Impact of tear film components on the conformational state of lysozyme deposited on contact lenses

PURPOSE: To investigate the impact of lactoferrin and lipids on the kinetic denaturation of lysozyme deposited on silicone and conventional hydrogel lenses, using a complex artificial tear solution (ATS). METHODS: Two silicone hydrogel lenses (AIR OPTIX AQUA; lotrafilcon B and ACUVUE OASYS; senofilcon A) and two conventional hydrogel lenses (ACUVUE 2; etafilcon A and PROCLEAR; omafilcon A) were incubated in four solutions: an ATS, ATS without lactoferrin, ATS without lipids, and ATS without lactoferrin and lipids. At various time points over a 28-day period, the percentage of active lysozyme per lens was determined using a fluorescence activity assay and an ELISA. RESULTS: After 28 days, the percentage of active lysozyme extracted from etafilcon A lenses in all solutions was significantly higher than all other lens materials (p < 0.001). For lotrafilcon B, senofilcon A, and omafilcon A lenses, lysozyme denaturation was greatest during the first week of incubation and before reaching a plateau (p > 0.05). The inclusion of lipids in the ATS significantly increased the lysozyme denaturation on both silicone hydrogel materials (p < 0.001), while in the presence of lactoferrin, lysozyme activity on senofilcon A lenses was significantly higher (p < 0.001). Lysozyme activity on both conventional lenses was not significantly affected by either lactoferrin or lipids (p > 0.05). CONCLUSIONS: Lactoferrin and lipids have an impact on the denaturation of lysozyme deposited onto silicone hydrogel contact lenses, while conventional hydrogel lenses were unaffected. Future in vitro studies should consider the impact of tear film components when investigating protein deposition and denaturation on contact lenses.