Location: Plant, Soil and Nutrition Research
2017 Annual Report
Objectives
1. In collaboration with international teams of plant breeders, we will develop lines of staple food crops such as beans, pearl millet, sorghum, rice, lentils and maize with improved Fe and Zn content and bioavailability.
1.A. Identify molecular markers and ultimately the genes that influence iron level and bioavailability in maize seed. Quantitative trait loci (QTL) mapping and an in-vitro digestion/Caco-2 cell culture model system will be used for this research sub-objective.
1.B. Identify molecular markers and ultimately the genes that influence iron level and bioavailability in lentils. Quantitative trait loci (QTL) mapping and an in-vitro digestion/Caco-2 cell culture model system will be used for this research sub-objective.
1.C. Identify agricultural and processing practices that enhance the nutritional quality of Fe in staple food crops.
1.D. Continue our work to identify compounds that promote or inhibit Fe bioavailability in staple food crops.
2. Evaluate a surgical duodenal loop model in poultry as a tool to measure bioavailability of health promoting phytochemicals.
2.A. Determine if absorption of selected phytochemicals can be measured in the poultry duodenal loop model.
2.B. Define bioavailability of specific phytochemicals from select foods using the validated duodenal loop model.
Approach
This project has two major objectives. The first is to develop lines of staple food crops with improved bioavailability and content of iron (Fe). To do so we will employ our established screening tools of an iron bioavailability bioassay and an animal model. In conjunction with these tools, we will make use of mass spectroscopy and marker assisted molecular breeding techniques. With these approaches, we will be able to identify and utilize regions of the plant genome that harbor genes associated with the enhanced food crop nutritional quality for Fe. To further complement the above approaches, we will continue our work on the identification of agricultural and food processing practices that enhance the bioavailability and content of Fe and Zn in staple food crops.
The second major objective of this project is to develop a method to measure and evaluate the bioavailability of functional phytochemicals from plant foods. To do so, we will assess the use of a surgical model utilizing the unique intestinal anatomy of the broiler chicken to measure absorption of compounds from the duodenal segment of the intestine. This approach uses an established surgical preparation involving anesthetized animals. Our initial efforts with this model will focus on compounds that are common to many staple food crops, fruits and vegetables. These phytochemicals will include the flavonoids epicatechin, quercitin, caffeic acid, chlorogenic acid and kaempferol. Enhancing our knowledge of bioavailability of health promoting phytochemicals will significantly improve efforts to develop more nutritious plant foods.
Progress Report
As stated in previous annual reports, the loss of our in-house collaborating maize breeder in 2014 resulted in a 5-7 year setback in our maize research. We have started to recover from that setback using another maize breeder and have identified genetic regions of interest. However, recent observations on Fe bioavailability from the embryo and endosperm components of the maize seed now indicate that the genetic mapping approach should be modified to identify genetic regions that contribute to more Fe in the endosperm (ie. floury part) of the seed rather than in the germ (ie. embryo) fraction. Recent studies indicate that the Fe of the endosperm fraction is more available for absorption, and thus of greater nutritional quality. This is a profound observation, as it strongly suggests that breeding for total Fe content, which could primarily direct Fe to the unavailable (germ) fraction, and could result in a misdirection for maize breeders leading them to produce maize with no benefit for Fe nutrition.
Our collaboration with ARS scientist bean breeder at Michigan State University has made significant progress on developing beans with enhanced Fe nutritional quality. We are identifying lines of yellow beans that cook up to 50% faster, have enhanced nutritional value for multiple nutrients in addition to Fe, and are being developed for improved plant architecture and yield. This improved Fe bioavailability in some lines is linked to the fast-cooking trait, and also appears to be partially due to a favorable profile of compounds (polyphenols) in the seed coat that have been shown to promote Fe bioavailability. This is the first color class of beans where varieties have been found to have a favorable (iron uptake promoting) profile of polyphenols in the seed coat. The yellow beans represent an emerging popular market class in the U.S. and are highly desired in many parts of Africa; thus, this bean research could have domestic impact by creating opportunities of a new market class, and international impact by providing bean varieties with enhanced Fe nutrition and thus alleviating Fe deficiency anemia.
Significant progress has been made on identifying the role of compounds (polyphenols) present in bean seed coats that influence iron bioavailability from beans. Until recently, it was thought that most if not all polyphenols found in bean seed coats inhibited iron uptake. Our studies have now shown that some polyphenols can promote iron bioavailability. We have identified the major inhibitory and promoting compounds and have also investigated the relative concentrations of each that result in net inhibitory or promotional effects. In general, we have found that the inhibitory polyphenols only have to be present at about 10% of the concentration of the promoting compounds to have strong inhibitory effect on iron bioavailability. This knowledge now enables scientists to target varieties within bean color classes, such as the yellow beans, that have the potential for increased iron bioavailability.
Progress was made with characterization and identification of the intestinal microbiome profile as related to dietary Zn intake. In a poultry model, a comparison between birds receiving a standard wheat based diet relative to those receiving a Zn biofortified wheat based diet indicated that dietary Zn content affected the relative abundances of intestinal microbial species. Through metagenomic analysis, we have evidence that predicted pathways responsible for macro- and micronutrient uptake are significantly depleted under Zn deficiency; along with concomitant decreases in beneficial short chain fatty acids. Such depletions may further impede optimal host Zn absorption. We also identified several candidate microbes that may play a significant role in modulating the bioavailability and utilization of dietary Zn during prolonged deficiency. Our results are the first to characterize a unique and dysbiotic cecal microbiota during Zn deficiency, and provide evidence for such microbial perturbations as potential effectors of the Zn deficient phenotype.
In related research, by using the red blood cell fatty acid ratio as a biomarker for Zn status, we were able to validate its reactiveness to dietary Zn in wheat based diets. These findings will allow to better understand the potential effects that dietary Zn has on various physiological process and on dietary Zn bioavailability and absorption.
Accomplishments
1. Development of a zinc status physiological biomarker system. Dietary zinc (Zn) deficiency affects 20% of the world’s population and the World Health Organization has alleviating Zn deficiency a priority. Alleviation of Zn deficiency has been difficult due to the lack of a sensitive and robust indicator of Zn nutritional status. Developing an animal model capable of using such a marker to predict human Zn status would be a more efficient process. To address this need, ARS researchers in Ithaca, New York have developed the red blood cell fatty acids ratio as a physiological biomarker of Zn status, and have successfully tested this measure in an established animal model. In addition, this biomarker was recently applied in a human trial and found to be reflective of Zn status.
2. Bean seed coats can promote or hinder absorption of iron. Polyphenols are a class of chemical compounds found in the seed coats of beans and other legumes. They have long been known to inhibit iron absorption in the human intestine; however, the specific compounds have not been clearly identified or characterized for effect. ARS researchers in Ithaca, New York have applied an established cell culture model to identify the specific compounds that inhibit iron, and have also identified compounds that promote iron absorption. In total, 48 compounds have been characterized. In general, the inhibitory compounds appear to dominate even when present at only 10% of the concentration of the promoting compounds. In the absence of the inhibitors, promoting polyphenols were shown to enhance iron absorption over a limited range of concentration. This observation is significant as such conditions and concentrations appear to exist in certain color classes of beans and other legumes. These findings have the potential to help breeders develop legumes with enhanced iron nutrition.
Review Publications
Tako, E.N., Bar, H., Glahn, R.P. 2016. The combined application of the Caco-2 cell bioassay coupled with in vivo (Gallus gallus) feeding trial represents an effective approach to predicting Fe bioavailability in humans. Nutrients. 8(11):732.
Glahn, R.P., Tako, E.N., Cichy, K.A., Wiesinger, J.A. 2016. The cotyledon cell wall of the common bean (phaseolus vulgaris) resists digestion in the upper intestine and thus may limit iron bioavailability. Food & Function. 7(7):3193-3200.
Siem, G., Tako, E.N., Ahn, C., Bodis, M., Glahn, R.P., Young, S. 2016. A novel in vivo model for assessing the impact of geophagic earth on iron status. Nutrients. 8(6):E362. doi:10.3390/nu8060362.
Hou, T., Kolba, N.J., Glahn, R.P., Tako, E. 2017. Intra-amniotic administration (Gallus gallus) of cicer arietinum and lens culinaris prebiotics extracts and duck egg white peptides affects calcium status and intestinal functionality. Nutrients. 9(7):785. doi:10.3390/nu9070785.
Guo, Z., Martucci, N., Moreno-Olivas, F., Mahler, G., Tako, E.N. 2017. Titanium dioxide nanoparticle ingestion alters nutrient absorption in an in vitro model of the small intestine. NanoImpact. 5:70-82.
Reed, S., Neuman, H., Glahn, R.P., Omry, K., Tako, E.N. 2017. Characterizing the gut (Gallus gallus) microbiota following the consumption of an iron biofortified Rwandan cream seeded carioca (Phaseolus Vulgaris L.) bean-based diet. PLoS One. 12(8):e0182431. https://doi.org/10.1371/journal.pone.0182431.
Wiesinger, J.A., Cichy, K.A., Glahn, R.P., Grusak, M.A., Brick, M., Thompson, H., Tako, E.N. 2016. Demonstrating a nutritional advantage to the fast cooking dry bean (Phaseolus vulgaris L.). Journal of Agricultural and Food Chemistry. 64(45):8592-8603.
Pacifici, S., Song, J., Zhang, C., Wang, Q., Glahn, R.P., Kolba, N.J., Tako, E.N. 2017. Intra amniotic administration of raffinose and stachyose affects the intestinal brush border functionality and alters gut microflora populations. Nutrients. 9(3):304. doi:10.3390/nu9030304.
Glahn, R.P., Cheng, Z., Giri, S. 2015. Extrinsic labelling of staple food crops with isotopic iron does not consistently result in full equilibration: Revisiting the methodology. Journal of Agricultural and Food Chemistry. 63(43):9621-9628.
