Significant reduction of the antiatherogenic effect of estrogen by long-term inhibition of nitric oxide synthesis in cholesterol-clamped rabbits

Effect of Coffee Consumption on Risk of Coronary Heart Disease in a Systematic Review and Meta-Analysis of Prospective Cohort Studies

Previous prospective studies have reported inconsistent findings on the association between coffee consumption and the risk of coronary heart disease (CHD). This study aimed to investigate their association using a meta-analysis of prospective studies. We searched PubMed and EMBASE for prospective cohort studies of the association between coffee consumption and the risk of CHD in the general population. We conducted a random-effects meta-analysis and also subgroup meta-analyses by various factors. Of 870 studies searched from databases, 32 prospective cohort studies were included in the final analysis. In the main meta-analysis of all studies, no significant association between coffee consumption and the risk of CHD was observed (relative risk [RR] 1.05, 95% confidence interval [CI] 0.97 to 1.14, I² = 64.9%). In the subgroup meta-analyses by gender, coffee consumption significantly increased the risk of CHD in men (RR 1.19, 95% CI 1.05 to 1.35, n = 17), whereas a nonsignificantly decreased risk of CHD was observed in women (RR 0.91, 95% CI 0.77 to 1.08, n = 11). Also, in the subgroup meta-analyses by follow-up period, coffee consumption significantly increased the risk of CHD in the follow-up of 20 years or longer (RR 1.16, 95% CI 1.06 to 1.27, n = 4) regardless of gender. In conclusion, in the current meta-analysis of prospective studies, we found that, overall, no significant association between coffee consumption and the risk of CHD was observed. However, coffee consumption showed a differential effect by gender, with an increased risk of CHD in men and a potentially decreased risk in women.

Long Term Sodium Nitrate Administration Positively Impacts Metabolic and Obesity Indices in Ovariectomized Rats

BACKGROUND

In postmenopausal women, nitric oxide (NO) deficiency is associated with obesity and type 2 diabetes (T2D). This study aims at determining the long-term effects of low-dose nitrate administration on metabolic and obesity indices in ovariectomized (OVX) rats.

METHODS

OVX rat model was induced using the two dorsolateral skin incision method. Two months after ovariectomy, rats were divided into three groups (n = 10/group): Control, OVX, and OVX+nitrate, and the latter received sodium nitrate at a dose of 100 mg/L in their drinking water for nine months. Fasting serum glucose and lipid profile were measured every month. A glucose tolerance test was performed at months 1, 3, and 9 (the end of the study). Obesity indices were calculated, and histological analyses were performed on the gonadal adipose tissues at month 9.

RESULTS

OVX rats had impaired fasting glucose, glucose intolerance, and dyslipidemia with higher obesity indices at month 9. Nitrate improved glucose and lipid metabolism in OVX rats and decreased body weight (6.9%), body mass index (12.5%), Lee index (5.4%), adiposity index (23.9%), abdominal circumference (10.5%), and thoracic circumference (17.1%). Also, nitrate decreased adipocyte area by 49% and increased adipocyte density by 193% in gonadal adipose tissue.

CONCLUSION

Long-term low-dose nitrate administration improves glucose and lipid metabolism in OVX rats in association with decreasing OVX-induced adiposity, increasing adipocyte density, and decreasing adipocyte area. These findings provide support for a potential therapeutic role of nitrate in postmenopausal women with some features of metabolic syndrome.

EP3 Blockade Adds to the Effect of TP Deficiency in Alleviating Endothelial Dysfunction in Atherosclerotic Mouse Aortas

Endothelial dysfunction, which leads to ischemic events under atherosclerotic conditions, can be attenuated by antagonizing the thromboxane-prostanoid receptor (TP) that mediates the vasoconstrictor effect of prostanoids including prostacyclin (PGI₂). This study aimed to determine whether antagonizing the E prostanoid receptor-3 (EP3; which can also be activated by PGI₂) adds to the above effect of TP deficiency (TP^-/-) under atherosclerotic conditions and if so, the underlying mechanism(s). Atherosclerosis was induced in ApoE^-/- mice and those with ApoE^-/- and TP^-/-. Here, we show that in phenylephrine pre-contracted abdominal aortic rings with atherosclerotic lesions of ApoE^-/-/TP^-/- mice, although an increase of force (which was larger than that of non-atherosclerotic controls) evoked by the endothelial muscarinic agonist acetylcholine to blunt the concurrently activated relaxation in ApoE^-/- counterparts was largely removed, the relaxation evoked by the agonist was still smaller than that of non-atherosclerotic TP^-/- mice. EP3 antagonism not only increased the above relaxation, but also reversed the contractile response evoked by acetylcholine in NO synthase-inhibited atherosclerotic ApoE^-/-/TP^-/- rings into a relaxation sensitive to I prostanoid receptor antagonism. In ApoE^-/- atherosclerotic vessels the expression of endothelial NO synthase was decreased, yet the production of PGI₂ (which evokes contraction via both TP and EP3) evoked by acetylcholine was unaltered compared to non-atherosclerotic conditions. These results demonstrate that EP3 blockade adds to the effect of TP^-/- in uncovering the dilator action of natively produced PGI₂ to alleviate endothelial dysfunction in atherosclerotic conditions.

Endothelial function and insulin resistance in early postmenopausal women with cardiovascular risk factors: importance of ESR1 and NOS3 polymorphisms

Cardiovascular benefits from estradiol activation of nitric oxide endothelial production may depend on vascular wall and on estrogen receptor alpha (ESR1) and nitric oxide synthase (NOS3) polymorphisms. We have evaluated the microcirculation in vivo through nailfold videocapillaroscopy, before and after acute nasal estradiol administration at baseline and after increased sheer stress (postocclusive reactive hyperemia response) in 100 postmenopausal women, being 70 controls (healthy) and 30 simultaneously hypertensive and diabetic (HD), correlating their responses to PvuII and XbaI ESR1 polymorphisms and to VNTR, T-786C and G894T NOS3 variants. In HD women, C variant allele of ESR1 Pvull was associated to higher vasodilatation after estradiol (1.72 vs 1.64 mm/s, p = 0.01 compared to TT homozygotes) while G894T and T-786C NOS3 polymorphisms were connected to lower increment after shear stress (15% among wild type and 10% among variant alleles, p = 0.02 and 0.04). The G variant allele of ESR1 XbaI polymorphism was associated to higher HOMA-IR (3.54 vs. 1.64, p = 0.01) in HD and higher glucose levels in healthy women (91.8 vs. 87.1 mg/dl, p = 0.01), in which increased waist and HOMA-IR were also related to the G allele in NOS3 G894T (waist 93.5 vs 88.2 cm, p = 0.02; HOMA-IR 2.89 vs 1.48, p = 0.05). ESR1 Pvull, NOS3 G894T and T-786C polymorphism analysis may be considered in HD postmenopausal women for endothelial response prediction following estrogen therapy but were not discriminatory for endothelial response in healthy women. ESR1 XbaI and G894T NOS3 polymorphisms may be useful in accessing insulin resistance and type 2 diabetes risks in all women, even before menopause and occurrence of metabolic disease.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Irradiation promotes Akt-targeting therapeutic gene delivery to the tumor vasculature

PURPOSE

To determine whether radiation-induced increases in nitric oxide (NO) production can influence tumor blood flow and improve delivery of Akt-targeting therapeutic DNA lipocomplexes to the tumor.

METHODS AND MATERIALS

The contribution of NO to the endothelial response to radiation was identified using NO synthase (NOS) inhibitors and endothelial NOS (eNOS)-deficient mice. Reporter-encoding plasmids complexed with cationic lipids were used to document the tumor vascular specificity and the efficacy of in vivo lipofection after irradiation. A dominant-negative Akt gene construct was used to evaluate the facilitating effects of radiotherapy on the therapeutic transgene delivery.

RESULTS

The abundance of eNOS protein was increased in both irradiated tumor microvessels and endothelial cells, leading to a stimulation of NO release and an associated increase in tumor blood flow. Transgene expression was subsequently improved in the irradiated vs. nonirradiated tumor vasculature. This effect was not apparent in eNOS-deficient mice and could not be reproduced in irradiated cultured endothelial cells. Finally, we combined low-dose radiotherapy with a dominant-negative Akt gene construct and documented synergistic antitumor effects.

CONCLUSIONS

This study offers a new rationale to combine radiotherapy with gene therapy, by directly exploiting the stimulatory effects of radiation on NO production by tumor endothelial cells. The preferential expression of the transgene in the tumor microvasculature underscores the potential of such an adjuvant strategy to limit the angiogenic response of irradiated tumors.

The atheroprotective effect of 17beta-estradiol depends on complex interactions in adaptive immunity

Estradiol prevents fatty streak formation in chow-fed atherosclerosis-prone apolipoprotein E (ApoE)-deficient mice. We previously reported that fatty streak development of immunodeficient ApoE(-/-)/recombination activating gene 2 (RAG-2(-/-)) double-deficient mice was insensitive to estradiol. In the present work, we demonstrate that the reconstitution of ApoE(-/-)/RAG-2(-/-) with bone marrow from immunocompetent ApoE(-/-)/RAG-2(+/+) mice restores the protective effect of estradiol on fatty streak constitution. We extended this demonstration to the model of low-density lipoprotein receptor-deficient mice, establishing the obligatory role of mature lymphocytes in this process. We then investigated whether the protective effect of estradiol was mediated by a specific lymphocyte subpopulation by studying the hormonal effect on fatty streak constitution in recently developed models of ApoE(-/-) mice deficient in selective T-lymphocyte subsets (either TCRalphabeta+, CD4+, CD8+, or TCRgammadelta+ lymphocytes) or B lymphocytes. In all these specifically immunodeficient mice, estradiol administration to ovariectomized mice conferred protection as in immunocompetent ApoE(-/-) mice, clearly demonstrating that no single lymphocyte subpopulation was specifically required for this effect. These results point to additional lymphocyte-dependent mechanisms such as modulating the interactions among lymphocytes and between lymphocytes and endothelial and/or antigen-presenting cells.

Novel action of estrone on vascular tissue: regulation of NOS and COX activity

The hypothesis tested in the present work is that estrone non-genomically regulates aortic nitric oxide synthase (NOS) and cyclooxygenase (COX) activities in female rats, and that such regulation depends on ovarian function. We found that physiological concentrations of estrone (E(1)) (0.1-10nM) significantly increased nitric oxide (NO) production (133 and 163% above control). The stimulatory action of E(1) on NOS activity was independent of calcium influx since the increase in NO elicited by the hormone was not affected by EGTA or verapamil. When COX activity was measured, we observed that estrone enhanced thromboxane (TXB(2)) production and prostacyclin (PGI(2)) release, but not prostaglandin (PGF(2), PGD(2), and PGE(2)) synthesis. Finally we demonstrated that the hormonal effect on NOS activity was not detected in rat aortic strips (RAS) isolated from animals deprived of ovarian activity (FR(-)) or ovariectomized rats (OVX). These results suggest that estrone exerts a direct, non-genomic action on rat aortic metabolism, which involves NOS and COX activation and depends on ovarian activity.

Hormone Therapy and Selective Estrogen Receptor Modulators for Prevention of Coronary Heart Disease in Postmenopausal Women

Coronary heart disease is the leading cause of morbidity and mortality in women older than the age of 50 in the United States today. Traditional cardiovascular risk factors (hyperlipidemia, glucose intolerance, and hypertension) are more clearly associated with significant cardiovascular risk after menopause. The increased incidence of cardiovascular events in postmenopausal women and the evidence that cardiovascular disease on average manifests a decade later in women compared with men suggests that estrogen deficiency may predispose women to a higher cardiovascular risk. Numerous biologic mechanisms have been proposed that relate use of hormone therapy (HT) to improved lipid profiles, insulin sensitivity, and vascular reactivity. Early observational trials in the last 2 decades showed a significant decrease in cardiovascular events. Recently published randomized clinical trial results, however, have led to uncertainty about the earlier established cardiovascular benefits of HT. To complicate issues further, alternative estrogenlike compounds, selective estrogen receptor modulators, are being introduced that appear to convey similar cardiovascular benefit and notably less cancer risk than HT. The newly released randomized trials on hormone and nonhormonal agents are reviewed.

The aging male: testosterone deficiency and testosterone replacement. An up-date

The significance of the age-related decline of androgens remains unclear in terms of cardiovascular risk, mood and cognition, and prostatic health. Although much research has been undertaken in this area and men's health has received still more attention in the latest years, there are no data based on randomized controlled clinical studies in aging men investigating the long-term effects of androgen replacement therapy on various aspects of the cardiovascular system, the immune system, body composition, and the brain. In men receiving long-term androgen replacement therapy, the safety aspects regarding the prostate are also an area of clinical importance. In this paper we present an up-dated review of the experimental and clinical evidence of androgen deficiency and androgen replacement therapy on carbohydrate metabolism, on coagulation and fibrinolysis, inflammatory effects, effects on lipoprotein metabolism, direct arterial effects, effects on body composition, effects on cognitive function and mood, and prostatic effects. The evidence clearly shows that data for the most part are conflicting, with only very few randomized studies available.

Dysfunction of endothelial nitric oxide synthase and atherosclerosis

Atherosclerosis is associated with an impairment of endothelium-dependent relaxations, which represents the reduced bioavailability of nitric oxide (NO) produced from endothelial NO synthase (eNOS). Among various mechanisms implicated in the impaired EDR in atherosclerosis, superoxide generated from dysfunctional eNOS has attracted attention. Under conditions in which vascular tissue levels of tetrahydrobiopterin (BH4), a cofactor for NOS, are deficient or lacking, eNOS becomes dysfunctional and produces superoxide rather than NO. Experimental studies in vitro have revealed that NO from eNOS constitutes an anti-atherogenic molecule. A deficiency of eNOS was demonstrated to accelerate atherosclerotic lesion formation in eNOS knockout mice. In contrast, eNOS overexpression with hypercholesterolemia may promote atherogenesis via increased superoxide generation from dysfunctional eNOS. Thus, eNOS may have 2 faces in the pathophysiology of atherosclerosis depending on tissue BH4 metabolisms. An improved understanding of tissue BH4 metabolisms in atherosclerotic vessels is needed, which would help in developing new strategies for the inhibition and treatment of atherosclerosis.

Estrogen alone or combined with medroxyprogesterone but not raloxifene reduce myocardial infarct size

We investigated whether estrogen protects the ischemic myocardium in oophorectomized female rabbits fed with a cholesterol-enriched diet, whether the addition of a progestin compound attenuates the beneficial effect of estrogen and whether raloxifene also limits myocardial necrosis. We treated 32 female oophorectomized hypercholesterolemic rabbits with (a) placebo (N=8, group I), (b) conjugated estrogens alone (N=8, group II), (c) conjugated estrogens combined continuously with medroxyprogesterone acetate (N=8, group III) and (d) raloxifene (N=8, group IV) all for 4 weeks. All rabbits underwent 30 min of ischemia and 120 min of reperfusion. Both infarct size (0.38+/-0.08 and 0.45+/-0.05 in groups II and III, respectively, vs. 0.78+/-0.07 in group I, P<0.005) and infarct size/risk zone% (26.34+/-4.18 and 35.01+/-4.39 in groups II and III, respectively, vs. 52.18+/-7.84 in group I, P<0.05) were significantly smaller in the estrogen treatment groups compared to placebo. No significant difference was observed between groups II and III. There was no significant difference between groups I and IV for infarct size (0.78+/-0.07 vs. 0.69+/-0.08, respectively) or for infarct size/risk zone% (52.18+/-7.84 vs. 47.17+/-4.3). Short-term estrogen protects ischemic myocardium in hypercholesterolemic oophorectomized female rabbits; this effect is not attenuated by the addition of a progestin compound. Raloxifene, however, does not decrease infarct size compared to placebo.

Adverse effects of a SERM (Levormeloxifene). Safety parameters and bone mineral density 12 months after treatment withdrawal

OBJECTIVE

Levormeloxifene is a selective estrogen receptor modulator (SERM). The development of the drug was discontinued due to intolerable adverse effects. This paper follow-up on the adverse events in a group of 234 women that was followed for 12 months without treatment after 12 months of treatment with levormeloxifene.

METHODS

Adverse events were recorded at all clinical visits. The double-layer thickness of the uterine endometrium was determined by transvaginal ultrasonography. Endometrial biopsies were obtained by pipelle. The biopsies taken at the entrance to the follow-up phase were taken under hysteroscopy-guidance. Bone mineral density of the total body, lumbar spine (L1-L4), hip and forearm was measured by dual-energy X-ray absorptiometry.

RESULTS

The most prominent adverse event was increased endometrial thickness over the pre-defined threshold of 8 mm. No cases of proliferative endometrium were reported. Following withdrawal of treatment the mean endometrial thickness approached baseline levels in a dose dependent manner. Hysteroscopic examinations showed that levormeloxifene was related to increased incidence of edema, vascularization and cysticity. In the levormeloxifene groups, a total of eight women had utero-vaginal prolapse and five women reported urinary incontinence (including worsening of a previously existing condition). Bone density in the spine and hip approached baseline levels during the 12 months of follow-up without treatment.

CONCLUSION

Endometrial thickening, seen in association with the use of some SERM's, may lead to harmful adverse effects more than 12 months after treatment is initiated. Levormeloxifene prevents the postmenopausal bone loss, but the lowest effective dose is unknown.

Value of the micropig model of menopause in the assessment of benefits and risks of postmenopausal therapies for cardiovascular and reproductive tissues

OBJECTIVE

To extend the comparative database demonstrating the cardioprotective benefits of estrogen therapy to an additional relevant species and to assess the usefulness of this model for studies designed to assess benefits and risks of postmenopausal therapies.

DESIGN

Prospective, randomized, controlled periclinical trial.

SETTING

Medical university animal facility.

ANIMAL(S)

Fifteen sexually mature Yucatan micropigs and 15 ovariectomized micropigs.

INTERVENTION(S)

Oral conjugated equine estrogens (CEE), 0.625 mg/d, or levormeloxifene, 37.5 mg/d, for 182 days.

MAIN OUTCOME MEASURE(S)

Coronary artery atherosclerosis was measured by digitization, uteri were weighed, and uterine and mammary tissues were evaluated histologically and morphometrically. Mean blood pressure was measured by oscillometry, C-reactive protein by enzyme-linked immunosorbent assay, and serum lipids by enzymatic methods.

RESULT(S)

Coronary artery atherosclerosis was reduced 51% in animals that received CEE compared with controls. Levels of C-reactive protein increased by 12% with both treatments. Serum lipid levels and mean blood pressure did not differ among groups. Levormeloxifene produced a 5.9-fold increase in the uterine-to-body weight ratio. Histologic and morphometric data indicate that levormeloxifene has uterotrophic and mammotrophic effects.

CONCLUSION(S)

The micropig model extends the comparative evidence for cardioprotection provided by estrogen therapy to an additional highly relevant species, thus supporting the rationale for a clinically beneficial role of estrogen for the heart. The marked uterine effects of levormeloxifene detected by this model are probably highly predictive of the adverse events that would be encountered in clinical trials.

Serum levels of the senescence biomarker clusterin/apolipoprotein J increase significantly in diabetes type II and during development of coronary heart disease or at myocardial infarction

Clusterin/apolipoprotein J (hereafter ApoJ) is a conserved secreted glycoprotein expressed by a wide array of tissues and being implicated in several physiological processes. ApoJ has been shown to associate with both normal in vitro aging, namely replicative senescence, as well as with stress induced premature senescence. In vivo, the protein is up-regulated in many severe physiological disturbances that relate to advanced aging, including accumulation in the artery wall during the development of atherosclerosis. In the current report we have expanded our previous studies that focus in the biological role of ApoJ during aging by addressing two interrelated issues: (a) we have examined the potential ApoJ association with in vivo aging and (b) we have studied whether its accumulation in the artery wall during the development of atherosclerosis is combined with a measurable increase of its serum levels, as well as, whether a similar effect occurs in diseases, such as diabetes type II, known to represent major risk factors of atherosclerosis. By combining a sandwich ELISA assay and immunoblotting analysis we demonstrate a measurable increase of ApoJ serum levels with age in males and provide evidence that, as compared to healthy donors, the serum ApoJ amount increases significantly in diabetic type II patients and in patients suffering from either a developing coronary heart disease, or myocardial infarction. The highest serum ApoJ levels were found during myocardial infarction but no correlation was observed with the number of vessels with documented atherosclerotic damage. In conclusion, this report illustrates that ApoJ accumulation in serum is probably coupled to a generalized stress mediated induction mechanism that is specifically related to certain diseases; moreover these data raise the possibility that elevated ApoJ levels in serum may represent a strong indication of vascular damage.

Estrogen modulation of endothelial nitric oxide synthase

Over the past decade, clinical and basic research has demonstrated that estrogen has a dramatic impact on the response to vascular injury and the development of atherosclerosis. Further work has indicated that this is at least partially mediated by an enhancement in nitric oxide (NO) production by the endothelial isoform of NO synthase (eNOS) due to increases in both eNOS expression and level of activation. The effects on eNOS abundance are primarily mediated at the level of gene transcription, and they are dependent on estrogen receptors (ERs), which classically serve as transcription factors, but they are independent of estrogen response element action. Estrogen also has potent nongenomic effects on eNOS activity mediated by a subpopulation of ERalpha localized to caveolae in endothelial cells, where they are coupled to eNOS in a functional signaling module. These observations, which emphasize dependence on cell surface-associated receptors, provide evidence for the existence of a steroid receptor fast-action complex, or SRFC, in caveolae. Estrogen binding to ERalpha on the SRFC in caveolae leads to G(alphai) activation, which mediates downstream events. The downstream signaling includes activation of tyrosine kinase-MAPK and Akt/protein kinase B signaling, stimulation of heat shock protein 90 binding to eNOS, and perturbation of the local calcium environment, leading to eNOS phosphorylation and calmodulin-mediated eNOS stimulation. These unique genomic and nongenomic processes are critical to the vasoprotective and atheroprotective characteristics of estrogen. In addition, they serve as excellent paradigms for further elucidation of novel mechanisms of steroid hormone action.

Reproductive hormones and cardiovascular disease mechanism of action and clinical implications

The bulk of the experimental data suggest beneficial effects of estrogen (both premenopausal use of OCs and postmenopausal use of ERT-HRT). An intriguing finding from the monkey studies is that social subordination, which induces estrogen deficiency in female monkeys, accelerates atherosclerosis premenopausally and predicts extent of postmenopausal atherosclerosis. This effect can be inhibited by exogenous estrogen, premenopausally. The results suggest that more effort on detecting and regulating premenopausal ovarian dysfunction may be justified. A complication in understanding estrogen action may be the result of varying extents of arterial damage. For example, primary prevention studies in both postmenopausal animals and women have provided strong evidence of atheroprotection with a variety of estrogens. In contrast, the results of secondary prevention studies [10,12] have in general suggested little cardioprotection with either ERT or HRT. Studies in rabbits suggest the antiatherogenic effect of estrogen may not be present when the endothelium is damaged [64]. The state of the endothelium may be critical for some estrogen actions. For those effects of estrogen that require the ER, be it ERalpha or ERbeta, the presence of the receptor may vary with age, disease state, or type of hormone therapy. If continuous combined HRT therapy decreases ER in the artery as it does in the uterus, this may eliminate those estrogen actions requiring the ER, but not others. Older women who have not been exposed to estrogens for many years may be more sensitive to some estrogen effects, and may need lower doses of ERT-HRT. Recent reports suggest that lower doses of estrogens maintain beneficial effects on lipoproteins and coagulation factors [95], while also requiring lower doses of progestogens to protect the uterus [96]. These beneficial findings are very promising in light of the improvements in CHD risk and decreased stroke risk reported with low-dose estrogens [5]. It ill be interesting to see if CRP is increased with lower doses of estrogens and whether these changes are associated with increased early risk of CHD. Perhaps older women with CHD are also more obese, may have diabetes, and may be more susceptible to inflammatory and thrombotic effects of higher doses of estrogens. There are many questions left unanswered. It is hoped that some of the answers may come from the WHI, which is a large prospective trial assessing ERT and HRT. The age range is also relatively large and may be able to determine if older women respond differently than younger women. Some initial data from the WHI have been made available suggesting a small increased risk in the first 2 years and a trend for decreasing risk in the last months of the first 2 years [34]. Just recently, the CEE + MPA arm of the study was stopped early by the data and-safety monitoring board as the overall health risks exceeded benefits with increases in both breast cancer and CVD [97]. The remainder of the study groups including an estrogen-only arm, are expected to continue until 2005.

Estriol retards and stabilizes atherosclerosis through an NO-mediated system

Estriol (E3) has little effect on the female genitals. E3 is used in hormone replacement therapy, particularly in Europe and Japan, since it obviates the need for progestin administration. However, the effect of E3 on atherosclerosis has not been elucidated. In this study, we evaluated the effect of E3 on the progression of atherosclerosis in a rabbit model. Thirty-six rabbits total were used. Twenty-eight were bilaterally oophorectomized, and 8 were not. The rabbits were divided into 5 groups and treated for 12 weeks as follows. Gp I (n = 8) was fed a high cholesterol diet (HCD; standard diet plus 0.5% cholesterol); Gp II (n = 8) was fed a HCD with E3 (0.3 mg/kg/day); Gp III (n = 8) was fed a HCD with 17beta estradiol (E2) (0.1 mg/kg/day); Gp IV (n = 8), the non oophorectomized group, was fed a HCD; and Gp NC was oophorectomized (n = 4), and fed a regular diet. E3 treatment increased the plasma E2 and E3 levels in Gp II. The plasma lipid levels were not altered by the E2 or E3 treatment. A HCD diminished the acetylcholine-induced NO mediated relaxation in the thoracic aorta. The E2 treatment (Gp III) and E3 treatment (Gp II) restored the aortic basal NO release and the aortic cyclic GMP levels, particularly effectively in the E3 group. E3 treatment also decreased the atherosclerotic area, and its effect was comparable with E2 (surface involvement: 41.2 +/- 5.1% in Gp I; 10.1 +/- 2.7% in Gp II; and 6.5 +/- 1.3% in Gp III). All four hyperlipidemic groups showed an increase of eNOS mRNA in the aortae, and this was especially pronounced in Gps II and III. The level of peroxynitrite, as determined by immunohistochemical nitrotyrosine staining, was lower in Gps II and III than in Gp I. E3 strongly activates NO-mediated systems, and could play a role in retarding the progression of atherosclerosis and in stabilizing atheroma.

Conjugated estrogen administration improves common carotid artery elastic properties in normotensive postmenopausal women

BACKGROUND

Various vascular effects of estrogens have been proposed to explain further the beneficial effect of replacement therapy in cardiovascular events.

HYPOTHESIS

The study was undertaken to assess the effect of conjugated estrogen on the elastic properties of the large arteries in normotensive, healthy, postmenopausal women.

METHODS

Toward this end, we investigated the acute effect of conjugated estrogen on the elastic properties of the common carotid artery (CCA) in 20 normotensive, healthy, postmenopausal women (age 54+/-3 years) at baseline and 20 min after the intravenous administration of 1.25 mg conjugated estrogens. The CCA distensibility was derived by a combination of surface ultrasonographic data and simultaneous blood pressure measurements at the brachial artery. The carotid pulsatility index, a measure of brain impedance, was determined electronically by tracing the CCA Doppler waveform.

RESULTS

At baseline, CCA distensibility had a negative correlation with both patients' age and time since menopause (r = -0.57 and r = -0.48, p < 0.05 for both cases). After estrogen administration, estradiol and estrone plasma levels were restored to the range of usual premenopausal values. Estrogen induced a significant increase in CCA distensibility by 0.92+/-0.005 dyne(-1) x cm2 x 10(-6) (from 2.03 to 2.95 dyne(-1) x cm2 x 10(-6)) and a significant reduction in CCA pulsatility index by 0.24+/-0.06, (from 2.17 to 1.93) (p < 0.001 for both cases). The improvement in CCA distensibility had a negative correlation with both patients' age and time since menopause (r= -0.46 and r = -0.44, respectively, p < 0.05 for both cases).

CONCLUSIONS

Acute conjugated estrogen administration induced an improvement in CCA elasticity and a reduction in brain impedance in normotensive, postmenopausal women. As the age of women and the time since menopause increased, the improvement in carotid distensibility decreased in such selected subjects.

Hormonal influence on the release of endothelial nitric oxide: gender-related dimorphic sensitivity of rat aorta for noradrenaline

Male gender shows a higher incidence of vascular disorders and this phenomenon could be explained by sexual dimorphic behaviour of vessels. Both gonadal hormones and endothelial nitric oxide (NO) are involved in the regulation of the vascular reactivity. This study aimed to evaluate a possible sexual dimorphic sensitivity of rat aorta for the catecholamine noradrenaline. To understand the role played by physiological concentrations of sex hormones, the experimental procedures were performed on isolated preparations from intact (sham-operated) and gonadectomized rats of both sexes. In parallel sets of experiments, the biosynthesis of NO was inhibited by N'-nitro-L-arginine methyl ester (L-NAME) to reveal any potential involvement of the endothelial modulator and its possible link with the endocrinous factor. In aortae from intact male and female rats, noradrenaline induced contractile effects with different potencies (mean+s.d. EC50 values 12.15 +/- 5.25 nM and 84.10 +/- 18.68 nM, respectively). Gonadectomy resulted in an increased sensitivity for noradrenaline in female vessels and a decreased sensitivity for the agonist in male vessels (EC50 values 25.64 +/- 5.04 nM and 21.70 +/ 1 1.13 nM, respectively). In aortae from intact male rats, the inhibition of NO biosynthesis resulted in a weak increase in sensitivity for noradrenaline (EC50 value 6.08 +/- 4.53 nM), whereas the increase was higher in vessels from intact female rats (EC50 value 10.38 +/- 8.40 nM). After treatment with L-NAME, aortae from gonadectomized male and female rats presented almost equivalent increases in sensitivity for the adrenergic agonist (EC50 values 6.02 +/- 3.63 nM and 9.10+/- 9.63 nM,respectively),and no significant difference in sensitivity could be recorded between intact and orchidectomized male rats, or between intact and ovariectomized female rats. It was concluded that rat aorta showed a sexual dimorphic sensitivity for noradrenaline and the female sex was more protected against the adrenergic contractile stimulus because of a higher release of endothelial NO. The gender-related difference in NO release was influenced by gonadal hormones, with the female hormones inducing an increase and the male hormones causing a reduction.

Interactions between endothelial nitric oxide synthase and sex hormones in vascular protection in mice

The vasculoprotective effects of sex hormones, particularly estrogens, have been attributed to their ability to increase the bioavailability of nitric oxide through activation of endothelial nitric oxide synthase (eNOS). To dissect the relative contribution in vivo of eNOS, sex hormones, and their interaction in two complex vascular phenotypes, hypertension and atherosclerosis, we used mice doubly deficient in eNOS and apoE (nnee) or lacking only apoE (NNee). Females and males were gonadectomized at 1 month of age and implanted either with control pellets or pellets releasing 17beta-estradiol (E2). Hormonally intact nnee mice have elevated blood pressure (BP) and increased atherosclerosis compared with NNee mice, but on removal of gonads, BP and atherosclerosis decreased significantly in nnee mice but not in NNee mice. Three months of treatment with exogenous E2 dramatically reduced atherosclerosis and significantly lowered BP in both NNee and nnee mice compared with animals treated with control pellets. Thus exogenous E2 has strong BP-lowering and atheroprotective effects in apoE-deficient mice, but eNOS is not essential for either effect. Endogenous sex hormones, on the other hand, cause significant damage to the vasculature in the absence of eNOS, but these effects are overridden by interactions between eNOS and sex hormones.

Effect of estrogen on endothelial function and angiogenesis

Animal studies evaluating gender difference, the effects of gonadectomy and estrogen replacement and clinical studies in post-menopausal women with and without estrogen replacement therapy (ERT) proved that estrogen exerts significant benefits on the cardiovascular system. Since effects on the plasma lipoprotein profile is responsible for only approximately 25-40% of the cardiovascular protection exerted by estrogens, it is postulated that direct effects of estrogen on the vascular wall must play an important role. Indeed, experimental and clinical evidence accumulated over the past decade, and reviewed briefly here, indicate that at least a part of cardiovascular benefits of 17 beta-estradiol can be attributed to the direct effect of the ovarian sex steroid hormone on vascular endothelial cells. Maintenance and upregulation of endothelial nitric oxide production and suppression of EDCF generation by 17 beta-estradiol may play an important role in preventing or reversing endothelial dysfunction, associated with atherosclerosis, hypertension and other cardiovascular diseases. Stimulation of angiogenesis (especially collateral vessel formation in ischemic tissues) by the ovarian steroid hormone could be beneficial in coronary artery disease, peripheral vascular disease, cerebral ischemia (stroke) and congestive heart failure. Despite these indisputable beneficial effects, several key questions remain to be answered in the future, including the better understanding of the apparently opposite effects of estrogen on prevention of cardiovascular disease vs. treatment of existing disease.

Centchroman, a selective estrogen receptor modulator, as a contraceptive and for the management of hormone-related clinical disorders

DL-Centchroman (67/20; INN: Ormeloxifene) synthesized at the Central Drug Research Institute, Lucknow, is a nonsteroidal once-a-week oral contraceptive. It was introduced in Delhi in July, 1991, marketed in India in 1992 as Saheli and Choice-7 (Hindustan Latex Ltd., Thiruvananthapuram) and Centron (Torrent Pharmaceuticals India Ltd., Ahmedabad), and included in the National Family Welfare Programme in 1995.5 According to post-marketing surveillance, approximately 100,000 women were using this pill and approximately 1100,000 menstrual cycles were covered until 1996. It is a unique need-oriented contraceptive being effective when taken immediately after coitus or routinely as a weekly pill and has the advantage of less frequent administration. Its contraceptive action is quickly reversible. It has long terminal serum halflife of 168 hr in women and exhibits duration of anti-implantation/estrogen antagonistic action of 120 hr, despite a short (24.1 hr) serum halflife, in the rat. In lactating women, it is excreted in milk in quantities considered unlikely to cause any deleterious effect on suckling babies. In phase II and III multicentric trials as a contraceptive, children born of method-and-user failure pregnancies showed normal milestones, without any congenital anomaly. Reports of its promising action in the management of certain hormone-related clinical disorders are available. It has an excellent therapeutic index and is considered safe for chronic administration.

Estrogens, progestins, selective estrogen receptor modulators, and the arterial tree

We reviewed studies of the effects of different estrogens, progestins, and selective estrogen receptor modulators at the coronary and carotid arterial sites to help determine their likely effects on cardiovascular morbidity and mortality. All English-language studies published between 1997 and 2000 on MEDLINE, Current Contents, and Best Evidence were reviewed, including in vitro, other animal, human physiologic, and clinical trial studies. We synthesize, assess limitations, and integrate across systems with the in vivo experience in humans to evaluate the clinical context. Estrogens have favorable direct effects in most circumstances, progestins oppose these effects, and early studies suggest that selective estrogen receptor modulators are protective. In some systems the dosage, route of delivery, and type of progestin may be important and risk factors may modulate hormone effects. The evaluation of endothelial dysfunction gives a unique in vivo opportunity to assess the vascular properties of hormones, although the relationship between the in vivo physiologic effects of hormones and clinical outcomes remains to be determined.

Estrogen-induced cardiorenal protection: potential cellular, biochemical, and molecular mechanisms

A number of cellular and biochemical processes are involved in the pathophysiology of glomerular and vascular remodeling, leading to renal and vascular disorders, respectively. Although estradiol protects the renal and cardiovascular systems, the mechanisms involved remain unclear. In this review we provide a discussion of the cellular, biochemical, and molecular mechanisms by which estradiol may exert protective effects on the kidneys and vascular wall. In this regard, we consider the possible role of genomic vs. nongenomic mechanisms and estrogen receptor-dependent vs. estrogen receptor-independent mechanisms in mediating the protective effects of estradiol on the renal and cardiovascular systems.

Alterations in EDHF-mediated hyperpolarization and relaxation in mesenteric arteries of female rats in long-term deficiency of oestrogen and during oestrus cycle

This study was undertaken to determine whether endothelium-dependent relaxations are altered in mesenteric arteries from young female rats during oestrus cycle and after castration. The contractile response to phenylephrine (Phe) was significantly enhanced in arteries from rats subjected to ovariectomy than in those from sham-operated (control) rats. Treatment of ovariectomized rats with 17beta-oestradiol returned the Phe response to the control level. Arteries from rats at the diestrus stage also exhibited greater contraction in response to Phe. In the presence of 100 microM N(G)-nitro-L-arginine (L-NOARG), the enhancement of the Phe contractile response associated with oestrogen deficiency was not observed. Endothelium-dependent relaxations elicited by acetylcholine (ACh) in arteries precontracted with Phe were significantly reduced in ovariectomized and diestrus rats regardless of whether endothelium-derived nitric oxide (NO) was blocked with L-NOARG. Treatment with 17beta-oestradiol prevented the reduced vascular relaxant response to ACh in ovariectomized rats. The reduction in the ACh responses observed in ovariectomized and diestrus rats was eliminated when 500 nM apamin and 100 nM charybdotoxin were present. ACh-induced endothelium-dependent hyperpolarizations were depressed in arteries from ovariectomized and diestrus rats. The hyperpolarizing response to ACh was significantly improved when ovariectomized rats were treated with 17beta-oestradiol. The resting membrane potentials and pinacidil-induced hyperpolarizations were unaffected by ovariectomy or the diestrus stage. These results suggest that oestrogen-deficient states of both short and long duration reduce the basal release of NO from the endothelium and specifically attenuate endothelium-dependent hyperpolarization and relaxation transduced by endothelium-derived hyperpolarizing factor.

Raloxifene and estrogen reduces progression of advanced atherosclerosis--a study in ovariectomized, cholesterol-fed rabbits

The present study investigated the effect of raloxifene, a selective estrogen receptor modulator (SERM), on aortic atherosclerosis in 80 ovariectomized, cholesterol-fed rabbits with pre-induced atherosclerosis. The animals were fed an atherogenic diet containing 240 mg cholesterol/day for 15 weeks, after this period a baseline control group was sacrificed. Thereafter, oral treatment was initiated with either estradiol 4 mg/day (n=20), raloxifene (210 mg/day) or placebo (n=20). In the treatment period of 39 weeks, the dietary cholesterol content was reduced to 80 mg cholesterol/day. Postmortem evaluation showed a significantly increased uterine weight induced by estradiol treatment (10.3+/-1.2 g), whereas raloxifene intervention caused a decreased uterus weight (1.21+/-0.1 g) when compared to placebo (2.48+/-0.47 g). Throughout the study, serum lipids increased in all groups to levels seen in very high risk humans. After 58 weeks the cholesterol content in the aorta was 3.18+/-0.54 micromol/cm(2) (38% reduction) in the estradiol group, 3.66+/-0.52 micromol/cm(2) (29% reduction) in the raloxifene group and 5.12+/-0.60 micromol/cm(2) in the placebo group. Analyses of the aortic cholesterol content corrected for time-averaged serum cholesterol revealed that both estradiol and raloxifene therapy significantly reduced the progression of atherosclerosis (P<0.01 for both) as compared to placebo.

GnRH agonist-suppressed expression of nitric oxide synthases and generation of peroxynitrite in adenomyosis

Because overproduction of nitric oxide (NO) and peroxynitrite is known to cause tissue injury, the expression of NO synthases (NOS) and generation of peroxynitrite were investigated in adenomyosis. Immunoreactivities to endothelial and inducible NOS demonstrated phase-dependent changes in normal endometrium, and in eutopic endometrium of adenomyosis. However, NOS were expressed throughout the menstrual cycle in ectopic endometrium from the majority of patients with adenomyosis. Nitrotyrosine, a footprint of peroxynitrite, was detected concomitantly with NOS protein. This suggested that high doses of NO and superoxide are produced in the ectopic endometrium, presumably by stimulation with bioactive molecules such as cytokines and growth factors. The expression of NOS and generation of peroxynitrite were markedly reduced by administration of gonadotrophin-releasing hormone agonists (GnRHa). The suppression of serum concentrations of nitrite/nitrate, stable metabolites of NO, by long-term administration of GnRHa was also demonstrated. The suppression of synthesis of NO and/or peroxynitrite may be part of both the therapeutic and adverse effects of GnRHa therapy.

Physiological concentration of 17beta-estradiol retards the progression of severe atherosclerosis induced by a high-cholesterol diet plus balloon catheter injury: role of NO

The molecular mechanisms of the antiatherosclerotic effects of estrogen are not yet known. We evaluated the effects of 17beta-estradiol (E(2)) on high cholesterol diet- (HCD; standard diet and 1% cholesterol) and balloon injury-induced atherosclerosis in female New Zealand White rabbits. The abdominal aortas of 40 oophorectomized (Groups 1 through 5) and 8 nonoophorectomized (Group 6) rabbits were injured by balloon catheter, and the animals were then divided into the following groups and treated for 10 weeks: Group 1, standard diet; Group 2, standard diet plus a moderate dose of E(2) (100 microg x kg(-1) x d(-1)); Group 3, HCD; Group 4, HCD plus a moderate dose of E(2); Group 5, HCD plus a low dose of E(2) (20 microg x kg(-1) x d(-1)); and Group 6, HCD in nonoophorectomized rabbits. After the treatment phase, plasma E(2) was increased up to 282.2+/-45.5 pg/mL in Group 2, 263.0+/-41.5 pg/mL in Group 4, 87. 9+/-18.8 pg/mL in Group 5, and 45.6+/-7.3 pg/mL in Group 6. HCD-mediated increases in plasma lipid levels were not changed by E(2) treatment, whereas E(2) decreased the aortic intimal thickening in Group 2 animals compared with those in Group 1 and reduced atherosclerosis in the thoracic and abdominal aortas of Group 4, 5, and 6 rabbits compared with those in Group 3. E(2) restored the impaired abdominal aortic endothelium-dependent relaxation of balloon-injured and HCD-supplemented rabbits, and E(2) increased basal nitric oxide (NO) release. The basal NO-releasing effect showed a significant, inverse relation with the severity of atherosclerosis. Plasma E(2) concentration also showed a significant, inverse relation with atherosclerotic area. In conclusion, physiological concentrations of E(2) can retard the progression of severe atherosclerosis and stabilize atheromas induced by HCD and balloon injury. The retardation may be partially mediated by endothelial NO function in vessels treated with E(2).

Dehydroepiandrosterone retards atherosclerosis formation through its conversion to estrogen: the possible role of nitric oxide

Dehydroepiandrosterone (DHEA) is speculated to have an antiatherosclerotic effect, although the mechanism of action remains unclear. The objective of the current study was to determine whether the antiatherosclerotic effect of DHEA is related to its conversion to estrogen and to define the role of nitric oxide (NO) in the antiatherosclerotic effect of DHEA. Forty-eight oophorectomized rabbits were divided into 5 groups and fed the following diets for 10 weeks: group 1, a regular rabbit diet plus 1% cholesterol (a high-cholesterol diet [HCD]); group 2, an HCD plus 0.3% DHEA; group 3, an HCD plus 0.3% DHEA and fadrozole (2.0 mg x kg(-1) x d(-1)), a specific aromatase inhibitor; group 4, an HCD plus 17beta-estradiol (20 microg x kg(-1) x d(-1)); and group 5, a regular diet. Atherosclerotic lesions, lipid deposition in aortic vessels, and basal and stimulated NO release were measured in the aforementioned groups of rabbits. NO release was measured by using an NO-selective electrode as well as by measuring vascular responses and the plasma NO metabolites nitrite and nitrate. The plasma total cholesterol level was increased, but there were no significant differences in lipid profile in the 4 groups of rabbits that were fed the HCD. The area occupied by atherosclerosis in the thoracic aorta was diminished by approximately 60% in the DHEA-treated rabbits (group 2) compared with the HCD group of rabbits (group 1); there was a corresponding 80% decrease in the estradiol group (group 4) but only a 30% decrease in the DHEA plus fadrozole group (group 3). In the aortas of rabbits from groups 1 and 3, the acetylcholine-induced and tone-related basal NO-mediated relaxations were diminished compared with those of the controls (group 5). However, these relaxations were restored in the aortas of group 2 and 4 rabbits, and an increase in NO release was observed in groups 2 and 4 compared with groups 1 and 3, as measured by an NO-selective electrode. Injection of neither solvent (20% ethanol/distilled water) nor fadrozole significantly affected the atherosclerotic area or the NO-related responses described above. We conclude that approximately 50% of the total antiatherosclerotic effect of DHEA was achieved through the conversion of DHEA to estrogen. NO may also play a role in the antiatherosclerotic effect of DHEA and 17beta-estradiol.

Metabolism of levormeloxifene, a selective oestrogen receptor modulator, in the Sprague-Dawley rat, Cynomolgus monkey and postmenopausal woman

1. The metabolic fate of levormeloxifene in the Sprague-Dawley rat, Cynomolgus monkey and postmenopausal volunteer has been investigated. 2. Two doses of [14C]levormeloxifene, 0.7 and 50 mg/kg, were given to the male and female rat and monkey, and a single 20-mg dose to the postmenopausal volunteer. 3. The primary route of excretion in all three species was the faeces. Metabolism was similar in all three species, with demethylation forming the major metabolite in the rat and postmenopausal volunteer. One of the major metabolites in the monkey involved an oxidative ring opening of a pyrrole ring. 4. The main site of metabolism of levormeloxifene is the liver and the majority of the drug and its metabolites is excreted via the faecal route. Metabolic pathways appear to be similar in the three species studied.

Raloxifene reduces atherosclerosis: studies of optimized raloxifene doses in ovariectomized, cholesterol-fed rabbits

OBJECTIVE

We have previously shown that raloxifene, a selective oestrogen receptor modulator, 35 mg/day inhibits atherosclerosis in ovariectomized, cholesterol-fed rabbits. This effect was only partial as compared to 17beta-oestradiol 4 mg/day; however, plasma raloxifene concentrations were low relative to those obtained in raloxifene-treated women. We therefore investigate the effects of raloxifene at higher doses.

DESIGN

The study on atherosclerosis in ovariectomized, cholesterol-fed rabbits (n = 80) compared raloxifene 70 mg/day and 210 mg/day to 17beta-oestradiol 4 mg/day and placebo.

RESULTS

After 48 weeks of therapy, the aortic cholesterol content in the 70 mg/day and 210 mg/day raloxifene treatment groups were 471 +/- 56 nmol/mg protein and 456 +/- 56 nmol/mg protein, respectively. This was significantly less than in the placebo group (654 +/- 69 nmol/mg protein; P < 0.05). In the oestrogen-treated group, the aortic cholesterol content was 357 +/- 62 nmol/mg protein (P < 0.01 as compared to placebo). Differences in serum lipids between the treatment groups could only partly explain the effect on aortic cholesterol content, indicating that additional anti-atherogenic mechanisms may contribute to the decrease in aortic atherosclerosis. This anti-atherosclerotic activity of raloxifene was observed at plasma concentrations comparable to those in postmenopausal women during raloxifene treatment.

CONCLUSIONS

We conclude that clinically relevant raloxifene treatment inhibits aortic atherosclerosis in ovariectomized, cholesterol-fed rabbits.

Protection by shear stress from collar-induced intimal thickening: role of nitric oxide

Nitric oxide (NO) has potent relaxant and antiproliferative effects on vascular smooth muscle cells, which may represent an important antiatherosclerotic mechanism. Since one of the major stimuli for NO release is flow-related shear stress, we have investigated (1) the effect of increased shear stress on neointimal formation induced in the rabbit carotid artery by enclosing the vessel in a nonconstrictive silicone soft collar and (2) the role of NO in the antiproliferative effect of increased shear stress. Forty-three New Zealand White rabbits were used. High shear stress in the left common carotid artery (CCA) was induced by ligature of the contralateral right internal carotid artery; intimal thickening was produced by the positioning a nonconstrictive silicone soft collar around the left CCA. To evaluate the role of NO, N(G)-nitro-L-arginine methyl ester (L-NAME) was orally administered at a subpressor dose. In all rabbits, arterial blood pressure, heart rate, arterial diameters, and blood flow velocities of both CCAs were determined at days 0, 3, 7, and 14. At the end of the study, all rabbits were euthanized, and histological analyses were performed on both CCAs of each animal. The presence of the collar was associated with a marked degree of intimal hyperplasia (intimal/medial area ratio 29+/-3.0% in collared arteries compared with 3+/-0.7% in sham control [noncollared] arteries, P<0.001). The increase in blood flow almost completely inhibited neointimal formation and induced an increase in arterial diameter of approximately 30%. The effects of increased blood flow were reversed by the administration of L-NAME. In conclusion, we demonstrate that in collar-induced intimal thickening, a chronic increase in shear stress (1) almost completely inhibits intimal thickening, and (2) this protective effect is mediated by NO production.

Effect of 17-beta estradiol on pre-existing atherosclerotic lesions: role of the endothelium

The atheroprotective effects of estrogen during the process of atherogenesis is well documented, whereas limited information is available about the effect of estrogen on pre-existing atherosclerotic lesions. After bilateral ovariectomy, 24 New Zealand White rabbits were randomized into three groups of eight animals each and subsequently fed a 0.5% cholesterol diet. In group I, the vessels were excised at day 84, whereas in group II, the cholesterol diet was continued for a total of 168 days. In group III, the animals were first fed with a cholesterol diet for 84 days; in the second phase of the experiment, the cholesterol diet was continued for a further 84 days with a combined estrogen treatment (1 mg estradiol valerate per kg body weight per week intramuscularly). At the end of the experiment, the proximal aortic arch, right carotid artery, thoracical aorta and abdominal aorta of each animal were excised and prepared for histological and immunohistological examination. By day 168, morphometrical analysis displayed a significantly lower plaque development under estrogen therapy in the carotid artery (0.08+/-0.18 mm(2) vs. 0.60+/-0.39 mm(2)), the thoracic aorta (0.56+/-0.94 mm(2) vs. 3.63+/-2.06 mm(2)), and in the abdominal aorta (0.55+/-0.70 mm(2) vs. 1.71+/-1.05 mm(2)) in comparison with the corresponding 168 day control group. However, estrogen treatment has failed to reduce further atherosclerotic plaque development in the aortic arch (9.42+/-1.79 mm(2) vs. 11. 64+/-3.29 mm(2)). Immunohistological detection of the 'anti-human factor VIII related antigen', i.e. the 'von Willebrand factor' (vWF), showed a significantly lower number of luminal cells positive for vWF in the aortic arch in the 84-day cholesterol group, compared with the corresponding controls of normocholesterolemic rabbits (65. 9+/-12.4% vs. 83.1+/-6.2%; P<0.05). Estradiol was able to inhibit the further progression of atherosclerosis when moderate vessel wall alterations were present, whereas pre-existing severe atherosclerosis was associated with a failure of the anti-atherosclerotic estrogen action. As suggested by the in situ detection of vWF as a morphological marker for endothelial cells, an intact endothelial layer might play an important role in mediating the beneficial effect of estrogen in the process of atherosclerosis.

The direct antiatherogenic effect of estrogen is present, absent, or reversed, depending on the state of the arterial endothelium. A time course study in cholesterol-clamped rabbits

BACKGROUND

This study further investigated the relationship between estrogen, arterial endothelium, and nitric oxide (NO) in cholesterol-clamped rabbits.

METHODS AND RESULTS

Rabbits were ovariectomized, balloon-injured in the thoracic aorta, and grouped to receive cholesterol-enriched chow together with either 17beta-estradiol or vehicle for 1, 2, 4, or 8 weeks. In the undamaged aorta, cholesterol accumulation of the placebo rabbits was significantly increased from week 4 to 8 (P<0.001). This increase was almost completely inhibited by estrogen (P<0.001). In the balloon-injured aorta, the estrogen and placebo rabbits accumulated similar amounts of cholesterol in the reendothelialized areas. In the deendothelialized areas, the estrogen group surprisingly accumulated significantly more cholesterol than the placebo group. This difference was apparent from week 2 and became significant at week 8 (P<0.01). Circulating nitrite/nitrate were significantly increased by estrogen at weeks 1, 2, and 4 but not at week 8. Similarly, in additional experiments, basal NO release was significantly higher in estrogen-treated than in placebo-treated rabbits after 4 (P<0.05) but not after 8 weeks. Stimulated NO release and endothelial NO synthase activity did not differ between groups. Mononuclear-endothelial cell binding was reduced by 50% by estrogen after 4 weeks (P<0.05). This difference, however, was abolished by coadministration of N(G)-nitro-L-arginine methyl ester, an inhibitor of NO production.

CONCLUSIONS

The direct antiatherogenic effect of estrogen was present, absent, or reversed, depending on the state of the arterial endothelium, and preceded by a transient increase in NO production followed by a reduced mononuclear-endothelial cell binding.

Interleukin-1beta-induced nitric oxide production in rat aortic endothelial cells: inhibition by estradiol in normal and high glucose cultures

Expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide (NO) production are associated with septic shock, atherosclerosis, and cytokine-induced vascular injury. Estrogen is known to impact vascular injury and vascular tone, in part through regulation of NO production. In the current study, we examined the effect of physiological concentrations of estradiol on interleukin-1beta (IL-1beta)-induced NO production in rat aortic endothelial cells (RAECs). 17Beta-estradiol significantly decreased IL-1beta-induced iNOS protein levels and reduced NO production in RAECs. High glucose (25 mM) elevated the increase in IL-1beta-induced iNOS protein and NO production. Nevertheless, estradiol still inhibited IL-1beta-induced iNOS and NO production even in the presence of high glucose. These data suggest that estradiol may exert its beneficial effects in part by inhibiting induction of endothelial iNOS, a possible mechanism for the protective effect of estradiol against diabetes-associated cardiovascular complications.

Lipoprotein modification and atherosclerosis in aging

The development of extensive atherosclerosis of major arteries of the heart, brain, and lower extremities is a particularly frequent problem in elderly individuals and is responsible for the majority of the cardiovascular morbidity and mortality in this population. Although the frequency and severity of this problem is well recognized, there has been relatively little investigation of the effects of aging on the development of atherosclerosis. Work by a number of investigators over the last 10-15 years has demonstrated that modifications of lipoproteins, resulting from oxidative stress, glycoxidation, formation of AGE, or other processes may play an important role in atherosclerosis. As described in this review, the aging process may enhance lipoprotein modification and atherosclerosis in several ways. Conditions such as hypertension, diabetes, and menopause all increase in frequency with advancing age and may contribute both directly and indirectly to lipoprotein modification and vascular injury.Additionally, in some studies of older animals and humans, there seems to be evidence for greater in vivo oxidative stress. Whether this is a specific consequence of aging and associated medical conditions, or related to differences in dietary fatty acid or antioxidant content or other lifestyle differences is currently unknown. One important consequence of this may be enhanced susceptibility of lipoproteins to oxidation. Additional study of lipoprotein modifications associated with aging is clearly needed, and may provide new insight and solutions to the common problem of atherosclerosis in the elderly.

Antiatherosclerotic activity of drugs in relation to nitric oxide function

Many studies have shown that loss of endothelium-derived nitric oxide is a major factor of ischemic episodes in patients with coronary artery disease and there is increasing evidence to suggest that nitric oxide might exert antiatherosclerotic actions. Based on these concepts, the results of animal studies on the effects of lipid lowering drugs, antioxidants, angiotensin converting enzyme inhibitors, Ca2+ channel blockers, estrogens and agents which modulate nitric oxide bioavailability are presented and compared to the results of patient studies and clinical trials. In spite of encouraging results obtained with antioxidants in animals, clinical trials could only show a clear positive effect of vitamin E treatment on the outcome of cardiovascular disease. Angiotensin converting enzyme inhibitors can ameliorate endothelial dysfunction in coronary heart disease, but their impact on disease progression remains unclear. There is evidence that estrogen replacement therapy in post-menopausal women may increase the bioavailability of nitric oxide. Finally, improved endothelial function and plaque stability clearly contribute to the clinical benefits of lipid lowering interventions, statins in particular. Taken together, these studies lend support to the concept that improving endothelial function and nitric oxide release might serve as valuable elements in the prevention or therapy of cardiovascular disease.

Effect of 17beta-estradiol in hypercholesterolemic rabbits with severe endothelial dysfunction

17beta-Estradiol prevents early vascular lesion development and may also affect advanced atherosclerosis. To test the antiatherosclerotic effect of estrogen under conditions that resemble more advanced human atherosclerosis with severe endothelial dysfunction, we have investigated the effect of 17beta-estradiol in hypercholesterolemic rabbits treated with the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME). Chronic L-NAME administration attenuated endothelial nitric oxide (EDNO)-mediated vascular responses leading to significantly accelerated atherosclerotic plaque development. 17beta-Estradiol treatment alone inhibited aortic lesion formation with concurrent increase in EDNO-mediated responses. The beneficial effect of estrogen persisted in the L-NAME-treated rabbits, suggesting that the antiatherogenic action of 17beta-estradiol involves NO-independent mechanisms as well. Serum cholesterol levels were not altered by any of the treatments. 17beta-Estradiol treatment significantly increased EDNO production under these conditions as well. The reduction in plaque size by 17beta-estradiol was always accompanied by increased EDNO production, suggesting a strong association between these two events. The results demonstrate that estrogen treatment may exert protection against atherosclerosis even in patients with severe endothelial dysfunction.

Effect of estrogen on aortic function in postmenopausal women

We hypothesized that estrogen may alter aortic elastic properties. The aortic pressure-diameter relation was obtained in 20 postmenopausal women, 10 without (group 1) and 10 with (group 2) proven coronary artery disease, before and after intravenous administration of 10 micrograms of 17beta-estradiol. Instantaneous aortic diameter was measured by an intravascular catheter developed in our institution simultaneously with aortic pressure at the same aortic level with a catheter-tipped micromanometer. At baseline, elastic properties of the aorta were decreased in group 2 compared with group 1. Compared with baseline, aortic distensibility was increased in both groups (P < 0.01 and P < 0.05 for groups 1 and 2, respectively) after estrogen administration, whereas the pressure-diameter loop was shifted downward along a different hypothetical line of elasticity, suggesting active changes in the aortic elastic properties. Furthermore, a significant reduction in wave reflection was found in both groups (P < 0.001). This action may contribute to the beneficial effects of estrogen on the cardiovascular system and may have future therapeutic implications in postmenopausal women.

Effect of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in the rat aorta

1. This study sought to evaluate whether the effects of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism. 2. Ovariectomized rats were treated daily with either 17-beta-estradiol-3-benzoate (100 microg kg(-1)) or vehicle for 1 week. 3. The effect of long-term 17-beta-estradiol treatment on the responses to cumulative doses of phenylephrine, 5-HT, calcium, potassium and 17-beta-estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17-beta-estradiol (5 and 10 microM) on the dose response curves for phenylephrine, 5-HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone-related basal release of nitric oxide (NO) was measured in rings with intact endothelium. 4. Long-term 17-beta-estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17-beta-estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium. 5. Long-term 17-beta-estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17-beta-estradiol had no effect. The tone-related release of NO was significantly increased after long-term exposure to 17-beta-estradiol. 6. In conclusion, this study indicate that the acute and long-term effects of 17-beta-estradiol in the rat aorta are mediated through different mechanisms. The long-term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17-beta-estradiol seems to be through an effect on the vascular smooth muscle cells.

Gender gap in aortic cholesterol accumulation in cholesterol-clamped rabbits: role of the endothelium and mononuclear-endothelial cell interaction

BACKGROUND

The purpose of the present study was to investigate plasma lipid-independent mechanisms for the sex difference in the development of atherosclerosis.

METHODS AND RESULTS

In the first experiment, 20 male and 20 female rabbits were balloon-injured in the middle thoracic aorta and maintained at the same plasma cholesterol level of approximately 25 mmol/L by use of individualized cholesterol feeding for 13 weeks. In the undamaged aorta, female rabbits had accumulated less than half the amount of cholesterol found in male rabbits (P<0.05). In the balloon-injured aorta, cholesterol accumulation was 3- to 4-fold higher than in the undamaged aorta, with no difference between groups. When cholesterol accumulation data for the balloon-injured aorta were separately assessed for blue (deendothelialized) and white (reendothelialized) tissue, blue tissue surprisingly revealed a reverse gender gap, ie, a significantly higher accumulation of cholesterol in females than in males (P<0.05). White tissue, which constituted the majority of the balloon-injured area, showed no difference in aortic cholesterol accumulation between groups. In the second experiment, 6 male and 6 female rabbits were fed standard rabbit pellets and 6 male and 6 female rabbits were fed a 0.5% cholesterol-enriched chow for 2 weeks. Mononuclear cell binding was 5-fold higher in aortic segments from hypercholesterolemic than from normocholesterolemic rabbits (P<0. 001). In hypercholesterolemic rabbits, cell binding was significantly lower in female than in male rabbits (P<0.05) and showed higher values in atherosclerosis-prone regions. These differences were not found in normocholesterolemic animals.

CONCLUSIONS

The present results suggest that female atheroprotection is independent of sex differences in plasma cholesterol but vitally dependent on the state of the arterial endothelium and involves mononuclear-endothelial cell adhesion as an early step.

Estrogens and atherosclerosis: phytoestrogens and selective estrogen receptor modulators

The development of atherosclerosis in animal models and the incidence of coronary heart disease in postmenopausal women are markedly reduced by estrogen treatment. Estrogen have acute beneficial effects on vascular reactivity and longer-term effects on critical steps in the pathogenesis of atherosclerosis. Phytoestrogens present in soybeans and other plant products are weak estrogens but appear to have potent beneficial effects on the arterial wall. The phytoestrogens have certain similarities to 'designer hormones' which are being developed to retain their beneficial effects on the cardiovascular system and the skeleton without having cancer promoting effects on the breast and endometrium.