Relative biological efficiency of protons at low and therapeutic doses in induction of 53BP1/γH2AX foci in lymphocytes from umbilical cord blood

Abstract

Purpose: In order to evaluate DNA damage induced by protons at low and radiotherapeutic doses at the therapeutic proton complex at Ružomberok, Slovak Republic, lymphocytes from umbilical cord blood (UCB) of the same four probands were irradiated in the dose range of 1–200 cGy with γ-rays and protons (200 MeV, irradiation in the Bragg peak).

Materials and methods: DNA repair γH2AX/53BP1 foci were analyzed by fluorescent microscopy and flow cytometry.

Results: Statistically significant effects of radiations were detected by fluorescent microscopy at all doses higher 1 cGy. Almost all distributions of foci in irradiated cells fitted to the Poisson distribution. In general, there was no difference in the levels of γH2AX and 53BP1 foci in irradiated cells. Flow cytometry was less sensitive and detected radiation induced effects at doses of 50 cGy and higher. Factorial analysis of variance in the whole studied dose range has shown no significant effect of radiation quality on number of γH2AX and 53BP1 foci. The ratio of proton-induced foci to γ-ray-induced foci was 0.86 ± 0.16 (53BP1) and 0.99 ± 0.34 (γH2AX) as measured by fluorescent microscopy and 0.99 ± 0.16 (γH2AX) as measured by flow cytometry at the radiotherapeutic dose of 2 Gy.

Conclusions: Both flow cytometry and fluorescent microscopy indicated that the average value of relative biological efficiency (RBE) at radiation doses ≥ 20 cGy was about 1.0. Our data that RBE increased at low doses ≤ 20 cGy are relevant both to the development of treatment modalities and exposures that take place during space exploration and should be verified by further studies.

Keywords::

• Protons
• cord blood lymphocytes
• DNA double-strand breaks

Acknowledgements

We are gratefully thankful to Prof. J. Kurty, Military Hospital, Ružomberok, Slovakia and Academician V. E. Balakin, the P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Protvino, Russia, for their great organizational help in irradiation with protons, Dr G. Kralik, St. Elisabeth Cancer Institute, Bratislava, Slovak Republic, for γ-irradiation of samples and Dr. S. Vasilyev, Institute of Medical Genetics, Tomsk, Russia, for help in statistical analysis. Dr M. Kubes, Eurocord-Slovakia, provided valuable assistance separating UCBC. Dr D.L. Davis, Environmental Health Trust, DC, USA, provided editorial comments.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

This work was supported by the Structural Funds of EU (Agency) by the Ministry of Education, Science, Research and Sport of the Slovak Republic (Protonbeam, ITMS: 26220220129), the Slovak Research and Development Agency (APVV 0669-10); the National Scholarship Program of the Slovak Republic (SAIA); and the VEGA Grant Agency (2/0150/11) of the Slovak Republic.