Uptake and release of preservatives from soft contact lens materials
Purpose: The purpose of this thesis was to examine the uptake and release of myristamidopropyl dimethylamine (MAPD) and polyhexamethylene biguanide (PHMB) from soft contact lens material using various in vitro models to determine the safety of the preservatives. Methods: Chapter 3: The detection of radioactive and non-radioactive MAPD were determined with UV-Vis spectroscopy and a radioactive beta counter. MAPD was prepared in phosphate buffered saline (PBS) solutions and different vial materials (glass and polyethylene). Chapter 4: To determine the uptake and release kinetics of 14C MAPD from reusable soft contact lens materials using radioactive labelling, five contemporary CLs were tested over a 1-day, and 7-day period. MAPD were extracted from contact lenses (CLs) with 2:1 chloroform:methanol at the end of each study. The radioactivity was measured using a beta scintillation counter. Chapter 5: To determine the uptake and release kinetics of 14C PHMB from reusable soft contact lens materials using radioactive labelling, five contemporary CLs were tested over a 1-day, and 7-day period. CLs were soaked in PHMB for 8 hours, followed by a release in PBS for 16 hours. PHMB were extracted from CLs with methanol at the end of each study. The experimental design was similar to Chapter 4. Chapter 6: To evaluate the cytotoxicity of MAPD and PHMB (from Chapter 4 and 5) released from reusable soft CLs on immortalized corneal epithelial cells (ICEC) and human corneal epithelial cells (HCEC). CLs were soaked in PBS containing either PHMB or MAPD for 8 hours. After incubation period, the lenses were placed in fresh PBS for 16 hours. The release media was exposed to ICEC and HCEC for 16 hours. Afterwards, two multipurpose solutions, MAPD (2.5 µg/mL, 5 µg/mL, 10 µg/mL) and PHMB (1 µg/mL, 5 µg/mL, 10 µg/mL) concentrations were tested against ICEC and HCEC. Cell viability was then measured using the alamarBlue™ assay. Results: Chapter 3: A mixture of radioactive and non-radioactive MAPD was able to be detected, resulting in a more cost-effective study. There were no differences in absorbance between PBS solutions. No differences in radioactivity were found between glass and polyethylene vials. However, polyethylene vials showed a more equal distribution of MAPD. The results suggest polyethylene vials are better suited for future radioactive kinetic studies (Chapter 4, Chapter 5). Chapter 4: Silicone hydrogel (SH) materials sorbed significantly more MAPD than the conventional hydrogel (CH) materials. However, the CH materials released a greater amount of MAPD than the SH materials. Over a 7-day period, similar results were found between SH and CH materials. Chapter 5: The CH material (etafilcon A) sorbed significantly more MAPD than the SH material (senofilcon A). Etafilcon A released more PHMB compared to all other lens types within a 24-hr period. Over a 7-day period, all CLs continued to sorb more PHMB, with no signs of saturation. The CH materials released more PHMB than the SH materials. Chapter 6: The amount of PHMB or MAPD released from CLs did not have an impact on corneal epithelial cell viability. PHMB and MAPD at concentrations of 5 µg/mL and higher showed significantly reduced cell viability. Direct exposure to multipurpose solutions also significantly reduced cell viability. Conclusion: This thesis provided a chemical and biological assay for assessing the impact of MAPD and PHMB from CLs. Radioactive labelling provided a sensitive method for assessing the uptake and release of MAPD (Chapter 4) and PHMB (Chapter 5) from reusable soft CLs. The uptake and release of MAPD and PHMB were different based on their chemical structure and properties. In chapter 6, MAPD and PHMB released from CLs were not cytotoxic to corneal epithelial cells. Direct exposure of multipurpose solutions and increasing concentrations of MAPD and PHMB significantly reduced cell viability. These models provide a valuable tool to predict future adverse events for new multipurpose solutions.
Cite this version of the work
Alan Yee (2022). Uptake and release of preservatives from soft contact lens materials. UWSpace. http://hdl.handle.net/10012/17877