title: Collagen cross-links reduce corneal permeability.
abstract: OBJECTIVE
  To investigate the relationship between corneal permeability and nonenzymatic cross-link density.
  
  
  METHODS
  Corneas were dissected from 90 cadaveric porcine eyes. Samples were incubated for 24 hours with control solution or methylglyoxal at concentrations of 0.01%, 0.10%, and 1.00%. Nonenzymatic cross-link density in treated and control groups was quantified by papain digest and fluorescence spectrophotometry. Control and treated corneas were mounted in a customized Ussing-type chamber connected to vertical tubing, and specific hydraulic conductivity was determined according to the descent of a column of degassed saline at room temperature. Permeability to diffusion of fluorescein in a static chamber was determined for a similar set of corneal samples.
  
  
  RESULTS
  Methylglyoxal treatment effectively increased nonenzymatic cross-link content, as indicated by the average fluorescence for each group. Specific hydraulic conductivity (m(2)) was reduced with increasing cross-link density. Similarly, the permeability coefficient for the fluorescein solute consistently decreased with increasing methylglyoxal concentration, indicating diffusion impedance resulting from the treatment.
  
  
  CONCLUSIONS
  Nonenzymatic cross-link density in the cornea can be significantly increased by treatment with methylglyoxal. Porcine cornea showed a nonlinear reduction in solute permeability and specific hydraulic conductivity with increasing cross-link density. This model suggests that age-related nonenzymatic cross-link accumulation can have a substantial impact on corneal permeability.
authors.affiliation: Department of Ophthalmology, University of California, San Francisco, San Francisco, California 94143-0730, USA. stewartj@vision.ucsf.edu
authors.forename: Jay M
authors.initials: JM
authors.lastname: Stewart
authors.forename: David S
authors.initials: DS
authors.lastname: Schultz
authors.forename: On-Tat
authors.initials: OT
authors.lastname: Lee
authors.forename: Monique L
authors.initials: ML
authors.lastname: Trinidad
mesh_terms: D000818:Animals; D001692:Biological Transport; D003094:Collagen / Q000378:metabolism*; D003315:Cornea / Q000187:drug effects / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D015194:Diffusion Chambers, Culture; D004797:Enzyme-Linked Immunosorbent Assay; D019793:Fluorescein / Q000378:metabolism; D010539:Permeability; D011765:Pyruvaldehyde / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D003432:Cross-Linking Reagents; D011765:Pyruvaldehyde; D003094:Collagen; D019793:Fluorescein