Effect of SNPs on iron metabolism

Evaluation of divalent metal transporter 1 (DMT1) (rs224589) polymorphism on blood lead levels of occupationally exposed individuals

Lead (Pb) is an environmental and public health toxicant. It affects various organ systems of the body, thereby disrupting their normal functions. To date, several genes that are known to influence the mechanism of action of lead and toxicity have been studied. Among them, the iron transporter gene, SLC11A2 (Solute Carrier 11 group A member 2) which codes for the transmembrane protein, DMT1 (Divalent Metal Transporter 1) has shown to transport other metals including zinc, copper, and lead. We investigated the influence of DMT1 polymorphism (rs224589) on blood lead (Pb-B) levels. In the present study, we enrolled 113 lead-exposed workers and performed a comprehensive biochemical analysis and genetic composition. The frequency of DMT1 variants observed in the total subjects (n = 113) was 42 % for homozygous CC wild type, 54 % for heterozygous CA, and 4 % for homozygous AA mutant. The heterozygous CA carriers presented higher Pb-B levels compared to wild type CC and mutant AA carriers. Further, a negative association was observed between Pb-B levels and hemoglobin in heterozygous CA carriers. Hence, C allele may be the risk allele that contributes to increased susceptibility to high Pb-B retention, and genotyping of DMT1 in lead exposed subjects might be used as a prognostic marker to impede organ damage due to lead toxicity.

GutSelf: Interindividual Variability in the Processing of Dietary Compounds by the Human Gastrointestinal Tract

Nutritional research is currently entering the field of personalized nutrition, to a large extent driven by major technological breakthroughs in analytical sciences and biocomputing. An efficient launching of the personalized approach depends on the ability of researchers to comprehensively monitor and characterize interindividual variability in the activity of the human gastrointestinal tract. This information is currently not available in such a form. This review therefore aims at identifying and discussing published data, providing evidence on interindividual variability in the processing of the major nutrients, i.e., protein, fat, carbohydrates, vitamins, and minerals, along the gastrointestinal tract, including oral processing, intestinal digestion, and absorption. Although interindividual variability is not a primary endpoint of most studies identified, a significant number of publications provides a wealth of information on this topic for each category of nutrients. This knowledge remains fragmented, however, and understanding the clinical relevance of most of the interindividual responses to food ingestion described in this review remains unclear. In that regard, this review has identified a gap and sets the base for future research addressing the issue of the interindividual variability in the response of the human organism to the ingestion of foods.

Evaluation of the effect of divalent metal transporter 1 gene polymorphism on blood iron, lead and cadmium levels

Divalent metal transporter 1 (DMT1), a member of the proton-coupled metal ion transporter family, mediates transport of ferrous iron from the lumen of the intestine into the enterocyte and export of iron from endocytic vesicles. It has an affinity not only for iron but also for other divalent cations including manganese, cobalt, nickel, cadmium, lead, copper, and zinc. DMT1 is encoded by the SLC11a2 gene that is located on chromosome 12q13 in humans and express four major mammalian isoforms (1A/+IRE, 1A/-IRE, 2/+IRE and 2/-IRE). Mutations or polymorphisms of DMT1 gene may have an impact on human health by disturbing metal trafficking. To study the possible association of DMT1 gene with the blood levels of some divalent cations such as iron, lead and cadmium, a single nucleotide polymorphism (SNP) (IVS4+44C/A) in DMT1 gene was investigated in 486 unrelated and healthy individuals in a Turkish population by method of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The genotype frequencies were found as 49.8% homozygote typical (CC), 38.3% heterozygote (CA) and 11.9% homozygote atypical (AA). Metal levels were analyzed by dual atomic absorption spectrometer system and the average levels of iron, lead and cadmium in the blood samples were 446.01 ± 81.87 ppm, 35.59 ± 17.72 ppb and 1.25 ± 0.87 ppb, respectively. Individuals with the CC genotype had higher blood iron, lead and cadmium levels than those with AA and CA genotypes. Highly statistically significant associations were detected between IVS4+44 C/A polymorphism in the DMT1 gene and iron and lead levels (p=0.001 and p=0.036, respectively), but no association was found with cadmium level (p=0.344). This study suggested that DMT1 IVS4+44 C/A polymorphism is associated with inter-individual variations in blood iron, lead and cadmium levels.

The A Allele of the -576G>A polymorphism of the transferrin gene is associated with the increased risk of age-related macular degeneration in smokers

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly in developed countries, and its pathogenesis is underlined by genetic and environmental factors. Oxidative stress is a major environmental risk factor of AMD; namely, AMD is associated with the increased level of reactive oxygen species, which may be produced in reactions catalyzed by iron present in the retina. Therefore, variability of the genes of iron metabolism may be important in the AMD risk. In the present study, we analyzed the association between AMD and the -576G>A polymorphism of the transferrin gene or the 1892C>T polymorphism of the transferrin receptor 2 (TFR2) gene in 278 patients with AMD and 105 controls. The former polymorphism is located in the promoter region of the transferrin gene and may affect the level of its transcription, while the latter is a synonymous mutation in the exon 16, which may affect the efficiency of translation of TFR2 mRNA. Transferrin and TFR2 are important in iron homeostasis. The A allele of the -576A>G polymorphism was significantly associated with the increased risk of AMD in tobacco smokers, whereas the 1892C>T polymorphism did not influence the risk of AMD related to smoking. Moreover, each polymorphism does not influence the risk of AMD associated with age, sex or the family history of the disease. In conclusion, the A allele of the -576A>G polymorphism of the transferrin gene may increase the risk of AMD in smokers.

Micronutrient bioavailability research priorities

A micronutrient bioavailability workshop, which involved international experts and members of the scientific community and the food industry, with interactive breakout sessions based on synectics principles, was organized by the International Life Sciences Institute Europe Addition of Nutrients to Food Task Force and the European Commission Network of Excellence European Micronutrient Recommendations Aligned. After presentations by experts, a series of "challenge statements" was discussed. The aim was to address topical issues, in particular those that linked bioavailability with the derivation of micronutrient requirements and dietary recommendations, to identify gaps in knowledge and to consider research priorities. Several generic research priorities were identified, including improving the quality of dietary surveys/food composition tables, the need for more metabolic studies that use stable isotopes and high-quality longer-term interventions, and the development of multifactorial mathematical models. Among the common recurrent factors identified as important were polymorphisms/genotype, consideration of the whole diet, chemical form of the micronutrient, and the determination of physiologic requirements. The involvement of all participants in the structured discussions ensured a broad overview of current knowledge, state-of-the-art research, and consideration of priorities for future research.

Nonheme-iron absorption in first-degree relatives is highly correlated: a stable-isotope study in mother-child pairs

BACKGROUND

Iron absorption in humans is highly variable even after iron status and dietary components that influence iron absorption are controlled for. Inherited factors may help explain this variance.

OBJECTIVE

Our objective was to compare nonheme-iron absorption from a noninhibitory, stable-isotope-labeled test meal in preschool-aged children and their mothers.

DESIGN

We provided 72 test meals based on degermed maize flour and milk powder and fortified with [(57)Fe]ferrous fumarate or [(58)Fe]ferrous sulfate to healthy Mexican preschool children [n = 18; mean (+/-SD) age: 3.6 +/- 1.0 y] and their mothers [n = 18; mean (+/-SD) age: 28.0 +/- 5.2 y]. Iron absorption was calculated on the basis of incorporation of isotopes into erythrocytes after 14 d and was adjusted for differences in iron status.

RESULTS

There was a wide variation in iron absorption from the test meals: in the mothers and children, the median fractional absorption of ferrous sulfate was 22.55% (range: 1.65-54.83%) and 5.51% (range: 2.23-17.20%), respectively (P < 0.0001). After adjustment for serum ferritin, the significant difference in absorption between mothers and their children disappeared. Despite this broad range of iron absorption, corrected fractional iron absorption from the ferrous fumarate-fortified (r(2) = 0.582) and the ferrous sulfate-fortified test meals (r(2) = 0.557) was strongly correlated in mothers and their children (P < 0.0001). There was a striking positive correlation between the mean corrected fractional iron absorption from both test meals in mothers and their children (r(2) = 0.782, P < 0.0001). In regression analyses that included age, sex, and hemoglobin, the only significant predictor of corrected fractional iron absorption in children was corrected fractional iron absorption in their mothers (standardized beta = 0.884, P < 0.001).

CONCLUSIONS

Nonheme-iron absorption exhibits a strong familial tendency. After differences in meal matrix and serum ferritin are accounted for, these data suggest that inheritance and/or shared environmental factors explain most of the variance in dietary iron absorption.