Longitudinal assessment of blood–brain barrier leakage during epileptogenesis in rats. A quantitative MRI study E.A. van Vliet a,b, ⁎, W.M. Otte c,d , J.A. Gorter a,b , R.M. Dijkhuizen c , W.J. Wadman a,b a Center for Neuroscience, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands b Epilepsy Institute in The Netherlands Foundation (Stichting Epilepsie Instellingen Nederland, SEIN), Heemstede, The Netherlands c Biomedical MR Imaging and Spectroscopy Group, Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands d Department of Pediatric Neurology, Rudolf Magnus Institute of Neuroscience, University medical Center Utrecht, Utrecht, The Netherlands abstract article info Article history: Received 19 July 2013 Revised 22 November 2013 Accepted 27 November 2013 Available online 7 December 2013 Keywords: Blood–brain barrier Magnetic resonance imaging Gadolinium Temporal lobe epilepsy Status epilepticus Fluorescein The blood–brain barrier (BBB) plays an important role in the homeostasis of the brain. BBB dysfunction has been implicated in the pathophysiology of various neurological disorders, including epilepsy in which it may contrib- ute to disease progression. Precise understanding of BBB dynamics during epileptogenesis may be of importance for the assessment of future therapies, including BBB leakage blocking-agents. Longitudinal changes in BBB integ- rity can be studied with in vivo magnetic resonance imaging (MRI) in combination with paramagnetic contrast agents. Although this approach has shown to be suitable to detect major BBB leakage during the acute phase in experimental epilepsy models, so far no studies have provided information on dynamics of the extent of BBB leakage towards later phases. Therefore a sensitive and quantitative approach was used in the present study, in- volving fast T1 mapping (dynamic approach) during a steady-state infusion of gadobutrol, as well as pre- and post-contrast T1-weighted MRI (post–pre approach). This was applied in an experimental epilepsy model in which previous MRI studies failed to detect BBB leakage during epileptogenesis. Adult male Sprague–Dawley rats were injected with kainic acid to induce status epilepticus (SE). MRI experi- ments were performed before SE (control) and during the acute (1 day) and chronic epileptic phases (6 weeks after SE). BBB leakage was quantified by fast T1 mapping (Look–Locker gradient echo MRI) with a time resolution of 48 s from 5 min before up to 45 min after 20 min step-down infusion of 0.2 M gadobutrol. In addition, T1-weighted MRI was acquired before and 45 min after infusion. MRI data were compared to post- mortem microscopic analysis using the BBB tracer fluorescein. Our MRI data showed BBB leakage, which was evident at 1 day and 6 weeks after SE in the hippocampus, ento- rhinal cortex, amygdala and piriform cortex. These findings were confirmed by microscopic analysis of fluoresce- in leakage. Furthermore, our MRI data revealed non-uniform BBB leakage throughout epileptogenesis. This study demonstrates BBB leakage in specific brain regions during epileptogenesis, which can be quantified using MRI. Therefore, MRI may be a valuable tool for experimental or clinical studies to elucidate the role of the BBB in epileptogenesis. © 2013 Elsevier Inc. All rights reserved. Introduction The blood–brain barrier (BBB) plays an important role in the homeo- stasis of the brain. Endothelial cells that are tightly connected via tight junctions protect the brain from the entry of potentially harmful sub- stances in the blood stream. BBB dysfunction that results in the entry of blood components in the extracellular space of the brain is observed in several disorders of the central nervous system, including epilepsy (Abbott et al., 2010). BBB dysfunction may also contribute to progres- sion of the disease (Friedman, 2011; Marchi et al., 2012; Van Vliet et al., 2007a; Vezzani et al., 2011). In experimental epilepsy models BBB leakage is detected using BBB tracers, commonly by post-mortem analysis of tracer accumulation in brain tissue. Longitudinal studies are warranted to more specifically relate BBB dysfunction to disease pro- gression, which could be achieved using in vivo contrast-enhanced magnetic resonance imaging (MRI). In patients' gadolinium (Gd)- based MR contrast agents such as Gd-diethylenetriaminepentacetate (Gd-DTPA) are routinely used to detect BBB opening (Dijkhuizen, 2011; Kassner and Thornhill, 2011). When the BBB is disrupted, the intravenously administered MR contrast agent leaks out of the blood vessels and accumulates in the brain parenchyma. This results in local shortening of the longitudinal MR relaxation time, T1. The changes in MR signal can be used to localize BBB disruption and to quantify the Neurobiology of Disease 63 (2014) 74–84 Abbreviations: BBB, blood–brain barrier; FSC, fluorescein; KA, kainic acid; SE, status epilepticus. ⁎ Corresponding author at: Swammerdam Institute for Life Sciences, Center for Neuroscience, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. Fax: +31 20 5257709. E-mail address: e.a.vanvliet@uva.nl (E.A. van Vliet). Available online on ScienceDirect (www.sciencedirect.com). 0969-9961/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.nbd.2013.11.019 Contents lists available at ScienceDirect Neurobiology of Disease journal homepage: www.elsevier.com/locate/ynbdi