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Miriam Heynen, Diana Trieu, Holly Irene Lorentz, Lyndon William Jones; Comparing and optimizing cholesterol extraction from hydrogel and silicone hydrogel contact lens materials. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6058.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the ability of 6 published extraction methods to extract cholesterol (CHOL) from silicone hydrogel (SH) and conventional hydrogel (CH) contact lenses, and to optimize the most efficient method for laboratory use.
8 different lens types (omafilcon A, etafilcon A, vifilcon A, comfilcon A, lotrafilcon B, galyfilcon A, senofilcon A, and balafilcon A) were incubated for 7 days at 37°C in an artificial tear solution containing radiolabelled 14C cholesterol. Lenses were extracted according to published protocols; A [2chloroform:1methanol (2C:1M), 2 x 3 h, 60 rpm], B [5toluene:1methanol, 0.5 h, sonicate], C [50%methanol, 3 h, 60 rpm], D [7chloroform:3methanol, 1 h, 60 rpm], E [2C:1M, 2 x 40 s, 1200 rpm], F [tetrahydrofuran, 1 h, 60 rpm]. Extracts were measured by liquid scintillation counting. Once the comparison was complete, the extraction method with the most robust extraction profile was optimized for its volume, time, and level of agitation.
Method A removed significantly more CHOL from all 5 SH lenses than all other extraction methods (p<0.002). Method B performed equal to method A (p>0.05) for 4 SH lenses except for lotrafilcon B, which had the most CHOL extracted with Method A (p<0.038). Method C removed significantly lower CHOL from all SH lenses (p<0.0002) compared to all other methods. In the CH group, Method B extracted the most CHOL from omafilcon A (p<0.025). The same amount of CHOL was extracted from etafilcon A and vifilcon A lenses using methods A-F (p>0.05). Due to the success of method A for most lens types, and its ease of use, it was chosen for further optimization. Modifying method A by increasing the extraction volume and adding vigorous shaking (900-1200 RPM), significantly improved the extraction of CHOL from balafilcon A and lotrafilcon B (p<0.015). Vifilcon A lenses showed improved CHOL extraction when method A was altered to use sonication (p<0.023). Modifications to method A did not change CHOL extraction in the remaining lenses.
No single method was superior for all lens types. Extraction efficiencies for the SH lenses were most sensitive to the type of solvent and level of agitation. The method that yielded the highest extraction efficiency of CHOL from SH lenses was 5 ml of 2C:1M shaken at 1200 rpm for 0.5 h at 37°C, twice. The best method for CH was 2 ml of 2C:1M, sonicated at 100 watts for 0.25 h at 37°C, twice.
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