Mesenchymal stem cell-based adjunctive therapy for Pseudomonas aeruginosa-induced keratitis: A proof-of-concept in-vitro study

PURPOSE

Pseudomonas aeruginosa-induced keratitis is one of the most severe and challenging forms of corneal infection, owing to its associated intense inflammatory reactions leading to corneal necrosis and dense corneal scar with loss of vision. Since mesenchymal stem cells (MSCs) are reported to possess antimicrobial and immunomodulatory properties, they can be tested as an adjuvant treatment along with the antibiotics which are the current standard of care. This study aims to investigate the anti-bacterial and immunomodulatory roles of human bone marrow MSC-derived conditioned medium (MSC-CM) in P. aeruginosa-infected human corneal epithelial cells (HCECs) in vitro.

METHODS

The effect of MSC-CM on the growth of clinical isolates of P. aeruginosa was evaluated by colony-forming unit assay. The expression of inflammatory cytokines (IL-6 and TNF-α) and an antimicrobial peptide (Lipocalin 2) in lipopolysaccharide-treated MSCs and HCECs was analyzed through ELISA. Corneal epithelial repair following infection with P. aeruginosa was studied through scratch assay.

RESULTS

Compared to control (P. aeruginosa (5*105) incubated in DMEM (1 ml) at 37 °C for 16 h), MSC-CM significantly: i) inhibits the growth of P. aeruginosa (159*109 vs. 104*109 CFU/ml), ii) accelerates corneal epithelial repair following infection with P. aeruginosa (9% vs. 24% closure of the wounded area after 12 h of infection), and iii) downregulates the lipopolysaccharide-induced expression of IL-6, TNF-α and Lipocalin 2 in HCECs. A combination of MSC-CM with an antibiotic, Ciprofloxacin moderately regulated the expression of IL-6, TNF-α, and Lipocalin 2.

CONCLUSION

MSC-CM holds promise as an adjunctive therapeutic approach for P. aeruginosa-induced corneal epithelial damage.

Complement Cascade 8 - Alpha and Calpain-2 in Extracellular Vesicles of Human Vitreous as Biomarkers of Infectious Endophthalmitis

Purpose

Extracellular vesicles (EVs) are messenger pigeons of the cells that communicate about cellular microenvironment. In this study, we evaluated the expression of C8α and calpain-2 in EVs from vitreous of patients with bacterial endophthalmitis to assess its utility as a diagnostic marker.

Methods

EVs were isolated from vitreous of patients with bacterial endophthalmitis (culture positive and culture negative) and noninfectious control by exosome isolation reagent and characterized, and the levels of C8α and calpain-2 was assessed by enzyme-linked immunosorbent assay in isolated EVs and direct vitreous. The receiver operating characteristic curve was generated to assess the diagnostic performance.

Results

Scanning electron microscopy (SEM) and dynamic light scattering (DLS) confirmed the presence of EVs having a diameter (nm) of 275.2 ± 93, 92 ± 22, and 77.28 ± 12 in culture-positive (CP), culture-negative (CN), and control respectively. The expression level (ng/mL) of C8α in the EVs obtained from CP was 144 ± 22 and CN was 31.2 ± 9.8, which was significantly higher (P < 0.01) than control 3.7 ± 2.4. Interestingly, C8α is not expressed directly in the vitreous of CN and controls. Calpain-2 was significantly downregulated (P ≤ 0.0001) in CP (0.94 ± 0.16) and CN (0.70 ± 0.14) than control. The sensitivity and specificity of 1 for C8α and calpain-2 in the EVs implied that its diagnostic accuracy was significant.

Conclusions

This study showed that the EV proteins C8α and calpain-2 could be suitable diagnostic markers for endophthalmitis. However, the presence of C8α in the EVs of CN samples but not in direct vitreous promises EVs as the future of diagnostics.

Translational Relevance

Expression levels of EV-calpain-2 and EV-C8α could diagnose CN bacterial endophthalmitis.

Tetraspanin CD9-derived peptides inhibit Pseudomonas aeruginosa corneal infection and aid in wound healing of corneal epithelial cells

Pseudomonas aeruginosa is a leading cause of corneal infection both within India and globally, often causing a loss of vision. Increasing antimicrobial resistance among the bacteria is making its treatment more difficult. Preventing initial bacterial adherence to the host membrane has been explored here to reduce infection of the cornea. Synthetic peptides derived from human tetraspanin CD9 have been shown to reduce infection in corneal cells both in vitro, ex vivo and in vivo. We found constitutive expression of CD9 in immortalized human corneal epithelial cells by flow cytometry and immunocytochemistry. The synthetic peptides derived from CD9 significantly reduced bacterial adherence to cultured corneal epithelial cells and ex vivo human cadaveric corneas as determined by colony forming units. The peptides also significantly reduced bacterial burden in a murine model of Pseudomonas keratitis and lowered the cellular infiltration in the corneal stroma. Additionally, the peptides aided corneal wound healing in uninfected C57BL/6 mice compared to control mice. These potential therapeutics had no effect on cell viability or proliferation of corneal epithelial cells and have the potential to be developed as an alternative therapeutic intervention.

Hyperkeratinization and Proinflammatory Cytokine Expression in Meibomian Glands Induced by Staphylococcus aureus

Purpose

This exploratory study aimed to investigate the morphological and pathological alterations of the meibomian gland (MG) with the Staphylococcus aureus crude extracts (SACEs) treatment.

Methods

Mouse MG explants were cultured and differentiated with or without SACEs for 48 hours. Explant's viability and cell death were determined by thiazolyl blue tetrazolium bromide (MTT) assay and TUNEL assay. MG morphology was observed by Hematoxylin and Eosin staining. Lipid droplet production was detected by Nile Red staining and LipidTox immunostaining. The pro-inflammatory cytokines were detected by ELISA. The relative gene and protein expression in MG explants was determined via quantitative RT-PCR, immunostaining, and immunoblotting. The components of the SACEs were analyzed by immunoblotting and silver staining.

Results

Our findings demonstrated that the SACEs treatment induced overexpression of keratin 1 (Krt1) in the ducts and acini of MG explants, accompanied by a decrease in viability and an increase in cell death in explants. Furthermore, the SACEs treatment dose-dependently increased the levels of TNF-α, IL-1β, and IL-6 in MG explants. The SACEs treatment induced activation of the nuclear factor kappa B (NF-κB) and AIM2 (absent in melanoma 2)/ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) inflammasome signaling pathway in explants. Further investigation showed expression of the key adipogenesis-related molecule peroxisome proliferator-activated receptor γ was decreased after SACEs treatment. However, no change was found in the lipid synthesis of MG explants after treatment with the SACEs. Staphylococcal enterotoxins B (SEB) was detected in the SACEs. SEB induced the overexpression of Krt1 and IL-1β in ducts and acini of MG explants.

Conclusions

Our findings confirm that Staphylococcus aureus induced hyperkeratinization and pro-inflammatory cytokines expression in MG explants ducts and acini. These effects might be mediated by SEB. Activation of the NF-κB and AIM2/ASC signaling pathway is involved in this process.

Wedelolactone ameliorates Pseudomonas aeruginosa-induced inflammation and corneal injury by suppressing caspase-4/5/11/GSDMD-mediated non-canonical pyroptosis

Pseudomonas aeruginosa (P. aeruginosa) keratitis, a worldwide leading cause of corneal perforation and blindness, which is associated with contact lens usage. Increasing evidence has indicated that pyroptosis, a novel proinflammatory programmed cell death, is linked with ocular diseases, little is known about the role of noncanonical pyroptosis in microbial keratitis. Here, we first indicated the involvement of noncanonical pyroptosis in P. aeruginosa keratitis and investigated whether wedelolactone (WDL), a major active component of Eclipta prostrate known to target caspase-11, could alleviate P. aeruginosa keratitis development. We found the expression of caspase-4/5/11 and cleaved GSDMD in corneas of P. aeruginosa keratitis patients, animal models and lipopolysaccharide (LPS)-induced primary cultured human corneal keratocytes (piHCKs) were increased. Combining ciprofloxacin with WDL significantly ameliorated the severity of P. aeruginosa keratitis, as manifested by decreased inflammatory responses and reduced corneal epithelial defects. Consistent with these findings, WDL also dose-dependently alleviated LPS-induced noncanonical pyroptosis by reversing the increased expression of caspase-4/5 and GSDMD in piHCKs. In summary, our results demonstrated that by targeting the activation of caspase-4/5/11, wedelolactone inhibited the development of P. aeruginosa keratitis and suppressed the release of proinflammatory cytokines. Wedelolactone may be a promising anti-inflammatory candidate to combat P. aeruginosa keratitis.

Oxygen Self-Supplying Nanotherapeutic for Mitigation of Tissue Hypoxia and Enhanced Photodynamic Therapy of Bacterial Keratitis

Hypoxia, a common characteristic of bacterial infections, is known to be closely associated with the emergence of multidrug-resistant bacteria, which hastens the need to develop advanced microbicides and antibacterial techniques. Photodynamic therapy is a promising strategy to reduce bacterial antibiotic resistance and employs photosensitizers, excitation light sources, and sufficient oxygen to generate toxic reactive oxygen species (ROS). The inherent limitation of PDT is that the generation of ROS is restricted by the hypoxic microenvironment in infection sites. Here, an oxygen self-supplying nanotherapeutic is developed to enhance antibacterial activity against multidrug-resistant bacteria on the basis of fluorinated boron dipyrromethene (BODIPY)-based glycomimetics. The nanotherapeutic not only could capture the bacteria efficiently but also was able to act as an oxygen carrier to relieve the hypoxic microenvironment of bacterial infections, thus achieving enhanced PDT efficacy. In a Pseudomonas aeruginosa infection of a rat cornea, typical administration of the nanotherapeutic decreased the infiltrate and showed a faster healing capacity in comparison with BODIPY-based glycomimetics. Self-supplying oxygen nanotherapeutics that relieve the hypoxic microenvironment and interfere with bacterial colonization have been shown to be a promising candidate for the management of drug-resistant microbial keratitis.

Integrative metabolomics and transcriptomics identifies itaconate as an adjunct therapy to treat ocular bacterial infection

The eye is highly susceptible to inflammation-mediated tissue damage evoked during bacterial infection. However, mechanisms regulating inflammation to protect the eye remain elusive. Here, we used integrated metabolomics and transcriptomics to show that the immunomodulatory metabolite itaconate and immune-responsive gene 1 (Irg1) are induced in bacterial (Staphylococcus aureus)-infected mouse eyes, bone-marrow-derived macrophages (BMDMs), and Müller glia. Itaconate levels are also elevated in the vitreous of patients with bacterial endophthalmitis. Irg1 deficiency in mice led to increased ocular pathology. Conversely, intraocular administration of itaconate protects both Irg1-/- and wild-type mice from bacterial endophthalmitis by reducing inflammation, bacterial burden, and preserving retinal architecture and visual function. Notably, itaconate exerts synergistic effects with antibiotics. The protective, anti-inflammatory effects of itaconate are mediated via activation of NRF2/HO-1 signaling and inhibition of NLRP3 inflammasome. Collectively, our study demonstrates the Irg1/itaconate axis is a regulator of intraocular inflammation and provides evidence for using itaconate, along with antibiotics, to treat bacterial infections.

ISG15 Acts as a Mediator of Innate Immune Response to Pseudomonas aeruginosa Infection in C57BL/6J Mouse Corneas

Purpose

IFN-stimulated gene (ISG) 15 is a type 1 IFN-induced protein and known to modify target proteins in a manner similar to ubiquitylation (protein conjugation by ISG15 is termed ISGylation). We sought to determine the role of ISG15 and its underlying mechanisms in corneal innate immune defense against Pseudomonas aeruginosa keratitis.

Methods

ISG15 expression in cultured human corneal epithelial cells (HCECs) and mouse corneas was determined by PCR and Western blot analysis. Gene knockout mice were used to define the role of ISG15 signaling in controlling the severity of P. aeruginosa keratitis, which was assessed with photographing, clinical scoring, bacterial counting, myeloperoxidase assay, and quantitative PCR determination of cytokine expression. Integrin LFA-1 inhibitor was used to assess its involvement of ISG15 signaling in P. aeruginosa-infected corneas.

Results

Heat-killed P. aeruginosa induced ISG15 expression in cultured HCECs and accumulation in the conditioned media. Isg15 deficiency accelerated keratitis progress, suppressed IFNγ and CXCL10, and promoted IL-1β while exhibiting no effects on IFNα expression. Moreover, exogenous ISG15 protected the corneas of wild-type mice from P. aeruginosa infection while markedly reducing the severity of P. aeruginosa keratitis in type 1 IFN-receptor knockout mice. Exogenous ISG15 increased bacteriostatic activity of B6 mouse corneal homogenates, and inhibition of LFA-1 exacerbated the severity of and abolished protective effects of ISG15 on P. aeruginosa keratitis.

Conclusions

Type 1 INF-induced ISG15 regulates the innate immune response and greatly reduces the susceptibility of B6 mouse corneas to P. aeruginosa infection in an LFA-1-dependent manner.

The Regulating Role of SB216763 in Pseudomonas aeruginosa Keratitis

BACKGROUND

Glycogen synthase kinase 3 beta (GSK3b) is a multifunctional molecule, which plays a critical role in the regulation of various signaling pathways including cell proliferation, growth and development, and inflammation. However, whether GSK3b is involved in the pathological process of Pseudomonas aeruginosa keratitis remains unknown.

METHODS

First, western blots were performed to measure the phosphorylated level of GSK3β at Ser9 (inactive form) in an animal model of Pseudomonas aeruginosa keratitis. Second, the keratitis model received the GSK3β inhibitor SB216763, and the inflammation of cornea was evaluated by clinical scores and slit photos. The expressions of inflammatory cytokines were assessed by real-time PCR, and the corneal bacterial burden was determined by plate count.

RESULTS

The phosphorylated level of GSK3β at Ser9 in the cornea markedly decreased after Pseudomonas aeruginosa infection. The inhibition of GSK3β by SB216763 significantly ameliorated the progress of corneal disease and alleviated corneal opacity. SB216763 suppressed the expression of inflammatory cytokines IL-6 and IL-1b, but exhibited no effects on TNF-a and IL-10 expression. SB216763 dramatically decreased cornea bacterial burden at 5 days after infection with Pseudomonas aeruginosa.

CONCLUSIONS

The activity of GSK3b was enhanced in Pseudomonas aeruginosa keratitis. The inhibition of GSK3β by SB216763 promoted host resistance against Pseudomonas aeruginosa keratitis, via down regulating inflammatory cytokines and bacterial burden.

The role of staphopain a in Staphylococcus aureus keratitis

Staphylococcus aureus is a common bacterial isolate from cases of microbial keratitis. The virulence factors that contribute to its pathogenicity during this disease have not been fully resolved. The aim of the current study was to examine the effects of the extracellular protease Staphopain A on corneal virulence. Two strains were used, one Staph 38 that gives a high pathology score during keratitis and a less virulent strain ATCC 8325-4. The effect of inhibition of Staphopain by general or specific protease inhibitors on adhesion of strains to fibronectin-coated glass or PMMA was determined. This was followed by an analysis of the effect of Staphopain A on the ability of the bacteria to adhere to and invade corneal epithelial cells. Finally, the effect of inhibiting Staphopain A on pathogenesis in a mouse model of keratitis was studied. Staphopain A increased the adhesion of strains to fibronectin-coated substrata and inhibition of Staphopain A reduced adhesion. The inhibition of Staphopain A by staphostatin A significantly decreased both association with and invasion into human corneal epithelial cells by 15-fold for strain Saur38. Inhibition of Staphopain A significantly reduced the pathology associated with S. aureus keratitis, reducing the infecting numbers of bacteria from 1.8x10⁵ to <1x10⁴ cells/cornea (p ≤ 0.001), significantly reducing the corneal pathology score (p ≤ 0.038) and reducing the numbers of infiltrating PMNs. This study shows that Staphopain increases adhesion and invasion of corneal cells due to increasing fibronectin binding and its inhibition has a significant impact on pathogenicity of S. aureus during keratitis.

S-layer Impacts the Virulence of Bacillus in Endophthalmitis

Purpose

Bacillus causes a sight-threating infection of the posterior segment of the eye. The robust intraocular inflammatory response in this disease is likely activated via host innate receptor interactions with components of the Bacillus cell envelope. S-layer proteins (SLPs) of some Gram-positive pathogens contribute to the pathogenesis of certain infections. The potential contributions of SLPs in eye infection pathogenesis have not been considered. Here, we explored the role of a Bacillus SLP (SlpA) in endophthalmitis pathogenesis.

Methods

The phenotypes and infectivity of wild-type (WT) and S-layer deficient (ΔslpA) Bacillus thuringiensis were compared. Experimental endophthalmitis was induced in C57BL/6J mice by intravitreally injecting 100-CFU WT or ΔslpA B. thuringiensis. Infected eyes were analyzed by bacterial counts, retinal function analysis, histology, and inflammatory cell influx. SLP-induced inflammation was also analyzed in vitro. Muller cells (MIO-M1) were treated with purified SLP. Nuclear factor-κB (NF-κB) DNA binding was measured by ELISA and expression of proinflammatory mediators from Muller cells was measured by RT-qPCR.

Results

Tested phenotypes of WT and ΔslpA B. thuringiensis were similar, with the exception of absence of the S-layer in the ΔslpA mutant. Intraocular growth of WT and ΔslpA B. thuringiensis was also similar. However, eyes infected with the ΔslpA mutant had significantly reduced inflammatory cell influx, less inflammatory damage to the eyes, and significant retention of retinal function compared with WT-infected eyes. SLP was also a potent stimulator of the NF-κB pathway and induced the expression of proinflammatory mediators (IL6, TNFα, CCL2, and CXCL-1) in human retinal Muller cells.

Conclusions

Taken together, our results suggest that SlpA contributes to the pathogenesis of Bacillus endophthalmitis, potentially by triggering innate inflammatory pathways in the retina.

Growth hormone-releasing hormone receptor mediates cytokine production in ciliary and iris epithelial cells during LPS-induced ocular inflammation

The receptor for growth hormone-releasing hormone (GHRH-R) has been shown to upregulate specifically in the ciliary and iris epithelial cells and infiltrating cells in the aqueous humor in a rat model of acute anterior uveitis. Treatment with GHRHR-R antagonist alleviates significantly these inflammatory responses. Herein we investigated whether the ciliary and iris epithelial cells can respond directly to lipopolysaccharide (LPS) without the influences of circulating leukocytes to produce inflammatory mediators through a GHRH-R mediated mechanism. In explant cultures of rat ciliary body and iris, LPS caused a substantial increase of GHRH-R in 24 h. Immunohistochemistry showed a localization of TLR4, the receptor for LPS, and an elevated expression of IL-6 and IL-1β in ciliary and iris epithelial cells after LPS treatment. LPS also elevated the level of IL-1β, IL-6, and iNOS and increased secretion of IL-1β and IL-6 from the explants. The GHRH-R antagonist, MIA-602, suppressed the elevated expression of IL-1β and IL-6, and reduced the release of IL-6. Such effects were not seen for the GHRHR agonist, MR-409. When co-cultured with leukocytes, expression of GHRH-R in the ocular explants was further enhanced during LPS treatment. Our results demonstrate a direct action of LPS on ciliary and iris epithelial cells to produce pro-inflammatory factors through a GHRH-R mediated mechanism, and suggest a role of these epithelial cells, in addition to the resident antigen presenting cells, in immune surveillance of the eye. Infiltrating leukocytes may enhance these inflammatory responses by regulating GHRH-R in ciliary and iris epithelial cells, in addition to their functions of synthesizing proinflammatory cytokines.

Association between possession of ExoU and antibiotic resistance in Pseudomonas aeruginosa

Virulent strains of Pseudomonas aeruginosa are often associated with an acquired cytotoxic protein, exoenzyme U (ExoU) that rapidly destroys the cell membranes of host cells by its phospholipase activity. Strains possessing the exoU gene are predominant in eye infections and are more resistant to antibiotics. Thus, it is essential to understand treatment options for these strains. Here, we have investigated the resistance profiles and genes associated with resistance for fluoroquinolone and beta-lactams. A total of 22 strains of P. aeruginosa from anterior eye infections, microbial keratitis (MK), and the lungs of cystic fibrosis (CF) patients were used. Based on whole genome sequencing, the prevalence of the exoU gene was 61.5% in MK isolates whereas none of the CF isolates possessed this gene. Overall, higher antibiotic resistance was observed in the isolates possessing exoU. Of the exoU strains, all except one were resistant to fluoroquinolones, 100% were resistant to beta-lactams. 75% had mutations in quinolone resistance determining regions (T81I gyrA and/or S87L parC) which correlated with fluoroquinolone resistance. In addition, exoU strains had mutations at K76Q, A110T, and V126E in ampC, Q155I and V356I in ampR and E114A, G283E, and M288R in mexR genes that are associated with higher beta-lactamase and efflux pump activities. In contrast, such mutations were not observed in the strains lacking exoU. The expression of the ampC gene increased by up to nine-fold in all eight exoU strains and the ampR was upregulated in seven exoU strains compared to PAO1. The expression of mexR gene was 1.4 to 3.6 fold lower in 75% of exoU strains. This study highlights the association between virulence traits and antibiotic resistance in pathogenic P. aeruginosa.

Intraocular Levels of Cefuroxime in Inflamed Rabbit Eyes

The pharmacokinetics of cefuroxime was studied in the inflamed rabbit eye employing subconjunctival, intravitreal and combined intravitreal-intravenous routes of administration to study the intraocular levels and the duration of minimum inhibitory concentrations (MIC) of the antibiotic in the vitreous and in the aqueous. A standard inoculum of viable S. aureus was injected into the vitreous of 36 pigmented rabbits to establish experimental endophthalmitis. A biological method was used for the antibiotic assay. Penetration of systemically and subconjunctivally administered-cefuroxime into the inflamed vitreous was poor. Intraocular inflammation increased the clearance of the intravitreally injected cefuroxime. A dose of 75 mg subconjunctivally produced levels in the aqueous far exceeding MIC for over six hours. Penetration of intravitreally injected cefuroxime into the aqueous was poor, inconsistent and short lasting. Following a single intravitreal injection of 1000 μg cefuroxime, levels exceeding the MIC for common ocular pathogens persisted in the vitreous for at least 24 hours but supplementation with intravenous cefuroxime neither increased the intraocular levels nor delayed the clearance of the intravitreally injected antibiotic.

Corneal Collagen Cross-linking: A Review of Clinical Applications

Corneal collagen cross-linking (CXL) has been shown to slow down or stop the progression of keratoconus. In addition, CXL has been applied in cases of corneal ectasia. Recent reports of the use of CXL in cases of infectious keratitis have generated further interest in this treatment modality. This review discusses the principle, clinical uses, and complications associated with CXL.

In vitro studies on the antimicrobial peptide human beta-defensin 9 (HBD9): signalling pathways and pathogen-related response (an American Ophthalmological Society thesis)

PURPOSE

Human β-defensins (HBDs) are an important part of the innate immune host defense at the ocular surface. Unlike other defensins, expression of HBD9 at the ocular surface is reduced during microbial infection, but activation of toll-like receptor 2 (TLR2) in corneal epithelial cells has been shown to up-regulate HBD9. Our purpose was to test the hypothesis that TLR2 has a key role in the signalling pathway(s) involved in the overexpression or underexpression of HBD9, and accordingly, different pathogens would induce a different expression pattern of HBD9.

METHODS

The in vitro RNAi silencing method and response to dexamethasone were used to determine key molecules involved in signalling pathways of HBD9 in immortalized human corneal epithelial cells. The techniques included cell culture with exposure to specific transcription factor inhibitors and bacteria, RNA extraction and cDNA synthesis, quantitative real-time polymerase chain reaction, and immunohistology.

RESULTS

This study demonstrates that TLR2 induces HBD9 mRNA and protein expression in a time- and dose-dependent manner. Transforming growth factor-β-activated kinase 1 (TAK1) plays a central role in HBD9 induction by TLR2, and transcription factors c-JUN and activating transcription factor 2 are also involved. Dexamethasone reduces TLR2-mediated up-regulation of HBD9 mRNA and protein levels in mitogen-activated protein kinase phosphatase 1 (MKP1)-dependent and c-JUN-independent manner. HBD9 expression differs with gram-negative and gram-positive bacteria.

CONCLUSIONS

TLR2-mediated MKPs and nuclear factor-κB signalling pathways are involved in HBD9 expression. TAK-1 is a key molecule. These molecules can be potentially targeted to modulate HBD9 expression. Differential expression of HBD9 with different bacteria could be related to differences in pathogen-associated molecular patterns of these organisms.

Role of TLR5 and flagella in bacillus intraocular infection

B. cereus possesses flagella which allow the organism to migrate within the eye during a blinding form of intraocular infection called endophthalmitis. Because flagella is a ligand for Toll-like receptor 5 (TLR5), we hypothesized that TLR5 contributed to endophthalmitis pathogenesis. Endophthalmitis was induced in C57BL/6J and TLR5−/− mice by injecting 100 CFU of B. cereus into the mid-vitreous. Eyes were analyzed for intraocular bacterial growth, retinal function, and inflammation by published methods. Purified B. cereus flagellin was also injected into the mid-vitreous of wild type C57BL/6J mice and inflammation was analyzed. TLR5 activation by B. cereus flagellin was also analyzed in vitro. B. cereus grew rapidly and at similar rates in infected eyes of C57BL/6J and TLR5−/− mice. A significant loss in retinal function in both groups of mice was observed at 8 and 12 hours postinfection. Retinal architecture disruption and acute inflammation (neutrophil infiltration and proinflammatory cytokine concentrations) increased and were significant at 8 and 12 hours postinfection. Acute inflammation was comparable in TLR5−/− and C57BL/6J mice. Physiological concentrations of purified B. cereus flagellin caused significant inflammation in C57BL/6J mouse eyes, but not to the extent of that observed during active infection. Purified B. cereus flagellin was a weak agonist for TLR5 in vitro. These results demonstrated that the absence of TLR5 did not have a significant effect on the evolution of B. cereus endophthalmitis. This disparity may be due to sequence differences in important TLR5 binding domains in B. cereus flagellin or the lack of flagellin monomers in the eye to activate TLR5 during infection. Taken together, these results suggest a limited role for flagellin/TLR5 interactions in B. cereus endophthalmitis. Based on this and previous data, the importance of flagella in this disease lies in its contribution to the motility of the organism within the eye during infection.

HGF signaling impacts severity of Pseudomonas aeruginosa keratitis

PURPOSE

To determine whether rapamycin altered corneal growth factor levels to impact severity of Pseudomonas aeruginosa keratitis.

METHODS

BALB/c mice were injected intraperitoneally with rapamycin or PBS and infected with P. aeruginosa. Corneas were harvested and mRNA levels of growth factors (EGF, HGF, FGF-7/KGF), receptors (EGFR, c-met, FGFR-2), and signaling molecules (PI3K, Akt, S6K1, and IGF-1R) tested. ELISA determined HGF/c-met, IGF-1, and Substance P (SP) protein levels. Corneal application of recombinant (r)HGF was assessed by clinical score, photography with a slit lamp, real-time RT-PCR (mRNA for mT0R, IL-10, IL-12, IL-18, PI3KCα, Akt), and ELISA (total and phosphorylated [p]c-met); rIGF-1 effects also were tested by ELISA. In vitro, RAW cells and peritoneal macrophages were stimulated with LPS ± rHGF ± c-met inhibitor (CI) and mTOR mRNA levels tested.

RESULTS

Rapamycin disparately regulated infected corneal mRNA levels of EGF/EGFR and FGF-7/FGFR-2, but HGF/c-met mRNA levels both increased. ELISA confirmed elevated HGF protein. Rapamycin did not change PI3KCα or Akt signaling molecule expression, downregulated S6K1, but upregulated IGF-1R mRNA levels; IGF-1 and SP proteins also were upregulated. After infection, topical rHGF versus PBS increased mRNA levels of IL-12p40, IL-18, PI3KCα, and Akt; mTOR and IL-10 mRNA were downregulated; rIGF-1 increased HGF protein. In vitro, rHGF and LPS lowered RAW cell and macrophage mTOR levels; CI addition restored them.

CONCLUSIONS

Collectively, these data provide evidence that enhanced corneal HGF levels increase signaling through the c-met receptor, decrease mTOR levels, and enhance proinflammatory cytokines, while decreasing anti-inflammatory cytokines, and that HGF signaling is central to disease outcome.

Galectin-1-mediated suppression of Pseudomonas aeruginosa-induced corneal immunopathology

Corneal infection with Pseudomonas aeruginosa leads to a severe immunoinflammatory lesion, often causing vision impairment and blindness. Although past studies have indicated a critical role for CD4(+) T cells, particularly Th1 cells, in corneal immunopathology, the relative contribution of recently discovered Th17 and regulatory T cells is undefined. In this study, we demonstrate that after corneal P. aeruginosa infection, both Th1 and Th17 cells infiltrate the cornea with increased representation of Th17 cells. In addition to Th1 and Th17 cells, regulatory T cells also migrate into the cornea during early as well as late stages of corneal pathology. Moreover, using galectin-1 (Gal-1), an immunomodulatory carbohydrate-binding molecule, we investigated whether shifting the balance among various CD4(+) T cell subsets can modulate P. aeruginosa-induced corneal immunopathology. We demonstrate in this study that local recombinant Gal-1 (rGal-1) treatment by subconjunctival injections significantly diminishes P. aeruginosa-mediated corneal inflammation through multiple mechanisms. Specifically, in our study, rGal-1 treatment significantly diminished corneal infiltration of total CD45(+) T cells, neutrophils, and CD4(+) T cells. Furthermore, rGal-1 treatment significantly reduced proinflammatory Th17 cell response in the cornea as well as local draining lymph nodes. Also, rGal-1 therapy promoted anti-inflammatory Th2 and IL-10 response in secondary lymphoid organs. Collectively, our results indicate that corneal P. aeruginosa infection induces a strong Th17-mediated corneal pathology, and treatment with endogenously derived protein such as Gal-1 may be of therapeutic value for the management of bacterial keratitis, a prevalent cause of vision loss and blindness in humans worldwide.

Role of Toll-like receptor (TLR) 2 in experimental Bacillus cereus endophthalmitis

Bacillus cereus causes a uniquely rapid and blinding intraocular infection, endophthalmitis. B. cereus replicates in the eye, synthesizes numerous toxins, and incites explosive intraocular inflammation. The mechanisms involved in the rapid and explosive intraocular immune response have not been addressed. Because Toll-like receptors (TLRs) are integral to the initial recognition of organisms during infection, we hypothesized that the uniquely explosive immune response observed during B. cereus endophthalmitis is directly influenced by the presence of TLR2, a known gram-positive pathogen recognition receptor. To address this hypothesis, we compared the courses of experimental B. cereus endophthalmitis in wild type C57BL/6J mice to that of age-matched homozygous TLR2(-/-) mice. Output parameters included analysis of bacterial growth, inflammatory cell (PMN) infiltration, cytokine/chemokine kinetics, retinal function testing, and histology, with N≥4 eyes/assay/time point/mouse strain. B. cereus grew at similar rates to10(8) CFU/eye by 12 h, regardless of the mouse strain. Retinal function was preserved to a greater degree in infected TLR2(-/-) eyes compared to that of infected wild type eyes, but infected eyes of both mouse strains lost significant function. Retinal architecture was preserved in infected TLR2(-/-) eyes, with limited retinal and vitreal cellular infiltration compared to that of infected wild type eyes. Ocular myeloperoxidase activities corroborated these results. In general, TNFα, IFNγ, IL6, and KC were detected in greater concentrations in infected wild type eyes than in infected TLR2(-/-) eyes. The absence of TLR2 resulted in decreased intraocular proinflammatory cytokine/chemokine levels and altered recruitment of inflammatory cells into the eye, resulting in less intraocular inflammation and preservation of retinal architecture, and a slightly greater degree of retinal function. These results demonstrate TLR2 is an important component of the initial ocular response to B. cereus endophthalmitis.

Immunohistochemical analysis of ocular platelet basic protein expression during infection with Pseudomonas aeruginosa

Platelet basic protein (PBP) and several of its derivatives are known to express a wide range of biological characteristics. It is the precursor of connective tissue activating peptide (CTAP-III), beta thromboglobulin (beta-TG) and neutrophil activating peptide (NAP-2), which is the proteolytic derived end product. The temporal ocular expression of the chemokine PBP before and during corneal infection over several days by Pseudomonas aeruginosa was examined by immunohistochemistry. Prior to corneal infection, immunohistochemical staining demonstrated the constitutive expression of PBP in the cornea, lens and retina. PBP expression was present in the corneal epithelium, stromal fibroblasts and endothelium. There was a temporal increase in PBP expression in the cornea after infection. The entire cornea exhibited extensive cellular infiltration by positive PBP staining infiltrating cells within 6 days post-infection. The cornea, lens and retina underwent extensive degradation within 5-6 days post-infection with some apparent selective increase in PBP staining in the lens and retina.

Penetration of Gatifloxacin Eye Drops into the Aqueous Humor in Humans

The authors topically administered gatifloxacin (GFLX) into the eye before cataract surgery and measured the concentrations of this agent to determine its penetration into aqueous humor. Seventy-seven patients with age-related cataracts who underwent cataract surgery were enrolled in this study. They received 0.3% GFLX ophthalmic solution 4 times at 30-min intervals, beginning 2 h before surgery. Aqueous humor was aspirated from the anterior chamber and assayed for GFLX concentration using high-performance liquid chromatography. The mean intraoperative GFLX concentration in aqueous humor was 0.485 +/- 0.328 microg/mL. GFLX level was 0.573 +/- 0.367 microg/mL in elderly patients, at least 70 years of age, and was significantly higher than that (0.322 +/- 0.135 microg/mL) in the patients less than 70 years old. This concentration was close to or higher than the minimum inhibitory concentrations required to inhibit the growth of 90% of major pathogens of endophthalmitis (MIC90), such as Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecalis associated with poor prognosis, other than Staphylococcus epidermidis, Pseudomonas aeruginosa, and MRSA (methicillin-resistant S. aureus) in vitro. The GFLX concentrations found in aqueous humor samples were sufficient to kill bacteria other than S. epidermidis, P. aeruginosa, and MRSA in vitro.

IFN-γ: Regulation of Nitric Oxide in theP. aeruginosa-Infected Cornea

PURPOSE

BALB/c mice are resistant to Pseudomonas aeruginosa (P. aeruginosa) keratitis and bacterial killing/stasis requires nitric oxide (NO). NO regulation in the cornea is unknown and was tested in this model.

METHODS

Nitrite detection, IFN-gamma-knockout mice, TNF-alpha neutralization, ELISA, aminoguanidine (AG) treatment, MPO, and plate counts were done.

RESULTS

Evidence shows (i) without IFN-gamma, nitrite levels are elevated, (ii) neutralization of TNF-alpha does not change nitrite levels, and (iii) absence of IFN-alpha and reduced NO synergistically increases disease progress and upregulates pro-inflammatory cytokines, PMN number, and bacterial load.

CONCLUSION

IFN-gamma regulates NO levels, and synergistic interaction between the two regulates disease outcome in resistant mice.

In Vitro Efficacy and Pharmacodynamic Indices for Antibiotics against Coagulase-Negative Staphylococcus Endophthalmitis Isolates

PURPOSE

To compare pharmacodynamic indices and minimal inhibitory concentrations for vancomycin, gatifloxacin, moxifloxacin, linezolid, and combined quinupristin and dalfopristin for historic and current human coagulase-negative staphylococcus (CoNS) endophthalmitis isolates.

DESIGN

Experimental study.

PARTICIPANTS

Fifty-nine CoNS endophthalmitis isolates retrieved from patients at the Bascom Palmer Eye Institute from 1993 through 2006.

METHODS

Coagulase-negative staphylococcal endophthalmitis isolates were recovered from the microbiology specimen bank, rehydrated, and processed for susceptibility testing using standard microbiological protocols. E tests were used to determine and compare mean inhibitory concentration for 50% of isolates (MIC50) and mean inhibitory concentration for 90% of isolates (MIC90) values. Peak concentration (C(max)) was defined as the maximum attainable aqueous concentration using topical or oral therapy, or both. The MIC50 and MIC90 values for each antibiotic are the minimum concentrations that inhibit 50% and 90% of CoNS endophthalmitis isolates, respectively. Significance was determined by the McNemar test. Pharmacodynamic indices (C(max)/MIC) were calculated using determined MIC values and published intraocular drug concentrations for topical and oral dosing. The pharmacodynamic index was defined as the achievable aqueous humor concentration of an antibiotic divided by the concentration of the antibiotic required to inhibit a specified percentage of microbiologic isolates.

MAIN OUTCOME MEASURES

Pharmacodynamic indices for new and conventional antibiotics.

RESULTS

General in vitro susceptibility patterns in descending order were vancomycin (100%), linezolid (100%), quinupristin and dalfopristin (98%), moxifloxacin (48%), and gatifloxacin (47%). The corresponding MIC50 and MIC90 values were vancomycin, 2 microg/ml and 3 microg/ml, respectively; linezolid, 1 microg/ml and 4 microg/ml; quinupristin and dalfopristin, 0.25 microg/ml and 0.5 microg/ml; moxifloxacin, 0.75 microg/ml and > or =32 microg/ml; and gatifloxacin, 2 microg/ml and > or =32 microg/ml. Pharmacokinetic indices (C(max)/MIC90) for topical dosing were all <1. There was a significant difference in the percent of isolates susceptible to combined quinupristin and dalfopristin, vancomycin, and linezolid compared with moxifloxacin and gatifloxacin. There was no statistical significance in CoNS susceptibility between the tested fluoroquinolones.

CONCLUSIONS

Vancomycin, linezolid, and combined quinupristin and dalfopristin were more effective in vitro than fluoroquinolones against CoNS in the current study. Reported aqueous concentrations of the antibiotics used in this study failed to provide adequate coverage for 90% of the CoNS endophthalmitis isolates.

Contact Lenses: Optimal Vision—Sub-Optimal Carrier?

The development of silicone hydrogel contact lenses with high oxygen permeabilities is a major step forward in vision correction. This advance in contact lenses material technology provides breakthrough levels of oxygen to the cornea. However, there are still important issues yet to be addressed by researchers, practitioners, and industry. Factors such as adequate correction for all refractive errors, microbial keratitis, comfort, and suitable lens care and lens biocompatibility are discussed from the authors' perspective.

Penetration of topically applied levofloxacin into eyes with thin-wall filtering bleb after trabeculectomy

PURPOSE

To investigate the comparative penetration of 0.3% levofloxacin eye drops into the aqueous humour between cataract patients with or without (control) thin-wall filtering blebs.

METHODS

One drop of 0.3% levofloxacin was administered to the eyes at 30-min intervals for 3.5 h before phacoemulcification for both groups. Aqueous humour samples (0.1-0.2 ml) were aspirated during surgery. The concentration of levofloxacin in the aqueous humour was determined by high-performance liquid chromatography. The Student's t-test, Pearson correlation, and chi(2) test were used to compare the data of the two groups. A P<0.05 was required for results to be considered statistically significant.

RESULTS

The levofloxacin concentration in the aqueous humour was significantly increased (P<0.0001) in the bleb (mean+SD: 3.7+/-2.3 microg/ml) vscontrol group (0.4+/-0.2 microg/ml). Intraocular pressure and the bleb area were not correlated with levofloxacin concentration.

CONCLUSION

The presence of thin-wall filtering blebs increases intraocular penetration of topically administered levofloxacin.

Spantide I decreases type I cytokines, enhances IL-10, and reduces corneal perforation in susceptible mice after Pseudomonas aeruginosa infection

PURPOSE

To determine the effects of blocking substance P (SP) interactions with its major receptor (NK1-R) using the antagonist spantide I in susceptible mice infected with Pseudomonas aeruginosa.

METHODS

Immunohistochemistry and enzyme immunosorbent assay (EIA) tested levels of SP in the cornea of B6 and BALB/c mice. B6 mice were treated with spantide, and after infection, slit lamp examination; clinical score; bacterial counts; and myeloperoxidase (MPO), RT-PCR, ELISA, and polymorphonuclear (PMN) cell chemotaxis assays were performed.

RESULTS

SP corneal levels were significantly elevated constitutively and after infection in the B6 more than in BALB/c mice. Spantide treatment of B6 mice significantly decreased the number of perforated corneas, bacterial counts, and PMNs. mRNA levels for type I cytokines (e.g., IFN-gamma) as well as MIP-2, IL-6, TNF-alpha, and IL-1beta (mRNA and protein) also were significantly reduced after spantide treatment. The type II cytokine IL-10 (mRNA and protein) was elevated, whereas TGF-beta mRNA levels were unchanged after spantide treatment. PMN chemotaxis was induced by SP and other neuropeptides in vitro, but was not affected by spantide I. mRNA for neurokinin-1-receptor-1 (NK-1R) was detected in the normal and infected corneas and on macrophages (Mphis), but not on PMNs (unstimulated or stimulated with endotoxin [LPS]). Spantide treatment of Mphis reduced IL-1beta after LPS+SP treatment but not after either alone.

CONCLUSIONS

The SP antagonist Spantide provides a novel approach to reduce type 1 and enhance the type 2 cytokine IL-10 in the infected cornea of B6 mice, leading to a significant reduction in corneal perforation and improved disease outcome.

A protective role for IL-6 in staphylococcal microbial keratitis

PURPOSE

To determine whether interleukin-6 (IL-6) plays a protective role in Staphylococcus aureus keratitis in a gene knockout (gko) mouse model and to determine whether IL-6 may be used as a therapy to modulate host responses and control bacterial infection, thereby reducing scarring.

METHODS

The eyes of IL-6 gko mice and wild-type mice were challenged topically with S. aureus and examined at 24 hours after infection. Keratitis was examined clinically and histologically. Bacterial and polymorphonuclear leukocytes (PMNs) were enumerated, and cytokine and chemokine levels were determined by ELISA. Exogenous IL-6 was administered to both IL-6 gko and wild-type mice, and clinical parameters were determined.

RESULTS

IL-6 gko mice showed more severe disease, with increased bacterial counts and PMNs, than did wild-type mice. Changes in levels of chemokines and cytokines were also observed. Administration of exogenous IL-6 resulted in an improved outcome in IL-6 gko mice, with a threefold reduction in bacterial load.

CONCLUSIONS

The data suggest an important regulatory role for IL-6 in modulating excessive inflammatory responses and in controlling bacterial proliferation. IL-6 may play a role in the priming and activation of neutrophils. It could represent a broad-spectrum therapy to improve outcomes in patients who have these potentially blinding infections.

Antibiotic effects of WP-0405, a thermo-setting ofloxacin gel, on methicillin-resistant Staphylococcus aureus keratitis in rabbits

PURPOSE

The chemotherapeutic effects and pharmacokinetics properties of WP-0405 (a thermo-setting in situ 0.3% ofloxacin-containing ophthalmic gel) and ofloxacin (a conventional 0.3% ofloxacin solution) on methicillin-resistant Staphylococcus aureus (MRSA) keratitis were compared in a rabbit model.

METHOD

The single-instillation pharmacokinetics of WP-0405 and ofloxacin in the cornea, aqueous humor, conjunctiva, and iris-ciliary body were determined in normal rabbit eyes. To compare the duration of antimicrobial action, WP-0405 or ofloxacin was instilled oncedaily in an early-treatment model of keratitis, and corneas were either removed immediately or 4 or 8 h postinstillation. In another experiment, WP-0405 was instilled two or three times daily to compare its antibiotic efficacy with three-times daily instillation of ofloxacin in the same early-treatment model of keratitis; corneas were then removed after determining the extent of the abscess area. In another experiment, WP-0405 was instilled four or eight times daily to compare its effects with eight-times daily instillation of ofloxacin in a late-treatment model of keratitis, and corneas were removed. The number of viable bacteria in the corneas was determined in all experiments.

RESULTS

Cmax and AUC0- in tissues treated with WP-0405 were 1.5-3.4-fold and 1.8-2.9-fold greater than those treated with ofloxacin, respectively. WP-0405 significantly reduced the number of viable bacteria for up to 8 h after a single instillation. WP-0405 not only significantly reduced the number of viable bacteria, but also the size of the abscess area at the same frequency of instillation. When compared to ofloxacin, WP-0405 exhibited an approximately equivalent antibiotic effect, with fewer administrations.

CONCLUSIONS

As a result of its pharmacokinetics, WP-0405 had a more potent, longer-acting antibiotic effect than did ofloxacin. Furthermore, because of its lower required instillation frequency, which would improve patient compliance, WP-0405 has great potential therapeutic benefits.

Regulation of Pseudomonas aeruginosa internalization after contact lens wear in vivo and in serum-free culture by ocular surface cells

PURPOSE

To determine the effects of contact lenses (CLs) and Pseudomonas aeruginosa (PA) infection on localization of cystic fibrosis transmembrane conductance regulator (CFTR) on corneal surface epithelial cells and the association between lipid raft formation and CFTR in mediating PA binding and internalization in ocular surface epithelium.

METHODS

CFTR immunolocalization was evaluated in vivo in rabbit corneal-conjunctival epithelium (with/without CL wear) before and after PA exposure and in serum-free human corneal epithelial cell culture (hTCEpi). Lipid raft formation was visualized with Alexa555-conjugated cholera toxin beta-subunit. Lipid raft involvement in PA internalization was assayed in vivo by gentamicin survival assays after topical filipin pretreatment. Involvement of CFTR in PA binding and internalization was evaluated by blockade with CFTR peptides or LPS.

RESULTS

CL wear in vivo enhanced anti-CFTR staining, but CFTR localization did not correlate with the PA binding by ocular surface cells. Conjunctival epithelial cells stained for CFTR but did not bind or internalize PA. Corneal epithelial cells in vivo did not stain for CFTR unless challenged by contact lens-induced hypoxia. PA internalization by hTCEpi was significantly inhibited by LPS (P < 0.01), but not by CFTR peptides. Remarkably, normal conjunctival epithelial cells showed lipid raft formation and CFTR staining but did not bind PA. Inhibition of raft formation by filipin blocked PA internalization in vivo after CL wear.

CONCLUSIONS

CFTR is not the predominant receptor for ocular surface PA infection, and after hypoxic CL challenge, neither lipid rafts nor CFTR localization alone predicts PA binding; however, lipid rafts are critical to CL-mediated PA internalization.

Prolonged hypoxia induces lipid raft formation and increases Pseudomonas internalization in vivo after contact lens wear and lid closure

PURPOSE

To investigate the effects of hypoxia on lipid raft formation and Pseudomonas aeruginosa internalization by the corneal epithelium with and without the physical effects of contact lens wear.

METHODS

One eye of each rabbit was randomly fitted with a low-Dk rigid gas-permeable contact lens (LDCTL) or closed with sutures, with the other as a control. After 1 day or 3 days, the rabbits were killed and bacterial invasion was assessed by gentamicin survival assay. Lipid rafts were identified by staining with FITC-conjugated beta subunit of cholera toxin. Corneal epithelial Bcl-2 expression was detected by Western blotting; surface epithelial cell size and thickness (epithelium and stroma) were measured by confocal microscopy.

RESULTS

One-day hypoxia induced no significant changes in P. aeruginosa internalization, Bcl-2 expression, or lipid raft formation except in one of four eyelid-closed eyes. After 3 days, P. aeruginosa internalization was increased significantly (P < 0.05) in LDCTL-wearing eyes and not significantly (P = 0.10) increased in eyelid-closed eyes. Both 3-day test conditions also induced lipid raft-forming cells that bound P. aeruginosa, albeit in different regions of the cornea (peripherally in LDCTL-wearing eyes and centrally in closed eyes); did not alter epithelial thickness or surface cell size; and appeared to decrease epithelial Bcl-2 expression.

CONCLUSIONS

This is the first direct comparison in vivo between two different methods inducing hypoxia on the corneal surface. Association of P. aeruginosa internalization with lipid raft formation in both conditions suggests a critical link among prolonged hypoxia, lipid raft formation, and susceptibility to P. aeruginosa infection. However, different distribution patterns of lipid raft-forming cells suggest physical effects of contact lens wear may direct localization of lipid raft-associated P. aeruginosa internalization on the corneal surface.

Penetration of second-, third-, and fourth-generation topical fluoroquinolone into aqueous and vitreous humour in a rabbit endophthalmitis model

AIMS

This study was designed to investigate the penetration of second-, third- and fourth-generation topical fluoroquinolone into aqueous and vitreous humour in a rabbit endophthalmitis model.

METHODS

Thirty New Zealand white rabbits were divided into six groups. Left eye was infected with an intravitreal inoculum of Staphylococcus aureus. Groups 1, 2, 3, 4, and 5 received topical ofloxacin, ciprofloxacin, lomefloxacin, levofloxacin, or moxifloxacin treatment 24 h after the inoculation, respectively. No treatment was given to group 6 as the control group (n=5). Aqueous and vitreous samples were obtained 30 min after the last drop. High-performance liquid chromatography was used to determine the fluoroquinolone concentration.

RESULTS

In the normal and inflamed eyes, mean aqueous concentrations of ofloxacin were 1.90 and 2.69 mug/ml, ciprofloxacin were 2.16 and 3.65 mug/ml, lomefloxacin were 3.54 and 1.19 mug/ml, levofloxacin were 2.89 and 9.41 mug/ml, and moxifloxacin were 4.92 and 43.33 mug/ml, respectively. Mean vitreous concentrations of ofloxacin were 0.25 and 0.07 mug/ml, ciprofloxacin were 0.08 and 0.32 mug/ml, lomefloxacin were 0.001 and 0.03 mug/ml, levofloxacin were 0.03 and 0.09 mug/ml, and moxifloxacin were 0.28 and 2.68 mug/ml, in normal and inflamed eyes, respectively. Moxifloxacin achieved a significantly higher concentration in aqueous and vitreous humour of infected eyes compared with ofloxacin (P<0.01), ciprofloxacin (P<0.05), lomefloxacin (P<0.01), and levofloxacin (P<0.05).

CONCLUSION

This study demonstrated that fourth-generation fluoroquinolone, moxifloxacin, seems to have better penetration to inflamed ocular tissues in rabbit.

Pseudomonas aeruginosa-induced inflammation in the rat extended-wear contact lens model

PURPOSE

To examine the early host response to Pseudomonas aeruginosa challenge in the extended contact lens-wearing rat model.

METHODS

Lewis rats were fitted with extended-wear lotrafilcon A hydrogel lenses in the left eye, and the right eye served as the control. Bacterial challenge was initiated in the experimental eye by fitting a bacteria-soaked contact lens and by topical delivery of the bacteria. On first detection of corneal opacity, slitlamp examination, histopathologic examination, viable bacteria counts, enzyme-linked immunosorbent assay, myeloperoxidase, Langerhans cell detection, and multiprobe ribonuclease protection assays were used to evaluate the early corneal response.

RESULTS

Analysis of bacterially challenged contact lens-wearing versus control rats showed Langerhans cells and polymorphonuclear neutrophils only in the experimentally challenged cornea. In addition, in the experimentally challenged cornea, ribonuclease protection and enzyme-linked immunosorbent analyses showed an upregulation of proinflammatory cytokines, including interleukins 1beta and 6, suggesting that with contact lens wear, these cytokines contribute to the early corneal response and, potentially, disease.

CONCLUSIONS

The contact lens-wearing rat model allows a unique analysis of the early effects of bacterial challenge in extended-wear contact lenses in the absence of corneal scarring, used in most rodent models. The rat model should be valuable to delineate further the effects of contact lens wear, including the testing of additional contact lens-related complications.

Expression of TNF-alpha, IL-1beta, and IFN-gamma in Staphylococcus epidermidis slime-positive experimental endophthalmitis is closely related to clinical inflammatory scores

PURPOSE

The purpose of this study was to investigate the expression of inflammatory cytokines TNF-alpha, IL-1beta, and IFN-gamma in the vitreous after experimentally induced endophthalmitis by a Staphylococcus epidermidis slime-producing strain.

METHODS

Seventy-two experimental Lewis rats received an intravitreal injection of 7000 viable organisms of Staphylococcus epidermidis slime-producing ATCC strain 35983, while 72 control rats received an intravitreal injection of sterile normal saline. Eyes were graded daily for signs of clinical inflammation and were removed 6, 12, 24, 48, 72 h, and 7 days after injection. Vitreous was obtained and titers of TNF-alpha, IL-1beta, and IFN-gamma were measured with established enzyme-linked immunosorbent assays.

RESULTS

In the experimental group, the clinical inflammatory score reached maximum (4+) within 24 h, while inflammation was almost abolished by day 7 (score 0-0.5+). Statistically increased levels of TNF-alpha and IL-1beta were detected in the experimental vitreous with maximum levels observed at 12 h. IFN-gamma was also detected in the experimental vitreous and reached maximum levels at 48 h. None of the cytokines examined was detected in sera at any time point in experimental or control rats.

CONCLUSIONS

The results of this study suggest that Staphylococcus epidermidis experimental endophthalmitis induces the expression of cytokines TNF-alpha, IL-1beta, and IFN-gamma in the vitreous. The time course of those cytokine expression levels is closely associated to the clinical presentation of this endophthalmitis model.

Silencing Toll-like receptor-9 in Pseudomonas aeruginosa keratitis

PURPOSE

To determine the effects of silencing Toll-like receptor (TLR) 9 signaling in Pseudomonas aeruginosa keratitis.

METHODS

Corneal TLR9 mRNA levels were tested by RT-PCR in C57BL/6 (B6, susceptible) and BALB/c (resistant) mice and compared. The response of B6 mice to CpG DNA, which binds TLR9, was tested after subconjunctival injection of mice with control or CpG DNA; TLR9, IL-1beta, macrophage inflammatory protein (MIP)-2, IL-4, IL-10, IL-12, IL-18, and IFN-gamma levels were measured by RT-PCR. Langerhans cells (LCs) were stimulated with CpG DNA and treated with TLR9 or control siRNA, and mRNA levels of TLR9, IL-1beta, and MIP-2 were detected by RT-PCR. In addition, IL-1beta levels were tested by ELISA. Then B6 mice were injected subconjunctivally with control or TLR9 siRNA before infection and treated topically afterward. Slit lamp, clinical score, RT-PCR, ELISA, myeloperoxidase assay, and plate counts were performed.

RESULTS

TLR9 mRNA levels were sixfold higher in B6 than in BALB/c corneas the day after injection. B6 mice injected with CpG DNA exhibited an increase in corneal mRNA for TLR9, IL-1beta, MIP-2, IL-12, and IFN-gamma over controls. LCs stimulated with CpG DNA and treated with TLR9 siRNA exhibited reduced TLR9, IL-1beta, and MIP-2 levels compared with controls. Finally, B6 mice treated with TLR9 siRNA showed decreases in corneal opacity, polymorphonuclear leukocyte number, IL-12 and IFN-gamma mRNA, IL-1beta, and MIP-2 protein compared with those treated with control siRNA. Fewer corneas perforated in these mice, but bacterial loads were higher than in controls.

CONCLUSIONS

Signaling through TLR9 appears important in P. aeruginosa keratitis, and silencing TLR9 signaling reduces inflammation but likely contributes to decreased bacterial killing in the cornea.

Ocular Pharmacokinetics of Moxifloxacin After Topical Treatment of Animals and Humans

The ocular penetration and pharmacokinetics of moxifloxacin in comparison to other fluoroquinolones (ofloxacin, ciprofloxacin, gatifloxacin, norfloxacin, levofloxacin, and lomefloxacin) have been determined by in vitro and ex vivo techniques, as well as in animal and human studies. This article reviews the original pharmacokinetics work performed by Alcon and other studies reported in the ocular fluoroquinolone literature. The results consistently demonstrate higher maximum concentrations for moxifloxacin relative to the other fluoroquinolones in ocular tissues with levels well above its minimum inhibitory concentrations for relevant ocular pathogens. This superior performance is due to the unique structure of moxifloxacin that combines high lipophilicity for enhanced corneal penetration with high aqueous solubility at physiological pH. The latter property creates a high concentration gradient at the tear film/corneal epithelial interface providing a driving force for better ocular penetration for moxifloxacin. In addition, the higher concentration of moxifloxacin in VIGAMOX (i.e., 0.5% vs. 0.3%) allows more antibiotic to be available to ocular tissues. It is clear from the array of studies summarized in this report that moxifloxacin penetrates ocular tissues better (two- to three-fold) than gatifloxacin, ciprofloxacin, ofloxacin, or levofloxacin. This consistent, enhanced penetration of topical moxifloxacin offers powerful advantages for ophthalmic therapy.

Overview of the Potency of Moxifloxacin Ophthalmic Solution 0.5% (VIGAMOX®)

Antibiotics have been the mainstay of therapy for infectious diseases since their origins in the 1940s. As microorganisms changed and resistance developed, more advanced antibiotics were ultimately needed to provide adequate coverage and spectrum. By selecting optimal antibiotics and dosing regimens, clinicians can avoid treatment failures and adverse events and can help prevent the emergence of further antibiotic resistance. The fourth-generation ophthalmic fluoroquinolones include moxifloxacin (VIGAMOX, Alcon Laboratories, Inc., Fort Worth, TX) and gatifloxacin (Zymar, Allergan, Irvine, CA), and they are now approved for the treatment of bacterial conjunctivitis. This review highlights four scientific methods that compare and rank antibiotic potencies and predict their clinical efficacy and their propensity to develop resistance: 1) in vitro assay for minimum inhibitory concentrations, 2) in vivo models for pharmacokinetic and pharamacodynamic properties, 3) therapeutic index or inhibitory quotient, and 4) in vitro assay for mutant prevention concentration. The fourth-generation ophthalmic fluoroquinolones perform well in these assays. Both antibiotics have better in vitro activity against gram-positive bacteria than ciprofloxacin or ofloxacin. Moxifloxacin penetrates better into ocular tissues than gatifloxacin and older fluoroquinolones; in vitro activity of moxifloxacin and gatifloxacin against gram-negative bacteria is similar to that of older fluoroquinolones. Moxifloxacin also has better mutant prevention characteristics than other fluoroquinolones. These findings support the use of the newer fluoroquinolones for the prevention and treatment of serious ophthalmic infections (e.g., keratitis, endophthalmitis) caused by susceptible bacteria.

Ophthalmic Infections and Their Anti-infective Challenges

This introduction provides an overview of the succeeding articles contained within this supplement on the new fourth-generation fluoroquinolone antibiotic product, moxifloxacin ophthalmic solution 0.5% (VIGAMOX, Alcon Laboratories, Inc., Fort Worth, TX). Moxifloxacin was developed specifically to address the increasing incidence of resistance to earlier-generation antibiotic molecules. Structural modifications to the moxifloxacin molecule have decreased the likelihood of the development of resistant organisms. This antibiotic has been shown to possess greater activity than previous-generation molecules against gram-positive bacteria while maintaining excellent potency against gram-negative organisms and nontuberculous (atypical) mycobacteria. Moxifloxacin ophthalmic solution 0.5% exhibits enhanced bioavailability due to a unique molecular structure that combines high lipophilicity for enhanced corneal penetration with high aqueous solubility at physiological pH. Numerous studies have shown that moxifloxacin ophthalmic solution 0.5% has high potency against a broad range of microbial species and a favorable profile in terms of safety and tolerability. The results presented in this supplement provide additional evidence for the potential benefits of moxifloxacin ophthalmic solution 0.5% in surgical prophylaxis and treatment of sight-threatening infections, such as bacterial conjunctivitis, endophthalmitis and keratitis.

Grepafloxacin Concentration in Ocular Tissues after Intravenous Infusion in Rabbits with Intraocular Inflammation

PURPOSE

To determine the penetration of grepafloxacin into ocular tissues during experimental ocular inflammation.

METHODS

10 albino and 10 pigmented rabbits underwent a continuous intravenous infusion of the drug 24 h after injecting Salmonella typhimurium toxin intravitreously, creating ocular inflammation. The animals were killed and grepafloxacin levels were determined in plasma and ocular tissues using high performance liquid chromatography.

RESULTS

Grepafloxacin levels achieved a steady-state plasma concentration of 1.5 microg/ml. The drug diffused more towards vascularized tissues (chorioretina and iris) in both albino and pigmented rabbits with a tissue/serum ratio higher than 1. Grepafloxacin showed more affinity to pigmented tissue, rising levels of 40,000-50,000 ng/g in the chorioretina and iris in pigmented animals. After inflammation, grepafloxacin intraocular penetration increased in albino animals with levels exceeding the minimum inhibitory concentration for the most common ocular pathogens.

CONCLUSION

Grepafloxacin intraocular penetration is higher in pigmented tissues. Ocular inflammation increases the drug penetration into the vitreous.

Interleukin-4 is not critical to pathogenesis in a mouse model of Pseudomonas aeruginosa corneal infection

PURPOSE

To determine the contribution of interleukin-4 (IL-4) to the initial host response during corneal infection with Pseudomonas aeruginosa in a mouse model.

METHODS

Corneas of 6- to 8-week-old IL-4(-/-) and wild-type mice were topically challenged with P. aeruginosa. Ocular tissue was collected 24 hr and 7 days postchallenge. Viable bacterial counts, myeloperoxidase assays, cytokine levels, and clinical and histological examinations were performed.

RESULTS

During challenge with P. aeruginosa, no differences were observed clinically, histologically, or in bacterial load between IL-4(-/-) and wild-type mice at either time point. However, differences in cytokine levels of IL-6, KC, and IL-10 were observed.

CONCLUSIONS

The data presented indicate that IL-4, a central Th2 cytokine, may not be critical to the pathogenesis or bacterial clearance in this model of P. aeruginosa bacterial keratitis during the early stages of the infectious process.

Effect of intravitreal dexamethasone on vitreous vancomycin concentrations in patients with suspected postoperative bacterial endophthalmitis

PURPOSE

To study intravitreal dexamethasone and vancomycin concentrations, when used together in patients with suspected postoperative bacterial endophthalmitis. Animal studies had suggested that dexamethasone might decrease the concentration of vancomycin.

DESIGN

Prospective randomized clinical trial in a tertiary referral center.

METHODS

Twenty-nine consecutive patients with suspected postoperative bacterial endophthalmitis underwent a vitreous biopsy followed by intravitreal injection of antibiotics (0.2 mg vancomycin, 0.05 mg gentamicin) and 400 mug dexamethasone or placebo. After 3-4 days, the intravitreal injection of antibiotics and dexamethasone or placebo was repeated. In 18 patients, a second biopsy was taken for repeat culture and measurement of vancomycin and dexamethasone concentrations.

RESULTS

In 20/29 patients (69%) the first vitreous cultures were positive; the second culture was negative in all cases. Thirteen out of 29 patients received dexamethasone. Dexamethasone concentrations showed an average of 25 ng/ml 3 days after injection, with an estimated half-life of 5.5 h. Vancomycin concentrations in patients given dexamethasone tended to be higher compared with those in the placebo group (P=0.061).

CONCLUSION

Intravitreal dexamethasone does not lead to decreased vancomycin concentrations, when given simultaneously in the treatment of patients with suspected bacterial endophthalmitis.

Hypoxia increases corneal cell expression of CFTR leading to increased Pseudomonas aeruginosa binding, internalization, and initiation of inflammation

PURPOSE

To investigate the effect of hypoxia-induced molecular responses of corneal epithelial cells on the surface of rabbit and human corneas and corneal cells in culture on interactions with Pseudomonas aeruginosa that may underlie increased susceptibility to keratitis.

METHODS

Organ cultures of rabbit and human corneal tissue, primary rabbit and human corneal cells, and transformed human corneal cells from a patient with cystic fibrosis and the same cell line corrected for expression of wild-type cystic fibrosis transmembrane conductance regulator (CFTR), the cellular receptor for P. aeruginosa, were exposed to hypoxic conditions for 24 to 72 hours. Changes in binding and internalization of P. aeruginosa were measured using cellular association and gentamicin-exclusion assays, and expression of CFTR and activation of NF-kappaB in response to hypoxia were determined by confocal laser microscopy and quantitative measurements of NF-kappaB activation.

RESULTS

Hypoxia induced in a time- and oxygen-concentration-dependent manner increased association and internalization of clinical isolates of P. aeruginosa in all cells tested. Hypoxia increased CFTR expression and NF-kappaB nuclear translocation in rabbit and human cells with wild-type CFTR. Corneal cells lacking CFTR had reduced NF-kappaB activation in response to hypoxia. Hypoxia did not affect the increase in corneal cell CFTR levels or NF-kappaB activation after P. aeruginosa infection.

CONCLUSIONS

Hypoxic conditions on the cornea exacerbate the binding and internalization of P. aeruginosa due to increased levels of CFTR expression and also induce basal NF-kappaB activation. Both of these responses probably exacerbate the effects of P. aeruginosa infection by allowing lower infectious doses of bacteria to induce disease and promote destructive inflammatory responses.

[Proinflammatory cytokines in the development of bacterial keratitis]

The production of proinflammatory cytokines IL-1alpha, IL1 2b, TNF-alpha and IL8 in lachrymal fluid was dynamically determined in 134 patients with uncomplicated and complicated clinical courses of primary (at exacerbation of the cornea) and secondary (with dystrophic changes in the cornea) keratitis. The level of proinflammatory cytokines in lachrymal fluid was found to essentially affect the clinical course in different types of keratitis.

Heat Treatment Enhances Healing Process of Experimental Pseudomonas Corneal Ulcer

We investigated the effects of hyperthermia on the healing process of experimental Pseudomonas corneal ulceration (PCU). Hartley guinea pigs were used to develop animal models of PCU. As a heat source, disposable chemical pocket warmers were applied. The healing process of PCU was compared between the heat-treated corneas and the control corneas. The severity of infection and the degree of angiogenesis were classified by a clinical scoring system. The animals were euthanized 14 days after infection and the corneas were submitted for histopathological examination. The expression of vascular endothelial growth factor (VEGF) was examined immunohistochemically. Comparative reverse transcription polymerase chain reaction was performed to measure the expression level of VEGF in the cornea. Hyperthermia significantly promoted corneal epithelization and neovascularization in the PCU model. Heat treatment significantly decreased the number of viable Pseudomonas organisms present in PCU. On immunohistochemistry, the heated cornea demonstrated more intense staining for VEGF. Comparative reverse transcription polymerase chain reaction showed upregulation of the expression level of VEGF mRNA in the heat-treated cornea. Hyperthermia accelerated the healing process of PCU with increased corneal neovascularization. Angiogenesis may play an important role in the PCU healing process, which is enhanced by the heat treatment.