Conversion of 5α‐Androstane‐3α,17β‐diol to bis[(4‐dimethylamino)phenyl carbamate] derivative for sensitive determination of its rat brain level by LC/ESI‐MS/MS

Abstract

Rationale5α‐Androstane‐3α,17β‐diol (3α,5α‐Adiol) is a testosterone‐derived neurosteroid and has anxiolytic and analgesic effects via γ‐aminobutyric acid type A receptors as with the progesterone‐derived neurosteroid, allopregnanolone (AP). Although the psychotropic drug‐evoked changes in the brain AP concentration have been intensively studied, those in the brain 3α,5α‐Adiol concentration remain poorly understood. One of the causes for this is the limited availability of a validated method for quantifying the brain 3α,5α‐Adiol with a sufficient sensitivity and specificity, which is described in this study.MethodsTo enhance the detectability of 3α,5α‐Adiol by electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS), derivatization with 4‐dimethylaminobenzoyl azide was employed. The brain sample was purified by solid‐phase extraction and the recovered 3α,5α‐Adiol and the deuterated internal standard were derivatized, then measured by liquid chromatography (LC)/ESI‐MS/MS with selected reaction monitoring.ResultsThe derivatized 3α,5α‐Adiol, i.e., the bis[(4‐dimethylamino)phenyl carbamate] derivative, provided the intense doubly‐protonated molecule as the precursor ion, then the specific product ion containing the 3α,5α‐Adiol‐skeleton by collision‐induced dissociation. The detectability of 3α,5α‐Adiol was eventually increased 1000‐fold by derivatization. Separation of the derivatized 3α,5α‐Adiol from its stereoisomers and interfering brain components was achieved using a SunShell Biphenyl column with an isopropyl alcohol‐containing mobile phase. A good linearity in the sufficient concentration range, acceptable precision and accuracy, and negligible matrix effect were demonstrated by the validation tests. The animal (rat) study using this method revealed that the brain 3α,5α‐Adiol levels were unaffected by the administration of fluoxetine (FLX) and clozapine (CLZ), in contrast to the significant increase of the AP levels.ConclusionAn LC/ESI‐MS/MS method capable of quantifying 3α,5α‐Adiol in the rat brain using a 20‐mg tissue was developed and validated. The brain levels of 3α,5α‐Adiol had an entirely different behavior from those of AP due to FLX and CLZ administration.