Irradiation of Mouse Brain Leads to Neuroinflammation and Delayed Infiltration of Immune Cells: Role of Interleukin-1 and CCR2 Signaling

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Neurobiology and Anatomy, 2010.Cranial irradiation is a common therapy for cancers of the head and neck, and stereotactic radiosurgery is becoming increasingly utilized to treat CNS disorders. The use of radiotherapy is restricted by the sensitivity of the surrounding normal CNS tissues to radiation. Exceeding the radio-tolerance of normal tissues can result in a multitude of side effects that manifest as early as the cessation of therapy to several years later and contribute to patient morbidity and mortality. Data from animal studies and the treatment of patients suggest that neuroinflammation plays a role in the etiology of these side effects, although the exact inflammatory mechanisms remain unknown. This thesis characterizes a model of cranial irradiation in C57BL/6 mice. Consistent with previous reports, we observed a multi-phasic inflammatory response in the transcript levels of multiple inflammatory cytokines, along with astrocyte, endothelial, and microglial activation. Surprisingly, no overt pathology consistent with radiation-induced necrosis could be detected for up to a year. Despite the lack of pathologic changes, CNS radiation resulted in an acute infiltration of neutrophils and delayed increases in the numbers of T cells, MHCII positive cells, and CD11c positive cells. CD11c positive cells were found to express MHCII, suggesting that these are mature dendritic cells. Infiltrating dendritic cells and T cells were shown to have a preference for white matter. Moreover, these neuroinflammatory changes were limited to areas of the brain apparently exposed to the radiation beam. Radiosensitivity varies between animal strains and species, with a majority of the previous CNS radiation studies being conducted in C3H mice and rats. Using our mouse model of cranial irradiation, the effect of strain on the neuroinflammatory response to radiation was also investigated. There were significant differences in the levels of proinflammatory cytokines at both early (four hours) and late (six months) time points following radiation. The numbers of MHCII positive cells were different between strains, both at baseline and following radiation, with increased numbers present in the C57BL/6 mouse strain. Differences were also found in ICAM-1 expression, T cells, and dendritic cells with normal aging between strains, which may contribute to the disparity seen in their response to radiation. IL-1 has numerous functions in the normal CNS, as well as being a potent proinflammatory molecule. IL-1 has been shown to be a participant in neuroinflammation associated with numerous CNS injuries and disorders, in both acute and chronic settings. IL-1 has the ability to recruit leukocytes from the periphery into the CNS in response to injury or inflammation. One of the signaling pathways involved is that of CCL2/CCR2, which is important for the recruitment of myeloid cells following CNS injury. We show that radiation results in a delayed, dose-dependent increase in peripherally-derived immune cell recruitment that was present until the conclusion of the study (six months). Infiltrating cells were limited to areas of the brain that were exposed to radiation. It was shown that radiation-induced cellular recruitment does not lead to an increased total number of myeloid cells in the brain. This infiltration was found to be dependent on CCR2, as animals transplanted with CCR2-deficient bone marrow displayed decreased myeloid cell recruitment. IL-1 signaling in peripheral immune cells was also shown to be important for radiation-induced immune cell recruitment to the CNS, in the context of normal aging and following radiation exposure, although it was not essential for the neuroinflammatory response to radiation. The work presented here demonstrates that cranial irradiation leads to a state of chronic inflammation in the CNS. This thesis also suggests that peripheral immune cells may play a role in the development of late developing radiation injury. Importantly, these experiments elucidate some of the inflammatory mediators involved in the cellular recruitment following radiation exposure. The fact that infiltrating cells were only found in areas of the brain that were exposed to radiation, at doses considered safe in human patients, may provide a means to therapeutically deliver genes to the CNS. Further studies will be required to more fully characterize pathways contributing to radiation-induced neuroinflammation and cellular recruitment

Additional file 1: Figure S1. of Brain radiation injury leads to a dose- and time-dependent recruitment of peripheral myeloid cells that depends on CCR2 signaling

Effect of head shielding during bone marrow depletion on immune cell infiltration. In this bone marrow transplant experiment, one set of animals experienced total body exposure to two doses of 6 Gy, while the other set was irradiated with head shielding. Both sets of animals were injected intravenously with 4 × 106 eGFP-expressing bone marrow cells via the tail vein. Six weeks were allowed for reconstitution, and then the animals were anesthetized intravenously with a ketamine/xylazine (90 mg/kg/8 mg/kg) mixture and brought down to the irradiator in a similar manner to those animals that were cranially irradiated (sham irradiated). Animals were returned to the vivarium and sacrificed at 6 months post-anesthetization. The numbers of eGFP+ cells per square millimeter were calculated for the fimbria/fornix, the corpus callosum/extreme capsule, and the hippocampus. The average numbers of cells for section were compared using two-tailed t tests. HS = Head Shielded; TBI = Total Body Irradiated. Graph bars represent means ± SEM, n = 6 mice per condition: *p ≤ 0.05, **p ≤ 0.01, and ***p ≤ 0.001. (TIFF 2826 kb

CIED malfunction in patients receiving radiation is a rare event that could be detected by remote monitoring

INTRODUCTION: An increasing number of patients with cardiac devices require radiation therapy for treatment of a variety of cancers. This study aimed to identify the incidence and predictors of cardiac implantable electronic devices (CIED) malfunction in a real-world population that has received radiation therapy. METHODS: This retrospective cohort study included 109 adult patients who received radiation therapy at the University of Rochester Medical Center, Radiation Oncology Department, between 2000 and 2015. Sixty patients had pacemakers and 49 had automatic implantable cardioverter defibrillators. Subjects received either high energy (16 MV) and/or low energy (6 MV) photon beams with or without electron beams (6-16 MeV). We included interrogations done from first day of radiation and up to 3 months\u27 postradiation therapy. Outcomes analyzed were device-related malfunctions and device-related clinical events. Fisher\u27s exact, Wilcoxon, and Kruskall-Wallis tests were used for bivariate analysis. Logistic regression with robust adjustment was used for multivariate analysis. RESULTS: We identified six device-related malfunctions. All events were minor and included partial settings reset leading to loss of historical data, pacing thresholds changes, lead impedance changes, and LV output increase. Two patients had device-related clinical events, including dyspnea and diaphragmatic-stimulation. In bivariate analysis, CIED malfunction was associated with CIED duration in situ. In multivariate analysis, there was no significant statistical association between adverse events and beam energy type, CIED location, or dose of radiation delivered to the target. CONCLUSIONS: CIED malfunctions are uncommon in real-world patients and associated with minor clinical events. In our cohort, remote CIED monitoring would have identified all events