Elevated plasma semicarbazide-sensitive amine oxidase (SSAO) activity in Type 2 diabetes mellitus complicated by retinopathy

Aims To measure plasma semicarbazide-sensitive amine oxidase (SSAO) activities and detect retinopathy in Type 2 diabetes mellitus (DM). Methods Cross-sectional, population-based. study of 65 diabetes patients (61 diagnosed from the age of 30 years) with or without retinopathy as determined by fundus photography in primary care. HbA(1c) was analysed by ion exchange chromatography on a Mono S for HbA(1c) column. SSAO activities were assayed radiometrically and formaldehyde-albumin adducts by ELISA in plasma samples from patients and 136 healthy controls. Results Subjects with diabetes had higher plasma SSAO activity, measured as nmol benzylamine.ml plasma(-1).h(-1) (mean 20.6), than controls (mean 14.3), P<0.0001; 95%;, confidence interval (CI) for difference 4.9-7.7. SSAO activity was higher in patients with retinopathy (mean 23.2) than in those without (mean 18.9), P=0.012; 95% CI for difference 1.0-7.5, and related to the HbA(1c) value, No statistically significant relationship between diabetes duration and SSAO activity was found. With HbA(1c) values and insulin treatment entered into a multiple logistic regression model, SSAO activity no longer predicted retinopathy, P increasing from 0.025 to 0.17. SSAO activity and the presence of any retinopathy were unrelated to titres of antibodies against formaldehyde-treated human serum albumin. Conclusions SSAO activity, earlier found to be elevated in Type 1 DM, is also elevated in Type 2 DM. The SSAO family of enzymes may be involved in the development of diabetic retinopathy, possibly by catalysing the formation of toxic metabolites. A potent and specific inhibitor of human SSAO might help prevent retinopathy in Type 1 and Type 2 DM.