Scientists supported by the National Heart, Lung, and Blood Institute (NHLBI) have been able to grow new tissue in the lungs of laboratory animals for the first time. Dr. Gloria De Carlo Massaro and Dr. Donald Massaro of the Georgetown University School of Medicine showed a 50 percent increase in the number of alveoli in the lungs of newborn rats treated with retinoic acid, a drug that is a derivative of Vitamin A. The alveoli are the smallest air spaces in the lungs and the site of the exchange of oxygen and carbon dioxide between the lungs and the bloodstream. The Massaros' study appears in the February issue of the American Journal of Physiology: Lung Cellular and Molecular Physiology.
"This is extremely exciting news," said NHLBI Director Dr. Claude Lenfant. "This is the first time that anyone has been able to grow new lung tissue in laboratory animals. It provides the first suggestion that some day we may be able to use an existing agent like retinoic acid to treat lung diseases like bronchopulmonary dysplasia in which the patient has insufficient alveoli to breathe efficiently.
"Nonetheless," he added, "a great deal more basic research is needed before we can begin work in patients. Until then, we caution that there is absolutely no evidence that Vitamin A supplementation is useful in treating lung disorders."
Bronchopulmonary dysplasia (BPD) is a condition that is becoming increasingly common as physicians improve their ability to save very low-birth-weight premature infants. Ten thousand new cases are now reported each year.
In babies who develop BPD, the lungs are immature and the structures that form the gas-exchange region of the lung don't subdivide as they should to form a sufficient number of alveoli to meet the body's oxygen needs. BPD has serious health and developmental consequences and represents a major health care cost to the nation, with initial treatment costs averaging $90,000 per baby.
In their study, the Massaros set out to test whether retinoic acid could reverse the effects of dexamethasone, an anti-inflammatory compound that is known to inhibit alveolar formation in rats. Using morphometry to quantify the alveoli, the Massaros found that administering retinoic acid to newborn rats also receiving dexamethasone reduced the effects of the dexamethasone. The rats formed three times more alveoli than they would have if they'd been treated with dexamethasone alone. Morphometry is a method of counting cell numbers.