Buccal cells as a non-invasive model for filaggrin protein expression and degradation in patients with atopic dermatitis.

Mutations in the filaggrin (FLG) gene are recognized as major genetic predispositions for atopic dermatitis (AD), yet characterization of FLG protein expression in human subjects remains limited due to the invasive nature of skin biopsies. The present study aimed to evaluate buccal cells as a non-invasive alternative for assessing FLG protein expression and degradation profiles in AD. Buccal cells were collected from 36 patients with AD and 36 healthy controls (aged 20-40 years). FLG gene expression was evaluated using reverse transcription quantitative PCR, while FLG protein expression was assessed by immunoblotting. Although FLG gene expression exhibited substantial variability, FLG protein levels remained relatively stable across samples. Notably, distinct FLG degradation profiles were observed in patients with AD, particularly involving low-molecular-weight fragments. Mild palmar hyperlinearity was identified in 11% of controls and 33% of patients with AD. In addition, buccal cell pellets from patients with AD exhibited increased viscosity compared with those from controls, which was not explained by mucin expression. These findings suggest that buccal cells provide a feasible, non-invasive epithelial model for investigating FLG protein dynamics, offering a complementary approach to skin-based studies. The observed alterations in degradation profiles and pellet viscosity offer new insights into epithelial barrier dysfunction and support the potential of protein-level approaches in AD research.