Hyaluronan reduces surfactant inhibition and improves rat lung function after meconium injury.

Hyaluronan (HA), an ionic polymer, is normally present in the alveolar subphase and is known to decrease lung surfactant inactivation caused by serum in vitro. In this study, we examined whether HA can ameliorate the inactivating effects of meconium in vitro and in vivo. Surface activities of various mixtures of Survanta, HA, and meconium were measured using a modified pulsating bubble surfactometer. With meconium, almost all surface activity measures were improved by the addition of HA of several molecular weights at a concentration of 0.25%. Anesthetized, paralyzed rats were maintained on positive-pressure ventilation. After lung injury by instillation of meconium, they were treated with Survanta, Survanta with HA, or control mixtures. Serial measures of blood gases and peak inspiratory pressure were recorded for the duration of the experiment. When the Survanta plus HA group was compared with the Survanta alone group, arterial oxygen tension averaged 117% higher, peak inspiratory pressure was 27% lower at the end of the experiment, and lung compliance also showed significant improvement. These results indicate that HA added to Survanta decreases inactivation caused by meconium in vitro and improves gas exchange and pulmonary mechanics of animals with meconium-induced acute lung injury.

Hyaluronan decreases surfactant inactivation in vitro.

Hyaluronan (HA) is an anionic polymer and a constituent of alveolar fluid that can bind proteins, phospholipids, and water. Previous studies have established that nonionic polymers improve the surface activity of pulmonary surfactants by decreasing inactivation of surfactant. In this work, we investigate whether HA can also have beneficial effects when added to surfactants. We used a modified pulsating bubble surfactometer to measure mixtures of several commercially available pulmonary surfactants or native calf surfactant with and without serum inactivation. Surface properties such as equilibrium surface tension, minimum and maximum surface tensions on compression and expansion of a surface film, and degree of surface area reduction required to reach a surface tension of 10 mN/m were measured. In the presence of serum, addition of HA dramatically improved the surface activities of all four surfactants and in some cases in the absence of serum as well. These results indicate that HA reduces inactivation of surfactants caused by serum and add evidence that endogenous HAs may interact with alveolar surfactant under normal and abnormal conditions.

Polyethylene glycol-surfactant for lavage lung injury in rats.

Addition of ionic and nonionic water-soluble polymers to pulmonary surfactants in the presence of inactivating substances prevents surfactant inactivation in vitro and improves lung function in several models of lung injury. However, a recent report found opposite effects when surfactant plus polyethylene glycol (PEG) was used to treat lung injury caused by saline lung lavage. Therefore, we examined the reasons why the polymer effect is less evident in the saline lung lavage lung injury model. We treated rats with lavage lung injury with a commercial lung surfactant extract derived from bovine lung (Survanta) with or without addition of PEG. Groups treated with Survanta + PEG had significantly higher static post mortem lung volumes than groups treated with Survanta. However, groups treated with Survanta + PEG had more tracheal fluid and no significant benefit in arterial oxygenation compared with the group treated with Survanta, despite our use of measures to reduce pulmonary edema. Measurements after intravascular injections of (125)I-labeled albumin confirmed that addition of PEG increased extravascular lung water and that this effect is mitigated by furosemide. We conclude that surfactant + PEG mixtures are less effective in lavage injury than in other forms of lung injury because of increased extravascular lung water.

Pulmonary collectins modulate strain-specific influenza a virus infection and host responses.

Collectins are secreted collagen-like lectins that bind, agglutinate, and neutralize influenza A virus (IAV) in vitro. Surfactant proteins A and D (SP-A and SP-D) are collectins expressed in the airway and alveolar epithelium and could have a role in the regulation of IAV infection in vivo. Previous studies have shown that binding of SP-D to IAV is dependent on the glycosylation of specific sites on the HA1 domain of hemagglutinin on the surface of IAV, while the binding of SP-A to the HA1 domain is dependent on the glycosylation of the carbohydrate recognition domain of SP-A. Here, using SP-A and SP-D gene-targeted mice on a common C57BL6 background, we report that viral replication and the host response as measured by weight loss, neutrophil influx into the lung, and local cytokine release are regulated by SP-D but not SP-A when the IAV is glycosylated at a specific site (N165) on the HA1 domain. SP-D does not protect against IAV infection with a strain lacking glycosylation at N165. With the exception of a small difference on day 2 after infection with X-79, we did not find any significant difference in viral load in SP-A(-/-) mice with either IAV strain, although small differences in the cytokine responses to IAV were detected in SP-A(-/-) mice. Mice deficient in both SP-A and SP-D responded to IAV similarly to mice deficient in SP-D alone. Since most strains of IAV currently circulating are glycosylated at N165, SP-D may play a role in protection from IAV infection.

Increased pulmonary blood flow does not alter surfactant protein gene expression in lambs within the first week of life.

Neonates and infants with congenital heart disease with increased pulmonary blood flow suffer morbidity from poor oxygenation and decreased lung compliance. In a previous experiment involving 4-wk-old lambs with pulmonary hypertension secondary to increased pulmonary blood flow following an in utero placement of an aortopulmonary vascular graft, we found a decrease in surfactant protein (SP)-A gene expression as well as a decrease in SP-A and SP-B protein contents. To determine the timing of these changes, the objective of the present study was to characterize the effect of increased pulmonary blood flow and pulmonary hypertension on SP-A, -B, and -C gene expressions and protein contents within the first week of life. Of eight fetal lambs that underwent the in utero placement of the shunt, there was no difference in the expression of SP-A, -B, and -C mRNA levels or SP-A and -B protein contents compared with age-matched controls. The results showed that, in this model of congenital heart disease with pulmonary hypertension and increased pulmonary blood flow, the effect of the shunt on SP gene expression and protein content was not apparent within the first week of life.

Effects of oligohydramnios on lung growth and maturation in the fetal rat.

Oligohydramnios (OH) retards fetal lung growth by producing less lung distension than normal. To examine effects of decreased distension on fetal lung development, we produced OH in rats by puncture of uterus and fetal membranes at 16 days of gestation; fetuses were delivered at 21 or 22 days of gestation. Controls were position-matched littermates in the opposite uterine horn. OH lungs had lower weights and less DNA, protein, and water, but no differences in saturated phosphatidylcholine, surfactant proteins (SP)-A and -B, and mRNA for SP-A, -B, -C, and -D. To evaluate effects on epithelial differentiation, we used RTI(40) and RTII(70), proteins specific in lung to luminal surfaces of alveolar type I and II cells, respectively. At 22 days of gestation, OH lungs had less RTI(40) mRNA (P < 0.05) and protein (P < 0.001), but RTII(70) did not differ from controls. With OH, type I cells (in proportion to type II cells) covered less distal air space perimeter (P < 0.01). We conclude that OH, which retards lung growth, has little effect on surfactant and impedes formation of type I cells relative to type II cells.