Influence of in vitro low-level gamma-radiation on the UV-induced DNA repair capacity of human lymphocytes - analysed by unscheduled DNA synthesis (UDS) and comet assay

Abstract

Unscheduled DNA synthesis (UDS) induced by ultraviolet radiation (UV) was studied in human lymphocytes after exposing blood samples in vitro to doses ranging between 1 and 10 mGy gamma-radiation, by way of measuring tritiated thymidine (3H-TdR) uptake in the DNA of these lymphocytes. The results indicate that samples pre-exposed to gamma-ray doses ranging between 2.5 and 4 mGy show higher UDS levels compared with those pre-exposed to doses of less than 2.5 or more than 4 mGy. These results were verified by studying the rate of removal of UV-induced photoproducts using the comet assay. The reason for the increase in DNA repair capacity in this dose range is discussed in comparison with earlier reports on this phenomenon. The DNA repair capacity with respect to inter-individual variability and age is also analysed. The study implies that the comet assay is a simple and sensitive visual method to track nucleotide excision repair and hence can be used to estimate UV-induced DNA repair in the place of the more reliable yet cumbersome and time-consuming, grain-counting autoradiographic technique.

Enhanced Nucleotide Excision Repair in Human Fibroblasts Pre‐exposed to Ionizing Radiation

“…This enhanced level of NER coincides with enhanced gene expression levels of XPC and DDB2, enhanced amounts of XPC and DDB2 proteins in chromatin and enhanced accumulation of XPC and DDB2 at local UV spots in X‐ray preirradiated cells. This upregulation of NER in X‐ray pretreated human fibroblasts is in line with increased UV‐induced DNA repair in IR preirradiated mammalian cells and mice, reported previously (18,19). In addition, this study presents for the first time mechanistic evidence that enhanced expression of XPC and DDB2 underlies this AR.…”

Dietary and genetic modulation of DNA repair in healthy human adults

“…Qiao et al (2002 a ) have found a 4·7-fold variation in NER capacity, measured using the host cell reactivation assay, in 102 healthy subjects (Qiao et al 2002 a ). Also, DNA repair of UV-induced damage, measured using the unscheduled DNA synthesis assay varies over an approximately 8-fold range, again in healthy control subjects (Mohankumar et al 1998). Amongst sixty-three young (mean age 21 years) healthy volunteers recruited to the Dietary Antioxidant Repair Trial there is a 10-fold inter-individual variation in NER capacity, measured using the host cell reactivation assay (see Fig.…”