Abstract
Opioids play crucial roles in the regulation of many important brain functions including pain, memory and neurogenesis. Activation of opioid receptors is reported to have neuroprotective effects following ischemic reperfusion injury. The objective of this study was to understand the role of biphalin and nociceptin, opioid receptor agonists, on blood-brain barrier (BBB) integrity during ischemic stroke. In this study, we aimed to measure the effect of biphalin and nociceptin on astrocytic glutamate uptake and on expression of excitatory amino acid transporter (EAAT) to study the indirect role of astrocytes on opioid receptor-mediated BBB protection during in vitro stroke conditions. We used mouse brain endothelial cells (bEnd.3) and primary astrocytes as in-vitro BBB model. Restrictive BBB properties were evaluated by measuring [14C] sucrose paracellular permeability and the redistribution of the tight junction proteins. The protective effect of biphalin and nociceptin on BBB integrity was assessed after exposing cells to oxygen-glucose deprivation (OGD) and glutamate. It was observed that combined stress (2mM glutamate and 2hours OGD) significantly reduced glutamate uptake by astrocytes however, biphalin and nociceptin treatment increased glutamate uptake in primary astrocytes. This suggests a role of increased astrocytic buffering capacity in opioid meditated protection of the BBB during ischemic stroke. It was also found that the combined stress significantly increased [14C] sucrose paracellular permeability in in-vitro BBB model. Biphalin and nociceptin treatment attenuated the effect of the combined stress, which was reversed by the opioid receptor antagonists, suggesting the role of opioid receptors in biphalin and nociception's BBB modulatory activity.
Significance Statement There is an unmet need for discovering new efficacious therapeutic agents to offset the deleterious effects of ischemic stroke. Given the confirmed roles of opioid receptors in the regulation of CNS functions, opioid receptor agonists have been studied as potential neuroprotective options in ischemic conditions. This study will greatly add to the knowledge about the cerebrovascular protective effects of opioid receptor agonists and provide insight about the mechanism of action of these agents.
- astrocytes
- blood-brain barrier
- excitotoxicity
- glutamate
- ischemia / reperfusion injury
- opioid receptors
- opioids
- Copyright © 2020 American Society for Pharmacology and Experimental Therapeutics