Biomarkers of radiation exposure in human lymphocytes: a multiparametric approach

Biomarkers are important in assessing the exposure and for predicting future adverse health outcomes. A study involving multiple end points following irradiation was initiated in our laboratory using human blood lymphocytes from healthy donors and normal human fibroblasts. Human cells were irradiated with very low doses (0.10 to 1.0 Gy) of γ-rays. Lymphocytes from five donors were irradiated and induced to proliferate for 52 to 60 hours and cytogenetic analysis was carried on metaphase chromosomes. Gene expression profiles using microarray analysis were generated from blood lymphocytes irradiated at G₀ state to identify signature genes of exposure to ionising radiation. Chromosome alterations induced were detected by using fluorescence in situ hybridisation (FISH) using telomere specific probe as well as by multi-colour FISH (mFISH). The effects of radiation on DNA damage studied by assessing micronuclei and γ-H2AX foci formation after exposure to radiation showed a dose dependent response. FISH based cytogenetic analysis revealed a dose-dependent increase in the percentage chromosome aberrations such as dicentrics and translocations. Micronucleus analysis also revealed a dose-dependent increase in the production and persistence of chromosome fragments in the irradiated lymphocytes. Effect on overall gene expression was investigated in human leukocytes using microarray technology. It was found that low doses of γ-irradiation induced differential gene expression. There were no marked differences on the differential gene expression profiles between the doses. However, the differentially expressed gene profiles were quite distinct in cells incubated for 2 h and 24 h subsequent to irradiation. Radiation induced biological response like cytokine production, which contributes to post irradiation pathophysiology was also investigated in human leukocytes. The findings were comparable to our microarray analyses, which revealed altered expressions of a variety of cytokines. We have performed similar experiments with high LET radiation (heavy ions). The results obtained in this study would, hopefully, provide us with functional relevance of early biomarkers of exposure. Previously, we have shown cells responding to environmental toxicants through biological networks that are engaged in the regulation of molecular functions such as DNA repair and oxidative stress. In order to illustrate radiation genomics as an effective tool in biological dosimetry, we propose predictive genomics as a promising approach to high-throughput radiation biodosimetry