Experimental Models for Fungal Keratitis: An Overview of Principles and Protocols

Zeolitic Imidazolate Framework-90 Treats Fungal Keratitis by Promoting Macrophage Apoptosis and Targeting Increased Mitochondrial Reactive Oxygen Species in Aspergillus Fumigatus

Background

Fungal keratitis is a severe vision-threatening corneal infection with a prognosis influenced by fungal virulence and the host's immune defense mechanisms. However, there is still a lack of effective drugs that attenuate fungal virulence while relieving the inflammatory response caused by fungal keratitis.

Purpose

Finding an effective treatment to solve these problems is particularly important.

Methods

We synthesized Zeolitic imidazolate framework-90 (ZIF-90) by water-based synthesis method and characterized it. In vitro experiments included mycelium electron microscopy, Cell Counting Kit-8 (CCK-8), and Enzyme-linked immunosorbent assay (ELISA). These trials verified the disruptive effects of ZIF-90 on morphology, cell membrane, cell wall, and biofilm formation of Aspergillus fumigatus (A. fumigatus). These experiments also demonstrated the impact of ZIF-90 on the proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Moreover, the effect of ZIF-90 on mitochondrial reactive oxygen species (mtROS) of cells and fungi was verified by MitoSOX Red Mitochondrial Superoxide Indicator (MitoSOX). In vivo, corneal toxicity test, establishment and treatment of mycotic keratitis mouse model, and immunofluorescence staining were used to evaluate the efficacy of ZIF-90 in the procedure of fungal keratitis. In addition, to investigate whether the metal-ligand zinc and the organic ligand imidazole acted as essential factors in ZIF-90, we investigated the in vitro antimicrobial and anti-inflammatory effects of ZIF-8, ZIF-67 and Metal-Organic Frameworks-74 (Zn) (MOF-74 (Zn)) by Minimum Inhibitory Concentration (MIC) and ELISA experiments.

Results

ZIF-90 has therapeutic effects on fungal keratitis, which could break the protective organelles of A. fumigatus, such as the cell wall. In addition, ZIF-90 can also be targeted to increase the amount of mtROS in fungi and promote apoptosis of macrophages. The results demonstrated that both zinc ions and imidazole possessed antimicrobial and anti-inflammatory effects. In addition, ZIF-90 exhibited better antifungal properties than ZIF-8, ZIF-67, and MOF-74 (Zn).

The Dual Pathogen Fusarium: Diseases, Incidence, Azole Resistance, and Biofilms

The increasing resistance of Fusarium species to nearly all first-line antifungal agents in clinical settings has led to its designation as a 'high-priority' human pathogen. As a dual pathogen, Fusarium spp. threaten both human health and crop production, impacting food security. Our recent drug profiling of clinical Fusarium isolates reveals resistance to several front-line antifungals, with notable cross-azole resistance observed in both clinical and plant-associated strains. While the overuse of agricultural azoles has been implicated in the selection of azole-resistant fungi such as Aspergillus, a similar mechanism has been assumed for Fusarium in clinical settings. However, direct genetic evidence supporting this hypothesis remains limited. In this review, part of our Special Interest (SI) series, we discuss the spectrum of human diseases caused by Fusarium. While incidence data are better established for human keratitis and onychomycosis, invasive fusariosis remains globally underreported. We propose reasons for this distinct clinical spectrum bias and explore the potential genetic basis of azole resistance.

Long Non-Coding RNA Osr2 Promotes Fusarium solani Keratitis Inflammation via the miR-30a-3p/ Xcr1 Axis

Purpose

Fungal keratitis (FK) is a challenging and sight-threatening corneal disease caused by fungal infections. Although long noncoding RNAs (lncRNAs) have been explored in various infectious diseases, their specific roles in FK remain largely unexplored.

Methods

A mouse model of FK was created by infecting corneal stromal cells with Fusarium solani. High-throughput lncRNA expression profiling was conducted on FK-affected corneal tissues to identify differentially expressed lncRNAs. Reverse transcription quantitative PCR (RT-qPCR) was used to validate the results. A competing endogenous RNA (ceRNA) network was constructed. Additionally, a specific antisense oligonucleotide (ASO) targeting lncRNA ENSMUST00000226838/Osr2 (Osr2) was developed for therapeutic evaluation. Inflammatory markers IL-1β, IL-6, and TNF-α were measured, and corneal inflammation was assessed through histological analysis and slit-lamp examination. Fluorescent in situ hybridization (FISH) was used to confirm Osr2 localization, whereas a dual-luciferase reporter assay verified interactions between Osr2 and miR-30a-3p.

Results

We identified 1143 differentially expressed lncRNAs in FK, with 701 upregulated and 442 downregulated. The ceRNA network analysis indicated that lncRNA Osr2 regulates Xcr1 expression through miR-30a-3p. Treatment with ASO-Osr2 significantly reduced corneal inflammation, and FISH confirmed lncRNA Osr2 distribution in both the nucleus and cytoplasm. Dual-luciferase assays demonstrated the interaction between Osr2 and miR-30a-3p, highlighting their potential roles in the progression of FK.

Conclusions

This study outlined the lncRNA expression profile in FK and established a ceRNA regulatory network, identifying lncRNA Osr2 as a crucial modulator of FK pathogenesis through its interaction with miR-30a-3p. These findings highlighted lncRNA Osr2 as a promising therapeutic target for the treatment of FK.

Antifungal susceptibility, clinical findings, and biofilm resistance of Fusarium species causing keratitis: a challenge for disease control

Fusarium keratitis (FK) is an important clinical condition that can lead to blindness and eye loss, and is most commonly caused by the Fusarium solani species complex (FSSC). This study evaluated the susceptibility of planktonic cells and biofilms of FSSC (n = 7) and non-FSSC (n = 7) isolates obtained from patients with keratitis from a semi-arid tropical region to amphotericin B (AMB), natamycin (NAT), voriconazole (VRZ), efinaconazole (EFZ), and luliconazole (LCZ). Analysis of clinical data showed that trauma was the most common risk factor for FK patients. Disease onset was longer in non-FSSC group (3-30 days) than in the FSSC group (3-7 days). FSSC strains were less susceptible to AMB and VRZ than non-FSSC strains (p < 0.05). Susceptibility to NAT, LCZ and EFZ was similar between isolates of FSSC and non-FSSC groups. Overall, patients infected with non-FSSC showed a better response to antifungal treatment. Corneal transplantation was more common in patients infected with FSSC (3/7) than in those infected with non-FSSC (1/7). Mature biofilms showed a poor response to antifungal treatment. Patients infected with Fusarium strains capable of forming antifungal tolerant biofilms had more complex therapeutic management, requiring two antifungals and/or corneal transplantation (p < 0.05). This study highlights the importance of mycological diagnosis and the antifungal susceptibility testing in the clinical management of FK. The ability of Fusarium to form antifungal tolerant biofilms poses a challenge to clinicians and urges the development of new antibiofilm therapeutics.

Zeolitic Imidazolate Framework-8 Offers an Anti-Inflammatory and Antifungal Method in the Treatment of Aspergillus Fungal Keratitis in vitro and in vivo

Background

Fungal keratitis is a serious blinding eye disease. Traditional drugs used to treat fungal keratitis commonly have the disadvantages of low bioavailability, poor dispersion, and limited permeability.

Purpose

To develop a new method for the treatment of fungal keratitis with improved bioavailability, dispersion, and permeability.

Methods

Zeolitic Imidazolate Framework-8 (ZIF-8) was formed by zinc ions and 2-methylimidazole linked by coordination bonds and characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Zeta potential. The safety of ZIF-8 on HCECs and RAW 264.7 cells was detected by Cell Counting Kit-8 (CCK-8). Safety evaluation of ZIF-8 on mice corneal epithelium was conducted using the Draize corneal toxicity test. The effects of ZIF-8 on fungal growth, biofilm formation, and hyphae structure were detected by Minimal inhibit concentration (MIC), crystal violet staining, Propidium Iodide (PI) testing, and calcofluor white staining. The anti-inflammatory effects of ZIF-8 on RAW 246.7 cells were evaluated by Quantitative Real-Time PCR Experiments (qPCR) and Enzyme-linked immunosorbent assay (ELISA). Clinical score, Colony-Forming Units (CFU), Hematoxylin-eosin (HE) staining, and immunofluorescence were conducted to verify the therapeutic effect of ZIF-8 on C57BL/6 female mice with fungal keratitis.

Results

In vitro, ZIF-8 showed outstanding antifungal effects, including inhibiting the growth of Aspergillus fumigatus over 90% at 64 μg/mL, restraining the formation of biofilm, and destroying cell membranes. In vivo, treatment with ZIF-8 reduced corneal fungal load and mitigated neutrophil infiltration in fungal keratitis, which effectively reduced the severity of keratitis in mice and alleviated the infiltration of inflammatory factors in the mouse cornea. In addition, ZIF-8 reduces the inflammatory response by downregulating the expression of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β after Aspergillus fumigatus infection in vivo and in vitro.

Conclusion

ZIF-8 has a significant anti-inflammatory and antifungal effect, which provides a new solution for the treatment of fungal keratitis.

Licochalcone A Ameliorates Aspergillus fumigatus Keratitis by Reducing Fungal Load and Activating the Nrf2/HO-1 Signaling Pathway

Fungal keratitis (FK) is a blinding corneal infectious disease. The prognosis is frequently unfavorable due to fungal invasion and an excessive host inflammatory response. Licochalcone A (Lico A) exhibits a broad spectrum of pharmacological activities, encompassing antifungal, anti-inflammatory, antioxidation, and antitumor properties. However, the role of Lico A has not yet been studied in FK. In this study, we discovered that Lico A could disrupt Aspergillus fumigatus (A. fumigatus) biofilms, inhibit fungal growth and adhesion to host cells, induce alterations of hyphal morphology, and impair the cell membrane and cell wall integrity and mitochondrial structure of A. fumigatus. Lico A can alleviate the severity of FK in mice, reduce neutrophil infiltration and fungal load, and significantly decrease the pro-inflammatory cytokines in mouse corneas infected with A. fumigatus. In vitro, we also demonstrated that Lico A increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) around the nucleus in human corneal epithelial cells (HCECs) stimulated with A. fumigatus. We verified that the anti-inflammatory effect of Lico A is associated with the activation of the Nrf2/HO-1 axis. These results indicated that Lico A could provide a protective role in A. fumigatus keratitis through its anti-inflammatory and antifungal activities.

A biomimetic human disease model of bacterial keratitis using a cornea-on-a-chip system

Bacterial keratitis is a common form of inflammation caused by the bacterial invasion of the corneal stroma after trauma. In extreme cases, it can lead to severe visual impairment or even blindness; therefore, timely medical intervention is imperative. Unfortunately, widespread misuse of antibiotics has led to the development of drug resistance. In recent years, organ-on-chips that integrate multiple cell co-cultures have extensive applications in fundamental research and drug screening. In this study, immortalized human corneal epithelial cells and primary human corneal fibroblasts were co-cultured on a porous polydimethylsiloxane membrane to create a cornea-on-a-chip model. The developed multilayer epithelium closely mimicked clinical conditions, demonstrating high structural resemblance and repeatability. By introducing a consistently defective epithelium and bacterial infection using the space-occupying method, we successfully established an in vitro model of bacterial keratitis using S. aureus. We validate this model by evaluating the efficacy of antibiotics, such as levofloxacin, tobramycin, and chloramphenicol, through simultaneously observing the reactions of bacteria and the two cell types to these antibiotics. Our study has revealed the barrier function of epithelium of the model and differentiated efficacy of three drugs in terms of bactericidal activity, reducing cellular apoptosis, and mitigating scar formation. Altogether, the cornea on chip enables the assessment of ocular antibiotics, distinguishing the impact on corneal cells and structural integrity. This study introduced a biomimetic in vitro disease model to evaluate drug efficacy and provided significant insights into the extensive effects of antibiotics on diverse cell populations within the cornea.

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Clinical efficacy of cyclosporin and natamycin for fungal keratitis

Objectives

To investigate the clinical efficacy of cyclosporin (CYSP) and natamycin (NAT) as a combination therapy in patients with fungal keratitis.

Methods

This is a retrospective study. A total of 64 patients (64 eyes) with fungal keratitis treated by Baoding No.1 Central Hospital between December 2018 and May 2022 according to their treatment methods were divided into a monotherapy (MT) group receiving NAT eye drops solely and a combination therapy (CT) group given CYSP eye drops in addition to the exact treatment provided for the MT group. The clinical responses, visual acuity changes, severity of eye symptoms, and adverse reactions were compared between the two groups.

Results

At two and four weeks post-treatment, the CT group had an overall response rate (ORR) significantly higher than that of the MT group (P< 0.05, respectively); both groups showed improved visual acuity and eye symptoms compared with the pre-treatment condition, and these improvements were more pronounced in the CT group (P < 0.05, respectively). Compared with the MT group, the CT group experienced a significantly shorter duration of eye symptoms (P < 0.05). The adverse reaction rate(ARR) was 9.38% in the CT group and 6.25% in the MT group, and the difference was not significant (P > 0.05).

Conclusion

Using CYSP and NAT as a combination therapy for fungal keratitis can substantially heighten the therapeutic effects, promote visual acuity recovery, and induce rapid remission of eye symptoms without increasing the risk of adverse reactions.

Aspergillus fumigatus Hypoxia Adaptation Is Critical for the Establishment of Fungal Keratitis

Purpose

The poor visual outcomes associated with fungal keratitis (FK) underscore a need to identify fungal pathways that can serve as novel antifungal targets. In this report, we investigated whether hypoxia develops in the FK cornea and, by extension, if fungal hypoxia adaptation is essential for virulence in this setting.

Methods

C57BL/6J mice were inoculated with Aspergillus fumigatus and Fusarium solani var. petroliphilum via topical overlay or intrastromal injection. At various time points post-inoculation (p.i.), animals were injected with pimonidazole for the detection of tissue hypoxia through immunofluorescence imaging. The A. fumigatus srbA gene was deleted through Cas9-mediated homologous recombination and its virulence was assessed in the topical infection model using slit-lamp microscopy and optical coherence tomography (OCT).

Results

Topical inoculation with A. fumigatus resulted in diffuse pimonidazole staining across the epithelial and endothelial layers within 6 hours. Stromal hypoxia was evident by 48 hours p.i., which corresponded to leukocytic infiltration. Intrastromal inoculation with either A. fumigatus or F. solani similarly led to diffuse staining patterns across all corneal cell layers. The A. fumigatus srbA deletion mutant was unable to grow at oxygen levels below 3% in vitro, and corneas inoculated with the mutant failed to develop signs of corneal opacification, inflammation, or fungal burden.

Conclusions

These results suggest that fungal antigen rapidly drives the development of corneal hypoxia, thus rendering fungal SrbA or related pathways essential for the establishment of infection. Such pathways may therefore serve as targets for novel antifungal intervention.

Local application of silver nitrate as an adjuvant treatment before deep lamellar keratoplasty for fungal keratitis poorly responsive to medical treatment

Objective

The purpose of this study is to evaluate the efficacy and safety of the local application of silver nitrate (LASN) as an adjuvant treatment before deep lamellar keratoplasty (DLKP) for fungal keratitis responding poorly to medical treatment.

Methods

A total of 12 patients (12 eyes) with fungal keratitis responding poorly to medical treatment (for at least 2 weeks) were included. LASN was performed using 2% silver nitrate, the ulcer was cleaned and debrided, and then, the silver nitrate cotton stick was applied to the surface of the ulcer for a few seconds. The effect of LASN was recorded. The number of hyphae before and after treatment was determined by confocal microscope. After the condition of the ulcer improved, DLKP was performed. Fungal recurrence, best-corrected visual acuity (BCVA), loose sutures, and endothelial cell density (ECD) were recorded in detail.

Results

Clinical resolution of corneal infiltration and edema was observed, and the ulcer boundary became clear in all 12 patients after 7-9 days of LASN. Confocal microscopy showed that the number of hyphae was significantly reduced. Ocular pain peaked on days 1 and 2 after treatment, and 9 patients (75%, day 1) and 1 patient (8.3%, day 2) required oral pain medication. During the follow-up period after DLKP, no fungal recurrence and loose sutures were observed. After the operation, the BCVA of all patients improved. The mean corneal ECD was 2,166.83 ± 119.75 cells/mm2.

Conclusion

The LASN was safe and effective and can be well tolerated by patients. Eye pain can be relieved quickly. LASN as an adjuvant treatment before DLKP might be a promising therapeutic strategy.

Host cell-type and pathogen-specific immunomodulatory functions of macrophage migration inhibitory factor (MIF) in infectious keratitis

Therapeutic management of inflammation in infectious keratitis (IK) requires new strategy and targets for selective immunomodulation. Targeting host cell-type specific inflammatory responses might be a viable strategy to curtail unnecessary inflammation and reduce tissue damage without affecting pathogen clearance. This study explores the possibility of pathogen and host cell-type dependent differences in the inflammatory pathways relevant in the pathogenesis of IK. Human corneal epithelial cell line (HCEC) and phorbol 12-myristate-13 acetate (PMA) differentiated THP-1 macrophage line were infected with either Aspergillus flavus conidia or Acanthamoeba castellanii trophozoites and the elicited inflammatory responses were studied in terms of gene expression and secretion of proinflammatory factors interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α) and an upstream inflammatory regulator and mediator protein-the Macrophage Migration Inhibitory Factor (MIF). Given the pleotropic mode of MIF function in diverse cell types relevant in many human diseases, we tested if MIF driven responses to infection is different in HCECs and THP-1 macrophages by studying its expression, secretion and involvement in inflammation by siRNA mediated knockdown. We also examined IK patient tear samples for MIF levels. Infection with A. flavus or A. castellanii induced IL-8 and TNF-α responses in HCECs and THP-1 macrophages but to different levels. Our preliminary human data showed that the level of secreted MIF protein was elevated in IK patient tear, however, MIF secretion by the two cell types were strikingly different in-vitro, under both normal and infected conditions. We found that HCECs released MIF constitutively, which was significantly inhibited with infection, whereas THP-1 macrophages were stimulated to release MIF during infection. MIF gene expression remained largely unaffected by infection in both the cell lines. Although MIF in HCECs appeared to be intracellularly captured during infection, MIF knockdown in HCECs associated with a partial reduction of the IL-8 and TNF-α expression produced by either of the pathogens, suggesting a pro-inflammatory role for MIF in HCECs, independent of its canonical cytokine like function. In contrast, MIF knockdown in THP-1 macrophages accompanied a dramatic increase in IL-8 and TNF-α expression during A. castellanii infection, while the responses to A. flavus infection remained unchanged. These data imply a host cell-type and pathogen specific distinction in the MIF- related inflammatory signaling and MIF as a potential selective immunomodulatory target in infectious keratitis.

The Role of Biofilms in Contact Lens Associated Fungal Keratitis

Biofilm formation is an important microbial strategy for fungal pathogens, such as Fusarium, Aspergillus, and Candida, to establish keratitis in patients wearing soft contact lenses. Despite the well-documented 2006 outbreak of Fusarium keratitis that eventually led to the withdrawal of the Bausch & Lomb multipurpose lens care solution ReNu with MoistureLoc ("MoistureLoc") from the global market, contact lens care systems and solutions currently available on the market do not specifically target fungal biofilms. This is partially due to the lack of recognition and understanding of important roles that fungal biofilms play in contact lens associated fungal keratitis (CLAFK). This review aims to reemphasize the link between fungal biofilms and CLAFK, and deepen our comprehension of its importance in pathogenesis and persistence of this medical device-related infection.

The essential role of N6-methyladenosine RNA methylation in complex eye diseases

There are many complex eye diseases which are the leading causes of blindness, however, the pathogenesis of the complex eye diseases is not fully understood, especially the underlying molecular mechanisms of N6-methyladenosine (m6A) RNA methylation in the eye diseases have not been extensive clarified. Our review summarizes the latest advances in the studies of m6A modification in the pathogenesis of the complex eye diseases, including cornea disease, cataract, diabetic retinopathy, age-related macular degeneration, proliferative vitreoretinopathy, Graves' disease, uveal melanoma, retinoblastoma, and traumatic optic neuropathy. We further discuss the possibility of developing m6A modification signatures as biomarkers for the diagnosis of the eye diseases, as well as potential therapeutic approaches.

Sertaconazole-Nitrate-Loaded Leciplex for Treating Keratomycosis: Optimization Using D-Optimal Design and In Vitro, Ex Vivo, and In Vivo Studies

This study aims to develop efficient topical therapy for keratomycosis using sertaconazolenitrate (STZN)-loaded leciplex (LP). The D-optimal design was used to optimize STZN-loaded LP by utilizing soy phosphatidylcholine (SPC) molar ratio (X₁), cationic surfactant molar ratio (X₂), and cationic surfactant type (X₃) as the independent variables, whereas their impact was studied for entrapment efficiency percent (EE; Y₁), particle size (PS; Y₂), polydispersity index (PDI; Y₃), zeta potential (ZP; Y₄), and permeability coefficient (Kp; Y₅). The optimized formula was evaluated regarding morphology, ex vivo permeation, mucoadhesion, stability, and in vivo studies. The optimized formula was spherical and showed EE of 84.87 ± 1.71%, PS of 39.70 ± 1.35 nm, PDI of 0.242 ± 0.006, ZP of +54.60 ± 0.24 mV, and Kp of 0.0577 ± 0.0001 cm/h. The ex vivo permeation study revealed that the optimized formula enhanced the Kp and corneal deposition by 2.78 and 12.49 folds, respectively, compared to the aqueous drug dispersion. Furthermore, the optimized formula was stable and revealed promising mucoadhesion properties. Finally, the in vivo studies showed that the optimized formula was superior to the drug dispersion in treating rats with induced keratomycosis. These results confirmed the capabilities of LP as a promising nanocarrier for treating ocular diseases topically.

Laccase-mediated functionalization of natamycin by gallic acids for the therapeutic effect on Aspergillus fumigatus keratitis

To improve the therapeutic effect of natamycin on fungal keratitis (FK), the grafted derivatives of natamycin and gallic acid were obtained, and the effects of the grafted derivatives on Aspergillus fumigatus (A. fumigatus) keratitis were investigated. The structure of natamycin grafted with gallic acid was identified by FT-IR and UV-Vis, and the successful synthesis of Gallic-Natamycin (GA-NAT) was proved. CCK-8 and the Draize eye test showed that GA-NAT had less cytotoxicity. Then, through in vitro antibacterial experiments such as minimum inhibitory concentration (MIC), adhesion, biofilm formation, and calcium fluorescence staining and in vivo experiments such as clinical score and plate counting, the results showed that GA-NAT had similar antifungal activity to natamycin, but had a better therapeutic effect than natamycin. Myeloperoxidase assay and immunofluorescence staining also showed that GA-NAT significantly inhibited neutrophil recruitment and activity. Moreover, It was further found that GA-NAT could inhibit the mRNA and protein expressions of LOX-1, TNF-α, and IL-1β. These results indicated that GA-NAT inhibited the fungal growth, reduced the neutrophil infiltration into cornea, and down-regulated the expression of inflammatory factors in lesions, which provides a new choice for FK treatment.

Pseudomonas Synergizes with Fluconazole against Candida during Treatment of Polymicrobial Infection

Polymicrobial infections are challenging to treat because we don't fully understand how pathogens interact during infection and how these interactions affect drug efficacy. Candida albicans and Pseudomonas aeruginosa are opportunistic pathogens that can be found in similar sites of infection such as in burn wounds and most importantly in the lungs of CF and mechanically ventilated patients. C. albicans is particularly difficult to treat because of the paucity of antifungal agents, some of which lack fungicidal activity. In this study, we investigated the efficacy of anti-fungal treatment during C. albicans-P. aeruginosa coculture in vitro and co-infection in the mucosal zebrafish infection model analogous to the lung. We find that P. aeruginosa enhances the activity of fluconazole (FLC), an anti-fungal drug that is fungistatic in vitro, to promote both clearance of C. albicans during co-infection in vivo and fungal killing in vitro. This synergy between FLC treatment and bacterial antagonism is partly due to iron piracy, as it is reduced upon iron supplementation and knockout of bacterial siderophores. Our work demonstrates that FLC has enhanced activity in clinically relevant contexts and highlights the need to understand antimicrobial effectiveness in the complex environment of the host with its associated microbial communities.

Rapidly dissolving microneedle patch of amphotericin B for intracorneal fungal infections

Chronic fungal infection of the cornea could lead to blindness if not treated properly. Topical amphotericin B (AMP-B) is considered the first treatment of choice for ocular fungal infection. However, factors related to its poor solubility and penetration through intact cornea lead to poor bioavailability. Microneedles (MNs) are emerging as a minimally invasive method to enhance ocular drug delivery. This study aims to investigate the potential use of biodegradable poly(vinylpyrrolidone) (PVP) and hyaluronic acid (HA)-based rapidly dissolving MNs for delivery of AMP-B to treat fungal infection. The data obtained illustrates PVP/HA MN arrays' reproducibility, good mechanical strength, and faster dissolution with 100% drug recovery. Multiphoton microscopic results revealed that MNs successfully penetrate the corneal tissue and enhance AMP-B permeation through corneal layers. Furthermore, PVP/HA MN arrays showed high solubility. Both PVP and HA successfully decreased AMP-B cytotoxicity when compared to free drug. More interestingly, the biocompatible MN formulations preserved the antifungal activity of AMP-B, as demonstrated by significant inhibition of fungal growth. Therefore, this study shows the feasibility of ocular delivery of the poorly soluble AMP-B using a fast-dissolving MN patch.

Mitochondria-Specific Aggregation-Induced Emission Luminogens for Selective Photodynamic Killing of Fungi and Efficacious Treatment of Keratitis

The development of effective antifungal agents remains a big challenge in view of the close evolutionary relationship between mammalian cells and fungi. Moreover, rapid mutations of fungal receptors at the molecular level result in the emergence of drug resistance. Here, with low tendency to develop drug-resistance, the subcellular organelle mitochondrion is exploited as an alternative target for efficient fungal killing by photodynamic therapy (PDT) of mitochondrial-targeting luminogens with aggregation-induced emission characteristics (AIEgens). With cationic isoquinolinium (IQ) moiety and proper hydrophobicity, three AIEgens, namely, IQ-TPE-2O, IQ-Cm, and IQ-TPA, can preferentially accumulate at the mitochondria of fungi over the mammalian cells. Upon white light irradiation, these AIEgens efficiently generate reactive ¹O₂, which causes irreversible damage to fungal mitochondria and further triggers the fungal death. Among them, IQ-TPA shows the highest PDT efficiency against fungi and negligible toxicity to mammalian cells, achieving the selective and highly efficient killing of fungi. Furthermore, we tested the clinical utility of this PDT strategy by treating fungal keratitis on a fungus-infected rabbit model. It was demonstrated that IQ-TPA presents obviously better therapeutic effects as compared with the clinically used rose bengal, suggesting the success of this PDT strategy and its great potential for clinical treatment of fungal infections.

A novel 3D culture model of fungal keratitis to explore host-pathogen interactions within the stromal environment

Fungal keratitis (FK) pathology is driven by both fungal growth and inflammation within the corneal stroma. Standard in vitro infection models ̶ involving co-culture of the pathogen and the corneal cells in tissue culture medium ̶ are sufficient to probe host responses to the fungus; however, they lack the physiological structure and nutrient composition of the stroma to accurately study fungal invasiveness and metabolic processes. We therefore sought to develop a culture model of FK that would allow for both host and fungal cell biology to be evaluated in parallel. Towards this end, we employed a previously described system in which primary human cornea fibroblasts (HCFs) are cultured on transwell membranes, whereupon they secrete a three-dimensional (3D) collagen matrix that resembles the human stroma. We demonstrated that two common mold agents of FK, Fusarium petroliphilum and Aspergillus fumigatus, penetrated into these constructs and caused a disruption of the collagen matrix that is characteristic of infection. HCF morphology appeared altered in the presence of fungus and electron microscopy revealed a clear internalization of fungal spores into these cells. Consistent with this apparent phagocyte-like activity of the HCFs, mRNA and protein levels for several pro-inflammatory cytokines/chemokines (including TNFα, IL-1β, IL-6, and IL-8) were significantly upregulated compared to uninfected samples. We similarly found an upregulation of several HCF metalloproteases (MMPs), which are enzymes that breakdown collagen during wound healing and may further activate pro-inflammatory signaling molecules. Finally, several fungal collagenase genes were upregulated during growth in the constructs relative to growth in tissue culture media alone, suggesting a fungal metabolic shift towards protein catabolism. Taken together, our results indicate that this 3D-stromal model provides a physiologically relevant system to study host and fungal cell pathobiology during FK.

Efficacy of adjuvant intrastromal and combination of intrastromal and intracameral voriconazole in <em>Aspergillus fumigatus</em>-induced moderate fungal keratitis in rabbits

BACKGROUND There is no in vivo evidence for the effectiveness of adjuvant intrastromal and combination of intrastromal and intracameral voriconazole (VCZ) for treating Aspergillus fumigatus keratitis. This study aimed to compare the efficacy of both agents against it.  METHODS A randomized, masked, controlled experimental study was conducted on 11 albino New Zealand white rabbits in which moderate fungal keratitis was induced by inoculating spores of A. fumigatus to the cornea. The rabbits were allocated into 3 groups: 50 μg/0.1 ml intrastromal VCZ injection, 50 μg/0.1 ml intrastromal VCZ and intracameral VCZ injections, and topical VCZ (control). The treatment was given 5 days after inoculation. Epithelial defect, infiltrate size, corneal ulcer depth, and hypopyon were evaluated clinically. Histopathological and mycological examinations were also done 14 days after treatment.  RESULTS All rabbits in the adjuvant treatment groups demonstrated a tendency of a better clinical response with decreasing size of epithelial defect (p = 0.679) and infiltrate (p = 0.755) than in the control group. Direct microscopy, corneal culture, and chop corneal tissue culture were still positive in most of the rabbits from all groups. Histopathological examination showed an increase of inflammatory cells after treatment in all groups, especially in rabbits which were inoculated with A. fumigatus spores in both eyes.  CONCLUSIONS An adjuvant combination of intrastromal and intracameral VCZ showed a tendency of better clinical response for A. fumigatus-induced moderate fungal keratitis in rabbits. 

The cGAS-STING signaling pathway contributes to the inflammatory response and autophagy in Aspergillus fumigatus keratitis

Fungal keratitis is a serious corneal infection, which can lead to significant visual impairment and blindness. The cGAS-STING signaling pathway has emerged as a key player in innate immunity by sensing of invading pathogens. However, the role of the cGAS-STING pathway in Aspergillus fumigatus (A. fumigatus) keratitis is still unknown. In this study, we showed that the cGAS-STING signaling pathway was activated in human corneal epithelial cells (HCECs) and in mouse corneas infected with A. fumigatus. Knockdown of cGAS reduced A. fumigatus-induced production of pro-inflammatory cytokines, including TNF-α, IL-1β, IL-6, and IFN-β. However, reconstruction of cGAS activity restored the inflammatory response in HCECs infected with A. fumigatus. A specific cGAS inhibitor, RU.521, could also significantly inhibit A. fumigatus-induced inflammatory cytokine expression. In addition, we found that cGAS was indispensable for the autophagy flux evoked by A. fumigatus infection. Moreover, inhibition of cGAS using siRNA or RU.521 alleviated the severity of A. fumigatus keratitis in the mouse cornea. Therefore, the cGAS-STING signaling pathway contributes to the progression of A. fumigatus keratitis and targeting this pathway may provide therapeutic potential.