title: A validated liquid chromatography-tandem mass spectrometry method for the quantitative determination of 4β-hydroxycholesterol in human plasma.
abstract: A novel liquid chromatography-tandem mass spectrometry method is described for the quantitative determination of the endogenous CYP 3A4/5 marker 4β-hydroxycholesterol in human K(2)-EDTA plasma. It is based on alkaline hydrolysis to convert esterified to free 4β-hydroxycholesterol, followed by analyte extraction from plasma by hexane and purification of the hexane extract by normal-phase solid-phase extraction. The analyte is chromatographically separated from endogenous isobaric plasma oxysterols and excess cholesterol by a 16-min reversed-phase gradient on a C18 column; detection is performed by atmospheric pressure photoionization tandem mass spectrometry in the positive ion mode, using toluene as a dopant. Using 400μl of plasma, 4β-hydroxycholesterol can be quantified in the concentration range 10.0-250nM. Validation results show that the method is sufficiently selective towards endogenous plasma sterols and capable of quantifying the analyte with good precision and accuracy. The analyte is sufficiently stable in all relevant matrices and solvents; the addition of the anti-oxidant butylated hydroxytoluene to prevent in vitro formation of 4β-hydroxycholesterol from cholesterol during storage or analysis is not necessary, provided that long-term frozen storage of plasma occurs at -70°C.
authors.affiliation: Bioanalytical Laboratory, PRA International, Westerbrink 3, 9405 BJ Assen, The Netherlands. merbelnicovande@praintl.com
authors.forename: Nico C
authors.initials: NC
authors.lastname: van de Merbel
authors.forename: Kees J
authors.initials: KJ
authors.lastname: Bronsema
authors.forename: Mischa W J
authors.initials: MW
authors.lastname: van Hout
authors.forename: Ralf
authors.initials: R
authors.lastname: Nilsson
authors.forename: Henrik
authors.initials: H
authors.lastname: Sillén
mesh_terms: D000975:Antioxidants / Q000737:chemistry; D015415:Biomarkers / Q000737:chemistry; D002138:Calibration; D002784:Cholesterol / Q000737:chemistry; D002853:Chromatography, Liquid / Q000379:methods*; D051544:Cytochrome P-450 CYP3A / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry; D006801:Humans; D006868:Hydrolysis; D006888:Hydroxycholesterols / Q000737:chemistry*; D007477:Ions; D008956:Models, Chemical; D015203:Reproducibility of Results; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000975:Antioxidants; D015415:Biomarkers; D006888:Hydroxycholesterols; D007477:Ions; C099828:cholest-5-ene-3,4-diol; D002784:Cholesterol; D004492:Edetic Acid; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human