OBJECTIVE -Previous studies have shown that in type 1 diabetes endothelial dysfunction persists even when glycemia is normalized. Moreover, oxidative stress has recently been demonstrated to be the mediator of hyperglycemia-induced endothelial dysfunction.RESEARCH DESIGN AND METHODS -Thirty-six type 1 diabetic patients and 12 control subjects were enrolled. The diabetic patients were divided into three groups. The first group was treated for 24 h with insulin, achieving a near-normalization of glycemia. After 12 h of this treatment, vitamin C was added for the remaining 12 h. The second group was treated for 24 h with vitamin C. After 12 h of this treatment, insulin was started, with achievement of near-normalization of glycemia for the remaining 12 h. The third group was treated for 24 h with both vitamin C and insulin, achieving near-normalization of glycemia.RESULTS -Neither normalization of glycemia nor vitamin C treatment alone was able to normalize endothelial dysfunction or oxidative stress. However, a combination of insulin and vitamin C normalized endothelial dysfunction and decreased oxidative stress to normal levels.CONCLUSIONS -This study suggests that long-lasting hyperglycemia in type 1 diabetic patients induces permanent alterations in endothelial cells, which may contribute to endothelial dysfunction by increased oxidative stress even when hyperglycemia is normalized.
Diabetes Care 30:649 -654, 2007T ype 1 diabetes is associated with increased incidence of macrovascular diseases (1).The accelerated macrovascular disease is due in part to the increased incidence of classic risk factors, such as hypertension and dyslipidemia (2). However, recent evidence suggests that hyperglycemia also plays a significant role (3).The endothelium is a major organ involved in the development of cardiovascular disease, even in diabetes (4). All risk factors involved in the pathogenesis of cardiovascular disease, such as dyslipidemia and hypertension, can induce endothelial dysfunction, which has largely been shown to be predictive of a future cardiovascular event (4).The presence of endothelial dysfunction has often been reported in diabetes (4). However, whereas several studies have shown that hyperglycemia induces endothelial dysfunction in both diabetic and nondiabetic subjects (5-7), a clear demonstration that control of hyperglycemia can restore/normalize endothelial function is still lacking. In particular, in type 1 diabetic patients endothelial dysfunction has been reported to be present even when normoglycemia was achieved (8,9). Furthermore, several studies indicated that hyperglycemia induces endothelial dysfunction through the generation of oxidative stress (for review, see ref. 10), which has been suggested to be the key player in the generation of diabetes complications, both micro-and macrovascular (11). Therefore, the aim of this study was to evaluate the distinct as well as the combined effect of controlling hyperglycemia and oxidative stress on endothelial function in type 1 diabetic patients.
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