Aims: 

Lipopolysacharide (LPS) and unconjugated bilirubin (UCB) are potentially neurotoxic insults, especially in the neonatal period when sepsis and jaundice are common conditions. However, the mechanisms underlying the passage of the exogenous and endogenous neurotoxins across the blood-brain barrier (BBB) towards the brain are still unclear. In this study, we applied transmission electron microscopy (TEM) analysis as a tool to dissect the ultrastructural alterations ocurring at the endothelial lining of the BBB by exposure to LPS and UCB that may favour their access into the brain.

Methods: 

Confluent monolayers of rat brain microvascular endothelial cells in primary culture were exposed to LPS (1 mg/ml), UCB (50 mM), their combination, or no addition (control), in the presence of human serum albumin (100 mM) to solubilize UCB, for 4 or 24 h, and morphological analysis was performed by TEM.

Results: 

Morphological analysis showed the presence of impaired mitochondria, dilated endoplasmic reticulum (ER) and high number of apoptotic bodies by both insults. It also revealed a loss of TJ by UCB, as well as an increase in the number of caveolae and shorter tight junctions in LPS-treated cells. Curiously, no significant difference due to 4 or 24 h treatment or aggravating effects resulted from the simultaneous exposure to both neurotoxins were observable in the cultures. These observations are supported by previous studies showing that both LPS and UCB induce endothelial cell death and lead to an increased permeability of the BBB, and that mitochondria and ER are important targets of UCB toxicity.

Conclusions: 

Transmission electron microscopic investigation proved a useful tool to add to molecular, biological and physiological techniques to obtain more accurate answers for the reason of the impairment of the BBB endothelium caused by LPS and UCB, and in showing some of the targets of these neurotoxins.

Support: 

FCT-PTDC/SAU-FCF/68819/2006