ARS | Publication request: Increased calcium bioavailability in mice fed genetically engineered plants lacking calcium oxalate

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2007
Publication Date: July 1, 2007
Repository URL: http://www.springerlink.com
Citation: Morris, J., Nakata, P.A., McConn, M., Brock, A., Hirschi, K.D. 2007. Increased calcium bioavailability in mice fed genetically engineered plants lacking calcium oxalate. Plant Molecular Biology. 64(5):613-618.

Interpretive Summary: Oxalate is an antinutrient that locks calcium up in the form of a calcium oxalate crystal. Calcium found in this crystalline form in foods can not easily be absorbed. To determine the feasibility of improving the absorbability of calcium from plant foods we tested calcium bioavailability in near isogenic plants that differ only in their ability to store calcium in the crystalline form. The plants were grown hydroponically in the presence of the radiotracer 45calcium to allow tracking of the absorbed calcium. Diets were formulated using leaves from the two labeled plant lines and the diets fed to mice. The ability of the mice to absorb and utilize the ingested calcium from the two diets was determined by measuring the amount of 45calcium incorporated into the femurs of the mice. The authors found that the leaves from the plant lacking crystals allowed for greater calcium absorption and utilization by the mice than the plant containing the crystals. Such a finding shows the feasibility of improving calcium availability in plant foods through genetic manipulation of its oxalate content. The study emphasizes the point that it is not just how much of a particular nutrient that you ingest in your diet that is important, but also the form of that nutrient. It is the form of the nutrient that governs its bioavailability meaning how much you will be able to absorb and utilize.

Technical Abstract: Bioavailable calcium affects bone formation and calcification. Here we investigate how a single gene mutation altering calcium partitioning in the model forage crop Medicago truncatula affects calcium bioavailability. Previously, the cod5 M. truncatula mutant was identified which contains identical calcium concentrations to wild-type, but contains no oxalate crystals. In this study, equal number of male and female mice were randomly grouped and then fed one of four 45Ca-containing diets: M. truncatula extrinsically or intrinsically labeled, and cod5 extrinsically or intrinsically labeled. Absorption of the tracer was determined in the legs one day after consumption. The absorption was similar in the M. truncatula and cod5 extrinsically labeled diets; however, in the intrinsically labeled diets, calcium absorption was 22.87% (P < 0.001) higher in mice fed cod5. Our study presents the first genetic evidence demonstrating the nutritional impact of removing oxalate crystals from foods.