Follow-up of plasma semicarbazide-sensitive amine oxidase activity and retinopathy in Type 2 diabetes mellitus

Plasma activity of the enzyme semicarbazide-sensitive amine oxidase (SSAO) is high in diabetes. Production of angiotoxic substances (an aldehyde, hydr ogen peroxide, and ammonia) in vessel walls is catalysed by SSAO, suggestin g a role for SSAO in the development of complications of diabetes. The obje ctive of the present study was to follow up plasma SSAO activity (measured radiometrically), HbA(1c) (using ion exchange chromatography), and retinopa thy (by fundus photography) after 2.8 years, in 34 patients with Type 2 dia betes. We also measured urinary levels of an SSAO substrate, methylamine, b y fluorometric high-performance liquid chromatography (HPLC). As at baselin e, plasma SSAO activity was now higher in subjects with retinopathy (mean 1 9.5) than in subjects without retinopathy (mean 16.0), 95% confidence inter val (CI) for difference 0.6-6.3 nmol benzylamine ml(-1) plasma h(-1). SSAO activity had not changed significantly since baseline, mean difference -1.6 5 and 95% CI for difference -3.76 to 0.46 nmol benzylamine ml(-1) plasma h( -1). Mean HbA(1c) level remained higher for patients with retinopathy (now 7.9%) compared to those without retinopathy (6.1%), 95% CI for difference 0 .6-3.0%. Comparing baseline and the present study, retinopathy was nonproli ferative; level had worsened for five and improved for two patients. Urinar y methylamine/creatinine ratio was lower in the group of patients with reti nopathy (mean 0.99) than in those without retinopathy (mean 1.78), 95% CI f or difference 0.1-1.5 mug mg(-1). The results of the present study are comp atible with a role for SSAO in the development of diabetic retinopathy. (C) 2001 Elsevier Science Inc. All rights reserved.