Effect of blood pressure and glycemic control on the plasma cell-free DNA in hemodialysis patients

Circulating cell-free DNA and its association with cardiovascular disease: what we know and future perspectives

PURPOSE OF REVIEW

The aim of this review is to explore a possible link between cell-free DNA (cfDNA) and cardiovascular disease (CVD), which may hold valuable potential for future diagnostics.

RECENT FINDINGS

cfDNA has become topic of high interest across several medical fields. cfDNA is used as a diagnostic biomarker in cancer, prenatal care, and transplantation. In addition, cfDNA may play an unrecognized role in biological processes that are involved in or underlying various disease states, for example, inflammation. Elevated levels of cfDNA are associated with various elements of CVD, cardio-metabolic risk factors, and autoimmune diseases. Mitochondrial cfDNA and neutrophil extracellular traps may play distinct roles. Total circulating cfDNA may reflect the unspecific accumulation of stressors and the organism's susceptibility and resilience to such stressors. As such, cfDNA, in a stressful situation, may provide predictive value for future development of CVD. We suggest exploring such possibility through a large-scale prospective cohort study of pregnant women.

SUMMARY

There is no doubt that cfDNA is a valuable biomarker. For CVD, its potential is indicated but less explored. New studies may identify cfDNA as a valuable circulating cardiovascular risk marker to help improve risk stratification.

NETs-Induced Thrombosis Impacts on Cardiovascular and Chronic Kidney Disease

Arterial and venous thrombosis constitute a major source of morbidity and mortality worldwide. Association between thrombotic complications and cardiovascular and other chronic inflammatory diseases are well described. Inflammation and subsequent initiation of thrombotic events, termed immunothrombosis, also receive growing attention but are still incompletely understood. Nevertheless, the clinical relevance of aberrant immunothrombosis, referred to as thromboinflammation, is evident by an increased risk of thrombosis and cardiovascular events in patients with inflammatory or infectious diseases. Proinflammatory mediators released from platelets, complement activation, and the formation of NETs (neutrophil extracellular traps) initiate and foster immunothrombosis. In this review, we highlight and discuss prominent and emerging interrelationships and functions between NETs and other mediators in immunothrombosis in cardiovascular disease. Also, with patients with chronic kidney disease suffering from increased cardiovascular and thrombotic risk, we summarize current knowledge on neutrophil phenotype, function, and NET formation in chronic kidney disease. In addition, we elaborate on therapeutic targeting of NETs-induced immunothrombosis. A better understanding of the functional relevance of antithrombotic mediators which do not increase bleeding risk may provide opportunities for successful therapeutic interventions to reduce thrombotic risk beyond current treatment options.

NETosis and kidney disease: what do we know?

Neutrophils are the most abundant leukocytes in the blood. They are rapidly mobilized from the circulation to sites of inflammation and/or infection. In affected tissues, neutrophils exhibit some dramatic antimicrobial functions, including degranulation, reactive oxygen species (ROS) production, phagocytosis, and formation of neutrophil extracellular traps (NETs). Like other cells of the immune system, after fulfilling their biological duties, they enter the path of death. Depending on the conditions, they may undergo different types of cell death (apoptosis, necrosis, necroptosis, autophagy, NETosis, and pyroptosis) that require the participation of multiple signaling pathways. NETosis is a unique neutrophil cell death mechanism that gives rise to different inflammatory and autoimmune pathological conditions. Recent studies have shown that NETosis also plays a role in the formation and/or progression of kidney diseases. This review discusses the underlying mechanism of NETosis and its relationship with some major kidney diseases in light of the current knowledge.

The influence of biological and lifestyle factors on circulating cell-free DNA in blood plasma

Research and clinical use of circulating cell-free DNA (cirDNA) is expanding rapidly; however, there remain large gaps in our understanding of the influence of lifestyle and biological factors on the amount of cirDNA present in blood. Here, we review 66 individual studies of cirDNA levels and lifestyle and biological factors, including exercise (acute and chronic), alcohol consumption, occupational hazard exposure, smoking, body mass index, menstruation, hypertension, circadian rhythm, stress, biological sex and age. Despite technical and methodological inconsistences across studies, we identify acute exercise as a significant influence on cirDNA levels. Given the large increase in cirDNA induced by acute exercise, we recommend that controlling for physical activity prior to blood collection is routinely incorporated into study design when total cirDNA levels are of interest. We also highlight appropriate selection and complete reporting of laboratory protocols as important for improving the reproducibility cirDNA studies and ability to critically evaluate the results.

Extremely High Cell-free DNA Levels Observed in Renal Allograft Patient With SARS-CoV-2 Infection

Beyond its widely recognized morbidity and mortality, coronavirus disease 2019 poses an additional health risk to renal allograft recipients. Detection and measurement of donor-derived cell-free DNA (dd-cfDNA), expressed as a fraction of the total cell-free DNA (cfDNA), has emerged as a noninvasive biomarker for allograft rejection. Here, we present a case report of a patient who was infected with severe acute respiratory syndrome coronavirus 2, 11 mo post-kidney transplant. The patient was serially monitored using an analytically and clinically validated massively multiplex PCR-based dd-cfDNA assay to assess allograft injury and risk for rejection. Over the course of infection, low dd-cfDNA fractions were observed (below the 1% cutoff) and were accompanied by unusually highly elevated levels of total cfDNA, which gradually declined as the infection resolved. The case study highlights the variability in total cfDNA levels during and after viral infection, and the need to consider both total and dd-cfDNA levels when clinically interpreting the results for allograft rejection. Furthermore, the study highlights the importance of serial testing, wherein an interplay between total cfDNA and dd-cfDNA can inform the optimization of a patient's immunosuppressive treatment regimen in response to infection.

Elevated Circulating Cell-Free DNA in Hemodialysis-Treated Patients Is Associated with Increased Mortality

BACKGROUND

Predicting the mortality risk of patients un-dergoing hemodialysis (HD) is challenging. Cell-free DNA (cfDNA) is released into circulation from dying cells, and its elevation is predictive of unfavorable outcome. In a pilot study, we found post-HD cfDNA level to be a predictor of all-cause mortality. Thus, the aim of this study was to confirm the prognostic power of cfDNA in a larger prospective cohort study conducted at 2 medical centers.

METHODS

CfDNA levels were measured by a rapid fluorometric assay on sera obtained before and after 1 HD session. One hundred fifty-three patients were followed up to 46 months for mortality during which time 47 patients died. We compared the predictive value of cfDNA to age, comorbidities, and standard blood tests.

RESULTS

Examining standard blood tests, only post-HD cfDNA levels were elevated in the non-survivor group compared to survivors (959 vs. 803 ng/mL, p = 0.04). Pre- and post-HD cfDNA levels correlated with age and diabetes. Patients with elevated cfDNA (>850 ng/mL) showed lower survival than those with normal levels. A Cox proportional hazard regression model demonstrated a significant hazard ratio of 1.92 for post-HD cfDNA levels. Logistic regression models showed that post-HD cfDNA was a significant predictor of mortality at 1-3 years with odd ratios of 4.61, 4.36, and 6.22, respectively.

CONCLUSIONS

Post-HD cfDNA level was superior to standard blood tests and could serve as a biomarker to assist in decision-making for HD-treated patients.

Plasma Concentrations of Extracellular DNA in Acute Kidney Injury

Current diagnostic methods of acute kidney injury (AKI) have limited sensitivity and specificity. Tissue injury has been linked to an increase in the concentrations of extracellular DNA (ecDNA) in plasma. A rapid turnover of ecDNA in the circulation makes it a potential marker with high sensitivity. This study aimed to analyze the concentration of ecDNA in plasma in animal models of AKI. Three different fractions of ecDNA were measured—total ecDNA was assessed fluorometrically, while nuclear ecDNA (ncDNA) and mitochondrial DNA (mtDNA) were analyzed using quantitative real-time PCR. AKI was induced using four different murine models of AKI-bilateral ureteral obstruction (BUO), glycerol-induced AKI (GLY), ischemia–reperfusion injury (IRI) and bilateral nephrectomy (BNx). Total ecDNA was significantly higher in BUO (p < 0.05) and GLY (p < 0.05) compared to the respective control groups. ncDNA was significantly higher in BUO (p < 0.05) compared to SHAM. No significant differences in the concentrations of mtDNA were found between the groups. The plasma concentrations of different fractions of ecDNA are dependent on the mechanism of induction of AKI and warrant further investigation as potential surrogate markers of AKI.

Cell free DNA as a diagnostic and prognostic marker for cardiovascular diseases

Release of cell free DNA (cfDNA) from damaged or dead cells routinely occurs in normal physiology. Recently, cfDNA has emerged as an essential biomarker in cardiovascular disease (CVD) of potential prognostic and diagnostic significance. Within the last decade, significant research efforts have been devoted to uncovering the mechanisms mediating cfDNA release and its outcome-predicting ability. The current review focuses on the pathways for cfDNA release in myocardial infarction, heart failure and hypertension, and discusses implementation of cfDNA monitoring to assess the overall development of these disease states and predict future complications.

Clinical relevance of cell-free mitochondrial DNA during the early postoperative period in kidney transplant recipients

Recent studies indicate that urinary mitochondrial DNA (mtDNA) is predictive of ischemic AKI and is related to delayed graft function (DGF) in renal transplantation. Nevertheless, the clinical implications and prognostic value of urinary mtDNA in kidney transplantation remain undetermined. Here, we aimed to evaluate the associations between cell-free mtDNA and clinical parameters, including pathological findings in allograft biopsy and post-transplant renal function. A total of 85 renal transplant recipients were enrolled, and blood and urine samples were collected at a median of 17 days after transplantation. Cell-free nuclear and mtDNA levels were measured by quantitative polymerase chain reaction for LPL and ND1 genes. Urinary cell-free mtDNA levels were significantly higher in patients with DGF (P < 0.001) and cases of deceased donor transplantation (P < 0.001). The subjects with acute rejection showed higher urinary mtDNA levels than those without abnormalities (P = 0.043). In addition, allograft functions at 9- and 12-month post-transplantation were significantly different between tertile groups of mtDNA independent of the presence of DGF or acute rejection, showing significantly better graft outcome in the lowest tertile group. Urinary cell-free mtDNA levels during the early post-transplant period are significantly associated with DGF, acute rejection in graft biopsy, and short-term post-transplant renal function.

Inevitable isolation and the change of stress markers in hemodialysis patients during the 2015 MERS-CoV outbreak in Korea

During the outbreak of Middle East respiratory syndrome coronavirus(MERS-CoV) in 2015, one hemodialysis patient was infected with MERS-CoV, and the remaining hemodialysis(HD) patients (n = 83) and medical staff (n = 12) had to undergo dialysis treatment in an isolated environment. This study was performed to investigate the effects of stress caused by dialysis treatment under isolation. Plasma samples from the HD patients and medical staff were collected at the time of isolation(M0), the following month(M1), and three months after isolation(M3). Parameters for stress included circulating cell-free genomic DNA(ccf-gDNA), circulating cell-free mitochondria DNA(ccf-mtDNA), and pentraxin-3(PTX-3). Decreased values of Hct, kt/v and ca x p were recovered after the end of two weeks of isolation. The levels of ccf-gDNA and ccf-mtDNA were the highest at M0 and decreased gradually in both HD patients and the medical staff. The normalization of ccf-gDNA and ccf-mtDNA was significantly delayed in HD patients compared with the response in the medical staff. PTX-3 increased only in HD patients and was highest at M0, and it then gradually decreased. Medical isolation and subnormal quality of care during the MERS outbreak caused extreme stress in HD patients. Plasma cell-free DNA and PTX-3 seems to be good indicators of stress and quality of care in HD patients.

Serum DNA integrity index as a potential molecular biomarker in endometrial cancer

Background

Circulating cell-free DNA (cfDNA) and its integrity index may represent a rapid and noninvasive “liquid biopsy” biomarker, which gives important complementary information for diagnosis, prognosis, and treatment stratification in cancer patients. The aim of our study was to evaluate the possible role of cfDNA and its integrity index as a complementary tool for endometrial cancer (EC) management.

Methods

Alu-quantitative real-time PCR (qPCR) analysis wasprformed on 60 serum samples from preoperative EC patients randomly recruited. Both cfDNA content and DNA integrity index were measured by qPCR-Alu115 (representing total cfDNA) and qPCR-Alu247 (corresponding to high molecular weight DNA) and correlated with clinicopathologic characteristics. Lymphovascular space invasion (LVSI) was detected by hematoxylin and eosin staining. In case of doubt, LVSI status was further evaluate by immunohistochemistry using anti-CD31 and anti-CD34 antibodies.

Results

Total cfDNA content significantly increases in high grade EC. A significant decrease of DNA integrity index was detected in the subset of hypertensive and obese high grade EC. Serum DNA integrity was higher in samples with LVSI. The ordinal regression analysis predicted a significant correlation between decreased integrity index values and hypertension specifically in tumors presenting LVSI.

Conclusions

Our study supports the utility of serum DNA integrity index as a noninvasive molecular biomarker in EC. We show that a correlation analysis between cfDNA quantitative and qualitative content and clinicopathologic features, such as blood pressure level, body mass index (BMI) and LVSI status, could represent a potential predictive signature to help stratification approaches in EC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-018-0688-4) contains supplementary material, which is available to authorized users.

Cell-free DNA: the role in pathophysiology and as a biomarker in kidney diseases

Cell-free DNA (cfDNA) is present in various body fluids and originates mostly from blood cells. In specific conditions, circulating cfDNA might be derived from tumours, donor organs after transplantation or from the foetus during pregnancy. The analysis of cfDNA is mainly used for genetic analyses of the source tissue -tumour, foetus or for the early detection of graft rejection. It might serve also as a nonspecific biomarker of tissue damage in critical care medicine. In kidney diseases, cfDNA increases during haemodialysis and indicates cell damage. In patients with renal cell carcinoma, cfDNA in plasma and its integrity is studied for monitoring of tumour growth, the effects of chemotherapy and for prognosis. Urinary cfDNA is highly fragmented, but the technical hurdles can now be overcome and urinary cfDNA is being evaluated as a potential biomarker of renal injury and urinary tract tumours. Beyond its diagnostic application, cfDNA might also be involved in the pathogenesis of diseases affecting the kidneys as shown for systemic lupus, sepsis and some pregnancy-related pathologies. Recent data suggest that increased cfDNA is associated with acute kidney injury. In this review, we discuss the biological characteristics, sources of cfDNA, its potential use as a biomarker as well as its role in the pathogenesis of renal and urinary diseases.

Short single-stranded DNA degradation products augment the activation of Toll-like receptor 9

Toll-like receptors encounter a diversity of degradation products in endosomes. TLR7 and TLR8 have been shown to be activated by RNA degradation products. Here we show that although TLR9 requires single-stranded DNA longer than 20 nucleotides for a robust response, TLR9 activation is augmented by CpG-containing oligodeoxyribonucleotides (sODNs) as short as 2 nucleotides, which, by themselves, do not induce activation in cell cultures, as well as in mice. sODNs also activate human TLR9 in combination with ODNs containing a single CpG motif that by themselves do not activate human TLR9. The specific sequence motif of sODN and colocalization of ODN and sODN suggest that the mechanism of activation involves binding of both ODN and sODN to TLR9. sODNs augment TLR9 activation by mammalian genomic DNA indicating the role of short DNA degradation products in the endosomes in response to infection or in autoimmune disease, particularly at limiting concentrations of ODNs.

DNA degradation products are frequently found in the endosome, but how they regulate the activation of Toll-like receptors is not known. Here the authors show that single-stranded DNA as short as two nucleotides can enhance the ability of longer DNA oligonucleotides to activate Toll-like receptors.

NETosis provides the link between activation of neutrophils on hemodialysis membrane and comorbidities in dialyzed patients

INTRODUCTION

Neutrophil extracellular traps (NETs) are formed by activated neutrophils during the process of NETosis in which the nuclear material is released into extracellular space, including DNA molecules, citrullinated histones, and neutrophil granule enzymes, such as elastase. This material forms networks that are able not only to physically entrap bacteria but also to provide elevated concentration of bactericidal components. Over the last years, it has become clear that NETs can also be formed under numerous sterile inflammatory conditions, i.e., thrombosis, cancer, SLE, atherosclerosis, and diabetes.

METHOD

We reviewed studies published until July 2016 to find possible associations between elevated cell-free DNA levels in dialyzed patients and the process of NETosis and its consequences.

RESULTS

The process of NETosis, its elevated activation, or impaired clearance provides the link between clinical conditions and elevated levels of cell-free DNA found in plasma after the hemodialytic procedure which itself is able to activate neutrophils via platelets and ROS formation. NETs stimulate thrombosis and endothelial damage, and their formation may contribute to the development of spectrum of comorbidities described in dialyzed patients.

CONCLUSION

The study of plasma cell-free DNA levels together with markers of NETosis could contribute to the evaluation of the influence of hemodialysis on the immune system of patients.