Membrane solubility of ethanol in chronic alcoholism. The effect of ethanol feeding and its withdrawal on the protection by alcohol of rat red blood cells from hypotonic hemolysis

Comparison of ethanol and acetaldehyde toxicity in rat astrocytes in primary culture

This study compared the effects of toxicity of ethanol and its first metabolite acetaldehyde in rat astrocytes through cell viability and cell proliferation. The cells were treated with different concentrations of ethanol in the presence or absence of a catalase inhibitor 2-amino-1,2,4 triazole (AMT) or with different concentrations of acetaldehyde. Cell viability was assessed using the trypan blue test. Cell proliferation was assessed after 24 hours and after seven days of exposure to either ethanol or acetaldehyde.We showed that both ethanol and acetaldehyde decreased cell viability in a dose-dependent manner. In proliferation studies, after seven days of exposure to either ethanol or acetaldehyde, we observed a significant dose-dependent decrease in cell number. The protein content study showed biphasic dose-response curves, after 24 hours and seven days of exposure to either ethanol or acetaldehyde. Co-incubation in the presence of AMT significantly reduced the inhibitory effect of ethanol on cell proliferation.We concluded that long-term exposure of astrocytes to ethanol is more toxic than acute exposure. Acetaldehyde is a much more potent toxin than ethanol, and at least a part of ethanol toxicity is due to ethanol's first metabolite acetaldehyde.

Influence of age on the stability of human erythrocyte membranes

This work evaluated the dependence of erythrocyte membrane stability on age, temperature (26, 32, 37, 42 and 47 degrees C), nutritional status, red cell count, red cell distribution width (RDW) and mean corpuscular volume (MCV) in human females (n = 67, 20-94 years). Erythrocyte membrane resistance to hypotonic lysis was expressed as the NaCl concentration (H(50)) capable of promoting 50% haemolysis. A nutritional evaluation was performed using the Mini Nutritional Assessment (MNA) instrument, which showed that 76.1% of the study group were well nourished and 23.9% were at risk of malnutrition. H(50) demonstrated a negative correlation with age at all temperatures. H(50) showed no correlation with either MNA scores or with any haematological indices. The power and significance of the correlations improved when we censored from the analyses those individuals at risk of malnutrition. The thermal dependencies lines for H(50) demonstrated higher values for females 20-39 years of age compared with those more than 60 years of age. These results suggest that erythrocyte resistance to hypotonicity (erythrocyte membrane stability), increased with age of study volunteers. This increased stability was more pronounced among well-nourished individuals.

Effects of brain membranes on 1H nuclear magnetic resonance signal intensity of ethanol in vitro

In vivo proton nuclear magnetic resonance (1H NMR) studies of ethanol in animal and human brains have shown that only a fraction of ethanol in brain is visible by NMR. The goals of these in vitro 1H NMR experiments were to determine: (1) whether the interaction of ethanol with brain membranes in vitro diminishes ethanol visibility; and (2) if a magnetization transfer (MT) effect can be observed for the interaction of ethanol with brain membranes in vitro. Furthermore, pilot studies were performed to determine if the brain membranes from rats chronically exposed to ethanol had a different effect on ethanol NMR visibility and spin-spin relaxation time (T2) than brain membranes obtained from control rats. Results show that the NMR visibility of ethanol is lower in rat brain membrane suspensions in vitro as compared to ethanol in saline solutions. The factors decreasing ethanol NMR visibility are T2 relaxation, water presaturation time, and off-resonance saturation by a frequency-dependent MT pulse. One-pulse NMR measurements without water presaturation showed that ethanol visibility was significantly increased by 15% in brain membrane suspensions of ethanol-fed rats, suggestive of decreased ethanol partitioning compared to controls. Furthermore ethanol in brain membrane suspensions from ethanol-fed rats showed smaller MT effects than from control rats. These results provide a mechanism for decreased NMR visibility of ethanol in brain, and suggest that chronic exposure to ethanol produces membrane changes which result in increased NMR visibility.

Differential in vitro effects of ethanol on glycerolipid acylation and biosynthesis in rat reticulocytes

Earlier reports have shown that, in human and rat red blood cells (RBC), ethanol modulates acylation reaction sin several membrane glycerolipid components. Little is known, however, about the kinetics and the mechanisms involved in the acylation changes. In the present study, we show that short-term in vitro exposure of intact rat reticulocytes to ethanol differentially modifies within minutes the incorporation of [3H]oleic acid in glycerolipids. A concentration-dependent inhibition of acyl incorporation was measured in phosphatidylcholine (PC) and phosphatidylethanolamine (PE). This effect did not involve inhibition of the corresponding acyltransferase activities and is likely to be due to ethanol-dependent decreases in phospholipase activities. In contrast, ethanol markedly stimulated [3H]oleic acid incorporation in phosphatidic acid (PA), diacylglycerol (DG) and, to a lesser extent, in triacylglycerol (TG). To determine the mechanisms of the latter increases, reticulocytes were pulsed with [14C]glycerol and assayed as a function of time for labeled biosynthetic precursors and products. We observed a very close correlation between time courses and amplitudes of the ethanol stimulation of acylation and biosynthesis reactions, suggesting that stimulation of acylation in PA, DG and TG is causally related at least partly to their increased biosynthesis. Further studies revealed that increases in glycerolipid acylation and biosynthesis in reticulocytes were: (a) readily reversible upon ethanol withdrawal; (b) detectable for clinically relevant concentration (50 mM) of ethanol; and (c) associated with concomitant increases in cell resistance to hemolysis. These changes may be relevant to the development of tolerance to ethanol.

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.

Biophysical and biochemical alterations in erythrocyte membranes from chronic alcoholics

Erythrocyte membranes from healthy controls and alcoholic patients, examined within 24 h of abstinence, were studied for basal membrane fluidity and membrane sensitivity to ethanol by fluorescence polarization of the apolar probe 1,6-diphenyl-1, 3,5-hexatriene (DPH) and its cationic derivative 1,4(trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The membrane partition (Kp) of ethanol and phenobarbital, and the concentrations of membrane-bound sialic acid and galactose, were also determined. The apolar hydrocarbon region of the membrane (DPH) was less fluid, in the alcoholics than in the controls (p less than 0.005). In the patients this membrane layer, as well as the polar lipid head group region (TMA-DPH), showed reduced fluidizing effect of ethanol (p less than 0.01). This resistance or tolerance to ethanol correlated with a markedly impaired (-59%, p less than 0.025) partition of ethanol into the membrane. The low Kp of ethanol in turn was partly related to reduced concentrations of polar carbohydrates such as sialic acid and galactose (p less than 0.01) at the membrane surface. The Kp of phenobarbital was reduced in the patients (-59%, p less than 0.005) but, apparently unrelated to the carbohydrate changes. These results indicate that in man, chronic alcohol abuse is associated with complex changes of membrane properties at different membrane levels e.g. at the charged surface, in the polar lipid head group region and in the hydrocarbon core. A partial basis for biophysical membrane tolerance to ethanol is suggested, implying that apart from phospholipid alterations, structural changes in membrane-bound glycoconjugates participate in this adaptive process.

Alcohol stimulates Na+/Ca2+ exchange in brain mitochondria

Ethanol, at low concentrations, specifically stimulates the Na(+)-dependent Ca2(+)-efflux in brain mitochondria. In addition, at higher concentrations, ethanol inhibits the Na(+)-independent Ca2(+)-efflux. The electrogenic Ca(+)-uptake system is not affected by ethanol. The specific stimulation of Na+/Ca2+ exchange reaches a maximum of 60% stimulation, with half-maximal stimulation at 130 mM ethanol. The inhibition of the Na(+)-independent efflux is proportional to the ethanol concentration, becoming significant only above 200 mM, with 50% inhibition at 0.5 M. The inhibition of the Na(+)-independent efflux is, in large part, due to an inhibition of the activation of the Cyclosporin-sensitive pore. Long-term ethanol-feeding had no effect on the Ca2+ transport systems and their sensitivity to acute ethanol treatment. It is suggested that the stimulation of the Na(+)-dependent Ca2(+)-efflux, which is the dominant Ca2+ efflux pathway in brain mitochondria, contributes to the intoxicating effects of ethanol.

A comparison of ethanol partitioning in biological and model membranes: nonideal partitioning is enhanced in synaptosomal membranes

The partitioning of ethanol into mouse brain synaptosomes at 37 degrees C was characterized as a function of ethanol concentration. In addition, the partitioning of ethanol into multilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles was characterized as a function of ethanol concentration and temperature. DPPC liposomes provided a model for ethanol partitioning into a phospholipid bilayer of defined composition allowing comparison to the more complex synaptosomal membrane. The values of the partition coefficients for ethanol depend on the convention used to express concentration in the partition coefficient ratio. We express these concentrations as mole fractions as ethanol in the membrane and aqueous phases. Ethanol partitioning is nonideal (ethanol membrane: buffer partition coefficients vary with total ethanol concentration). In synaptosomes, the partition coefficients vary markedly with concentration and asymptotically approach zero at higher concentrations. In the DPPC system, the variation of the partition coefficient is less pronounced, but significant. The ethanol: DPPC partition coefficients decrease by a factor of 2 at ethanol concentrations above 3.2 x 10(-3) M. This suggests a model involving at least two distinguishable types of interactions of ethanol with the membrane. Ethanol appears to undergo both bulk phase partitioning into the membrane bilayer core and nonspecific binding to the membrane surface. In pure DPPC, bulk phase hydrophobic partitioning predominates. In synaptosomes, nonspecific surface binding appears to be a major interaction. Temperature studies indicate ethanol partitioning into DPPC increases above the phospholipid gel to liquid crystalline phase transition temperature. This suggests a preferred partitioning of ethanol into fluid state lipid. However, significant membrane concentrations of ethanol are found in gel state DPPC.

Hemolysis by aliphatic alcohols and saponin measured by the coil planet centrifugation method

Using the coil planet centrifugation method, the mechanism of hemolysis by alcohols and saponin was investigated. With this technique, erythrocytes are introduced into a gradient of hemolytic agents in saline, which is prepared in a long coiled polyethylene tube. The tube is centrifuged so that the cells move from a low to a high concentration of hemolytic agent. When the cells lyse, they release hemoglobin which remains stationary, and therefore hemolytic potency can be determined spectrophotometrically by the distance the cells move before lysing. We found that alcohols caused hemolysis at a particular concentration, whereas saponin-induced hemolysis was dependent on the amount of saponin accumulated in the environment of the cell. In addition, alcohols with longer carbon chains were more potent hemolytic agents than those with shorter chains, but each additional carbon group produced less of an increase in hemolysis per mole of alcohol. This chain-length dependency is consistent with a previous study on in vivo alcohol-induced hemolysis. The coil planet centrifugation method is also adaptable to comparative studies on the mechanism of other types of hemolysis, such as immune or drug-induced lysis, and to toxicological studies.

Membrane tolerance to ethanol is rapidly lost after withdrawal: a model for studies of membrane adaptation

The structural properties of liver microsomes and erythrocytes obtained from rats that had been chronically administered ethanol were examined by electron spin resonance (ESR) following ethanol withdrawal for 1-10 days. Membranes obtained from control animals exhibited considerable molecular disordering upon the addition of ethanol in vitro (50-100 mM). Conversely, microsomal and erythrocyte membranes from alcoholic animals were resistant to this disordering by ethanol (membrane tolerance). These membrane properties were also apparent in lipid bilayers comprised of either total lipids or phospholipids isolated from the control and alcoholic animals. While several weeks of ethanol administration were required for both erythrocytes and microsomes to develop membrane tolerance, erythrocytes from alcoholic animals were disordered by ethanol in vitro after the animals had been withdrawn from ethanol for only 1 day. The same rapid loss of tolerance was observed in microsomes after 2 days of withdrawal. The same time course for the loss of tolerance was observed in lipid bilayers prepared from the total lipid and phospholipid extracts. No significant differences in the cholesterol/phospholipid ratio were observed between the microsomal or erythrocyte membranes isolated before and after withdrawal. Thus, alterations in the microsomal and erythrocyte phospholipids, and not cholesterol content, were responsible for conveying membrane tolerance. Membrane structural properties can be rapidly adjusted in a mammalian system in response to the withdrawal of the external membrane perturbant ethanol. The withdrawal model, which begins with established membrane tolerance and leads to rapid and complete loss of tolerance, provides a model to analyze the compositional changes responsible for this tolerance to disordering by ethanol.