Are there endogenous estrone fatty acyl esters in human plasma or ovarian follicular fluid?

Background: Estrone and its sulfated esters are the most abundant estrogens in blood in men and in women after the menopause. However, previous studies on the esterification of estrone with fatty acids have yielded conflicting results, some studies reporting high nanomolar concentrations of estrone fatty acyl esters in plasma.

Methods: We developed an estrone radioimmunoassay (RIA) method to determine endogenous concentrations of estrone and after saponification, applied it to male and female plasma. In addition, the concentration of estrone fatty acyl esters in ovarian follicular fluid was analyzed by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results: By estrone RIA, we did not find measurable amounts of estrone fatty acyl esters in male or female plasma, except for one premenopausal woman who had the highest plasma concentration of nonesterified estrone. The concentration of hydrolyzed estrone fatty acyl esters determined by LC-MS/MS in follicular fluid obtained from women undergoing ovarian stimulation was below the limit of quantification of <10 pmol/l (<2.7 ng/l).

Conclusions: In contrast to previous data by others, our study suggests that estrone fatty acyl esters are in most cases not detectable in plasma of healthy men or healthy nonpregnant women.