Concentrations of granulocyte colony-stimulating factor in human milk after in vitro simulations of digestion

Human milk contains proteins that survive digestion in the neonatal gastroi ntestinal tract. Our group and others have reported that granulocyte colony -stimulating factor (G-CSF), a hematopoietic cytokine that influences neutr ophil proliferation and differentiation, is present in human milk. We also reported that specific receptors for G-CSF are expressed on the villous ent erocytes of neonates. However, the physiologic role of milk-borne G-CSF is not known. Thus, we sought to evaluate the capacity of human milk to protec t G-CSF against proteolytic degradation after exposure to gastric secretion s obtained from preterm (PT) and term (T) neonates at pH concentrations of 3.2, 5.8, and 7.4. Specifically, we examined degradation of 1) endogenous G -CSF in PT (n = 15) and T (n = 15) human milk; 2) recombinant human G-CSF ( rhG-CSF) added to a protein-free buffer (n = 10, 5 PT and 5 T); and 3) rhG- CSF added to human milk (n = 12, 6 PT and 6 T), various commercially prepar ed infant formulas tit = 15), and cow's milli (n = 5). Endogenous G-CSF and rhG-CSF added to human milk resisted degradation at 1 and 2 h. However, wh en rhG-CSF was added to commercial formulas, >95% was degraded at 1 and 2 h at each pH level. Similarly, approximately 60% of rhG-CSF added to cow's m ilk was degraded at 1 and 2 h. We conclude that I) endogenous G-CSF and rhG -CSF added to human milk are protected from degradation after exposure to g astric secretions at physiologic pH levels, 2) rhG-CSF added to infant form ulas is not protected from degradation, and 3) it is likely that the G-CSF present in human milk is biologically available to the neonate.