Biofortification of Rice with Zinc: Assessment of the Relative Bioavailability of Zinc in a Caco-2 Cell Model and Suckling Rat Pups

Abstract

Staple foods, such as rice, can now be enriched in micronutrients through conventional breeding (i.e., biofortification) to enhance dietary intake of vulnerable populations. The objectives of this study were (1) to establish a rapid, high capacity Caco-2 cell model to determine the relative bioavailability of zinc (Zn) from samples of staple food breeding lines for potential use as a guideline for selection/breeding and (2) to determine the relative bioavailability of Zn from conventional rice varieties and one Zn-biofortified type. Polished or undermilled, parboiled rice samples were digested in vitro with pepsin and pH adjustment, and by pancreatic enzymes. Zn uptake from digested samples was measured in Caco-2 cells in culture. A previously validated rat pup model was also used to assess Zn absorption in vivo, using gastric intubation and (65)Zn labeling. Pups were killed after 6 h, and radioactivity in tissues and in small intestine perfusate and cecum-colon contents was used to measure Zn bioavailability. A biofortified rice variety contained substantially more Zn than conventional varieties, with no change in phytate content. Absorbed Zn (μg/g rice) was significantly higher from the new variety in both the in vitro Caco-2 cell model (2.1-fold) and the rat pup model (2.0-fold). Results from the two models were highly correlated, particularly for the polished samples. Biofortification of rice with Zn results in significantly increased Zn uptake in both models. Since results from the Caco-2 cell model correlated well with those from rat pups, this cell model is likely to predict results in human populations and can be used for screening purposes.

Bioavailability of iron and zinc as affected by phytic acid content in rice grain

“…Hunt et al () reported that Processing (milling) of rice grain reduces the PA resulting in improvement of Zn bioavailability. Jou, Du, Hotz, and Lönnerdal () also reported that uptake of Zn was more from milled rice by Caco‐2 cells than from brown rice. Hence, it can be concluded that PA and total P contents are quantitatively associated and variety or species‐dependent.…”

Bioavailability of iron, zinc, and provitamin A carotenoids in biofortified staple crops

“…It is important that the extrinsic labeling is validated by comparisons with intrinsic labeling experiments, which are reliable. It has been shown that extrinsic labeling can be used for nonheme iron (as in plant foods) and zinc absorption studies in humans . Numerous studies have also investigated carotenoid metabolism using 14 C‐ and 13 C‐labeled compounds .…”

“…The absolute percentage of zinc absorption from high‐zinc rice predicted by an algorithm was inaccurate . Results of in vitro and rat pup studies differed from human and algorithm data in that they did not show a decreased percentage of zinc absorption with a higher zinc intake from biofortified rice …”

“…Since phytate:zinc molar ratios of the rice breeds studied ranged from 19 to 52, it is not surprising that no effect of phytate concentration on zinc absorption was observed in the study. Past studies indicate that the inhibitory effect is only linear for phytate:zinc molar ratios between 2.9 and 11.4, while higher molar ratios do not show a further effect . In an experiment performed in this study, there were significant decreases in zinc uptake with phytate:zinc molar ratios between 2.5 and 20.…”

The road to micronutrient biofortification of rice: progress and prospects

“…These results suggest that at least in the case of NAS overexpression lines, there is no need to co-express phytase or metalloproteins to increase bioavailability. Recently it was shown that biofortification of rice with Zn significantly increases Zn uptake in Caco-2 as well as in rat pups, and are suggested to be the same in human populations (Jou et al, 2012). Feeding tests in humans may be the next step toward the release of biofortified lines.…”