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Frank V. Bright, Peter Maziarz, Micheal Liu, Jinzhong Zhang, Mohinder Merchea; PHMB and PQ-1 Impact On A Liposome Corneal Surface Membrane Model. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6491.
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Transient ocular surface fluorescence due to MPS preservative exposure has been implicated as an injury of the cornea. This study assessed molecular level interactions of the disinfectant agents PHMB or PQ-1 used in soft contact lens multi-purpose solutions (MPS) and corneal epithelium using an in-vitro cell model.
An anionic liposome model of the corneal epithelial surface was prepared by using a previously published protocol. 1,6-Diphenyl-1,3,5-hexatriene (DPH), a well-known lipid membrane probe, was used to assess the membrane integrity. Fluorescein was used as the fluorescent probe in association with the liposomes. The steady-state fluorescence anisotropy (a measure of interactions between molecules) was measured by using an SLM model 8100 spectrofluorometer. Liposome integrity was assessed by measuring the shift in melting point temperature (Tm) of model liposomes exposed to preservative concentrations from 0 ppm to 100 ppm. A reduction in integrity was indicative of a damaged cell membrane component.
Free fluorescein demonstrated no statistically significant liposome interaction (p>0.05). PHMB (tagged with fluorescein) demonstrated an association to the liposomes (p<0.0002). The melting point temperature of liposomes at physiological temperature of 37C demonstrated a) no statistically significant shift when exposed to PHMB from 0ppm to 100ppm (p>0.05) and b) no statistically significant reduction in the melting point temperature of liposomes exposed to PQ-1 from 0ppm to 6ppm (p>0.05). Exposure of PQ-1 at levels of 8ppm or greater demonstrated liposome disruption.
PHMB and PQ-1 are used in varying concentrations in MPS. Preservative associated transient hyperfluorescence (PATH) has been interpreted as damage of the corneal surface based on its macroscopic clinical appearance, and is reported to occur more with PHMB in comparison to PQ-1. This study demonstrated that PHMB has a non-destructive interaction with the liposome surface chemistry. At concentrations 100x higher than found in commercially available MPS products, PHMB did not damage the phospholipid bilayer components that comprise the most superficial surface of the corneal epithelium. Alternatively, PQ-1 demonstrated a threshold of 8ppm when disruption of phospholipid bilayer components was observed. This study suggests that evaluation of PATH clinically is an inappropriate assessment of cell surface integrity or biocompatibility. Further study is recommended to better understand MPS products and ocular tissue at the molecular level.
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