Lipoidal estradiol (LE2) is the variety of

endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, es ...

C17β long-chain

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

s of

estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development of f ...

which are formed as

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

s of estradiol. Important examples of these esters include estradiol arachidonate, estradiol lineolate,

estradiol oleate Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...

estradiol palmitate Estradiol palmitate (brand name Esmopal), or estradiol monopalmitate, also known as estradiol 17β-hexadecanoate, is a naturally occurring steroidal estrogen and an estrogen ester – specifically, the C17β palmitate ester of estradiol. It occu ...

, and

estradiol stearate Estradiol stearate (E2-17-St), also known as estradiol octadecanoate and sold under the brand name Depofollan, is a naturally occurring estrogen and an estrogen ester – specifically, the C17β stearate ester of estradiol. It occurs in the body ...

. LE2 are

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

s but do not bind to the

estrogen receptor Estrogen receptors (ERs) are a group of proteins found inside cells. They are receptors that are activated by the hormone estrogen ( 17β-estradiol). Two classes of ER exist: nuclear estrogen receptors (ERα and ERβ), which are members of the ...

, instead acting as

prohormone A prohormone is a committed Precursor (chemistry), precursor of a hormone consisting of peptide hormones synthesized together that has a minimal hormonal effect by itself because of its expression-suppressing structure, often created by protein fol ...

s of estradiol. Relative to estradiol, they have far longer-lasting durations of effect due to their much slower rates of

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

and clearance. It has been hypothesized that LE2 may serve as a store of estrogen for when estradiol levels become low. LE2 are highly

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...

and

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

and are found in highest concentrations in

adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular e ...

and other estrogen-sensitive tissues and in low but detectable concentrations in circulation, with none

excreted Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after lea ...

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

. They have been referred to as the "endogenous counterparts of the synthetic esters of estrogens" like

estradiol valerate Estradiol valerate (EV), sold for use by mouth under the brand name Progynova and Primiwal E4 and for use by injection under the brand names Delestrogen and Progynon Depot among others, is an estrogen medication. It is used in hormone therapy fo ...

and

estradiol cypionate Estradiol cypionate (EC), sold under the brand name Depo-Estradiol among others, is an estrogen (medication), estrogen medication which is used in Hormone replacement therapy, hormone therapy for menopausal symptoms and hypoestrogenism, low estrog ...

. Two of the estradiol esters that compose LE2, estradiol palmitate and estradiol stearate, have been developed and marketed for medical use as long-acting estrogens for use via

depot Depot ( or ) may refer to: Places * Depot, Poland, a village * Depot Island, Kemp Land, Antarctica * Depot Island, Victoria Land, Antarctica * Depot Island Formation, Greenland Brands and enterprises * Maxwell Street Depot, a restaurant in ...

intramuscular injection Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles have ...

. Estradiol is esterified into LE2 by

lecithin–cholesterol acyltransferase Lecithin–cholesterol acyltransferase (LCAT, also called phosphatidylcholine–sterol O-acyltransferase) is an enzyme, in many animals including humans, that converts free cholesterol into cholesteryl ester (a more hydrophobic form of cholester ...

(LCAT).

References

Estradiol esters Estranes Estrogens Human metabolites Prodrugs {{genito-urinary-drug-stub

See also

References