Extracellular DNA Level in the Blood of Irradiated Rats

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.

Alteration of mtDNA copy number, mitochondrial gene expression and extracellular DNA content in mice after irradiation at lethal dose

High steady-state transcriptional activity is essential for normal mitochondrial function. The requisite transcription rate is satisfied in part by high copy number of mitochondrial DNA (mtDNA). In the present study, we analyze mtDNA copy number by real-time PCR in nucleated blood cells from control mice and mice exposed to 1- or 10-Gy X-radiation. Transcription of the oxidative phosphorylation-associated genes cytb, atp6, nd4, nd2 and d-loop region was monitored in these nucleated blood cells similarly by real-time PCR. We observed a 50% decrease in the ratio of mitochondrial to nuclear DNA (mtDNA/nDNA) in blood cells, while the mtDNA/nDNA ratio in serum increased. After a lethal 10-Gy dose of X-irradiation, we observed an 80% decrease in the number of circulating lymphocytes. In response to a 10-Gy radiation dose, we observed transiently increased mtDNA/nDNA ratio and transcription within the initial 5 h post-treatment. At 24-72 h, the mtDNA/nDNA ratio in surviving cells was reduced to the level observed in blood cells irradiated with 1 Gy. We observed a decrease in the serum mtDNA/nDNA ratio due to an increase in nDNA content rather than a decrease in mtDNA. Taken together, results presented herein suggest that the mtDNA/nDNA ratio may be of clinical value potentially as a diagnostic tool, particularly in oncology patients undergoing radiation therapy.

Postradiation DNA polymorphism

The presence of DNA molecules with tumor-specific genetic alterations has been demonstrated in the plasma of cancer patients. Such plasma DNA fragments may be immunogenic and provide immunologic support to the malignant cells. Further, the tumor-specific plasma DNA may participate in the adaptive processes of the tumor cells in the cancer host. The mechanisms of the latter are unclear. However, from the standpoint of the resistance problem, understanding of DNA transformation after exposure of extreme factors is of great interest.