Effect of endogenous estrogen on endothelial function in women with coronary heart disease and its mechanism

ADMA metabolism and clearance

The plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is the resultant of many processes at cellular and organ levels. Post-translational methylation of arginine residues of pro teins plays a crucial role in the regulation of their functions, which include processes such as transcription, translation and RNA splicing. Because protein methylation is irreversible, the methylation signal can be turned off only by proteolysis of the entire protein. Consequently, most methylated proteins have high turnover rates. Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH). Some ADMA escapes degradation and leaves the cell via cationic amino acid transporters. These trans porters also mediate uptake of ADMA by neighboring cells or distant organs, thereby facilitating active interorgan transport. Clearance of ADMA from the plasma occurs in small part by urinary excretion, but the bulk of ADMA is degraded by intracellular DDAH, after uptake from the circulation. This review discusses the various processes involved in ADMA metabolism: protein methylation, proteolysis of methylated proteins, metabolism by DDAH, and interorgan transport. In addition, the role of the kidney and the liver in the clearance of ADMA is highlighted.

Sex differences in cardiovascular ageing

Despite recent progress in identifying and narrowing the gaps in cardiovascular outcomes between men and women, general understanding of how and why cardiovascular disease presentations differ between the sexes remains limited. Sex-specific patterns of cardiac and vascular ageing play an important role and, in fact, begin very early in life. Differences between the sexes in patterns of age-related cardiac remodelling are associated with the relatively greater prevalence in women than in men of heart failure with preserved ejection fraction. Similarly, sex variation in how vascular structure and function change with ageing contributes to differences between men and women in how coronary artery disease manifests typically or atypically over the adult life course. Both hormonal and non-hormonal factors underlie sex differences in cardiovascular ageing and the development of age-related disease. The midlife withdrawal of endogenous oestrogen appears to augment the age-related increase in cardiovascular risk seen in postmenopausal compared with premenopausal women. However, when compared with intrinsic biological differences between men and women that are present throughout life, this menopausal transition may not be as substantial an actor in determining cardiovascular outcomes.

Neighborhood socioeconomic status during childhood versus puberty in relation to endogenous sex hormone levels in adult women

BACKGROUND

Socioeconomic adversity in early life is related to cardiovascular risk in adulthood; however, no studies have examined whether such adversity may be related to endogenous sex hormones, which are themselves associated with cardiovascular outcomes, or whether the timing of adversity exposures (childhood vs. puberty) matters.

OBJECTIVE

The goal of the current study was to separately examine neighborhood socioeconomic status (SES) during periods of childhood and puberty in relation to adulthood levels of endogenous sex hormones (estradiol [E2], testosterone), sex hormone binding globulin (SHBG), and a derived index of bioavailable testosterone (free androgen index).

METHODS

In a sample of 143 premenopausal women (mean age = 36.8 [SD = 5.5]; 51.7% White, 32.2% African American, 5.6% Latina, 7.0% Chinese, and 3.5% Filipina), retrospective reports of residential address information in designated periods of childhood and puberty were used to derive U.S. census-based neighborhood SES composite scores characterizing the socioeconomic environments of women during these periods.

RESULTS

In covariate-adjusted analyses, higher neighborhood SES in puberty predicted higher levels of SHBG in adulthood, but neighborhood SES during childhood did not (standardized regression coefficient = .24, p = .01 vs. standardized regression coefficient = .04, p = .75, respectively). Neighborhood SES was not predictive of other hormones (E2, testosterone, and free androgen index).

DISCUSSION

The current findings suggest that puberty may be a time of particular vulnerability to the effects of neighborhood SES on SHBG levels, which have been linked to cardiovascular risk factor profiles and atherosclerotic disease progression.

Modulation of endothelial function by Korean red ginseng (Panax ginseng C.A. Meyer) and its components in healthy individuals: a randomized controlled trial

AIMS

Ginseng root and its derivatives remain atop the most widely used medicinal herbs in cardiovascular disease, despite inadequate substantiation of efficacy. We previously reported the potential of Korean red ginseng (KRG) to affect vascular tone by decreasing arterial wave reflection via an unknown mechanism. Given the preclinical link between ginseng intake and vasoactivity related to nitric oxide (NO) production, we sought to directly evaluate the effects of KRG root and its major root components, on an established noninvasive measure of endothelial function.

METHODS

In an acute, randomized, placebo-controlled, double-blind, crossover design, 16 healthy participants (9M:7F, age:30 ± 9y, BMI: 24 kg ±3 kg/m(2) , systolicBP/diastolicBP: 109 ± 11/66 ± 8 mmHg) on four occasions were administered: KRG root (3 g), KRG ginsenosides extract, KRG polysaccharides extract, and cornstarch control. Extracted fractions were delivered at doses bioequivalent to those found in 3 g of KRG. Flow-mediated vasodilatation (FMD) assessment, preceding a brachial blood pressure measurement, was performed at baseline and at 90 and 180 min posttreatment to assess endothelial function.

RESULTS

KRG significantly improved FMD posttreatment. Maximal vasodilatation of Δ2.57 ± 2.8% occurred at 180 min compared with control (Δ-0.83 ± 2.7%, P = 0.003 for all comparisons). The ginsenoside extract produced a comparable response (Δ1.75 ± 2.6%), but not the polysaccharide fraction (Δ0.10 ± 2.7%). Brachial blood pressure remained unchanged for all treatments (P = 0.45).

CONCLUSIONS

KRG acutely improved endothelial function in healthy individuals, which appears to be attributable to its ginsenoside containing fraction. Our data confirm preclinical data and support the potential for these compounds as targets for therapeutic strategies in disorders involving endothelial dysfunction.

Menopausal hormone treatment cardiovascular disease: another look at an unresolved conundrum

Cardiovascular disease (CVD) is the most common cause of death in women. Before the Women's Health Initiative (WHI) hormone trials, evidence favored the concept that menopausal hormone treatment (MHT) protects against CVD. WHI studies failed to demonstrate CVD benefit, with worse net outcomes for MHT versus placebo in the population studied. We review evidence regarding the relationship between MHT and CVD with consideration of mechanisms and risk factors for atherogenesis and cardiac events, results of observational case-control and cohort studies, and outcomes of randomized trials. Estrogen effects on CVD risk factors favor delay or amelioration of atherosclerotic plaque development but may increase risk of acute events when at-risk plaque is present. Long-term observational studies have shown ∼40% reductions in risk of myocardial infarction and all-cause mortality. Analyses of data from randomized control trials other than the WHI show a ∼30% cardioprotective effect in recently menopausal women. Review of the literature as well as WHI data suggests that younger and/or more recently menopausal women may have a better risk-benefit ratio than older or remotely menopausal women and that CVD protection may only occur after >5 years; WHI women averaged 63 years of age (12 years postmenopausal) and few were studied for >6 years. Thus, a beneficial effect of long-term MHT on CVD and mortality is still an open question and is likely to remain controversial for the foreseeable future.

Endogenous sex steroid levels and cardiovascular disease in relation to the menopause: a systematic review

Heart disease remains a major cause of death among women in the United States. This article focuses on physiologic endogenous estrogen levels with a systematic review of literature related to endogenous sex steroid levels and coronary artery disease (CAD) among postmenopausal women with natural or surgical menopause. There is adequate reason to seek evidence for associations of circulating estrogen levels and CAD. In the future, even if ovarian senescence-associated hormonal changes are confirmed to be associated with CAD in cohort studies of postmenopausal women, there may be other components explaining the gender differences in CAD patterns.

Impaired endothelial function in pediatric patients with turner syndrome and healthy controls: a case-control study

Background

Turner Syndrome women are at high risk of vascular disease and the assessment of early risk factors in Turner Syndrome girls is an emerging focus of research. Our objective was to evaluate endothelial function (EF), a preclinical measure of atherosclerosis, in Turner Syndrome girls compared with controls.

Methods

A cross-sectional case-control study of Turner Syndrome girls and healthy controls. Subjects underwent fasting insulin and glucose with calculation of HOMA-IR, fasting lipid profile, anthropometrics, and EF testing using peripheral arterial tonometry (PAT). Subjects, aged 10-18 years, had karyotype-confirmed Turner Syndrome; growth hormone (GH), thyroxine and estrogen use were not exclusion criteria. Controls were age- and BMI-matched healthy girls. Fifteen Turner Syndrome and 15 controls were recruited.

Results

Turner Syndrome girls had lower height, higher HDL and higher waist:height ratio than controls. PAT-hyperemia ratio (RH-PAT) scores were lower in Turner Syndrome (1.64 ± 0.34 vs. 2.08 ± 0.32, p = 0.002) indicating impaired EF. Among Turner Syndrome, RH-PAT did not vary with estrogen therapy or with karyotype 45,XO compared with other karyotypes. However, endothelial function was better in GH-treated compared with GH-untreated Turner Syndrome (1.80 ± 0.36 vs. 1.4 + 0.22, p = 0.02) although there were no differences in HOMA-IR, adiponectin or IGF-1.

Conclusion

Girls with Turner Syndrome exhibit impaired endothelial function compared with controls, which may explain higher risk for vascular disease. GH may protect endothelial function in Turner Syndrome.

Serum homocysteine and asymmetric dimethylarginine levels in patients with premature ovarian failure: a prospective controlled study

OBJECTIVE

To investigate serum homocysteine and asymmetric dimethylarginine (ADMA) levels in patients with premature ovarian failure (POF).

STUDY DESIGN

A total of 69 women, 32 with POF and 37 apparently healthy women were included in the study. Fasting blood samples were drawn to measure serum homocysteine and ADMA levels using ELISA method.

RESULTS

The study and control group had a mean age of 37.3 + 2.6, 37.5 + 2.5 years; a mean homocysteine level of 13.54 + 5.19, 12.71 + 3.99 mmol/l and a mean ADMA level of 1.32 + 0.27, 1.26 + 0.36 mmol/l, respectively. There were no statistically significant differences between the two groups in terms of homocysteine and ADMA levels (with p values of 0.465 and 0.423, respectively). A negative significant correlation was found between estradiol and ADMA (p <0.05).

CONCLUSION

Homocysteine and ADMA levels did not change in comparison with the control group, which suggests that estrogen deficiency in patients with POF does not have any effect on homocysteine and asymmetric dimethylarginine levels.

The influence of physiological and surgical menopause on coronary heart disease risk markers

OBJECTIVE

To investigate the influence of physiological and surgical menopause on serum concentrations of coronary heart disease (CHD) risk markers and sex hormones.

DESIGN

Physiological menopausal transition was investigated in two studies. In a longitudinal study, 16 women were followed from 2 years before until 2 years after physiological menopause. In a case-control study, 27 early postmenopausal women were compared with 27 age-matched late premenopausal women. Surgical menopause was investigated in 11 women undergoing a prophylactic bilateral salpingo-oophorectomy. The following parameters were measured: serum concentrations of estradiol, follicle-stimulating hormone, inhibin A, inhibin B, asymmetric dimethylarginine, lipids, leptin, homocysteine, C-reactive protein, and coenzyme Q10, as well as weight and body mass index.

RESULTS

After physiological and surgical menopause, serum estradiol and inhibin A and B decreased, whereas follicle-stimulating hormone increased (all P values < 0.01). Serum asymmetric dimethylarginine, total and low-density lipoprotein cholesterol, and leptin concentrations were significantly higher in postmenopausal women compared with premenopausal women (all P values < 0.05). Serum homocysteine concentrations increased significantly during the physiological menopausal transition. Total and low-density lipoprotein cholesterol increased after surgical menopause (both P values = 0.01). None of the other parameters studied were influenced significantly by the menopausal transition. No difference in change in the various CHD risk markers investigated was observed between physiological and surgical menopause.

CONCLUSIONS

The CHD risk profile was affected unfavorably by both physiological and surgical menopause. Changes in most CHD risk markers were small, despite the substantial changes in hormonal parameters.

Altered endothelial function in asymptomatic male adolescents with type 1 diabetes

OBJECTIVE

While adult men and women with diabetes experience similar rates of cardiovascular disease, early microvascular complications show significant gender differences during adolescence. The goal of this study was to determine whether a gender contrast in a preclinical stage of atherosclerosis, or endothelial dysfunction, is present in pediatric diabetic patients.

METHODS

Reactive hyperemia-peripheral arterial tonometry (RH-PAT), a noninvasive method to assess endothelial dysfunction, was used. Measurements were performed at rest and after hyperemia in 20 diabetic subjects and 20 age- and gender-matched nondiabetics, aged 12-16 years. Confounding risk factors for endothelial dysfunction, including smoking, obesity, and hypertension, were excluded.

RESULTS

RH-PAT was lower for male diabetic subjects vs. controls (n = 12, 1.60 +/- 0.32 vs. 1.92 +/- 0.28, P < .001). RH-PAT was similar in female diabetic patients vs. controls. Male and females with type 1 diabetes subjects had equivalent metabolic control (HbA1C 7.48 +/- 1.0 vs. 7.51 +/- 0.9) and lipid profiles. No difference was observed in age, HbA1C, and diabetes duration, between male and female diabetic subjects. However, diabetic female patients had a greater body mass index (24.2 +/- 2.5 vs. 20.6 +/- 2.0, P = .003) and were more mature in pubertal status as compared with diabetic male patients.

CONCLUSION

Endothelial dysfunction was present in adolescent male diabetic subjects as measured using RH-PAT. Considering that endothelial dysfunction is reversible, early detection of this process may have therapeutic and prognostic implications in this young age group.

SEX HORMONES AND THE CARDIOVASCULAR SYSTEM: EFFECTS ON ARTERIAL FUNCTION IN WOMEN

1. It has long been hypothesized that oestrogen may be cardioprotective. This hypothesis is supported by diverse and comprehensive mechanistic studies in animals and humans. Consistently, in observational studies, oestrogen use in post-menopausal women significantly reduced cardiovascular disease. Contrastingly, large interventional trials focusing on chronic disease prevention in older post-menopausal women have suggested neutral (oestrogen alone) or adverse (combined oestrogen/progestin preparations) cardiovascular effects. 2. The negative initial interpretation and extrapolation of the early randomized, controlled interventional trials, primarily the Women's Health Initiative, has recently been theoretically reconciled with the positive mechanistic and observational studies. As a new interventional literature emerges, it has been suggested that if oestrogen is used from menopause onwards it is likely to be protective, but if instituted after endothelial damage has occurred in an oestrogen-deficient post-menopausal state, the beneficial vessel wall effects are not observed and the procoagulant effects result in overall increased cardiovascular risk. 3. The present article reviews the literature on arterial function and oestrogen use in the setting of the early endothelial protection theory. This theory is generally supported by the data on oestrogen effects on arterial function. In general, in studies of premenopausal women the effects of oestrogen were positive, with similar benefits noted if oestrogen was used early after menopause. However, where hormone therapy was commenced some years after menopause, the beneficial effects on arterial function were not observed. In clinical practice, hormone therapy is primarily used at menopause for the treatment of menopausal symptoms. The data on arterial function reviewed herein, along with emerging interventional human studies, suggest that the cardiovascular effects of this practice are not adverse.

Effects of intranasal versus oral hormone therapy on asymmetric dimethylarginine in healthy postmenopausal women: a randomized study

OBJECTIVE

Oral estrogens reduce asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, and an independent risk factor for cardiovascular disease. This study was conducted to compare the effect on ADMA between intranasal and oral 17beta-estradiol (E2) combined with norethisterone (acetate) (NET(A)) administration in postmenopausal women.

METHODS

In a two-center, randomized, double-blind, comparative study 90 healthy postmenopausal women (age 56.6+/-4.7 years) received daily continuous combined intranasal E2/NET 175 microg/275 microg (n=47) or oral E2/NETA 1 mg/0.5 mg (n=43) for one year. At baseline, week 12 and 52, plasma concentrations of ADMA, arginine and symmetric dimethylarginine (SDMA) were measured by high-performance liquid chromatography.

RESULTS

Oral E2/NETA reduced ADMA concentrations (-7.4%; 95% confidence interval (CI) -10.4 to -4.4%), while intranasal E2/NET had no effect (-0.8%; 95% CI -3.7 to 2.1%) after 52 weeks. In both groups, arginine was transiently decreased compared to baseline at week 12 (intranasal: -6.1%; 95% CI -9.1 to -3.0%; oral: -6.5%; 95% CI -10.9 to -2.1%). Only oral E2/NETA reduced SDMA concentrations.

CONCLUSIONS

Oral administration of E2/NETA reduced ADMA and SDMA concentrations, whereas intranasal administration did not. Both treatments transiently reduced arginine. The decrease in ADMA by oral estrogens could be a key phenomenon in the modulation of nitric oxide synthesis by postmenopausal hormone therapy.

Plasma markers of NO synthase activity in women after ovarian hyperstimulation: influence of estradiol on ADMA

The beneficial effects of estrogen on vasculature are partially explained by an estrogen-induced increase in nitric oxide (NO) synthesis. Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of NO synthase. In the present study, the effect of 17beta-estradiol (E2) on ADMA and NO synthesis was investigated both in vivo and in vitro. Plasma NO and ADMA levels were measured in healthy women at a low menstrual estrogenic stage (E2 < 100 pg/ml) and in women who were undergoing ovarian hyperstimulation (E2 > 2000 pg/ml) before in vitro fertilization embryo transfer. Primary human umbilical vein endothelial cell (HUVEC) cultures were incubated with and without 100 nM E2 for 24 hours and the NO and ADMA levels of the media were measured. A nitric oxide analyzer was used for the detection of NO metabolites. ADMA and L-arginine were measured by high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde. The IVF patients with high plasma E2 concentrations had significantly lower (48%, n = 12) plasma ADMA and higher (56%, n = 14) NO levels than the women at a low estrogenic stage. The incubation of HUVEC cultures with estradiol resulted in a significant decrease (47%, n = 10) in ADMA and an increase (46%, n = 10) in NO concentration in the culture media. Estradiol, by reducing ADMA, may therefore facilitate NO synthesis in endothelial cells. The protective effects of estradiol on vasculature may partly be related to a reduction in ADMA levels.

ADMA metabolism and clearance

The plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is the resultant of many processes at cellular and organ levels. Post-translational methylation of arginine residues of proteins plays a crucial role in the regulation of their functions, which include processes such as transcription, translation and RNA splicing. Because protein methylation is irreversible, the methylation signal can be turned off only by proteolysis of the entire protein. Consequently, most methylated proteins have high turnover rates. Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH). Some ADMA escapes degradation and leaves the cell via cationic amino acid transporters. These transporters also mediate uptake of ADMA by neighboring cells or distant organs, thereby facilitating active interorgan transport. Clearance of ADMA from the plasma occurs in small part by urinary excretion, but the bulk of ADMA is degraded by intracellular DDAH, after uptake from the circulation. This review discusses the various processes involved in ADMA metabolism: protein methylation, proteolysis of methylated proteins, metabolism by DDAH, and interorgan transport. In addition, the role of the kidney and the liver in the clearance of ADMA is highlighted.

Is the estrogen controversy over? Deconstructing the Women's Health Initiative study: a critical evaluation of the evidence

The Women's Health Initiative (WHI) hormone trials have been widely interpreted as demonstrating that combined menopausal hormone therapy (HT) fails to protect against-and may increase-cardiovascular disease (CVD), stroke, and dementia in menopausal women, regardless of whether initiated early in the menopause or later. This conclusion does not agree with results of large epidemiological studies showing protection by HT and by estrogen replacement alone (ET) against CVD and dementia. One possible reason for this inconsistency is that the epidemiologic data are confounded by "healthy user bias." Another possible explanation is that most women in the observational studies initiated ET or HT at or near the menopausal transition, at which point there is little or no arterial injury, whereas, in the WHI studies, older women, averaging approximately 12 years postmenopausal, many of whom would have had significant asymptomatic atherosclerosis, were treated. Substantial data demonstrate atheropreventive effects of estrogen before vascular damage occurs, whereas adverse effects of oral estrogen on thrombosis and inflammation may predominate once complex atheromas are present. Similarly, the excess of dementia observed in older WHI women treated with oral conjugated estrogen could be due to cerebral thromboses (multi-infarct dementia). Given the uncertain relevance of the WHI (and other published randomized clinical trials) to initiation of HT in perimenopausal women, and its subsequent continuation for atheroprevention, new trials will be needed to resolve whether early intervention with estrogen may prevent CVD and/or dementia. The Kronos Early Estrogen Prevention Study (KEEPS), which began in mid-2005, is a randomized, controlled multicenter trial of HT in recently menopausal women. It will examine surrogate end points as well as risk factors for atherosclerosis.

Oral, more than transdermal, oestrogen therapy lowers asymmetric dimethylarginine in healthy postmenopausal women: a randomized, placebo-controlled study

OBJECTIVE

To compare the effects of oral and transdermal hormone therapy (HT) on asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in postmenopausal women.

DESIGN

In a multicentre, placebo-controlled, double-blind study, 152 hysterectomized healthy women were randomized to receive daily transdermal 17beta-oestradiol (tE2, n = 33), or oral micronized 17beta-oestradiol either unopposed (oE2, n = 37), or continuous combined with gestodene (oE2 + G, n = 33), or placebo (n = 49) for 13, 28-day treatment cycles. Plasma concentrations of ADMA, arginine and symmetric dimethylarginine (SDMA) were measured at baseline and in treatment cycles 4 and 13 with a high-performance liquid chromatography method.

RESULTS

After 13 cycles all active treatment groups showed a significant reduction in ADMA compared with placebo: tE2, -4.0% (95% CI: -7.5 to -0.6%); oE2, -7.7% (95% CI: -10.9 to -4.4%) and oE2 + G, -7.5% (95% CI: -10.8 to -4.3%). ancova showed a significantly larger reduction in the oral groups compared with the transdermal group (tE2 vs. oE2 and tE2 vs. oE2 + G, both P < 0.01). Oral, but not transdermal treatment, significantly reduced arginine compared with placebo. All active treatments reduced SDMA; however, this was only statistically significant in the oE2 group.

CONCLUSION

Reduction of ADMA was more pronounced after oral than after tE2 administration. Adding gestodene to oral 17beta-oestradiol did not alter the reduction of ADMA. The clinical implications of these findings remain uncertain; however, the decrease of ADMA by 17beta-oestradiol could be a key phenomenon in the modulation of nitric oxide synthesis by postmenopausal HT.