Increase of Cell-Free Nuclear and Mitochondrial DNA Content in the Urine of Rats after X-ray Irradiation or Bleomycin Administration

Abstract

Purpose: To study the content of cell-free mitochondrial DNA (cf-mtDNA) and cell-free nuclear DNA (cf-nDNA) in urine of rats exposed to ionizing radiation, and after injection of a cytostatic drug bleomycin.
 Material and methods: Wistar male rats aged 3 months were used in the experiments. Rats were irradiated at a doses of 3, 5, and 8 Gy. Bleomycin was administered intraperitoneally in concentrations of 3, 7, and 10 mg/kg. The DNA content was measured by real-time PCR. 
 Results: The results showed an increase in the level of the number of cf-nDNA and cf-mtDNA fragments in urine of irradiated rats. It was shown that the content of cf-nDNA and cf-mtDNA has a linear dependence on the X-ray dose. Thus, the maximum number of mtDNA and nDNA copies was recorded for 12–24th hours after irradiation. The number of PCR amplification products of cf-mtDNA is 2–3 times higher than those of cf-nDNA. Data analysis of the content of cf-nDNA and cf-mtDNA in rat urine after introduction of bleomycin also showed elevated levels compared with control animals. It was shown that the content of cf-nDNA and cf-mtDNA has a linear dependence on the dose of the chemotherapeutic drug. 
 Conclusion: Thus, it has been shown that it is possible to overcome the transrenal (renal) barrier in animals with cf-mtDNA and cf-nDNA and pass them into the urine after X-ray irradiation, as well as after the administration of bleomycin. The dose dependence of the identified effects was found. The increased content of cell-free DNA in the urine can be considered as a potential biomarker for assessing the level of genotoxic load during radiation damage to the body, as well as when exposed to other genotoxic agents.