Deoxyribonuclease I Activity, Cell-Free DNA, and Risk of Liver Cancer in a Prospective Cohort

Cell-Free DNA Promotes Inflammation in Patients With Oral Lichen Planus via the STING Pathway

Background

Damaged and dead cells release cell-free DNA (cfDNA) that activates cyclic GMP–AMP (cGAMP) synthase (cGAS), which leads to the activation of stimulator of interferon genes (STING) via the second messenger cGAMP. STING promotes the production of inflammatory cytokines and type I interferons to induce an inflammatory response. Oral lichen planus (OLP), a chronic autoimmune disease involving oral mucosa characterized by the apoptosis of keratinocytes mediated by T-lymphocytes, is related to the activation of multiple inflammatory signaling pathways. Currently, the relationship between cfDNA and OLP has not been confirmed. We hypothesized that cfDNA may be a potential therapeutic target for OLP.

Methods

cfDNA was extracted from the saliva and plasma of OLP patients; its concentration was measured using the Quanti-iT-PicoGree kit and its relationship with OLP inflammation was assessed. cfDNA of OLP patients (cfDNA-OLP) was transfected into THP-1 macrophages and the expression of inflammatory factors was investigated by performing quantitative real time PCR (qRT-PCR), western blotting, and enzyme-linked immunosorbent assay (ELISA). STING expression was analyzed in the tissues of OLP patients and healthy controls using immunohistochemical staining and western blotting. siRNA was used to knockdown STING expression in THP-1 macrophages, and the inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) secreted by cells following cfDNA-OLP transfection were detected using ELISA. Finally, the effect of the cationic polymer PAMAM-G3 was evaluated on the treatment of inflammation induced by cfDNA-OLP.

Results

The concentration of cfDNA in the saliva and plasma of OLP patients was considerably higher than that of healthy controls, and it positively correlated with the levels of inflammatory cytokines and clinical characteristics. cfDNA-OLP induced an inflammatory response in THP-1 macrophages. STING expression was significantly higher in OLP tissues than in the gingival tissues of healthy controls. STING knockdown suppressed cfDNA-OLP-induced inflammation in THP-1 macrophages. PAMAM-G3 inhibited the inflammatory response caused by cfDNA-OLP.

Conclusion

The cfDNA level is increased in OLP patients, and the STING pathway activated by cfDNA-OLP might play a critical role in OLP pathogenesis. Treatment with PAMAM-G3 reduced the inflammation induced by cfDNA-OLP, and therefore, may be a potential treatment strategy for OLP.

cfDNA and DNases: New Biomarkers of Sepsis in Preterm Neonates-A Pilot Study

INTRODUCTION

An early and accurate diagnosis of early onset neonatal sepsis (EONS) and late onset neonatal sepsis (LONS) is essential to improve the outcome of this devastating conditions. Especially, preterm infants are at risk. Reliable biomarkers are rare, clinical decision-making depends on clinical appearance and multiple laboratory findings. Markers of NET formation and NET turnover might improve diagnostic precision. Aim of this study was to evaluate the diagnostic value of NETs in sepsis diagnosis in neonatal preterm infants.

METHODS

Plasma samples of neonatal preterm infants with suspected sepsis were collected. Blood samples were assayed for markers of NET formation and NET turnover: cfDNA, DNase1, nucleosome, NE, and H3Cit. All clinical findings, values of laboratory markers, and epidemiological characteristics were collected retrospectively. Two subpopulations were created to divide EONS from LONS. EMA sepsis criteria for neonatal sepsis were used to generate a sepsis group (EMA positive) and a control group (EMA negative).

RESULTS

A total of 31 preterm neonates with suspected sepsis were included. Out of these, nine patients met the criteria for sepsis according to EMA. Regarding early onset neonatal sepsis (3 EONS vs. 10 controls), cfDNA, DNase I, nucleosome, and CRP were elevated significantly. H3Cit and NE did not show any significant elevations. In the late onset sepsis collective (6 LONS vs. 12 controls), cfDNA, DNase I, and CRP differed significantly compared to control group.

Role of Cell-Free DNA and Deoxyribonucleases in Tumor Progression

Many studies have reported an increase in the level of circulating cell-free DNA (cfDNA) in the blood of patients with cancer. cfDNA mainly comes from tumor cells and, therefore, carries features of its genomic profile. Moreover, tumor-derived cfDNA can act like oncoviruses, entering the cells of vulnerable organs, transforming them and forming metastatic nodes. Another source of cfDNA is immune cells, including neutrophils that generate neutrophil extracellular traps (NETs). Despite the potential eliminative effect of NETs on tumors, in some cases, their excessive generation provokes tumor growth as well as invasion. Considering both possible pathological contributions of cfDNA, as an agent of oncotransformation and the main component of NETs, the study of deoxyribonucleases (DNases) as anticancer and antimetastatic agents is important and promising. This review considers the pathological role of cfDNA in cancer development and the role of DNases as agents to prevent and/or prohibit tumor progression and the development of metastases.

Human Recombinant DNase I (Pulmozyme®) Inhibits Lung Metastases in Murine Metastatic B16 Melanoma Model That Correlates with Restoration of the DNase Activity and the Decrease SINE/LINE and c-Myc Fragments in Blood Cell-Free DNA

Tumor-associated cell-free DNAs (cfDNA) play an important role in the promotion of metastases. Previous studies proved the high antimetastatic potential of bovine pancreatic DNase I and identified short interspersed nuclear elements (SINEs) and long interspersed nuclear elements (LINEs)and fragments of oncogenes in cfDNA as the main molecular targets of enzyme in the bloodstream. Here, recombinant human DNase I (commercial name Pulmozyme^®), which is used for the treatment of cystic fibrosis in humans, was repurposed for the inhibition of lung metastases in the B16 melanoma model in mice. We found that Pulmozyme^® strongly reduced migration and induced apoptosis of B16 cells in vitro and effectively inhibited metastases in lungs and liver in vivo. Pulmozyme^® was shown to be two times more effective when administered intranasally (i.n.) than bovine DNase I, but intramuscular (i.m.) administration forced it to exhibit as high an antimetastatic activity as bovine DNase I. Both DNases administered to mice either i.m. or i.n. enhanced the DNase activity of blood serum to the level of healthy animals, significantly decreased cfDNA concentrations, efficiently degraded SINE and LINE repeats and c-Myc fragments in the bloodstream and induced apoptosis and disintegration of neutrophil extracellular traps in metastatic foci; as a result, this manifested as the inhibition of metastases spread. Thus, Pulmozyme^®, which is already an approved drug, can be recommended for use in the treatment of lung metastases.

Deoxyribonucleases and Their Applications in Biomedicine

Extracellular DNA, also called cell-free DNA, released from dying cells or activated immune cells can be recognized by the immune system as a danger signal causing or enhancing inflammation. The cleavage of extracellular DNA is crucial for limiting the inflammatory response and maintaining homeostasis. Deoxyribonucleases (DNases) as enzymes that degrade DNA are hypothesized to play a key role in this process as a determinant of the variable concentration of extracellular DNA. DNases are divided into two families-DNase I and DNase II, according to their biochemical and biological properties as well as the tissue-specific production. Studies have shown that low DNase activity is both, a biomarker and a pathogenic factor in systemic lupus erythematosus. Interventional experiments proved that administration of exogenous DNase has beneficial effects in inflammatory diseases. Recombinant human DNase reduces mucus viscosity in lungs and is used for the treatment of patients with cystic fibrosis. This review summarizes the currently available published data about DNases, their activity as a potential biomarker and methods used for their assessment. An overview of the experiments with systemic administration of DNase is also included. Whether low-plasma DNase activity is involved in the etiopathogenesis of diseases remains unknown and needs to be elucidated.

Inhibition of nuclease activity by a splice-switching oligonucleotide targeting deoxyribonuclease 1 mRNA prevents apoptosis progression and prolong viability of normal human CD4+ T-lymphocytes

The nuclease activity of deoxyribonuclease 1 (DNase I) is regulated by alternative splicing (AS) of its mRNA. The aim of this study was to define the ability of a splice-switching oligonucleotide (SSO) that base-paired with DNase I pre-mRNA to induce AS and inhibit nuclease activity in human T, B and NK lymphocytes. The SSO for DNase I could significantly downregulate the expression of full-length active DNase I and upregulate a truncated splice variant with a deleted exon 4. Such an induction of AS resulted in inhibition of nuclease activity and slowed apoptosis progression in anti-CD95/FAS stimulated lymphocytes. These results should facilitate further investigations of apoptosis regulation in lymphocytes and demonstrate that SSOs for DNase I are promising cytoprotective agents.

DNase I improves corneal epithelial and nerve regeneration in diabetic mice

DNase I has been reported to improve diabetic wound healing through the clearance of neutrophils extracellular traps (NETs) caused by neutrophil aggregation. However, the function of DNase I on diabetic corneal wound healing remains unclear. Here, we investigated the effect and mechanism of topical DNase I application on diabetic mouse corneal epithelial and nerve regeneration. Corneal epithelial defects, inflammatory response, regeneration‐related signalling pathways, oxidative stress, corneal innervation and sensation were examined and compared between the diabetic and normal mice. The results confirmed firstly the increased NETs production during the delayed corneal epithelial wound healing of diabetic mice, which was significantly improved through either DNase I or Cl‐amidine administration. Mechanistically, DNase I improved inflammation resolution, reactivated epithelial regeneration‐related signalling pathways and attenuated the accumulation of reactive oxygen species (ROS). Moreover, DNase I application also promoted corneal nerve regeneration and restored the impaired corneal sensitivity in diabetic mice. Therefore, these results indicate that topical DNase I application promotes corneal epithelial wound healing and mechanical sensation restoration in diabetic mice, representing the potential therapeutic approach for diabetic keratopathy.

Analysis of deoxyribonuclease activity by conjugation-free fluorescence polarisation in sub-nanolitre droplets

We report the analysis of deoxyribonuclease (DNase) activity by conjugation-free fluorescence polarisation in a droplet-based microfluidic chip. DNase is a DNA cleaving enzyme and its activity is important in the maintenance of normal cellular functions. Alterations in DNase activity have been implicated as the cause of various cancers and autoimmune diseases. To date, various methods for the analysis of DNase activity have been reported. However, they are not cost effective due to the requirement of large sample volumes and the need for the conjugation of fluorescent dyes. In this study, we have used ethidium bromide (EtBr), a DNA intercalating reagent, as a fluorescent reporter without any prior conjugation or modification of DNA. Degradation of DNA by DNase 1 was monitored at a steady state by making changes in the fluorescence polarisation of EtBr in droplets with a volume of 330 picolitre at a 40 hertz frequency under visible light. Using this technique, we successfully determined the half-maximal inhibitory concentration (IC₅₀) of ethylenediaminetetraacetic acid (EDTA) for the inhibition of DNase 1 activity to be 1.56 ± 0.91 mM.

Circulating cell-free DNA fragment analysis by microchip electrophoresis and its relationship with DNase I in cardiac diseases

Circulating cell-free DNA (cfDNA) has been directly related to cancer, diabetes, stroke, systemic lupus erythematosus, trauma, rheumatoid arthritis, inflammation, infection, and myocardial infarction (MI). In this study, plasma cfDNA was extracted from the plasma of cardiac disease patients and the cfDNA fragment distribution as well as the relationships between cfDNA concentration and deoxyribonuclease I (DNase I) activity enzyme implicated in double-stranded DNA processing were examined. Results revealed that the cfDNA concentrations in patients with MI and cardiac angina were significantly higher than that in healthy control subjects. Microchip electrophoresis of plasma cfDNA revealed a single fragment (150-200 bp) in some healthy control subjects and three fragments (150-200 bp, 300-400 bp, and 500-600 bp) in all cardiac patient samples. Moreover, a cfDNA ratio of 150-200 bp/500-600 bp was significantly more prevalent in MI patients than in patients with other cardiac diseases (chest pain, cardiac angina, atrial fibrillation and cardiac failure). In addition, a positive correlation between DNase I activity and cfDNA concentration was observed. These results suggest that the plasma cfDNA in cardiac disease patients may originate from apoptosis and that the 150-200 bp/500-600 bp ratio for cfDNA may be a novel diagnostic indicator for MI.