Phospholipids of Animal and Marine Origin: Structure, Function, and Anti-Inflammatory Properties

Molecules 
2017
, 
22
, 1964 
3 of 31 
unsaturated fatty acids that act as precursors for the synthesis of pro-inflammatory mediators called 
eicosanoids (prostaglandins (PGs), thromboxanes (TX), leukotrienes (LT), and lipoxins (LX)) [10,11].
Even though the main function of PLs is to support the formation and biofunctionality of cell 
membranes, there are specific varied PLs that perform specialised functions in the subcellular 
micelles and organelles. For example, PLs are structural and functional constituents of the surface 
monolayers of lipoproteins (which transport lipids to tissues via the blood stream), the pleura and 
alveoli of the lung and are constituents of the pericardium, joints, peritoneal and gastrointestinal 
surfactants, while together with cholesterol and bile acids they form mixed micelles in the 
gallbladder for fat emulsification [12]. In addition, some PLs act as lipid mediators of inflammation 
that have the ability to influence immunological processes at the cellular level (i.e., PAF) [7]. PLs also 
contain bound PUFAs to be released on demand as precursors of prostaglandins and other 
eicosanoids [11], while other PLs and their metabolites are a source of secondary messengers in cell 
signalling (e.g., diacylglycerols, phosphoinositides, etc.) [13], and carry out essential functions 
within organelles such as the mitochondria [14]. Therefore, not only are PLs integral structural lipids 
in cell membrane formation, function and integrity, but research has also identified that they possess 
a plethora of additional functions in various cell types and organisms, which will be discussed 
further in this review. 
Figure 1.
The most common structures of phospholipids are depicted: phospholipids with a glycerol 
backbone (GPLs); sphingomyelin as a representative of a sphingosine-backbone phospholipid 
(SPLs); and alkyl-phospholipids (Alkyl-GPLs) that have a fatty chain linked with an ether-bond at 
the 
sn
-1 position of the glycerol backbone. 
1.2. Glycerophospholipid and Sphingophospholipid Biosynthesis 
In mammalian cells, GPL synthesis requires a diacylglycerol unit, which is provided by either 
diacylglycerol or CDP-diacylglycerol. The generation of these precursors initiates through the 
enzyme glycerol-3-phosphate acyltransferase (situated in the external leaflet of the mitochondrial 
membrane and of the endoplasmic reticulum), which links a fatty acid-CoA (generally a SFA) to the 
sn
-1 position of glycerol-3-phosphate to generate lyso-PA. Acylglycerol-3-acyltransferase is required 
for the subsequent formation of PA in the endoplasmic reticulum, whereby it esterifies another fatty