Highly glycated oxyhaemoglobin impairs nitric oxide relaxations in human mesenteric microvessels

Aims/hypothesis. It has been recently shown that glycated human haemoglobin induces endothelial dysfunction in rat vessels by generating superoxide an ions that interfere with nitric oxide mediated responses. Our study analyse d the effect of glycated human haemoglobin on the endothelium-dependent rel axations of human vessels. Methods. Omental microvessels were obtained from patients (without diabetes , hypertension or vascular disease) during surgery and mounted in a small v essel myograph to study their vasoactive responses (vessels from 3-7 patien ts for each set of experiments). Results. Cumulative vasodilatory responses to bradykinin (10 nmol/l to 3 mu mol/l) were induced in vessels precontracted with 35-50 mmol/l potassium c hloride. Addition of 100 mu mol/l N-G-nitro-L-arginine methyl ester reduced the relaxation evoked by bradykinin, but preincubation with both N-G-nitro -L-arginine methyl ester and 10 mu mol/l indomethacin was needed to abolish it. Bradykinin-induced responses were inhibited by 1 mu mol/l non-glycated oxyhaemoglobin whereas no effect was obtained with 10 nmol/l oxyhaemoglobi n. At these low concentrations (10 nmol/l), glycated human oxyhaemoglobin c aused an impairment of bradykinin-induced relaxation when the percentage of glycation was 10% or higher. This effect was prevented by preincubating th e vessels with ascorbic acid (10 mu mol/l), superoxide dismutase (100 U/ml) and gliclazide (1 and 10 mu mol/l), but not with indomethacin (10 mu mol/l ), catalase (400-600 U/ml), dimethylthiourea (1 mmol/l) or glibenclamide (1 0 mu mol/l). In vessels preincubated with N-G-nitro-L-arginine methyl ester (100 mu mol/l), glycohaemoglobin did not add any additional effect. Conclusion/interpretation. Highly glycated human oxyhaemoglobin, at physiol ogical plasmatic concentrations, impairs nitric oxide-mediated responses by a mechanism involving superoxide anions but not cyclooxygenase derivatives .