Attenuation of senile pruritus by PAC-14028-mediated downregulation of the NF-κB and MAPK pathways

Objective: Senile pruritus is a specific type of itching that occurs in elderly persons. Previously, we assessed antagonism of the nonselective ligand-gated cation channel transient receptor potential vanilloid 1 (TRPV1; capsaicin receptor or vanilloid receptor 1) and attenuation of atopic dermatitis by the non-steroidal TRPV1 antagonist PAC-14028 in clinical studies. The findings led us to postulate that PAC-14028 may also reduce itching in elderly people by antagonizing the TRPV1 pathway. In this study, we evaluated whether PAC-14028 modulates inflammatory markers present in senile pruritus. Materials and Methods: HaCaT, RAW264.7, and differentiated THP-1 cells under itching-inducing conditions were treated with zymosan or IL-17A and variety of experimental approaches such as molecular modeling simulations, site-directed mutagenesis, overexpression strategies, confocal microscopy, mRNA analyses, and immunoprecipitation/Western blotting analyses were assessed to check changes in inflammatory markers and explore the underlying mechanisms of PAC-14028 activity. Results: In the bioinformatic analyses, skin inflammation markers were found to be closely related to TRPV1, and the MAPK and NF-κB pathways were upregulated when TRPV1 was activated. In HaCaT cells, PAC-14028 was found to directly bind to TRPV1, inhibiting inflammatory cytokine gene expression and downstream MAPK and NF-κB signaling under various skin inflammatory conditions. Conclusions: By combining the results of multiple assays, we were able to elucidate the molecular mechanism of PAC-14028 to TRPV1. Taken together, the findings indicate that PAC-14028 as a potential therapeutic agent for elderly people with pruritus.