Targeting hypoxia: the role of ethanolic extract of Coptis chinensis Franch. in modulating HIF-1α/IL-17 axis in oropharyngeal candidiasis

Ethnopharmacological relevance: Oropharyngeal candidiasis (OPC), primarily induced by Candida albicans, poses a significant threat to oral health due to the hypoxic microenvironment established by C. albicans biofilms. Coptis chinensis Franch., a traditional Chinese medicine first documented in Shennong's Classic of the materia medica, has been traditionally employed in the treatment of infectious diseases, including OPC. The ethanolic extract of C. chinensis Franch. (EECF), which is a compound obtained through ethanol extraction from the herb, demonstrates significant therapeutic potential against Fungal oral mucosal infections, such as those caused by Candida albicans. However, the possible effects of EECF on hypoxic microenvironment which is key to OPC are unclear. Thus, we hypothesized that EECF may alleviate the hypoxic microenvironment induced by C. albicans Infection and modulate the host hypoxia-induced inflammatory response, thereby contributing to the treatment of OPC.

Purpose: We aim to investigate the potential mechanism of action of EECF for the treatment of OPC by exploring the effects of EECF on the hypoxic microenvironment generated by the C. albicans biofilm and the hypoxia inducible factor-1α (HIF-1α) and activation of immune pathways of host.

Materials and methods: We investigated EECF's inhibitory effects on C. albicans biofilm formation using Karl Koffler fluorescent whitener staining, XTT assay, and quantitative real-time polymerase chain reaction (qRT-PCR). In a murine OPC model, therapeutic efficacy was evaluated through hematoxylin-eosin staining, Schiff's periodinium staining, and Fungal load quantification. Epithelial barrier protection was assessed via Transwell assays measuring KB cell layer penetration. Mechanistic studies examined EECF's impact on HIF-1α/c-Fos/MKP1/IL-17 pathways using qRT-PCR, western blotting, and immunofluorescence. Finally, gene silencing/overexpression experiments verified the effects of HIF-1α modulation by EECF.

Results: In vitro studies revealed EECF inhibits C. albicans hyphal growth, biofilm formation, and cyclic adenosine monophosphate (cAMP) production under both normoxic and hypoxic conditions, accompanied by downregulation of CYR1 and EFG1 in the cAMP pathway. In a murine OPC model, EECF treatment reduced oral Fungal burden, repaired tongue papillary architecture, protected mucosal integrity, and suppressed hypoxic microenvironment formation in tongue tissues while modulating HIF-1α/c-Fos/MKP1/IL-17 axis-related genes/proteins. In vitro cellular assays demonstrated EECF impaired C. albicans penetration of KB cell barriers and attenuated infection-induced hypoxia through inhibition of HIF-1α/c-Fos/MKP1/IL-17 pathway components. Hypoxic cellular experiments confirmed EECF's inhibitory effects on these pathways were maintained under low-oxygen conditions. Functional gene validation confirmed EECF regulates the HIF-1α/IL-17 axis through modulation of HIF-1α gene expression.

Conclusion: Our findings demonstrate that EECF suppresses C. albicans biofilm formation by inhibiting Fungal cAMP signaling, which attenuates hypoxia-induced HIF-1α/IL-17 activation in oral epithelial cells, leading to reduced Fungal burden and inflammatory pathology. Thus, our results support potential of EECF as a potent therapeutic agent for OPC, and warrant further investigation into its clinical applicability as a precision treatment for fungal-host interaction dysregulation.

Biofilm; Candida albicans; Ethanolic extract of C. chinensis franch.; HIF-1α/IL-17 axis; Hypoxic microenvironment; Oropharyngeal candidiasis.