Interactions of hinokitiol with fungal membrane lipids in model systems

Hinokitiol (β-thujaplicin) is a naturally occurring substance of antimicrobial properties, which can be used e.g. as a cosmetic preservative. In this work the influence of hinokitiol on the monolayers and bilayers formed from fungal membrane lipids (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine - POPE; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine - POPC and ergosterol) was investigated. These studies aimed to investigate the effect of hinokitiol on fungal membranes, being indicated as a target for this compound. In this context, the affinity of hinokitiol for ergosterol-containing membranes was of particular interest. The in vitro antifungal activity of hinokitiol was also determined. The results showed that hinokitiol is active against the Candida species tested and exhibits stronger antifungal than antibacterial activity. Moreover, hinokitiol alters the properties of model membranes and the observed effects correlated with ergosterol content in the system. Namely, the higher the ergosterol content, the greater the fluidizing and destabilising effect of hinokitiol and its removal from the model. Moreover, hinokitiol is not able to penetrate into ergosterol membranes; instead, causes strong destabilization of the film and dragging the monolayer material into the subphase. Thus, hinokitiol changes properties of model membrane by the exclusion of the molecules from the interface. The results evidenced differences in the interactions of hinokitiol with ergosterol vs phospholipids, and the interactions of hinokitiol with the membrane depend on the presence and levels of ergosterol. Thus, ergosterol can be a molecular target for this compound. Moreover, the presence of ergosterol in fungal membranes and its lack in bacteria membranes may explain stronger antifungal vs antibacterial effect of hinokitiol.