Medical interventions for acanthamoeba keratitis

Nitric oxide: an old drug but with new horizons in ophthalmology-a narrative review

Background and Objective

Based on basic knowledge and prior research on nitric oxide (NO), the potential of NO for treating eye diseases is reviewed, and the possibility of NO-based eye drops in clinical practice and the future potential of NO in ophthalmology are discussed.

Methods

A PubMed search was performed for English-language original reports and reviews using the following key words: nitric oxide, eye, ocular, and drug.

Key Content and Findings

NO is synthesized in the human body by NO synthase (NOS) from L-arginine or through enzyme-dependent reduction of dietary nitrate. Three types of NOS (eNOS, nNOS, and iNOS) are abundantly expressed in the eye under normal physiologic or pathologic conditions. The biological effect of NO in the eye is dose dependent. Low intraocular NO concentrations, produced by eNOS or nNOS, have various cellular effects, including vasodilation, intraocular pressure (IOP) regulation, and neuroprotection. iNOS induced under pathologic ocular conditions produces high NO concentrations in the local environment and mediates tissue inflammation, ocular cell apoptosis, and neurodegeneration. In particular, increased iNOS has been reported in glaucoma and retinal ischemic or degenerative diseases. NO plays a vital role in ocular injury. NO can facilitate ocular surface wound healing while eradicating pathogens such as bacteria and Acanthamoeba in chemical burns or infectious keratitis. Furthermore, NO has antifibrotic activity via the cyclic guanosine monophosphate (cGMP) signaling pathway. NO causes smooth muscle relaxation, which can be used to inhibit myopia progression in children. NO can be a stem cell modulator and may help in treating ocular stem cell disorders.

Conclusions

Because of its diverse biologic effects, NO can be a key player in regulating ocular inflammation in various ocular diseases, aiding ocular surface wound healing, controlling IOP in glaucoma, alleviating retinal disease, and suppressing myopia progression. Although there remain limitations to the effective use of highly unstable state, gaseous NO, the role of NO in the field of ophthalmology can be greatly expanded through the development of novel NO donors and effective delivery platforms.

Assessment of genotypes, endosymbionts and clinical characteristics of Acanthamoeba recovered from ocular infection

Introduction

Acanthamoeba is an emerging pathogen, infamous for its resilience against antiprotozoal compounds, disinfectants and harsh environments. It is known to cause keratitis, a sight-threatening, painful and difficult to treat corneal infection which is often reported among contact lens wearers and patients with ocular trauma. Acanthamoeba comprises over 24 species and currently 23 genotypes (T1-T23) have been identified.

Aims

This retrospective study was designed to examine the Acanthamoeba species and genotypes recovered from patients with Acanthamoeba keratitis (AK), determine the presence of endosymbionts in ocular isolates of Acanthamoeba and review the clinical presentations.

Methodology

Thirteen culture-confirmed AK patients treated in a tertiary eye care facility in Hyderabad, India from February to October 2020 were included in this study. The clinical manifestations, medications and visual outcomes of all patients were obtained from medical records. The Acanthamoeba isolates were identified by sequencing the ribosomal nuclear subunit (rns) gene. Acanthamoeba isolates were assessed for the presence of bacterial or fungal endosymbionts using molecular assays, PCR and fluorescence in situ hybridization (FISH).

Results

The mean age of the patients was 33 years (SD ± 17.4; 95% CI 22.5 to 43.5 years). Six (46.2%) cases had AK associated risk factors; four patients had ocular trauma and two were contact lens wearers. A. culbertsoni (6/13, 46.2%) was the most common species, followed by A. polyphaga and A. triangularis. Most of the isolates (12/13) belonged to genotype T4 and one was a T12; three sub-clusters T4A, T4B, and T4F were identified within the T4 genotype. There was no significant association between Acanthamoeba types and clinical outcomes. Eight (61.5%) isolates harboured intracellular bacteria and one contained Malassezia restricta. The presence of intracellular microbes was associated with a higher proportion of stromal infiltrates (88.9%, 8/9), epithelial defect (55.6%, 5/9) and hypopyon (55.6%, 5/9) compared to 50% (2/4), 25% (1/4) and 25% (1/4) AK cases without intracellular microbes, respectively.

Conclusions

Genotype T4 was the predominant isolate in southern India. This is the second report of T12 genotype identified from AK patient in India, which is rarely reported worldwide. The majority of the Acanthamoeba clinical isolates in this study harboured intracellular microbes, which may impact clinical characteristics of AK.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07741-4.

In vitro anti-Acanthamoeba activity of the commercial chitosan and nano-chitosan against pathogenic Acanthamoeba genotype T4

Acanthamoeba keratitis (AK) is a rare but serious infection of the eye and can lead to blindness. The effective and safe medical therapy remains unclear for AK until present. Antimicrobial activity and biological characteristic of chitosan encourage screening of it against Acanthamoeba. Thus, in vitro anti-amoebic activities of commercial chitosan and nano-chitosan were tested on pathogenic Acanthamoeba genotype T4, a causative agent of human AK. The Acanthamoeba spp. was isolated from the keratitis patient. The Acanthamoeba genotype T4 was approved using PCR method followed by sequencing technique. Chitosan nanoparticles was prepared using ionic gelation method and characterized by their physicochemical properties. In the present study, the in vitro activity of serial dilutions (12.5, 25, 50, 100, and 200 µL/mL) of commercial chitosan and nano-chitosan were evaluated against Acanthamoeba trophozoites and cysts. The finding of nano-chitosan particle size by DLS was 118 nm with a PDI of about 0.134. Zeta potential value was found to be 42.7 mV. The obtained results showed that the tested chitosan and nano-chitosan presented anti-amoebic activities dependent to time and concentration. The inhibitory effect of the chitosan and nano-chitosan is enhanced by increasing the concentration and incubation time. The inhibitory effect of nano-chitosan on both trophozoites and cyst was more than chitosan. According to the results, nano-chitosan shows the potent activity against Acanthamoeba T4 and could be used for the development of novel and safe therapeutic approaches in the future.

Current understanding and therapeutic management of contact lens associated sterile corneal infiltrates and microbial keratitis

Contact lenses are widely prescribed in clinical practice with multiple applications and advantages. However, contact lenses can be associated with various complications which range from innocuous to severe. Clinicians thus not only need to possess the ability to prescribe the most appropriate contact lenses for each individual patient but also be able to recognise and manage any associated complications. This review examines the existing literature on the management of corneal infiltrative events associated with soft contact lenses, including microbial keratitis, particularly in the context of practising in Australia. The definitions and diagnosis of corneal infiltrative events, as well as the current understanding of their aetiologies, will be explored. The various aspects of a successful management will be discussed, including the applications of therapeutic agents such as antimicrobial and anti-inflammatory agents, the role of microbiological investigations, and strategies to improve long-term prognosis. The currently available evidence supporting management options will be presented, highlighting the relative abundance of high-level evidence on management protocols, antimicrobial selection and treatment duration for microbial keratitis; and the relative paucity of studies and trials for sterile corneal infiltrative events, despite this condition being much more commonly encountered in clinical practice.

Challenges in Acanthamoeba Keratitis: A Review

To review challenges in the diagnosis and management of Acanthamoeba keratitis (AK), along with prognostic factors, in order to help ophthalmologists avoid misdiagnosis, protracted treatment periods, and long-term negative sequelae, with an overarching goal of improving patient outcomes and quality of life, we examined AK studies published between January 1998 and December 2019. All manuscripts describing clinical manifestations, diagnosis, treatment, prognosis, and challenges in short- and long-term management were included. The diagnosis of AK is often challenging. An increased time between symptom onset and the initiation of appropriate therapy is associated with poorer visual outcomes. The timely initiation of standardized antiamoebic therapies improves visual outcomes, decreases the duration of treatment, and reduces the chances of needing surgical intervention. In clinical practice, AK diagnosis is often missed or delayed, leading to poorer final visual outcomes and a negative impact on patient morbidity and quality of life.

Effectiveness and Safety of Topical Chlorhexidine and Vitamin E TPGS in the Treatment of Acanthamoeba Keratitis: A Survey on 29 Cases

This study aimed to test the effectiveness of a solution of chlorhexidine (CHX) and D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) in the treatment of Acanthamoeba keratitis (AK) via a prospective, interventional case series study. Twenty-nine consecutive patients with AK were enrolled. At baseline, best-corrected visual acuity (BCVA), slit lamp examination, confocal microscopy, and polymerase chain reaction (PCR) were performed. Topical therapy with CHX 0.02% and VE-TPGS 0.2% was administered hourly/24 h for the first day, hourly in the daytime for the next three days, and finally, every two hours in the daytime up to one month. BCVA and ocular inflammation were recorded after two weeks, four weeks, and three months from baseline. Mean logMAR BCVA significantly improved at two weeks (0.78) compared to baseline (1.76), remaining stable over time (0.80 at four weeks, 0.77 at three months). Ocular inflammation improved in 14 eyes at 2 weeks, with further slow improvements in all cases. At three months, no patient had signs of corneal inflammation. The presence of corneal scars was first recorded at the two-week follow-up, with an enlargement at the four-week follow-up. At the three-month follow-up, 19 eyes still showed corneal opacities. In conclusion, the tested solution was shown to be effective for the treatment of AK. Furthermore, it might represent a good first-line treatment.

Reliability of the Evidence Addressing Treatment of Corneal Diseases: A Summary of Systematic Reviews

Importance

Patient care should be informed by clinical practice guidelines, which in turn should be informed by evidence from reliable systematic reviews. The American Academy of Ophthalmology is updating its Preferred Practice Patterns (PPPs) for the management of the following 6 corneal diseases: bacterial keratitis, blepharitis, conjunctivitis, corneal ectasia, corneal edema and opacification, and dry eye syndrome.

Objective

To summarize the reliability of the existing systematic reviews addressing interventions for corneal diseases.

Data Source

The Cochrane Eyes and Vision US Satellite database.

Study Selection

In this study of published systematic reviews from 1997 to 2017 (median, 2014), the Cochrane Eyes and Vision US Satellite database was searched for systematic reviews evaluating interventions for the management of any corneal disease, combining eyes and vision keywords and controlled vocabulary terms with a validated search filter.

Data Extraction and Synthesis

The study classified systematic reviews as reliable when each of the following 5 criteria were met: the systematic review specified eligibility criteria for inclusion of studies, conducted a comprehensive literature search for studies, assessed risk of bias of the individual included studies, used appropriate methods for quantitative syntheses (meta-analysis) (only assessed if meta-analysis was performed), and had conclusions that were supported by the results of the systematic review. They were classified as unreliable if at least 1 criterion was not met.

Main Outcomes and Measures

The proportion of systematic reviews that were reliable and the reasons for unreliability.

Results

This study identified 98 systematic reviews that addressed interventions for 15 corneal diseases. Thirty-three of 98 systematic reviews (34%) were classified as unreliable. The most frequent reasons for unreliability were that the systematic review did not conduct a comprehensive literature search for studies (22 of 33 [67%]), did not assess risk of bias of the individual included studies (13 of 33 [39%]), and did not use appropriate methods for quantitative syntheses (meta-analysis) (12 of 17 systematic reviews that conducted a quantitative synthesis [71%]). Sixty-five of 98 systematic reviews (66%) were classified as reliable. Forty-two of the 65 reliable systematic reviews (65%) addressed corneal diseases relevant to the 2018 American Academy of Ophthalmology PPPs; 33 of these 42 systematic reviews (79%) are cited in the 2018 PPPs.

Conclusions and Relevance

One in 3 systematic reviews addressing interventions for corneal diseases are unreliable and thus were not used to inform PPP recommendations. Careful adherence by systematic reviewers and journal editors to well-established best practices regarding systematic review conduct and reporting might help make future systematic reviews in eyes and vision more reliable.

Oral miltefosine for refractory Acanthamoeba keratitis

Purpose

To report the first case of Acanthamoeba keratitis treated with oral miltefosine in the United States.

Observations

A 17-year-old female with a history of orthokeratology contact lens wear presented after five months of left eye pain, redness, and photophobia. She was previously treated with antivirals and topical corticosteroids for presumed herpetic disease. She was found to have a large central ring infiltrate and corneal cultures were positive for Acanthamoeba. The infection progressed despite hourly PHMB 0.02% and chlorhexidine 0.02%, and oral vorizonazole. The patient was started on oral miltefosine 50 mg 3 times per day. Following one week of treatment, repeat cultures were positive for Acanthamoeba and therefore, the concentration of chlorhexidine was increased from 0.02% to 0.06% and PHMB was changed to propamidine isetionate (Brolene 0.1%). There was definite clinical improvement after five weeks of treatment with oral miltefosine, topical chlorhexidine 0.06% and propamidine isetionate 0.1%.

Conclusions and importance

Acanthamoeba keratitis is a challenging entity to treat and often associated with a poor prognosis. Oral miltefosine may offer additional therapeutic benefit in cases of refractory Acanthamoeba keratitis.

Evaluation of Oxasqualenoids from the Red Alga Laurencia viridis against Acanthamoeba

Acanthamoeba genus is a widely distributed and opportunistic parasite with increasing importance worldwide as an emerging pathogen in the past decades. This protozoan has an active trophozoite stage, a cyst stage, and is dormant and very resistant. It can cause Acanthamoeba keratitis, an ocular sight-threatening disease, and granulomatous amoebic encephalitis, a chronic, very fatal brain pathology. In this study, the amoebicidal activity of sixteen Laurencia oxasqualenoid metabolites and semisynthetic derivatives were tested against Acanthamoeba castellanii Neff. The results obtained point out that iubol (3) and dehydrothyrsiferol (1) possess potent activities, with IC₅₀ values of 5.30 and 12.83 µM, respectively. The hydroxylated congeners thyrsiferol (2) and 22-hydroxydehydrothyrsiferol (4), active in the same value range at IC₅₀ 13.97 and 17.00 µM, are not toxic against murine macrophages; thus, they are solid candidates for the development of new amoebicidal therapies.

Effect of Nitric Oxide on Acanthamoeba castellanii

Purpose

Acanthamoeba keratitis is a well-known intractable corneal infectious disease. We investigated the anti-Acanthamoeba effect of exogenous nitric oxide (NO).

Methods

Acanthamoeba castellanii was axenically cultured and exposed to various concentrations of NO donors, such as sodium nitrite, sodium nitroprusside (SNP), and NO-releasing silica nanoparticles (coated in branched polyethylene imine, size:100 nm), for 1 to 7 days (sodium nitrite and SNP: 0, 0.1, 1, 10, 100, and 1000 μM; silica nanoparticles: 0, 6.25, 12.5, 25, 50, and 100 μg/mL). Human corneal epithelial cells (HCECs) were cultured and exposed to sodium nitrite, SNP (0, 0.1, 1, 10, 100, and 1000 μM), and silica nanoparticles for 1, 2, and 3 days.

Results

Sodium nitrite and SNP showed a dose-dependent inhibitory effect on A. castellanii viability. A more prominent inhibitory effect was observed with SNP (less than 10% of organisms survived at 7-day culture with 1000 μM) compared with sodium nitrite. However, more cytotoxicity on HCEC was observed with SNP. NO-releasing silica nanoparticles were successfully internalized into the amoebic cytoplasm and accumulated in large vacuoles. Although blank silica nanoparticles had no inhibitory effect on A. castellanii viability, NO-releasing silica nanoparticles showed a dose-dependent amoebicidal effect. Furthermore, no cystic transformation of A. castellanii was observed under a phase contrast microscope or transmission electron microscope after exogenous NO treatment.

Conclusions

Our results demonstrated the anti-Acanthamoeba effect of exogenous NO. This finding suggests that NO-releasing drug platforms, including nano-carriers, can be a promising therapeutic strategy for Acanthamoeba keratitis.

Associated factors, diagnosis and management of Acanthamoeba keratitis in a referral Center in Southern China

BACKGROUND

To analyse the associated factors, diagnosis, clinical manifestations and therapeutic effects of Acanthamoeba keratitis at a tertiary ophthalmic centre in Southern China.

METHODS

A retrospective clinical study was performed in fifteen patients who were admitted to Zhongshan Ophthalmic Centre (ZOC) from January 2004 to December 2014. The patients' pathogenesis-associated factors were analysed, and preoperative diagnoses were determined using corneal scraping cultures and/or confocal microscopy followed. All diagnoses were confirmed by postoperative pathological examinations. At follow-up, best-corrected visual acuity (BCVA), the recurrence rate and graft transparency were evaluated to assess therapeutic effects.

RESULTS

The main pathogenic factors observed in the fifteen patients were a history of injury or a foreign body entering the eyes (12 cases). In all, Acanthamoeba keratitis was preoperatively diagnosed in 5 cases using corneal scraping cultures or confocal microscopy. Ocular symptoms included redness, photophobia, tearing, and blurred vision. Penetrating keratoplasty was performed in thirteen patients, and postoperative pathological examinations were performed to confirm these diagnoses. The logarithm of the minimum angle of resolution (logMAR) of visual acuity was significantly improved after keratoplasty (p < 0.01). No recurrence was observed, and approximately 90% of the corneal grafts were found to be transparent during the follow-up period.

CONCLUSIONS

Corneal trauma may be the main pathogenic factor that causes Acanthamoeba keratitis in southern China. Corneal scraping combined with confocal microscopy was helpful for achieving a correct diagnosis. Early keratoplasty combined with amoebicidal therapy is an effective treatment strategy in Acanthamoeba keratitis.

Medical interventions for acanthamoeba keratitis

BACKGROUND

Acanthamoeba are microscopic, free-living, single-celled organisms which can infect the eye and lead to Acanthamoeba keratitis (AK). AK can result in loss of vision in the infected eye or loss of eye itself; however, there are no formal guidelines or standards of care for the treatment of AK.

OBJECTIVES

To evaluate the relative effectiveness and safety of medical therapy for the treatment of AK.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015, Issue 1), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), PubMed (1948 to January 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to January 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 9 January 2015.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of medical therapy for AK, regardless of the participants' age, sex, or etiology of disease. We included studies that compared either anti-amoeba therapy (drugs used alone or in combination with other medical therapies) with no anti-amoeba therapy or one anti-amoeba therapy with another anti-amoeba therapy.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results and full-text reports, assessed risk of bias, and abstracted data. We used standard methodological procedures as set forth by the Cochrane Collaboration.

MAIN RESULTS

We included one RCT (56 eyes of 55 participants) in this review. The study compared two types of topical biguanides for the treatment of AK: chlorhexidine 0.02% and polyhexamethylene biguanide (PHMB) 0.02%. All participants were contact lens wearers with a median age of 31 years. Treatment duration ranged from 51 to 145 days. The study, conducted in the UK, was well-designed and had low risk of bias overall.Outcome data were available for 51 (91%) of 56 eyes. Follow-up times for outcome measurements in the study were not reported. Resolution of infection, defined as control of ocular inflammation, relief of pain and photosensitivity, and recovery of vision, was 86% in the chlorhexidine group compared with 78% in the PHMB group (relative risk (RR) 1.10, 95% confidence intervals (CI) 0.84 to 1.42). In the chlorhexidine group, 20 of 28 eyes (71%) had better visual acuity compared with 13 of 23 eyes (57%) in the PHMB group at final follow-up (RR 1.26, 95% CI 0.82 to 1.94). Five participants required therapeutic keratoplasty: 2 in the chlorhexidine group compared with 3 in the PHMB group (RR 0.55, 95% CI 0.10 to 3.00). No serious adverse event related to drug toxicity was observed in the study.

AUTHORS' CONCLUSIONS

There is insufficient evidence to evaluate the relative effectiveness and safety of medical therapy for the treatment of AK. Results from the one included study yielded no difference with respect to outcomes reported between chlorhexidine and PHMB. However, the sample size was inadequate to detect clinically meaningful differences between the two groups as indicated by the wide confidence intervals of effect estimates.