Quantification and kinetics of 25-hydroxyvitamin D3 by isotope dilution liquid chromatography/thermospray mass spectrometry.
A liquid chromatography/thermospray mass spectrometry method has been developed and used to measure the plasma levels and half-life of 25-hydroxyvitamin D3 in adults. The mean plasma levels of 25-hydroxyvitamin D3 averaged 40 ng ml-1 (n = 4) in summer and 30 ng ml-1 (n = 6) in winter. The method was also used to determine the half-life of serum 25-hydroxyvitamin D3 in subjects maintained on either high or low-fiber diets who had been given an intravenous infusion of (6,19,19-2H3)25-hydroxyvitamin D3 sufficient to label 5% of their estimated body pools. The half-life was determined to be 10.4 days (n = 4), which is approximately 50% of the currently accepted value of 19 days, determined using radiolabeled methods. This difference may be due to kinetic isotope effects arising as a result of the tritiated compounds being labeled at sites that undergo Cyt-P450-catalyzed oxidations.
Vicchio
D
D
Section on Metabolic Analysis and Mass Spectrometry, NIH, Bethesda, Maryland 20892.
Yergey
A
A
O'Brien
K
K
Allen
L
L
Ray
R
R
Holick
M
M
D000328:Adult; D002112:Calcifediol / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D002853:Chromatography, Liquid; D006207:Half-Life; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry
D002112:Calcifediol