Do Circulating Histones Represent the Missing Link among COVID-19 Infection and Multiorgan Injuries, Microvascular Coagulopathy and Systemic Hyperinflammation?

Monocyte distribution width alterations and cytokine storm are modulated by circulating histones

OBJECTIVES

Extracellular histone levels are associated with the severity of many human pathologies, including sepsis and COVID-19. This study aimed to investigate the role of extracellular histones on monocyte distribution width (MDW), and their effect on the release of cytokines by blood cells.

METHODS

Peripheral venous blood was collected from healthy subjects and treated with different doses of a histone mixture (range 0-200 μg/mL) to analyze MDW modifications up-to 3 h and digital microscopy of blood smears. Plasma obtained after 3 h of histone treatment were assayed to evaluate a panel of 24 inflammatory cytokines.

RESULTS

MDW values significantly increased in a time- and dose-dependent manner. These findings are associated with the histone-induced modifications of cell volume, cytoplasmic granularity, vacuolization, and nuclear structure of monocytes, promoting their heterogeneity without affecting their count. After 3 h of treatment almost all cytokines significantly increased in a dose-dependent manner. The most relevant response was shown by the significantly increased G-CSF levels, and by the increase of IL-1β, IL-6, MIP-1β, and IL-8 at the histone doses of 50, 100, and 200 µg/mL. VEGF, IP-10, GM-CSF, TNF-α, Eotaxin, and IL-2 were also up-regulated, and a lower but significant increase was observed for IL-15, IL-5, IL-17, bFGF, IL-10, IFN-γ, MCP-1, and IL-9.

CONCLUSIONS

Circulating histones critically induce functional alterations of monocytes mirrored by MDW, monocyte anisocytosis, and hyperinflammation/cytokine storm in sepsis and COVID-19. MDW and circulating histones may be useful tools to predict higher risks of worst outcomes.

COVID-19 and Biomarkers: The Contribution of the Journal

Three years after coronavirus disease 2019 (COVID-19) was declared a pandemic by the World Health Organization (WHO), several features of the pathogenesis and innate immune response to SARS-CoV-2 (severe acute respiratory syndrome coronavirus disease 2) have now been clarified [...].

THE ROLE OF NEUTROPHIL EXTRACELLULAR TRAPS (NETS) IN THE IMMUNOPATHOGENESIS OF SEVERE COVID-19: POTENTIAL IMMUNOTHERAPEUTIC STRATEGIES REGULATING NET FORMATION AND ACTIVITY

The role of neutrophil granulocytes (NG) in the pathogenesis of COVID-19 is associated with the recruitment of NG into inflammatory foci, activation of their functions and enhanced formation of neutrophil extracellular networks (NETs). In this review, we analyzed a fairly large volume of scientific literature devoted to the peculiarities of the formation of NETs, their role in the pathogenesis of COVID-19, participation in the occurrence of immunothrombosis, vasculitis, acute respiratory distress syndrome, cytokine storm syndrome, multi-organ lesions. Convincing data are presented that clearly indicate the significant involvement of NETs in the immunopathogenesis of COVID-19 and the associated severe complications resulting from the intensification of the inflammation process, which is key for the course of infection caused by the SARS-CoV-2 virus. The presented role of NG and NETs, along with the role of other immune system cells and pro-inflammatory cytokines, is extremely important in understanding the development of an overactive immune response in severe COVID-19. The obtained scientific results, available today, allow identifying the possibilities of regulatory effects on hyperactivated NG, on the formation of NETs at various stages and on limiting the negative impact of already formed NETs on various tissues and organs. All of the above should help in the creation of new, specialized immunotherapy strategies designed to increase the chances of survival, reduce the severity of clinical manifestations in patients with COVID-19, as well as significantly reduce mortality rates. Currently, it is possible to use existing drugs and a number of new drugs are being developed, the action of which can regulate the amount of NG, positively affect the functions of NG and limit the intensity of NETs formation. Continuing research on the role of hyperactive NG and netosis, as well as understanding the mechanisms of regulation of the phenomenon of formation and restriction of NETs activity in severe COVID-19, apparently, are a priority, since in the future the new data obtained could become the basis for the development of targeted approaches not only to immunotherapy aimed at limiting education and blocking negative effects already formed NETs in severe COVID-19, but also to immunotherapy, which could be used in the complex treatment of other netopathies, first of all, autoimmune diseases, auto-inflammatory syndromes, severe purulent-inflammatory processes, including bacterial sepsis and hematogenous osteomyelitis.

Deciphering the role of monocyte and monocyte distribution width (MDW) in COVID-19: an updated systematic review and meta-analysis

The SARS-CoV-2 infection is characterized by both systemic and organ hyper-thromboinflammation, with a clinical course ranging from mild up-to critical systemic dysfunction and death. In patients with coronavirus disease 2019 (COVID-19) the monocyte/macrophage population is deeply involved as both trigger and target, assuming the value of useful diagnostic/prognostic marker of innate cellular immunity. Several studies correlated morphological and immunophenotypic alterations of circulating monocytes with clinical outcomes in COVID-19 patients, concluding that monocyte distribution width (MDW) may retain clinical value in stratifying the risk of disease worsening. Through an electronic search in Medline and Scopus we performed an updated literature review and meta-analysis aimed to explore the association between increased MDW levels and illness severity in COVID-19 patients, deciphering role(s) and function(s) of monocytes in the harmful network underlining SARS-CoV-2 infection. We found that significantly elevated MDW values were frequently present in COVID-19 patients who developed unfavorable clinical outcomes, compounded by a significant association between monocyte anisocytosis and SARS-CoV-2 outcomes. These findings suggest that blood MDW index and its scatter plot could represent useful routine laboratory tools for early identification of patients at higher risk of unfavorable COVID-19 and for monitoring the progression of viral infection, clinical outcomes, and therapeutic efficacy throughout hospitalization. According to this evidence, therapeutic decisions in patients with SARS-CoV-2 infection could benefit from monitoring MDW value, with administration of drugs limiting thrombo-inflammation due to monocyte hyper-activation in patients with severe/critical COVID-19 disease.

What is the impact of circulating histones in COVID-19: a systematic review

The infectious respiratory condition COVID-19 manifests a clinical course ranging from mild/moderate up-to critical systemic dysfunction and death linked to thromboinflammation. During COVID-19 infection, neutrophil extracellular traps participating in cytokine storm and coagulation dysfunction have emerged as diagnostic/prognostic markers. The characterization of NET identified that mainly histones, have the potential to initiate and propagate inflammatory storm and thrombosis, leading to increased disease severity and decreased patient survival. Baseline assessment and serial monitoring of blood histone concentration may be conceivably useful in COVID-19. We performed a literature review to explore the association among increased circulating levels of histones, disease severity/mortality in COVID-19 patients, and comparison of histone values between COVID-19 and non-COVID-19 patients. We carried out an electronic search in Medline and Scopus, using the keywords "COVID-19" OR "SARS-CoV-2" AND "histone" OR "citrullinated histones" OR "hyperhistonemia", between 2019 and present time (i.e., June 07th, 2022), which allowed to select 17 studies, totaling 1,846 subjects. We found that substantially elevated histone values were consistently present in all COVID-19 patients who developed unfavorable clinical outcomes. These findings suggest that blood histone monitoring upon admission and throughout hospitalization may be useful for early identification of higher risk of unfavorable COVID-19 progression. Therapeutic decisions in patients with SARS-CoV-2 based on the use of histone cut-off values may be driven by drugs engaging histones, finally leading to the limitation of cytotoxic, inflammatory, and thrombotic effects of circulating histones in viral sepsis.

Fibrin structure, viscoelasticity and lysis face the interplay of biorelevant polyions

PURPOSE OF REVIEW

In the past 5 decades, heparins have been widely used as anticoagulants in the prevention and treatment of thrombosis. Subsequent development of heparin variants of various size and charge facilitated the discovery of their multiple biological actions and nonanticoagulant benefits. Platelet-derived or microbial polyphosphates, as well as DNA released in the course of neutrophil extracellular trap-formation are additional polyanions, which can modulate the development and stability of thrombi associated with cancer or inflammation. In this review, we focus on the size-dependent and electric charge-dependent modulatory effects of the three polyanions of different chemical structure.

RECENT FINDINGS

The polycationic histones have been recognized as potential biomarkers and therapeutic targets in several diseases related to inflammation and thrombosis. Since combating histones with activated protein C or heparin could cause unwanted bleeding, the quest for nonanticoagulant histone-neutralizing agents is ongoing. Polyanions may neutralize or exaggerate certain histone-mediated effects depending on their electric charge, size and histone effects under investigation. Several prothrombotic effects of polyphosphates and DNA are also size-dependent.

SUMMARY

The efficiency of future therapeutics targeting prothrombotic polyanions or histones is not a simple matter of electric charge, but may rely on a delicate combination of size, charge and chemical composition.

Circulating histones contribute to monocyte and MDW alterations as common mediators in classical and COVID-19 sepsis

Objective

Histone proteins are physiologically involved in DNA packaging and gene regulation but are extracellularly released by neutrophil/monocyte extracellular traps and mediate thrombo-inflammatory pathways, associated to the severity of many human pathologies, including bacterial/fungal sepsis and COVID-19. Prominent and promising laboratory features in classic and viral sepsis emphasize monocyte distribution width (MDW), due to its ability to distinguish and stratify patients at higher risk of critical conditions or death. No data are available on the roles of histones as MDW modifiers.

Design

Comparison of MDW index was undertaken by routine hematology analyzer on whole blood samples from patients with COVID-19 and Sepsis. The impact of histones on the MDW characteristics was assessed by the in vitro time-dependent treatment of healthy control whole blood with histones and histones plus lipopolysaccharide to simulate viral and classical sepsis, respectively.

Measurements and main results

We demonstrated the breadth of early, persistent, and significant increase of MDW index in whole blood from healthy subject treated in vitro with histones, highlighting changes similar to those found in vivo in classic and viral sepsis patients. These findings are mechanistically associated with the histone-induced modifications of cell volume, cytoplasmic granularity and vacuolization, and nuclear structure alterations of the circulating monocyte population.

Conclusions

Histones may contribute to the pronounced and persistent monocyte alterations observed in both acute classical and viral sepsis. Assessment of the biological impact of circulating histone released during COVID-19 and sepsis on these blood cells should be considered as key factor modulating both thrombosis and inflammatory processes, as well as the importance of neutralization of their cytotoxic and procoagulant activities by several commercially available drugs (e.g., heparins and heparinoids).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04138-2.

Impaired fibrinolysis in severe Covid-19 infection is detectable in early stages of the disease

BACKGROUND

A significant degree of mortality and morbidity in Covid-19 is due to thromboembolic disease. Coagulopathy has been well described in critically unwell patients on ICU. There is less clear evidence regarding these changes at the time of presentation to the Emergency Department and the progression of disease over time.

OBJECTIVE

We sought to investigate whether coagulation markers can predict severity and how they change over the disease course.

METHODS

Patients presenting to a single University Teaching Hospital were recruited and followed up if PCR was positive. Alongside routine blood testing, Rotational Thromboelastometry (ROTEM) was performed. Outcome data was recorded for all patients, and ROTEM values were compared across outcome groups.

RESULTS

Extem and Intem Maximum Lysis were significantly reduced in those who died or required an ICU admission, indicating a reduced ability to break down clot mass in the most critically unwell patients.

CONCLUSION

Comparisons between groups demonstrated that one distinguishing feature between those who require ICU admission or die of Covid-19 compared with those who survive a hospital stay to discharge was the extent to which fibrinolysis could occur. Mortality and morbidity in Covid-19 infection appears in part driven by an inability to break down clot mass.