Estradiol Replacement Timing and Obesogenic Diet Effects on Body Composition and Metabolism in Postmenopausal Macaques

Metabolic effects of late-onset estradiol replacement in high-fat-fed ovariectomized mice

Background

Decreased estrogen levels in postmenopausal women negatively impact metabolic health. It is known that estradiol (E2) replacement can reverse this condition. However, there is no consensus on whether the effects mediated by E2 depend on the starting time of E2 replacement after menopause. We aimed to investigate the effects of different onset E2 treatments on glucose tolerance and metabolic parameters in high-fat-fed ovariectomized mice.

Material and methods

Eight-week-old female C57BL/6J mice were divided into three groups: SHAM, OVX, and E2, to evaluate three different time points of E2 replacement after ovariectomy: early (after 4 weeks), intermediate (after 12 weeks), and late replacement (after 20 weeks). E2 groups received treatment through subcutaneous pellets.

Results

E2 replacement improved the parameters analyzed independently of the time since ovariectomy, reducing body weight gain and fat mass, as well as increasing the percentage of lean mass. Glucose intolerance, fasting insulin, HOMA-IR, and cholesterol levels were also reduced after treatment with E2. In the liver, there was a decrease in triacylglycerol (TAG) deposition, with no difference in the expression of SREBP1 and ERα proteins. In the muscle, there was a decrease in TAG deposition. In periuterine adipose tissue, there was an increase in the expression of SREBP1, FASN, and SCD, with no difference in the expression of ERα.

Conclusions

Our findings reinforce the critical role of E2 in regulating both glucose and lipid metabolism and indicate that E2 action on metabolic health was not dependent on time since ovariectomy for the parameters analyzed.

The aged female rhesus macaque as a translational model for human menopause and hormone therapy

Progress in understanding the causes of physiological and behavioral changes in post-menopausal women is hampered by the paucity of animal models that accurately recapitulate these age-associated changes. Here we evaluate the translational potential of female rhesus macaques (Macaca mulatta). Like women, these long-lived diurnal primates show marked neuroendocrine changes during aging, as well as perturbed sleep-wake cycles and cognitive decline. Furthermore, the brains of old rhesus macaques show some of the same pathological hallmarks of Alzheimer's disease as do humans, including amyloidosis and tauopathology. Importantly, unlike humans, rhesus macaques can be maintained under tightly controlled environmental conditions, such as photoperiod, temperature and diet, and tissues can be collected with zero postmortem interval; this makes them especially suitable for studies aimed at elucidating underlying molecular mechanisms. Recent findings from female macaques are helping to elucidate how sex-steroids influence gene expression within the brain and contribute to the maintenance of cognitive function and amelioration of age-associated pathologies. Taken together, these findings emphasize the translational value of female rhesus macaques as a model for elucidating causal mechanisms that underlie normative and pathological changes in post-menopausal women. They also provide a pragmatic platform upon which to develop safe and effective therapies.

Effect of ovariectomy and high-fat diet on the expression of estrogen receptors and adipose tissue metabolism in wistar rats

This study addresses the increasing prevalence of obesity, especially among postmenopausal. Estrogen plays a crucial role in regulating adipose tissue in women, with its absence after menopause associated with metabolic complications. The study aimed to determine the lipolytic activity in different adipose tissue depots of ovariectomized rats submitted to a high-fat diet. Also, to analyze the expression of estrogen receptors in adipose tissues and perform histological and morphometric analyzes of these deposits. Female rats were ovariectomized (O) or sham operated (S). The animals were divided into groups: ovariectomized with high-fat diet (OF), sham-operated with high-fat diet (SF), ovariectomized with control diet (OC) or sham-operated with control diet as the control group (SC). After 24 weeks of consuming the diets, rats were killed and adipose tissue deposits were removed. Polymerase chain reaction was performed to analyze the expression of estrogen receptors in adipose tissues, lipolysis assay and histological analysis. Both the high-fat diet and ovariectomy increased body weight and adiposity. There was hypertrophy of adipocytes. Estrogen replacement therapy modulate lipolytic activity in different adipose depots, with different responses in relation to estrogen receptors. Estrogen receptor expression varied between fat depots. Mesenteric adipose tissue showed greater sensitivity to estrogen compared with others. Estrogen increased lipolytic activity in some fat depots, reducing in others. Expression of ERs depends of hormonal status and adipose tissue location, which may explain distinct actions of estrogen on the metabolism of adipose tissue and on the production of adipokines by them.

Effect of hormone replacement therapy on amyloid beta (Aβ) plaque density in the rhesus macaque amygdala

Background

Amyloid beta (Aβ) plaque density was examined in the amygdala of rhesus macaques, to elucidate the influence of age, diet and hormonal environment.

Methods

Luminex technology was used to measure cerebrospinal fluid (CSF) concentrations of Aβ40 and Aβ42 across three decades, while immunohistochemistry was used to examine Aβ plaque density in the amygdala.

Results

Aβ40 was found to be the predominant isoform of Aβ in the CSF, but neither Aβ40 or Aβ42 concentrations showed an age-related change, and the ratio of Aβ42 to Aβ40 showed only a marginal increase. Significantly fewer Aβ plaques were detected in the amygdala of old ovariectomized animals if they received estradiol HRT (p < 0.001); similar results were obtained regardless of whether they had been maintained on a regular monkey chow for ∼48 months or on a high-fat, high-sugar, Western-style diet for ∼30 months.

Conclusion

The results demonstrate that HRT involving estrogen can reduce Aβ plaque load in a cognitive brain region of aged non-human primates. The results from this translational animal model may therefore have clinical relevance to the treatment of AD in post-menopausal women, whether used alone, or as a supplement to current pharmacological and monoclonal antibody-based interventions.

Pathological Markers of Alzheimer's Disease and Related Dementia in the Rhesus Macaque Amygdala

Rhesus macaques develop amyloid-β (Aβ) plaques during old age, but it is unclear how extensively they express other pathological hallmarks of dementia. Here we used immunohistochemistry to examine expression of phosphorylated tau (pTau) protein and cytoplasmic inclusions of TAR DNA binding protein 43 kDa (TDP-43) within the amygdala of young and old males, and also in old surgically-menopausal females that were maintained on regular or obesogenic diets. Only one animal, a 23-year-old female, showed pTau expression and none showed TDP-43 inclusions. What genetic and/or environmental factors protect macaques from expressing more severe human neuro-pathologies remains an interesting unresolved question.

Effect of estradiol replacement on hippocampal concentrations of estrogens in aged rhesus macaques maintained on an obesogenic diet

Replacement involving estrogens has proven efficacy at treating a wide range of disorders that develop with menopause or after surgical removal of the ovaries. Here, we tested whether an estradiol (E2) replacement paradigm that recapitulates physiological E2 levels in the circulation also recapitulates physiological E2 levels within the hippocampus. E2 was delivered continuously to old ovariectomized (OVX) rhesus macaques, maintained on a high-fat, high-sugar Western-style diet (WSD) for ∼30 months, via subcutaneous implants; this resulted in physiological concentrations of both estrone (E1) and E2 in the circulation (determined by LC-MS/MS). Surprisingly, however, hippocampal concentrations of E2 were markedly (P < 0.01) higher than in ovary-intact animals maintained on a regular chow diet. The data suggest that E2 replacement paradigms that appear to recapitulate physiological E2 concentrations in the circulation may produce hyper-physiological E2 levels within some brain areas, especially when individuals are maintained on a WSD.

The Regulation of Adipose Tissue Health by Estrogens

Obesity and its' associated metabolic diseases such as type 2 diabetes and cardiometabolic disorders are significant health problems confronting many countries. A major driver for developing obesity and metabolic dysfunction is the uncontrolled expansion of white adipose tissue (WAT). Specifically, the pathophysiological expansion of visceral WAT is often associated with metabolic dysfunction due to changes in adipokine secretion profiles, reduced vascularization, increased fibrosis, and enrichment of pro-inflammatory immune cells. A critical determinate of body fat distribution and WAT health is the sex steroid estrogen. The bioavailability of estrogen appears to favor metabolically healthy subcutaneous fat over visceral fat growth while protecting against changes in metabolic dysfunction. Our review will focus on the role of estrogen on body fat partitioning, WAT homeostasis, adipogenesis, adipocyte progenitor cell (APC) function, and thermogenesis to control WAT health and systemic metabolism.

Effects of estradiol supplementation on the brain transcriptome of old rhesus macaques maintained on an obesogenic diet

Obesity, the cessation of ovarian steroids with menopause, and age are risk factors for mood disorders, dementia, and Alzheimer's disease (AD). However, immediate hormone therapy (HT) after menopause may have beneficial effects in different brain regions involved in memory and cognition. To more closely replicate the age, endocrine, and metabolic environment of obese postmenopausal women, either on or off HT, middle-aged female rhesus macaques were ovariectomized/hysterectomized (OvH) and maintained on a high-fat, high-sugar, obesogenic Western-style diet (WSD) for 30 months; half of the animals received HT immediately after OvH and half served as placebo controls. RNAseq of the occipital (OC) and prefrontal cortex (PFC), hippocampus (HIP), and amygdala (AMG) identified 293, 379, 505, and 4993 differentially expressed genes (DEGs), respectively. Pathway enrichment analysis identified an activation of neuroinflammation in OC and HIP, but an inhibition in the AMG with HT. Synaptogenesis, circadian rhythm, mitochondrial dysfunction, mTOR, glutamate, serotonin, GABA, dopamine, epinephrine/norepinephrine, glucocorticoid receptor signaling, neuronal NOS, and amyloid processing were exclusively enriched in AMG. As compared to the placebo control group, most of these signaling pathways are downregulated after HT, suggesting a protective effect of HT in OvH females under a WSD. Overall, our results suggest that a chronic obesogenic diet may induce a wide range of alterations in multiple signaling pathways that are linked to age-associated brain pathology and dementia. In these individuals, HT seems to have a protective effect against neuroinflammation, amyloid beta depositions, and tau tangle formation.

Serum ischemia-modified albumin level returns to its premenopausal level with 1-year hormone therapy in healthy menopausal women

Introduction

To assess the effect of hormone therapy (HT) on serum ischemia modified albumin (IMA) levels in healthy menopausal women.

Material and methods

Thirty surgical menopausal women who were admitted to our menopausal polyclinic during a 1-year period and diagnosed with menopause and planned to have HT for menopausal symptoms were enrolled in this prospective study. The serum İMA levels were recorded before and after (3 months, 6 months, 12 months later) hormone treatment (2 mg estradiol hemihydrate).

Results

The mean age of women was 47.60 ± 2.34 years. The mean serum IMA levels were 0.610 ± 0.096 absorbance units (ABSU) at the beginning and 0.484 ± 0.080 ABSU after 3 months of hormone therapy. Following 6 months of hormone therapy, serum IMA level was 0.546 ± 0.075, and reached 0.580 ± 0.089 ABSU following 12 months of therapy.

Conclusions

These findings suggest that HT may not block the menopause induced ischemia process. Although HT had a positive effect on serum IMA levels following 3 months’ use, serum IMA levels returned to baseline levels after 12 months’ use. Based on this study’s findings, long-term use of HT may not have a positive effect on cardiovascular disease protection.

Longitudinal Effects of Immediate and Delayed Estradiol on Cognitive Performance in a Spatial Maze and Hippocampal Volume in Menopausal Macaques Under an Obesogenic Diet

The consumption of a diet high in fat and refined sugars has several health risks, including the development of cognitive decline and neurodegeneration. For women, menopause carries additional health risks that may interact with a high-fat diet in negative ways. Some symptoms of menopause, including cognitive impairments, can be modulated by hormone replacement therapy (HRT), but the hormonal formulation and the timing of the treatment relative to the onset of menopause are critical factors determining its efficacy. Little is known about how obesogenic, high-fat, high-sugar diets interact with HRT in menopause to affect cognition and neurodegeneration. Given the high prevalence of the consumption of an obesogenic Western-style diet, understanding how the effects of HRT are modulated by an obesogenic diet is critical for developing optimized therapeutic strategies for peri- and post-menopausal women. In this study, we investigated by magnetic resonance imaging (MRI) the effects of either immediate or delayed estradiol hormone therapy on cognition and neuroanatomy following ovo-hysterectomy (OvH) of aged, female rhesus macaques on an obesogenic diet. The macaques were followed for 2.5 years after ovo-hysterectomy, with four time points at which anatomical MRIs were acquired. Analysis of hippocampal volumes revealed an interaction between time point and treatment; hippocampal volumes in the delayed estrogen group, but not the immediate estrogen group, increased over time compared to those in untreated controls. Performance on a hippocampal-dependent spatial maze task showed improved performance in estrogen treated animals compared to OvH macaques given placebo. These results indicate that HRT may contribute to beneficial cognitive outcomes after menopause under an obesogenic diet.

Mini-review: Aging of the neuroendocrine system: Insights from nonhuman primate models

The neuroendocrine system (NES) plays a crucial role in synchronizing the physiology and behavior of the whole organism in response to environmental constraints. The NES consists of a hypothalamic-pituitary-target organ axis that acts in coordination to regulate growth, reproduction, stress and basal metabolism. The growth (or somatotropic), hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-thyroid (HPT) axes are therefore finely tuned by the hypothalamus through the successive release of hypothalamic and pituitary hormones to control the downstream physiological functions. These functions rely on a complex set of mechanisms requiring tight synchronization between peripheral organs and the hypothalamic-pituitary complex, whose functionality can be altered during aging. Here, we review the results of research on the effects of aging on the NES of nonhuman primate (NHP) species in wild and captive conditions. A focus on the age-related dysregulation of the master circadian pacemaker, which, in turn, alters the synchronization of the NES with the organism environment, is proposed. Finally, practical and ethical considerations of using NHP models to test the effects of nutrition-based or hormonal treatments to combat the deterioration of the NES are discussed.

Aging Reduces Estradiol Protection Against Neural but Not Metabolic Effects of Obesity in Female 3xTg-AD Mice

Vulnerability to Alzheimer's disease (AD) is increased by several risk factors, including midlife obesity, female sex, and the depletion of estrogens in women as a consequence of menopause. Conversely, estrogen-based hormone therapies have been linked with protection from age-related increases in adiposity and dementia risk, although treatment efficacy appears to be affected by the age of initiation. Potential interactions between obesity, AD, aging, and estrogen treatment are likely to have significant impact on optimizing the use of hormone therapies in postmenopausal women. In the current study, we compared how treatment with the primary estrogen, 17β-estradiol (E2), affects levels of AD-like neuropathology, behavioral impairment, and other neural and systemic effects of preexisting diet-induced obesity in female 3xTg-AD mice. Importantly, experiments were conducted at chronological ages associated with both the early and late stages of reproductive senescence. We observed that E2 treatment was generally associated with significantly improved metabolic outcomes, including reductions in body weight, adiposity, and leptin, across both age groups. Conversely, neural benefits of E2 in obese mice, including decreased β-amyloid burden, improved behavioral performance, and reduced microglial activation, were observed only in the early aging group. These results are consistent with the perspective that neural benefits of estrogen-based therapies require initiation of treatment during early rather than later phases of reproductive aging. Further, the discordance between E2 protection against systemic versus neural effects of obesity across age groups suggests that pathways other than general metabolic function, perhaps including reduced microglial activation, contribute to the mechanism(s) of the observed E2 actions. These findings reinforce the potential systemic and neural benefits of estrogen therapies against obesity, while also highlighting the critical role of aging as a mediator of estrogens' protective actions.

Estradiol treatment improves biological rhythms in a preclinical rat model of menopause

The perimenopausal transition at middle age is often associated with hot flashes and sleep disruptions, metabolic changes, and other symptoms. Whereas the mechanisms for these processes are incompletely understood, both aging (AG) and a loss of ovarian estrogens play contributing roles. Furthermore, the timing of when estradiol (E) treatment should commence and for how long are key clinical questions in the management of symptoms. Using a rat model of surgical menopause, we determined the effects of regimens of E treatment with differing time at onset and duration of treatment on diurnal rhythms of activity and core temperature and on food intake and body weight. Reproductively mature (MAT, ∼4 months) or AG (∼11 months) female rats were ovariectomized, implanted intraperitoneally with a telemetry device, and given either a vehicle (V) or E subcutaneous capsule implantation. Rats were remotely recorded for 10 days per month for 3 (MAT) or 6 (AG) months. To ascertain whether delayed onset of treatment affected rhythms, a subset of AG-V rats had their capsules switched to E at the end of 3 months. Another set of AG-E rats had their capsules removed at 3 months to determine whether beneficial effects of E would persist. Overall, activity and temperature mesor, robustness, and amplitude declined with AG. Compared to V treatment, E-treated rats showed (1) better maintenance of body weight and food intake; (2) higher, more consolidated activity and temperature rhythms; and (3) higher activity and temperature robustness and amplitude. In the AG arm of the study, switching treatment from V to E or E to V quickly reversed these patterns. Thus, the presence of E was the dominant factor in determining stability and amplitude of locomotor activity and temperature rhythms. As a whole, the results show benefits of E treatment, even with a delay, on biological rhythms and physiological functions.

Estradiol Replacement Timing and Obesogenic Diet Effects on Body Composition and Metabolism in Postmenopausal Macaques

Whether hormone replacement therapy has beneficial metabolic effects in postmenopausal women remains controversial because of between-study differences in menopausal duration, estrogen formulations, and diet. Additionally, animal studies have not reflected the typical human obesogenic, Western-style diet (WSD). In this study, we determined the effects of immediate 17β-estradiol (ImE) or delayed 17β-estradiol treatment on weight and metabolism parameters in old ovo-hysterectomized rhesus macaques consuming a WSD over a 30-month period. The placebo and ImE groups exhibited progressive gains in weight and fat mass, which ImE initially attenuated but did not prevent. Progression of insulin resistance (IR) was lessened by ImE compared with placebo under both fasting and IV glucose-stimulated conditions, plateauing in all groups between 24 and 30 months. Consequently, relative euglycemia was maintained through lower stimulated insulin levels with ImE than with placebo. Bone mineral density decreased in the placebo group but was maintained in the ImE group, whereas bone mineral content was unaffected by placebo and increased with ImE. Daily activity was reduced while macaques consumed a WSD and was not affected by ImE. Over time, total cholesterol, triglyceride, very-low-density cholesterol, high-density lipoprotein cholesterol (HDL-C), non-HDL-C, and IL-8 levels increased or trended upward in all animals, with only the change in HDL-C affected by ImE. Delayed estrogen treatment (months 24 to 30) had no significant impact on body composition or glucometabolic parameters. In summary, detrimental WSD-induced changes in body composition and metabolism were only temporarily ameliorated by ImE, with the important exception of glucose homeostasis, which benefited from E replacement even as body composition worsened.