| Objective To compare differences in genetic effects and dose-effect relationship induced by different radionuclides to provide experimental date for evaluating on their genetic toxicity.Methods Twenty-four Wistar male rats were randomly divided into one control group and three radon inhaled groups(60, 90, and 120 working level month(WLM)), with each group of 6 rats. All the radon-exposed rats were exposed in the HD-3 multifunctional radon-room. The tracheal-bronchial epithelial(TBE) cells were isolated using pronase digestion and cell brushing, and the blood samples were obtained by cardiac puncture. Genetic toxicity of radon and late fussion products was detected by measuring the biological endpoints of hypoxanthine phosphoribosyl transferase (hprt) mutation and micronuclei(MN) rate and DNA damage. The micronuclei rate(MNR) was detected by cytokinesis-blocked(CB) micronuclei assay, and the hprt mutation was detected according to the multinucleated cells method, and DNA damage was detected by single cell gel electrophoresis(SCGE). The tracheal-bronchial epithelial cells were cultured in F12 media, and screened in selective F12 media. The transformed cell lines were collected at 8th generation for reversed transcript polymerase chain reaction(RT-PCR) , and confirmed with western blot assay. The p53 and p16 expression of lung tissue were detected according to strept actividin-biotin complex(SABC) method, and cox-2 expression was detected by the streptavidin-peroxidase(SP) method. SPSS 10.0 was used for statistical analysis on dose-effect and dose-rate-effect relationship.Results About 1.30×106 tracheal-bronchial epithelial cells were obtained from each rat with a cell survival rate of 84.19 percent. The mutant frequency(y) of hprt in the lymphocytes and tracheal-bronchial epithelial cells increased with the accumulated doses(x), which could be described by the following functions: y = 4E-05x2 + 0.0008x + 1.0324; and y = 2E-05x2 + 0.0012x + 1.0538. The dose-effect relationship between the accumulated doses(x) and the MN rates (y) of the lymphocytes and the epithelial cells were given by the following functions: y = 0.1272x + 2.6546; and y = 0.0006x2 - 0.0203x + 4.8598. Two transformed cell lines from 90 and 120 WLM dose group rats were obtained and named as A and B. in which the expression of the p53 and cox-2 mRNA increased, while the expression of p16 decreased. The expression of p53 and cox-2 protein also increased and p16 decreased in a dose dependent manner. The relationships between MNR and accumulative doses or dose rate induced by late fission products could be described by y = 4.5407+1.3958x-0.0266x2 and y = 4.5659+0.5167x-0.0034x2 respectively. Comparative analysis revealed that the hprt mutation and MNR induced by unit dose fission products changed significantly at the low-dose region, while the effect induced by unit radon presented different features.The hprt/MNR of the same dose decreased for both radon and fission products.Conclusions1. p53, p16 and cox-2 gene may play an important role in tracheal-bronchial epithelial cells transformation in radon-exposed rats. A good dose-effect relationship between changes in micronuclei and hprt mutation and doses exposed indicated that these two biological endpoints might be used as potential biomarkers of radon exposure.2. The hprt mutation and micronuclei were two sensitive endpoints in reflecting genetic effects of the late fission products. A dose-response relationship was established at the low-dose region.3. The dose-response relationship for radon and fission products were different due to their different entry route and radiation type, but they showed a common feature in that the hprt/MNR decreased with the dose suggesting more fragments loss of genetic material as doses going high.
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