Neuroprotection by hypercapnia in brain ischemic injury followed by persistent hypoxia: an in vivo and in vitro experimental study

Abstract Backgrounds: Therapeutic hypercapnia was shown to have a potential neuroprotective role in our previous studies in a rat model of ischemia followed by hypoxia; however, it is unknown how hypercapnia affects blood-brain barrier (BBB) function under hypoxic conditions in cerebral ischemia. We aimed to observe the BBB permeability changes in response to cerebral ischemia followed by acute hypoxia or hypercapnic hypoxia using in vivo and in vitro models.Methods: Adult rats underwent unilateral common carotid artery ligation, at 60 min of ligation, they were exposed to systemic hypoxia with ventilation of 15% oxygen (O2) combined with 8% carbon dioxide (CO2) for 180 min. Cerebral blood flow, BBB integrity, infarct volume and behavior were assessed in this study. In vitro, rat brain microvascular endothelial cells (BMECs) were isolated and cultured under O2 (1% or 21%) with or without 15% CO2 for 6 h. Cell viability and transendothelial electrical resistance (TEER) were measured. The ZO-1 and occludin protein levels were explored in BMECs by Western blotting.Results: Arterial blood O2 (PaO2) tensions averaged 56.1 mmHg during simple hypoxia, and arterial blood CO2 tensions (PaCO2) were maintained at normal values or 60–80 mmHg. Hypercapnia treatment significantly reduced brain infarct volume and pathophysiological changes in hypoxic ischemia rats. Furthermore, in the in vitro experiment, hypercapnia significantly improved the growth condition of BMECs, reduced endothelial cell permeability and attenuated the loss of ZO-1 and occludin protein in BMECs induced by hypoxia. Conclusions: Hypercapnia exerts beneficial effects on the BBB permeability in the rat model of hypoxic-ischemic injury and recovers the neurologic status especially within one week, possibly by preventing the loss of tight junction proteins.