Endogenous testosterone and endothelial function in postmenopausal women

Experimental benefits of sex hormones on vascular function and the outcome of hormone therapy in cardiovascular disease

Cardiovascular disease (CVD) is more common in men and postmenopausal women than premenopausal women, suggesting vascular benefits of female sex hormones. Experimental data have shown beneficial vascular effects of estrogen including stimulation of endothelium-dependent nitric oxide, prostacyclin and hyperpolarizing factor-mediated vascular relaxation. However, the experimental evidence did not translate into vascular benefits of hormone replacement therapy (HRT) in postmenopausal women, and HERS, HERS-II and WHI clinical trials demonstrated adverse cardiovascular events with HRT. The lack of vascular benefits of HRT could be related to the hormone used, the vascular estrogen receptor (ER), and the subject’s age and preexisting cardiovascular condition. Natural and phytoestrogens in small doses may be more beneficial than synthetic estrogen. Specific estrogen receptor modulators (SERMs) could maximize the vascular benefits, with little side effects on breast cancer. Transdermal estrogens avoid the first-pass liver metabolism associated with the oral route. Postmenopausal decrease and genetic polymorphism in vascular ER and post-receptor signaling mechanisms could also modify the effects of HRT. Variants of cytosolic/nuclear ER mediate transcriptional genomic effects that stimulate endothelial cell growth, but inhibit vascular smooth muscle (VSM) proliferation. Also, plasma membrane ERs trigger not only non-genomic stimulation of endothelium-dependent vascular relaxation, but also inhibition of [Ca²⁺]i, protein kinase C and Rho kinase-dependent VSM contraction. HRT could also be more effective in the perimenopausal period than in older postmenopausal women, and may prevent the development, while worsening preexisting CVD. Lastly, progesterone may modify the vascular effects of estrogen, and modulators of estrogen/testosterone ratio could provide alternative HRT combinations. Thus, the type, dose, route of administration and the timing/duration of HRT should be customized depending on the subject’s age and preexisting cardiovascular condition, and thereby make it possible to translate the beneficial vascular effects of sex hormones to the outcome of HRT in postmenopausal CVD.

Cardiovascular and cancer safety of testosterone in women

PURPOSE OF REVIEW

To examine the recent data pertaining to the relationships between testosterone and cardiovascular disease (CVD) and cancer in women.

RECENT FINDINGS

Despite the entrenched belief that higher blood levels of testosterone increase the risk of CVD in women, data from recent observational studies mostly show an inverse relationship between testosterone and CVD risk. One pilot study suggests favorable effects of nonoral testosterone treatment of women with established congestive cardiac failure which merits further evaluation. The relationship between endogenous testosterone production and breast cancer risk remains contentious, with recent studies indicating either no relationship, or a possible increase in risk when estrone and estradiol are not taken into account. No randomized controlled trial of testosterone therapy has been sufficiently large or of sufficient duration to establish whether such treatment may influence breast cancer occurrence. There does not appear to be an association between testosterone and endometrial cancer, or other malignancies on review of published studies.

SUMMARY

Testosterone is inversely associated with increased CVD risk in women, whereas low sex hormone binding globulin increases CVD risk. The relationship between testosterone and breast cancer remains unclear, although a clear signal of risk has not emerged from studies of women treated with testosterone therapy over the past decade.

Androgenicity and venous endothelial function in post-menopausal women

BACKGROUND

Endothelial dysfunction is one of the early signs of cardiovascular damage. High androgen levels have been related to inflammatory endothelial markers in pre- and post-menopausal women.

AIM

This cross-sectional study aimed at investigating whether free androgen index (FAI) [estimated by dividing total testosterone (nmol/l) by SHBG (nmol/l) x 100] is related to endothelial function during post-menopause.

SUBJECTS AND METHODS

Twenty-six post-menopausal women were assessed with the dorsal hand vein compliance technique. Acetylcholine (Ach) and sodium nitroprusside (SNP) dose-response curves were constructed to test endothelium-dependent and independent relaxation, respectively.

RESULTS

Mean age was 54 yr (+/-4) and median time since menopause was 6 yr (interquartile range: 3-9). Patients were stratified according to FAI levels into two groups: FAI greater than or less than the group median of 2.5. Waist-to-hip ratio (WHR) was significantly higher in the group with FAI>2.5, as well as median dose of Ach for maximal vasodilation [720 (360-3600) ng/min with FAI>2.5 vs 36 (0.36-360) ng/min with FAI<or=2.5; p=0.005]. Maximal vasodilation with SNP was similar in both groups. Positive correlations were observed between Ach doses and maximal vasodilation and FAI (r=0.473, p=0.015), waist (r=0.510, p= 0.011), and WHR (r=0.479, p=0.021). SHBG was negatively correlated with Ach doses (rs=-0.400, p=0.043).

CONCLUSIONS

This study suggests that FAI, even within normal limits, is related to early changes in endothelial function in healthy post-menopausal women. Longitudinal studies are required to determine the clinical relevance of these findings.

Extremes of endogenous testosterone are associated with increased risk of incident coronary events in older women

CONTEXT

Few studies have examined whether endogenous testosterone is associated with the development of coronary heart disease (CHD) in women.

OBJECTIVE

This study tested the association of total testosterone (total T) and bioavailable T (BioT) levels with risk of incident coronary events among older community-dwelling women.

DESIGN, SETTING, AND PARTICIPANTS

This was a prospective, population-based study of 639 postmenopausal women, aged 50-91 (mean, 73.8) yr who had serum testosterone measurements at baseline (1984-87) and who were followed for incident CHD events through 2004.

MAIN OUTCOME MEASURES

A total of 134 incident CHD events occurred during follow-up [45 nonfatal myocardial infarctions, 79 fatal myocardial infarctions, and 10 coronary revascularizations].

RESULTS

The median follow-up was 12.3 yr. Age-adjusted CHD risk estimates were similar for the four highest total T quintiles relative to the lowest, suggesting a low threshold. In age-adjusted analyses, the lowest total T quintile (</=80 pg/ml) was associated with a 1.62-fold increased risk of incident CHD [95% confidence interval (CI), 1.10-2.39] compared to higher levels. BioT showed a U-shaped association with incident CHD. Age-adjusted risk for the lowest and highest BioT quintiles relative to the third were 1.79 (95% CI, 1.03-3.16) and 1.96 (95% CI, 1.13-3.41), respectively. Additional adjustment for lifestyle, adiposity, estradiol, and ovarian status, or for CHD risk factor covariates, had minimal influence on results.

CONCLUSIONS

An optimal range of testosterone may exist for cardiovascular health in women, with increased risk of CHD events at low levels of testosterone overall and at high levels of the bioavailable fraction of testosterone.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Review: Endothelial dysfunction: A potential tool in gender related cardiovascular disease

The overwhelming importance of distinctive cardiovascular disease profile in women has stimulated enormous efforts to disclose its cause. In this review, we discuss vascular endothelium as a potential phenotypic marker for the genetic difference. As it is a potentially modifiable factor for cardiovascular disease, every effort should be made to detect it, either directly or indirectly, at the earliest in females who are at risk, so that the future cardiovascular events might be prevented.

Androgens stimulate endothelial progenitor cells through an androgen receptor-mediated pathway

BACKGROUND AND OBJECTIVE

Testosterone (T) treatment has recently been shown to induce an increase in the number of endothelial progenitor cells (EPCs) through a possible effect on bone marrow. Hypogonadotrophic hypogonadal (HH) men have low circulating EPCs that increase significantly after T treatment. Moreover, expression of the androgen receptor (AR) has been demonstrated by immunohistochemistry in these cells, suggesting that T might also have a direct effect on EPC function. In the present study we investigated the expression and function of the AR in human EPCs and the in vitro effect of androgens on EPC function. Design and patients EPCs obtained from healthy male anonymous blood donors were analysed after androgen stimulation with and without AR antagonist administration (flutamide).

RESULTS

Reverse transcriptase polymerase chain reaction (RT-PCR), Western blotting and immunofluorescence analyses demonstrated the expression of AR mRNA and protein in human EPCs. Stimulation of these cells with the synthetic androgen methyltrienolone (R1881) caused AR translocation in the nucleus, suggesting its activation. Colony forming unit (CFU), proliferation and migration assays under different doses of R1881 demonstrated a dose-dependent increase in EPC proliferation, migration and colony formation. All these effects are abolished by flutamide pretreatment.

CONCLUSIONS

This study showed that the increase in the proliferation, migration and colony formation activity of EPCs induced by androgens is an AR-mediated pathway. Androgen exerts these effects at concentrations that are physiologically present in men and therefore further studies are needed to clarify the clinical significance of these effects in normal and pathological conditions.