Hormonal, lipoprotein, and vascular effects of the selective estrogen receptor modulator raloxifene in hypercholesterolemic men

Raloxifene, soy phytoestrogens and endothelial function in postmenopausal women

OBJECTIVE

To compare the effects of raloxifene and soy phytoestrogens on endothelial function in healthy, postmenopausal women.

DESIGN

Randomized, double-blind, placebo-controlled, cross-over trial. Subjects (n = 22; mean age 58.5 years) underwent endothelial function testing at baseline and following 6 weeks of daily raloxifene 60 mg, soy phytoestrogens 55 mg, and placebo in random sequence with intervening 6-week wash-out periods. Endothelial function was assessed as flow-mediated vasodilatation (FMD) of the brachial artery using high-resolution ultrasound; digital flux was measured with laser Doppler velocimetry.

RESULTS

Baseline (pretreatment) FMD was almost within normal range at 9.6% (+/-6.4). FMD did not change from baseline within any treatment group, and no between-group differences were detected. FMD values following treatment with raloxifene, soy, and placebo were 10.3% (+/-12.3), 8.3% (+/-7.7), and 9.5% (+/-4.4), respectively. Area under curve ratios showed no treatment differences for digital velocimetry.

CONCLUSIONS

In this study, neither raloxifene nor soy enhanced endothelial function in postmenopausal women. However, the cohort had relatively normal endothelial function at baseline. Further study is required to determine if particular subgroups of postmenopausal women derive vascular benefit from the use of selective estrogen receptor modulators or soy phytoestrogens.

Raloxifene treatment enhances brain activation during recognition of familiar items: a pharmacological fMRI study in healthy elderly males

Raloxifene is a selective estrogen receptor modulator that may delay the onset of mild cognitive impairment in elderly women. Effects of raloxifene treatment on mental performance in males remain to be investigated. In a previous functional magnetic resonance imaging (fMRI) study, we showed that raloxifene treatment enhanced brain activation in elderly males during encoding of new information (faces) into memory. The current study used fMRI in the same group of subjects to screen for effects of raloxifene treatment on brain function during face recognition. Healthy elderly males (n=28; mean age 63.6 years, SD 2.4) were scanned at baseline and after 3 months of treatment with either raloxifene 120 mg (n=14) or placebo (n=14) in a randomized, double-blind, placebo-controlled study design. Functional data were analyzed in an event-related fashion with respect to correct hits and correct rejections using FSL software. Performance data were analyzed with respect to recognition accuracy, latency, and response bias. Functional effects of treatment were found on brain activation related to correct hits only. When compared to placebo treatment, raloxifene treatment enhanced brain activation in the left posterior parahippocampal area (Z=3.9) and right inferior prefrontal cortex (Z=3.5). Recognition accuracy scores remained stable in the raloxifene group, whereas the placebo group showed a small but significant decrease in accuracy scores (p=0.02). No significant effects were found on response bias or latency. In conclusion, raloxifene treatment affects brain function during memory performance in a way that may reflect increased arousal during initial encoding, with downstream effects on brain function during retrieval of information. Behaviorally, such neurofunctional effects may actively block decreased memory performance as a result of context-dependency. The validity of these predictions can be tested in large-scale clinical trials.

Raloxifene exposure enhances brain activation during memory performance in healthy elderly males; its possible relevance to behavior

Raloxifene is a selective estrogen receptor modulator (SERM) that is prescribed in females only, but its use in male subjects is increasingly considered. With a growing number of patients having potential benefit from raloxifene, the need for an assessment of its effects on brain function is growing. Effects of estrogens on brain function are very subtle and difficult to detect by neuropsychological assessment. Functional imaging techniques, however, have been relatively successful in detecting such changes. This study used functional magnetic resonance imaging (fMRI) to examine effects of raloxifene treatment on memory function. Healthy elderly males (n = 28; mean age 63.6 years, SD 2.4) were scanned during performance on a face encoding paradigm. Scans were made at baseline and after 3 months of treatment with either raloxifene (n = 14) or placebo (n = 14). Treatment effects were analyzed using mixed-effects statistical analysis (FSL). Activation during task performance involved bilateral parietal and prefrontal areas, anterior cingulate gyrus, and inferior prefrontal, occipital, and mediotemporal areas bilaterally. When compared to placebo, raloxifene treatment significantly enhanced activation in these structures (Z > 3.1), except for mediotemporal areas. Task performance accuracy diminished in the placebo group (P = 0.02), but remained constant in the raloxifene group (P = 0.60). In conclusion, raloxifene treatment enhanced brain activation in areas spanning a number of different cognitive domains, suggesting an effect on cortical arousal. Such effects may translate into small effects on behavior, including effects on attention and working memory performance, executive functions, verbal skills, and episodic memory. Further neuropsychological assessment is necessary to test the validity of these predictions.

Effect of raloxifene on activated protein C (APC) resistance in postmenopausal women and on APC resistance and homocysteine levels in elderly men

Raloxifene, a selective estrogen receptor modulator, like hormonal replacement therapy increases the risk of venous thromboembolism in postmenopausal women. A possible explanation for the increased thrombotic risk could be an increase in acquired resistance to activated protein C (APC). In two randomized, placebo-controlled, double-blind studies we determined the effect of raloxifene on the normalized APC sensitivity ratios (nAPCsr). The nAPCsr were determined with the thrombin generation-based APC resistance test. In the first study 83 postmenopausal women (age, 51.1 +/- 2.7 years) randomly received daily 0.625 mg conjugated equine estrogen and 2.5 mg medroxyprogesterone acetate (n=17), 60 mg raloxifene (n=23), 150 mg raloxifene (n=20) or placebo (n=23) for 24 months. At baseline and after 6, 12 and 24 months the nAPCsr were measured. In the second study 30 elderly men (age, 64.4 +/- 2.4 years) randomly received 120 mg raloxifene (n=15) or placebo (n=15) for 3 months. At baseline and after 3 months the nAPCsr and fasting homocysteine levels were measured. In postmenopausal women conjugated equine estrogen/medroxyprogesterone acetate significantly increased the nAPCsr from 1.26 +/- 0.82 to 2.87 +/- 0.86 at 24 months (P <0.0005 compared with placebo). Raloxifene had no significant effect on nAPCsr compared with placebo in both women and men. The results did not change after excluding carriers of factor V Leiden. Also fasting homocysteine levels were not affected by raloxifene in the aging men. It is concluded that raloxifene, in contrast to combined hormonal replacement therapy, does not increase APC resistance.

Raloxifene treatment is associated with increased serum estradiol and decreased bone remodeling in healthy middle-aged men with low sex hormone levels

In healthy middle-aged men, raloxifene treatment was associated with increased serum estradiol and decreased biochemical markers of bone turnover in subjects with estradiol levels below a threshold of 101.8 pM.

INTRODUCTION

We investigated the effects of the selective estrogen receptor modulator raloxifene on bone remodeling in healthy middle-aged men.

MATERIALS AND METHODS

Forty-three healthy eugonadal men (mean age, 56 years; range, 49-70 years) were enrolled in a randomized placebo-controlled, double-blind, two-sequence crossover study. The subjects received either raloxifene 120 mg/day or placebo for 6 weeks, followed by a 2-month washout period, before crossing over. To predict changes of urinary total deoxypyridinoline/creatinine on raloxifene treatment, we used a logistic regression model to determine cut-off values of sex hormones for highest sensitivity and specificity.

RESULTS

In the whole group, raloxifene treatment was associated with an increase in serum sex hormones, that is, total testosterone (+13%, p < 0.01), bioavailable testosterone (+11%, p = 0.02), total estradiol (+11%, p < 0.002), and bioavailable estradiol (+11%, p = 0.035), and with a decrease in serum osteocalcin (-13%, p < 0.05) and serum total alkaline phosphatase (-6%, p < 0.05). Other biochemical markers of bone turnover remained unchanged. Using a logistic regression model to predict changes in urinary deoxypyridoline, we calculated thresholds for total (101.8 pM) and bioavailable (4.79 pM) estradiol, as well as for total (19.4 nM) and bioavailable (0.35 nM) testosterone. Raloxifene treatment was associated with an increase in serum estradiol and decrease in biochemical markers of bone turnover in men with estradiol values below these estradiol thresholds, without any significant change in subjects with values above them. Similarly, raloxifene treatment was associated with an increase in serum testosterone and a decrease in biochemical markers of bone turnover in those with baseline testosterone values below the testosterone thresholds. The association between antiresorptive effects of raloxifene and low sex hormone levels was more pronounced for estradiol than for testosterone.

CONCLUSIONS

The antiresorptive effect of raloxifene was only detectable in men with low baseline estradiol levels. Unlike in postmenopausal women, the increase of estradiol may contribute to the antiresorptive effect of raloxifene in men.

Selective estrogen receptor modulator effects on serum lipoproteins and vascular function in postmenopausal women and in hypercholesterolemic men

Epidemiological observations, clinical mechanistic studies, and basic laboratory research suggest that estrogen therapy is associated with beneficial cardiovascular effects in postmenopausal women. Estrogen has a multitude of biological effects that may account for this apparent benefit (which remains to be proved in randomized clinical trials), including favorable effects on the lipid profile, increased endothelial nitric oxide bioactivity, and enhanced fibrinolysis. However, long-term estrogen therapy increases the risk of breast and endometrial cancers. Raloxifene, a benzothiophene derivative that binds to the estrogen receptor, is a selective estrogen receptor modulator, producing estrogen-agonist effects in some tissues (liver, bone) and estrogen-antagonistic effects in others (breast, uterus), and may prove to be an option for women with atherosclerosis or its risk factors. This review updates the current knowledge of the biological effects of selective estrogen receptor modulators of potential cardiovascular importance in postmenopausal women.