Analysis of Using I¹²⁵ Radiolabeling for Quantifying Protein on Contact Lenses

ABSTRACT

Purpose: To investigate the accuracy of I¹²⁵ radiolabeling to quantitatively determine the deposition of protein onto various commercially available contact lens (CL) materials.

Methods: Commercially available silicone hydrogel and conventional hydrogel CL materials were examined for times ranging from 10 s to 1 week. Adsorption of free I¹²⁵ was measured directly for the CL. The use of dialyzing labeled proteins and/or using NaI to compete with free I¹²⁵ uptake was investigated as ways to minimize effects due to free I¹²⁵.

Results: At all time points and with all lens materials, there was 0.3 μg/lens or greater of apparent mass attributable to free I¹²⁵ uptake. Dialyzing labeled proteins significantly reduced free I¹²⁵ uptake for all materials investigated. The benefit of using dialyzed protein was most prominent at shorter times, as free I¹²⁵ is continuously generated over time. Using NaI can reduce free I¹²⁵ uptake for some lens materials, but this is shown to directly affect protein deposition on some materials.

Conclusions: Periodic replenishment of incubation solutions with freshly dialyzed labeled protein to limit free I¹²⁵ generation is recommended, but the incorporation of NaI onto the buffer solution is not. Irrespective of the exact procedure to limit free I¹²⁵ uptake, extra steps must be performed to quantify the amount of I¹²⁵ adsorbed onto contact lens materials, to determine thresholds of confidence with respect to the actual protein deposition that occurs.

• Contact lens
• free I¹²⁵
• I¹²⁵ radiolabeling
• protein deposition
• silicone hydrogel

ACKNOWLEDGMENTS

The authors thank Dr. Heather Sheardown (Ph.D.) at McMaster University for providing the facilities for radiolabeling proteins.

DECLARATION OF INTEREST

Over the past 3 years one of the authors (LJ) has received research support or honoraria from the following companies: Abbott Medical Optics, Advanced Vision Research, Alcon, AlgiPharma, Allergan, Bausch & Lomb, CIBA Vision, CooperVision, Essilor, J&J Vision Care, Oculus, TearScience, Visioneering Technologies. The work is funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada.