January 2020
Yinku Liang, Hongbo Duan, Ping Zhang, Hao Han, Feixiong Gao, Yunxiang Li, and Zhongyang Xu
Abstract
In this study, six compounds were isolated and purified from dandelion, and only sample I exhibited notable antifungal effect on Candida albicans (CA). high-performance liquid chromatography-diode-array detector-electrospray ionization-tandem mass spectrometry analysis showed that sample I comprised 4-coumaric acid, ferulic acid, quercetin pentoside, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, luteolin, and two unknown compounds, at a relative percent composition of 11.45, 3.96, 10.48, 34.24, 3.91, 11.80, 3.65 and 4.21%, respectively. Further antimicrobial experiments showed that the minimum inhibitory concentration of sample I was 32.0 mg/ml, and sample I mainly acts on bacterial growth in the exponential phase of CA growth. Optical density and infrared analyses conclusively suggested that sample I damages the structure of CA cells, particularly the cell wall and cell membrane, resulting in macromolecule leakage of intracellular nucleic acids and cell metabolism disruption. In conclusion, dandelion sample I was reported to increase CA cell membrane permeability by affecting the glycosidic bond in β-(1–3)-D glucan and destroying the cell wall, ultimately leading CA to death.
Discussion
According to the literature, dandelion crude extract has notable bacteriostatic activity and is effective against a variety of bacteria, including Bacillus subtilis, Staphylococcus aureus (45), Escherichia coli, Pseudomonas aeruginosa (46), methicillin-resistant Staphylococcus aureus, Bacillus cereus (47), Vibrio harveyi (48), Pseudomonas aeruginosa, Paracoccus bacillus (49), and other microorganisms.
Studies of the fungistatic activity in CA have revealed that the mechanism involves alterations in the gene encoding of the target enzyme lanosterol 14-α demethylase or overexpression of the efflux pump genes containing cerebellar degeneration related protein (CDR)1, CDR2, and multidrug resistance mutation 1 (50). Ding et al (51) reported that the molecular mechanism underlying the ATB-induced apoptosis of CA cells is based on the inhibition of tubulin polymerization, leading to G2/M phase cell cycle arrest. CA also has a strong effect on mycelial development and cell membrane morphology, properties that are related to abnormal actin skeleton and subsequent translational defects of hyphae-associated factors (52). The 20-polymer peptide Ib-AMP1 exhibits a specific fungistatic effect on CA by inhibiting different cellular processes rather than cell membrane ion channels or pores (53). Caspofungin hinders the growth of CA by restricting the synthesis of CA cell wall β-glucan (42).
Overall, existing research shows that the mechanism of antifungal activity in CA is very complex, and more extensive and comprehensive investigations are needed to properly elucidate this mechanism. At present, to the best of our knowledge, no studies have evaluated the antifungal activity of DAIS against CA.
In this study, the active ingredients in dandelion were extracted, isolated, and analyzed. The results demonstrated that among six different dandelion extracts, only sample I exhibited marked antifungal activity against CA, with an inhibition zone diameter of 10.38 mm recorded at sample I concentration of 53.2 mg/ml. HPLC-ESI-MS/MS analysis revealed that the main chemical components in sample I are 4-coumaric acid, ferulic acid, quercetin pentoside, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, luteolin, and two unknown components, with relative percentages of 11.45, 3.96, 10.48, 34.24, 3.91, 11.80, 3.65 and 4.21%, respectively. Therefore, 3,5-di-O-caffeoylquinic acid is the most abundant component.
The results of preliminary antifungal activity analyses show that the concentration of dandelion sample I is significantly correlated with the growth inhibition effect of CA. Comparing the absorbances of different concentrations of sample group, the MIC of DAIS was identified as 32.0 mg/ml.
Kinetically, it was found that dandelion sample I mainly inhibits CA growth in the exponential phase. Furthermore, SEM images showed that DAIS are capable of damaging the membranes of CA cells, leading to cell surface depression, wrinkling, increased cell membrane permeability, macromolecule leakage, and ultimately, disordered cell metabolism.
This suggests that inhibition of CA growth by DAIS may be related to the damaging effect of the latter on the cell membranes of the former. In addition, infrared spectrometry indicated that sample I destroy the glycosidic bond of β-(1–3)-D-glucan in CA cell walls, thereby changing its structure. In summary, dandelion sample I was proposed to increase the permeability of CA by destroying its cell wall and membrane, ultimately delaying cellular growth or leading to cell death.
Sample I was reported to include eight chemical components; comparing the antifungal activity of these identified constituents with previous literature, these identified compounds did not have antifungal activities against CA. Thus, these two unknown compounds could exert antifungal activities against CA or there may be a synergistic effect between these unknown compounds with these identified compound; further investigation is required.
In the present study, we reported that dandelion sample I, composed of 4-coumaric acid, ferulic acid, quercetin pentoside, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, luteolin, and two unknown components, exhibits good antifungal activity against CA. Our findings provide a basis for novel approaches to screen for anti-VVC drugs. However, further investigation is needed to determine the antifungal activities of the individual components, as well as the synergistic effects.
