Activity of Lysozyme Deposited on Conventional and Silicone Hydrogel Contact Lenses as a Function of Time

Abstract

Purpose:: To determine the activity of hen egg lysozyme (HEL) deposited on various conventional and silicone hydrogel (SH) contact lenses as a function of time using an in vitro model.

Methods:: Optima FW (OFW), Acuvue (AV), Proclear (PC), Focus Night&Day (FND), O₂Optix (O2), PureVision (PV), Acuvue Advance (AA) and Acuvue OASYS (AO) contact lenses (n=5) were incubated in a phosphate-buffered solution (PBS, pH7.4) containing HEL (1.9mg/ml) for time periods ranging from 1 hour to 28 days at 37°C with constant shaking. Following the specified doping period, the lenses were rinsed briefly in PBS to remove unbound HEL and extracted with either 50:50 0.2% trifluoroacetic acid: acetonitrile (TFA:ACN) (OFW, AV, PC, FND, O2, PV) or 50:50 0.02% TFA:ACN (AO, AA). The extracts were lyophilized to dryness and the samples were assessed for lysozyme activity by a modified micrococcal assay and total lysozyme was determined by SDS PAGE and Western blotting.

Results:: HEL deposited on AV lenses exhibited a gradual reduction in activity over the first 3 days and there was no further significant decrease in activity over time (p>0.05). There was a gradual reduction in activity over the first week for PV & AA lenses (p<0.05) and over two weeks with OFW & PC lenses (p<0.05) with no further decrease in activity over time for all these lenses (all p>0.05). With FND, O2 and AO lenses there was a decrease in activity until 28 days of doping. At the end of 28 days, HEL deposited on AV exhibited the greatest activity (90±3%) and this was statistically different from all other lens types (p<0.001). HEL deposited on OFW (17.8±4%), FND (23.4±4%) and O2 (24±5%) exhibited the lowest activity. HEL deposited on other lens materials exhibited intermediate activity (PC, 38±3%; AA, 62.3±8; AO, 47±6; and PV, 61±7).

Conclusions:: The reduction in activity of HEL deposited on contact lenses is time dependant and the rate of reduction varies between lens materials. This variation between lenses could be due to the differences in surface/ bulk material properties or the location of lysozyme on these lenses. The results from this study reiterate that levels of lysozyme denaturation are highly variable between materials.

Keywords: contact lens • cornea: tears/tear film/dry eye • protein structure/function