Poly(propylene oxide)-poly(ethylene oxide) block copolymer mediated rescue of diseased blood-brain barrier

Abstract

Brain microvascular endothelial cells (BMECs) comprise the blood-brain barrier (BBB), which serves as the vital interface between the vasculature and the central nervous system and controls transport into and out of the brain. During many pathological conditions, BBB dysfunction causes or exacerbates neurological injury. Amphiphilic block copolymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) have been extensively employed in biomedical applications. One specific type of PPO-PEO block copolymers called poloxamer 188 (P188) has demonstrated wide utility as a cell membrane stabilizer in various disease settings, including in animal models of neurological injuries where P188 treatment improved BBB function. While animal models have substantiated the use of P188 for protecting the BBB and biophysical studies have enlightened our understanding of how P188 interacts with lipid bilayers, how P188 specifically affects the function and phenotype of the BMECs has not be thoroughly investigated. Furthermore, researchers have mainly focused on P188, but exploration of other hydrophilic dominant PPO-PEO block copolymers is warranted. In this work, we utilized an in vitro model of the BBB to specifically interrogate the impact of P188 and related PPO-PEO block copolymers to damaged BBB. Human induced pluripotent stem cell-derived BMECs were used as an in vitro model of the BBB to study the state of the BBB in childhood cerebral adrenoleukodystrophy and ischemic stroke. We established that P188 and PPO-PEO diblock copolymers can protect or rescue the BBB during certain disease conditions, leading to mitigation of disease phenotype and improved barrier function. To investigate the localization of a PPO-PEO diblock copolymer in cells, we employed confocal fluorescence microscopy and established groundwork for fluorophore-free, live-cell imaging via confocal Raman microscopy. Elucidation of the cellular responses to PPO-PEO block copolymer treatment of damaged BMECs in vitro could bridge the gap between studies using non-living biophysical systems and in vivo studies to allow for translational research that may enable the development of therapeutic solutions for neurological diseases.