Changes in human endothelial cells and astrocytes of the blood-brain barrier (BBB) in cerebral malaria : using in vitro BBB models

During cerebral malaria (CM), sequestration of Plasmodium falciparum infected red blood cells (PRBC) to the blood-brain barrier (BBB) is associated with BBB disruption and long-term neurological sequelae in CM survivors, possibly linked to the activation of astrocytes. The aim of this study was to investigate the indirect effect of sequestration of PRBC during CM on endothelial cells and astrocytes of the BBB using two in vitro BBB models, the human brain endothelial cell (HBEC)-alone and the HBEC-astrocyte BBB models. This is the first time the HBEC-astrocyte BBB has been used to study sequestration in cerebral malaria. The HBEC-astrocyte BBB formed a tighter BBB over 5 days as indicated by the significantly higher transendothelial electrical resistance (TEER) than the HBEC-alone BBB. Inflammatory mediators released in response to coculturing of PRBC with HBEC caused a statistically significant increase in HBEC-alone BBB permeability but had no effect on the HBEC-astrocyte BBB integrity. However, these inflammatory mediators caused activation of astrocytes in the HBEC-astrocyte BBB shown by an increase in the adhesion molecule ICAM-1 and astrocyte marker GFAP in the astrocyte supernatant, and the increased expression of the protease ADAMTS-4 in astrocytes. A novel study was performed to investigate the effect of serum from malaria patients on HBEC-alone BBB integrity in vitro. Results showed that serum from uncomplicated malaria, severe malaria and CM patients caused an increase in HBEC-alone BBB permeability, with a more pronounced increase with serum from CM patients. This suggests that inflammatory mediators present in the serum of malaria patients had the ability to disrupt endothelial integrity. Our results suggest that during CM, sequestration of PRBC to the BBB results in the release of inflammatory mediators that cause astrocyte activation. Activated astrocytes released inflammatory cytokines that could cause damage to neurons and this could be responsible for the neurological sequelae observed in some CM survivors.