Bone mass and soy isoflavones in socially housed, premenopausal macaques

Effect of soy isoflavones on thyroid hormones in intact and ovariectomized cynomolgus monkeys (Macaca fascicularis)

OBJECTIVE

Soy isoflavones are commonly used to alleviate menopause-related symptoms. Postmenopausal women are at increased risk for hypothyroidism, and there are concerns that isoflavones may be detrimental to thyroid health. The aim of this study was to examine the effects of soy protein and isoflavones on thyroid function and the relationship between thyroid function and ovarian function.

METHODS

Adult female cynomolgus monkeys (Macaca fascicularis) were randomized to consume two diets differing only in protein source: casein-lactalbumin (n = 44) or soy protein with isoflavones (n = 41). After 34 months, all animals were ovariectomized via laparotomy. Half of the monkeys from each diet treatment group continued to consume their preovariectomy treatment phase diet (either isolated soy protein [n = 19] or casein-lactalbumin [n = 21]) for an additional 34 months. The remaining animals did not continue their diets and thus were not considered further. Circulating progesterone, triiodothyronine, thyroxine, and thyroid-stimulating hormone were measured at baseline. Thyroid hormones were remeasured during each treatment phase.

RESULTS

Dietary soy increased triiodothyronine in preovariectomized monkeys and prevented a decline in thyroxine after surgical menopause (both P's < 0.05). Mean progesterone concentrations were positively correlated with triiodothyronine at baseline in preovariectomized monkeys (P < 0.01).

CONCLUSIONS

Progesterone levels and triiodothyronine are positively correlated in macaques. Dietary soy increases triiodothyronine in preovariectomized monkeys and prevents a decline in thyroxine after surgical menopause. The outcomes observed in this study suggest that soy protein and isoflavone consumption does not adversely affect-and may even preserve-thyroid function in postmenopausal women.

Dietary soy effects on mammary gland development during the pubertal transition in nonhuman primates

While epidemiologic studies suggest that soy intake early in life may reduce breast cancer risk, there are also concerns that exposure to soy isoflavones during childhood may alter pubertal development and hormonal profiles. Here, we assessed the effect of a high-soy diet on pubertal breast development, sex hormones, and growth in a nonhuman primate model. Pubertal female cynomolgus monkeys were randomized to receive a diet modeled on a typical North American diet with one of two protein sources for approximately 4.5 years: (i) casein/lactalbumin (CL, n = 12, as control) or (ii) soy protein isolate with a human equivalent dose of 120 mg/d isoflavones (SOY, n = 17), which is comparable to approximately four servings of soy foods. Pubertal exposure to the SOY diet did not alter onset of menarche, indicators of growth and pubertal progression, or circulating estradiol and progesterone concentrations. Greater endometrial area was seen in the SOY group on the first of four postmenarchal ultrasound measurements (P < 0.05). There was a subtle effect of diet on breast differentiation whereby the SOY group showed higher numbers of differentiated large-sized lobular units and a lower proportion with immature ducts following menarche (P < 0.05). Numbers of small lobules and terminal end buds and mammary epithelial cell proliferation did not differ by diet. Expression of progesterone receptor was lower in immature lobules of soy-fed animals (P < 0.05). Our findings suggest that consumption of soy starting before menarche may result in modest effects consistent with a more differentiated breast phenotype in adulthood.

Phytoestrogens and bone health at different reproductive stages

BACKGROUND

Isoflavones are an alternative to hormonal therapy for the relief of menopausal symptoms. Since isoflavones interact with estrogen receptors it has been hypothesized that such substances may have an effect on bone health.

OBJECTIVE

To clarify the effect of isoflavones on bone at experimental and clinical level, and to identify areas that require further clarification and research.

METHOD

A systematic review of studies involving isoflavones and bone health was performed, and a specific search on isoflavone's mechanism of action and the importance of equol production was made based on Internet search engines, MEDLINE (1966-October 2012) and the Cochrane Controlled Clinical Trials Register. This search was supplemented by a handsearch of reference lists of selected papers.

RESULTS

In vitro and animal studies show a positive effect of isoflavones on bone which has not been clearly confirmed by long-term human trials. Equol producers seem to present a more positive response to isoflavone intervention. Isoflavone rich diets could help maintain peak bone mass in premenopausal women. The effect of isoflavones in perimenopausal women is insufficiently studied but it seems to attenuate bone loss in the menopausal transition. In postmenopause, isoflavones may present a modest benefit but its clinical relevance in preventing osteoporotic fractures remains to be determined.

CONCLUSIONS

The present review suggests that isoflavone increase bone mineral density and decrease the bone turnover resorption markers. The effect of soy isoflavones on BMD is mediated by equol production, reproductive status, supplement type, isoflavone dose and intervention duration.

Greater Skeletal Gains in Ovary Intact Rats at Maturity Are Achieved by Supplementing a Standardized Extract of Butea monosperma Stem Bark that Confers Better Bone Conserving Effect following Ovariectomy and Concurrent Treatment Withdrawal

With a longitudinally designed study, we tested whether an acetone soluble fraction (ASF) from the stem bark of Butea monosperma resulted in maximizing bone gain in rats during growth and maturation and thus protected against osteopenia following ovariectomy (OVx) with concomitant treatment withdrawal. Female rats at weaning were given ASF (100 mg/kg/d) or vehicle for 12 weeks, and baseline skeletal parameters (micro-CT) and total plasma antioxidant status (TAS) were measured. At this stage, one group was OVx and the other group was sham operated. Vehicle group (untreated) after OVx was given E2 or continued with vehicle (OVx control). ASF group after OVx was given vehicle (ASF withdrawn, ASFW). After another 12 weeks, all groups were killed and various skeletal parameters were determined. ASF resulted in substantially better skeletal parameters and higher plasma TAS over control at maturity. Rats treated with ASF before OVx had reduced rates of bone loss compared to OVx control. Twelve weeks after OVx, the ASFW group exhibited better trabecular microarchitectural preservation, bone turnover profiles, increased cortical deposition, and biomechanical strength over the OVx control, and the effects were comparable to OVx + E2 group. ASF supplementation during skeletal growth could maximize bone accrual and could confer increased resistance to post-OVx osteopenia despite treatment withdrawal.

Response to an adequate dietary intake of vitamin D3 modulates the effect of estrogen therapy on bone density

INTRODUCTION

This study analyzed associations between plasma vitamin D(3) (25OHD(3)) and bone mineral density (BMD) and whether the effects of conjugated equine estrogens (CEE) on BMD are modulated by 25OHD(3).

METHODS

Fifty cynomolgus monkeys were fed a diet containing 25OHD(3) (providing a woman's equivalent of 1000 IU/day of 25OHD3). The monkeys underwent bilateral oophorectomy and were randomized to either CEE (equivalent of 0.45 mg/day) (n=25) or placebo (n=25) and continued receiving the same diet. 25OHD(3) and BMD were measured at randomization and after 6 months. BMD also was measured after 20 months (equivalent to 6 human years). Associations between 25OHD(3) and BMD were subsequently analyzed.

RESULTS

Baseline 25OHD(3) plasma concentrations varied from 26 to 95 ng/mL (mean±standard deviation [SD] 54 ± 15 ng/mL). Higher plasma concentrations of 25OHD(3) were associated with a significantly increased BMD. Monkeys on both CEE and placebo had increased BMD over 20 months; however, the increase was not significantly different (0.034 g/cm(2) vs. 0.020 g/cm(2), respectively; p=0.064). The 20-month BMD increased significantly with CEE treatment in those with higher vs. lower 25OHD(3) concentrations (p=0.027). The percent change in BMD over 20 months also increased significantly with CEE treatment in those with higher vs. lower 25OHD(3) concentrations (p=0.018). A higher 25OHD(3) concentration had no significant effect on BMD in those receiving placebo.

CONCLUSIONS

Monkeys fed a diet containing 1000 IU/day equivalent of 25OHD(3) have a wide range of plasma 25OHD(3) concentrations. Those receiving CEE with higher 25OHD(3) concentrations had higher BMDs, suggesting 25OHD(3) and CEE have synergistic effects on BMD.

Effect of ovarian aging on androgen biosynthesis in a cynomolgus macaque model

OBJECTIVE

The role of androgens in chronic disease pathogenesis, cognitive function and libido during menopause is of increasing interest. The aim of this study was to characterize the distribution and expression of androgenic proteins in the macaque ovary and to investigate the relationship between serum androgen concentrations, follicle number, and the persistence of androgenesis in the aging macaque ovary.

METHODS

The subjects were 26 adult female cynomolgus macaques. Ovaries were immunostained for cytochrome P450 17α-hydroxylase/17-20 lyase (P450c17), 3β-hydroxysteroid dehydrogenase (3βHSD), and cytochrome b5 (cytb5). Based on primordial follicle counts, animals were divided into tertiles (low (≤200), intermediate (226-1232), and high (2372-4356)) to evaluate differences in androgen staining and changes in serum androgen concentrations following ovariectomy.

RESULTS

Positive immunostaining for P450c17 and cytb5 within the theca interna layer of growing follicles persisted in advanced atretic follicles and secondary interstitial cells (residual stromal cells). Ovaries with low follicle numbers had less staining for all androgenic proteins compared to ovaries with higher numbers of growing follicles. Immunostaining for cytb5 was the most reliable marker for persistent androgenesis in ovaries with minimal primordial follicle numbers (<100) and residual stromal cells. Following ovariectomy, a significant decrease in testosterone (-27.7%, -30.8%, -27.5%; p < 0.01) and androstenedione (-33.4%, -35.7%, -46.0%; p < 0.01) was observed in monkeys with low, intermediate, and high primordial follicle counts, respectively.

CONCLUSIONS

Despite low follicle numbers, the aging macaque ovary retains the necessary proteins for androgenesis within residual stromal cells and contributes to peripheral androgen concentrations.

The effect of diet and cardiovascular risk on ovarian aging in cynomolgus monkeys (Macaca fascicularis)

OBJECTIVE

The aim of this study was to determine the relationships among dietary protein source, cardiovascular risk, reproductive hormones, and ovarian aging.

METHODS

Adult female cynomolgus monkeys (Macaca fascicularis) were assigned randomly to one of two diets containing saturated fat and cholesterol, differing only by protein source: (1) casein-lactalbumin (n = 29) or (2) soy protein with isoflavones (n = 32). Cardiovascular risk markers and reproductive hormones were measured at baseline and after 32 months of treatment, at which time the ovaries were removed and serially sectioned and ovarian follicles were counted in every 100th section.

RESULTS

Casein-lactalbumin-fed monkeys had fewer primordial, primary, and secondary follicles (all P values < 0.05) than did their soy-fed counterparts. Antimüllerian hormone was significantly correlated with all follicle types (r values > or = 0.66, P < 0.001) for casein-fed monkeys and was significantly correlated with primary (rsoy = 0.47, P = 0.005) and secondary (rsoy = 0.45, P = 0.007) follicles in soy-fed monkeys. No significant associations were seen between any of the other reproductive hormones measured and follicle counts. Casein-lactalbumin-fed monkeys had a more atherogenic lipoprotein profile and increased atherosclerosis extent (P < 0.05), but despite these differences in cardiovascular risk between monkeys fed with casein-lactalbumin and monkeys fed with soy, none of the individual cardiovascular risk markers measured in this study explained the relationship between dietary protein source and follicle counts (linear regression, all P values > 0.05).

CONCLUSIONS

Diet influences the rate of follicular depletion in cynomolgus macaques; however, the mechanism for this effect remains undetermined.

Reproductive aging and risk for chronic disease: Insights from studies of nonhuman primates

Reproductive aging and ovarian senescence have considerable public health relevance because they are associated with increased risk for coronary heart disease (CHD), osteoporosis and other degenerative conditions including cognitive decline and potentially the metabolic syndrome. It has been suggested that the hormonal dysregulation that occurs during the perimenopausal transition may play a role in the initiation of pathobiological changes (e.g., adverse lipid profiles, atherosclerotic plaques) that will increase risk for chronic disease (e.g., CHD) during the postmenopausal years. Moreover, these early changes are suspected to establish a trajectory of disease progression that may be difficult to alter if interventions are not begun until after menopause. Even a slight increase in the rate of disease progression during the pre- or perimenopausal years could have substantial consequences for health and quality of life over the postmenopausal lifespan. Thus, the years leading up to menopause may offer a "critical window" for interventions aimed at reducing the postmenopausal disease burden. The relationship between perimenopausal hormonal dysregulation and the risk for chronic disease is poorly understood due, in large part, to the lack of appropriate animal models of the perimenopausal transition and natural menopause. In this review we assesses studies of nonhuman primates (NHPs) evaluated in various reproductive stages (naturally pre-, peri- and postmenopausal, surgically menopausal) and their contribution to our understanding about risk factors for chronic disease. Finally, because large numbers of naturally perimenopausal and menopausal NHPs are not available for research at present, experimental approaches that have the potential to hasten the onset of the perimenopausal transition will be described.

Plasma lipid-dependent and -independent effects of dietary soy protein and social status on atherogenesis in premenopausal monkeys: implications for postmenopausal atherosclerosis burden

OBJECTIVE

: Atherosclerosis developed during premenopausal years predicts postmenopausal atherosclerosis burden. The objective of this study was to determine the effects of dietary soy protein isolate (SPI) and social status on atherogenesis and arterial gene expression in a premenopausal monkey model.

DESIGN

: Socially housed premenopausal cynomolgus macaques (n = 84) were fed an atherogenic diet deriving protein from casein/lactalbumin or SPI (containing 1.88 mg isoflavones/g). After 36 months of diet consumption, iliac artery biopsies were assessed for atherosclerosis and expression of mRNA transcripts related to inflammation, macrophage and T-cell content, and estrogen receptors (ERs).

RESULTS

: SPI reduced plaque size (P < 0.05), total plasma cholesterol, non-high-density lipoprotein cholesterol (HDLc), and the total plasma cholesterol/HDLc ratio (all P < 0.003), while increasing triglycerides (P < 0.006) and HDLc (P < 0.0001). Arterial mRNA for CD68 (P < 0.001), CD3 (P < 0.02), and CD4 (P < 0.001) and inflammatory markers monocyte chemotactic protein-1, intercellular adhesion molecule-1, and interleukin-6 (all P < 0.0001) were also lower in the group receiving SPI. For most outcomes, this effect remained even after adjustments for plaque size and plasma lipid concentrations. Arterial ER-alpha was inversely associated with atherosclerosis (P < 0.02) and increased with SPI (P < 0.001). Subordinate monkeys had lower ER-beta (P < 0.02) and higher interleukin-6 (P < 0.05) transcripts but did not differ from dominant monkeys in extent of atherosclerosis (P > 0.9).

CONCLUSIONS

: Premenopausal consumption of SPI had plasma lipid-independent beneficial effects on the pathobiological processes involved in atherosclerotic plaque development, thus potentially establishing the basis for reduced postmenopausal complications. Dominant social status provided similar, albeit less extensive, benefits in risk markers.

Ovarian dysfunction and the premenopausal origins of coronary heart disease

OBJECTIVE

The menopausal loss of cyclic ovarian function is believed to contribute to coronary heart disease (CHD). However, ovarian function varies substantially throughout the premenopausal years, with disruptions in hormonal activity ranging from mild to profound. Here we propose our "precocious acceleration" hypothesis, which holds that to the extent cyclic ovarian function affords protection against CHD, even mild ovulatory abnormalities in young women will accelerate development of this disease.

DESIGN

Data relating to the expression and incidence of premenopausal ovarian dysfunction in women and its relationship to CHD are reviewed. Also reviewed are the results from experiments conducted with socially housed cynomolgus monkeys (Macaca fascicularis), focused on the causes, occurrence, and pathobiological sequelae of premenopausal ovarian dysfunction. The implications of the foregoing material for understanding the health of peri- and postmenopausal women are then considered.

RESULTS

Epidemiological and clinical studies indicate that common premenopausal reproductive abnormalities (manifested along a continuum from mild subclinical alterations to complete suppression) are associated with increased risk of CHD. This increased risk is probably mediated by different pathways, depending on whether the reproductive deficits relate to hypoestrogenemia (functional hypothalamic anovulatory syndrome) or hyperandrogenemia (polycystic ovary syndrome). Furthermore, although clinically obvious expressions of these syndromes affect perhaps 10% of premenopausal women, evidence suggests that a much larger number may experience subclinical dysfunction capable of increasing CHD risk.

CONCLUSIONS

Epidemiological data and systematic studies in nonhuman primates provide initial support for the precocious acceleration hypothesis, suggesting that efforts to protect the health of postmenopausal women would best begin during the premenopausal years.