Concentrations of Granulocyte Colony-Stimulating Factor in Human Milk after in Vitro Simulations of Digestion

Abstract

Human milk contains proteins that survive digestion in the neonatal gastrointestinal tract. Our group and others have reported that granulocyte colony-stimulating factor (G-CSF), a hematopoietic cytokine that influences neutrophil proliferation and differentiation, is present in human milk. We also reported that specific receptors for G-CSF are expressed on the villous enterocytes 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 protect G-CSF against proteolytic degradation after exposure to gastric secretions 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 prepared infant formulas (n = 15), and cow's milk (n = 5). Endogenous G-CSF and rhG-CSF added to human milk resisted degradation at 1 and 2 h. However, when 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 milk was degraded at I and 2 h. We conclude that 1) endogenous G-CSF and rhG-CSF added to human milk are protected from degradation after exposure to gastric secretions at physiologic pH levels, 2) rhG-CSF added to infant formulas is not protected from degradation, and 3) it is likely that the G-CSF present in human milk is biologically available to the neonate.

Excretion of Granulocyte Colony-Stimulating Factor into Human Breast Milk

“…Endogenous G-CSF in human milk is reportedly protected from degradation and is, therefore, absorbed from specific receptors for G-CSF expressed on the villous enterocytes. However, exogenously administered G-CSF excreted into milk is not protected from degradation and is, therefore, not absorbed in vitro [6, 7, 8, 9]. In our patient, because she stopped breastfeeding, we could not determine the G-CSF absorption from enterocytes or the blood concentration in her infant, but we found that G-CSF, administered subcutaneously for the harvest of peripheral blood stem cells, was excreted into milk.…”

Maternal surfactant protein A influences the immunoprotective properties of milk in a murine model

“…G-CSF is present in human milk and the G-CSF receptor is present in newborn intestines (23,24). Further, cytokines and chemokines may be functional postingestion (25). Thus, milk proteins have the potential for physiologic function in the newborn.…”

Presence of Macrophage Migration Inhibitory Factor in Human Milk: Evidence in the Aqueous Phase and Milk Fat Globules

“…It is still unclear, however, how milk cytokines can avoid inactivation and retain their biologic activity through the gastrointestinal tract. Human milk contains factors limiting proteolysis (37,38) or increasing the pH of the stomach, thereby protecting cytokines from degradation after exposure to gastric secretion (39). Compartmentalization in different fractions of human milk has also been suggested as an additional mechanism of protection (2).…”