Differences in ICAM‐1 and TNF‐α expression between large single fraction and fractionated irradiation in mouse brain

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Abstract
Purpose: To elucidate the brain molecular response to irradiation. The expression of the intercellular adhesion molecule (ICAM‐1) and tumour necrosis factor‐α (TNF‐α) in the mouse brain was compared after single‐dose and fractionated whole‐brain irradiation. Materials and methods: Mice received a single dose of 2, 10 or 20 Gy or a fractionated dose (2 Gy day−1) of 10, 20 or 40 Gy. ICAM‐1, and TNF‐α mRNA expression were quantified by the highly sensitive real‐time polymerase chain reaction technique. Expression of ICAM‐1 protein was quantified by dual‐labelled monoclonal antibody assay. Results: After a 20‐Gy single dose, there was an increase in ICAM‐1 and TNF‐α mRNA levels (14‐ and 11‐fold, respectively) as well as a significant increase in the level of ICAM‐1 protein (p=0.0243). The expression of ICAM‐1 and TNF‐α mRNA increased at the end of the 40‐Gy fractionated regimen (3.55‐ and 2.30‐fold, respectively). Conclusions: The molecular response of the brain to single‐dose irradiation was rapid, while its response to fractionated irradiation was slow. This finding is consistent with clinical observations and could be of use when designing strategies to mitigate radiation sequelae.