Age-dependent changes of serum oxygen radical scavenger capacity and haemoglobin glycosylation in non-insulin-dependent diabetic patients

Background: Contradictory results have been reported in the literature conc erning the correlation between glycosylated haemoglobin (HbA1c) and peroxid ation level in serum of diabetic patients. Objective: To evaluate this corr elation in type 2 diabetic patients by comparing the level of HbA1c with th e oxygen radical absorbance capacity (ORAC(OH)) of serum. Methods: One hund red and five type 2 diabetic patients were enroled for the study. After hav ing obtained informed consent, venous blood samples were drawn after overni ght fast at the time of routine diabetic check-ups. The blood was collected in plain and EDTA (1 mg/ml) tubes. Glycosylated haemoglobin (HbA1c) was de termined by cation-exchange chromatography (HPLC), and spectrophotometric d etection (Diamat Analyzer, BioRad). Serum was used for biochemical determin ations performed by standard laboratory procedures and for ORAC(OH) analysi s. This last parameter was determined measuring the loss of beta -phycoeryt rin fluorescence due to oxidation by hydroxyl radicals generated by Cu2+ an d H2O2, in the presence and absence of serum. Seventy-eight control age-mat ched subjects were obtained from the personnel staff of our Research Depart ment and old healthy subjects, selected on the basis of Senieur Protocol, w ere relatives of the above mentioned personnel. Results: When the populatio n of diabetic patients was taken as a whole, a decrease of ORAC(OH) has bee n observed compared to the controls. Moreover, negative correlations were f ound comparing ORAC(OH) either with HbA1c (r = -0.213; p = 0.029) and with the age of patients (r = -0.27; p = 0.005). To better understand the effect of age, the data were re-examined dividing the diabetics into two populati ons, i.e. under and over 65 years of age. An age-dependent decrease of ORAC (OH) and an increase in HbA1c levels has been observed comparing these two populations; however, the correlation between the two parameters remained s tatistically significant only in the oldest group (r = -0.31; p = 0.026). C onclusions: Present data point to an involvement of oxidative stress in the glycation of haemoglobin especially in old diabetic patients, and provide support for the potential use of an antioxidant therapy in these patients, irrespective of their glycaemic control. Copyright (C) 2001 S, Karger AG, B asel.