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Little is known about the mechanism(s) of endothelial dysfunction in diabetes. In this study, the effect of nonenzymatic glycated LDL, a phenomenon induced by elevated D-glucose levels associated with diabetes, on porcine aortic endothelial cells was investigated. Two fractions of LDL from diabetic patients were separated by affinity column chromatography and are referred to herein as fraction alpha (nonglycated LDL) and fraction beta (glycated LDL). Incubation of endothelial cells for 24 h with total LDL isolated from diabetic subjects (dLDL) increased the release of superoxide anions (*O2-) by fivefold, while no effect of LDL isolated from healthy individuals (nLDL) was found. Fraction beta, but not fraction alpha, evoked the *O2- release. In vitro-glycated LDL mimicked the effect of dLDL/fraction beta on *O2- release that correlated with its degree of glycation (R2 = 0.96). Moreover, nitric oxide (NO) stability (measured with a porphyrinic-based electrode) and NO bioactivity (measured by its ability to elevate cellular cGMP levels) were reduced in cells treated with dLDL by 46 and 41%, respectively. dLDL (but not nLDL or fraction alpha) abolished shear stress-induced L-arginine uptake. The inhibitory effect of dLDL on shear stress-induced L-arginine uptake was mimicked by in vitro-glycated LDL. The efficiency of in vitro-glycated LDL to diminish shear stress-evoked L-arginine uptake correlated with the extent of glycation (R2 = 0.88). Moreover, dLDL, but not nLDL or fraction alpha, reduced shear stress-mediated cGMP formation and NOx production by 47 and 88%, respectively. This effect was also mimicked by in vitro-glycated LDL, correlating with its degree of glycation (R2 = 0.86). Under these experimental conditions, glycated LDL reduced shear stress-induced increase in NO synthesis by inhibition of shear stress-stimulated L-arginine uptake and NO bioactivity due to increased endothelial cell *O2- release. These properties may contribute to the reduced vasodilatory response and the vascular complications in diabetes. [ABSTRACT FROM AUTHOR]

Alterations of vascular smooth muscle function have been implicated in the development of vascular complications and circulatory dysfunction in diabetes. However, little is known about changes in smooth muscle contractility and the intracellular mechanisms contributing to altered responsiveness of blood vessels of diabetic patients. Therefore, smooth muscle and endothelial cell function were assessed in 20 patients with diabetes and compared with 41 age-matched control subjects. In rings from uterine arteries, smooth muscle sensitivity to K+, norepinephrine (NE), and phenylephrine (PE) was enhanced by 1.4-, 2.3-, and 9.7-fold, respectively, and endothelium-dependent relaxation was reduced by 64% in diabetic patients, as compared with control subjects. In addition, in freshly isolated smooth muscle cells from diabetic patients, an increased perinuclear Ca2+ signaling to K+ (30 mmol/l >73%; 60 mmol/l >68%) and NE (300 nmol/l >86%; 10 micromol/l >67%) was found. In contrast, subplasmalemmal Ca2+ response, which favors smooth muscle relaxation caused by activation of Ca2+-activated K+ channels, was reduced by 38% in diabetic patients as compared with control subjects, indicating a significant change in the subcellular Ca2+ distribution in vascular smooth muscle cells in diabetic patients. In contrast to the altered Ca2+ signaling found in freshly isolated cells from diabetic patients, in cultured smooth muscle cells isolated from control subjects and diabetic patients, no difference in the intracellular Ca2+ signaling to stimulation with either K+ or NE was found. Furthermore, production of superoxide anion (*O2-) in intact and endothelium-denuded arteries from diabetic patients was increased by 150 and 136%, respectively. Incubation of freshly isolated smooth muscle cells from control subjects with the *O2- -generating system xanthine oxidase/hypoxanthine mimicked the effect of diabetic patients on subcellular Ca2+ distribution in a superoxide dismutase-sensitive manner. We conclude that in diabetic subjects, smooth muscle reactivity is increased because of changes in subcellular Ca2+ distribution on cell activation. Increased *O2- production may play a crucial role in the alteration of smooth muscle function. [ABSTRACT FROM AUTHOR]