Identification of botanicals that unmask beta-glucan from the cell surface of an opportunistic fungal pathogen

Authors: ZHANG, JIN - University Of Mississippi; AGARWAL, AMEETA - University Of Mississippi; FENG, QIN - University Of Mississippi; TRIPATHI, SIDDHARTH - University Of Mississippi; KHAN, IKHLAS - University Of Mississippi; PUGH, NIRMAL - University Of Mississippi

Submitted to: Journal of Dietary Supplements
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2023
Publication Date: 4/18/2023
Citation: Zhang, J., Agarwal, A., Feng, Q., Tripathi, S.K., Khan, I.A., Pugh, N.D. 2023. Identification of botanicals that unmask beta-glucan from the cell surface of an opportunistic fungal pathogen. Journal of Dietary Supplement. https://doi.org/10.1080/19390211.2023.2201355.
DOI: https://doi.org/10.1080/19390211.2023.2201355

Interpretive Summary: Fungal pathogens contain a polysaccharide called beta-glucan in their cell walls that is detected by host immune cells. Detection of beta-glucans results in activation of the immune cells and thereby plays an important role in the clearance of fungal infections. However, because beta-glucans are masked by an outer layer of other compounds, fungal pathogens can evade detection by host immune cells. In this study, we developed a method to identify whether botanicals contain compounds capable of unmasking beta-glucans. A collection of botanicals were evaluated that have been used in traditional medicine for their antifungal properties. Several botanicals were identified to contain compounds that unmasked beta-glucan. These results indicate that the purported antifungal activities attributed to some botanicals may be due, at least in part, to the presence of compounds that exhibit beta-glucan unmasking activity. Enhanced exposure of cell wall beta-glucans would allow the host to build resilience against fungal infections by helping the immune system to detect the pathogen and mount a more effective clearance mechanism. This method, together with traditional anti-fungal assays, may therefore serve as a valuable tool for substantiating the use of botanicals in preventing and/or treating fungal infections.

Technical Abstract: The polysaccharide, beta-glucan, which is present in the cell walls of fungal pathogens, is recognized by Dectin-1 expressed on host immune cells, and plays an important role in the clearance of fungal infections. However, because beta-glucan is masked by an outer layer of mannoproteins, fungal pathogens are able to evade detection by host immune cells during the commensal phase of their life and also during early stages of infection. In this study, we have developed a microplate-based screen to identify beta-glucan unmasking activity exhibited by botanicals. This screen measures the activity of a reporter gene in response to the transcriptional activation of NF-'B due to the interaction between beta-glucan on the fungal cell surface and the beta-glucan receptor, Dectin-1 present on host immune cells. In this proof-of-concept study, we screened a collection of botanicals (10 plants and some of their reported pure compound actives) that have been used in traditional medicine for their antifungal properties. Several hits were identified in samples that unmasked beta-glucan at sub-inhibitory concentrations. The hit samples were confirmed by fluorescent staining with a beta-glucan antibody, verifying that the samples identified in the screen did indeed unmask beta-glucan. These results indicate that the purported antifungal activities attributed to some botanicals may be due, at least in part, to the presence of compounds that exhibit beta-glucan unmasking activity. Enhanced exposure of cell wall beta-glucans would allow the host to build resilience against fungal infections by helping the immune system to detect the pathogen and mount a more effective clearance mechanism. This screen, together with direct killing/growth inhibition assays, may therefore serve as a valuable tool for substantiating the use of botanicals in preventing and/or treating fungal infections.