- Olfactory (smell) nerve endings have been found to occur in locations outsides the nose where they perform several important functions that influence general health and disease
- Targeting olfactory receptors newly developed drug treatments can be useful for several diseases including cancer
- Until recently, it was believed that olfactory receptors were only present in the nose and their function was limited to sensing smell
Olfactory nerve endings or receptors occur in almost all parts of the body and may have several important functions, that are still not fully determined according to a recent review of more than 200 scientific studies on this subject. The functions of these extra-nasal olfactory nerve endings can be potentially used in the diagnosis and developing treatment of many diseases including cancer. The review article appears in the July issue of Physiological Reviews.
According to scientists from Ruhr-University Bochum in Germany, "Olfactory receptors occur in nearly the entire human body, [and] they appear to be substantially more functionally important than previously suggested. In addition to the receptors playing a major role in the sense of smell, several essential normal body processes (physiological) and disease (pathophysiological) processes have been described as mediated by human olfactory receptors, including cell growth, cell death, cell migration and secretion."
Important Functions of Olfactory Nerve Endings (Receptors) Outside Nose In Health and Disease
- Regulation of normal heart function
- Activation of olfactory receptors in the immune system can cause death of specific types of leukemia cells
- Olfactory receptors in skin improve wound healing and increase formation of new skin cells to replace damaged and dead skin cells
- Activation of olfactory receptors in the testes increases motility of sperms
- Smell receptors in the prostate gland reduce multiplication and spread of prostate cancer cells in men
- Smell receptors in liver decrease growth and spread of cancer cells
- Olfactory receptors in digestive tract can cause abnormal bowel function leading to diarrhea or constipation but have been shown to improve digestion
- Smell receptors in the digestive tract reduce multiplication and spread of cells
Olfactory Receptors Measurement as Possible Biomarkers of Cancer and Other DiseasesIt is evident from the previous discussion that olfactory receptors have several important functions in almost all organs of the body which can have important applications in the clinical setting. Sometimes the levels of expression of these receptors can change and this can in turn result in disease.
- For example, overexpression of a certain subtype of smell receptors in the prostate has been associated with cancer growth and spread
- Overexpression of another subtype of olfactory receptors in the bowel has been shown to increase the growth and spread of bowel cancer
- Abnormal expression of smell receptors in a disorderly manner has been shown to occur in neurodegenerative brain diseases (progressive brain disease with worsening memory, thinking and understanding capacity as well as poor sensation and progressive limitation of mobility and performing daily activities).
Thus measurements of the expression levels of these receptors can therefore be used as biomarkers (substances that can be used in diagnosis of disease) to diagnose specific conditions as well as treating these conditions by developing drugs that target and modify these receptors
Activation of Olfactory Receptors by Scents to Help Regulate Body FunctionsSeveral naturally occurring volatile scents can be used to stimulate the olfactory receptors which may be beneficial to general health. These chemical scents may be produced within the body (endogenous) or administered externally (exogenous).
Exogenous agents include β-ionone (roses and berries), thymol (thyme), citronellal (citrus species), geraniol (rose oil and citronella oil) and citronellol (pelargonium). Endogenous agents include byproducts of the cholesterol synthesis pathway and fatty acids.
ConclusionIn conclusion, the extensive presence and potential diverse roles of olfactory receptors throughout the body indicate these are not pure smell receptors but general chemoreceptors governing several normal as well as abnormal disease processes in the body. Therefore targeting them to modify their function in regulating these processes including cancer and other diseases is a definite possibility for the future in addition to using them as biomarkers.
However, the identification and characterization of smell receptors outside the nose is by no means complete and still has a long way to go and could become the focus of new and exciting research projects to gain better understanding and scope of these little known structures.
- Desiree Maßberg and Hanns Hatt "Human Olfactory Receptors: Novel Cellular Functions Outside of the Nose" American Physiological Society (2018) https://doi.org/10.1152/physrev.00013.2017