Bioengineers on the brink of breaching blood-brain barrier

Imagine the brain as an air traffic control tower, overseeing the crucial and complex operations of the body's "airport." This tower, essential for coordinating the ceaseless flow of neurological signals, is guarded by a formidable layer that functions like the airport's security team, diligently screening everything and everyone, ensuring no unwanted intruders disrupt the vital workings inside.

However, this security, while vital, comes with a significant drawback: sometimes a "mechanic"—in the form of critical medication needed for treating neurological disorders—is needed inside the control tower to fix arising issues. But if the security is too stringent, denying even these essential agents entry, the very operations they're meant to protect could be jeopardized.

Now, researchers led by Michael Mitchell of the University of Pennsylvania are broaching this long-standing boundary in biology, known as the blood-brain barrier, by developing a method akin to providing this mechanic with a special keycard to bypass security. Their findings, published in the journal Nano Letters, present a model that uses lipid nanoparticles (LNPs) to deliver mRNA, offering new hope for treating conditions like Alzheimer's disease and seizures—not unlike fixing the control tower's glitches without compromising its security.

"Our model performed better at crossing the blood-brain barrier than others and helped us identify organ-specific particles that we later validated in future models," says Mitchell, associate professor of bioengineering at Penn's School of Engineering and Applied Science, and senior author on the study. "It's an exciting proof of concept that will no doubt inform novel approaches to treating conditions like traumatic brain injury, stroke, and Alzheimer's."

Search for the key

To develop the model, Emily Han, a Ph.D. candidate and NSF Graduate Research Fellow in the Mitchell Lab and first author of the paper, explains that it started with a search for the right in vitro screening platform, saying, "I was combing through the literature, most of the platforms I found were limited to a regular 96-well plate, a two-dimensional array that can't represent both the upper and lower parts of the blood-brain barrier, which correspond to the blood and brain, respectively."

Han then explored high-throughput transwell systems with both compartments but found they didn't account for mRNA transfection of the cells, revealing a gap in the development process. This led her to create a platform capable of measuring mRNA transport from the blood compartment to the brain, as well as transfection of various brain cell types including endothelial cells and neurons.

"I spent months figuring out the optimal conditions for this new in vitro system, including which cell growth conditions and fluorescent reporters to use," Han explains. "Once robust, we screened our library of LNPs and tested them on animal models. Seeing the brains express protein as a result of the mRNA we delivered was thrilling and confirmed we were on the right track."

The team's platform is poised to significantly advance treatments for neurological disorders. It's currently tailored for testing a range of LNPs with brain-targeted peptides, antibodies, and various lipid compositions. However, it could also deliver other therapeutic agents like siRNA, DNA, proteins, or small molecule drugs directly to the brain after intravenous administration.