Magnolol as a potent antifungal agent inhibits Candida albicans virulence factors via the PKC and Cek1 MAPK signaling pathways

Abstract

Magnolol, a lignin compound extracted from Magnolia officinalis Cortex, has been found to have prominent antifungal effects against Candida albicans. However, the specific mechanism still remains unclear. Therefore, this study aimed to further explore the inhibition mechanism of magnolol against Candida albicans virulence factors and the related signaling pathways. By an XTT reduction assay, a hyphal formation assay, confocal laser scanning microscopy, transmission electron microscopy, a calcofluor white staining assay, and a cell wall β-glucan quantitative detection assay, we evaluated the inhibitory effects of magnolol against the adhesion, hyphal formation, biofilm viability, biofilm spatial structure, and cell wall ultrastructure of Candida albicans. Moreover, by RNA sequencing and qRT-PCR, we confirmed the effects of magnolol in inhibiting the gene expression of Candida albicans virulence factors and the related signaling pathways. The results revealed that the adhesion and hyphal formation of Candida albicans were inhibited significantly by magnolol. The viability and spatial structures of Candida albicans biofilms were further weakened. Candida albicans ultrastructure showed partial thinning of cell walls and even rupture, with cytoplasmic leakage. The cell wall intergrity and β-glucan content were also radically reduced. Moreover, magnolol caused significant inhibition of the expression of Candida albicans adhesion, invasion, hyphal formation, biofilm formation, β-1,3-glucan synthesis, and hydrolase secretion-related genes, including ALS1, ALS3, EFG1, EAP1, FKS1, FKS2, PLB2, and SAP2. Furthermore, the PKC pathway-related genes (RHO1, PKC1, BCK1, MKK2, MKC1) and Cek1 pathway-related genes (CDC42, CST20, STE11, HST7, CEK1) were also significantly downregulated, indicating that the inhibition of magnolol against Candida albicans virulence factors might be related to PKC and Cek1 MAPK signaling pathways. In conclusion, the findings of this study confirmed the inhibition mechanism of magnolol against Candida albicans virulence factors, which might be related to PKC and Cek1 MAPK pathways, thus laying the theoretical foundation for its clinical antifungal applications.

Mechanistic insights of magnolol antimicrobial activity against Mycoplasma using untargeted metabolomic analyses

“…Magnolol is one of major bioactive isolates from Magnolia officinalis that has many pharmacological activities, including anticancer-, anti-inflammatory-, antifungal-, and antioxidant activities ( Zhang et al., 2019 ; Xie et al., 2022 ). This study showed that magnolol significantly inhibited the growth of various mycoplasma in vitro , including M. synoviae , M. gallisepticum , and M. hyopneumoniae , The MICs of magnolol against various mycoplasma were determined at 15.63 µg/mL, and the inhibitory effect was dose-dependent ( Figures 1 , 2 ).…”

“…Magnolol is a traditional Chinese medicine derived from Magnolia officinalis Cortex that displays potent antibacterial-, antifungal-, anti-inflammatory-, and antioxidant activities ( Zhang et al., 2019 ). Magnolol or its derivatives have remarkable antibacterial and antifungal activities against Candida albicans ( Behbehani et al., 2017 ; Xie et al., 2022 ), Streptococcus mutans ( Greenberg et al., 2007 ); Staphylococcus aureus ( Guo et al., 2021 ), Alternaria alternata ( Wang et al., 2020 ), Rhizoctonia solani ( Mo et al., 2021 ), Fusarium ( Oufensou et al., 2019 ), Magnaporthe grisea ( Choi et al., 2009 ), and Penicillium expansum ( Chen et al., 2019 ). Magnolol could damage the integrity of fungal cells and interfere with cell metabolism to inhibit the growth of R. solani and A. alternata ( Wang et al., 2020 ; Mo et al., 2021 ).…”

“…Magnolol could damage the integrity of fungal cells and interfere with cell metabolism to inhibit the growth of R. solani and A. alternata ( Wang et al., 2020 ; Mo et al., 2021 ). Magnolol caused significant inhibition of gene expression that are related to adhesion, invasion, hyphal formation, biofilm formation, and metabolic enzymes in C. albicans ( Xie et al., 2022 ). Magnolol or its derivatives have excellent antibacterial and anti-infective activity by destroying bacterial cell membranes ( Guo et al., 2021 ).…”

Old and new strategies in therapy and diagnosis against fungal infections

“…Moreover, the impaired activation of MAPK-Mkc1 decreased the resistance to ergosterol biosynthesis inhibitors opening the doors to potential upstream agents able to deplete Mkc1 or, in a similar way, Cek1 and Hog1 (Singh et al 2009 ; LaFayette et al 2010 ). In this regard, magnolol negatively affects C. albicans virulence factors by inhibiting PKC and MAPK-Cek1 signaling (Xie et al 2022 ). Finally, another option concerns the inhibition of chaperons of the heat-shock protein family which are involved in the cascades.…”

The effect of herbal medicine in innate immunity to Candida albicans

“…Magnolol (5,5'-diallyl-2,2'-dihydroxybiphenyl) (The chemical structure of magnolol in Figure 2E) is a polyphenolic binaphthalene compound and a structural isomer of honokiol. Magnolia officinalis Cortex (M. officinalis), as a primary component of traditional Chinese medicine formulae, was widely used for the treatment of infectious diseases associated with pathogenic microorganisms, such as constipation, diarrhea, asthma, phlegm, and malaria (110). Magnolol and honokiol are isolated from the stem bark of a TCM Magnolia officinalis and have a variety of beneficial activities, including anti-inflammatory, antimicrobial, antioxidant, antiangiogenic, anticancer, neuroprotective, cardiovascular protective (111).…”