Cell-free chromatin: A newly described mediator of systemic inflammation

Cytokine Storm as a Cellular Response to dsDNA Breaks: A New Proposal

Pathogenesis of cytokine storm is poorly understood. In this article we propose a new mechanism and suggest innovative therapeutic avenues for its prevention. We have reported that particles of cell-free chromatin (cfCh) that are released from the billions of cells that die in the body everyday can illegitimately integrate into genomes of healthy cells to trigger dsDNA breaks. The latter leads to apoptosis and/or intense activation of inflammatory cytokines in the affected cells. We hypothesise that a similar phenomenon of dsDNA breaks and inflammation is involved in cytokine storm. The abundant cfCh particles that are released from dying host cells following viral/microbial invasion initiate a cascading effect of more cell death resulting in a vicious cycle of further DNA damage, apoptosis and hyper-inflammation which culminate in cytokine storm. We propose that this unrelenting vicious cycle of cellular DNA damage and cytokine storm may be the underlying cause of high mortality from severe COVID-19. We discuss results of our preclinical studies wherein we have shown that endotoxin induced cytokine storm in mice can be reversed by three different agents that have the ability to inactivate cfCh. These agents may be worthy of investigation in clinical trials to reduce mortality from COVID-19.

A New Perspective on the Origin of DNA Double-Strand Breaks and Its Implications for Ageing

It is estimated that 10-50 DNA double-strand breaks (DSBs) occur in a nucleated human cell per cell cycle. We reviewed the present state of knowledge and hypothesized that the currently accepted mechanisms cannot explain such high frequency of DSBs occurring daily under normal physiological conditions. We propose an alternative model that implicates illegitimate genomic integration into healthy cells of cell-free chromatin (cfCh) particles released from the billions of cells that die in the body every day. Repeated genomic integration of cfCh may have catastrophic consequences for the cell, such as DSBs, their faulty repair by nonhomologous end joining (NHEJ) followed by apoptosis with release of more cfCh which would integrate into genomes of surrounding cells. This can creates a vicious cycle of cfCh integration, DSBs, NHEJ, and more apoptosis, thereby providing a potential explanation as to why so many billions of cells die in the body on a daily basis. We also recount the recent observation that cfCh integration and the resulting DSBs activate inflammatory cytokines. This leads us to propose that concurrent DSBs and induction of inflammation occurring throughout life may be the underlying cause of ageing, degenerative disorders, and cancer. Finally, we discuss the prospect that agents that can inactivate/degrade cfCh may hold the key to making healthy ageing a realizable goal.

Plasma Nucleosomes in Primary Breast Cancer

Simple Summary

Nucleosomes composed of DNA and histone proteins enter the extracellular space and end eventually in the circulation when cells die. In blood plasma, they could represent a nonspecific marker of cell death, potentially useful for noninvasive monitoring of cancer. The aim of this study was to analyze circulating nucleosomes in relation to patient/tumor characteristics and prognosis in nonmetastatic breast cancer. This study included 92 patients with breast cancer treated with surgery. Plasma nucleosomes were detected in samples taken in the morning on the day of surgery. Circulating nucleosomes were positively associated with the systemic inflammation but not with other patient/tumor characteristics. Patients with lower nucleosomes had lower risk of disease recurrence compared to patients with higher nucleosomes. Our data suggest that plasma nucleosomes in nonmetastatic breast cancer are associated with systemic inflammation and might have a prognostic value. The underlying mechanisms require further studies.

Abstract

When cells die, nucleosomes composed of DNA and histone proteins enter the extracellular space and end eventually in the circulation. In plasma, they might serve as a nonspecific marker of cell death, potentially useful for noninvasive monitoring of tumor dynamics. The aim of this study was to analyze circulating nucleosomes in relation to patient/tumor characteristics and prognosis in primary breast cancer. This study included 92 patients with breast cancer treated with surgery for whom plasma isolated was available in the biobank. Plasma nucleosomes were detected in samples taken in the morning on the day of surgery using Cell Death Detection ELISA kit with anti-histone and anti-DNA antibodies. Circulating nucleosomes were positively associated with the systemic inflammatory index (SII), but not with other patient/tumor characteristics. Patients with high SII in comparison to low SII had higher circulating nucleosomes (by 59%, p = 0.02). Nucleosomes correlated with plasma plasminogen activator inhibitor-1, IL-15, IL-16, IL-18, and hepatocyte growth factor. Patients with lower nucleosomes had significantly better disease-free survival (HR = 0.46, p = 0.05). In a multivariate analysis, nucleosomes, hormone receptor status, HER2 status, lymph node involvement, and tumor grade were independent predictors of disease-free survival. Our data suggest that plasma nucleosomes in primary breast cancer are associated with systemic inflammation and might have a prognostic value. The underlying mechanisms require further studies.

Pre-analytical issues in liquid biopsy – where do we stand?

It is well documented that in the chain from sample to the result in a clinical laboratory, the pre-analytical phase is the weakest and most vulnerable link. This also holds for the use and analysis of extracellular nucleic acids. In this short review, we will summarize and critically evaluate the most important steps of the pre-analytical phase, i.e. the choice of the best control population for the patients to be analyzed, the actual blood draw, the choice of tubes for blood drawing, the impact of delayed processing of blood samples, the best method for getting rid of cells and debris, the choice of matrix, i.e. plasma vs. serum vs. other body fluids, and the impact of long-term storage of cell-free liquids on the outcome. Even if the analysis of cell-free nucleic acids has already become a routine application in the area of non-invasive prenatal screening (NIPS) and in the care of cancer patients (search for resistance mutations in the EGFR gene), there are still many unresolved issues of the pre-analytical phase which need to be urgently tackled.

Cell-free chromatin particles released from dying host cells are global instigators of endotoxin sepsis in mice

We have earlier reported that cell-free chromatin (cfCh) particles that are released from dying cells, or those that circulate blood, can readily enter into healthy cells, illegitimately integrate into their genomes and induce dsDNA breaks, apoptosis and intense activation of inflammatory cytokines. We hypothesized that sepsis is caused by cfCh released from dying host cells following microbial infection leading to bystander host cell apoptosis and inflammation which are perpetuated in a vicious cycle with release of more cfCh from dying host cells. To test this hypothesis we used three cfCh inactivating agents namely 1) anti-histone antibody complexed nanoparticles which inactivate cfCh by binding to histones; 2) DNase I which inactivates cfCh by degrading its DNA component, and 3) a novel pro-oxidant combination of Resveratrol and Copper which, like DNase I, inactivates cfCh by degrading its DNA component. Female C57 BL/6 mice, 6–8 weeks old, were administered a single i.p. injection of LPS at a dose of 10 mg/Kg or 20 mg/Kg with or without concurrent treatment with the above cfCh inactivating agents. Administration of cfCh inactivating agents concurrently with LPS resulted in prevention of following pathological parameters: 1) release of cfCh in extra-cellular spaces of brain, lung and heart and in circulation; 2) release of inflammatory cytokines in circulation; 3) activation of DNA damage, apoptosis and inflammation in cells of thymus, spleen and in PBMCs; 4) DNA damage, apoptosis and inflammation in cells of lung, liver, heart, brain, kidney and small intestine; 5) liver and kidney dysfunction and elevation of serum lactate; 6) coagulopathy, fibrinolysis and thrombocytopenia; 7) lethality. We conclude that cfCh that are released from dying host cells in response to bacterial endotoxin represents a global instigator of sepsis. cfCh inactivation may provide a novel approach to management of sepsis in humans.