Lysophospholipid and fatty acid inhibition of pulmonary surfactant: Non-enzymatic models of phospholipase A2 surfactant hydrolysis

Abstract

Secretory A(2) phospholipases (sPLA(2)) hydrolyze surfactant phospholipids cause surfactant dysfunction and are elevated in lung inflammation. Phospholipase-mediated surfactant hydrolysis may disrupt surfactant function by generation of lysophospholipids and free fatty acids and/or depletion of native phospholipids. In this study, we quantitatively assessed multiple mechanisms of sPLA(2)-mediated surfactant dysfunction using non-enzymatic models including supplementation of surfactants with exogenous lysophospholipids and free fatty acids. Our data demonstrated lysophospholipids at levels >or=10 mol% of total phospholipid (i.e., >or=10% hydrolysis) led to a significant increase in minimum surface tension and increased the time to achieve a normal minimum surface tension. Lysophospholipid inhibition of surfactant function was independent of the lysophospholipid head group or total phospholipid concentration. Free fatty acids (palmitic acid, oleic acid) alone had little effect on minimum surface tension, but did increase the maximum surface tension and the time to achieve normal minimum surface tension. The combined effect of equimolar free fatty acids and lysophospholipids was not different from the effect of lysophospholipids alone for any measurement of surfactant function. Surfactant proteins did not change the percent lysophospholipids required to increase minimum surface tension. As a mechanism that causes surfactant dysfunction, depletion of native phospholipids required much greater change (equivalent to >80% hydrolysis) than generation of lysophospholipids. In summary, generation of lysophospholipids is the principal mechanism of phospholipase-mediated surfactant injury in our non-enzymatic models. These models and findings will assist in understanding more complex in vitro and in vivo studies of phospholipase-mediated surfactant injury.

High-throughput evaluation of pulmonary surfactant adsorption and surface film formation

“…Deactivation of surfactant by serum components and by inflammatory mediators leaked into the alveolar spaces is thought to be a major determinant of the respiratory failure in acute respiratory distress associated with lung injury (16,47). The surface-inhibitory activity of proteins such as albumin (8,48), fibrinogen (49), C-reactive protein (9,50), or lipases (51) toward surfactant has been well documented, as well as the deactivating effect of metabolites such as neutral lipids (46,52), FFAs (53), bile salts (54), heme derivatives (55), or lysophospholipids (33,53). Lung injury with different sources and to different extents is probably associated with particular complex and possibly multifactorial profiles of surfactant deactivation that have been only preliminarly characterized.…”

Multiple Roles of Phospholipase A2during Lung Infection and Inflammation

“…The lipid component of surfactant predominantly consists of PC, but also contains a small percentage of phosphatidylglycerol, phosphatidylinositol, and phosphatidylethanolamine (PE) (51). Various sPLA 2 isoforms have different specificities for hydrolyzing particular phospholipid substrates with particular head groups.…”

Inactivation of Pulmonary Surfactant by Lysophosphatidylcholine

“…In inflammatory lung diseases, hydrolysis of surfactant PL by phospholipase generates lysophospholipids. Such degradation not only can deplete active surfactant lipids, but also releases products like lysophosphatidylcholines (lysoPC) and free fatty acids that are severe biophysical inhibitors of surfactant activity (2). If such compounds are present in a mixture with PS, their intrinsic surface active behavior can reduce the adsorption of surfactant constituents into the interface, or alter film properties during dynamic cycling, or both.…”