Impact of radiation dose and post-irradiation time on the patterns of gene expression in human peripheral blood lymphocytes exposed to X-rays

Using DNA Microarray technique, we have earlier shown that exposure to ã-radiation affected a large number of genes, appropriately referred to as radiation response genes (RRG), in human peripheral blood lymphocytes (HPBL). Further analysis of the expression of these RRGs revealed that some of these genes were up-regulated while a relatively larger number of genes were down-regulated. Based on our data and limited information available in literature, it is apparent that radiation induced modulation of gene expression is a process dependent on multiple parameters like the dose, dose rate, post-irradiation period, etc. From these studies, we identified 20 'candidate' RRGs in HPBL exposed to low doses of ã-rays. Out of the 20 candidate RRGs, we have taken up 9 genes in this investigation for its validation by quantitative real-time PCR (qPCR). We followed their expression patterns by qPCR as a function of radiation dose and post-irradiation time period using GAPDH and 18S genes as normalizer genes. The objective of our work is to identify stable and persistent RRGs in HPBL following ex vivo X-ray irradiation of blood. Freshly drawn blood from consenting volunteers was exposed to different doses of X-rays at a low dose rate. Sham exposed blood sample served as the control. Total RNA was isolated from blood either immediately (0 h) or after 12 h and 24 h post-irradiation incubation in a CO₂ incubator at standard conditions. cDNA was prepared from the isolated RNA. qPCR was performed at optimized conditions. This study presents data from 12 individual donors of both genders and different ages. Among the tested genes, expression of CDKN1A and ZNF440 genes showed linear dose response curves in relation to dose and post-irradiation incubation period. In this, while the former exhibited a direct correlation, the latter showed an inverse trend. The presentation shall dwell on the significance of these results in the domain of molecular bio-dosimetry. (author)