In a paper published in the journal Physiological Reviews, Drs. Désirée Maßberg and Hanns Hatt — of the Department of Cell Physiology at Ruhr University Bochum in Germany — sum up our current knowledge about olfactory receptors and suggest some applications.
The authors claim that these highly specialized chemical-sniffing proteins are found not only in the nose but also in the "testis, lung, intestine, skin, heart, and blood."
In addition, distinct types of olfactory receptors — different to those of healthy cells — are found in abundance in cancer cells.
The body's 'chemoreceptors'
Since 2003, when Dr. Hatt's team was the first to show that olfactory receptors have roles beyond odor-detection in the nose, he and others have detailed their function in more than 20 types of tissue in the human body.
Using state-of-the-art DNA tools, they identified that each type of tissue has 5–80 different kinds of olfactory receptor.
Essentially, a receptor is a protein or cluster of proteins that sits in the cell membrane and will only react when it encounters a specific molecule that is able to bind to it — much like a unique key opening its matching lock. This triggers a series of molecular events inside the cell.
Olfactory receptors get their name from the fact that they were first discovered in nasal tissue.
However, as they began finding them in other parts of the body, scientists realized that olfactory receptors "don't really have much to do with smelling as such," Dr. Hatt explains. "Rather, we should refer to them in more general terms, namely as chemoreceptors," he adds.
Opportunities in health and medicine
The large variety of olfactory receptors — and the molecules that activate them — gives scope for these to trigger an enormous selection of signaling pathways that lead to different cell responses.
Scientists have revealed that once activated, olfactory receptors can make cells divide, proliferate, move, and release chemical messengers. They also influence pathways that lead to cell death.
The study authors note that cancer cells often carry large numbers of olfactory receptors that are different to those of healthy cells. They suggest that these could be used in cancer diagnosis — for instance, as markers of tumor progression.
They might also offer opportunities for treatment of tumors that are easy to reach with odorants, such as in bladder and intestinal cancers.
Manipulating olfactory receptors could also help control other biological processes, such as digestion, skin regeneration, and hair growth. Dr. Hatt suggests that this could open up opportunities for their use in "the field of wellness and healthcare."
More research needed
The investigators call for more detailed research to further explore the potential use of olfactory receptors in medicine and healthcare.
Dr. Hatt says that we not only need to "decode" the many types of olfactory receptor, but also identify and analyze the large number of odorants that trigger them.
After that, it is likely that there will be major challenges in translating the findings from the laboratory into the clinic.
When that is done, he predicts that using odorants as receptor blockers will "open up a comprehensive and effective broad spectrum" of new approaches in pharmacology.
"Unfortunately, the activating odorants of only about 50 of the 350 human olfactory receptors have been identified to date."
Dr. Hanns Hatt