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.

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.

Resolvin D1 protects against Aspergillus fumigatus keratitis in diabetes by blocking the MAPK-NF-κB pathway

Fungal keratitis (FK) is one of the main causes of blindness in China. People with diabetes are susceptible to corneal epithelial disease, even fungal keratitis. At present, there are few studies on this disease. Resolvins (Rv) has been reported as a mediators that exert crucial anti-inflammatory and immune regulation roles in serval diseases. In order to investigate the roles and underlying mechanism of Resolvins D1 (RvD1) on the Aspergillus fumigatus (A. fumigatus) keratitis in diabetes, we established in vivo and in vitro models of A. fumigatus keratitis, which were then exposed to high glucose. The expression levels of RvD1, 5-lipoxygenase (5-LOX), and 15-lipoxygenase (15-LOX) in A. fumigatus keratitis patients with diabetes were determined through Enzyme Linked Immunosorbent Assay (ELISA), Western blot and immunohistochemistry. Reactive Oxygen Species (ROS) production, ELISA, flow cytometry, Hematoxylin-Eosin (HE) staining and fungal loading determination were conducted to evaluate the severity of A. fumigatus infection. Lymphangiogenesis and angiogenesis were examined by immunofluorescence assay. Western blot was applied to detect the proteins of the MAPK-NF-κB pathway. The results showed that RvD1 diminished the high glucose-induced oxidative stress and inflammatory response, as evidenced by the reduction of ROS production, Interleukin-6 (IL-6), Interleukin-8 (IL-8), Heme Oxygenase-1 (HMOX-1), and the elevation of Cyclooxygenase-2 (COX2), Superoxide Dismutase (SOD-1), and Glutathione Peroxidase-2 (GPX2) levels in A. fumigatus-infected Human Corneal Endothelial Cells (HCECs). Additionally, lymphangiogenesis and angiogenesis prominently decreased after intervention with RvD1. Furthermore, RvD1 significantly reduced the levels of p-MEK1/2 and p-ERK1/2, and restrained the NF-κB and GPR32 activation. The above results showed that RvD1 protects against A. fumigatus keratitis in diabetes by suppressing oxidative stress, inflammatory response, fungal growth, and immunoreaction via modulating MAPK-NF-κB pathway. RvD1 provides clues for the therapeutic targets of Fungal keratitis complicated with diabetes.

IL-36α Exerts Proinflammatory Effects in Aspergillus fumigatus Keratitis of Mice Through the Pathway of IL-36α/IL-36R/NF-κB

Purpose

To explore the role of IL-36α in corneas infected by Aspergillus fumigatus.

Methods

The experimental group was comprised of 15 corneas with fungal keratitis, and 15 healthy donor corneas were included in the control group. IL-36α was detected in normal and infected corneas of humans and C57BL/6 mice. Mice corneas were infected with A. fumigatus with or without pretreatment of recombinant mouse (rm) IL-36α and IL-36α neutralizing antibody (Ab). Primary macrophages were stimulated with 75% ethanol-killed A. fumigatus with or without pretreatment of rmIL-36α. The severity of the disease was documented by clinical score and photographs with a slit lamp. PCR, western blot, and immunostaining were used to determine the expression of IL-36α, IL-1β, IL-6, and TNF-α. Polymorphonuclear neutrophilic leukocyte infiltration was assessed by myeloperoxidase (MPO) assay and flow cytometry. Macrophage infiltration was tested by immunofluorescent staining and flow cytometry.

Results

IL-36α mRNA and protein were significantly elevated in human and mice corneas after infection. The rmIL-36α treatment of C57BL/6 mice increased clinical score, MPO levels, macrophage infiltration, and expression of the proinflammatory cytokines IL-1β, IL-6, and TNF-α compared with the infected controls, which showed a decrease due to IL-36α Ab treatment. In primary macrophages, IL-36α expression was also significantly increased by A. fumigatus. The rmIL-36α treatment upregulated IL-1β, IL-6, and phosphorylated nuclear factor (NF)-κB expression, which was significantly inhibited by rmIL-36Ra.

Conclusions

IL-36α act as a proinflammatory cytokine in A. fumigatus keratitis by promoting the infiltration of neutrophils and macrophages and increasing the secretion of IL-1β, IL-6, and TNF-α, in addition to regulating expression of phosphorylated NF-κB.

Antimicrobial Nitric Oxide Releasing Contact Lens Gels for the Treatment of Microbial Keratitis

Microbial keratitis is a serious sight threatening infection affecting approximately two million individuals worldwide annually. While antibiotic eye drops remain the gold standard treatment for these infections, the significant problems associated with eye drop drug delivery and the alarming rise in antimicrobial resistance has meant that there is an urgent need to develop alternative treatments. In this work, a nitric oxide releasing contact lens gel displaying broad spectrum antimicrobial activity against two of the most common causative pathogens of microbial keratitis is described. The contact lens gel is composed of poly-ε-lysine (pεK) functionalized with nitric oxide (NO) releasing diazeniumdiolate moieties which enables the controlled and sustained release of bactericidal concentrations of NO at physiological pH over a period of 15 h. Diazeniumdiolate functionalization was confirmed by Fourier transform infrared (FTIR), and the concentration of NO released from the gels was determined by chemiluminescence. The bactericidal efficacy of the gels against Pseudomonas aeruginosa and Staphylococcus aureus was ascertained, and between 1 and 4 log reductions in bacterial populations were observed over 24 h. Additional cell cytotoxicity studies with human corneal epithelial cells (hCE-T) also demonstrated that the contact lens gels were not cytotoxic, suggesting that the developed technology could be a viable alternative treatment for microbial  keratitis.

Blowing epithelial cell bubbles with GumB: ShlA-family pore-forming toxins induce blebbing and rapid cellular death in corneal epithelial cells

Medical devices, such as contact lenses, bring bacteria in direct contact with human cells. Consequences of these host-pathogen interactions include the alteration of mammalian cell surface architecture and induction of cellular death that renders tissues more susceptible to infection. Gram-negative bacteria known to induce cellular blebbing by mammalian cells, Pseudomonas and Vibrio species, do so through a type III secretion system-dependent mechanism. This study demonstrates that a subset of bacteria from the Enterobacteriaceae bacterial family induce cellular death and membrane blebs in a variety of cell types via a type V secretion-system dependent mechanism. Here, we report that ShlA-family cytolysins from Proteus mirabilis and Serratia marcescens were required to induce membrane blebbling and cell death. Blebbing and cellular death were blocked by an antioxidant and RIP-1 and MLKL inhibitors, implicating necroptosis in the observed phenotypes. Additional genetic studies determined that an IgaA family stress-response protein, GumB, was necessary to induce blebs. Data supported a model where GumB and shlBA are in a regulatory circuit through the Rcs stress response phosphorelay system required for bleb formation and pathogenesis in an invertebrate model of infection and proliferation in a phagocytic cell line. This study introduces GumB as a regulator of S. marcescens host-pathogen interactions and demonstrates a common type V secretion system-dependent mechanism by which bacteria elicit surface morphological changes on mammalian cells. This type V secretion-system mechanism likely contributes bacterial damage to the corneal epithelial layer, and enables access to deeper parts of the tissue that are more susceptible to infection.

Staphylococcus aureus alpha-hemolysin impairs corneal epithelial wound healing and promotes intracellular bacterial invasion

Colonization by Staphylococcus aureus (S. aureus) has been implicated in many infectious and wound healing disorders. This study was performed to characterize the pathogenic role of S. aureus alpha-hemolysin (alpha-toxin) in corneal epithelial wound healing and infectious keratitis in the setting of a corneal wound. The effect of wild-type and isogenic Hla mutant (α-hemolysin gene deleted) S. aureus bacteria and conditioned media on corneal epithelial wound healing was tested in vitro using a scratch assay and in vivo using a murine epithelial debridement model. The invasiveness of wild-type and Hla mutant S. aureus was evaluated in vitro in human corneal epithelial cells and in vivo in a murine model of infectious keratitis following total epithelial debridement. S. aureus and its conditioned media significantly delayed epithelial wound closure both in vitro (P < 0.05) and in vivo (P < 0.05). The effect of S. aureus on wound healing was significantly diminished with the Hla mutant strain (P < 0.05). Likewise, compared to the wild-type strain, the Hla mutant strain demonstrated significantly reduced ability to invade corneal epithelial cells in vitro (P < 0.05) and infect murine corneas following total epithelial debridement in vivo (P < 0.05). In conclusion, S. aureus alpha-hemolysin plays a major role in the pathologic modulation of corneal epithelial wound healing and the intracellular invasion of the bacteria. Limiting colonization by S. aureus and/or blocking alpha-hemolysin may provide a therapeutic approach for corneal wound healing and infectious disorders.

Contact lens wear and the diabetic corneal epithelium: A happy or disastrous marriage?

Diabetes mellitus is an epidemic in the US and abroad. With the advent of new contact lens technology, the use of contact lenses as glucose sensors in lieu of the traditional finger stick is quickly becoming realized. This has the potential to rapidly expand the contact lens market into this growing patient population. The independent cellular and physiological effects of contact lens wear and diabetes on the corneal epithelium have been described. However, little evidence exists to date to support whether there is increased risk associated with contact lens wear in diabetes. The focus of this review is to discuss what is known about the cellular effects of contact lenses on the corneal epithelium, the pathophysiological changes in the corneal epithelium that occur in diabetes, and whether an increased risk for corneal epithelial damage and/or infection may negatively impact safety in diabetic contact lens wearers. Available data indicates that there are inherent risks associated with contact lens wear in diabetics. Importantly, eye care practitioners fitting contact lenses in the diabetic patient need to carefully consider the duration of disease, the level of glycemic control, the presence of retinopathy, and the patient's overall health.

Indoleamine 2,3-Dioxygenase Is Involved in the Inflammation Response of Corneal Epithelial Cells to Aspergillus fumigatus Infections

Indoleamine 2,3-dioxygenase (IDO), which is mainly expressed in activated dendritic cells, is known as a regulator of immune responses. However, the role of IDO in immune responses against fungal corneal infection has not been investigated. To evaluate the regulatory mechanisms of IDO in fungal inflammation, we resorted to human corneal epithelial cells (HCECs), known as the first barrier of cornea against pathogenic microorganisms. We found that IDO was significantly up-regulated in corneal epithelium infected with Aspergillus fumigatus (A. fumigatus) and HCECs incubated with spores of A. fumigatus. Furthermore, IDO inhibitor (1-methyltryptophan, 1-MT) enhanced inflammatory cytokines IL-1β and IL-6 expression which were up-regulated by A. fumigatus spores infection. Dectin-1, as one of the important C-type lectin receptors, can identify β-glucan, and mediate fungal innate immune responses. In the present study, pre-treatment with curdlan, a Dectin-1 agonist, further enhanced IDO expression compared with A. fumigatus stimulation. While laminarin, the Dectin-1 specific inhibitor, partially inhibited IDO expression stimulated by A. fumigatus. Further studies demonstrated inhibition of IDO activity amplified the expressions of inflammatory cytokines IL-1β and IL-6 induced by activation of Dectin-1. These results suggested that IDO was involved in the immune responses of fungal keratitis. The activation of Dectin-1 may contribute to A. fumigatus spores-induced up-regulation of IDO.

A Novel Innate Response of Human Corneal Epithelium to Heat-killed Candida albicans by Producing Peptidoglycan Recognition Proteins

Fungal infections of the cornea can be sight-threatening and have a worse prognosis than other types of microbial corneal infections. Peptidoglycan recognition proteins (PGLYRP), which are expressed on the ocular surface, play an important role in the immune response against bacterial corneal infections by activating toll-like receptors (TLRs) or increasing phagocytosis. However, the role of PGLYRPs in innate immune response to fungal pathogens has not been investigated. In this study, we observed a significant induction of three PGLYRPs 2–4 in primary human corneal epithelial cells (HCECs) exposed to live or heat-killed Candida albicans (HKCA). The C-type lectin receptor dectin-1 plays a critical role in controlling Candida albicans infections by promoting phagocytic activity and cytokine production in macrophages and dendritic cells. Here, we demonstrate that dectin-1 is expressed by normal human corneal tissue and primary HCECs. HKCA exposure increased expression of dectin-1 on HCECs at mRNA and protein levels. Interestingly, dectin-1 neutralizing antibody, IκB-α inhibitor BAY11-7082, and NF-κB activation inhibitor quinazoline blocked NF-κB p65 nuclear translocation, as well as the induction of the PGLYRPs by HKCA in HCECs. Furthermore, rhPGLYRP-2 was found to suppress colony-forming units of Candida albicans in vitro. In conclusion, these findings demonstrate that dectin-1 is expressed by human corneal epithelial cells, and dectin-1/NF-κB signaling pathway plays an important role in regulating Candida albicans/HKCA-induced PGLYRP secretion by HCECs.

Pseudomonas aeruginosa utilizes the type III secreted toxin ExoS to avoid acidified compartments within epithelial cells

Invasive Pseudomonas aeruginosa (PA) can enter epithelial cells wherein they mediate formation of plasma membrane bleb-niches for intracellular compartmentalization. This phenotype, and capacity for intracellular replication, requires the ADP-ribosyltransferase (ADPr) activity of ExoS, a PA type III secretion system (T3SS) effector protein. Thus, PA T3SS mutants lack these capacities and instead traffic to perinuclear vacuoles. Here, we tested the hypothesis that the T3SS, via the ADPr activity of ExoS, allows PA to evade acidic vacuoles that otherwise suppress its intracellular viability. The acidification state of bacteria-occupied vacuoles within infected corneal epithelial cells was studied using LysoTracker to visualize acidic, lysosomal vacuoles. Steady state analysis showed that within cells wild-type PAO1 localized to both membrane bleb-niches and vacuoles, while both exsA (transcriptional activator) and popB (effector translocation) T3SS mutants were only found in vacuoles. The acidification state of occupied vacuoles suggested a relationship with ExoS expression, i.e. vacuoles occupied by the exsA mutant (unable to express ExoS) were more often acidified than either popB mutant or wild-type PAO1 occupied vacuoles (p < 0.001). An exoS-gfp reporter construct pJNE05 confirmed that high exoS transcriptional output coincided with low occupation of acidified vacuoles, and vice versa, for both popB mutants and wild-type bacteria. Complementation of a triple effector null mutant of PAO1 with exoS (pUCPexoS) reduced the number of acidified bacteria-occupied vacuoles per cell; pUCPexoSE381D which lacks ADPr activity did not. The H⁺-ATPase inhibitor bafilomycin rescued intracellular replication to wild-type levels for exsA mutants, showing its viability is suppressed by vacuolar acidification. Taken together, the data show that the mechanism by which ExoS ADPr activity allows intracellular replication by PA involves suppression of vacuolar acidification. They also show that variability in ExoS expression by wild-type PA inside cells can differentially influence the fate of individual intracellular bacteria, even within the same cell.

MicroRNA-762 is upregulated in human corneal epithelial cells in response to tear fluid and Pseudomonas aeruginosa antigens and negatively regulates the expression of host defense genes encoding RNase7 and ST2

Mucosal surfaces regulate defenses against infection and excessive inflammation. We previously showed that human tears upregulated epithelial expression of genes encoding RNase7 and ST2, which inhibited Pseudomonas aeruginosa invasion of human corneal epithelial cells. Here, microRNA microarrays were used to show that a combination of tear fluid exposure (16 h) then P. aeruginosa antigens (3 h) upregulated miR-762 and miR-1207, and down-regulated miR-92 and let-7b (all > 2-fold) in human corneal epithelial cells compared to P. aeruginosa antigens alone. RT-PCR confirmed miR-762 upregulation ∼ 3-fold in tear-antigen exposed cells. Without tears or antigens, an antagomir reduced miR-762 expression relative to scrambled controls by ∼50%, increased expression of genes encoding RNase7 (∼80 %), ST2 (∼58%) and Rab5a (∼75%), without affecting P. aeruginosa internalization. However, P. aeruginosa invasion was increased > 3-fold by a miR-762 mimic which reduced RNase7 and ST2 gene expression. Tear fluid alone also induced miR-762 expression ∼ 4-fold, which was reduced by the miR-762 antagomir. Combination of tear fluid and miR-762 antagomir increased RNase7 and ST2 gene expression. These data show that mucosal fluids, such as tears, can modulate epithelial microRNA expression to regulate innate defense genes, and that miR-762 negatively regulates RNase7, ST2 and Rab5a genes. Since RNase7 and ST2 inhibit P. aeruginosa internalization, and are upregulated by tear fluid, other tear-induced mechanisms must counteract inhibitory effects of miR-762 to regulate resistance to bacteria. These data also suggest a complex relationship between tear induction of miR-762, its modulation of innate defense genes, and P. aeruginosa internalization.

The effects of silicone hydrogel lens wear on the corneal epithelium and risk for microbial keratitis

Previous studies using animal models and human clinical trials have demonstrated that the use of low-oxygen-transmissible contact lens materials produce corneal epithelial surface damage resulting in increased Pseudomonas aeruginosa (PA) adhesion and raft-mediated internalization into surface corneal epithelial cells. These findings led to the testable clinical predictions that (1) microbial keratitis (MK) risk is expected to be the greatest during the first 6 months of wear; (2) there is no difference between 6 and 30 night extended wear; and (3) that wear of hyperoxygen-transmissible lenses would reduce the reported incidence of infection. Subsequent epidemiologic studies have confirmed the first two predictions; however, increased oxygen transmissibility with silicone hydrogel (SiHy) lens wear has not altered the overall incidence of MK. In this review, more recent clinical and basic studies that investigate epithelial alterations and bacterial adhesion to corneal epithelial cells after the wear of SiHy lenses with and without concomitant exposure to chemically preserved multipurpose solutions (MPS) will be examined. The collective results of these studies demonstrate that even in the absence of lens-related hypoxia, MPS induce ocular surface changes during SiHy lens wear that are associated with a pathophysiologic increase in PA adherence and internalization in the corneal epithelium, and therefore, predict a greater risk for PA-MK. In addition, new data supporting an interactive role for inflammation in facilitating PA adherence and internalization in the corneal epithelium will also be discussed.

Detection of virulence factors in Serratia strains isolated from contact lens-associated corneal ulcers

PURPOSE

This paper reports on the microbiological findings pertaining to three Serratia isolates from soft contact lens-related corneal ulcers, which represent a complication of contact lens wear reported with increasing frequency.

METHODS

Bacterial identification and antibiotic susceptibility testing were performed using the Vitek system. Serratia's ability to form biofilm, produce gelatinase, elastase and alkaline protease, and invade human corneal epithelial (HCE) cells was investigated. The isolates' susceptibility to the following disinfectants was tested: (a) ReNu MultiPlus(®) , containing polyaminopropyl biguanide 0.0001%; (b) Opti-Free Express(®) , containing polyquaternium-1 0.001% and myristamidopropyldimethylamine 0.0005%; (c) Opti-Free Replenish(®) , containing polyquaternium-1 0.001% and myristamidopropyldimethylamine 0.0005%, and (d) Oxysept Comfort(®) , a one-step 3% hydrogen peroxide-catalase system.

RESULTS

Two Serratia marcescens and one Serratia liquefaciens were identified. All the strains were susceptible to aminoglycosides and fluoroquinolones. No isolate formed biofilm or significantly invaded HCE cells; all produced alkaline protease and gelatinase, but not elastase. Opti-Free Express(®) and Opti-Free Replenish(®) were active against S. liquefaciens, but failed to kill the S. marcescens isolates within the minimum recommended time (6 hours). ReNu MultiPlus(®) needed 6 hours to kill one strain of S. marcescens, which is 2 hours more than recommended. Conversely, Oxysept Comfort(®) was always effective within the minimum recommended time (6 hours).

CONCLUSIONS

The ability to produce alkaline protease and gelatinase may play a major role in the pathogenesis of contact lens-related Serratia keratitis. Several types of contact lens solutions may be ineffective in eradicating Serratia from contaminated contact lens cases within the minimum recommended time. Only exposure to Oxysept Comfort(®) was always effective against Serratia in this study.

Inhibition of macrophage migration inhibitory factor ameliorates ocular Pseudomonas aeruginosa-induced keratitis

Pseudomonas aeruginosa causes severe sight-threatening corneal infections, with the inflammatory response to the pathogen being the major factor resulting in damage to the cornea that leads to loss of visual acuity. We found that mice deficient for macrophage migration inhibitory factor (MIF), a key regulator of inflammation, had significantly reduced consequences from acute P. aeruginosa keratitis. This improvement in the outcome was manifested as improved bacterial clearance, decreased neutrophil infiltration, and decreased inflammatory responses when P. aeruginosa-infected MIF knock out (KO) mice were compared to infected wild-type mice. Recombinant MIF applied to infected corneas restored the susceptibility of MIF deficient mice to P. aeruginosa-induced disease, demonstrating that MIF is necessary and sufficient to cause significant pathology at this immune privileged site. A MIF inhibitor administered during P. aeruginosa-induced infection ameliorated the disease-associated pathology. MIF regulated epithelial cell responses to infection by enhancing synthesis of proinflammatory mediators in response to P. aeruginosa infection and by promoting bacterial invasion of corneal epithelial cells, a correlate of virulence in the keratitis model. Our results uncover a host factor that elevates inflammation and propagates bacterial cellular invasion, and further suggest that inhibition of MIF during infection may have a beneficial therapeutic effect.

Expression of surfactant protein D in human corneal epithelial cells is upregulated by Pseudomonas aeruginosa

We reported previously that surfactant protein D (SP-D) was present in human tears and corneal epithelial cells, and that it contributed to tear fluid protection of those cells against Pseudomonas aeruginosa invasion. This suggested a role in ocular innate immunity. Here, we explored the effects of bacterial challenge on SP-D expression by human corneal epithelial cells. Results showed that these cells produced and secreted SP-D constitutively in culture, and that production (mRNA, protein) and secretion of SP-D were upregulated after exposure to heat-killed P. aeruginosa or to purified flagellin or lipopolysaccharide. To begin exploring the mechanism for flagellin-mediated SP-D induction, cells were exposed to purified flagellin or flagellin mutated in the TLR-5-binding domain (L94A, L88A) which reduces IL-8 secretion by A549 respiratory cells. Mutated flagellin did not upregulate IL-8 expression in corneal epithelial cells, but did induce SP-D responses. Mitogen-activated protein kinase inhibitors, especially the JNK inhibitor SP600125, reduced secretion of SP-D, but not production, in the presence of P. aeruginosa. These data show that while SP-D and IL-8 corneal responses are each induced by P. aeruginosa or its antigens, they can involve different regions of the same ligand. The data suggest that separate mechanisms may regulate SP-D secretion and production by human corneal epithelia.

Archipelago Keratitis

OBJECTIVE

To describe archipelago keratitis, a presumed clinical variant of herpetic epithelial keratitis.

DESIGN

Case series.

PARTICIPANTS

A series of 6 patients with an unusual form of superficial keratitis.

METHODS

History, including age, gender, clinical evolution, and treatment; slit-lamp biomicroscopy findings; in vivo confocal microscopy findings; and corneal epithelial scrapings were analyzed.

MAIN OUTCOME MEASURES

Clinical ocular examination, a diagnostic workup including corneal scraping for herpesvirus polymerase chain reaction, in vivo confocal microscopy, and therapeutic outcome.

RESULTS

The authors describe a series of 6 patients with keratitis consisting of foci of epithelial erosions associated with subepithelial nummular inflammatory infiltrates and disposed in a radial, centripetal, archipelagolike pattern originating from the limbus. All the patients had a past history of herpetic epithelial keratitis, herpetic vesicles on the ipsilateral lid, or both. Polymerase chain reaction-based screening for herpes simplex virus 1 and 2 in corneal scrapings demonstrated positive results in 2 patients. In vivo corneal confocal microscopy revealed focal areas of hyperreflective epithelial cells and hyperreflective subepithelial dendritic structures overlying activated keratocytes. All the patients improved with oral valacyclovir treatment followed by topical steroid therapy.

CONCLUSIONS

Archipelago keratitis may be a new clinical variant of herpetic keratitis, reflecting herpetic dissemination from the limbus to the center of the cornea.

Functions of MUC16 in corneal epithelial cells

PURPOSE

The membrane-associated mucin MUC16, a heavily O-glycosylated transmembrane protein, is expressed by the ocular surface epithelia and localized on the tips of the surface microplicae. Although its functions in the ocular surface glycocalyx are unknown, it is thought that MUC16 provides a disadhesive barrier to the epithelial membrane. Two other membrane-associated mucins expressed by ocular surface epithelia, MUC1 and MUC4, are multifunctional and have signaling capabilities through their cytoplasmic tails and EGF-like domains, respectively. The MUC16 cytoplasmic tail has not been characterized, but, because it contains a polybasic amino acid sequence, it potentially interacts with the actin cytoskeleton through ezrin/radixin/moesin (ERM) actin-binding proteins.

METHODS

The interaction of MUC16 with the actin cytoskeleton through ERMs was investigated using cytoplasmic tail peptides and ERM pull-down experiments. MUC16 functions were determined using RNA interference in immortalized human corneal-limbal epithelial (HCLE) cells. The effect of MUC16 knockdown on microplicae structure in HCLE cells was determined using scanning and immunoelectron microscopy. HCLE cells were incubated with rose bengal dye to measure the role of MUC16 in ocular surface barrier function. Binding of fluorescently labeled Staphylococcus aureus to HCLE cells was measured to determine the role of MUC16 in the protection of pathogen adherence on the ocular surface epithelium.

RESULTS

MUC16 cytoplasmic tail peptides bound the N-terminus of ERMs, with no detectable binding of MUC1 and MUC4 peptides. No effect on surface membrane projections could be detected in HCLE cells after MUC16 suppression; however, HCLE cells incubated with rose bengal showed that exclusion of the dye was significantly reduced in cells with MUC16 suppression. In addition, S. aureus binding to HCLE cells was significantly increased with MUC16 suppression.

CONCLUSIONS

These results suggest that MUC16 is a multifunctional molecule linked to the actin cytoskeleton. The expression of MUC16 in the ocular surface glycocalyx helps provide a disadhesive protective barrier for the epithelial surface.

Post-LASIK Epithelial Dendritic Defect Associated With Alternaria

PURPOSE

To report a case of a dendritic epithelial defect with interface inflammation associated with Alternaria sp. after laser in situ keratomileusis (LASIK) surgery.

METHODS

A case report of a 46-year-old woman who presented with a dendritic epithelial defect and interface inflammation after LASIK surgery.

RESULTS

After an apparent post-LASIK herpes simplex keratitis with related interface inflammation failed to respond to medical therapy, cornea culture results were positive for Alternaria fungal sp. 2 weeks and 6 days after presentation. Viral cultures and polymerase chain reaction were negative for herpes simplex virus. Six months after penetrating keratoplasty (and 1 year after LASIK), the patient underwent a cataract extraction OD. Best-corrected visual acuity 18 months after the original LASIK procedure was 20/25 OD.

CONCLUSIONS

Alternaria keratitis may present with a dendritic epithelial defect with interface inflammation mimicking herpes simplex virus.

Comparison of Antibiotic Effect and Corneal Epithelial Toxicity of Levofloxacin and Moxifloxacin In Vitro

PURPOSE

To compare the bacterial susceptibility and corneal epithelial toxicity of levofloxacin and moxifloxacin in the human corneal epithelial cells (HCECs).

METHODS

We used 2 types of strains, ie, American Type Culture Collection strains and resistant strains. The former included Staphylococcus aureus, coagulase-negative staphylococci, Pseudomonas aeruginosa, and Serratia marcescens, The latter were methicillin-resistant Staphylococcus aureus; methicillin-resistant, coagulase-negative Staphylococcus sp.; and ciprofloxacin-resistant P. aeruginosa. The HCECs were incubated with each bacterial population for 1 hour and exposed to both antibiotics for 1 hour. The colony-forming units of viable bacteria per well were expressed as base 10 logarithms. To determine corneal epithelial toxicity, we exposed the HCECs to each antibiotic agent, and the viable epithelial cells were quantified by the MTT assay. We also observed the wound healing rate of injured HCECs cultured in each antibiotic agent for 24 hours.

RESULTS

In bacterial susceptibility testing of antibiotics, levofloxacin was less effective for Serratia marcescens than moxifloxacin (P < 0.05). However, both moxifloxacin and levofloxacin showed the same efficacy against Gram-positive bacteria, P. aeruginosa, and resistant strains (P > 0.05). Moxifloxacin showed a higher toxicity than levofloxacin when the HCECs were exposed to the respective antibiotics for 2 and 24 hours (P < 0.05). The moxifloxacin inhibited the effect of wound healing in HCEC injury, but levofloxacin did not (P < 0.05).

CONCLUSIONS

There was no significant difference in antibiotic effects between moxifloxacin and levofloxacin on most bacterial strains, except for Serratia marcescens. On the other hand, levofloxacin seemed to be safer than moxifloxacin in HCECs.

Pseudomonas aeruginosa infection and inflammation during contact lens wear: a review

Infection and inflammation during contact lens wear is often associated with microbial contamination of lenses. Several different types of microbes that colonize lenses can lead to infection and inflammation, but the most common cause of infection (microbial keratitis; MK) remains the Gram-negative bacterium Pseudomonas aeruginosa. P. aeruginosa has a battery of cell-associated and extracellular virulence factors it can use to initiate and maintain infection. Its ability to produce proteases, to either invade or kill corneal cells, and to coordinate expression of virulence factors via quorum-sensing have been shown to be important during MK. Another important factor that contributes to the destruction of the cornea during MK is excessive activation of the host defense system. P. aeruginosa can activate several pathways of the immune system during MK, and activation often involves receptors on the corneal epithelial cells called toll-like receptors (TLRs). These TLRs recognize e.g., lipopolysaccharide or flagella from P. aeruginosa and activate the epithelial cells to produce inflammatory mediators such as cytokines and chemokines. These cytokines or chemokines recruit white blood cells, predominantly polymorphonuclear leukocytes, to the infection in order that they can phagocytose and kill the P. aeruginosa. However, continued recruitment and presence of these polymorphonuclear neutrophils and other white blood cells in the corneal tissue leads to destruction of corneal cells and tissue components. This can ultimately lead to scarring and vision loss.

Gemella haemolysans infectious crystalline keratopathy

PURPOSE

To report a case of infectious crystalline keratopathy caused by Gemella haemolysans.

METHODS

Observational case report. A 65-year-old woman underwent penetrating keratoplasty for contact lens-related Acanthamoeba keratitis and developed a nonhealing epithelial defect. Despite continued prophylaxis with topical gatifloxacin, small superficial stromal opacities were noted and cultured 6 months after penetrating keratoplasty. The opacities coalesced into a fine, crystalline keratopathy in the superficial stroma with persistent overlying epithelial defect.

RESULTS

Culture results from corneal scraping showed more than 100 colonies of G. haemolysans. Topical vancomycin was instituted, with complete resolution of the crystalline keratopathy and epithelial defect over the next 2 months.

CONCLUSIONS

G. haemolysans can be a causative organism of infectious crystalline keratopathy. This infection can arise in a postkeratoplasty patient despite prophylaxis with a fourth-generation fluoroquinolone.

Current concepts: contact lens related Pseudomonas keratitis

Despite the development of silicone hydrogel lenses, Pseudomonas aeruginosa (PA) continues to be the leading cause of contact lens related microbial keratitis. Understanding the pathogenesis of PA-mediated corneal infection is critical to the development of new prevention and treatment strategies. Recently intracellular invasion of surface corneal epithelial cells by PA has been revisited as an important element in the infection process. This review identifies the mechanisms involved, and examines the roles of the lens, hypoxia alone, PA stain, cystic fibrosis transmembrane receptor protein (CFTR), and membrane lipid rafts in mediating intracellular invasion in both in vitro and in vivo conditions. Non-toxic blockade of raft formation in vitro or in vivo effectively abrogates PA internalization and may represent a unique, new strategy to prevent or ameliorate lens-related PA microbial keratitis.

Staphylococcus aureus-induced corneal inflammation is dependent on Toll-like receptor 2 and myeloid differentiation factor 88

Toll-like receptors (TLRs) expressed by the corneal epithelium represent a first line of host defense to microbial keratitis. The current study examined the role of TLR2, TLR4, and TLR9 and the common adaptor molecule myeloid differentiation factor 88 (MyD88) in a Staphylococcus aureus model of corneal inflammation. The corneal epithelia of C57BL/6, TLR2(-/-), TLR4(-/-), TLR9(-/-), and MyD88(-/-) mice were abraded using a trephine and epithelial brush and were exposed to heat- or UV-inactivated S. aureus clinical strain 8325-4 and other clinical isolates. Corneal thickness and haze were measured by in vivo confocal microscopy, neutrophil recruitment to the corneal stroma was quantified by immunohistochemistry, and cytokine production was measured by enzyme-linked immunosorbent assay. The exposure of corneal epithelium to S. aureus induced neutrophil recruitment to the corneal stroma and increased corneal thickness and haze in control C57BL/6 mice but not in TLR2(-/-) or MyD88(-/-) mice. The responses of TLR4(-/-) and TLR9(-/-) mice were similar to those of C57BL/6 mice. S. aureus-induced cytokine production by corneal epithelial cells and neutrophils was also significantly reduced in TLR2(-/-) mice compared with that in C57BL/6 mice. These findings indicate that S. aureus-induced corneal inflammation is mediated by TLR2 and MyD88 in resident epithelial cells and infiltrating neutrophils.

Salicylic acid reduces the production of several potential virulence factors of Pseudomonas aeruginosa associated with microbial keratitis

PURPOSE

Pseudomonas aeruginosa is a common cause of contact-lens-related microbial keratitis. This bacterium is becoming increasingly resistant to antibiotics, and even if the infection can be treated with antibiotics, damage to the cornea resulting from the combined effect of bacteria and host factors can lead to loss of vision. The purpose of this study was to test the effect of salicylic acid on the production of potential virulence factors during the growth of P. aeruginosa.

METHODS

Bacterial cells were grown in a subinhibitory concentration of salicylic acid, and supernatants were collected and analyzed for presence of proteases by using zymography and hydrolysis of chromogenic substrates. The supernatants were also analyzed for the amount of acetylated homoserine lactones by using bacterial reporter strains. Pseudomonas cells from salicylic acid cultures were analyzed for their twitching and swimming motility as well as their ability to invade or cause the death of corneal epithelial cells.

RESULTS

Growth in a subinhibitory concentration of salicylic acid resulted in a significant reduction in the number of bacterial cells and a reduction in the rate of the number of bacteria increasing during logarithmic growth, but the time to reach the stationary phase of growth was unchanged. These changes in growth pattern affected the amount of acylated homoserine lactones produced by P. aeruginosa 6294. Also affected by growth in salicylic acid was the ability of strain 6294 to show twitching or swimming motility. Salicylic acid also reduced the invasion of strain 6294 into corneal epithelial cells and the epithelial cell death caused by strain 6206. Furthermore, production of proteases by P. aeruginosa was significantly reduced by growth in salicylic acid.

CONCLUSIONS

The results of this study clearly demonstrate that salicylic acid has a significant impact on several potential virulence factors of P. aeruginosa that may be involved in the production of microbial keratitis. These effects were probably mediated by reduction in the cell density and concomitant reduction in the quorum-sensing signaling molecules, the acylated homoserine lactones, produced by P. aeruginosa.

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.

Effects of Moraxella (Branhamella) ovis culture filtrates on bovine erythrocytes, peripheral mononuclear cells, and corneal epithelial cells

Infectious bovine keratoconjunctivitis (IBK) is a highly contagious ocular disease that affects cattle of all ages and that occurs worldwide. Piliated hemolytic Moraxella bovis is recognized as the etiologic agent of IBK. According to data from the Nebraska Veterinary Diagnostic Laboratory System, however, Moraxella (Branhamella) ovis has been isolated with increasing frequency from cattle affected with IBK. The objective of this study was, therefore, to examine M. ovis field isolates for the presence of the putative virulence factors of M. bovis. Culture filtrates from selected M. ovis field isolates demonstrated hemolytic activity on bovine erythrocytes and cytotoxic activity on bovine peripheral blood mononuclear cells and corneal epithelial cells. The hemolytic activity of the culture filtrates was attenuated after heat treatment. Polyclonal antibodies raised against the M. bovis hemolysin-cytotoxin also recognized a protein of approximately 98 kDa in a Western blot assay. These data indicate that the M. ovis field isolates examined produce one or more heat-labile exotoxins and may suggest that M. ovis plays a role in the pathogenesis of IBK.

Interaction of Pseudomonas aeruginosa with human tear fluid components

PURPOSE

Reflex human tears bind Pseudomonas aeruginosa bacteria and prevent them from invading corneal epithelial cells. In this study, we assessed the effect of eye closure and the role of sialoglycoprotein (SG) in tears on bacterial binding and invasion.

METHODS

Human tears (reflex and closed-eye) were collected using a microcapillary tube. Reflex tears were separated into 13 fractions by high-performance liquid chromatography while high-molecular-weight components from closed-eye tears were separated into an SG/mucin fraction and a nonmucin fraction. Bacterial binding was quantified by viable counts and bacterial invasion was tested using the gentamicin survival technique.

RESULTS

Closed-eye tears bound significantly more bacteria than open-eye tears. Fractionation of reflex tears showed that 11 out of the 13 fractions bound bacteria, while all 13 fractions significantly reduced bacterial invasion of corneal epithelial cells. Surprisingly, the SG/mucin component of closed-eye tears resisted bacterial binding and had no significant effect on bacterial invasion.

CONCLUSIONS

P. aeruginosa bacteria bind more efficiently to closed-eye tears than to open-eye tears. The mechanism by which tears bind bacteria and protect against invasion does not require SG/mucin, as this fraction of closed-eye tears does not contain either activity.

Inflammatory responses of corneal epithelial cells to Pseudomonas aeruginosa infection

PURPOSE

We hypothesized that corneal epithelium plays a role in the innate immune response by sensing the presence of pathogens and providing signals that activate the corneal defense system. We sought to determine the mechanisms involved in the activation of the signaling pathways and subsequent production of proinflammatory cytokines in human corneal epithelial cells (HCECs) in response to Pseudomonas aeruginosa infection.

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary cultures of HCECs were exposed to P. aeruginosa (PA01 strain) with or without the presence of the NF-kappaB inhibitor kamebakaurin, the p38 inhibitor SB203580, or the JNK inhibitor SP600125. IkappaB-alpha phosphorylation and degradation and p38 and JNK phosphorylation were assessed at different time points by Western blot analysis. Interleukin (IL)-6, IL-8, and TNF-alpha levels were determined by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Exposure of HUCL cells and primary HCECs to P. aeruginosa resulted in rapid activation of NF-kappaB as indicated by an increase in IkappaB-alpha phosphorylation observed within 15 min and by IkappaB-alpha degradation, which peaked in 1 hr. Two stress-activated mitogen-activated protein kinases, p38 and JNK, were also activated as their phosphorylation was induced by P. aeruginosa infection. Concomitant with the activation of these Toll-like receptor-mediated signaling pathways, transcriptional expression and subsequent secretion of IL-6 and IL-8 in HUCL cells were also induced by P. aeruginosa. Presence of the NF-kappaB inhibitor kamebakaurin in culture medium blocked P. aeruginosa-induced NF-kappaB activation and inhibited IL-6, IL-8, and TNF-alpha expression and secretion. Inhibition of p38 or JNK also resulted in a decrease in bacteria-induced expression and secretion of these cytokines.

CONCLUSIONS

P. aeruginosa triggers an innate immune response in HCECs, and NF-kappaB and, to a lesser extent, the p38/JNK signal pathways are responsible for P. aeruginosa-induced proinflammatory cytokine production in these cells.

Internalization of Pseudomonas aeruginosa is mediated by lipid rafts in contact lens-wearing rabbit and cultured human corneal epithelial cells

PURPOSE

The internalization of Pseudomonas aeruginosa (PA) in nasal and tracheal epithelium has recently been shown to involve the formation of cholesterol- and sphingolipid-rich plasma membrane domains (lipid rafts). The purpose of this study was to investigate the role of lipid rafts in PA internalization by corneal epithelium in vivo, in vitro, and after contact lens wear.

METHODS

Lipid raft formation was evaluated in rabbit corneas with and without contact lens wear and a human corneal epithelial (hTCEpi) cell line before and after PA infection with cornea-pathogenic strains by staining with FITC-conjugated cholera toxin beta-subunit, known to bind the lipid raft component GM1. Bacterial internalization was assessed by gentamicin survival assay. The role of lipid rafts in PA internalization was evaluated by pretreatment of hTCEpi cells with cholesterol metabolism inhibitors. The interaction of PA with lipid rafts was confirmed by flow cytometry.

RESULTS

Contact lens wear in rabbits induced lipid raft formation in occasional surface corneal epithelial cells. Subsequent PA exposure showed preferential binding to lipid raft-forming cells, leading to lipid raft aggregation and PA internalization. A similar sequence of lipid raft formation and PA internalization was also observed in hTCEpi for all PA strains. Internalization of all PA strains was blocked by three cholesterol metabolism inhibitors (P < 0.01). Flow cytometry showed an association of PA with rafts.

CONCLUSIONS

These findings demonstrate that contact-lens-mediated PA internalization involves lipid raft formation. Also, hTCEpi cells may be used as an experimental model for studying further the molecular mechanism(s) of PA infection in the corneal epithelium.

Non-steroidal anti inflammatory agents decrease bacterial colonisation of contact lenses and prevent adhesion to human corneal epithelial cells

PURPOSE

To investigate non-steroidal anti-inflammatory agents (NSAIDs), salicylic acid, sodium diclofenac and ketorolac for inhibition of bacterial colonization of contact lenses (CL) and human corneal epithelial cells (HCE).

METHODS

CLs pre-colonised with Pseudomonas aeruginosa, Haemophilus influenzae, Staphylococcus epidermidis and Streptococcus pneumoniae were exposed overnight to NSAIDs and the number of viable bacteria on the CLs were calculated. Cytotoxicity of NSAIDs to HCE cells was evaluated with the MTT assay. Viable counts were used to measure the adhesion of P. aeruginosa and S. epidermidis to HCE cells in the presence of the least cytotoxic NSAID.

RESULTS

All NSAIDs significantly decreased bacterial colonization of CLs in a dose-dependent manner. Salicylic acid (100 mM) completely inhibited colonisation of all species tested and was the least cytotoxic. Salicylic acid also prevented adhesion of P. aeruginosa and S. epidermidis to HCE (60% and 58% inhibition at 60 mM at 2 hours).

CONCLUSIONS

Salicylic acid demonstrated potential as a compound for incorporation into anti-bacterial strategies to prevent bacterial contamination of contact lenses. This study highlighted the potential for NSAIDs as anti-bacterial agents and indicates that this class of compound should be investigated for other suitable candidates.

Induction of cytokines from polymorphonuclear leukocytes and epithelial cells by ocular isolates of Serratia marcescens

PURPOSE

During contact lens wear, bacterial contamination of the lens can lead to the development of microbial keratitis (MK) or contact lens induced acute red eye (CLARE). Inflammatory mediators released by the host may heighten the response. We have examined the ability of human corneal epithelial cells and polymorphonuclear leukocytes (PMNs) to release cytokines upon stimulation with bacteria.

METHODS

Serratia marcescens strains were added to corneal epithelial cells or PMNs. After incubations of up to 20 hours, supernatants were assayed for the presence of inflammatory mediators by ELISA.

RESULTS

All strains stimulated PMNs to release IL-8 and LTB(4). Epithelial cells did not release LTB(4). IL-8 was released after exposure to most S. marcescens isolates. A sub-group of strains stimulated the release of TNF-alpha from corneal epithelial cells.

CONCLUSIONS

S. marcescens can stimulate the release of inflammatory mediators from both PMNs and corneal epithelial cells. This release could be important in the progression and resolution of MK and CLARE.

Polyphosphate kinase 1 and the ocular virulence of Pseudomonas aeruginosa

PURPOSE

To determine the role of polyphosphate kinase 1 (PPK1) in the ocular virulence of Pseudomonas aeruginosa.

METHODS

Using a mouse model of infection, P. aeruginosa strains PAO1, PAOM5 (an isogenic mutant of PAO1 deficient in PPK1), and PAOM5+PPK1 (the mutant complemented with PPK1 on plasmid pHEPAK11) were compared for ocular virulence. These strains were also characterized with respect to traits associated with survival and pathogenicity in an ocular environment.

RESULTS

The PPK1-deficient strain PAOM5 was significantly less virulent than either wild-type PAO1 or the complemented mutant (P <0.016). Loss of virulence was not associated with serum sensitivity or diminished adherence to the cornea. However, PAOM5 has an increased susceptibility to oxidative stress and was cleared from corneal tissue significantly better (P <0.006) than either the wild-type or restored strain. Furthermore, the PPK1-deficient mutant produced significantly less (P <0.022) pyocyanin.

CONCLUSIONS

PPK1 is essential for a successful ocular infection by P. aeruginosa. The loss of ocular virulence is probably due to the dysregulation of multiple genes, including those responsible for stress response.

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.

Pseudomonas aeruginosa corneal binding after 24-hour orthokeratology lens wear

PURPOSE

To examine the effect of short-term 24-hr orthokeratology lens (OKL) wear on Pseudomonas aeruginosa binding, epithelial surface cell morphology, epithelial sheet thickness, and stromal thickness in a rabbit model.

METHODS

Seventeen New Zealand white rabbits were treated according to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. Partial membranectomy was performed on all rabbits 1 week before the experiments. Baseline values for epithelial and stromal thickness and epithelial surface cell size were determined by in vivo confocal microscopy in one randomly chosen eye (n = 6). One week later, rabbits were fitted in the same eye with a hyper oxygen-transmissible OKL. Twenty-four hours later, confocal microscopy was repeated. The second group of rabbits (n = 6) was fitted with an OKL in one randomly chosen eye for 24 hr. P. aeruginosa binding to the corneal epithelium was assessed for the control corneas and those exposed to the test lens. Scanning electron microscopy was performed on a third group of rabbits to assess epithelial surface damage (n = 5).

RESULTS

There was a statistically significant difference (P<0.001) in P. aeruginosa binding between the control (1.11 +/- 0.74 x 10(5) colony-forming units per cornea) and the OKL-wearing eyes (2.74 +/- 0.69 x 10(5) colony-forming units per cornea). The central epithelium thinned by 6.5% after lens wear (48.2 +/- 1.9 microm to 45 +/- 1.7 microm, P=0.005); however, central stromal thickness increased by 7.3% (322 +/- 22 microm to 345 +/- 29 microm, P=0.006). Compared with the baseline value, central epithelial cell size increased significantly from 1,253 +/- 140 mm(2) to 1,627 +/- 393 mm(2) (29.4%, P=0.02). Scanning electron microscopy showed increased surface epithelial damage associated with OKL wear.

CONCLUSIONS

This prospective, masked, pilot study showed that 24-hr hyper oxygen-transmissible OKL wear induced a statistically significant increase in P. aeruginosa binding to the epithelium of the rabbit cornea, accompanied by central epithelial thinning, stromal thickening, and surface cell damage assessed by scanning electron microscopy. Collectively, the data suggest that despite adequate lens oxygen transmissibility, the mechanical pressure inherent in the OKL design exerted on the corneal surface appears to be associated with increased adherence of P. aeruginosa to surface corneal epithelial cells, which may pose an increased risk for lens-related microbial keratitis, especially in overnight (i.e., closed-eye) wearing conditions. Future studies are needed to determine whether these results are similar in human wear and how P. aeruginosa binding during OKL wear compares with other lens-wearing modalities, such as daily or continuous soft lens wear.

Innate immune response of corneal epithelial cells to Staphylococcus aureus infection: role of peptidoglycan in stimulating proinflammatory cytokine secretion

PURPOSE

This study sought to elucidate the innate immune responses of cultured human corneal epithelial cells (HCECs) to infection by the Gram-positive bacterium Staphylococcus aureus and to determine the underlying mechanisms.

METHODS

HUCL, a telomerase-immortalized HCEC line, and primary cultures of HCECs were challenged with live or heat-killed S. aureus, its exoproducts, or cell wall components lipoteichoic acid (LTA) and peptidoglycan (PGN). IkappaB-alpha phosphorylation and degradation as well as phosphorylation of MAPKs, p38, and JNK-1/2, were assessed by Western blot analysis. The expression of interleukin (IL)-6, IL-8, TNF-alpha, and beta-defensin-2 were determined using RT-PCR and secretion of IL-6, IL-8, TNF-alpha, and beta-defensin were measured using enzyme-linked immunosorbent assay and immunoblot analysis of culture medium.

RESULTS

Exposure of HUCL cells to live, but not heat-killed, S. aureus resulted in NF-kappaB activation in a time-dependent manner, as assessed by the increase in IkappaB-alpha phosphorylation and degradation. Live bacteria also activated the p38 and JNK pathways. The effects of live bacteria on HUCL cells may be attributable to bacterial exoproducts, since the conditioned medium of S. aureus also effectively stimulated these signaling pathways. PGN, but not LTA, activated the NF-kappaB and MAPK pathways in a dose- and time-dependent manner. Concomitant with activation of NF-kappaB and MAPKs, transcriptional expression of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were induced in cells challenged with bacterial exoproducts and PGN. Secretion of IL-6, IL-8, TNF-alpha, and beta-defensin-2 were also significantly increased in HCECs in response to bacterial exoproducts and PGN challenge.

CONCLUSIONS

Corneal epithelial cells possess the ability to recognize the presence of Gram-positive bacteria and to initiate the innate immune responses by the expression and/or release of proinflammatory cytokines and beta-defensin-2 in the cornea.

Role of EGFR transactivation in preventing apoptosis in Pseudomonas aeruginosa-infected human corneal epithelial cells

PURPOSE

To determine the role of epidermal growth factor (EGF) receptor (EGFR)-mediated signaling pathways in preventing infection-induced apoptosis in human corneal epithelial cells (HCECs).

METHODS

Epithelial monolayers of a telomerase-immortalized HCEC line, HUCL, and primary culture of HCECs were infected with Pseudomonas aeruginosa in the presence of the EGFR inhibitor tyrphostin AG1478, the extracellular signal-regulated kinase (ERK) inhibitor U0126, the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, the heparin-binding EGF-like growth factor (HB-EGF) antagonist CRM197, the HB-EGF neutralizing antibody, or the matrix metalloproteinase inhibitor GM6001. The activation of EGFR was analyzed by immunoprecipitation using EGFR antibodies, followed by Western blot analysis with phosphotyrosine antibody. Phosphorylation of ERK and Akt, a major substrate of PI3K, and generation of cleaved caspase-3 and poly (ADP-ribose) polymerase (PARP) were determined by Western blot analysis. Apoptotic cells were characterized by positive staining of active caspase-3, loss of mitochondrial cytochrome c, and condensation of chromosomes. Apoptosis was also confirmed by measuring caspase-3 activity and assessing the generation of cleaved caspase-3 and PARP.

RESULTS

P. aeruginosa infection of HUCL cells resulted in EGFR activation and EGFR-dependent ERK1/2 and PI3K phosphorylation. Inhibition of EGFR, ERK1/2, and PI3K activities with kinase-specific inhibitors (AG1478, U0126, and LY294002, respectively) resulted in an increase in the number of apoptotic cells, in elevated cellular caspase-3 activity, and/or in increased cleaved PARP in P. aeruginosa-infected HUCL cells or primary culture of HCECs. Blocking HB-EGF ectodomain shedding by inhibition of matrix metalloproteinase-mediated proteolysis, downregulation of HB-EGF, or neutralization of its activity retarded infection-induced EGFR transactivation and, as a consequence, increased infection-induced HUCL apoptosis.

CONCLUSIONS

Bacterial infection of HCECs induces EGFR transactivation through HB-EGF ectodomain shedding. EGFR and its downstream ERK and PI3K signaling pathways play a role in preventing epithelial apoptosis in the early stage of bacterial infection.

Role of Pseudomonas aeruginosa ExsA in penetration through corneal epithelium in a novel in vivo model

PURPOSE

The scarified cornea keratitis model was modified to study Pseudomonas aeruginosa infection of healing corneal epithelium. The new model was then used to study the role of ExsA, a transcriptional activator of P. aeruginosa, in bacterial penetration through injured and healing corneal epithelia.

METHODS

Scratch-injured corneas of C57BL/6 mice were allowed to heal for 0, 6, 9, or 12 hours before inoculation with a cytotoxic (6206) or invasive (PAO1) P. aeruginosa strain. Disease progression was monitored for 14 days. The integrity of the healing epithelium was studied in uninfected eyes by fluorescein staining and by histologic examination. In other experiments, the effect of bacterial exsA mutation was studied after 0, 6, or 12 hours of healing. Three hours after infection, these eyes were used to quantify early bacterial colonization levels by viable counts, or they were sectioned to study bacterial penetration through the epithelium by microscopy.

RESULTS

Corneas remained susceptible to infection 6 but not 12 hours after scratch injury. By 6 hours, the previously exposed stroma was already completely covered by several layers of epithelial cells. Fluorescein staining unexpectedly occurred even after 12 hours of healing time, showing that resistance to infection preceded full restoration of epithelial barrier function. Mutation of exsA reduced both bacterial colonization levels and penetration through the epithelium 3 hours after bacterial inoculation, but only in the 6-hour healing situation, and only for the cytotoxic strain (PA103). Mutation of exsA in the invasive strain (PAO1) had no effect on 3-hour colonization or penetration levels under any circumstances.

CONCLUSIONS

The 6-hour healing infection model showed a role for ExsA in early interactions with the corneal epithelium that was not detectable with the conventional (0-hour) scratch model. Comparison of the 6- and 12-hour healing models, which showed that factors additional to barrier function contribute to defense against infection, could be used to gain new insights into corneal defense mechanisms, and the methods used by bacteria to circumvent them.

[Infection immunology in silicone hydrogel contact lenses for continuous wear--a review]

BACKGROUND

The patient's wish for permanent refractive solution and optimal comfort must be weighed against the risk of infections. In order to meet these wishes and the demand for minimising associated risks, hyperoxygen-transmissible silicone hydrogel contact lenses have been developed.

METHODS

Colonisation and sensitivity to antibiotics of bacteria in vitro, expression of bacterial ligands of the corneal epithelium (rabbit model), and the morphology of complications in patients have been reported to characterise HOTL.

RESULTS

Bacterial adherence to hydrophobic silicone elastomers is low. The reduction of sensitivity towards antibiotics is higher for PMMA-adherent bacteria with respect to the conventional antibiotics compared to the silicone-elastomer adherent bacteria. Colonising bacteria are not significantly different in asymptomatic CL wearers concerning CFU and species: asymptomatic: CNS (54 vs. 47 %), propioni- (43 vs. 48 %), coryne- (6 vs. 10 %) and gram-negative bacteria (2 vs. 3 %), S. aureus (2 vs. 1 %), and in patients with keratitis are not significantly different concerning species: CLARE (H. influenzae, S. pneumoniae), CLPU (S. aureus, S. pneumoniae), IK (P. aeruginosa), however, concerning the CFU (gram-negative) 23.7 % (keratitis) vs. 3.8 %, (asymptomatic), S. pneumoniae 7.6 % vs. 0.6 %. The epithelial expression of bacterial ligands like WGA is lower for HOTL (3230 p/750 micro) than for low oxygen-transmissible (4611 p/750 micro) consistent with a decreased adherence of pseudomonas of 5.31 - 5.98 vs. 5.9 - 7.81 bacteria/cell. Asymptomatic morphological anomalies and keratitis are less frequent in HOTL. Apoptosis-induced desquamation and the central epithelial thickness decreased. In a one-year study of 504 patients wearing continuous wear HOTL for 30 days, corneal staining was seen in 10.6 vs. 10.5 % 30-day 7 day extended wear, infiltrates in 2.3 vs. 4.6 %, epithelial oedema in 3.6 vs. 2.0 % und tarsal conjunctival anomalies in 3.0 vs. 1.6 %. Individual reports on infectious keratitis in HOTL wearers have been published.

CONCLUSIONS

Fewer morphological anomalies and a decreased incidence of infections (on the basis of duration of wear) can be associated with the higher oxygen transmission of HOTL. From the clinical point of view, colonisation of HOTL with the same bacterial species as in conventional biomaterials, and the extended wear demand clear patient counseling and vigilant follow-up by an ophthalmologist.

Contact lens infections: can they ever be eradicated?

Since their introduction, the most significant complication of wearing soft contact lenses has been the development of vision-threatening microbial keratitis. In lens-wearing corneas, microbial infection is thought to develop in the absence of overt injury, leading to the hypothesis that microbe interactions with the corneal epithelium are critical to the pathogenesis of this disease. Thus, we have focused our research efforts on understanding microbial virulence mechanisms aimed at corneal epithelial cells and the innate defenses that normally protect them using the gram-negative bacterium Pseudomonas aeruginosa as a model organism. This report summarizes those results and explores their relevance to understanding contact lens-related infections.

Effects of daily and overnight wear of hyper-oxygen transmissible rigid and silicone hydrogel lenses on bacterial binding to the corneal epithelium: 13-month clinical trials

PURPOSE

For 14 years, the U. S. Food and Drug Administration (FDA) and eye care practitioners have strongly discouraged patients from sleeping in contact lenses. In the past 9 months however, the FDA has approved three new hyper-oxygen transmissible lenses for up to 30-night extended wear. Is this a great advance or another clinical triumph of hope over experience? What should the public know? What should patients do?

METHODS

Our research group has studied all three new lenses in prospective, randomized, masked, parallel clinical trials in a single center. As an outcome measure, we looked at whether lens wear caused more bacterial binding to surface corneal cells.

RESULTS

Compared with conventional lens use, the new lenses caused no or only small increases in bacterial binding in either daily or extended wear. Furthermore, the increases seen stratified with known infection risks by both lens type (hard or soft) and wearing schedule. Indeed, early epidemiologic reports indicate that this new generation of lenses may reduce lens-related microbial infection risks by 10- to 40-fold.

CONCLUSION

This represents a true clinical paradigm shift of the first magnitude in safety of contact lens wear. Taken together, this data suggest that patients will soon replace their current, conventional lenses with this new generation of materials for any schedule of wear.

Effects of contact lens care solutions on surface exfoliation and bacterial binding to corneal epithelial cells

PURPOSE

The purpose of this study is to assess the effects of commercially available contact lens wetting solutions on bacterial binding and cell exfoliation rates in human corneal epithelium.

METHODS

The effects of four contact lens care solutions were tested: ReNu Multi Plus (Bausch & Lomb, Rochester, NY) multipurpose solution; OPTI-FREE Express (Alcon, Ft. Worth, TX) multipurpose solution; Complete Blink-N-Clean (Allergan, Irvine, CA) lens drops; and Lens Plus (Allergan) rewetting drops.

STUDY DESIGN

Prospective, double-masked, randomized crossover clinical trial (N = 20 subjects).

OUTCOME MEASURES

Measures of outcome included binding of Pseudomonas aeruginosa (PA) to exfoliated corneal epithelial cells, and the rate of surface cell exfoliation. Cells were collected at the baseline (pretreatment) examination and 4 days later, after subjects used the assigned solution six times daily and once again immediately before cell collection (posttreatment). Following cell collection, patients underwent 1 week of recovery, during which no drops were used, and random cross-over assignment to the next test solution.

RESULTS

Use of test solutions increased PA binding, with a range of + 11.9% to + 58.2%. Analyzed together, PA binding increased significantly (+ 29%; P = 0.02, paired t-test); Lens Plus solution alone raised PA binding levels significantly (P = 0.022, 2-way ANOVA, Student-Newman-Keuls [SNK] test). Exfoliation rates were decreased from -7% to -52.7%. Analyzed together, cell exfoliation decreased significantly (P = 0.004; Wilcoxon signed rank test). Individual use of OPTI-FREE decreased exfoliation significantly (P = 0.019: 2-way ANOVA, SNK test).

CONCLUSIONS

Topical application of common commercial contact lens care solutions increases PA binding and reduces corneal surface cell exfoliation. Similar effects have also been reported with contact lens wear. Taken together, the data suggest that the use of lens solution itself may play a role in increasing PA binding to corneal epithelial cells and, hence, might potentially contribute inadvertently to increased risk for lens-related microbial keratitis.

The causes of and cures for contact lens-induced peripheral ulcer

PURPOSE

Contact lens-induced peripheral ulceration (CLPU) is a relatively common adverse response associated with wearing hydrogel lenses, especially on an extended wear schedule. Bacteriologic examination of lenses at the time of an event has demonstrated an association with Staphylococci spp. We sought to investigate the causes of CLPU in a rabbit model of contact lens wear.

METHODS

Rabbits wore contact lenses for a period of 24 hr in the presence or absence of bacteria or in presence or absence of epithelial scratches made in the periphery of the cornea before lens wear. Bacteria tested were a strain of Staphylococcus aureus or a strain of Staphylococcus epidermidis isolated from human CLPUs. Rabbits were also challenged with S. aureus in the presence of an epithelial defect and in the absence of a contact lens. Corneas were monitored by slitlamp, histology, and microbial culture after 24 hr.

RESULTS

No CLPU-like lesions were detected under the following conditions: corneal scratch plus lens wear with no bacteria; corneal scratch plus S. epidermidis colonized lenses; corneal scratch without lens wear and with S. aureus applied to eyes; no scratch plus S. aureus colonized lenses; and corneal scratch plus contact lenses colonized by dead S. aureus. CLPU-like lesions were found only when the corneas were scratched and contact lenses colonized by viable S. aureus were applied to the eye. The histology of the lesions demonstrated a frank epithelial break with underlying stromal infiltration. Only low numbers of bacteria could be cultivated from the corneas with CLPU-like lesions. The CLPU-like lesions shared many similarities with CLPU in humans.

CONCLUSION

CLPU-like lesions were only produced by S. aureus and not S. epidermidis in the presence of an epithelial abrasion and contact lens. Thus, we hypothesize that to reduce the incidence of CLPU, contact lenses designed to reduce corneal interaction and repel microbial colonization should be produced.

Pseudomonas aeruginosa binds to extracellular matrix deposited by human corneal epithelial cells

PURPOSE

To measure the effect of extracellular matrix substrate, pH, and O(2) on Pseudomonas aeruginosa binding.

METHODS

Extracellular matrix substrates were prepared from human corneal epithelial cells cultured in 2% or 20% O(2). P. aeruginosa strains ATCC 19660 or PAO1 (suspended in pH 7.0 or 7.5 buffer) were cultured on extracellular matrix substrates in 2% or 20% O(2). The mean number of adherent bacteria per counted per field +/- SEM (n = 15) was determined for combinations of bacteria, extracellular matrix substrate, pH, and O(2). Binding in the presence of antibodies directed against laminin-5 was also measured.

RESULTS

Extracellular matrix substrates produced by cells cultured in 20% O(2), combined with an environment of pH 7.0, provided the least favorable conditions for binding of strain 19660. In contrast, extracellular matrix substrates produced by cells cultured in 2% O(2), combined with an environment of pH 7.0, provided the most favorable conditions for binding of strain 19660. Binding of PAO1, however, as a function of extracellular matrix substrate and pH, did not similarly compare with binding of strain 19660. Antibodies against laminin-5 chains served to increase the number of strain 19660 bacteria bound to extracellular matrix substrates compared with the control.

CONCLUSIONS

The extracellular matrix secreted by hypoxic corneal epithelial cells is a substrate for binding of P. aeruginosa. Results in previous studies have shown that hypoxic extracellular matrix contains less laminin-5 protein than normoxic matrix. The antibody studies in this report suggest that the decrease in laminin-5 content in hypoxic matrix, relative to matrix secreted by normoxic corneal epithelium, may be responsible for increased bacterial adhesion.

Pseudomonas aeruginosa strains with lipopolysaccharide defects exhibit reduced intracellular viability after invasion of corneal epithelial cells

Pseudomonas aeruginosa is a leading cause of infectious keratitis. Many ocular isolates of this bacterium invade corneal epithelial cells in vitro and in vivo. Antibiotic survival assays have shown that a complete core lipopolysaccharide is required for full epithelial invasion by P. aeruginosa. In this study, we show that P. aeruginosa mutants with defects in their lipopolysaccharide core and O antigen exhibited reduced viability after internalization by corneal epithelial cells. Restoration of lipopolysaccharide core and O antigen expression by complementation with the plasmid pLPS1 restored intracellular survival. P. aeruginosa strains with a complete lipopolysaccharide survived and replicated within the cells. The data suggest that lipopolysaccharide is involved in the intracellular survival and/or replication of P. aeruginosa, indicating an additional mechanism by which this important virulence factor may contribute to the pathogenesis of corneal infection.

Effects of daily and overnight wear of a novel hyper oxygen-transmissible soft contact lens on bacterial binding and corneal epithelium: a 13-month clinical trial

OBJECTIVE

To test prospectively a new biologic rationale for an advanced hyper oxygen-transmissible lens (HOTL) providing prospects for safer daily (DW) or extended (EW) contact lens wear.

DESIGN

Prospective, randomized, double-masked, single-center, 13-month clinical trial.

PARTICIPANTS

One hundred sixty-eight patients completed the DW study (1 month): control lens (n = 70); HOTL (n = 98). One hundred thirty-six patients finished 1 year of EW: controls (n = 56), HOTL (n = 25, 6 nights; n = 55, 30 nights).

TESTING

Irrigation chamber to collect corneal surface cells, confocal microscopy, tear collection at baseline, 2, and 4, weeks of DW, and 24 hours, 1, 3, 6, 9, and 12 months of EW.

MAIN OUTCOME MEASURES

(1) Pseudomonas aeruginosa (PA) binding to exfoliated corneal surface cells; (2) central epithelial thickness (CET); (3) superficial cell area (SCA); (4) epithelial surface cell exfoliation (DESQ); and (5) tear lactate dehydrogenase (LDH).

RESULTS

Daily wear with control lens increased PA binding from 5.90 +/- 2.60 to 7.81 +/- 3.04 bacteria per cell (P < 0.01); HOTL wear increased PA binding significantly less (5.31 +/- 1.87-5.98 +/- 2.26; P < 0.01). Daily wear produced no significant changes in CET or SCA. Significant decreases in DESQ were seen with both lenses with no significant intergroup differences. Tear LDH increased significantly in DW with HOTL wear versus control (P = 0.0017), but not after 1 month of subsequent EW (P = 0.533). One to 3 months of EW with control lens showed significantly higher PA binding than HOTL wear (P < 0.01); binding adaptively decreased thereafter, returning to baseline at 9 to 12 months. Lens EW produced significantly enlarged SCA, thinning of CET (except 6-night HOTL wear), and decreased DESQ (P < 0.01). Some adaptive recovery was seen with CET and DESQ, but not SCA; importantly, the data indicated no significant difference between 6- or 30-night EW for all outcomes.

CONCLUSIONS

Hyper oxygen-transmissible lens wear (DW or EW) produced significantly decreased PA binding compared with control lens wear, with no significant difference in wearing schedule (6 nights vs. 30 nights); additionally, there was a remarkable and unexpected adaptive recovery in the first 6 months of all soft lens wear, with a return to baseline PA binding levels and partial recovery for the other outcomes except SCA at 1 year. These results suggest that HOTL use should result in a decrease in the incidence of and risk(s) for lens-related microbial keratitis and that further epidemiologic studies should consider time in adapted EW in future risk and incidence analyses.