Human breast milk contains a unique substance that may protect newborn infants from necrotizing enterocolitis (NEC), according to a study presented at the annual meeting of the American College of Surgeons.
Overall, NEC affects 7% of babies admitted to the neonatal intensive care unit, and kills as many as 50% of them, but it almost never occurs in breast-fed infants. “We know that breast milk is somehow protective against this disease,” said Dr. Elizabeth Pontarelli, MD, research fellow at Children’s Hospital in Los Angeles.
NEC occurs primarily in premature, pre-term and low birth weight infants, as well as those with cardiac defects who have insufficient oxygen flow to the intestines.
“In NEC, the intestine becomes extremely inflamed, and the inflammation process causes the clotting of small vessels that supply blood, and the intestines will actually die,” she explained. “As a result, a whole cascade of things happens. Inflammation causes the intestinal barrier to break down so that bacteria can cross over, get into the blood and cause a systemic infection.”
Breast Feeding Lowers Prevalence
While NEC occurs in fewer than 1% of breast-fed pre-term or LBW infants, the disease affects between 10 and 20% of those who are formula-fed. The markedly lower prevalence of NEC among breast-fed babies has led some researchers to hypothesize that breast milk contains something that is somehow protective.
Dr. Pontarelli’s research turns on a protein being referred to as “P-glycoprotein (PGP)-like factor.”
“PGP exists in the epithelial cell of the intestine, as well as the liver, the kidney, and the brain as part of the brain-blood barrier. PGP goes across the membrane, connecting the inside with the outside of the cell, and functions mostly in cells that have the ability to extract things from the body,” said Dr. Pontarelli.
Earlier work by Dr. Henri Ford at Children’s Hospital Los Angeles, showed that expression of PGP down-regulates intestinal inflammation, and moreover, that breast milk seemed to induce intestinal PGP expression. This led to the question of what specific breast milk components were responsible for this apparently protective effect.
Dr. Pontarelli and her colleagues treated cells from a self-renewing intestinal epithelial cell line with human breast milk obtained from six healthy human volunteers who had children in hospital daycare.
“The active fraction of breast milk was obtained by removing lipids and precipitating with ammonium sulfate.” They initially identified hundreds of breast milk proteins, eventually zeroing in on a smaller number of proteins with PGP-producing activity. Researchers then tested the endothelial cell lines with the various proteins to determine whether they could prevent bacterially-induced apoptosis.
The effect of the protein seemed to peak between four and eight hours after incubation, and reduced bacterially-induced apoptosis from 19% to 4%. Dr. Pontarelli believes that in vivo, the protein in the breast milk prevents a baby’s premature intestine from over-reacting to bacteria. The data were published in the Journal of the American College of Surgeons in September.
The findings provided an interesting turn in a line of research that began 18 years ago.
“Originally, we thought we were studying PGP, and we thought the breast milk was up-regulating PGP in the intestine, but the experiments did not turn out the way we expected. What we thought was PGP in the cells was actually something in the breast milk,”explained Dr. Pontarelli.
Breast milk’s preventive powers against NEC are only one of the many factors which lead physicians to advocate for breast-feeding, according to Dr. Pontarelli. “There’s excellent evidence that points to the conclusion that mothers should breast feed whenever possible. Breast-feeding reduces the risk of allergies, asthma and obesity, andit may increase the baby’s IQ,” she said.
“Some ICUs are going breast milk only, and they’re not giving babies formula any more,” Dr. Pontarelli said, adding that other institutions are banking donor breast milk.”
“Unfortunately, when the baby is born prematurely, the mother may not have developed the appropriate hormones to produce breast milk. Then, the mother is frequently in a different hospital than the baby. We sometimes have dads transport the milk over, but most of those babies are too underdeveloped to have a suck mechanism, so we have to feed the baby through a tube. Or the baby may be intubated, because its lungs are not fully developed, in which case the baby can’t suck,” she explained.
“So, it become more important to determine at which stages of breast feeding this PGP factor is maximal, to see if, as a formula supplement, it would serve the same effective purpose as it does when it is in the breast milk,” she noted.