The Potential Mechanisms Underlying Delayed On-Set of Radiation Necrosis of Brains: Time of Biological Events

Abstract

Cerebral radiation necrosis (RN) is a delayed complication of radiation therapy for brain tumours, leading to neurological anomalies and death. The biological events underlying the phase of developing RN has yet to be clarified. Thus further understanding of the mechanisms is essential to develop effective therapies. Similar to clinical RN, mice develop delayed necrosis 5 weeks after Gamma knife induced radiation. Using the window of opportunity, before necrotic brain damage, the study from our group demonstrated the activation of glial cell and elevation of Cx43 from week 1-3 after the radiation. As the part of the project, my study investigated earlier biological changes associated with the BBB leakage and inflammation by examining pro-inflammation cytokine, inflammasome, and gliosis from 6 hours after the radiation. Mouse brains were collected at six, twenty-four, 96 hours, one, two and three weeks after unilateral radiation. Immunohistochemistry was used to observe GFAP for astrocytes, IB4 for microglia and fibrinogen for BBB leakage. Immunofluorescence was used to observe Cx43 for gap-junction/hemichannels of capillaries Il-1β and NLRP3 for inflammation were performed on coronal brain sections. Images were analyzed using ImageJ. Data were analyzed using Prisim. Compared to the control hemispheres, the activation of astrocytes was observed 6 hours after radiation and the elevation of Cx43 expression from 24 hours after radiation. IL-1β expression and microglial activation were from 96 hours after radiation. The presence of fibrinogen through leaking BBB was detected from week1. The expression of Cx43 was bilateral with an increase in the control side 96 hours when compared to 6 hours’ time point. My results may suggest that the activation of astrocytes and opening of gapjunctions/ hemichannels initiated the pro-inflammatory cytokines, for example, IL-1β, leading to the glial cell associated acute inflammation. The activated glial cells could be the contributor to BBB breakdown which may lead to chronic inflammation and radiation necrosis. The pharmacological blockage of Cx43 gap-junction may further confirm its role in initiating RN.