mRNA Levels of Placental Iron and Zinc Transporter Genes Are Upregulated in Gambian Women with Low Iron and Zinc Status

Abstract

Background: The role of the placenta in regulating micronutrient transport in response to maternal status is poorly understood.Objective: We investigated the effect of prenatal nutritional supplementation on the regulation of placental iron and zinc transport.Methods: In a randomized trial in rural Gambia [ENID (Early Nutrition and Immune Development)], pregnant women were allocated to 1 of 4 nutritional intervention arms: 1) iron and folic acid (FeFol) tablets (FeFol group); 2) multiple micronutrient (MMN) tablets (MMN group); 3) protein energy (PE) as a lipid-based nutrient supplement (LNS; PE group); and 4) PE and MMN (PE+MMN group) as LNS. All arms included iron (60 mg/d) and folic acid (400 μg/d). The MMN and PE+MMN arms included 30 mg supplemental Zn/d. In a subgroup of ∼300 mother-infant pairs, we measured maternal iron status, mRNA levels of genes encoding for placental iron and zinc transport proteins, and cord blood iron levels.Results: Maternal plasma iron concentration in late pregnancy was 45% and 78% lower in the PE and PE+MMN groups compared to the FeFol and MMN groups, respectively (P < 0.001). The mRNA levels of the placental iron uptake protein transferrin receptor 1 were 30-49% higher in the PE and PE+MMN arms than in the FeFol arm (P < 0.031), and also higher in the PE+MMN arm (29%; P = 0.042) than in the MMN arm. Ferritin in infant cord blood was 18-22% lower in the LNS groups (P < 0.024). Zinc supplementation in the MMN arm was associated with higher maternal plasma zinc concentrations (10% increase; P < 0.001) than in other intervention arms. mRNA levels for intracellular zinc-uptake proteins, in this case zrt, irt-like protein (ZIP) 4 and ZIP8, were 96-205% lower in the PE+MMN arm than in the intervention arms without added zinc (P < 0.025). Furthermore, mRNA expression of ZIP1 was 85% lower in the PE+MMN group than in the PE group (P = 0.003).Conclusion: In conditions of low maternal iron and in the absence of supplemental zinc, the placenta upregulates the gene expression of iron and zinc uptake proteins, presumably in order to meet fetal demands in the face of low maternal supply. The ENID trial was registered at www.controlled-trials.com as ISRCTN49285450.

Keywords: intervention; iron; lipid-based nutrient supplement; mRNA; micronutrient; placenta; prenatal; transporter; zinc.

FIGURE 1

Subject flowchart summarized according to Consolidated Standards of Reporting Trials. FeFol, iron and folic acid; MMN, multiple micronutrient; PE, protein energy.

FIGURE 2

Maternal plasma concentrations of hemoglobin (A), ferritin (B), hepcidin (C), iron (D), sTfR (E), transferrin (F), and UIBC (G) at booking and 20 and 30 wk of pregnancy, by intervention arm. Data were analyzed by repeated-measures 2-factor ANOVA, adjusted for gestational age and maternal BMI at booking, season of birth, maternal parity, and log-transformed C-reactive protein. Significance of supplementation (P_s), week (P_w), and its interaction (P_sw) for each concentration are as follows: hemoglobin: P_s = 0.023, P_w < 0.001, P_sw < 0.001; ferritin: P_s < 0.001, P_w < 0.001, P_sw < 0.001; hepcidin: P_s < 0.001, P_w < 0.001, P_sw < 0.001; iron P_s < 0.001, P_w < 0.001, P_sw < 0.001; sTfR: P_s = 0.019, P_w = 0.005, P_sw < 0.001; transferrin: P_s = 0.003, P_w < 0.001, P_sw < 0.001; and UIBC: P_s < 0.001, P_w < 0.001, P_sw < 0.001. Then, for each time point, data were analyzed by 1-factor ANOVA adjusted for the variables listed above. When the effect of supplementation was significant, this ANOVA was followed by the post hoc t test. Transferrin and UIBC are presented as adjusted means ± SEMs (n = 71–75). Hemoglobin, ferritin, hepcidin, and iron were log-transformed before analysis and are presented as the back-transformed adjusted means and their corresponding back-transformed 95% CIs (n = 66–75). Means at a given time point without a common letter differ, P < 0.05. FeFol, iron and folic acid; MMN, multiple micronutrient; PE, protein energy; sTfR, serum soluble transferrin receptor; UIBC, unbound iron-binding capacity.

FIGURE 3

Maternal plasma zinc concentrations at 30 wk of gestation, by intervention arm. Data were analyzed by 1-factor ANOVA, adjusted for gestational age and maternal BMI at booking, season of birth, and maternal parity. Values are adjusted means ± SEMs (n = 71–74). Means without a common letter differ, P < 0.05 (post hoc t test). FeFol, iron and folic acid; MMN, multiple micronutrient; PE, protein energy.

FIGURE 4

Placental mRNA expression of TfR1 relative to the ubiquitin housekeeper, by intervention arm. Placental samples with an RNA integrity number >4 were analyzed. Log-transformed data were analyzed by 1-factor ANOVA, adjusted for gestational age and maternal BMI at booking, season of birth, and maternal parity. Values are back-transformed adjusted means and their corresponding back-transformed 95% CIs (n = 69–73). Means without a common letter differ, P < 0.05. FeFol, iron and folic acid; MMN, multiple micronutrient; PE, protein energy; TfR1, transferrin receptor 1.

FIGURE 5

Placental mRNA expression of the zinc uptake genes ZIP1 (A), ZIP4 (B), and ZIP8 (C), relative to the ubiquitin housekeeper, by intervention arm. Placental samples with an RNA integrity number >4 were analyzed. Log-transformed data were analyzed by 1-factor ANOVA, adjusted for gestational age and maternal BMI at booking, season of birth, and maternal parity. Values are back-transformed adjusted means and their corresponding back-transformed 95% CIs (n = 69–73). Means without a common letter differ, P < 0.05. FeFol, iron and folic acid; MMN, multiple micronutrient; PE, protein energy; ZIP, zrt, irt-like protein.

FIGURE 6

Cord blood concentrations of Hb (A), iron (B), and ferritin (C), by intervention arm. Data were analyzed by 1-factor ANOVA, adjusted for gestational age and maternal BMI at booking, season of birth, and maternal parity. Values are adjusted means ± SEMs (n = 50–61). Means without a common letter differ, P < 0.05. conc., concentration; FeFol, iron and folic acid; Hb, hemoglobin; MMN, multiple micronutrient; PE, protein energy.