Peculiarities of DNA damage caused by exogenous nitric oxide combined with fractionated low dose ionizing radiation in normal and tumor cells.

UNLABELLED: The aim of this study was to investigate the reaction of normal and tumor cells to genotoxic effect of widespread environmental factors - exogenous nitric oxides and ionizing radiation. METHODS: The animals were treated with NO (125 mg/m(3)) and low dose ionizing radiation (10 acute exposures with 0.1 Gy each). Genotoxicity was estimated in vivo in rats peripheral blood lymphocytes, bone marrow cells and tumor cells of Guerin carcinoma. DNA damages were assessed by alkaline single-cell gel electrophoresis. RESULTS: Exogenous nitric oxides as well as irradiation caused significant increase of DNA damage in all types of investigated cells. The genotoxic effect increased in the order: peripheral blood lymphocytes < bone marrow cells < Guerin carcinoma cells. The greatest genotoxic effect was registered in Guerin carcinoma cells on terminal phase of tumor growth in rats exposed to NO and low dose ionizing radiation. CONCLUSIONS: Long-term exposure to common environmental factors (exogenous nitric oxides and ionizing radiation) capable to induce DNA damage in different cells. Severity of the genotoxic effect depends on cell type and nature of impacting factors. NO caused more significant DNA damage than low dose ionizing radiation but the highest level of DNA damage was observed after their joint action. Obtained results confirm the real threat of cancer risk increase under combined action of common environmental factors of different nature.

Nitric oxide coordinates development of genomic instability in realization of combined effect with ionizing radiation.

UNLABELLED: The aim of this study was to investigate the ability of environmental nitrogen oxides or natural nitric oxide (NO) donors to modify free radicals ba-lance and development of genomic instability alone or in combination with ionizing radiation. METHODS: Genotoxicity and cytogenetic abnormalities were assessed in vitro in peripheral blood lymphocytes (PBL) isolated from healthy humans or in vivo in rats PBL. Human PBL were treated with physiologically relevant NO donor - S-Nitrosoglutathione and X-ray irradiation. The inhalation treatment of animals with NO was carried out in chamber with purified gaseous NO mixed inside with air. Levels of S-Nitrosohemoglobin and methemoglobin in the blood were assessed with electron paramagnetic resonance. The total level of reactive oxygen and nitrogen species in PBL was determined fluorometrically, and serum levels of reactive oxygen species was determined by spectrophotometric assay. DNA damages were assessed by alkaline single-cell gel electrophoresis. The frequency of chromosomal aberrations in human PBL measured with the conventional cytogenetic assay in metaphase cells on short-term (52 h) and long-term (72 h) cultures. RESULTS: Environmental nitrogen oxides or release of NO from stable complexes with biomolecules (such as S-Nitrosothiols) intensified generation of free radicals, DNA damage and development of genomic instability alone or in combination with ionizing radiation. Treatment of PBL by S-Nitrosoglutathione caused prevalent induction of chromatid type but irradiation - chromosome aberrations. The dose dependence of chromatid-type aberrations observed in human PBL after combined influence of S-Nitrosoglutathione and ionizing radiation indicates a crucial role of NO in the formation of chromosomal instability. CONCLUSION: NO can deregulate free radicals balance resulted in genotoxic effect, posttranslational modification of repair enzymes and thus coordinated development of genomic instability and increase of cancer risk.

Exogenous nitric oxide potentiate DNA damage and alter DNA repair in cells exposed to ionising radiation.

UNLABELLED: The aim of this study was to investigate impact of exogenous nitric oxide (NO) on generation of different types of DNA damages, their transformation, and specificity of DNA repair in cells treated with ionizing radiation (IR). METHODS: levels of single-strand and double-strand breaks assessed in peripheral blood lymphocytes (PBL) isolated from healthy humans and treated in vitro with NO donor -- S-nitrosoglutathione (GSNO) and IR. The rate of DNA repair estimated after 30 and 60 min of PBL treatment. The visualization and measuring the number of prompt and delayed DNA damages, including strand breaks, apurinic and thermolabile sites performed with single-cell gel electrophoresis. RESULTS: IR caused dose-dependent generation of single strand breaks (SSBs), double strand breaks (DSBs), and heat-labile sites (HLS) in cell DNA. However, particularly destructive was combined treatment IR with GSNO as NO donor that leads to a significant increase of DNA damage and a dose-dependent inhibition of the DNA repair rate. Obtained data proofs the ability of NO to inhibit fast and slow stages of SSBs, DSBs, and HLS repair resulting in significant growth of genotoxic effect. DNA breaks generation from HLS is able to affect DSBs yields especially in cells with altered DNA repair. The process of DNA repair of delayed DSBs formed from HLS was quite different from removal of DNA damages occurring immediately after treatment and was characterized by IR dose dependent inhibition of DNA repair. CONCLUSION: High level of DNA strand breaks, that are generated after the combined treatment with NO and IR, are accumulated for quite a long time after exposure due to altered DNA repair, indicating the development of genetic instability and increase of carcinogenic risk for organism exposed to combination of harmful environmental factors.