The Brain-Blood Barrier and the Future of Medical Treatments

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The blood-brain barrier is a biological structure that acts to maintain a homeostatic environment within the Central Nervous System(CNS). You can think of it as your brain’s wall of defense. The blood-brain barrier is known as a diffusion barrier because it is semipermeable. This means that it only allows some substances to enter the brain while preventing other harmful substances from circulating in the bloodstream and the brain. This can be thought of as a filtration or vetting system.

This semipermeable barrier is achieved through endothelial cells. Endothelial cells line the inside of every blood vessel in the body and form a one-cell-thick later called the endothelium.  The blood-brain barrier is a layer of endothelial cells that selectively allow entry of molecules needed for brain function. Unlike these other blood vessels in the body, the endothelial cells in the brain are tightly wedged together which creates the semipermeable boundary between the brain and bloodstream. The molecules that are permitted entry through this boundary are amino acids, oxygen, glucose, and water. This ensures that the right balance of hormones, nutrients, and water is flowing throughout the brain.

Research surrounding the blood-brain barrier and medical treatments has many challenges. Most drug treatments are unable to pass through the barrier, which is why drug development for brain diseases have poor success rates compared to the development of drugs in other areas of the body. In cancer, for example, the blood–brain barrier is largely responsible for the failure of brain of cancer treatments. The blood-brain barrier actively pumps selected molecules into or out of the brain and can prevent the drugs from entering the brain. In many instances where the cancer drugs do manage to cross the blood-brain barrier, they are promptly kicked back out by active efflux pumps<. Another issue with the blood-brain barrier and cancer treatments lies in the fact that the molecules that can easily slip across the barrier tend to be small and highly lipid-soluble. This presents a challenge since many lipid-insoluble biological drugs have improved outcomes for many other types of cancer.

Despite the challenges of the blood-brain barrier and cancer treatments, studies have proven that your brain’s wall of defense can also act as a potential noninvasive treatment tool for many neurological diseases. Through extensive studies, scientists have found that very small compounds or compounds that are lipid-soluble can pass through the endothelial cells of the blood-brain barrier with almost no effort. These compounds include antidepressants, anti-anxiety medications, alcohol, cocaine, and many other hormones. The passing of larger molecules such as glucose or insulin is also possible with the help of transporter proteins.

Blood-brain barrier research does not stop there. There are currently several ways that researchers are attempting to combat the challenges of the blood-brain barrier and medical treatments. One example of this is the development of cyclic peptides that can enhance the penetration of the blood-brain barrier. This is achieved by attaching the cyclic peptides to the surface of nanoparticles. This creates a drug nanocarrier for drug delivery through the blood-brain barrier, which is promising for the future effectiveness of drug delivery to the brain.

The future of medical treatments through the use of the blood-brain barrier continues to move forward. As scientists continue to explore this biological barrier, new and noninvasive treatments will arise to address cancer and other neurological diseases.

References:
NCBI: https://www.ncbi.nlm.nih.gov/books/NBK519556/
Science Daily: https://www.sciencedaily.com/releases/2019/10/191011095933.htm
Cure Alzheimer’s Fund: https://curealz.org/the-research/topics-of-interest/blood-brain-barrier/
Nature: https://www.nature.com/articles/d41586-018-06707-4
Pharma Tech: https://pharma.nridigital.com/pharma_jul20/breaking_blood-brain_barrier_neurology