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CARDIOVASCULAR

17-Estradiol Antagonizes the Down-Regulation of Endothelial Nitric-Oxide Synthase and GTP Cyclohydrolase I by High Glucose: Relevance to Postmenopausal Diabetic Cardiovascular Disease

Department of Geriatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan (A.M.-A., T.H., Q.F.D., A.I.); Department of Pharmacology, Fujita Health University School of Medicine, Toyoake, Japan (H.S., T.N.); and Department of Pharmacology, School of Medicine, University of Toyama, Toyama, Japan (Y.H.)

In postmenopausal women, the risk of diabetic cardiovascular disease drastically increases compared with that of men or premenopausal women. However, the mechanism of this phenomenon has not yet been clarified. We hypothesized that the beneficial effects of estrogen on endothelial function may be relevant to protection against hyperglycemia-induced vascular derangement. Bovine aortic endothelial cells were incubated for 72 h in the presence and absence of the physiological concentration of 17-estradiol (17-E2) under normal and high-glucose conditions. The presence of 17-E2 significantly counteracted the reduction in basal nitric oxide production under high-glucose conditions. This finding was associated with the recovery of endothelial nitric-oxide synthase (eNOS) protein expression, tetrahydrobiopterin (BH4) levels, and the activity and gene expression of GTP cyclohydrolase I (GTPCH-I), a rate-limiting enzyme for BH4 synthesis. Both the gene transfer of estrogen receptor using adenovirus and treatment with the protein kinase C inhibitor bisindolylmaleimide I significantly enhanced the effects of 17-E2 treatment under high-glucose conditions, whereas these effects were abolished by the estrogen receptor antagonist ICI 182,780 (faslodex). Transfection of small-interfering RNA targeting eNOS resulted in a marked reduction in GTPCH-I mRNA under both normal and high-glucose conditions, but this reduction was strongly reversed by 17-E2. These results suggest that the activation of ER with 17-E2 can counteract high-glucose-induced down-regulation of eNOS and GTPCH-I in endothelial cells. Therefore, estrogen deficiency may result in an exaggeration of hyperglycemia-induced endothelial dysfunction, leading to the development of cardiovascular disease in postmenopausal diabetic women.

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