PARENT SESSION
1:30 PM to 3:30 PM
Sunday, April 21, 2002
Poster Session 6 Normal Tissue Biology II
Room: Nevada Exhibition Center

(P11-93) Radiation-induced acute blood-brain barrier disruption is mediated by the acid sphingomyelinase pathway .

Li, Yu-Qing^*,1, Jain, Vipan¹, Haimovitz-Friedman, Adriana², Wong, Shun¹, ¹ Princess Margaret Hospital, Toronto, Ontario, Canada² Memorial Sloan-Kettering Cancer Center, New York, NY

ABSTRACT-
Acute disruption of blood-brain barrier (BBB) is well recognised following radiation therapy (XRT) to the central nervous system (CNS). In this study, we assessed the genetic regulation of acute vascular endothelial cell death and BBB disruption in the CNS after XRT. Adult rats were given graded single doses of X-ray to the cervical spinal cord. At different time intervals after XRT, the irradiated spinal cord was processed for histologic and immunohistochemical analysis. In rat spinal cord, there was a dose-dependent apoptotic response during the first 24 h after XRT. Apoptotic cells consisted of both endothelial and glial cells as described previously. Using immunohistochemistry for laminin or factor VIII, a dose-dependent reduction in endothelial cell density (20.5%, 22.1% and 39.3% after doses of 22, 30 and 50 Gy respectively compared to control) was observed at 24 h after XRT. This was associated with a similar dose-dependent disruption in BSCB as demonstrated by albumin immunohistochemistry. XRT-induced apoptosis in endothelial cells has been shown to be dependent on the acid sphingomyelinase (ASMase) pathway. After a single dose of 50 Gy to the cervical spinal cord of ASMase +/+ mice, there was a 47.7% reduction in endothelial cell density at 24 h compared to non-irradiated controls (33.8/mm² vs 17.6/mm², p = 0.03). No decrease of endothelial cell density was observed in ASMase -/- mice (29.1/mm² vs 27.7/mm²). Disruption of BSCB was assessed using albumin immunohistochemistry and ip injection of Evans blue dye. In the irradiated (50 Gy) spinal cord of ASMase +/+ mice at 24 h, there was evidence of albumin immunoreactivity and Evans blue dye staining around microvessels. Non-irradiated controls and the irradiated spinal cord of ASMase-/- mice demonstrated no evidence of leakage. Reduction in endothelial density at 24 h after a single dose of 50 Gy in p53 +/+ mouse spinal cord was similar to that observed in p53 -/- animals. Both p53 +/+ and -/- mice demonstrated albumin immunoreactivity around vessels after XRT. We conclude that there is a causal association of acute BSCB disruption with apoptosis of endothelial cells in the CNS after XRT. Furthermore, acute BSCB disruption following XRT is mediated by the ASMase pathway, but not the p53 pathway. (supported by NCIC)

KEYWORDS: Apoptosis, Blood-spinal cord barrier, Central nervous system, Acid sphingomyelinase