# Estrone sulfate

Estrone sulfate, also known as E1S, E1SO4 and estrone 3-sulfate, is a natural, endogenous steroid and an estrogen ester and conjugate.
In addition to its role as a natural hormone, estrone sulfate is used as a medication, for instance in menopausal hormone therapy; for information on estrone sulfate as a medication, see the estrone sulfate (medication) article.

## Biological function

E1S itself is biologically inactive, with less than 1% of the relative binding affinity of estradiol for the ERα and ERβ. However, it can be transformed by steroid sulfatase, also known as estrogen sulfatase, into estrone, an estrogen. Simultaneously, estrogen sulfotransferases, including SULT1A1 and SULT1E1, convert estrone to E1S, resulting in an equilibrium between the two steroids in various tissues. Estrone can also be converted by 17β-hydroxysteroid dehydrogenases into the more potent estrogen estradiol. E1S levels are much higher than those of estrone and estradiol, and it is thought to serve as a long-lasting reservoir for estrone and estradiol in the body. In accordance, E1S has been found to transactivate the estrogen receptor at physiologically relevant concentrations. This was diminished with co-application of irosustat (STX-64), a steroid sulfatase inhibitor, indicating the importance of transformation of estrone sulfate into estrone in the estrogenicity of E1S.
Unlike unconjugated estradiol and estrone, which are lipophilic compounds, E1S is an anion and is hydrophilic. As a result of this, whereas estradiol and estrone are able to readily diffuse through the lipid bilayers of cells, E1S is unable to permeate through cell membranes. Instead, estrone sulfate is transported into cells in a tissue-specific manner by active transport via organic-anion-transporting polypeptides (OATPs), including OATP1A2, OATP1B1, OATP1B3, OATP1C1, OATP2B1, OATP3A1, OATP4A1, and OATP4C1, as well as by the sodium-dependent organic anion transporter (SOAT; SLC10A6).
E1S, serving as a precursor and intermediate for estrone and estradiol, may be involved in the pathophysiology of estrogen-associated diseases including breast cancer, benign breast disease, endometrial cancer, ovarian cancer, prostate cancer, and colorectal cancer. For this reason, enzyme inhibitors of steroid sulfatase and 17β-hydroxysteroid dehydrogenase and inhibitors of OATPs, which prevent activation of E1S into estrone and estradiol, are of interest in the potential treatment of such conditions.
vte Affinities and estrogenic potencies of estrogen esters and ethers at the estrogen receptors :
| Estrogen | Other names | RBATooltip Relative binding affinity (%)$^a$ | REP (%)$^b$ | REP (%)$^b$ |
| Estrogen | Other names | ER | ERα | ERβ |
| Estradiol | E2 | 100 | 100 | 100 |
| Estradiol 3-sulfate | E2S; E2-3S | ? | 0.02 | 0.04 |
| Estradiol 3-glucuronide | E2-3G | ? | 0.02 | 0.09 |
| Estradiol 17β-glucuronide | E2-17G | ? | 0.002 | 0.0002 |
| Estradiol benzoate | EB; Estradiol 3-benzoate | 10 | 1.1 | 0.52 |
| Estradiol 17β-acetate | E2-17A | 31–45 | 24 | ? |
| Estradiol diacetate | EDA; Estradiol 3,17β-diacetate | ? | 0.79 | ? |
| Estradiol propionate | EP; Estradiol 17β-propionate | 19–26 | 2.6 | ? |
| Estradiol valerate | EV; Estradiol 17β-valerate | 2–11 | 0.04–21 | ? |
| Estradiol cypionate | EC; Estradiol 17β-cypionate | ?$^c$ | 4.0 | ? |
| Estradiol palmitate | Estradiol 17β-palmitate | 0 | ? | ? |
| Estradiol stearate | Estradiol 17β-stearate | 0 | ? | ? |
| Estrone | E1; 17-Ketoestradiol | 11 | 5.3–38 | 14 |
| Estrone sulfate | E1S; Estrone 3-sulfate | 2 | 0.004 | 0.002 |
| Estrone glucuronide | E1G; Estrone 3-glucuronide | ? | <0.001 | 0.0006 |
| Ethinylestradiol | EE; 17α-Ethynylestradiol | 100 | 17–150 | 129 |
| Mestranol | EE 3-methyl ether | 1 | 1.3–8.2 | 0.16 |
| Quinestrol | EE 3-cyclopentyl ether | ? | 0.37 | ? |
| Footnotes: $^a$ = Relative binding affinities (RBAs) were determined via in-vitro displacement of labeled estradiol from estrogen receptors (ERs) generally of rodent uterine cytosol. Estrogen esters are variably hydrolyzed into estrogens in these systems (shorter ester chain length -> greater rate of hydrolysis) and the ER RBAs of the esters decrease strongly when hydrolysis is prevented. $^b$ = Relative estrogenic potencies (REPs) were calculated from half-maximal effective concentrations (EC$_{50}$) that were determined via in-vitro β‐galactosidase (β-gal) and green fluorescent protein (GFP) production assays in yeast expressing human ERα and human ERβ. Both mammalian cells and yeast have the capacity to hydrolyze estrogen esters. $^c$ = The affinities of estradiol cypionate for the ERs are similar to those of estradiol valerate and estradiol benzoate (figure). Sources: See template page. |||||

## Chemistry

E1S, also known as estrone 3-sulfate or as estra-1,3,5(10)-trien-17-one 3-sulfate, is a naturally occurring estrane steroid and a derivative of estrone. It is an estrogen conjugate or ester, and is specifically the C3 sulfate ester of estrone. Related estrogen conjugates include estradiol sulfate, estriol sulfate, estrone glucuronide, estradiol glucuronide, and estriol glucuronide, while related steroid conjugates include dehydroepiandrosterone sulfate and pregnenolone sulfate.
The logP of E1S is 1.4.

## Biochemistry
### Biosynthesis

E1S is produced via estrogen sulfotransferases from the peripheral metabolism of the estrogens estradiol and estrone. Estrogen sulfotransferases are expressed minimally or not at all in the gonads. In accordance, E1S is not secreted in meaningful amounts from the gonads in humans. However, measurable amounts of estrogen sulfates are said to be secreted by the ovaries in any case.
vte Production rates, secretion rates, clearance rates, and blood levels of major sex hormones :
| Sex | Sex hormone | Reproductive phase | Blood production rate | Gonadal secretion rate | Metabolic clearance rate | Reference range (serum levels) | Reference range (serum levels) |
| Sex | Sex hormone | Reproductive phase | Blood production rate | Gonadal secretion rate | Metabolic clearance rate | SI units | Non-SI units |
| Men | Androstenedione | – | 2.8 mg/day | 1.6 mg/day | 2200 L/day | 2.8–7.3 nmol/L | 80–210 ng/dL |
| Men | Testosterone | – | 6.5 mg/day | 6.2 mg/day | 950 L/day | 6.9–34.7 nmol/L | 200–1000 ng/dL |
| Men | Estrone | – | 150 μg/day | 110 μg/day | 2050 L/day | 37–250 pmol/L | 10–70 pg/mL |
| Men | Estradiol | – | 60 μg/day | 50 μg/day | 1600 L/day | <37–210 pmol/L | 10–57 pg/mL |
| Men | Estrone sulfate | – | 80 μg/day | Insignificant | 167 L/day | 600–2500 pmol/L | 200–900 pg/mL |
| Women | Androstenedione | – | 3.2 mg/day | 2.8 mg/day | 2000 L/day | 3.1–12.2 nmol/L | 89–350 ng/dL |
| Women | Testosterone | – | 190 μg/day | 60 μg/day | 500 L/day | 0.7–2.8 nmol/L | 20–81 ng/dL |
| Women | Estrone | Follicular phase | 110 μg/day | 80 μg/day | 2200 L/day | 110–400 pmol/L | 30–110 pg/mL |
| Women | Estrone | Luteal phase | 260 μg/day | 150 μg/day | 2200 L/day | 310–660 pmol/L | 80–180 pg/mL |
| Women | Estrone | Postmenopause | 40 μg/day | Insignificant | 1610 L/day | 22–230 pmol/L | 6–60 pg/mL |
| Women | Estradiol | Follicular phase | 90 μg/day | 80 μg/day | 1200 L/day | <37–360 pmol/L | 10–98 pg/mL |
| Women | Estradiol | Luteal phase | 250 μg/day | 240 μg/day | 1200 L/day | 699–1250 pmol/L | 190–341 pg/mL |
| Women | Estradiol | Postmenopause | 6 μg/day | Insignificant | 910 L/day | <37–140 pmol/L | 10–38 pg/mL |
| Women | Estrone sulfate | Follicular phase | 100 μg/day | Insignificant | 146 L/day | 700–3600 pmol/L | 250–1300 pg/mL |
| Women | Estrone sulfate | Luteal phase | 180 μg/day | Insignificant | 146 L/day | 1100–7300 pmol/L | 400–2600 pg/mL |
| Women | Progesterone | Follicular phase | 2 mg/day | 1.7 mg/day | 2100 L/day | 0.3–3 nmol/L | 0.1–0.9 ng/mL |
| Women | Progesterone | Luteal phase | 25 mg/day | 24 mg/day | 2100 L/day | 19–45 nmol/L | 6–14 ng/mL |
| Notes and sources Notes: "The concentration of a steroid in the circulation is determined by the rate at which it is secreted from glands, the rate of metabolism of precursor or prehormones into the steroid, and the rate at which it is extracted by tissues and metabolized. The secretion rate of a steroid refers to the total secretion of the compound from a gland per unit time. Secretion rates have been assessed by sampling the venous effluent from a gland over time and subtracting out the arterial and peripheral venous hormone concentration. The metabolic clearance rate of a steroid is defined as the volume of blood that has been completely cleared of the hormone per unit time. The production rate of a steroid hormone refers to entry into the blood of the compound from all possible sources, including secretion from glands and conversion of prohormones into the steroid of interest. At steady state, the amount of hormone entering the blood from all sources will be equal to the rate at which it is being cleared (metabolic clearance rate) multiplied by blood concentration (production rate = metabolic clearance rate × concentration). If there is little contribution of prohormone metabolism to the circulating pool of steroid, then the production rate will approximate the secretion rate." Sources: See template. ||||||||

### Distribution

Whereas free steroids like estradiol are lipophilic and can enter cells via passive diffusion, steroid conjugates like E1S are hydrophilic and are unable to do so. Instead, steroid conjugates require active transport via membrane transport proteins to enter cells.
Studies in animals and humans have had mixed findings on uptake of exogenously administered E1S in normal and tumorous mammary gland tissue. This is in contrast to substantial uptake of exogenously administered estradiol and estrone by the mammary glands. Another animal study found that E1S wasn't taken up by the uterus but was taken up by the liver, where it was hydrolyzed into estrone.

### Metabolism

The elimination half-life of E1S is 10 to 12 hours. Its metabolic clearance rate is 80 L/day/m$^2$.
Ovarian tumors have been found to express steroid sulfatase and have been found to convert E1S into estradiol. This may contribute to the often elevated levels of estradiol observed in women with ovarian cancer.
* vte Metabolic pathways of estradiol in humans
* Estradiol
* Estrone sulfate
* Estrone glucuronide
* 2-Hydroxyestrone
* Estrone
* 4-Hydroxyestrone
* 2-Methoxyestrone
* 16α-Hydroxyestrone
* 4-Methoxyestrone
* 17-Epiestriol
* Estriol
* 16-Epiestriol
* 17β-HSD
* EST
* STS
* UGT1A3 UGT1A9
* CYP450
* CYP450
* COMT
* CYP450
* COMT
* unidentified
* 17β-HSD
* unidentified
* Description: The metabolic pathways involved in the metabolism of estradiol and other natural estrogens (e.g., estrone, estriol) in humans. In addition to the metabolic transformations shown in the diagram, conjugation (e.g., sulfation and glucuronidation) occurs in the case of estradiol and metabolites of estradiol that have one or more available hydroxyl (–OH) groups. Sources: See template page.

### Levels

E1S levels have been characterized in humans. E1S using radioimmunoassay (RIA) have been reported to be 0.96 ± 0.11 ng/mL in men, 0.96 ± 0.17 ng/mL during the follicular phase in women, 1.74 ± 0.32 ng/mL during the luteal phase in women, 0.74 ± 0.11 ng/mL in women taking oral contraceptives, 0.13 ± 0.03 ng/mL in postmenopausal women, and 2.56 ± 0.47 ng/mL in postmenopausal women on menopausal hormone therapy. In addition, E1S levels in pregnant women were 19 ± 5 ng/mL in the first trimester, 66 ± 31 ng/mL in the second trimester, and 105 ± 22 ng/mL in the third trimester. E1S levels are about 10 to 15 times higher than those of estrone in women.