17 Beta-estradiol increases nitric oxide and prostaglandin I2 production by cultured human uterine arteries only in histologically normal specimens

S-equol Partially Restored Endothelial Nitric Oxide Production in Isoflavone-deficient Ovariectomized Rats

BACKGROUND

S-equol is known as an estrogenic substance, but its ability to restore vascular endothelial function is unknown. The aim of this study was to investigate the impact of S-equol on endothelial function and intimal thickening under isoflavone- and estrogen-deficient circumstances.

METHODS

Twelve-week-old female Sprague-Dawley rats were bilaterally ovariectomized and assigned to one of the 3 groups: control, isoflavone-deficient (ID), or ID plus equol (n = 12, respectively). The control group received a normal diet containing isoflavones, while ID and ID plus equol groups received isoflavones-free diet. At 16th week, subcutaneous administration of S-equol (200 μg/d) started in the ID plus equol group. At 18th week, endothelial denudation of the left common carotid artery was performed in all groups, and thoracic and carotid arteries were collected at 20th week.

RESULTS

In thoracic artery, endothelium-dependent relaxation, cyclic guanosine monophosphate levels in the tissue, and endothelial nitric oxide (NO) synthase expression and phosphorylation were significantly higher in the groups of ID plus equol and control than in the ID. The ratio of intima to media of the injured carotid artery in the control group was the lowest.

CONCLUSIONS

Removal of dietary soy isoflavones decreased endothelium-derived NO level in ovariectomized rats. S-equol supplementation partially improved NO-related endothelial function.

Possible involvement of altered arginase activity, arginase type I and type II expressions, and nitric oxide production in occurrence of intimal hyperplasia in premenopausal human uterine arteries

In the present experiments, we tried to elucidate whether changes in arginase activity and protein expression of arginase I and II are involved in the occurrence of intimal hyperplasia in premenopausal human uterine arteries. They were obtained from thirty-four patients undergoing total abdominal hysterectomy with informed consent for the present study. All specimens were assessed histologically and the intima/media ratio (%) was evaluated as an index of the intimal hyperplasia. Thirteen patients out of 34 had histologically normal arteries (intima/media ratio = 18.1 +/- 0.7%), whereas the remaining 21 patients had various degrees of intimal hyperplasia (intima/media ratio = 32.7 +/- 2.3%), and these specimens were categorized as hyperplasic. Intimal hyperplasia was accompanied by impaired cyclic GMP production, enhanced overall arginase activity, and up-regulations of arginase I and II in endothelial cells and of arginase II in the smooth muscle layer. Pearson's correlation coefficient analyses revealed the close relationships among the arginase activities in endothelial cells and smooth muscle layer, the intimal/media ratio, and cyclic GMP production. These results suggest that the enhanced arginase activity and expressions of two arginase subtypes shed new light on the processes associated with the occurrence of intimal hyperplasia in premenopausal human uterine arteries.

Possible involvement of enhanced arginase activity due to up-regulated arginases and decreased hydroxyarginine in accelerating intimal hyperplasia with hyperglycemia

The present study was designed to investigate the roles of enhanced arginase activity due to up-regulated arginases and the decreased hydroxyarginine for accelerating intimal hyperplasia with hyperglycemia. Thirteen weeks after injection of alloxan or physiological saline, endothelial denudation of the carotid artery was performed to induce intimal hyperplasia. The intimal hyperplasia occurred on 4 weeks following denudation was significantly accelerated by hyperglycemia. The method to measure L-arginine, endogenous NOS inhibitors such as monomethylarginine and asymmetric dimethylarginine, and hydroxyarginine as an intermediate of NO production simultaneously was established with the aid of high-performance liquid chromatography. In hyperglycemia group, the impaired cyclic GMP production as an indicator of NO production in endothelial cells was accompanied by the enhanced arginase activity together with increased expression of arginase I and II proteins, accumulated endogenous NOS inhibitors, reduced concentration of hydroxyarginine, and decreased DDAH activity in endothelial cells. However, NOS activity per se remained unchanged in the hyperglycemia group. Authentic hydroxyarginine inhibited arginase activity in a concentration-dependent manner. The inhibition of arginase with hydroxyarginine at a reduced concentration with hyperglycemia became significantly lower than that for the control. These results suggest that the accelerated intimal hyperplasia with hyperglycemia is closely related to the impaired NO production in endothelial cells, which results from accumulation of endogenous NOS inhibitors and accelerated arginase activity together with up-regulation of arginase I and II proteins. Decreased DDAH activity would bring about the accumulation of endogenous NOS inhibitors. Furthermore, reduced concentration of hydroxyarginine with hyperglycemia possibly results in an enhanced arginase activity in vivo, implicating partly in the impairment of NO production.

Roles of accumulated endogenous nitric oxide synthase inhibitors, enhanced arginase activity, and attenuated nitric oxide synthase activity in endothelial cells for pulmonary hypertension in rats

Nitric oxide (NO) has been suggested to play a key role in the pathogenesis of pulmonary hypertension (PH). To determine which mechanism exists to affect NO production, we examined the concentration of endogenous nitric oxide synthase (NOS) inhibitors and their catabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) activity and protein expression (DDAH1 and DDAH2) in pulmonary artery endothelial cells (PAECs) of rats given monocrotaline (MCT). We also measured NOS and arginase activities and NOS protein expression. Twenty-four days after MCT administration, PH and right ventricle (RV) hypertrophy were established. Endothelium-dependent, but not endothelium-independent, relaxation and cGMP production were significantly impaired in pulmonary artery specimens of MCT group. The constitutive NOS activity and protein expression in PAECs were significantly reduced in MCT group, whereas the arginase, which shares l-arginine as a common substrate with NOS, activity was significantly enhanced in PAECs of MCT group. The contents of monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), but not symmetric dimethylarginine (SDMA), were increased in PAECs of MCT group. The DDAH activity and DDAH1, but not DDAH2, protein expression were significantly reduced in PAECs of MCT group. These results suggest that the impairment of cGMP production as a marker of NO production is possibly due to the blunted endothelial NOS activity resulting from the downregulation of endothelial NOS protein, accumulation of endogenous NOS inhibitors, and accelerated arginase activity in PAECs of PH rats. The decreased overall DDAH activity accompanied by the downregulation of DDAH1 would bring about the accumulation of endogenous NOS inhibitors.

Estrogen replacement effectively improves the accelerated intimal hyperplasia following balloon injury of carotid artery in the ovariectomized rats

Present experiments were designed to investigate the effects of ovariectomy (OVX) and estrogen replacement (ER) on neointimal formation after balloon injury of the rat carotid artery. Young adult female rats were divided into 3 groups of sham operation (control), ovariectomy, and ovariectomy plus estrogen replacement. Estrogen replacement was initiated by implanting a sustained release pellet containing water-soluble 17beta-estradiol 1 week after the ovariectomy. Carotid arteries were harvested 2 weeks after the balloon injury for determinations. The balloon injury caused intimal hyperplasia, which was accompanied by the impaired endothelium-dependent relaxation and cyclic GMP production, and accumulation of asymmetric dimethylarginine (ADMA) as an endogenous NOS inhibitor. Bilateral ovariectomy accelerated the intimal hyperplasia. The acceleration was accompanied by the enhanced impairment of NO production, attenuated reendothelialization, and enhanced accumulation of ADMA. The estrogen replacement improved the accelerated intimal hyperplasia with concomitant improvement of the impaired NO production and accumulated asymmetric dimethylarginine, and facilitated reendothelialization. These results suggests that the enhanced impairment of NO production, which possibly results from the accumulated asymmetric dimethylarginine and lack of reendothelialization, may contribute to the acceleration of intimal hyperplasia by ovariectomy and that estrogen replacement effectively improves the intimal hyperplasia by restoring the impaired NO production through reducing endogenous NOS inhibitor and facilitating reendothelialization.

Accumulated endogenous nitric oxide synthase inhibitors, enhanced arginase activity, attenuated dimethylarginine dimethylaminohydrolase activity and intimal hyperplasia in premenopausal human uterine arteries

The present study was designed to investigate the involvement of nitric oxide synthase (NOS), endogenous NOS inhibitors, arginase, which shares L-arginine as a common substrate with NOS, and dimethylarginine dimethylaminohydrolase (DDAH) as a metabolizing enzyme of NOS inhibitors in the occurrence of intimal hyperplasia in premenopausal human uterine arteries. Fifty-two uterine arteries were obtained from 52 patients undergoing total hysterectomy with an informed consent for the present study. All specimens were assessed histologically and the intima:media ratio (%) was evaluated as an index of intimal hyperplasia. Nineteen specimens were found to be histologically normal (intima:media ratio=16.1+/-0.8%), whereas remaining 33 specimens were categorized as intimal hyperplasia (intima:media ratio=34.4+/-1.5%). The intimal hyperplasia was associated with the impaired cyclic GMP production without change in endothelial NOS activity per se, accumulation of endogenous NOS inhibitors in endothelial cells, attenuated DDAH activity in endothelial cells and enhanced arginase activity in endothelial cells and smooth muscle layer. These findings suggest that the impaired cyclic GMP production as a marker of NO production is possibly due to the accumulated endogenous NOS inhibitors and enhanced arginase activity, which, in turn, closely relates to the occurrence of intimal hyperplasia, and that the impaired DDAH activity would result in the accumulation of endogenous NOS inhibitors in endothelial cells. Because of the enhanced arginase activity in endothelial cells and smooth muscle layer, the accelerated polyamine biosynthetic pathway may be implicated in the occurrence of intimal hyperplasia in premenopausal human uterine arteries.

Regulation of nitric oxide-dependent vasodilation in coronary arteries of estrogen receptor-alpha-deficient mice

Estrogen has been shown to increase endothelium-dependent vasodilation and expression of endothelial nitric oxide (NO) synthase (eNOS); however, the role of estrogen receptors in mediating estrogen effects on endothelial function remains to be elucidated. The purpose of this study was to test the hypothesis that estrogen modulates NO-dependent vasodilation of coronary arteries through its action on estrogen receptor-alpha (ER-alpha) to increase protein levels of eNOS and Cu/Zn superoxide dismutase (SOD-1). Vasodilation to acetylcholine (ACh) and sodium nitroprusside was assessed in isolated coronary arteries from intact and ovariectomized female wild-type (WT) and ER-alpha knockout (ERalphaKO) mice. Protein levels for eNOS and SOD-1 were also evaluated. Vasodilation to ACh was not significantly altered in ERalphaKO mice compared with WT mice. Ovariectomy reduced responsiveness to ACh in ERalphaKO mice but not WT mice. Responses to sodium nitroprusside were not altered by disruption of ER-alpha or by ovariectomy. Supplementation with estrogen restored ACh-induced vasodilation in ovariectomized ERalphaKO mice. eNOS protein was reduced in ERalphaKO mice compared with WT mice. Ovariectomy caused a further reduction in eNOS protein in ERalphaKO mice, but this reduction was reversed by estrogen treatment. SOD-1 protein levels were increased by disruption of ER-alpha. Ovariectomy reduced SOD-1 protein in ERalphaKO mice, but this reduction was partially reversed by estrogen replacement. These results suggest that estrogen modulation of eNOS protein content is mediated in part through ER-alpha. NO-dependent responses are preserved in ERalphaKO mice, possibly through increased SOD-1 expression and enhanced bioavailability of NO.

Possible involvement of facilitated polyol pathway in augmentation of intimal hyperplasia in rabbits with alloxan-induced hyperglycemia

Present experiments were designed to investigate whether the facilitated polyol pathway is involved in the augmentation of intimal hyperplasia with hyperglycemia. Twelve weeks after a single bolus intravenous injection of alloxan (100 mg/kg) or saline, rabbits underwent a unilateral endothelial denudation of the carotid artery. Intimal hyperplasia was evident 4 weeks after denudation and significantly augmented in hyperglycemic animals treated with alloxan. This effect was accompanied by the enhanced accumulation of endogenous NOS inhibitors (N(G)-monomethyl-l-arginine [l-NMMA] and asymmetric, N(G),N(G)-dimethyl-l-arginine [ADMA]) in regenerated endothelial cells, impairment of NO production and release, and enhanced accumulation of endothelin-1 (ET-1) within the vessel wall. Sorbitol levels in aortic endothelial cells and within the smooth muscle layer were significantly increased with hyperglycemia. All these changes associated with hyperglycemia were significantly reduced in animals treated with the selective aldose reductase inhibitor fidarestat (3 mg/kg/d). These findings suggest that the facilitated polyol pathway possibly plays an important role for the augmentation of intimal hyperplasia caused by the hyperglycemic state.