The blood-brain barrier that was discovered in the 1960s is an effective and strong set or a network of blood vessels that stands in between the brain and the rest of the body. This barrier acts as a protective wall, preventing the entry of foreign substances and allowing only the essential nutrients to enter. The brain’s blood vessels, like all other blood vessels in the body, are lined with endothelial cells, which act as an interface between circulating blood and the vessel wall. The endothelial cells in the brain, however, are closely wedged together, forming a virtually impermeable barrier between the brain and the bloodstream, unlike most blood vessels in the body. This nature of resistance sometimes prevents life-saving drugs from being able to repair the injured or diseased brain.  

Scientists have discovered that molecules that are very small and/or fat-soluble, such as antidepressants, anti-anxiety drugs, alcohol, cocaine, and many hormones, can easily pass through the endothelial cells that make up the blood-brain barrier. Larger molecules, such as glucose or insulin, must, on the other hand, be carried around by proteins. These transporter proteins, which are found in the blood vessel walls of the brain, snag and drag specific molecules from the blood into the brain. Drugs that can cross the blood-brain barrier could help researchers create more effective treatments for central nervous system disorders like Alzheimer’s, depression, and epilepsy. Scientists are looking into a variety of methods to do this, including using Trojan horses to smuggle drugs through the barrier and using ultrasound to temporarily weaken the barrier to allow drugs into the brain.  There are several mechanisms by which drugs can cross the blood-brain barrier (BBB):

1. Passive movement of water-soluble agents across the BBB is negligible because of the tight junctions between endothelial cells.
2. Small, lipid-soluble agents, such as antidepressants, cross the BBB via diffusion through endothelial cells.
3. Specialized transport proteins transport glucose, amino acids, and drugs like vinca alkaloids and cyclosporin, across the BBB.
4. Receptors mediate the transcytosis of proteins like insulin and transferrin.
5. Proteins, such as albumin, are adsorbed and transported across the BBB by transcytosis.
6. Efflux transporters counter passive diffusion by pumping foreign agents, such as non-sedating antihistamines, out of the brain.

How can nanotechnology help?

The best way to move drugs through the BBB is to use a safe method that does not damage the barrier. Nanobiotechnology-based delivery methods provide the best chances for achieving this ideal among the various approaches available. Some strategies necessitate multifunctional NPs that combine regulated BBB passage with targeted delivery of therapeutic cargo to the brain’s intended site of action. The delivery of drugs and biological therapeutics for brain tumors through the BBB is a significant application of nanobiotechnology.  Although there are currently some limitations and concerns for the potential neurotoxicity of NPs, the future prospects for NP-based therapeutic delivery to the brain are excellent.