Inhibition of allergen‐mediated mast cell activation by rosemary extract (Rosmarinus officinalis L.)
Authors: Yousef Michael , Hicks Natalie J. , Boyd Tylar , Tsiani Evangelia , MacNeil Adam J. 
Published: June 2021

The prevalence of allergic inflammatory disorders is increasing at an alarming rate, with 40–50% of school‐aged children suffering today and more than 25% of people living in a developed nation presently diagnosed or expected to develop, an allergic disease in their lifetime. This trend places a large economic burden on healthcare systems with $20B spent on treating these disorders in the USA in 2007. Mast cells are immune sentinels and a driving force in both normal and pathological contexts of inflammation. Allergen detection by the immune system results in production of allergen‐specific immunoglobulin E (IgE) antibodies. These antibodies bind to their high‐affinity receptor FcɛRI, which is constitutively expressed on the surface of mast cells. Crosslinking of FcɛRI by allergen‐bound IgE antibodies leads to mast cell degranulation (e.g. histamine) resulting in an early phase response, and the release of newly synthesized pro‐inflammatory mediators, contributing to a late phase response. The mitogen‐activated protein kinase (MAPK) family and, nuclear factor‐κ‐light‐chain‐enhancer of activated B cells (NF‐κB) pathways have been established to be driving mechanisms behind mast cell‐induced inflammation. Rosemary extract (RE) is rich in polyphenols, including rosmarinic acid (RA), carnosic acid (CA), and carnosol (CO), which have been shown to inhibit the MAPK and NF‐κB pathways in other cellular contexts in vitro and in in vivo animal models. However, the effect of these polyphenols on mast cell activation and degranulation has not been explored. Therefore, the aim of this study was to evaluate the potential of RE in modulating mast cell activation and FcɛRI signaling via these pathways toward understanding the mechanism of action and functional outcomes. Mast cells were sensitized with anti‐TNP IgE and were stimulated with the cognate allergen (TNP‐BSA) under stem cell factor (SCF) potentiation, and treated with 0 – 25 μg/mL RE. Samples were then collected for β‐hexosaminidase assay, quantitative polymerase chain reaction (qPCR), enzyme‐linked immunosorbent assay (ELISA) and, western blotting analysis. The β‐hexosaminidase assay demonstrated that RE treatment inhibited mast cell degranulation dose‐dependently to a maximum (down to 15% of control) at 25 μg/mL (p<0.001) RE. qPCR analysis showed that RE treatment at 25 μg/mL resulted in decreased gene expression of IL6 at both 60 and 120 mins (p<0.05), IL13 at 120 mins (p<0.05), TNF at 120 mins (p<0.05), CCL1 at both 60 (p<0.01) and 120 mins (p<0.05), CCL3 at both 60 and 120 minutes (p<0.05), and Rcan1 at 120 mins (p<0.05). ELISA analysis further supported the qPCR data showing decreases in pro‐inflammatory IL‐6 at 12 hrs (p<0.05) and TNF at 24 hrs (p<0.05). Western blot analysis demonstrated that RE treatment at both 5 and 25 μg/mL inhibited phosphorylation of p38‐MAPK at 5 mins. This work enhances our current understanding of mast cell functional modulation, mast cell signaling, and mechanistic activities of RE with relevance to innate defences and allergy.Support or Funding InformationSupported by the Natural Sciences and Engineering Research Council of Canada (NSERC); Canada Foundation for Innovation (CFI); Government of Ontario; and Brock University.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.