Ethanolamine glycerophospholipids

In mammalian and plant tissues this component usually occurs in lesser amounts than phosphatidylcholine. In bacteria, it is the principal phospholipid present.

After the discovery of 2-aminoethylphosphonic acid in lipid extracts of the sea anemone (Kittredge JS et al., Biochemistry 1962, 1, 624), unusual phosphatidylethanolamine analogues containing a carbon-phosphorus bond instead of the classical carbon-oxygen-phosphorus bond have been described in marine invertebrates and protozoa (Tetrahymena pyriformis). They were first reported in 1966 in Tetrahymena as glycerophosphonolipids (Liang CR et al., Biochim Biophys Acta 1966, 125, 548) but, later, they were identified in that species as derivative of chimyl alcohol (Thomson GA, Biochemistry 1967, 6, 2015) : an alcohol is linked with an ether bond in sn-1 of the glycerol molecule. These phosphonolipids, often termed phosphonylethanolamine, are extremely resistant to acid or enzymatic hydrolysis. They were proposed as a possible artificial pulmonary surfactant.

The alk-1'-enyl, acyl derivative (ethanolamine plasmalogen) occurs widely in nature, mainly present in high concentration in the white matter (myelin) of the nervous system, in the heart and the kidney. It is practically absent in plants and bacteria (except in obligate anaerobes).

The fatty acid acylated at the 2-position of glycerol is most frequently polyunsaturated (arachidonic or docosahexaenoic acid). The function of ethanolamine plasmalogen remains obscure, hypotheses concerning their role in arachidonic acid reservoir and protection of other lipids against oxidation (through their vinyl group) were suggested (Leray C et al. Lipids 2002, 37, 285). A function in the mediation of cellular cholesterol efflux has been also discovered (Mandel H et al., Biochem Biophys Res Comm 1998, 250, 369). The plasmalogen synthesis via the peroxisomal pathway was shown to decrease with age and more severely in patients suffering Alzheimer disease. A precise link between plasmalogen levels and that pathology remains to be defined.  
For an extensive review on functions and biosynthesis of plasmalogens in health and disease, refer to the paper by Brites P et al. (Brites P et al., Biochim Biophys Acta 2004, 1636, 219).
A graphical chart of the metabolism of plasmalogens may be found on the BioCarta web site

The alkyl-, acyl-derivative (1-alkyl-, 2-acyl-sn-glycero-3-phosphorylethanolamine) is present in small amount in all phospholipid extracts.

It was first isolated from bovine erythrocytes but is present also in reasonably amount in bone marrow, platelets, certain protozoa and molluscs.

N-methyl and N,N-dimethyl phosphatidylethanolamine

These groups have either N-methylethanolamine or N,N-dimethylethanolamine substituted for ethanolamine in their structure. Bremer (Biochim Biophys Acta 1959, 35, 287) proposed a possible role of these compounds in interconversions from phosphatidylethanolamine to phosphatidylcholine in rat liver. This was confirmed later and extensively studied in nervous tissues.
N-Methyl phosphatidylethanolamine has been detected in a Gram-positive bacteria Clostridium acetobutylicum (Lepage C et al., J Gen Microbiol 1987, 133, 103).

Phosphatidylethanolamine-hydroxy-alkenals

Phosphatidylethanolamine can be covalently modified in vitro and in cellular systems by hydroxy-alkenals, such as 4-hydroxy-2-nonenal (4-HNE; from n-6 fatty acids), 4-hydroxy-2-hexenal (4-HHE; from n-3 fatty acids), and 4-hydroxy-dodecadienal (4-HDDE; from the 12-lipoxygenase product of arachidonic acid), to form PE-alkenal Michael adducts (Guichardant M et al., Free Rad Biol Med 1998, 25, 1049; Bacot S et al., J Lipid Res 2007, 48, 816). Below, the adduct formed between PE and 4-HHE is shown.

Several experimental results suggest that these adducts could be used as specific markers of membrane disorders occurring in pathophysiological states with associated oxidative stress and might affect cell function.

N-acetyl phosphatidylethanolamine

That unusual phosphatidylethanolamine derivative was described in a filamentous fungus, Absidia corymbifera, and formed about 6% of total membrane lipids (Batrakov SG et al., Biochim Biophys Acta 2001, 1531, 169).

The main fatty acids (R and R') are 16:0, 18:0 and 18:2

N-ethoxycarbonyl phosphatidylethanolamine 

Another unusual PE derivative was, as the previous one, isolated from Absidia corymbifera, N-ethoxycarbonyl phosphatidylethanolamine and formed about 9% of total membrane lipids (Batrakov SG et al., Biochim Biophys Acta 2001, 1531, 169).

The fatty acid pattern is similar to N-acetyl PE but also with a prominent proportion of 18:3. 

N-acyl phosphatidylethanolamine

This complex lipid containing three fatty acid chains was isolated in 1965 by Bomstein (Biochem Biophys Res Comm 1965, 21, 49) from wheat flour. Later, it was shown to be present in quite all grains (pea seeds, oats and soya beans) but its presence was also reported in microorganisms, fish, and in mammalian tissues (Schmid HHO et al., Prog Lipid Res 1990, 29, 1). In oat lipids the major N-acylated fatty acids are 16:0, 18:2 and 18:1 (Holmbäck J et al., Lipids 2001, 36, 153-165). In animal cells (heart, brain, liver and skeletal muscle), the N-acyl chain is frequently palmitic or stearic acid. The mechanism proposed for the synthesis of this complex phospholipid includes the action of an N-acyl transferase catalyzing an exchange reaction between the sn-1 position of phospholipids (probably phosphatidylcholine) and the primary amine of phosphatidylethanolamine.

Recent reports indicate the importance of N-acyl phosphatidylethanolamine as precursors for N-acylethanolamines, which in turn play a physiological role during germination of seeds (Chapman KD et al., Plant Physiol 1999, 120, 1157) and in defense systems in plants (Tripathy S et al., Plant Physiol 1999, 121, 1299).

N-Acylated ethanolamines were first isolated from preparations of egg yolk, peanut oils, and soybeans due to their anti-inflammatory and anti-allergienic properties (Kuehl FA et al., J Am Chem Soc 1957, 79, 5577). Interestingly, a unique N-acyl phosphatidylethanolamine was proposed in the brain as a source of N-arachidonoyl ethanolamine (named also anandamide, from the Sanskrit "ananda" that means bliss), this metabolite appears to be formed (with a molecule of phosphatidic acid) by phospholipase D action. Further investigations provide evidence for a multistep pathway by the sequential actions of hydrolases and glycerophosphodiesterase (Simon GM et al., J Biol Chem 2008, 283, 9341).