7alpha-Methyl-ethinyl estradiol is not a metabolite of tibolone but a chemical stress artifact.
OBJECTIVE
This study was conducted to establish whether 7alpha-methyl-ethinyl estradiol (7alpha-MEE) in plasma from postmenopausal women treated with tibolone is a metabolite or an artifact.


METHODS
Clinical samples with known levels of tibolone metabolites, plus plasma samples spiked with tibolone and metabolites, were analyzed for levels of 7alpha-MEE using liquid chromatography-mass spectometry (LC-MS/MS) with and without derivatization.


RESULTS
Approximately 20 to 40 pg/mL 7alpha-MEE was detected using LC-MS/MS with derivatization in plasma samples from postmenopausal women treated with tibolone. In plasma samples spiked with 200 ng/mL tibolone or Delta-tibolone, LC-MS/MS with derivatization revealed the generation of around 200 and 36 pg/mL 7alpha-MEE, respectively, whereas LC-MS/MS without derivatization showed no detectable chemical conversion of tibolone to 7alpha-MEE. Generation of 7alpha-MEE is increased by the "stress conditions" used in the derivatization procedure; simply drying the sample also shows this artifactual conversion. The major active and sulfated 3-hydroxy metabolites of tibolone are not converted to 7alpha-MEE. Without derivatization, and avoiding stress conditions, no detectable levels (<20 pg/mL) of 7alpha-MEE were found in plasma samples from postmenopausal women treated with single (eight participants at 13 time points) or multiple (seven participants at 18 time points) doses of tibolone.


CONCLUSIONS
7alpha-MEE is not a metabolite of tibolone but is a chemical artifact generated during analytical procedures with derivatization. Using LC-MS/MS without derivatization, 7alpha-MEE cannot be demonstrated in plasma from postmenopausal women after single or multiple doses of tibolone.
Dröge
Melloney J
MJ
ABL Laboratories, Assen, The Netherlands.
Oostebring
Freddy
F
Oosting
Ep
E
Verheul
Herman A M
HA
Kloosterboer
Helenius J
HJ
D002853:Chromatography, Liquid; D004958:Estradiol / Q000031:analogs & derivatives* / Q000737:chemistry; D020847:Estrogen Receptor Modulators / Q000008:administration & dosage* / Q000737:chemistry* / Q000378:metabolism; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008875:Middle Aged; D009652:Norpregnenes / Q000008:administration & dosage* / Q000737:chemistry* / Q000378:metabolism; D017698:Postmenopause; D012680:Sensitivity and Specificity
C513611:7alpha-methyl ethinylestradiol; D020847:Estrogen Receptor Modulators; D009652:Norpregnenes; D004958:Estradiol; C027385:tibolone