Mechanism of antifungal activity and therapeutic action of β-ionone on Aspergillus fumigatus keratitis via suppressing LOX1 and JNK/p38 MAPK activation

Chelerythrine ameliorates Aspergillus fumigatus keratitis through suppressing the LOX-1/p38 MAPK signaling pathway

PURPOSE

Aspergillus fumigatus (A. fumigatus) keratitis is a type of infectious corneal disease that significantly impairs vision. The objective of this study is to evaluate the therapeutic potential of chelerythrine (CHE) on A. fumigatus keratitis.

METHODS

The antifungal activity of CHE was assessed through various tests including the minimum inhibitory concentration test, scanning electron microscopy, transmission electron microscopy, propidium iodide uptake test and plate count. Neutrophil infiltration and activity were assessed using immunofluorescence staining and the myeloperoxidase test. RT-PCR, western blotting assay, and ELISA were performed to measure the expression levels of proinflammatory cytokines (IL-1β and IL-6), NF-E2-related factor (Nrf2), heme oxygenase-1 (HO-1), and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), as well as to determine the ratio of phosphorylated-p38 (p-p38) mitogen-activated protein kinase (MAPK) to p38 MAPK.

RESULTS

In vitro, CHE inhibited the growth of A. fumigatus conidia, reduced fungal hyphae survival, and prevented fungal biofilm formation. In vivo, CHE reduced the severity of A. fumigatus keratitis and exhibited an excellent anti-inflammatory effect by blocking neutrophil infiltration. Furthermore, CHE decreased the expression levels of proinflammatory cytokines and LOX-1 at both mRNA and protein levels, while also decreasing the p-p38 MAPK/p38 MAPK ratio. Additionally, CHE increased the expression levels of Nrf2 and HO-1.

CONCLUSION

CHE provides protection against A. fumigatus keratitis through multiple mechanisms, including reducing fungal survival, inducing anti-inflammatory effects, enhancing Nrf2 and HO-1 expression, and suppressing the signaling pathway of LOX-1/p38 MAPK.

Anti-Inflammatory Efficacy of Nanobody Specific to β-Glucan on a Fungal Cell Wall in a Murine Model of Fungal Keratitis

Purpose: to explore the anti-inflammatory effects of a nanobody (Nb) specific to β-glucan on fungal keratitis (FK). Methods: in order to verify the therapeutic and anti-inflammatory efficacy of Nb in FK, the severity of inflammation was assessed with inflammatory scores, hematoxylin-eosin (HE) staining, and myeloperoxidase (MPO) assays. In corneas of mice of FK model and human corneal epithelial cells stimulated by fungal hyphae, real-time reverse transcriptase polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay were used to detect the expression levels of inflammatory cytokines and pattern recognition receptors (PRRs). In vivo, macrophages and neutrophils infiltration in the cornea stroma was detected by immunofluorescence (IFS) staining. Results: In murine models infected with Aspergillus fumigatus (A. fumigatus), Nb treatment could reduce the inflammatory scores. HE staining and MPO results showed Nb significantly alleviated corneal edema and reduced inflammatory cell infiltration 3 days post-infection. In addition, the expression levels of LOX-1 and Dectin-1 were significantly decreased in the Nb group in vivo. The expression of chemokines CCL2 and CXCL2 also decreased in the Nb group. Compared with the PBS group, the number of macrophages and neutrophils in the Nb group was significantly decreased, which was shown in IFS results. Moreover, Nb attenuated the expression of Dectin-1, LOX-1, and inflammatory mediators, including IL-6 and IL-8 in vitro. Conclusion: our study showed that Nb could alleviate FK by downregulating the expression of PRRs and inflammatory factors as well as reducing the infiltration of macrophages and neutrophils.

Resveratrol has neuroprotective effects and plays an anti-inflammatory role through Dectin-1/p38 pathway in Aspergillus fumigatus keratitis

PURPOSE

To determine the antifungal, anti-inflammatory and neuroprotective effects of resveratrol (RES) in Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

Cytotoxicity assay and Draize eye assay were performed to assess the toxicity of RES. The antifungal effect of RES was assessed by minimal inhibitory concentration, scanning or transmission electron microscopy, propidium iodide uptake assay, and Calcofluor white staining. Phosphorylation of p38 MAPK, mRNA and protein levels of Dectin-1 and related inflammatory factors were measured by qRT-PCR, ELISA and Western blot in vitro and in vivo. Clinical score, HE staining, plate count, and myeloperoxidase test were used to observe the progress of fungal keratitis. IF staining, qRT-PCR, and the Von Frey test were selected to assess the neuroprotective effects of RES.

RESULTS

RES suppressed A. fumigatus hyphae growth and altered hyphae morphology in vitro. RES decreased the expression of Dectin-1, IL-1β and TNF-α, as well as p38 MAPK phosphorylation expression, and also decreased clinical scores, reduced inflammatory cell infiltration and neutrophil activity, and decreased fungal load. RES also protected corneal basal nerve fibers, down-regulated mechanosensitivity thresholds, and increased the mRNA levels of CGRP and TRPV-1..

CONCLUSION

These evidences revealed that RES could exert antifungal effects on A. fumigatus and ameliorate FK through suppressing the Dectin-1/p38 MAPK pathway to down-regulate IL-1β, IL-6, etc. expression and play protective effect on corneal nerves.

Formononetin protects against Aspergillus fumigatus Keratitis: Targeting inflammation and fungal load

PURPOSE

To investigate the potential treatment of formononetin (FMN) on Aspergillus fumigatus (A. fumigatus) keratitis with anti-inflammatory and antifungal activity.

METHODS

The effects of FMN on mice with A. fumigatus keratitis were evaluated through keratitis clinical scores, hematoxylin-eosin (HE) staining, and plate counts. The expression of pro-inflammatory factors was measured using RT-PCR, ELISA, or Western blot. The distribution of macrophages and neutrophils was explored by immunofluorescence staining. The antifungal properties of FMN were assessed through minimum inhibitory concentration (MIC), propidium iodide (PI) staining, fungal spore adhesion, and biofilm formation assay.

RESULTS

In A. fumigatus keratitis mice, FMN decreased the keratitis clinical scores, macrophages and neutrophils migration, and the expression of TNF-α, IL-6, and IL-1β. In A. fumigatus-stimulated human corneal epithelial cells (HCECs), FMN reduced the expression of IL-6, TNF-α, IL-1β, and NLRP3. FMN also decreased the expression of thymic stromal lymphopoietin (TSLP) and thymic stromal lymphopoietin receptor (TSLPR). Moreover, FMN reduced the levels of reactive oxygen species (ROS) induced by A. fumigatus in HCECs. Furthermore, FMN inhibited A. fumigatus growth, prevented spore adhesion and disrupted fungal biofilm formation in vitro. In vivo, FMN treatment reduced the fungal load in mice cornea at 3 days post infection (p.i.).

CONCLUSION

FMN demonstrated anti-inflammatory and antifungal properties, and exhibited a protective effect on mouse A. fumigatus keratitis.

Plumbagin inhibits fungal growth, HMGB1/LOX-1 pathway and inflammatory factors in A. fumigatus keratitis

To investigate the anti-inflammatory and antifungal effects of plumbagin (PL) in Aspergillus fumigatus (A. fumigatus) keratitis, the minimum inhibitory concentration (MIC), time-killing curve, spore adhesion, crystal violet staining, calcium fluoride white staining, and Propidium Iodide (PI) staining were employed to assess the antifungal activity of PL in vitro against A. fumigatus. The cytotoxicity of PL was assessed using the Cell Counting Kit-8 (CCK8). The impact of PL on the expression of HMGB1, LOX-1, TNF-α, IL-1β, IL-6, IL-10 and ROS in A. fumigatus keratitis was investigated using RT-PCR, ELISA, Western blot, and Reactive oxygen species (ROS) assay. The therapeutic efficacy of PL against A. fumigatus keratitis was assessed through clinical scoring, plate counting, Immunofluorescence and Hematoxylin-Eosin (HE) staining. Finally, we found that PL inhibited the growth, spore adhesion, and biofilm formation of A. fumigatus and disrupted the integrity of its cell membrane and cell wall. PL decreased IL-6, TNF-α, and IL-1β levels while increasing IL-10 expression in fungi-infected mice corneas and peritoneal macrophages. Additionally, PL significantly attenuated the HMGB1/LOX-1 pathway while reversing the promoting effect of Boxb (an HMGB1 agonist) on HMGB1/LOX-1. Moreover, PL decreased the level of ROS. In vivo, clinical scores, neutrophil recruitment, and fungal burden were all significantly reduced in infected corneas treated with PL. In summary, the inflammatory process can be inhibited by PL through the regulation of the HMGB-1/LOX-1 pathway. Simultaneously, PL can exert antifungal effects by limiting fungal spore adhesion and biofilm formation, as well as causing destruction of cell membranes and walls.

Pseudolaric acid B exerts an antifungal effect and targets SIRT1 to ameliorate inflammation by regulating Nrf2/NF-κB pathways in fungal keratitis

Fungal keratitis (FK) is a vision-threatening infection. We aimed to explore the antifungal and anti-inflammatory effects of pseudolaric acid B (PAB) on FK and the underlying mechanisms involved. Network pharmacology utilized to acquire the potential target genes, and silent information regulator 1 (SIRT1) was consistently downregulated in Gene Expression Omnibus dataset and clinical samples. Molecular docking analysis showed that PAB and SIRT1 had good binding activity. No toxicity was observed in vivo and in vitro with a PAB concentration below 0.3 μM. PAB exerted its antifungal activity by destroying the integrity of hyphae, and alleviated the severity of FK in rats by decreasing clinical scores, fungal burden and inhibiting inflammatory cell infiltration. PAB increased SIRT1 to regulate the crosstalk between nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor kappa-B (NF-κB), decreasing the levels of inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6; and pattern recognition receptors, C-type lectin domain containing 7A (Dectin-1), lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1), toll like receptor (TLR)-2, and TLR4 both in vivo and in vitro. However, this anti-inflammatory effect of PAB was abolished by the SIRT1 inhibitor EX527. This study provides new evidence that PAB has antifungal and anti-inflammatory effects in FK and may provide a novel therapeutic strategy for the treatment of FK.

Schaftoside reduces inflammation in Aspergillus fumigatus keratitis through the inhibition of the TLR4/MyD88 pathway

PURPOSE

The purpose of this research study was to investigate the impact of schaftoside on Aspergillus fumigatus (A. fumigatus) keratitis and elucidate its underlying mechanisms.

METHODS

In order to establish safe experimental concentrations of schaftoside in human corneal epithelial cells (HCECs), RAW264.7 cells, and mouse models, various techniques were employed including cytotoxicity assay (CCK-8) assay, cell scratch assay, and Draize test. The therapeutic effect of schaftoside was assessed using slit-lamp biomicroscopy, clinical scores, as well as determination of neutrophil infiltration through hematoxylin and eosin (HE) staining, immunofluorescence (IF) staining, and myeloperoxidase (MPO) assay. The levels of Toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 (MyD88), pro-inflammatory mediators interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-6 were determined using quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and IF techniques.

RESULTS

Schaftoside at a concentration of 160 μM displayed no harmful side effects on HCECs, RAW cells, and mouse corneas, rendering it suitable for further experiments. In a murine fungal keratitis model, schaftoside mitigated the severity of fungal keratitis by inhibiting neutrophil infiltration and reducing MPO activity. Both in vitro and in vivo experiments demonstrated that schaftoside treatment suppressed the upregulation of IL-1β, TNF-α, and IL-6 expression, while also downregulating the expressions of TLR4 as well as MyD88 at both mRNA and protein levels.

CONCLUSIONS

Schaftoside demonstrated a protective effect against A. fumigatus keratitis by reducing corneal damage through inhibition of neutrophil recruitment and downstream inflammatory cytokines. The anti-inflammatory properties of schaftoside in A. fumigatus keratitis may involve modulation of the TLR4/MyD88 pathway.

Aspergillus fumigatus-Derived Extracellular Vesicles Mitigate Fungal Keratitis by Modulating the Immune Cell Function

Fungal keratitis (FK) is a refractory global disease characterized by a high incidence of blindness and a lack of effective therapeutic options, and Aspergillus fumigatus (A. fumigatus, AF) is one of the most common causative fungi. This study aimed to investigate the role of extracellular vesicles (EVs) from A. fumigatus in the immune cell function and their protective role in A. fumigatus keratitis in order to explore their therapeutic potential. First, we isolated and characterized the EVs (AF-derived EVs). In vitro, we stimulated RAW264.7 cells and polymorphonuclear cells with AF-derived EVs. The expression levels of inflammatory factors increased in both immune cells along with an M1 polarization variation of RAW264.7 cells. After being incubated with AF-derived EVs, both immune cells exhibited an increased conidia-phagocytic index and a decreased conidia survival rate. In vivo, we injected EVs subconjunctivally on mice resulting in a heightened production of secretory immunoglobulin A (sIgA) in tear fluid. By the injection of EVs on mice in advance, a significant reduction in severity of A. fumigatus FK was witnessed by lower clinical scores, inflammatory appearances, and mitigated fungal load. Collectively, these results positioned AF-derived EVs as a promising and innovative immune therapy for combating FK, while also providing a platform for further investigation into developing an optimal formulation for modulating inflammation in the context of FK.

Floral Volatile Organic Compounds Change the Composition and Function of the Endophytic Fungal Community in the Flowers of Osmanthus fragrans

Endophytic fungi in flowers influence plant health and reproduction. However, whether floral volatile organic compounds (VOCs) affect the composition and function of the endophytic fungal community remains unclear. Here, gas chromatography-mass spectrometry (GC-MS) and high-throughput sequencing were used to explore the relationship between floral VOCs and the endophytic fungal community during different flower development stages in Osmanthus fragrans 'Rixiang Gui'. The results showed that the composition of the endophytic fungal community and floral VOCs shifted along with flowering development. The highest and lowest α diversity of the endophytic fungal community occurred in the flower fading stage and full blooming stage, respectively. The dominant fungi, including Dothideomycetes (class), Pleosporales (order), and Neocladophialophora, Alternaria, and Setophoma (genera), were enriched in the flower fading stage and decreased in the full blooming stage, demonstrating the enrichment of the Pathotroph, Saprotroph, and Pathotroph-Saprotroph functions in the flower fading stage and their depletion in the full blooming stage. However, the total VOC and terpene contents were highest in the full blooming stage and lowest in the flower fading stage, which was opposite to the α diversity of the endophytic fungal community and the dominant fungi during flowering development. Linalool, dihydro-β-ionone, and trans-linalool oxide(furan) were key factors affecting the endophytic fungal community composition. Furthermore, dihydro-β-ionone played an extremely important role in inhibiting endophytic fungi in the full blooming stage. Based on the above results, it is believed that VOCs, especially terpenes, changed the endophytic fungal community composition in the flowers of O. fragrans 'Rixiang Gui'. These findings improve the understanding of the interaction between endophytic fungi and VOCs in flowers and provide new insight into the mechanism of flower development.

The therapeutic role and mechanism of 4-Methoxycinnamic acid in fungal keratitis

Fungal keratitis is an infectious vision-threatening disease that has a poor prognosis, and the clinical therapeutic drugs have multiple limitations, such as epithelial toxicity and low bioavailability. Therefore, new antifungal treatment strategies must be developed. 4-Methoxycinnamic acid (MCA) is a widely occurring natural phenolic acid that has been proven to have multiple effects, such as antibacterial, antifungal, anti-inflammatory, neuroprotective, and inhibiting cancer. In this research, we explored the effects and underlying mechanisms of MCA on A. fumigatus keratitis and the antifungal effects of the combination of MCA and natamycin (NATA) on A. fumigatus. We found that MCA exerts antifungal effects by inhibiting the synthesis of the fungal cell wall, changing the permeability of fungal cell membranes. Moreover, the MCA-NATA combination exhibited synergy for A. fumigatus. In addition, MCA exerted an anti-inflammatory effect by downregulating the inflammatory factors (IL-1β, TNF-α, IL-6, and iNOS) in C57BL/6 mice and RAW264.7 cells. The anti-inflammatory mechanism of MCA was associated with the Mincle signal pathway. In summary, MCA acts as a potential therapeutic drug for fungal keratitis and a potential antifungal sensitizer for natamycin. MCA inhibits fungal cell wall synthesis, destroys the permeability of fungal cell membranes, and mediates the anti-inflammatory, immune response of the host.

Hinokitiol inhibits Aspergillus fumigatus by interfering with the cell membrane and cell wall

Hinokitiol (β-thujaplicin) is an important component of the essential oil extracted from Chamaecyparis obtuse, which prevents the decay and decomposition of temple and shrine buildings in Japan. Hinokiol has been shown to have a detrimental effect on various fungi such as Candida albicans and saprophytic fungi. However how hinokitiol works against Aspergillus fumigatus (A. fumigatus) has not been claimed. This study aims to investigate the adverse effects of hinokitiol on the disruption of the cell wall and cell membrane of A. fumigatus and to explore possible potential mechanisms or pathways. According to our results, hinokitiol negatively altered mycelium morphology, growth density, and cell plasma composition content. When incubated with human corneal epithelial cells (HCECs), hinokitiol saw a safe effect with concentrations below 12 μg/ml. Hinokitiol was shown to increase the cell membrane's permeability by decreasing the cell membrane's ergosterol content. The integrity of the cell wall was disrupted, as well as a significant increase in chitin degradation and chitinase activity. As determined by RNA-seq results, subsequent analysis, and qRT-PCR, altered transcript levels of cell walls and cell membranes-related genes (such as eglC) illustrated how hinokitiol affected the genetic profile of A. fumigatus. With this study, we recommend hinokitiol as an effective anti-A. fumigatus agent by reducing the amounts of key components in the cell wall and membrane by preventing production and accelerating breakdown.

Benzyl isothiocyanate improves the prognosis of Aspergillus fumigatus keratitis by reducing fungal load and inhibiting Mincle signal pathway

Aspergillus fumigatus keratitis is a potential blinding disease associated with A. fumigatus invasion and excessive inflammatory response. Benzyl isothiocyanate (BITC) is a secondary metabolite with broad antibacterial and anti-inflammatory activity extracted from cruciferous species. However, the role of BITC in A. fumigatus keratitis has not been discovered yet. This study aims to explore the antifungal and anti-inflammatory effects and mechanisms of BITC in A. fumigatus keratitis. Our results provided evidences that BITC exerted antifungal effects against A. fumigatus by damaging cell membranes, mitochondria, adhesion, and biofilms in a concentration-dependent manner. In vivo, fungal load and inflammatory response including inflammatory cell infiltration and pro-inflammatory cytokine expression were reduced in BITC-treated A. fumigatus keratitis. Additionally, BITC significantly decreased Mincle, IL-1β, TNF-α, and IL-6 expression in RAW264.7 cells that stimulated by A. fumigatus or Mincle ligand trehalose-6,6-dibehenate. In summary, BITC possessed fungicidal activities and could improve the prognosis of A. fumigatus keratitis by reducing fungal load and inhibiting the inflammatory response mediated by Mincle.