72 - The Effect of Different Zinc Concentrations on the Stiffness of the Crystalline Lens

Poster Board Number: 72
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Odd poster #s – first hour
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Co-authors:

Vivian Choh - University of Waterloo

Abstract Body : Introduction and Objective: Aquaporins are specialized water channels. A volume change through permeable aquaporins may be necessary for the lens' ability to change shape during accommodation. This study aimed to determine the effects of zinc, an agonist that increases aquaporin 0 (AQP0) permeability in oocytes, on the biomechanics of chicken lenses.



Material and Methods: Hatchling White Leghorn chickens (Gallus gallus domesticus) were reared for 14 days before being sacrificed. Both eyes were enucleated and immersed in oxygenated Tyrode’s solution (TS). Lenses were dissected out and one lens from each bird was treated one of with three concentrations of zinc chloride (20 [n=6], 40 [n=7], and 80 [n=13] μg/ml in TS for 15 min, at room temperature; RT), while the other lens (control lens) was incubated in TS (15 min, RT). Lenses were compressed using the CellScale Micro Tester G2, and force-compression data were generated and fit to an exponential curve with the equation y=y₀ + ae^bx; the unitless b-coefficient of the exponential equation was used to assess stiffness as it describes how rapidly the force increases as the compression distance increases. The effects of zinc-treated vs control lenses were analyzed for each zinc concentration using a paired t-test.



Results: The b-coefficient value for the lenses treated with 80 μg/ml of zinc averaged to 4.4 ± 0.5 while the mean value for control lenses was significantly lower (p = 0.01) at 4.0 ± 0.4, indicating that zinc-treated lenses were stiffer. However, the stiffness of lenses treated with 20 μg/ml and 40 μg/ml of zinc were not different from those treated with vehicle only (p=0.67 and p=0.56, respectively).



Conclusions: The compression data show that treatment with a high dose of zinc led to stiffer lenses but lower doses did not seem to have an effect. AQP0 typically plays a role in allowing water to enter the lens fiber. Since zinc is known to open AQP0 channel, we speculate that the zinc-associated increase in stiffness may have been mediated by increased water content through the AQP0 channels.



Significance/Implications: Zinc affects the lens stiffness only at specific concentrations. However, as water permeability was not measured in this study, the AQP0-associated mechanism of lens stiffening cannot be confirmed. It is reported that zinc only affects AQP0 and does not have an effect on AQP1 and other channels that also allow water to flow out of the lens. It is unclear whether targeting other AQPs would lead to changes in stiffness. Further study is needed to determine zinc's action on the biomechanics of the lens.



Funding sources: The research is funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Optometric Education Trust Fund (COETF).