Regiospecific esterification of estrogens by lecithin:cholesterol acyltransferase

Lecithin:cholesterol acyltransferase (LCAT), the enzyme that esterifies cholesterol in blood, also esterifies other steroids at the 3beta-hydroxyl. These steroids, like cholesterol, are delta5-3beta-hydroxysteroids, such as pregnenolone and dehydroepiandrosterone. One unusual LCAT substrate is the estrogen, estradiol, which is esterified at the 17beta-hydroxyl. The esterification of estradiol by LCAT has been reported to produce a powerful antioxidant that protects low density lipoprotein (LDL) from oxidation. We investigated the substrate specificity of LCAT, comparing the esterification of four different steroids (estradiol, estriol, testosterone, and 5-androstene-3beta, 17beta-diol) by human LCAT in blood and by acyl-coenzyme A:acyltransferase in tissue (placenta and fat). Estradiol was esterified only at the D ring 17beta-hydroxyl group in both blood and tissue. In contrast, although testosterone has a D ring structure identical to that of estradiol, and it was esterified at the 17beta-hydroxyl by acyl-coenzyme A:acyltransferase in tissue, it was not esterified by LCAT. When 5-androstenediol was the substrate in the tissues, both the 3beta- and 17beta-esters were synthesized, but the major product was the 17beta-ester. Conversely, although 5-androstenediol was an excellent substrate for LCAT, only the 3beta-hydroxyl was esterified. No 17beta-ester was formed. The comparison of the esterification of estriol by acyl-coenzyme A:acyltransferase and LCAT was also surprising. In the tissues, estriol is esterified at both D ring hydroxyls, and both are esterified about equally. Although estriol is an extremely polar estrogen, it is esterified by LCAT, albeit at a very slow rate. Although again both D ring hydroxyls were esterified, the LCAT esterification site was mainly at the 17beta-hydroxyl. Esterification of estriol at the 17beta-hydroxyl in preference to the 16alpha-hydroxyl is especially striking, because the 17beta-hydroxyl group is sterically shielded by the C-18 methyl group, making esterification at this position energetically much more difficult. Furthermore, these studies demonstrate that esterification of the 17beta-hydroxyl group by LCAT is unique to estrogens. It suggests that this unusual regiospecific esterification of C-17 of the estrogens underlies a distinct stereochemical requirement for the powerful antioxidant action that has reported for the estradiol esters formed by LCAT.

7alpha-Iodo and 7alpha-fluoro steroids as androgen receptor-mediated imaging agents

We have synthesized several 7alpha-fluoro (F) and 7alpha-iodo (I) analogues of 5alpha-dihydrotestosterone (5alpha-DHT) and 19-nor-5alpha-dihydrotestosterone (5alpha-NDHT) and tested them for binding to the androgen receptor and for their biological activity in an in vitro assay with cells that have been engineered to respond to androgens. The relative binding affinity to the androgen receptor determined in competition assays showed that in the androstane series the fluoro steroids have the highest affinity and that F-17alpha-CH3-DHT (4) has a higher affinity than 5alpha-DHT. All other steroids were somewhat less potent than 5alpha-DHT with F-DHT (2) = I-17alpha-CH3-DHT (3) >/= F-NDHT (6) > F-17alpha-CH3-NDHT (8) = I-DHT (1) >/= I-NDHT (5) > I-17alpha-CH3-NDHT (7). The relative biological activity in cells transfected with the androgen receptor and an androgen responsive reporter gene is 4 >> 5alpha-DHT > 2 > 6 > 3 >/= 1 >/= 8 >/= 5 > 7. The iodinated compound, I-17alpha-CH3-DHT (3), with the highest binding activity was synthesized labeled with 125I and was shown to bind with high affinity, Ka = 1.9 x 10(10) L/mol, and low nonspecific binding to the androgen receptor in rat prostatic cytosol. However, when radiolabeled [125I]-17alpha-CH3-DHT ([125I]3) was injected into castrated male rats, it showed very poor androgen receptor-mediated uptake into the rat prostate. This was unexpected in light of its superior receptor binding properties and its protection by the 17alpha-methyl group from metabolic oxidation at C-17. However, the biological potency of I-17alpha-CH3-DHT (3) was not as high as would have been expected. When I-DHT (1) and I-17alpha-CH3-DHT (3) were incubated in aqueous media at 37 degrees C they rapidly decomposed, but they were stable at 0 degrees C. The fluorinated analogue 4 treated similarly at 37 degrees C was completely stable. The products of the decomposition reaction of I-DHT (1) at 37 degrees C were identified as iodide and principally 17beta-hydroxy-5alpha-androst-7-en-3-one. The temperature dependence of this elimination reaction explains the inconsistency between the high binding to the androgen receptor (measured at 0 degrees C) and the low biological activity, as well as the poor androgen receptor mediated concentration in vivo. The fluorinated analogue F-17alpha-CH3-DHT (4) has both high affinity for the androgen receptor and high stability in aqueous media. Of the compounds tested, 4 has the highest affinity for the androgen receptor as well as the highest androgenic activity. Thus it is likely that F-17alpha-CH3-DHT 4 labeled with 18F will be an excellent receptor-mediated diagnostic imaging agent.

Iodinated and fluorinated steroid 2'-aryl-[3,2-c] pyrazoles as potential glucocorticoid receptor imaging agents

We have synthesized several halogenated steroids as potential glucocorticoid receptor mediated imaging agents. These compounds are analogs of aryl-pyrazolo steroids, similar to the potent glucocorticoid, cortivazol. Compounds containing the halogens, iodine, bromine, and fluorine, as well as the E- and Z-iodovinyl side chain at the para position of 2'-phenyl-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole were prepared. They were tested as ligands for the glucocorticoid receptor by competition for the binding of [3H]dexamethasone and for glucocorticoid potency by the induction of alkaline phosphatase in HeLa cells. None of the iodinated steroids were good ligands for the glucocorticoid receptor or potent glucocorticoids. The bromo analog was only slightly better than the iodinated steroids as a ligand, and it had a potency in the HeLa cell assay about half that of dexamethasone. The fluoro analog good binding to the glucocorticoid receptor and was a very potent glucocorticoid, approximately seven times that of dexamethasone. Consequently, it appears that the fluoro steroid, 2'-(4-fluorophenyl)-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole, when labeled with 18F, would make an excellent glucocorticoid receptor-mediated imaging agent for positron emission tomography.

Sex and the developing brain: suppression of neuronal estrogen sensitivity by developmental androgen exposure

The developmental effects of androgen play a central role in sexual differentiation of the mammalian central nervous system. The cellular mechanisms responsible for mediating these effects remain incompletely understood. A considerable amount of evidence has accumulated indicating that one of the earliest detectable events in the mechanism of sexual differentiation is a selective and permanent reduction in estrogen receptor concentrations in specific regions of the brain. Using quantitative autoradiographic methods, it has been possible to precisely map the regional distribution of estrogen receptors in the brains of male and female rats, as well as to study the development of sexual dimorphisms in receptor distribution. Despite previous data suggesting that the left and right sides of the brain may be differentially responsive to early androgen exposure, there is no significant right-left asymmetry in estrogen receptor distribution, in either sex. Significant sex differences in receptor density are, however, observed in several regions of the preoptic area, the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus, particularly in its most rostral and caudal aspects. In the periventricular preoptic area of the female, highest estrogen receptor density occurs in the anteroventral periventricular region: binding in this region is reduced by approximately 50% in the male, as compared to the female. These data are consistent with the hypothesis that androgen-induced defeminization of feminine behavioral and neuroendocrine responses to estrogen may involve selective reductions in the estrogen sensitivity of critical components of the neural circuitry regulating these responses, mediated in part through a reduction in estrogen receptor biosynthesis.

A direct stereoselective synthesis of 7 beta-hydroxytestosterone

Although 7 beta-hydroxytestosterone is a known product of hepatic androgen metabolism, there are no published methods for its chemical synthesis except from the equally difficult to obtain 7 beta-hydroxy-4-androstene-3,17-dione. We found that several seemingly straightforward routes for its synthesis failed. Consequently, we tried to produce 7 beta-hydroxytestosterone by enzymatic oxidation of 5-androstene-3 beta, 7 beta, 17 beta-triol with cholesterol oxidase (Brevibacterium sp.), a procedure previously used to synthesize 7 beta-hydroxy-4-cholesten-3-one from 3 beta, 7 beta-dihydroxycholesterol (Alexander and Fisher 1995). However, 5-androstene-3 beta, 7 beta, 17 beta-triol was, at best, a very poor substrate for the enzyme leading to the production of 7 beta-hydroxytestosterone in only trace amounts. Thus, we explored a strategy for the enzymatic synthesis in which a C8-ester at C-17 (5-androstene-3 beta, 7 beta, 17 beta-triol 17-caprylate) would serve to mimic the bulky and hydrophobic side chain of cholesterol and thus allow the C19-steroid to act as an effective substrate. When this ester was incubated with cholesterol oxidase, it was converted efficiently to 7 beta-hydroxytestosterone-17-caprylate. Attempts to remove the ester group by several mild hydrolytic procedures caused elimination of the 7 beta-hydroxyl group; we, therefore, obtained 7 beta-hydroxytestosterone by incubation of the intermediate ester with porcine lipase.

7 alpha-iodine-125-iodo-5 alpha-dihydrotestosterone: a radiolabeled ligand for the androgen receptor

We describe the preparation of 7 alpha-[125I]iodo-5 alpha-dihydrotestosterone (7 alpha-[125I]IDHT) and its characterization as a ligand for the androgen receptor.

METHODS

We designed a route to prepare the radioiodine-labeled androgen on microscale through treatment of the 7 beta-tosylate of 7 beta-hydroxy-5 alpha-dihydrotestosterone-17 beta-p-nitro-benzoate with Na125I, followed by alkaline hydrolysis. The radiolabeled steroid was tested as a ligand for the androgen receptor in cytosol from MCF-7 cells, and for its in vivo tissue distribution in the rat. In addition, we tested 7 alpha-[125I]IDHT as a ligand in a novel assay for the detection and quantification of the ligand activated androgen receptor by in vitro autoradiography.

RESULTS

The above synthetic route produced the 17 beta-p-nitrobenzoate of 7 alpha-[125I]IDHT in carrier-free form and in good yield. The 17 beta-ester was removed with alkali and the resulting 7 alpha-[125I]IDHT was purified by HPLC. 7 alpha-[125I]IDHT bound with high affinity, Kd = 0.26 nM, to the androgen receptor and showed low nonspecific binding. Since the ligand was carrier free and thus of very high specific activity, approximately 2,200 Ci/mmole, the sensitivity of the assay was much greater than with [3H]R1881, the classical androgen receptor ligand with which it was compared. When tested as a ligand for in vitro autoradiography, 7 alpha-[125I]IDHT produced excellent autoradiograms of the activated receptor with very low nonspecific binding and with only overnight exposure of the film.

CONCLUSION

These studies demonstrate that 7 alpha-[125I]IDHT is an excellent ligand for the androgen receptor.

Regulation of estrogen receptor concentrations in the rat brain: effects of sustained androgen and estrogen exposure

To determine whether estrogen and androgens either alone or in combination downregulate estrogen receptors in the brain, ovariectomized/adrenalectomized female rats received one of the following four treatments: (1) one subcutaneously placed Silastic capsule containing 10% estradiol in cholesterol, (2) one capsule containing 10% estradiol and two capsules containing 100% 5 alpha-dihydrotestosterone (DHT), (3) two capsules containing DHT, or (4) empty Silastic capsules (control animals). Animals were killed 4 or 8 days after capsule insertion and the occupied, unoccupied and total estrogen receptor content in specific brain nuclei was determined by quantitative in vitro autoradiography. To determine if the effects of the androgen were reversible, DHT capsules were removed after 4 days from half of the estradiol+DHT-treated rats, and the animals were killed 4 days later. Estradiol downregulated estrogen receptor expression in the periventricular preoptic area, medial preoptic area, bed nucleus of the stria terminalis (BNST), arcuate nucleus (ARC), ventromedial nucleus (VMN), and medial and cortical amygdala, decreasing receptor content by 30-41% in animals treated for 4 days, and by 44-60% in animals treated for 8 days with estradiol alone. DHT treatment in combination with estradiol further decreased estrogen receptor content in the BNST, ARC and VMN, relative to the estradiol-only animals. DHT in the absence of estrogen was without effect. In animals in which the DHT capsules were removed after 4 days of exposure, allowing the estradiol to remain for a further 4 days, estrogen receptor levels were indistinguishable from those measured in control animals treated for 8 days with estradiol alone. These results demonstrate that sustained estrogen exposure downregulates levels of estrogen receptor in the brain and confirm that DHT synergizes with estrogen in inducing this response in some, but not all, target neuronal groups.

Sexual differentiation of estrogen receptor concentrations in the rat brain: effects of neonatal testosterone exposure

This study tests the hypothesis that sex differences in estrogen receptor (ER) expression in the rat hypothalamus and preoptic area may at least partly result from androgen exposure during the immediate postnatal period. Male rats were castrated and female rats were injected with androgen, at either 15-30 min, 24 h or 10 days after birth. ER distribution in the brain was evaluated by in vitro autoradiography at 28 days of age. Males castrated immediately after birth exhibited higher ER levels in the preoptic area and the ventromedial and arcuate nuclei of the hypothalamus than either control males or males castrated on day 10. Females injected at birth with testosterone propionate exhibited reduced ER binding in the same brain regions. These data suggest that postnatal androgen secretion prior to postnatal day 10 permanently alters patterns of ER expression in the brain.

Origin of estradiol fatty acid esters in human ovarian follicular fluid

The estradiol fatty acid esters are the most potent of the naturally occurring steroidal estrogens. These esters are present predominantly in fat, where they are sequestered until they are hydrolyzed by esterases. Thus they act as a preformed reservoir of estradiol. We have previously shown that ovarian follicular fluid from patients undergoing gonadotropin stimulation contains very high amounts of estradiol fatty acid esters (approximately 10(-7) M). The source of these esters is unknown. They can be formed by esterification of estradiol in the follicular fluid by lecithin:cholesterol acyltransferase (LCAT), or in the ovary by an acyl coenzyme A:acyltransferase. In order to determine which of these enzymatic processes is the source of the estradiol esters in the follicular fluid, we incubated [3H]estradiol with follicular fluid and cells isolated from human ovarian follicular fluid and characterized the fatty acid composition of the [3H]estradiol esters biosynthesized in each. In addition, we characterized the endogenous estradiol fatty acid esters in the follicular fluid and compared them to the biosynthetic esters. The fatty acid composition of the endogenous esters was different than those synthesized by the cellular acyl coenzyme A:acyltransferase, and the same as the esters synthesized by LCAT, demonstrating that the esters are produced in situ in the follicular fluid. Although the role of these estradiol esters in the ovary is not known, given their remarkable estrogenic potency it is highly probable that they have an important physiological role.

Long-lived testosterone esters in the rat

Over the past decade it has become increasingly clear that steroid hormones are enzymatically esterified with fatty acids. These steroidal esters are the natural analogs of synthetic esters that are used therapeutically. One such family of pharmacological steroids is the synthetic alkyl esters of testosterone, androgens with great hormonal potency. We have investigated whether testosterone esters exist naturally by using the rat as a model. Most tissues of male rats, including blood, have very little if any ester (quantified by immunoassay as a nonpolar saponifiable metabolite), but fat and testes have sizable quantities, approximately 3 ng of testosterone equivalents per g of tissue. Testosterone in fat averages 9 ng/g. The fat from female rats and long-term (> 2 weeks) castrated males has no detectable testosterone ester. The presence of testosterone esters was confirmed by GC/MS, which clearly showed the presence of testosterone in the hydrolyzed ester fraction of fat from intact males but not long-term castrates. Upon castration, testosterone levels in the fat completely disappear within 6 hr. To the contrary, it is not until 48 hr after castration that a measurable fall in the testosterone ester fraction was observed; even after 10 days a small amount of ester is still present in the fat. These experiments demonstrate the existence of a previously unknown androgen with a potentially important physiological impact; testosterone esters, natural analogs of potent therapeutic agents, occur in the fat where they can serve as a reservoir of preformed androgen to stimulate neighboring target tissues.

A comparison of the esterification of steroids by rat lecithin:cholesterol acyltransferase and acyl coenzyme A:cholesterol acyltransferase

Although fatty acid esters of several steroids have been found in both blood and tissues, their biosynthetic origins are uncertain. For example, the fatty acid esters of delta 5-3 beta-hydroxysteroids pregnenolone and dehydroepiandrosterone (DHEA) are synthesized in tissues by an acyl coenzyme A:acyltransferase. These esters are not secreted, and the circulating esters are formed in blood by lecithin:cholesterol acyltransferase (LCAT). Fatty acid esters of corticosterone (B) and estradiol (E2) are also present in both blood and tissues, but unlike the delta 5-3 beta-hydroxysteroids, their structures are so different from cholesterol that it would not necessarily follow that they are esterified by the same enzyme. We have examined the esterification of the steroids DHEA, B, and E2 in blood and tissue, in comparison to the esterification of cholesterol, using as a model plasma and hepatic microsomes from the rat. All of the steroids were esterified in plasma, but at very different rates: cholesterol > DHEA >> E2 = B. The LCAT inhibitor, 5.5'-dithiobis-(2-nitrobenzoic acid), inhibited the esterification of all of the substrates. DHEA inhibited the esterification of cholesterol, albeit only at high concentration. The fatty acid compositions of the cholesterol and DHEA esters were analyzed, and they were found to be identical, with arachidonate the predominant ester, greater than 60%. In hepatic microsomes, the rate of esterification was different than plasma: cholesterol > E2 > or = DHEA >> B. Although B was esterified in both plasma and hepatic microsomes, the rate was exceedingly slow in both. The acyl coenzyme A:cholesterol acyltransferase inhibitor, N'-(2,4-difluorophenyl)-N-[[4-(2,2-dimethylpropyl)phenyl]- methyl]-N-heptylurea, blocked the esterification of cholesterol almost completely, but surprisingly, it had no effect on the esterification of the other steroids. The fatty acid esters of cholesterol, E2, and DHEA synthesized in the hepatic microsomes were analyzed. The composition of the cholesterol esters from the microsomes was very different than the esters of DHEA and E2. These results show that all of the steroids tested are esterified by LCAT, and consequently that blood LCAT is the probable source of the circulating steroidal esters. Most interesting are the studies of microsomal esterification. It has been presumed that similar to blood, the esterification of steroids in tissues is carried out by the same enzyme that esterifies cholesterol.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of occupied and unoccupied estrogen receptors in the rat brain: effects of physiological gonadal steroid exposure

In vitro autoradiographic methods have been developed for selective measurement of occupied and unoccupied estrogen receptors (ERs) in brain tissue sections. Addition of protamine sulfate traps unoccupied ERs in the tissue sections, allowing them to be detected after a short period of incubation with labeled estrogen. Occupied ERs are assessed, after washing in buffer without protamine to eliminate unoccupied receptor, by incubating the sections for 2 h at 37 C to exchange isotopically labeled steroid for the endogenous unlabeled ligand. Total ER binding capacity is estimated by summing the values for occupied and unoccupied ER. In all brain regions of normal females, ER occupation is low at estrus, reflecting the very low levels of circulating estradiol present at this stage of the estrous cycle, rising to approximately 50% of binding capacity at proestrus. By contrast, in intact males ER occupation varies considerably between brain regions, from a high of 55% of binding capacity in the bed nucleus of the stria terminalis to a low of 21% in the hypothalamic arcuate nucleus. Gonadectomy or treatment of intact males with the aromatase inhibitor 4-hydroxy androstenedione greatly reduces or eliminates ER occupation, depending on the brain region. In both sexes, changes in levels of endogenous gonadal steroids have little effect on total (occupied plus unoccupied) ER concentrations, with the exception of the hypothalamic ventromedial nucleus of the female, in which total ER concentration declines at estrus. These results are consistent with the hypothesis that local aromatization may be the primary determinant of regional ER occupation in the brain of the male rat, in contrast to the female, in which high levels of ER occupation are found only during the preovulatory estrogen surge. Although physiological changes in circulating estradiol and aromatizable androgen concentrations induce large changes in ER occupation, they have little effect on total ER content in most regions of the brain, suggesting that previous reports of changes in ER messenger RNA levels under different conditions of gonadal steroid exposure may not be directly reflected in steady state levels of the cognate receptor site.

Sex differences in the development of estrogen receptors in the rat brain

The mechanisms involved in sexual differentiation of the brain remain incompletely defined. In mammals, testosterone secretion by the male during early development permanently alters the capacity of the brain to respond to circulating estrogen. In rats, this change in estrogen responsiveness is associated with a reduction in estrogen receptor (ER) levels in the periventricular region of the preoptic area (PVP), the medial preoptic nucleus (MPO), and the hypothalamic ventromedial nucleus (VMN) of the male. To determine whether these differences represent a response to early testosterone exposure or a secondary consequence of gonadal secretions at puberty, ER levels were measured by quantitative in vitro autoradiography in the brains of rats killed at intervals between 1-10 and 28-49 days of age. As early as 24 hr after birth, ER sex differences in the MPO and PVP are already quantitatively similar to those observed in adulthood. A sex difference in the VMN emerges later, between 5 and 10 days of age. Differences between brain regions are also observed in the rate of ER development after the first week of life, ER concentrations in the PVP and MPO being close to adult levels within 1 day of birth, in contrast to the VMN where they increase markedly between Day 10 and adulthood in both sexes. These observations suggest that changes in ER concentrations may be one of the earliest hallmarks of brain sexual differentiation. Sex differences in ER in different brain regions may, however, be expressed asynchronously, providing a possible mechanism for variation in the duration of "critical periods" for testosterone-mediated organization of specific CNS functions.

Androgen treatment decreases estrogen receptor binding in the ventromedial nucleus of the rat brain: a quantitative in vitro autoradiographic analysis

Androgens oppose the actions of estrogen on a number of neuroendocrine functions in the rat including prolactin and gonadotropin secretion and the activation of the female pattern of sex behavior. Although in nonneural tissues antiestrogenic actions of androgens have been related to actions at the level of the estrogen receptor, previous attempts to demonstrate effects of nonaromatizable androgens on estrogen receptor levels in the brain have been unsuccessful, possibly because of the poor anatomical resolution of the methods used. We have used a new in vitro autoradiographic assay combined with an 125I-labeled estrogen receptor ligand to test the hypothesis that the nonaromatizable androgen, 5 alpha-dihydrotestosterone (5 alpha-DHT), may act to reduce estrogen binding in specific regions of the brain involved in reproductive neuroendocrine and behavioral responses. This in vitro autoradiographic method allows selective measurement of occupied estrogen receptors in tissue sections. Gonadectomized/adrenalectomized rats were divided into two groups per sex. All animals received daily injections of estradiol benzoate (EB: 40 micrograms/kg body wt) for 4 days. Animals in the 5 alpha-DHT treatment group received 5 alpha-DHT (10 mg/kg body wt) every 12 h for 4 days, while animals in the control group received vehicle injections. Animals were killed 4 h after the final EB/5 alpha-DHT injection and their brains processed for in vitro autoradiography. As previously reported, higher levels of estrogen binding were observed in the ventrolateral aspect of the ventromedial nucleus (vIVMN) and the periventricular and medial preoptic area of the female compared to the male.(ABSTRACT TRUNCATED AT 250 WORDS)

Pubertal development of estrogen receptors in the rat brain

The regional distribution of estrogen receptors (ER) was studied in the brain of the female rat over the peripubertal period. Increases were observed in nuclear ER occupation as well as cytosolic progestin receptor induction in the period leading up to the time of vaginal opening, consistent with an increased availability of estrogen to the brain. ER binding capacity, however, was remarkably similar in pre- and postpubertal rats. Using a microdissection-based nuclear ER assay, small increases in the total ER content of the hypothalamic ventromedial and arcuate nuclei were observed in the female at around the time of the onset of reproductive cyclicity. In vivo autoradiographic studies confirmed the existence of a small increase in estrogen binding in these two brain regions at around the time of vaginal opening, as well as transient increases in estrogen retention within the preoptic area and bed nucleus of the stria terminalis. These changes in estrogen binding in the brain may play a role in pubertal alterations in the feedback sensitivity of the brain to circulating estrogen.

Partial demasculinization and feminization of sex behavior in male rats by in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin is not associated with alterations in estrogen receptor binding or volumes of sexually differentiated brain nuclei

In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure partially demasculinizes and feminizes sexual behavior in adult male rats, presumably by causing incomplete sexual differentiation of the central nervous system (CNS). Our objective was to determine if TCDD exposure affects other aspects of sexual differentiation of the CNS. Because sex differences in the estrogen receptor system are thought to play a role in sexually dimorphic estrogen-mediated responses, and because estrogen is an important activator of both male and female sex behavior, the possible effect of TCDD exposure on estrogen binding in specific brain nuclei was examined. In addition, we investigated effects of in utero and lactational TCDD exposure on sex differences in the volumes of brain nuclei which are dependent on steroid hormone stimulation during the period of CNS sexual differentiation. Pregnant Holtzman rats were given TCDD (0.7 microgram/kg, po) or vehicle (control) on gestation Day 15. Offspring were exposed to TCDD in utero and via lactation and then assessed in adulthood. Demasculinized sexual behavior was evidenced in the TCDD-exposed males by increased intromission latencies and a greater number of intromissions prior to ejaculation. These males were then castrated, primed with ovarian steroids, and tested for feminine sexual behavior. In utero and lactational TCDD exposure increased both the frequency and intensity of lordotic behavior, indicating that the males were partially feminized. To determine if TCDD exposure had a generalized effect on estrogen receptor concentrations the arcuate nucleus, cortical and medical amygdala and the bed nucleus of the stria terminalis, previously found to have equivalent numbers of estrogen receptors in males and females, were evaluated in littermates of the rats whose sexual behavior had been assessed. TCDD had no effect in either sex. To determine if TCDD exposure had an effect specific to sexual differentiation of the brain, estrogen receptor concentrations in the medial preoptic nucleus (MPO), ventrolateral aspect of the ventro-medial nucleus, and periventricular preoptic area were assessed. As expected, females had higher estrogen receptor concentrations in these nuclei than did males, but TCDD exposure did not affect estrogen receptor concentrations in any of these sexually dimorphic brain nuclei. The volumes of sexually dimorphic brain nuclei were examined in additional littermates. In control rats, the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in males than in females whereas the MPO is larger in females than in males. TCDD exposure had no effect on the volume of either the SDN-POA or MPO in either males or females.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis and evaluation of 7 alpha-iodo-5 alpha-dihydrotestosterone as a potential radioligand for androgen receptor

7 alpha-Iodo-17 beta-hydroxy-5 alpha-androstan-3-one (7 alpha-iodo-5 alpha-dihydrotestosterone, 7 alpha-IDHT) has been synthesized as a potential radioligand for the detection and measurement of androgen receptor and for imaging of androgen-receptor-containing tissues when labeled with the gamma-emitting radionuclides 125I and 123I, respectively. In vitro binding studies show that 7 alpha-IDHT binds with high affinity to the rat and human androgen receptor (RBA = 74) compared to R1881 (RBA = 100). Further, this compound showed high specificity for the androgen receptor. 7 alpha-IDHT showed only a marginal affinity for the progestin receptor and even less affinity for the estrogen receptor. No binding was detected to the glucocorticoid receptor. These characteristics make 7 alpha-IDHT a potentially ideal agent for imaging and evaluation of androgen-receptor-containing tissues.

Rapid stimulation of rhodamine 123 efflux from multidrug-resistant KB cells by progesterone

Rhodamine 123 is a mitochondrial dye that is retained for prolonged periods by carcinoma cells. While investigating causes of retention of this dye, we found that 10 microM progesterone caused a rapid stimulation of efflux of rhodamine 123 within 15 min from KB V20C cells, which overexpress the multidrug resistance pump. Progesterone did not stimulate efflux from KB cells that do not overexpress the pump, and verapamil blocked rhodamine 123 efflux in the presence or absence of progesterone, indicating that rhodamine 123 is removed from KB V20C cells by the multidrug resistance pump. Progesterone, however, is unlikely to stimulate rhodamine 123 efflux by simply increasing pump activity for two reasons: (1) progesterone inhibited the efflux of daunomycin from KB V20C cells, so it did not stimulate efflux of all drugs, and (2) progesterone inhibited efflux of rhodamine 123 from L1210/VMDRC cells and had little effect on Adr MCF7 cells; both overexpress the multidrug resistance pump. In the experiments with KB V20C cells, progesterone was the most active steroid tested. At 10 microM, progesterone caused a 70-fold stimulation, desoxycorticosterone, testosterone, promegestone and estradiol about 20-fold, and others had little or no effect. Progesterone may act by a non-genomic mechanism to decrease intracellular binding of rhodamine 123, making the dye accessible to the multidrug resistance pump.

In vitro autoradiographic visualization of occupied estrogen receptors in the rat brain with an iodinated estrogen ligand

Methods have been developed for the selective measurement of occupied estrogen receptors (ER) in brain tissue sections. Cryostat sections of unfixed tissue were incubated with radiolabeled estrogen at physiological temperatures, displacing endogenous receptor-bound estrogen by radioligand and thereby allowing the receptor complexes to be visualized autoradiographically after washing to remove nonspecifically bound steroid. The resultant autoradiographs were analyzed by computer-assisted densitometry. Synthetic 11 beta-methoxy-substituted radiolabeled estrogens gave the best autoradiographic images, as a result of reduced nonspecific labeling, although [3H]-estradiol was also used successfully. With the synthetic ER ligand 11 beta-methoxy 16 alpha-[125I]-iodo-estradiol, exposure times of less than 24 hr generated acceptable autoradiographs; with 3H-labeled estrogens, exposures of 3 months or more may be required. The method is sufficiently sensitive to detect physiological changes in ER occupation and to allow determination of receptor affinities and saturation binding capacities in discrete cell groups identified in sections from individual animals.

The isolation and characterization of estradiol-fatty acid esters in human ovarian follicular fluid. Identification of an endogenous long-lived and potent family of estrogens

The estradiol-fatty acid esters are highly potent and long-lived estrogens that were first isolated and identified from in vitro biosynthetic experiments (Mellon-Nussbaum S., Ponticorvo, L., Schatz, F., and Hochberg, R. B. (1982) J. Biol. Chem. 257, 5678-5684). Other studies have indicated that these esters exist endogenously, but the evidence is indirect, resting solely on the presence of a nonpolar saponifiable metabolite. Although there are similar reports of other naturally occurring fatty acid esters of biologically active steroid hormones, likewise, none has been isolated and characterized. In this study we have found that follicular fluid from the ovaries of women stimulated with gonadotrophins contains relatively large amounts of a nonpolar saponifiable derivative of estradiol (approximately 10(-7)M), which we presumed to be fatty acid esters. Using a combination of chromatographic techniques we isolated these estradiol metabolites and identified them by mass spectral analysis. They are a mixture of five different estradiol-17 fatty acid esters. The amount of each present was determined by separating the esters by reversed phase high performance liquid chromatography and then quantifying each peak by radioimmunoassay and UV absorption. The esters of estradiol are predominantly unsaturated, with linoleate the most abundant comprising 43% of the total. The other esters are: palmitate (20%), arachidonate (19%), oleate (14%), and stearate (4%). Thus these studies conclusively demonstrate the existence of these unusually powerful estrogens.

7 alpha-Methyl-17 alpha-(E-2'-[125I]iodovinyl)-19-nortestosterone: a new radioligand for the detection of androgen receptor

We have synthesized two gamma-emitting, 125I-labeled steroids, E- and Z-7 alpha-methyl-17 alpha-(2'-[125I]iodovinyl)-19-nortestosterone [125I](E- and Z-MIVNT) for specific labeling of androgen receptors. [125I]E- and [125I]Z-MIVNT were synthesized stereospecifically from E- and Z-7 alpha-methyl-17 alpha-(2'-tri-n-butylstannyl-vinyl)-19-nortestosterone. The tin adducts were prepared by addition of tri-n-butyltin hydride to 7 alpha-methyl-17 alpha-ethynyl-19-nortestosterone, and after purification they were converted in high yield to the [125I]MIVNT isomers by reaction with 125I (generated in situ by oxidation of [125I]iodide with chloramine T). The 125I-labeled products were purified by high-performance liquid chromatography, and their mass determined with an ultraviolet detector (specific activity of both, approximately 2,200 Ci/mmol). In rat prostate cytosol, [125I]E-MIVNT bound with high affinity to a single class of binding sites. Nonspecific binding in the presence of 5 alpha-dihydrotestosterone was relatively low, and compared favorably with that obtained in parallel studies with [3H]methyltrienolone (R1881). The E-isomer bound prostate cytosol with at least twice the affinity of the Z-isomer; therefore, the interaction of the E-isomer with the androgen receptor as well as other steroid receptors was studied in greater detail. Complexes of the androgen receptor with [125I]E-MIVNT as well as [3H]R1881 dissociate very slowly at 4C (kdiss for both = 0.04 h-1). Displacement studies showed that the interaction of [125I]E-MIVNT with the androgen receptor is highly specific. Competition studies showed that unlabeled E-MIVNT binds poorly to other steroid receptors in rat tissue cytosols. These binding properties make [125I]E-MIVNT a promising ligand for study of the androgen receptor, and [123I]E-MIVNT a potential imaging agent for the detection of androgen-dependent tumors, such as prostate cancer.

Aromatase and testosterone fatty acid esters: the search for a cryptic biosynthetic pathway to estradiol esters

The estradiol fatty acid esters (lipoidal derivatives, LE2) are extremely potent estrogens that accumulate in fat, including fat of menopausal women. These steroidal esters are protected from metabolism and are converted to the free, biologically active steroid through the action of esterases. Previous studies have shown that biosynthetic pathways in the adrenal gland exist in which steroid fatty acid esters are substrates. This led us to determine whether a cryptic aromatase pathway exists in which testosterone esters could be converted directly into LE2. We tested a representative fatty acid ester, testosterone stearate, both as an inhibitor and as a substrate for the aromatase enzyme from human placental microsomes. This ester had neither activity. In addition, we tested [1 beta-3H]testosterone acetate as a substrate for this enzyme complex, measuring the production of 3H2O as evidence of aromatization. Although the rate of reaction was considerably slower than that of testosterone, 3H2O was produced. However, when [2, 4, 6, 7-3H]testosterone acetate was incubated and the steroidal products isolated, we found that hydrolysis of the substrate had occurred. Both [3H]-labeled testosterone and estradiol were found, and very little if any [3H]estradiol acetate was formed. Thus, we conclude that an aromatase pathway involving testosterone esters does not exist and that the sole source of LE2 is through direct esterification of estradiol.

Measurement of estradiol-17-fatty acid esters in human tissues

We have developed a gas chromatographic/mass spectral method for the sensitive and reproducible measurement of estradiol-17-fatty acid esters in human tissues and blood. To provide an internal standard for quantification, a trideuterated analog of a representative estradiol ester is added to the tissues. Estradiol (E2) released from the nonpolar ester fraction by alkaline hydrolysis is derivatized to form the ditrimethylsilyl ether and then analyzed by gas chromatographic/mass spectral, monitoring the molecular ions mass per U charge of the ditrimethylsilyl derivative of E2 and [2H3]E2. There are low but detectable levels of E2 ester in the blood of cycling females; there are none in urine. While the E2 ester is present in breast cyst fluid, its concentration, 77-140 pmol/L, is considerably less than E2, 110-2,863 pmol/L. But there is a large amount of E2 ester in fat. In premenopausal women the average E2 ester in fat (sc and omental) is 957 +/- 283 38 fmol/g (SEM); in women who are menopausal less than 12 yr, the E2 ester in fat is 669 +/- 158 fmol/g; in women who are menopausal at least 15 yr, the fat level is 399 +/- 146 fmol/g. Muscle from the same women have lower concentrations of the ester; in 8 out of 12 muscle specimens it was not detectable. The E2 esters are extremely potent estrogens. Although they are hormonally active they require enzymatic hydrolysis to exert their hormonal action. These studies show that these long chain esters of E2 are sequestered in fatty tissues, wherein they represent a protected store of preformed hormone. Under the proper stimulation, adipose tissue can activate the estrogenic signal through the action of hormonally sensitive esterases. Thus, through signaling between estrogen sensitive tissues and neighboring fat cells, a local paracrine loop may exist.

Estrogen receptors colocalize with low-affinity nerve growth factor receptors in cholinergic neurons of the basal forebrain

The rodent and primate basal forebrain is a target of a family of endogenous peptide signaling molecules, the neurotrophins--nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3--and of the gonadal steroid hormone estrogen, both of which have been implicated in cholinergic function. To investigate whether or not these ligands may act on the same neurons in the developing and adult rodent basal forebrain, we combined autoradiography with 125I-labeled estrogen and either nonisotopic in situ hybridization histochemistry or immunohistochemistry. We now report colocalization of intranuclear estrogen binding sites with the mRNA and immunoreactive protein for the low-affinity nerve growth factor receptor, which binds all three neurotrophins, and for the cholinergic marker enzyme choline acetyltransferase (acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6). Colocalization of estrogen and low-affinity nerve growth factor receptors implies that their ligands may act on the same neuron, perhaps synergistically, to regulate the expression of specific genes or gene networks that may influence neuronal survival, differentiation, regeneration, and plasticity. That cholinergic neurons in brain regions subserving cognitive functions may be regulated not only by the neurotrophins but also by estrogen may have considerable relevance for the development and maintenance of neural substrates of cognition. If estrogen-neurotrophin interactions are important for survival of target neurons, then clinical conditions associated with estrogen deficiency could contribute to the atrophy or death of these neurons. These findings have implications for the subsequent decline in those differentiated neural functions associated with aging and Alzheimer disease.