Ischaemic stroke disintegrates communications within a controlled ensemble of cells that constitutes the blood-brain barrier. Therapeutic hypothermia may act as a neuroprotectant during intra- and post-ischaemic injuries. Hence, this study focuses on the effects of oxygen-glucose deprivation mediated ischaemic injury on the barrier in the absence or presence of hypothermia.

 An in vitro model of human blood-brain barrier, composed of human brain microvascular endothelial cells, astrocytes and pericytes, was subjected to oxygen-glucose deprivation (OGD) in the absence or presence of hypothermia in a time-dependent fashion. Following treatments, the integrity and function of blood-brain barrier was assessed by transendothelial electrical resistance and paracellular flux of high and low molecular weight permeability markers i.e. Evan’s blue albumin (EBA) and sodium fluorescein (NaF), respectively. Levels of pro-inflammatory cytokines were assessed in all three cell lines using specific ELISA-based kits. To study the rate of apoptosis, caspase-3/7 enzyme activities and percentage of DNA fragmented cells were measured.

Blood-brain barrier (BBB) accounts for a selective transition of ions and molecules from cerebral circulation to the brain parenchyma. The BBB is formed by endothelial cells, surrounded by basement membrane and astrocytes, pericytes and neurons, where astrocytes and tight junction proteins are known to significantly contribute to the overall tightness of the BBB. However, various cerebral conditions, notably acute ischaemic attack compromises the BBB integrity and thus contribute to ensuing oedema formation. Amongst the cells that make up the BBB, endothelial cells and astrocytes are known to be the potent producers of pro-inflammatory cytokines, notably interleukin- 1β (IL-1β) and tumor necrosis factor-alpha (TNF-α). As the cytokines may cross the BBB, they have long been implicated in early breakdown of the endothelial barrier. Recent studies have demonstrated that diminished expressions of tight junction proteins and reduced BBB-associated cell viability also play major roles in inducing cytokine-induced BBB damage. TNF-α is a pleiotropic inflammatory cytokine, usually demonstrates a bi-phasic release pattern. The BBB-associated endothelial cells contain TNF receptor-1 whereas IL-1β which tend to work synergistically with TNF-α at the site of ischaemic injury has a late releasing property usually after 6 to 24 h post-ischaemic attack. IL-1β also induces vasogenic oedema, triggers the endothelium for leukocyte adherence and contributes to influx of calcium. The release of cytokines at the site of injury is mainly followed by chemokines such as monocyte chemoattractant protein-1 and cytokine-induced neutrophil chemoattractant. Apoptosis, an active metabolic and genetically encoded death pathway, constitutes another major mechanism in ischaemiainduced neurovascular injury. Ischaemic signalling pathway may be employed by cytotoxic T cells, whose product, granzyme B, directly cleaves procaspase molecules, thereby activating the caspase enzymes in cells targeted for destruction. The barrier breakdown at high concentrations of cytokines correlates with caspase-3/7 activation via Jun amino-terminal kinases and protein kinase C signaling pathways

With Regards,
Sara Giselle
Associate Managing Editor
Journal of Stroke Research & Therapy