Gut protection provided by odorants in food

A research team led by Professor Lee Sung-joon of the Division of Food Bioscience and Technology at the College of Life Sciences and Biotechnology, Korea University, has published a paper entitled ‘Activation of ectopic olfactory receptor 544 induces GLP-1 secretion and regulates gut inflammation’ on November 1st in the scientific journal Gut Microbes (IF: 10.245).
- Title of Paper  : Activation of ectopic olfactory receptor 544 induces GLP-1 secretion and regulates gut inflammation;https://doi.org/10.1080/19490976.2021.1987782) 

There are various nutrients and odorants in food. These odorants enhance the flavor of food and regulate our appetite, and when absorbed into the body, they act as functional substances that have diverse biological effects.

Through a signal delivery process, food odorants transmit odorant information to the brain through olfactory receptors in the nasal olfactory epithelium cells. Recent research has shown that olfactory receptors are widely ectopically expressed in various tissues such as the kidney, liver, muscle, and fat, as well as in immune cells.

On this basis, Professor Lee's study assumed that because olfactory receptors are expressed in the tissues of the gut, a digestive organ, as target proteins for these odorants they enhance the health efficacy of odorants in food.

The research team found that olfactory receptor 544 (Olfr544) is widely expressed ectopically in the small intestine and colon of mice, and that azelaic acid (AzA) produced by various grains such as wheat, barley, oatmeal, and sorghum functions as a ligand for Olfr544 and activates cAMP-PKA-CREB signaling. In this study, treating the small intestine endocrine cells of mice with AzA led to the induction of the cAMP-PKA-CREB signaling axis and the increase of the secretion of GLP-1, an enteroendocrine hormone with anti-obesity effects, while the induction of the GLP-1 secretion was negated in cells with Olfr544 gene knockdown and in Olfr544-deficient mice. This result indicates that AzA increased the secretion of GLP-1 on Olfr544. Gut microbiome analysis revealed that AzA increased the levels of Bacteroides acidifaciens. In fecal metabolomics analysis, the levels of metabolites that are correlated with anti-obesity and antioxidant effects were elevated by AzA, thereby improving intestinal permeability by inhibiting inflammatory cytokine expression and preventing the gut inflammation associated with obesity.

This study is of great scientific significance as it revealed that olfactory receptors, which account for 3% of the human genome, are expressed in intestinal tissues and perform biological functions. Upon the publication of the paper, a patent was applied for regarding the findings on the capacity of AzA to relieve gut inflammation and increase the secretion of GLP-1. Findings from the study can be used to develop food materials, pharmaceuticals, and healthy functional foods that can give a boost to the secretion of enteroendocrine hormones and alleviate colonic inflammation.
 
The research outcome's significance is confirmed by the fact that the paper was published in a scientific journal that is ranked in the world’s top 7% on the Journal Citation Reports (JCR) list for microbiology. Since joining Korea University in 2004, the corresponding author Professor Lee Sung-joon has published more than 140 SCI papers and mentored 50 or more graduates, while undertaking basic research projects and applied commercialization studies.

This research was conducted with support from the National Research Foundation of Korea through the foundation’s Mid-Career Researcher Program and Creative Research Program.