Reductions of phospholipase A₂ inhibition of pulmonary surfactant with hyaluronan

ABSTRACT

In acute lung injuries, secretory phospholipase A₂ (sPLA₂) inhibits surfactants by hydrolyzing phospholipids. Because hyaluronan (HA) reduces hydrolysis of phospholipids by sPLA₂, and because sPLA₂ inhibits surfactant in vitro, the authors hypothesized HA would reduce sPLA₂ inhibition. Surfactants were used alone or mixed with HA and/or sPLA₂ then tested for surface activity in 2 separate assays, or for sPLA₂ activity. Equilibrium surface pressures were identical for surfactant with or without HA. sPLA₂ inhibited surface activity but this inhibitory effect was reduced with HA by 14% in the spreading trough and by 63% in a modified bubble surfactometer. Hyaluronan caused a modest reduction (39%) of sPLA₂ breakdown of labeled phospholipid. Therefore hyaluronan reduces inhibition of surfactants by sPLA₂ in vitro, and reduces the activity of the enzyme.

KEYWORDS :

• hyaluronan
• inhibition
• phospholipase
• surfactant