Lipoidal estradiol (LE2) is the variety of endogenous C17β long-chain fatty acid estersofestradiol which are formed as metabolites of estradiol.[1][2] Important examples of these esters include estradiol arachidonate, estradiol lineolate, estradiol oleate, estradiol palmitate, and estradiol stearate.[1][2] LE2 are estrogens but do not bind to the estrogen receptor, instead acting as prohormones of estradiol.[1][2] Relative to estradiol, they have far longer-lasting durations of effect due to their much slower rates of metabolism and clearance.[1][2] It has been hypothesized that LE2 may serve as a store of estrogen for when estradiol levels become low.[1][2] LE2 are highly lipophilic and hydrophobic and are found in highest concentrations in adipose tissue and other estrogen-sensitive tissues and in low but detectable concentrations in circulation, with none excretedinurine.[1][2] They have been referred to as the "endogenous counterparts of the synthetic esters of estrogens" like estradiol valerate and estradiol cypionate.[1][2]
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 intramuscular injection.[3][4]
Estradiol is esterified into LE2 by lecithin–cholesterol acyltransferase (LCAT).[5]
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