Acanthamoeba keratitis: persistent organisms without inflammation after 1 year of topical chlorhexidine

Lactase can target cellular differentiation of Acanthamoeba castellanii belonging to the T4 genotype

The free living Acanthamoeba spp. are ubiquitous amoebae associated with potentially blinding disease known as Acanthamoeba keratitis (AK) and a fatal central nervous system infection granulomatous amoebic encephalitis (GAE). With the inherent ability of cellular differentiation, it can phenotypically transform to a dormant cyst form from an active trophozoite form. Acanthamoeba cysts are highly resistant to therapeutic agents as well as contact lens cleaning solutions. One way to tackle drug resistance against Acanthamoeba is by inhibiting the formation of cysts from trophozoites. The biochemical analysis showed that the major component of Acanthamoeba cyst wall is composed of carbohydrate moieties such as galactose and glucose. The disaccharide of galactose and glucose is lactose. In this study, we analyzed the potential of lactase enzyme to target carbohydrate moieties of cyst walls. Amoebicidal assessment showed that lactase was ineffective against trophozoite of A. castellanii but enhanced amoebicidal effects of chlorhexidine. The lactase enzyme did not show any toxicity against normal human keratinocyte cells (HaCaT) at the tested range. Hence, lactase can be used for further assessment for development of potential therapeutic agents in the management of Acanthamoeba infection as well as formulation of effective contact lens disinfectants.

Novel Map Biopsy Technique to Define the Extent of Infection Before Penetrating Keratoplasty for Acanthamoeba Keratitis

PURPOSE

The purpose of this study was to report a novel approach of prepenetrating keratoplasty (PKP) corneal map biopsies to define the extent of Acanthamoeba cyst infiltration in recalcitrant Acanthamoeba keratitis.

METHODS

Corneal map biopsies were performed 1 week before PKP. Four biopsies, 1 from each peripheral corneal quadrant, were obtained to delineate the extent of microscopic infection. Histological results of these map biopsies were used to determine the size and location of the subsequent PKP.

RESULTS

In our first case, map biopsies revealed Acanthamoeba cysts in 2 of the 4 biopsies. This led to an inferotemporally eccentric 8.5-mm PKP. The final histology report indicated that the closest resection margin was 0.08 mm. In our second case, the peripheral map biopsies were clear and an inferiorly eccentric 8.25-mm PKP was performed. The final histology report indicated that the closest resection margin was 2.3 mm. Both grafts have remained clear at 6 months postoperatively.

CONCLUSIONS

Map biopsies of the cornea can achieve total removal of the corneal tissues infested with Acanthamoeba cysts and prevent reinfection of the donor graft.

Amoebicidal activity of cationic carbosilane dendrons derived with 4-phenylbutyric acid against Acanthamoeba griffini and Acanthamoeba polyphaga trophozoites and cysts

Amoebae from the genus Acanthamoeba are important pathogens responsible for severe illnesses in humans such as Acanthamoeba keratitis and granulomatous amoebic encephalitis. In the last few decades, AK diagnoses have steadily increased. Most patients suffering from AK were contact lens users and the infection was related to poor hygiene. However, therapy is not yet well established, and treatments may last for several months due to resistance. Moreover, these treatments have been described to generate cytotoxicity. Therefore, there is an urgent need to develop new therapeutic strategies against AK. In this study, the amoebicidal activity of different generation cationic carbosilane dendrons derived with 4-phenylbutyric acid was demonstrated against Acanthamoeba polyphaga and Acanthamoeba griffini trophozoites and cysts. In addition, the combination of chlorhexidine digluconate and the most effective dendron (ArCO2G2(SNMe3I)4) showed an in vitro effect against Acanthamoeba trophozoites and cysts, reducing the minimal trophozoite amoebicidal concentration as well as concentrations with cysticidal activity.

In vitro activity of Camellia sinensis (green tea) against trophozoites and cysts of Acanthamoeba castellanii

The effect of Camellia sinensis (green tea) on the growth of Acanthamoeba castellanii trophozoites was examined using a microplate based-Sulforhodamine B (SRB) assay. C. sinensis hot and cold brews at 75% and 100% concentrations significantly inhibited the growth of trophozoites. We also examined the structural alterations in C. sinensis-treated trophozoites using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This analysis showed that C. sinensis compromised the cell membrane integrity and caused progressive destruction of trophozoites. C. sinensis also significantly inhibited the parasite's ability to form cysts in a dose-dependent manner and reduced the rate of excystation from cysts to trophozoites. C. sinensis exhibited low cytotoxic effects on primary corneal stromal cells. However, cytotoxicity was more pronounced in SV40-immortalized corneal epithelial cells. Chromatographic analysis showed that both hot and cold C. sinensis brews contained the same number and type of chemical compounds. This work demonstrated that C. sinensis has anti-acanthamoebic activity against trophozoite and cystic forms of A. castellanii. Further studies are warranted to identify the exact substances in C. sinensis that have the most potent anti-acanthamoebic effect.

Acanthamoeba Keratitis: Current Status and Urgent Research Priorities

Background:

First discovered in the early 1970s, Acanthamoeba keratitis has remained a major eye infection and presents a significant threat to the public health, especially in developing countries. The aim is to present a timely review of our current understanding of the advances made in this field in a comprehensible manner and includes novel concepts and provides clear directions for immediate research priorities.

Methods:

We undertook a search of bibliographic databases for peer-reviewed research literature and also summarized our published results in this field.

Results:

The present review focuses on novel diagnostic and therapeutic strategies in details which can provide access to management and treatment of Acanthamoeba keratitis. This coupled with the recently available genome sequence information together with high throughput genomics technology and innovative approaches should stimulate interest in the rational design of preventative and therapeutic measures. Current treatment of Acanthamoeba keratitis is problematic and often leads to infection recurrence. Better understanding of diagnosis, pathogenesis, pathophysiology and therapeutic regimens, would lead to novel strategies in treatment and prophylaxis.

The impact of vinegar on pathogenic Acanthamoeba astronyxis isolate

Acanthamoeba keratitis (AK) is a severe corneal disease that was reported by WHO as the second most common infectious cause of blindness after trachoma; contact lens wear is considered one of the main risk factors in its transmission. Thus, the treatment of AK is crucial but, the inability of medical agents to completely eradicate the resistant cyst, together with their toxic effects, suggest that new agents are needed. Vinegar has been known long ago as a simple and available disinfectant with antimicrobial effects, so the present study aimed to test the effect of different concentrations of vinegar solution on Acanthamoeba astronyxis isolate, along the period of 1 h in comparison to parasite and chlorhexidine controls. Post hoc test analysis revealed a highly significant difference between the vinegar-treated parasites and both controls, as regards the viable and non-viable mean cysts count. Vinegar concentration of 5% exhibited the highest mean of non-viable cysts along the time intervals, while the lowest was shown with 0.04% where also, no viable cysts were detected at 60 min. All tested concentrations behaved in a time-dependent manner. There was a positive correlation with a significant outcome between the different concentrations and the mean of the non-viable parasites along time. Transmission electron microscopy of treated cysts revealed corrugated altered cell wall with loss of ridges and detachment and shrinkage of content. Treated trophozoites showed flattening of the acanthopodia with thinned out plasma membrane and degenerated cytoplasmic content. The study highlighted the potential use of vinegar as an adjuvant in the prevention and treatment of AK.

Miltefosine and polyhexamethylene biguanide: a new drug combination for the treatment of Acanthamoeba keratitis

BACKGROUND

In this study, a series of compounds - miltefosine, polyhexamethylene biguanide, chlorhexidine and propamidine isethionate - and combinations of the latter three agents with miltefosine were prepared and used in a rat model for the topical treatment of Acanthamoeba keratitis.

METHODS

The corneas of rats were infected with Acanthamoeba hatchetti. On the fifth day, all corneas were microscopically examined in order to determine the grade of infections. Nine groups were then prepared: miltefosine (65.12 μg/mL); chlorhexidine (0.02%); polyhexamethylene biguanide (0.02%), propamidine isethionate (0.1%), miltefosine plus chlorhexidine, miltefosine plus polyhexamethylene biguanide; miltefosine plus propamidine isethionate; infected control; and a non-infected control group. The treatment was continued for 28 days. After the treatment, the corneas were excised and used for Acanthamoeba culture to investigate the presence of Acanthamoeba growth. For the determination of cytotoxicity of the drugs on L929 cells, colorimetric assays were performed.

RESULTS

The best treatment results were obtained from the polyhexamethylene biguanide plus miltefosine group; the ratio of fully recovered eyes was 28.4%. It was proven that the miltefosine-polyhexamethylene biguanide combination yielded the highest anti-acanthamoebal activity in that approximately 86% of the eyes were cleared from amoebae. The cytotoxicity values of the miltefosine and the control groups were compared with other groups and found to be statistically different (P < 0.05).

CONCLUSION

This in vivo study demonstrates that a miltefosine-polyhexamethylene biguanide combination is highly effective for the treatment of Acanthamoeba keratitis.

Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and application of statins as a novel effective therapeutic approach against Acanthamoeba infections

Acanthamoeba is an opportunistic pathogen in humans, whose infections most commonly manifest as Acanthamoeba keratitis or, more rarely, granulomatous amoebic encephalitis. Although there are many therapeutic options for the treatment of Acanthamoeba, they are generally lengthy and/or have limited efficacy. Therefore, there is a requirement for the identification, validation, and development of novel therapeutic targets against these pathogens. Recently, RNA interference (RNAi) has been widely used for these validation purposes and has proven to be a powerful tool for Acanthamoeba therapeutics. Ergosterol is one of the major sterols in the membrane of Acanthamoeba. 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is an enzyme that catalyzes the conversion of HMG-CoA to mevalonate, one of the precursors for the production of cholesterol in humans and ergosterol in plants, fungi, and protozoa. Statins are compounds which inhibit this enzyme and so are promising as chemotherapeutics. In order to validate whether this enzyme could be an interesting therapeutic target in Acanthamoeba, small interfering RNAs (siRNAs) against HMG-CoA were developed and used to evaluate the effects induced by the inhibition of Acanthamoeba HMG-CoA. It was found that HMG-CoA is a potential drug target in these pathogenic free-living amoebae, and various statins were evaluated in vitro against three clinical strains of Acanthamoeba by using a colorimetric assay, showing important activities against the tested strains. We conclude that the targeting of HMG-CoA and Acanthamoeba treatment using statins is a novel powerful treatment option against Acanthamoeba species in human disease.

Successful treatment of chronic stromal acanthamoeba keratitis with oral voriconazole monotherapy

PURPOSE

To describe the treatment of chronic stromal Acanthamoeba keratitis (AK) with oral voriconazole monotherapy.

METHODS

All cases of chronic stromal AK recalcitrant to traditional therapy subsequently treated with systemic voriconazole seen at the University of Illinois Eye and Ear Infirmary between June 2003 and July 2009 were reviewed for clinical presentation, clinical course, and outcome.

RESULTS

Three eyes of 2 patients were identified with culture-confirmed chronic stromal AK unresponsive to traditional antiacanthamoebal therapies, requiring topical corticosteroids to maintain corneal clarity. Oral voriconazole 200 mg twice daily achieved a rapid but transient reduction of inflammation and elimination of corticosteroid dependency but, in both patients, recrudesced approximately 6 weeks after its discontinuation. Subsequent repeated and/or extended use of oral voriconazole alone resulted in complete resolution ranging from 7 to 11 months off all medications with final best-corrected visual acuity ranging from 20/20 to 20/25.

CONCLUSIONS

Recalcitrant chronic Acanthamoeba stromal keratitis was successfully treated with extended systemic voriconazole administration with good preservation of vision. The clinical resolution of chronic stromal keratitis in our 2 cases suggests that voriconazole may have a larger role in the treatment of AK.

Functional dissection of adenylate cyclase R, an inducer of spore encapsulation

Cyclic AMP acting on protein kinase A controls sporulation and encystation in social and solitary amoebas. In Dictyostelium discoideum, adenylate cyclase R (ACR), is essential for spore encapsulation. In addition to its cyclase (AC) domain, ACR harbors seven transmembrane helices, a histidine kinase domain, and two receiver domains. We investigated the role of these domains in the regulation of AC activity. Expression of an ACR-YFP fusion protein in acr(-) cells rescued their sporulation defective phenotype and revealed that ACR is associated with the nuclear envelope and endoplasmic reticulum. Loss of the transmembrane helices (ΔTM) caused a 60% reduction of AC activity, but ΔTM-ACR still rescued the acr(-) phenotype. The isolated AC domain was properly expressed but inactive. Mutation of three essential ATP-binding residues in the histidine kinase domain did not affect the AC activity or phenotypic rescue. Mutation of the essential phosphoryl-accepting aspartate in receivers 1, 2, or both had only modest effects on AC activity and did not affect phenotypic rescue, indicating that AC activity is not critically regulated by phosphorelay. Remarkably, the dimerizing histidine phosphoacceptor subdomain, which in ACR lacks the canonical histidine for autophosphorylation, was essential for AC activity. Transformation of wild-type cells with an ACR allele (ΔCRA) that is truncated after this domain inhibited AC activity of endogenous ACR and replicated the acr(-) phenotype. Combined with the observation that the isolated AC domain was inactive, the dominant-negative effect of ΔCRA strongly suggests that the defunct phosphoacceptor domain acquired a novel role in enforcing dimerization of the AC domain.

Clinical experience with Acanthamoeba keratitis at the cole eye institute, 1999-2008

PURPOSE

To review the clinical presentations, risk factors, medical and surgical management, and outcomes of patients with Acanthamoeba keratitis (AK).

METHODS

Retrospective review of laboratory and medical records of all patients suspected of having AK from January 1999 through May 2008 at Cole Eye Institute.

RESULTS

Twenty-nine eyes of 26 patients were identified as having either culture- or tissue-proven AK or presumed AK based on clinical examination and complete response to full course of treatment. The most common risk factors identified for AK were history of contact lens wear (89.7%) and exposure to contaminated water (27.6%). Clinical presentations included early AK (superficial disease) in 37.9% of eyes or late AK (deep stromal disease with or without epithelial disease) in 62.1% of eyes. All early AK cases had best-corrected visual acuity of 20/30 or better at last follow-up, whereas only 55.6% of late AK cases achieved 20/30 or better. Eight eyes underwent penetrating keratoplasty. One patient demonstrated viable-appearing cysts in the corneal button, despite 15 months of maximum medical treatment and 5 months off all medical treatments. Over the nearly 10-year period, there was no significant increase in the number of cases seen each year.

CONCLUSIONS

The most common risk factor for AK continues to be contact lens wear. AK requires prolonged and intense treatment, although good final visual acuity can be achieved. Potentially viable Acanthamoeba cysts can still persist in a noninflamed cornea after extensive medical therapy, supporting the practice that corneal transplantation after presumably resolved cases of AK should be followed with vigilance to detect the earliest signs of recurrent disease.

Evaluation of three different methods to establish animal models of Acanthamoeba keratitis

PURPOSE

To produce animal models of Acanthamoeba keratitis and to evaluate the advantages and adaptation range of each of the three methods employed.

MATERIALS AND METHODS

Mice and Wistar rats in three groups of 15 rats and 15 mice each were used to establish the models. Right corneas in group A were scratched and challenged with Acanthamoeba. Those in group B were scratched and covered with contact lenses incubated with Acanthamoeba. Those in group C received an intrastromal injection of Acanthamoeba. Five rats and 5 mice in each group were used for histopathological investigations and the other 10 in each group were used for clinical evaluation. The models were evaluated by slit lamp examination, microscopic examination and culture of corneal scrapings, HE staining of corneal sections, and pathological scoring of the infections.

RESULTS

Four rats and 6 mice in group A, 7 rats and 8 mice in group B, and 10 rats and 10 mice in group C developed typical Acanthamoeba keratitis.

CONCLUSION

Corneal scratching alone has the lowest infection rate, while scratching and then covering with contaminated contact lenses has a moderate rate of infection and most closely mimics what happens in most human infections. Intrastromal injection of Acanthamoeba gives a much higher infection rate and more severe Acanthamoeba keratitis.

Treatment with voriconazole in 3 eyes with resistant Acanthamoeba keratitis

PURPOSE

To report the use of topical voriconazole 1% (Vfend; Pfizer Inc, New York, New York, USA) ophthalmic solution for Acanthamoeba keratitis (AK) resistant to treatment with chlorhexidine (PerioChip; Dexel Pharma Technologies, Jerusalem, Israel).

DESIGN

Retrospective case series.

METHODS

Three eyes of 2 patients with culture-proven AK were treated at a tertiary care institution, and their charts were reviewed. Topical voriconazole 1% was instituted as second-line treatment for AK unresponsive to standard treatment with chlorhexidine and hexamidine. Treatment with voriconazole 1% was started at 1-hour intervals. Improvement was assessed and defined by absence of clinical signs of active infection and visual improvement.

RESULTS

One patient with unilateral AK and 1 patient with bilateral AK who remained culture-positive for Acanthamoeba despite ongoing treatment with chlorhexidine and hexamidine were treated with voriconazole 1% topical solution as an adjuvant. Both patients were contact lens wearers. Of 3 eyes additionally treated with voriconazole, 2 eyes had clinical resolution of disease. One eye demonstrated recurrent disease after penetrating keratoplasty that resolved after intrastromal injection of voriconazole.

CONCLUSIONS

We report the use of topical and intrastromal voriconazole in successfully treating AK in cases of chlorhexidine- and hexamidine-resistant Acanthamoeba. Voriconazole may be a promising adjuvant agent in treating AK.

Differential effects of α-helical and β-hairpin antimicrobial peptides against Acanthamoeba castellanii

In this work we evaluated the ability of different types of antimicrobial peptides to promote permeabilization and growth inhibition of Acanthamoeba castellanii trophozoites, which cause eye keratitis. We used cationic α-helical peptides P5 and P6, corresponding to the N-terminus of the pore-forming protein from Triatoma infestans, a blood-sucking insect, and a β-hairpin amphipathic molecule (gomesin), of the spider Acanthoscurria gomesiana haemocytes. A. castellanii permeabilization was obtained after 1 h incubation with micromolar concentrations of both types of peptides. While permeabilization induced by gomesin increased with longer incubations, P5 permeabilization did not increase with time and occurred at doses that are more toxic for SIRC cells. P5, however, at doses below the critical dose used to kill rabbit corneal cells was quite effective in promoting growth inhibition. Similarly, P5 was more effective when serine protease inhibitor was added simultaneously to the permeabilization assay. High performance chromatography followed by mass spectrometry analysis confirmed that, in contrast to gomesin, P5 is hydrolysed by A. castellanii culture supernatants. We conclude that the use of antimicrobial peptides to treat A. castellanii infections requires the search of more specific peptides that are resistant to proteolysis.

The potential pathogenicity of chlorhexidine-sensitive Acanthamoeba strains isolated from contact lens cases from asymptomatic individuals in Tenerife, Canary Islands, Spain

Pathogenic strains of the genus Acanthamoeba are causative agents of a serious sight-threatening infection of the eye known as Acanthamoeba keratitis. The prevalence of this infection has risen in the past 20 years, mainly due to the increase in number of contact lens wearers. In this study, the prevalence of Acanthamoeba in a risk group constituted by asymptomatic contact lens wearers from Tenerife, Canary Islands, Spain, was evaluated. Contact lenses and contact lens cases were analysed for the presence of Acanthamoeba isolates. The isolates' genotypes were also determined after rDNA sequencing. The pathogenic potential of the isolated strains was subsequently established using previously described molecular and biochemical assays, which allowed the selection of three strains with high pathogenic potential. Furthermore, the sensitivity of these isolates against two standard drugs, ciprofloxacin and chlorhexidine, was analysed. As the three selected strains were sensitive to chlorhexidine, its activity and IC(50) were evaluated. Chlorhexidine was found to be active against these strains and the obtained IC(50) values were compared to the concentrations of this drug present in contact lens maintenance solutions. It was observed that the measured IC(50) was higher than the concentration found in these maintenance solutions. Therefore, the ineffectiveness of chlorhexidine-containing contact lens maintenance solutions against potentially pathogenic strains of Acanthamoeba is demonstrated in this study.