Assessing the mammary gland of nonhuman primates: effects of endogenous hormones and exogenous hormonal agents and growth factors

ERBB Receptors and Their Ligands in the Developing Mammary Glands of Different Species: Fifteen Characters in Search of an Author

The ERBB tyrosine kinase receptors and their ligands belong to a complex family that has diverse biological effects and expression profiles in the developing mammary glands, where its members play an essential role in translating hormone signals into local effects. While our understanding of these processes stems mostly from mouse models, there is the potential for differences in how this family functions in the mammary glands of other species, particularly in light of their unique histomorphological features. Herein we review the postnatal distribution and function of ERBB receptors and their ligands in the mammary glands of rodents and humans, as well as for livestock and companion animals. Our analysis highlights the diverse biology for this family and its members across species, the regulation of their expression, and how their roles and functions might be modulated by varying stromal composition and hormone interactions. Given that ERBB receptors and their ligands have the potential to influence processes ranging from normal mammary development to diseased states such as cancer and/or mastitis, both in human and veterinary medicine, a more complete understanding of their biological functions should help to direct future research and the identification of new therapeutic targets.

Impact of 6 month conjugated equine estrogen versus estradiol-treatment on biomarkers and enriched gene sets in healthy mammary tissue of non-human primates

OBJECTIVE

To identify distinctly regulated gene markers and enriched gene sets in breast tissue of cynomolgus monkeys (Macaca fascicularis) treated for six months with either conjugated equine estrogens (CEE) or estradiol (E2) by analysis of corresponding mRNA levels of genes associated with breast development, carcinogenesis, apoptosis and immune regulation. Additionally, translation of three nuclear markers was analyzed.

METHODS

RNA from breast biopsies and necropsies was isolated from two independent study trials from Ethun et al. (CEE) and Foth et al. (E2) after 6 month of treatment duration. RNA was subjected to qRT-PCR and MicroArray analysis. Immunohistochemical stainings were performed for the estrogen receptor alpha subunit (ERa), the progesterone receptor (PGR) and the proliferation marker Ki67.

RESULTS

We identified a total of 36 distinctly enriched gene sets. Thirty-one were found in the CEE treatment group and five were found in the E2 treatment group, with no overlap. Furthermore, two individual genes IGFBP1 and SGK493 were upregulated in CEE treated animals. Additional targeted qRT-PCR analysis of ten specific estrogen-related genes showed upregulation of three genes (TFF1, PGR and GREB1) after CEE treatment, respectively one gene (TFF1) after E2 treatment. Immunohistochemical stains of breast biopsies showed a significant increase in expression of the PGR marker after CEE treatment.

CONCLUSIONS

In this study we identified enriched gene sets possibly induced by CEE or E2 treatment in various processes associated with cancer biology and immunology. This preliminary translational data supports the concept that different estrogen types have different effects on healthy breast tissue and may help generate hypotheses for future research.

Unique Transcriptomic Changes Underlie Hormonal Interactions During Mammary Histomorphogenesis in Female Pigs

Successful lactation and the risk for developing breast cancer depend on growth and differentiation of the mammary gland (MG) epithelium that is regulated by ovarian steroids (17β-estradiol [E] and progesterone [P]) and pituitary-derived prolactin (PRL). Given that the MG of pigs share histomorphogenic features present in the normal human breast, we sought to define the transcriptional responses within the MG of pigs following exposure to all combinations of these hormones. Hormone-ablated female pigs were administered combinations of E, medroxyprogesterone 17-acetate (source of P), and either haloperidol (to induce PRL) or 2-bromo-α-ergocryptine. We subsequently monitored phenotypic changes in the MG including mitosis, receptors for E and P (ESR1 and PGR), level of phosphorylated STAT5 (pSTAT5), and the frequency of terminal ductal lobular unit (TDLU) subtypes; these changes were then associated with all transcriptomic changes. Estrogen altered the expression of approximately 20% of all genes that were mostly associated with mitosis, whereas PRL stimulated elements of fatty acid metabolism and an inflammatory response. Several outcomes, including increased pSTAT5, highlighted the ability of E to enhance PRL action. Regression of transcriptomic changes against several MG phenotypes revealed 1669 genes correlated with proliferation, among which 29 were E inducible. Additional gene expression signatures were associated with TDLU formation and the frequency of ESR1 or PGR. These data provide a link between the hormone-regulated genome and phenome of the MG in a species having a complex histoarchitecture like that in the human breast, and highlight an underexplored synergy between the actions of E and PRL during MG development.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the nonhuman primate used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Investigating the role of endogenous estrogens, hormone replacement therapy, and blockade of estrogen receptor-α activity on breast metabolic signaling

Purpose

Menopause is associated with an increased risk of estrogen receptor-positive (ER +) breast cancer. To characterize the metabolic shifts associated with reduced estrogen bioavailability on breast tissue, metabolomics was performed from ovary-intact and ovariectomized (OVX) female non-human primates (NHP). The effects of exogenous estrogen administration or estrogen receptor blockade (tamoxifen treatment) on menopause-induced metabolic changes were also investigated.

Methods

Bilateral ovariectomies were performed on female cynomolgus macaques (Macaca fascicularis) to model menopause. OVX NHP were then divided into untreated (n = 13), conjugated equine estrogen (CEE)-treated (n= 13), or tamoxifen-treated (n = 13) subgroups and followed for 3 years. Aged-matched ovary-intact female NHP (n = 12) were used as a premenopausal comparison group. Metabolomics was performed on snap-frozen breast tissue.

Results

Changes in several different metabolic biochemicals were noted, particularly in glucose and fatty acid metabolism. Specifically, glycolytic, Krebs cycle, acylcarnitines, and phospholipid metabolites were elevated in breast tissue from ovary-intact NHP and OVX + CEE in relation to the OVX and OVX + tamoxifen group. In contrast, treatment with CEE and tamoxifen decreased several cholesterol metabolites, compared to the ovary-intact and OVX NHP. These changes were accompanied by elevated bile acid metabolites in the ovary-intact group.

Conclusion

Alterations in estrogen bioavailability are associated with changes in the mammary tissue metabolome, particularly in glucose and fatty acid metabolism. Changes in these pathways may represent a bioenergetic shift in gland metabolism at menopause that may affect breast cancer risk.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06354-w.

The evolution of perennially enlarged breasts in women: a critical review and a novel hypothesis

The possession of permanent, adipose breasts in women is a uniquely human trait that develops during puberty, well in advance of the first pregnancy. The adaptive role and developmental pattern of this breast morphology, unusual among primates, remains an unresolved conundrum. The evolutionary origins of this trait have been the focus of many hypotheses, which variously suggest that breasts are a product of sexual selection or of natural selection due to their putative role in assisting in nursing or as a thermoregulatory organ. Alternative hypotheses assume that permanent breasts are a by-product of other evolutionary changes. We review and evaluate these hypotheses in the light of recent literature on breast morphology, physiology, phylogeny, ontogeny, sex differences, and genetics in order to highlight their strengths and flaws and to propose a coherent perspective and a new hypothesis on the evolutionary origins of perennially enlarged breasts in women. We propose that breasts appeared as early as Homo ergaster, originally as a by-product of other coincident evolutionary processes of adaptive significance. These included an increase in subcutaneous fat tissue (SFT) in response to the demands of thermoregulatory and energy storage, and of the ontogenetic development of the evolving brain. An increase in SFT triggered an increase in oestradiol levels (E2). An increase in meat in the diet of early Homo allowed for further hormonal changes, such as greater dehydroepiandrosterone (DHEA/S) synthesis, which were crucial for brain evolution. DHEA/S is also easily converted to E2 in E2-sensitive body parts, such as breasts and gluteofemoral regions, causing fat accumulation in these regions, enabling the evolution of perennially enlarged breasts. Furthermore, it is also plausible that after enlarged breasts appeared, they were co-opted for other functions, such as attracting mates and indicating biological condition. Finally, we argue that the multifold adaptive benefits of SFT increase and hormonal changes outweighed the possible costs of perennially enlarged breasts, enabling their further development.

Nonhuman primate model in mammary gland biology and neoplasia research

Research on breast cancer pathogenesis, prevention and drug development remains an important field as this disease is still one of the leading causes of cancer death worldwide. Nonhuman primates, particularly macaque species, may serve as a highly translational animal model in breast cancer studies due to their similarity with humans in genetics, anatomy, reproductive and endocrine physiology including mammary gland development profile. The use of nonhuman primates in biomedical research, however, requires high ethical standards and an increasing expectation to improve strategies to replace, reduce and refine their use. Here, we discuss some key features of nonhuman primate mammary gland biology relevant to their strengths and limitations as models in studies of breast development and cancer risk.

Mammosphere Culture of Mammary Cells from Cynomolgus Macaques (Macaca fascicularis)

The mammary gland contains adult stem cells that are capable of self-renewal. Although these cells hold an important role in the biology and pathology of the breast, the studies of mammary stem cells are few due to the difficulty of acquiring and expanding undifferentiated adult stem cell populations. In this study, we developed mammosphere cultures from frozen mammary cells of nulliparous cynomolgus macaques (Macaca fascicularis) as a culture system to enrich mammary stem cells. Small samples of mammary tissues were collected by surgical biopsy; cells were cultured in epithelial cell growth medium and cryopreserved. Cryopreserved cells were cultured into mammospheres, and the expression of markers for stemness was evaluated by using quantitative PCR analysis. Cells were further differentiated by using 2D and 3D approaches to evaluate morphology and organoid budding, respectively. The study showed that mammosphere culture resulted in an increase in the expression of mammary stem cell markers with each passage. In contrast, markers for epithelial cells and pluripotency decreased across multiple passages. The 2D differentiation of the cells showed heterogeneous morphology, whereas 3D differentiation allowed for organoid formation. The results indicate that mammospheres can be successfully developed from frozen mammary cells derived from breast tissue collected from nulliparous cynomolgus macaques through surgical biopsy. Because mammosphere cultures allow for the enrichment of a mammary stem cell population, this refined method provides a model for the in vitro or ex vivo study of mammary stem cells.

Age at reproductive debut: Developmental predictors and consequences for lactation, infant mass, and subsequent reproduction in rhesus macaques (Macaca mulatta)

OBJECTIVES

The age at which females initiate their reproductive career is a critical life-history parameter with potential consequences on their residual reproductive value and lifetime fitness. The age at reproductive debut may be intimately tied to the somatic capacity of the mother to rear her young, but relatively little is known about the influence of age of first birth on milk synthesis within a broader framework of reproductive scheduling, infant outcomes, and other life-history tradeoffs.

MATERIAL AND METHODS

Our study investigated the predictors of age at first reproduction among 108 captive rhesus macaque (Macaca mulatta) females, and associations with their milk synthesis at peak lactation, infant mass, and ability to subsequently conceive and reproduce.

RESULTS

The majority of females reproduced in their fourth year (typical breeders); far fewer initiated their reproductive career one year earlier or one year later (respectively early and late breeders). Early breeders (3-year-old) benefited from highly favorable early life development (better juvenile growth, high dominance rank) to accelerate reproduction, but were impaired in milk synthesis due to lower somatic resources and their own continued growth. Comparatively, late breeders suffered from poor developmental conditions, only partially compensated by their delayed reproduction, and evinced compromised milk synthesis. Typical breeders not only produced higher available milk energy but also had best reproductive performance during the breeding and birth seasons following primiparity.

DISCUSSION

Here, we refine and extend our understanding of how life-history tradeoffs manifest in the magnitude, sources, and consequences of variation in age of reproductive debut. These findings provide insight into primate reproductive flexibility in the context of constraints and opportunities.

Why primate models matter

Research involving nonhuman primates (NHPs) has played a vital role in many of the medical and scientific advances of the past century. NHPs are used because of their similarity to humans in physiology, neuroanatomy, reproduction, development, cognition, and social complexity-yet it is these very similarities that make the use of NHPs in biomedical research a considered decision. As primate researchers, we feel an obligation and responsibility to present the facts concerning why primates are used in various areas of biomedical research. Recent decisions in the United States, including the phasing out of chimpanzees in research by the National Institutes of Health and the pending closure of the New England Primate Research Center, illustrate to us the critical importance of conveying why continued research with primates is needed. Here, we review key areas in biomedicine where primate models have been, and continue to be, essential for advancing fundamental knowledge in biomedical and biological research.

Differential responses to JNJ-37822681, a specific and fast dissociating dopamine D2 receptor antagonist, in cynomolgus monkey and Sprague-Dawley rat general toxicology studies: clinical observations, prolactin levels, mammary histopathology findings and toxicokinetics

JNJ-37822681 is a potent, specific and fast dissociating dopamine D2 receptor antagonist intended for the treatment of schizophrenia. Its nonclinical toxicological profile was investigated in a series of general repeat dose toxicity studies in cynomolgus monkeys and Sprague-Dawley rats. The maximum duration of treatment was 9 and 6 months, respectively. Interspecies differences were noted in the response to JNJ-37822681 in terms of extrapyramidal (EPS)-like clinical signs and prolactin-mediated tissue changes in the mammary gland. Monkeys showed severe EPS-like clinical signs such as abnormal posture, abnormal eye movements and hallucination-like behavior at relatively low exposures compared to those associated with EPS in patients with schizophrenia. The high sensitivity of the monkey to JNJ-37822681-induced EPS-like signs was unexpected based on the fast dissociating properties of the compound. Rats, however, were not prone to EPS. Elevated serum prolactin levels were found in rats and monkeys. While rats showed slight to moderate prolactin-related tissue changes upon histopathological examination in all studies, which among others affected the mammary gland, only minor mammary gland tissue changes were noted in monkeys. Prolactin levels were only slightly increased in patients with schizophrenia receiving relatively high dose levels of JNJ-37822681. The monkey toxicology studies did not provide an exposure-based safety margin, while in rats adverse effects were only noted at exposures considerably higher than those achieved at efficacious plasma concentrations in the clinic. Overall, the available data suggest that the cynomolgus monkey showed better predictivity towards the nature of JNJ-37822681-associated adverse events in humans than the Sprague-Dawley rat.

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.

Effects of bazedoxifene acetate with and without conjugated equine estrogens on the breast of postmenopausal monkeys

OBJECTIVE

Concerns about increased breast cancer risk with estrogen and progestin therapy have led to an increased interest in progestin alternatives. The main objective of this study was to determine if bazedoxifene acetate (BZA), a new selective estrogen receptor modulator, will antagonize the proliferative and transcriptional effects of conjugated equine estrogens (CEE) in the breast.

METHODS

As part of a 20-month preclinical trial, 95 ovariectomized cynomolgus macaques (Macaca fascicularis) were randomized to receive no treatment or treatment with BZA (20 mg/d), CEE (0.45 mg/d), or BZA and CEE in combination (women's daily equivalent doses). The data presented here include breast effects after 6 months of treatment. Endpoints included histomorphometry, histopathological evaluations, gene microarray assays, polymerase chain reaction quantification of specific estrogen receptor α (ER-α) activity markers, and immunohistochemical detection of sex steroid receptors, and the proliferation marker Ki67.

RESULTS

BZA + CEE and BZA resulted in significantly less total epithelial density, lobular enlargement, and Ki67 immunolabeling in the terminal ducts compared with CEE alone (P < 0.05 for all). The addition of BZA to CEE antagonized the expression of ER-α-regulated genes such as GREB1 and TFF1 (P < 0.01 for both), whereas BZA alone had minimal effects on ER-α-mediated transcriptional activity. BZA and BZA + CEE did not significantly up-regulate genes related to cell cycle progression and proliferation. BZA with and without CEE also resulted in less lobular and terminal duct ER-α immunolabeling compared with control and CEE (P < 0.0001 for all).

CONCLUSIONS

These findings demonstrate that BZA given at a clinically relevant dose is an estrogen antagonist in the breast, supporting the idea that CEE + BZA may provide a lower breast cancer risk profile compared with traditional estrogen + progestin therapies.

Scientific and Regulatory Policy Committee (SRPC) Paper

Hormonally mediated effects on the female reproductive system may manifest as pathologic changes of endocrine-responsive organs and altered reproductive function. Identification of these effects requires proper assessment, which may include investigative studies to profile female reproductive hormones. Here, we briefly describe normal hormonal patterns across the estrous or menstrual cycle and provide general guidance on measuring female reproductive hormones and characterizing hormonal disturbances in nonclinical toxicity studies. Although species used in standard toxicity studies share basic features of reproductive endocrinology, there are important species differences that affect both study design and interpretation of results. Diagnosing female reproductive hormone disturbances can be complicated by many factors, including estrous/menstrual cyclicity, diurnal variation, and age- and stress-related factors. Thus, female reproductive hormonal measurements should not generally be included in first-tier toxicity studies of standard design with groups of unsynchronized intact female animals. Rather, appropriately designed and statistically powered investigative studies are recommended in order to properly identify ovarian and/or pituitary hormone changes and bridge these effects to mechanistic evaluations and safety assessments. This article is intended to provide general considerations and approaches for these types of targeted studies.

Life stage differences in mammary gland gene expression profile in non-human primates

Breast cancer (BC) is the most common malignancy of women in the developed world. To better understand its pathogenesis, knowledge of normal breast development is crucial, as BC is the result of disregulation of physiologic processes. The aim of this study was to investigate the impact of reproductive life stages on the transcriptional profile of the mammary gland in a primate model. Comparative transcriptomic analyses were carried out using breast tissues from 28 female cynomolgus macaques (Macaca fascicularis) at the following life stages: prepubertal (n = 5), adolescent (n = 4), adult luteal (n = 5), pregnant (n = 6), lactating (n = 3), and postmenopausal (n = 5). Mammary gland RNA was hybridized to Affymetrix GeneChip(®) Rhesus Macaque Genome Arrays. Differential gene expression was analyzed using ANOVA and cluster analysis. Hierarchical cluster analysis revealed distinct separation of life stage groups. More than 2,225 differentially expressed mRNAs were identified. Gene families or pathways that changed across life stages included those related to estrogen and androgen (ESR1, PGR, TFF1, GREB1, AR, 17HSDB2, 17HSDB7, STS, HSD11B1, AKR1C4), prolactin (PRLR, ELF5, STAT5, CSN1S1), insulin-like growth factor signaling (IGF1, IGFBP1, IGFBP5), extracellular matrix (POSTN, TGFB1, COL5A2, COL12A1, FOXC1, LAMC1, PDGFRA, TGFB2), and differentiation (CD24, CD29, CD44, CD61, ALDH1, BRCA1, FOXA1, POSTN, DICER1, LIG4, KLF4, NOTCH2, RIF1, BMPR1A, TGFB2). Pregnancy and lactation displayed distinct patterns of gene expression. ESR1 and IGF1 were significantly higher in the adolescent compared to the adult animals, whereas differentiation pathways were overrepresented in adult animals and pregnancy-associated life stages. Few individual genes were distinctly different in postmenopausal animals. Our data demonstrate characteristic patterns of gene expression during breast development. Several of the pathways activated during pubertal development have been implicated in cancer development and metastasis, supporting the idea that other developmental markers may have application as biomarkers for BC.

Long-term ovariectomy alters social and anxious behaviors in semi-free ranging Japanese macaques

Symptoms of anxiety and depression often occur in young women after complete hysterectomy and in older women during menopause. There are many variables that are hard to control in human population studies, but that are absent to a large extent in stable nonhuman primate troops. However, macaques exhibit depressive and anxious behaviors in response to similar situations as humans such as isolation, stress, instability or aggression. Therefore, we hypothesized that examination of behavior in ovariectomized individuals in a stable macaque troop organized along matriarchal lineages and in which individuals have social support from extended family, would reveal effects that were due to the withdrawal of ovarian steroids without many of the confounds of human society. We also tested the hypothesis that ovariectomy would elicit and increase anxious behavior in a stressful situation such as brief exposure to single caging. Japanese macaques (Macaca fuscata) were ovariectomized (Ovx) or tubal-ligated (intact controls) at 3 years of age and allowed to mature for 3 years in a stable troop of approximately 300 individuals. Behaviors were recorded in the outdoor corral in the third year followed by individual temperament tests in single cages. There was no obvious difference in anxiety-related behaviors such as scratching between Ovx and tubal-ligated animals in the corral. Nonetheless, compared to tubal-ligated animals, Ovx animals exhibited a significant decrease in (1) positive social behavior, (2) initiating dominance behavior, (3) time receiving grooming, (4) locomoting, (5) mounting behavior, and in (6) consort behavior. However, Ovx females exhibited a significant increase in (1) consummatory behavior and (2) object play compared to tubal-ligated controls. In the individual temperament tests, Ovx individuals exhibited an increase in anxiety-related behaviors. There was no difference in adrenal weight/body weight suggesting that neither group was under chronic stress. These data indicate that ovarian hormones enable females to successfully navigate their social situation and may reduce anxiety in novel situations.

Overview of the marmoset as a model in nonclinical development of pharmaceutical products

Callithrix jacchus (common marmoset) is one of the more primitive non-human primate species and is used widely in fundamental biology, pharmacology and toxicology studies. Marmosets breed well in captivity with good reproductive efficiencies and their sexual maturity is reached within 18 months of age allowing for rapid expansion of colonies and early availability of sexually mature animals permitting an earlier assessment of product candidates in the adult. Their relatively small size allows a reduction in material requirements leading to a reduction in development time and cost. Fewer animals are also required due to their ability to be used in both pharmacology and toxicology (nonclinical) studies. These factors, alongside a better understanding of their optimal nutrient and welfare requirements over recent years, facilitate the generation of a more cohesive and robust dataset. With the growth of biotechnology-derived pharmaceuticals, non-human primate use has, by necessity, also increased; nevertheless, there is also a growing public call for minimizing their use. Utilizing, the more primitive marmoset species may provide the optimal compromise and once the scientific rationale has been carefully considered and their use justified, there are several advantages to using the marmoset as a model in nonclinical development of pharmaceutical products.

Cyclic Morphological Changes in the Beagle Mammary Gland

Interpretation of chemical-induced effects on the female beagle mammary gland can be difficult owing to the wide variation of normal glandular morphology. In this retrospective study, morphological features of the gland in four (proestrus, estrus, diestrus, and anestrus) phases of the cycle are described. The gland was quiescent (inactive) in proestrus and estrus. In diestrus, with the rise of progesterone, four (I–IV) distinct morphological changes were evident. In phase I, there was exuberant stromal and ductal proliferation. In phase II, there was early lobular development with branching ducts and alveolar proliferation. In phase III, there was an abundance of glandular tissue with large lobules containing secretory material, whereas phase IV had features of early regression, increased interlobular connective tissue, and eosinophilic secretions in distended ducts and acini. In early anestrus, ducts were distended, with eosinophilic secretions with alveolar regression, whereas regression was complete in late anestrus. Glandular morphology was slightly variable in the mammary chain within the same dog. Progesterone receptor expression was prominent in estrus and early diestrus, and peak estrogen receptor expression was noted in diestrus II. Expression of proliferation marker ki-67 was highest in diestrus I, followed by diestrus II. There was excellent concordance between the estrous stage and the glandular morphology.

Endometrial profile of tamoxifen and low-dose estradiol combination therapy

PURPOSE

Combination estrogen + progestin therapy has been associated with increased breast cancer risk in postmenopausal women. Selective estrogen receptor modulators (SERM) are potential alternatives to progestins, although the endometrial safety of estrogen + SERM co-therapies is not known. The goal of this study was to evaluate the endometrial profile of low-dose estradiol and the SERM tamoxifen alone and in combination.

EXPERIMENTAL DESIGN

Twenty-four postmenopausal female cynomolgus macaques were randomized by social group to receive placebo, low-dose micronized estradiol (E(2); 0.25 mg/1,800 kcal), the SERM tamoxifen (Tam; 20 mg/1,800 kcal), or E(2) + Tam for 4 months in a parallel-arm design.

RESULTS

Tamoxifen alone resulted in overlapping but distinct effects compared with E(2). Both E(2) and Tam increased uterine weight and endometrial thickness, whereas only E(2) increased endometrial proliferation. Morphologic effects were similar for Tam and E(2) + Tam, which both induced stromal fibrosis and cystic change. Tamoxifen inhibited E(2)-induced proliferation and expression of genes related to cell cycle progression while exhibiting mixed agonist and antagonist effects on gene markers of estrogen receptor activity. The gene expression profile for E(2) + Tam was distinct from either E(2) or Tam alone but dominated by the Tam effect for estrogen-regulated genes. Tam also attenuated E(2) effects on both vaginal maturation and cervical epithelial height.

CONCLUSIONS

These findings characterize a novel phenotype resulting from estrogen + SERM co-therapy. The predominance of Tam effects on endometrial proliferation, morphology, and transcriptional profiles suggests that endometrial risks for E(2) + Tam may be similar to Tam alone.

Estrogen/isoflavone interactions in cynomolgus macaques (Macaca fascicularis)

Soy isoflavones are phytoestrogenic components of dietary soy, which are widely consumed for their potential health benefits. Soy isoflavones appear to decrease breast and endometrial cancer risk in human observational studies, but paradoxically stimulate growth of breast cancer cells in culture and uterine enlargement in rodents. We have shown that these compounds are not estrogenic in cynomolgus monkeys even at relatively high doses, but that they reduce estrogen-induced proliferative responses of the breast and endometrium. This effect may be mediated through estrogen receptor interactions and/or modulation of endogenous estrogen metabolism. Interindividual variation in isoflavone absorption and metabolism contributes to the degree of estrogen antagonistic effect. Our recent studies have also shown that individual isoflavone metabolites such as glyceollins may have unique selective estrogen receptor modulator-like activity, acting as tissue-specific antagonists without agonist activity. Rodent studies and human epidemiologic data suggest that timing of exposure and dose relative to endogenous estrogen concentrations are important determinants of effect, and studies of dietary soy on breast development and pubertal maturation are under way. Because soy isoflavones are both abundant in standard monkey chow diets and widely available as dietary supplements for human beings, these findings have broad relevance to the health of human and nonhuman primates.

Hormone interactions confer specific proliferative and histomorphogenic responses in the porcine mammary gland

Mammary gland growth and morphogenesis are regulated by interactions between hormones as much as by their individual actions. The effect of these interactions on the mammary gland phenotype in species other than rodents is relatively undefined. We investigated the individual and combined effects of estrogen (E), progestin (P), and prolactin (PRL) on mammary gland development in gilts. Pigs were shown to have a ductal-lobular parenchyma that underwent hormone-stimulated progression of terminal ductal lobular unit (TDLU) morphogenesis similar to that in the human breast. Ovariectomy plus hypoprolactinemia abolished mammary gland growth. Estrogen alone stimulated mammary epithelial cell proliferation, terminal bud formation, and the progression of TDLU1 structures to a TDLU2 morphotype. Maximal epithelial cell proliferation, DNA content, parenchymal area, and morphological development of the porcine mammary gland were realized following treatment with E+PRL or E+P+PRL. In contrast, P alone did not promote epithelial cell proliferation, TDLU type progression, mammary gland growth, or morphogenesis. These data indicate that interactions between E and PRL are the main determinants of growth and morphogenesis in the porcine mammary gland.

Mammary gland and endometrial effects of testosterone in combination with oral estradiol and progesterone

OBJECTIVE

The goal of this pilot study was to evaluate the effects of testosterone (T) cotherapy on mammary gland and endometrial measures in a postmenopausal primate model.

METHODS

Twenty-five surgically postmenopausal cynomolgus monkeys were randomized by social group to receive daily treatment with (1) placebo, (2) oral micronized 17beta-estradiol (1 mg/d equivalent in women) + progesterone (200 mg/d equivalent in women) (E + P), or (3) E + P with T administered via subcutaneous pellets for 8 weeks at a high dose (15 mg) followed by 8 weeks at a low dose (1.5 mg) (E + P + T). The main outcome measures were breast and endometrial epithelial proliferation, as measured by Ki67/MIB1 immunolabeling.

RESULTS

Intralobular breast proliferation did not differ significantly among groups after 8 weeks of treatment but was marginally higher (P = 0.03) in the E + P + T group after 16 weeks of treatment. No significant increase in proliferation was seen for E + P alone. Comparable changes in mammary gland markers of estrogen-receptor activity were seen for the E + P and E + P + T groups. In the endometrium, the addition of T did not increase endometrial glandular proliferation or estrogen-receptor activity or result in any distinct histologic changes.

CONCLUSIONS

The findings of this study do not support the idea that T antagonizes the effects of combined hormone therapy on breast proliferation or markers of estrogen-receptor activity. Overall, the short-term effects of T cotherapy on the mammary gland and endometrium were minimal.

Selected Background Findings and Interpretation of Common Lesions in the Female Reproductive System in Macaques

The authors describe a selection of normal findings and common naturally occurring lesions in the reproductive system of female macaques, including changes in the ovaries, uterus, cervix, vagina, and mammary glands. Normal features of immature ovaries, uteri, and mammary glands are described. Common non-neoplastic lesions in the ovaries include cortical mineralization, polyovular follicles, cysts, ovarian surface epithelial hyperplasia, and ectopic ovarian tissue. Ovarian neoplasms include granulosa cell tumors, teratomas, and ovarian surface epithelial tumors. Common non-neoplastic uterine findings include loss of features of normal cyclicity, abnormal bleeding, adenomyosis, endometriosis, epithelial plaques, and pregnancy-associated vascular remodeling. Hyperplastic and neoplastic lesions of the uterus include endometrial polyps, leiomyomas, and rarely endometrial hyperplasia and endometrial adenocarcinoma. Vaginitis is common. Cervical lesions include endocervical squamous metaplasia, polyps, and papillomavirus-associated lesions. Lesions in the mammary gland are most often proliferative and range from ductal hyperplasia to invasive carcinoma. Challenges to interpretation include the normal or pathologic absence of menstrual cyclicity and the potential misinterpretation of sporadic lesions, such as epithelial plaques or papillomavirus-associated lesions. Interpretation of normal and pathologic findings is best accomplished with knowledge of the life stage, reproductive history, and hormonal status of the animal.

Physiology and Endocrinology of the Ovarian Cycle in Macaques

Macaques provide excellent models for preclinical testing and safety assessment of female reproductive toxicants. Currently, cynomolgus monkeys are the predominant species for (reproductive) toxicity testing. Marmosets and rhesus monkeys are being used occasionally. The authors provide a brief review on physiology and endocrinology of the cynomolgus monkey ovarian cycle, practical guidance on assessment and monitoring of ovarian cyclicity, and new data on effects of social housing on ovarian cyclicity in toxicological studies. In macaques, cycle monitoring is achieved using daily vaginal smears for menstruation combined with cycle-timed frequent sampling for steroid and peptide hormone analysis. Owing to requirements of frequent and timed blood sampling, it is not recommended to incorporate these special evaluations into a general toxicity study design. Marmosets lack external signs of ovarian cyclicity, and cycle monitoring is done by regular determinations of progesterone. Cynomolgus and marmoset monkeys do not exhibit seasonal variations in ovarian activity, whereas such annual rhythm is pronounced in rhesus monkeys. Studies on pair- and group-housed cynomolgus monkeys revealed transient alterations in the duration and endocrinology of the ovarian cycle followed by return to normal cyclicity after approximately six months. This effect is avoided if the animals had contact with each other prior to mingling. These experiments also demonstrated that synchronization of ovarian cycles did not occur.

The Mammary Glands of Macaques

This review describes the normal biology and physiology of the mammary gland in macaques, including the typical histologic appearance across the life span (development, reproductive maturity, lactation, and senescence). The molecular events regulating breast morphogenesis are described, as well as systemic and local hormonal regulators of mammary gland proliferation, differentiation, and function. Similarities and differences to the human breast are described. Regulatory events are illuminated by discussion of genetically modified mouse models. Tissue response markers, including immunohistochemical markers of proliferation and other hormonally induced changes and studies to date, regarding the effects of exogenous hormones, are briefly summarized. In general, estrogens stimulate progesterone receptor expression and proliferation in the mammary gland, and combinations of estrogens and progestogens cause greater proliferation than estrogens alone. Evaluation of novel chemical agents in macaques requires careful evaluation of age and hormonal context to avoid the confounding effects of mammary gland development, past reproductive history, and other influences on mammary gland morphology. The expression of proliferation markers and progesterone receptors may be used as biomarkers to measure chemically induced hormonal effects.

Estrogen effects on epithelial proliferation and benign proliferative lesions in the postmenopausal primate mammary gland

Proliferative lesions of the mammary gland are risk markers and potential precursors for the development of breast cancer in postmenopausal women. In this study we evaluated mammary epithelial proliferation and proliferative lesions in a group of 63 aged postmenopausal macaques randomized by social group to receive one of three experimental diets for 8 months: (1) control; (2) control with 17beta-estradiol (E2) at the human equivalent dose of 1.0 mg per day; and (3) control with the soy phytoestrogen equol (EQ) at the human equivalent dose of 105 mg per day. In normal mammary epithelium, treatment with E2 but not EQ resulted in greater proliferation, epithelial area, and progesterone receptor expression (P<0.05 for all). Mammary lesions included columnar cell change (26/63), columnar cell hyperplasia with and without atypia (13/63), atypical ductal hyperplasia (6/63), and atypical lobular hyperplasia (3/63). Lesions were most common within terminal ductal lobular units. The prevalence of columnar cell hyperplasia (total and atypical cases) was higher in animals treated with E2 compared to control (P<0.05 for both). Compared to normal mammary epithelium, columnar cell lesions (CCLs) showed greater constitutive expression of estrogen receptor-alpha across all groups (P<0.001) and greater expression of progesterone receptor in response to E2 (P<0.01). Independent of treatment, animals with CCLs on histology had greater gene expression of estrogen receptor-alpha and markers of estrogen receptor activity (trefoil factor 1) and proliferation (gene for Ki67 antigen) at a site contralateral to the CCL (P<0.05 for all). These findings demonstrate that the terminal ductal lobular units of the postmenopausal mammary gland contain morphologically distinct cell populations that may hyperrespond to E2 exposure, resulting in specific types of hyperplastic lesions.

Effects of lasofoxifene on the uterus, vagina, and breast in ovariectomized cynomolgus monkeys (Macaca fascicularis)

OBJECTIVE

The purpose of this study was to assess the effects of lasofoxifene on the reproductive system in ovariectomized nonhuman primates.

STUDY DESIGN

This was a 2-year, randomized study. Adult female macaques (Macaca fascicularis) were assigned randomly into 5 groups: ovariectomized, placebo-treated controls (n = 22); sham-ovariectomized, placebo-treated controls (n = 24); ovariectomized animals given 0.021 mg Premarin kg/d (conjugated equine estrogen; n = 25); lasofoxifene at 1.0 mg/kg/d (n = 23); or lasofoxifene at 5.0 mg/kg/d (n = 25). Outcomes included organ weights and histopathologic findings.

RESULTS

Lasofoxifene did not increase uterine weight or endometrial thickness and did not change mammary, vaginal, or cervical histologic condition. Mild endometrial fibrosis and cystic change were seen in lasofoxifene-treated animals, in contrast to significant uterine weight increases and endometrial hyperplasia induced by conjugated equine estrogen.

CONCLUSION

Lasofoxifene did not increase uterine weight and produced minor histologic uterine changes at the doses that were given and had no effect on the breast, vagina, or cervix.