Update on the Management of Infectious Keratitis

The Role of Pneumococcal Virulence Factors in Ocular Infectious Diseases

Streptococcus pneumoniae is a gram-positive, facultatively anaerobic pathogen that can cause severe infections such as pneumonia, meningitis, septicemia, and middle ear infections. It is also one of the top pathogens contributing to bacterial keratitis and conjunctivitis. Though two pneumococcal vaccines exist for the prevention of nonocular diseases, they do little to fully prevent ocular infections. This pathogen has several virulence factors that wreak havoc on the conjunctiva, cornea, and intraocular system. Polysaccharide capsule aids in the evasion of host complement system. Pneumolysin (PLY) is a cholesterol-dependent cytolysin that acts as pore-forming toxin. Neuraminidases assist in adherence and colonization by exposing cell surface receptors to the pneumococcus. Zinc metalloproteinases contribute to evasion of the immune system and disease severity. The main purpose of this review is to consolidate the multiple studies that have been conducted on several pneumococcal virulence factors and the role each plays in conjunctivitis, keratitis, and endophthalmitis.

Fenretinide Inhibits Neutrophil Recruitment and IL-1β Production in Aspergillus fumigatus Keratitis

Purpose:

Fungal keratitis is a major cause of corneal ulcers, resulting in significant visual impairment and blindness. Fenretinide, a derivative of vitamin A, has been shown to suppress inflammation in a multitude of diseases. In this study, we aimed to characterize the effect of fenretinide in Aspergillus fumigatus keratitis of the eye in a mouse model.

Methods:

In vivo and in vitro experiments were performed in mouse models and THP-1 macrophage cell cultures infected with A. fumigatus, respectively. Experimental subjects were first pretreated with fenretinide, and then the effect of the compound was assessed with clinical evaluation, neutrophil staining, myeloperoxidase assay, quantitative polymerase chain reaction (qRT-PCR), and western blot.

Results:

We confirmed that fenretinide contributed to protection of corneal transparency during early mouse A. fumigatus keratitis by reducing neutrophil recruitment, decreasing myeloperoxidase (MPO) levels and increasing apoptosis. Compared with controls, fenretinide impaired proinflammatory cytokine interleukin 1 beta (IL-1β) production in response to A. fumigatus exposure with contributions by lectin-type oxidized LDL receptor 1 (LOX-1) and c-Jun N-terminal kinase (JNK).

Conclusions:

Together, these findings demonstrate that fenretinide may suppress inflammation through reduced neutrophil recruitment and inflammatory cytokine production in A. fumigatus keratitis.

Therapeutic use of fluorinated nucleosides – progress in patents

Fluorinated nucleosides constitute a large class of chemotherapeutics approved for clinical use. The pharmacokinetic and pharmacodynamic properties of a drug can be affected, as a consequence of modulation of electronic, lipophilic and steric parameters, by the introduction of fluorine into the structure of drug-like molecule. Herein, we focus on fluorinated-nucleoside analogs, their therapeutic use and applications based on the patent literature from 2014 to 2018. We briefly discuss the clinical properties of anticancer and antiviral fluorine-containing nucleos(t)ides US FDA-approved or in development, and highlight their resistance mechanisms and limitations in the clinic. We emphasize patent inventions related to improved synthetic methods toward selected nucleos(t)ide analogs including the phosphoramidate sofosbuvir and 18F-labeled nucleosides FLT and FMAU, used as a 18F-PET tracers.

Infectious Keratitis: Microbiological Review of 297 Cases

Infectious keratitis is a serious ocular infection that can lead to loss of vision. The aim of this study was to investigate the microbiological characteristics of this infection at the University Hospital of Guadalajara (Spain). We retrospectively reviewed all cases diagnosed between January 2010 and December 2016. During the 7-year study period, 297 corneal scrapes corresponding to 298 patients were performed. Antibiotic treatment prior to the culture was administered in 59 cases (19.9%). Contact lens wear was the most common risk factor (33.2%). Bacterial keratitis accounted for 64.6% of cases, viral keratitis for 3.4%, and fungal keratitis for 1%. A total of 241 bacterial strains were identified. Gram-positive isolates represented 87.1%, and gram-negative 12.7%. Coagulase-negative Staphylococcus strains were the most common microorganisms isolated (30.3%). When gram-positive microorganisms were analyzed, the sensitivity prevalence rates for vancomycin (VCM), levofloxacin, gentamicin (GM), and tobramycin (TO) were 99.4%, 84.6%, 87.9%, and 88.3%, respectively. For the gram-negative organisms, the sensitivity prevalence rates for ceftazidime, ciprofloxacin, GM, and TO were 83.3%, 93.5%, 96.3%, and 100%, respectively. Our study revealed strong predominance of gram-positive microorganisms. We suggest empirically treating bacterial keratitis originating in our area with VCM and TO, especially severe bacterial keratitis and pretreated cases in the community without a clinical response.

Opportunistic ocular infections in the setting of HIV

PURPOSE OF REVIEW

The aim of this review is to highlight recent changes in opportunistic ocular infections (OOIs) in the era of modern combination antiretroviral therapy (cART), in the setting of HIV-infected patients.

RECENT FINDINGS

Improvements in modern cART has led to a progressive decline in the incidence of OOIs and mortality among patients with AIDS. Not only has there been a decreasing incidence of cytomegalovirus (CMV) retinitis, but there also has been a decline in progression of such retinitis when it does occur in AIDS patients, since the introduction of cART. Nevertheless, CMV retinitis remains the major cause of vision loss in AIDS patients. Although the incidence of CMV retinitis has declined overall, the incidence of ocular syphilis has increased during the cART era. Moreover, the impact of having HIV plays a role with respect to multidrug-resistant (MDR) tuberculosis and has resulted in a high prevalence of presumed ocular tuberculosis in HIV/MDR-TB co-infected patients. Although immune reconstitution uveitis (IRU) has been an important cause of visual deficits in developed countries, OOIs remain an important cause of blindness in the developing world.

SUMMARY

Reconstituting the immune system with effective cART while increasing accessibility of screening examinations is key to the success of blindness prevent in HIV-infected individuals, particularly in developing countries.

The HIV Integrase Inhibitor Raltegravir Inhibits Felid Alphaherpesvirus 1 Replication by Targeting both DNA Replication and Late Gene Expression

Alphaherpesvirus-associated ocular infections in humans caused by human alphaherpesvirus 1 (HHV-1) remain challenging to treat due to the frequency of drug application required and the potential for the selection of drug-resistant viruses. Repurposing on-the-market drugs is a viable strategy to accelerate the pace of drug development. It has been reported that the human immunodeficiency virus (HIV) integrase inhibitor raltegravir inhibits HHV-1 replication by targeting the DNA polymerase accessory factor and limits terminase-mediated genome cleavage of human betaherpesvirus 5 (HHV-5). We have previously shown, both in vitro and in vivo, that raltegravir can also inhibit the replication of felid alphaherpesvirus 1 (FeHV-1), a common ocular pathogen of cats with a pathogenesis similar to that of HHV-1 ocular disease. In contrast to what was reported for HHV-1, we were unable to select for a raltegravir-resistant FeHV-1 strain in order to define any basis for drug action. A candidate-based approach to explore the mode of action of raltegravir against FeHV-1 showed that raltegravir did not impact FeHV-1 terminase function, as described for HHV-5. Instead, raltegravir inhibited DNA replication, similarly to HHV-1, but by targeting the initiation of viral DNA replication rather than elongation. In addition, we found that raltegravir specifically repressed late gene expression independently of DNA replication, and both activities are consistent with inhibition of ICP8. Taken together, these results suggest that raltegravir could be a valuable therapeutic agent against herpesviruses.IMPORTANCE The rise of drug-resistant herpesviruses is a longstanding concern, particularly among immunocompromised patients. Therefore, therapies targeting viral proteins other than the DNA polymerase that may be less likely to lead to drug-resistant viruses are urgently needed. Using FeHV-1, an alphaherpesvirus closely related to HHV-1 that similarly causes ocular herpes in its natural host, we found that the HIV integrase inhibitor raltegravir targets different stages of the virus life cycle beyond DNA replication and that it does so without developing drug resistance under the conditions tested. This shows that the drug could provide a viable strategy for the treatment of herpesvirus infections.

Virucidal, antiviral and immunomodulatory activities of β-escin and Aesculus hippocastanum extract

OBJECTIVES

β-Escin, one of the constituents of Aesculus hippocastanum L. (Hippocastanaceae) seed extract (AH), inhibits NF-κB activation, which plays an important role in HSV-1 replication. The aim was to examine the antiherpetic activity of β-escin and AH, as well as their effect on the activation of NF-κB and AP-1 and cytokine secretion in epithelial cells and macrophages.

METHODS

Cell viability was evaluated using MTT assay, and antiviral and virucidal activity was determined by plaque assay. The effect on NF-κB and AP-1 signalling pathways activation was determined by a luciferase reporter assay, and cytokine production was measured by ELISA.

KEY FINDINGS

β-Escin and AH had virucidal and anti-HSV-1 activities, and the antiviral activity was discovered for other enveloped viruses (VSV and Dengue). Moreover, β-escin and AH significantly reduced NF-κB and AP-1 activation and cytokine production in macrophages stimulated with HSV-1 and TLRs ligands. However, an enhanced activation of these pathways and an increase in the levels of pro-inflammatory cytokines in β-escin and AH-treated HSV-1-infected epithelial cells were found.

CONCLUSIONS

This study demonstrates virucidal and broad-spectrum antiviral activities for β escin and AH. Besides, β-escin and AH modulate cytokine production depending on the stimuli (viral or non-viral) and the cell type under study.

Comparison of anterior segment optical coherence tomography findings in acanthamoeba keratitis and herpetic epithelial keratitis

This study is to investigate the characteristic features of Acanthamoeba keratitis (AK) that differentiating it from herpetic epithelial keratitis (HEK) using anterior segment optical coherence tomography (AS-OCT). Medical records of three eyes of each AK and herpetic keratitis who had AS-OCT examination were reviewed in this study. Slit-lamp biomicroscopy and AS-OCT was performed on the initial visit and on every follow-up visits in all patients. In all three AK cases, reflective bands in the corneal stroma that correspond to the area of radial keratoneuritis were observed. The depth of the reflective bands varied in each case. After AK treatment, slit-lamp biomicroscopy confirmed that radial keratoneuritis had resolved and AS-OCT confirmed that reflective bands in the corneal stroma had also disappeared in all patients. Unlike the AS-OCT results found in AK, highly reflective HEK lesions were observed only in the subepithelial area, not in the stroma. AS-OCT seems to be helpful analyzing the specific depth of the lesion which enables to distinguish AK from HEK.

Depletion of the Insulator Protein CTCF Results in Herpes Simplex Virus 1 Reactivation In Vivo

Herpes simplex virus 1 (HSV-1) establishes a lifelong latent infection in host peripheral neurons, including the neurons of the trigeminal ganglia (TG). HSV-1 can reactivate from neurons to cause recurrent infection. During latency, the insulator protein CTCF occupies DNA binding sites on the HSV-1 genome, and these sites have been previously characterized as functional enhancer-blocking insulators. Previously, CTCF was found to be dissociated from wild-type virus postreactivation but not in mutants that do not reactivate, indicating that CTCF eviction may also be an important component of reactivation. To further elucidate the role of CTCF in reactivation of HSV-1, we used recombinant adeno-associated virus (rAAV) vectors to deliver a small interfering RNA targeting CTCF to peripheral neurons latent with HSV-1 in rabbit TG. Our data show that CTCF depletion resulted in long-term and persistent shedding of infectious virus in the cornea and increased ICP0 expression in the ganglia, indicating that CTCF depletion facilitates HSV-1 reactivation.IMPORTANCE Increasing evidence has shown that the insulator protein CTCF regulates gene expression of DNA viruses, including the gammaherpesviruses. While CTCF occupation and insulator function control gene expression in DNA viruses, CTCF eviction has been correlated to increased lytic gene expression and the dissolution of transcriptional domains. Our previous data have shown that in the alphaherpesvirus HSV-1, CTCF was found to be dissociated from the HSV-1 genome postreactivation, further indicating a global role for CTCF eviction in the transition from latency to reactivation in HSV-1 genomes. Using an rAAV8, we targeted HSV-1-infected peripheral neurons for CTCF depletion to show that CTCF depletion precedes the shedding of infectious virus and increased lytic gene expression in vivo, providing the first evidence that CTCF depletion facilitates HSV-1 reactivation.

Biofilm testing of microbiota: An essential step during corneal scrap examination in Egyptian acanthamoebic keratitis cases

PURPOSE

To detect co-infections in the culture-proven acanthamoebic keratitis (AK) cases, and to test the capability of biofilm formation in the isolated microbiota. The clinical findings, habit of wearing contact lens and in-vitro antibiotic resistance were analyzed further according to the biofilm formation capability.

METHODS

After clinical examination, corneal scraps and swabs were taken from 240 clinically suspected AK cases, for Acanthamoeba and microbiological cultures. In cases of keratoplasty, trimmed corneal tissue was collected and sent for histopathological examination. Scanning electron microscopy was done for some samples. Biofilm formation capability was investigated using a tissue culture plate method. Antibiotic resistance pattern was determined using a modified-Kirby-Bauer disc diffusion method.

RESULTS

In 102 AK culture proven cases, 11 had no co-infection, 74 had a single co-infection and 17 had double co-infections. Enterobactericae and Aspergillus were the commonest bacterial and fungal isolates, respectively. Regarding the biofilm formation, 64.7% of Enterobactericae, 50% of Pseudomonas aeuroginosa, 43.75% of Staph aureus, 76.92% of Streptococcus pneumoniae, 28.57% of Corynebacterium, 60% of α-haemolytic streptococci, 40% of Acinetobacter, 100% of Candida and 77.8% Aspergillus isolates were biofilm producers. Severe manifestations were more frequently reported in cases co-infected with biofilm producers than with non-biofilm producers. Generally, high percentages of the biofilm forming bacterial isolates were sensitive to antibiotics in-vitro.

CONCLUSIONS

Routine investigations for co-infection and biofilm formation in addition to Acanthamoeba culture are strongly recommended in suspected AK cases. Co-infection with biofilm producers may precipitate extrinsic in-vivo drug resistance despite of the in-vitro sensitivity. Designing a biofilm-dissolving topical drug is highly recommended to enhance the response to the standard therapeutic regimen especially in the resistant AK cases.

CTCF Binding Sites in the Herpes Simplex Virus 1 Genome Display Site-Specific CTCF Occupation, Protein Recruitment, and Insulator Function

There are seven conserved CTCF binding domains in the herpes simplex virus 1 (HSV-1) genome. These binding sites individually flank the latency-associated transcript (LAT) and the immediate early (IE) gene regions, suggesting that CTCF insulators differentially control transcriptional domains in HSV-1 latency. In this work, we show that two CTCF binding motifs in HSV-1 display enhancer blocking in a cell-type-specific manner. We found that CTCF binding to the latent HSV-1 genome was LAT dependent and that the quantity of bound CTCF was site specific. Following reactivation, CTCF eviction was dynamic, suggesting that each CTCF site was independently regulated. We explored whether CTCF sites recruit the polycomb-repressive complex 2 (PRC2) to establish repressive domains through a CTCF-Suz12 interaction and found that Suz12 colocalized to the CTCF insulators flanking the ICP0 and ICP4 regions and, conversely, was removed at early times postreactivation. Collectively, these data support the idea that CTCF sites in HSV-1 are independently regulated and may contribute to lytic-latent HSV-1 control in a site-specific manner.IMPORTANCE The role of chromatin insulators in DNA viruses is an area of interest. It has been shown in several beta- and gammaherpesviruses that insulators likely control the lytic transcriptional profile through protein recruitment and through the formation of three-dimensional (3D) chromatin loops. The ability of insulators to regulate alphaherpesviruses has been understudied to date. The alphaherpesvirus HSV-1 has seven conserved insulator binding motifs that flank regions of the genome known to contribute to the establishment of latency. Our work presented here contributes to the understanding of how insulators control transcription of HSV-1.

Expert practice patterns and opinions on corneal cross-linking for infectious keratitis

Objective

To assess the current opinion and practice patterns from cornea experts regarding the benefit of corneal cross-linking (CXL) for infectious keratitis (IK).

Methods and analysis

An international survey was distributed to corneal specialists via an internet survey. The survey data collected were analysed with descriptive statistics.

Results

A survey was sent to 190 recipients, and 29 (15%) respondents completed the survey with an average of 7 years’ experience using CXL. A majority of respondents (66%) used CXL to treat IK due to bacterial, fungal, protozoan or unknown aetiology. Main indications to use CXL as adjuvant therapy were worsening infiltrate diameter or depth despite therapy (74%), followed by antibiotic resistance (68%), corneal thinning (53%), poor compliance with medication (26%) and other reasons (21%). Most respondents felt CXL would be at least moderately helpful as an adjuvant therapy for bacterial (96%) or fungal (75%) keratitis; about half (46%) thought it would be helpful for acanthamoeba keratitis. As sole therapy, fewer respondents believed CXL would be at least moderately helpful to treat bacterial (75%), fungal (58%) and acanthamoeba (43%) keratitis.

Conclusion

The survey offered insights into current expert practices and opinions of using CXL as therapy for IK. The results of this survey serve to guide in the design of future clinical studies.