Exercise is a potent stimulus for enhancing circulating DNase activity

Response of Circulating Free Cellular DNA to Repeated Exercise in Men with Type 1 Diabetes Mellitus

Background: Intense exercise leads to neutrophil extracellular traps (NETs) formation, which triggers cell disintegration. NET, as well as other processes of apoptosis, necrosis, and spontaneous secretion, result in increased levels of cell-free DNA (cf-DNA) in the circulation. An increment of cf-DNA is also observed in autoimmune diseases, such as type 1 diabetes mellitus (T1DM). Repeated exhaustive exercises are an impulse for physiological adaptation; therefore, in this case-control study, we compared the exercise-induced increase in cf-DNA in men with T1DM and healthy controls to determine the development of the tolerance to exercise. Methods: Volunteers performed a treadmill run to exhaustion at a speed matching 70% of their personal VO2 max at three consecutive visits, separated by a 72 h resting period. Blood was collected before and after exercise for the determination of plasma cell-free nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) by real-time PCR, blood cell count and metabolic markers. Results: Each bout of exhaustive exercise induced a great elevation of cf n-DNA levels. An increase in cf mt-DNA was observed after each run. However, the significance of the increase was noted only after the second bout in T1DM participants (p < 0.02). Changes in cf-DNA concentration were transient and returned to baseline values during 72 h of resting. The exercise-induced increment in circulating cf n-DNA and cf mt-DNA was not significantly different between the studied groups (p > 0.05). Conclusions: Cf-DNA appears to be a sensitive marker of inflammation, with a lower post-exercise increase in individuals with T1DM than in healthy men.

Extracellular vesicle-associated DNA: ten years since its discovery in human blood

Extracellular vesicles (EVs) have emerged as key players in intercellular communication, facilitating the transfer of crucial cargo between cells. Liquid biopsy, particularly through the isolation of EVs, has unveiled a rich source of potential biomarkers for health and disease, encompassing proteins and nucleic acids. A milestone in this exploration occurred a decade ago with the identification of extracellular vesicle-associated DNA (EV-DNA) in the bloodstream of a patient diagnosed with pancreatic cancer. Subsequent years have witnessed substantial advancements, deepening our insights into the molecular intricacies of EV-DNA emission, detection, and analysis. Understanding the complexities surrounding the release of EV-DNA and addressing the challenges inherent in EV-DNA research are pivotal steps toward enhancing liquid biopsy-based strategies. These strategies, crucial for the detection and monitoring of various pathological conditions, particularly cancer, rely on a comprehensive understanding of why and how EV-DNA is released. In our review, we aim to provide a thorough summary of a decade's worth of research on EV-DNA. We will delve into diverse mechanisms of EV-DNA emission, its potential as a biomarker, its functional capabilities, discordant findings in the field, and the hurdles hindering its clinical application. Looking ahead to the next decade, we envision that advancements in EV isolation and detection techniques, coupled with improved standardization and data sharing, will catalyze the development of novel strategies exploiting EV-DNA as both a source of biomarkers and therapeutic targets.

Exercise-Induced Cell-Free DNA Correlates with Energy Expenditure in Multiple Exercise Protocols

PURPOSE

Exercise-induced cell-free DNA (ei-cfDNA) has been studied in response to various types of exercise. Its correlation with exercise intensity and duration has been observed consistently. However, comprehensive measurements and exploration of the tissue of origin are lacking. The aim of this study is to establish precise connections between exercise variables and the distribution of tissue of origin, aiming to provide further evidence supporting its use as a biomarker for exercise.

METHODS

Twelve self-identified active adults (six men and six women) performed a crossover study starting with either endurance testing or resistance testing under different intensities and protocols. We obtained blood before and after each exercise session and measured the levels of cfDNA and determined its tissue of origin utilizing cell type-specific DNA methylation patterns in plasma.

RESULTS

We found that when duration and intensity are fixed, ei-cfDNA fold change correlates with energy expenditure ( P = 0.001) in endurance testing and years trained ( P = 0.001) in resistance testing. Most of the ei-cfDNA comes from increases in white blood cells (~95%) where neutrophils make up the majority (~74%) and the distribution is different between exercise modalities and protocols.

CONCLUSIONS

This study highlights the potential of exercise-induced cfDNA as a biomarker for exercise, showing correlations with energy expenditure and a consistent pattern of tissue origin. Additional research is needed to investigate potential sex differences in the response of cfDNA to exercise, further exploring its clinical implications.

The value of plasma cell-free DNA levels as biomarker in patients with eating disorders: A preliminary study

OBJECTIVE

Circulating cell-free DNA (cfDNA) holds promise as a rapid and convenient biomarker for identifying individuals with eating disorders. To investigate this hypothesis, we measured plasma cfDNA in patients with different eating disorders.

METHODS

In this study, 110 participants (98 patients with eating disorders divided into 30 patients with bulimia nervosa, 33 patients with anorexia nervosa (AN) Restricting subtype, 35 patients with AN Binge-eating/purging subtype and 12 controls) were enrolled. We measured both cell-free nuclear DNA (cf-nDNA) and cell-free mitochondrial DNA (cf-mtDNA) from plasma using two specific droplet digital PCR assays each, referring to two amplicon sizes.

RESULTS

Levels of plasma cf-nDNA and cf-mtDNA showed no significant differences between control participants and those with eating disorders. However, we observed a higher proportion of long cf-nDNA fragments in patients with eating disorders, suggesting its potential as a biomarker for eating disorders.

CONCLUSION

This is the first study of cfDNA in patients with eating disorders. Our findings highlight the potential for qualitative exploration of cfDNA, although not of quantitative interest. Full characterization of cfDNA may serve as a valuable biomarker for eating disorders and provide some insights into the hidden mechanisms underlying the chronic development of these conditions. Future studies are needed to confirm or refute this hypothesis.

Interleukin-4 during post-exercise recovery negatively correlates with the production of phagocyte-generated oxidants

Exhaustive run induced a biphasic oxidative response of circulating phagocytes in 16 amateur sportsmen. The first phase involved an increment just after exercise of enhanced whole blood chemiluminescence normalized per phagocyte count, whereas in the second phase a decrement from 1 h post-exercise and ongoing till 24 h. We tested whether plasma Interleukin IL-4, IL-8, IL-10 and Tumor Necrosis Factor α concentrations change in response to exhaustive run and whether there are associations between their levels and delta resting. Moreover, IL-8 and IL-10 significantly increased immediately post-exercise and after 1 h, but later normalized. Tumor necrosis factor α rose by 1.1-times only just after exercise. However, none of these cytokines showed any correlation with the investigated chemiluminescence. Exercise did not alter plasma concentrations of IL-4. However, pre-exercise IL-4 negatively correlated with measured luminescence just after exercise (ρ = -0.54, p < 0.05), and also tended to be negatively associated with decrements of the second phase at 1 h post-exercise ρ = -0.45, p = 0.08. It is suggested that plasma IL-4, by a negative association with blood phagocytes oxidants production, could be involved in the maintenance of proper balance between oxidants and anti-oxidants during strenuous exercise and post-exercise recovery.

Physical Exercise Promotes DNase Activity Enhancing the Capacity to Degrade Neutrophil Extracellular Traps

(1) Background: An unhealthy lifestyle is a significant contributor to the development of chronic diseases. Physical activity can benefit primary and secondary prevention. Higher DNase activity is associated with favourable outcomes after cardiovascular (CV) events. In this study, we aimed to investigate the influence of consequent endurance exercise on DNase activity. (2) Methods: 98 subjects with at least one CV risk factor but the physical ability to perform endurance training were included. Individuals performed a bicycle stress test at the beginning and after 8 months to assess physical performance. In between, all participants were instructed to engage in guideline-directed physical activity. Blood samples were drawn in two-month intervals to assess routine laboratory parameters, cell-free DNA (cfDNA), and DNase activity. (3) Results: Prevailing CV risk factors were overweight (65.9%), a positive family history (44.9%), hypertension (32.7%) and smoking (20.4%). Performance changed by 7.8 ± 9.1% after 8 months. Comparison of baseline to 8 months revealed a decrease in cfDNA and an increase in DNase activity. This effect was driven by participants who achieved a performance gain. (4) Conclusions: Regular physical activity might improve CV health by increasing DNase activity and thereby, the capacity to lower pro-inflammatory signalling, complementing measures of primary and secondary prevention.

Associations of circulating cell-free DNA, C-reactive protein, and cardiometabolic risk among low-active smokers with elevated depressive symptoms

Background and aims

Cell-free DNA (cfDNA) is elevated in several disease states. Metabolic syndrome is a constellation of factors associated with poor cardiometabolic outcomes. This study examined associations of cfDNA from the nucleus (cf-nDNA) and mitochondria (cf-mtDNA), C-reactive protein (CRP), and metabolic syndrome risk, in low-active smokers with depressive symptoms.

Methods

Participants (N = 109; mean age 47) self-reported medical history. Physical activity was determined by accelerometry and anthropometrics were measured. Blood was collected and analyzed for cf-nDNA, cf-mtDNA, CRP, triglycerides, high-density lipoprotein, hemoglobin A1c. A continuous metabolic syndrome composite risk score was calculated. Relationships of cf-nDNA, cf-mtDNA, CRP, and cardiometabolic risk were examined with correlations and linear regression.

Results

CRP and cf-nDNA were significantly associated with metabolic syndrome risk (r = .39 and r = .31, respectively), cf-mtDNA was not (r = .01). In a linear regression, CRP and cf-nDNA significantly predicted the metabolic syndrome risk score, findings that remained significant controlling for age, gender, nicotine dependence, and physical activity.

Conclusions

Associations of cf-nDNA with both CRP and metabolic risk suggest a role for cf-nDNA in inflammatory processes associated with metabolic syndrome. The negative findings for cf-mtDNA suggest distinct roles for cf-nDNA and cf-mtDNA in these processes.

Changes in Specific Biomarkers Indicate Cardiac Adaptive and Anti-inflammatory Response of Repeated Recreational SCUBA Diving

Objective

Recreational SCUBA (rSCUBA) diving has become a highly popular and widespread sport. Yet, information on molecular events underlying (patho)physiological events that follow exposure to the specific environmental conditions (hyperbaric conditions, coldness, immersion, and elevated breathing pressure), in which rSCUBA diving is performed, remain largely unknown. Our previous study suggested that repeated rSCUBA diving triggers an adaptive response of cardiovascular and immune system. To elucidate further molecular events underlying cardiac and immune system adaptation and to exclude possible adverse effects we measured blood levels of specific cardiac and inflammation markers.

Methods

This longitudinal intervention study included fourteen recreational divers who performed five dives, one per week, on the depth 20–30 m that lasted 30 min, after the non-dive period of 5 months. Blood samples were taken immediately before and after the first, third, and fifth dives. Copeptin, immunoglobulins A, G and M, complement components C3 and C4, and differential blood count parameters, including neutrophil-to-lymphocyte ratio (NLR) were determined using standard laboratory methods. Cell-free DNA was measured by qPCR analysis and N-glycans released from IgG and total plasma proteins (TPP), were analyzed by hydrophilic interaction ultra-performance liquid chromatography.

Results

Copeptin level increased after the first dive but decreased after the third and fifth dive. Increases in immunoglobulins level after every dive and during whole studied period were observed, but no changes in C3, C4, and cfDNA level were detected. NLR increased only after the first dive. IgG and TPP N-glycosylation alterations toward anti-inflammatory status over whole studied period were manifested as an increase in monogalyctosylated and core-fucosylated IgG N-glycans and decrease in agalactosylated TPP N-glycans.

Conclusion

rSCUBA diving practiced on a regular basis promotes anti-inflammatory status thus contributing cardioprotection and conferring multiple health benefits.

Exhaustive Exercise Increases Spontaneous but Not fMLP-Induced Production of Reactive Oxygen Species by Circulating Phagocytes in Amateur Sportsmen

Strenuous exercise alters the oxidative response of blood phagocytes to various agonists. However, little is known about spontaneous post exercise oxidant production by these cells. In this cross-over trial, we tested whether an exhaustive treadmill run at a speed corresponding to 70% of VO2max affects spontaneous and fMLP-provoked oxidant production by phagocytes in 18 amateur sportsmen. Blood was collected before, just after, and 1, 3, 5 and 24 h post exercise for determination of absolute and normalized per phagocyte count spontaneous (a-rLBCL, rLBCL) and fMLP-induced luminol-enhanced whole blood chemiluminescence (a-fMLP-LBCL, fMLP-LBCL). a-rLBCL and rLBCL increased by 2.5- and 1.5-times just after exercise (p < 0.05) and then returned to baseline or decreased by about 2-times at the remaining time-points, respectively. a-fMLP-LBCL increased 1.7- and 1.6-times just after and at 3 h post-exercise (p < 0.05), respectively, while fMLP-LBCL was suppressed by 1.5- to 2.3-times at 1, 3, 5 and 24 h post-exercise. No correlations were found between elevated post-exercise a-rLBCL, a-fMLP-LBCL and run distance to exhaustion. No changes of oxidants production were observed in the control arm (1 h resting instead of exercise). Exhaustive exercise decreased the blood phagocyte-specific oxidative response to fMLP while increasing transiently spontaneous oxidant generation, which could be a factor inducing secondary rise in antioxidant enzymes activity.

Differences in Immune Response During Competition and Preparation Phase in Elite Rowers

Background: Metabolic stress is high during training and competition of Olympic rowers, but there is a lack of biomedical markers allowing to quantify training load on the molecular level. We aimed to identify such markers applying a complex approach involving inflammatory and immunologic variables. Methods: Eleven international elite male rowers (age 22.7 ± 2.4 yrs.; VO₂max 71 ± 5 ml·min^-1·kg^-1) of the German National Rowing team were monitored at competition phase (COMP) vs. preparation phase (PREP), representing high vs. low load. Perceived stress and recovery were assessed by a Recovery Stress Questionnaire for Athletes (RESTQ-76 Sport). Immune cell activation (dendritic cell (DC)/macrophage/monocytes/T-cells) was evaluated via fluorescent activated cell sorting. Cytokines, High-Mobility Group Protein B1 (HMGB1), cell-free DNA (cfDNA), creatine kinase (CK), uric acid (UA), and kynurenine (KYN) were measured in venous blood. Results: Rowers experienced more general stress and less recovery during COMP, but sports-related stress and recovery did not differ from PREP. During COMP, DC/macrophage/monocyte and T-regulatory cells (T_reg-cell) increased (p = 0.001 and 0.010). HMGB1 and cfDNA increased in most athletes during COMP (p = 0.001 and 0.048), while CK, UA, and KYN remained unaltered (p = 0.053, 0.304, and 0.211). Pro-inflammatory cytokines IL-1β (p = 0.002), TNF-α (p < 0.001), and the chemokine IL-8 (p = 0.001) were elevated during COMP, while anti-inflammatory Il-10 was lower (p = 0.002). Conclusion: COMP resulted in an increase in biomarkers reflecting tissue damage, with plausible evidence of immune cell activation that appeared to be compensated by anti-inflammatory mechanisms, such as T_reg-cell proliferation. We suggest an anti-inflammatory and immunological matrix approach to optimize training load quantification in elite athletes.

Mitochondrial DNA and Exercise: Implications for Health and Injuries in Sports

Recently, several studies have highlighted the tight connection between mitochondria and physical activity. Mitochondrial functions are important in high-demanding metabolic activities, such as endurance sports. Moreover, regular training positively affects metabolic health by increasing mitochondrial oxidative capacity and regulating glucose metabolism. Exercise could have multiple effects, also on the mitochondrial DNA (mtDNA) and vice versa; some studies have investigated how mtDNA polymorphisms can affect the performance of general athletes and mtDNA haplogroups seem to be related to the performance of elite endurance athletes. Along with several stimuli, including pathogens, stress, trauma, and reactive oxygen species, acute and intense exercise also seem to be responsible for mtDNA release into the cytoplasm and extracellular space, leading to the activation of the innate immune response. In addition, several sports are characterized by a higher frequency of injuries, including cranial trauma, associated with neurological consequences. However, with regular exercise, circulating cell-free mtDNA levels are kept low, perhaps promoting cf-mtDNA removal, acting as a protective factor against inflammation.

cfDNA Changes in Maximal Exercises as a Sport Adaptation Predictor

Changes of circulating free plasma DNA (cfDNA) are associated with different types of tissue injury, including those induced by intensive aerobic and anaerobic exercises. Observed changes are dependent from induced inflammation, and thus it may be a potential marker for athletic overtraining. We aimed to identify the response of cfDNA to different types of exercise, with association to exercise intensity as a potential marker of exercise load. Fifty volunteers (25 athletes and 25 physically active men) were assigned to the study and performed maximal aerobic (Bruce test) and anaerobic (Wingate Anaerobic Test) test. Blood samples for cfDNA analysis were collected at four time-points: before, 2-5 min after, 30 min after and 60 min after each type of maximal physical activity. The two-way ANOVA revealed a significant effect of group factor on serum cfDNA concentrations (32.15% higher concentration of cfDNA in the athletes). In turn the results of the post hoc test for the interaction of the repeated measures factor and the group showed that while the concentration of cfDNA decreased by 40.10% in the period from 30 min to 60 min after exercise in the control group, the concentration of cfDNA in the group of athletes remained at a similar level. Our analysis presents different responses depending on the intensity and duration of exercise. Our observations imply that formation of cfDNA is associated with response to physical activity but only during maximal effort.

Stress and circulating cell-free mitochondrial DNA: A systematic review of human studies, physiological considerations, and technical recommendations

Cell-free mitochondrial DNA (cf-mtDNA) is a marker of inflammatory disease and a predictor of mortality, but little is known about cf-mtDNA in relation to psychobiology. A systematic review of the literature reveals that blood cf-mtDNA varies in response to common real-world stressors including psychopathology, acute psychological stress, and exercise. Moreover, cf-mtDNA is inducible within minutes and exhibits high intra-individual day-to-day variation, highlighting the dynamic regulation of cf-mtDNA levels. We discuss current knowledge on the mechanisms of cf-mtDNA release, its forms of transport ("cell-free" does not mean "membrane-free"), potential physiological functions, putative cellular and neuroendocrine triggers, and factors that may contribute to cf-mtDNA removal from the circulation. A review of in vitro, pre-clinical, and clinical studies shows conflicting results around the dogma that physiological forms of cf-mtDNA are pro-inflammatory, opening the possibility of other physiological functions, including the cell-to-cell transfer of whole mitochondria. Finally, to enhance the reproducibility and biological interpretation of human cf-mtDNA research, we propose guidelines for blood collection, cf-mtDNA isolation, quantification, and reporting standards, which can promote concerted advances by the community. Defining the mechanistic basis for cf-mtDNA signaling is an opportunity to elucidate the role of mitochondria in brain-body interactions and psychopathology.

The Nexus of cfDNA and Nuclease Biology

Cell-free DNA (cfDNA) is a widely used noninvasive biomarker for diagnosis and prognosis of multiple disease states. Emerging evidence suggests that cfDNA might not just be passive waste products of cell death but could have a physiological and pathological function in inflammation and autoimmunity. The balance of cfDNA generation and clearance may thus be vital in health and disease. In particular, plasma nuclease activity has been linked to multiple pathologies including cancer and systemic lupus erythematosus (SLE) and associated with profound changes in the nonrandom fragmentation of cfDNA. Lastly, in this review, we explore the effects of DNA fragmentation factor B (DFFB), DNASE1L3, and DNASE1 on cfDNA levels and their fragmentomic profiles, and what these recent insights reveal about the biology of cfDNA.

Comprehensive cell type decomposition of circulating cell-free DNA with CelFiE

Circulating cell-free DNA (cfDNA) in the bloodstream originates from dying cells and is a promising noninvasive biomarker for cell death. Here, we propose an algorithm, CelFiE, to accurately estimate the relative abundances of cell types and tissues contributing to cfDNA from epigenetic cfDNA sequencing. In contrast to previous work, CelFiE accommodates low coverage data, does not require CpG site curation, and estimates contributions from multiple unknown cell types that are not available in external reference data. In simulations, CelFiE accurately estimates known and unknown cell type proportions from low coverage and noisy cfDNA mixtures, including from cell types composing less than 1% of the total mixture. When used in two clinically-relevant situations, CelFiE correctly estimates a large placenta component in pregnant women, and an elevated skeletal muscle component in amyotrophic lateral sclerosis (ALS) patients, consistent with the occurrence of muscle wasting typical in these patients. Together, these results show how CelFiE could be a useful tool for biomarker discovery and monitoring the progression of degenerative disease.

Tissue damage and turnover lead to the release of DNA in the blood and can be used to monitor changes in tissue state. Here, the authors developed a tool to accurately estimate the proportion of cell types contributing to cell-free DNA in the blood, with an application to pregnant women and ALS patients.

Circulating cell free DNA response to exhaustive exercise in average trained men with type I diabetes mellitus

It is believed that neutrophils extracellular traps (NETs) formation is responsible for the increase in cf DNA after exercise. Since T1DM is accompanied by enhanced NETs generation, we compared exercise-induced increase in cf DNA in 14 men with T1DM and 11 healthy controls and analyzed its association with exercise load. Subjects performed a treadmill run to exhaustion at speed corresponding to 70% of their personal VO2max. Blood was collected before and just after exercise for determination of plasma cf nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) by real-time PCR, blood cell count and metabolic markers. Exercise resulted in the increase in median cf n-DNA from 3.9 ng/mL to 21.0 ng/mL in T1DM group and from 3.3 ng/mL to 28.9 ng/mL in controls. Median exercise-induced increment (∆) in cf n-DNA did not differ significantly in both groups (17.8 ng/mL vs. 22.1 ng/mL, p = 0.23), but this variable correlated with run distance (r = 0.66), Δ neutrophils (r = 0.86), Δ creatinine (r = 0.65) and Δ creatine kinase (r = 0.77) only in controls. Pre- and post-exercise cf mt-DNA were not significantly different within and between groups. These suggest low usefulness of Δ cf n-DNA as a marker of exercise intensity in T1DM men.

Reliability of gastrointestinal barrier integrity and microbial translocation biomarkers at rest and following exertional heat stress

PURPOSE

Exertional heat stress adversely distrupts (GI) barrier integrity and, through subsequent microbial translocation (MT), negativly impacts health. Despite widespread application, the temporal reliability of popular GI barrier integity and MT biomarkers is poorly characterised.

METHOD

Fourteen males completed two 80-min exertional heat stress tests (EHST) separated by 7-14 days. Venous blood was drawn pre, immediately- and 1-hr post both EHSTs. GI barrier integrity was assessed using the serum Dual-Sugar Absorption Test (DSAT), Intestinal Fatty-Acid-Binding Protein (I-FABP) and Claudin-3 (CLDN-3). MT was assessed using plasma Lipopolysaccharide Binding Protein (LBP), total 16S bacterial DNA and Bacteroides DNA.

RESULTS

No GI barrier integrity or MT biomarker, except absolute Bacteroides DNA, displayed systematic trial order bias (p ≥ .05). I-FABP (trial 1 = Δ 0.834 ± 0.445 ng ml^-1 ; trial 2 = Δ 0.776 ± 0.489 ng ml^-1 ) and CLDN-3 (trial 1 = Δ 0.317 ± 0.586 ng ml^-1 ; trial 2 = Δ 0.371 ± 0.508 ng ml^-1 ) were increased post-EHST (p ≤ .01). All MT biomarkers were unchanged post-EHST. Coefficient of variation and typical error of measurement post-EHST were: 11.5% and 0.004 (ratio) for the DSAT 90-min postprobe ingestion; 12.2% and 0.004 (ratio) at 150-min postprobe ingestion; 12.1% and 0.376 ng ml^-1 for I-FABP; 4.9% and 0.342 ng ml^-1 for CLDN-3; 9.2% and 0.420 µg ml^-1 for LBP; 9.5% and 0.15 pg µl^-1 for total 16S DNA; and 54.7% and 0.032 for Bacteroides/total 16S DNA ratio.

CONCLUSION

Each GI barrier integrity and MT translocation biomarker, except Bacteroides/total 16S ratio, had acceptable reliability at rest and postexertional heat stress.

Changes in plasma hydroxyproline and plasma cell-free DNA concentrations after higher- versus lower-intensity eccentric cycling

PURPOSE

We examined changes in plasma creatine kinase (CK) activity, hydroxyproline and cell-free DNA (cfDNA) concentrations in relation to changes in maximum voluntary isometric contraction (MVIC) torque and delayed-onset muscle soreness (DOMS) following a session of volume-matched higher- (HI) versus lower-intensity (LI) eccentric cycling exercise.

METHODS

Healthy young men performed either 5 × 1-min HI at 20% of peak power output (n = 11) or 5 × 4-min LI eccentric cycling at 5% of peak power output (n = 9). Changes in knee extensor MVIC torque, DOMS, plasma CK activity, and hydroxyproline and cfDNA concentrations before, immediately after, and 24-72 h post-exercise were compared between groups.

RESULTS

Plasma CK activity increased post-exercise (141 ± 73.5%) and MVIC torque decreased from immediately (13.3 ± 7.8%) to 48 h (6.7 ± 13.5%) post-exercise (P < 0.05), without significant differences between groups. DOMS was greater after HI (peak: 4.5 ± 3.0 on a 10-point scale) than LI (1.2 ± 1.0). Hydroxyproline concentration increased 40-53% at 24-72 h after both LI and HI (P < 0.05). cfDNA concentration increased immediately after HI only (2.3 ± 0.9-fold, P < 0.001), with a significant difference between groups (P = 0.002). Lack of detectable methylated HOXD4 indicated that the cfDNA was not derived from skeletal muscle. No significant correlations were evident between the magnitude of change in the measures, but the cfDNA increase immediately post-exercise was correlated with the maximal change in heart rate during exercise (r = 0.513, P = 0.025).

CONCLUSION

Changes in plasma hydroxyproline and cfDNA concentrations were not associated with muscle fiber damage, but the increased hydroxyproline in both groups suggests increased collagen turnover. cfDNA may be a useful metabolic-intensity exercise marker.

Cell-free nucleic acid patterns in disease prediction and monitoring-hype or hope?

Interest in the use of cell-free nucleic acids (CFNAs) as clinical non-invasive biomarker panels for prediction and prevention of multiple diseases has greatly increased over the last decade. Indeed, circulating CFNAs are attributable to many physiological and pathological processes such as imbalanced stress conditions, physical activities, extensive apoptosis of different origin, systemic hypoxic-ischemic events and tumour progression, amongst others. This article highlights the involvement of circulating CFNAs in local and systemic processes dealing with the question, whether specific patterns of CFNAs in blood, their detection, quantity and quality (such as their methylation status) might be instrumental to predict a disease development/progression and could be further utilised for accompanying diagnostics, targeted prevention, creation of individualised therapy algorithms, therapy monitoring and prognosis. Presented considerations conform with principles of 3P medicine and serve for improving individual outcomes and cost efficacy of medical services provided to the population.

Methods for Regulating and Monitoring Resistance Training

Individualisation can improve resistance training prescription. This is accomplished via monitoring or autoregulating training. Autoregulation adjusts variables at an individualised pace per performance, readiness, or recovery. Many autoregulation and monitoring methods exist; therefore, this review’s objective was to examine approaches intended to optimise adaptation. Up to July 2019, PubMed, Medline, SPORTDiscus, Scopus and CINAHL were searched. Only studies on methods of athlete monitoring useful for resistance-training regulation, or autoregulated training methods were included. Eleven monitoring and regulation themes emerged across 90 studies. Some physiological, performance, and perceptual measures correlated strongly (r ≥ 0.68) with resistance training performance. Testosterone, cortisol, catecholamines, cell-free DNA, jump height, throwing distance, barbell velocity, isometric and dynamic peak force, maximal voluntary isometric contractions, and sessional, repetitions in reserve-(RIR) based, and post-set Borg-scale ratings of perceived exertion (RPE) were strongly associated with training performance, respectively. Despite strong correlations, many physiological and performance methods are logistically restrictive or limited to lab-settings, such as blood markers, electromyography or kinetic measurements. Some practical performance tests such as jump height or throw distance may be useful, low-risk stand-ins for maximal strength tests. Performance-based individualisation of load progression, flexible training configurations, and intensity and volume modifications based on velocity and RIR-based RPE scores are practical, reliable and show preliminary utility for enhancing performance.

Increased Hepcidin Levels During a Period of High Training Load Do Not Alter Iron Status in Male Elite Junior Rowers

The liver-derived hormone hepcidin plays a key role in iron metabolism by mediating the degradation of the iron export protein ferroportin 1 (FPN1). Circulating levels of hepcidin and the iron storage protein ferritin are elevated during the recovery period after acute endurance exercise, which can be interpreted as an acute phase reaction to intense exercise with far-reaching consequences for iron metabolism and homeostasis. Since absolute and functional iron deficiency (ID) potentially lead to a loss of performance and well-being, it is surprising that the cumulative effects of training stress on hepcidin levels and its interplay with cellular iron availability are not well described. Therefore, the aim of this study was to determine serum levels of hepcidin at six time points during a 4-week training camp of junior world elite rowers preparing for the world championships and to relate the alterations in training load to overall iron status determined by serum ferritin, transferrin, iron, and soluble transferrin receptor (sTfR). Serum hepcidin levels increased significantly (p = 0.02) during the initial increase in training load (23.24 ± 2.43 ng/ml) at day 7 compared to the start of training camp (11.47 ± 3.92 ng/ml) and turned back on day 13 (09.51 ± 3.59 ng/ml) already, meeting well the entrance level of hepcidin at day 0. Serum ferritin was significantly higher at day 7 compared to all other timepoints with exception of the subsequent time point at day 13 reflecting well the time course pattern of hepcidin. Non-significant changes between training phases were found for serum iron, transferrin, and sTfR levels as well as for transferrin saturation, and ferritin-index (sTfR/log ferritin). Our findings indicate that hepcidin as well as ferritin, both representing acute phase proteins, are sensitive to initial increases in training load. Erythropoiesis was unaffected by iron compartmentalization through hepcidin. We conclude that hepcidin is sensitive to rigorous changes in training load in junior world elite rowers without causing short-term alterations in functional iron homeostasis.

Decreased integrity of exercise-induced plasma cell free nuclear DNA - negative association with the increased oxidants production by circulating phagocytes

Strenuous exercise increases circulating cell free DNA (cfDNA) and stimulates blood phagocytes to generate reactive oxygen species (ROS) which may induce DNA strand breaks. We tested whether: (A) elevated cfDNA in response to three repeated bouts of exhaustive exercise has decreased integrity; (B) each bout of exercise increases luminol enhanced whole blood chemiluminescence (LBCL) as a measure of ROS production by polymorphonuclear leukocytes. Eleven men performed three treadmill exercise tests to exhaustion separated by 72 hours of resting. Pre- and post-exercise concentrations and integrity of cf nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) and resting (r) and fMLP (n-formyl-methionyl-leucyl-phenylalanine)-stimulated LBCL were determined. Each bout increased concentrations of cf n-DNA by more than 10-times which was accompanied by about 2-times elevated post-exercise rLBCL and fMLP-LBCL. Post-exercise cf n-DNA integrity (integrity index, I_229/97) decreased after the first (0.59 ± 0.19 vs. 0.48 ± 0.18) and second (0.53 ± 0.14 vs. 0.44 ± 0.17) bout of exercise. There were negative correlations between I_229/97 and rLBCL (ƍ = –0.37), and I_229/97 and fMLP-LBCL (ƍ = –0.40) – analysis of pooled pre- and post-exercise data (n = 66). cf mt- DNA integrity (I_218/78) did not alter in response to exercise. This suggests an involvement of phagocyte ROS in cf n-DNA strand breaks in response to exhaustive exercise.

Time course of recovery is similar for the back squat, bench press, and deadlift in well-trained males

This study examined the time course of recovery following resistance exercise sessions in the back squat, bench press, and deadlift. Twelve well-trained males (age: 24.5 ± 3.8 years, body mass: 84.01 ± 15.44 kg, training age: 7.1 ± 4.2 years) performed 4 sets to failure at 80% of a 1-repetition maximum (1RM) on the squat, bench press, and deadlift in successive weeks. The bench press was always performed in week 2 with the squat and deadlift order counterbalanced between weeks 1 and 3. Indirect muscle damage and performance fatigue was assessed immediately before and after exercise and at 24 h, 48 h, 72 h, and 96 h postexercise. Outcome measures included limb swelling, joint range of motion, delayed onset muscle soreness, average concentric velocity (ACV) at 70% of 1RM, creatine kinase, lactate dehydrogenase, and cell-free DNA (cfDNA). Most measures demonstrated a main time effect (p < 0.05) within conditions; however, no between condition (p > 0.05) differences existed. ACV decreased in the squat condition for up to 72 h (p = 0.02, –8.61%) and in the bench press (p < 0.01, –26.69%) immediately postexercise but did not decline during the deadlift condition (p > 0.05). There was a main time effect for increased cfDNA in the squat (p < 0.01) and bench press (p < 0.05), but not the deadlift (p = 0.153). Further, immediately postexercise increases in cfDNA were directly related (p < 0.05) to changes in ACV in all 3 conditions. These results suggest that the deadlift does not result in greater muscle damage and recovery time than the squat and bench press following volume-type training in well-trained men. Further, acute changes in cfDNA may predict performance during the recovery period.

Comparison for immunophysiological responses of Jeju and Thoroughbred horses after exercise

OBJECTIVE

The study was conducted to investigate variations in the immunophysiological responses to exercise-induced stress in Jeju and Thoroughbred horses.

METHODS

Blood samples were collected from the jugular veins of adult Jeju (n = 5) and Thoroughbred (n = 5) horses before and after 30 min of exercise. The hematological, biochemical, and immunological profiles of the blood samples were analyzed. Blood smears were stained and observed under a microscope. The concentration of cell-free (cf) DNA in the plasma was determined using real time polymerase chain reaction (PCR). Peripheral blood mononuclear cells (PBMCs) and polymorphonuclear cells were separated using Polymorphprep, and the expression of various stress-related and chemokine receptor genes was measured using reverse transcriptase (RT) and real-time PCR.

RESULTS

After exercise, Jeju and Thoroughbred horses displayed stress responses with significantly increased rectal temperatures, cortisol levels, and muscle catabolism-associated metabolites. Red blood cell indices were significantly higher in Thoroughbred horses than in Jeju horses after exercise. In addition, exercise-induced stress triggered the formation of neutrophil extracellular traps (NETs) and reduced platelet counts in Jeju horses but not in Thoroughbred horses. Heat shock protein 72 and heat shock protein family A (Hsp70) member 6 expression is rapidly modulated in response to exercise-induced stress in the PBMCs of Jeju horses. The expression of CXC chemokine receptor 4 in PBMCs was higher in Thoroughbred horses than in Jeju horses after exercise.

CONCLUSION

In summary, the different immunophysiological responses of Jeju and Thoroughbred horses explain the differences in the physiological and anatomical properties of the two breeds. The physiology of Thoroughbred horses makes them suitable for racing as they are less sensitive to exercise-induced stress compared to that of Jeju horses. This study provides a basis for investigating the link between exercise-induced stresses and the physiological alteration of horses. Hence, our findings show that some of assessed parameters could be used to determine the endurance performance of horses.

Sex, Age, and Bodyweight as Determinants of Extracellular DNA in the Plasma of Mice: A Cross-Sectional Study

Extracellular DNA (ecDNA) is studied as a possible biomarker, but also as a trigger of the immune responses important for the pathogenesis of several diseases. Extracellular deoxyribonuclease (DNase) activity cleaves ecDNA. The aim of our study was to describe the interindividual variability of ecDNA and DNase activity in the plasma of healthy mice, and to analyze the potential determinants of the variability, including sex, age, and bodyweight. In this experiment, 58 adult CD1 mice (41 females and 31 males) of a variable age (3 to 16 months old) and bodyweight (females 25.7 to 52.1 g, males 24.6 to 49.6 g) were used. The plasma ecDNA was measured using a fluorometric method. The nuclear ecDNA and mitochondrial ecDNA were quantified using real-time PCR. The deoxyribonuclease activity was assessed using the single radial enzyme diffusion method. The coefficient of variance for plasma ecDNA was 139%, and for DNase 48%. Sex differences were not found in the plasma ecDNA (52.7 ± 73.0 ηg/mL), but in the DNase activity (74.5 ± 33.5 K.u./mL for males, and 47.0 ± 15.4 K.u./mL for females). There were no associations between plasma ecDNA and bodyweight or the age of mice. Our study shows that the variability of plasma ecDNA and DNase in adult healthy mice is very high. Sex, age, and bodyweight seem not to be major determinants of ecDNA variability in healthy mice. As ecDNA gains importance in the research of several diseases, it is of importance to understand its production and cleavage. Further studies should, thus, test other potential determinants, taking into account cleavage mechanisms other than DNase.

Acute psychological stress increases serum circulating cell-free mitochondrial DNA

Intrinsic biological mechanisms transduce psychological stress into physiological adaptation that requires energy, but the role of mitochondria and mitochondrial DNA (mtDNA) in this process has not been defined in humans. Here, we show that similar to physical injury, exposure to psychological stress increases serum circulating cell-free mtDNA (ccf-mtDNA) levels. Healthy midlife adults exposed on two separate occasions to a brief psychological challenge exhibited a 2-3-fold increase in ccf-mtDNA, with no change in ccf-nuclear DNA levels, establishing the magnitude and specificity for ccf-mtDNA reactivity. In cell-based studies, we show that glucocorticoid signaling - a consequence of psychological stress in humans - is sufficient to induce mtDNA extrusion in a time frame consistent with stress-induced ccf-mtDNA increase. Collectively, these findings provide evidence that acute psychological stress induces ccf-mtDNA and implicate neuroendocrine signaling as a potential trigger for ccf-mtDNA release. Further controlled work is needed to confirm that observed increases in ccf-mtDNA result from stress exposure and to determine the functional significance of this effect.

Circulating, Cell-Free DNA for Monitoring Player Load in Professional Football

Purpose: Player monitoring in elite sport settings is becoming increasingly important. Questionnaire-based methods and biomarkers such as circulating, cell-free DNA (cfDNA) are suggested for load monitoring. cfDNA concentrations were shown to increase depending on total distance covered in football and were associated with overtraining in weight lifters. Thus, the objective of this study was to examine whether cfDNA is feasible as a monitoring tool in elite football players. Methods: Capillary blood samples from 22 male elite football players were collected over 4 mo of a regular season. Sampling was conducted the day before, 1 day after, or several days after regular-season games and/or training. In addition, each player filled in a visual analogue scale (VAS) questionnaire including the items "general perceived exertion," "muscular fatigue," and "mental fatigue." Performance during training and games was tracked by the Catapult system and with the OPTA system, respectively. Results: cfDNA values were significantly elevated in players the day after regular-season games (1.4-fold; P = .0004) in line with the scores of the VAS. Both parameters showed significantly higher values during midweek-game weeks. cfDNA concentrations correlated with training data, and VAS was correlated with the tracking of the season games. However, cfDNA and VAS did not correlate with each other. Conclusions: cfDNA concentrations at rest and VAS scores are influenced by previous load in professional football players. Future studies will reveal whether cfDNA might serve as a practically applicable marker for player load in football players.

Circulating cell-free nucleic acids as biomarkers in colorectal cancer screening and diagnosis - an update

Introduction: Screening methods for one of the most frequently diagnosed malignancy, colorectal cancer (CRC), have limitations. Circulating cell-free nucleic acids (cfNA) hold clinical relevance as screening, prognostic and therapy monitoring markers. Area covered: In this review, we summarize potential CRC-specific cfNA biomarkers, the recently developed sample preparation techniques, their applications, and pitfalls. Expert opinion: Automated extraction of cfDNA is highly reproducible, however, cfDNA yield is less compared to manual isolation. Quantitative and highly sensitive detection techniques (e.g. digital PCR, NGS) can be applied to analyze genetic and epigenetic changes. Detection of DNA mutations or methylation in cfDNA and related altered levels of mRNA, miRNA, and lncRNA may improve early cancer recognition, based on specific, CRC-related patterns. Detection of cfDNA mutations (e.g. TP53, KRAS, APC) has limited diagnostic sensitivity (40-60%), however, methylated DNA including SEPT9, SFRP1, SDC2 can be applied with higher sensitivity (up to 90%) for CRC. Circulating miRNAs (e.g. miR-21, miR-92, miR-141) provide comparably high sensitivity for CRC as the circulating tumor cell mRNA markers (e.g. EGFR, CK19, CK20, CEA). Automation of cfNA isolation coupled with quantitative analysis of CRC-related, highly sensitive biomarkers may enhance CRC screening and early detection in the future.

Circulating Cell-Free DNA in Physical Activities

The interest about circulating cell-free DNA (cfDNA) concentration increased from several years because of its correlation with various conditions like osteoarthritis, cancers, stroke, and sepsis; recently it has become an important marker for overtraining syndrome or performance diagnostics.Several studies have demonstrated that cfDNA increases in vigorous and exhausting exercise but also endurance exercise. Acute effect of exercise on cfDNA concentration seems to be correlated to stress factor, while chronic effect is associated with necrosis and apoptosis.The intensity and duration seem to have effects on the variation of cfDNA concentration that is strongly correlated with other metabolic markers like acid lactate and creatine kinase, recognized as markers of muscle damage. Variation of cfDNA value could be used to predict overtraining syndrome.

The Potential Clinical Utility of Circulating Tumor DNA in Esophageal Adenocarcinoma: From Early Detection to Therapy

Esophageal adenocarcinoma (EAC) is a lethal cancer requiring improved screening strategies and treatment options due to poor detection methods, aggressive progression, and therapeutic resistance. Emerging circulating tumor DNA (ctDNA) technologies may offer a unique non-invasive strategy to better characterize the highly heterogeneous cancer and more clearly establish the genetic modulations leading to disease progression. The presented review describes the potential advantages of ctDNA methodologies as compared to current clinical strategies to improve clinical detection, enhance disease surveillance, evaluate prognosis, and personalize treatment. Specifically, we describe the ctDNA-targetable genetic markers of prognostic significance to stratify patients into risk of progression from benign to malignant disease and potentially offer cost-effective screening of established cancer. We also describe the application of ctDNA to more effectively characterize the heterogeneity and particular mutagenic resistance mechanisms in real-time to improve prognosis and therapeutic monitoring strategies. Lastly, we discuss the inconsistent clinical responses to currently approved therapies for EAC and the role of ctDNA to explore the dynamic regulation of novel targeted and immunotherapies to personalize therapy and improve patient outcomes. Although there are clear limitations of ctDNA technologies for immediate clinical deployment, this review presents the prospective role of such applications to potentially overcome many of the notable hurdles to treating EAC patients. A deeper understanding of complex EAC tumor biology may result in the progress toward improved clinical outcomes.

Techniques of using circulating tumor DNA as a liquid biopsy component in cancer management

Precision medicine in the clinical management of cancer may be achieved through the diagnostic platform called “liquid biopsy”. This method utilizes the detection of biomarkers in blood for prognostic and predictive purposes. One of the latest blood born markers under investigation in the field of liquid biopsy in cancer patients is circulating tumor DNA (ctDNA). ctDNA is released by tumor cells through different mechanisms and can therefore provide information about the genomic make-up of the tumor currently present in the patient. Through longitudinal ctDNA-based liquid biopsies, tumor dynamics may be monitored to predict and assess drug response and/or resistance. However, because ctDNA is highly fragmented and because its concentration can be extremely low in a high background of normal circulating DNA, screening for clinical relevant mutations is challenging. Although significant progress has been made in advancing the detection and analysis of ctDNA in the last few years, the current challenges include standardization and increasing current techniques to single molecule sensitivity in combination with perfect specificity. This review focuses on the potential role of ctDNA in the clinical management of cancer patients, the current technologies that are being employed, and the hurdles that still need to be taken to achieve ctDNA-based liquid biopsy towards precision medicine.

The diverse origins of circulating cell-free DNA in the human body: a critical re-evaluation of the literature

Since the detection of cell-free DNA (cfDNA) in human plasma in 1948, it has been investigated as a non-invasive screening tool for many diseases, especially solid tumours and foetal genetic abnormalities. However, to date our lack of knowledge regarding the origin and purpose of cfDNA in a physiological environment has limited its use to more obvious diagnostics, neglecting, for example, its potential utility in the identification of predisposition to disease, earlier detection of cancers, and lifestyle-induced epigenetic changes. Moreover, the concept or mechanism of cfDNA could also have potential therapeutic uses such as in immuno- or gene therapy. This review presents an extensive compilation of the putative origins of cfDNA and then contrasts the contributions of cellular breakdown processes with active mechanisms for the release of cfDNA into the extracellular environment. The involvement of cfDNA derived from both cellular breakdown and active release in lateral information transfer is also discussed. We hope to encourage researchers to adopt a more holistic view of cfDNA research, taking into account all the biological pathways in which cfDNA is involved, and to give serious consideration to the integration of in vitro and in vivo research. We also wish to encourage researchers not to limit their focus to the apoptotic or necrotic fraction of cfDNA, but to investigate the intercellular messaging capabilities of the actively released fraction of cfDNA and to study the role of cfDNA in pathogenesis.

Circulating, cell-free DNA as a marker for exercise load in intermittent sports

Background

Attempts to establish a biomarker reflecting individual player load in intermittent sports such as football have failed so far. Increases in circulating DNA (cfDNA) have been demonstrated in various endurance sports settings. While it has been proposed that cfDNA could be a suitable marker for player load in intermittent sports, the effects on cfDNA of repeated sprinting as an essential feature in intermittent sports are unknown. For the first time, we assessed both alterations of cfDNA due to repeated maximal sprints and due to a professional football game.

Methods

Nine participants were subjected to a standardised sprint training session with cross-over design of five maximal sprints of 40 meters with either “short” (1 minute) or “long” pauses (5 minutes). Capillary cfDNA and lactate were measured after every sprint and venous cfDNA before and after each series of sprints. Moreover, capillary cfDNA and lactate values were taken in 23 professional football players before and after incremental exercise testing, during the course of a training week at rest (baseline) and in all 17 enrolled players following a season game.

Results

Lactate and venous cfDNA increased more pronounced during “short” compared to “long” (1.4-fold, p = 0.032 and 1.7-fold, p = 0.016) and cfDNA correlated significantly with lactate (r = 0.69; p<0.001). Incremental exercise testing increased cfDNA 7.0-fold (p<0.001). The season game increased cfDNA 22.7-fold (p<0.0001), while lactate showed a 2.0-fold (p = 0.09) increase compared to baseline. Fold-changes in cfDNA correlated with distance covered during game (spearman’s r = 0.87, p = 0.0012), while no correlation between lactate and the tracking data could be found.

Discussion

We show for the first time that cfDNA could be an objective marker for distance covered in elite intermittent sports. In contrast to the potential of more established blood-based markers like IL-6, CK, or CRP, cfDNA shows by far the strongest fold-change and a high correlation with a particular load related aspect in professional football.

Serial perioperative cell-free DNA levels in donors and recipients undergoing living donor liver transplantation

BACKGROUND

Effect of anaesthesia and surgery on cell-free DNA (cfDNA) is not known. Given that surgical stress augments inflammation and injury, we hypothesized that levels of cfDNA will fluctuate during perioperative period. Therefore, in this study serial perioperative cfDNA concentration was measured in donors and recipients undergoing living donor liver transplantation (LDLT).

METHODS

Baseline, post-induction, intraoperative and post-operative plasma cfDNA levels were evaluated in 21 donors and recipients each, by Sytox green method. In addition, qPCR was performed in a subset of samples.

RESULTS

Baseline cfDNA levels were higher in recipients (37.62 ng/ml) than in donors (25.49 ng/ml). A decrease in cfDNA was observed following anaesthesia induction in both recipients (11.90 ng/ml) and donors (10.75 ng/ml). When the kinetics of the cfDNA was monitored further, an increase was noted intraoperatively in donors (46.18 ng/ml) and recipients (anhepatic phase: 56.25 ng/ml, reperfusion phase: 54.36 ng/ml). cfDNA levels remained high post-operatively. One recipient who developed post-operative sepsis had the highest cfDNA level (94.72 ng/ml).

CONCLUSION

Plasma cfDNA levels are high in recipients indicative of liver injury. Lower cfDNA levels following induction may be attributed to the subduing effect of anaesthetic agents on cell death. High cfDNA levels seen in intra- and post-operative phases reflect cellular trauma and inflammation. This similar pattern of fluctuation of cfDNA level in donors and recipients is suggestive of its possible utility as a surgical stress marker. In addition, comparable cfDNA levels in anhepatic and reperfusion phase reflect less ischemia reperfusion injury during LDLT.

Acute effects of strength exercises and effects of regular strength training on cell free DNA concentrations in blood plasma

Creatine kinase (CK) is a marker for muscle cell damage with limited potential as marker for training load in strength training. Recent exercise studies identified cell free DNA (cfDNA) as a marker for aseptic inflammation and cell damage. Here we overserved in a pilot study the acute effects during strength exercise and chronic effects of regular strength training on cfDNA concentrations over a period of four weeks in three training groups applying conservation training (CT) at 60% of the 1 repetition maximum, high intensity-low repetition training (HT) at 90% of the 1 repetition maximum and differential training (DT) at 60% of the 1 repetition maximum. EDTA-plasma samples were collected before every training session, and on the first and last training day repeatedly after every set of exercises. CfDNA increased significantly by 1.62-fold (mean (±SD) before first exercise: 8.31 (2.84) ng/ml, after last exercise 13.48 (4.12) ng/ml) across all groups within a single training session (p<0.001). The increase was 1.77-fold higher (mean (±SD) before first exercise: 12.23 (6.29) ng/ml, after last exercise 17.73 (11.24) ng/ml) in HT compared to CT (mean (±SD) before first exercise: 6.79 (1.28) ng/ml, after last exercise 10.05 (2.89) ng/ml) (p = 0.01). DNA size analysis suggested predominant release of short, mononucleosomal DNA-fragments in the acute exercise setting, while we detected an increase of mostly longer, polynucleosomal cfDNA-fragments at rest before the training session only at day two with a subsequent return to baseline (p<0.001). In contrast, training procedures did not cause any alterations in CK. Our results suggest that during strength exercise short-fragmented cfDNA is released, reflecting a fast, aseptic inflammatory response, while elevation of longer fragments at baseline on day two seemed to reflect mild cellular damage due to a novel training regime. We critically discuss the implications of our findings for future evaluations of cfDNA as a marker for training load in strength training.

Kinetic analysis, size profiling, and bioenergetic association of DNA released by selected cell lines in vitro

Although circulating DNA (cirDNA) analysis shows great promise as a screening tool for a wide range of pathologies, numerous stumbling blocks hinder the rapid translation of research to clinical practice. This is related directly to the inherent complexity of the in vivo setting, wherein the influence of complex systems of interconnected cellular responses and putative DNA sources creates a seemingly arbitrary representation of the quantitative and qualitative properties of the cirDNA in the blood of any individual. Therefore, to evaluate the potential of in vitro cell cultures to circumvent the difficulties encountered in in vivo investigations, the purpose of this work was to elucidate the characteristics of the DNA released [cell-free DNA (cfDNA)] by eight different cell lines. This revealed three different forms of cfDNA release patterns and the presence of nucleosomal fragments as well as actively released forms of DNA, which are not only consistently observed in every tested cell line, but also in plasma samples. Correlations between cfDNA release and cellular origin, growth rate, and cancer status were also investigated by screening and comparing bioenergetics flux parameters. These results show statistically significant correlations between cfDNA levels and glycolysis, while no correlations between cfDNA levels and oxidative phosphorylation were observed. Furthermore, several correlations between growth rate, cancer status, and dependency on aerobic glycolysis were observed. Cell cultures can, therefore, successfully serve as closed-circuit models to either replace or be used in conjunction with biofluid samples, which will enable sharper focus on specific cell types or DNA origins.

Repeated bouts of exhaustive exercise increase circulating cell free nuclear and mitochondrial DNA without development of tolerance in healthy men

Objective

Acute single strenuous exercise increases circulating cell free DNA (cf DNA). We tested whether three repeated bouts of exhaustive exercise induced the cf DNA response without development of tolerance in healthy men.

Methods

Eleven average-trained men (age 34.0±5.2 years, body mass index 26.2±3.1 kg/m2, maximal oxygen consumption—VO₂max 49.6±4.5 ml/kg*min) performed three treadmill exercise tests to exhaustion at speed corresponding to 70% VO₂max separated by 72 hours of resting. Blood was collected before and after each bout of exercise for determination of cell free nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) by real-time PCR, selected markers of muscle damage, and blood cell count.

Results

Each bout induced the increase (p<0.05) in plasma cf n-DNA: from 3.4±1.4 to 38.5±27.5, from 4.1±3.3 to 48.5±26.2, and 3.1±1.6 to 53.8±39.9 ng/mL after the first, second, and third exercise, respectively. In a congruent way, cf mt-DNA rose significantly after the second (from 229±216 to 450±228*103 GE/mL) and third bout of exercise (from 173±120 to 462±314*103 GE/mL).

Pre-exercise cf mt-DNA decreased (p<0.05) by 2-times (from 355±219 before the first bout to 173±120*103 GE/mL before the third bout) over the study period and were accompanied by significant increase in white blood cells, platelets, creatine kinase, creatinine and lactate after each bout. However, the exercise induced percentage increment of cf n-DNA was always many times higher than corresponding increments of the afore-mentioned markers at any occasion.

Conclusions

Repeated bouts of exhaustive exercise induced remarkable increase in circulating cf n-DNA without signs of tolerance development. Baseline cf mt-DNA decreased in response to series of strenuous exercise. Since percentage increments of cf n-DNA in response to exercise were many times higher than those observed for other markers, measurement of circulating cf n-DNA could be a sensitive tool for monitoring acute exercise effects in human body.

Circadian Rhythm of Methylated Septin 9, Cell-Free DNA Amount and Tumor Markers in Colorectal Cancer Patients

To determine the level of cell-free DNA (cfDNA), Septin 9 (SEPT9) and tumor markers (CEA, AFP, CA19-9, TPA, CA72-4). Plasma samples were collected four times a day (06:00, 12:00, 18:00, 24:00) from 9 patients with CRC (5 stage I-II, 4 stage III-IV), from one with colorectal adenoma and from one healthy control. CfDNA was isolated, quantified and bisulfite-converted. CfDNA and methylated SEPT9 were determined by RT-PCR. Plasma levels of conventional tumor markers were also measured. The lowest cfDNA concentrations were observed at 24:00 and 18:00 in stage I-III patients. In stage IV samples low cfDNA level (mean 48.2 ng/ml) were observed at several time points (6:00, 12:00, 18:00). The highest cfDNA levels were measured at 6:00 and 12:00 in CRC I-III stages and at 24:00 in stage IV samples (78.65 ng/ml). Higher in-day differences were found in stage II (43-48%) than in stage I samples (22%). Interestingly, the highest SEPT9 methylation level was found at 24:00 in most CRC cases, in contrast to the cfDNA levels. At 24:00, all cancer and adenoma cases were positive for SEPT9 methylation. At other time points (6:00, 12:00, 18:00) only 77.7% of CRC samples showed SEPT9 positivity. Stage I samples were SEPT9 positive only at 24:00. CEA and CA19-9 levels displayed correlation with the amount of cfDNA in case of late stage cases. Daytime activity can influence SEPT9 positivity in cases with low concentration of cfDNA. Thus, it may improve screening sensitivity by collecting samples earlier in the morning.

A historical and evolutionary perspective on the biological significance of circulating DNA and extracellular vesicles

The discovery of quantitative and qualitative differences of the circulating DNA (cirDNA) between healthy and diseased individuals inclined researchers to investigate these molecules as potential biomarkers for non-invasive diagnosis and prognosis of various pathologies. However, except for some prenatal tests, cirDNA analyses have not been readily translated to clinical practice due to a lack of knowledge regarding its composition, function, and biological and evolutionary origins. We believe that, to fully grasp the nature of cirDNA and the extracellular vesicles (EVs) and protein complexes with which it is associated, it is necessary to probe the early and badly neglected work that contributed to the discovery and development of these concepts. Accordingly, this review consists of a schematic summary of the major events that developed and integrated the concepts of heredity, genetic information, cirDNA, EVs, and protein complexes. CirDNA enters target cells and provokes a myriad of gene regulatory effects associated with the messaging functions of various natures, disease progression, somatic genome variation, and transgenerational inheritance. This challenges the traditional views on each of the former topics. All of these discoveries can be traced directly back to the iconic works of Darwin, Lamarck, and their followers. The history of cirDNA that has been revisited here is rich in information that should be considered in clinical practice, when designing new experiments, and should be very useful for generating an empirically up-to-date view of cirDNA and EVs. Furthermore, we hope that it will invite many flights of speculation and stimulate further inquiry into its biological and evolutionary origins.

Circulating cell-free nucleic acids as biomarkers in colorectal cancer screening and diagnosis

Screening methods for the most frequent diagnosed malignant tumor, colorectal cancer (CRC), have limitations. Circulating cell-free DNA (cfDNA) analysis came into focus as a potential screening test for CRC. Detection of epigenetic and genetic alterations of cfDNA as DNA methylation or DNA mutations and related ribonucleic acids may improve cancer detection based on unique, CRC-specific patterns. In this review the authors summarize the CRC-specific nucleic acid biomarkers measured in peripheral blood and their potential as screening markers. Detection of DNA mutation has inadequate sensitivity; however, methylated DNA can be established with higher sensitivity from CRC plasma samples. The ribonucleic acid based miRNA studies represented higher sensitivity for CRC as compared with mRNA studies. Recently, isolation of cfDNA has become automated, highly reproducible and a high throughput method. With automated possible diagnostic tools, a new approach may be available for CRC screening as liquid biopsy.

Extracellular DNA: A Bridge to Cancer

DNase I is a secreted enzyme whose function has been presumed to control "waste management" in the human system, by degrading DNA that leaks from dead and dying cells. Emerging studies have instead yielded evidence that DNase I plays a central role in newly defined dynamics of immune and autoimmune diseases, as well as cancer and vascular disorders, including thrombosis. Cancer cells have been reported to be associated with distinctive extracellular structures that facilitate aggregation and implantation. The fact that DNA is a component of such structures and that it plays a role in cancer development is illustrated by direct evidence: DNase I added to tumor cells eliminates the structures and inhibits tumorigenicity of some cancer cell lines. DNase I injected into experimental animals, moreover, results in significant inhibition of metastasis. Despite independent observations of such phenomena in diverse cancers for over 50 years, the potential for using DNase I as a clinical tool to prevent or treat cancer remains unexplored. The discovery of neutrophil extracellular traps has yielded a conceptual framework for interpreting how extracellular DNA may function in cancer development and why it may prove to be an important clinical target in stopping cancer outside the cell.

Detecting cancer biomarkers in blood: challenges for new molecular diagnostic and point-of-care tests using cell-free nucleic acids

As we move into the era of individualized cancer treatment, the need for more sophisticated cancer diagnostics has emerged. Cell-free (cf) nucleic acids (cf-DNA, cf-RNA) and other cellular nanoparticulates are now considered important and selective biomarkers. There is great hope that blood-borne cf-nucleic acids can be used for 'liquid biopsies', replacing more invasive tissue biopsies to analyze cancer mutations and monitor therapy. Conventional techniques for cf-nucleic acid biomarker isolation from blood are generally time-consuming, complicated and expensive. They require relatively large blood samples, which must be processed to serum or plasma before isolation of biomarkers can proceed. Such cumbersome sample preparation also limits the widespread use of powerful, downstream genomic analyses, including PCR and DNA sequencing. These limitations also preclude rapid, point-of-care diagnostic applications. Thus, new technologies that allow rapid isolation of biomarkers directly from blood will permit seamless sample-to-answer solutions that enable next-generation point-of-care molecular diagnostics.

Direct measurement of cell-free DNA from serially collected capillary plasma during incremental exercise

To investigate the kinetics of cell-free DNA (cfDNA) due to exercise, we established a direct real-time PCR for the quantification of cfDNA from unpurified capillary plasma by amplification of a 90- and a 222-bp multilocus L1PA2 sequence. Twenty-six male athletes performed an incremental treadmill test. For cfDNA measurement, capillary samples were collected serially from the fingertip preexercise, during, and several times postexercise. Venous blood was drawn before and immediately after exercise to compare capillary and venous cfDNA values. To elucidate the strongest association of cfDNA accumulations with either cardiorespiratory or metabolic function during exercise, capillary cfDNA values were correlated with standard measures like heart rate, oxygen consumption, or lactate concentrations. The venous cfDNA concentrations were significantly higher compared with the capillary plasma, but in both fractions cfDNA increased 9.8-fold and the values correlated significantly ( r = 0.796). During incremental treadmill running, the capillary cfDNA concentrations increased nearly parallel to the lactate values. The values correlated best with heart rate and energy expenditure, followed by oxygen consumption, Borg values, and lactate levels (0.710 ≤ r ≥ 0.808). With this article, we present a sensitive procedure for the direct quantification of cfDNA in unpurified capillary plasma instead of purified venous plasma. Further studies should investigate the differences between capillary and venous cfDNA that might mirror different physiological mechanisms. Enhanced cardiorespiratory function during exercise might lead to the accumulation of cfDNA via the release of stress hormones that already increase at intensities below the anaerobic threshold. Furthermore, cfDNA might be released by neutrophil extracellular traps.