Tag: blood-brain barrier

Categories : Medical Research & Technology Neurodegenerative DiseasesTags :

MRI and Ultrasound Combo Opens Blood-brain Barrier

On By ModernMedia
In a mouse model study of MRI-guided focused ultrasound-induced blood-brain barrier (BBB) opening at MRI field strengths ranging from ­approximately 0 T (outside the magnetic field) to 4.7 T, the static magnetic field dampened the detected microbubble cavitation signal and decreased the BBB opening volume. Credit: Washington University School of Medicine in St. Louis

Using a combination of ultrasound, MRI field strength and microbubbles can open the blood-brain barrier (BBB) and allow therapeutic drugs to reach the diseased brain location with MRI guidance. 

Using the physical phenomenon of cavitation, it is a promising technique that has been shown safe in patients with various brain diseases, such as Alzheimer’s diseases, Parkinson’s disease, ALS, and glioblastoma.
While MRI has been commonly used for treatment guidance and assessment in preclinical research and clinical studies, until now, researchers did not know the impact that MRI scanner’s magnetic field had on the BBB opening size and drug delivery efficiency.

Hong Chen, associate professor of biomedical engineering at Washington University in St. Louis, and her lab have found for the first time that the magnetic field of the MRI scanner decreased the BBB opening volume by 3.3-fold to 11.7-fold, depending on the strength of the magnetic field, in a mouse model. The findings were in Radiology.

Prof Chen conducted the study on four groups of mice. After they were injected microbubbles, three groups received focused-ultrasound sonication at different strengths of the magnetic field: 1.5 T (teslas), 3 T and 4.7 T, and one group was never exposed to the field. 

The researchers found that the microbubble cavitation activity, or the growing, shrinking and collapse of the microbubbles, decreased by 2.1 decibels at 1.5 T; 2.9 decibels at 3 T; and 3 decibels at 4.7 T, compared with those that had received the dose outside of the magnetic field. Additionally, the magnetic field decreased the BBB opening volume by 3.3-fold at 1.5 T; 4.4-fold at 3 T; and 11.7-fold at 4.7 T. No tissue damage from the procedure was seen.

Following focused-ultrasound sonication, the team injected a model drug, Evans blue dye, to investigate whether the magnetic field affected drug delivery across the BBB. The images showed that the fluorescence intensity of the Evans blue was lower in mice that received the treatment in one of the three strengths of magnetic fields compared with mice treated outside the magnetic field. The Evans blue trans-BBB delivery was decreased by 1.4-fold at1.5 T, 1.6-fold at 3.0 T and 1.9-fold at 4.7 T when compared with those treated outside of the magnetic field.

“The dampening effect of the magnetic field on the microbubble is likely caused by the loss of bubble kinetic energy due to the Lorentz force acting on the moving charged lipid molecules on the microbubble shell and dipolar water molecules surrounding the microbubbles,” said Yaoheng (Mack) Yang, a doctoral student in Prof Chen’s lab and the lead author of the study.

“Findings from this study suggest that the impact of the magnetic field needs to be considered in the clinical applications of focused ultrasound in brain drug delivery,” Prof Chen said.

In addition to brain drug delivery, cavitation is also used in several other therapeutic techniques, such as histotripsy, the use of cavitation to mechanically destroy regions of tissue, and sonothrombolysis, a therapy used after acute ischaemic stroke. The magnetic field’s damping effect on cavitation is expected to affect the treatment outcomes of other cavitation-mediated techniques when MRI-guided focused-ultrasound systems are used.

Source: Washington University in St. Louis

Journal information: Yang, Y., et al. (2021) Static Magnetic Fields Dampen Focused Ultrasound–mediated Blood-Brain Barrier Opening. Radiology. doi.org/10.1148/radiol.2021204441. 

Categories : GeneticsTags :

New Study Finds Critical Flaw in Blood-brain Model

On By ModernMedia

The wrong kind of cells have been used to make in vitro models of the blood-brain barrier, which now throws a decade’s worth of research into question.

The present in vitro human blood-brain barrier model was developed in 2012. By inducing differentiated adult cells, such as skin cells, into developing into stem cells, the pluripotent stem cells obtained from the process are then transformed into nearly any type of mature cell. This includes the type of endothelial cell that lines brain and spinal cord blood vessels, and making a unique barrier that acts as a gatekeeper, restricting potentially dangerous substances, antibodies, and immune cells from entering the brain from the bloodstream.

“The blood-brain barrier is difficult to study in humans and there are many differences between the human and animal blood-brain barrier. So it’s very helpful to have a model of the human blood-brain barrier in a dish,” said co-study leader Dritan Agalliu, PhD, associate professor at Columbia University Vagelos College of Physicians and Surgeons.

Agalliu had noticed that these endothelial cells produced in this manner, did not behave like normal endothelial cells in the human brain. “This raised my suspicion that the protocol for making the barrier’s endothelial cells may have generated cells of the wrong identity,” said Agalliu.
“At the same time the Weill Cornell Medicine team had similar suspicions, so we teamed up to reproduce the protocol and perform bulk and single-cell RNA sequencing of these cells.”

Upon analysis, the researchers discovered that the supposed human brain endothelial cells were missing several key proteins found in natural endothelial cells and had more in common with epithelial cells, which is not usually found in the brain.

The team also identified three genes that, when activated within induced pluripotent cells, lead to the creation of cells that behave more like actual endothelial cells. More work is still needed, Agalliu says, to create endothelial cells that produce a reliable model of the human blood-brain barrier. His team is working to address this problem.

“The misidentification of human brain endothelial cells may be an issue for other types of cells made from induced pluripotent cells such as astrocytes or pericytes that form the neurovascular unit,” said Agalliu. The protocols to produce these cells were drawn up prior to the advent of single-cell technologies that are better at identifying cells.

“Cell misidentification remains a major problem that needs to be addressed in the scientific community in order to develop cells that mirror those found in the human brain. This will allow us to use these cells to study the role of genetic risk factors for neurological disorders and develop drug therapies that target the correct cells that contribute to the blood-brain barrier.”

Source: Medical Xpress