Activation of PI3K/Akt pathway mediated by estrogen receptors accounts for estrone-induced vascular activation of cGMP signaling.

Estrone (E1) produces remarkable vascular effects, including relaxation, modulation of proliferation, apoptosis and cell adhesion. This study investigated the role of estrogen receptors and endothelial signaling pathways in the vascular relaxation promoted by E1. Aortic rings from male Wistar rats (250-300 g) were contracted with phenylephrine and stimulated with graded concentrations of E1. The concentration-dependent relaxation induced by E1 was abolished after removal of the endothelium or incubation with the estrogen receptor antagonist ICI 182,780. G protein-coupled estrogen receptor antagonism did not alter the E1 effect. Pretreatment of endothelium-intact arteries with inhibitors of nitric oxide synthase, guanylyl cyclase, calmodulin (CaM) and PI3K reduced the E1-induced vasorelaxation. Incubation with inhibitors of the MEK/ERK1/2 or p38MAPK pathways did not alter the E1 vasorelaxation. Similarly, inhibition of cyclooxygenase or blockade of potassium channels did not change the E1 effect. Western blot analysis evidenced that E1 induces phosphorylation of eNOS, PI3K and Akt in rat aorta. Our data demonstrate that E1 induces aortic vascular relaxation through classic estrogen receptors activation on the endothelium. We also identify CaM and PI3K/Akt pathways as critical mediators of the NO-cGMP signaling activation by E1. These findings contribute to the notion that this estrogen regulates arterial function and represents another link, besides 17ß-estradiol (E2), between postmenopause and vascular dysfunction.

Increased O-GlcNAcylation of Endothelial Nitric Oxide Synthase Compromises the Anti-contractile Properties of Perivascular Adipose Tissue in Metabolic Syndrome.

Under physiological conditions, the perivascular adipose tissue (PVAT) negatively modulates vascular contractility. This property is lost in experimental and human obesity and in the metabolic syndrome, indicating that changes in PVAT function may contribute to vascular dysfunction associated with increased body weight and hyperglycemia. The O-linked ß-N-acetylglucosamine (O-GlcNAc) modification of proteins (O-GlcNAcylation) is a unique posttranslational process that integrates glucose metabolism with intracellular protein activity. Increased flux of glucose through the hexosamine biosynthetic pathway and the consequent increase in tissue-specific O-GlcNAc modification of proteins have been linked to multiple facets of vascular dysfunction in diabetes and other pathological conditions. We hypothesized that chronic consumption of glucose, a condition that progresses to metabolic syndrome, leads to increased O-GlcNAc modification of proteins in the PVAT, decreasing its anti-contractile effects. Therefore, the current study was devised to determine whether a high-sugar diet increases O-GlcNAcylation in the PVAT and how increased O-GlcNAc interferes with PVAT vasorelaxant function. To assess molecular mechanisms by which O-GlcNAc contributes to PVAT dysfunction, thoracic aortas surrounded by PVAT were isolated from Wistar rats fed either a control or high sugar diet, for 10 and 12 weeks. Rats chronically fed a high sugar diet exhibited metabolic syndrome features, increased O-GlcNAcylated-proteins in the PVAT and loss of PVAT anti-contractile effect. PVAT from high sugar diet-fed rats for 12 weeks exhibited decreased NO formation, reduced expression of endothelial nitric oxide synthase (eNOS) and increased O-GlcNAcylation of eNOS. High sugar diet also decreased OGA activity and increased superoxide anion generation in the PVAT. Visceral adipose tissue samples from hyperglycemic patients showed increased levels of O-GlcNAc-modified proteins, increased ROS generation and decreased OGA activity. These data indicate that O-GlcNAcylation contributes to metabolic syndrome-induced PVAT dysfunction and that O-GlcNAcylation of eNOS may be targeted in the development of novel therapies for vascular dysfunction in conditions associated with hyperglycemia.

Metformin reduces the stimulatory effect of obesity on in vivo Walker-256 tumor development and increases the area of tumor necrosis.

AIMS: The objective of this study was to analyze the influence of obesity and insulin resistance on tumor development and, in turn, the effect of insulin sensitizing agents. MAIN METHODS: Male offspring of Wistar rats received monosodium glutamate (400mg/kg) (obese) or saline (control) from the second to sixth day after birth. Sixteen-week-old control and obese rats received 5×10(5) Walker-256 tumor cells, subcutaneously injected into the right flank. Some of the obese and control rats received concomitant treatment with metformin (300mg/kg) by gavage. At the 18th week, obesity was characterized. The percentage of rats that developed tumors, the tumor relative weight and the percentage of cachexia incidence were analyzed. The tumor tissue was evaluated histologically by means of hematoxylin and eosin staining. KEY FINDINGS: Metformin did not correct the insulin resistance in obese rats. The tumor development was significantly higher in the obese group, whereas metformin treatment reduced it. After pathological analysis, we observed that the tumor tissues were similar in all groups except for adipocytes, which were found in greater quantity in the obese and metformin-treated obese groups. The area of tumor necrosis was higher in the group treated with metformin when compared with the untreated one. SIGNIFICANCE: Metformin reduced Walker-256 tumor development but not cachexia in obese rats. The reduction occurred independently of the correction of insulin resistance. Metformin increased the area of necrosis in tumor tissues, which may have contributed to the reduced tumor development.