13C Natural Abundance of Serum Retinol Is a Novel Biomarker for Evaluating Provitamin A Carotenoid-Biofortified Maize Consumption in Male Mongolian Gerbils [Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions]

Background: Crops such as maize, sorghum, and millet are being biofortified with provitamin A carotenoids to ensure adequate vitamin A (VA) intakes. VA assessment can be challenging because serum retinol concentrations are homeostatically controlled and more sensitive techniques are resource-intensive.

Objectives: We investigated changes in serum retinol relative differences of isotope amount ratios of ¹³C/¹²C (¹³C) caused by natural ¹³C fractionation in C₃ compared with C₄ plants as a biomarker to detect provitamin A efficacy from biofortified (orange) maize and high-carotene carrots.

Methods: The design was a 2 x 2 x 2 maize (orange compared with white) by carrot (orange compared with white) by a VA fortificant (VA+ compared with VA–) in weanling male Mongolian gerbils (n = 55), which included a 14-d VA depletion period and a 62-d treatment period (1 baseline and 8 treatment groups; n = 5–7/group). Liver VA and serum retinol were quantified, purified by HPLC, and analyzed by GC combustion isotope ratio mass spectrometry for ¹³C.

Results: Treatments affected liver VA concentrations (0.048 ± 0.039 to 0.79 ± 0.24 μmol/g; P < 0.0001) but not overall serum retinol concentrations (1.38 ± 0.22 μmol/L). Serum retinol and liver VA ¹³C were significantly correlated (R² = 0.92; P < 0.0001). Serum retinol ¹³C differentiated control groups that consumed white maize and white carrots (–27.1 ± 1.2 ¹³C) from treated groups that consumed orange maize and white carrots (–21.6 ± 1.4 ¹³C P < 0.0001) and white maize and orange carrots (–30.6 ± 0.7 ¹³C P < 0.0001). A prediction model demonstrated the relative contribution of orange maize to total dietary VA for groups that consumed VA from mixed sources.

Conclusions: Provitamin A efficacy and quantitative estimation of the relative contribution to dietary VA were demonstrated with the use of serum retinol ¹³C. This method could be used for maize efficacy or effectiveness studies and with other C₄ crops biofortified with provitamin A carotenoids (e.g., millet, sorghum). Advantages include no extrinsic tracer dose, 1 blood sample, and higher sensitivity than serum retinol concentrations alone.

From: Gannon, B. M., Pungarcher, I., Mourao, L., Davis, C. R., Simon, P., Pixley, K. V., Tanumihardjo, S. A. http://redirect.viglink.com?u=http%3A%2F%2Fjn.nutrition.org%2Fcgi%2Fcontent%2Fshort%2F146%2F7%2F1290%3Frss%3D1&key=ddaed8f51db7bb1330a6f6de768a69b8