Compartmental models of vitamin a and β-carotene metabolism in women

Abstract

We have developed compartmental models of vitamin A and β-carotene (βC) metabolism in women living under controlled conditions on diets with known concentrations of vitamins and carotenoids. Fourteen healthy adult women were given either retinyl-d4 acetate, or βC-D8 before breakfast. Natural and stable-isotopes of retinol and βC were collected in serum for up to 95 days or 20 days, respectively. Stable isotopes were separated from other components and measured by GC-MS or HPLC-UV. Preformed retinyl-d4 acetate metabolism in all women tested can be accurately described by a simple four-compartment model. However, the model did not fit one women initially, when she had marginal vitamin A status. We tested the hypothesis that dietary changes of βC intake have important roles on the kinetics of vitamin A metabolism. Dietary changes of βC intake did not influence the turnover rate of retinol in any compartment. However, it did result in changes in steady-state masses and residence times of retinol in several compartments. A working compartmental model for βC metabolism was developed. The kinetics of retinol-d4 formed from βC is more complicated than the pre- formed retinol-d4. Results suggest that βC-d8 readily converts into retinol-d4 with high inter-individual variability.