Establishing a Pertinent In vitro Model of the Blood Brain Barrier to Elucidate the Mechanisms of Invasion and Drug Permeability to the Brain

Abstract

The maintenance of homeostasis in the brain relies on the restrictive permeability of the blood brain barrier (BBB). Neurological disorders, neurodegeneration, infectious insults, and tumor metastasis to the brain are all consequences of the loss of structural integrity of the BBB. Specific to Lebanon, 80% of the Lebanese population is thought to be infected with Toxoplasma gondii (T. gondii). Chronic toxoplasmosis (CT) is established after the parasite crosses the BBB to form cysts in the brain. The latter is associated with primary neuropathies, neuropsychiatric and behavioral disorders as well as brain cancers. Furthermore, 1 in 8 women will develop breast cancer in their lifetime. One of the most devastating consequences of breast cancer development and progression is secondary metastasis to the brain. Hence, it is imperative to find a relevant way to study the BBB to curb the deleterious side effects of it being breached. Current models fail to recapitulate the fundamental properties required to mirror the pathophysiological features of the BBB, leaving a gap in the application and translation of the research for medical application. Therefore, there is a need for effective modeling of the BBB to elucidate mechanisms of a variety of diseases including parasitic infection, metastasis of cancer to the brain, and to assess current drugs for BBB permeability and for novel drug screening. In this study, we developed a three-dimensional (3D) model that recapitulates the physiological and molecular properties of the BBB in vitro. This was achieved using a trans-well, cell-cell and cell-matrix interaction model. This model uniquely uses primary human endothelial cells and astrocytes, as well as subendothelial basement membrane to faithfully mimic the cyto-architecture of the BBB. Barrier permeability was then assessed using trans epithelial/ endothelial electrical resistance (TEER) and a variety of permeability tracers. We used this model as a platform to assess the invasion of Toxoplasma gondii (T. gondii) to the brain and breast cancer metastasis. This novel BBB model will contribute to the assessment of known drugs that are BBB permeable as well as discovering novel drugs that can be delivered to the brain. In doing so, we hope to extricate the molecular mechanisms of these breaches of the BBB to contribute to the amelioration of the outcomes of diagnoses of T. gondii infection or metastatic breast cancer.