Interaction of radiation- and bleomycin-induced lesions and influence of glutathione level on the interaction

Radiation-induced exchange aberrations are thought to arise as a consequence of misrejoining of free ends of DNA double strand breaks (dsbs). In quiescent mammalian cells this process of misrejoining is prevalently taken up by the non-homologous end joining (NHEJ) process. In order to investigate the role of glutathione (GSH) in DNA dsb rejoining, the interaction of the lesions induced by bleomycin (Blem) and by radiation was studied since the lesions caused by both have similar and apparent rapid rates of repair. Endogenous GSH was depleted by buthionine sulfoximine (BSO) and chromosome aberrations (CAs) of human lymphocytes were scored from first cycle metaphases. Gamma radiation was administered 2 h after Blem treatment in combined studies. In the case of BSO, the treatment was given 3 h before Blem treatment. The BSO-treated samples showed higher sensitivity to radiation than BSO-untreated ones. Combined treatment of Blem and radiation induced higher frequency of CAs, in particular the exchange aberrations and interstitial deletions. However, such increased frequency of exchange aberrations was reduced drastically and the frequency of terminal deletions was increased significantly when combined treatment was given to BSO-pretreated cells. The consistent level of Ku70 protein in all the treated samples, with undetectable level of Rad51 in the G0-lymphocytes indicates the involvement of NHEJ pathway in misrejoining of DNA dsbs. It may be hypothesized that reduction in the frequency of exchange aberrations as induced by Blem + radiation combined treatment in BSO-treated samples could be because of reduced NHEJ pathway.