Courtesy of Genentech
Delivering medications to the brain could become easier, thanks to molecules that can escort drugs through the notoriously impervious sheath that separates blood vessels from neurons. In a proof-of-concept study in monkeys, biologists used the system to reduce levels of the protein amyloid-β, which accumulates in the brain plaques associated with Alzheimer's disease1.


The blood–brain barrier is a layer of cells lining the inner surface of the capillaries that feed the central nervous system. It is nature's way of protecting the delicate brain from infectious agents and toxic compounds, while letting nutrients and oxygen in and waste products out. Because the barrier strictly regulates the passage of larger molecules and often prevents drug molecules from entering the brain, it has long posed one of the most difficult challenges in developing treatments for brain disorders.
Several approaches to bypassing the barrier are being tested, including nanoparticles that are small enough to pass through the barrier's cellular membranes and deliver their payload; catheters that carry a drug directly into the brain; and ultrasound pulses that push microbubbles through the barrier. But no approach has yet found broad therapeutic application.
Neurobiologist Ryan Watts and his colleagues at the biotechnology company Genentech in South San Francisco have sought to break through the barrier by exploiting transferrin, a protein that sits on the surface of blood vessels and carries iron into the brain. The team created an antibody with two ends. One end binds loosely to transferrin and uses the protein to transport itself into the brain. And once the antibody is inside, its other end targets an enzyme called β-secretase 1 (BACE1), which produces amyloid-β. Crucially, the antibody binds more tightly to BACE1 than to transferrin, and this pulls it off the blood vessel and into the brain. It locks BACE1 shut and prevents it from making amyloid-β.
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