Dietary L-serine modifies free amino acid composition of maternal milk and lowers the body weight of the offspring in mice

Abstract

The growth of offspring is affected not only by the protein in maternal milk but also by the free amino acids (FAAs) contained in it. L-Serine (L-Ser) is known as an important FAA for the development of the central nervous system and behavioral activity. However, it is not clear whether L-Ser is transported into the pool of FAAs contained in milk and thereby affects the growth of offspring. Using mice, the current study investigated the effects of dietary L-Ser during pregnancy and lactation on milk and plasma FAA composition, as well as on growth, behavior, and plasma FAAs of offspring. Dietary L-Ser did not significantly affect the maternal, anxiety-like, or cognitive behaviors of either the dam or the offspring. The FAA composition notably differed between plasma and milk in dams. In milk, dietary L-Ser increased free L-Ser levels, while glutamic acid, L-alanine, D-alanine and taurine levels were decreased. The body weight of the offspring was lowered by dietary L-Ser. The concentrations of plasma FAAs in 13-day-old offspring (fed only milk) were not altered, but 20-day-old offspring (fed both milk and parental diet) showed higher plasma L-Ser and D-Ser concentrations as a result of the dietary L-Ser treatment. In conclusion, the present study found that dietary L-Ser transported easily from maternal plasma to milk and that dietary L-Ser treatment could change the FAA composition of milk, but that an enhanced level of L-Ser in milk did not enhance the plasma L-Ser level in the offspring.

Orally administrated D-arginine exhibits higher enrichment in the brain and milk than L-arginine in ICR mice

“…Similar results have been confirmed about serine (Ser). In maternal milk, L-Ser levels increased by about 120 nmol/ml in mice fed the diet containing 2% L-Ser as compared to the control diet [14]. On the other hand, milk D-Ser levels in the mice fed with 0.5% D-Ser diet was over 2,000 nmol/ml higher than that in the mice fed with control diet (Aso et al, unpublished data).…”

Differences in free amino acid concentrations in milk between Wistar and Wistar Kyoto rats

“…Therefore, the patterns of change in free amino acid concentrations in milk were similar between WIS and WKY rats. The previous study reported that dietary L-Ser decreased body weight of offspring in mice [17]. Dietary L-Ser increased free L-Ser concentration in the milk of dams, but it did not influence free L-Ser in plasma in 13-day-old offspring.…”

“…Milk proteins are synthesized by free amino acids, peptides, proteins and glucose in plasma, and modification of the free amino acid profile in maternal plasma also influences the free amino acid profile in milk [17]. Differences in free amino acid concentrations in milk were observed between WIS and WKY rats; however, there were no significant interactions between the strains and lactation stages.…”

“…In this study, free L-Ser concentration in the milk of WKY rats was higher than that of WIS rats, but the level of increment may not influence the level of L-Ser in plasma of offspring as reported by Nagamachi et al . [17]. Free L-Ser, D-Ile, L-Leu and L-Arg concentration in milk of WKY rats were significantly higher than the WIS rats.…”

“…In addition, the relationships between free amino acid concentrations in plasma and depression or injection of antidepressants were investigated using male WIS and WKY rats [18]. However, free amino acid concentration in the milk could not be predicted by the free amino acid concentration in plasma, since the pattern of free amino acids was mostly different between milk and plasma [17, 25]. This fact suggested that free amino acids in plasma are used for milk protein synthesis and/or are metabolized differently for each free amino acid.…”