Insulin-like growth factors I and II and their binding proteins in human milk: Effect of heat treatment on IGF and IGF binding protein stability

Insulin-like growth factors (IGF-I and-II) are peptide growth factors that contribute to the growth-promoting properties of human milk. IGFs in extra cellular fluids are associated with high-affinity binding proteins (IGFBPs). In this study, IGF-I and-II, and IGFBPs in human milk were characterized, and the stability of the IGFs and IGFBPs to heat treatment was investigated. IGF-I and-II were quantified by radioimmunoassays of acid-chromatographed samples, and IGFBPs were characterized using Western ligand blotting. The concentration (mean ± SD) of IGF-I in human milk was 1.5 ± 0.5 (μg/L, compared to 2.7 ± 0.7 μg/L for IGF-II. Heat treatment did not significantly affect either IGF-I or-II content. Human milk contains a single, nonglycosylated, IGFBP, with an apparent Mr of 31 k, which was immu-noprecititable by an antibody to IGFBP-2. Stability of the IGFBP to heat treatment was assessed and was not significantly affected by heat treatment. Therefore, both IGF-I and-II, and the IGFBP in human milk appear to be stable under heat treatment conditions routinely used for processing banked human milk.