Measuring Changes in Brain Endothelial Barrier Integrity with Two Impedance-based Biosensors in Response to Cancer Cells and Cytokines

Summary

Here we demonstrate the technique of using impedance-based biosensors: ECIS and cellZscope, for measuring brain endothelial barrier strength. We detail the preparation and technique of adding various stimuli to an in vitro model of the brain endothelium. We measure, record, and give a representative analysis of the findings.

Abstract

The blood-brain barrier (BBB) protects the brain parenchyma against harmful pathogens in the blood. The BBB consists of the neurovascular unit, comprising pericytes, astrocytic foot processes, and tightly adhered endothelial cells. Here, the brain endothelial cells form the first line of barrier against blood-borne pathogens. In conditions like cancer and neuroinflammation, circulating factors in the blood can disrupt this barrier. Disease progression significantly worsens post barrier disruption, which permits access to or impairment of regions of the brain. This significantly worsens the prognoses, particularly due to limited treatment options available at the level of the brain. Hence, emerging studies aim to investigate potential therapeutics that can prevent these detrimental factors in the blood from interacting with the brain endothelial cells.

The commercially available Electric Cell-Substrate Impedance Sensing (ECIS) and cellZscope instruments measure the impedance across cellular monolayers, such as the BBB endothelium, to determine their barrier strength. Here we detail the use of both biosensors in assessing brain endothelial barrier integrity upon the addition of various stimuli. Crucially, we highlight the importance of their high-throughput capability for concurrent investigation of multiple variables and biological treatments.

Introduction

This article discusses current trends in the assessment of microvascular cells. We specifically detail the use of two commercially available platforms for measuring the barrier properties of cerebral microvascular endothelial cells. Endothelial cells are blood-facing cells, which line the vessel wall. However, cerebral microvessels are unique as they help form the protective blood-brain barrier (BBB)^1,2,3. The BBB functions to regulate the transport of molecules from the blood to the brain. Peripheral diseases that affect the central nervous system (CNS) are commonly linked t....

Protocol

1. Using ECIS to monitor changes in brain endothelial barrier integrity in response to various treatments

1. Setting up the software, array station, and machine
   1. Connect the 96-well array station to the machine. Place the array station in a plastic bag and place it in the incubator at least 1 h before the assay to allow it to warm up. Remove the plastic bag immediately before the experiment.
   2. Once ready, turn on the machine and open the corresponding software on the computer. Press the Setup button under the Collect Data tab. The software will complete a connection check, which wil....

Results

Interpreting ECIS impedance data

Understanding optimal experimental conditions
Herein the data can be directly viewed using the software (Figure 2A) or exported for analysis and graph plotting (Figure 2B). Figure 2A shows an example of data displayed on the actual software interface. The left graph shows an example of a disrupted connection due to improper lo.......

Discussion

Therapeutic studies on diseases that affect the BBB must consider the importance of brain endothelial barrier integrity and regulation. For example, brain endothelial barrier disruption is critically investigated in the metastasis of cancer to the brain from other anatomical sites. This is because the brain endothelium forms the first barrier against circulating tumor cells. As mentioned earlier in the introduction, in vitro studies on endothelial barrier integrity need to be reproducible, non-invasive, label-fr.......

Materials

Name	Company	Catalog Number	Comments
aMEM	Gibco	12561072	Melanoma cell base media
cellZscope array	nanoAnalytics	cellZscope2; software v4.3.1	TER measuring biosensor array
Collagen I—rat tail	Gibco	A1048301	ECM substrate for coating
dibutyryl-cAMP	Sigma-Aldrich	D0627	Brain endothelial media supplement
ECIS array	Applied Biophysics	ECIS ZΘ; software v1.2.163.0	Rb/Alpha measuring biosensor array
ECIS plate	Applied Biophysics	96W20idf	96-well biosensor plate
FBS	Sigma-Aldrich	12203C-500ML
GlutaMAX	Gibco	305050-061	Brain endothelial media supplement
hCMVEC	Applied Biological Materials	T0259	Brain endothelial cell line
hEGF	PeproTech	PTAF10015100	Brain endothelial media supplement
Heparin	Sigma-Aldrich	H-3393	Brain endothelial media supplement
hFGF	PeproTech	PTAF10018B50	Brain endothelial media supplement
Hydrocortison	Sigma-Aldrich	H0888	Brain endothelial media supplement
IL-1β	PeproTech	200-01B	Cytokine
Insulin-Transferrin-Sodium Selenite	Sigma-Aldrich	11074547001	Melanoma cell media supplement
M199	Gibco	11150-067	Brain endothelial cell base media
MilliQ water			Deionized water
PBS 1x	Gibco	10010-023
TNFα	PeproTech	300-01A	Cytokine
Transwell insert	Corning	CLS3464	Porous membrane insert
TrypLE Express Enzyme	Gibco	12604021	Dissociation reagent