Cinnamaldehyde reduces inflammatory responses in chronic rhinosinusitis by inhibiting TRPM8 expression

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.

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.

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.