Year: 2013
Type: dissertation
Abstract: The blood-brain barrier restricts the passage of many drugs into the brain.This restrictive barrier is created by the presence of many features, such as the tight junctions between the brain capillary endothelial cells and efflux transporter proteins (e.g., P-glycoprotein), all of which limit the transport of many compounds into the brain.In the early phase of drug development, cell based in vitro models are used to predict blood-brain barrier permeability of new drug candidates.In order to make appropriate predictions, it is important to be aware of the usefulness and limitations of these in vitro models.In addition, the relevance of the in vitro models needs to be assessed against their in vivo counterparts.Primary bovine brain microvessel endothelial cells (BBMECs) have been used as an in vitro blood-brain barrier model, since primary cells most closely represent the in vivo situation.However, the functionality of the efflux proteins and the in vivo relevance of the monocultured BBMECs have not been comprehensively assessed.Therefore, the general objective of this study was to evaluate the suitability of the monocultured BBMEC model for use in drug permeability studies.The BBMEC model was confirmed as being leaky.One reason for this could be the partial perinuclear localization of the tight junction protein occludin.P-glycoprotein was found to be expressed and correctly localized in the monocultured BBMECs.However, P-glycoprotein expression was significantly higher in the BBMECs cultured on filter inserts.Although Pglycoprotein was shown to be functional in the BBMECs, no efflux was detected in the bidirectional transport studies.The molecular descriptors determining the passive drug permeability across the BBMEC model were similar with those present in epithelial cell models, suggesting that there are no clear differences between passive drug permeability in the endothelial and epithelial cell models when drugs need to be classified into different categories.In addition, no clear differences were found in the in vitro-in vivo correlations between BBMEC model and epithelial cell models, indicating that the predictive value of endothelial and epithelial cell models is similar when passive transport of drugs is being evaluated in vitro.In conclusion, the monocultured BBMEC model was able to predict the in vivo brain entry of mainly passively transported drugs.In addition, undetected efflux suggests that the use of BBMEC model may pose a high risk of obtaining false negative results for drug candidates that are potential P-glycoprotein substrates.However, BBMECs are suitable for evaluating cellular mechanisms, such as in cellular uptake studies, where the tightness of the cell monolayer is not crucial.
Author: Jenni J. Hakkarainen
Language: English
Subfield: Neurology
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
Funders: Itä-Suomen Yliopisto, Tekes
OpenAlex ID: W3094830078