Cellular damage in vitro

Summary

Aim: The cellular damage of ionising radiation depends on dose, physical radiation quality (e. g. LET) and intracellular radionuclide uptake. The influence of two beta emitters (¹⁸⁸Re and ¹³¹I) on the thyroid cell line PC Cl3 was studied. Furthermore, we analysed the effect of intracellular accumulation. Methods: The thyroid cell line PC Cl3 was irradiated with ¹⁸⁸Re-perrhenate or ¹³¹I-sodium iodide in presence or absence of perchlorate. The initial DNA-damage was measured in the comet assay as olive tail moment (OTM). The colony forming assay detects the clonogenic cell survival as surviving fraction. Additional the intracellular radionuclide uptake was quantified. Results: Dose response curves were established for irradiation with ¹⁸⁸Re-perrhenate or ¹³¹I-iodine under various extra- and intracellular activity distribution conditions. In the presence of perchlorate DNA-damage and clonogenic cell survival for both radionuclides were comparable. In the absence of perchlorat radionuclide uptake of 1.39% (¹³¹I) and 4.14% (¹⁸⁸Re) were measured causing twofold higher radiotoxicity. Although ¹³¹I uptake was lower than ¹⁸⁸Re uptake the OTM values were higher und surviving fractions were lower. Conclusions: ¹³¹I, compared to ¹⁸⁸Re, has lower mean beta energy and a higher LET, and therefore, it induced a higher DNA-damage even at lower intracellular uptake. An additional explanation for the higher radiotoxicity of ¹³¹I could be the higher dose exposition caused by crossfire through neighborhood cells.

Zusammenfassung

Ziel: Die Zellschädigung durch ionisierende Strahlung wird durch die absorbierte Dosis, strahlenphysikalische Eigenschaften (z. B. LET) sowie die intrazelluläre Radionuklidlokalisation beeinflusst. An der Schilddrüsenzelle PC Cl3 sollte der Einfluss zweier Betastrahler (¹⁸⁸Re und ¹³¹I) mit unterschiedlicher mittlerer Betaenergie sowie der Einfluss der intrazellulären Akkumulation auf das Ausmaß des DNASchadens untersucht werden. Methoden: Die PC Cl3-Zellen wurden in An- bzw. Abwesenheit von Perchlorat mit ¹⁸⁸Re und ¹³¹I inkubiert. Im Komet-Assay wurde die Höhe des initialen DNA-Schadens an Hand des OTM (olive tail moment) quantifiziert. Das klonogene Zell überleben wurde mit dem Koloniebildungstest durch Bestimmung der Überlebensfraktion ermittelt. Parallel zu allen Versuchen wurde die intrazelluläre Radionuklidaufnahme durch Uptake-Experimente gemessen. Ergebnisse: Dosis/Wirkungskurven für die Bestrahlung mit ¹⁸⁸Re und ¹³¹I unter variabler extra- und intrazellulärer Verteilung der Radioaktivität wurden erstellt. Bei Inkubation mit Perchlorat waren initialer Schaden und klonogenes Überleben für ¹³¹I und ¹⁸⁸Re vergleichbar. Ohne Perchlorat wurden zwischen 1,39% (¹³¹I) und 4,14% (¹⁸⁸Re) der inkubierten Aktivität intrazellulär nachgewiesen, was die Radiotoxizität etwa verdoppelte. Trotz des geringeren Uptakes von ¹³¹I gegenüber ¹⁸⁸Re konnte ein höheres OTM und eine geringere Überlebensfraktion nachgewiesen werden. Schlussfolgerungen: Der im Vergleich zu ¹⁸⁸Re niederenergetischere Betastrahler ¹³¹I hat einen höheren LET und verursachte im Vergleich zu ¹⁸⁸Re trotz geringerer intrazellulärer Konzentration höhere DNA-Schäden. Die höhere Radiotoxizität von ¹³¹I könnte mit einem höheren Dosiseintrag durch die Nachbarzellbestrahlung erklärt werden.

Keywords

Comet assay - colony forming assay - ¹³¹I - ¹⁸⁸Re - intracellular radionuclide uptake - PC Cl3

Schlüsselwörter

Komet-Assay - Koloniebildungstest - ¹³¹I - ¹⁸⁸Re - intrazelluläre Radionuklidaufnahme - PC Cl3

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