Features of Brain Damage after Neutron Irradiation of the Head and Modification of the Damage by Lactoferrin.

Purpose: The purpose of the study was to investigate the effect of γ,n-irradiation of the mouse head on the brain cells damage, behavior, and cognition and to examine the possibility of using lactoferrin (LF) to alleviate radiation-induced impairments.

Materials And Methods: Mouse heads were irradiated in a beam of neutrons and gamma rays from the IR-8 nuclear reactor. The brain cells of control and irradiated mice were isolated using Percoll. Neurons and resting and activated microglial cells were analyzed using the fluorescently labeled antibodies and flow cytometry. The level of DNA double-strand breaks in neurons was determined by γH2AX histone content. Cytokine gene expression in the hippocampus was studied by RT-PCR. Behavior and cognitive functions were studied using the open field, Morris water maze, and novel object recognition tests. LF was isolated from female colostrum by preparative ion-exchange chromatography and purified by affinity chromatography on heparin-Sepharose.

Results: γ,n-Irradiation of the mouse head at a dose of 1.5 Gy led to an increase in the level of DNA double-strand breaks in neurons. Twenty-four hours after irradiation the total number of cells and the number of neurons in the isolated fraction of brain cells decreased, but the number of microglial cells remained unchanged. The number of resting and activated microglia did not change within 3-72 h after γ,n-irradiation. The expression level of the TNFα, IL-1β, and IL-6 genes increased 2 months after γ,n-irradiation of the mouse head at a dose of 1.5 Gy, indicating the development of neuroinflammation. At this time, irradiated mice demonstrated the anxiety-like behavior and impaired spatial and episodic memory. A single i.p. administration of human LF to mice immediately after γ,n-irradiation of the head did not affect the observed radiation-induced disturbances, but decreased the gene expression levels of TNFα, IL-1β, and IL-6 pro-inflammatory cytokines and increased the gene expression level of TGFβ anti-inflammatory cytokine in the hippocampus 2 months after radiation exposure. The obtained results indicate a partial decrease in the level of hippocampal neuroinflammation of irradiated animals treated with LF.

Conclusions: γ,n-Irradiation of the mouse head at a dose of 1.5 Gy leads to DNA damage of neurons and the decrease in the number of neurons. Microglia cells are more resistant to such radiation exposure. Late after head-only γ,n-irradiation, mice develop neuroinflammation, which is detected by an increase in the pro-inflammatory cytokine gene expression in the hippocampus and also by anxiety-like behavior and impaired cognitive functions. A single LF administration leads to a partial decrease in the neuroinflammation level, but does not affect the other studied parameters. The optimal dosing regimen of LF remains to be determined to preserve cognitive functions after γ,n-irradiation of the brain.