Biochemical markers of type III and I collagen: association with retinopathy and neuropathy in Type 1 diabetic subjects

Aims Connective tissue alterations may contribute to the development of dia betic long-term complications in eyes, kidneys and peripheral nerves. Colla gen deposition may be increased in micro- and macrovascular disease in diab etic subjects. We tested whether biochemical markers of type III and I coll agen metabolism are associated with retinopathy and neuropathy in Type 1 di abetes. Methods A total of 28 patients, mean age 43.4 +/- 9.5 (sd) and duration of diabetes 25.2 +/- 9.7 years, were studied. Stereoscopic colour fundus photo graphs were taken for assessment of retinopathy which was classified as no, background or proliferative. Concentrations of aminoterminal propeptide of type III procollagen (PIIINP), carboxyterminal propeptide of type I procol lagen (PICP) and carboxyterminal cross-linked telopeptide of type I collage n (ICTP) in serum and urinary excretion of cross-linked N-telopeptides of t ype I collagen (NTX) and deoxypyridinoline crosslinks (DPyr) into urine wer e measured. Results Average serum PIIINP was higher in subjects with proliferative (3.2 +/- 1.1 mug/l) than without proliferative retinopathy (2.5 +/- 0.6 mug/l) (P = 0.03). Average serum PICP was higher in subjects without retinopathy ( 181.7 +/- 19.5 mug/l) than in subjects with background retinopathy (132.1 /- 42.7 mug/l) (P = 0.02). Concentrations of other collagen markers were no t different in subjects with or without retinopathy. No association between collagen markers and neuropathy was found. Conclusions The increased synthesis of type III collagen, reflecting deposi tion of matrix and basement membrane connective tissue, may be involved in the pathogenesis of proliferative retinopathy in Type 1 diabetic subjects. On the other hand, we observed decreased synthesis of Type I collagen, whic h can result in weakened vascular integrity in subjects with retinopathy.