Cinnamaldehyde reduces inflammatory responses in chronic rhinosinusitis by inhibiting TRPM8 expression.

Objective: This study aimed to investigate the effects of cinnamaldehyde (CA) intervention on transient receptor potential melastatin 8 (TRPM8) expression in human nasal epithelial cells (HNECs) and mouse models of chronic rhinosinusitis (CRS) and determine the alleviating effects of CA on CRS.

Methods: HNECs were treated with CA, and the protein levels and mRNA expression of pro-inflammatory cytokines, namely, interleukin-25 (IL-25), IL-33, and thymic stromal lymphopoietin (TSLP), were measured by enzyme-linked immunosorbent assay and real-time reverse-transcription polymerase chain reaction (RT-PCR). TRPM8 expression levels were examined by RT-PCR and western blot. The C57BL/6 mice were randomly divided into three groups (control group, model group, CA group). The model and CA groups were induced by intranasal drip intervention of ovalbumin (OVA) three times a week for 9 weeks. Each mouse was individually observed in a single cage to record the frequency of nose scratching and sneezing within 10 minutes. Histologic examination of nasal mucosa in mice was done using hematoxylin-eosin staining to compare the degree of inflammation. Pro-inflammatory cytokine levels and TRPM8 expression levels were measured in mouse nasal lavage fluid.

Results: In vitro experiments demonstrated that CA intervention in HNECs significantly reduced the protein and mRNA of IL-25, IL-33, TSLP, and TRPM8. In vivo analysis showed that the CA group exhibited fewer nose scratching and sneezing symptoms and reduced nasal mucosal inflammation as well as lower levels of IL-25, IL-33, and TSLP in nasal lavage fluid and tissues than the model group.