Increase in DNA single-strand break rejoining by continuous exposure of human mononuclear blood cells to radioiodine (131I) in vitro

• Published in: International journal of radiation biology 1997, Vol.72 (5), p.607-613
• Main Authors: HENGSTLER, J. G, BOCKISCH, A, FUCHS, J, GRIMM, W, ZAPF, A.-O, LADE, K, MEINERT, R, OESCH-BARTLOMOWICZ, B, TANNER, B, OESCH, F
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; Molecular genetics; Mutagenesis. Repair
• ISSN: 0955-3002; 1362-3095
• DOI: 10.1080/095530097143103

Radioiodine (131I) induced a dose- and timedependent increase in DNA single-strand breaks (DNA-ssb) in human (G0) mononuclear blood cells (MNC) in vitro. Incubation of MNC with 22 MBq 131I/ml at 4 C caused a linear, timedependent induction of DNA-ssb (increase in elution rate: 24.7 10 -3 h -1 per 100 min incubation with 131I). However, if MNC were incubated at 37 C a decrease in the slope of the time-effect curve was observed after about 300 min incubation with 22 or 30 MBq 131I/ml. The goodness of fit of different regression models was assessed by Akaike's Information Criterion (AIC). The best fit was obtained for a non-linear model (y = a + bx + cx 0.5; AIC = 53.5; where x is incubation time and y is elution rate), whereas other models including the linear regression model (y = a + bx ; AIC 38.6) were worse. As the total induction of DNA-ssb at 4 C was constant with time, the decrease in the slope of the time-effect curve (DNA-ssb versus time) at 37 C can be interpreted as an increase in rejoining of DNA-ssb. Inhibition of both RNA and protein synthesis clearly increased the extent of DNA-ssb observable after incubation with 131I. Thus, during continuous exposure of MNC to 131I, proteins were synthesized which rejoined DNA- ssb. However, incubation of MNC with 131I (44 MBq/ml) at 37 C under conditions expected to lead to inhibition of RNA and/or protein synthesis still resulted in a decrease of the slope of the time-effect curve, indicating a stimulation of DNA-ssb rejoining. Thus, we favour the hypothesis that the increase in the activity of DNA-ssb rejoining, besides de novo synthesis of repair enzymes, is also caused by a post-translational stimulation of DNA-repair enzymes and that this stimulation possibly is mediated by DNAfragments.