Estradiol fatty acid esters in adipose tissue and serum of pregnant and pre- and postmenopausal women

Role of Estrogen and Its Receptors in Adipose Tissue Glucose Metabolism in Pre- and Postmenopausal Women

CONTEXT

Reduced estrogen levels in postmenopausal women predispose them to metabolic side effects, including insulin resistance and type 2 diabetes; however, the cellular mechanisms are not well understood.

OBJECTIVE

This work aimed to study the expression of estrogen receptors in adipose tissue from pre- and postmenopausal women and the effects of estradiol (E2) on glucose uptake of adipocytes.

METHODS

Subcutaneous (SAT) and visceral adipose tissue (VAT) obtained from pre- and postmenopausal women (19-51 and 46-75 years old, respectively) were used to measure gene expression of ESR1 and ESR2. SAT tissue was incubated with E2, and glucose uptake and estrogen receptor levels were measured. Polymorphisms in ESR1 and ESR2 were addressed in public databases to identify single nucleotide polymorphisms associated with metabolic traits.

RESULTS

ESR2 expression was lower in pre- vs postmenopausal women, corresponding to lower ESR1:ESR2 gene expression ratio in postmenopausal women. In premenopausal women, the expression of ESR1 was higher in VAT than in SAT. In both pre- and postmenopausal women, ESR2 expression was lower in VAT than in SAT. In late, but not pre- or early postmenopausal women, E2 reduced glucose uptake and GLUT4 protein and increased expression of ESR2. ESR1 polymorphisms were associated with weight, body fat distribution, and total cholesterol, and ESR2 polymorphisms were associated with total cholesterol and triglyceride levels and with body fat percentage.

CONCLUSION

E2 inhibits glucose utilization in human adipocytes in late postmenopausal women. Changes in glucose utilization over time since menopause may be explained by a lower ESR1:ESR2 ratio. This can have clinical implications on the timing of estrogen treatment in postmenopausal women.

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Dorsal epidural "Spindle Cell Lipoma" in a pregnant female

Background

Spindle cell lipoma (SCL) constitutes just 1.5% of all lipomatous tumors. They typically occur in the upper back and shoulders. Here, we report a 37-year-old female presenting with a SCL in the dorsal epidural thoracic spine, during her 9^th month of pregnancy.

Case Description

A 37-year-old female presented with a subacute (2 months) progressive paraparesis during her ^9th month of pregnancy. The MR showed a dorsal epidural mass at the D8 level. Following a cesarean section, the patient underwent a laminectomy for tumor excision. Microscopically, the lesion proved to be a SCL. At 5-year follow-up, there was no tumor recurrence.

Conclusion

SCL represents a variant of benign lipomas that may occur in the dorsal thoracic spine. Gross total excision may be followed by a benign clinical course without recurrence or malignant degeneration. Very atypical SCLs need closer follow-up to avoid the misdiagnosis of liposarcoma.

Simultaneous quantification of estrogens and glucocorticoids in human adipose tissue by liquid-chromatography-tandem mass spectrometry

The presence of estrogens, androgens and glucocorticoids as well as their receptors and steroid converting enzymes in adipose tissue has been established. Their contribution to diseases such as obesity, diabetes and hormone-dependent cancers is an active area of research. Our objective was to develop a LC-MS/MS method to quantify bioactive estrogens and glucocorticoids simultaneously in human adipose tissue. Estrogens and glucocorticoids were extracted from adipose tissue samples using solid-phase extraction. Estrogens were derivatized using 1-(2,4-dinitro-5-fluorophenyl)-4-methylpiperazine (PPZ) and methyl iodide to generate a permanently charged molecule (MPPZ). Steroids were separated and quantified by LC-MS/MS. The limit of quantitation for the steroids was between 15 and 100 pg per sample. Accuracy and precision were acceptable (<20%). Using this method, estradiol, estrone, cortisone and cortisol were quantified in adipose tissue from women with and without breast cancer. This novel assay of estrogens and glucocorticoids by LC-MS/MS coupled with derivatization allowed simultaneous quantification of a panel of steroids in human adipose tissue across the endogenous range of concentrations encountered in health and disease.

Steroid biosynthesis in adipose tissue

Tissue-specific expression of steroidogenic enzymes allows the modulation of active steroid levels in a local manner. Thus, the measurement of local steroid concentrations, rather than the circulating levels, has been recognized as a more accurate indicator of the steroid action within a specific tissue. Adipose tissue, one of the largest endocrine tissues in the human body, has been established as an important site for steroid storage and metabolism. Locally produced steroids, through the enzymatic conversion from steroid precursors delivered to adipose tissue, have been proven to either functionally regulate adipose tissue metabolism, or quantitatively contribute to the whole body's steroid levels. Most recently, it has been suggested that adipose tissue may contain the steroidogenic machinery necessary for the initiation of steroid biosynthesis de novo from cholesterol. This review summarizes the evidence indicating the presence of the entire steroidogenic apparatus in adipose tissue and discusses the potential roles of local steroid products in modulating adipose tissue activity and other metabolic parameters.

Bringing GC-MS profiling of steroids into clinical applications

Abnormalities of steroid biosynthesis and excretion are responsible for the development and prevention of endocrine disorders, such as metabolic syndromes, cancers, and neurodegenerative diseases. Due to their biochemical roles in endocrine system, qualitative and quantitative analysis of steroid hormones in various biological specimens is needed to elucidate their altered expression. Mass spectrometry (MS)-based steroid profiling can reveal the states of metabolites in biological systems and provide comprehensive insights by allowing comparisons between metabolites present in cells, tissues, or organisms. In addition, the activities of many enzymes related to steroid metabolism often lead to hormonal imbalances that have serious consequences, and which are responsible for the progress of hormone-dependent diseases. In contrast to immunoaffinity-based enzyme assays, MS-based methods are more reproducible in quantification. In particular, high-resolution gas chromatographic (GC) separation of steroids with similar chemical structures can be achieved to provide rapid and reproducible results with excellent purification. GC-MS profiling therefore has been widely used for steroid analysis, and offers the basis for techniques that can be applied to large-scale clinical studies. Recent advances in analytical technologies combined with inter-disciplinary strategies, such as physiology and bioinformatics, will help in understanding the biochemical roles of steroid hormones. Therefore, comprehensive analytical protocols in steroid analysis for different research purposes may contribute to the elucidation of complex metabolic processes relevant to steroid function in many endocrine disorders, and in the identification of diagnostic biomarkers.

An innovative LC-MS/MS-based method for determining CYP 17 and CYP 19 activity in the adipose tissue of pre- and postmenopausal and ovariectomized women using 13C-labeled steroid substrates

CONTEXT

Does adipose tissue produce steroid hormones like an endocrine organ?

OBJECT

To clarify whether adipose tissue produces sex steroid hormone like an endocrine organ, we estimated several key steroid hormone levels, as well as CYP17 and CYP19 activity, in ovariectomized, pre- and postmenopausal women by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

SUBJECTS AND METHODS

The subjects were 19 premenopausal (n = 12), postmenopausal (n = 4), and ovariectomized women (n = 3) aged 27-68 years. Serum, visceral adipose and sc adipose samples were taken from these subjects and stored at -70°C. The levels of cortisol, cortisone, progesterone (Prog), androstenedione, dehydroepiandrosterone, estrone, estradiol (E2), and T in serum and adipose tissue were estimated simultaneously by LC-MS/MS. CYP17 and CYP19 activity in tissues were assayed with the use of (13)C-labeled steroid precursors and LC-MS/MS-based estimation of the metabolites.

RESULTS

E2 and Prog levels in the sera of postmenopausal or ovariectomized women were less than 10% of those in premenopausal women. No marked variations were seen in other hormones. Estrone, androstenedione, dehydroepiandrosterone, and Prog levels in the visceral and sc tissues of postmenopausal and ovariectomized women were 9-60 times higher than those in serum, whereas E2 and T levels were 3- to 7-fold higher than those in serum, and cortisol and cortisone levels were 20% of those found for serum. CYP17 in adipose tissue was found to have 17-hydroxylase and 20,17-lyase activity, with each catalytic activity being essentially equal. Therefore, CYP17 in adipose tissue is of the testicular/ovarian type but not adrenal type, which has 17-hydroxylase activity dominant. The presence of CYP19 activity in adipose tissue was approximately 3% of CYP17.

CONCLUSION

Our findings suggest that adipose tissue acts as an endocrine organ, with CYP17 and CYP19 activity playing an essential role in sex steroid hormone biosynthesis.

17β-Estradiol and estradiol fatty acyl esters and estrogen-converting enzyme expression in adipose tissue in obese men and women

CONTEXT

Obesity is associated with increased circulating 17β-estradiol (E₂), but less is known about E₂ concentrations in adipose tissue. In addition to E₂, adipose tissue synthesizes E₂ fatty acyl esters (E₂-FAE).

OBJECTIVE

The aim was to compare estrogen concentrations and expression of estrogen-converting enzymes in adipose tissue between severely obese men and women.

DESIGN AND SETTING

Tissue samples were obtained during elective surgery in University Central Hospital in the years 2008 through 2011.

PATIENTS

We studied 14 men and 22 premenopausal women undergoing bariatric surgery and 10 control women operated for nonmalignant reasons.

INTERVENTIONS

Paired samples were taken from abdominal sc and visceral adipose tissue and serum and analyzed for E₂ and E₂-FAE by fluoroimmunoassay and liquid chromatography-tandem mass spectrometry. mRNA expression of genes was analyzed by quantitative PCR.

RESULTS

Compared with men, E₂ levels in sc adipose tissue in obese women were higher, along with higher relative mRNA expression of steroid sulfatase and 17β-hydroxysteroid dehydrogenases 1, 7, and 12. In men, E₂-FAE concentrations in adipose tissue were similar to E₂ but in women significantly lower compared with E₂. Adipose tissue E₂-FAE and serum E₂-FAE levels correlated positively in obese subjects. Serum E₂ did not significantly correlate with E₂ concentration or mRNA expression of genes in adipose tissue in obese men or women.

CONCLUSIONS

The production of E₂ by the large adipose mass was not reflected by increased circulating E₂ concentrations in severely obese men or women. However, adipose tissue may contribute to concentrations of serum E₂-FAE.

The impact of gender and serum estradiol levels on HDL-mediated reverse cholesterol transport

OBJECTIVE

Premenopausal women have a lower incidence of cardiovascular disease compared to men of the same age. Endogenous oestrogens, especially estradiol, presumably protect against atherosclerosis by a variety of mechanisms. Reverse cholesterol transport (RCT) mechanisms also provide protection against this disease. RCT is defined as the removal of cholesterol from peripheral macrophage foam cells, via high-density lipoproteins (HDL), and cholesterol transportation to the liver for excretion. We have previously shown in a preliminary study that HDL, isolated from premenopausal women, enhanced macrophage cholesterol efflux compared to HDL derived from age-matched male subjects.

MATERIALS AND METHODS

Here, we expanded this study by analysing a larger population of healthy volunteers and evaluated the capacity of HDL derived from women with high or low serum E2 concentrations, mainly representing premenopausal and postmenopausal women, respectively, or men (each group consisting of 30 subjects) to facilitate cholesterol removal from human THP-1 macrophages. HDL isolated from serum samples was incubated with [(3)H] cholesterol oleate-loaded macrophages for 16 h, after which cholesterol efflux to HDL was determined.

RESULTS

No significant differences in the efflux-promoting ability of HDL existed among the three groups. Relevant plasma factors involved in further steps of RCT, such as cholesterol ester transfer protein (CETP), phospholipid transfer protein (PLTP) and lecithin:cholesterol acyltransferase (LCAT) activities were also analysed, but no differences were observed among the study groups.

CONCLUSION

The results do not support a role for estradiol status or gender in modifying the initial step of RCT as a protective mechanism against cardiovascular disease.

Adipose tissue: friend or foe?

The perception of adipose tissue has changed considerably with the dramatic increase in the incidence of obesity and obesity-related comorbidities over the past 3 decades. Excess fat is no longer associated with wealth, but is instead recognized as a risk factor for many diseases. Adipose tissue is increasingly being identified as a vital, complex endocrine organ, and not simply as a fat store. Not all fat is created equal--regional, developmental, structural, and functional variations exist. Epicardial adipose tissue is a metabolically active organ producing a number of factors that modulate cardiac structure and function. The global epidemic of obesity and metabolic syndrome imposes a major disease burden, particularly of cardiovascular disease. In this Review, we describe the various types of adipose tissue--their developmental biology, differentiation, cell heterogeneity, and functional characteristics. We discuss the link between adipose tissue and inflammation, the signaling factors released by adipose tissue, as well as cardiac adiposity and its relevance to cardiovascular diseases. Finally, we review the myocardial regenerative potential of adipose-tissue-derived stem cells. We believe that a thorough understanding of adipose tissue is of great clinical value.

Fatty acyl esterification and deesterification of 17β-estradiol in human breast subcutaneous adipose tissue

CONTEXT

Adipose tissue has an important role in peripheral estrogen synthesis. One of the metabolic pathways of estradiol (E(2)) is its conversion to lipophilic fatty acyl esters.

OBJECTIVE

The aim was to study the metabolism of E(2) fatty acyl esters in adipose tissue and, specifically, the role of hormone-sensitive lipase (HSL) in steroid ester hydrolysis.

DESIGN AND SETTING

Tissue samples were obtained during elective surgery in University Central Hospital in the years 2008-2011.

PATIENTS

Women undergoing reduction mammoplasty (n = 27) or surgery for breast cancer (n = 16) participated in the study.

INTERVENTIONS

Two sc adipose tissue samples were taken from different quadrants of the breast. Radiolabeled steroids were incubated with tissue homogenate (esterase assay) or microsomal fraction (acyl transferase assay). E(2) and E(2) fatty acyl ester concentrations were determined by fluoroimmunoassay or liquid chromatography-tandem mass spectrometry.

MAIN OUTCOME MEASURES

We evaluated the hydrolysis rate of E(2) fatty acyl esters as well as the esterification rate of E(2); we also related tissue concentrations of E(2) and E(2) esters to serum estrogen concentrations.

RESULTS

Compared to esters of dehydroepiandrosterone and cholesterol, the hydrolysis of E(2) esters was much slower, whereas the esterification rate of E(2) was higher. The hydrolysis of E(2) esters in adipose tissue was reduced by 33-51% by inhibition of HSL. Estrogen concentration in sc adipose tissue was higher than in serum in both pre- and postmenopausal women.

CONCLUSIONS

E(2) fatty acyl esters in adipose tissue surrounding the mammary gland may act as a reservoir for conversion back to biologically active E(2). This is partly dependent on HSL activity.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Quantitative determination of dehydroepiandrosterone fatty acyl esters in human female adipose tissue and serum using mass spectrometric methods

Dehydroepiandrosterone-fatty acyl esters (DHEA-FAE) are naturally occurring water-insoluble metabolites of DHEA, which are transported in plasma exclusively by lipoproteins. To find out whether DHEA, like estradiol, might be stored in adipose tissue in FAE form, we set up a mass spectrometric method to quantify DHEA-FAE and free DHEA in human adipose tissue and serum. The method consists of chromatographic purification steps and final determination of hydrolyzed DHEA-FAE and free DHEA, which was carried out by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). Our results showed that no detectable amounts of DHEA-FAE could be found in adipose tissue although 32-178 pmol/g of free DHEA were determined by GC-MS and LC-MS/MS. The DHEA-FAE concentrations in serum quantified by GC-MS were 1.4±0.7 pmol/ml in premenopausal women (n=7), and 0.9±0.4 pmol/ml in postmenopausal women (n=5). Correspondingly, the free DHEA concentrations were 15.2±6.3 pmol/ml and 6.8±3.0 pmol/ml. In addition, the mean proportions of DHEA-FAE of total DHEA (DHEA-FAE+free DHEA) in serum were 8.6% and 11.2% in pre- and postmenopausal women, respectively. Serum DHEA-FAE concentration was below quantification limit for LC-MS/MS (signal-to-noise ratio, S/N=10), while free DHEA concentrations varied between 5.8 and 23.2 pmol/ml. In conclusion, the proportion of DHEA-FAE of total DHEA in serum was approximately 9%. However, in contrast to our previous findings for estradiol fatty acid esters in adipose tissue which constituted about 80% of total estradiol (esterified+free), the proportion of DHEA-FAE of total DHEA was below 5%. Four to ten times higher concentrations of free DHEA were quantified in adipose tissue compared to those in serum.

Fatty acid esters of steroids: synthesis and metabolism in lipoproteins and adipose tissue

At the end of the last century ideas concerning the physiological role of the steroid fatty acid ester family were emerging. Estrogens, fatty acylated at C-17 hydroxyl group and incorporated in lipoproteins were proposed to provide antioxidative protection to these particles. A large number of studies involving non-estrogenic adrenal steroids, and their fatty acylated forms, demonstrated their lipoprotein-mediated transport into cells and subsequent intracellular activation, suggesting a novel transport mechanism for lipophilic steroid derivatives. After these important advances the main focus of interest has shifted away from C-19 and C-21 steroids to fatty acylated estrogens. However, interest in their lipoprotein-mediated transport has decreased because only minute amounts of these derivatives were detected in circulating lipoproteins, and their antioxidative activity remained unconfirmed under physiological circumstances. It now appears that the overwhelming majority of estradiol in postmenopausal women resides in adipose tissue, most of it in esterified form. This is poorly reflected in plasma levels which are very low. Recent data suggest that estrogen fatty acid esters probably represent a storage form. The future focus of investigation is likely to be on firstly, the enzymatic mechanisms regulating the esterification and de-esterification of estradiol and other steroids residing in adipose tissue and secondly, on the role of insulin and other hormones in the regulation of these enzymatic mechanisms. Thirdly, as a large proportion of fatty acid esterified C-19 and C-21 non-estrogenic steroids is transported in lipoproteins and as they are important precursors of androgens and estrogens, this field should be investigated further.

Mass spectrometric profiling of saturated fatty acid esters of steroids separated by high-temperature gas chromatography

An efficient analytical method for simultaneous determination of 12 SFEs in serum is described. The method involves solid-phase extraction to isolate of SFEs from interfering species, especially cholesteryl esters, conversion to trimethylsilyl (TMS) ether derivatives for the direct analysis by gas chromatography-mass spectrometry (GC-MS) using a high temperature MXT-1 (Silcosteel-treated stainless steel) capillary column. All SFEs as their TMS derivatives were well separated with excellent peak shapes within 12 min. Overall recoveries ranged from 88% to 119%, with a detection limits for SFEs ranged from 2 to 30 microg L(-1). The linearity as correlation coefficient was higher than 0.99 except for pregnenolone-3-arachidate (r(2)=0.98) in the concentration range of 5-3000 microg L(-1). Ten serum samples obtained from volunteers were also analyzed and quantitatively determined of DHEA-3-palmitate and pregnenolone-3-stearate in 1.8-1195.8 microg L(-1) concentration. The devised high temperature GC-MS method could be useful for identification of SFEs in biological specimens including serum.

Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Dehydroepiandrosterone-fatty acyl esters (DHEA-FAE) belong to a unique family of naturally occurring hydrophobic steroid hormone derivatives that are transported in circulating lipoproteins and may act as a source of dehydroepiendrosterone (DHEA) and other biologically active steroid hormones in cells. Here, we studied the metabolic fate of low-density lipoprotein-associated [(3)H]DHEA-FAE ([(3)H]DHEA-FAE-LDL) and the possible role of lysosomal acid lipase (LAL) in the hydrolysis of DHEA-FAE in cultured human cells. When HeLa cells were incubated with [(3)H]DHEA-FAE-LDL, the accumulation of label in the cellular fraction increased with incubation time and could be inhibited by excess unlabeled LDL, suggesting LDL receptor or LDL receptor-related receptor-dependent uptake. During 48 h of chase, decreasing amounts of [(3)H]DHEA-FAE were found in the cellular fraction, while in the medium increasing amounts of unesterified [(3)H]DHEA and its two metabolites, [(3)H]-5alpha-androstanedione (5alpha-adione) and [(3)H]androstenedione (4-adione), appeared. As LDL-cholesteryl ester hydrolysis is dependent on LAL activity, we depleted LAL from HeLa cells using small interfering RNAs and compared the hydrolysis of [(3)H]DHEA-FAE-LDL and [(3)H]cholesteryl-FAE-LDL. The results demonstrated a more modest but significant reducing effect on the hydrolysis of [(3)H]DHEA-FAE compared with [(3)H]cholesteryl-FAE. Moreover, experiments in LAL-deficient human fibroblasts (Wolman disease patient cells) showed that [(3)H]DHEA-FAE hydrolysis was not completely dependent on LAL activity. In summary, LDL-transported [(3)H]DHEA-FAE entered cells via LDL receptor or LDL receptor-related receptor-mediated uptake, followed by intracellular hydrolysis and further metabolism into 5alpha-adione and 4-adione that were excreted from cells. Although LAL contributed to the deesterification of DHEA-FAE, it was not solely responsible for the hydrolysis.