A Fragile Existence:
Discoveries help overcome newborn vulnerabilities

BY SHAWNE NEEPER

FALL 2004 -- As he struggles mightily to draw his life's first breath, a three-pound premature newborn spurs doctors and nurses into action. Within the hour, the baby is settled in the intensive care unit, beneath a handkerchief-sized blanket, covered by a clear-plastic germ shield, and connected to tubes that pump lifesaving oxygen into his underdeveloped lungs.

A Healthy Glow: A healing blue light bathes a 1-day-old baby boy who is developing a case of neonatal jaundice.

But his safety is short-lived. Over the course of the next day, staff in the Neonatal Intensive Care Unit (NICU) notice that the whites of his eyes have begun to turn a disturbing yellow. The sickly tint spreads from his face down his body in a matter of hours, alerting his doctors to a dangerous case of neonatal jaundice. To stop the disease's rapid progression, a nurse places soft, padded goggles over his eyes and thumbnail-sized ears then switches on a wide lamp over his head that will bathe him in healing blue light.

Breathing difficulties and jaundice are two of the most common threats to newborns, and premature delivery increases a baby's vulnerability to these and other problems. To boost the prospects for these fragile newborns, physicians and researchers at Lucile Packard Children's Hospital and Stanford University are combining their clinical and scientific expertise. From research on the genetic underpinnings of lung disease in infants, to development of a breath analyzer that detects jaundice in its earliest stages, their work is creating new hope for these tiniest of babies.

Bilirubin Buildup

One of the pioneers in studying jaundice is David Stevenson, M.D., Packard Hospital's neonatology chief, who has been practicing at Stanford, and now Packard, for more than two decades. Whether trying to prevent or treat jaundice, "it's all a matter of balance," he says – balance between creation and destruction of a brownish-yellow culprit called bilirubin.

Jaundice results from the breakdown of red blood cells. As old cells are removed, they release the oxygen-carrying molecule hemoglobin. Special enzymes convert the hemoglobin into bilirubin, which is then removed by the liver. But in babies prone to severe jaundice, excess red blood cell turnover or poor liver function causes a buildup of bilirubin. As the pigment accumulates, its yellow hue permeates the skin, eyes, and the brain – where it can cause permanent hearing loss and movement problems. Too much buildup can even kill a newborn.

Today, clinicians fight jaundice with bright light, a treatment known as phototherapy, which has been evolving over the last 40 years. Exposure to over-the-crib lamps or new fiber optic blankets causes a chemical reaction in the bilirubin under the infant's skin. This reaction makes bilirubin easier to eliminate from the body.

The first phototherapy lamps used white light; but now it's clear that a particular shade of blue works best, bathing the babies in a pool of aqua light. "That wavelength is exactly right to affect bilirubin," Stevenson says. But he is working on an even better option, collaborating with Stanford University engineers to create a baby jumper, no thicker than most T-shirts, that will glow blue on the inside with the light of light-emitting diodes (LED's). The therapeutic garment will keep a newborn warm and avoid exposing sensitive young eyes to bright light as it helps clear away the extra bilirubin.

In another effort to advance jaundice treatments, William Rhine, M.D., medical director of the neonatal intensive care unit, and his colleagues are comparing different phototherapy strategies to gauge their effects on a baby's development. In this study, newborns who are treated for jaundice will undergo follow-up tests of brain function at age 3, and the researchers will compare the results of the various treatments.

"There are no good measures of infant brain injury from phototherapy," says Rhine. "To get a relevant measure of long-term health impact of the treatment, we must look later in life, which means following hundreds of children for three years. It's an expensive proposition, but necessary to determine the important, real-life results from different therapies."

No Waiting Required

But before they can treat jaundice, doctors must first detect it. Too often, babies are discharged from the hospital after birth, only to return for emergency care of sudden jaundice. Rather than wait for visible, potentially damaging bilirubin accumulation, Stevenson has been searching for ways to identify highrisk babies before jaundice sets in. The trail led to carbon monoxide, a by-product of bilirubin production. Together with colleagues across the globe, Stevenson showed that babies who are at risk for jaundice have excess carbon monoxide in their breath. As a result of this work, two companies have introduced new breath analysis machines; the latest appeared on the market this year.

"Now you don't have to wait for pigment to accumulate; you can see the problem before the child is jaundiced," Stevenson says.

The next hope for these at-risk babies lies in experimental drugs that reduce bilirubin production to prevent jaundice. The new drugs block heme oxygenase (HO), a key enzyme in conversion of hemoglobin to bilirubin. These drugs decrease bilirubin levels when first administered, but the body senses the change, and ramps up production of the HO enzyme to compensate. So Stevenson is seeking a drug that blocks HO without causing this compensatory increase in HO gene expression. His long-time collaborator, Christopher Contag, Ph.D., has a unique tool for the search.

Glowing Clues

Contag, assistant professor of pediatrics and neonatology, studies the underlying biochemistry and gene mechanisms of disease within living animals. By attaching a gene from the North American firefly to the gene for HO, Contag created a mouse that literally lights up on the inside as it produces the bilirubinmaking enzyme. To photograph where and how much HO is created, Contag places each mouse inside a black, light-sealed box the size and shape of a dorm-room refrigerator. A super-sensitive detector picks up as few as four photons from the mouse. By looking for changes in the amount of light emitted during drug treatment, Contag can evaluate whether a potential jaundice therapy is causing compensatory increases in HO gene expression.

Contag Mice: Glowing genes track bilirubin production in the liver and kidneys.

A drug that decreases HO enzyme production could prevent bilirubin buildup and stop jaundice before it begins. But HO has roles in other body systems, including the immune response, opening the question of serious side effects.

"We don’t yet know the importance of heme oxygenase in infection," says Stacy Burns, Ph.D., a postdoctoral researcher in Contag's lab. If newborns, especially preterm babies, with their undeveloped immune systems, are exposed to an HO-blocking drug, "How will this affect their response to infection?" Burns asks.

To study how the immune system develops, Burns traces an infection's path through the body in mice of varying ages by exposing them to bacteria containing a light-producing gene. The light betrays the bacteria’s location as it progresses from the gut to the liver and spleen. Burns then samples tissue from those areas to search for genes that are active in adults, but not in newborn mice. She hopes the results will reveal a key element that is missing in the immature immune response – something that might be boosted to help babies fight infection.

Struggle for Air

Infants who are born prematurely face not only greater risk of jaundice, but also a life-threatening struggle for air. Almost all preemies require breathing tubes to support their underdeveloped lungs. While the ventilation is necessary to keep some babies alive, it also creates risk of lung damage due to infection and, possibly, due to the breathing support itself.

Healthy lung tissue	Damaged lung tissue

Richard Bland, M.D., professor of pediatrics, studies lung development and mechanical ventilation. Bland demonstrated that ventilation causes the immature lungs of newborn sheep to develop fewer air sacs, called alveoli, and fewer small blood vessels, called capillaries – impairing the normal exchange of oxygen and carbon dioxide. These abnormalities mimic a type of chronic lung disease called bronchopulmonary dysplasia, Bland says, which was first described by doctors at Stanford almost 40 years ago. This condition develops most often in infants who are born very prematurely and require a lengthy period of ventilation. Bland proposed that the air pressure from ventilation over-stretches the immature lung tissue, causing abnormal development of the lungs’ elastic structure.

In support of that theory, Bland showed that ventilated lungs have an excess of elastin, a protein that is partially responsible for the lungs' stretchy quality. Healthy developing lung tissue contains elastin at well-organized, pinpoint locations. In contrast, ventilated lung tissue is besotted with thick, disorganized bands of the protein, presumably leading to the abnormal formation of alveoli and blood vessels. To explore the causes and potential treatments, Bland is examining gene expression for elastin and related proteins. By understanding how ventilation alters gene expression in lung tissue, he hopes to prevent the cascade of events that disrupts normal lung development and leads to this crippling form of chronic lung disease.

"You're paying a price" for ventilation in premature infants, agrees NICU medical director Rhine. Ventilation is often necessary to keep a preterm infant alive, but the line between enough and too much is not known. "We're trying to get off ventilation sooner," Rhine says. This fall, the NICU will join a National Institutes of Health study of ventilation’s long-term risks and benefits.

Breathing Easier

The beneficiary of all this work is resting back in the NICU on his second day of life, nestled in fleecy blankets, circled by life-supporting wires and tubes. A quiet "shu-u-sh" from his ventilator carries the needed oxygen to his lungs. The yellow tint in his skin is bathed in a health-giving blue glow. Thanks to ongoing research, his jaundice was treated immediately. Now his caregivers will watch for the earliest signs that he can breathe on his own so that everyone, including his parents, can breathe a little easier.