Stem cells show promise for treating a range of neurological conditions, including Parkinson's, strokes and Alzheimer's, but it is tricky getting them into the brain. Perhaps inhaling stem cells might be the answer - if mice are anything to go by.
Other options all have their drawbacks. Drilling through the skull and injecting the stem cells is painful and carries some risks. You can also inject them into the bloodstream but only a fraction reach their target due to the blood-brain barrier.
The nose, however, might be a viable alternative. In the upper reaches of the nasal cavity lies the cribriform plate, a bony roof that separates the nose from the brain. It is perforated with pin-size holes, which are plugged with nerve fibres and other connective tissue. Since proteins, bacteria and viruses can enter the brain this way, Lusine Danielyan at the University Hospital of TÃ¼bingen in Germany, and her colleagues, wondered if stem cells would also migrate into the brain through the cribriform plate.
To test their idea, they dripped a suspension of fluorescently labelled stem cells into the noses of mice. The mice snorted them high into their noses, and the cells migrated through the cribriform plate. Then they travelled either into the olfactory bulb - the part of the brain that detects and deciphers odours - or into the cerebrospinal fluid lining the skull, migrating across the brain. The stem cells then moved deeper into the brain.
The mice snorted stem cells high into their noses and large numbers of them migrated into the brain. "We found that the cells could squeeze through these holes, which are far below their own diameter and into the brain," says Danielyan, who presented her findings at the Strategies for Engineered Negligible Senescence meeting in Cambridge, UK, this week.
When the researchers pre-treated the nasal membrane of the mice with an enzyme called hyaluronidase to loosen the junctions between epithelial cells, even more stem cells entered the brain through the nose.
Other researchers have shown that you can also deliver therapeutic proteins such as neural growth factor into the brain in this way. If the results of this study can be repeated in humans, snorting stem cells might be a way of getting large numbers of cells into the brain without surgery. Repeated doses could also be given in the form of nasal drops.
John Sinden, chief scientific officer at ReNeuron in Guildford, UK, says the results are interesting and that less invasive ways of delivering cells to the brain are needed. "A problem may arise if cells migrate to inappropriate locations that could then become a tumour risk," he cautions. "One needs to discover exactly where the cells are going in both brain and the [rest of the body] in order to understand whether this poses a problem or not."