The expression profile of redox genes in human monocytes exposed in vitro to γ radiation

Abstract Background It is known that γ radiation is rapidly triggering in cells and in the surrounding medium a hydrogen peroxide burst through water radiolysis, which may have early and late consequence on the viability and functions of irradiated cells. Investigations on monocytes and macrophages are of utmost importance for assessing radiation risks, considering that they are highly responsive to danger/damage signals, are master regulators of the immune response and actively contribute to repair processes in tissues damaged by radiation. Aim In the present study we investigated the expression changes of redox genes in SC monocytes exposed in vitro to γ rays, aiming to identify delayed disturbances of the redox gene network in exposed cells. Methods SC monocytes were exposed to γ radiation in the dose range of 1–5 Gy, at various dose rates (1.6 Gy/h, 4 Gy/h and 10 Gy/h). Cells were further cultivated and were analyzed at various time points after irradiation (24 h and 48 h) regarding cell viability and the expression profile of 84 redox genes critically involved in oxidative stress and antioxidant responses, addressing ROS metabolism, oxidative stress responsive genes, antioxidant genes and pathway activity signature genes. Results Over-expression of particular genes encoding various members of the NADPH oxidase family or myeloperoxidase evidenced an increased potential of irradiated cells to generate reactive oxygen or nitrogen species, especially superoxide anion. Alternatively, up-regulation of genes encoding antioxidant molecules indirectly proved that an increased oxidative activity occurred in irradiated monocytes. Redox-mediated cellular deregulation was evidenced by the over-expression of the BNIP3 gene which is involved in cell death by apoptosis or autophagy, and was complemented by the up-regulation of the DUSP1 gene involved in cell cycle arrest and functional silencing of monocytes. At lower doses and dose rates, an enhanced molecular fingerprint of antioxidant responses mediated by the cytoprotective transcription factor NRF2 was found, albeit not being able to avoid the observed reduction of biabl cells in irradiated cell cultures. Moreover, only a low transcriptional activity of NRF2 was registered at higher doses which probably inflicted profound oxidative damages that compromised critical cellular defense mechanisms. Conclusion Pathway-focused analysis of redox gene expression allowed us to highlight delayed oxidative alterations in monocytes exposed in vitro to γ rays, indicating that a chronic oxidative activity is persisting long after irradiation. Moreover, we emphasized that the necessity to boost the endogenous antioxidant system in normal cells exposed to higher doses of γ rays, in order to protect them against the deleterious effects of radiation. A therapeutic option might be the pharmacological activation of the transcription factor NRF2 which can rapidly react to even small increases in intracellular oxidants and to regulate the expression of many antioxidant and cytoprotective genes.