Diabetic retinopathy risk correlates with intracellular concentrations of the glycoxidation product Nepsilon-(carboxymethyl) lysine independently of glycohaemoglobin concentrations.
OBJECTIVE
We investigated whether either the amount of diabetes-induced intracellular oxidative stress or the concentration of hyperglycaemia-induced advanced glycation endproducts is associated with the risk of diabetic retinopathy.


METHODS
We measured concentrations of the glycoxidation product Nepsilon-(carboxymethyl)lysine and two non-oxidation-dependent advanced glycation end-products (methylglyoxal-derived and 3-deoxyglucosone-derived) in CD45RA+ T-cells from 21 Type I (insulin-dependent) diabetic patients with and without diabetic retinopathy and from age-matched nondiabetic control subjects.


RESULTS
Intracellular concentrations of both oxidation-dependent Nepsilon-(carboxymethyl)lysine and oxidation-independent advanced glycation endproducts were increased in memory T-cells from diabetic patients. Nepsilon-(carboxymethyl)lysine: diabetic median-24176 arbitrary units/mg protein (95% confidence interval 18690-34099 arbitrary units/mg protein); nondiabetic-9088 arbitrary units/mg protein (confidence interval 6994-10696 arbitrary units/mg protein; p < 0.0001). Methylglyoxal-derived advanced glycation end products: diabetic-5430 arbitrary units/ mg protein (confidence interval 3458-13610); nondiabetic-271 arbitrary units/mg protein (confidence interval 61-760 arbitrary units/mg protein; p< 0.0001). 3-Deoxyglucosone-derived advanced glycation end products: diabetic-8070 arbitrary units/mg protein (confidence interval 7049-16551 arbitrary units/mg protein); nondiabetic-1479 arbitrary units/ mg protein (confidence interval 1169-3170; p< 0.0001). Only Nepsilon-(carboxymethyl)lysine concentrations, however, inversely correlated with the duration of retinopathy-free diabetes (r = -0.51; p < 0.02). Diabetes-dependent Nepsilon-(carboxymethyl)lysine accumulation did not correlate with age, diabetes duration, or averaged glycohaemoglobin concentrations. In vitro experiments wih menadione and lymphocytes confirmed that Nepsilon-(carboxymethyl)lysine concentrations reflect intracellular oxidative stress.


CONCLUSIONS
Monitoring intracellular concentrations of increased oxidative stress in long-lived CD45RA+ lymphocytes by markers such as Nepsilon-(carboxymethyl)lysine possibly identifies a subgroup of patients at high risk for microvascular complications.
Hammes
H P
HP
3rd Medical Department, Centre of Internal Medicine, Justus-Liebig-University, Giessen, Germany.
Brownlee
M
M
Lin
J
J
Schleicher
E
E
Bretzel
R G
RG
D000328:Adult; D003847:Deoxyglucose / Q000031:analogs & derivatives; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003930:Diabetic Retinopathy / Q000097:blood*; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D017127:Glycation End Products, Advanced / Q000097:blood; D006801:Humans; D017493:Leukocyte Common Antigens / Q000032:analysis; D008239:Lysine / Q000031:analogs & derivatives* / Q000097:blood; D008297:Male; D008875:Middle Aged; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D011765:Pyruvaldehyde; D012307:Risk Factors; D013601:T-Lymphocytes / Q000737:chemistry* / Q000276:immunology
D003847:Deoxyglucose; D006442:Glycated Hemoglobin; D017127:Glycation End Products, Advanced; D017493:Leukocyte Common Antigens; D008239:Lysine; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D011765:Pyruvaldehyde; C060458:3-deoxyglucose; C048496:N(6)-carboxymethyllysine