Numerous studies to date have shown that olfactory receptors are relevant not only for smell perception, but that they also play a significant physiological and pathophysiological role in all organs. An overview of receptors detected so far and of the functions they fulfil within the human body is provided by Prof Dr Dr Dr habil. Hanns Hatt and Dr Désirée Maßberg from the Department for Cellphysiology at Ruhr-Universität Bochum, published in the journal Physiological Reviews; online preview available on June 13, 2018. They elaborate, for example, potential clinical applications, especially with regard to cancer diagnosis and therapy, and they discuss the steps scientists have yet to take to ensure that the receptors' full potential can be used for applications in the medical field, but also in health and care products.
Different cell biological effects
In 2003, the team headed by Hanns Hatt demonstrated for the first time that olfactory receptors fulfil important functions in tissues outside of the nose; subsequently, the researchers in Bochum and in other labs successfully described the role of olfactory receptors in more than 20 different types of human tissue. Most up to date DNA sequencing methods were instrumental for the collection of new information about quantitative and specific distribution patterns. It emerged that 5 to 80 different types of olfactory receptors can be found per tissue.
"Olfactory receptors outside the nose, however, don't really have much to do with smelling as such," says Hanns Hatt. "Rather, we should refer to them in more general terms, namely as chemoreceptors." If a molecule activates such a receptor, it may stimulate the cells to multiply, move, or release specific chemical transmitters. Cell death is also affected by olfactory receptors. Cell-biological effects are many and varied precisely because olfactory receptors have the ability to switch on different signalling pathways in cells.
Olfactory receptors in cancer cells
Cancer cells often contain specific olfactory receptors in large amounts - often different ones to those found in healthy cells. In their article, the authors from Bochum describe that olfactory receptors can thus be used as specific markers for tumours and their metastases and, consequently, be useful for cancer diagnosis. Moreover, Hatt and Maßberg consider them to have potential for cancer therapy, especially in the case of tumours that are easily accessible for odorants, e.g. in intestinal or bladder cancer.
"In addition, applications in the field of wellness and healthcare are likewise conceivable," elaborates Hanns Hatt. Skin regeneration, intestinal digestion, and hair growth can be regulated via olfactory receptors. This therapeutic method is already being applied for tissue repair and for promoting digestion.
In-depth research necessary
In order to exploit the receptors' potential in the areas outlined above, the authors point out that ongoing in-depth research will remain necessary. "Unfortunately, the activating odorants of only about 50 of the 350 human olfactory receptors have been identified to date," illustrates Hanns Hatt. He considers it an essential research goal to decode additional olfactory receptors, to find the relevant signalling pathways, and to shed light on the function of receptors in a living body.
"Another major challenge is transferring basic-research findings into clinical applications," explains Hatt. "In future, deploying odorants for activating or blocking receptors will open up a comprehensive and effective broad spectrum of novel therapeutic approaches in the field of pharmacology."