We present a sensitive tracer method, suitable for in vivo human research, that uses β-[14C]carotene coupled with accelerator mass spectrometry (AMS) detection. Using this approach, the concentration-time course of a physiological (306 μg; 200 nCi) oral dose of β-[14C]carotene was determined for 209 days in plasma. Analytes included β-[14C]carotene, [14C]retinyl esters, [14C]retinol, and several [14C]retinoic acids. There was a 5.5-h lag between dosing and the appearance of 14C in plasma. Labeled β-carotene and [14C]retinyl esters rose and displayed several maxima with virtually identical kinetic profiles over the first 24-h period; elevated [14C]retinyl ester concentrations were sustained in the plasma compartment for >21 h postdosing. The appearance of [14C]retinol in plasma was also delayed 5.5 h postdosing and its concentration rose linearly for 28 h before declining. Cumulative urine and stool were collected for 17 and 10 days, respectively, and 57.4% of the dose was recovered in the stool within 48 h postdosing. The stool was the major excretion route for the absorbed dose. The turnover times (1/kel) for β-carotene and retinol were 58 and 302 days, respectively. Area under the curve analysis of the plasma response curves suggested a molar vitamin A value of 0.53 for β-carotene, with a minimum of 62% of the absorbed β-carotene being cleaved to vitamin A. In summary, AMS is an excellent tool for defining the in vivo metabolic behavior of β-carotene and related compounds at physiological concentrations. Further, our data suggest that retinyl esters derived from β-carotene may undergo hepatic resecretion with VLDL in a process similar to that observed for β-carotene.—Dueker, S. R., Y. Lin, B. A. Buchholz, P. D. Schneider, M. W. Lamé, H. J. Segall, J. S. Vogel, and A. J. Clifford. Long-term kinetic study of β-carotene, using accelerator mass spectrometry in an adult volunteer. J. Lipid Res. 2000. 41: 1790–1800.
