Supervisors info:
Αλέξανδρος Γεωργακίλας, Αναπλ. Καθηγητής, ΣΕΜΦΕ, ΕΜΠ
Βασίλειος Γοργούλης, Καθηγητής, Ιατρική, ΕΚΠΑ
Γεωργία Τερζούδη, Ερευνήτρια Α, Υγειοφυσική, ΕΚΕΦΕ Δημόκριτος
Summary:
During the last years there is a growing body of evidence showing that the effects of ionizing radiation (IR), are not restricted only to the irradiated cells, but are also extended in tissues and cells out of the irradiation field. The consequence of IR in non-irradiated cells in the vicinity of directly irradiated ones as well as at distant sites is called bystander and/or distant effect of IR respectively. The underlying mechanisms are still obscure although the release of soluble factors including cytokines is implicated in the effect of IR distantly. In order to investigate the molecular mechanisms taking place in the so called distant effect, we examined the impact of leg-irradiated treated mice with X-ray beams of low energy with 10Gy and 40Gy on their intestines as well as distant sites. We used irradiation of Broad Beam (BB) and irradiation of micro beams (MRT). We examined 24 and 96 hours after the irradiation. Irradiation and tissue isolation took place at the accelerator of Australian Synchrotron IMBL of Peter McCallum Institute in the Melbourne’s University and they shipped frozen in the Department of Histology and Embryology of the Medical School of Athens where the experiments were carried out. By employing immunohistochemistry (IHC) in frozen sections we found significantly increased levels of 8-oxoguanine (8-oxoG), a marker of oxidative stress and DNA damage, in both 10 Gy and 40 Gy irradiated mice in comparison with untreated mice, in both BB and MRT IR. Specifically, 8-oxoG levels in stroma cells were up to 3.8 times and in epithelial cells 7 times elevated in 40Gy and 10Gy of BB IR respectively in relation to non-irradiated mice. As for MRT IR and 10Gy, the corresponding levels were 4 and 5 times elevated. Of note, mice irradiated with 10Gy exhibited markedly reduced levels of ki67, cellular proliferation markers, which were further decreased in mice treated with 40Gy, 2.5 times elevated, versus controls, implying increased cellular damage which leads to cell cycle arrest. As for the cellular proliferation of the intestine epithelial cells of mice which irradiated with MRT there is no differentiation in relation to non-irradiated mice. There was a small decrease in the number of oxidative damage of the DNA at the 96 hours compared to 24 hours after irradiation. This may be interpreted that cells have begun repairing their damages, but it certainly indicates that 24 hours are enough to show the phenomenon at its maximum intensity. We also see up to 6 times elevated levels of senescence in IR treated mice with BB. Finally, there was an increase in inflammatory reaction of the epithelial intestinal cells of the mice irradiated in the foot by both BB and MRT. For BB IR, nuclear p65 was up to 2.2 times while for MRT up to 2.4 times elevated versus controls. This leads us to the conclusion that some of the responsible for the distant effect factors are cytokines, immune cells, such as macrophages, etc. These factors can cause oxidative stress and induce secondary inflammatory responses and activation of the immune system to the various sites of the organism.
Keywords:
Distant effect of IR, DNA damage due to IR, Bystander effect of IR, Oxidative damages of DNA, Inflammatory response of distant tissues
