Lung Surfactant Phospholipid Molecular Species in Health and Disease

Abstract

I. Introduction 3II. Composition of Surfactant Phospholipid Molecular Species inthe Adult Lungs 6III. Molecular Species of Surfactant Phospholipid During FetalDevelopment 9IV. Molecular Species of Phospholipid During PostnatalDevelopment 9V. Modification of Surfactant Phospholipid Molecular Species inDisease States 10A. Respiratory Syncytial Virus Bronchiolitis 10B. Respiratory Diseases in Children 10C. Asthma 11D. Acute Respiratory Distress Syndrome 11VI. Conclusion 12References 12I. IntroductionThe importance of the phospholipid component for the physiological function oflung surfactant has been recognized for many years. However, the effects ofdevelopment and disease on the detailed phospholipid composition of surfactanthave received relatively little attention until recently, largely because of lack ofsensitivity and specificity of the analytical methods available. Phospholipidsare characterized either as glycerophospholipids, with fatty acids esterified atthe sn-1 and sn-2 positions of the glycerophosphate backbone of the molecule,or as sphingolipids, with a fatty acid esterified to a sphingosine phosphatemoiety (Fig. 1.1). The head group attached to the phosphate of glycerophospho-lipids can be choline, ethanolamine, serine, glycerol, or inositol to give, respect-ively, phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn),phosphatidylserine (PtdSer), phosphatidylglycerol (PtdGly), or phosphatidyl-inositol (PtdIns). The vast majority of sphingolipids have choline esterified tothe phosphate to generate sphingomyelin. Within each of these phospholipidclasses, there is a spectrum of individual molecular species, defined by the com-bination of esterified fatty acids attached to the glycerol. Generally, membraneglycerophospholipids tend to have palmitoyl (16:0)1 or stearoyl (18:0) at theirsn-1 position and unsaturated fatty acids esterified at sn-2. The esterified fattyacid in sphingolipids is generally saturated, but can often contain as many as22 or 24 carbon atoms.