Use of collagen shields containing amphotericin B in the treatment of experimental Candida albicans-induced keratomycosis in rabbits

MicroRNA-122 ameliorates corneal allograft rejection through the downregulation of its target CPEB1

Transplant rejection is a major cause of corneal transplantation failure. MicroRNAs (miRNAs) are a family of small RNAs that regulates gene expression in a sequence-specific manner. miRNAs have recently been shown to have important roles in human organ transplantation, but reports of miRNAs directly associated with corneal transplantation rejection remain limited. To investigate the role of miRNAs during corneal allograft rejection, we established a mouse penetrating keratoplasty model and used microarrays to screen for differentially expressed miRNAs. Our results revealed that the expression of miR-122 was significantly decreased in the allogeneic group. Consistent with this result, the expression of cytoplasmic polyadenylation element-binding protein-1 (CPEB1), a direct target of miR-122, was significantly increased. Further analysis demonstrated that miR-122 inhibited inflammatory cytokine-induced apoptosis in corneal keratocytes through the downregulation of its target CPEB1. We also found that increased miR-122 expression significantly reduced the risk of corneal transplantation rejection. Thus, our results indicate that miR-122 is an important miRNA associated with corneal graft rejection and can be used as a therapeutic target for the prevention of immune rejection after keratoplasty.

Development and Effects of FTY720 Ophthalmic Solution on Corneal Allograft Survival

Fingolimod (FTY720), a novel class of sphingosine 1-phosphate receptor modulators, has received special interest among ophthalmologists, particularly given that oral administration of FTY720 has proven to effectively treat corneal graft rejection in animal models. However, no studies have examined the performance of FTY720 as an ophthalmic solution in reducing corneal rejection in high-risk corneal rejection models, and the stability and ocular irritation profile of FTY720 ophthalmic solution are also unknown. Thus, we developed 0.1%, 0.2% and 0.5% FTY720 ophthalmic solutions and evaluated their chemical stabilities under various storage conditions with high- performance liquid chromatography. To investigate the ocular irritancy of the FTY720 ophthalmic solution, New Zealand albino rabbits were subjected to the Draize test. Furthermore, classic, well-established rat allogenic penetrating keratoplasty models were used to investigate the anti-rejection efficacy of the tested FTY720 ophthalmic solutions. We found that the non-irritating 0.5% FTY720 ophthalmic solution could prolong corneal allograft survival in rats with significant efficacy for about one month. Furthermore, no significant concentration changes occurred in any of the types of FTY720 ophthalmic solutions within three months. These results revealed crucial profiles of FTY720 ophthalmic solutions and warrant further investigation and optimization of FTY720 in the anti-rejection therapy after keratoplasty.

Efficacy Profile of Intracameral Amphotericin B. The Often Forgotten Step

PURPOSE

The objectives of this study were to assess visual and structural outcomes in mycotic keratitis after conventional treatment (topical and systemic antifungals) and intracameral amphotericin B (ICAMB), and to evaluate any complications.

DESIGN

This was a prospective, nonrandomized, nonblinded interventional study.

METHODS

This study was conducted on 104 eyes of 104 patients with fungal corneal ulcers. Patients were categorized into 2 groups: group A, who received conventional topical and systemic antifungal medications, and group B, who received ICAMB in the dose of 5 to 10 μg in 1 mL of 5% dextrose. Response to treatment was evaluated. Results of the 2 groups were compared with appropriate statistical indices.

RESULTS

The mean final visual acuity in patients in group B receiving ICAMB was 1.22 ± 0.31 logMAR units. The improvement in mean visual acuity was 1.40 ± 0.2 logMAR units. In group A, mean visual outcome was 1.25 ± 0.73 logMAR units. There was an improvement by 0.55 ± 0.30 logMAR units. Healing with varying degrees of opacification occurred in a significant number of patients (81.48%) treated with ICAMB as compared with conventional treatment (Z = 2.24, P < 0.05). Complications, such as sloughing, occurred in significantly fewer patients treated with ICAMB as compared with conventional treatment (Z = 2.29, P < 0.05).

CONCLUSIONS

In cases of keratomycosis where response to local and systemic antifungal treatment is not evident after 7 days, ICAMB can be safely administered to prevent the progression of ulcers and the development of complications.

Self-aggregated nanoparticles based on amphiphilic poly(lactic acid)-grafted-chitosan copolymer for ocular delivery of amphotericin B

Background

The purpose of this study was to develop a self-aggregated nanoparticulate vehicle using an amphiphilic poly(lactic acid)-grafted-chitosan (PLA-g-CS) copolymer and to evaluate its potential for ocular delivery of amphotericin B.

Methods

A PLA-g-CS copolymer was synthesized via a “protection-graft-deprotection” procedure and its structure was confirmed by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, and X-ray diffraction spectra. Amphotericin B-loaded nanoparticles based on PLA-g-CS (AmB/PLA-g-CS) were prepared by the dialysis method and characterized for particle size, zeta potential, and encapsulation efficiency. Studies of these AmB/PLA-g-CS nanoparticles, including their mucoadhesive strength, drug release properties, antifungal activity, ocular irritation, ocular pharmacokinetics, and corneal penetration were performed in vitro and in vivo.

Results

Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, and X-ray diffraction spectra showed that the PLA chains were successfully grafted onto chitosan molecules and that crystallization of chitosan was suppressed. The self-aggregated PLA-g-CS nanoparticles had a core-shell structure with an average particle size of approximately 200 nm and zeta potentials higher than 30 mV. Amphotericin B was incorporated into the hydrophobic core of the nanoparticles with high encapsulation efficiency. Sustained drug release from the nanoparticles was observed in vitro. The ocular irritation study showed no sign of irritation after instillation of the PLA-g-CS nanoparticles into rabbit eyes. The minimal inhibitory concentration of the AmB/PLA-g-CS nanoparticles showed antifungal activity similar to that of free amphotericin B against Candida albicans. The in vivo ocular pharmacokinetic study suggested that the PLA-g-CS nanoparticles have the advantage of prolonging residence time at the ocular surface. The corneal penetration study showed that the PLA-g-CS nanoparticles could penetrate into the cornea.

Conclusion

Our results suggest that this nanoparticulate vehicle based on a PLA-g-CS copolymer might be a promising system for effective ocular delivery of amphotericin B.

Corneal Graft Rejection

Penetrating keratoplasty is the most widely practiced type of transplantation in humans. Irreversible immune rejection of the transplanted cornea is the major cause of human allograft failure in the intermediate and late postoperative period. This immunological process causes reversible or irreversible damage to the grafted cornea in several cases despite the use of intensive immunosuppressive therapy. Corneal graft rejection comprises a sequence of complex immune responses that involves the recognition of the foreign histocompatibility antigens of the corneal graft by the host's immune system, leading to the initiation of the immune response cascade. An efferent immune response is mounted by the host immune system against these foreign antigens culminating in rejection and graft decompensation in irreversible cases. A variety of donor- and host-related risk factors contribute to the corneal rejection episode. Epithelial rejection, chronic stromal rejection, hyperacute rejection, and endothelial rejection constitute the several different types of corneal graft rejection that might occur in isolation or in conjunction. Corneal graft failure subsequent to graft rejection remains an important cause of blindness and hence the need for developing new strategies for suppressing graft rejection is colossal. New systemic pharmacological interventions recommended in corneal transplantation need further evaluation and detailed guidelines. Two factors, prevention and management, are of significant importance among all aspects of immunological graft rejection. Preventive aspects begin with the recipient selection, spread through donor antigenic activity, and end with meticulous surgery. Prevention of corneal graft rejection lies with reduction of the donor antigenic tissue load, minimizing host and donor incompatibility by tissue matching and suppressing the host immune response. Management of corneal graft rejection consists of early detection and aggressive therapy with corticosteroids. Corticosteroid therapy, both topical and systemic, is the mainstay of management. Addition of immunosuppressive to the treatment regimen helps in quick and long term recovery. Knowledge of the immunopathogenesis of graft rejection may allow a better understanding of the immunological process thus helping in its prevention, early detection and management.

Current perspectives on ophthalmic mycoses

Fungi may infect the cornea, orbit and other ocular structures. Species of Fusarium, Aspergillus, Candida, dematiaceous fungi, and Scedosporium predominate. Diagnosis is aided by recognition of typical clinical features and by direct microscopic detection of fungi in scrapes, biopsy specimens, and other samples. Culture confirms the diagnosis. Histopathological, immunohistochemical, or DNA-based tests may also be needed. Pathogenesis involves agent (invasiveness, toxigenicity) and host factors. Specific antifungal therapy is instituted as soon as the diagnosis is made. Amphotericin B by various routes is the mainstay of treatment for life-threatening and severe ophthalmic mycoses. Topical natamycin is usually the first choice for filamentous fungal keratitis, and topical amphotericin B is the first choice for yeast keratitis. Increasingly, the triazoles itraconazole and fluconazole are being evaluated as therapeutic options in ophthalmic mycoses. Medical therapy alone does not usually suffice for invasive fungal orbital infections, scleritis, and keratitis due to Fusarium spp., Lasiodiplodia theobromae, and Pythium insidiosum. Surgical debridement is essential in orbital infections, while various surgical procedures may be required for other infections not responding to medical therapy. Corticosteroids are contraindicated in most ophthalmic mycoses; therefore, other methods are being sought to control inflammatory tissue damage. Fungal infections following ophthalmic surgical procedures, in patients with AIDS, and due to use of various ocular biomaterials are unique subsets of ophthalmic mycoses. Future research needs to focus on the development of rapid, species-specific diagnostic aids, broad-spectrum fungicidal compounds that are active by various routes, and therapeutic modalities which curtail the harmful effects of fungus- and host tissue-derived factors.

Collagen corneal shields

Collagen corneal shields were developed as a corneal bandage lens and are currently indicated for ocular surface protection following surgery and in traumatic and nontraumatic corneal conditions. Collagen shields are manufactured from porcine or bovine collagen and three different collagen shields are currently available with dissolution times of 12, 24, and 72 hours. The theoretical, experimental, and clinical evidence supports a role for collagen corneal shields as a drug delivery device and in the promotion of epithelial and stromal healing. Presoaking the collagen shield in a pharmacological agent with adjunctive topical treatment represents the most efficacious method of utilizing collagen shields for drug delivery. In microbial keratitis collagen shields can enhance drug delivery, promote epithelial and stromal healing, neutralize collagenases, and reduce corneal inflammation. This review will examine the evidence that supports the role of collagen shields in drug delivery and corneal wound healing. Despite a large volume of experimental (animal) work, studies on human subjects, particularly randomized controlled trials, are lacking. The authors are advocating the reassessment of the application and benefits of corneal collagen shields to clinical practice.

Intracameral amphotericin B: initial experience in severe keratomycosis

PURPOSE

Fungal keratitis is a significant cause of ocular morbidity in India. The most commonly implicated fungi are Aspergillus spp. Patients often present with hypopyon, which usually contains fungal elements. The treatment is difficult owing to poor intraocular penetration of most available antifungal agents. This study evaluated the results of intracameral injection of amphotericin B in natamycin resistant cases of severe keratomycosis.

METHODS

Three patients of culture proven Aspergillus flavus corneal ulcer with hypopyon not responding to topical natamycin 5%, amphotericin B 0.15%, and oral itraconazole were administered intracameral amphotericin B. The first case received 7.5 microg in 0.1 mL followed by two subsequent injections of 10 microg in 0.1 mL each, the second case received two injections of 10 microg in 0.1 mL, and the third patient received a single dose of 10 microg in 0.1 mL. Culture of the aqueous sample also grew A. flavus in all three cases.

RESULTS

All three cases responded favorably, with the ulcer and hypopyon clearing completely. There was no clinical evidence of corneal or lenticular toxicity in any patient.

CONCLUSIONS

Intracameral amphotericin B may be a useful modality in the treatment of severe keratomycosis not responding to topical natamycin. It ensures adequate drug delivery into the anterior chamber and may be especially useful to avoid surgical intervention in the acute stage of the disease.

Keratomycosis after cataract surgery

PURPOSE

To evaluate cases and results of keratomycosis that developed after cataract surgery.

SETTING

Hospital de Guipúzcoa, San Sebastián, Spain.

METHODS

This retrospective study comprised 8 patients who developed keratomycosis soon after cataract surgery.

RESULTS

Culture analysis revealed 7 cases of Aspergillus fumigatus and 1 of Aspergillus flavus. After medical treatment with antifungal agents, 6 cases resolved and 2 required evisceration.

CONCLUSIONS

The presence of fungi in corneal ulcers that develop after cataract surgery should be considered. Initiation of early treatment determines the prognosis. Among the therapeutic options, collagen shields soaked in amphotericin B may be effective.

Efficacious topical treatment for murine cutaneous leishmaniasis with ethanolic formulations of amphotericin B

The goal of the present study was to evaluate the antileishmanial effects of topically applied lipid-based formulations containing amphotericin B (AmB) in CBA mice as a model for human cutaneous leishmaniasis. Such treatment, if efficacious, is expected to be superior to systemic treatments since, by acting in a localized manner, it will require lower, and therefore less toxic, drug dosages. Three preparations of AmB complexed to polar lipids were tested: Fungizone (mixed micelles composed of AmB and deoxycholate), Amphocil (AmB and cholesteryl sulfate complex), and ABPLC (AmB and phospholipid complex). All these formulations killed parasites in vitro with similar efficacies but were ineffective when they were applied topically. However, Amphocil and ABPLC, but not Fungizone, when dispersed in an aqueous solution containing 5 to 25% ethanol, induced a statistically significant improvement in lesion size from week 2 or 3 onward (a total of 15 mg of AmB per kg of body weight was applied over 3 weeks). AmB biodistribution measurements following topical application of Amphocil, determined by high-pressure liquid chromatography, showed that AmB was detectable in the skin but not in the internal organs. Application of at least 10 times more drug was necessary to obtain detectable levels of AmB in the internal organs. After application of therapeutic doses of ABPLC, very low levels of AmB were detected in the internal organs. These experiments show for the first time that AmB administered topically as a complex either with cholesteryl sulfate or with phospholipids and in the presence of ethanol can penetrate the skin and kill sensitive organisms in a localized manner by using very low total drug concentrations.

Treatment of fungal corneal ulcers with amphotericin B ointment

PURPOSE

To report two patients with severe fungal corneal ulcers who were treated successfully with topical amphotericin B ointment.

METHODS

Two eyes of two patients developed corneal ulcers and hypopyon after corneal foreign body removal. Aspergillus fumigatus and Fusarium solani were isolated in Patients 1 and 2, respectively. By antifungal susceptibility testing, amphotericin B was shown to have the lowest minimal inhibitory concentration.

RESULT

Topical administration of amphotericin B ointment resulted in dramatic improvement in fungal corneal ulcers.

CONCLUSIONS

Antifungal susceptibility tests may aid with selection of antifungal agents. Amphotericin B ointment is one of the promising therapies for keratomycosis caused by antimycotic-resistant fungi.

Impregnation of collagen corneal shields with liposomes: uptake and release of hydrophilic and lipophilic marker substances

PURPOSE

Liposomes and collagen corneal shields (CCS) have been used as ophthalmic drug delivery devices. With regard to a possibly combined application, we studied the effects of surface charge and bilayer fluidity of liposomes on their uptake and release by CCS.

METHODS

12-hours-CCS were soaked in large unilamellar liposomes, which had been labelled with 4,5-carboxyfluorescein (CF) and N-(lissamine rhodamine B sulfonyl)-diacyl-phosphatidylethanolamine (PE-RhB) in the aqueous space and in the liposome bilayer, respectively. Released fluorophores were determined fluorometrically in the elution buffer at intervals from 1 to 240 min after immersion.

RESULTS

The CF concentration in the CCS soaked in a CF solution was two to seven times higher than immersion in the liposome suspensions. Among those, the negatively charged, cholesterol-containing preparation led to the highest CF concentration in the CCS. The PE-RhB concentration was highest after soaking the CCS in neutral, cholesterol-free liposomes. All types of liposomes were found inside the CCS by freeze fracture electron microscopy. The release kinetics data indicate a first order release. More than 90% of CF was released by the CCS within the first 30 min. This was equal after soaking the CCS in the CF solution or in liposomes. With DOPC-liposomes, the maximal release was already attained after 10 min. In general, the differences in the release kinetics of both hydrophilic and lipophilic markers, obtained by the various liposome types were small.

CONCLUSIONS

Our results indicate that surface charge and bilayer fluidity are of minor importance for the interaction with collagen corneal shields. However, since the release kinetics of a liposome-encapsulated hydrophilic or lipophilic substance are similar to the release of a non-encapsulated drug, the combination of liposomes with collagen shields may be useful mainly with respect to the encapsulation of drugs which do not penetrate the ocular surface as well as to prolong corneal contact time of the liposomes.