In Vitro Assessment of Medical Device Toxicity: Interactions of Benzalkonium Chloride With Silicone-Containing and p-HEMA–Containing Hydrogel Contact Lens Materials
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PURPOSE: To analyze the interactions of benzalkonium chloride (BAK) with silicone-containing (lotrafilcon A and galyfilcon A) and p-HEMA-containing (etafilcon A and vifilcon A) hydrogel contact lenses and to examine the possibility of using sodium fluorescein permeability assay (SFPA), 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the bovine lens assay in conjunction with confocal laser scanning microscopy (CLSM) as a battery of in vitro alternatives to evaluate the potential toxicity of soft contact lenses. METHODS: Four soft contact lens types (Focus Monthly [vifilcon A], Focus NIGHT & DAY [lotrafilcon A], ACUVUE Advance With Hydraclear [galyfilcon A], and SUREVUE [etafilcon A]) were soaked for 24 hours in various concentrations of BAK (1%, 0.1%, 0.01%, and 0.001%) in 20-mL glass vials. After 24 hours, the lenses were gently washed in Hanks' Balanced Salt Solution (HBSS), placed in 5 mL of HBSS, and incubated for a total of 7 days at 37 degrees C, 5% CO2. BAK released into HBSS (i.e., the extract) was recovered from the vials and used as the test chemical in the SFPA (epithelium integrity), MTT assay (cellular viability), and the bovine lens assay with CLSM (mitochondrial metabolism and optical properties). The amount of BAK extracted from the various contact lenses was measured using an Abbe refractometer. Negative controls consisted of HBSS and contact lenses subjected to the same conditions as the treated contact lenses, but without BAK. RESULTS: Extracts obtained from soaking Focus Monthly lenses in BAK caused the most damage to the epithelium and mitochondrial metabolism. However, at 0.1% BAK extraction, all lens extracts showed increased levels of back vertex distance variability of the cultured bovine lens. CONCLUSIONS: Unexpectedly, lenses extracted with HBSS showed SFPA and MTT assay responses and an observed effect on the bovine lens epithelium visualized by CLSM, indicating that unknown chemical agents may be leached from contact lens polymers.
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