Beyond the null hypothesis--do the HERS results disprove the estrogen/coronary heart disease hypothesis?

Effects of Conventional or Lower Doses of Hormone Replacement Therapy in Postmenopausal Women

OBJECTIVE

The effects of hormone replacement therapy (HRT) can affect many aspects relevant to cardiovascular disease, including vasomotor function, inflammation, and hemostasis. Recent studies have demonstrated that current doses of HRT exert a mixture of both protective and adverse effects. In the current study, we compared the effects of lower doses of HRT (L-HRT) and conventional doses of HRT (C-HRT) on a variety of relevant cardiovascular parameters.

METHODS AND RESULTS

This randomized, double-blind, crossover study included 57 women who received micronized progesterone 100 mg with either conjugated equine estrogen 0.625 mg (C-HRT) or 0.3 mg (L-HRT) daily for 2 months. L-HRT showed comparable effects to C-HRT on high-density lipoprotein cholesterol and triglyceride levels, but not on low-density lipoprotein cholesterol levels. C-HRT and L-HRT significantly improved the percent flow-mediated dilator response to hyperemia from baseline values (both P<0.001) by a similar degree (P=0.719). C-HRT significantly increased high-sensitivity C-reactive protein (hsCRP) levels from baseline values (P<0.001); however, L-HRT did not significantly change hsCRP (P=0.874). C-HRT and L-HRT significantly decreased antithrombin III from baseline values (P<0.001 and P=0.042, respectively). C-HRT significantly increased prothrombin fragment 1+2 (F1+2) from baseline values (P<0.001); however, L-HRT did not significantly change F1+2 (P=0.558). Of interest, the effects of C-HRT and L-HRT on hsCRP, antithrombin III, and F1+2 were significantly different (all P<0.001). C-HRT and L-HRT significantly reduced plasma PAI-1 antigen levels from baseline values (P=0.002 and P=0.038, respectively) to a similar degree (P=0.184).

CONCLUSIONS

Compared with C-HRT, L-HRT has comparable effects on lipoproteins, flow-mediated dilation, and PAI-1 antigen levels. However, L-HRT did not increase hsCRP or F1+2 levels, and it decreased antithrombin III less than C-HRT.

Significant differential effects of hormone therapy or tibolone on markers of cardiovascular disease in postmenopausal women: a randomized, double-blind, placebo-controlled, crossover study

OBJECTIVE

The objective was to compare the effects of tibolone and hormone therapy (HT) on lipid profile, vasodilation, and factors associated with inflammation and hemostasis.

METHODS AND RESULTS

Fifty-three women received micronized progesterone (MP, 100 mg) with conjugated equine estrogen (CEE, 0.625 mg) or tibolone (2.5 mg) daily for 2 months, with a 2-month washout period. Compared with HT, tibolone significantly reduced total cholesterol (P<0.001), triglyceride (P<0.001), and HDL cholesterol (P<0.001) levels as well as triglyceride/HDL cholesterol ratios (P<0.001) but not LDL cholesterol levels. Tibolone significantly improved flow-mediated brachial artery dilator response to hyperemia from baseline values (P<0.001) by a magnitude similar to that found with HT (P=0.628). Compared with tibolone, which showed no changes, HT significantly increased high-sensitivity C-reactive protein (hsCRP, P=0.030) and reduced antithrombin III (P<0.001). HT and tibolone significantly increased prothrombin fragment 1+2 (F1+2) from baseline values (P<0.001 and P=0.004, respectively). The effects of HT and tibolone on hsCRP, antithrombin III, and F1+2 were significantly different. HT and tibolone significantly reduced plasma levels of plasminogen activator inhibitor type 1 antigen from baseline levels (P=0.006 and P=0.005, respectively) to a similar degree (P=0.988).

CONCLUSIONS

Tibolone significantly improved flow-mediated brachial artery dilator response by a magnitude similar to that found with CEE+MP; however, tibolone did not significantly change hsCRP and antithrombin III, and tibolone increased F1+2 less than did CEE+MP.

Can a healthy endothelium influence the cardiovascular effects of hormone replacement therapy?

Emerging clinical and observational evidences suggest that estrogen confers physiologic benefits that are receptor mediated and depend on the integrity and functional status of the endothelium within the coronary vasculature. In postmenopausal women, estrogen replacement therapy (ERT) and hormone replacement therapy (HRT) regimens can enhance the lipoprotein panel; blunt the expression of numerous cytokines, chemokines, and other proinflammatory mediators of endothelial injury and vascular smooth muscle cell proliferation; up-regulate endothelial nitric oxide synthase activity and nitric oxide production; and augment fibrinolysis potential and vasodilator capacity (diminish arterial resistance). Advancing age and atherosclerotic injury to the vessel wall tend to deplete estrogen receptors, compromise endothelial function, promote thrombus formation, and thus potentially diminish the efficacy of ERT and HRT. Therefore, optimizing the clinical benefits of these regimens in postmenopausal women depends largely on promoting a healthy endothelium through life-style modifications that diminish coronary risk.

Strategies for the prevention of atherosclerotic progression in women

Atherosclerosis is an inflammatory and fibrotic process that begins early in life in females. The pathogenesis involves the oxidation of the low-density lipoprotein molecule aggravated by smoking, hypertension, lipid abnormalities, and hormonal changes. Risks for progression of atherosclerosis can now be tabulated for the female based on age, cholesterol, smoking, high-density lipoprotein, and systolic blood pressure. During the reproductive years, emphasis should be placed on lifestyle changes, but women at increased risk for diabetes should be aggressively treated with lipid-lowering agents. During the menopausal phase of life, an important consideration is the use of hormone replacement along with lifestyle changes, smoking cessation, blood pressure control, and lipid modification. In the female with established coronary heart disease, standard cardiac medications are indicated along with more aggressive approaches to risk factors and target goals for cholesterol, low-density lipoprotein, and triglycerides. The effect of hormone replacement in established coronary artery disease is uncertain. Therefore, strategies for slowing the progression of atherosclerosis should begin during the reproductive years, with particular emphasis in patients during menopause and in patients with coronary heart disease.

Pharmacological approaches to preserving and restoring coronary endothelial function

There is compelling evidence that the endothelium is critical to normal coronary vascular function and that endothelial dysfunction, generally indicated by an impairment of endothelium-dependent vasodilatation, is an important component of coronary artery disease (CAD). Endothelial cells synthesise and release a number of factors, including prostacyclin, nitric oxide (NO), endothelium-derived hyperpolarising factor (EDHF) and endothelin, which are important in the regulation of vascular tone and the control of platelet and leukocyte adhesion, aggregation and migration. NO appears to be the critical factor in the preservation of normal coronary vascular function and there is a well-established correlation between CAD and an impairment of NO activity. Thus, to preserve endothelial function, drugs have been used to either increase the synthesis of NO, or to decrease its breakdown. Fortuitously, compounds such as the HMG-CoA reductase inhibitors, angiotensin (AT) converting enzyme inhibitors (ACEIs), AT receptor antagonists and oestrogen, which have been introduced into clinical practice because of other beneficial effects, have also been shown to improve coronary endothelial function through a variety of mechanisms. In addition, L -arginine, the substrate for NO synthesis, and the anti-oxidants ascorbate and alpha-tocopherol, are able to increase NO synthesis and bioavailability respectively. Studies in experimental animals strongly support the ability of these agents to enhance the activity of endothelium-derived NO but clinical trials have failed to demonstrate reversal of established CAD. Whether these agents preserve endothelial function and prevent the development of CAD remains to be established.

Lipid disorders: justification of methods and goals of treatment

Dyslipidemia is a major risk factor for coronary heart disease (CHD). While some uncertainty exists about the clinical significance of improving high-density lipoprotein cholesterol and triglyceride levels, large primary- and secondary-prevention studies aimed at lowering low-density lipoprotein cholesterol levels with statins have convincingly reduced CHD events and total mortality. Despite the strong clinical evidence and widely publicized treatment guidelines, many hyperlipidemic patients receive inadequate lipid-lowering treatment. This failure to achieve clinical treatment goals may be due to poor physician adherence to treatment guidelines, patient noncompliance, and the presence of concomitant medical conditions that modify typical hyperlipidemia management. This review considers the challenges and available strategies to optimize lipid management in patients at risk for CHD.

Hormone replacement therapy for prevention of coronary heart disease: current evidence

Postmenopausal estrogen replacement, with or without progestin therapy, has a generally favorable impact on lipids, improves endothelial function, and has anti-inflammatory and antioxidant effects. These properties should favorably impact coronary risk; indeed, epidemiologic studies have consistently associated hormone replacement therapy with reduced coronary risk. Nonetheless, the Heart & Estrogen/progestin Replacement Study (HERS), a randomized, placebo-controlled, secondary prevention trial of conjugated estrogen with progestin, found no overall reduction in coronary events among women assigned to active hormone treatment. This review explores the role of estrogen replacement among interventions intended to prevent coronary heart disease in the post-HERS era.

Myocardial Akt Activation and Gender

Abstract —Cardiovascular disease risk is higher in men than women, but the basis for this discrepancy remains controversial. Estrogenic stimulation of the myocardium or isolated cardiomyocytes has been purported to exert multiple beneficial effects associated with inhibition of maladaptive responses to pathogenic insults. This report describes a significant difference between the sexes in myocardial activation of Akt, a protein kinase that regulates a broad range of physiological responses including metabolism, gene transcription, and cell survival. We find that young women possess higher levels of nuclear-localized phospho-Akt 473 relative to comparably aged men or postmenopausal women. Both localization of phospho-Akt 473 in myocardial nuclei of sexually mature female mice versus males and Akt kinase activity in nuclear extracts of hearts from female mice versus males are elevated. Cytosolic localization of phospho-forkhead, a downstream nuclear target of Akt, is also increased in female relative to male mice, suggesting a potential mechanism for cardioprotective nuclear signaling resulting from Akt activation. Phospho-Akt 473 levels and localization at cardiac nuclei are similarly increased in transgenic mice with myocardium-specific expression of insulin-like growth factor I, a proven stimulus for Akt activation. Phospho-Akt 473 is also localized to the nucleus of cultured cardiomyocytes after exposure to 17β-estradiol or genistein (a phytoestrogen in soy protein–based diets), and neonatal exposure of litters to genistein elevated nuclear phospho-Akt 473 localization. The activation of Akt in a gender-dependent manner may help explain differences observed in cardiovascular disease risk between the sexes and supports the potential beneficial effects of estrogenic stimulation.

[Hormone replacement therapy in ischemic heart disease prevention in women. Arguments in favor]

Numerous evidence have suggested a physiologic action of sexual steroids upon the cardiovascular system and the coherence of epidemiological studies have raised the possibility of a positive action of estradiol in preventing cardiovascular disease, specially through atheroma inhibition and other vascular wall-related mechanisms. From an experimental point of view, some clinical trials have demonstrated an improvement in some intermediate clinical variables, such as hypercholesterolemia and hypertension, after the administration of estradiol. Nonetheless, the HERS study, the first secondary prevention trial of estrogen and cardiovascular disease, failed to demonstrate these positive actions suggested by epidemiological studies and the efficacy of estradiol in the treatment of postmenopausal women with cardiovascular disease has been questioned. In spite of this, the HERS study has also been questioned because of different pitfalls in its development and, for some authors, it is inconclusive. Therefore, at present, it is not possible to make an evidence based clinical decision regarding the key question about the real actions of estradiol in the prevention of cardiovascular disease in postmenopausal women.

Effect of medroxyprogesterone acetate plus estradiol on endothelium-dependent vasodilation in postmenopausal women

The addition of medroxyprogesterone acetate (MPA) is widely accepted to remove the endometrial-cancerogenic effect of estrogen replacement therapy in postmenopausal women. To evaluate the effect of MPA on endothelial function, we measured flow-mediated vasodilation of brachial arteries after transient occlusion in a randomized, double-blind, placebo-controlled study; we concluded that the addition of MPA attenuates the favorable effects of estradiol on endothelium-dependent vasodilation.