Protein-lipid interaction on the surface of a hydrophilic contact lens in vitro

PURPOSE: To investigate the mechanism of protein-lipid interactions responsible for biofilm formation on the surface of hydrophilic contact lenses in vitro. METHODS: New, never-worn hydrophilic contact lenses were individually incubated in a protein-only, lipid-only, or combination protein-lipid artificial tear solution for 24 hours at 37 degrees C with constant stirring. Deposited lipids were removed with a methanol based extraction procedure, separated using high-performance, thin layer chromatography and quantitatively analyzed densitometrically. Deposited proteins were extracted with 4M urea, separated using gel electrophoresis and quantitatively analyzed densitometrically. RESULTS: The presence of protein in the artificial tear solution has a profound effect on the nature of lipid deposition for each group of hydrophilic lens, whereas the presence of lipid has a significant effect on the nature of protein deposition for only a group IV lens. In addition, the presence of lipid deposits on a group IV lens decreases the adsorption of lysozyme, while the presence of protein deposits reduces the amount of total lipid adhering to a group II lens. CONCLUSIONS: Protein adsorption on a group IV lens renders the lens surface less hydrophilic and, thereby, more susceptible to lipid deposition, which in turn increases surface hydrophobicity and inhibits additional protein deposition. For a group II lens, positively charged protein competes with and replaces some of the polar lipids attached to the lens. Thus, the interaction of protein and lipid on a lens surface most prone to a particular contaminant apparently makes it less likely for that contaminant to bind.