Review of clinical and basic approaches of fungal keratitis

Oriented cellulose hydrogel: Directed tissue regeneration for reducing corneal leukoplakia and managing fungal corneal ulcers

Fungal corneal ulcer is one of the leading causes of corneal blindness in developing countries. Corneal scars such as leukoplakia are formed due to inflammation, oxidative stress and non-directed repair, which seriously affect the patients' subsequent visual and life quality. In this study, drawing inspiration from the oriented structure of collagen fibers within the corneal stroma, we first proposed the directional arrangement of CuTA-CMHT hydrogel system at micro and macro scales based on the 3D printing extrusion method combined with secondary patterning. It played an antifungal role and induced oriented repair in therapy of fungal corneal ulcer. The results showed that it effectively inhibited Candida albicans, Aspergillus Niger, Fusarium sapropelum, which mainly affects TNF, NF-kappa B, and HIF-1 signaling pathways, achieving effective antifungal functions. More importantly, the fibroblasts interacted with extracellular matrix (ECM) of corneal stroma through formation of focal adhesions, promoted the proliferation and directional migration of cells in vitro, induced the directional alignment of collagen fibers and corneal stromal orthogonally oriented repair in vivo. This process is mainly associated with MYLK, MYL9, and ITGA3 molecules. Furthermore, the downregulation the growth factors TGF-β and PDGF-β inhibits myofibroblast development and reduces scar-type ECM production, thereby reducing corneal leukoplakia. It also activates the PI3K-AKT signaling pathway, promoting corneal healing. In conclusion, the oriented CuTA-CMHT hydrogel system mimics the orthogonal arrangement of collagen fibers, inhibits inflammation, eliminates reactive oxygen species, and reduces corneal leukoplakia, which is of great significance in the treatment of fungal corneal ulcer and is expected to write a new chapter in corneal tissue engineering.

Purification, characterization of an entomopathogenic fungal lectin from Purpureocillium lilacinum and its involvement in pathogenesis leading to mycotic keratitis

A lectin PCL, from Purpureocillium lilacinum a saprophytic, filamentous fungus was purified from the crude extract of the mycelia using 70% ammonium sulphate precipitation followed by affinity chromatography on mucin-Sepharose 4 B column. PCL is a monomer with an apparent molecular mass of 18.5 kDa as revealed by SDS-PAGE under both reducing and non-reducing conditions. PCL is a blood group non-specific lectin and has highest affinity towards chitin, mucin, asialomucin, fetuin with a MIC of 0.15 µg/mL and also recognizes L-fucose, galactose, lactose, N-acetyl galactosamine, hyaluronic acid. PCL is stable up to 60 °C and within the pH range 4-8. To understand its role in pathogenesis, effect of PCL was evaluated on human corneal epithelial cells (HCECs). PCL showed strong glycan mediated binding to HCECs and PCL showed proinflammatory response at lower concentrations by stimulating secretion of IL-6, 8. In contrast PCL at higher concentrations revealed opposite effect of HCECs growth inhibition. All these results collectively support the involvement of PCL in mediating host pathogen interactions possibly leading to pathogenesis. In addition, considering the entomopathogenic effect of Purpureocillium lilacinum, PCL may be attributed for this beneficiary effect, which needs to be explored.

Comparison of Accelerated and Standard Corneal Collagen Cross-Linking Treatments in Experimental Fungal Keratitis for Aspergillus fumigatus

Introduction. To compare accelerated and standard corneal collagen cross-linking (CXL) treatments in experimental Aspergillus keratitis models. Methods. Twenty-six New Zealand rabbits were divided into two groups: a 1% voriconazole combined with standard CXL group, and a 1% voriconazole combined with accelerated CXL group. The ulcer area, corneal opacity, and corneal neovascularization score were measured via slit-lamp imaging, and the corneal and corneal epithelial thickness and ulcer depth were measured via anterior segment optical coherence tomography (AS-OCT). The duration of the hyphae was observed via in vivo confocal microscopy (IVCM), and the cornea was taken for pathological examination after modeling and at the end of the study to determine the hyphae and corneal repair. The observation times were as follows: at successful modeling (day 0) and at 1, 4, 7, 14, 21, and 28 days after the intervention. Results. The area and depth of the ulcer decreased in both groups after CXL (all $P<0.05$ ). Interestingly, the ulcer area in the accelerated CXL group still tended to increase on the first day after CXL although the difference was not statistically significant ( $P=0.6649$ ). On the 21st and 28th days after CXL, the ulcer area and depth of the standard CXL group were larger and deeper than those of the accelerated CXL group (all $P<0.05$ ). The ulcer healing time in the accelerated CXL group was 18.67 ± 6.21 days, while that in the standard CXL group was 23.55 ± 4.72 days, and the difference was statistically significant ( $P=0.0475$ ). Conclusions. Both accelerated and standard CXL can significantly inhibit the progression of Aspergillus keratitis corneal ulcers and promote ulcer healing. The accelerated CXL was superior to the standard CXL, which could control infection faster and promote ulcer healing. However, it is important to note that there may be a risk of early deterioration of the ulcer with accelerated CXL.

Comparison of Corneal Collagen Cross-Linking and Voriconazole Treatments in Experimental Fungal Keratitis for Aspergillus fumigatus

Aims

To compare the antifungal efficacy of corneal cross-linking (CXL) and voriconazole in experimental Aspergillus keratitis models.

Methods

Thirty-nine New Zealand rabbits were divided into three groups: a control group, a voriconazole group (M group), and a voriconazole combined with CXL group (CXL-M group). The ulcer area was measured via slit lamp imaging, the corneal and corneal epithelial thickness, and ulcer depth was measured via anterior segment optical coherence tomography (AS-OCT). The existence time of the hyphae was observed via in vivo confocal microscopy (IVCM), and the cornea was taken for pathological examination after modeling and at the end of the study to determine the hyphae and corneal repair. The observation times were as follows: at successful modeling and at 1, 4, 7, 14, 21, and 28 days after intervention.

Results

In the CXL-M group, ulcer area and depth decreased continuously from Day 4 to Day 28 after CXL (all P &lt; 0.05). In the CXL-M group, ulcer area and depth were smaller than those in the other two groups from Day 4 to Day 21 after CXL (all P &lt; 0.05, except ulcer area in the CXL-M vs. M group on Day 21). The duration of hyphae in the CXL-M group was significantly shorter than in the other two groups (P = 0.025). On Day 28, in CXL-M group, corneal thickness was thicker than baseline (P &lt; 0.05). Meanwhile, in CXL-M group, corneal and corneal epithelial thickness were significantly thinner than in the other two groups (P &lt; 0.001). The CXL-M group had no complications, such as corneal perforation, at the end of the study.

Conclusions

Voriconazole combined with CXL is effective in treating Aspergillus-infected keratitis. Combined therapy could effectively inhibit Aspergillus, accelerate corneal repair, and shorten the course of the disease.

Antifungal activity of [K3]temporin-SHa against medically relevant yeasts and moulds

Few antifungal agents are currently available for the treatment of fungal infections. Antimicrobial peptides (AMPs), which are natural molecules involved in the innate immune response of many organisms, represent a promising research method because of their broad killing activity. The aim of this study was to assess the activity of a frog AMP, [K³]temporin-SHa, against some species of yeasts and moulds, and to further explore its activity against Candida albicans. MIC determinations were performed according to EUCAST guidelines. Next, the activity of [K³]temporin-SHa against C. albicans was explored using time-killing curve experiments, membrane permeabilization assays, and electron microscopy. Finally, chequerboard assays were performed to evaluate the synergy between [K³]temporin-SHa and amphotericin B or fluconazole. [K³]temporin-SHa was found to be active in vitro against several yeasts with MIC between 5.5 and 45 µM. [K³]temporin-SHa displayed rapid fungicidal activity against C. albicans (inoculum was divided into two in less than an hour and no viable colonies were recovered after 5 h) with a mechanism that could be due to membrane permeabilization. [K³]temporin-SHa was synergistic with amphotericin B against C. albicans (FICI = 0.303). [K³]temporin-SHa could represent an additional tool to treat several Candida species and C. neoformans.

Interactions of thymic stromal lymphopoietin with interleukin-4 in adaptive immunity during Aspergillus fumigatus keratitis

AIM

To investigate the potential interactions of thymic stromal lymphopoietin (TSLP) with interleukin-4 (IL-4) in adaptive immunity during fungal keratitis (FK).

METHODS

An FK mouse model was induced with Aspergillus fumigatus (AF) hyphal infection. Mice were divided into several groups: untreated, phosphate buffer saline (PBS), infected with AF, and pretreated with a scrambled siRNA, a TSLP-specific siRNA (TSLP siRNA), murine recombinant TSLP (rTSLP), immunoglobulin G (IgG), murine recombinant IFN (rIFN-γ), murine recombinant IL-4 (rIL-4), rIL-13, murine recombinant IL-17A (rIL-17A), and murine recombinant IL-17F (rIL-17F) groups. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) or Western blot were performed to determine mRNA and protein levels in the inflamed cornea. Cytokine locations were observed by immunofluoresence staining after AF hyphal infection.

RESULTS

Compared to those in the untreated group, TSLP and T helper type 1 (Th1) cytokine levels in the AF group were upregulated at 24h post infection (hpi), and those of T helper type 2 (Th2) and T helper type 17 (Th17) cytokines were increased at 5d post infection (dpi). Th2 cytokine levels were decreased in the TSLP siRNA-pretreated group and increased in the rTSLP-pretreated group compared with the AF group. The TSLP level was increased in the rIL-4-pretreated group, but there were no significant changes among the other groups. Immunofluorescence staining showed cytokine locations after AF hyphal infection.

CONCLUSION

TSLP induces a Th2 immune response and promots Th2 T cell differentiation in vivo. IL-4 promotes TSLP secretion. Therefore, TSLP with IL-4 regulates adaptive immunity in FK.

Comparison of modified corneal cross-linking with intrastromal voriconazole for the treatment of fungal corneal ulcer

The present study aimed to evaluate the efficacy of modified corneal cross-linking (CXL) for the treatment of fungal corneal ulcers compared with that following intrastromal voriconazole injection. In total, 31 patients with fungal corneal ulcers treated at The General Hospital of Northern Theater Command between October 2017 and October 2019 were enrolled. Among them, 10 eyes were treated with ultraviolet A (UV-A)/riboflavin CXL (CXL group), whilst 21 eyes were treated with debridement combined with intrastromal voriconazole (stromal injection group). Preoperative microbiological examination was performed in both groups, and evaluated using Fisher's exact test. Postoperatively, infection control and total efficacy rates, localized lesion, ulcer healing rate 1 week after surgery, visual acuity and complications were evaluated using Fisher's exact test, however visual acuity was analyzed by mixed-model ANOVA. The results showed that the pre-operative species distribution between the CXL and stromal injection groups did not significantly differ. The infection control rate in the CXL group was notably higher compared with that in the stromal injection group (P=0.04). Furthermore, the total efficacy rate in the CXL group was also markedly higher compared with that in the stromal injection group, though no statistically significant differences were observed. Localized lesions were observed in nine eyes (90.0%) in the CXL group and nine eyes (42.9%) in the stromal injection group (P=0.02). However, the rate of ulcer healing at 1 week postoperatively and the logarithm of the minimum angle of resolution (logMAR) of visual acuity were not found to be significantly different between the two groups. In terms of complications, with the exception of one patient in the CXL group exhibiting loss of corneal transparency and one patient in the stromal injection group presenting with partial corneal thinning, no other forms of complications were observed. In conclusion, the present study suggested that CXL could have a beneficial impact for treating fungal corneal ulcers in the aspects of infection control, localized lesions and accelerated epithelialization. In addition, except the loss of corneal transparency, this treatment approach could be applied with reduced risks of adverse events.

A 10-Year Retrospective Clinical Analysis of Fungal Keratitis in a Portuguese Tertiary Centre

Purpose

To determine the microbiological profile, risk factors, treatment and surgical intervention rates of fungal keratitis at a tertiary referral centre.

Methods

A retrospective review of microbiological and medical records from hospitalised patients treated for fungal keratitis at Centro Hospitalar Universitário de São João from 2009 to 2019 was conducted.

Results

Overall, 43 patients were included in our study. The mean age of patients was 63.7 years and 46.5% were men. In culture were isolated 22 (51.2%) filamentous fungi and 21 (48.8%) yeast. Candida species (n = 20, 46.5%), Fusarium species (n = 10, 23.4%) and Aspergillus species (n = 4, 9.3%) were the most common isolated species. Important risk factors were contact lens use (n = 24, 55.8%), long-term users of topical corticosteroids (n = 19, 44.2%) and previous keratitis (n = 19, 44.2%). Yeast isolates had a statistically significant higher prevalence in long-term users of topical corticosteroids compared to filamentous ones (p = 0.043). Twenty-four cases (55.8%) required surgical intervention, of which 23 cases underwent therapeutic penetrating keratoplasty. Ocular complications, such as evisceration was noted in 12 patients (27.9%) and endophthalmitis in 5 (11.6%). No statistically significant changes of best corrected visual acuity (BCVA) were found after treatment (p = 0.687).

Conclusion

Most patients with fungal keratitis have associated risk factors. Filamentous and yeast species have equally prevalent etiologies. In general, our results mirror how difficult and challenging the approach and treatment of fungal keratitis could be.

Do Ophthalmic Solutions of Amphotericin B Solubilised in 2-Hydroxypropyl-γ-Cyclodextrins Possess an Extended Physicochemical Stability?

Fungal keratitis is a sight-threatening disease for which amphotericin B eye drops is one of the front-line treatments. Unfortunately, there are currently no commercial forms available, and there is little data concerning the long-term stability of compounded formulations based on intravenous dosages forms. New formulations of amphotericin B ophthalmic solutions solubilised with γ-cyclodextrins have shown promising in-vitro results, but stability data is also lacking. The objective of this study was therefore to investigate the stability of a formulation of ready-to-use amphotericin B solubilised in 2-hydroxypropyl-γ-cyclodextrins (AB-HP-γ-CD), for 350 days. An amphotericin B deoxycholate (ABDC) formulation was used as a comparator. Analyses used were the following: visual inspection, turbidity, osmolality and pH measurements, amphotericin B quantification by a stability-indicating liquid chromatography method, breakdown product research, and sterility assay. AB-HP-γ-CD formulation showed signs of chemical instability (loss of amphotericin B) after 28 and 56 days at 25 °C and 5 °C. Adding an antioxidant (ascorbic acid) to the formulation did not improve stability. ABDC formulation showed signs of physical instability (increased turbidy and amphotericin B precipitation) after 28 days and 168 days at 25 °C and 5 °C. As such, AB-HP-γ-CD formulation does not provide long-term stability for ophthalmic amphotericin B solutions.

In Vitro Topical Delivery of Chlorhexidine to the Cornea: Enhancement Using Drug-Loaded Contact Lenses and β-Cyclodextrin Complexation, and the Importance of Simulating Tear Irrigation

Microbial keratitis is a severe, sight-threatening condition caused by various pathogens. Eyedrops are the standard delivery modality for treating these disorders; however, blinking reflex, elevated tear production, and nasolacrimal drainage eliminate much of the instilled dose within a few seconds. Therefore, eyedrops must be applied repeatedly for prolonged periods. The present study aimed to probe more effective ocular delivery of chlorhexidine based upon drug-loaded hydrogel contact lenses and β-cyclodextrin (β-CD), while also determining the effect of constant irrigation with simulated tear fluid (STF) in in vitro experiments. Chlorhexidine digluconate (as 0.2 and 2% solutions, β-CD inclusion complexes, and loaded hydrogel contact lenses) were applied to enucleated porcine eyes as single or multiple 10 μL doses, or as drug-loaded contact lenses, with and without β-CD. The corneas were then excised and drug-extracted quantified by high-performance liquid chromatography (HPLC). The effect of constant irrigation by STF was evaluated to test the effect of increased tear production on corneal delivery. Potential antimicrobial activity of the delivered drug was also assessed. Results showed that drug-loaded contact lenses delivered the greatest amount of chlorhexidine into the cornea over a 24 h period, while the eyedrop solution comparator delivered the least. The β-CD significantly enhanced chlorhexidine delivery to the cornea from eyedrop solution, although contact lenses loaded with chlorhexidine-β-CD failed to enhance delivery. β-CD within the hydrogel matrix impeded drug release. Constant irrigation with STF significantly reduced the amount of drug delivered to the cornea in all cases. Chlorhexidine retained antimicrobial activity in all delivery methods. Hydrogel contact lenses loaded with chlorhexidine delivered significantly higher levels to the cornea compared to eyedrops, either multiple hourly doses or a single dose. They also offer reduced application, in particular, to a nonulcerated corneal infection. Finally, the importance of fully accounting for tear production in in vitro ocular delivery experiments was highlighted.

[Fungal keratitis after penetrating keratoplasty]

The article presents a case of fungal keratitis after penetrating keratoplasty (PKP). A 35-years old patient had previously undergone surgical removal of an intraocular foreign body and developed chronic keratouveitis and epithelial-endothelial corneal dystrophy. PKP and early postoperative period were uneventful. The patient was frequently monitored with anterior segment photos. Two weeks later, fungal keratitis occurred on the edge of the donor flap. Direct microscopic evaluation revealed fungus spores and filaments, but growth of fungi in culture was negative. Instillation of steroids and antibiotics was discontinued, specific therapy included fluconazole and amphotericin B. Despite the ongoing treatment, keratitis has repeatedly recurred, and infiltrates were scraped. Topical and systemic voriconazole was administered instead of fluconazole in combination with regular scarification. After 3 weeks of treatment with voriconazole, stable corneal epithelialization was achieved and the cornea has restored its transparency. During 1.5 years of the follow-up, keratitis did not reccur; sutures were removed, corrected visual acuity increased to 1.0. Patients who had undergone PKP are at risk of developing fungal keratitis. Frequent monitoring of such patients contributes to early diagnosis of infectious complications. In the absence of officinal antifungal eye drops, specialist has to supply the patient with ex tempore antimycotic agents and change the treatment according to its effectiveness in each specific case.

An Omics Approach to Diagnosing or Investigating Fungal Keratitis

Fungal keratitis (FK) is one of the most severe corneal infectious diseases. FK often leads to poor visual prognosis and thus requires accurate diagnosis. Conventional approaches, including clinical diagnoses, smears, and cultures, often fail to provide reliable diagnostic value. Omics approaches, such as those using genomic, metagenomic, and tear proteomic data sources, provide promising features for improving the diagnosis and monitoring the progression of FK. Genomic approaches are based mainly on detecting amplicons of ribosomal RNA genes, and internal transcribed spacers are gradually gaining popularity in clinical practices. A metagenomic approach based on 16S rRNA genes may help monitor the dynamic change of conjunctival microbiota associated with an FK event, whereas that based on shot-gun and 18S rRNA target enrichment sequencing could have the potential to diagnose FK using clinical samples. A tear proteomic approach may provide comprehensive information about ocular surface defense and injury during FK. Representative up- and down-regulated proteins during FK could also be used as biomarkers to determine the clinical course and develop a treatment strategy in different stages of FK. Consequently, a personalized tear proteomic approach will soon play a key role in FK management.

Altered spontaneous brain activity patterns in patients with corneal ulcer using amplitude of low-frequency fluctuation: An fMRI study

The aim of the present study was to investigate the altered spontaneous brain activity in patients with corneal ulcer (CU) through the amplitude of low-frequency fluctuation (ALFF) technique and the association with their visual performance. A total of 40 patients with CU and 40 healthy controls (HCs) matched for sex, age and educational level were enrolled. Resting-state functional magnetic resonance imaging (rs-fMRI) was performed to examine the probands. Spontaneous cerebral activity variations were investigated using the ALFF technique. The average ALFF values of the CU patients and the HCs were classified by utilizing receiver operating characteristic (ROC) curves. Contrary to HCs, the CU patients had significantly lower ALFF values in the left cerebellar anterior lobe, right middle frontal gyrus and left middle frontal gyrus, but higher ALFF values in the right cerebellar inferior lobe, left cerebellar inferior lobe, left inferior temporal gyrus, right fusiform gyrus, left superior frontal gyrus, right angular gyrus and bilateral superior frontal gyrus. ROC curve analysis of each brain region indicated that the accuracy of ALFF value specificity between the CU and HCs of the area under the curve was perfect. In conclusion, abnormal spontaneous activities were detected in numerous brain regions of CU patients, which may provide useful information for understanding the dysfunction of CU. These activity changes in brain regions may be used as effective clinical indicators for CU.

Evaluation of corneal cross-linking as adjuvant therapy for the management of fungal keratitis

PURPOSE

To evaluate the efficacy of corneal cross-linking (CXL) as adjuvant therapy for the treatment of fungal ulcerative keratitis.

METHODS

Forty-one patients with fungal ulcerative keratitis were recruited and assigned into two randomized controlled groups. These groups were treated with CXL combined with antifungal medications (CXL-M) or antifungal medications alone (M). The ulcers were assessed by slit-lamp biomicroscopy, slit-lamp images, in vivo confocal microscopy (IVCM), and anterior segment optical coherence tomography (AS-OCT). The patients were followed up before surgery/first visit (FV), 1 day after surgery, 1 and 2 weeks, and 1, 2, 3, 4, 5, and 6 months after surgery/FV.

RESULTS

In the cured patients, the area of corneal ulcers, the duration of ulcer healing, the time to non-observed fungal hyphae by IVCM, the number of antifungal medications, the frequency of administered medications, and the maximum ulcer depth decreased significantly after CXL (all P < 0.05) compared with the M group. There were no significant differences in either corneal thickness or epithelial thickness of ulcers after healing between 5 and 6 months after surgery in the CXL-M group, while these were increased significantly at 6 months compared with 5 months after FV in the M group (both P < 0.05).

CONCLUSIONS

In our study, CXL accelerated healing of the fungal ulcers, shortened the treatment duration, and minimized the need for medications and surgery. It appears that CXL is an effective procedure and adjuvant therapy for managing fungal keratitis.

Self-implantable double-layered micro-drug-reservoirs for efficient and controlled ocular drug delivery

Eye diseases and injuries impose a significant clinical problem worldwide. Safe and effective ocular drug delivery is, however, challenging due to the presence of ocular barriers. Here we report a strategy using an eye patch equipped with an array of detachable microneedles. These microneedles can penetrate the ocular surface tissue, and serve as implanted micro-reservoirs for controlled drug delivery. The biphasic drug release kinetics enabled by the double-layered micro-reservoirs largely enhances therapeutic efficacy. Using corneal neovascularization as the disease model, we show that delivery of an anti-angiogenic monoclonal antibody (DC101) by such eye patch produces ~90% reduction of neovascular area. Furthermore, quick release of an anti-inflammatory compound (diclofenac) followed by a sustained release of DC101 provides synergistic therapeutic outcome. The eye patch application is easy and minimally invasive to ensure good patient compliance. Such intraocular drug delivery strategy promises effective home-based treatment of many eye diseases.

Treatment for eye injuries and diseases is most efficient when delivered directly into the eye. Here, the authors developed a patient-friendly eye patch equipped with an array of detachable microneedles, through which drugs can be delivered through the cornea for an extended period of time.