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Use of GADD45A and CDKN1A Gene Expression Changes as Biomarker in Assessment of DNA Damage for Ionizing Radiation Exposure

The present study aims to determination of GADD45 and CDKN1A expression genes as a biomarkers for ionizing radiation in white mice Mus musculus Balb/C by using the real-time quantitative PCR assay. Seventy- two white mice (36 males and 36 females) were divided into two groups; their whole body was exposed to 5 cGy and 100 cGy of X-ray radiation at a dose rate of 200 cGy/min, in addition to the control group. Total RNA was isolated using Trizol method from liver samples of mice after 6, 48 hours and 10 days of exposure to radiation as well as of the control group. Complementary DNA was used in amplification of genes used in the present study, two types of primers pairs were selected for the genes amplification Growth arrest and DNA-damage inducible A (GADD45A) and Cyclin-dependent kinase inhibitor 1A (CDKN1A), which have a relation with ionizing radiation in addition to the primers for internal control (β-actin) gene. The size amplified product were 95 bp and 162 bp nitrogen-base pair for GADD45A and CDKN1A genes, respectively. The existence of significant elevation p <0.05 in the amount of gene expression of the GADD45A gene in samples of mice liver exposed to doses 5 cGy and 100 cGy after 6 hours of exposure to radiation. It was found that this gene having up-regulation level after 6 hours in the liver of mice exposed to these doses in comparison with the control group. The presence of a significant reduction (p <0.05) in the amount of gene expression of the CDKN1A gene in samples of mice liver exposed to doses 5 cGy and 100 cGy after 6 hours of exposure to radiation and this reduction continued after 24 hours and 10 days. Moreover, it was found that this gene had a down-regulation level after 6 hours in the liver of mice exposed to these doses in comparison with the control group. The organizational level in the high dose of 100 cGy is higher than that at the low dose 5 cGy. In conclusion, the results indicated that there is a possibility of using the changes in the level of GADD45A and CDKN1A genes expression as useful biomarkers in assessment of DNA damage for low and high radiation exposure.