Partial purification and characterization of epidermal growth factor in human breast milk

Human epidermal growth factor (hEGF), a potent growth stimulator of many tissues in culture, has been isolated from human urine and subsequently identified in many human biological fluids including breast milk. In this study, partial purification and characterization of hEGF-like substance(s) in human milk were performed using homologous hEGF radioimmunoassay (RIA) and radioreceptor assay (RRA). hEGF-like material(s) was extracted from pooled human milk by ethanol precipitation, followed by adsorption to cation- and anion-exchange resin. DEAE-Sephadex G-25 ion-exchange chromatography of human milk extracts revealed three major components with hEGF activity (peak I, II, III) eluted with a linear gradient by ammonium acetate. The competitive binding curves for these components were parallel to those for standard hEGF in both RIA and RRA. The apparent molecular weight of peak I was approximately 6,500 and that of peak II and III was approximately 7,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The pI value for peak I was approximately 4.5 and that for peaks II and III was approximately 5.0 by isoelectric focusing. These data are comparable to the size and charge heterogeneity of hEGF in human urine extracts. In conclusion, the major components of hEGF in human milk appear to be physicochemically, immunologically and biologically (receptor binding activity) indistinguishable from hEGF of urinary origin.