Reductions of phospholipase A(2) inhibition of pulmonary surfactant with hyaluronan.

In acute lung injuries, secretory phospholipase A(2) (sPLA(2)) inhibits surfactants by hydrolyzing phospholipids. Because hyaluronan (HA) reduces hydrolysis of phospholipids by sPLA(2), and because sPLA(2) inhibits surfactant in vitro, the authors hypothesized HA would reduce sPLA(2) inhibition. Surfactants were used alone or mixed with HA and/or sPLA(2) then tested for surface activity in 2 separate assays, or for sPLA(2) activity. Equilibrium surface pressures were identical for surfactant with or without HA. sPLA(2) 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 sPLA(2) breakdown of labeled phospholipid. Therefore hyaluronan reduces inhibition of surfactants by sPLA(2) in vitro, and reduces the activity of the enzyme.