Early-Life Iron Deficiency Reduces Brain Iron Content and Alters Brain Tissue Composition Despite Iron Repletion: A Neuroimaging Assessment

Abstract

Early-life iron deficiency has lifelong influences on brain structure and cognitive function, however characterization of these changes often requires invasive techniques. There is a need for non-invasive assessment of early-life iron deficiency with potential to translate findings to the human clinical setting. In this study, 28 male pigs were provided either a control diet (CONT; n = 14; 23.5 mg Fe/L milk replacer) or an iron-deficient diet (ID; n = 14; 1.56 mg Fe/L milk replacer) for phase 1 of the study, from postnatal day (PND) 2 until 32. Twenty pigs (n = 10/diet from phase 1 were used in phase 2 of the study from PND 33 to 61, where all pigs were provided a common iron-sufficient diet, regardless of their phase 1 dietary iron status. All pigs were subjected to magnetic resonance imaging at PND 32 and again at PND 61, and quantitative susceptibility mapping was used to assess brain iron content at both imaging time-points. Data collected on PND 61 were analyzed using voxel-based morphometry and tract-based spatial statistics to determine tissue concentration difference and white matter tract integrity, respectively. Quantitative susceptibility mapping outcomes indicated reduced iron content in the pons, medulla, cerebellum, left cortex, and left hippocampus of ID pigs compared with CONT pigs, regardless of imaging time-point. In contrast, iron contents were increased in the olfactory bulbs of ID pigs compared with CONT pigs. Voxel-based morphometric analysis indicated increased grey and white matter concentrations in CONT pigs compared with ID pigs that were evident at PND 61. Differences in tissue concentrations were predominately located in cortical tissue as well as the cerebellum, thalamus, caudate, internal capsule, and hippocampi. Tract-based spatial statistics indicated increased fractional anisotropy values along subcortical white matter tracts in CONT pigs compared with ID pigs that were evident on PND 61. All described differences were significant at p ≤ 0.05. Results from this study indicate that neuroimaging can sensitively detect structural and physiological changes due to early-life iron deficiency, including grey and white matter volumes, iron contents, as well as reduced subcortical white matter integrity, despite a subsequent period of dietary iron repletion.

Keywords: brain iron; iron deficiency; iron repletion; myelination; neurodevelopment; pediatric nutrition; pig.

Figure 1

Measures of average iron content in brain regions were influenced by dietary iron status, regardless of imaging time-point. Because there was no significant interaction between diet and magnetic resonance imaging (MRI) day, this figure only shows the significant main effects of diet, regardless of time. Reduced iron content in the pons (p < 0.001), medulla (p = 0.018), cerebellum (p = 0.005), left cortex (p = 0.004), and left hippocampus (p < 0.001) was observed in ID pigs compared with CONT pigs. Iron content of the olfactory bulb was increased (p = 0.043) in ID pigs compared with CONT pigs. Note that as iron content increases, quantitative susceptibility measures values change from diamagnetic (negative values) to paramagnetic (positive values). Abbreviations: control (CONT); iron deficient (ID). * Main effect of early-life dietary iron status, differs by p < 0.05.

Figure 2

Pictured here is a population-averaged pig brain, with a statistical heat map indicating differences in grey matter between dietary treatment groups. The range of red-to-yellow indicates the degree of statistical difference from significant pseudo-t values of 3.80 to 7.35, respectively, in voxels where CONT pigs exhibited increased grey matter concentrations compared with ID pigs (i.e., CONT grey matter > ID grey matter). Clusters that range from dark-to-light blue indicate increasing significance from significant pseudo-t values of 4.30 to 5.55, respectively, in voxels where ID pigs exhibit increased grey matter compared with CONT pigs (i.e., ID grey matter > CONT grey matter). (A) Brain images in coronal orientation and (B) Brain images in axial orientation. Abbreviations: control (CONT); iron deficient (ID).

Figure 3

Pictured here is a population-averaged pig brain, with a statistical heat map indicating differences in white matter between dietary treatment groups. The range of red-to-yellow indicates the degree of statistical difference from significant pseudo-t values of 4.00 to 6.40, respectively, in voxels where CONT pigs exhibited increased white matter concentrations compared with ID pigs (i.e., CONT white matter > ID white matter). Notably, no differences were observed where ID pigs exhibited increased white matter concentrations compared with CONT pigs. (A) Brain images in coronal orientation and (B) Brain images in axial orientation. Abbreviations: control (CONT); iron deficient (ID).

Figure 4

Pictured here is a population-averaged pig brain, with a statistical heat map indicating differences in white matter tract development between dietary treatment groups. Fractional anisotropy (FA) differences along predetermined white matter tracts where CONT pigs exhibited higher (p < 0.05) FA values compared with ID pigs. Representative slices were chosen to highlight areas in which FA values in CONT pigs were higher than in ID pigs. The range of red-to-yellow indicates degree of statistical difference from p = 0.05 to p = 0.001, respectively. Brain images in coronal orientation. Abbreviations: control (CONT); fractional anisotropy (FA); iron deficient (ID).