Could it be that the most widespread and devastating gastrointestinal disease affecting premature babies could be conquered simply by adding a common polypeptide, epidermal growth factor (EGF), to infant formula? And if so, exactly how does it work, and why?
Necrotizing enterocolitis (NEC) affects some 10,000 infants annually in the U.S., and over 90% are formula-fed before onset of NEC. At greatest risk are small, premature infants, and infants fed concentrated formulas. Estimates of mortality vary widely, up to 40%. International rates of incidence and mortality are thought to be similar.
Although there is no effective treatment, the incidence of NEC among formula-fed babies is estimated at six to 10 times higher than breast-fed babies, indicating important direct benefits of mother’s milk.
“Using a neonatal animal model of NEC, we have shown that when one protein found in breast milk -- epidermal growth factor (EGF) -- is added to formula, the incidence of NEC decreases by 50% compared to animals fed formula alone,” Jessica A. Clark, the lead author in a research study at the Department of Pediatrics, University of Arizona, said.
“Under conditions designed to induce NEC in neonatal rats, we found that EGF treatment alters the balance of cell death and cell survival gene expression so that neonatal intestinal cells are able to survive, short-circuiting the usual NEC progression, and enabling normal intestinal growth,” Clark added.
The complete team includes: Jessica A. Clark, Tara A. Saunders, Sarah M. Doelle, Hana Holubec, Robert H. Lane, Melissa D. Halpern and Bohuslav Dvorak, all from the Department of Pediatrics, University of Arizona, Tucson.
Finding how EGF protects intestinal cells
“Since there is currently no effective preventative treatment for NEC, it is essential that we understand the molecular mechanism of EGF protective or healing effects so that an adequate human therapy can be developed,” Clark said. In the meantime, she added, “development should start right away of an infant formula fortified with growth factors such as EGF.”
The current experiment was designed to see if EGF could protect enterocytes from apoptosis, or cell death, prior to the full onset of NEC. The Bcl-2 family of proteins is an important class of molecules that regulates intestinal cell apoptosis. Gene expression of two major Bcl-2 family members, Bcl-2 and Bax were measured after neonatal rats were exposed to conditions that induce NEC. Three groups of neonatal rats were involved: dam-fed (DF), formula fed (NEC) and formula plus 500 ng/ml EGF (NEC+EFG).
Researchers found that Bc1-2 mRNA was reduced and Bax mRNA was elevated in NEC compared to DF (p £ .01). EGF increased Bc1-2 mRNA while Bax mRNA was decreased (p £ 0.05). Bax/Bc1-2 mRNA and protein were markedly decreased in NEC+EGF animals compared to the NEC group. Cleaved caspase-3 positive epithelial cells, indicating cells undergoing apoptosis, were reduced in EGF-treated animals compared to animals with NEC (p £ 0.001).
“The most exciting finding was that EGF treatment altered the balance of cell death and cell survival gene expression such that the intestinal cells are able to survive,” Clark said. “In other words, we saw that the breast milk protein EGF protects the intestine from developing NEC.” Therefore, supplementing commercially available infant formula with EGF may be one way to prevent NEC in human babies.
Next steps and funding
Clark said that the next step “will be to further understand the molecular mechanism of the EGF healing effect in NEC, such as the EGF receptor signaling cascades that are used to promote cell survival. We are currently working on developing an in vitro system, using cultured intestinal epithelial cells, to study these signaling cascades.”
Research was supported by an American Physiological Society Porter Physiology Fellowship (Clark) and by the National Institutes of Health (Dvorak).