title: Sclera as a surrogate marker for determining AGE-modifications in Bruch's membrane using a Raman spectroscopy-based index of aging.
abstract: OBJECTIVE
  Raman spectroscopy is an effective probe of advanced glycation end products (AGEs) in Bruch's membrane. However, because it is the outermost layer of the retina, this extracellular matrix is difficult to analyze in vivo with current technology. The sclera shares many compositional characteristics with Bruch's membrane, but it is much easier to access for in vivo Raman analysis. This study investigated whether sclera could act as a surrogate tissue for Raman-based investigation of pathogenic AGEs in Bruch's membrane.
  
  
  METHODS
  Human sclera and Bruch's membrane were dissected from postmortem eyes (n = 67) across a wide age range (33-92 years) and were probed by Raman spectroscopy. The biochemical composition, AGEs, and their age-related trends were determined from data reduction of the Raman spectra and compared for the two tissues.
  
  
  RESULTS
  Raman microscopy demonstrated that Bruch's membrane and sclera are composed of a similar range of biomolecules but with distinct relative quantities, such as in the heme/collagen and the elastin/collagen ratios. Both tissues accumulated AGEs, and these correlated with chronological age (R(2) = 0.824 and R(2) = 0.717 for sclera and Bruch's membrane, respectively). The sclera accumulated AGE adducts at a lower rate than Bruch's membrane, and the models of overall age-related changes exhibited a lower rate (one-fourth that of Bruch's membrane) but a significant increase with age (P < 0.05).
  
  
  CONCLUSIONS
  The results suggest that the sclera is a viable surrogate marker for estimating AGE accumulation in Bruch's membrane and for reliably predicting chronological age. These findings also suggest that sclera could be a useful target tissue for future patient-based, Raman spectroscopy studies.
authors.affiliation: Centre for Vision and Vascular Science, School of Medicine and Dentistry, Queen's University Belfast, Belfast, United Kingdom.
authors.forename: J Renwick
authors.initials: JR
authors.lastname: Beattie
authors.forename: Anna M
authors.initials: AM
authors.lastname: Pawlak
authors.forename: John J
authors.initials: JJ
authors.lastname: McGarvey
authors.forename: Alan W
authors.initials: AW
authors.lastname: Stitt
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D015415:Biomarkers / Q000378:metabolism*; D016570:Bruch Membrane / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D017127:Glycation End Products, Advanced / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D012590:Sclera / Q000378:metabolism*; D013059:Spectrum Analysis, Raman; D014019:Tissue Donors; D019207:beta Carotene / Q000378:metabolism
chemical_list: D015415:Biomarkers; D005136:Eye Proteins; D017127:Glycation End Products, Advanced; D019207:beta Carotene