The Concentration of Liver-Expressed Antimicrobial Peptide 2 in Human Milk and Infant Plasma Is Positively Associated with Adiposity and Body Weight in the First Year of Life

The liver-expressed antimicrobial peptide 2 (LEAP2) is a recently recognized anorectic and glucose-regulating hormone with an unknown role in lactation. The objectives of this study were as follows: 1) to assess LEAP2 presence in human milk and putative associations with infant body weight and adiposity in the first year of life, 2) to evaluate the impact of maternal weight status on LEAP2 concentration, and 3) to explore the relationship between infant plasma LEAP2 concentration and body weight and adiposity. This prospective cohort observational study assessed LEAP2 concentration in plasma and milk from lactating women with normal weight (n = 26) or overweight or obesity (OW/OB, n = 26) at 6 mo postpartum and in 6-mo-old infant plasma, examining associations with metabolic and anthropometric variables at 6 mo and 1 y. Maternal plasma and milk leptin and insulin concentrations were also measured. LEAP2 expression in milk fat globules and single-cell-RNA-sequencing datasets was evaluated. LEAP2 was detected in all milk samples assessed (2.08 ± 0.65 ng/mL) and was positively associated with infant triceps (P = 0.022, Cohen f2 = 1.25) and subscapular (P = 0.008, f2 = 0.68) skinfolds at 1 y old. Maternal LEAP2 was positively associated with insulin (P = 0.005, f2 = 0.30) and prepregnancy body mass index (BMI) (P = 0.040, f2 = 0.17) and negatively associated with gestational weight gain (P = 0.008, f2 = 0.25) and postpartum weight retention (P = 0.036, f2 = 0.15). Maternal LEAP2 was higher in plasma (P = 0.039), but not milk of lactating women with OW/OB. Infant plasma LEAP2 (1.98 ± 0.28 ng/mL) was positively associated with weight (P = 0.004, f2 = 0.63), BMI (P = 0.049, f2 = 0.37), and weight-for-length (P = 0.024, f2 = 0.35) z-scores at 1 y old, predominantly in males. No evidence for LEAP2 mRNA expression was found in mammary cells. Milk LEAP2 is a bioactive component that plays a role in infant fat accretion in the first year of life. Although maternal LEAP2 responds to weight change in pregnancy and lactation, infant plasma LEAP2 might be involved in body weight regulation in early life. This trial was registered at clinicaltrials.gov as NCT05798676.