Dimerization of tear lysozyme on hydrophilic contact lens polymers

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.

Impact of fluorescent probes on albumin sorption profiles to ophthalmic biomaterials

Bovine serum albumin (BSA) was conjugated to three organic fluorescent probes, 5-(4,6-dichloro-s-triazin-2-ylamino)fluorescein hydrochloride (DTAF), Rhodamine B isothiocyanate (RITC), and Lucifer yellow VS (LY). The protein sorption profile to one pHEMA-based (etafilcon A) and three silicone hydrogel (SH) contact lens types (lotrafilcon B, balafilcon A and senofilcon A) was determined using confocal laser scanning microscopy. In addition, all lenses were incubated in dye solutions containing the fluorescent probe alone; and in a separate experiment BSA accumulation was quantified using radiolabeling. The different fluorescent conjugates showed similar sorption profiles for the pHEMA-based lens, but marked differences for all SH lenses. Lotrafilcon B accumulated more protein on the surface as compared to the matrix, independent of the fluorescent probe used for conjugation. Protein sorption varied for senofilcon A, with DTAF-BSA sorbing primarily to the surface region, while the other conjugates penetrated in equal amounts into the matrix. Balafilcon A exhibited smaller differences between conjugates, with LY-BSA allowing the protein to fully penetrate the matrix, while the other conjugates showed minor surface adsorption. Sorption curves of unbound dyes were often similar compared to the conjugated results. BSA profiles to pHEMA-based and silicone hydrogel lenses were highly dependent on the fluorescent probe used and none of the probes accurately reflected quantitative protein levels for the lens materials investigated.

Quantitative and conformational characterization of lysozyme deposited on balafilcon and etafilcon contact lens materials

PURPOSE

To determine whether differences in lysozyme deposition and/or activity exist on worn etafilcon and balafilcon contact lenses following care with a polyquaternium-based system (PQ) or a polyhexanide-based system (PHMB).

METHODS

Following acid-based deposit extraction, lysozyme concentration was determined via Western blotting and lysozyme activity was determined by a micrococcyl assay.

RESULTS

Lysozyme deposition on etafilcon lenses was greater following disinfection with the PHMB-based system (1551 +/- 371 micro g/lens vs 935 +/- 271 micro g/lens; p < 0.001). Deposition on balafilcon lenses was not influenced by the care regimen (10 +/- 3.5 micro g/lens vs 10 +/- 5 micro g/lens; p = 0.89). For both materials, the percentage of denatured lysozyme was greater when they were exposed to the PHMB-based system (28 vs 21%; p = 0.05 (etafilcon) and 57 vs 40%; p = 0.04 (balafilcon)).

CONCLUSIONS

The quantity and conformation of lysozyme deposited on hydrogel contact lens materials is significantly influenced by both lens material and care regimen.

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.

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.

The application of counter immunoelectrophoresis (CIE) in ocular protein studies

This paper focuses on the effects of wear regime on the deposition pattern of important immunoregulatory proteins on FDA Group IV etafilcon-A lenses. Specifically, the aim was to assess the extent to which the daily disposable wear modality produces a different deposition of proteins from the conventional daily wear regime which is coupled with cleaning and disinfection. Counter immunoelectrophoresis (CIE) was employed to detect individual proteins in lens extracts from individual patients and focused on the analysis of five proteins, IgA, IgG, lactoferrin, albumin and kininogen. Deposition was monitored as a function of time; significantly lower deposition was detected on the daily disposable lenses.

Biological and mechanical characteristics of the interface between a new swelling anchor and bone

We recently evaluated the peak pullout loads for anchors made from our new copolymeric swelling-type material compared with anchors made of a nonswelling material. In vitro and in vivo peak pullout loads of these anchors were evaluated after different intervals of implantation in the lateral femoral condyles of New Zealand White rabbits. Scanning electron microscopy and energy dispersive x-ray analyses were additionally performed on selected retrieved samples after pullout to examine the characteristics of bone attachment to the implant. The mean peak pullout load was greater for the swelling anchors than for the nonswelling anchors after 48 hours in vitro (46.0 +/- 15.8 compared with 10.8 +/- 9.1 N, p = 0.0541). After 2 weeks in vivo, it was significantly greater for the swelling anchors than for the nonswelling controls (177.7 +/- 41.3 compared with 53.7 +/- 17.5 N, p = 0.0024). The peak pullout load was also greater for the swelling anchors after 8 weeks in vivo; however, this difference was less pronounced than at 2 weeks (101.8 +/- 35.0 compared with 58.9 +/- 9.7 N, p = 0.0508). Furthermore, the swelling implants tended to induce bone deposition at the bone-implant interface. Results from this investigation reveal that the new family of dynamic implants has potential for applications requiring fixation to cancellous or osteoporotic bone.