Analysis of protein and mucin components deposited on hydrophilic contact lenses

A Review of Techniques to Measure Protein Sorption to Soft Contact Lenses

PURPOSE

To compare and critically evaluate a variety of techniques to measure the quantity and biological activity of protein sorption to contact lenses over short time periods.

METHODS

A literature review was undertaken investigating the major techniques to measure protein sorption to soft contact lens materials, with specific reference to measuring protein directly on lenses using in situ, ex situ, protein structural, and biological activity techniques.

RESULTS

The use of in situ techniques to measure protein quantity provides excellent sensitivity, but many are not directly applicable to contact lenses. Many ex situ techniques struggle to measure all sorbed proteins, and these measurements can have significant signal interference from the lens materials themselves. Techniques measuring the secondary and tertiary structures of sorbed proteins have exhibited only limited success.

CONCLUSIONS

There are a wide variety of techniques to measure both the amount of protein and the biological activity of protein sorbed to soft contact lens materials. To measure the mass of protein sorbed to soft contact lenses (not just thin films) over short time periods, the method of choice should be I radiolabeling. This technique is sensitive enough to measure small amounts of deposited protein, provided steps are taken to limit and measure any interaction of the iodine tracer with the materials. To measure the protein activity over short time periods, the method of choice should be to measure the biological function of sorbed proteins. This may require new methods or adaptations of existing ones.

Extraction Efficiency of an Extraction Buffer Used to Quantify Lysozyme Deposition on Conventional and Silicone Hydrogel Contact Lens Materials

PURPOSE

Extracting lysozyme from Food and Drug Administration group IV etafilcon lenses by using 0.2% trifluoroacetic acid and acetonitrile (TFA/ACN) is a well-established procedure. TFA/ACN has been the extraction buffer of choice for extracting proteins from silicone hydrogel contact lenses. The purpose of this study was to determine the efficiency of TFA/ACN in extracting lysozyme from silicone hydrogel and etafilcon lenses by using an in vitro model.

METHODS

ACUVUE 2, Focus NIGHT & DAY, O2 Optix, PureVision, and ACUVUE Advance lenses were incubated in simple lysozyme solution and a complex artificial tear solution consisting of multiple tear components containing lysozyme labeled with iodine 125. All the silicone hydrogel lenses were incubated for 28 days, whereas the ACUVUE 2 lenses were incubated for 7 days at 37 degrees C with constant rotation. After the incubation period, radioactive counts were determined, and the lenses were placed in an appropriate volume of the buffer for 24 hours in darkness. The lenses were removed from the buffer, and radioactive counts were determined again.

RESULTS

Extraction efficiencies for lysozyme from the artificial tear solution were 97.2% +/- 1.2% for ACUVUE 2, 64.3% +/- 6.2% for Focus NIGHT & DAY, 62.5% +/- 5.6% for O2 Optix, 53.5% +/- 5.8% for PureVision, and 89.2% +/- 3.4% for ACUVUE Advance. Results were similar for the lysozyme extracted after incubating in the simple lysozyme solution.

CONCLUSIONS

TFA/ACN is extremely efficient at extracting lysozyme deposited on etafilcon lenses. However, it does not extract all the lysozyme deposited on silicone hydrogel lenses, and alternative extraction procedures should be sought.

Combination of serum eye drops with hydrogel bandage contact lenses in the treatment of persistent epithelial defects

BACKGROUND

The treatment of persistent epithelial defects (PED) with autologous serum eye drops is often combined with conventional medication such as artificial tears and topical antibiotics, but until now no report exists on the use of a bandage contact lens (BCL) in combination with autologous serum eye drops in the treatment of PEDs. We report six eyes (five patients) which were all treated with autologous serum eye drops in combination with an FDA group IV hydrogel contact lens.

METHODS

Five patients aged 36-88 years, were suffering from six PEDs for 73.5+/-46.9 days due to rheumatoid sterile corneal ulcer (n=1), neurotrophic keratopathy (n=3) or partial limbal stem cell deficiency (n=1). All patients had been unsuccessfully treated with conventional therapy before. Three of them had already had an amniotic membrane transplantation and two had undergone a keratoplasty; however, the epithelial defect persisted or recurred. In all cases, an FDA group IV hydrogel contact lens (Biomedics 55, ocufilcon D, 55% water content) was fitted and serum eye drops applied 8 times a day.

RESULTS

The PED healed in five of six eyes after a treatment period of 14.2+/-8.9 days. In one eye the PED became smaller, but it took 90 days until the lesion healed completely. In three eyes (two patients) white deposits appeared on the surface of the BCL during the treatment after 12.3+/-5.1 days. Because no signs of inflammation were observed and since the epithelial defect improved, a new identical lens was applied and the medication continued unaltered. The surface of contaminated and non-contaminated BCLs were analyzed by scanning electron microscopy and SDS gel-electrophoresis. The scanning electron microscopic examination presented a coating of amorphous material with a wrinkled appearance and many corpuscular deposits. There was no indication of bacterial colonisation. The SDS gel-electrophoresis showed a small band at 65 kDa, probably albumin.

CONCLUSION

These findings suggest that the combination of a therapeutic contact lens and serum eye drops can be successfully used in the treatment of persistent epithelial defects. Deposition of albumin may occur on the surface of the contact lenses, which, in the small group presented here, caused no unwanted effects.

Stabilization of Lysozyme Mass Extracted From Lotrafilcon Silicone Hydrogel Contact Lenses

PURPOSE

Lysozyme deposits extracted from lotrafilcon silicone hydrogel (SH) contact lens materials demonstrate a loss in total mass as a function of storage time when assessed by Western blotting. This loss represents a potential source of error when quantifying total lysozyme deposition on SH lenses. The purpose of this study was to devise a method whereby lysozyme mass would be preserved over time to allow for its accurate quantitation after its removal from SH lenses.

METHODS

Lysozyme deposits from 12 human worn lotrafilcon lenses were extracted using a 50:50 mixture of 0.2% trifluoroacetic acid and acetonitrile. Extracts were lyophilized to dryness, then resuspended in either reconstitution buffer (10 mM Tris-HCl, 1 mM EDTA) or modified reconstitution buffer (reconstitution buffer + 0.9% saline). BIOSTAB Biomolecule Storage Solution (Sigma-Aldrich) was added to one half of the samples from each buffer group. One microliter of each of the samples was immediately subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blotting, whereas the remaining volume was aliquoted and stored at -20 degrees C or -70 degrees C and subjected to the same procedures after 48 h of storage. Comparison of lysozyme band intensity in stored vs. fresh samples enabled calculation of percentage mass loss of lysozyme.

RESULTS

Samples stored at -20 degrees C in reconstitution buffer with no BIOSTAB demonstrated a 33% loss in mass over 48 h of storage. Identical samples stored at -70 degrees C in modified reconstitution buffer with BIOSTAB added demonstrated <1% loss in mass. Statistical analysis indicated that buffer composition (p < 0.001), storage temperature (p = 0.04), and addition of BIOSTAB (p < 0.001) were all important in controlling loss of mass over time.

CONCLUSION

We have optimized a procedure whereby the extracted mass of lysozyme deposits found on lotrafilcon SH lenses can be preserved, thus enabling accurate quantitation after extraction and resuspension.

Comparing the extent of protein build-up on several disposable lenses by two spectrophotometric methods

This study aims to quantify levels of protein build-up on high-water ionic (Type IV) disposable contact lenses worn by patients, by two spectrophotometric methods, previously validated only with conventional lenses. Forty lenses were analyzed and the related results were compared. The Ninhydrine-Lysozyme method and the Coomassie Blue Albumin one agreed in identifying the most spoiled lenses. Etafilcon A attracted significantly more protein than the other materials tested, which were in the following decreasing order of protein spoilation: Ocuflcon D, Ocufilcon A and Vasurfilcon A. These similar findings suggest that it is possible to use the above mentioned analysis methods for an accurate evaluation of the contamination of several materials of disposable/frequent replacement lenses as for conventional lenses.

The effect of eye closure on protein and complement deposition on Group IV hydrogel contact lenses: relationship to tear flow dynamics

PURPOSE

This study was designed to determine the effect of overnight eye closure on the rate and composition of protein deposition on high water content ionic matrix soft contact lenses (Group IV SCLs) and to extrapolate from this data information on the probable change in the rate of reflex-type tear secretion associated with eye closure.

METHODS

Group IV SCLs were temporally sampled after equivalent periods of wear under closed eye (C) or open eye (O) conditions. Lenses were rinsed in saline and the majority of the tightly bound protein extracted at 90 degrees C in 40% urea, containing 1% SDS, 1 mM DTT, 100 mM Tris-HCl (pH 8.00). Residual protein was determined by Coomassie staining of the extracted lenses and densitometric analysis. Extracted protein was quantitated and separated by SDS-PAGE. Gels were either stained with Coomassie blue or reversibly stained with imidazole-zinc and blotted. Blots were PAS stained, or lectin and antibody probed for glycoproteins, secretory IgA (sIgA), IgG, lysozyme and complement C3. Laboratory simulated deposition studies were carried out on unworn lenses exposed to HPLC purified lysozyme.

RESULTS

The protein in the saline rinse, to a large degree mirrored the composition of tear fluid in which the lens had been residing (O or C). This would suggest that the saline wash consists of residual tear fluid and loosely adherent protein. In contrast, the urea extracts were highly homogeneous consisting primarily of lysozyme and to lesser extent lysozyme dimer. This supports the contention that the Group IV SCL functions in the eye much as cationic exchange resin selectively absorbing lysozyme. C extracts also proved relatively enriched in trace amounts of sIgA, IgG and complement C3 and its breakdown products. High levels of C3 and C3 breakdown products were specifically recovered only in the C worn lens extracts from a subject experiencing unilateral contact lens associated corneal infiltrates from the affected eye. In all subjects, markedly less protein (lysozyme) was recovered in urea extracts of lenses exposed to 7-8 h of closed eye as compared to open eye wear (0.20 +/- .08 versus 0.79 +/- .15 mg/lens (n = 6)). Temporal studies further revealed that deposition was linearly related to duration of wear during the initial phase of conditioning film formation giving rise to rate constants for lysozyme deposition of 2.2 +/- 0.29 (n = 5) and 0.20 +/- 0.06 microgram/min (n = 4) under open and closed eye conditions respectively. With further wear, deposition eventually reached a steady state. Under laboratory conditions, lysozyme was much rapidly and quantitatively removed from solution in a manner following a hyperbolic plot. This suggests that during the initial phase of deposition the rate of deposition is limited by the capacity of the tear fluid to deliver lysozyme to the lens surface under these two extremes of conditions.

CONCLUSIONS

Eye closure profoundly affects the rate of lysozyme deposition on Group IV hydrogels and the composition of minor biofilm constituents in a manner that could affect biocompatibility. Findings support the contention that eye closure results in a > 90% reduction in the rate of reflex-type tear secretion.

Characterization of lacrymal component accumulation on worn soft contact lens surfaces by atomic force microscopy

The purpose of this study was to investigate lacrymal component accumulation on a soft contact lens (SCL) surface after various periods of continuous wear, using the recently developed atomic force microscopy (AFM). AFM allowed high resolution images of unworn and worn SCL, and presented two main advantages. 1. The SCL are analysed under nearly physiological conditions without being dried or destroyed. So the same SCL was analysed at various times during a long wearing period. To identify the deposited tear proteins, a qualitative analysis of solubilized deposit by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) on 4-15% gradient minigels was performed as well. We present typical images which emphasize the importance of the coating by lacrymal components. AFM analysis of worn SCL showed the deposition on the surface of a uniform lacrymal component coating (named deposit type I) with a progressive accumulation of numerous discrete granules (named deposit type II). SDS-PAGE of extracted deposits revealed the main tear proteins as: IgA, lactoferrin, tear lipocalin and lysozyme and the unknown protein of molecular weight 30,000. There is no clear difference in the protein patterns of the two types of deposits. Furthermore, a particular mode of use of AFM is described to illustrate the potential of this technique as a local tool for measuring protein coating thickness. Thus, for analysis of protein deposits on SCL surfaces, SDS-PAGE on minigels and AFM were easy and rapid to perform. When associated, these two techniques could find use in a wide range of worn SCL evaluation and most generally in biocompatibility evaluation studies.

Separation of human tear proteins with ceramic hydroxyapatite high-performance liquid chromatography

Human tear protein, which consists mainly of albumin, lysozyme, and lactoferrin, was assayed with high-performance liquid chromatography using a new ceramic hydroxyapatite column. Proteins were eluted at room temperature using a 20-min linear gradient from 95:5% A/B buffer to 0:100% A/B buffer (buffer A, distilled water; buffer B, 400 mM KH2PO4 containing 240 mM NaOH). The proteins eluted at 1.2 min for albumin, 8.5 min for lysozyme, and 20.4 and 21.7 min for lactoferrin, respectively. The assays may be performed in 30 min.

Detection of protein deposition on contact lens type polymeric hydrogels by Coomassie blue R staining

Using an aqueous solvent of high methanol content, we have been able to extend the use of Coomassie blue R protein staining to contact lens-type acrylate hydrogels of 35-80% water content. Protein deposition on a wide range of hydrogels was compared after exposure to protein and there was good agreement between in vitro and in vivo studies to assess deposit resistance. Staining was sensitive down to a 2 micrograms lysozyme/cm2 zone extending from one polymer surface to the other, and linear with protein content up to 40 micrograms/cm2. The staining method permits unusual deposit morphologies to be easily visualized and is best used for qualitative or semiquantitative evaluation of protein deposition during the development of new polymeric materials. We propose a new classification system for protein deposition based on the degree of Coomassie blue R staining.

The role of tears in preventing protein deposition on contact lenses

Recently the presence of a coating inhibitory factor was described in human tears which can prevent the binding of proteins to a solid phase. In these earlier studies depositions of lactoferrin and IgG onto plastic was studied. In the study described here, peroxidase conjugated albumin was used as a model to investigate the effect of human tears on the binding of proteins to plastic surfaces. We investigated the question whether contact lens deposits are associated with decreased levels of this factor in the tearfilm of contact lens wearers. The mean value of the coating inhibiting activity in the tears of the controls did not differ significantly from contact lens wearers without deposits. The contact lens wearers with deposits on their lenses, had a lower mean coating inhibiting activity than the contact lens wearers without deposits. No significant difference was seen in coating inhibiting activity in tears obtained from individuals before and after they had worn lenses for three weeks. Also no difference was observed in the coating inhibiting activity on the eyes of persons who were wearing a lens in one eye only. The results of our study show that a too low activity of the coating inhibiting factor in tears is associated with deposits on contact lenses.