Golden Rice is an effective source of vitamin A

Abstract

Background: Genetically engineered "Golden Rice" contains up to 35 microg beta-carotene per gram of rice. It is important to determine the vitamin A equivalency of Golden Rice beta-carotene to project the potential effect of this biofortified grain in rice-consuming populations that commonly exhibit low vitamin A status.

Objective: The objective was to determine the vitamin A value of intrinsically labeled dietary Golden Rice in humans.

Design: Golden Rice plants were grown hydroponically with heavy water (deuterium oxide) to generate deuterium-labeled [2H]beta-carotene in the rice grains. Golden Rice servings of 65-98 g (130-200 g cooked rice) containing 0.99-1.53 mg beta-carotene were fed to 5 healthy adult volunteers (3 women and 2 men) with 10 g butter. A reference dose of [13C10]retinyl acetate (0.4-1.0 mg) in oil was given to each volunteer 1 wk before ingestion of the Golden Rice dose. Blood samples were collected over 36 d.

Results: Our results showed that the mean (+/-SD) area under the curve for the total serum response to [2H]retinol was 39.9 +/- 20.7 microg x d after the Golden Rice dose. Compared with that of the [13C10]retinyl acetate reference dose (84.7 +/- 34.6 microg x d), Golden Rice beta-carotene provided 0.24-0.94 mg retinol. Thus, the conversion factor of Golden Rice beta-carotene to retinol is 3.8 +/- 1.7 to 1 with a range of 1.9-6.4 to 1 by weight, or 2.0 +/- 0.9 to 1 with a range of 1.0-3.4 to 1 by moles.

Conclusion: Beta-carotene derived from Golden Rice is effectively converted to vitamin A in humans. This trial was registered at clinicaltrials.gov as NCT00680355.

FIGURE 1

Photograph of the labeling chamber (A) and system components used to produce polished Golden Rice-2 (B). Components of the labeling system: 1, Golden Rice-2 in deuterated nutrient solution at seed fill stage; 2, carbon dioxide sensor; 3, tower fan for air mixing; 4, air conditioning unit; 5, dehumidifier; 6, collection tub for transpired heavy water from plants (collected from dehumidifier); 7, carbon dioxide supply; 8, water-free air.

FIGURE 2

Experimental design for the Golden Rice human study. Three sets of dashed lines are used to amplify the overall time period to progressively larger scales. The first order (upper scale) includes the entire 36-d study and sampling period. The second order (middle scale) represents days 1–15 of more frequent blood sampling. Each cell on the horizontal time axis represents a 24-h period, with the division line representing the fasting blood collection time (0 h). The cells in black represent days 1 and 8, the days on which the tracers were ingested. The third order (lower scale) is common for these 2 dosing and high-multiple blood-sampling days (days 1 and 8), with each cell on the time axis representing 1 h. The 0 time represents the first blood sampling of the day, and all other numbers represent the times of subsequent sampling (in h) relative to the time of first sampling. The anchor symbols represent the oral dosing of the tracer. The arrows indicate the times at which blood samples were collected. d, day in the study; h, hour after study dose or after fasting blood sample, RAc, retinyl acetate.

FIGURE 3

Chromatogram of Golden Rice carotenoids. Each labeled chromatographic peak represents an identified carotenoid compound: 1, lutein; 2, anhydrolutein; 3, zeaxanthin; 4, cryptoxanthin; 5, 13-cis β-carotene; 6, all-trans β-carotene; 7, 9-cis β-carotene.

FIGURE 4

Deuterium enrichment profile of Golden Rice β-carotene analyzed by liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (positive ion mode). Hydroponic labeling does not produce uniform enrichment, but rather a range of isotopomers. The vertical axis represents the signal intensity. The horizontal axis represents the mass (M + H⁺ = mass plus hydrogen atom with positive charge) of the isotopomers. Unlabeled β-carotene is shown with a mass of 537. The most abundant isotopomer of labeled β-carotene (with 9 deuterium atoms) is represented by an m/z of 546. The enrichment of Golden Rice β-carotene is 86%.

FIGURE 5

Enrichment mass spectrometric profile of serum retinol samples collected from one subject. Top panel: profile obtained before ingestion of the labeled dose; data are an average of 11.3–11.6 min on the gas chromatography–mass spectrometry (GC/MS) chromatogram for a sample collected on day 1, 0 h. Middle panel: profile obtained after ingestion of the reference dose; data are an average of 13.7–13.8 min on the GC/MS chromatogram for a sample collected on day 1, 13 h after the [¹³C₁₀]retinyl acetate dose. Bottom panel: profile obtained after ingestion of the labeled Golden Rice dose; data are an average of 11.3–11.6 min on the GC/MS chromatogram for a sample collected on day 9, 24 h after the Golden Rice meal. Arrows indicate signal intensities that were greater than the abundance values on the y axis.

FIGURE 6

Calculated labeled retinol species in the circulation of a representative volunteer, throughout the course of the study, after consumption of [¹³C₁₀]retinyl acetate on day 1 and after a deuterium-labeled Golden Rice β-carotene dose on day 8.

FIGURE 7

Serial measurements of deuterium-labeled β-carotene in the circulation of a representative volunteer. Values are presented for the 25 d of monitoring after the oral dose of labeled Golden Rice.