Chronic ethanol administration induced an increase in phosphatidylserine in guinea pig synaptic plasma membranes

Mechanism of Action of Thymosinα1: Does It Interact with Membrane by Recognition of Exposed Phosphatidylserine on Cell Surface? A Structural Approach

Thymosinα1 is a peptidic hormone with pleiotropic activity, which is used in the therapy of several diseases. It is unstructured in water solution and interacts with negative regions of micelles and vesicles assuming two tracts of helical conformation with a structural flexible break in between. The studies of the interaction of Thymosinα1 with micelles of mixed dipalmitoylphosphatidylcholine and sodium dodecylsulfate and vesicles with mixed dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylserine, the latter the negative component of the membranes, by (1)H and natural abundance (15)N NMR are herewith reported, reviewed, and discussed. The results indicate that the preferred interactions are those where the surface is negatively charged due to sodium dodecylsulfate or due to the presence of dipalmitoylphosphatidylserine exposed on the surface. In fact the unbalance of dipalmitoylphosphatidylserine on the cellular surface is an important phenomenon present in pathological conditions of cells. Moreover, the direct interaction of Thymosinα1 with K562 cells presenting an overexposure of phosphatidylserine as a consequence of resveratrol-induced apoptosis was carried out.

Metabolism and functions of phosphatidylserine in mammalian brain

Phosphatidylserine (PtdSer) is involved in cell signaling and apoptosis. The mechanisms regulating its synthesis and degradation are still not defined. Thus, its role in these processes cannot be clearly established at molecular level. In higher eukaryotes, PtdSer is synthesized from phosphatidylethanolamine or phosphatidylcholine through the exchange of the nitrogen base with free serine. PtdSer concentration in the nervous tissue membranes varies with age, brain areas, cells, and subcellular components. At least two serine base exchange enzymes isoforms are present in brain, and their biochemical properties and regulation are still largely unknown because their activities vary with cell type and/or subcellular fraction, developmental stage, and differentiation. These peculiarities may explain the apparent contrasting reports. PtdSer cellular levels also depend on its decarboxylation to phosphatidylethanolamine and conversion to lysoPtdSer by phospholipases. Several aspects of brain PtdSer metabolism and functions seem related to the high polyunsaturated fatty acids content, particularly docosahexaenoic acid (DHA).

Effect of ethanol on ATP-induced phospholipases C and D and serine base exchange in glioma C6 cells

The effect of extracellular ATP, a nucleotide receptor agonist in the central nervous system, was investigated in glioma C6 cells on the intracellular Ca2+ level and the formation of phosphatidylethanol and phosphatidic acid in the presence and absence of ethanol (150 mM). In the cells prelabeled with [14C]palmitic acid, 100 microM ATP induced both the hydrolysis and the transphosphatidylation reactions leading to the formation of [14C]phosphatidic acid; addition of ethanol generated [14C]phosphatidylethanol. However, ATP-mediated increase in the level of [14C]phosphatidic acid was not inhibited by ethanol. Furthermore, ethanol augmented ATP-induced transient and sustained increase in the intracellular Ca2+ concentration, whereas ethanol alone did not produce any change in the intracellular Ca2+ level. These results indicate that in glioma C6 cells, ATP induces activation of polyphosphoinositide-specific phospholipase C and phospholipase D and that ethanol enhances this effect. In the present investigation we have also shown that long-term (2 days) ethanol treatment, at concentration relevant to chronic alcoholism (100 mM), decreased the incorporation of [14C]serine into phosphatidylserine. Since the effect of ethanol on ATP-induced activities of phospholipase C and phospholipase D and on serine base-exchange in glioma C6 cells differs significantly from that in cultured neuronal cells, these results may contribute to a better understanding of the mechanisms of ethanol action in cells of glial origin.

A developmental profile of the effects of ethanol on the levels of chick brain phospholipids

The effects of embryonic exposure to ethanol on brain phospholipid levels were studied by injecting various concentrations of ethanol, ranging from 0 to 149 microns kg-1 egg, into fertile chicken eggs at 0 days of incubation. At 7, 9, 11, 15 and 18 days of incubation, brains were collected and the levels of total phospholipids and various phospholipid classes were measured. Although embryonic exposure to ethanol failed to influence total phospholipid levels, ethanol-induced changes in the levels of individual phospholipid classes were observed. Ethanol-induced increases in the levels of phosphatidylethanolamine (PE) and phosphatidylserine (PS) and ethanol-induced decreases in the levels of phosphatidylcholine (PC) were observed at 9, 11, 15 and 18 days of incubation. Ethanol-induced decreases in brain sphingomyelin (SP) levels were observed at 7 and 18 days of development. These ethanol-induced changes in brain phospholipid levels preceded detectable alcohol dehydrogenase (ADH) activities in both brain and liver.

Ethanol alters brain phospholipid levels which correlate with altered brain morphology

The effects of embryonic exposure on brain phospholipid levels were studied by injecting various concentrations of ethanol into fertile chicken eggs at 0 days of development. At 18 days of development, the levels of total phospholipids and various phospholipid classes were assayed in brain tissue and correlated to neuron densities within the cerebral hemispheres and the optic lobes. Although ethanol concentrations ranging from 0 to 3700 microns/Kg egg wt. failed to influence either total brain weight or total brain phospholipid levels, ethanol-induced changes in the levels of individual phospholipid classes were observed. When injected with 7 microns of ethanol/Kg egg wt., a 2- to 3-fold increase in brain phosphatidylethanolamine (PE) levels were observed with reduced levels of brain phosphatidylcholine (PC) and brain sphingomyelin (SP). When injected with 74 microns of ethanol/Kg egg wt., ethanol-induced increases in brain phosphatidylserine (PS) and PE were observed with ethanol-induced decreases in brain PC and SP. Cell fractionation studies demonstrated ethanol-induced increases in brain PE and PS and ethanol-induced decreases in brain PC and SP in nuclear, mitochondrial, and microsomal membranes. These ethanol-induced alterations in brain phospholipid profiles correlated with ethanol-induced reductions in neuron densities within the cerebral hemispheres and optic lobes.

Ethanol potentiates the uptake of [14C]serine into phosphatidylserine by base-exchange reaction in NG 108-15 cells

Phospholipid base-exchange enzymes catalyze the incorporation of nitrogenous bases into phosphoglycerides by a calcium-dependent mechanism. In this study, we describe the effect of ethanol on the incorporation of radioactive serine, choline and ethanolamine into their respective phospholipids in a neuroblastoma x glioma hybrid cell line (NG 108-15). Long term ethanol exposure induced a potentiation of the incorporation of [14C]serine into phosphatidylserine. Moreover, the phosphorus content of PS was found to be increased after long-term ethanol exposure. No concomitant changes in the phosphorus content of other phospholipids were observed. The results indicate that in NG 108-15 cells, the incorporation of radiolabelled serine into PS is potentiated during chronic ethanol exposure.

Reversible inhibition by ethanol of Mg(2+)-dependent phosphatidate phosphohydrolase: an in vitro study in the rat reticulocyte

By using a tracer method, we demonstrate that short-term in vitro exposure of intact rat reticulocytes to ethanol elicits a biphasic response of cell-bound Mg(2+)-dependent phosphatidate phosphohydrolase (PAP). An initial concentration-dependent (200-750 mM) activity decrease is rapidly (< 10 min) followed by reversal of the inhibition in the presence of ethanol, suggesting the development of a cell resistance to the inhibitory agent. Addition to the cell suspension of propranolol (100 microM), a known PAP inhibitor, does elicit PAP inhibition but unlike ethanol, inhibition is not followed by a return with time to control value. Ethanol-induced inhibition of cell-bound PAP was also demonstrated in cell-free extracts, where the Mg(2+)-dependent activity was decreased both in the particulate and soluble fractions. In the intact cells, the transient PAP inhibition occurs in concomitance with an overall increase in total glycerolipid biosynthesis, which is constant over 60-min incubation. We suggest that the biphasic mode of response to ethanol of Mg(2+)-dependent PAP activity may play a role in the mechanism of membrane adaptation to ethanol, and thereby to the pathogenesis of alcoholism.

Effects of chronic ethanol administration on poly-phosphoinositide metabolism in the mouse brain: variance with age

Using a procedure in which poly-phosphoinositides (poly-PI) in C57Bl mouse brain were labeled with [32P]Pi or [32P]ATP, the effects of chronic ethanol administration and age on metabolism of these anionic phospholipids were examined. Within 4 h after intracerebral injection, both labeled precursors were effectively incorporated into membrane phospholipids with high proportions of labeling among phosphatidylcholine, phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate. With few exceptions, the phospholipid labeling patterns in different brain regions, e.g. cortex, hippocampus and hypothalamus, were similar. However, when the brain homogenate was subjected to differential and sucrose-Ficoll gradient centrifugation, different phospholipid labeling patterns were observed in the subcellular membrane fractions. Young adult mice given an ethanol (5% w/v) liquid diet for 2 months showed an increase in the levels of labeled phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-bisphosphate and phosphatidylserine in the cortex and hippocampus as compared to the pair-fed controls, but these changes were not observed in the hypothalamus. In another study, 12- and 26-month-old mice were administered either an ethanol (8 g/kg in two doses daily) or a control diet by gavage for 3 weeks. The 12-month-old group given the ethanol diet showed an increase in labeled poly-PI which was found largely in the synaptosomal fraction. Surprisingly, the 26-month-old mice given the same ethanol paradigm showed a decrease in labeled poly-PI. Consistent with our previous observations, the 26-month-old mice showed a higher proportion of labeled poly-PI in the synaptosomal fraction as compared to the younger age group.(ABSTRACT TRUNCATED AT 250 WORDS)

In utero ethanol exposure decreases the biosynthesis of phosphatidylserine in rat pup cerebrum

Phosphatidylserine is enriched in the brain and has been implicated to play a role in regulating neuronal membrane functions. In this study, three experimental protocols were used to examine the effects of in utero ethanol exposure on phosphatidylserine biosynthesis in rat pup brain, namely, (1) assay of the serine base-exchange enzyme activity in brain microsomes, (2) incubation of brain slices with [3H] serine, and (3) incorporation in vivo of [3H]serine into phosphatidylserine as well as serine-related phospholipids in brain. Results from all three protocols point to a decrease in phosphatidylserine biosynthesis in newborn rat pup cerebrum on exposure to ethanol in utero compared with the pair-fed controls. When in utero ethanol-exposed pups were nursed by mothers given a chow diet, the differences gradually returned to control levels by 17 days of age. The decrease in phosphatidylserine biosynthesis may be important in explaining some of the neuronal deficits associated with in utero ethanol exposure.

Resistance to ethanol disordering of membranes from ethanol-fed rats is conferred by all phospholipid classes

Phospholipids extracted from liver microsomes and mitochondria of ethanol-fed rats retained the resistance to membrane disordered by ethanol which is observed in the intact isolated membranes. The lipid extracts were separated into the major phospholipid classes (phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol from microsomes and phosphatidylcholine, phosphatidylethanolamine and cardiolipin from mitochondria) by preparative TLC. The extent of membrane disordering by ethanol of phospholipid vesicles composed of a mixture of phospholipids from ethanol-fed rats and controls was determined from the reduction of the order parameter of the spin-probe 12-doxyl-stearate. In contrast to previous reports, we found that all phospholipid classes from ethanol-fed rats confer resistance to disordering by ethanol. To a first approximation the extent of resistance was proportional to the fraction of lipids from ethanol-fed rats, regardless of the phospholipid head-group. Subtle differences between phospholipid classes may exist but were too small to measure accurately. Except for phosphatidylethanol, incorporation of anionic phospholipids did not have a significant effect on the sensitivity of phospholipid vesicles to the disordering effect of ethanol. Vesicles prepared from mixtures of various dioleoyl phospholipids and natural phospholipids did not indicate a clear effect of fatty acid saturation on the sensitivity to disordering by ethanol. Although the precise molecular changes that occur in phospholipids from ethanol-fed rats have not been fully characterized it appears that subtle changes in all phospholipid classes contribute to the resistance to ethanol disordering of these membranes.

Chronic ethanol ingestion modifies liver microsomal phosphatidylserine inducing resistance to hydrolysis by exogenous phospholipase A2

Chronic ethanol ingestion leads to the acquisition of a tolerance to membrane lipid disordering, a lowered partition coefficient to hydrophobic compounds and a resistance to the hydrolysis of the phospholipids by exogenous phospholipase A2. Anionic phospholipids have been implicated as being responsible for the resistance to lipid disordering and a number of modifications to these phospholipids are known to occur as a result of chronic ethanol-ingestion. In this study the basis of the resistance to phospholipase A2 in hepatic microsomes was investigated. It was found that chronic ethanol-induced modifications to each of the major phospholipid classes was responsible to some extent for the resistance to phospholipase A2, however, PS was particularly potent considering it is a compositionally minor constituent. The effect was interpreted as a reduced ability to activate the phospholipase A2 since PS acts as an essential activator of phospholipase A2 (along with PI). Fatty acid analysis revealed that the chronic ethanol-treatment resulted in a elevated level of docosahexaenoate with a parallel reduction in arachidonate in phosphatidylserine. Lipid packing and organization is important in the regulating the level of exogenous phospholipase A2 activity but the activity was not found to correlate with lipid order of different phosphatidylserine species. It is concluded that subtle differences in the molecular species arrangement or disposition around the enzyme may be responsible for the altered phospholipase A2 interaction with the membrane induced by chronic ethanol-treatment. One implication of this study is that other anionic phospholipid dependent membrane proteins, of which there are many known examples, may also be modified as a result of chronic ethanol-ingestion.

Ethanol alters the transfer of arachidonic acid to ethanolamine plasmalogens in C-6 glioma cells

In this study, the effects of ethanol exposure on uptake and metabolism of arachidonic acid by C-6 glioma cells in culture was examined. Labeled arachidonic acid was effectively taken up by the phospholipids of these cells and radioactivity was initially incorporated into phosphatidylinositols and phosphatidylcholines, reaching a peak between 4 and 6 hours. However, the labeling of ethanolamine plasmalogens continued to show an increase with time after labeled arachidonic acid has been exhausted in the medium. Since over 90% of labeled arachidonic acid was already taken up by the cells after 4 hours of exposure, the continued increase in labeling of ethanolamine plasmalogens is attributed to a transacylation mechanism. Cells grown in 150 mM ethanol for 2 days did not show a change in the overall incorporation of labeled arachidonic acid into phospholipids but showed a significant increase in labeling of ethanolamine plasmalogens, which was marked by a concomitant decrease in labeling of phosphatidylcholines. Ethanol exposure also resulted in a significant increase in the transfer of labeled arachidonic acid to triacylglycerols. Changes in phospholipid and triacylglycerol labeling pattern positively correlated with increasing ethanol concentration from 75 to 300 mM. Besides, most ethanol effects were readily noticeable after 24 hours of exposure. These data suggest a specific effect of ethanol on promoting the transacylase process for biosynthesis of ethanolamine plasmalogens as well as the acyltransferase for biosynthesis of triacylglycerols.

Effects of acute ethanol administration on stimulated parotid secretion in the rat

Young adult male rats previously never exposed to ethanol were given a single dose of 4 ml of 35% (v/v) ethanol in water by direct intragastric intubation (approximate weight related dose = 5.2 g/kg). Control rats were given distilled water in the same volume by the same route or were given no intragastric fluids. After administration of Valium-Hypnorm anesthesia, parotid salivary secretion was stimulated by subcutaneous pilocarpine HCI (10 mg/kg), and accurately timed samples were collected. No differences were recorded in the rate of salivary flow during the initial (5-min) high-flow phase of secretion, but during the subsequent 25-min phase of secretion the output in ethanol-treated rats was depressed by 60% compared to controls (p less than 0.01). Furthermore, electrolyte analyses of this saliva indicated that salivary ductal resorptive activity might be diminished in the presence of high blood ethanol. However, when rats were previously habitually exposed to ethanol at a twice daily dose of 4 ml of 35% (v/v) ethanol in water, the inhibitory action of acute ethanol administration was abolished. Moreover, in these rats there was significantly depressed [Na+] in both high-flow and low-flow saliva samples (p less than 0.01) with little change in [Na+] occurring at higher flow rates. This suggests the possibility of enhanced ductal resorption developing in rats exposed to long-term ethanol feeding.

The influence of cholesterol on synaptic fluidity and dopamine uptake

The present study examined how the synaptic cholesterol/phospholipid ratio influences membrane fluidity and a transmembrane process of the dopaminergic system, dopamine uptake. Fluorescence polarization of DPH was used as a measure of membrane fluidity. The cholesterol content of synaptosomal and synaptic plasma membranes was altered using a lipid transfer protein. The results of the present study demonstrate that the transmembrane process of dopamine uptake may be inhibited by an elevated synaptic cholesterol/phospholipid ratio, which correlates with increased fluorescence polarization. Specifically, a 10-30% increase in the cholesterol/phospholipid ratio resulted in an approximately 20% increase in fluorescence polarization, a 3- to 6-fold increase in Km, a 4-fold increase in Vmax, and a marked decrease in the Vmax/Km (the first order rate constant for dopamine uptake at low substrate concentrations).

Effect of ethanol on the maturation of the spontaneous transmitter release by regenerated nerve endings

The cellular mechanisms involved in the theratogentic action of ethanol are not well known, but neuron outgrowth and synaptogenesis are regarded as the periods in which ethanol causes its major damage in the nervous system. The effects of chronic treatment with ethanol on the maturation of the spontaneous transmitter release by regenerated nerve endings in the rat were studied. The sciatic nerve was crushed and miniature end plate potentials (mepps) were recorded intracellularly in the re-innervated extensor digitorum longus muscle at different points in time after denervation; end plate potentials (epps) were also recorded. Two main effects were observed in the re-innervated muscles of ethanol-treated rats: (1) the appearance of spontaneous and evoked transmitter release was delayed and (2) the subsequent increase in frequency of mepps is faster. The possible mechanisms involved in these effects are discussed.

Effects of ethanol on arachidonic acid incorporation into lipids of a plasma membrane fraction isolated from brain cerebral cortex

In the presence of ATP, MgCl2, and CoASH, somal plasma membranes isolated from rat cerebral cortex were active in transferring arachidonic acid to phosphatidylinositols, phosphatidylcholines, and triacylglycerols. Ethanol (350-525 mM) added to the incubation mixture inhibited arachidonic acid incorporation into phospholipids, while it enhanced the incorporation into triacylglycerols. Under these conditions, ethanol was found to react with arachidonic acid to form arachidonoyl ethyl ester. The incorporation of labeled arachidonic acid into glycerolipids as well as the synthesis of ethyl esters required the presence of ATP and CoASH for maximal activity. Nevertheless, each uptake process exhibited a unique pH profile. The esterification of arachidonic acid was not specific for ethanol as other aliphatic alcohols (e.g., propanol and butanol) were also able to react with labeled arachidonic acid to form the respective esters. Somal plasma membranes isolated from mice after chronic ethanol administration showed an increase in arachidonoyl transfer to both phospholipids and triacylglycerols. When these membranes were challenged with ethanol (325 mM), those isolated from the chronic ethanol group showed a greater increase in the labeling of triacylglycerols and ethyl esters than those from controls. Thus, different acyltransferases exhibite different responses to the effects of ethanol in vitro and in vivo.

Membrane effects of ethanol: bulk lipid versus lipid domains

It has been well-established that ethanol fluidizes the bulk lipid of membranes and that this effect may alter cell function and be involved in ethanol sensitivity and tolerance. This hypothesis has been supported in several studies, however, there is also a considerable amount of data that do not support such an explanation, e.g., direct effect of ethanol on proteins, other membrane acting drugs, temperature effects, effects of ethanol on aged membranes and inconsistent effects of chronic ethanol consumption on lipid content. This review examined the bulk membrane fluidization hypothesis in light of those data and proposed a modification of the bulk membrane hypothesis that is based on recent data that show that ethanol and other alcohols have a specific effect on the structural properties of different membrane domains. This specific effect of ethanol is discussed within the context of how changes in fluidity of domains may alter membrane function.

The influence of dolichols on fluidity of mouse synaptic plasma membranes

Dolichols are isoprenologues which constitute an important component of biological membranes. However, an understanding of the effects of dolichols on the organization and dynamics of biological membranes has not been forthcoming. The experiments reported here are aimed at understanding the effects of dolichols on the physical properties of mouse brain synaptic plasma membranes. The effect of dolichols incorporated into mouse brain synaptic plasma membranes on fluorescent and electron spin resonance probes sensing the hydrophobic core differed from that of probes reporting closer to the surface of membrane bilayers. Dolichols significantly (P less than 0.01) lowered the polarization, limiting anisotropy, and order parameter of diphenylhexatriene in synaptic plasma membranes and liposomes extracted from synaptic plasma membranes, without changing the rotational relaxation time. Similarly, dolichol increased the fluidity reported by 16-doxylstearic acid in synaptic plasma membranes or liposomes extracted from synaptic plasma membranes. In contrast, dolichols exerted no effect on those properties for trans-parinaric acid or 5-doxylstearic acid in synaptic plasma membranes or liposomes derived therefrom. Dolichols can dramatically alter the structure and dynamics of lipid motion in synaptic plasma membranes and these effects are dependent on the location of the probe in the membrane.

Effects of chronic ethanol administration on rat brain phospholipid metabolism

Alterations in brain phospholipid metabolism were observed after chronic ethanol administration for 16 days to developing rats. Animals were injected intraperitoneally with 32Pi 16 h prior to killing. Overall uptake of 32Pi by brain did not differ between the control and ethanol-treated groups, which were killed 2 h and 24 h after the last ethanol feeding. Except for an increase in the labeling of myelin after ethanol treatment, the amount of radioactivity recovered in the synaptosomal-mitochondrial and plasma membrane fractions of control and ethanol-treated groups was not different. Relative to the radioactivity of phosphatidylcholines, which indicated no change, there were increases (20-44%) in labeling of ethanolamine plasmalogens, phosphatidic acids, and phosphatidylinositols in cortical synaptosomes from the 2-h ethanol-treated group. In the plasma membrane fractions, however, increases (9-14%) in labeling of phosphatidylserines and phosphatidylinositols were observed in both 2- and 24-h ethanol-treated groups. In both membrane fractions, there was an obvious increase (44-86%) in labeling of polyphosphoinositides at 24 h after withdrawal from ethanol. Results thus indicate an adaptive increase in the biosynthesis of ethanolamine plasmalogen and brain acidic phospholipids due to chronic ethanol administration. Furthermore, the increase in labeling of polyphosphoinositides in the 24-h withdrawal group may reflect the hypoactivity associated with ethanol withdrawal.

Changes in lipid composition of rat heart mitochondria after chronic ethanol administration

Triacylglycerols and phospholipids of mitochondria from heart ventricular muscle were analyzed following chronic ethanol administration (2 and 10 g/kg of body weight/day) to adult rats for 21 days via intragastric intubation. Triacylglycerols were elevated 57% in the high ethanol group as compared to controls, but cholesterol level was not altered. Most of the phospholipids, including lysophospholipids, showed a small increase in level after ethanol administration. However the greatest increase (50%) occurred in ethanolamine plasmalogens. Although small changes in the acyl group composition of phosphatidylethanolamines and phosphatidylcholines were observed, the acyl group profile of cardiolipin remained unaltered. It is concluded that myocardial membranes respond to the disordering effects of ethanol by altering the synthesis of selected lipids more than through altering the phospholipid acyl group composition. Some of these changes may be responsible for altered mitochondrial functions in the myocardium.

Anionic glycerophospholipids in platelets from alcoholics

Studies on ethanol-exposed animals have revealed changes in anionic phospholipids in brain membranes. The intention of this study was to investigate whether there was a similar effect on man. Assuming platelets to be an adequate model for CNS synaptosomes, concentration and fatty acid composition of anionic phospholipids, phosphatidylserine (PS) and phosphatidylositol (PI) in the platelet membrane from alcoholics after a debauche period were examined and compared to controls. Ethanol effects on neutral lipids were also analysed in order to obtain a comprehensive view. No quantitative difference was found in anionic phospholipids between alcoholics and controls. Fatty acid composition of individual phospholipids revealed significant changes which were more obvious in neutral phospholipids than in anionic. Oleic acid was increased and linoleic and arachidonic acids were decreased. After 1 week of detoxification, the abnormalities did not decrease, on the contrary they increased and total phospholipid concentration per platelet was significantly higher than in controls. It is concluded that the ethanol toxicity on bone marrow hampers the use of platelets as a model for synaptosomes but that the observed lipid abnormalities might play a major role in the impairment of platelet function in alcoholics.

Chronic ethanol increases liver plasma membrane fluidity

Purified plasma membrane fractions of cultured well-differentiated Reuber H35 hepatoma cells were studied after growth in the presence or absence of ethanol. Growth of cells in the presence of ethanol significantly increased plasma membrane 5'-nucleotidase activity but did not influence sodium-potassium adenosinetriphosphatase activity. Fluorescence polarization of lipophilic probes was used to study membrane lipid structure. Steady-state polarization of diphenylhexatriene (DPH), a probe of the hydrophobic core, was significantly lower in plasma membranes from cells grown in 80 mM ethanol for 3 weeks, compared to controls. Decreased polarization of DPH in plasma membranes was observed after 3-weeks growth of cells in as little as 1 mM ethanol. A 1-h exposure to 80 mM ethanol had no effect. Altered DPH polarization was due to a decrease in the order parameter of the probe. The rotational correlation time of the probe was virtually unchanged. Chronic ethanol treatment of cells did not alter the polarization of the membrane surface probe trimethylammoniodiphenylhexatriene. Plasma membranes from cells grown in 80 mM ethanol had decreased contents of both phospholipid and unesterified cholesterol, but the cholesterol to phospholipid ratio was unchanged. The percentages of sphingomyelin and phosphatidylserine in plasma membrane phospholipids were significantly decreased after ethanol treatment, while the phosphatidylcholine/sphingomyelin ratio was increased by 42%. Vesicles prepared from total plasma membrane lipids of ethanol-treated cells, as well as vesicles prepared from polar lipids alone, showed the same alterations in DPH polarization as did plasma membranes. The importance of ethanol metabolism in the observed plasma membrane changes was demonstrated in two ways.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol and membrane lipids

Although ethanol is known to exert its primary mode of action on the central nervous system, the exact molecular interaction underlying the behavioral and physiological manifestations of alcohol intoxication has not been elucidated. Chronic ethanol administration results in changes in organ functions. These changes are reflective of the adaptive mechanisms in response to the acute effects of ethanol. Biophysical studies have shown that ethanol in vitro disorders the membrane and perturbs the fine structural arrangement of the membrane lipids. In the chronic state, these membranes develop resistance to the disordering effects. Tolerance development is also accompanied by biochemical changes. Although ethanol-induced changes in membrane lipids have been implicated in both biophysical and biochemical studies, measurements of membrane lipids, such as cholesterol content, fatty acid unsaturation, phospholipid distribution, and ganglioside profiles, have not produced conclusive evidence that any of these parameters are directly involved in the action of ethanol. On the other hand, there is increasing evidence indicating that although ethanol in vitro produces a membrane-fluidizing effect, the chronic response to this effect is not to change the membrane bulk lipid composition. Instead, changes in membrane lipids may pertain to small metabolically active pools located in certain subcellular fractions. Most likely, these lipids are involved in important membrane functions. For example, the increase in PS in brain plasma membranes may provide an explanation for the adaptive increase in synaptic membrane ion transport activity, especially (Na,K)-ATPase. There is also evidence that the lipid pool involved in the deacylation-reacylation mechanism (i.e., PI and PC with 20:4 groups) is altered after ethanol administration. An increase in metabolic turnover of these phospholipid pools may have important implications for the membrane functional changes. Obviously, there are other lipid-metabolizing enzyme systems that may exert similar effects but have not yet been investigated in detail. From the results of these studies, it is concluded that the multiple actions of ethanol are associated with changes in enzymic systems important in the functional expression of the membranes.

Synaptic membrane phospholipids: effects of maternal ethanol consumption

The cholesterol and phospholipid content and phospholipid composition were determined in synaptic membranes from the 17- to 31-day-old offspring of rats that were pair-fed either a control or 6.6% (v/v) ethanol liquid diet on a chronic basis prior to parturition. At all ages examined, the major synaptic membrane phospholipid was phosphatidyl choline (greater than 40%). Other prominent synaptic membrane phospholipids included phosphatidyl ethanolamine (approximately 17 to 21%), ethanolamine plasmalogen (approximately 5 to 16%), and phosphatidyl serine (approximately 13%). Smaller proportions of sphingomyelin (4 to 7%), phosphatidyl inositol (approximately 1%), and phosphatidic acid (approximately 1%) were detected. Between 17 and 31 days of age, there was a significant decrease in the proportion of phosphatidyl choline and a significant increase in the proportion of ethanolamine plasmalogen. When the offspring of control and ethanol-treated rats were compared, no significant differences were found in either the yield of synaptic membrane protein, or in the concentration of synaptic membrane cholesterol and total phospholipid. However, the proportion of ethanolamine plasmalogen was significantly decreased in the 24-day-old offspring of ethanol-treated rats, suggestive of a delay in the normal development-related increase of this lipid. In addition, there was a small increase in the proportion of sphingomyelin in the 31-day-old offspring of ethanol-treated rats.

Changes in lipid composition of cortical synaptosomes from different age groups of mice

Lipid composition of cortical synaptosomes differed with age in C57BL/6NNIA mice. Significant age differences were observed for cholesterol and the ratio of cholesterol to total phospholipid phosphorus content. The phospholipid to protein ratio of individual phospholipids also increased with age with diacyl-sn-glycero-3-phosphocholine (PC) increasing the most. Acyl group composition of individual phospholipids, however, showed little age difference. The double bond index for PC decreased significantly with age. Changes in membrane composition may help explain differences in the effects of ethanol on the physical and biochemical properties of membranes from different age groups that have been reported previously.

Increased acidic phospholipids in rat brain membranes after chronic ethanol administration

Two types of plasma membranes isolated from rat brain cortex were used to study the membrane-perturbing properties of ethanol. Rats administered ethanol in the form of a liquid diet showed an increase in levels of phosphatidylserines, phosphatidylinositols and phosphatidic acids as compared to controls. The results present evidence that chronic ethanol treatment results in an increase in the acidic phospholipids in brain membranes. This type of membrane modification may have important implications for the function of membrane transport enzymes such as (Na+, K+)-ATPase, which also increases in activity upon chronic ethanol administration.