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Disposition of ¹⁴C-β-carotene following delivery with autologous triacylglyceride-rich lipoproteins
Publish date: Feb 03, 2007
Author: Stephen R. Dueker, Le Thuy Vuong, Brian Faulkner, Bruce A. Buchholz, John S. Vogel
Source: Nuclear Instruments and Methods in Physics Research B 259 (2007) 767–772

Following ingestion, a fraction of β-carotene is cleaved into vitamin A in the intestine, while another is absorbed intact and distributed among tissues and organs. The extent to which this absorbed β-carotene serves as a source of vitamin A is unknown in vivo. In the present study we use the attomole sensitivity of accelerator mass spectrometry (AMS) for ¹⁴C to quantify the disposition of ¹⁴C-β-carotene (930 ng; 60.4 nCi of activity) after intravenous injection with an autologous triacylglyceride-rich lipoprotein fraction in a single volunteer. Total ¹⁴C was quantified in serial plasma samples and also in triglyceride-rich, and low density lipoprotein, subfractions. The appearance of ¹⁴C-retinol, the circulating form of vitamin A in plasma, was determined by chromatographic separation of plasma retinol extracts prior to AMS analysis. The data showed that ¹⁴C concentrations rapidly decayed within the triglyceride-rich lipoprotein fractions after injection, whereas low density lipoprotein ¹⁴C began a significant rise in ¹⁴C 5 h post dose. Plasma ¹⁴C-retinol also appeared at 5 h post dose and its concentrations were maintained above baseline for >88 days. Based upon comparisons of ¹⁴C-retinol concentrations following an earlier study with orally dosed ¹⁴C-β-carotene, a molar vitamin A value of the absorbed β-carotene of 0.19 was derived, meaning that 1 mole of absorbed β-carotene provides 0.19 moles of vitamin A. This is the first study to show that infused β-carotene contributes to the vitamin A economy in humans in vivo.

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