The oral mucosa is a crucial physical barrier in the oral cavity, protecting underlying tissues from microbial invasion, physical and chemical stimuli. This barrier function is maintained by the stratified oral epithelium and tight junction proteins. When this barrier is compromised, oral diseases such as periodontitis and oral lichen planus can occur, which are often associated with elevated levels of inflammatory markers, including IL-6, IL-8, TNFα and IL-1ß. In addition to its protective function, the oral epithelium also acts as a barrier to topical drugs, reducing their efficacy. Nanocarriers, such as core-multishell nanocarriers (CMS-NCs), offer a promising approach to improve drug delivery across the oral mucosa.
This study investigated cellular events in oral inflammation and the potential of CMS nanocarriers as a topical anti-inflammatory treatment for oral mucosa. Both 2D and 3D cell culture systems were used as research models. Characterization of the 3D model showed properties very similar to in vivo conditions, including a tissue architecture of multilayered epithelium and lamina propria with fibroblasts, tight junction formation and cell differentiation. Treatment of the models with TNFα induced inflammation, as evidenced by increased levels of IL-6 and IL-8, and led to enhanced claudin-1 expression, which in turn improved membrane integrity. In addition, wound healing was accelerated by TNFα. These results suggest a protective role of epithelial cells in the early phase of inflammation. Furthermore, activation of the ERK/MAPK signaling by TNFα contributed to IL-8 secretion, highlighting a potential target therapeutic target to reduce oral inflammation.
This study further examined the application of CMS nanocarriers as a topical anti-inflammatory treatment for the oral mucosa using dexamethasone-loaded CMS nanocarrier (Dx-CMS). Using an enzyme-linked immunosorbent assay (ELISA), Dx-CMS was shown to reduce IL-6 and IL-8 secretion more efficiently than ethanolic dexamethasone solution or dexamethasone-containing cream. However, CMS nanocarriers showed reduced adhesion in the presence of saliva, highlighting the need to improve their mucoadhesive properties. Mussel-inspired catechol functionalization is a promising approach to overcome this limitation. Using CMS nanocarriers coupled or loaded with fluorescent dyes, it was shown that CMS nanocarrier with 8% catechol content (CMS-C0.08) exhibited better mucoadhesive properties than the non-functionalized CMS nanocarrier. Furthermore, the anti-inflammatory activity of dexamethasone-loaded CMS-C0.08 (Dx-CMS-C0.08) was evaluated and compared to the dexamethasone-loaded non-functionalized CMS nanocarrier (Dx-CMS). Both Dx-CMS and Dx-CMS-C0.08 showed comparable anti-inflammatory effect when applied to the 3D oral mucosal model for 24 and 48 h. However, when applied dynamically on cell monolayers, which reflects the dynamic environment of the oral mucosa and the practical application in the treatment, Dx-CMS-C0.08 exhibited a better anti-inflammatory effect than Dx-CMS.
Overall, this study provides valuable insights into the cellular mechanisms of oral inflammation and highlights the potential of catechol-functionalized CMS nanocarrier, particularly CMS-C0.08, as an effective topical drug delivery system to improve the treatment of oral inflammatory diseases. Finally, this study highlights the importance of the human 3D model, which is able to better simulate in vivo conditions compared to conventional 2D cell culture systems and could serve as an important alternative to animal models in further investigations.
