Abstract
Tryptophan, critical for infant neurodevelopment, is limited in infant formulas. Tryptophan-rich α-lactalbumin is abundant in human milk but limited in bovine milk, and its metabolism in developing infants remains unclear. We developed an α-lactalbumin-enriched formula and conducted a feeding study with neonatal piglets to comprehensively monitor tryptophan utilization across serum, urine, liver, and brain using gas chromatography mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR)-based metabolomics. Enrichment of α-lactalbumin led to higher circulating tryptophan and increased serotonin levels in the striatum. It also increased metabolic products from the kynurenine and indole pathways, which were predominantly excreted in urine. Despite these increases, the activity of the kynurenine pathway in the liver was lower, possibly mediated by reduced circulating cortisol, thus increasing brain tryptophan availability and favoring serotonin synthesis. These findings provide mechanistic insights that can guide the development of infant formulas to better mimic the metabolic profile of breastfed infants.