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A radiation-induced blood-brain barrier (BBB) breakdown has been supposed to explain the acute radiation syndrome and the delayed brain radiation injury, but it has been clearly demonstrated only at high doses. In a previous study (Diserbo et al., 2002), we showed that non-lethal total body irradiation produced an early transient increase in BBB permeability in rats but the underlying mechanisms of radiation-induced BBB breakdown remain unclear. In the present work, the effects of ionizing radiation were studied on an in vitro BBB model. Gamma irradiation induced an increase in [(14)C]-sucrose BBB permeability that can be detected 72 h after exposure at doses up to 4 Gy. This increase was more important 8 days after irradiation and could be limited by dexamethasone treatment. An increase in fluorescein and FITC-dextrans (4 kDa/70 kDa) permeability was also observed, which can be related to a substantial opening of endothelial cell tight-junctions but without massive modification of tight-junction protein (ZO-1, ZO-2, claudin-5, occludin) immunolabeling even 8 days after 25 Gy exposure. Formation of actin stress fibers occurred in endothelial cells 8 days after 25 Gy exposure. A progressive decrease in cellular density associated with a simultaneous spreading of the endothelial cells was also observed after irradiation. Anti-γH2AX immunolabeling was used to investigate both DNA double-strand break induction and repair rates in endothelial cells. It revealed long-lasting DNA double-strand breaks after gamma irradiation. A better understanding and awareness of these phenomena are essential for designing appropriate pharmacotherapy in radiation-therapy and treatment of accidental overexposure., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The blood-brain barrier (BBB) is critical to maintain cerebral homeostasis. In this study, we examined the effects of exposure to electromagnetic pulse (EMP) on the functional integrity of BBB and, on the localization and expression of tight junction (TJ) proteins (occludin and ZO-1) in rats. Animals were sham or whole-body exposed to EMP at 200 kV/m for 400 pulses. The permeability of BBB in rat cerebral cortex was examined by using Evans Blue (EB) and lanthanum nitrate as vascular tracers. The localization and expression of TJ proteins were assessed by western blot and immunofluorescence analysis, respectively. The data indicated that EMP exposure caused: (i) increased permeability of BBB, and (ii) altered localization as well as decreased levels of TJ protein ZO-1. These results suggested that the alteration of ZO-1 may play an important role in the disruption of tight junctions, which may lead to dysfunction of BBB after EMP exposure., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

Disruption of the blood-brain barrier (BBB) is a key feature of radiation injury to the central nervous system. Studies suggest that endothelial cell apoptosis, gene expression changes, and alteration of the microenvironment are important in initiation and progression of injury. Although substantial effort has been directed at understanding the impact of radiation on endothelial cells and oligodendrocytes, growing evidence suggests that other cell types, including astrocytes, are important in responses that include induced gene expression and microenvironmental changes. Endothelial apoptosis is important in early BBB disruption. Hypoxia and oxidative stress in the later period that precedes tissue damage might lead to astrocytic responses that impact cell survival and cell interactions. Cell death, gene expression changes, and a toxic microenvironment can be viewed as interacting elements in a model of radiation-induced disruption of the BBB. These processes implicate particular genes and proteins as targets in potential strategies for neuroprotection.

Using intravital microscopy and a closed window method, we measured irradiation-induced changes in the vascular permeability and cell interactions in microcirculation networks of the rat pia mater; the same effects were monitored in the cremaster muscle as a control. The closed cranial window has many advantages, including long-term direct visualization of microcirculation. The method allows for repeated testing of the same vessel or network, thereby reducing variability. The method also allows for measurement of permeability changes and the accompanying leukocyte-endothelial cell interactions in the same network or vessel, which permits correlative studies of these phenomena. However, this method is not without challenges. The optical conditions are difficult, because the brain is three-dimensional and its parenchyma is more complex than the thinner, flatter peripheral tissues. To overcome this limitation, we performed a dynamic background subtraction. The background is dynamically related to vessel intensity, and changes in intensity were determined by eliminating the effects of neighboring and underlying vessels. We applied this method to studying the effects of ionizing radiation on the blood-brain barrier (BBB) permeability and cell interactions and the modulation of these effects by anti-ICAM-1 antibodies. Our results demonstrate that this method is sensitive to changes in these properties of the BBB.

We assessed the acute effects of radiation on the rat blood-brain barrier. A cranial window model and intravital microscopy were used to measure changes in permeability and leukocyte adhesion in pial vessels after a localized, single dose of 20 Gy. Permeability was assessed using five sizes of fluorescein isothiocyanate (FITC)-dextran molecules (4.4-, 10-, 38.2-, 70-, and 150-kDa) with measurements performed before and 2, 24, 48, 72 and 96 h after irradiation for the 4.4 and 38.2-kDa molecules and before and 24 h after irradiation for the other three molecules. To demonstrate the nature of blood-brain barrier permeability, we concurrently studied the permeability of microvessels in the cremaster muscle. In both tissues, permeability to FITC-dextran was significantly greater 24 h after irradiation than before (P<0.05). The exception was that radiation did not affect the permeability of pial vessels to the 150-kDa molecule. The particle-size dependence of the permeability changes in the brain were indicative of altered integrity of endothelial tight junctions and occurred concomitantly with an increase in cell adhesion which was determined by fluorescent labeling of leukocytes with rhodamine 6G. An early inflammatory response to irradiation was apparent in the brain 2 h after irradiation. The numbers of rolling and adherent leukocytes increased significantly and peaked at 24 h. Injection with the anti-ICAM-1 mAb significantly reduced leukocyte adhesion and permeability thereby linking the two processes. These findings provide a target to reduce radiation-related permeability and cell adhesion and potentially the side effects of radiation in the CNS.