Extended Latanoprost Release from Commercial Contact Lenses: In Vitro Studies Using Corneal Models

In this study, we compared, for the first time, the release of a 432 kDa prostaglandin analogue drug, Latanoprost, from commercially available contact lenses using in vitro models with corneal epithelial cells. Conventional polyHEMA-based and silicone hydrogel soft contact lenses were soaked in drug solution ( solution in phosphate buffered saline). The drug release from the contact lens material and its diffusion through three in vitro models was studied. The three in vitro models consisted of a polyethylene terephthalate (PET) membrane without corneal epithelial cells, a PET membrane with a monolayer of human corneal epithelial cells (HCEC), and a PET membrane with stratified HCEC. In the cell-based in vitro corneal epithelium models, a zero order release was obtained with the silicone hydrogel materials (linear for the duration of the experiment) whereby, after 48 hours, between 4 to 6 of latanoprost (an amount well within the range of the prescribed daily dose for glaucoma patients) was released. In the absence of cells, a significantly lower amount of drug, between 0.3 to 0.5 , was released, (). The difference observed in release from the hydrogel lens materials in the presence and absence of cells emphasizes the importance of using an in vitro corneal model that is more representative of the physiological conditions in the eye to more adequately characterize ophthalmic drug delivery materials. Our results demonstrate how in vitro models with corneal epithelial cells may allow better prediction of in vivo release. It also highlights the potential of drug-soaked silicone hydrogel contact lens materials for drug delivery purposes.     

Development of a Curved,Stratified, In Vitro Model to Assess Ocular Biocompatibility

Purpose

To further improve in vitro models of the cornea, this study focused on the creation of a three-dimensional, stratified, curved epithelium; and the subsequent characterization and evaluation of its suitability as a model for biocompatibility testing.

Methods

Immortalized human corneal epithelial cells were grown to confluency on curved cellulose filters for seven days, and were then differentiated and stratified using an air-liquid interface for seven days before testing. Varying concentrations of a commercial ophthalmic solution containing benzalkonium chloride (BAK), a known cytotoxic agent, and two relevant ocular surfactants were tested on the model. A whole balafilcon A lens soaked in phosphate buffered saline (BA PBS) was also used to assess biocompatibility and verify the validity of the model. Viability assays as well as flow cytometry were performed on the cells to investigate changes in cell death and integrin expression.

Results

The reconstructed curved corneal epithelium was composed of 3–5 layers of cells. Increasing concentrations of BAK showed dose-dependent decreased cell viability and increased integrin expression and cell death. No significant change in viability was observed in the presence of the surfactants. As expected, the BA PBS combination appeared to be very biocompatible with no adverse change in cell viability or integrin expression.

Conclusions

The stratified, curved, epithelial model proved to be sensitive to distinct changes in cytotoxicity and is suitable for continued assessment for biocompatibility testing of contact lenses. Our results showed that flow cytometry can provide a quantitative measure of the cell response to biomaterials or cytotoxic compounds for both the supernatant and adherent cell populations. As a specifically designed in vitro model of the corneal epithelium, this quantitative model for biocompatibility at the ocular surface may help improve our understanding of cell-material interactions and reduce the use of animal testing.     

Quantification of protein deposits on silicone hydrogel materials using stable-isotopic labeling and multiple reaction monitoring

This study was designed to use multiple reaction monitoring (MRM) for accurate quantification of contact lens protein deposits. Worn lenses used with a multipurpose disinfecting solution were collected after wear. Individual contact lenses were extracted and then digested with trypsin. MRM in conjunction with stable-isotope-labeled peptide standards was used for protein quantification. The results show that lysozyme was the major protein detected from both lens types. The amount of protein extracted from contact lenses was affected by the lens material. Except for keratin-1 (0.83?±?0.61 vs 0.77?±?0.20, p?=?0.81) or proline rich protein-4 (0.11?±?0.04 vs 0.15?±?0.12, p?=?0.97), the amounts of lysozyme, lactoferrin, or lipocalin-1 extracted from balafilcon A lenses (12.9?±?9.01, 0.84?±?0.50 or 2.06?±?1.6, respectively) were significantly higher than that extracted from senofilcon A lenses (0.88?±?0.13, 0.50?±?0.10 or 0.27?±?0.23, respectively) (p?相似文献   

Quantification of protein deposits on silicone hydrogel materials using stable-isotopic labeling and multiple reaction monitoring

This study was designed to use multiple reaction monitoring (MRM) for accurate quantification of contact lens protein deposits. Worn lenses used with a multipurpose disinfecting solution were collected after wear. Individual contact lenses were extracted and then digested with trypsin. MRM in conjunction with stable-isotope-labeled peptide standards was used for protein quantification. The results show that lysozyme was the major protein detected from both lens types. The amount of protein extracted from contact lenses was affected by the lens material. Except for keratin-1 (0.83 ± 0.61 vs 0.77 ± 0.20, p = 0.81) or proline rich protein-4 (0.11 ± 0.04 vs 0.15 ± 0.12, p = 0.97), the amounts of lysozyme, lactoferrin, or lipocalin-1 extracted from balafilcon A lenses (12.9 ± 9.01, 0.84 ± 0.50 or 2.06 ± 1.6, respectively) were significantly higher than that extracted from senofilcon A lenses (0.88 ± 0.13, 0.50 ± 0.10 or 0.27 ± 0.23, respectively) (p < 0.05). The amount of protein extracted from contact lenses was dependent on both the individual wearer and the contact lens material. This may have implications for the development of clinical responses during lens wear for different people and with different types of contact lenses. The use of MRM-MS is a powerful analytical tool for the quantification of specific proteins from single contact lenses after wear.     

Effect of nutrient limitation on adhesion characteristics of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes a variety of diseases in humans including lung and ocular infections. Infections of the cornea are usually associated with wearing contact lenses and can result in loss of vision. This study aimed to determine the effect of carbon or nitrogen limitation on the adhesion to contact lenses of a strain of Ps. aeruginosa isolated from contact lens-related corneal inflammation. Cells were grown in a continuous culture apparatus in varying levels of glucose or ammonia to effect nutrient limitation. Adhesion to contact lenses was measured as total counts and viable counts. The cell surface hydrophobicity and charge were measured using adhesion to surface-modified Sepharose. Changes in lipopolysaccharide were determined using 1D SDS-PAGE and changes in cell-surface proteins were measured using 2D gel electrophoresis. The more the cultures were nitrogen limited, the greater the increase in adhesion to unworn hydrogel contact lenses 0.3 x 10(3) - 2.2 x 10(3) cells/mm2 on Etafilon A lenses. Cells that were carbon limited showed a greater increase in adhesion to contact lenses when the lenses had been coated in artificial tears. It appeared that lipopolysaccharide may have been involved in the constitutive adhesion to unworn lenses that occurred during C-limitation, whereas changes in the outer membrane proteins contributed to the increased adhesion under nitrogen limitation, or the change in adhesion that occurred to carbon-limited cells using contact lenses coated in artificial tears. Nine cell-surface proteins appeared during nitrogen limitation with kDa/pI of 75/4.8, 4.9, 5.0; 62/5.6; 89/6.5; 38/6.4; 28/1.5; 18/6.4; 12/4.5. Any or all of these may have been involved in the increased adhesion and further experiments are underway to examine this possibility.     

Direct detection of proteins adsorbed on synthetic materials by matrix-assisted laser desorption ionization-mass spectrometry.

The irreversible accumulation of biological material on synthetic surfaces ("biofouling") adversely affects for instance contact lenses, implantable biomedical devices, biosensors, water purification, transport and storage systems, and marine structures. It is shown here that proteins adsorbed on contact lenses can be detected directly, rapidly, and conveniently, with high sensitivity, by matrix-assisted laser desorption ionization (MALDI)-mass spectrometry. This new approach allows detection of minor (and major) proteinaceous constituents of biofouled layers on samples retrieved from clinical usage and in vitro protein adsorption studies, at levels substantially below monolayer coverage. Identification of the detected biological molecules can be done by comparison of the detected mass peaks with known protein molecular masses or with spectra recorded of pure compounds or by separate biochemical assays. The MALDI mass spectra recorded on different contact lenses contain peaks assignable to lysozyme and a number of smaller proteins. Such sensitive characterization of the early stages of biofouling enhances the understanding of protein/materials interactions and assists in designing guided strategies toward control of biological adsorption processes.     

Adhesion of Pseudomonas aeruginosa,Achromobacter xylosoxidans,Delftia acidovorans,Stenotrophomonas maltophilia to contact lenses under the influence of an artificial tear solution

Abstract

Corneal infection is a devastating sight-threatening complication that is associated with contact lens (CL) wear, commonly caused by Pseudomonas aeruginosa. Lately, Achromobacter xylosoxidans, Delftia acidovorans, and Stenotrophomonas maltophilia have been associated with corneal infection. This study investigated the adhesion of these emerging pathogens to CLs, under the influence of an artificial tear solution (ATS) containing a variety of components commonly found in human tears. Two different CL materials, etafilcon A and senofilcon A, either soaked in an ATS or phosphate buffered saline, were exposed to the bacteria. Bacterial adhesion was investigated using a radio-labeling technique (total counts) and plate count method (viable counts). The findings from this study revealed that in addition to P. aeruginosa, among the emerging pathogens evaluated, A. xylosoxidans showed an increased propensity for adherence to both CL materials and S. maltophilia showed lower viability. ATS influenced the viable counts more than the total counts on CLs.     

Deletion of JAM-A causes morphological defects in the corneal epithelium

Junctional adhesion molecule-A (JAM-A, JAM-1, F11R) is an Ig domain containing transmembrane protein that has been proposed to function in diverse processes including platelet activation and adhesion, leukocyte transmigration, angiogenesis, epithelial cell shape and endothelial cell migration although its function in vivo is less well established. In the mouse eye, JAM-A protein expression is first detected at 12.5 dpc in the blood vessels of the tunica vasculosa, while it is first detected in both the corneal epithelium and lens between 13.5 and 14.5 dpc. In the corneal epithelium, JAM-A levels remain appreciable throughout life, while JAM-A immunostaining becomes stronger in the lens as the animals age. Both the cornea and lens of mice lacking an intact JAM-A gene are transparent until at least a year of age, although the cells of the JAM-A null corneal epithelium are irregularly shaped. In wild-type mice, JAM-A protein is found at the leading edge of repairing corneal epithelial wounds, however, corneal epithelial wound repair was qualitatively normal in JAM-A null animals. In summary, JAM-A is expressed in the corneal epithelium where it appears to regulate cell shape.     

Soft contact lenses

A series of 55 patients were fitted with a new type of hydrophilic soft contact lens. These were found more comfortable than hard contact lenses and they had a protective and pain-relieving action in cases of chronic corneal disease. Vision was not as good as with hard contact lenses and a greater potential danger of infection was found. They are preferred by many patients despite the noticeable thick edge and the difficulty of obtaining an identical replacement.     

The effects of non-ionic polymeric surfactants on the cleaning of biofouled hydrogel materials

Block co-polymer surfactants have been used for cleaning hydrogel medical devices that contact the body (eg contact lenses) because of their biocompatibility. This work examined the relationship between concentration and detergency of two non-ionic polymeric surfactants (Pluronic F127 and Triton X-100) for cleaning protein soil, with anionic surfactants (sodium dodecyl sulfate and sodium laureth sulfate) as positive controls. Surface plasmon resonance was used to quantify removal of simulated tear soil from self-assembled monolayer surfaces, and a microplate format was used to study the removal of fluorescently labeled soil proteins from contact lenses. While detergency increased as a function of concentration for anionic surfactants, it decreased with concentration for the two polymeric surfactants. The fact that the protein detergency of some non-ionic polymeric surfactants did not increase with concentration above the critical micelle concentration could have implications for optimizing the tradeoff between detergency and biocompatibility.     

Geometric optical optimization of the corneal lens of Notonecta glauca

The optimal shape of the corneal lens of the water bug backswimmer (Notonecta glauca) and the optimal shape and position of the thin transition layer between the distal and proximal units of its cornea are theoretically determined. Using a geometric optical method, first the shape of a geometric interface between the lens units is determined, which eliminates the longitudinal spherical aberration. This interface is investigated for differently formed thick lenses when the medium in contact with the entrance surface of the lens is water or air. The optimal transition layer for the amphibious backswimmer is that, the boundaries of which are the theoretical interfaces for water and air, and the refractive index varies continuously in it. The optimal shape of the corneal lens is determined, with the disadvantageous lenses, with respect to the possible minimal spherical aberration and amount of reflected light from the transition layer, being rejected. The optimal position of the transition layer in the cornea can be obtained from the minimization of the amount of diffracted light on the marginal connection of the layers. The optimal corneal lens for backswimmer has ellipsoid boundary surfaces; the optimal transition layer in it is thin bell-shaped, at the marginal connection of which there is no dimple, the maximum of the layer is on the margin of the cornea. The shape of the theoretically optimal corneal lens, the shape and position of the theoretically optimal transition layer agree well with those of Notonecta glauca. The question posed, the geometric optical method used and the results presented are of general importance, and not only with respect to vision in the bug Notonecta, but also in the fossil trilobites, or in the wave guide theories which have been employed in similar modelling problems, in design of system of lenses without spherical aberration, for example.     

In vivo measurement of age-related stiffening in the crystalline lens by Brillouin optical microscopy

The biophysical and biomechanical properties of the crystalline lens (e.g., viscoelasticity) have long been implicated in accommodation and vision problems, such as presbyopia and cataracts. However, it has been difficult to measure such parameters noninvasively. Here, we used in vivo Brillouin optical microscopy to characterize material acoustic properties at GHz frequency and measure the longitudinal elastic moduli of lenses. We obtained three-dimensional elasticity maps of the lenses in live mice, which showed biomechanical heterogeneity in the cortex and nucleus of the lens with high spatial resolution. An in vivo longitudinal study of mice over a period of 2 months revealed a marked age-related stiffening of the lens nucleus. We found remarkably good correlation (log-log linear) between the Brillouin elastic modulus and the Young's modulus measured by conventional mechanical techniques at low frequencies (~1 Hz). Our results suggest that Brillouin microscopy is potentially useful for basic and animal research and clinical ophthalmology.     

The phase relationships between the diurnal rhythms in axial length and choroidal thickness and the association with ocular growth rate in chicks

Eyes of young chickens show diurnal oscillations in axial length and choroidal thickness that are out of phase. In eyes responding to myopic defocus induced by prior form deprivation, the two rhythms shift into phase. In order to elucidate the possible role for these rhythms in ocular growth regulation, they were measured under visual conditions that altered ocular growth rate. (1) Form deprivation to myopic defocus. Eyes of chicks were monocularly deprived for 5 days. Diffusers were removed. (2) Myopic defocus to hyperopic defocus. Eyes wore positive lenses for 6 days; lenses were removed. (3) Hyperopic to myopic defocus. Eyes wore negative lenses for 5 days; lenses were removed. Eyes were measured using A-scan ultrasonography at 6-h intervals for 24 h over various cycles. The rhythms shift into phase in eyes slowing their growth in response to myopic defocus in all three conditions. This shift precedes by 1 day the decrease in growth in both lens conditions, and is concomitant with it in recovering eyes. There is a positive correlation between the phase difference and growth rate. In conclusion, there is a consistent association between growth rate and phase relationships of the rhythms in axial elongation and choroidal thickness.     

Hyperosmolaric contrast agents in cartilage tomography may expose cartilage to overload-induced cell death

In clinical arthrographic examination, strong hypertonic contrast agents are injected directly into the joint space. This may reduce the stiffness of articular cartilage, which is further hypothesized to lead to overload-induced cell death. We investigated the cell death in articular cartilage while the tissue was compressed in situ in physiological saline solution and in full strength hypertonic X-ray contrast agent Hexabrix^TM. Samples were prepared from bovine patellae and stored in Dulbecco’s Modified Eagle’s Medium overnight. Further, impact tests with or without creep were conducted for the samples with contact stresses and creep times changing from 1 MPa to 10 MPa and from 0 min to 15 min, respectively. Finally, depth-dependent cell viability was assessed with a confocal microscope. In order to characterize changes in the biomechanical properties of cartilage as a result of the use of Hexabrix?, stress-relaxation tests were conducted for the samples immersed in Hexabrix? and phosphate buffered saline (PBS). Both dynamic and equilibrium modulus of the samples immersed in Hexabrix? were significantly (p<0.05) lower than those of the samples immersed in PBS. Cartilage samples immersed in physiological saline solution showed load-induced cell death primarily in the superficial and middle zones. However, under high 8–10 MPa contact stresses, the samples immersed in full strength Hexabrix? showed significantly (p<0.05) higher number of dead cells than the samples compressed in physiological saline, especially in the deep zone of cartilage. In conclusion, excessive loading stresses followed by tissue creep might increase the risk for chondrocyte death in articular cartilage when immersed in hypertonic X-ray contrast agent, especially in the deep zone of cartilage.     

Dipeptidyl peptidase IV (DPPIV) activity in the tear fluid as an indicator of the severity of corneal injury: a histochemical and biochemical study

Comparative histochemical and biochemical studies on the catalytically active protease Dipeptidyl peptidase IV (DPPIV), have been performed in the rabbit cornea and the tear fluid using a sensitive fluorogenic substrate, Gly-Pro-7-amino-4-Trifluoromethyl Coumarine (AFC). In both normal and experimentally injured corneas, DPPIV activity was detected histochemically and in the tear fluid biochemically. In contrast to the normal cornea where DPPIV activity was absent and in the tear fluid where it was low, during continuous wearing of contact lenses or repeated irradiation of the cornea with UVB rays, slight DPPIV activity appeared first in the superficial layers of the corneal epithelium, while later increased activity was present in the whole epithelium. This paralleled elevated DPPIV activity in the tear fluid. Moreover, during continuous contact lens wear, the increased DPPIV activity in the tear fluid was, in many cases, coincidental with the presence of capillaries in the limbal part of the corneal stroma. After severe alkali burns when corneal ulcers appeared, collagen fragments were active for DPPIV, which was associated with high DPPIV activity in the tear fluid. In conclusion, Gly-Pro-AFC was found to be useful for comparative histochemical and biochemical studies on DPPIV activity in the experimentally injured rabbit eye. Using the method of the tear film collection by a short touch of substrate punches to the respective site of the cornea or conjunctiva we can show that in experimental injuries (wearing of contact lenses, irradiation of the cornea with UVB rays), the damaged corneal cells were the main source for DPPIV activity in the tear fluid. It is suggested that the activity of DPPIV measured in the tear fluid might serve as an indicator of early corneal disorders, e.g. corneal vascularization related to contact lens wear.     

Developmental aspects of galectin-3 expression in the lens

In order to investigate the temporal and spatial expression pattern of the lectin galectin-3 during lens development we performed immunohistochemical studies using monoclonal and polyclonal antibodies against galectin-3 on paraffin sections of human, mouse and rat eyes. Galectin-3 has been shown to be involved in various biological functions related to cell adhesion, proliferation, apoptosis and differentiation in other tissues. In the human lens, galectin-3 shows a selective expression pattern during lens development. It is present in all cells of the early lens vesicle and at later stages it is strongly expressed during the elongation phase in differentiating primary lens fibres. From about 7 weeks onwards the anterior lens epithelium fails to express galectin-3. Adult lenses, however, exhibit immunoreactivity in the anterior epithelial cells and in the early differentiating secondary fibres of the lens' outer cortex prior to the onset of degradation of the nuclei. In contrast to the observed expression pattern in prenatal human lenses, mouse and rat lenses exhibited immunoreactivity for galectin-3 during postnatal and adult stages only. At these stages, the expression pattern closely resembles that seen in the corresponding human lenses. The spatiotemporal pattern of galectin-3 distribution during lens development favours a role of this lectin in adhesion processes and in the regulation of programmed organelle elimination during lens cell differentiation.     

A biphasic model for micro-indentation of a hydrogel-based contact lens

The stiffness and hydraulic permeability of soft contact lenses may influence its clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications; e.g., lesions. It is therefore important to determine these properties in the design of comfortable contact lenses. Micro-indentation provides a nondestructive means of measuring mechanical properties of soft, hydrated contact lenses. However, certain geometrical and material considerations must be taken into account when analyzing output force-displacement (F-D) data. Rather than solely having a solid response, mechanical behavior of hydrogel contact lenses can be described as the coupled interaction between fluid transport through pores and solid matrix deformation. In addition, indentation of thin membranes ( approximately 100 microm) requires special consideration of boundary conditions at lens surfaces and at the indenter contact region. In this study, a biphasic finite element model was developed to simulate the micro-indentation of a hydrogel contact lens. The model accounts for a curved, thin hydrogel membrane supported on an impermeable mold. A time-varying boundary condition was implemented to model the contact interface between the impermeable spherical indenter and the lens. Parametric studies varying the indentation velocities and hydraulic permeability show F-D curves have a sensitive region outside of which the force response reaches asymptotic limits governed by either the solid matrix (slow indentation velocity, large permeability) or the fluid transport (high indentation velocity, low permeability). Using these results, biphasic properties (Young's modulus and hydraulic permeability) were estimated by fitting model results to F-D curves obtained at multiple indentation velocities (1.2 and 20 microm/s). Fitting to micro-indentation tests of Etafilcon A resulted in an estimated permeability range of 1.0 x 10(-15) to 5.0 x 10(-15) m(4)N s and Young's modulus range of 130 to 170 kPa.     

GROWTH OF LENS AND OCULAR ENVIRONMENT: ROLE OF NEURAL RETINA IN THE GROWTH OF MOUSE LENS AS REVEALED BY AN IMPLANTATION EXPERIMENT

The lens of 6-day-old normal mouse was implanted into the lentectomized eye of adult mouse to examine the effect of retina upon the growth of the implanted lens in vivo. The implanted lens grew normally and its transparency was kept for more than 5 months after implantation. The connection between the implanted lens and the ciliary part of the recipient iris was well established with the regeneration of zonular fibers from the recipient. In young lenses implanted reversely into adult eyes, the epithelial cells facing the retina elongated and a new epithelium was formed on the corneal side of the lens within 5 days. Young lenses implanted either in normal or reverse orientation into eyes from which the retina was previously removed did not grow. The cells of the original lens epithelium of these lenses were randomly accumulated beneath the posterior lens capsule, while the anterior portion of the implanted lenses became an epithelial structure without cell elongation. These results suggest that the growth of the implanted lens may be dependent on the retina of the adult eye.     

Single cell level detection of Escherichia coli in microfluidic device

Detection of Escherichia coli K-12 in phosphate buffered saline (PBS) was demonstrated in a Y-channel polydimethylsiloxane (PDMS) microfluidic device through optical fiber monitoring of latex immunoagglutination. The latex immunoagglutination assay was performed for serially diluted E. coli solutions using 0.92-microm highly carboxylated polystyrene particles conjugated with polyclonal anti-E. coli. Pre-treatments such as cell lysis or culturing to enhance the signal were not used. Proximity optical fibers around the view cell of the device were used to quantify the increase in 45 degrees forward light scattering of the immunoagglutinated particles. In order to reduce false positive signals caused by antibodies binding to non-viable E. coli cells or free antigens in solution, target solutions were washed three times, and then the results were compared to non-washing treatments. The detection limit was found to be less than 10 cfu ml(-1) (1 cfu per device) without PBS washing (thus detecting non-viable cells and free antigens), or less than 40 cfu ml(-1) (4 cfu per device) with PBS washing (thus detecting viable E. coli cells only).