Aromatase activity and bone loss

Protective role of exercise on breast cancer-related osteoporosis in women undergoing aromatase inhibitors: A narrative review

Hormone therapy following surgery reduces the risk of breast cancer (BC) recurrence and progression of hormone-sensitive BC, especially in postmenopausal women. Despite the antitumor efficacy of hormone therapy, particularly of aromatase inhibitors, they cause long-term side effects, mainly bone density reduction. Exercise can slow the rate of bone loss, which reduces the risk of fractures from osteoporosis, and could be an integrative treatment able to mitigate the BC treatment side effects positively impacting bone health. This narrative review aims to discuss studies on the effect of exercise on bone health in BC women undergoing aromatase inhibitors, highlighting the possible role of exercise as complementary to conventional therapies. Additionally, according to the literature revision, exercise practical applications to improve bone health in these patients are summarized.

Aromatase Inhibition Eliminates Sexual Receptivity Without Enhancing Weight Gain in Ovariectomized Marmoset Monkeys

Context

Ovarian estradiol supports female sexual behavior and metabolic function. While ovariectomy (OVX) in rodents abolishes sexual behavior and enables obesity, OVX in nonhuman primates decreases, but does not abolish, sexual behavior, and inconsistently alters weight gain.

Objective

We hypothesize that extra-ovarian estradiol provides key support for both functions, and to test this idea, we employed aromatase inhibition to eliminate extra-ovarian estradiol biosynthesis and diet-induced obesity to enhance weight gain.

Methods

Thirteen adult female marmosets were OVX and received (1) estradiol-containing capsules and daily oral treatments of vehicle (E2; n = 5); empty capsules and daily oral treatments of either (2) vehicle (VEH, 1 mL/kg, n = 4), or (3) letrozole (LET, 1 mg/kg, n = 4).

Results

After 7 months, we observed robust sexual receptivity in E2, intermediate frequencies in VEH, and virtually none in LET females (P = .04). By contrast, few rejections of male mounts were observed in E2, intermediate frequencies in VEH, and high frequencies in LET females (P = .04). Receptive head turns were consistently observed in E2, but not in VEH and LET females. LET females, alone, exhibited robust aggressive rejection of males. VEH and LET females demonstrated increased % body weight gain (P = .01). Relative estradiol levels in peripheral serum were E2 >>> VEH > LET, while those in hypothalamus ranked E2 = VEH > LET, confirming inhibition of local hypothalamic estradiol synthesis by letrozole.

Conclusion

Our findings provide the first evidence for extra-ovarian estradiol contributing to female sexual behavior in a nonhuman primate, and prompt speculation that extra-ovarian estradiol, and in particular neuroestrogens, may similarly regulate sexual motivation in other primates, including humans.

Osteoporosis and musculoskeletal complications related to therapy of breast cancer

Aromatase inhibitors (AIs) are the treatment of choice for the majority of postmenopausal women with estrogen receptor (ER) positive breast cancers in early and advanced stage settings. One of most frequent side effects of AIs is bone loss that is of sufficient magnitude to increase risk of osteoporotic fractures. Osteoporosis is primarily a complex genetic disease with few modifiable risk factors. As the lifespan increases, and breast mortality decreases, more women with breast cancer will be at risk of osteoporotic fractures, or falls that result in fractures. The screening, prevention, and treatment of osteoporosis do not differ in women with or without breast cancer. Rather, breast cancer treatments, including AIs, chemotherapy-induced ovarian failure, and gonadotropin-releasing hormone (GnRH) agonists, all decrease estrogen, which causes net bone resorption, leading some women to experience fracture. Occurring in about fifty-percent of women, AI-induced arthralgia is one of the most common side effects, and causes of nonadherence and discontinuation. Registry studies show that nonadherence and discontinuation may contribute to higher breast cancer mortality. Thus, understanding the mechanisms, risk factors, and interventions to mitigate symptoms of AI-induced arthralgia is a high priority.

Dehydroepiandrosterone and Bone

In humans, dehydroepiandrosterone (DHEA), secreted mainly from the adrenal cortex, and its sulfate ester, DHEAS, are the most abundant circulating steroids. DHEA/DHEAS possess pleiotropic effects in human aging, bone, metabolic diseases, neurologic function/neurodegenerative diseases, cancer, immune system and disorders, cardiovascular diseases, diabetes, muscle function, sexual dysfunction, and other health conditions. The age-related reduced levels of DHEA and DHEAS are associated with bone mineral density measures of osteopenia and osteoporosis. Clinical, epidemiological, and experimental studies indicate that DHEA replacement therapy may be beneficial for bone health through its inhibition of skeletal catabolic IL-6 and stimulation of osteoanabolic IGF-I-mediated mechanisms. Studies with primary cultures of human bone marrow-derived mesenchymal stem cells (hMSCs) were used to show that DHEA stimulates osteoblastogenesis. The in vitro stimulation of both osteoblastogenesis and IGF-I gene expression by DHEA in hMSCs requires IGF-I receptor, PI3K, p38 MAPK, or p42/44 MAPK signaling pathways. The in vitro inhibition of IL-6 secretion in hMSCs by DHEA was more consistent and extensive than by estradiol or dihydrotestosterone. In summary, evidence from us and others indicates that DHEA may be useful for treating bone diseases through its inhibition of skeletal catabolic IL-6 and stimulation of anabolic IGF-I-mediated mechanisms.

Seasonal expression of P450arom and estrogen receptors in scented glands of muskrats (Ondatra zibethicus)

Male muskrats have one pair of scented glands that grow and involute annually. To investigate the annual changes in the scented gland, we measured the expressions of aromatase cytochrome P-450 (P450arom) and estrogen receptors (ERs) in the scented glands. P450arom was expressed in glandular cells and epithelial cells in the scented glands during the breeding season, and only in glandular cells during the nonbreeding season. ERα and ERβ were also detected in different types of cells in the scented gland during the breeding and nonbreeding seasons. Both mRNA and protein levels of P450arom, ERα, and ERβ were higher in the scented glandular tissues during the breeding season than those during the nonbreeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed microRNAs might be the genes encoding P450arom and ERs. In conclusion, the seasonal changes in the expression of P450arom and ERs may be involved in the regulation of scented gland functions.

Testosterone supplementation, glucocorticoid milieu and bone homeostasis in the ageing male

Male ageing is entwined with a continuous fall in free testosterone levels, which contributes to the pathogenesis of bone loss. Glucocorticoid excess, either dependent on the ageing process or iatrogenically induced, was found to additionally impair the bone structure and metabolism. Cautious testosterone supplementation in this respect may positively affect the glucocorticoid milieu and bone homeostasis, while testosterone-induced changes in the glucocorticoid output could serve as a determinant of bone-related therapeutic outcome. Namely, bone mineral content/density, the parameters of trabecular bone structure as well as bone strength are enhanced, serum calcitonin levels tend to increase, while serum osteocalcin, serum parathyroid hormone and urinary calcium decrease, all upon testosterone administration to the ageing male. In parallel, testosterone application decreases glucocorticoid secretion in the animal models of male ageing, while clinical data in this field are still inconsistent. Importantly, a physiological link exists between testosterone-induced changes in glucocorticoid levels and the tendency of bone status improvement in the ageing male. We believe that the assessment of circulating adrenocorticotropic hormone concentrations together with glucocorticoid levels, reflecting the hypothalamic-pituitary-adrenal axis feedback loop operativeness during testosterone supplementation, represents a well-balanced bone-related therapeutic update.

Testosterone application decreases the capacity for ACTH and corticosterone secretion in a rat model of the andropause

The culminating phase of ageing in males-andropause is characterized by enhanced activity of the hypothalamic-pituitary-adrenal axis and frequent glucocorticoid excess. In parallel, free testosterone deficiency provides the baseline hormonal milieu for the ageing male. The aim of this study was to illustrate (using diverse microscopic and biochemical methodologies) the effects of testosterone application on the capacity for adrenocorticotropic hormone (ACTH) and corticosterone secretion in a rat model of the andropause. Middle-aged Wistar rats were divided into sham-operated (SO; n=8), orchidectomized (Orx; n=8) and testosterone treated orchidectomized (Orx+T; n=8) groups. Testosterone propionate (5 mg/kg b.w./day) was administered for three weeks, while SO and Orx groups received the vehicle alone. ACTH cells and the adrenal cortex were stained using immuno-histochemical, immuno-fluorescent and histochemical procedures. Circulating concentrations of testosterone, estradiol, ACTH and corticosterone, as well as the adrenal tissue corticosterone levels were measured by immunoassays. Testosterone application led to increased (p<0.05) serum concentrations of sex steroids. Consequently, in Orx+T rats the ACTH cell nuclei volume increased (p<0.05) by 34%, while the volume density of ACTH cells and their relative intensity of fluorescence decreased (p<0.05) by 46% and 21%, respectively, in comparison with the corresponding parameters in the Orx group. Testosterone also induced vasodilatation in the adrenocortical zona fasciculata, and decreased (p<0.05) the ACTH concentrations and adrenal tissue corticosterone levels by 38% and 31%, respectively, compared to the Orx group. In conclusion, testosterone administration caused a decrease in the capacity for ACTH and corticosterone secretion in a rat model of the andropause.

Morbid obesity attenuates the skeletal abnormalities associated with leptin deficiency in mice

Leptin-deficient ob/ob mice are morbidly obese and exhibit low total bone mass and mild osteopetrosis. In order to disassociate the skeletal effects of leptin deficiency from those associated with morbid obesity, we evaluated bone mass, architecture, gene expression, and indices of bone turnover in WT mice, ob/ob mice allowed to feed ad libitum (ob/ob), and ob/ob mice pair-fed equivalent to WT mice (pair-fed ob/ob). Mice were maintained at 32 °C (thermoneutral) from 6 to 18 weeks of age to minimize differences in resting energy expenditure. ob/ob mice were heavier, had more abdominal white adipose tissue (WAT), and were hyperglycemic compared with WT mice. Femur length, bone mineral content (BMC) and bone mineral density, and midshaft femur cortical thickness were lower in ob/ob mice than in WT mice. Cancellous bone volume (BV) fraction was higher but indices of bone formation and resorption were lower in ob/ob mice compared with WT mice; reduced bone resorption in ob/ob mice resulted in pathological retention of calcified cartilage. Pair-fed ob/ob mice were lighter and had lower WAT, uterine weight, and serum glucose than ob/ob mice. Similarly, femoral length, BMC, and cortical thickness were lower in pair-fed ob/ob mice compared with ob/ob mice, as were indices of cancellous bone formation and resorption. In contrast, bone marrow adiposity, calcified cartilage, and cancellous BV fraction were higher at one or more cancellous sites in pair-fed ob/ob mice compared with ob/ob mice. These findings indicate that the skeletal abnormalities caused by leptin deficiency are markedly attenuated in morbidly obese ob/ob mice.

A comprehensive network and pathway analysis of human deafness genes

OBJECTIVE

To perform comprehensive network and pathway analyses of the genes known to cause genetic hearing loss.

STUDY DESIGN

In silico analysis of deafness genes using ingenuity pathway analysis (IPA).

METHODS

Genes relevant for hearing and deafness were identified through PubMed literature searches and the Hereditary Hearing Loss Homepage. The genes were assembled into 3 groups: 63 genes that cause nonsyndromic deafness, 107 genes that cause nonsyndromic or syndromic sensorineural deafness, and 112 genes associated with otic capsule development and malformations. Each group of genes was analyzed using IPA to discover the most interconnected, that is, "nodal" molecules, within the most statistically significant networks (p < 10).

RESULTS

The number of networks that met our criterion for significance was 1 for Group 1 and 2 for Groups 2 and 3. Nodal molecules of these networks were as follows: transforming growth factor beta1 (TGFB1) for Group 1, MAPK3/MAPK1 MAP kinase (ERK 1/2) and the G protein coupled receptors (GPCR) for Group 2, and TGFB1 and hepatocyte nuclear factor 4 alpha (HNF4A) for Group 3. The nodal molecules included not only those known to be associated with deafness (GPCR), or with predisposition to otosclerosis (TGFB1), but also novel genes that have not been described in the cochlea (HNF4A) and signaling kinases (ERK 1/2).

CONCLUSION

A number of molecules that are likely to be key mediators of genetic hearing loss were identified through three different network and pathway analyses. The molecules included new candidate genes for deafness. Therapies targeting these molecules may be useful to treat deafness.

Pharmacokinetic evaluation of toremifene and its clinical implications for the treatment of osteoporosis

INTRODUCTION

Toremifene is a triphenylethylene selective estrogen receptor modulator (SERM) that differs from tamoxifen in a single chloride ion addition on a side chain, resulting in a potentially more favorable toxicity profile.

AREAS COVERED

This article reviews the pharmacokinetics of toremifene and its potential use for the treatment of osteoporosis. This article was based on articles found through a literature search containing the terms 'toremifene' and 'SERMs.'

EXPERT OPINION

Toremifene can be administered orally with an excellent bioavailability. The overall pharmacokinetic profile is remarkably similar to tamoxifen. Toremifene is highly metabolized in the liver and is eliminated primarily in the feces following enterohepatic circulation. Some of its metabolites retain biological activity. This SERM was approved by the FDA for the treatment of estrogen receptor-positive metastatic breast cancer and is under investigation for its potential skeletal benefits in men on androgen deprivation therapy. Despite the positive preclinical and clinical evidences for the prevention of bone loss and fractures, the chemopreventive effect on prostate cancer remains to be confirmed and an increased risk of venous thromboembolism was evidenced in a large Phase III trial. Thus, additional data are required to establish the full clinical profile of this compound and its potential advantages over antiresorptive agents commonly in use for the treatment of osteoporosis.