Naturally occurring menopause in cynomolgus monkeys: changes in hormone, lipid, and carbohydrate measures with hormonal status

The Influence of Diet on Metabolism and Health Across the Lifespan in Nonhuman Primates

The macro and micronutrient composition and the overall quantity of the diet are important predictors of physical and psychological health and, as a consequence, behavior. Translational preclinical models are critical to identifying the mechanisms underlying these relationships. Nonhuman primate models are particularly instrumental to this line of research as they exhibit considerable genetic, social, and physiological similarities, as well as similarities in their developmental trajectories to humans. This review aims to discuss recent contributions to the field of diet and metabolism and health using nonhuman primate models. The influence of diet composition on health and physiology across the lifespan will be the primary focus, including recent work examining the impact of maternal diet programming of offspring physiologic and behavioral developmental outcomes.

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.

Nonhuman primates at the intersection of aging biology, chronic disease, and health: An introduction to the American journal of primatology special issue on aging, cognitive decline, and neuropathology in nonhuman primates

Aging across the Primate Order is poorly understood because ages of individuals are often unknown, there is a dearth of aged animals available for study, and because aging is best characterized by longitudinal studies which are difficult to carry out in long-lived species. The human population is aging rapidly, and advanced age is a primary risk factor for several chronic diseases and conditions that impact healthspan. As lifespan has increased, diseases and disorders of the central nervous system (CNS) have become more prevalent, and Alzheimer's disease and related dementias have become epidemic. Nonhuman primate (NHP) models are key to understanding the aging primate CNS. This Special Issue presents a review of current knowledge about NHP CNS aging across the Primate Order. Similarities and differences to human aging, and their implications for the validity of NHP models of aging are considered. Topics include aging-related brain structure and function, neuropathologies, cognitive performance, social behavior and social network characteristics, and physical, sensory, and motor function. Challenges to primate CNS aging research are discussed. Together, this collection of articles demonstrates the value of studying aging in a breadth of NHP models to advance our understanding of human and nonhuman primate aging and healthspan.

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.

Single-Cell Transcriptomic Atlas of Primate Ovarian Aging

Molecular mechanisms of ovarian aging and female age-related fertility decline remain unclear. We surveyed the single-cell transcriptomic landscape of ovaries from young and aged non-human primates (NHPs) and identified seven ovarian cell types with distinct gene-expression signatures, including oocyte and six types of ovarian somatic cells. In-depth dissection of gene-expression dynamics of oocytes revealed four subtypes at sequential and stepwise developmental stages. Further analysis of cell-type-specific aging-associated transcriptional changes uncovered the disturbance of antioxidant signaling specific to early-stage oocytes and granulosa cells, indicative of oxidative damage as a crucial factor in ovarian functional decline with age. Additionally, inactivated antioxidative pathways, increased reactive oxygen species, and apoptosis were observed in granulosa cells from aged women. This study provides a comprehensive understanding of the cell-type-specific mechanisms underlying primate ovarian aging at single-cell resolution, revealing new diagnostic biomarkers and potential therapeutic targets for age-related human ovarian disorders.

Age-related nomograms of serum anti-Mullerian hormone levels in female monkeys: Comparison of rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) monkeys

AMH is regarded as a promising predictor for ovarian reserve in humans and non-human primate, and widely used in human medicine to predict ovarian response to gonadotropin, menopause and premature ovarian failure. However, large data set on the range of AMH levels in nonhuman primates is still scarce, which limited its applications largely. In this study, age-related AMH nomograms of rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) were produced and compared. 219 rhesus and 529 cynomolgus monkeys ranging from infancy to adult were included. In total, the mean serum AMH levels in cynomolgus monkeys were higher than that of rhesus monkeys (14.6 ± 5.3 ng/ml vs 9.5 ± 6.0 ng/ml, P < 0.001). AMH was inversely correlated with age (r = -0.371, P < 0.001) in rhesus, while the negative correlation did not reach statistical significance in cynomolgus monkeys (r = -0.044, P = 0.156). The maximum mean AMH levels were attained at the subgroup of 4-11 yr and the lowest AMH levels were obtained at the subgroup of ≧12 yr in both primates, corresponding to their fertility potential. In rhesus monkeys, from 1 to 11 years old, AMH level remained stable (1-3 yr: ß = 2.784, P = 0.340; 4-11 yr: r = 0.100, P = 0.110) whereas from 12 yr onward, an inverse correlation between AMH and age (r = -0.450, P = 0.02) was observed. Similarly, AMH appeared stable from 1 to 3 yr (ß = -2.289, P = 0.429) and showed an inverse correlation with age (r = -0.521, P < 0.001) from 12 yr onward in cynomolgus monkeys, while a positive correlation was observed (r = 0.156, P = 0.001) from 4 to 11 yr. AMH levels were relatively stable across the menstrual cycle in both primates and no seasonal difference for AMH levels was observed in rhesus monkeys. Body mass index did not affect serum AMH levels in both primates. Our nomograms of serum AMH provide a reference guide on AMH longitudinal distribution by age for Macaca monkeys and might facilitate its applications.

Species Comparison of Postnatal Development of the Female Reproductive System

The postnatal development of the female reproductive system in laboratory animals and humans is reviewed. To enable a meaningful species comparison of the developing female reproductive system, common definitions of developmental processes were established with a focus made on aspects that are similar across species. A species comparison of the key endocrine, morphologic, and functional (onset of ovarian cycles and ability to reproduce) features of postnatal development of the female reproductive system is provided for human, nonhuman primate, dog, rat, and also mouse, minipig, and rabbit where possible. Species differences in the timing and control of female sexual maturation are highlighted. Additionally, a species comparison of the type and timing of female reproductive ovarian cycles was compiled. Human development provided the frame of reference, and then other common laboratory species were compared. The comparison has inherent challenges because the processes involved and sequence of events can differ greatly across species. Broad strokes were taken to assign a particular average age to an event and are to be used with caution. Methods of evaluation of postnatal female reproductive development in laboratory animals are discussed. Lastly, control rodent data from one of the author's laboratory on vaginal opening, first estrus, estrous cyclicity, and the histopathology involved with the developing female rat and mouse are presented. The information provided in this review is intended to be a resource for the design and interpretation of juvenile animal toxicity testing and ultimately, the relevance of the data to characterize potential risks for women and girls. Birth Defects Research 110:163-189, 2018. © 2017 Wiley Periodicals, Inc.

The Impact of Age on the Female Reproductive System

Evaluation of the female reproductive system in a general toxicity setting can be challenging for the toxicologic pathologist due to the cyclic nature of the estrous and menstrual cycles, timing of puberty and reproductive senescence, and species differences. Age in particular can have a significant impact on the histologic appearance of the female reproductive system and create challenges when trying to distinguish test article-related findings from normal developmental or senescent changes. This review describes the key physiologic and histologic features of immaturity, the transition through puberty, sexual maturity, and reproductive senescence in the female reproductive system, with an emphasis on practical applications for the toxicologic pathologist, and includes recommendations for distinguishing and documenting these developmental periods. Rats and cynomolgus monkeys are used as examples throughout with correlations to clinically observed end points to better aid the toxicologic pathologist in understanding how age may impact study interpretation.

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.

Improvements of vaginal atrophy without systemic side effects after topical application of Pueraria mirifica, a phytoestrogen-rich herb, in postmenopausal cynomolgus macaques

The estrogenic efficacy of topical vaginal application of Pueraria mirifica extract (PM) on the restoration of vaginal atrophy, and the presence of any systemic side effects, were investigated in postmenopausal cynomolgus macaques. Twelve postmenopausal cynomolgus macaques, with complete cessation of menstruation for at least 5 years before start of this experiment, were divided into three groups. They received a topical vaginal application daily of 0.1 or 1% (w/w) PM cream or a conjugated equine estrogen (CEE) cream (a mixture of estrone, equilin, 17β-dihydroequilin, 17α-estradiol and 17α-dihydroequilin at 0.625 mg total estrogen/g cream) for 28 days. Estrogenic efficacy was assessed weekly by vaginal cytology assay and vaginal pH measurement, whilst the plasma luteinizing hormone (LH) and sex skin coloration levels were determined at the end of each treatment period to evaluate the systemic side effects. PM significantly increased the proportion of superficial cells in a dose-dependent manner, with a similar efficacy between 1% (w/w) PM and CEE. Together with increased vaginal maturation, PM decreased the vaginal pH to acidic levels, as observed in the CEE group. PM induced no detected systemic side effects, whilst CEE decreased the plasma LH level and increased the reddish color of the sex skin during the posttreatment period. Topical vaginal treatment with PM stimulated the maturation of the vaginal epithelium without causing systemic side effects in postmenopausal monkeys. The implication is that PM could be a safer alternative to treat vaginal atrophy in postmenopausal women.

Animal models for the effective development of atrophic vaginitis therapies: possibilities and limitations

INTRODUCTION

Vaginal atrophy (VA) is an inflammation of the vagina that develops when there is a significant decrease in levels of the estrogen. Prolonged periods of hypoestrogenism may induce severe VA and treatment is essential. This is a significant problem which requires more focused attention for the development of existing and future therapies.

AREAS COVERED

This review evaluates the suitable animal models of VA, including: mice, rodents and non-human primates. It focuses particularly on the possibilities and limitations of these in vivo models for the effective development of VA therapies.

EXPERT OPINION

Hormone replacement therapy (HRT) has been prescribed and successfully used for VA. However, some studies have shown that HRT may be linked to an increased risk of breast cancer, coronary heart diseases and others risks. Thus, there is a growing interest in effective and safe alternatives to VA symptoms. There are, however, a number of things that must be considered for future drug discovery efforts. One major consideration is what animal model should be used and whether the model is appropriate for the study aim. Similarly, research studies must also consider the influencing factors on these animal models, so that these models can effectively mimic the actual disease. The authors also highlight the need to standardize research parameters to produce more reliable and reproducible data.

Nonhuman primates and other animal models in diabetes research

Animal models are important for determining the pathogenesis of and potential treatments for obesity and diabetes. Nonhuman primates (NHPs) are particularly useful for studying these disorders. As in humans, type 2 diabetes mellitus is the most common form of diabetes in NHPs and occurs more often in older obese animals, with a metabolic progression from insulin resistance (IR) and impaired glucose tolerance to overt diabetes. Histopathologic changes in pancreatic islets are also similar to those seen in humans with diabetes. Initially, there is islet hyperplasia with abundant insulin production to compensate for IR, followed by insufficient insulin production with replacement of islets with islet-associated amyloid. Diabetic NHPs also have adverse changes in plasma lipid and lipoprotein concentrations, biomarkers of obesity, inflammation, and oxidative stress, and protein glycation that contribute to the numerous complications of the disease. Furthermore, sex hormones, pregnancy, and environmental factors (e.g., diet and stress) affect IR and can also contribute to diabetes progression in NHPs. Additionally, due to their similar clinical and pathologic characteristics, NHPs have been used in many pharmacological studies to assess new therapeutic agents. For these reasons, NHPs are particularly valuable animal models of obesity and diabetes for studying disease pathogenesis, risk factors, comorbidities, and therapeutic interventions.

Analysis of glucose metabolism in cynomolgus monkeys during aging

This study was designed to investigate the effect of aging on the glucose metabolism on cynomolgus (Macaca fascicularis) monkeys. A total of 33 cynomolgus monkeys in three aged groups were monitored for glucose levels, serum parameters in fasting state and somatometric measurements. Intravenous glucose tolerance test (IVGTT) and insulin tolerance test (ITT) were also performed. Aging associated changes lies in the less secretion of insulin and C-peptide during IVGTT in cynomolgus monkeys. It was also found that impaired insulin sensitivity occurred in female monkeys during aging based on HOMA-IR and K(ITT) value. In addition, triglyceride level also rose with the increase of age. Less insulin secretion and impaired insulin sensitivity in female were the characteristic during the aging of cynomolgus monkeys in this study. Body mass index, weight and waist hip rate may be the relevant factors in insulin resistance of cynomolgus monkeys.

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.

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.

TNFRSF11A and TNFSF11 are associated with age at menarche and natural menopause in white women

OBJECTIVE

Menarche and menopause mark the lower and upper limits of the female reproductive period. The timing of these events influences women's health in later life. The onsets of menarche and menopause have a strong genetic basis. We tested two genes, TNFRSF11A (RANK) and TNFSF11 (RANKL), for their association with age at menarche (AM) and age at natural menopause (ANM).

METHODS

Nineteen single nucleotide polymorphisms (SNPs) of TNFRSF11A and 12 SNPs of TNFSF11 were genotyped in a random sample of 306 unrelated white women. This sample was analyzed for the association of the SNPs and common haplotypes with AM. Then, a subsample of 211 women with natural menopause was analyzed for the association of both genes with ANM. Smoking, alcohol intake, and duration of lactation were applied as covariates in the association analyses.

RESULTS

Three polymorphisms of TNFSF11 were associated with AM: rs2200287 (P = 0.005), rs9525641 (P = 0.039), and rs1054016 (P = 0.047). Two SNPs of this gene, rs346578 and rs9525641, showed an association with ANM (P = 0.007 and P = 0.011, respectively). Two SNPs of TNFRSF11A were associated with AM (rs3826620; P = 0.022) and ANM (rs8086340; P = 0.015). Multiple SNP-SNP and SNP-environment interaction effects on AM and ANM were detected for both genes. One polymorphism of TNFRSF11A, rs4436867, was not directly associated with either trait but indicated significant interactions with four TNFSF11 polymorphisms on ANM. Two other TNFRSF11A polymorphisms, rs4941125 and rs7235803, showed interaction effects with several TNFSF11 polymorphisms on AM. Both genes manifested significant interaction with the duration of breast-feeding in their effect on ANM.

CONCLUSIONS

The TNFRSF11A and TNFSF11 genes are associated with the onset of AM and ANM in white women.

Validation of multi-detector computed tomography as a non-invasive method for measuring ovarian volume in macaques (Macaca fascicularis)

The purpose of this study was to validate low radiation dose, contrast-enhanced, multi-detector computed tomography (MDCT) as a non-invasive method for measuring ovarian volume in macaques. Computed tomography scans of four known-volume phantoms and nine mature female cynomolgus macaques were acquired using a previously described, low radiation dose scanning protocol, intravenous contrast enhancement, and a 32-slice MDCT scanner. Immediately following MDCT, ovaries were surgically removed and the ovarian weights were measured. The ovarian volumes were determined using water displacement. A veterinary radiologist who was unaware of actual volumes measured ovarian CT volumes three times, using a laptop computer, pen display tablet, hand-traced regions of interest, and free image analysis software. A statistician selected and performed all tests comparing the actual and CT data. Ovaries were successfully located in all MDCT scans. The iliac arteries and veins, uterus, fallopian tubes, cervix, ureters, urinary bladder, rectum, and colon were also consistently visualized. Large antral follicles were detected in six ovaries. Phantom mean CT volume was 0.702+/-SD 0.504 cc and the mean actual volume was 0.743+/-SD 0.526 cc. Ovary mean CT volume was 0.258+/-SD 0.159 cc and mean water displacement volume was 0.257+/-SD 0.145 cc. For phantoms, the mean coefficient of variation for CT volumes was 2.5%. For ovaries, the least squares mean coefficient of variation for CT volumes was 5.4%. The ovarian CT volume was significantly associated with actual ovarian volume (ICC coefficient 0.79, regression coefficient 0.5, P=0.0006) and the actual ovarian weight (ICC coefficient 0.62, regression coefficient 0.6, P=0.015). There was no association between the CT volume accuracy and mean ovarian CT density (degree of intravenous contrast enhancement), and there was no proportional or fixed bias in the CT volume measurements. Findings from this study indicate that MDCT is a valid non-invasive technique for measuring the ovarian volume in macaques.

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.

Serum antimüllerian hormone predicts ovarian reserve in a monkey model

OBJECTIVE

A monkey model of the menopausal transition (perimenopause) would facilitate efforts to understand better the effect of hormonal fluctuations during this life phase on the initiation of chronic diseases associated with the postmenopausal years. Antimüllerian hormone (AMH) is a promising marker of ovarian reserve (primordial follicle number) in women. Here, we describe the relationship between AMH and ovarian reserve in cynomolgus monkeys (Macaca fascicularis) estimated to be 12 to 15 years of age (approximately 36-45 y in women).

METHODS AND RESULTS

The results of daily vaginal swabbing (to detect menses) and thrice weekly blood sampling for 12 weeks indicate that AMH is relatively stable across the menstrual cycle (intraclass correlation, approximately 0.80), with a slight although significant (P < 0.02) reduction (approximately 1.4-fold) on days 2 to 5 postovulation. Substantial interindividual variation in AMH concentrations were observed between monkeys, with values ranging from 4.46 +/- 0.17 to 18.80 +/- 0.71 ng/mL (mean +/- SE). Antimüllerian hormone concentrations were reduced by approximately 63% after the removal of one ovary (7.6 +/- 0.77 vs 2.75 +/- 0.37 ng/mL; P < 0.001; n = 19) and were below the level of detection after the removal of both ovaries (5.8 +/- 0.42 to <0.05 ng/mL; P < 0.001; n = 84), suggesting that the ovary is likely to be either the major or the sole source of AMH in the monkey. Finally, we examined the association between AMH and primordial, primary, and secondary follicles in 29 monkeys and found significant associations with all follicle types (r = 0.78, r = 0.66, and r = 0.80, respectively; P < 0.01).

CONCLUSIONS

The relationship between AMH and ovarian reserve in the monkey is similar to that in women, suggesting that monkeys may be a useful model for studying hormonal fluctuations across the menopausal transition.

No clear association between female hormonal aspects and osteoarthritis of the hand, hip and knee: a systematic review

OBJECTIVE

Incidence of OA rises steeply in women of age >50 years; the climacteric period for women. The simultaneous occurrence of these events suggests an association between OA and changes in female hormonal aspects. This systematic review studies the assumed association between OA and aspects concerning the fertile period (duration, endogenous hormones, age at menarche/menopause) and the menopause [menopausal status, years since menopause (YSM) and surgical menopause].

METHODS

Medline and EMBASE were searched for articles assessing associations between hand/hip/knee OA and female hormonal aspects. Methodological quality was assessed systematically, and results were summarized in a best-evidence synthesis.

RESULTS

Sixteen studies were included in the present study. For most hormonal aspects no association was found. Conflicting evidence was found for an association of age at menarche with Herberden's nodes (HNs) and hand ROA, YSM with knee ROA and ovariectomy with hip OA. An increased risk was seen for low estradiol serum levels in the early follicular phase with incident knee ROA, age at menarche being < or =11 years old with total hip replacement, being post-menopausal and YSM with the presence of HN. A protective effect was seen for age at menopause being > or =52 years with total knee replacement. Evidence level was limited for all.

CONCLUSIONS

The assumed relationship between the female hormonal aspects and OA was not clearly observed in this review. The relationship is perhaps too complex, or other aspects, yet to be determined, play a role in the increased incidence in women aged >50 years.

Effect of 17beta-oestradiol replacement on vascular responsiveness in ovariectomized diabetic rats

1. Women with functional ovaries exhibit a gender advantage in terms of the prevalence of cardiovascular diseases. However, whether this gender bias pertains in diabetes is unknown. 2. The aim of the present study was to examine the effects of 17beta-oestradiol (E2) on vascular responsiveness in normal and diabetic ovariectomized (OVX) rats. Aged-matched female rats were divided into four groups as follows: (i) OVX; (ii) OVX + E2 treated; (iii) diabetic OVX; and (iv) diabetic OVX + E2 treated. Bilateral ovariectomy was performed and streptozotocin was used to induce experimental diabetes. Rats were treated with 1 mg/kg per day, p.o., E2 for 8 weeks. 3. Although E2 treatment had no effect on blood glucose levels in normal and diabetic OVX rats, it significantly reduced systolic blood pressure and prevented diabetes-induced loss of bodyweight gain. 4. In segments of the thoracic aorta, concentration-dependent vasoconstrictor responses to KCl and phenylephrine were significantly attenuated following E2 treatment in both the normal and diabetic groups. The sarcoplasmic/endoplasmic reticulum calcium ATPase inhibitor thapsigargin (10(-6) mol/L) and the Ca(2+) channel blocker nifedipine (10(-6) mol/L) inhibited the transient vasoconstriction to PE in all groups. The constrictor effect of PE was increased by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-6) mol/L), but was reduced by superoxide dismutase (SOD; 100 U/mL) and the cyclo-oxygenase inhibitor indomethacin (10(-6) mol/L) in all groups. Responses to acetylcholine (ACh; 10(-6) mol/L) demonstrated reduced endothelium-dependent relaxation in non-E2-treated groups. Relaxation responses to ACh were increased by 100 U/mL SOD and 10(-6) mol/L indomethacin, but were reduced by 10(-6) mol/L l-NAME in all groups. There were no differences among the four groups in terms of relaxation responses to sodium nitroprusside (10(-11) to 10(-6) mol/L). 5. In conclusion, the results of the present study suggest that oestrogen treatment has beneficial effects on vascular function in both diabetic and non-diabetic OVX rats due to Ca(2+) regulation and anti-oxidation.

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.

Menopause in nonhuman primates?

A gradual alteration in the mechanisms underlying reproduction and fertility characterizes the aging process in human females. These changes culminate in menopause, conventionally defined as a cessation of menstrual cycles that marks the end of reproductive capacity. In fact, a central and defining event in menopause is the discontinuation of ovulation, which is correlated with a number of structural and functional changes in the reproductive axis. Despite several decades of research, a degree of uncertainty remains as to whether nonhuman primates undergo menopause, and whether they are suitable models of human reproductive senescence. We review some of the controversies that have clouded our understanding of reproductive aging in nonhuman primates, including issues of definition, timing, comparability of data from wild versus captive populations, and cross-species comparisons. The existing data support the view that menopause occurs in a number of primate species and is not unique to humans.

Menstrual cycles continue into advanced old age in the common chimpanzee (Pan troglodytes)

A long postreproductive lifespan may distinguish women from all other female primates. A long-held consensus among reproductive scientists has been that our closest living relative, the chimpanzee (Pan troglodytes), experiences menstrual cycles until death. However, a recent study of biannual assessments of gonadotropins, but lacking observations of menstruation, concluded that menopause occurs in chimpanzees between 35 and 40 yr of age. A separate report, but on wild chimpanzees, documented fertility through the 40-44 age range in all populations studied. These contradictory reports pose questions about differences between wild and captive populations and about assessments of menopause. The present study revisits this controversy by analyzing longitudinal records of anogenital swelling and menstruation in 89 female chimpanzees aged 6 to 59 yr (n = 2386 records on cycle length), monitored for most of their adult lives at the Yerkes National Primate Research Center. Twenty of these chimpanzees were observed past 39 yr of age; all 20 displayed menstrual cycles beyond this age, as confirmed by at least two observations of menses about 35 days apart. Three of these were older than 50 yr and still displayed menstrual cycles. Only the oldest female appeared menopausal, with cycles of anogenital swelling ceasing 2 yr prior to her death at age 59. Random-effects statistical modeling reveals a slight decrease in cycle length until 20 yr of age and a slight lengthening thereafter. Mean cycle length across the lifespan is 35.4 days. Our findings, based upon actual observations of menstrual cycles, suggest that menopause in the chimpanzee is rare, occurring near the end of the lifespan.

Mammary gland development in early pubertal female macaques

Ductal morphogenesis of the mammary gland occurs largely in the early pubertal period under the influence of ovarian sex hormones. In this study we characterized developing ductal structures in breast tissue of 14 female prepubertal or early pubertal rhesus monkeys (average age, 2.6 +/- 0.1 years). Serum estradiol concentrations ranged from < 5.0 to 61.2 pg/ml, while progesterone concentrations were low in all animals (< 0.6 ng/ml). No corpora lutea were seen on ovarian histology. The most immature mammary glands contained multilayered ducts frequently ending in distinctive terminal end bud structures. Transitional ducts had variably stratified columnar epithelium, often with prominent rounded myoepithelial cells and loose periductal stroma. Mature ducts had simple cuboidal luminal epithelium, flattened myoepithelium, and associated lobular development, typical of the premenopausal breast. Expression of estrogen receptor alpha was significantly higher in immature ducts compared to mature ducts, while progesterone receptor expression, epithelial proliferation, and cytokeratin expression did not show a relationship to the maturity of the ducts. These findings identify dynamic morphologic changes occurring in the primate breast during early puberty and suggest that estradiol (rather than progesterone) is the predominant hormonal stimulus for early ductal and lobular development.

Are the available experimental models of type 2 diabetes appropriate for a gender perspective?

Several experimental models have so far been developed to improve our knowledge of the pathogenetic mechanisms of type 2 diabetes mellitus (T2D), to determine the possible pharmacological targets of this disease and to better evaluate diabetes-associated complications, e.g. the cardiovascular disease. In particular, the study of T2D gained the attention of several groups working with different animal species: rodents, cats or pigs, as well as other non-human primate species. Each of these species provided useful and different clues. However, T2D has to be considered as a gender-associated disease: sex differences play in fact a key role in the onset as well as in the progression of the disease and a higher mortality for cardiovascular diseases is detected in diabetic women with respect to men. The results obtained from all the available animal models appear to only partially address this issue so that the search for more precise information in this respect appears to be mandatory. In this review we summarize these concepts and literature in the field and propose a reappraisal of the various animal models for a study of T2D that would take into consideration a gender perspective.

Hormone therapy effects on social behavior and activity levels of surgically postmenopausal cynomolgus monkeys

The purpose of the experiments reported here was to investigate central nervous system effects of commonly prescribed postmenopausal hormone therapies in a primate model, the cynomolgus monkey (Macaca fascicularis). The results of two experiments are reported. In the first, ovariectomized adult cynomolgus monkeys were treated for eight weeks each with oral micronized 17beta-estradiol (E2) (n=23), E2+medroxyprogesterone acetate (MPA) (n=23), E2+progesterone (P4) (n=23), and placebo (n=23) using a crossover design. In the second, ovariectomized adult cynomolgus monkeys were treated for eight weeks with oral micronized E2+oral micronized P4 (n=10), or E2+intravaginal micronized P4 delivered via a Silastic ring (n=8), or oral placebo and intravaginal placebo (n=5), using a parallel arm design. Behavior was recorded during weeks two through four. Cerebrospinal fluid (CSF) and blood were sampled, and 24h heart rate recorded by telemetry during weeks five through seven. Monoaminergic metabolites were assayed in CSF, and cortisol was assayed in serum. There were no significant effects of treatment on CSF monoaminergic metabolites or heart rate. E2+MPA increased cortisol concentrations. While there were some differences in effects between experiments, both progestogens and both routes of administration increased time spent resting, particularly resting in body contact, resulting in increased passive affiliative interaction. Thus, synthetic progestogens appear to be as sedating as progesterone, and the ring delivery system does not appear to protect the central nervous system from effects of progestogens. Further research is needed to explore social context as an important feature of behavioral response to steroid hormone regimens and to verify and extend knowledge of systemic effects of vaginal ring-delivered progestogens.

Mechanism of gender-specific differences in aortic stiffness with aging in nonhuman primates

BACKGROUND

Our hypothesis was that the changes in vascular properties responsible for aortic stiffness with aging would be greater in old male monkeys than old female monkeys.

METHODS AND RESULTS

We analyzed the effects of gender differences in aging on in vivo measurements of aortic pressure and diameter and on extracellular matrix of the thoracic aorta in young adult (age, 6.6+/-0.5 years) versus old adult (age, 21.2+/-0.2 years) monkeys (Macaca fascicularis). Aortic stiffness, as represented by the pressure strain elastic modulus (Ep), increased more in old male monkeys (5.08+/-0.81; P<0.01) than in old females (3.06+/-0.52). In both genders, collagen density was maintained, collagen-bound glycation end products increased, and collagen type 1 decreased. However, elastin density decreased significantly (from 22+/-1.5% to 15+/-1.2%) with aging (P<0.05) only in males. Furthermore, only old males were characterized by a decrease (P<0.05) in collagen type 3 (an isoform that promotes elasticity) and an increase in collagen type 8 (an isoform that promotes the neointimal migration of vascular smooth muscle cells). In contrast to the data in monkeys, collagen types 1 and 3 both increased significantly in aging rats.

CONCLUSIONS

There are major species differences in the effects of aging on aortic collagen types 1 and 3. Furthermore, because alterations in collagen density, collagen content, hydroxyproline, and collagen advanced glycation end products were similar in both old male and female monkeys, these factors cannot be responsible for the greater increase in stiffness in old males. However, changes in collagen isoforms and the decrease in elastin observed only in old males likely account for the greater increase in aortic stiffness.

Increased apoptosis and myocyte enlargement with decreased cardiac mass; distinctive features of the aging male, but not female, monkey heart

We studied gender-specific changes in aging cardiomyopathy in a primate model, Macaca fascicularis, free of the major human diseases, complicating the interpretation of data specific to aging in humans. Left ventricular (LV) weight/body weight decreased, p<0.05, in old males but did not change in old females. However, despite the decrease in LV weight, mean myocyte cross-sectional area in the old males increased by 51%. This increase in myocyte size was not uniform in old males, i.e., it was manifest in only 20-30% of all the myocytes from old males. In old males there was a 4-fold increase in frequency of myocyte apoptosis without any increase in proliferation-capable myocytes assessed by Ki-67 expression. Apoptosis was unchanged in old female monkey hearts, whereas the frequency of myocytes expressing Ki-67 declined 90%. These results, opposite to findings from rodent studies, indicate distinct differences in which male and female monkeys maintain functional heart mass during aging. The old male hearts demonstrated increased apoptosis, which more than offset the myocyte hypertrophy. Interestingly, the hypertrophy was not uniform and there was no significant increase in myocyte proliferation.

Destruction of primordial ovarian follicles in adult cynomolgus macaques after exposure to 4-vinylcyclohexene diepoxide: a nonhuman primate model of the menopausal transition

OBJECTIVE

To determine whether the 4-vinylcyclohexene diepoxide (VCD)-treated mouse menopause model, which involves accelerated atresia of primordial follicles and induces gradual ovarian failure (while sparing the ovarian stroma), can be adapted to nonhuman primates.

DESIGN

Controlled periclinical trial (nonhuman primates).

SETTING

Comparative Medicine Clinical Research Center.

ANIMAL(S)

Four adult female cynomolgus monkeys.

INTERVENTION(S)

Once-daily i.m. injections for 15 days as follows: vehicle or VCD doses of 80 mg/kg, 160 mg/kg, 250 mg/kg. Ovaries were removed 27 days after treatment, and pathological determinations were made at necropsy.

MAIN OUTCOME MEASURE(S)

Baseline and interim hematologic and biochemical measures, physical exams, and body weights. Follicle counts and organ evaluation at necropsy.

RESULT(S)

A nearly complete elimination of primordial, intermediate, primary and secondary follicles was achieved with 250 mg/kg VCD. A 50% reduction in primordial and primary follicles was observed with 160 mg/kg VCD. No effect of 80 mg/kg VCD per day was observed. Clinical health measures remained within normal range except for transient, mild increases in liver enzymes and an inflammatory response at the injection site with 250 mg/kg. Postmortem evaluations (9 months) revealed no gross or histological lesions in the organs studied.

CONCLUSION(S)

These results demonstrate that the monkey ovary is susceptible to VCD and that as in rodents, primordial and primary follicles are targeted selectively.

Old World Nonhuman Primate Models of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a major health problem of increasing incidence. To better study the pathogenesis and potential therapeutic agents for this disease, appropriate animal models are needed. Old World nonhuman primates (NHPs) are a useful animal model of type 2 diabetes; like humans, the disease is most common in older, obese animals. Before developing overt diabetes, NHPs have a period of obesity-associated insulin resistance that is initially met with compensatory insulin secretion. When either a relative or absolute deficiency in pancreatic insulin production occurs, fasting glucose concentrations begin to increase and diabetic signs become apparent. Pathological changes in pancreatic islets are also similar to those seen in human diabetics. Initially there is hyperplasia of the islets with abundant insulin production typically followed by replacement of islets with islet-associated amyloid. Diabetic NHPs have detrimental changes in plasma lipid and lipoprotein concentrations, lipoprotein composition, and glycation, which may contribute to progression of atherosclerosis. As both the prediabetic condition (similar to metabolic syndrome in humans) and overt diabetes become better defined in monkeys, their use in pharmacological studies is increasing. Likely due to their genetic similarity to humans and the similar characteristics of the disease in NHPs, NHPs have been used to study recently developed agonists of the peroxisome proliferators-activated receptors. Importantly, agonists of the different receptor subclasses elicit similar responses in both humans and NHPs. Thus, Old World NHPs are a valuable animal model of type 2 diabetes to study disease progression, associated risk factors, and potential new treatments.