Phospholipid precursors

Anandamide is believed to be synthesized from a phospholipid precursor, /V-arachidonoyl-phosphatidylethanolamine, catalysed by phospholipase D (Di Marzo et al. 1998). The other proposed route of synthesis is from condensation of arachidonic acid and ethanolamine, although this has yet to be demonstrated in living cells. 2-AG is formed in a calcium-dependent manner, and mediated by the enzymes phospholipase C and diacylglycerol lipase (Kondo et al. 1998 Stella et al. 1997). 

Like other arachidonate-derived endogenous compounds the endocannabinoids seem to be synthesized and released by cells on demand. The hydrolysis of phospholipid precursors, also probably embedded in the... 

Lopes, J.M., Hirsch, J.P., Chorgo, P.A., Schulze, K.L., and Henry, S.A., 1991, Analysis of sequences in the INOl promoter that are involved in its regulation by phospholipid precursors. Nucleic Acids Res. 19 1687-1693. 

Lands WEM, and Samuelsson B. (1968). Phospholipid precursors rfpmstaglndms, Biochini. Kophys. Acta 164,426-429. 

Lands WEM, SamuelssonB Phospholipid precursors of prostaglandins. Biochim. Biophvs. Ada. 164 426,1968... 

The subject of phospholipase assays has been concisely reviewed [1-5]. A standard approach employs phospholipids with radioisotopes incorporated into specific positions in the molecule. By the appropriate choice of labeling, the specificity of the enzymes can readily be established and as little as a few picomoles of product can be detected. The use of isotopes has been helpful in the measurement of phospholipase activity using the membranes of whole cells or isolated subcellular fractions previously labeled with radioactive phospholipid precursors. 

Hansen, H.H., Hansen, S.H., Schousboe, A., and Hansen, H.S. (2000) Determination of the phospholipid precursor of anandamide and other Al-acylethanolamine phospholipids before and after sodium azide-induced toxicity in cultured neocortical neurons. Journal of Neurochemistry 75 861-871. 

Unlike the classical neurotransmitters, PGs are not stored prior to use but are rapidly synthesized upon demand from phospholipid precursors. Activation and translocation of cytosolic phospholipase Aj causes the release of free arachidonic acid and the initiation of PG synthesis. A variety of endogenous as well as environmental stimuli have been shown to initiate this process, which takes place on the endoplasmic reticulum and Golgi apparatus of most cells. 

Cardiac TG usually occur as droplets of various sizes within the cells and do not appear to be membrane enclosed (Rouser et ai, 1968). They are readily mobilized for energy production or serve as phospholipid precursors. On the other hand, the phospholipids occur almost exclusively in the membranous structures of the cell (McMurray, 1973). Cholesterol also occurs in membranes, has a condensing effect, and controls the movement of the hydrocarbon chains of phospholipids (Papahadjopoulos, 1973). 

FIGURE 10.1 Chemical structures of typical OxPCs generated by peroxidation of paknitoyl-arachidonoyl-phosphatidylcholine. The figure presents a few most common molecular species selected from dozens of molecular species produced by nonenzymatic oxidation of a single precursor phospholipid. Note that oxidation can either add oxy functions to the full-size carbon chain or induce chain fragmentation. Both types of modifications produce phospholipids with abnormal properties and biological activities that were not characteristic of unoxidized phospholipid precursors. 

Serine is a rather unsatisfactory phospholipid precursor because its different pathways of metabolism can label the phospholipids in different ways ... 

Serine Constituent of phospholipids precursor of sphingolipids precursor of ethanolamine... 

In these experiments rat brain slices were incubated with some phospholipid precursors (choline, arachidonic acid, etc,), and the effect of prostaglandins upon their incorporation and renewal in phospholipids was investigated. When tritiated ethanolamine was used, as the lipid precursor, radioactivity was found not only into ethanolamine phosphoglycerides (EPG) but also in smaller amounts... 

Biosynthesis of NAPE utilizes phosphatidylethanolamine (PE) as the immediate phospholipid precursor. We have demonstrated this both by direct feeding of radiolabeled phosphatidylethanolamine (unpublished data) and by use of radiolabeled PE formed by feeding microsomes either [ C]ethanolamine or CDP-[ C]ethanolamine under conditions for PE synthesis, followed by removal of the water soluble label and assaying NAPE synthesis under conditions of the latter synthesis. The former procedure produces PE by an exchange reaction, the second by ethanolaminephosphotransferase [6]. PE formed by either reaction could be utilized for NAPE synthesis. 

Before the discovery of anandamide, many aspects of the biogenesis of NAEs had been unraveled in a series of experiments carried out in the laboratory of Harald H.O. Schmid. These studies indicated that formation of NAEs likely proceeds from the hydrolytic cleavage of a phospholipid precursor, N-acylphos-phatidylethanolamine (NAPE), rather than from the condensation reaction of fatty acids with ethanolamine which had been suggested by earlier studies (ref. 32 and see below). Our own work on primary cultures of rat brain neurons corroborated and extended the pathway predicted by Schmid and coworkers (Fig. 6.10). 

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