Dissecting the anti-allergic potential of carnosic acid during IgE and IL-33-mediated mast cell activation

Abstract

Mast cells are critical immune sentinels and essential regulators of inflammation, most notably recognized for their central role in allergic inflammation. Allergen-induced cross-linkage of FcεRI complexes initiates a biphasic mast cell response, characterized by the immediate degranulation of preformed mediators and the delayed production and release of pro-inflammatory cytokine and chemokines. As a result of mast cells being the main perpetrators of the inflammatory responses associated with allergy, identifying novel mast cell stabilizing compounds is an area of intense investigation worldwide in an effort to alleviate the severity of the allergy epidemic. Carnosic acid (CA), a major polyphenolic constituent of the Lamiaceae family herbs has been shown to exhibit potent anti-inflammatory effects on other cellular models, but it’s role as a potential modulator of mast cell activation is currently undefined. Therefore, the purpose of this dissertation was to dissect the anti-allergy potential of CA in a mast cell model. Here, study 1 identified that out of the 3 major polyphenols derived from rosemary, CA showed the most promise as an inhibitor of mast cell responses, impairing mast cell degranulation and cytokine/chemokine release at increased concentrations, warranting its further investigation. Study 2 followed up on our previous investigation, to fully uncover the therapeutic potential of CA and its underlying mechanism of action. Here, we found that CA significantly impairs critical inflammatory responses during both the early and late phase response of allergic inflammation by targeting and inhibiting the upstream tyrosine kinase Syk, a novel mechanistic finding. To further establish CA as a mast cell stabilizer, study 3 determined its inhibitory effects following IL-33-induced mast cell activation in the presence or absence of allergen and SCF activation. Here, we found that similar to study 2, CA treatment significantly impaired the secretory mechanisms responsible for pro-inflammatory mediator release as IL-33-activated signaling and gene expression of mediators was significantly increased despite a decrease in secretion. Finally, study 4 investigated the role of CA treatment during the mast cell differentiation process. We determined that the presence of CA during differentiation has a dramatic effect on the presence of key mast cell surface receptors, and differentially regulates the inflammatory response following activation with allergen and or IL-33. Collectively, the findings of this dissertation help to establish the potential therapeutic utility of CA in a mast cell model of allergic and IL-33-mediated mast cell activation. We expect that the data presented will help the progression of future research identifying novel anti-allergy compounds and will contribute to better understanding the mechanisms responsible for mast cell function in various pathological contexts.