Contact Lens Care & Compliance
Protein on Contact Lenses Isn’t Necessarily a Bad Thing
BY MICHAEL A. WARD, MMSC, FAAO
Research has demonstrated that certain tear proteins can remain biologically active on worn soft contact lenses (Dobson et al, 2011). This implies that lysozyme and other tear proteins may maintain their antimicrobial properties even after attaching to hydrogel lenses. We are accustomed to thinking of proteins as detrimental lens deposits that need to be removed. This brings that thinking into question.
A Look at Lysozyme
Lysozyme is part of our innate immune system and is abundant in a number of human secretions including tears, saliva, and mucus. Alexander Fleming first identified lysozyme’s antimicrobial properties in 1922. Lysozyme is a muramidase enzyme that kills bacteria by catalyzing the hydrolysis of peptidoglycans, specifically between the n-acetylmuramic acid (NAM) and n-acetylglucosamine (NAG), thus breaking down the bacterial cell walls. It is primarily effective against Gram-positive organisms (e.g. Staphylococcus sp., Streptococcus sp.), which have much higher amounts of peptidoglycans in their cell walls.
Recently published in the journal Science, Choi et al (2012) at the University of California - Irvine have demonstrated the biologic activity of lysozyme using nanocircuit architecture. They were able to tether a single lysozyme molecule to a single-walled carbon nd electronically monitor changes in molecular configurations during enzymatic activity. They reported that when lysozyme is active, it closes its configuration to wrap around bacterial substrates, producing microsecond electronic signals. Researchers monitored and recorded the transistor-generated signals to identify enzymatic activities of lysozyme. This is an exquisitely sensitive assay for enzyme activity that will further our understanding of human tear proteins and their contributions to ocular surface health.
At last year’s Association for Research in Vision and Ophthalmology meeting, Dobson et al presented a poster on their investigation of the direct antimicrobial proteins extracted from patient-worn lenses (etafilcon A) after the lenses were treated with different lens care solutions. Their data showed that after being exposed to a solution that contains ingredients known to stabilize proteins, tear proteins absorbed to soft lenses possessed potent antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. Lysozyme becomes more biologically active against Gram-negative bacteria when in the presence of ethylene diamine tetra acetate (EDTA), which breaks down their outer cell wall membrane.
Some Thoughts and Questions
Tear protein activity will likely be affected by choice of lens material (water content, ionicity), lens care product composition, other tear film properties (pH, osmolarity, microbial floral composition), and other environmental factors. Protein accumulations, particularly denatured proteins, on contact lens surfaces have been associated with inflammatory events such as giant papillary conjunctivitis (GPC). Is this a too-limited view on the interaction of tear proteins and contact lenses? If multipurpose solution products can maintain biologic activity of soft lens-attached tear proteins, would it promote or lessen the potential for GPC? Beyond our understanding that denatured proteins bound to contact lenses can lead to complications, is there more that we should know about tear proteins and their relationship to contact lens wear and care? CLS
For references, please visit www.clspectrum.com/references.asp and click on document #197.
|Mr. Ward is an instructor in ophthalmology at Emory University School of Medicine and director, Emory Contact Lens Service. He has also been an advisor for Alcon, AMO, and B+L. You can reach him at firstname.lastname@example.org.|