Brain phosphatidylethanolamine

Because altered sodium channels have been implicated in kdr and kdr-like resistance phenomena in insects, basic research on the biochemistry and molecular biology of this molecule, which plays a central role in normal processes of nervous excitation in animals, is of immediate relevance. The results of recent investigations of the voltage-sensitive sodium channels of vertebrate nerves and muscles have provided unprecedented insight into the structure of this large and complex membrane macromolecule. Sodium channel components from electric eel electroplax, mammalian brain, and mammalian skeletal muscle have been solubilized and purified (for a recent review, see Ref. 19). A large a subunit (ca. 2 60 kDa) is a common feature of all purified channels in addition, there is evidence for two smaller subunits ( Jl and J2 37-39 kDa) associated with the mammalian brain sodium channel and for one or two smaller subunits of similar size associated with muscle sodium channels. Reconstitution experiments with rat brain channel components show that incorporation of the a and pi subunits into phospholipid membranes in the presence of brain lipids or brain phosphatidylethanolamine is sufficient to produce all of the functional properties of sodium channels in native membranes (AA). Similar results have been obtained with purified rabbit muscle (45) and eel electroplax (AS.) sodium channels. 

Selected Fatty Acid Composition of Brain Phosphatidylethanolamine (PE) and Phosphatidylcholine (PC) ... 

Fig. 2. The effect of y-linolenic acid (GLA) and a-linolenic acid (ALA) supplementations on the changes (%) of arachidonic acid (AA ) and docosahexaenoic acid (DHA ) in liver and brain phosphatidylethanolamine (PE).

Additionally, Abedin et al. (29) reported that there were dose-dependent DHA increases in neural tissues, including retinal phospholipid and brain phosphatidylethanolamine. AA levels in these tissues were resistant to dietary manipulation. In our study, we also observed similar DHA and AA accumulation profiles (unpublished data). 

These compounds constimte as much as 10% of the phospholipids of brain and muscle. StmcmraUy, the plasmalogens resemble phosphatidylethanolamine but possess an ether link on the sn- carbon instead of the ester link found in acylglycerols. Typically, the alkyl radical is an unsamrated alcohol (Figure 14-10). In some instances, choline, serine, or inositol may be sub-stimted for ethanolamine. 

Materials. Egg phosphatidylcholine (PC), bovine brain phosphatidylserine (PS) were obtained from Avanti Polar Lipids Inc. (Birmingham, AL) and cholesterol was from Sigma (St. Louis, MO). Ganglioside GMj, bovine, was obtained from Calbiochem (San Diego, CA). Diethylenetriamine pentaacetic acid distearylamide complex (DPTA-SA) was synthesized according to ref. 17 and nlIn-DTPA-SA was prepared as described (7). This lipophilic radiolabel is not transferred to the serum components from liposomes (unpublished data), nor is it rapidly metabolized in vivo (7). The synthesis of N-(glutaryl)phosphatidylethanolamine(NGPE) has been described (18). Dipalmitoyl deoxyfluorouridine(dpFUdR) was synthesized as described (24). 

Cadas H, di Tomaso E, Piomelli D. Occurrence and biosynthesis of endogenous cannabinoid precursor, A-arachidonyl phosphatidylethanolamine, in rat brain. J Neurosci 1997 17 1226-1242. 

To date the evidence seems to favor the binding of tumor promoter to phospholipid in the cell membrane. Specific binding of [3h]TPA to mouse epidermal particulate matter is susceptible to phospholipases C and A2, less susceptible to protease, and completely resistant to glycosidase (32). Photoaffinity labelling studies with [20-3h]-phorbol 12-p-azidobenzoate 13-benzoate indicates that the irreversible binding of this photolabile phorbol ester to mouse brain membrane is predominantly to the phospholipid (specifically phosphatidylethanolamine and phosphatidylserine) portion rather than to the protein portion (33). 

Guan Z., Wang Y., Cairns N. J., Lantos P L., Dallner G., and Sindelar P. J. (1999). Decrease and structural modifications of phosphatidylethanolamine plasmalogen in the brain with Alzheimer disease. J. Neuropathol. Exp. Neurol. 58 740-747. 

Anandamide is present in brain cells in very low concentrations [44-47]. Apparently it is released (presumably mostly when needed) through cleavage catalysed by phospholipase D from /V-arachidonoyl phosphatidyl etha-nolamide, which is formed by a calcium-dependent enzyme activity which catalyses the transfer of arachidonic acid (and other fatty acids) from various donor phospholipids to phosphatidylethanolamine (see Figure 5.4) [48, 49], In animal post mortem brains kept at room temperature, the concentration of anandamide gradually increases [44, 45], It would be of interest to find out whether anandamide concentrations also increase in vivo in brain after trauma, indicating a possible role for this fatty acid amide. Preliminary experiments by Dr. E. Shohami (unpublished) have shown that administration... 

Most of the lipids of the neutral fraction were eluted at the solvent front when the chloroform/methanol/water solvent system, which is suitable for the separation of the acidic fraction, was used. We then tried solvent systems which can separate more hydrophobic lipids. Using the hexane/ ethyl acetate/ethanol/0.1% aqueous ammonia solvent system, we could separate phospholipids (Fig. 2B) and glycolipids (data not shown). A 5-mg amount of a neutral fraction from human brain lipids was applied to TC-CCC by using hexane/ethyl acetate/ethanol/0.1% aqueous ammonia (5 5 5 4). Phosphatidylcholine (PC), sphingomyelin (SPM), and lysophosphatidylcholine (lysoPC) were successively eluted. Phosphatidylethanolamine (PE) and lyso-phosphatidylethanolamine (lysoPE) and other minor phospholipid components were retained as the column contents with this solvent system. Cerebroside (fr. 28/36) and some... 

Properties Yellowish, amorphous substance characteristic odor and taste. Insoluble in water and acetone soluble in chloroform and ether slightly soluble in alcohol. A group of phospholipids in which two fatty acids (Rt and R2) form ester linkages with the two hydroxyl groups of glycerophosphoric acid, and either ethanolamine or serine (Rj) forms an ester linkage with the phosphate group. Cephalins are therefore either phosphatidylethanolamine or phosphatidylserine. They are associated with lecithins found in brain tissue, nerve tissue, and egg yolk. 

Burstein and Hunter (1995) observed that THC stimulated the biosynthesis of anandamide in neuroblastoma cells employing either ethanolamine or arachidonic acid as the label. Anandamide bios5mthesis has also been shown to occur in primary cultures of rat brain neurons labelled with [H]-ethanolamine when stimulated with ionomycin, a Ca ionophore (Di Marzo et al. 1994). These authors proposed an alternate model for the biosynthesis of anandamide in which N-arachidonoyl phosphatidyl ethanolamine is cleaved by a phospholipase D activity to yield phosphatidic acid and ararchidonoylethanolamide. This model is based upon extensive studies undertaken by Schmid and collaborators (1990), who have shown that fatty acid ethanolamide formation results from the N-acylation of phosphatidyl ethanolamine by a transacylase to form N-acyl phosphatidylethanolamine. Possibly resulting from postmortem changes, this compound is subsequently hydrolyzed to the fatty acid ethanolamide and the corresponding phosphatide by a phosphodiesterase, phospholipase D. 

Phosphatidylethanolamines, or cephalins (so-called because they were first obtained from brain tissue), can be synthesized by reactions analogous to those of de novo synthesis of phosphatidylcholine. Ethanolamine is first phosphorylated by ATP and ethanolamine kinase to phosphoethanolamine, which then reacts with CTP to form CDP-ethanolamine. CTPrphosphoethanolamine cytidylyltransferase is not located on the endoplasmic reticulum, nor do fatty acids activate it as they do the analogous enzyme of phosphatidylcholine synthesis. Finally, 1,2-diacylglycerol phosphoethanolamine transferase catalyses the reaction of diacylglycerol with CDP-ethanolamine to form phosphatidylethanolamine. 

Phosphatidylethanolamines can also be synthesized by decarboxylation of phosphatidylserine and in mammals principally through action of the Ca -mediated base exchange enzyme (Figure 19-3). Phosphatidylserine production in liver occurs at the cytosolic face of the endoplasmic reticulum. In brain tissue, this phospholipid accounts for up to 15% of the total phospholipid content. 

The a,jS-unsaturated fatty ether is an aldehydogenie group because its hydrolysis releases an a -unsaturated primary alcohol that readily tautomerizes to an aldehyde. Choline, ethanolamine, and serine plasmalogens are found in cardiac and skeletal muscle, brain, and liver. The biosynthesis of phosphatidylethanolamine is shown in Figure 19-5. 

Fig. 2. Graphical representation of study by Abedin and co-workers. The lower panel presents the dietary fatty acid concentrations fed for 12 to 15-wk-old guinea pigs. The Lo LCP diet is intermediate in LCP content for human breast milks Hi LCP has threefold higher LCP concentrations. The upper panel shows the outcome variable, DHA concentration in brain or retina phosphatidylethanolamine (PE). Brain and retina DHA were similar between animals fed the Hi LNA diet or Lo LCP. (Based on data from Abedin, Lien, Vingrys, Sinclair, 1999).

In our previous reports, we have shown that infant rhesus monkeys born from mothers fed an n-3 fatty acid-deficient diet and then also fed a deficient diet after birth developed low levels of n-3 fatty acids in the brain and retina and impairment in visual function (Neuringer et al., 1984, Connor et al., 1984, Neuringer et al., 1986). The specific biochemical markers of the n-3-deficient state were a marked decline in the DHA of the cerebral cortex and a compensatory increase in n-6 fatty acids, especially docosapenta-enoic acid (22 5n-6). Thus, the sum total of the n-3 and n-6 fatty acids remained similar, about 50% of the fatty acids in phosphatidylethanolamine and phosphatidylserine, indicating the existence of mechanisms in the brain to conserve polyunsaturation of membrane phospholipids as much as possible despite the n-3-deficient state. 

Dramatic changes in the fatty acids of the frontal cortex were detected within 1 wk after the fish-oil diet was given as demonstrated in the individual data in the frontal lobe biopsy specimens from five juvenile monkeys. All four major phospholipid classes of the brain underwent extensive remodeling of their constituent fatty acids. The data in Fig. 3 is for the fatty acids of phosphatidylethanolamine from each of the five experimental monkeys. By 12-28 wk, the total n-3 fatty acids increased from 4% to 36%of total fatty acids (Connor et al., 1990b). The major increase was in DHA, from 4% to 29%, whereas EPA and 22 5n-3, another n-3 fatty acid found in fish oil, each increased from 0% to almost 3%. To be emphasized, as will be discussed later, is the apparent conversion of EPA to DHA in the brain. The total n-6 fatty acids reciprocally decreased from 44% to 16% of the total fatty acids, with the major reduction occurring in 22 5n-6, from 18% to 2%, and 22 4n-6, from 12% to 4%. There was also a moderate decrease of arachidonic acid from 12.8% to 8.9% of total fatty acids. Again, a major remodeling of the phospholipid fatty acids from n-6 to n-3 fatty acids was evident. 

As emphasized, dietary fatty acids produced drastic modification of the molecular species of brain ethanolamine phospholipids. Hargreaves and Clandinin reported similar findings in the rat (Connor et al., 1997). Using argentation thin-layer chromatography (TLC), which is unable to resolve individual molecular species, they fed fish-oil or linseed-oil diets to rats, which resulted in an increased microsomal and synaptic membrane content of phosphatidylethanolamine species containing six double bonds, and a decrease in species containing five double bonds, compared with animals fed soy or safflower oil. 

The reversibility of n-3 fatty acid deficiency in the monkey cerebral cortex was relatively rapid in our study. Effects of fish-oil feeding were seen within 1 wk after its initiation. By that time, DHA in the phosphatidylethanolamine of the cerebral cortex had more than doubled. The DHA concentration in phosphatidylethanolamine reached the control value of 22% in 6-12 wk after fish-oil feeding. We and others have demonstrated that the uptake of DHA and other fatty acids occurs within minutes after their intravenous injection bound to albumin (Pitkin et al., 1972). Furthermore, DHA is taken up by the brain in preference to other fatty acids (Pitkin et al., 1972). In contrast to the rapid incorporation of DHA from 4% to 13% in the first week, 22 5n-6 only decreased form 23% to 20% during the first week (Holub and Kuksis, 1978). This asymmetry may indicate that DHA did not exclusively displace 22 5n-6 from the sn-2 position of brain phospholipids. 

In this study, the half-life of DHA of phosphatidylethanolamine in the cerebral cortex was similar to the half-lives of DHA in plasma and erythrocyte phospholipids, roughly 21 d. These data suggest that the blood-brain barrier present for cholesterol (Olendorf, 1975, Trapp and Bemson, 1977) and other substances may not exist for the fatty acids of the plasma phospholipids because of the relatively rapid uptake of plasma DHA into the brain. The mechanisms of transport of these fatty acids remain to be investigated. 

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