A Descriptive and Quantitative Immunohistochemical Study Demonstrating a Spectrum of Platelet Recruitment Patterns Across Pulmonary Infections Including COVID-19

Antiplatelet therapy prior to COVID-19 infection impacts on patients mortality: a propensity score-matched cohort study

One of the major pathomechanisms of COVID-19 is the interplay of hyperinflammation and disruptions in coagulation processes, involving thrombocytes. Antiplatelet therapy (AP) by anti-inflammatory effect and inhibition of platelet aggregation may affect these pathways. The aim of this study was to investigate if AP has an impact on the in-hospital course and medium-term outcomes in hospitalized COVID-19 patients. The study population (2170 COVID-19 patients: mean ± SD age 60 ± 19 years old, 50% male) was divided into a group of 274 patients receiving any AP prior to COVID-19 infection (AP group), and after propensity score matching, a group of 274 patients without previous AP (non-AP group). Patients from the AP group were less frequently hospitalized in the intensive care unit: 9% vs. 15%, 0.55 (0.33-0.94), developed less often shock: 9% vs. 15%, 0.56 (0.33-0.96), and required less aggressive forms of therapy. The AP group had more coronary revascularizations: 5% vs. 1%, 3.48 (2.19-5.55) and strokes/TIA: 5% vs. 1%, 3.63 (1.18-11.2). The bleeding rate was comparable: 7% vs. 7%, 1.06 (0.54-2.06). The patients from the AP group had lower 3-month mortality: 31% vs. 39%, 0.69 (0.51-0.93) and didn't differ significantly in 6-month mortality: 34% vs. 41%, 0.79 (0.60-1.04). When analyzing the subgroup with a history of myocardial infarction and/or coronary revascularization and/or previous stroke/transient ischemic attack and/or peripheral artery disease, AP had a beneficial effect on both 3-month: 37% vs. 56%, 0.58 (0.40-0.86) and 6-month mortality: 42% vs. 57%, 0.63 (0.44-0.92). Moreover, the favourable effect was highly noticeable in this subgroup where acetylsalicylic acid was continued during hospitalization with reduction of in-hospital: 19% vs. 43%, 0.31 (0.15-0.67), 3-month: 30% vs. 54%, 044 (0.26-0.75) and 6-month mortality: 33% vs. 54%, 0.49 (0.29-0.82) when confronted with the subgroup who had acetylsalicylic acid suspension during hospitalization. The AP may have a beneficial impact on hospital course and mortality in COVID-19 and shouldn't be discontinued, especially in high-risk patients.

Pulmonary Parenchymal Changes in COVID-19 Survivors

BACKGROUND

As the COVID-19 pandemic moves into the survivorship phase, questions regarding long-term lung damage remain unanswered. Previous histopathologic studies are limited to autopsy reports. We studied lung specimens from COVID-19 survivors who underwent elective lung resections to determine whether postacute histopathologic changes are present.

METHODS

This multicenter observational study included 11 adult COVID-19 survivors who had recovered but subsequently underwent unrelated elective lung resection for indeterminate lung nodules or lung cancer. We compared these against an age- and procedure-matched control group who never contracted COVID-19 (n = 5) and an end-stage COVID-19 group (n = 3). A blinded pulmonary pathologist examined the lung parenchyma focusing on 4 compartments: airways, alveoli, interstitium, and vasculature.

RESULTS

Elective lung resection was performed in 11 COVID-19 survivors with asymptomatic (n = 4), moderate (n = 4), and severe (n = 3) COVID-19 infections at a median 68.5 days (range 24-142 days) after the COVID-19 diagnosis. The most common operation was lobectomy (75%). Histopathologic examination identified no differences between the lung parenchyma of COVID-19 survivors and controls across all compartments examined. Conversely, patients in the end-stage COVID-19 group showed fibrotic diffuse alveolar damage with intra-alveolar macrophages, organizing pneumonia, and focal interstitial emphysema.

CONCLUSIONS

In this study to examine the lung parenchyma of COVID-19 survivors, we did not find distinct postacute histopathologic changes to suggest permanent pulmonary damage. These results are reassuring for COVID-19 survivors who recover and become asymptomatic.

Platelet‐leukocyte interactions in COVID‐19: Contributions to hypercoagulability, inflammation, and disease severity

A State of the Art lecture titled "Platelet-leukocyte interactions in COVID-19: Contributions to hypercoagulability, inflammation and disease severity" was presented at the International Society for Thrombosis and Hemostasis (ISTH) congress in 2021. Severe coronavirus disease 2019 (COVID-19) has been associated with a high incidence of coagulopathy and thromboembolic events that contributes to disease severity and poor outcomes. Therefore, understanding the mechanisms of COVID-19-associated hypercoagulability and thromboinflammation has gained great interest. Here, we review the mechanisms involved in platelet activation and platelet interactions with leukocytes during COVID-19. We highlight recent evidence that platelet activation, platelet-monocyte, and platelet-neutrophil interactions in COVID-19 support pathological thromboinflammation, including in driving tissue factor expression and NETosis, which have been associated with thromboembolic complication and poor outcomes in critically ill patients. The contributions of platelet-leukocyte interactions to COVID-19 immunoregulation, inflammation, and hypercoagulability, as well as their potential implications in disease severity and therapeutic strategies, will be discussed. Finally, we summarize relevant new data on this topic presented during the 2021 ISTH Congress.

Upregulation of cytokine signalling in platelets increases risk of thrombophilia in severe COVID-19 patients

Abnormal coagulation dynamics, including disseminated intravascular coagulopathy, pulmonary embolism, venous thromboembolism and risk of thrombosis are often associated with the severity of COVID-19. However, very little is known about the contribution of platelets in above pathogenesis. In order to decipher the pathophysiology of thrombophilia in COVID-19, we recruited severely ill patients from ICU, based on the above symptoms and higher D-dimer levels, and compared these parameters with their asymptomatic counterparts. Elevated levels of platelet-derived microparticles and platelet-leukocyte aggregates suggested the hyperactivation of platelets in ICU patients. Strikingly, platelet transcriptome analysis showed a greater association of IL-6 and TNF signalling pathways in ICU patients along with higher plasma levels of IL-6 and TNFα. In addition, upregulation of pathways like blood coagulation and hemostasis, as well as inflammation coexisted in platelets of these patients. Further, the increment of necrotic pathway and ROS-metabolic processes in platelets was suggestive of its procoagulant phenotype in ICU patients. This study suggests that higher plasma IL-6 and TNFα may trigger platelet activation and coagulation, and in turn aggravate thrombosis and hypercoagulation in severe COVID-19 patients. Therefore, the elevated IL-6 and TNFα, may serve as potential risk factors for platelet activation and thrombophilia in these patients.

Platelet-monocyte interaction amplifies thromboinflammation through tissue factor signaling in COVID-19

Accumulating evidence into the pathogenesis of COVID-19 highlight a hypercoagulability state with high risk of life-threatening thromboembolic complications. However, the mechanisms of hypercoagulability and their link to hyperinflammation remain poorly understood. Here we investigate functions and mechanisms of platelet activation and platelet-monocyte interactions in inflammatory amplification during SARS-CoV2 infection. We used a combination of immunophenotyping, single cell analysis, functional assays and pharmacological approaches to gain insights on mechanisms. Critically ill COVID-19 patients exhibited increased platelet-monocyte aggregates formation. We identified a subset of inflammatory monocytes presenting high CD16 and low HLA-DR expression as the subset mainly interacting with platelets during severe COVID-19. Single cell RNAseq analysis indicated enhanced fibrinogen receptor Mac-1 in monocytes from severe COVID-19 patients. Monocytes from severe COVID-19 patients displayed increased platelet binding and hyperresponsiveness to P-selectin and fibrinogen with respect to TFN-α and IL-1β secretion. Platelets were able to orchestrate monocyte responses driving TF expression, inflammatory activation and inflammatory cytokines secretion in SARS-CoV-2 infection. Platelet-monocyte interactions ex-vivo and in SARS-CoV-2 infection model in vitro reciprocally activated monocytes and platelets, inducing the heightened secretion of a wide panel of inflammatory mediators. We identified platelet adhesion as a primary signaling mechanism inducing mediator secretion and TF expression, while TF signaling played major roles in amplifying inflammation by inducing proinflammatory cytokines, especially TNF-α and IL-1β. Our data identify platelet-induced TF expression and activity at the crossroad of coagulation and inflammation in severe COVID-19.

A guide to molecular and functional investigations of platelets to bridge basic and clinical sciences

Platelets have been shown to be associated with pathophysiological process beyond thrombosis, demonstrating critical additional roles in homeostatic processes, such as immune regulation, and vascular remodeling. Platelets themselves can have multiple functional states and can communicate and regulate other cells including immune cells and vascular smooth muscle cells, to serve such diverse functions. Although traditional platelet functional assays are informative and reliable, they are limited in their ability to unravel platelet phenotypic heterogeneity and interactions. Developments in methods such as electron microscopy, flow cytometry, mass spectrometry, and 'omics' studies, have led to new insights. In this Review, we focus on advances in platelet biology and function, with an emphasis on current and promising methodologies. We also discuss technical and biological challenges in platelet investigations. Using coronavirus disease 2019 (COVID-19) as an example, we further describe the translational relevance of these approaches and the possible 'bench-to-bedside' utility in patient diagnosis and care.

Of vascular defense, hemostasis, cancer, and platelet biology: an evolutionary perspective

We have established considerable expertise in studying the role of platelets in cancer biology. From this expertise, we were keen to recognize the numerous venous-, arterial-, microvascular-, and macrovascular thrombotic events and immunologic disorders are caused by severe, acute-respiratory-syndrome coronavirus 2 (SARS-CoV-2) infections. With this offering, we explore the evolutionary connections that place platelets at the center of hemostasis, immunity, and adaptive phylogeny. Coevolutionary changes have also occurred in vertebrate viruses and their vertebrate hosts that reflect their respective evolutionary interactions. As mammals adapted from aquatic to terrestrial life and the heavy blood loss associated with placentalization-based live birth, platelets evolved phylogenetically from thrombocytes toward higher megakaryocyte-blebbing-based production rates and the lack of nuclei. With no nuclei and robust RNA synthesis, this adaptation may have influenced viral replication to become less efficient after virus particles are engulfed. Human platelets express numerous receptors that bind viral particles, which developed from archetypal origins to initiate aggregation and exocytic-release of thrombo-, immuno-, angiogenic-, growth-, and repair-stimulatory granule contents. Whether by direct, evolutionary, selective pressure, or not, these responses may help to contain virus spread, attract immune cells for eradication, and stimulate angiogenesis, growth, and wound repair after viral damage. Because mammalian and marsupial platelets became smaller and more plate-like their biophysical properties improved in function, which facilitated distribution near vessel walls in fluid-shear fields. This adaptation increased the probability that platelets could then interact with and engulf shedding virus particles. Platelets also generate circulating microvesicles that increase membrane surface-area encounters and mark viral targets. In order to match virus-production rates, billions of platelets are generated and turned over per day to continually provide active defenses and adaptation to suppress the spectrum of evolving threats like SARS-CoV-2.

Post-mortem lung tissue: the fossil record of the pathophysiology and immunopathology of severe COVID-19

The lungs are the main site that is affected in severe COVID-19, and post-mortem lung tissue provides crucial insights into the pathophysiology of severe disease. From basic histology to state-of-the-art multiparameter digital pathology technologies, post-mortem lung tissue provides snapshots of tissue architecture, and resident and inflammatory cell phenotypes and composition at the time of death. Contrary to early assumptions that COVID-19 in the lungs is a uniform disease, post-mortem findings have established a high degree of disease heterogeneity. Classic diffuse alveolar damage represents just one phenotype, with disease divisible by early and late progression as well as by pathophysiological process. A distinct lung tissue state occurs with secondary infection; extrapulmonary causes of death might also originate from a pathological process in the lungs linked to microthrombosis. This heterogeneity of COVID-19 lung disease must be recognised in the management of patients and in the development of novel treatment strategies.

α-Ketoglutarate Inhibits Thrombosis and Inflammation by Prolyl Hydroxylase-2 Mediated Inactivation of Phospho-Akt

Background

Phospho-Akt1 (pAkt1) undergoes prolyl hydroxylation at Pro125 and Pro313 by the prolyl hydroxylase-2 (PHD2) in a reaction decarboxylating α-ketoglutarate (αKG). We investigated whether the αKG supplementation could inhibit Akt-mediated activation of platelets and monocytes, in vitro as well as in vivo, by augmenting PHD2 activity.

Methods

We treated platelets or monocytes isolated from healthy individuals with αKG in presence of agonists in vitro and assessed the signalling molecules including pAkt1. We supplemented mice with dietary αKG and estimated the functional responses of platelets and monocytes ex vivo. Further, we investigated the impact of dietary αKG on inflammation and thrombosis in lungs of mice either treated with thrombosis-inducing agent carrageenan or infected with SARS-CoV-2.

Findings

Octyl αKG supplementation to platelets promoted PHD2 activity through elevated intracellular αKG to succinate ratio, and reduced aggregation in vitro by suppressing pAkt1(Thr308). Augmented PHD2 activity was confirmed by increased hydroxylated-proline and enhanced binding of PHD2 to pAkt in αKG-treated platelets. Contrastingly, inhibitors of PHD2 significantly increased pAkt1 in platelets. Octyl-αKG followed similar mechanism in monocytes to inhibit cytokine secretion in vitro. Our data also describe a suppressed pAkt1 and reduced activation of platelets and leukocytes ex vivo from mice supplemented with dietary αKG, unaccompanied by alteration in their number. Dietary αKG significantly reduced clot formation and leukocyte accumulation in various organs including lungs of mice treated with thrombosis-inducing agent carrageenan. Importantly, in SARS-CoV-2 infected hamsters, we observed a significant rescue effect of dietary αKG on inflamed lungs with significantly reduced leukocyte accumulation, clot formation and viral load alongside down-modulation of pAkt in the lung of the infected animals.

Interpretation

Our study suggests that dietary αKG supplementation prevents Akt-driven maladies such as thrombosis and inflammation and rescues pathology of COVID19-infected lungs.

Funding

Study was funded by the Department of Biotechnology (DBT), Govt. of India (grants: BT/PR22881 and BT/PR22985); and the Science and Engineering Research Board, Govt. of India (CRG/000092).

Alterations in platelets during SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) is a pandemic syndrome caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. SARS-CoV-2 infection induces a process of inflammation and thrombosis supported by an altered platelet activation state. This platelet activation is peculiar being characterized by the formation of platelet-leukocytes rather than platelet–platelet aggregates and by an increased procoagulant potential supported by elevated levels of TF positive platelets and microvesicles.

Therapeutic strategies targeting, beyond systemic inflammation (i.e. with tocilizumab, an anti interleukin-6 receptor), this state of platelet activation might therefore be beneficial. Among the antithrombotic drugs proposed as candidates to treat patients with SARS-CoV-2 infection, antiplatelet drugs, such as aspirin are showing promising results.

Platelet-leukocyte interactions in the pathogenesis of viral infections

Evolving evidence demonstrates that platelets have major roles in viral syndromes through previously unrecognized viral sensing and effector functions. Activated platelets and increased platelet-leukocyte aggregates are observed in clinical and experimental viral infections. The mechanisms and outcomes of platelet-leukocyte interactions depend on the interacting leukocyte as well as on the pathogen and pathological conditions. In this review, we discuss the mechanisms involved in platelet interactions with leukocytes and its functions during viral infections. We focus on the contributions of human platelet-leukocyte interactions to pathophysiological and protective responses during viral infections of major global health relevance, including acquired immunodeficiency syndrome (AIDS), dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), influenza pneumonia, and COVID-19.

A series of COVID-19 autopsies with clinical and pathologic comparisons to both seasonal and pandemic influenza

Autopsies of patients who have died from COVID‐19 have been crucial in delineating patterns of injury associated with SARS‐CoV‐2 infection. Despite their utility, comprehensive autopsy studies are somewhat lacking relative to the global burden of disease, and very few comprehensive studies contextualize the findings to other fatal viral infections. We developed a novel autopsy protocol in order to perform postmortem examinations on victims of COVID‐19 and herein describe detailed clinical information, gross findings, and histologic features observed in the first 16 complete COVID‐19 autopsies. We also critically evaluated the role of ancillary studies used to establish a diagnosis of COVID‐19 at autopsy, including immunohistochemistry (IHC), in situ hybridization (ISH), and electron microscopy (EM). IHC and ISH targeting SARS‐CoV‐2 were comparable in terms of the location and number of infected cells in lung tissue; however, nonspecific staining of bacteria was seen occasionally with IHC. EM was unrevealing in blindly sampled tissues. We then compared the clinical and histologic features present in this series to six archival cases of fatal seasonal influenza and six archival cases of pandemic influenza from the fourth wave of the ‘Spanish Flu’ in the winter of 1920. In addition to routine histology, the inflammatory infiltrates in the lungs of COVID‐19 and seasonal influenza victims were compared using quantitative IHC. Our results demonstrate that the clinical and histologic features of COVID‐19 are similar to those seen in fatal cases of influenza, and the two diseases tend to overlap histologically. There was no significant difference in the composition of the inflammatory infiltrate in COVID‐19 and influenza at sites of acute lung injury at the time of autopsy. Our study underscores the relatively nonspecific clinical features and pathologic changes shared between severe cases of COVID‐19 and influenza, while also providing important caveats to ancillary methods of viral detection.