Loss of Blood-Brain Barrier Integrity in a KCl-Induced Model of Episodic Headache Enhances CNS Drug Delivery

Abstract

Cortical spreading depression (CSD) in the CNS is suggested as a common mechanism contributing to headache. Despite strong evidence for CNS involvement in headache disorders, drug development for headache disorders remains focused on peripheral targets. Difficulty in delivering drugs across the blood-brain barrier (BBB) may partially account for this disparity. It is known, however, that BBB permeability is increased during several CNS pathologies. In this study, we investigated BBB changes in response to KCl-induced CSD events and subsequent allodynia in rats. Cortical KCl injection in awake, freely moving rats produced facial allodynia with peak intensity between 1.5 and 3 h and CSD induction within 0.5–2 h postinjection. Brain perfusion of 14C-sucrose as a marker of BBB paracellular permeability revealed increased leak in the cortex, but not brainstem, beginning 0.5 h post-KCl injection and resolving within 6 h; no changes in tight junction (TJ) proteins occludin or claudin-5 expression were observed. Acute pretreatment with topiramate to inhibit CSD did not prevent the increased BBB paracellular permeability. CNS delivery of the abortive anti-migraine agent sumatriptan was increased in the cortex 1.5 h post-KCl injection. Surprisingly, sumatriptan uptake was also increased in the brainstem following CSD induction, suggesting regulation of active transport mechanisms at the BBB. Together, these results demonstrate the ability of CSD events to produce transient, time-dependent changes in BBB permeability when allodynia is present and to mediate access of clinically relevant therapeutics (i.e., sumatriptan) to the CNS.

Functional NHE1 expression is critical to blood brain barrier integrity and sumatriptan blood to brain uptake

“…Previously we have shown that CSD events in vivo increase paracellular uptake of 14 Csucrose, but not Evans Blue albumin [36], in line with above findings. To further investigate the role of NHE1 in the maintenance of BBB integrity, we assessed the uptake of the medium sized FITC-dextran (4000 Da) after cortical injection of aCSF or KCl ± the NHE1 inhibitor, zoniporide.…”

“…Thirty-min pretreatment with zoniporide (10 nM) significantly increased TEER values in both conditions (Fig 1A and 1B) To determine if KCl-mediated reductions in TEER were associated with paracellular leak, we next assessed 14 C-sucrose uptake after the KCl pulse. 14 C-sucrose as a marker of BBB paracellular permeability was used in these studies in line with our former in vivo experiments, in which elevated cortical uptake of 14 C-sucrose was observed after induction of CSD [36]. The uptake of 14 C-sucrose through the monolayer of bEnd.3 cells were significantly increased during KCl-pulse ( Fig 1C) (aCSF: 100.0±5.6% of vehicle-treated vs. KCl: 146.8±8.5% of vehicletreated, p<0.0001, as assessed by one-way ANOVA with Tukey post-test, n = 9-11/group, F (4,48) = 16.08).…”

“…Prior to assessing NHE1 contribution in vivo, we investigated the induction of periorbital allodynia following cortical KCl injections in female rats as previously reported in male rats [36,37]. Cortical KCl (0.5μL 1M) but not aCSF (0.5μL) induced significant periorbital allodynia that lasted for >24h (Fig 4).…”

“…Cortical KCl-induced CSD events cause transient, time-and regional dependent changes in BBB integrity [36] and functional NHE1 expression was altered in CSD tissue. It is wellknown that the neurovascular unit (NVU) throughout the parenchyma is comprised of endothelial cells, pericytes, astrocytes, neurons, and microglia [30].…”

“…Dural cannulation was performed as previously described [36,37]. Briefly, anesthesia was induced with intraperitoneal 80:10 mg/kg ketamine:xylazine or 45:5:2 mg/kg cocktail of ketamine:xylazine:acepromazine.…”