Free fatty acids created during the digestion of infant formula cause cellular death that may contribute to necrotizing enterocolitis, a severe intestinal condition that is often fatal and occurs most commonly in premature infants, according to a study by University of California, San Diego bioengineers.
Their report, which was based on in vitro tests comparing the digestion of fresh human breast milk and nine different infant formulas, was published online in the journal Pediatric Research. Scientists have long known that premature infants fed formula are more likely to develop necrotizing enterocolitis than those fed breast milk. The condition is the leading cause of death from gastrointestinal diseases in premature infants, but the underlying mechanism has not been understood. Alexander Penn, a research scientist working in the Microcirculation Laboratory of bioengineering Professor Geert Schmid-Schönbein from the UC San Diego Jacobs School of Engineering, believes they have come closer to an answer.
Penn and others had previously determined that the partially digested food in a mature, adult intestine is capable of killing cells, due to the presence of free fatty acids which have a “detergent” capacity that damages cell membranes. The intestines of healthy adults and older children have a mature mucosal barrier that may prevent damage due to free fatty acids. However, the intestine is leakier at birth, particularly for preterm infants, which could be why they are more susceptible to necrotizing enterocolitis.
Therefore, the researchers wanted to know what happens to breast milk as compared to infant formula when they are exposed to digestive enzymes. They “digested,” in vitro, infant formulas marketed for full term and preterm infants as well as fresh human breast milk using pancreatic enzymes or fluid from an intestine. They then tested the formula and milk for levels of free fatty acids. They also tested whether these fatty acids killed off three types of cells involved in necrotizing enterocolitis: epithelial cells that line the intestine, endothelial cells that line blood vessels, and neutrophils, a type of white blood cell that is a kind of “first responder” to inflammation caused by trauma in the body.
Overwhelmingly, the digestion of formula led to cellular death, or cytotoxicity – in less than 5 minutes in some cases – while breast milk did not. For example, digestion of formula caused death in 47 percent to 99 percent of neutrophils while only 6 percent of them died as a result of milk digestion. The study found that breast milk appears to have a built-in mechanism to prevent cytotoxicity. The research team believes most food, like formula, releases high levels of free fatty acids during digestion, but that breast milk is digested in a slower, more controlled, process.