title: Glycation and glycoxidation studies in vitro on isolated human vitreous collagen.
abstract: BACKGROUND
  Structural and functional impairment in vitreous collagen plays an important role in the pathogenesis of diabetic retinopathy. Collagen being a long-lived protein is prone to both glycation and glycoxidation, resulting in accumulation of advanced glycation end products (AGE). The objective of our study was to explore the extent of glycation by glucose, and iron- and copper-mediated glycoxidation of human vitreous collagen, and also to study the beneficial effects of lysine, inositol and aminoguanidine as antiglycating and anti-cross linking agents.
  
  
  METHODS
  Vitreous from human donor eyeballs was pooled and collagen was extracted using 0.9 M NaCl. Collagen was estimated by measuring the hydroxyproline content. The extracted collagen was used for glycation and glycoxidation studies. Glycation studies were conducted using U14C glucose, along with anti-glycating agents, such as lysine and aminoguanidine. Metal-mediated glycoxidation studies were done by measuring collagen content in cyanogen bromide insoluble fraction, in the presence and absence of an anti-cross linking agent, inositol.
  
  
  RESULTS
  Human vitreous collagen extractable with 0.9 M NaCl was glycated by glucose at 5 and 10 mM concentrations under physiological conditions of temperature and pH. An anti-glycating effect was exhibited by lysine, inositol and aminoguanidine, of which lysine was the best (76% antiglycating activity) followed by inositol. Inositol was also found to be useful in inhibiting glycoxidation.
  
  
  CONCLUSIONS
  Vitreous collagen undergoes glycation, as well as iron- and copper-mediated glycoxidation, leading to possible structural and functional impairment. Glycation and glycoxidation are inhibited, significantly by lysine and inositol respectively.
authors.affiliation: Biochemistry Research Department, Vision Research Foundation, Sankara Nethralaya, Chennai, India.
authors.forename: Konerirajapuram N
authors.initials: KN
authors.lastname: Sulochana
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Ramprasad
authors.forename: Karnuakaran
authors.initials: K
authors.lastname: Coral
authors.forename: Soundarajan
authors.initials: S
authors.lastname: Lakshmi
authors.forename: Ranganathan
authors.initials: R
authors.lastname: Punitham
authors.forename: Angayarkanni
authors.initials: A
authors.lastname: Narayanasamy
authors.forename: Sivaramakrishna
authors.initials: S
authors.lastname: Ramakrishnan
mesh_terms: D000818:Animals; D002417:Cattle; D003094:Collagen / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D006909:Hydroxyproline / Q000032:analysis; D010084:Oxidation-Reduction; D014822:Vitreous Body / Q000737:chemistry*
chemical_list: D003094:Collagen; D005947:Glucose; D006909:Hydroxyproline