Trace level quantification of deuterated 17β-estradiol and estrone in ovariectomized mouse plasma and brain using liquid chromatography/tandem mass spectrometry following dansylation reaction

A sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method coupled with dansylation was developed for the simultaneous quantification of exogenously administered deuterated 17beta-estradiol-d(4) (E2-d(4)) and its metabolite, estrone-d(4) (E1-d(4)), in mouse plasma and brain homogenates. The dansylation reaction was simple, fast, and sensitive, and a lower limit of quantification of 50 pg/mL was achieved by using 50 muL of mouse plasma. Interference from endogenous 17beta-estradiol and estrone in plasma and brain samples was minimized by the use of deuterated-E2 as well by utilizing ovariectomized (OVX) mice. The recovery of dansylated derivative exceeded 83% and the reaction was completed within approximately 3 min. The intra- and inter-day assay precision were better than 12.9% and assay accuracy ranged between 92-104% for E1-d(4) and E2-d(4) in plasma, respectively. The absorption of E2-d(4) at both 1 and 3 mg/kg P.O. was rapid, reaching peak plasma concentrations (C-max) at 5 min post-dose that was the earliest time point obtained, and were 1.1 and 13.8 ng/mL, respectively; the C-max values for the estrone metabolite, E1-d(4), were 1.1 and 43.2 ng/mL, respectively. The area-under-the-plasma-time curve (AUC(0-2h)) values were determined to be 0.65 and 2.90 ng (.) h/mL for E2-d(4) and 0.77 and 6.74 ng (.) h/mL for E1-d(4), respectively, at 1 and 3 mg/kg. The mean brain-to-plasma ratio for E1-d(4) and E2-d(4) after P.O. administration of E2-d(4) to the OVX mice at 1 and 3 mg/kg indicated that both E1-d(4) and E2-d(4) were present in the brain as well as in the circulation. Copyright (C) 2004 John Wiley Sons, Ltd.