Low-molecular-weight DNA in blood plasma as an index of the influence of ionizing radiation

The Effects of Low-Frequency Noise on Rats: Evidence of Chromosomal Aberrations in the Bone Marrow Cells and the Release of Low-Molecular-Weight DNA in the Blood Plasma

Objectives:

Evaluation of the effect of low-frequency noise (LFN) on the frequency of chromosomal aberrations in the bone marrow cells and on the content of low-molecular-weight DNA (lmwDNA) in the blood plasma of rats.

Materials and Methods:

A total of 96 male Wistar rats were exposed to either single (17 min session) or multiple (17 min session repeated five times a week for 13 weeks) LFN, with the maximum range below 250 Hz and the sound pressure levels (SPLs) at 120 and 150 dB, respectively. The rats in the control groups were not subjected to any impact. The frequency of chromosomal aberrations in the bone marrow cells and the levels of lmwDNA in the blood plasma were measured afterwards.

Results:

It has been detected that a single LFN exposure with either corresponding SPLs had a significant increase in the frequency of chromosomal aberrations (more than 10-fold) compared to the controls (0.9 ± 0.3%) and resulted in the appearance of dicentric chromosomes in the aberration spectrum, both of which are evident for the occurrence of deoxyribonucleic acid double strand breaks triggered by the exposure. Furthermore, the lmwDNA levels in the blood plasma measured the following day after a single LFN exposure were significantly higher (7.7- and 7.6-fold, respectively) than that in the control group (11.0 ± 5.4 ng/ml), and such levels were maintained higher (4.8- and 2.1-fold, respectively) in the week after a single LFN exposure for the SPL of 120 and 150 dB, respectively, compared to the control group (18.8 ± 1.6 ng/ml). Similar results were obtained from the group with multiple LFN exposures (36.4- and 22.4-fold, respectively) compared to the control (17.7 ± 1.7 ng/ml) and suggest the enhancement of cellular apoptosis as a result of the LFN impact.

Conclusion:

Presumably, the LFN may have possible mutagenic effects and cause massive cell death.

Comparative Analysis of Harmful Physical Factors Effect on the Cell Genome

Exposure to either to low-frequency noise or ionizing radiation causes an increase in the number of chromosomal aberrations in the bone marrow cells and the level of low-molecular-weight DNA in the blood plasma of experimental animals. The dynamics of the content of low-molecular-weight DNA increasing after exposure to low-frequency noise and ionizing radiation differs significantly. Both exposures are able to provide a direct damaging effect on DNA.

Human circulating ribosomal DNA content significantly increases while circulating satellite III (1q12) content decreases under chronic occupational exposure to low-dose gamma- neutron and tritium beta-radiation

A single exposure to ionizing radiation (IR) results in an elevated cell-free DNA (cfDNA) content in the blood plasma. In this case, the cfDNA concentration can be a marker of the cell death in the organism. However, a chronic exposure to a low-dose IR enhances both the endonuclease activity and titer of antibodies to DNA in blood plasma, resulting in a decrease of the total concentration of circulating cfDNA in exposed people. In this case, the total cfDNA concentration should not be considered as a marker of the cell death in an exposed body. We assumed that a pool of the cfDNA circulating in the exposed people contains DNA fragments, which are resistant to a double-strand break formation in the environment of the elevated plasma endonuclease activity, and can be accumulated in the blood plasma. In order to test this hypothesis, we studied the content of GC-rich sequences (69%GC) of the transcribed region of human ribosomal repeat (rDNA), as well as the content of AT-rich repeat (63%AT) of satellite III (1q12) in the cfDNA samples obtained from 285 individuals. We have found that a chronic exposure to gamma-neutron radiation (N=88) and tritium β-radiation (N=88) evokes an increase of the rDNA content (RrDNA index) and a decrease of the satellite III content (RsatIII index) in the circulating cfDNA as compared with the cfDNA of non-exposed people (N=109). Such index that simultaneously displays both the increase of rDNA content and decrease of satellite III content in the cfDNA (RrDNA/RsatIII) can be recommended as a marker of chronic processes in the body that involve the elevated cell death rate and/or increased blood plasma endonuclease activity.

Radioprotective combination of α-tocopherol and ascorbic acid promotes apoptosis that is evident by release of low-molecular weight DNA fragments into circulation

PURPOSE

Genotoxic stresses, including irradiation, lead to the apoptosis of damaged cells and the release of DNA fragments into circulation. Both α-tocopherol acetate and ascorbic acid possess antioxidant and radioprotective properties. Interestingly, depending on a particular experimental system, the treatment with vitamins may demonstrate either apoptosis-promoting or apoptosis-suppressing effects.

MATERIALS AND METHODS

Adult Wistar male rats received total body irradiation with 2-100 Gy doses, while non-irradiated rats served as controls. Oral gavages with vitamins were administered either 10 min or 1 h before irradiation. Control groups were similarly treated with water. Blood samples were collected at 5 h post irradiation. The levels and the composition of circulating DNA were profiled. Chromosomal aberrations were assessed 24 h after irradiation.

RESULTS

A substantial dose-dependent increase in circulating low-molecular weight (LMW) DNA levels was observed after whole body irradiation. An order-of-magnitude increase in the proportion of bone marrow cells with chromosomal abnormalities was observed after irradiation at 2 Gy. Single vitamin preparations were not protective, while the combination of α-tocopherol (10 mg/kg) and ascorbic acid (20 mg/kg) displayed a protective effect evident from marked decrease in chromosomal aberrations. In animals treated with a combination of the vitamins only, substantial increases in the release of LMW DNA were observed.

CONCLUSIONS

Radioprotective combination of α-tocopherol and ascorbic acid promotes apoptosis that is evident by release of low-molecular weight DNA into circulation. We hypothesize that the pretreatment with vitamins provides radioprotection, at least in part, by aiding non-inflammatory, apoptotic elimination of most damaged cells. The microevolutionary nature of observed adaptive response provides mechanistic foundation for the phenomenon of hormesis.

Human circulating plasma DNA significantly decreases while lymphocyte DNA damage increases under chronic occupational exposure to low-dose gamma-neutron and tritium β-radiation

The blood plasma of healthy people contains cell-fee (circulating) DNA (cfDNA). Apoptotic cells are the main source of the cfDNA. The cfDNA concentration increases in case of the organism's cell death rate increase, for example in case of exposure to high-dose ionizing radiation (IR). The objects of the present research are the blood plasma and blood lymphocytes of people, who contacted occupationally with the sources of external gamma/neutron radiation or internal β-radiation of tritium N = 176). As the controls (references), blood samples of people, who had never been occupationally subjected to the IR sources, were used (N = 109). With respect to the plasma samples of each donor there were defined: the cfDNA concentration (the cfDNA index), DNase1 activity (the DNase1 index) and titre of antibodies to DNA (the Ab DNA index). The general DNA damage in the cells was defined (using the Comet assay, the tail moment (TM) index). A chronic effect of the low-dose ionizing radiation on a human being is accompanied by the enhancement of the DNA damage in lymphocytes along with a considerable cfDNA content reduction, while the DNase1 content and concentration of antibodies to DNA (Ab DNA) increase. All the aforementioned changes were also observed in people, who had not worked with the IR sources for more than a year. The ratio cfDNA/(DNase1×Ab DNA × TM) is proposed to be used as a marker of the chronic exposure of a person to the external low-dose IR. It was formulated the assumption that the joint analysis of the cfDNA, DNase1, Ab DNA and TM values may provide the information about the human organism's cell resistivity to chronic exposure to the low-dose IR and about the development of the adaptive response in the organism that is aimed, firstly, at the effective cfDNA elimination from the blood circulation, and, secondly - at survival of the cells, including the cells with the damaged DNA.

Cell-free DNA in the urine of rats exposed to ionizing radiation

Investigation of cell-free DNA (cf-DNA) in body fluids, as a potential biomarker for assessing the effect of ionizing radiation on the organism, is of considerable interest. We investigated changes in the contents of cell-free mitochondrial DNA (cf-mtDNA) and cell-free nuclear DNA (cf-nDNA) in the urine of X-ray-exposed rats. Assays of cf-mtDNA and cf-nDNA were performed by a real-time PCR in rat urine collected before and after irradiation of animals with doses of 3 and 5 Gy. We also determined the presence of mutations in urine cf-mtDNA, as recognized by Surveyor nuclease. A sharp increase in cf-mtDNA and cf-nDNA in the urine of irradiated rats was observed within 24 h after exposure, followed by a decrease to normal levels. In all cases, the contents of cf-mtDNA fragment copies (estimated by gene tRNA) were significantly higher than those of cf-nDNA estimated by gene GAPDH. A certain portion of mutant cf-mtDNA fragments was detected in the urine of exposed rats, whereas they were absent in the urine of the same animals before irradiation. These preliminary data also suggest that the increased levels of urine cf-mtDNA and cf-nDNA may be a potential biomarker for noninvasive assessment of how the organism responds to ionizing radiation influence.

Increased circulating cell-free DNA levels and mtDNA fragments in interventional cardiologists occupationally exposed to low levels of ionizing radiation

Circulating cell-free DNA (ccf-DNA) and mtDNA (ccf-mtDNA) have often been used as indicators of cell death and tissue damage in acute and chronic disorders, but little is known about changes in ccf-DNA and ccf-mtDNA concentrations following radiation exposure. The aim of the study was to investigate the impact of chronic low-dose radiation exposure on serum ccf-DNA levels and ccf-mtDNA fragments (mtDNA-79 and mtDNA-230) of interventional cardiologists working in high-volume cardiac catheterization laboratory to assess their possible role as useful radiation biomarkers. We enrolled 50 interventional cardiologists (26 males; age = 48.4 ± 10 years) and 50 age- and gender-matched unexposed controls (27 males; age = 47.6 ± 8.3 years). Quant-iT™ dsDNA High-Sensitivity assay was used to measure circulating ccf-DNA isolated from serum samples. Quantitative analysis of mtDNA fragments was performed by real-time PCR. No significant relationships were found between ccf-DNA and ccf-mtDNA, and age, gender, smoking, or other clinical parameters. Ccf-DNA levels (44.2 ± 31.1 vs. 30.6 ± 19.2 ng/ml, P = 0.013), ccf-mtDNA-79 (2.6 ± 2.1 vs. 1.1 ± 0.8, P < 0.01), and ccf-mtDNA-230 copies (2.0 ± 1.8 vs. 1.04 ± 0.9, P = 0.02) were significantly higher in interventional cardiologists compared with the non-exposed group. In a subset (n = 15) of interventional cardiologists with a reliable reconstruction of cumulative professional exposure (59.7 ± 48.4 mSv; range: 1.4-182 mS), ccf-DNA (53.2 ± 41.3 vs. 36.4 ± 22.9 and 32.2 ± 20.5, P = 0.08), mtDNA-79 (2.4 ± 2.1 vs. 2.03 ± 1.7 and 1.09 ± 0.82, P = 0.05), and mtDNA-230 (2.0 ± 2.2 vs. 1.5 ± 1.4 and 1.04 ± 0.9, P = 0.09) tended to be significantly increased in high-exposure subjects compared with both low-exposure interventional cardiologists and controls. Our results provide evidence for a possible role of circulating DNA as a relevant biomarker of cellular damage induced by exposure to chronic low-dose radiation.

Fluoroplast-polyaniline-coated adsorbent for one-step isolation of DNA for PCR detection of viral hepatitides (HBV and TTV)

AIMS

To demonstrate the effectiveness of application of the adsorbent successively modified with nano-layers of fluoroplast and polyaniline for one-step isolation of DNA of hepatitis B virus and transfusion-transmitted virus from human serum.

MATERIALS & METHODS

The technique is based on the application of the spin-cartridges containing porous adsorbent for one-step viral DNA isolation from serum followed by polymerase chain reaction.

RESULTS

The developed adsorbent was shown to be effective for one-step isolation of viral DNA from serum samples for polymerase chain reaction diagnostics.

CONCLUSION

The effectiveness of the developed adsorbent application for isolation of viral DNA from serum for polymerase chain reaction diagnostics was confirmed in comparison with standard methods. Thus, the facile sample preparation method of viral DNA isolation was elaborated.

Oxidized extracellular DNA as a stress signal that may modify response to anticancer therapy

An increase in the levels of oxidation is a universal feature of genomic DNA of irradiated or aged or even malignant cells. In case of apoptotic death of stressed cells, oxidized DNA can be released in circulation (cfDNA). According to the results of the studies performed in vitro by our group and other researchers, the oxidized cfDNA serves as a biomarker for a stress and a stress signal that is transmitted from the "stressed" area i.e. irradiated cells or cells with deficient anti-oxidant defenses to distant (bystander) cells. In recipient cells, oxidized DNA stimulates biosynthesis of ROS that is followed up by an increase in the number of single strand and double strand breaks (SSBs and DSBs), and activation of DNA Damage Response (DDR) pathway. Effects of oxidized DNA are considered similar to that of irradiation. It seems that downstream effects of irradiation, in part, depend on the release of oxidized DNA fragments that mediate the effects in distant cells. The responses of normal and tumor cell to oxidized DNA may differ. It seems that tumor cells are more sensitive to oxidized DNA-dependent DNA damage, while developing pronounced adaptive response. This may suggest that in chemotherapy or irradiation-treated human body, the release of oxidized DNA from dying cancer cells may give a boost to remaining malignant cells by augmenting their survival and stress resistance. Further studies of the effects of oxidized DNA in both in vitro and in vivo systems are warranted.

A new biodosimetric method: branched DNA-based quantitative detection of B1 DNA in mouse plasma

A simple and accurate method for measuring the biological effects of radiation is of increasing importance, especially in mass casualty scenarios. We have therefore developed a new biodosimetric technique targeting circulating B1 DNA in mouse plasma by branched DNA signal amplification for rapid quantification of plasma DNA. This technology targets repetitive elements of the B1 retrotransposon in the mouse genome, followed by signal amplification using Panomics Quantigene 2.0 reagents. Evaluation was conducted concerning precision, accuracy and linearity. Plasma samples were collected from mice 0-24 h after 0-10 Gy total body irradiation (TBI). The average inter- and intra-assay coefficients of variance were 8.7% and 12.3%, respectively. The average recovery rate of spiked DNA into plasma was 89.5%. This assay revealed that when BALB/c and NIH Swiss mice were exposed to 6 Gy TBI, plasma B1 DNA levels increased significantly at 3 h post-TBI, peaked at 9 h and gradually returned toward baseline levels in 24 h. A dose-dependent change in plasma DNA was observed at 9 h post-TBI; the dose-response relation was monotonic, exhibiting linearity for BALB/c mice from 3 to 6 Gy (r = 0.993) and NIH Swiss mice from 3 to 7 Gy (r = 0.98). This branched DNA-based assay is reliable, accurate and sensitive in detecting plasma B1 DNA quantitatively. A radiation dose-correlated increase in plasma B1 DNA was demonstrated in BALB/c and NIH Swiss mice in the dose range from 3 to 6 Gy, suggesting that plasma B1 DNA has potential as a biomarker for radiation biological effect.

B1 sequence-based real-time quantitative PCR: a sensitive method for direct measurement of mouse plasma DNA levels after gamma irradiation

PURPOSE

Current biodosimetric techniques for determining radiation exposure have inherent delays, as well as quantitation and interpretation limitations. We have identified a new technique with the advantage of directly measuring circulating DNA by amplifying inter-B1 regions in the mouse genome, providing a sensitive method for quantitating plasma DNA.

METHODS AND MATERIALS

Real-time quantitative polymerase chain reaction (PCR) was used to detect levels of DNA by amplifying inter-B1 genomic DNA in plasma samples collected at 0-48 h from mice receiving 0-10 Gy total- or partial-body irradiation ((137)Cs gamma-ray source at approximately 1.86 Gy/min; homogeneity: +/- 6.5%).

RESULTS

The correlation coefficient between DNA levels and the threshold cycle value (C(T)) was 0.996, and the average recoveries of DNA in the assay were 87%. This assay revealed that when BALB/c mice were exposed to 10 Gy total-body irradiation (TBI), plasma DNA levels gradually increased beginning at 3 h after irradiation, peaked at 9 h, and returned to baseline within 48 h. Increased plasma DNA levels were also detected following upper-torso or lower-torso partial-body irradiation; however, TBI approximately doubled those plasma DNA levels at the same radiation dose. This technique therefore reflects total body cell damage. The advantages of this assay are that DNA extraction is not required, the assay is highly sensitive (0.002 ng), and results can be obtained within 2.5 h after collection of plasma samples.

CONCLUSIONS

A radiation dose-dependent increase of plasma DNA was observed in the dose range from 2 to 10 Gy, suggesting that plasma DNA may be a useful radiation biomarker and adjunct to existing cell-based assays.

Circulating Nucleic Acids and Diabetic Complications

Diabetes mellitus is a major health problem across the world. Diabetic retinopathy (DR) and nephropathy are two of the major complications of diabetes. DR is the leading cause of blindness and diabetic nephropathy is the leading cause of end-stage renal failure. We have examined the potential value of circulating nucleic acids in the detection and monitoring of these two complications of diabetes. mRNA for nephrin was significantly higher in all diabetics compared to healthy controls and it was significantly higher in normoalbuminuric patients compared to healthy controls. This may indicate progression to microalbuminuric stage. Circulating rhodopsin mRNA was detectable in healthy subjects and in diabetic patients. It was significantly raised in diabetic patients with retinopathy. Higher rhodopsin mRNA in diabetic patients without retinopathy suggests that some of them may go on to develop it or already have it subclinically. Circulating nucleic acids have the potential to be noninvasive molecular tests for diabetic complications.

Radiation-induced genomic instability is associated with DNA methylation changes in cultured human keratinocytes

The mechanism by which radiation-induced genomic instability is initiated, propagated and effected is currently under intense scrutiny. We have investigated the potential role of altered genomic methylation patterns in the cellular response to irradiation and have found evidence for widespread dysregulation of CpG methylation persisting up to 20 population doublings post-irradiation. Similar effects are seen with cells treated with medium from irradiated cells (the 'bystander effect') rather than subjected to direct irradiation. Using an arbitrarily primed methylation sensitive PCR screening method we have demonstrated that irradiation causes reproducible alterations in the methylation profile of a human keratinocyte cell line, HPV-G, and have further characterised one of these sequences as being a member of a retrotransposon element derived sequence family on chromosome 7; MLT1A. Multiple changes were also detected in the screen, which indicate that although the response of cells is predominantly hypermethylation, specific hypomethylation occurs as well. Sequence specific changes are also reported in the methylation of the pericentromeric SAT2 satellite sequence. This is the first demonstration that irradiation results in the induction of heritable methylation changes in mammalian cells, and provides a link between the various non-radiological instigators of genomic instability, the perpetuation of the unstable state and several of its manifestations.

Extracellular circulating nucleic acids in human plasma in health and disease

The concentration of extracellular DNA and RNA in blood plasma of healthy donors, trauma patients, patients with breast and lung cancer, nonmalignant breast tumors and nonmalignant lung diseases were estimated. Significant amounts of extracellular RNA were found in plasma of trauma patients. The concentration of DNA and RNA in plasma of trauma patients correlates with the extent of posttraumatic organ failure. Extracellular RNA was not found in the plasma of breast cancer patients and patients with nonmalignant breast tumors, whereas a very high concentration of extracellular RNA was found in patients with malignant and nonmalignant diseases of lung.

Cell-surface-bound nucleic acids: Free and cell-surface-bound nucleic acids in blood of healthy donors and breast cancer patients

Concentrations of extracellular DNA and RNA in the blood of healthy donors and patients with malignant and nonmalignant breast tumors were investigated. Cell-surface-bound extracellular DNA and RNA were detached by PBS-EDTA treatment or mild trypsin treatment of erythrocytes and leukocytes. In healthy donors, almost all extracellular nucleic acids (98%) are bound at the surface of blood cells. In the blood of cancer patients, extracellular nucleic acids were found in plasma and not at the cell surface. In patients with nonmalignant breast tumors, extracellular nucleic acids were found both at the surface of blood cells and in plasma. In healthy donors, the cell-surface-bound DNA is represented by 20-kbp DNA fragments and smaller fragments that varied in amounts in different fractions.