Genome-wide association and genomic prediction for iron and zinc concentration and iron bioavailability in a collection of yellow dry beans

Dry bean is a nutrient-dense food targeted in biofortification programs to increase seed iron and zinc levels. The underlying assumption of breeding for higher mineral content is that enhanced iron and zinc levels will deliver health benefits to the consumers of these biofortified foods. This study characterized a diversity panel of 275 genotypes comprising the Yellow Bean Collection (YBC) for seed Fe and Zn concentration, Fe bioavailability (FeBio), and seed yield across 2 years in two field locations. The genetic architecture of each trait was elucidated via genome-wide association studies (GWAS) and the efficacy of genomic prediction (GP) was assessed. Moreover, 82 yellow breeding lines were evaluated for seed Fe and Zn concentrations as well as seed yield, serving as a prediction set for GP models. Large phenotypic variability was identified in all traits evaluated, and variations of up to 2.8 and 13.7-fold were observed for Fe concentration and FeBio, respectively. Prediction accuracies in the YBC ranged from a low of 0.12 for Fe concentration, to a high of 0.72 for FeBio, and an accuracy improvement of 0.03 was observed when a QTN, identified through GWAS, was used as a fixed effect for FeBio. This study provides evidence of the lack of correlation between FeBio estimated in vitro and Fe concentration and highlights the potential of GP in accurately predicting FeBio in yellow beans, offering a cost-effective alternative to the traditional assessment of using Caco2 cell methodologies.

Iron Bioavailability of Maize Is Improved by Degermination for Some but Not All Genotypes: Enhancing Maize Nutrition With Biofortification and Processing

Objectives

To evaluate bioavailable Fe, total Fe concentration and phytate concentration of whole and degerminated maize in a diverse panel of 52 genotypes. This work sought to expand upon previous work which identified the germ fraction of the maize kernel as an inhibitory component for Fe bioavailability.

Methods

Samples were degerminated manually by scalpel dissection of the germ fraction. Samples were then cooked, lyophilized, and milled to a flour. Iron bioavailability was evaluated with the Caco-2 Cell Bioassay. Iron concentration was measured by ICP-ES. Phytate concentration was determined via a colorimetric assay for total phytate phosphorous (Megazyme Phytate Kit, Megazyme International).

Results

In 30 of the maize genotypes, bioavailable Fe increased when degerminated, thus indicating a higher fractional Fe uptake as the amount of Fe decreased by more than 70%. The remaining 22 genotypes showed no change or a decrease in Fe bioavailability with degermination. These results confirm previous research showing that the germ fraction is a strong inhibitory component for many maize varieties. Degermination greatly reduced phytate content and phytate:Fe molar ratio; Fe concentrations were positively correlated with phytate, and negatively correlated with phytate:Fe molar ratios for most maize groups. While the high phytate content of the germ fraction likely plays a role, only degerminated yellow maize indicated a significant correlation between Fe bioavailability and phytate concentration, and only pigmented maize indicated a correlation between Fe bioavailability and phytate:Fe molar ratio. Other factors in the maize germ and endosperm fractions are likely relevant to changes in Fe bioavailability.

Conclusions

This study suggests that Fe nutrition from maize can be enhanced by processing (degermination) and or by selecting varieties where the inhibitory effect of the germ fraction is relatively low.

Funding Sources

Funded by the United States Department of Agriculture, Agricultural Research Service.

An In Vitro Analysis and In Vivo Trial Demonstrating the Improved Iron Bioavailability of White Beans (Phaseolus vulgaris L.) After Processing Into Pasta

Objectives

The cotyledon cell wall of the common bean can be a factor in Fe bioavailability. This study evaluated the iron bioavailability of two bean varieties (white or black) either boiled (intact cell walls) or extruded into pasta formulated from heat treated bean flour as the major ingredient (100% bean flour; broken cell walls).

Methods

In vitro Fe bioavailability was determined via the Caco-2 Cell Bioassay. In vivo Fe bioavailability was measured by the capacity of a bean-based or bean pasta-based diet to generate and maintain total body hemoglobin iron (Hb-Fe) during a 6 week poultry feeding trial.

Results

The iron and phytate concentrations of the bean-based and bean pasta-based diets consisting of tomato paste, carrot, cabbage, milk, potato and corn oil were not significantly different. The Caco-2 cell bioassay predicted that the white bean pasta diet would have the highest Fe bioavailability, closely followed by the white bean diet. The bioassay predicted the black bean diet and the black bean pasta diet would have significantly lower Fe bioavailability. For the in vivo studies, animals fed the white bean pasta diet (broken cell walls) had significantly (p ≤ 0.05) higher hemoglobin, Hb-Fe and hemoglobin maintenance efficiencies than animals fed a white bean, black bean or black bean pasta-based diet. Although cotyledon cells were broken, the iron bioavailability of the black bean pasta was not improved after processing into pasta. The low iron bioavailability of black beans was associated with their high concentrations of seed coat procyanidin, cinnamtannin and anthocyanidin compounds that have a negative impact on the absorption of iron.

Conclusions

This study shows that white colored dry bean possesses a combination of traits that result in improved iron bioavailability after processing into pasta. The enhanced Fe bioavailability from the white bean pasta is likely due to the breakage of the cotyledon cell wall during processing, thus allowing enhanced bioaccessibility of the intracellular Fe. In the black bean pasta diet, this enhancement was not observed due to the presence of the seed coat polyphenols which interacted with the released intracellular Fe and prevented Fe absorption.

Funding Sources

Funded by the United States Department of Agriculture, Agricultural Research Service.

On-Farm Evaluation in Uganda of Iron Concentration and Iron Bioavailability in the Fast Cooking Manteca Yellow Bean (Phaseolus vulgaris L.)

Objectives

To evaluate the genotype by environment (GxE) influence on Fe concentration and Fe bioavailability of select fast cooking bean varieties in Uganda.

Methods

This study compared two fast cooking Manteca genotypes (Ervilha, Cebo) to eight other white, yellow and red mottled genotypes, which included farmer local check varieties NABE15 and Masindi yellow. Genotypes were produced as a group across nine on-farm locations in Uganda over two field seasons. Cooking time was standardized with a Mattson cooking device and iron bioavailability was measured with a Caco-2 bioassay, which measures ferritin formation (ng ferritin/mg cell protein) relative to a navy bean reference control (cv. Merlin) as an indicator of iron uptake. Iron concentration was measured via inductively coupled plasma emission spectroscopy (ICP-ES).

Results

Iron concentrations of the cooked beans were highly variable across Uganda with low board sense heritability (plot basis 0.40). Iron concentrations in cooked seed ranged from 41 to 97 mg/g, with a mean of 67 mg/g across the nine production environments. Iron bioavailability ranged from 8 to 116% of navy bean control and was highly heritable (plot basis 0.80) among this subset of white, yellow and red beans. The fast cooking white (Blanco Fanesquero) and two Manteca yellow beans consistently had the highest iron bioavailability (64 – 116% of control) across all locations in Uganda. There was a significant negative association (r = −0.438, p ≤ 0.05) between cooking time and iron bioavailability of the white, yellow and red beans produced in Uganda.

Conclusions

This study demonstrates the high iron bioavailability trait of the two fast cooking Manteca yellow beans are stable across different production environments in Uganda. This study presents evidence that breeding for fast cooking times in yellow beans is not only a valuable end-use quality trait beneficial to smallholder farmers in Uganda, but could also be a sustainable approach for delivering more bioavailable iron to consumers in East Africa. The high variability of Fe concentration within genotypes raises concern that high Fe concentration can be a sustainable trait in Uganda.

Funding Sources

U.S. Agency for International Development (USAID), U.S. Department of Agriculture (USDA).

Iron Biofortification of the Common Bean: Assessment of Bean Iron Concentration and Iron Bioavailability from Markets and Breeder Collections in East Africa

Objectives

To assess the practicality and assumptions of the high Fe concentration approach for bean Fe biofortification in east Africa.

Methods

A collection of 76 marketplace samples (East Africa Marketplace Collection; EAMC) were assembled, consisting of multiple color classes from locations in Uganda, Rwanda, Democratic Republic of Congo, Burundi, Ethiopia, Kenya and Tanzania. In addition, because market samples can be a mixture of seed varieties within a market class, 170 samples from the Africa CIAT Collection were also assembled that represent beans of common markets in the region. Iron concentration was measured via inductively coupled plasma emission spectroscopy (ICP-ES) and Fe bioavailability via an established Caco-2 cell bioassay. Using these measures, the following assumptions of high Fe bean Fe biofortification approach were assessed: 1) the average Fe concentration in beans currently consumed in east Africa is approximately 50 μg/g (dry weight), 2) a 40 μg/g increase (target value 90 μg/g) can be sustained through traditional breeding, and 3) iron bioavailability from the biofortified bean will not decrease substantially to negate the increase in Fe concentration.

Results

The average EAMC bean Fe concentration was 72 μg/g, ranging from 52–93 μg/g, with a couple of outlying varieties at 105 μg/g (MAC9) and 129 μg/g (MAC49). The Africa CIAT collection averaged 67.5 μg/g with a range of 51–90 μg/g. The 18 biofortified varieties within the EAMC averaged 73 μg/g (range of 55–94 μg/g), which is essentially equal to the overall mean (70 μg/g) and range (54–93 μg/g) of the non-biofortified bean varieties in the EAMC. Using a Caco-2 cell bioassay to measure Fe bioavailability of the EAMC, the biofortified varieties did not deliver any additional Fe relative to non-biofortified varieties.

Conclusions

The results indicate that the assumptions of the high Fe bean breeding approach are not met in the typical east African market place. Furthermore, based on the Fe content and bioavailability data collected from this study, the biofortified bean varieties from these markets are providing no additional dietary Fe. An alternative approach for bean Fe biofortification, such as enhanced Fe bioavailability should be pursued.

Funding Sources

USDA.

Polyphenolic Profiles of Yellow Bean Seed Coats and Their Relationship with Iron Bioavailability

Previous work with Caco-2 cell cultures has shown that individual polyphenols can either promote or inhibit iron uptake. This investigation was designed to characterize the relationship between iron bioavailability and seed coat polyphenol composition in a panel of 14 yellow beans representing five market classes with the potential for fast cooking time and high iron content. The study included two white and two red mottled bean lines, which represent high and low iron bioavailability capacity in dry beans, respectively. Polyphenols were measured quantitatively by high-performance liquid chromatography-mass spectrometry (HPLC-MS)/UV and iron bioavailability of seed coat extracts was measured in Caco-2 assays. Thirteen of the yellow bean seed types contained high concentrations (up to 35.3 ± 2.7 μmol/g) of kaempferol 3-glucoside (k 3-g), a known promoter of iron uptake. A general association between the ratio of promoting to inhibiting polyphenols (P/I) and iron uptake was observed. The presence of iron uptake inhibiting condensed tannins proportionately countered the promotional effects of kaempferol compounds. Unidentified factors present in seed coats other than polyphenols also appeared to affect iron uptake.

A Combined In Vitro (Caco-2 Cell) and In Vivo (Gallus gallus) Assessment Reveals the Iron Benefits of Consuming the Fast Cooking Manteca Yellow Bean (Phaseolus vulgaris L.) (P10-114-19)

Objectives

The common dry bean (Phaseolus vulgaris L.) is a globally produced pulse crop and an important source of protein and micronutrients for millions of people across Latin America and Africa. In these regions, energy for cooking is expensive or scarce and long cooking times deter consumers from purchasing beans. In addition, many of the preferred black and red seed types have phytate and polyphenols that limit the absorption of trace minerals. Yellow beans are unique because their seed coats are rich in kaempferol 3-glucoside, a recently discovered promoter of iron absorption. Several market classes of yellow beans are sold throughout Latin America and Africa, where they are marketed at premium prices for their fast cooking tendencies. Exploring the yellow bean's unique heritage to develop new fast cooking varieties that deliver more absorbable iron would be useful for regions where inhabitants have limited access to fuelwood for cooking. This study compared the iron bioavailability of three fast cooking yellow beans from Africa with contrasting seed coat colors (Manteca, Amarillo, Njano) to slower cooking white and red kidney commercial varieties from North America (Table 1).

Methods

Cooked beans were formulated into diets with the complementary food crops of potato, rice and cabbage. Iron bioavailability was measured as ferritin formation in an in vitro digestion Caco-2 bioassay and the ability to maintain total body iron hemoglobin (Hb-Fe) during a 6 week in vivo (Gallus gallus) feeding trial.

Results

Animals fed yellow bean diets had faster growth rates, accumulated more dietary iron and had higher Hb-Fe than animals fed either kidney bean diet (Figure 1). In contrast to yellow beans, the kidney beans had almost no kaempferol 3-glucoside (Table 2). When compared to the other four bean based diets, the fast cooking Manteca yellow bean diet had the highest Caco-2 ferritin formation in vitro (Table 3) and delivered the largest increase in Hb-Fe in vivo (Figure 1).

Conclusions

Through the added benefit of fast preparation times and improved iron quality after cooking, this study provides evidence that the Manteca market class is worthy of germplasm enhancement as a new convenience food to help alleviate trace mineral deficiencies in regions where beans are widely accepted as a dietary staple.

Funding Sources

USDA-NIFA.

Supporting Tables, Images and/or Graphs

The cotyledon cell wall and intracellular matrix are factors that limit iron bioavailability of the common bean (Phaseolus vulgaris)

Strategies that enhance the Fe bioavailability of the bean are of keen interest to nutritionists, bean breeders and growers.

Iron deficiency: Differential effects on monoamine transporters

In this study, we extend previous work on iron deficiency and dopamine (DA) transporters to include an examination of central serotonin (5-HT) and noradrenergic (NE) transporters. Rats were fed either iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. In males, an additional group of iron deficient animals (IR) were given iron supplementation. DA, 5-HT, and NE transporter binding was done in situ on thin sections. ID males, but not females, decreased DA transporter binding in the nucleus accumbens, caudate putamen and substantia nigra by 20-40%. ID males also had a 20-30% reduction in 5-HT transporter binding in several areas (nucleus accumbens, olfactory tubercle, colliculus) while in ID females there was 15-25% increased serotonin transporter binding in the olfactory tubercle, zona incerta, anteroventral thalamic nucleus and vestibular nucleus. Iron deficiency reduced 3H-nisoxetine binding to the NE transporter in locus ceruleus and anteroventral thalamic nucleus in males but not females. Only some of the changes observed in DA, serotonin and NE transporter binding were reversible by iron supplementation. These findings show that iron deficiency affects monoamine systems related to homeostasis and in most cases males appear to be more vulnerable than females.

Iron deficiency affects acoustic startle response and latency, but not prepulse inhibition in young adult rats

Iron deficiency is associated with alterations in dopamine and serotonin transporters as well as changes in dopamine receptor (DR) density, monoamine concentrations, and in vivo extracellular contents of monoamines in terminal fields. Human infants with iron deficiency have both delayed maturation as well as lengthened central conduction times in auditory evoked potential studies. The current study utilizes the magnitude of the acoustic startle response (ASR), prepulse inhibition (PPI), and mean latency to maximum startle response (T(max)), to examine the functional integrity of response to environmental cues. Male and female rats consumed iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. ID rats of both sexes had 20-60% reductions in ASR when compared to CN rats but there was no effect on PPI. T(max) was significantly longer by 10-20% in females, but not males. Dopamine transporter density was significantly lower in putamen, nucleus accumbens, and olfactory tubercle in males, but not female rats while the serotonin transporter was significantly different from control animal density in five of 14 brain regions. Norepinephrine transporter density was lower in the locus ceruleus of ID male rats but was unaffected in ID female rats. Regression modeling of ASR with brain monoamine transporters and receptors showed hematocrit, norepinephrine transporter (NET) in dentate gyrus, and D1R in the nucleus accumbens account for nearly 49% of the variance in ASR. T(max) was not significantly associated with any of the independent variables. We conclude that iron deficiency affects the startle response, but not the inhibitory circuits involved in prepulse inhibition. Importantly, sex also strongly influenced these behavioral responses. Future studies, perhaps pharmacologic in nature, are necessary to ascertain whether iron deficiency modifies the contribution of monoaminergic systems to responses to environmental stimuli.

Thy1 expression in the brain is affected by iron and is decreased in Restless Legs Syndrome

Thy-1 is a cell adhesion molecule that plays a regulatory role in the vesicular release of neurotransmitters. The objective of this study is to examine the relationship between iron status and Thy1 expression in neuronal systems of varying complexity. Pheochromocytoma cell (PC12) cells were used to explore whether there was a direct relation between cellular iron status and Thy1 expression. Iron chelation significantly decreased expression of Thy1 in PC12 cells in a dose and time dependent manner. Transferrin receptor expression was increased with iron chelation demonstrating that a global decrease in protein synthesis could not account for the Thy1 changes. We also examined brain homogenates from adult rats that were nursed by dams on an iron deficient (ID) diet and found a significant decrease in Thy1 compared to control rats. Finally, the substantia nigra from individuals with Restless Legs Syndrome reportedly has lower than normal amounts of iron. Therefore, we examined this brain region from individuals with the clinical diagnosis of primary Restless Legs syndrome (RLS) and found the concentration of Thy1 was less than half that of controls. The results of these studies support the novel concept that there is a relationship between Thy1 and iron and point to a novel mechanism by which iron deficiency can affect brain function. They also indicate a possible mechanism by which iron deficiency compromises dopaminergic transmission in RLS, providing a potentially important link between decreased brain iron and the responsiveness to levodopa and iron supplementation treatment in RLS.

Recurrent infectious mononucleosis caused by Epstein-Barr virus with persistent splenomegaly

We present the clinical case of a 20-year-old male soldier who appeared in general good physical condition. He suffered from infectious mononucleosis caused by Epstein-Barr virus that had recurred 2 years after the first serologically documented episode. The detected splenomegaly persisted in the healthy young man, who otherwise showed no apparent immune deficiency. To our knowledge, this is an extremely rare condition.