients with cardiovascular disease (CVD). During the COVID-19 pandemic, hospitalizations for acute CVD, including heart failure, myocardial infarction (MI), and stroke, have declined precipitously. Population deaths due to cardiovascular causes were increased over this period and may also inform public health responses and policy efforts in states. CVD is associated with increasing mortality among hospitalized COVID-19 patients. Identifying the significant risk factors is urgent to reduce the risk of hospitalized patients. Therefore, in this study, we aimed to overview the immune-inflammatory responses of COVID-19 and its effect on the CVD such as heart failure, congenital heart disease, coronary heart disease, ischemic heart disease, hypertensive problems, and other diseases of circulatory system. Also, the COVID-19’s impact on the heart, CVD, summarizing the pathophysiological basis and the clinical management of these patients, and ultimately reduce mortality.^8–10

Pathology and pathogenesis

SARS-CoV-2 uses the angiotensin-converting enzyme-2 (ACE2) receptor for cell entry in humans. The predominant lung injury pattern in COVID-19 was identified as diffuse alveolar hemorrhage and damage accompanied by platelet–fibrin–microthrombi in the pulmonary vessels. On the postmortem analysis, congested and diffusely edematous of the lung parenchyma, and clinical diagnosis of ARDS were observed. Pathologic features accompanying the interstitial and intra-alveolar exudate have dilated alveolar and collapsed alveoli, capillary congestion, formation of hyaline membrane, and pneumocytes desquamation. Viral particles within pneumocytes type 1 and 2, and localized SARS-CoV-2 antigen to the ACE2 bronchiolar epithelium are dominant. The microthrombosis was present in the small- and medium-pulmonary arterial vessels and CD61 megakaryocytes were increased in alveolar capillaries. In COVID-19, direct viral invasion via the ACE2 receptor may trigger endotheliitis and contribute to endothelial injury.^1,11,12

Patients with COVID-19 have infiltration of the mononuclear inflammatory cells (lymphocytes and macrophages) in the lung parenchyma. The infiltrated lymphocytes are T cells (CD4 and CD8) in the bronchioles and alveoli, and CD4 T-cells are predominance, which aggregate around small vessels that often contained microthrombi. The CD68 macrophages were also localized in the alveolar lumen.^1,13,14

Immune-inflammatory response

Innate immunity, as the first line of defense, has a key role in inhibiting in the COVID-19. Pathogen-associated molecular patterns (PAMPs) of the SARS-CoV-2 such as viral genomic single-stranded ribonucleic acid (ssRNA), replication of double-stranded ribonucleic acid, and proteins are recognized by pattern-recognition receptors (PRRs). Coronavirus ssRNA is sensed by endosomal toll-like receptors (TLR)3 and TLR7. Likewise, RIG-I and MDA5, as cytoplasmic RNA sensors, mediate signaling in the induction of antiviral interferon responses and respond to coronavirus RNAs. Stimulator of interferon genes (SING), as another PRR, is a cytosolic DNA sensor, and SING-mediated signaling was reported following coronavirus infections. The PAMP-PRR interactions result in the transcription factor activation of inflammation promoting, which contribute to the expression of interferon-I (IFN-I) and other proinflammatory cytokines.^15–17 Viral replication also stimulates the production of chemokines such as IL8, IP10, and MCP1, leading to the accumulation of new sources for proinflammatory mediators. SARS-CoV Viroporin 3a stimulates the NLR-P3 inflammasome and the secretion of IL-1β, which contributes to pyroptosis. Adaptive immune response against COVID-19 is categorized into humoral via neutralizing antibodies (IgM and/or IgG) and cellular responses via CD8+ cytotoxic T cells against intracellular viruses. Both of the elements are regulated by antigen-specific CD4+ T cells.^15,18–20

Cytokine storm

In COVID-19 patients, enhanced clinical inflammatory markers were prognostic of mortality and disease severity. ARDS is higher in the patients with elevated C-reactive protein (CRP), lactate dehydrogenase (LDH), ferritin, PGF, VEGF, FGF, G-CSF, GM-CSF, IP-10, MCP-1, MIP-1a and b, IFN-γ, TNF-α, IL-1b, IL-2, IL-6, IL-7, and IL-8 levels.^1,21,22

SARS-CoV-2, as a cytopathic virus, induces cell death during replication. Viral replication in cells causes high levels of pyroptosis (inflammatory form of programed cell death), that is hyper-inflammatory response to SARS-CoV-2 infection and releases IL-1b from cells. Resident alveolar macrophages and lung epithelial cells detect the PAMP such as viral RNA, using several PRR. The PRR and IL-1R activation stimulate the secretion of pro-inflammatory cytokines, which recruit activated T cells and macrophages to the infection site, whereby these immune effector cells potentiate inflammatory reaction with additional cytokine secretion and lung parenchyma destruction.^1,23–25 The cytokine profile in COVID-19 patients is Th1 and classic M1 macrophage is predominant. Also, ACE2-infected pneumocytes express high levels of pro-inflammatory cytokines (i.e., IL-1b, MCP-1, IL-6, and TNF-α). On the other hand, severe COVID-19 patients have increased TLR, IL-1R, and downstream signaling molecules (i.e., TRAF6, IRAK1, IRAK4, MYD88, and p65) expression that have strong effect on inflammation. Therefore, identifying the exact drivers of the pathologic inflammation and immune markers that predict a hyperinflammatory response to SARS-CoV-2 infection is important.^1,24,26,27

CVD and COVID-19

The CVD and hypertension are the most common comorbidities in patients with COVID-19, which are associated with the severity of COVID-19. The several cardiovascular biomarkers are elevated in severe COVID-19 cases. Angiotensin I is converted to angiotensin II by ACE1 and angiotensin II is converted to angiotensin 1–7 (Ang 1–7) by ACE2 that induces vasodilatory response. However, ACE inhibitor/angiotensin-receptor blocker therapy in patients increase the risk of SARS-CoV-2 infection and severity. In addition, in patients with CVD, the cardiotoxicity of antiviral therapies with cardiovascular drugs should be paid attention in COVID-19.^28–31

These involvements of the cardiovascular with COVID-19 can be explained by the several mechanisms. First, the systemic oxidative stress in SARS that is induced by hypoxemia directly damages cardiomyocytes, via mitochondrial damage and intracellular acidosis. Second, ACE2 receptors on the cardiovascular system can dysregulate the renin–angiotensin–aldosterone system (RAAS), leading to ventricular remodeling that alters myocardial demand and further induces cardiomyocyte damage. Third, in the CS of COVID-19 infection, mononuclear inflammatory infiltrate cells in cardiac interstitial are dominant. Finally, local and systemic effects of immune system induce cardiac microvasculature damage resulting in perfusion defects.^28,32–35

The cumulative cardiomyocyte damage elucidated may result in increased levels of hscTn1, CK, troponin, furthermore, D-dimer, and prothrombin levels in hypercoagulable state which are associated with poor outcomes in COVID-19 patients. Elevation of the troponin is associated with the increased risk of mortality and adverse outcomes in COVID-19 patients. Therefore, in COVID-19 patients, coronary angiography and primary percutaneous coronary intervention are necessary.^28,36,37

Cardiovascular cellular pathogenesis

The SARS-CoV-2 enters into the cells via binding to the ACE2. SARS-CoV-2 internalizes and downregulates the ACE2 expression on the cell surface. Since ACE2 converts angiotensin I and II to angiotensin 1–9 and 1–7 cardioprotective peptides, its loss on cell surface potentiates cardiac damage. In addition, the ACE2 loss on endothelium exacerbates endothelial dysfunction, inflammation, and thrombosis. Also, the reduced ACE2 induces cytokine release through dysregulating RAAS, depresses ACE2/Mas receptor axis, and activates ACE2/bradykinin B1R/DABK axis. The cardiac complications in COVID-19 patients can be divided into electrical and mechanical dysfunction. In arrhythmias, the electrical aberrance is seen, whereas vascular, pericardial, myocardial, and valvular complications arise due to mechanical dysfunction.^38–42

Arrhythmia in COVID-19 patients can be secondary activated by pulmonary disease, drug side effects, electrolyte imbalance, protein kinase C (PKC), and direct oxidized Ca2+/CAMKII (calmodulin-dependent protein kinase II). PKC is activated by angiotensin II and can initiate arrhythmias. Hypo Ca2+ and hypo Mg2+ are commonly seen in COVID-19 patients due to angiotensin II-mediated urinary excretion. The hypoxia in ARDS increases the arrhythmias risk. The upregulated angiotensin II activates NADPH oxidase (increases the reactive oxygen species (ROS)) that oxidizes the CaMKII into ox-CaMKII and the ox-CaMKII in turn phosphorylates RyR2, and increases diastolic sarcoplasmic Ca2+ leak that induces atrial and ventricular arrhythmias. In COVID-19, the inflammation dysregulates the post-translational modification of cardiac ion channels resulting in arrhythmia.^38,43–45

Elevated angiotensin II facilitates inflammatory cascade, elevated IL-6, and VEGF. These pro-inflammatory cytokines promote fibrosis and inflammation that present as pericarditis. On the other side, SARS-CoV-2 can cause pericarditis which progresses to pericardial effusion and can further complicate Takotsubo cardiomyopathy. In COVID-19, myocardial dysfunction presents as acute coronary syndrome, myocarditis, cardiomyopathy, heart failure, and shock. SARS-CoV-2 can induce systemic inflammatory response syndrome through a combination of CS and dysregulated immune activity which leads to myocardial dysfunction. In the CS of the SARS-CoV-2 infection, cytokines contribute to the damage of the myocard by facilitating the release of ROS, endogenous NO, and superoxide anion.^38,46–48 Finally, damage-associated molecular proteins (DAMPs) like heat-shock proteins, HMGB1, oxidized lipoproteins, and histones are released from the damaged myocardial cells and further activate the inflammation and also myocytes damage. These excessive DAMPs create an ongoing defective inflammatory cycle resulting in septic/COVID-19 cardiomyopathy. The ACE2 is broadly expressed on the stromal fibroblasts of the cardiac valves, especially aortic valves and in stenotic valves, the ACE2 expression is downregulated. The depression of ACE2/angiotensin-(1–7)/Mas receptor axis potentiates inflammation, fibrosis, and valvular sclerosis (Figure 1). These downstream effects of COVID-19 result in the damage of the valves, which may present chronically due to the slow progressive nature of cardiac valvular disease.^38,49,50

Figure 1.

The SARS-Cov-2 enters via respiration and is localized in pneumocytes via ACE2- that is dominant in bronchiolar epithelium and can active immune response (innate and adaptive) against COVID-19. Pneumonia and ARDS are main problems in COVID-19. Inflammation, pro-inflammatory cytokines release, and CS lead to the structural and functional (mechanical and electrical) CVD (cardiomyopathy, endomyocardial, pericarditis, arrhythmia, etc.) and coagulopathy (microthrombi, thromboembolism, ischemia, DIC, etc.).

ANG, angiotensin; ACE, angiotensin-converting enzyme; ARDS, acute respiratory distress syndrome; CS, cytokine storm; CVD, cardiovascular disease; DIC, disseminated intravascular coagulation.

Myocardial injury

COVID-19 patients with myocardial injury have elevated CRP, procalcitonin, and NT-proBNP that are associated with increased risk of in-hospital mortality. The mechanism of myocardial injury in COVID-19 may involve a direct myocyte injury with viral infection, and significant inflammation provoked by cytokine dysregulation.^5,51–54

Endomyocardial biopsies from COVID-19 patients demonstrated the presence of lymphocytic infiltrates in the right ventricular myocardium, cardiomyocyte hypertrophy, and necrosis, and also macrophage infiltration in the myocardium. Potential etiologies with the COVID-19 include myocarditis, cardiac microvascular and coronary disease, ischemic injury, septic cardiomyopathy, Takotsubo’s cardiomyopathy, and secondary hypoxic injury.^5,55,56

Non-invasive diagnostic tools such as electrocardiography (ECG) and cardiac imaging (including echocardiography, magnetic resonance imaging, and computed tomography imaging) determine the extent of cardiac structure and function in the setting of COVID-19 infection. ECG abnormalities, such as PR depression and ST elevation, may be observed in myocarditis, but these are not conclusive.^5,57,58

Coagulopathy

Overproduction of pro-inflammatory cytokines in the immune response to SARS-CoV-2 activates the coagulation cascade. Some cytokines facilitate the adhesion of platelets by increasing the production of Von Willebrand factor. Moreover, high levels of IL-1, IL-6, TNF-α, and thrombin promote clot formation in COVID-19 patients by activating platelets. Also, thrombin activates the PAR-1, and endothelial cells (ECs) upregulate the expression of tissue factor (TF) at mucosal surfaces. Tissue factor activates the extrinsic pathway of the coagulation, downregulates the activated protein C that is an inhibitor of clotting, and inhibits the fibrinolytic processes. Moreover, plasminogen activator inhibitor-1 upregulation blocks the plasminogen activation, thus decreases the breakdown of fibrin clots.^5,59–62

An imbalance between coagulants and anti-coagulants promotes the pro-coagulation state. This can explain the presence of pulmonary microthrombi and disseminated intravascular coagulation (DIC) diagnosed in critically COVID-19 patients. The formation of microthrombi increases venous thromboembolism incidence and its related problems.^5,63–65

Thrombotic complications

There are substantial evidences for a significant risk of thrombosis in COVID-19 patients. Complications may include pulmonary embolism (PE), deep-vein thrombosis, systemic arterial embolism, ischemia, and MI. Usually, these patients have abnormal coagulation parameters, such as D-dimer and activated partial thromboplastin time. Important risk factors of the venous thrombosis involve endothelial injury, stasis, and a hypercoagulable state, together known as Virchow’s triad.^66–71

Inflammation has a main role in thrombosis through perpetuating a hypercoagulable state and endothelial injury that can be done via fibrinolysis reduction, stimulation of the TF pathway, and NETosis. Also, complement activation is involved in thrombosis. The C3a and membrane attack complex (C5b-9) are involved in platelet activation and C5a enhances plasma and cellular TF expression. These intravascular pulmonary microthrombi are linked to the development of hypoxemia in the early stages of ARDS in COVID-19. Primary pulmonary thrombosis could be underpinned by ACE2-mediated CS, endothelial injury, and the development of a hypercoagulable state in patients with COVID-19.^66,72–74

Myocardial and microvascular injuries by SARS-CoV-2 cause sub-endothelium and collagen exposure, which lead to platelet activation and possible contact pathway activation follows polyphosphate release in platelet degranulation. Endothelial trauma actives the TF pathway via the cleavage of FVII to FVIIa and also, ACE2-SARS-CoV-2 interactions dysregulate the kallikrein/kinin system. Inflammation due to SARS-CoV-2 generates inflammatory mediators such as CRP and pro-inflammatory cytokines. IL-6 is a key regulator of fibrinogen transcription and increases the level of plasma fibrinogen. Interestingly, SARS-CoV-2’ RNAs have interaction with platelets via TLR7 and 9 in a similar way to stimulate cytokine releasing and leukocytes activation.^66,75–77

The balance between thrombolysis and thrombus is maintained by tissue-type plasminogen activator (tPA), urinary-type plasminogen activator (uPA), and their inhibitor PAI-1. In COVID-19 patients, impaired tPA and uPA fibrinolytic function further perpetuates a pro-thrombotic state. Hyperactivity of the fibrinolytic is supported by significant rises in D-dimer. On the other side, pro-inflammatory cytokines trigger EC activation and the release of PAI-1 and tPA. DIC is a potentially lethal mechanism that leads to multi-organ dysfunction and fibrinolysis derangement in COVID-19. The DIC pathophysiology in SARS-CoV-2 includes EC, leukocyte, and platelet activation, fibrin deposition, resulting in diffuse inflammation and coagulopathy.^66,78–80

It was proposed that the COVID-19 microthrombus phenotype aligns more closely with complement-mediated thrombotic microangiopathy that is supported by the presence of anemia, elevated LDH, and renal dysfunction in severe SARS-CoV-2 cases. Microvascular dysfunction in SARS-CoV-2 via ACE2 receptor interactions and mannan-binding lectin serine protease (MASP) MASP-2 in the lectin pathway of complement activation is done. MASP-1 and -2 can cleave prothrombin to form thrombin and activate FXIII and fibrinogen, but future studies are needed to address the role of MASPs in COVID-19.^66,81–83

Immuno-inflammatory biomarkers in CVD

Several immune-inflammatory biomarkers were explored in COVID-19 patients for possible monitoring of patients with CVD and treatment, which include full blood cells count, D-dimer, APTT and prothrombin time, cytokines, CRP, and other inflammatory markers such as CRP, fibrinogen, ferritin, IL-2, 6, 7, and TNF-α.^66,84–86

D-dimer is an important prognostic marker for COVID-19 mortality. Thrombocytopenia in SARS-CoV-2 is observed due to intravascular pulmonary microthrombus formation. However, thrombocytopenia in COVID-19 rarely results in a bleeding phenotype. Elevation of the inflammatory markers is observed 7–14 days after initial onset. IL-6, as a main inflammatory cytokine, decreased during intensive care unit (ICU) admission. CRP is also elevated in the hospitalized COVID-19 patients. Furthermore, CRP levels are linked with elevated cardiac troponins and also myocardial injury. Serum ferritin, as a potential prognostic inflammatory marker in COVID-19, is a cellular damage marker.^66,87–90 Elevated ferritin is associated with ICU admission and in-hospital mortality. Troponins T and I as cardiac-specific markers are highly sensitive to myocardial damage and released into the blood following heart trauma or infection. Elevated troponin is associated with myocarditis, MI, and PE resulting in myocardial ischemia. Troponin is consistently elevated in SARS-Cov-2 infection and considered a marker of poor prognosis. However, it should be confirmed in ICU admission patients, in-hospital mortality, and comorbidity.^{36,66,91–95}

Lung vascular immunopathology

Pathology of the lung in COVID-19 patients shows marked hemorrhage and microvascular thrombosis linked to interstitial and alveolar inflammation. Lung-restricted vascular immunopathology, as diffuse pulmonary intravascular coagulopathy in COVID-19, is an early stage of DIC. The immune mechanism underlying pulmonary interstitial and alveolar inflammation triggers extensive immunothrombosis.^96–100

IL-1, IL-6, and TNF-α trigger EC activation and dysfunction, determine vessel wall permeability, vasculopathy, thromboinflammatory, ventilation perfusion mismatch, and a clinical phenotype of refractory ARDS. Innate immune response, dysregulation of ACE2 expression, and adaptive antiviral immune responses in COVID-19 contribute to extensive pulmonary immunovascular coagulopathy, pulmonary immunothrombosis, and diffuse pulmonary intravascular coagulopathy.^96,101–110

Pulmonary artery problems in COVID-19

One of the serious COVID-19 complication is thrombosis, and prophylactic anticoagulation to prevent thrombosis and reduce mortality is necessary.^111,112 In-hospital, the acute PE rate is higher in ICU patients than in hospitalized general wards that may reflect a more severe pro-coagulant state. Therefore, the higher rate in COVID-19 patients makes it urgent to establish the antithrombotic treatment to minimize the risk in patients. Indeed, the immunothrombosis scenario is triggered by the SARS-CoV-2 infection, and EC dysfunction in the pulmonary microvasculature plays an important role in the thromboinflammatory processes. In this regard, CS and macrophage activation syndrome could trigger activating the coagulation cascade. Immune responses in local lymph nodes against pathogens (such as corona virus) can have strong effect on target tissue. At least, immunothrombosis prevention by standard thromboprophylaxis and available anticoagulant regiments is necessary.^113–115

One of the potential pulmonary morbidities in COVID-19 patients is the tendency to thromboembolic phenomena. Also, chronic thromboembolic pulmonary hypertension (CTEPH) was reported in a series of patients with acute PE after COVID-19 pneumonia. It is possible that recovered patients from COVID-19 may develop the chronic thromboembolic disease, CTEPH, and PH secondary to lung disease.^116,117 In COVID-19 patients (even in non-advanced disease), pulmonary parenchymal damage and altered hemodynamics determine pulmonary hypertension and right ventricular involvement.¹¹⁸ Post-PE clinical syndrome results from the mix of heterogeneous factors, from deconditioning to hemodynamic derangements. And also, the combination of viral pneumonia and ARDS is a possible precursor to pulmonary fibrosis.¹¹⁹ Therefore, immunomodulatory and anti-complement treatments to reduce the inflammatory cascade in COVID-19 are necessary and in routine, post-COVID-19 follow-up should be done in all COVID-19 patients.

Concluding remarks

COVID-19 infection is linked to myocardial injury and leads to severe disease progression. The main mechanism of myocardial injury is immune-inflammatory responses against SARS-Cov-2. SARS-CoV-2 with its receptor, the ACE2 involve in CVD and by inflammation and cytokines, involve immune system with cardiovascular system. ARDS is the main issue in COVID-19 patients that is initiated by cytokine hyper secretion and can have dangerous effect on cardiovascular system, and coagulopathy is another problem in COVID-19 patients. The interplay between the inflammation, immune response, coagulation, and CVD in COVID-19 requires further research, to establish their pathophysiology mechanism of the disease in further detail. In addition, the relationship between CVD pathogenesis and immune response in SARS-Cov-2 infection needs deep survey to have applicable prophylactic and therapeutic protocols for control and management of CVD in COVID-19 patients. Therefore, more attention to cardiovascular injury and CVD in patients with COVID-19 infection is necessary for prevention and limitation of the morbidity and mortality.