Anemia in infancy is associated with alterations in systemic metabolism and microbial structure and function in a sex-specific manner: an observational study

Abstract

Background: Anemia is a term that describes low hemoglobin concentrations and can result from micronutrient deficiencies, infection, or low birth weight. Early-life anemia, particularly iron-deficiency anemia (IDA) is associated with several negative metabolic, developmental, and cognitive outcomes, some of which persist into adulthood.

Objective: The aim of this study was to investigate alterations in systemic metabolism and fecal microbial diversity and functionality associated with anemia and IDA in male and female infants from Iquitos, Peru.

Design: Cross-sectional stool and serum samples were collected from 95 infants (53 boys and 42 girls) at 12 mo of age. The fecal microbiome was assessed by using 16S ribosomal RNA gene sequencing, and the fecal and serum metabolomes were quantified using 1H-nuclear magnetic resonance.

Results: The prevalence of anemia was 64%, with a greater proportion of anemia in male infants attributed to iron deficiency. Metabolically, anemia was associated with decreased concentrations of tricarboxylic acid cycle metabolites in both sexes (males: succinate, P = 0.031; females: fumarate, P = 0.028). In addition, anemic male infants exhibited significantly lower serum concentrations of several amino acids compared with nonanemic male infants. Although no specific structural or functional differences in the microbiota were observed with anemia in general, likely due the heterogeneity of its etiology, IDA affected the microbiome both structurally and functionally. Specifically, the abundance of butyrate-producing bacteria was lower in IDA subjects of both sexes than in nonanemic, non-iron-deficient subjects of the same sex (females: Butyricicoccus, P = 0.041; males: Coprococcus, P = 0.010; Roseburia, P = 0.027). IDA male infants had higher concentrations of 4-hydroxyphenyllactate (P < 0.001) and putrescine (P = 0.042) than those without IDA, whereas IDA female infants exhibited higher concentrations of leucine (P = 0.011) and valine (P = 0.003).

Conclusions: Sexually dimorphic differences associated with anemia and IDA are suggestive of greater mitochondrial dysfunction and oxidative stress in male infants compared with female infants, and alterations in microbial structure and function may further contribute. Differences in metabolic pathways associated with anemia and IDA in each sex point to potential mechanisms for the associated lasting cognitive deficits. This trial is registered at clinicaltrials.gov as NCT03377777.

FIGURE 1

Participant flow chart and number of samples included in analyses. All infants who were included in the study (n = 95) provided a serum sample to determine iron status and for serum metabolome analysis. A subset provided fecal samples for fecal microbiome and metabolome analyses. The total number and the number of subjects with IDA providing fecal samples are indicated. IDA, iron-deficiency anemia.

FIGURE 2

Anemic male infants (n = 38) exhibited lower serum concentrations of succinate and several amino acids in comparison to nonanemic male infants (n = 15). Anemic female infants (n = 23) only exhibited lower serum concentrations of fumarate when compared with nonanemic female infants (n = 19). Within each sex, the effect of anemia was assessed using single-factor ANCOVA with height-for-age z score as a covariate. The gray and white triangles indicate metabolites that are significantly lower (P ≤ 0.05) in anemic males compared with nonanemic males and in anemic females compared with nonanemic females, respectively. OAA, oxaloacetate; TCA cycle, tricarboxylic acid cycle; αKG, α-ketoglutarate.

FIGURE 3

The fecal microbiome and metabolome differ between IDA and reference subjects. PCoA of the unweighted UniFrac distance, rarefied to the lowest read count, of the fecal microbiome in IDA and reference subjects in male (n = 26) (A) and female (n = 19) (B) infants. PCA showing centroids of the fecal metabolome in male (n = 26) (C) and female (n = 18) (D) infants compared with reference (non–iron-deficient and nonanemic) subjects. IDA, iron-deficiency anemia; PC, principal component; PCA, principal components analysis; PCoA, Principal Coordinates Analysis.

FIGURE 4

The fecal microbiome of male infants exhibits taxonomic differences between IDA and reference subjects. The relative abundances of the microbes between IDA (n = 19) and reference (n = 7) males were assessed using ANCOVA accounting for age and HAZ. Gray boxes identify taxa that differ (P < 0.05) between IDA and reference subjects. HAZ, height-for-age z score; IDA, iron-deficiency anemia.

FIGURE 5

mTOR has a role in energy metabolism and hemoglobin synthesis. mTOR activity promotes hemoglobin production and improves oxygen consumption and oxidative capacity of the mitochondria by increasing the activity of several TCA cycle and ET chain enzymes. ID alone will downregulate the expression of both aconitase and ALA synthase through altering the stability of their mRNA transcripts. In addition, ID creates a second layer of impairment by inhibiting mTOR activity. ALA, δ-aminolevulinic acid; ET, electron transport; Hb, hemoglobin; ID, iron deficiency; mTOR, mechanistic target of rapamycin; OAA, oxaloacetate; TCA cycle, tricarboxylic acid cycle.

FIGURE 6

Mitochondrial dysfunction in anemic males may lead to hepatic fatty acid accumulation. Typically, triglycerides are taken up from the bloodstream, releasing free glycerol in the process (40). These fatty acids are then transported into the mitochondria and converted to acetyl CoA, which can enter the TCA cycle, be used for ketone body production, or be transported to the cytosol for cholesterol synthesis. In anemic male infants, no differences in glycerol concentrations were observed, indicating that cellular uptake of triglycerides is unchanged. However, mitochondrial dysfunction could impair the uptake of fatty acids into the mitochondria, resulting in the accumulation of cytosolic fatty acids and the development of fatty liver in anemic males. Because anemic female infants exhibited decreased concentrations of glycerol, this may indicate a decreased cellular fatty acid uptake and lower risk of fatty acid accumulation; TCA cycle, tricarboxylic acid cycle.

FIGURE 7

Balanced mTOR activity is critical for neuronal and glial energy metabolism, maturation of oligodendrocytes, myelination, and long-term potentiation (67–73). Considering the extensive role of mTOR in neurodevelopment, its inhibition by ID, hypoxia, low energy status, and decreased amino acid concentrations associated with anemia in anemic males could have several negative ramifications on neurodevelopment in early life. ID, iron deficiency; LTP, long-term potentiation; MBP, myelin basic protein; mTOR, mechanistic target of rapamycin; mTORC1, mechanistic target of rapamycin complex 1; OL, oligodendrocyte; PLP, proteolipid protein.