Oxidative Stress Alters Blood-Brain Barrier Integrity

Abstract

The blood-brain barrier (BBB) is located at the level of the cerebral microvasculature and is critical to maintain central nervous system (CNS) homeostasis. The tight junction (TJ) protein complexes between endothelial cells at the BBB are primarily responsible for limiting paracellular diffusion of substances from the blood to the CNS. The BBB’s functional integrity is compromised in a number of disease states which affect the CNS, suggesting BBB dysfunction causes or contributes to many diseases of the CNS. A common component of most of these diseases is oxidative stres. Oxidative stress is associated with hypoxia-reoxygenation (HR) and peripheral inflammatory pain (PIP). Both HR and PIP have been shown to compromise BBB functional integrity. Using in vivo rat models of HR and PIP, we examined the role of ROS on BBB permeability as well as the TJ protein occludin using the free radical scavenger tempol. First, we subjected rats to HR with or without pre-treatment with tempol (200 mg/kg). We showed that tempol prevents up-regulation of the cellular stress marker heat shock protein 70 at the BBB during HR. Next we showed tempol reverses HR-mediated BBB permeability increase to ¹⁴C-sucrose, a marker of BBB paracellular permeability. Tempol also attenuated changes in the structure and localization of occludin, suggesting ROS produced during HR alter occludin and lead to disruption of BBB. We then investigated whether ROS production have similar effects on occludin and BBB permeability during PIP by administering 3% λ-carrageenan into the hind paw of rats. We found tempol attenuated carrageenan-induced increase in paw edema and thermal hyperalgesia. Tempol also attenuated up-regulation of the cellular stress marker NF-κB in cerebral microvessels. Tempol significantly decreased BBB permeability to ¹⁴C sucrose during PIP. We found PIP reduces disulfide bonds in occludin oligomeric assemblies thought to be important in maintaining the structural integrity of the BBB. Tempol significantly inhibited disulfide bond reduction, suggesting ROS mediate BBB disruption during inflammatory pain by reducing occludin disulfide bonding. Taken together, these findings show the involvement of ROS during HR and PIP contributes to BBB dysfunction by altering the structure of high molecular weight occludin oligomeric assemblies.