The Grasshopper: A Novel Model for Assessing Vertebrate Brain Uptake

Abstract

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.

Barrier mechanisms in the Drosophila blood-brain barrier

“…Mayer et al ( 2009 ) identified Mdr65 in a screen for increased BBB permeability to the P-glycoprotein substrate Rhodamine B. Mdr65 is also required at the BBB to protect the brain from various P-glycoprotein xenobiotic substrates, and sensitivity of the Mdr65 mutants to these xenobiotics can be rescued by expression of human P-glycoprotein specifically in the SPG cells, confirming that Mdr65 provides an evolutionarily conserved chemoprotective transport barrier at the invertebrate BBB. Interestingly, recent work in the migratory locust ( Locusta migratoria ) and the desert locust ( Schistocerca gregaria ) has shown that P-glycoprotein-like xenobiotic transporters also provide a transcellular barrier in the locust brain (Nielsen et al, 2011 ; Andersson et al, 2013 ). These findings advance the possibilities of using insect models to study the roles of xenobiotic efflux transporters at the BBB (see below).…”

“…Using the grasshopper system, Nielsen et al ( 2011 ) showed that co-administration of a P-glycoprotein inhibitor with a test P-glycoprotein substrate rendered the BBB more permeable to the P-glycoprotein substrate. Furthermore, Andersson et al ( 2013 ) were able to use this methodology to distinguish P-glycoprotein substrates from non-substrates using liquid chromatography-mass spectrometry to measure the drug content in the brain, either in the absence or presence of a P-glycoprotein inhibitor. This confirmed that P-glycoprotein substrates could be identified using this model system.…”

Identification of a Functional Homolog of the Mammalian CYP3A4 in Locusts

“…Currently, two insect BBB models have been reported using locusts as model insects (Nielsen et al, 2011;Andersson et al, 2013). An ex vivo model has been developed and allows application of test items directly to entire brains isolated prior to testing.…”

Molecular Determinants of blood–brain Barrier Permeation

“…For instance, the use of insect cells from the grasshopper ( Locusta migratoria ) has several key aspectct which are close enough in function for the easy development of in vitro cell cultures which can be used to screen compounds for BBB permeability. [29, 43, 44] Additionally, the zebrafish ( Danio rerio ) has also been used successfully as surrogate model for the BBB permeability studies of compounds. [45, 46]…”