Alzheimer's disease and other neurodegenerative disorders could soon be treated with nose drops. Researchers in Minnesota say that the nasal passage holds great promise as a conduit for delivering drugs into the brain, as the olfactory system provides a direct link between the brain and the outside world.
Getting drugs into the brain is one of neuroscience's challenges. The molecules of many drugs are too large to cross the blood-brain barrier, the tightly woven cells in the blood vessels in and around the brain that form a kind of protective fence guarding brain tissue. Nerve growth factor, a promising treatment for Alzheimer's disease, is one such drug. Injecting NGF does not work, and procedures such as grafting NGF-producing cells directly into the brain are expensive and risky.
But William Frey, a neuroscientist at the Alzheimer's Research Center at the Regions Hospital in St Paul, woke one morning with the idea of using nose drops to carry NGF to the brains of his patients. "I knew that bad things could get in this way," he says. "It occurred to me that maybe good things could get in this way too."
Olfactory nerves are unusual in that they run straight from the olfactory bulb in the brain to the nasal cavity, where they come into contact with "odorants" in the air. But occasionally, Frey points out, the odd anatomy of the olfactory system can be dangerous because it provides a way for some viruses, such as herpes, to sneak into the brain. In one study, even tiny gold particles sprayed into the noses of monkeys were traced along the olfactory nerves and into the animals' brains.
So Frey and his colleagues decided to see if NGF could be delivered in
nose drops. After anaesthetising 12 rats, the researchers gave half the animals
drops in their noses over 30 minutes and injected the rest with NGF. They found
that within an hour, a significant amount of NGF had made its way not only into
the olfactory bulb, but also i
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