Dissecting the Molecular Mechanism of Colistin Resistance in mcr-1 Bacteria

Colistin or polymyxin B is the last resort antibiotic to treat infections of multidrug-resistant Gram-negative bacteria by disrupting their outer membranes. The recent emergence of Gram-negative bacteria that demonstrate colistin resistance, particularly plasmid-mediated mobile colistin resistance (mcr), poses a big challenge to the treatment of multidrug resistance infections. Using molecular dynamics simulations, we explore the mechanism of colistin resistance in a model lipid A bilayer mimicking the Gram-negative mcr-1 bacterial outer membrane. The simulation results reveal that the outer membrane of normal Gram-negative bacteria is stabilized by salt bridges between positively charged divalent ions and negatively charged phosphate groups of the membranes. In the presence of positively charged polymyxin B, these salt bridges are disrupted, and calcium is released into the aqueous phase, resulting in membrane disruption. In contrast, the lipid A in the outer membrane of mcr-1 bacteria has a novel modification, this being a covalently attached phosphoethanolamine group. This group enables the formation of a large number of hydrogen bonds between the amine and phosphate groups, resulting in an electrostatic net on the membrane. This extensive noncovalent electrostatic cross-linking between the lipid molecules collectively enhances the membrane stability and results in resistance to the action of cationic peptides such as polymyxin B. The simulation results shed new atomistic insights for understanding the mechanistic basis of colistin resistance and provide clues for the design of new membrane disruptors and permeabilizers to treat mcr-1 infections.

Age-associated changes in human tear proteome

Background

Prevalence of many eye and ocular surface diseases increases with age. While the clinical characteristics and pathophysiologic mechanisms of these conditions are often either known or extensively studied, the effects of normal aging on tear film and ocular surface have not been as widely researched.

Methods

In order to examine the effects of aging on tear fluid proteomics, tear fluid samples were collected preoperatively from 115 subjects undergoing strabismus or refractive surgery using glass microcapillary tubes. In addition to their refractive error or strabismus, the subjects did not have any other current, known eye diseases. The non-pooled samples were analysed using NanoLC-TripleTOF implementing a sequential window acquisition of all theoretical fragment ion spectra mass spectrometry, resulting in quantified data of 849 proteins.

Results

According to correlation results, 17 tear proteins correlated significantly with increased age and many of these proteins were connected to inflammation, immune response and cell death. According to enrichment analysis, growth and survival of cells decreased while immune response and inflammation increased with aging. We also discovered several well-known, activated and inhibited upstream regulators, e.g. NF-κB, which has been previously connected to aging in numerous previous studies.

Conclusions

Overall, the results show the common age-dependent alterations in tear fluid protein profile, which demonstrate similar age-associated alterations of biological functions previously shown in other tissue and sample types.

Electronic supplementary material

The online version of this article (10.1186/s12014-019-9233-5) contains supplementary material, which is available to authorized users.

The Asia Cornea Society Infectious Keratitis Study: A Prospective Multicenter Study of Infectious Keratitis in Asia

PURPOSE

To survey the demographics, risk factors, microbiology, and outcomes for infectious keratitis in Asia.

DESIGN

Prospective, nonrandomized clinical study.

METHODS

Thirteen study centers and 30 sub-centers recruited consecutive subjects over 12-18 months, and performed standardized data collection. A microbiological protocol standardized the processing and reporting of all isolates. Treatment of the infectious keratitis was decided by the managing ophthalmologist. Subjects were observed for up to 6 months. Main outcome measures were final visual acuity and the need for surgery during infection.

RESULTS

A total of 6626 eyes of 6563 subjects were studied. The majority of subjects were male (n = 3992). Trauma (n = 2279, 34.7%) and contact lens wear (n = 704, 10.7%) were the commonest risk factors. Overall, bacterial keratitis was diagnosed in 2521 eyes (38.0%) and fungal keratitis in 2166 eyes (32.7%). Of the 2831 microorganisms isolated, the most common were Fusarium species (n = 518, 18.3%), Pseudomonas aeruginosa (n = 302, 10.7%), and Aspergillus flavus (n = 236, 8.3%). Cornea transplantation was performed in 628 eyes to manage ongoing infection, but 289 grafts (46%) had failed by the end of the study. Moderate visual impairment (Snellen vision less than 20/60) was documented in 3478 eyes (53.6%).

CONCLUSION

Demographic and risk factors for infection vary by country, but infections occur predominantly in male subjects and are frequently related to trauma. Overall, a similar percentage of bacterial and fungal infections were diagnosed in this study. Visual recovery after infectious keratitis is guarded, and corneal transplantation for active infection is associated with a high failure rate.

Comparison of iTRAQ and SWATH in a clinical study with multiple time points

Background

Advances in mass spectrometry have accelerated biomarker discovery in many areas of medicine. The purpose of this study was to compare two mass spectrometry (MS) methods, isobaric tags for relative and absolute quantitation (iTRAQ) and sequential window acquisition of all theoretical fragment ion spectra (SWATH), for analytical efficiency in biomarker discovery when there are multiple methodological constraints such as limited sample size and several time points for each patient to be analyzed.

Methods

A total of 140 tear samples were collected from 28 glaucoma patients at 5 time points in a glaucoma drug switch study. Samples were analyzed with iTRAQ and SWATH methods using NanoLC-MSTOF mass spectrometry.

Results

We discovered that even though iTRAQ is faster than SWATH with respect to analysis time per sample, it loses in sensitivity, reliability and robustness. While SWATH analysis yielded complete data of 456 proteins in all samples, with iTRAQ we were able to quantify 477 proteins in total but on average only 125 proteins were quantified in a sample. 283 proteins were common in the datasets produced by the two methods. Repeatability of the methods was assessed by calculating percent relative standard deviation (% RSD) between replicate MS analyses: SWATH was more repeatable (56% of proteins < 20% RSD), compared to iTRAQ (43% of proteins < 20% RSD). Despite the overall benefits of SWATH, both methods showed less than 1 log fold change difference in the expression of 74% common proteins. In addition, comparison to MS/MS peptide results using 8 isotopically labeled peptide standards, SWATH and iTRAQ showed similar results in terms of accuracy. Moreover, both methods detected similar trends in a longitudinal analysis of protein expression of two known tear biomarkers.

Conclusions

Overall, we conclude that SWATH should be preferred for biomarker discovery studies when analyzing limited volumes of clinical samples collected at multiple time points.

Trial Registeration

The study was approved by the Ethics Committee at Tampere University Hospital and was registered in EU clinical trials register (EudraCT Number: 2010-021039-14).

Comparative proteomic analysis of human embryonic stem cell-derived and primary human retinal pigment epithelium

Human embryonic stem cell-derived retinal pigment epithelial cells (hESC-RPE) provide an unlimited cell source for retinal cell replacement therapies. Clinical trials using hESC-RPE to treat diseases such as age-related macular degeneration (AMD) are currently underway. Human ESC-RPE cells have been thoroughly characterized at the gene level but their protein expression profile has not been studied at larger scale. In this study, proteomic analysis was used to compare hESC-RPE cells differentiated from two independent hESC lines, to primary human RPE (hRPE) using Isobaric tags for relative quantitation (iTRAQ). 1041 common proteins were present in both hESC-RPE cells and native hRPE with majority of the proteins similarly regulated. The hESC-RPE proteome reflected that of normal hRPE with a large number of metabolic, mitochondrial, cytoskeletal, and transport proteins expressed. No signs of increased stress, apoptosis, immune response, proliferation, or retinal degeneration related changes were noted in hESC-RPE, while important RPE specific proteins involved in key RPE functions such as visual cycle and phagocytosis, could be detected in the hESC-RPE. Overall, the results indicated that the proteome of the hESC-RPE cells closely resembled that of their native counterparts.

Membrane-targeting AM-0016 kills mycobacterial persisters and shows low propensity for resistance development

Aim: To test the hypothesis that targeting the cytoplasmic membrane may be an effective way to kill persister mycobacteria and delay the emergence of resistance. Methods: In vitro activity of AM-0016, a novel xanthone-based antibacterial, was assessed against growing and persister tubercle bacilli. Resistance mutation frequencies were determined. Biochemical membrane and electron microscopic analyses were carried out. Results: AM-0016 rapidly sterilized growing tubercle bacillus cultures and displayed strong bactericidal activity against persister bacteria. Spontaneous resistance mutation frequency was lower than 10-8. Exposure to AM-0016 resulted in rapid collapse of the membrane potential. Imaging revealed deformation of the cell envelope. Conclusion: Targeting the cytoplasmic membrane may be an attractive approach to eliminate persister mycobacteria and slow down the emergence of genetic drug resistance.

Effects of Punctal Occlusion on Clinical Signs and Symptoms and on Tear Cytokine Levels in Patients with Dry Eye

PURPOSE

To investigate changes in signs, symptoms, and tear cytokines following punctal plug occlusion in patients with dry eye.

METHODS

A single-center study was conducted at Singapore Eye Research Institute. Nonabsorbable punctal plugs were inserted in the lower punctum of both eyes in patients with moderate dry eye. Over 3 weeks, in the more severe eye, dry eye symptoms, fluorescein corneal staining, Schirmer I (without topical anesthesia) test, tear film breakup time (TFBUT), and safety were assessed. Cytokine and matrix metalloproteinase-9 (MMP-9) levels in tear samples were measured.

RESULTS

Twenty-nine patients (mean age 49.8 years) with moderate dry eye were evaluated. At baseline, mean (standard deviation) global symptoms score was 53.8 (26.5), Schirmer I test score was 5.1 (2.8) mm, and TFBUT was 2.2 (0.6) seconds. After 3 weeks, punctal occlusion significantly reduced global irritation symptoms score (P<.001) and decreased fluorescein staining in all zones (P<.01) except the inferior zone (P=.42). No significant association between levels of cytokines or MMP-9 and either TFBUT or global irritation symptoms were observed at baseline. Levels of several cytokines and MMP-9 were higher in patients with Schirmer I test scores ≤8 mm at baseline. After 3 weeks of punctal occlusion, no significant changes in overall cytokine or MMP-9 levels were observed.

CONCLUSIONS

Punctal plug occlusion provided symptomatic relief and reduced fluorescein staining in all except the inferior zone. However, insertion of punctal plugs had minimal effect on tear cytokines and MMP-9 levels, suggesting a need for earlier treatment with anti-inflammatory agents for management of dry eye disease.

Prophylactic Vancomycin Drops Reduce the Severity of Early Bacterial Keratitis in Keratoprosthesis

BACKGROUND

Artificial cornea transplantation, keratoprosthesis, improves vision for patients at high risk of failure with human cadaveric cornea. However, post-operative infection can cause visual loss and implant extrusion in 3.2-17% of eyes. Long-term vancomycin drops are recommended following keratoprosthesis to prevent bacterial keratitis. Evidence, though, in support of this practice is poor. We investigated whether prophylactic vancomycin drops prevented bacterial keratitis in an animal keratoprosthesis model.

METHODOLOGY

Twenty-three rabbits were assigned either to a prophylactic group (n = 13) that received vancomycin 1.4% drops 5 times/day from keratoprosthesis implantation to sacrifice, or a non-prophylactic group (n = 10) that received no drops. All rabbits had Staphylococcus aureus inoculation into the cornea at 7-12 days post-implantation and were sacrificed at predetermined time-points. Prophylactic and non-prophylactic groups were compared with slit-lamp photography (SLP), anterior segment optical coherence tomography (AS-OCT), and histology, immunohistochemistry and bacterial quantification of excised corneas. Corneal vancomycin pharmacokinetics were studied in 8 additional rabbits.

RESULTS

On day 1 post-inoculation, the median SLP score and mean±SEM AS-OCT corneal thickness (CT) were greater in the non-prophylactic than the prophylactic group (11 vs. 1, p = 0.049 and 486.9±61.2 vs. 327.4±37.1 μm, p = 0.029 respectively). On days 2 and 4, SLP scores and CT were not significantly different. Immunohistochemistry showed a greater CD11b+ve/non-CD11b+ve cell ratio in the non-prophylactic group (1.45 vs. 0.71) on day 2. Bacterial counts were not significantly different between the two groups. Corneal vancomycin concentration (2.835±0.383 μg/ml) exceeded minimum inhibitory concentration (MIC) for Staphylococcus aureus only after 16 days of vancomycin drops. Two of 3 rabbits still developed infection despite bacterial inoculation after 16 days of prophylactic drops.

CONCLUSIONS

Prophylactic vancomycin drops provided short-term benefit, but did not prevent infection. Achieving MIC in the cornea was not sufficient to prevent Staphylococcus aureus keratitis. Patients should continue to be counselled regarding the risk of infection following keratoprosthesis.

Comparative proteomics reveals human pluripotent stem cell-derived limbal epithelial stem cells are similar to native ocular surface epithelial cells

Limbal epithelial stem cells (LESCs) are tissue-specific stem cells responsible for renewing the corneal epithelium. Acute trauma or chronic disease affecting LESCs may disrupt corneal epithelial renewal, causing vision threatening and painful ocular surface disorders, collectively referred to as LESC deficiency (LESCD). These disorders cannot be treated with traditional corneal transplantation and therefore alternative cell sources for successful cell-based therapy are needed. LESCs derived from human pluripotent stem cells (hPSCs) are a prospective source for ocular surface reconstruction, yet critical evaluation of these cells is crucial before considering clinical applications. In order to quantitatively evaluate hPSC-derived LESCs, we compared protein expression in native human corneal cells to that in hPSC-derived LESCs using isobaric tag for relative and absolute quantitation (iTRAQ) technology. We identified 860 unique proteins present in all samples, including proteins involved in cell cycling, proliferation, differentiation and apoptosis, various LESC niche components, and limbal and corneal epithelial markers. Protein expression profiles were nearly identical in LESCs derived from two different hPSC lines, indicating that the differentiation protocol is reproducible, yielding homogeneous cell populations. Their protein expression profile suggests that hPSC-derived LESCs are similar to the human ocular surface epithelial cells, and possess LESC-like characteristics.

Climatic droplet keratopathy: an old disease in new clothes

Climatic droplet keratopathy (CDK) is an acquired and potentially handicapping cornea degenerative disease that is highly prevalent in certain rural communities around the world. It predominantly affects males over their forties. It has many other names such as Bietti's band-shaped nodular dystrophy, Labrador keratopathy, spheroidal degeneration, chronic actinic keratopathy, oil droplet degeneration, elastoid degeneration and keratinoid corneal degeneration. CDK is characterized by the haziness and opalescence of the cornea's most anterior layers which go through three stages with increasing severity. Globular deposits of different sizes may be histopathologically observed under the corneal epithelium by means of light and electron microscopy. The coalescence and increased volume of these spherules may cause the disruption of Bowman's membrane and the elevation and thinning of the corneal epithelium. The exact aetiology and pathogenesis of CDK are unknown, but they are possibly multifactorial. The only treatment in CDK advanced cases is a corneal transplantation, which in different impoverished regions of the world is not an available option. Many years ago, the clinical and histological aspects of this disease were described in several articles. This review highlights new scientific evidence of the expanding knowledge on CDK's pathogenesis which will open the prospect for new therapeutic interventions.

Elevated expression of matrix metalloproteinase-9 and inflammatory cytokines in keratoconus patients is inhibited by cyclosporine A

PURPOSE

The present study was designed to understand the role of inflammatory cytokines secreted by corneal epithelial cells in keratoconus (KC) and the response to treatment with cyclosporine A (CyA).

METHODS

The study involved 129 Indian KC patients clinically graded according to Amsler-Krumeich classification and 20 healthy, nonectatic subjects as controls. Tear levels of matrix metalloproteinase-9 (MMP9), interleukin-6 (IL6), and tumor necrosis factor-α (TNFα) were measured using ELISA kits. Gene expression was measured by qPCR in corneal epithelial cells obtained by debridement from subjects undergoing ocular surface surgeries. In addition, epithelial cells were stimulated with TNFα and treated with CyA to study its role on MMP9 expression. Finally, 20 KC patients (27 eyes) with inflammatory symptoms were treated with topical CyA application.

RESULTS

We observed that MMP9, TNFα, and IL6 levels were strongly upregulated at the mRNA level in KC patient epithelia. Similarly, tears collected from KC patients exhibited high levels of MMP9 and IL6 protein. Cyclosporine A treatment significantly reduced the mRNA expression levels of IL6 and TNFα in both short- and long-term treatments; however, it reduced MMP9 levels only in long-term treatment in cultured corneal epithelial cells. Subsequent treatment of KC patients with CyA for approximately 6 months reduced tear MMP9 levels and led to local reduction in corneal curvatures as determined by corneal topography maps.

CONCLUSIONS

The data indicate that corneal epithelium contributes to elevated MMP9 and inflammatory cytokine expression in tears of KC patients. Cyclosporine A treatment reduced MMP9 and inflammatory cytokine levels in an in vitro inflammation model system. In KC patients, CyA treatment reduced MMP9 levels measured in tears with concomitant arrest of disease progression. Therefore, CyA might be a novel treatment strategy in KC patients but requires additional evaluation in larger cohorts. (ClinicalTrials.gov number, NCT01746823.).

Proteomic and gene expression patterns of keratoconus

Keratoconus is a progressive corneal thinning disease associated with significant tissue remodeling activities and activation of a variety of signaling networks. However, it is not understood how differential gene and protein expression direct function in keratoconus corneas to drive the underlying pathology, ectasia. Research in the field has focused on discovering differentially expressed genes and proteins and quantifying their levels and activities in keratoconus patient samples. In this study, both microarray analysis of total ribonucleic acid (RNA) and whole proteome analyses are carried out using corneal epithelium and tears from keratoconus patients and compared to healthy controls. A number of structural proteins, signaling molecules, cytokines, proteases, and enzymes have been found to be deregulated in keratoconus corneas. Together, the data provide clues to the complex process of corneal degradation which suggest novel ways to clinically diagnose and manage the disease. This review will focus on discussing these recent advances in the knowledge of keratoconus biology from a gene expression and function point-of-view.

High Refractive Index Inorganic-Organic Interpenetrating Polymer Network (IPN) Hydrogel Nanocomposite toward Artificial Cornea Implants

The use of artificial cornea implants has received increasing attention for treating cornea-related diseases and vision errors due to the low side effects. To achieve long-term successful vision correction, stable and biocompatible materials of high refractive index (RI) need to be developed. Herein, we developed an interpenetrating polymer network (IPN) hydrogel containing well-dispersed ZnS nanoparticles (∼3 nm) covalently linked to the first polymer network, poly(2-hydroethyl methacrylate) (PHEMA). The second polymer network used was poly(acrylic acid) (PAA). The resultant ZnS/PHEMA/PAA IPN nanocomposite is clear and transparent at both dry and hydrated states with their RIs measured to be as high as 1.65 and 1.49, respectively. The equilibrium water content of the hydrogel nanocomposite reached 60.2% which is reasonably near to that of cornea. The material exerted minimal cytotoxicity toward primary epidermal keratinocyte cells. The high RI IPN hydrogel nanocomposite developed here might be an excellent candidate for artificial cornea implants.

Effect of structural parameters of peptides on dimer formation and highly oxidized side products in the oxidation of thiols of linear analogues of human beta-defensin 3 by DMSO

The purpose of this study was to examine the effects of structural parameters of peptides on their oxidation by DMSO, including location of cysteine, effect of adjunct group participation, molecular hydrophobicity, steric hindrance or the accessibility of thiol group and peptide conformation, on oxidation rates, dimer formation and associated side products. We designed and synthesized two series of linear cysteine-containing analogues of human beta-defensin 3 (the C1-peptides with cysteine at the N-terminus residue 1, the C29-peptides with cysteine located at residue 29 in the centre of peptide), which were used for preparation of disulphide-linked homodimers. HPLC-ESI-MS was used to monitor the oxidation process and to characterize the molecular weights of dimers and side products of high oxidation. The formations of dimers and side products were dependent on the position of cysteines. Hydrophobicity generally rendered the thiol groups less accessible and hence exposed them to slow oxidation to form dimers (or even fail to form dimers during the timescale of observation). Molecular dynamics simulations showed that the exposure of cysteines (and sulphurs) of the C1-peptides was much larger than for the C29-peptides. The larger hydrophobic side chains tended to enable clustering of the side chains that sequester cysteine, particularly in the C29-peptides, which provided a molecular explanation for the observed trends in oxidation rates. Together with molecular modelling, we propose a reaction mechanism to elucidate the oxidation results of these peptides.

Use of multiple methods for genotyping Fusarium during an outbreak of contact lens associated fungal keratitis in Singapore

Background

In Singapore, an outbreak of fungal keratitis caused by members of the Fusarium solani species complex (FSSC) was identified in March 2005 to May 2006 involving 66 patients. Epidemiological investigations have indicated that improper contact lens wear and the use of specific contact lens solutions were risk factors.

Methods

We assessed the genetic diversity of the isolates using AFLP, Rep-PCR, and ERIC-PCR and compared the usefulness of these typing schemes to characterize the isolates.

Results

AFLP was the most discriminative typing scheme and appears to group FSSC from eye infections and from other infections differently.

Conclusion

There was a high genomic heterogeneity among the isolates confirming that this was not a point source outbreak.

Defensins knowledgebase: a manually curated database and information source focused on the defensins family of antimicrobial peptides

The defensins knowledgebase is a manually curated database and information source focused on the defensin family of antimicrobial peptides. The current version of the database holds a comprehensive collection of over 350 defensin records each containing sequence, structure and activity information. A web-based interface provides access to the information and allows for text-based searching on the data fields. In addition, the website presents information on patents, grants, research laboratories and scientists, clinical studies and commercial entities pertaining to defensins. With the rapidly increasing interest in defensins, we hope that the knowledgebase will prove to be a valuable resource in the field of antimicrobial peptide research. The defensins knowledgebase is available at .

Transglutaminase Participates in UVB-Induced Cell Death Pathways in Human Corneal Epithelial Cells

PURPOSE

Ultraviolet light (UVB) is known to cause apoptosis in human corneal epithelial cells. This study evaluates the role of transglutaminase in regulating tumor necrosis factor (TNF) receptor clustering as well as caspase activation in UVB-induced apoptosis in human corneal epithelial cells.

METHODS

A human corneal epithelial cell line was used. A single dose of UVB (20 mJ/cm2) was used as a stimulus. Cell viability and cell death were investigated by MTT, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL), and caspase-3 assays. Immunofluorescent staining was used to investigate TNF receptor-I clustering at various time intervals after UVB. Short interfering RNA was used to knock down transglutaminase-2 expression. Fluorescein-cadaverine uptake was used to assess transglutaminase activity. A noncovalent peptide delivery system was used to transfect guinea pig liver transglutaminase into corneal epithelial cells.

RESULTS

UVB increased transglutaminase activity, reduced cell viability, and increased TUNEL staining. UVB or TNF-alpha promoted TNF-receptor-I clustering, a process inhibited by the transglutaminase inhibitor, mono-dansyl cadaverine. UVB also increased activated caspase-3, in a manner suppressible by mono-dansyl cadaverine. Intracellular delivery of exogenous transglutaminase markedly increase caspase-3 activation compared with the vehicle control.

CONCLUSIONS

Transglutaminase enzymatic activity is involved in corneal epithelial cell death after UVB and appears to participate in two steps regulating this process, clustering of TNF receptor-I and caspase-3 activation.

Deposition of Particles on Ocular Tissues and Formation of Krukenberg Spindle, Hyphema, and Hypopyon

Eye diseases, such as Krukenberg’s spindle, hyphema, and hypopyon, are related to the deposition of specific particles such as pigmentary cells, leukocytes, and erythrocytes. These particles are circulated by the aqueous humor (AH) and tend to deposit in regions of low velocities or high resistance. In the present paper, numerical simulations are reported of the AH flow and particle transport, and the particle concentration predictions are qualitatively compared to clinical images. The particle concentration distributions provide an understanding of the likely sources of deposition and the origin of the deposited particles. Pigmentary cells are seen to concentrate in a vertical band on the corneal surface consistent with clinical observations of Krukenberg’s spindle. Leukocytes and erythrocytes are seen to collect at the bottom of the anterior chamber similar to the observations made for hypopyon and hyphema. These results confirm the potential of using numerical calculations in order to obtain a better understanding of the particle transport and deposition patterns in the anterior chamber of the eye.

An outbreak of Fusarium keratitis associated with contact lens wear in Singapore

CONTEXT

Fungal keratitis is a potentially blinding condition that is rarely seen with contact lens wear.

OBJECTIVE

To describe a nationwide outbreak of fungal keratitis caused by Fusarium species among contact lens wearers in Singapore.

DESIGN, SETTING, AND PATIENTS

Nationwide, hospital-based case series. All cases of fungal keratitis among contact lens wearers in all ophthalmology departments in Singapore were reviewed along with the charts of all contact lens wearers with culture-proven fungal keratitis from March 2005 through May 2006. A standardized telephone interview was conducted to obtain additional clinical information.

MAIN OUTCOME MEASURE

Diagnosis of Fusarium keratitis associated with contact lens wear.

RESULTS

During the study period, 66 patients (68 affected eyes) were diagnosed with Fusarium keratitis associated with contact lens wear; the estimated annual national incidence is 2.35 cases per 10,000 contact lens wearers (95% confidence interval, 0.62-7.22). Patients ranged in age from 13 to 44 years (mean [SD], 27.1 [8.4] years), of which 32 (48.5%) were men. The vast majority (65 patients; 98.5%) wore soft, disposable contact lenses; 62 patients (93.9%) reported using 1 brand of contact lens cleaning solution (ReNu, Bausch & Lomb, Rochester, NY), including 42 patients (63.6%) who recalled using ReNu with MoistureLoc. Most patients (81.8%) reported poor contact lens hygiene practices, including overnight use of daily wear contact lenses (19.7%), and use of contact lenses past the replacement date (43.9%). The final best-corrected visual acuity ranged from 20/20 to 20/80. Five patients (5 eyes; 7.4%) required emergency therapeutic or tectonic corneal transplantation.

CONCLUSIONS

A new and evolving epidemic of Fusarium keratitis associated with contact lens wear was found in Singapore. Physicians and eye care practitioners worldwide need to be aware of the likelihood of similar outbreaks emerging among contact lens wearers.

Expression and regulation of cornified envelope proteins in human corneal epithelium

PURPOSE

Stratified squamous epithelial cells assemble a specialized protective barrier structure on their periphery, termed the cornified envelope. The purpose of this study was to evaluate the presence and distribution of cornified envelope precursors in human corneal epithelium, their expression in human corneal epithelial cell cultures, and the effect of ultraviolet radiation (UVB) and transglutaminase (TG) inhibition on their expression.

METHODS

Tissue distribution of small proline-rich proteins (SPRRs) and filaggrin and involucrin was studied in human cornea sections by immunofluorescence staining. Primary human corneal epithelial cells (HCECs) from limbal explants were used in cell culture experiments. A single dose of UVB at 20 mJ/cm2 was used to stimulate these cells, in the presence or absence of mono-dansyl cadaverine (MDC), a TG inhibitor. SPRR2 and involucrin protein levels were studied by immunofluorescence staining and Western blot analysis. Gene expression of 12 proteins was investigated by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

In human cornea tissue, SPRR1, SPRR2, filaggrin, and involucrin protein expression were detected in the central and peripheral corneal and limbal epithelium. In HCECs, SPRR2 and involucrin proteins were detected in the cytosolic fraction, and involucrin levels increased after UVB. Both SPRR2 and involucrin levels accumulated in the presence of MDC. Nine genes including involucrin, SPRR (types 1A, 1B, 2A, 2B, and 3), late envelope protein (LEP) 1 and 16, and filaggrin were expressed by HCECs. SPRR 4, loricrin, and LEP 6 transcripts were not detected. UVB downregulated SPRR (2A, 2B) and LEP 1 transcripts.

CONCLUSIONS

Various envelope precursors are expressed in human corneal epithelium and in HCECs, acute UVB stress differentially alters their expression in HCECs. The expression of envelope precursors and their rapid modulation by UVB supports the role of these proteins in the regulation of ocular surface stress. TG function may be relevant in the regulation of soluble precursors in UVB-stimulated corneal epithelium.

Expression of insulin-like growth factor binding protein-3 in pterygium tissue

BACKGROUND

Pterygium is a fibrovascular overgrowth from the conjunctiva onto the cornea. The pathogenesis of this common ocular surface disorder is not well understood and the only treatment is surgical removal.

METHODS

DNA microarray analysis of primary pterygium tissue was carried out using uninvolved conjunctiva tissue as a comparison for gene expression levels. Real time polymerase chain reaction (PCR) was used to verify the mRNA level of expression for genes changed in pterygium. Western blot analysis and immunohistochemistry showed protein expression levels and the tissue distribution.

RESULTS

Microarray analysis revealed that mRNA levels of a number of genes were changed in primary pterygium. In particular the gene for insulin-like growth factor binding protein-3, (IGFBP3), which modulates the effects of insulin-like growth factor on cells was significantly decreased. Both the message and protein expression of IGFBP3 in pterygium were decreased compared to normal, uninvolved conjunctiva.

CONCLUSION

Decreased levels of IGFBP3 protein have been strongly correlated with the presence of cancer. Identification of the low level of expression of IGFBP3 in pterygium suggests that the pathway controlling cell proliferation has lost an important control mechanism, which may explain the continued growth of pterygium.

Human Limbal Progenitor Cell Characteristics are Maintained in Tissue Culture

Introduction: Acute central serous chorioretinopathy (CSCR) afflicts young middle-aged males in the Western population. We aimed to analyse patient demographics and to determine the angiographic characteristics of acute CSCR in an Asian population. Materials and Methods: This is a retrospective study of all patients presenting with acute CSCR who had fundal fluorescein angiograms performed within a 4-year period (between 1 January 1998 and 31 December 2001). Results: The fluorescein angiograms of 128 patients were analysed. The majority were male (109/128) with a male-to-female ratio of 5.7:1. The age range of patients was 26 to 60 years, with a mean age of 41 years. The majority of patients (84%) were aged 30 to 50 years. With regard to racial distribution, 83% were Chinese, 6% were Malays and 11% were Indians or of other races. Unilateral disease was found in 74 patients (58%) and 52 had bilateral disease. The macula was the most common site of fluorescein leakage and was found in 97 patients (76%). Almost half the patients (44%) had more than one site of disease involvement (i.e., multifocal). The inkblot leakage pattern was found in 103 patients (80%). Conclusions: The patient demographics of acute CSCR in our population were compared to that reported in the West. The gender ratio was similar, with males being afflicted 6 to 10 times more compared to females. There was no racial predilection found for acute CSCR in the local population. We also found a significant proportion of patients with bilateral and multifocal disease compared to the West. The inkblot pattern of leakage was the most common pattern seen on angiography. There were a significant number of cases with bilateral and multifocal involvement, exceeding those reported in non-Asian populations. Key words: Cell culture, Feeder layer, Limbal epithelial cells, Progenitor cells, Stem cells

Human limbal progenitor cell characteristics are maintained in tissue culture

INTRODUCTION

To determine the differentiation of human limbal epithelial cells in tissue culture.

MATERIALS AND METHODS

Epithelial cells from the human limbus (n = 29) were isolated and cultured in supplemental hormonal epithelial medium (SHEM) in the presence of mitomycin C-treated 3T3 feeder layer. Confluent cells were airlifted to form multiple layers. The expression of cytokeratin 3 (K3), cytokeratin 12 (K12), involucrin, connexin 43 (Cx43), proliferation cell nuclear antigen (PCNA) and p63 was studied in normal and airlifted cells by immunohistochemistry. Expression levels of K3 and K12 mRNA were examined by real-time polymerase chain reaction (PCR).

RESULTS

The colony-forming efficiency of primary cultured (P0) cells was about 19.35 +/- 6.46% (mean +/- SD, n = 7). Real-time PCR analysis showed that the transcription level of K3 and K12 in cultured cells was lower than in freshly isolated limbal cells or cells from central cornea (P <0.01). Few cells were positive for K3 in P0 or P1 cells [(1.99 +/- 1.27)% (n = 7, P0) and (3.96 +/- 1.35)% (n = 4, P1), P = 0.046]. More cells at all levels were found to stain positive for PCNA and p63 as compared to K3, K12 and involucrin. After air-lifting, cell sheets of 3 to 5 epithelial cell layers formed. Involucrin showed positive staining in suprabasal layers of the cell sheets while connexin 43 was only observed in the basal layer. Staining of K3 remained sparse.

CONCLUSIONS

Human limbal cells isolated from cadaveric tissues were able to proliferate in vitro and exhibited a phenotype with characteristics similar to that of the limbal stem or progenitor cells.

Numerical Solution of Ocular Fluid Dynamics in a Rabbit Eye: Parametric Effects

Numerical calculations of the aqueous humor dynamics in the anterior chamber of a rabbit's eye are presented to delineate the basic flow mechanisms. The calculations are based on a geometrical model of the eye, which represents the Trabecular meshwork (TM) as a multilayered porous zone of specified pore sizes and void fraction. The outer surface of the cornea is assumed to be at a fixed temperature (corresponding to the ambient temperature), while the iris surface is assumed to be at the core body temperature. Results are obtained for both the horizontal upward-facing orientation of the eye, and the vertical orientation of the eye. Parameters varied include: the temperature difference between the iris and the cornea to underscore the important role of buoyancy in driving the aqueous humor flow; and, the pupil size reflecting different levels of ambient light. Buoyancy is observed to be the dominant driving mechanism for the convective motion in both orientations of the eye. Variations in the pupil size appear to have little influence on the IOP or flow distribution in view of the dominant role of buoyancy in controlling the flow motion. The study provides distributions of the shear stress and flow patterns and delineates the important role of the eye-orientation on these results.

Formation of collagen-glycosaminoglycan blended nanofibrous scaffolds and their biological properties

The development of blended collagen and glycosaminoglycan (GAG) scaffolds can potentially be used in many soft tissue engineering applications since the scaffolds mimic the structure and biological function of native extracellular matrix (ECM). In this study, we were able to obtain novel nanofibrous collagen-GAG scaffolds by electrospinning collagen blended with chondroitin sulfate (CS), a widely used GAG, in a mixed solvent of trifluoroethanol and water. The electrospun collagen-GAG scaffold with 4% CS (COLL-CS-04) exhibited a uniform fiber structure with nanoscale diameters. A second collagen-GAG scaffold with 10% CS consisted of smaller diameter fibers but exhibited a broader diameter distribution due to the different solution properties in comparison with COLL-CS-04. After cross-linking with glutaraldehyde vapor, the collagen-GAG scaffolds became more biostable and were resistant to collagenase degradation. This is evidently a more favorable environment allowing increased proliferation of rabbit conjunctiva fibroblast on the scaffolds. Incorporation of CS into collagen nanofibers without cross-linking did not increase the biostability but still promoted cell growth. The potential of applying the nanoscale collagen-GAG scaffold in tissue engineering is significant since the nanodimension fibers made of natural ECM mimic closely the native ECM found in the human body. The high surface area characteristic of this scaffold may maximize cell-ECM interaction and promote tissue regeneration faster than other conventional scaffolds.

The in vitro and in vivo proliferative capacity of serum-free cultivated human conjunctival epithelial cells

PURPOSE

To investigate the in vitro and in vivo proliferative capacity of human conjunctival epithelial cells cultured in serum-free media, and to compare this with current methods that utilize serum-containing media and 3T3 feeder layers.

METHODS

Human conjunctival epithelial cells were cultivated in serum-free media alone, serum-free media with a 3T3 feeder layer, and serum-containing media with a 3T3 feeder layer. The areas of outgrowth, colony-forming efficiencies and number of population doublings were compared. The in vivo proliferative potential was assessed by analyzing the number of cells generated by the implantation of cultured cells into athymic mice. Cultured cells were evaluated for the expression of cytokeratins K3, K4, K12, K19, as well as the gel-forming goblet cell mucin, MUC5AC.

RESULTS

Cells cultivated in serum-free media, serum-free media and feeder cells, and serum-containing media and feeder cells achieved colony-forming efficiencies of 14.5 +/- 4.1%, 10.1 +/- 3.1%, and 20.4 +/- 6.7%, respectively, and number of population doublings of 24.8 +/- 4.3, 14.8 +/- 3.6, and 30.0 +/- 5.0, respectively. Nine-day old athymic mice conjunctival cysts derived from serum-free cultures comprised 1.29 x 10(6) +/- 0.46 x 10(6) cells, while cysts derived from serum-containing cultures comprised 1.30 x 10(6) +/- 0.53 x 10(6) cells. The degree of epithelial stratification was similar in both conditions. Serum-free cultivated conjunctival cells retained their in vivo characteristics and expressed K4, K19 and MUC5AC. The presence of MUC5AC mRNA in these cells was confirmed by RT-PCR.

CONCLUSIONS

Conjunctival epithelial cells propagated in serum-free media demonstrated a similar in vivo proliferative capability, as compared to serum-containing media with 3T3 feeder cells. This has important clinical implications, as the serum-free ex vivo expansion of cells for clinical transplantation overcomes the problems associated with the use of animal serum and cells.

Early gene expression in the rat cortex after experimental traumatic brain injury and hypotension

To determine c-fos and egr-1 mRNA levels in the rat cortex after traumatic brain injury (TBI) and TBI plus hemorrhagic hypotension (HH). Sprague-Dawley rats were subjected to TBI. HH was induced by removing 5 ml of blood from the jugular vein for a duration of 20 min. Cortical tissue was harvested at 0 and 120 min, and mRNA levels of the immediate early genes c-fos, egr-1 were obtained. Rats that sustained TBI alone had increased c-fos and egr-1 mRNA expression at 120 min that was significant. Additionally, c-fos mRNA levels after TBI alone were significantly higher than c-fos mRNA levels after TBI+HH at 120 min. Levels of egr-1 mRNA after TBI alone at 120 min were not significantly higher than egr-1 mRNA levels after TBI+HH at 120 min.

Response of GAP-43 and p75 in human neuromas over time after traumatic injury

OBJECTIVE

GAP-43 and p75 are proteins that promote growth cone and neurite formation, elongation, and arborization in regenerating nerve axons. The objectives of this study were to determine whether GAP-43 and the low-affinity nerve growth factor receptor p75 are elevated in traumatic neuromas and whether there is a correlation between the relative amount of GAP-43 or p75 and demographic characteristics such as time elapsed between injury and repair.

METHODS

Traumatic neuromas from 21 randomly selected patients were studied, and the charts were reviewed. Specimens were collected at the time of nerve resection and grafting. Immunohistochemical analysis was performed on each sample and normal human nerve with antibodies to GAP-43 and p75. Western blot and computerized gel analyses were performed.

RESULTS

All neuroma specimens harvested within 13 months of injury exhibited markedly elevated GAP-43 levels compared with normal nerve. Specimens harvested at 14 months or more after injury showed precipitously lower GAP-43 levels, similar to or less than those of normal nerve. The correlation between the amount of intra-axonal GAP-43 and postinjury time interval was statistically significant, P = 0.0038. High GAP-43 levels were also correlated with transection injury, high postoperative sensory grade, and pain. p75 levels were elevated, without consistent variation in our population.

CONCLUSION

These preliminary data suggest that the expression of intra-axonal GAP-43 may vary over time after injury, remaining elevated for approximately the first year, then decreasing abruptly to normal or subnormal levels. These results correlate with clinical experience, indicating that peripheral nerves should be repaired relatively early if repair is indicated.

Herpes simplex virus type-1 infection of corneal epithelial cells induces apoptosis of the underlying keratocytes

The purpose of this study was to determine whether primary corneal infection with Herpes simplex virus (HSV)-1 induces keratocyte apoptosis in the rabbit. New Zealand white rabbit eyes were inoculated with HSV-1 strain 17 Syn+. Rabbits that developed slit lamp signs of epithelial infection were killed between 12 and 120 hr post infection. One cornea of each animal was fresh-frozen for TUNEL assay to detect DNA fragmentation in situ. The other cornea was fixed for transmission electron microscopy (TEM). Mechanical scrape wounded rabbit corneas were included as positive controls. DNA fragmentation consistent with apoptosis was detected in anterior keratocytes of corneas at 18, 24, and 48 hr after primary infection with HSV-1 and 2 hr after an epithelial scrape, but not in unwounded control corneas. Electron microscopic evidence of keratocyte apoptosis that included chromatin condensation, chromatin fragmentation, and cellular blebbing with formation of membrane bound cell fragments was detected in mechanical scrape wounded corneas and infected rabbit corneas at 12, 18, 24, 48, and 120 hr after infection, but not in unwounded control corneas. This study suggests that anterior stromal keratocyte apoptosis occurs following primary HSV-1 infection of the corneal epithelium. Previous studies have demonstrated that corneal epithelial scrape wounds induce apoptosis in the underlying keratocyte cells. We hypothesize that soluble mediators released by epithelial injury mediate anterior keratocyte apoptosis and that one of the physiologic functions of this epithelial-stromal apoptosis system is to limit viral extension.