Tempo-iMG™ and Tempo-iOligo™ were cited by scientists in a nature.com study where they built a 3D in vitro organoid model of the blood brain barrier (BBB). They chose to build their BBB model based on a composition of multiple neural and glial cell types. By utilizing Tempo Bioscience’s iPSC-derived microglia and oligodendrocyte progenitor cells in this BBB model, researchers could perform specific assays to evaluate the functionality of this model and suggest its utility for developing patient-relevant scientific applications.
Scientists from the Wake Forest Institute for Regenerative Medicine investigated how to create a more “human-like” BBB model that would help scientists develop therapeutics that can pass through this highly selective and dynamic barrier. Currently, BBB models lack the ability to model the highly-specific interconnectivity of the human brain. To better represent and model the human BBB, researchers created a spheroid model that included multiple neural and glial cell types that could form tight junctions, and selective in their membrane permeability. Furthermore, this spheroid model can demonstrate the interactions between the BBB and surrounding brain tissue which has direct implications for drug development. Diseases such as multiple sclerosis, Alzheimer’s, and amyotrophic lateral sclerosis have lacked accurate patient relevant models and therefore therapeutic development has been stalled over the past decade. Studies such as “Recent progress and new challenges in modeling of human pluripotent stem cell-derived blood-brain barrier” and “Challenges of Integrative Disease Modeling in Alzheimer’s Disease” describe the faults of non-human based models and how improvements are needed for better modeling. With a comprehensive BBB model, drug development for these devastating diseases can progress more efficiently and safely.
What types of cells make up an accurate BBB model? What role do iPSC-derived cell types play?
Prior to this study, in vitro BBB models only utilized endothelial cells, pericytes, and astrocytes from animal models and immortalized cell lines. In this study, researchers created a spheroid organoid model that contained six canonical cell types found within the brain; the three previously listed, as well as iPSC-derived microglia, oligodendrocytes, and neurons. The addition of these iPSCs allowed researchers to create a BBB model that exhibited tight junction interconnectivity and BBB selectivity of specific molecules, such as mercury, across the membrane. Furthermore, the use of iPSC-derivative cell types specifically allowed researchers to conclude that their 3D spheroid model was physiologically relevant for modeling the human BBB.
Assessing BBB Expression of Tight Junctions, Adherens Junctions, and Transport Proteins
To determine if the BBB organoid model constructed was effective, researchers needed to determine that the particular microvasculature was distributed and functioning properly. For example, tight and adherens junctions must link microvascular endothelial cells to prevent foreign substance diffusion as we discuss in “What is the Blood Brain Barrier? Part 1 of a Series.” Researchers were able to identify that the spheroid showed BBB tight junction biomarkers by using immunofluorescent staining. To demonstrate the model’s functional aspects , researchers monitored the effect of hypoxia, a common trigger of neurologic injury that comes from ischemic stroke and traumatic brain injury, on the 3D BBB spheroid model. In a previous study of a 2D transwell system, hypoxia was shown to induce permeability and alter tight junction formation. When hypoxic conditions were tested on the BBB spheroid, researchers found that tight junction and adheren proteins’ localization were disrupted. This suggested that this organoid model could be a physiologically relevant model for studying hypoxia-caused conditions such as ischemia.
Neurotoxicity Assessment of BBB Selective Permeability
As previously established, the BBB’s regulated and selective permeability is a key feature that must be maintained to accurately model the influx and efflux of a variety of molecules including nutrients. To do so, researchers evaluated charge selectivity using inorganic mercury II salts which are toxic but unable to cross the BBB. Researchers compared the frequency of cell death on organoids containing all six cell types that had blood-brain barriers (BBB+) compared to organoids composed of neural cells that do not have a BBB (BBB-). Researchers measured toxicity by evaluating ATP production utilizing Promega’s CellTiter Luminescent Cell Viability Assay; a lowered rate of ATP production would indicate the organoid was killed by the mercury II salts. In BBB+ organoids, researchers found a higher rate of ATP production compared to BBB- organoids, which demonstrated that the blood brain barrier in this model organoid protected the cells from being killed by the mercury. This validates this BBB model’s membrane selectivity which is important for future exploration in understanding compounds passing through the BBB.
Why are these results significant?
These results are significant because researchers demonstrated the ability of this 3D Spheroid BBB to model an adult human BBB. As we discussed in “What is the Blood Brain Barrier? Part 1 of a Series,” the BBB’s complexity has posed significant difficulties for the progress of pharmaceutical development. Having a more human relevant model will encourage efficient drug development.
Where do Tempo products fit in?
In this study, researchers aimed to improve the current BBB models, and utilized Tempo-iMG™ and Tempo-iOligo™ to better represent a human blood brain barrier. Key characteristics of the human BBB, such as effective microvasculature and membrane permeability, were reflected in this study. As previously described, the use of iPSCs can significantly improve therapeutic development
Tempo Bioscience, as of October 19th 2022, announced new products, Tempo-iBMEC™ and Tempo-iPeri™, which are cells derived from human iPSCs and are critical for modeling the human blood-brain barrier. These products serve the industry’s drug development needs and improve the evaluation of a variety of drug candidates across the human blood-brain-barrier.