title: Enzymatic quantification of cholesterol and cholesterol esters from silicone hydrogel contact lenses.
abstract: OBJECTIVE
  The purpose of this work was to develop an enzymatic method of quantification of cholesterol and cholesterol esters derived from contact lenses, both in vitro and ex vivo.
  
  
  METHODS
  Lotrafilcon B (O2 Optix; CIBA Vision, Inc., Duluth, GA) and galyfilcon A (Acuvue Advance; Vistakon, Inc., Jacksonville, FL) silicone hydrogel contact lenses were independently incubated in cholesterol oleate solutions varying in concentrations. After incubation, the lenses were removed and underwent two separate 2:1 chloroform-methanol extractions. After in vitro studies, 10 human subjects wore both lotrafilcon B and galyfilcon A contact lenses for 7 days. The lenses also underwent two separate 2:1 chloroform-methanol extractions. All in vitro and ex vivo samples were quantified with a cholesterol esterase enzymatic reaction.
  
  
  RESULTS
  Calibration curves from quantifications of in vitro contact lens samples soaked in successively decreasing concentrations of cholesterol oleate yielded coefficients of determination (R(2)) of 0.99 (lotrafilcon B) and 0.97 (galyfilcon A). For in vitro contact lens samples, galyfilcon A was associated with an average cholesterol oleate extraction of 39.85 +/- 48.65 microg/lens, whereas lotrafilcon B was associated with 5.86 +/- 3.36 microg/lens (P = 0.05) across both extractions and all incubation concentrations. For ex vivo contact lens samples, there was significantly more cholesterol and cholesterol esters deposited on galyfilcon A (5.77 +/- 1.87 microg/lens) than on lotrafilcon B (2.03 +/- 1.62 microg/lens; P = 0.0005).
  
  
  CONCLUSIONS
  This is an efficient and simple method of quantifying total cholesterol extracted from silicone hydrogel contact lenses and, potentially, the meibum and/or tear film. Certain silicone hydrogel materials demonstrate more affinity for cholesterol and its esters than do others.
authors.affiliation: Ohio State University, Columbus, Ohio 43218-2342, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pucker
authors.forename: Mirunalni
authors.initials: M
authors.lastname: Thangavelu
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Nichols
mesh_terms: D000328:Adult; D002784:Cholesterol / Q000032:analysis*; D002788:Cholesterol Esters / Q000032:analysis*; D003263:Contact Lenses, Hydrophilic; D057075:Enzyme Assays; D005260:Female; D006801:Humans; D020100:Hydrogels / Q000737:chemistry*; D008297:Male; D011446:Prospective Studies; D012828:Silicones / Q000737:chemistry*
chemical_list: D002788:Cholesterol Esters; D020100:Hydrogels; D012828:Silicones; C540499:galyfilcon A; C524582:lotrafilcon B; C014409:cholesteryl oleate; D002784:Cholesterol