Estrogen therapy replenishes vascular tetrahydrobiopterin and reduces oxidative stress in ovariectomized rats

Novel Role of 5-Methyl-(6S)-Tetrahydrofolate in Mediating Endothelial Cell Tetrahydrobiopterin in Pregnancy and Implications for Gestational Hypertension

BACKGROUND

Folate intake during pregnancy is essential for fetal development and maternal health. However, the specific effects of folic acid (FA) and 5-methyl-(6S)-tetrahydrofolate (5-MTHF) on the prevention and treatment of hypertensive disorders of pregnancy remain unclear. We investigated whether FA and 5-MTHF have different effects on endothelial cell tetrahydrobiopterin (BH4) metabolism in pregnancy and the possible consequences for endothelial NO generation, maternal blood pressure, and fetal growth.

METHODS

We analyzed the maternal blood pressure in pregnant wild-type (Gch1fl/fl) and Gch1fl/fl Tie2cre mice treated with either FA or 5-MTHF starting before pregnancy, mid-pregnancy or late pregnancy. BH4, superoxide, and NO bioavailability were determined in mouse and human models of endothelial cell BH4 deficiency by high-performance liquid chromatography.

RESULTS

In vitro studies in mouse and human endothelial cells showed that treatment with 5-MTHF, but not FA, elevated BH4 levels, reduced superoxide production, and increased NO synthase activity. In primary endothelial cells isolated from women with hypertensive pregnancies, exposure to 5-MTHF, but not FA, restored the reduction in BH4 levels and NO synthase activity. In vivo studies in mice revealed that oral treatment with 5-MTHF, but not FA, prevented and treated hypertension in pregnancy when administered either before or during pregnancy, respectively, and normalized placental and fetal growth restriction if administered from mid-gestation onward.

CONCLUSIONS

Collectively, these studies identify a critical role for 5-MTHF in endothelial cell function in pregnancy, related to endothelial cell BH4 availability and NO synthase activity. Thus, 5-MTHF represents a novel therapeutic agent that may potentially improve endothelial function in hypertensive disorders of pregnancy by targeting endothelial cell BH4.

Effects of dietary soy content on cerebral artery function and behavior in ovariectomized female mice

As females age, they transition through menopause, experiencing a decrease in estrogen and an increase in cardiovascular and neurodegenerative disease risk. Most standard rodent chows contain phytoestrogen-rich soybean meal, which can mimic the effects of estrogen. Understanding the impact of this soybean meal on vascular outcomes is crucial to proper experimental design. Thus, this study aimed to compare the effects of standard and soy-free chows on cerebral artery endothelial function and cognitive function in ovariectomized mice. Young female C57Bl/6J mice (n = 43; ∼6 mo) were randomly assigned to three groups: sham, ovariectomy (OVX), or ovariectomy on a diet containing soy (OVX + Soy). In posterior cerebral arteries, the OVX mice had a 27% lower maximal response to insulin compared with the sham mice. The OVX + Soy mice had a 27% greater maximal vasodilation to insulin compared with the OVX mice and there were no differences in vasodilation between the OVX + Soy and sham groups. The group differences in vasodilation were mediated by differences in nitric oxide bioavailability. The OVX + Soy mice also had greater insulin receptor gene expression in cerebral arteries compared with the OVX mice. However, no differences in aortic or cerebral artery stiffness were observed between groups. Interestingly, the OVX + Soy group scored better on nesting behavior compared with both sham and OVX groups. In summary, we found that ovariectomy impairs insulin-mediated vasodilation in cerebral arteries, but a diet containing soy mitigates these effects. These findings highlight the importance of considering dietary soy when performing vascular and behavioral tests in mice, particularly in females.NEW & NOTEWORTHY To properly design experiments, we must consider how variables like diet impact our outcomes, particularly the effects of soy on females. We found that cerebral artery vasodilation in response to insulin was impaired in ovariectomized female mice compared with intact shams. However, ovariectomized mice fed a soy diet had a preserved cerebral artery insulin-mediated vasodilation. These results highlight that the effects of diet on vascular function may explain inconsistencies found between studies.

Estrogen and the Vascular Endothelium: The Unanswered Questions

Premenopausal women have a lower incidence of cardiovascular disease (CVD) compared with their age-matched male counterparts; however, this discrepancy is abolished following the transition to menopause or during low estrogen states. This, combined with a large amount of basic and preclinical data indicating that estrogen is vasculoprotective, supports the concept that hormone therapy could improve cardiovascular health. However, clinical outcomes in individuals undergoing estrogen treatment have been highly variable, challenging the current paradigm regarding the role of estrogen in the fight against heart disease. Increased risk for CVD correlates with long-term oral contraceptive use, hormone replacement therapy in older, postmenopausal cisgender females, and gender affirmation treatment for transgender females. Vascular endothelial dysfunction serves as a nidus for the development of many cardiovascular diseases and is highly predictive of future CVD risk. Despite preclinical studies indicating that estrogen promotes a quiescent, functional endothelium, it still remains unclear why these observations do not translate to improved CVD outcomes. The goal of this review is to explore our current understanding of the effect of estrogen on the vasculature, with a focus on endothelial health. Following a discussion regarding the influence of estrogen on large and small artery function, critical knowledge gaps are identified. Finally, novel mechanisms and hypotheses are presented that may explain the lack of cardiovascular benefit in unique patient populations.

Role of BH4 deficiency as a mediator of oxidative stress-related endothelial dysfunction in menopausal women

Endothelial function (brachial artery flow-mediated dilation [FMD]) is reduced in estrogen-deficient postmenopausal women, mediated, in part, by reduced nitric oxide (NO) bioavailability, secondary to tetrahydrobiopterin (BH4) deficiency and oxidative stress. FMD is increased, but not fully restored, in postmenopausal women after acute intravenous vitamin C (VITC; superoxide scavenger) or oral BH4 supplementation. In vitro studies demonstrate that coadministration of VITC with BH4 prevents endothelial nitric oxide synthase (eNOS) uncoupling and reductions in NO by peroxynitrite. To investigate mechanisms of endothelial dysfunction in women, we assessed the separate and combined effects of VITC and BH4 to determine whether coadministration of VITC + BH4 improves FMD in healthy postmenopausal women (n = 19, 58 ± 5 yr) to premenopausal (n = 14, 36 ± 9 yr) levels, with exploratory testing in perimenopausal women (n = 8, 51 ± 3 yr). FMD was measured during acute intravenous infusions of saline (control) and VITC (∼2-3 g) ∼3 h after a single dose of oral BH4 (KUVAN, 10 mg/kg body wt) or placebo (randomized crossover, separated by ∼1 mo). Under the placebo condition, FMD was reduced in postmenopausal compared with premenopausal women during the saline infusion (5.6 ± 0.7 vs. 11.6 ± 0.9%, P < 0.001) and increased in postmenopausal women during VITC (+3.5 [1.4, 5.6]%, P = 0.001) and acute BH4 (+1.8 [0.37, 3.2]%, P = 0.01) alone. Coadministration of VITC + BH4 increased FMD in postmenopausal women (+3.0 [1.7, 4.3]%, P < 0.001), but FMD remained reduced compared with premenopausal women (P = 0.02). Exploratory analyses revealed that VITC + BH4 did not restore FMD in perimenopausal women to premenopausal levels (P = 0.045). Coadministration of VITC + BH4 does not restore FMD in menopausal women, suggesting that additional mechanisms may be involved.NEW & NOTEWORTHY Endothelial function is reduced across the menopausal stages related to increased oxidative stress associated with estrogen deficiency. In vitro studies demonstrate that coadministration of VITC with BH4 prevents endothelial nitric oxide synthase (eNOS) uncoupling and reductions in NO by peroxynitrite; however, this remains untested in humans. We demonstrate that the coadministration of BH4 + VITC does not restore endothelial function in perimenopausal and postmenopausal women to the level of premenopausal women, suggesting that other mechanisms contribute.

Moving beyond inclusion: Methodological considerations for the menstrual cycle and menopause in research evaluating effects of dietary nitrate on vascular function

Recent reports have acknowledged the underrepresentation of women in the field of dietary nitrate (NO₃^-) research. Undoubtedly, greater participation from women is warranted to clarify potential sex differences in the responses to dietary NO₃^- interventions. However, careful consideration for the effects of sex hormones - principally 17β-estradiol - on endogenous nitric oxide (NO) synthesis and dietary NO₃^- reductase capacity is necessary for improved interpretation and reproducibility of such investigations. From available literature, we present a narrative review describing how hormonal variations across the menstrual cycle, as well as with menopause, may impact NO biosynthesis catalyzed by NO synthase enzymes and NO₃^- reduction via the enterosalivary pathway. In doing so, we address methodological considerations related to the menstrual cycle and hormonal contraceptive use relevant for the inclusion of premenopausal women along with factors to consider when testing postmenopausal women. Adherence to such methodological practices may explicate the utility of dietary NO₃^- supplementation as a means to improve vascular function among women across the lifespan.

Nitric Oxide Regulates Estrus Cycle Dependent Colonic Motility in Mice

Women are more susceptible to functional bowel disorders than men and the severity of their symptoms such as diarrhea, constipation, abdominal pain and bloating changes over the menstrual cycle, suggesting a role for sex hormones in gastrointestinal function. Nitric oxide (NO) is a major inhibitory neurotransmitter in the gut and blockade of nitric oxide synthase (NOS; responsible for NO synthesis) increases colonic motility in male mice ex vivo. We assessed the effects of NOS inhibition on colonic motility in female mice using video imaging analysis of colonic motor complexes (CMCs). To understand interactions between NO and estrogen in the gut, we also quantified neuronal NOS and estrogen receptor alpha (ERα)-expressing myenteric neurons in estrus and proestrus female mice using immunofluorescence. Mice in estrus had fewer CMCs under control conditions (6 ± 1 per 15 min, n = 22) compared to proestrus (8 ± 1 per 15 min, n = 22, One-way ANOVA, p = 0.041). During proestrus, the NOS antagonist N-nitro-L-arginine (NOLA) increased CMC numbers compared to controls (189 ± 46%). In contrast, NOLA had no significant effect on CMC numbers during estrus. During estrus, we observed more NOS-expressing myenteric neurons (48 ± 2%) than during proestrus (39 ± 1%, n = 3, p = 0.035). Increased nuclear expression of ERα was observed in estrus which coincided with an altered motility response to NOLA in contrast with proestrus when ERα was largely cytoplasmic. In conclusion, we confirm a cyclic and sexually dimorphic effect of NOS activity in female mouse colon, which could be due to genomic effects of estrogens via ERα.

The poorly conducted orchestra of steroid hormones, oxidative stress and inflammation in frailty needs a maestro: Regular physical exercise

This review outlines the various factors associated with unhealthy aging which includes becoming frail and dependent. With many people not engaging in recommended exercise, facilitators and barriers to engage with exercise must be investigated to promote exercise uptake and adherence over the lifespan for different demographics, including the old, less affluent, women, and those with different cultural-ethnic backgrounds. Governmental and locally funded public health messages and environmental facilitation (gyms, parks etc.) can play an important role. Studies have shown that exercise can act as a conductor to balance oxidative stress, immune and endocrine functions together to promote healthy aging and reduce the risk for age-related morbidities, such as cardiovascular disease and atherosclerosis, and promote cognition and mood over the lifespan. Like a classic symphony orchestra, consisting of four groups of related musical instruments - the woodwinds, brass, percussion, and strings - the aging process should also perform in harmony, with compassion, avoiding the aggrandizement of any of its individual parts during the presentation. This review discusses the wide variety of molecular, cellular and endocrine mechanisms (focusing on the steroid balance) underlying this process and their interrelationships.

Protective Effects of Estrogen on Cardiovascular Disease Mediated by Oxidative Stress

Perimenopause is an important stage of female senescence. Epidemiological investigation has shown that the incidence of cardiovascular disease in premenopausal women is lower than that in men, and the incidence of cardiovascular disease in postmenopausal women is significantly higher than that in men. This phenomenon reveals that estrogen has a definite protective effect on the cardiovascular system. In the cardiovascular system, oxidative stress is considered important in the pathogenesis of atherosclerosis, myocardial dysfunction, cardiac hypertrophy, heart failure, and myocardial ischemia. From the perspective of oxidative stress, estrogen plays a regulatory role in the cardiovascular system through the estrogen receptor, providing strategies for the treatment of menopausal women with cardiovascular diseases.

Decline in endothelial function across the menopause transition in healthy women is related to decreased estradiol and increased oxidative stress

Endothelial function declines progressively across stages of the menopause transition; however, the mechanisms contributing to this decline are unknown. We hypothesized that differences in endothelial function among pre-, peri, and postmenopausal women are related to differences in estradiol and oxidative stress. Brachial artery flow-mediated dilation (FMD) was measured in 87 healthy women categorized by menopause stage (24 premenopausal, 17 early and 21 late perimenopausal, and 25 postmenopausal) before and after 3 days of ovarian hormone suppression (gonadotropin releasing hormone antagonist [GnRHant]) alone, and an additional 3 days of GnRHant with concurrent transdermal estradiol or placebo add-back treatment. In 82 women, FMD during acute vitamin C (antioxidant) infusion was measured before and after GnRHant + add-back. Before GnRHant, FMD was different among groups (p < 0.005; reduced across stages of menopause). Vitamin C increased FMD in late peri- and post- (p < 0.005) but not pre- or early perimenopausal women (p > 0.54). After GnRHant alone, FMD decreased in pre- and peri- (p < 0.01), but not postmenopausal women, and was restored to premenopausal levels by estradiol add-back in the pre- and perimenopausal groups. Vitamin C improved FMD in pre-, peri-, and postmenopausal women on GnRHant + placebo. There was no effect of vitamin C on FMD in women on GnRHant + estradiol. These observations support the concept that the decline in endothelial function across the menopause transition is related to the loss of ovarian estradiol. The decline in estradiol may alter redox balance, thereby increasing oxidative stress and impairing endothelial function.

Is Cardiac Diastolic Dysfunction a Part of Post-Menopausal Syndrome?

Post-menopausal women exhibit an exponential increase in the incidence of heart failure with preserved ejection fraction compared with men of the same age, which indicates a potential role of hormonal changes in subclinical and clinical diastolic dysfunction. This paper reviews the preclinical evidence that demonstrates the involvement of estrogen in many regulatory molecular pathways of cardiac diastolic function and the clinical data that investigates the effect of estrogen on diastolic function in post-menopausal women. Published reports show that estrogen deficiency influences both early diastolic relaxation via calcium homeostasis and the late diastolic compliance associated with cardiac hypertrophy and fibrosis. Because of the high risk of diastolic dysfunction and heart failure with preserved ejection fraction in post-menopausal women and the positive effects of estrogen on preserving cardiac function, further clinical studies are needed to clarify the role of endogenous estrogen or hormone replacement in mitigating the onset and progression of heart failure with preserved ejection fraction in women.

Modulatory influence of sex hormones on vascular aging

This review summarizes a presentation given during the "Countermeasures to Cardiovascular Aging Symposium" that was part of the American Physiological Society Conference on Cardiovascular Aging: New Frontiers and Old Friends held in Westminster, CO, in August 2017. Endothelial dysfunction, a characteristic of vascular aging, is a major risk factor for age-associated cardiovascular diseases. In women, the decline in endothelial function is attenuated until menopause, whereafter the rate of decline accelerates to match that seen in men. Sex differences in the decline in endothelial function have been attributed to changes in sex hormones with aging. Women have a progressive impairment in endothelial function across the stages of the menopause transition, related in part to declining estradiol levels. In contrast to women, little is known about the impact of declining testosterone levels on endothelial function in men. Some evidence suggests greater endothelial dysfunction in men with low testosterone compared with men with higher testosterone. The underlying causes of endothelial dysfunction with sex hormone deficiency are unknown but may be related to endothelial nitric oxide synthase dysfunction and oxidative stress. Lifestyle behaviors, including habitual endurance exercise, attenuates and reverses the age-associated decline in endothelial function in older men. However, in older women, these exercise adaptations are diminished or absent, possibly related to estrogen deficiency. Understanding how declines in sex hormones contribute to the vascular aging process in both women and men will inform effective sex-specific intervention strategies to preserve vascular health and prevent cardiovascular diseases.

Role of glutathione biosynthesis in endothelial dysfunction and fibrosis

Glutathione (GSH) biosynthesis is essential for cellular redox homeostasis and antioxidant defense. The rate-limiting step requires glutamate-cysteine ligase (GCL), which is composed of the catalytic (GCLc) and the modulatory (GCLm) subunits. To evaluate the contribution of GCLc to endothelial function we generated an endothelial-specific Gclc haplo-insufficient mouse model (Gclc e/+ mice). In murine lung endothelial cells (MLEC) derived from these mice we observed a 50% reduction in GCLc levels compared to lung fibroblasts from the same mice. MLEC obtained from haplo-insufficient mice showed significant reduction in GSH levels as well as increased basal and stimulated ROS levels, reduced phosphorylation of eNOS (Ser 1177) and increased eNOS S-glutathionylation, compared to MLEC from wild type (WT) mice. Studies in mesenteric arteries demonstrated impaired endothelium-dependent vasodilation in Gclc(e/+) male mice, which was corrected by pre-incubation with GSH-ethyl-ester and BH4. To study the contribution of endothelial GSH synthesis to renal fibrosis we employed the unilateral ureteral obstruction model in WT and Gclc(e/+) mice. We observed that obstructed kidneys from Gclc(e/+) mice exhibited increased deposition of fibrotic markers and reduced Nrf2 levels. We conclude that the preservation of endothelial GSH biosynthesis is not only critical for endothelial function but also in anti-fibrotic responses.

Sex differences in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a vascular disorder with a high case fatality rate in the instance of rupture. AAA is a multifactorial disease, and the etiology is still not fully understood. AAA is more likely to occur in men, but women have a greater risk of rupture and worse prognosis. Women are reportedly protected against AAA possibly by premenopausal levels of estrogen and are, on average, diagnosed at older ages than men. Here, we review the present body of research on AAA pathophysiology in humans, animal models, and cultured cells, with an emphasis on sex differences and sex steroid hormone signaling.

Endothelial dysfunction occurs independently of adipose tissue inflammation and insulin resistance in ovariectomized Yucatan miniature-swine

In rodents, experimentally-induced ovarian hormone deficiency increases adiposity and adipose tissue (AT) inflammation, which is thought to contribute to insulin resistance and increased cardiovascular disease risk. However, whether this occurs in a translationally-relevant large animal model remains unknown. Herein, we tested the hypothesis that ovariectomy would promote visceral and perivascular AT (PVAT) inflammation, as well as subsequent insulin resistance and peripheral vascular dysfunction in female swine. At sexual maturity (7 months of age), female Yucatan mini-swine either remained intact (control, n = 9) or were ovariectomized (OVX, n = 7). All pigs were fed standard chow (15-20 g/kg), and were euthanized 6 months post-surgery. Uterine mass and plasma estradiol levels were decreased by ∼10-fold and 2-fold, respectively, in OVX compared to control pigs. Body mass, glucose homeostasis, and markers of insulin resistance were not different between control and OVX pigs; however, OVX animals exhibited greater plasma triglycerides and triglyceride:HDL ratio. Ovariectomy enhanced visceral adipocyte expansion, although this was not accompanied by brachial artery PVAT adipocyte expansion, AT inflammation in either depot, or increased systemic inflammation assessed by plasma C-reactive protein concentrations. Despite the lack of AT inflammation and insulin resistance, OVX pigs exhibited depressed brachial artery endothelial-dependent vasorelaxation, which was rescued with blockade of endothelin receptor A. Together, these findings indicate that in female Yucatan mini-swine, increased AT inflammation and insulin resistance are not required for loss of ovarian hormones to induce endothelial dysfunction.

BH4 improves postprandial endothelial function after a high-fat meal in men and postmenopausal women

OBJECTIVE

The timing and duration of menopause is important when evaluating the risk for cardiovascular disease in postmenopausal women, likely related in part to nitric oxide (NO) bioavailability. The flow-mediated dilation (FMD) test is a noninvasive assessment of NO bioavailability in humans, and tetrahydrobiopterin (BH4) is essential for NO synthesis. A high-fat meal (HFM) has been used to increase lipemia and reduce NO bioavailability. Thus, this study sought to determine if menopausal transition has any impact on the postprandial endothelial function response to a HFM, and evaluate the effect of BH4 on postprandial endothelial function in postmenopausal women and men.

METHODS

Utilizing a randomized, double-blind, placebo-controlled design, sex-steroid hormones and FMD were determined in 30 older adults (10 postmenopausal women aged below 3 y [W < 3], 10 postmenopausal women aged above 10 y [W > 10], and 10 men) at baseline and 4 hours after the ingestion of a HFM alone or a HFM with BH4 (HFM + BH4; 5 mg/kg).

RESULTS

Data are presented as mean ± SEM. Independent of treatment, postprandial testosterone was significantly (P < 0.05) decreased in men (-64 ± 11 ng/dL), whereas no changes were observed in W < 3 or W > 10 group. In addition, concentrations of progesterone were higher (P = 0.019) and the testosterone/estradiol ratio was lower (P = 0.026) in all groups after the ingestion of HFM + BH4 compared with the ingestion of HFM alone. Overall, an increase in FMD was observed after the ingestion of HFM + BH4 (Δ1.9% ± 0.6%), whereas no change in FMD was observed after the ingestion of HFM alone (Δ-0.7% ± 0.6%).

CONCLUSIONS

Co-ingestion of BH4 with a HFM not only alters the sex-steroid hormone ratio, it improves postprandial FMD after a HFM regardless of postmenopause status or sex.

Diabetes and menopause aggravate age-dependent deterioration in arterial stiffness

OBJECTIVE

The present study was designed to evaluate the effects of menopause status and diabetes on arterial stiffness, metabolic parameters, and inflammatory parameters in premenopausal and postmenopausal women with and without type 2 diabetes mellitus.

METHODS

In the present study, 186 women were divided into three groups: group 1 includes 42 premenopausal women without type 2 diabetes mellitus, group 2 includes 85 postmenopausal women without diabetes, and group 3 includes 59 postmenopausal women with diabetes. Blood glucose, hemoglobin A1c, insulin, lipids, C-reactive protein, homeostasis model assessment-insulin resistance, aldosterone, and renin were measured. Pulse wave velocity (PWV) and augmentation index (AI) were determined using SphygmoCor (version 7.1; AtCor Medical, Sydney, Australia).

RESULTS

PWV and AI values increased from group 1 to group 3 in a continuous fashion. Postmenopausal women with and without diabetes exhibited significantly increased AI compared with premenopausal women without diabetes (P < 0.0001 and P < 0.0001, respectively). PWV was significantly higher in postmenopausal women with diabetes mellitus than in premenopausal and postmenopausal women without diabetes mellitus (P = 0.007 and P = 0.002, respectively).

CONCLUSIONS

Postmenopausal women without diabetes have significantly higher AI compared with premenopausal women without type 2 diabetes mellitus. The combination of diabetes and postmenopause status is associated with further deterioration of AI and PWV independently of age, body mass index, and other cardiovascular risk factors.

Sex-based differential regulation of oxidative stress in the vasculature by nitric oxide

Background

Nitric oxide (^•NO) is more effective at inhibiting neointimal hyperplasia following arterial injury in male versus female rodents, though the etiology is unclear. Given that superoxide (O₂^•−) regulates cellular proliferation, and ^•NO regulates superoxide dismutase-1 (SOD-1) in the vasculature, we hypothesized that ^•NO differentially regulates SOD-1 based on sex.

Materials and methods

Male and female vascular smooth muscle cells (VSMC) were harvested from the aortae of Sprague-Dawley rats. O₂^•− levels were quantified by electron paramagnetic resonance (EPR) and HPLC. sod-1 gene expression was assayed by qPCR. SOD-1, SOD-2, and catalase protein levels were detected by Western blot. SOD-1 activity was measured via colorimetric assay. The rat carotid artery injury model was performed on Sprague-Dawley rats ±^•NO treatment and SOD-1 protein levels were examined by Western blot.

Results

In vitro, male VSMC have higher O₂^•− levels and lower SOD − 1 activity at baseline compared to female VSMC (P < 0.05). ^•NO decreased O₂^•− levels and increased SOD − 1 activity in male (P<0.05) but not female VSMC. ^•NO also increased sod− 1 gene expression and SOD − 1 protein levels in male (P<0.05) but not female VSMC. In vivo, SOD-1 levels were 3.7-fold higher in female versus male carotid arteries at baseline. After injury, SOD-1 levels decreased in both sexes, but ^•NO increased SOD-1 levels 3-fold above controls in males, but returned to baseline in females.

Conclusions

Our results provide evidence that regulation of the redox environment at baseline and following exposure to ^•NO is sex-dependent in the vasculature. These data suggest that sex-based differential redox regulation may be one mechanism by which ^•NO is more effective at inhibiting neointimal hyperplasia in male versus female rodents.

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The baseline redox environment in the vascular is sex-dependent.

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Nitric oxide differentially affects the vascular redox environment between the sexes.

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Nitric oxide decreases superoxide (O₂^.) levels, by increasing SOD-1 activity, sod1 gene expression and SOD-1 protein levels in male vascular smooth muscle cells, but not in females.

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Sex-based differential redox regulation may be one mechanism by which is more effective at inhibiting neointimal hyperplasia in male versus female rodents.

Vascular Aging across the Menopause Transition in Healthy Women

Vascular aging, featuring endothelial dysfunction and large artery stiffening, is a major risk factor for developing cardiovascular disease (CVD). In women, vascular aging appears to be accelerated during the menopause transition, particularly around the late perimenopausal period, presumably related to declines in ovarian function and estrogen levels. The mechanisms underlying endothelial dysfunction and large artery stiffening with the menopause transition are not completely understood. Oxidative stress and the proinflammatory cytokine tumor necrosis factor-α contribute to endothelial dysfunction and large artery stiffening in estrogen-deficient postmenopausal women. Habitual endurance exercise attenuates the age-related increase in large artery stiffness in estrogen-deficient postmenopausal women and can reverse arterial stiffening to premenopausal levels in estrogen-replete postmenopausal women. In contrast, estrogen status appears to play a key permissive role in the adaptive response of the endothelium to habitual endurance exercise in that endothelial improvements are absent in estrogen-deficient women but present in estrogen-replete women. We review here the current state of knowledge on the biological defects underlying vascular aging across the menopause transition, with particular focus on potential mechanisms, the role of habitual exercise in preserving vascular health, and key areas for future research.

Efficacy of a low dose of estrogen on antioxidant defenses and heart rate variability

This study tested whether a low dose (40% less than the pharmacological dose of 17-β estradiol) would be as effective as the pharmacological dose to improve cardiovascular parameters and decrease cardiac oxidative stress. Female Wistar rats (n = 9/group) were divided in three groups: (1) ovariectomized (Ovx), (2) ovariectomized animals treated for 21 days with low dose (LE; 0.2 mg), and (3) high dose (HE; 0.5 mg) 17-β estradiol subcutaneously. Hemodynamic assessment and spectral analysis for evaluation of autonomic nervous system regulation were performed. Myocardial superoxide dismutase (SOD) and catalase (CAT) activities, redox ratio (GSH/GSSG), total radical-trapping antioxidant potential (TRAP), hydrogen peroxide, and superoxide anion concentrations were measured. HE and LE groups exhibited an improvement in hemodynamic function and heart rate variability. These changes were associated with an increase in the TRAP, GSH/GSSG, SOD, and CAT. A decrease in hydrogen peroxide and superoxide anion was also observed in the treated estrogen groups as compared to the Ovx group. Our results indicate that a low dose of estrogen is just as effective as a high dose into promoting cardiovascular function and reducing oxidative stress, thereby supporting the approach of using low dose of estrogen in clinical settings to minimize the risks associated with estrogen therapy.

Endothelial dysfunction and enhanced contractility in microvessels from ovariectomized rats: roles of oxidative stress and perivascular adipose tissue

Ovarian hormone loss increases reactive oxidative species, endothelial dysfunction, and cardiovascular disease. Because perivascular adipose tissue (PVAT) regulates endothelial function, we hypothesized that reactive oxidative species in PVAT mediate adverse microvascular effects of ovarian hormone deficiency. Rats were ovariectomized or sham operated and given vehicle or tempol for 6 weeks. Mesenteric resistance arterioles from ovariectomized compared with sham-operated rats had dysfunctional responses to acetylcholine (ACh) including decreased ACh-induced endothelium-dependent relaxation (50±6% versus 72±2%) and endothelium-dependent relaxation factor (17±4% versus 37±2%) and increased endothelium-dependent contracting factor (27±5% versus 9±3%). OVX rat mesenteric arterioles had increased contractions to the thromboxane/prostanoid receptor agonist U-46 619 (58±3% versus 40±5%) and increased reactive oxidative species (tempo-9-AC fluorescence) with U-46 619 (0.65±0.17 versus 0.14±0.06 Δ unit) or ACh (0.49±0.09 versus 0.09±0.05 Δ unit) and increased p22(phox) protein expression (0.89±0.05 versus 0.18±0.04 Δ unit), whereas nitric oxide activity (DAF-FM [4-amino-5-methylamino-2',7'-difluorofluorescein diacetate] fluorescence) with ACh was reduced (0.39±0.1 versus 0.70±0.10 Δ unit). No differences were found in endothelium-dependent hyperpolarizing factor or contractile responses to phenylephrine. PVAT enhanced ACh-induced relaxation, endothelium-dependent relaxation factor, and nitric oxide only in sham-operated rats. Tempol prevented ovariectomy-induced endothelial dysfunction and restored the enhancing effects of PVAT on ACh-induced relaxation, endothelium-dependent relaxation factor, and nitric oxide in ovariectomized rat vessels, but both tempol and PVAT were required to normalize the enhanced U-46 619 contractions after ovariectomy. In conclusion, ovariectomy redirects endothelial responses from relaxation to contraction by reducing vascular nitric oxide, augmenting thromboxane/prostanoid receptor signaling, and attenuating the vasodilatory effects of PVAT, all of which were dependent on reactive oxidative species.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

Endothelial relaxation mechanisms and oxidative stress are restored by atorvastatin therapy in ovariectomized rats

The studies on hormone replacement therapy (HRT) in females with estrogen deficiency are not conclusive. Thus, non-estrogen therapies, such as atorvastatin (ATO), could be new strategies to substitute or complement HRT. This study evaluated the effects of ATO on mesenteric vascular bed (MVB) function from ovariectomized (OVX) female rats. Female rats were divided into control SHAM, OVX, and OVX treated with 17β-estradiol (EST) or ATO groups. The MVB reactivity was determined in organ chambers, vascular oxidative stress by dihydroethidine staining, and the expression of target proteins by western blot. The reduction in acetylcholine-induced relaxation in OVX rats was restored by ATO or EST treatment. The endothelium-dependent nitric oxide (NO) component was reduced in OVX rats, whereas the endothelium-derived hyperpolarizing factor (EDHF) component or prostanoids were not altered in the MVBs. Endothelial dysfunction in OVX rats was associated with oxidative stress, an up-regulation of iNOS and NADPH oxidase expression and a down-regulation of eNOS expression. Treatment with ATO or EST improved the NO component of the relaxation and normalized oxidative stress and the expression of those signaling pathways enzymes. Thus, the protective effect of ATO on endothelial dysfunction caused by estrogen deficiency highlights a significant therapeutic benefit for statins independent of its effects on cholesterol, thus providing evidence that non-estrogen therapy could be used for cardiovascular benefit in an estrogen-deficient state, such as menopause.

Characterization of the cardiac renin angiotensin system in oophorectomized and estrogen-replete mRen2.Lewis rats

The cardioprotective effects of estrogen are well recognized, but the mechanisms remain poorly understood. Accumulating evidence suggests that the local cardiac renin-angiotensin system (RAS) is involved in the development and progression of cardiac hypertrophy, remodeling, and heart failure. Estrogen attenuates the effects of an activated circulating RAS; however, its role in regulating the cardiac RAS is unclear. Bilateral oophorectomy (OVX; n = 17) or sham-operation (Sham; n = 13) was performed in 4-week-old, female mRen2.Lewis rats. At 11 weeks of age, the rats were randomized and received either 17 β-estradiol (E2, 36 µg/pellet, 60-day release, n = 8) or vehicle (OVX-V, n = 9) for 4 weeks. The rats were sacrificed, and blood and hearts were used to determine protein and/or gene expression of circulating and tissue RAS components. E2 treatment minimized the rise in circulating angiotensin (Ang) II and aldosterone produced by loss of ovarian estrogens. Chronic E2 also attenuated OVX-associated increases in cardiac Ang II, Ang-(1–7) content, chymase gene expression, and mast cell number. Neither OVX nor OVX+E2 altered cardiac expression or activity of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and Ang II type 1 receptor (AT1R). E2 treatment in OVX rats significantly decreased gene expression of MMP-9, ACE2, and Ang-(1–7) mas receptor, in comparison to sham-operated and OVX littermates. E2 treatment appears to inhibit upsurges in cardiac Ang II expression in the OVX-mRen2 rat, possibly by reducing chymase-dependent Ang II formation. Further studies are warranted to determine whether an E2-mediated reduction in cardiac chymase directly contributes to this response in OVX rats.

Estrogen therapy, independent of timing, improves cardiac structure and function in oophorectomized mRen2.Lewis rats

OBJECTIVE

mRen2.Lewis rats exhibit exacerbated increases in blood pressure, left ventricular (LV) remodeling, and diastolic impairment after the loss of estrogens. In this same model, depletion of estrogens has marked effects on the cardiac biopterin profile concomitant with suppressed nitric oxide release. With respect to the establishment of overt systolic hypertension after oophorectomy (OVX), we assessed the effects of timing long-term 17β-estradiol (E2) therapy on myocardial function, myocardial structure, and the cardiac nitric oxide system.

METHODS

OVX (n = 24) or sham operation (Sham; n = 13) was performed in 4-week-old female mRen2.Lewis rats. After randomization, OVX rats received E2 immediately (OVX + E2-early; n = 7), E2 at 11 weeks of age (OVX + E2-late; n = 8), or no E2 at all (OVX; n = 9).

RESULTS

E2-early was associated with lower body weight, less hypertension-related cardiac remodeling, and decreased LV filling pressure compared with OVX rats without E2 supplementation. E2-late similarly attenuated the adverse effects of ovarian hormone loss on tissue Doppler-derived LV filling pressures and perivascular fibrosis, and significantly improved myocardial relaxation or mitral annular velocity (e'). Early and late exposures to E2 decreased dihydrobiopterin, but only E2-late yielded significant increases in cardiac nitrite concentrations.

CONCLUSIONS

Although there are some similarities between E2-early and E2-late treatments in relation to preservation of diastolic function and cardiac structure after OVX, the lusitropic potential of E2 is most consistent with late supplementation. The cardioprotective effects of E2-late are independent of blood pressure and may have occurred through regulation of cardiac biopterins and nitric oxide production.

Potentiation of vascular oxidative stress and nitric oxide-mediated endothelial dysfunction by high-fat diet in a mouse model of estrogen deficiency and hyperandrogenemia

Estrogen deficiency is associated with increased cardiovascular risk due, in part, to hypertension, endothelial dysfunction, obesity, and hypercholesterolemia. Underlying mechanisms for this remain unclear. Here, we investigated whether high-fat intake aggravates vascular dysfunction through oxidative stress and inflammation, which could predispose to cardiovascular injury in conditions of estrogen deficiency, such as menopause. We studied female homozygous follitropin receptor knock out (FORKO) mice, which have hormonal features of clinical menopause and hypertension and wild-type (WT) and heterozygote mice (HTZ), fed a standard or high-fat diet for 4 months. Vascular function and structure were evaluated in arterial segments by pressurized myography. Acetylcholine (ACh)-induced vasodilation was reduced in FORKO vs. WT mice (P < .001). N(varpi)-nitro-l-arginine-methyl-ester inhibited Ach-induced relaxation in all groups on normal chow and in WT and HTZ on high-fat diet (FD) but had no effect in fat-fed FORKO mice. Antioxidant cocktail (superoxide dismutase, catalase, Tempol) increased ACh responses only in high-fat diet FORKO mice (P < .05). Vascular media-to-lumen ratio was increased and reactive oxygen species (ROS) generation, nitrotyrosine formation, and plasma nitrite levels were augmented in fat-fed FORKO vs. FORKO on normal chow. High-fat diet did not influence vascular inflammatory responses in any group. Our data demonstrate that FORKO mice have altered nitric oxide-sensitive vasorelaxation and vascular remodeling, which are aggravated by high-fat diet. Underlying mechanisms for this may involve decreased NO formation and increased generation of ROS and nitrotyrosine. These findings suggest that high-fat intake potentiates vascular damage in estrogen-deficient states, an effect involving increased oxidative stress.

Altered neuronal nitric oxide synthase in the aging vascular system: implications for estrogens therapy

Ovarian dysfunction at any age is associated with increased cardiovascular risk in women; however, therapeutic effects of exogenous estrogens are age dependent. Estradiol (E2) activates neuronal nitric oxide synthase (nNOS) in vascular cells. Because nNOS is prone to uncoupling under unfavorable biochemical conditions (as seen in aging), E2 stimulation of nNOS may lack vascular benefits in aging. Small mesenteric arteries were isolated from female Sprague Dawley rats, 3 or 12 months old, who were ovariectomized (Ovx) and treated with placebo or E2 for 4 wk. Vascular relaxation to exogenous E2 (0.001-100 μmol/liter) ± selective nNOS inhibitor (N-propyl-l-arginine, 2 μmol/liter) or pan-NOS inhibitor [Nω-nitro-l-arginine methyl ester (l-NAME), 100 μmol/liter] was examined on wire myograph. NOS expression was measured by Western blotting in thoracic aortas, in which superoxide generation was detected as dihydroethidium (DHE) fluorescence. E2 relaxations were impaired in Ovx conditions. E2 treatment (4 wk) normalized vascular function in young rats only. Both l-N-propyl-l-arginine and l-NAME blunted E2 relaxation in young controls, but only l-NAME did so in aging controls. NOS inhibition had no effect on acute E2 relaxation in Ovx rats, regardless of age or treatment. nNOS expression was similar in all animal groups. However, nNOS inhibition increased DHE fluorescence in young controls, whereas it reduced it in aging or Ovx animals. In E2-treated animals of either age, superoxide production was NOS independent. In conclusion, nNOS contributed to vascular relaxation in young, but not aging rats, where its enzymatic function shifted toward superoxide production. Thus, nNOS dysfunction may explain a mechanism of impaired E2 signaling in aging conditions.

Premenopausal women exhibit an inherent protection of endothelial function following a high-fat meal

Endogenous estrogens likely increase blood flow and subsequently shear stress but have also been associated with improved endothelial function and cardiovascular protection. In contrast, a high-fat meal is thought to reduce endothelial function and increase cardiovascular risk. Therefore, we tested the hypotheses that fluctuating hormones across the menstrual cycle (1) facilitate an increase in shear rate and explain phase-specific differences in flow-mediated dilation (FMD) and (2) provide vascular protection against the insult of a high-fat meal. Flow-mediated dilation was determined at baseline and 4 hours following a high-fat meal in young women during the menses (M), follicular (F), and luteal (L) phases of the menstrual cycle. Male control participants were studied once. 17β-Estradiol was elevated (P < .05) during the F (5.3 ± 0.7 pg/mL) and L (5.2 ± 0.6 pg/mL) phases when compared to the M (3.9 ± 0.5 pg/mL) phase, and this was accompanied by an elevated FMD in the F and L phases (12.4 ± 1.4% and 11.2 ± 0.9%, respectively) compared to M (8.0 ± 0.9) with no change in shear rate. Female postprandial FMD was similar throughout the menstrual cycle, while men exhibited a 50% reduction (6.4 ± 1 to 3.3 ± 1%; P < .05). Interestingly, the postprandial FMD response was not associated with concentrations of either 17β-estradiol or progesterone. Despite acutely changing ovarian hormones across the menstrual cycle, shear stress is invariant and therefore does not account for the changes in FMD. Additionally, young women appear to have an inherent vascular protection from the insult of a high-fat meal, perhaps helping to explain sex-specific differences in cardiovascular risk.

Dynamic oxidative stress and DNA damage induced by oestrogen deficiency and protective effects of puerarin and 17β-oestradiol in ovariectomized rats

Oxidative stress plays an essential role in the pathogenesis of cardiovascular diseases and osteoporosis resulting from oestrogen deficiency in the postmenopausal period. In this report, we observed a dynamic change of oxidative stress and DNA damage after ovariectomy in female rats. We then compared phytoestrogen puerarin and 17β-oestradiol (E₂) in their effects on oestrogen deficiency-induced oxidative stress and DNA damage. Serum total antioxidant capacity (TAC), malondialdehyde (MDA) and lymphocytes DNA damage (comet%) were measured. There was a gradual increase in oxidative stress in the ovariectomized (OVX) rats over time after ovariectomy, as compared to rats receiving sham operation. OVX rats that were on puerarin and E₂ showed increased TAC and decreased MDA in the serum, as well as decreased lymphocytes comet%. Puerarin appeared to have a more powerful protective effect on DNA oxidative damage than E₂. The study indicates that postmenopausal women may benefit from phytoestrogen puerarin.

Tetrahydrobiopterin improves endothelial function and decreases arterial stiffness in estrogen-deficient postmenopausal women

The mechanisms mediating arterial stiffening with aging and menopause are not completely understood. We determined whether administration of tetrahydrobiopterin (BH(4)), a critical cofactor for endothelial nitric oxide synthase to produce nitric oxide, would increase vascular endothelial-dependent vasodilatory tone and decrease arterial stiffness in estrogen-deficient postmenopausal women. Additionally, we examined whether the beneficial effects of estrogen on vascular function were possibly related to BH(4). Arterial stiffness (carotid artery compliance) and endothelial-dependent vasodilation [brachial artery flow-mediated dilation (FMD)] were measured in postmenopausal (n = 24; 57 ± 1 yr, mean ± SE) and eumenorrheic premenopausal (n = 9; 33 ± 2 yr) women before and 3 h after the oral administration of BH(4). Subsequently, in postmenopausal women, vascular testing (before and after BH(4)) was repeated following randomization to either 2 days of transdermal estradiol or placebo. Baseline carotid artery compliance and brachial artery FMD were lower in postmenopausal than in premenopausal women (P < 0.0001). BH(4) administration increased carotid artery compliance (0.61 ± 0.05 to 0.73 ± 0.04 mm(2)·mmHg(-1)·10(-1) vs. baseline, P < 0.0001) and brachial artery FMD (P < 0.001) in postmenopausal women but had no effect in premenopausal women (P = 0.62). Carotid artery compliance (0.59 ± 0.05 to 0.78 ± 0.06 mm(2)·mmHg(-1)·10(-1), P < 0.001) and FMD increased in postmenopausal women in response to estradiol (P = 0.02) but were not further improved with the coadministration of BH(4), possibly because estrogen increased BH(4) bioavailability. Carotid artery compliance and FMD increased with BH(4) in the placebo group (P = 0.02). Although speculative, these results suggest that reduced vascular BH(4) may be an important contributor to arterial stiffening in estrogen-deficient postmenopausal women, related in part to reduced endothelial-dependent vasodilatory tone.

Gender bias in gastroparesis: is nitric oxide the answer?

Accumulating evidence suggests that gender-related differences are prominent in gastric motility functions in both health and disease. Women are more susceptible to gastroparesis than men. Though the mechanism(s) involved are not fully understood, impairment of the nitrergic system is one of the main factors responsible for the disease. Uncoupling of neuronal nitric oxide synthase (nNOS) causes a decreased synthesis of NO leading to a reduction in smooth muscle relaxation. Tetrahydrobiopterin (BH(4)) (an essential cofactor for nNOS) is a key regulator of nNOS activity for stomach dysfunction and gastroparesis. In addition, BH(4) has been shown to be a potent antioxidant and anti-inflammatory agent. Well established by results from our laboratory, a diminished intracellular (BH(4):total biopterin) ratio in diabetic female rats significantly impairs nNOS activity and function. Recent research has been focused on BH(4) biosynthesis and gastroparesis because reduced BH(4) cofactor levels can alter the production of NO by nNOS. Researchers are now paying more attention to the possibility of using BH(4) as a therapeutic strategy in gastroparesis. The purpose of this review is to provide an overview of the regulation and function of nNOS by sex hormones and BH(4) and its potential role in the treatment of gastroparesis.

Tetrahydrobiopterin restores diastolic function and attenuates superoxide production in ovariectomized mRen2.Lewis rats

After oophorectomy, mRen2.Lewis rats exhibit diastolic dysfunction associated with elevated superoxide, increased cardiac neuronal nitric oxide synthase (nNOS) expression, and diminished myocardial tetrahydrobiopterin (BH₄) content, effects that are attenuated with selective nNOS inhibition. BH₄ is an essential cofactor of nNOS catalytic activity leading to nitric oxide production. Therefore, we assessed the effect of 4 wk BH₄ supplementation on diastolic function and left ventricular (LV) remodeling in oophorectomized mRen2.Lewis rats compared with sham-operated controls. Female mRen2.Lewis rats underwent either bilateral ovariectomy (OVX) (n = 19) or sham operation (n = 13) at 4 wk of age. Beginning at 11 wk of age, OVX rats were randomized to receive either BH₄ (10 mg/kg · d) or saline, whereas the sham rats received saline via sc mini-pumps. Loss of ovarian hormones reduced cardiac BH₄ when compared with control hearts; this was associated with impaired myocardial relaxation, augmented filling pressures, increased collagen deposition, and thickened LV walls. Additionally, superoxide production increased and nitric oxide decreased in hearts from OVX compared with sham rats. Chronic BH₄ supplementation after OVX improved diastolic function and attenuated LV remodeling while restoring myocardial nitric oxide release and preventing reactive oxygen species generation. These data indicate that BH₄ supplementation protects against the adverse effects of ovarian hormonal loss on diastolic function and cardiac structure in mRen2.Lewis rats by restoring myocardial NO release and mitigating myocardial O₂⁻ generation. Whether BH₄ supplementation is a therapeutic option for the management of diastolic dysfunction in postmenopausal women will require direct testing in humans.

Neuronal nitric oxide synthase inhibition improves diastolic function and reduces oxidative stress in ovariectomized mRen2.Lewis rats

OBJECTIVE

The loss of estrogen in mRen2.Lewis rats leads to an exacerbation of diastolic dysfunction. Because specific neuronal nitric oxide synthase (nNOS) inhibition reverses renal damage in the same model, we assessed the effects of inhibiting neuronal nitric oxide on diastolic function, left ventricular remodeling, and the components of the cardiac nitric oxide system in ovariectomized (OVX) and sham-operated mRen2.Lewis rats treated with N5-(1-imino-3-butenyl)-L-ornithine (L-VNIO; 0.5 mg/kg per day for 28 d) or vehicle (saline).

METHODS

Female mRen2.Lewis rats underwent either bilateral oophorectomy (OVX; n = 15) or sham operation (or surgical procedure) (sham; n = 19) at 4 weeks of age. Beginning at 11 weeks of age, the rats were randomized to receive either L-VNIO or vehicle.

RESULTS

The surgical loss of ovarian hormones, particularly estrogen, led to exacerbated hypertension, impaired myocardial relaxation, diminished diastolic compliance, increased perivascular fibrosis, and increased relative wall thickness. The cardiac tetrahydrobiopterin-to-dihydrobiopterin levels were lower among OVX rats compared with sham-operated rats, and this altered cardiac biopterin profile was associated with enhanced myocardial superoxide production and decreased nitric oxide release. L-VNIO decreased myocardial reactive oxygen species production, increased nitrite concentrations, attenuated cardiac remodeling, and improved diastolic function.

CONCLUSIONS

Impaired relaxation, diastolic stiffness, and cardiac remodeling were found among OVX mRen2.Lewis rats. A possible mechanism for this unfavorable cardiac phenotype may have resulted from a deficiency in available tetrahydrobiopterin and subsequent increase in nNOS-derived superoxide and reduction in nitric oxide synthase metabolites within the heart. Selective nNOS inhibition with L-VNIO attenuated cardiac superoxide production and limited remodeling, leading to improved diastolic function in OVX mRen2.Lewis rats.

Dehydroepiandrosterone protects against oxidative stress-induced endothelial dysfunction in ovariectomized rats

Cardiovascular disease is less frequent in premenopausal women than in age-matched men or postmenopausal women. Moreover, the marked age-related decline in serum dehydroepiandrosterone (DHEA) level has been associated to cardiovascular disease. The aim of this study was to evaluate the effects of DHEA treatment on vascular function in ovariectomized rats. At 8 weeks of age, female Wistar rats were ovariectomized (OVX) or sham (SHAM) operated and 8 weeks after surgery both groups were treated with vehicle or DHEA (10mg kg⁻¹ week⁻¹) for 3 weeks. Aortic rings were used to evaluate the vasoconstrictor response to phenylephrine (PHE) and the relaxation responses to acetylcholine (ACh) and sodium nitroprusside (SNP). Tissue reactive oxygen species (ROS) production and SOD, NADPH oxidase and eNOS protein expression were analysed. PHE-induced contraction was increased in aortic rings from OVX compared to SHAM, associated with a reduction in NO bioavailability. Furthermore, the relaxation induced by ACh was reduced in arteries from OVX, while SNP relaxation did not change. The incubation of aortic rings with SOD or apocynin restored the enhanced PHE-contraction and the impaired ACh-relaxation only in OVX. DHEA treatment corrected the increased PHE contraction and the impaired ACh-induced relaxation observed in OVX by an increment in NO bioavailability and decrease in ROS production. Besides, DHEA treatment restores the reduced Cu/Zn-SOD protein expression and eNOS phosphorylation and the increased NADPH oxidase protein expression in the aorta of OVX rats. The present results suggest an important action of DHEA, improving endothelial function in OVX rats by acting as an antioxidant and enhancing the NO bioavailability.

Ovariectomy in aged versus young rats augments matrix metalloproteinase-mediated vasoconstriction in mesenteric arteries

OBJECTIVE

Ovarian deficiency is known to undermine vasoprotective mechanisms and accelerate cardiovascular disease in postmenopausal women. In a rat model of menopause (aged ovariectomized [Ovx] rats), we recently revealed a vasoconstrictor pathway mediated by matrix metalloproteinases (MMPs) via cleavage of big endothelin-1 (ET-1). However, the specific impact of aging and/or Ovx on this pathway remains unknown. We hypothesized that aging exacerbates MMP-mediated vasoconstriction in an ovary-deficient state.

METHODS

Young and aged female Sprague-Dawley rats, either intact or Ovx, were assessed for MMP-dependent vasoreactivity. Dose responses to big ET-1 in the absence or presence of an MMP inhibitor (GM6001) were tested on small mesenteric arteries using a pressure myograph system. MMP levels in the vascular tissue were measured by gelatin zymography.

RESULTS

Both young Ovx and aged Ovx animals demonstrated a similar increase in the vasoconstriction to big ET-1 compared with the age-matched intact groups. MMP inhibition attenuated big ET-1 response in both Ovx groups and aged controls, but this effect was more pronounced in aged Ovx arteries (area under the curve reduction, 3.8 +/- 0.6 units in aged Ovx rats vs 1.5 +/- 0.5 units in young Ovx rats or 1.8 +/- 0.6 units in aged intact rats; P < 0.05). MMP-2 activity in the vascular tissue increased with age and was further augmented by Ovx.

CONCLUSIONS

Regardless of age, ovarian loss increases vascular reactivity to big ET-1, which is mediated, in part, by MMP. Superimposed with advancing age, ovarian deficiency further increases the proconstrictor role of MMP, which corresponds with higher MMP-2 levels in the aging vessel wall. MMP-mediated vasoconstriction may be a mechanism contributing to vascular dysfunction in postmenopausal women.

Accelerated postmenopausal cognitive decline is restricted to women with normal BMI: longitudinal evidence from the Betula project

In order to determine whether cognitive performance is influenced by the menopausal transition, we tested cognitive performance at three time points, sampled women in earlier as well as later stages of the menopausal transition (40-65 years of age), and assessed the moderating influence of body mass index (BMI) on rate of change. Multilevel analyses were used to model change in cognitive performance as a function of number of years post menopause over and above chronological age. We investigated change in the menopausal transition for 10 cognitive outcomes in 193 women who were postmenopausal during the last test wave. The model, controlling for age and education, showed that postmenopausal women within the normal range of BMI (BMI 18.5-25) displayed more rapid decline than women with BMI above 25 for measures of visuospatial ability and episodic memory. In addition, there was an accelerated rate of change post menopause for all women on verbal fluency. The results support the notion that the diminished postmenopausal production of endogenous estrogen may have a slight negative influence on cognitive abilities, but mainly for women within a normal BMI range.

Effect of 17beta-oestradiol replacement on vascular responsiveness in ovariectomized diabetic rats

1. Women with functional ovaries exhibit a gender advantage in terms of the prevalence of cardiovascular diseases. However, whether this gender bias pertains in diabetes is unknown. 2. The aim of the present study was to examine the effects of 17beta-oestradiol (E2) on vascular responsiveness in normal and diabetic ovariectomized (OVX) rats. Aged-matched female rats were divided into four groups as follows: (i) OVX; (ii) OVX + E2 treated; (iii) diabetic OVX; and (iv) diabetic OVX + E2 treated. Bilateral ovariectomy was performed and streptozotocin was used to induce experimental diabetes. Rats were treated with 1 mg/kg per day, p.o., E2 for 8 weeks. 3. Although E2 treatment had no effect on blood glucose levels in normal and diabetic OVX rats, it significantly reduced systolic blood pressure and prevented diabetes-induced loss of bodyweight gain. 4. In segments of the thoracic aorta, concentration-dependent vasoconstrictor responses to KCl and phenylephrine were significantly attenuated following E2 treatment in both the normal and diabetic groups. The sarcoplasmic/endoplasmic reticulum calcium ATPase inhibitor thapsigargin (10(-6) mol/L) and the Ca(2+) channel blocker nifedipine (10(-6) mol/L) inhibited the transient vasoconstriction to PE in all groups. The constrictor effect of PE was increased by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-6) mol/L), but was reduced by superoxide dismutase (SOD; 100 U/mL) and the cyclo-oxygenase inhibitor indomethacin (10(-6) mol/L) in all groups. Responses to acetylcholine (ACh; 10(-6) mol/L) demonstrated reduced endothelium-dependent relaxation in non-E2-treated groups. Relaxation responses to ACh were increased by 100 U/mL SOD and 10(-6) mol/L indomethacin, but were reduced by 10(-6) mol/L l-NAME in all groups. There were no differences among the four groups in terms of relaxation responses to sodium nitroprusside (10(-11) to 10(-6) mol/L). 5. In conclusion, the results of the present study suggest that oestrogen treatment has beneficial effects on vascular function in both diabetic and non-diabetic OVX rats due to Ca(2+) regulation and anti-oxidation.

The influence of estrogen and progesterone on parasympathetic vasodilatation in the rat submandibular gland

Previous studies suggest that NO- and PGI(2)-independent pathways play a greater role in parasympathetic vasodilatation in the submandibular glands (SMG) of female than of male rats. Thus, the purpose of this study was to determine whether estrogen and progesterone influence the relative contributions of NO and PGI(2) to parasympathetic vasodilatation in the SMG. Vascular responses to chorda-lingual nerve stimulation were examined in sham-operated (SHAM) and ovariectomized (OVX) female rats and in OVX rats treated with either 17beta-estradiol alone or a combination of 17beta-estradiol and progesterone. Compared with SHAM animals, increases in vascular conductance in OVX rats were reduced at 1, 2 and 5 Hz (p<0.05). Blood flow responses in OVX+17beta-estradiol and OVX+17beta-estradiol+progesterone rats were indistinguishable from those observed in SHAM animals. Indomethacin had no effect on vasodilatation in SHAM and OVX+17beta-estradiol rats, but increased vascular responses in OVX animals (p<0.02). The addition of L-NAME resulted in a significant reduction in vasodilatation at all frequencies. In OVX rats treated with both estrogen and progesterone, indomethacin caused a reduction in vasodilatation and L-NAME further diminished the remaining responses. Under all conditions, vasodilatation was due largely, if not exclusively, to direct parasympathetic rather than antidromic sensory nerve activation. Finally, both neuronally-derived and endothelium-derived NO appeared to be responsible for the NO-dependent vasodilatation, but endothelium-derived NO became increasingly important as the frequency of stimulation increased. We conclude that estrogen and progesterone influence parasympathetic vasodilatation through combined effects on NO-, PGI(2)- and non-NO/PGI(2)-mediated pathways.

Estrogen deficiency-induced alterations of vascular MMP-2, MT1-MMP, and TIMP-2 in ovariectomized rats

BACKGROUND

Matrix metalloproteinases (MMPs) activity may modulate hypertension-related accumulation of extracellular matrix (ECM) in arteries. We tested whether estrogen deficiency induces alterations of vascular collagen, MMP-2, membrane-type 1-MMP (MT1-MMP), or tissue inhibitor of metalloproteinases-2 (TIMP-2) expression in ovariectomized rats, which may be associated with postmenopausal hypertension.

METHODS

Estrogen deficiency was induced by ovariectomy (Ovx) in female rats. Time-course changes of aortic MMPs protein expression were evaluated. Treatment with tempol or aminoguanidine was used to examine the role of oxidative stress and nitric oxide (NO) on these changes.

RESULTS

The level of the active-form MMP-2 was markedly reduced during 1-4 weeks after Ovx, with a significant increase in collagen accumulation and increased MT1-MMP expression. Although active-form MMP-2 and collagen progressively returned to normal levels, the markedly increased collagen deposition appeared again at 8 weeks and persisted until 12 weeks, followed by induction of MMP-2 and MT1-MMP at 12 weeks. The TIMP-2 level reduced for 2 weeks after Ovx, but soon returned to normal. Treatment with 17beta-estradiol (E(2)), tempol, or aminoguanidine for 6 weeks prevented Ovx-induced blood pressure elevation and apparently reversed the MMPs changes.

CONCLUSIONS

In an initial period, E(2) deficiency induces a reduction of active-form MMP-2 leading to collagen accumulation, and induction of MT1-MMP, which may be a compensatory response to degrade collagen. At a latter stage, the concurrent elevation of active-form MMP-2 and MT1-MMP expression may be adaptive responses to regulate ECM composition in the vascular wall. Oxidative stress and NO contribute to activity modulation of vascular MMPs in Ovx rats.

Certain progestins prevent the enhancing effect of 17beta-estradiol on NO-mediated inhibition of platelet aggregation by endothelial cells

OBJECTIVE

Estro-progestin treatments have been associated with an increased risk of thromboembolic events in postmenopausal women. This study examined whether progestins affect the stimulatory effect of estrogens on the endothelial formation of nitric oxide (NO), a potent antithrombotic factor.

METHODS AND RESULTS

Experiments were performed with human endothelial cells. Endothelial NO synthase (eNOS) and GTP cyclohydrolase I (GTPCH I) mRNA expression was assessed by RT-PCR, eNOS protein by Western blotting, NO formation by electron spin resonance spectroscopy, and platelet aggregation by an aggregometer. Medroxyprogesterone acetate (MPA), progesterone, levonorgestrel, and nomegestrol acetate prevented the 17beta-estradiol (17beta-E)-induced expression of eNOS mRNA and protein. MPA and progesterone reduced the 17beta-E-induced formation of NO and potentiation of the inhibitory effect of endothelial cells on platelet aggregation whereas levonorgestrel and nomegestrol acetate were without effect. Moreover, MPA and progesterone prevented the 17beta-E-induced expression of GTPCH I mRNA. Mifepristone, a glucocorticoid and progesterone receptor antagonist, and L-sepiapterin prevented the inhibitory effect of MPA and progesterone on platelet aggregation.

CONCLUSIONS

Certain progestins, including MPA, attenuate the 17beta-E-induced NO-mediated inhibition of platelet aggregation by endothelial cells through preventing both eNOS and GTPCH I expression most likely via activation of glucocorticoid receptors.

Sex differences in control of blood pressure: role of oxidative stress in hypertension in females

In general, blood pressure is higher in normotensive men than in age-matched women, and the prevalence of hypertension in men is also higher until after menopause, when the prevalence of hypertension increases for women. It is likely then that the mechanisms by which blood pressure increases in men and women with aging may be different. Although clinical trials to reduce blood pressure with antioxidants have typically not been successful in human cohorts, studies in male rats suggest that oxidative stress plays an important role in mediating hypertension. The exact mechanisms by which oxidative stress increases blood pressure have not been completely elucidated. There may be several reasons for the discrepancies between clinical and animal studies. In this review, the data obtained in selected clinical and animal studies are discussed, and the hypothesis is put forward that oxidative stress may not be as important in mediating hypertension in females as has been shown previously in male rats. Furthermore, it is likely that differences in genetics, age, length of time with hypertension, endothelial dysfunction, and sex are all factored in to modulate the responses to antioxidants in humans. As such, future clinical trials should be designed and powered to evaluate the effects of oxidative stress on blood pressure separately in men and women.

Cardiac hypertrophy is associated with altered thioredoxin and ASK-1 signaling in a mouse model of menopause

Oxidative stress is implicated in menopause-associated hypertension and cardiovascular disease. The role of antioxidants in this process is unclear. We questioned whether the downregulation of thioredoxin (TRX) is associated with oxidative stress and the development of hypertension and target-organ damage (cardiac hypertrophy) in a menopause model. TRX is an endogenous antioxidant that also interacts with signaling molecules, such as apoptosis signal-regulated kinase 1 (ASK-1), independently of its antioxidant function. Aged female wild-type (WT) and follitropin receptor knockout (FORKO) mice (20-24 wk), with hormonal imbalances, were studied. Mice were infused with ANG II (400 ng x kg(-1) x min(-1); 14 days). Systolic blood pressure was increased by ANG II in WT (166+/-8 vs. 121+/-5 mmHg) and FORKO (176+/-7 vs. 115+/-5 mmHg; P<0.0001; n=9/group) mice. In ANG II-infused FORKO mice, cardiac mass was increased by 42% (P<0.001). This was associated with increased collagen content and augmented ERK1/2 phosphorylation (2-fold). Cardiac TRX expression and activity were decreased by ANG II in FORKO but not in WT (P<0.01) mice. ASK-1 expression, cleaved caspase III content, and Bax/Bcl-2 content were increased in ANG II-infused FORKO (P<0.05). ANG II had no effect on cardiac NAD(P)H oxidase activity or on O(2)(*-) levels in WT or FORKO. Cardiac ANG II type 1 receptor expression was similar in FORKO and WT. These findings indicate that in female FORKO, ANG II-induced cardiac hypertrophy and fibrosis are associated with the TRX downregulation and upregulation of ASK-1/caspase signaling. Our data suggest that in a model of menopause, protective actions of TRX may be blunted, which could contribute to cardiac remodeling independently of oxidative stress and hypertension.

Vascular effects of estrogen and progestins and risk of coronary artery disease: importance of timing of estrogen treatment

The effects of estrogen and progestins on the vascular wall have drawn major medical attention, and significant controversy over various studies has been developed. Several experimental and observational studies have shown cardioprotective effects; however, prospective randomized trials showed an increase in cardiovascular events in postmenopausal women on estrogen/ medroxyprogesterone acetate treatment. The most significant parameter for cardiovascular benefit of estrogen seems to be the interval since the onset of menopause. In the early postmenopausal years, estrogen has beneficial effects on the vascular wall by inhibition of atherosclerosis progression, whereas in the late postmenopause, adverse effects like upregulation of the plaque inflammatory processes and plaque instability may develop. The effects of progestins on the cardiovascular system are not as clear and may differ according to the choice of progestins that is used. The aim of this review is to summarize the effects of estrogen and progestins on the vascular wall and their clinical implications.

Estrogen reduces aldosterone, upregulates adrenal angiotensin II AT2 receptors and normalizes adrenomedullary Fra-2 in ovariectomized rats

We studied the effect of ovariectomy and estrogen replacement on expression of adrenal angiotensin II AT1 and AT2 receptors, aldosterone content, catecholamine synthesis, and the transcription factor Fos-related antigen 2 (Fra-2). Ovariectomy increased AT1 receptor expression in the adrenal zona glomerulosa and medulla, and decreased adrenomedullary catecholamine content and Fra-2 expression when compared to intact female rats. In the zona glomerulosa, estrogen replacement normalized AT1 receptor expression, decreased AT1B receptor mRNA, and increased AT2 receptor expression and mRNA. Estrogen treatment decreased adrenal aldosterone content. In the adrenal medulla, the effects of estrogen replacement were: normalized AT1 receptor expression, increased AT2 receptor expression, AT2 receptor mRNA, and tyrosine hydroxylase mRNA, and normalized Fra-2 expression and catecholamine content. We demonstrate that the constitutive adrenal expression of AT1 receptors, catecholamine synthesis and Fra-2 expression are partially under the control of reproductive hormones. Our results suggest that estrogen treatment decreases aldosterone production through AT1 receptor downregulation and AT2 receptor upregulation. AT2 receptor upregulation and modulation of Fra-2 expression may participate in the estrogen-dependent normalization of adrenomedullary catecholamine synthesis in ovariectomized rats. The AT2 receptor upregulation and the decrease in AT1 receptor function and in the production of the fluid-retentive, pro-inflammatory hormone aldosterone partially explain the protective effects of estrogen therapy.

Discoordinate regulation of renal nitric oxide synthase isoforms in ovariectomized mRen2. Lewis rats

Estrogen depletion markedly exacerbates hypertension in female congenic mRen2. Lewis rats, a model of tissue renin overexpression. Because estrogen influences nitric oxide synthase (NOS) and NO may exert differential effects on blood pressure, the present study investigated the functional expression of NOS isoforms in the kidney of ovariectomized (OVX) mRen2. Lewis rats. OVX-mRen2. Lewis exhibited an increase in systolic blood pressure (SBP) of 171 +/- 5 vs. 141 +/- 7 mmHg (P < 0.01) for intact littermates. Renal cortical mRNA and protein levels for endothelial NOS (eNOS) were reduced 50-60% (P < 0.05) and negatively correlated with blood pressure. In contrast, cortical neuronal NOS (nNOS) mRNA and protein levels increased 100 to 300% (P < 0.05). In the OVX kidney, nNOS immunostaining was more evident in the macula densa, cortical tubules, and the medullary collecting ducts compared with the intact group. To determine whether the increase in renal nNOS expression constitutes a compensatory response to the reduction in renal eNOS, we treated both intact and OVX mRen2. Lewis rats with the selective nNOS inhibitor L-VNIO from 11 to 15 wk of age. The nNOS inhibitor reduced blood pressure in the OVX group (185 +/- 3 vs. 151 +/- 8 mmHg, P < 0.05), but pressure was not altered in the intact group (146 +/- 4 vs. 151 +/- 4 mmHg). In summary, exacerbation of blood pressure in the OVX mRen2. Lewis rats was associated with the discoordinate regulation of renal NOS isoforms. Estrogen sensitivity in this congenic strain may involve the influence of NO through the regulation of both eNOS and nNOS.