Iron Bioavailability of Maize Hemoglobin in a Caco-2 Cell Culture Model

Abstract

Maize (Zea mays) is an important staple crop in many parts of the world but has low iron bioavailability, in part due to its high phytate content. Hemoglobin is a form of iron that is highly bioavailable, and its bioavailability is not inhibited by phytate. It was hypothesized that maize hemoglobin is a highly bioavailable iron source and that biofortification of maize with iron can be accomplished by overexpression of maize globin in the endosperm. Maize was transformed with a gene construct encoding a translational fusion of maize globin and green fluorescent protein under transcriptional control of the maize 27 kDa γ-zein promoter. Iron bioavailability of maize hemoglobin produced in Escherichia coli and of stably transformed seeds expressing the maize globin−GFP fusion was determined using an in vitro Caco-2 cell culture model. Maize flour fortified with maize hemoglobin was found to have iron bioavailability that is not significantly different from that of flour fortified with ferrous sulfate or bovine hemoglobin but is significantly higher than unfortified flour. Transformed maize grain expressing maize globin was found to have iron bioavailability similar to that of untransformed seeds. These results suggest that maize globin produced in E. coli may be an effective iron fortificant, but overexpressing maize globin in maize endosperm may require a different strategy to increase bioavailable iron content in maize KeywordsInterdepartmental Genetics Graduate Program, biofortification, hemoglobin, iron bioavailability, transgenic maize ABSTRACT: Maize (Zea mays) is an important staple crop in many parts of the world but has low iron bioavailability, in part due to its high phytate content. Hemoglobin is a form of iron that is highly bioavailable, and its bioavailability is not inhibited by phytate. It was hypothesized that maize hemoglobin is a highly bioavailable iron source and that biofortification of maize with iron can be accomplished by overexpression of maize globin in the endosperm. Maize was transformed with a gene construct encoding a translational fusion of maize globin and green fluorescent protein under transcriptional control of the maize 27 kDa γ-zein promoter. Iron bioavailability of maize hemoglobin produced in Escherichia coli and of stably transformed seeds expressing the maize globin−GFP fusion was determined using an in vitro Caco-2 cell culture model. Maize flour fortified with maize hemoglobin was found to have iron bioavailability that is not significantly different from that of flour fortified with ferrous sulfate or bovine hemoglobin but is significantly higher than unfortified flour. Transformed maize grain expressing maize globin was found to have iron bioavailability similar to that of untransformed seeds. These results suggest that maize globin produced in E. coli may be an effective iron fortificant, but overexpressing maize globin in maize endosperm may require a different strategy to increase bioavailable iron content in maize.

Iron Bioavailability in Low Phytate Pea

“…The same soybean ferritin gene was also introduced into rice and resulted in a 2 times higher iron concentration, but iron bioavailability was not directly tested (Lucca et al, 2001). Bodnar et al (2013) tried to increase iron bioavailability by increasing heme iron level in maize endosperm. They overexpressed a maize globin gene to increase the hemoglobin level, however, they determined that iron bioavailability did not differ between the transformed and untransformed seeds.…”

Wheat Vacuolar Iron Transporter TaVIT2 Transports Fe and Mn and Is Effective for Biofortification

“…Samples were incubated at 37°C on a rolling table for 90 min. Next, the pH of the samples was gradually adjusted to pH 5.5, bile (0.007 g mL 21 ) and pancreatin (0.001 g mL 21 ) digestive enzymes were added, the pH was adjusted to 7, and the samples were incubated for an additional 1 h. At the end of the simulated digestion, samples were centrifuged at 3,000g for 10 min, the gastrointestinal enzymes were heated inactivated at 80°C for 10 min and centrifuged as before, and the resultant supernatant was used subsequently for iron uptake experiments similar to Bodnar et al (2013) with little modification. A volume of 0.5 mL of wheat digestate was diluted in 0.5 mL of Eagle's MEM and applied over Caco-2 cell monolayers grown on collagen-coated 12-well plates.…”

Micromilling Enhances Iron Bioaccessibility from Wholegrain Wheat

“…18,19 Consequently, transgenic transformation of cereals and other food crops became an attractive option for improving iron nutrition in human populations. 20,21 Plants have been genetically modified to yield grains that express ferritin, 22 phytase, 23,24 hemoglobin, 25,26 or coexpression of ferritin and phytase in an attempt to improve iron nutrition. 27 Biofortification is still in its developmental phase and is beset by numerous challenges both technical and emotive.…”