Characterization of a novel brain barrier ex vivo insect-based P-glycoprotein screening model.

In earlier studies insects were proposed as suitable models for vertebrate blood-brain barrier (BBB) permeability prediction and useful in early drug discovery. Here we provide transcriptome and functional data demonstrating the presence of a P-glycoprotein (Pgp) efflux transporter in the brain barrier of the desert locust (Schistocerca gregaria). In an in vivo study on the locust, we found an increased uptake of the two well-known Pgp substrates, rhodamine 123 and loperamide after co-administration with the Pgp inhibitors cyclosporine A or verapamil. Furthermore, ex vivo studies on isolated locust brains demonstrated differences in permeation of high and low permeability compounds. The vertebrate Pgp inhibitor verapamil did not affect the uptake of passively diffusing compounds but significantly increased the brain uptake of Pgp substrates in the ex vivo model. In addition, studies at 2°C and 30°C showed differences in brain uptake between Pgp-effluxed and passively diffusing compounds. The transcriptome data show a high degree of sequence identity of the locust Pgp transporter protein sequences to the human Pgp sequence (37%), as well as the presence of conserved domains. As in vertebrates, the locust brain-barrier function is morphologically confined to one specific cell layer and by using a whole-brain ex vivo drug exposure technique our locust model may retain the major cues that maintain and modulate the physiological function of the brain barrier. We show that the locust model has the potential to act as a robust and convenient model for assessing BBB permeability in early drug discovery.

The grasshopper: a novel model for assessing vertebrate brain uptake.

The aim of the present study was to develop a blood-brain barrier (BBB) permeability model that is applicable in the drug discovery phase. The BBB ensures proper neural function, but it restricts many drugs from entering the brain, and this complicates the development of new drugs against central nervous system diseases. Many in vitro models have been developed to predict BBB permeability, but the permeability characteristics of the human BBB are notoriously complex and hard to predict. Consequently, one single suitable BBB permeability screening model, which is generally applicable in the early drug discovery phase, does not yet exist. A new refined ex vivo insect-based BBB screening model that uses an intact, viable whole brain under controlled in vitro-like exposure conditions is presented. This model uses intact brains from desert locusts, which are placed in a well containing the compound solubilized in an insect buffer. After a limited time, the brain is removed and the compound concentration in the brain is measured by conventional liquid chromatography-mass spectrometry. The data presented here include 25 known drugs, and the data show that the ex vivo insect model can be used to measure the brain uptake over the hemolymph-brain barrier of drugs and that the brain uptake shows linear correlation with in situ perfusion data obtained in vertebrates. Moreover, this study shows that the insect ex vivo model is able to identify P-glycoprotein (Pgp) substrates, and the model allows differentiation between low-permeability compounds and compounds that are Pgp substrates.

Models for predicting blood-brain barrier permeation.

The endothelial blood-brain barrier (BBB) ensures an optimal environment for proper neural function in vertebrates; however, it also creates a major obstacle for the medical treatment of brain diseases. Despite significant progress in the development of various in vitro and in silico models for predicting BBB permeation, many challenges remain and, so far, no model is able to meet the early drug discovery demands of the industry for reliability and time and cost efficiency. Recently, it was found that the grasshopper (Locusta migratoria) brain barrier has similar functionality as the vertebrate BBB. The insect model can thus be used as a surrogate for the vertebrate BBB as it meets the demands required during the drug discovery phase.