Concentrations of Purine Metabolites Are Elevated in Fluids from Adults and Infants and in Livers from Mice Fed Diets Depleted of Bovine Milk Exosomes and their RNA Cargos

Abstract

Background Humans and mice absorb bovine milk exosomes and their RNA cargos. Objectives The objectives of this study were to determine whether milk exosome– and RNA-depleted (ERD) and exosome- and RNA-sufficient (ERS) diets alter the concentrations of purine metabolites in mouse livers, and to determine whether diets depleted of bovine milk alter the plasma concentration and urine excretion of purine metabolites in adults and infants, respectively. Methods C57BL/6 mice were fed ERD (providing 2% of the microRNA cargos compared with ERS) and ERS diets starting at age 3 wk; livers were collected at age 7 wk. Plasma and 24-h urine samples were collected from healthy adults who consumed (DCs) or avoided (DAs) dairy products. Spot urine samples were collected from healthy infants fed human milk (HM), milk formula (MF), or soy formula (SF) at age 3 mo. Purine metabolites were analyzed in liver, plasma, and urine; mRNAs and microRNAs were analyzed in the livers of female mice. Results We found that 9 hepatic purine metabolites in ERD-fed mice were 1.76 ± 0.43 times the concentrations in ERS-fed mice (P < 0.05). Plasma concentrations and urine excretion of purine metabolites in DAs was ≤1.62 ± 0.45 times the concentrations in DCs (P < 0.05). The excretion of 13 purine metabolites in urine from SF infants was ≤175 ± 39 times the excretion in HM and MF infants (P < 0.05). mRNA expression of 5′-nucleotidase, cytosolic IIIB, and adenosine deaminase in mice fed ERD was 0.64 ± 0.52 and 0.60 ± 0.28 times the expression in mice fed ERS, respectively. Conclusion Diets depleted of bovine-milk exosomes and RNA cargos caused increases in hepatic purine metabolites in mice, and in plasma and urine from human adults and infants, compared with exosome-sufficient controls. These findings are important, because purines play a role in intermediary metabolism and cell signaling.

Biological Properties of Milk-Derived Extracellular Vesicles and Their Physiological Functions in Infant

“…Similarly, the concentration of urinary purine metabolites was significantly higher in infants fed with soy milk or formula than breast-fed infants. This difference suggested that the absence of breast milk-derived exosomes could affect normal brain function in infants (Aguilar-Lozano et al, 2018). A longitudinal study indicated that psychomotor development is higher in breastfeeding babies than in babies fed with formula milk or soy milk.…”

Milk-Derived Exosomes and Metabolic Regulation

“…Aberrant metabolism of purines has been implicated in the loss of SLM in mice fed the ERD diet. The purine metabolites adenosine and ATP play an important role in SLM, and hepatic levels of purine metabolites were substantially higher in mice fed the ERD diet compared with ERS controls (138,139). Effects of milk feeding on purine metabolites were similar in human cohorts compared with the changes observed in mice: The concentrations of purine metabolites were higher in plasma and urine in human milk avoiders compared with milk consumers and in infants fed soy formula compared with infants fed human milk or milk formula (139).…”

“…The purine metabolites adenosine and ATP play an important role in SLM, and hepatic levels of purine metabolites were substantially higher in mice fed the ERD diet compared with ERS controls (138,139). Effects of milk feeding on purine metabolites were similar in human cohorts compared with the changes observed in mice: The concentrations of purine metabolites were higher in plasma and urine in human milk avoiders compared with milk consumers and in infants fed soy formula compared with infants fed human milk or milk formula (139). The mechanisms by which milk exosomes and RNA cargos alter purine metabolism is unknown, although the authors proposed that miR-362-3p and miR-30a-5p in milk exosomes might be responsible for the differential expression of 5 × -nucleotidase, cytosolic IIIB, and adenosine deaminase in livers from mice fed ERD or ERS diets.…”

Human milk extracellular vesicle miRNA expression and associations with maternal characteristics in a population-based cohort from the Faroe Islands

“…Milk EVs are released by the luminal epithelium and have been demonstrated to survive digestion in vitro and may be taken up by recipient cells in the infant 6 – 10 . These milk EVs can then induce changes in gene expression in vitro 6 , induce systemic metabolic alterations in vivo 9 , and may play a role in newborn immunity 11 – 13 .…”