DNA damage in lymphocytes after irradiation with ²¹¹At and ¹⁸⁸Re

Summary

Aim: Ionising radiation produces many types of DNA lesions of different complexity. High linear energy transfer (LET) types of radiation are biological more effective than low LET radiation. In the present work we applied the single cell gel electrophoreses (comet assay) to study the induction of initial DNA damage, efficiency of repair and residual DNA damage in lymphocytes after treatment with ²¹¹At and ¹⁸⁸Re. Methods: Peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood of healthy donors and irradiated with ²¹¹At and ¹⁸⁸Re at different doses. The comet assay was performed under alkaline and neutral conditions in order to detect the initial DNA damage and its repair. The measure of damage was % tail DNA (percentage of DNA in the tail). Results: After treatment of cells with ¹⁸⁸Re the initial DNA damage (% tail DNA) detected with the alkaline comet assay was higher than the damage measured for ²¹¹At. The neutral comet assay estimated higher tail intensities for ²¹¹At in contrast to ¹⁸⁸Re. Compared with the complete repair (10%) after irradiation with ¹⁸⁸Re, the radiotoxicity of alpha particles indicated reduced rejoining of DNA strand breaks (60–80% residual damage). Rejoining of DNA damage measured by the neutral comet method detected about 70% unrepaired strand breaks for ²¹¹At and ¹⁸⁸Re. Conclusions: There are major differences between the repair of strand breaks caused by ¹⁸⁸Re and ²¹¹At detected by the alkaline comet assay. The DNA-damage induced by the high LET Emitter ²¹¹At remains nearly unrepaired detected by both alkaline and neutral comet assay. Represented data following irradiation of lymphocytes with alpha and beta particles demonstrated higher biological effectiveness of ²¹¹At by factors of 2.0–2.5.

Zusammenfassung

Energiereiche Strahlung verursacht in Abhängigkeit von den strahlenphysikalischen Eigenschaften (linearer Energietransfer, LET) der Radionuklide Zellschäden unterschiedlicher Komplexität. DNA-Strangbrüche können mit dem Komet-Assay nachgewiesen werden. Ziel ist die Untersuchung von DNA-Schäden und deren Reparatur nach Bestrahlung mit ²¹¹At und ¹⁸⁸Re. Methoden: Periphere mononukleäre Blutzellen wurden mit ²¹¹At oder ¹⁸⁸Re bestrahlt. Die DNA-Schäden wurden mit dem alkalischen und neutralen Komet-Assay quantifiziert. Neben der Bestimmung von Initialschäden erfolgte die Ermittlung der residualen DNA-Strangbrüche. Ergebnisse: Im alkalischen Komet-Assay wurden nach Exposition mit ¹⁸⁸Re höhere DNA-Schäden als nach ²¹¹At detektiert. Die Messung der initialen DNASchäden mit dem neutralen Assay ergab für ²¹¹At eine höhere Radiotoxizität als für ¹⁸⁸Re. Das Verhältnis ESB zu DSB ist beim Beta-Emitter ¹⁸⁸Re zur Seite der ESB verschoben. Der Vergleich der Reparaturkapazitäten im alkalischen Komet-Assay zeigte nach Bestrahlung mit ¹⁸⁸Re eine Reparatur auf 10% der Initialschäden, während nach Exposition mit ²¹¹At 60 % – 80 % der DNA-Schäden unrepariert blieben. Die im neutralen Komet-Assay analysierte DNA-Reparatur ermittelte für ²¹¹At sowie für ¹⁸⁸Re Residualschäden in Höhe von 70 % – 80 %. Schlussfolgerung: Mit dem neutralen Komet-Assay konnte anhand der Detektion der Initialschäden sowie der DSB-Reparatur eine höhere biologische Wirkung von ²¹¹At im Vergleich zu ¹⁸⁸Re bestimmt werden. Die höheren Residualschäden nach DNA-Reparatur weisen auf die Existenz komplexerer Schäden nach Exposition mit ²¹¹At im Vergleich zu ¹⁸⁸Re hin. Unter Berücksichtigung der Spezifität der Komet-Assay-Versionen ermöglicht die Kombination der Teste eine partielle Aussage zur Qualität der DNA-Schäden.

Keywords

Comet assay - ²¹¹At - ¹⁸⁸Re - strand breaks - repair - lymphocytes

Schlüsselwörter

Komet-Assay - DNA-Strangbrüche - DNAReparatur - ²¹¹At - ¹⁸⁸Re

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