Differential accumulation of advanced glycation end products in the courseof diabetic retinopathy

Aims/hypothesis. Glycated proteins, formed by reaction of glucose and prote in, react further yielding numerous, mostly undefined advanced glycation en d products (AGE). The recently characterized imidazolone-type AGE (AG-1) is non-oxidatively formed involving 3-deoxyglucosone whereas some AGEs, parti cularly N-epsilon-(carboxymethyl)lysine (CML), are formed only in the prese nce of oxygen. Methods. To study the possible contribution of oxidative and non-oxidative AGE formation in the development of diabetic retinopathy antibodies directe d against CML-type and imidazolone-type AGEs were characterized by dot blot analysis and used to localize these well-characterized epitops in the reti nas from diabetic rats (early course) and from human Type I (insulin-depend ent) diabetes mellitus with laser-treated proliferative diabetic retinopath y (late course). Results. In non-diabetic rats CML was moderately positive in neuroglial and vascular structures of nondiabetic rat retinas and increased strongly in d iabetic retinas. Anti-imidiazolone antibody staining was strongly positive only in diabetic capillaries. Advanced human diabetic retinopathy showed st rong CML-immunolabelling of the entire retina whereas control samples showe d moderate staining of neuroglial structures only with the polyclonal CML-a ntibody. Anti-imidiazolone antibody staining was faint in the inner retina of control sections but were strong throughout the entire diabetic retina. Immunolabelling for the AGE-receptor was congruent with a marker of Muller cells. Conclusion/interpretation. Our data indicate that the oxidatively formed CM L is present in non-diabetic retinas as a regular constituent but increases in diabetes both in neuroglial and vascular components. Imidazolone-type A GE are restricted to microvessels and spread during later stages over the e ntire retina, co-localizing with the expression of ACE-receptor.