A 'new' estrogen metabolite: an epoxide of estrone as a sulfated steroid

Current heightened recognition of the importance of sulfated steroids led to the examination of conjugates in media from incubations of estrogens in tissues from the reproductive tract of stallions. Previously, we had reported a 'new' unidentified metabolite of estrone (E1) and [3H]-E1, located between 17β-estradiol (E2) and E1 reference standards on chromatography (HPLC) and identified tentatively as a stable 5α,6α-estrone epoxide. Stallion tissues were minced and incubated for 2 h with [3H]-E1 (1 × 106 cpm). Solid-phase extraction of unconjugated and conjugated steroids from media was followed by liquid scintillation counting (LSC), where radioactivity was mostly in the conjugate fractions (>80%). HPLC of conjugated steroids used an isocratic solvent system of acetonitrile/water (8:92) at 700 µL/min with detection by LSC. A radioactive peak between reference standards of E1 and E2 sulfates was examined, after solvolysis, in a second solvent system. Sulfated steroids yielded largely E1, whereas acid treatment of the unconjugated E1 epoxide had earlier formed 6α-OH-E1 almost exclusively. With sulfatase enzyme, at neutral pH, radioactivity was also seen mostly as E1 with trace amounts of polar material. Reduction with KBH4, however, led also to desulfation; radioactivity had alignment with E2 but even more had low retention times as for 6α/6β-OH-E2. These findings point to a different hydrolysis for desulfation; even more, they reveal an additional oxygen atom at C6 and are supportive of biological formation of 5α,6α-epoxides of E1 and E2. As possible alternatives to catechol estrogens, implicated in cancer, the 'new' estrogen metabolites and their sulfated forms may have special interest.

Patterns of conceptus development and of progesterone concentrations in maternal blood preceding spontaneous early pregnancy failure in mares

Sixteen cases of spontaneous pregnancy loss (11 of singletons and five of pairs of twins) are described. The losses occurred between gestation Days 13 and 25 in 12 mares being monitored almost daily by transrectal ultrasonography (for measurement of conceptus growth) and blood sampling (for determination of maternal plasma progesterone concentrations as evidence of luteolysis) in experimental studies of early pregnancy. In 10 of the 16 cases the uterus was flushed and eight conceptuses were recovered for morphological assessment. Five of the 11 losses of singletons occurred before Day 16 and, with one exception, were preceded or accompanied by luteolysis. The remaining six singleton pregnancies failed after Day 16, with two cases evidencing luteolysis beforehand. Thus, overall, 6/11 singleton losses were associated with luteolysis while 5/11 were not. The five cases of simultaneous loss or degeneration of twin conceptuses all occurred on Day 19 or 20, preceded by luteolysis in only one case. These observations suggest that while the causes of spontaneous early pregnancy failure are multifactorial, luteolysis might contribute to the problem more often than has been previously contended.

A stable epoxide of estrone: Evidence for formation of a 'new' estrogen metabolite

Oxidative metabolism of estrogens is an important feature in liver and some non-hepatic tissues. In initial studies on estrogen metabolism in tissues from the reproductive tract of the stallion, where testicular estrogen secretion is remarkably high, a prominent radiolabeled product from [³H]-estrone (E1) was noted on chromatography; it had a retention time (Rt) between 17β-estradiol (E2) and E1. Unexpectedly, when non-radiolabeled E1 was the substrate no UV absorption at 280nm was seen at the Rt for the [³H]-labeled product-suggesting a non-aromatic ring A. The following efforts were made to reveal more about the nature of the "unknown" compound. Reduction and acetylation showed, separately, the presence of a single keto and hydroxyl group. Exposure to acid gave a single radiolabeled peak with Rt of 6α-hydroxy-E1-suggesting the presence of a third molecule of oxygen. Mass spectrometry with limited material was inconclusive but supportive for a formula of C₁₈H₂₂O_3. Thus, an epoxide involving the aromatic ring of E1 is suggested as a labile intermediate in the formation of the "unknown" metabolite. Estrogen epoxides as labile, reactive intermediates have been considered as potential precursors of the 2- and 4-hydroxy catechol estrogens with implications in breast cancer [Soloway, 2007]. Because of the association of the "unknown" metabolite with 6α-hydroxy-E1, the structural form proposed for the stable epoxide is that for 5α,6α-epoxy-estrone. This represents an alternative to the production of the 2- and 4-hydroxy-catechol estrogens. The broad range in normal tissues where the "unknown" compound was shown to be a persistent metabolite (e.g. mouse mammary glands, ovary, uterus, brain, muscle, equine conceptus, stallion and domestic boar reproductive tracts) suggests more general biological implications.

Biosynthesis of oestrogen by the early equine embryo proper

The embryo proper in early equine pregnancy has recently been shown to have a remarkable capacity for metabolism of oestrogens. High concentrations of oestrogens in yolk-sac fluid could provide substrate for local metabolism in tissues of the embryo proper and this activity could have significance for early development. Due to the high level of oestrogen metabolism in the embryo proper we examined the possibility that it could also biosynthesise oestrogens. Conceptuses were collected in the fourth week of pregnancy (n=23) and the embryo was separated from extraembryonic tissues for incubation with [(3)H]androstenedione. Steroids were recovered from media by solid-phase extraction and eluted as unconjugated and conjugated fractions. Profiles of free and sulfoconjugated fractions, as well as the phenolic steroids extracted from them, were obtained by chromatography. Oestrone and oestradiol were seen clearly, indicating oestrogen biosynthesis, and the presence of more polar products, arising from metabolism of the primary oestrogens, gave further evidence that the embryo was capable of oestrogen biosynthesis. Aromatase activity was also demonstrated by detection of tritium loss, as (3)H(2)O, from incubations (n=3) with [1β-(3)H]androstenedione. It is suggested that its oestrogen biosynthesis may have significance for the remarkable development of the vasculature in the embryo proper at this stage.

The in vitro metabolism of cortisol by ovarian follicles of rainbow trout (Oncorhynchus mykiss): comparison with ovulated oocytes and pre-hatch embryos

Mid-vitellogenic stage rainbow trout (Oncorhynchus mykiss) ovarian follicles (both intact and yolk free (YF)), ovulated oocytes and embryos were co-incubated with [2,4,6,7-3H]cortisol for 18 h to determine the degree and nature of the metabolism and biotransformation of the glucocorticoid. There was evidence of the conversion of cortisol to the less biologically potent glucocorticoid, cortisone, and the formation of glucocorticoid sulphates (both cortisol and cortisone) for all cell and tissue samples, suggesting the presence of 11β-hydroxysteroid dehydrogenase (11β-HSD) and glucocorticoid sulphotransferase (GST) activity at all stages; however, GST activity was particularly marked in both intact and YF ovarian follicles, suggesting an important role of follicles in limiting the exposure of oocyte to maternal cortisol. As there was no evidence of 11β-HSD or GST activity in ovarian fluid, the findings affirm that ovarian follicles (probably the thecal and granulosa cells) provide a barrier against the transfer of cortisol to the oocytes by forming sulphated steroids, whereas ovulated oocytes and early embryos have a more limited capacity to either metabolize or conjugate cortisol and are therefore more vulnerable at the post-ovulatory and early embryonic stages to increases in exposure to the glucocorticoid.

Relationship between the timing of prostaglandin-induced luteolysis and effects on the conceptus during early pregnancy in mares

To advance the understanding of early pregnancy and pregnancy failure in horses, this study determined how luteolysis induced by cloprostenol (an analogue of prostaglandin F2α) affects conceptus development. Mares were injected on Days 12, 14, 16 or 18 of pregnancy with either cloprostenol (treatment groups, total n = 83 pregnancies) or saline (controls, n = 81), and growth of the conceptuses was monitored and compared by daily ultrasonography until they were collected transcervically on Days 15–22, 1–4 days after the injections. The comparisons were extended in the recovered conceptuses by counting somites, measuring the volume and osmolality of yolk-sac fluid and its concentrations of proteins, estrone sulfate and progesterone, and by assessing the morphology of the capsule and vascular system. When luteolysis was initiated on or before Day 16, most pregnancies survived until the time of collection and the conceptuses in respective treated and control groups on Days 15–20 were very similar except for some effects of treatment on the capsule and vascular development. In contrast, after luteolysis was initiated on Day 18, abortion often ensued within 3 days and most conceptuses collected had degenerated, therein constituting a predictable system in which to study the pathogenesis of a particular cause of pregnancy failure.

Diaryl dimers of estradiol and of estrone may be formed as major metabolites by mouse mammary glands

The formation of a novel estrogen metabolite by mammary tissues was investigated. Polar and nonpolar metabolites of endogenous estrogens are formed in liver and other tissues. Polar products such as the catechol estrogens are implicated in tumorigenesis in breast tissue, whereas a nonpolar metabolite, 2-methoxyestradiol, may be protective. Diaryl ether dimers, as a novel form, have been reported as nonpolar products from liver microsomes. We have noted major amounts of nonpolar metabolites in other tissues that were neither 2-methoxyestrogens nor estrogen fatty acid esters. The possible formation of such novel metabolites by breast tissues from adult nulliparous mice with [(3)H]-labeled estrogens as substrates was considered. Steroids were recovered from media by solid-phase extraction and profiles were obtained from HPLC (acetonitrile:water). Saponification was done with an internal standard of estradiol stearate. Major amounts of nonpolar metabolites were formed in all instances, with one or two principal peaks. Alkaline hydrolysis had no effect on the nonpolar product(s) but released estradiol from its stearate. Strong acid treatment also had no effect as shown by HPLC. Thus, it is suggested that diaryl dimers of estrogens may be formed as major metabolites by mouse mammary glands.

Estrogen metabolism by the equine embryo proper during the fourth week of pregnancy

Estrogen production by the trophoblast is considered important in early equine pregnancy and leads to high concentrations in yolk-sac (Y-S) fluid. The embryo proper is a potential site for their action. We examined estrogen metabolism in the embryo proper because some actions of estrogens are derived from locally formed metabolites. The embryo proper, as well as separated extraembryonic tissues, of conceptuses collected about day 25 of pregnancy, were incubated with 3[H]-estrone (E1) and 3[H]-estradiol (E2). Steroids were recovered from media by solid-phase extraction and eluted separately as unconjugated and conjugated fractions. Profiles of free and sulfo-conjugated fractions were obtained by HPLC. Some differences and similarities were noted for the embryo proper as compared to the extraembryonic tissues. No reduction of E1 to E2 was noted for the embryo proper and allantois, but some was seen with the bilaminar Y-S wall. Less conversion of E2 to E1 occurred in the embryo proper than in the extraembryonic tissues. Profiles for hydrolyzed sulfates from incubation of the embryo proper were very similar for both substrates, mainly with E1 present. Thus, low levels of reductase and high levels of oxido- activities were apparent for the 17β-hydroxysteroid dehydrogenase enzymes. Further evidence of an active role for the embryo proper was seen as minor, polar products, and an unknown compound eluting between E2 and E1. These findings show, for the first time, that the embryo proper can metabolize estrogens that are found in Y-S fluid – a function of potential significance at this stage in its development.

The presence of 19-norandrostenedione and its sulphate form in yolk-sac fluid of the early equine conceptus

C(18) neutral steroid formation by cytochrome P450 aromatase has been recorded for several equine and porcine tissues. High activity of P450 aromatase is reflected in the quantities of estrogens in yolk-sac (y-s) fluid of early equine conceptuses. In a previous study of y-s fluid we detected large amounts of androgens by radioimmunoassay (RIA), using an antiserum for androstenedione (A(4)). Here, we report that RIA, following chromatography, gave tentative identification of the major peak as norandrostenedione (19-norA) not as A(4). Furthermore, even greater quantities of 19-norA seemed to be present in y-s fluid as a sulphoconjugate, as noted from extraction, solvolysis, HPLC, followed by RIA. Confirmation of these unusual findings was attained after further purification with two HPLC systems and definitive identification by LC-MS with an authentic standard of 19-norA. Initial extraction of the steroid sulphate as a methylene-blue complex also yielded 19-norA suggesting that the 3-enol form had enabled sulphoconjugation. The biological significance of retention mainly as a sulphate is not known; however, the large amounts of 19-norA found in the fluid accords well with reports on the catalytic activity shown in vitro by the blastocyst isozyme of P450 aromatase in the pig and horse.

The boar testis: the most versatile steroid producing organ known

A review of the remarkable production of steroids by the testes of the boar is presented, with the principal aims of highlighting the achievements of the Leydig cells and, at the same time, pointing to the considerable deficiencies in our understanding of its biological relevance. The onset of gonadal steroidogenesis at an early stage of sex differentiation and the pattern of pre- and postnatal secretion of steroids are outlined. This is followed by a list of steroids identified in extracts of the boar testis, with emphasis on those that can reasonably be assumed to be secretory products of the Leydig cells. For example, the high concentrations of 16-unsaturated C19 and sulphoconjugated compounds are noted. Next, an impressive list of steroids found in venous blood from the boar testis is given; among them are the 16-unsaturated steroids, the oestrogens and dehydroepiandrosterone, all mainly in the form of sulphates. However, the list also includes some less likely members, such as 11-OH and 19-OH androgens as well as 5alpha-reduced steroids. Lastly, the high concentrations of steroids reported in testicular lymph, especially sulphates, are mentioned. Although roles for testosterone are uncontested, and even for the pheromone-like C19 steroids, there is little that can be said with assurance about the other compounds listed. Some speculations are made on their possible contributions to the reproductive physiology of the boar. This is done to provoke interest and, perhaps, even action towards reaching a more complete understanding of the biological significance of the steroidogenic powers of porcine Leydig cells.

Estrogen Metabolism in the Equine Conceptus and Endometrium During Early Pregnancy in Relation to Estrogen Concentrations in Yolk-Sac Fluid1

Because estradiol (E(2)) production by the early equine conceptus is considered crucial to the establishment of pregnancy, the amounts of E(2), estrone (E(1)), and their sulfates (E(2)S, E(1)S) were measured by RIA in yolk-sac fluid of 63 conceptuses collected by transcervical lavage over the period of 11-26 days after ovulation. Amounts increased significantly with age of conceptus, especially for E(1)S. Then, the metabolism of E(2), which may be highly relevant for its action, was examined in the conceptus and endometrium over the period when the conceptus ceases to migrate within the uterus. Eleven conceptuses collected mainly on Days 12, 15, and 18, with endometrial biopsy samples taken immediately thereafter, were used for steroid metabolic studies. Trophoblastic and endometrial tissues were incubated with [(3)H]-labeled E(2) or E(1), and with [(14)C]-E(1) in one experiment. Steroids were recovered from the media by solid-phase extraction (SPE) and eluted separately as unconjugated and conjugated fractions. Conjugation increased from Day 12 for the trophoblast (more so by bilaminar than trilaminar tissues on Day 18) and was much greater for endometrium, with almost all as sulfoconjugates. HPLC profiles of free and sulfate fractions were obtained from a gradient of acetonitrile/water. Interconversion (E(2) right harpoon over left harpoon E(1)) by trophoblast varied with development; it favored E(2) in older conceptuses, more in bilaminar than trilaminar tissues. Some more polar products were also noted, with loss of tritium seen as [(3)H](2)O at SPE, and confirmed by HPLC in a second system with authentic reference steroids. Almost all radioactivity in the endometrium was present as E(2) in both free and sulfate fractions. It was concluded that local metabolism of E(2) is quantitatively significant and may play an important role in the actions of the large amounts of estradiol produced by the early equine conceptus.

Estradiol-17beta sulfotransferase activity in canine osteosarcoma D17 cells

Estrogen sulfatase and sulfotransferase (EST) activities are present in breast cancer tissues but there are no reports on EST in cancerous bone cells. We incubated [(3)H]estradiol-17beta with cells from a canine osteosarcoma D17 line for periods up to 24 h. Radioactive steroids were recovered from the media and separated into unconjugated and conjugated fractions using Sep-Pak C18 cartridges. The conjugate fraction was solvolyzed and the resulting free steroids were obtained from a second C18 cartridge. Little metabolism was apparent in 4 h of incubation, but by 24 h as much as one half of the radioactivity was seen in the conjugate fraction. Most of the conjugates were recovered as sulfates in all three experiments. HPLC profiles showed a limited metabolism of estradiol to other compounds except for estrone, which was clearly present in both free and sulfate fractions. These results suggest that EST may have a role in the local metabolism of estrogens in bone.

Androgen and estrogen metabolism in the reproductive tract and accessory sex glands of the domestic boar (Sus scrofa)

Steroid metabolism in target tissues has relevance in assessing biological response. We have investigated the metabolism of testosterone and estrogens in the reproductive tract and accessory sex glands in the boar. Seminal vesicles were taken from four 6-mo-old animals; and seminal vesicles, prostate, vas deferens, and regions of the epididymis were taken from two mature boars (10 and 24 mo old). Tissues were incubated in 5 ml medium (TC-199) at 34 degrees C under 5% CO(2) and 95% air for 2 h with (3)H-labeled testosterone, estrone, and estradiol-17beta. Aliquots of spent media were taken to measure radioactivity before separation of unconjugated and conjugated steroids on Waters C(18) Sep-Pak cartridges. Sulfoconjugated steroids and glucuronidates were recovered in series from C(18) cartridges after solvolysis and enzyme hydrolysis, respectively. Profiles of metabolites for free and hydrolyzed fractions were obtained from gradient HPLC with acetonitrile:water on a reversed-phase C(18) column. No clear evidence of conjugation was seen for testosterone metabolites. 5alpha-Dihydrotestosterone was the principal metabolite, but the amounts formed depended on the source, with little from the epididymal tissues and seminal vesicles, but greater quantities from the vas deferens (>25%) and prostate (>30%). The most noteworthy feature of estrogen metabolism was the extent of conjugation by all tissues. Almost all radioactivity in the conjugate fractions for the epididymis and vas was present as sulfates. Glucuronidates were seen for the prostate and were the dominant form of conjugation (about 60%) for the seminal vesicles. A striking parallel existed for the profiles of estrogen metabolites from all tissues for unconjugated and hydrolyzed fractions. Only in quantitative terms were some distinctions noted. These overall findings underscore a need to consider local metabolism of steroid hormones in target tissues of the male reproductive system.

Metabolism of oestrone and oestradiol-17beta to conjugated steroids by the accessory sex glands of the male pig

Oestrogens are secreted in large amounts by boar testes and are known to have a synergistic effect with testosterone on the production of large volumes of seminal plasma. Thus, oestrogens play a role in regulating the large accessory sex glands in the boar. Since testosterone metabolites (e.g. 5alpha-dihydrotestosterone) account for much of its action in target tissues we have looked at the metabolism of oestrogens in the accessory sex glands of the male pig. Tissues from seminal vesicles and bulbourethral glands of 6-week-old castrate and intact males, and 12-week-old castrate animals, were incubated with (3)H-labelled oestrone and oestradiol-17beta. Aliquots of spent culture medium and of methanolic tissue extracts were taken to measure radioactivity, prior to separation of unconjugated and conjugated steroids on Waters C(18) Sep-Pak cartridges. About one-third of the radioactivity appeared as conjugates in the media from both glands with each oestrogen. Subsequently, sulphoconjugated steroids and glucuronidates were recovered in series from C(18) cartridges after solvolysis and enzyme hydrolysis respectively. Furthermore, about one-third of the conjugated fraction in each case remained unhydrolysed after these treatments. In conclusion, it is clear that a study of the actions of oestrogens on these glands must consider the dynamics of metabolism of the oestrogens presented to them by the testes and would include conjugation of steroids by the glands themselves.

Postnatal decline in gonadal secretion of dehydroepiandrosterone and 3 beta-hydroxyandrosta-5,7-dien-17-one in the newborn foal

Dehydroepiandrosterone (DHEA) and 3 beta-hydroxyandrosta-5,7-dien-17-one (7-dehydro-DHEA) are secreted in large quantities by the remarkably hypertrophied fetal gonads of both sexes in the pregnant mare. Their secretion serves as the fetal component of a feto-placental unit for oestrogen production in equine pregnancies. They are secreted in large amounts but show a decline in late pregnancy when the fetal gonads regress and levels of oestrogens in the mare fall as a consequence. We have examined the levels of these precursor steroids in the newborn foal in the first days after birth. DHEA and 7-dehydro-DHEA were measured in peripheral plasma in a direct RIA with a DHEA antibody which cross-reacts with 7-dehydro DHEA (> 150%). Subsequent studies were performed with solid-phase extraction, separation of unconjugated from conjugated steroids, and HPLC fractionation followed by RIA. Detection on HPLC at 254 and 280 nm was compared with results from RIA. It was concluded that DHEA is the major steroid produced by the gonads at birth. The concentrations are highly variable in the first day of postnatal life (70.45 +/- 63.06 ng/ml, n = 52) and decline rapidly to < 2 ng/ml (n = 6) at 96 h after birth. At this time the sulphate form is also seen, with an increasing ratio of DHEAS/DHEA as the value for total DHEA falls. The mechanism and significance of the apparent abrupt decline in gonadal steroidogenesis in the newborn foal remain unknown.

Estrogen concentrations in semen of the stallion

Large amounts of estrogens are secreted by the tests of the mature stallion. In a recent study by Claus et al. [Claus, Dimmick, T., Gimenez, T., Hudson, L.W., 1992. Estrogens and prostaglandin F2 alpha in the semen and blood plasma of stallions. Theriogenology 38, 687-693.], it was stated that high levels of estrogens were also present in semen. As a preliminary step to study possible implications for fertility in the stallion, we have measured estrone sulphate (E1S), the principal estrogen in blood, in both seminal plasma and spermatozoa. Semen was collected from four Standardbred stallions at each of two stud farms in Southern Ontario during the breeding season (March-May) in 1994 and 1995, respectively, and from five stallions at the second farm in 1996. Blood samples from the jugular vein were also taken at the time of semen collection in 1996. Gel-free semen samples (n = 98, 1994-1995, n = 12, 1996) and blood were stored at -20 degrees C until analysis. Sperm was removed from thawed samples (1 ml) by centrifugation, washed 5 x with saline solution and extracted with 80% methanol. Seminal plasma (200 microliters) was diluted with absolute methanol (800 microliters), vortexed and centrifuged before aliquots were taken for radioimmunoassay (RIA). Blood plasma was diluted with RIA buffer (1:10), and all aliquots were assayed using an antiserum for direct measurement of E1S. Concentrations of E1S (ng ml-1) ranged from 0.73-8.15 (n = 110) in seminal plasma and from 64.7-153.5 (n = 12) in blood plasma. E1S concentration in the sperm pellet from 1 ml of semen had a mean value of 1.3 ng and a range of 0.54-2.48 ng (n = 53 from four animals). The amounts of E1S in total gel-free ejaculates (n = 22) from four stallions range 26-121 ng. It was concluded that the high concentrations of E1S in peripheral blood of the stallion are reflected in lesser, but high levels of the steroid in the ejaculate. E1S concentrations were quite variable in seminal plasma among stallions but less so for collections from an individual animal. The presence of E1S in washed spermatozoa requires further study.

Plasma levels of several androgens and estrogens from birth to puberty in male domestic pigs

Plasma concentrations for several androgens and estrogens were determined in male domestic pigs from birth to eight months of age. Samples (N = 6) of blood were collected from Yorkshire males at weekly intervals from birth to four weeks, and thereafter at monthly intervals to eight months. Radioimmunoassays were done without extraction from plasma for dehydroepiandrosterone sulphate, androstenedione and estrone sulphate. Other steroids were measured after solid-phase extraction, separate elution of unconjugated and conjugated fractions, and solvolysis of sulpho-conjugated steroids (testosterone, 5 alpha-androstane-3 beta, 17 beta-diol, epiandrosterone, 19-nortestosterone and estradiol-17 beta). All steroids showed a peak in plasma levels at 2-4 weeks after birth. Concentrations remained low from 2-5 months and rose markedly thereafter. Most steroids were present in much greater quantities as sulpho-conjugated compounds. Concentrations of testosterone sulphate and testosterone were similar (9.4 mumol/l) at three weeks but the sulphated form predominated after six months of age. This study shows that during postnatal development the testes of the domestic pig are remarkably active in steroidogenesis with a peak at 2-4 weeks after birth. Also, the range of steroid products seen at this stage is comparable to that shown by the mature boar.