Lack of exposure to amniotic fluid could be the reason that preterm infants are more susceptible to the gastrointestinal inflammatory disease known as necrotizing enterocolitis (NEC), according to McGowan Institute for Regenerative Medicine affiliated faculty member and senior author David Hackam, M.D., Ph.D., Watson Family Professor of Surgery, Department of Surgery, Pitt School of Medicine, and co-director of the Fetal Diagnosis and Treatment Center at Children's Hospital, and researchers at Children's Hospital of Pittsburgh of UPMC and the University of Pittsburgh School of Medicine. In their report in the Proceedings of the National Academy of Sciences, they show that feeding amniotic fluid to young mice reduced the risk of NEC in an experimental model, suggesting new therapeutic avenues for warding off the deadly condition.
Dr. Hackam noted that NEC is the leading cause of death from gastrointestinal disease in babies, and most commonly affects those who are born 6 to 8 weeks too early. Twelve to 15 percent of all premature babies develop NEC.
"The disease occurs when these tiny babies are about 2 to 3 weeks of age," he said. "At first, they are a little sick, but seem OK. Then, often without warning, they stop tolerating their feeds, their bellies become swollen and, in many cases, they become critically ill within hours. When I operate on them, I see patches of dead intestinal tissue that needs to be removed. It is devastating for families."
The causes of NEC are not well understood, he added. In previous research, his team determined that a molecular switch called Toll-lie receptor 4 (TLR4) was turned on in intestinal tissue affected by NEC. Healthy infants born at term have relatively low levels of TLR4 in the gut. The protein is important in fending off infection because it is involved in the recognition of bacteria, leading the researchers to posit that unlike in healthy newborns, something goes wrong with the TLR4 response when preemies get colonized with normal gut flora.
"One big difference between a 34-week-old baby developing in its mother's uterus and one in the neonatal intensive care unit is that the first one is floating in and swallowing amniotic fluid," Dr. Hackam said. "Early delivery means that exposure to the fluid is gone, so we speculated that components of the fluid could help prevent NEC by keeping TLR4 in check."
In the study, the researchers showed that injecting small amounts of amniotic fluid into the intestine of premature mice, or feeding the fluid to them, stopped NEC from developing. That's because the fluid is rich in epidermal growth factor (EGF), a wound healing protein; when the researchers removed it from the fluid or blocked or removed the EGF receptor on intestinal cells, amniotic fluid no longer had a protective effect.
"It appears that EGF in amniotic fluid is able to shut off TLR4 activity and prevent NEC," Dr. Hackam said. "Perhaps if we one day banked amniotic fluid after premature delivery, we could give it to newborns at risk for the problem. We also could identify a drug that inhibits TLR4 activity to try to save these babies."
The research team includes lead author Misty Good, M.D., assistant professor of pediatrics, University of Pittsburgh School of Medicine; and others from Children's Hospital and University of Pittsburgh School of Medicine.
Illustration: McGowan Institute for Regenerative Medicine.
Abstract (Amniotic fluid inhibits Toll-like receptor 4 signaling in the fetal and neonatal intestinal epithelium. Misty Good, Richard H. Siggers, Chhinder P. Sodhi, Amin Afrazi, Feras Alkhudari, Charlotte E. Egan, Matthew D. Neal, Ibrahim Yazji, Hongpeng Jia, Joyce Lin, Maria F. Branca, Congrong Ma, Thomas Prindle, Zachary Grant, Sapana Shah, Dennis Slagle II, Jose Paredes, John Ozolek, George K. Gittes, and David J. Hackam. Proceedings of the National Academy of Sciences if the United States of America; published online before print June 25, 2012.)