Long-term kinetic study of beta-carotene, using accelerator mass spectrometry in an adult volunteer

We present a sensitive tracer method, suitable for in vivo human research, that uses beta-[C-14]carotene coupled with accelerator mass spectrometry (A MS) detection. Using this approach, the concentration-time course of a phys iological (306 mug; 200 nCi) oral dose of beta-[C-14]carotene was determine d for 209 days in plasma. Analytes included beta-[C-14]carotene, [C-14]reti nyl esters, [C-14]retinol, and several [C-14]retinoic acids. There was a 5. 5-h lag between dosing and the appearance of C-14 in plasma. Labeled beta - carotene and [C-14]retinyl esters rose and displayed several maxima with vi rtually identical kinetic profiles over the first 24-h period; elevated [C- 14]retinyl ester concentrations were sustained in the plasma compartment fo r >21 h postdosing. The appearance of [C-14]retinol in plasma was also dela yed 5.5 h postdosing and its concentration rose linearly for 28 h before de clining. Cumalative urine and stool were collected for 17 and 10 days, resp ectively and 57.4% of the dose was recovered in the stool within 48 h postd osing. The stool was the major excretion route for the absorbed dose. The t urnover times (I/k(el)) for beta -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 beta -carotene, with a minim um of 62% of the absorbed beta -carotene being cleaved to vitamin A. In sum mary, AMS is an excellent tool for defining the in vivo metabolic behavior of beta -carotene and related compounds at physiological concentrations. Fu rther, our data suggest that retinyl esters derived from beta -carotene may undergo hepatic resecretion with VLDL in a process similar to that observe d for beta -carotene.