Reduction of the sialic acid and galactose concentrations in erythrocyte membranes in alcoholics

A shift in microvillus membrane fucosylation to sialylation by ethanol ingestion in rat intestine

The luminal surface of enterocytes is covered with glycocalyx which is rich in glycoproteins. Ethanol ingestion is shown to induce morphological and biochemical changes in the intestine. In this study, the effect of ethanol ingestion on membrane glycoproteins has been investigated. Chemical analysis of microvillus membranes revealed an increase in hexose and sialic acid contents, but a reduction in fucose levels in ethanol-fed rats compared with controls. The observed changes were apparent in animals fed with ethanol for 35-56 days compared with controls. Lectin-binding assay indicated an increase in Wheat germ agglutinin (affinity for GlcNAc/sialic acid) and a decrease in Aleuria aurantia (affinity for alpha-L: -fucose) reactivity of brush borders in ethanol-fed animals for 4-8 weeks. Western blot analysis using biotin-labeled Wheat germ agglutinin revealed increased binding to proteins of M(r) 66-205 kDa in ethanol-fed rats compared with controls. The binding of Aleuria aurantia to membrane proteins of M(r) 97-185 kDa was reduced in ethanol-fed animals. These findings suggest that long-term ethanol feeding modulates the sialylation and fucosylation processes of microvillus membrane proteins in rat intestine. This could affect the intestinal digestive and absorptive functions in chronic alcoholism.

Biological water and its role in the effects of alcohol

Alcohol and water compete with each other on target membrane molecules, specifically, lipids and proteins near the membrane surface. The basis for this competition is the hydrogen bonding capability of both compounds. But alcohol's amphiphilic properties give it the capability to be attracted simultaneously to both hydrophobic and hydrophilic targets. Thus, alcohol could bind certain targets preferentially and displace water, leading to conformational consequences. This article reviews the clustering and organized character of biological water, which modulates the conformation of membrane surface molecules, particularly receptor protein. Any alcohol-induced displacement of biological water on or inside of membrane proteins creates the opportunity for allosteric change in membrane receptors. This interaction may also prevail in organelles, such as the Golgi apparatus, which have relatively low concentrations of bulk water. Target molecules of particular interest in neuronal membrane are zwitteronic phospholipids, gangliosides, and membrane proteins, including glycoproteins. FTIR and NMR spectroscopic evidence from model membrane systems shows that alcohol has a nonstereospecific binding capability for membrane surface molecules and that such binding occurs at sites that are otherwise occupied by hydrogen-bonded water. The significance of these effects seems to lie in the need to learn more about biological water as an active participant in biochemical actions. Proposed herein is a new working hypothesis that the molecular targets of ethanol action most deserving of study are those where water is trapped and there is little bulk water. Proteins (enzymes and receptors) certainly differ in this regard, as do organelles.

Effects of ethanol on neuroblastoma cells in culture: role of gangliosides in neuritogenesis and substrate adhesion

Murine Neuro-2A neuroblastoma cells were exposed to ethanol in culture under two experimental paradigms: (1) short-term (24 hr or less) and low concentrations (0.05 to 0.5%; 8.5 to 86 mM) and (2) long-term (48 hr at 0.5%; 86 mM). Long-term ethanol exposure did not affect Neuro-2A viability, determined by DNA synthesis or the ability to exclude Trypan Blue. Similarly, long-term ethanol treatment did not inhibit differentiation, exhibited by the extension of neurites, promoted by either dibutyryl-cyclic-AMP or by incubation with exogenous ganglioside GM1. The incorporation of exogenous ganglioside GM1 into plasma membranes was not influenced by varying concentrations of ethanol (up to 1.2%; 204 mM). In contrast, ethanol did influence Neuro-2A cell attachment to collagen in a dualistic manner. During short-term ethanol exposure, cell attachment was enhanced. However, when cells were initially exposed to ethanol for 48 hr a marked inhibition of subsequent attachment was observed. Long-term ethanol exposure also inhibited attachment to other substrata, including laminin, fibronectin and vitronectin. Incubation of Neuro-2A cells with either exogenous ganglioside GM1 or a mixture of brain gangliosides partially reversed the inhibition of attachment to collagen. This reversal did not appear to be due to any one particular ganglioside structure, however. Mixed brain gangliosides were fractionated into three fractions, according to the number of sialic acid residues. Each of the three fractions were equally effective in partially restoring Neuro-2A cell attachment to collagen after long-term ethanol treatment. The results suggest that the mechanism by which these effects occur is at the level of plasma membrane fluidity, because both ethanol and glycosphingolipid content are known to influence membrane lateral mobility, although other mechanisms, such as changes in headgroup hydration, are possible.

Alcohol intoxication and sialic acid in erythrocyte membrane and in serum transferrin

Microheterogeneity of serum transferrin as well as erythrocyte membrane sialic acid content were examined in alcoholic patients and healthy controls. Both the sialic acid content of erythrocyte membranes and of the circulating transferrin were significantly lower in alcoholic patients than in controls. A moderate daily ethanol intake (less than 80 g) allowed to observe a proportional relationship between alcohol intake and the carbohydrate deficient forms of transferrin, and also a correlation between alcohol intake and the membrane sialic acid content. This supports the hypothesis of ubiquitary alterations of glycosylations in connection to ethanol intoxication. Additional disturbances could explain the absence of correlations between membrane sialic acid, pattern of abnormal forms of serum transferrin, and alcohol intake in heavy alcoholic patients.

The effect of abstinence in alcoholics of erythrocyte gangliosides

The pattern of gangliosides in membranes of erythrocytes was examined in healthy and in alcoholic subjects on the second and on the 28th day of detoxification therapy. The GM3 and GD3 fraction were decreased significantly in alcoholics on the 2nd day. After 4 weeks of abstinence all changes had returned to the level of healthy subjects.

[Abnormal gangliosides in the plasma of alcoholics]

Gangliosides were isolated from plasma of alcoholics. The pattern of gangliosides was compared with that of healthy humans. Up to seven fractions of gangliosides could be detected. In healthy subjects the following pattern was found: GM3 38.2%, SPG 6.0%, GD3 30.2%, GD1a 10.6%, GD1b 4.8%, GT1b 7.9%, GQ1b 2.2%. In alcoholics, significant differences were observed in the main ganglioside fractions GM3 (52.6%) and GD3 (17.5%).

Differences in susceptibility of rat liver and brain sialidases to ethanol and gangliosides

Based on reports that ethanol can decrease the level of sialic acid (SA) (neuraminic acid) in several tissues, we tested the hypothesis that ethanol promotes SA cleavage by enhancing the activity of sialidases (neuraminidases). We also investigated whether brain and liver sialidases have the same response to ethanol and gangliosides, especially since our prior studies have demonstrated that gangliosides could antagonize ethanol-induced behavior. Experiments were conducted on homogenates of brain and liver and of liver slices of adult rats. In liver slices, cleavage of SA did not fall in proportion to the ethanol-induced inhibition of sialidase; in fact, at 0.1 M ethanol, free SA increased, even though sialidase was inhibited. Brain sialidase activity on endogenous sialoglycoconjugates was much more resistant to ethanol than liver sialidase and was fully active even in concentrations as high as 1 M. When gangliosides were incubated with liver slices in the absence of ethanol, sialidase was markedly stimulated. The ethanol-induced inhibition of sialdase in liver slices was mimicked by sorbitol, suggesting that the inhibition may be caused by a shift in redox state as a result of increased NADH. The ethanol metabolite, acetaldehyde, does not seem to be a factor, because sialidase inhibition still occurred when slices were incubated with ethanol containing pyrazole. The results indicate that ethanol promotes the accumulation of free SA in liver without stimulating sialdase; our other work suggests that the cause is an increase in accessibility to sialoglycoconjugates rather than decreased utilization of SA. Brain and liver sialidases clearly respond differently to both ethanol and gangliosides.

Ethanol promotes hydrolysis of 3H-labeled sialoconjugates from brain of mice in vitro

Acute administration of ethanol reportedly decreases total sialic acid in brain. Here, we tested the hypothesis in brain and liver that the decrement is due to increased hydrolysis of sialoglycoconjugates. Mouse tissue slices were pulse-labeled with N-[3H]acetyl-D-mannosamine, the precursor of sialic acid. Incorporation was linear for up to 4 hr of incubation. When the labeled slices were incubated with three concentrations of ethanol (0.1, 0.5, and 1 M) for 5 hr, labeled liver sialoconjugates were significantly affected only at 0.5 and 1 M ethanol, whereas labeled brain sialoconjugates were markedly decreased even at 100 mM ethanol. Sialidase activity decreased steadily with increasing concentration of ethanol, indicating that the increased hydrolysis was not attributable to an enhanced sialidase activity. n-Propanol and t-butanol had the same degradative effect as ethanol on sialocompounds; and 3 mM pyrazole, an inhibitor of alcohol dehydrogenase (ADH), had no effect on ethanol-induced degradation of sialocompounds. The protein/DNA ratio in liver showed a steady decrease with increasing ethanol. The data thus confirm the in vivo reports of ethanol-enhanced cleavage and rule out any increase in sialidase activity as a major cause.

Carbohydrate-deficient transferrin (CDT) in serum in women with early alcohol addiction

Carbohydrate-deficient transferrin (CDT) in serum was determined by micro anion exchange chromatography and a transferrin radioimmune assay in 58 consecutive women treated for early alcohol dependence compared, with 62 healthy females with an alcohol consumption of 0-15 g of ethanol/day. The upper normal CDT level was 74 mg/l. CDT was elevated above this value in 83% of the alcoholic women with an intake of 60 g of ethanol/day or more for at least 7 days within the preceding two weeks. CDT values were significantly positively correlated with daily alcohol consumption but not with GT, ASAT, ALAT or MCV. During abstinence CDT level declined exponentially with a half-life of 14 +/- 3 days. The results indicated that CDT may be as sensitive and specific a marker in women with early alcohol addiction as in previously studied male alcoholics. The amount of alcohol consumed appeared to be more important than sex or liver function. Determination of CDT may thus offer a means for early objective diagnosis and adequate treatment also of women in early stages of alcoholism.

[Abnormal erythrocyte membrane gangliosides in alcoholism]

The pattern of gangliosides in membranes of erythrocytes was examined in healthy donors and in alcoholic subjects. Seven different gangliosides could be detected. In healthy donors the following pattern was found: GM3 = 17.6%, SPG = 43.1%, GD3 = 9.1%, GD1a = 12.8%, FucGD1b = 5.2%, GT1b = 6.7% and GX = 5.7%. The GM3 and FucDG1b fraction were decreased statistically significantly in alcoholics.

Gangliosides, or sialic acid, antagonize ethanol intoxication

Because ethanol elicits a dose-dependent hydrolysis of brain sialogangliosides, we tested the possibility that injected gangliosides might antagonize intoxicating doses of ethanol. Clear anti-intoxication effects were seen at 24 hr post-injection of mixed mouse-brain gangliosides at 125-130 mg/kg, but not at lower or higher doses. Sleep time was reduced on the order of 50%, and roto-rod agility was significantly enhanced. Sialic acid (SA) similarly antagonized ethanol; however, the precursor of SA, N-acetyl-D-mannosamine, as well as ceramide and asialoganglioside did not.

Membrane glycoconjugates as potential mediators of alcohol effects

1. Membrane glycoconjugates include glycoproteins and glycolipids that have many important functions in a wide variety of tissues, especially brain. 2. Alcohol's ability to fluidize and swell plasma membranes could be expected to alter the orientation and conformation of the embedded glycoconjugates. 3. Both kinds of glycoconjugates can contain terminal moieties of sialic acid, which has been shown to be decreased by single doses of alcohol. Chronic exposure to alcohol may have no effect on sialic acid, except in very young animals. 4. Glycolipids containing sialic acid (gangliosides) are also decreased by acute doses of alcohol, but chronic alcohol has little effect. Thus, gangliosides may have a role in the development and expression of tolerance. 5. Glycoproteins containing sialic acid may also be involved in alcohol action, but there has been less research in this area. 6. Alcohol-induced disruptions in membrane glycoconjugates could affect the important cellular functions that glycoconjugates have, and thus research on alcohol effects on glycoconjugates could lead to important discoveries of diagnostic and therapeutic value for alcohol abuse and alcoholism.

Micro anion exchange chromatography of carbohydrate-deficient transferrin in serum in relation to alcohol consumption (Swedish Patent 8400587-5)

A new simplified and rapid method for detection and quantitation of "carbohydrate-deficient transferrin" in serum is described. The method is based on isocratic anion exchange chromatography of isotransferrins in disposable microcolumns followed by a double antibody transferrin radioimmune assay. This technique, which separates all transferrin components isoelectric above pH 5.65, showed a very good reproducibility and accuracy with a coefficient of variation between 5 and 9%. 77 alcoholic patients could be clearly separated from 80 healthy "normal consumers" and 33 total abstainers with a specificity of 100% and a sensitivity of 91%. The values were significantly correlated to the amount of alcohol consumed during the latest month, and declined in abstaining alcoholics with a mean biological half-life of 17 days. Elevated levels occasionally appeared in healthy individuals after daily consumption of 60 g of ethanol during a 10-day period. In a sample of 187 patients with nonalcohol-related conditions only 2% false-positive values were found. This method is suggested as a potential tool for detecting and monitoring alcohol abuse.

Glycoprotein sialyl- and galactosyl transferase activities in erythrocyte membranes in alcoholic patients and healthy controls

In investigating possible mechanisms underlying carbohydrate deficiencies in serum transferrin and erythrocyte membranes in alcoholics, a total of 27 alcoholic patients and 27 healthy controls were examined for the activities of sialytransferase in serum and erythrocyte membranes and galactosyltransferase in erythrocyte membranes. The enzymes were assayed with endogenous and different exogenous glycoprotein acceptors and with [14C] CMP-sialic acid and [14C] UDP-galactose as substrates. No decrease in enzyme activities were found in alcoholic patients compared to controls, indicating that chronic ethanol abuse does not exert any direct inhibitory effect on these glycosyltransferases in isolated erythrocyte membranes or on sialytransferase in serum. Further studies of the effect of ethanol on the metabolism of complex carbohydrates are clearly necessary.

Carbohydrate composition of serum transferrin in alcoholic patients

Previous studies have shown that sialic acid-deficient isotransferrins appear in serum during chronic alcohol abuse. In this investigation whole serum transferrin from alcoholic patients and healthy controls was isolated by antitransferrin affinity chromatography and the total levels of sialic acid, galactose, N-acetylglucosamine, and mannose were analyzed. The results showed that the concentrations of sialic acid and galactose as well as N-acetylglucosamine were reduced in all of the alcoholics studied. These findings indicate that chronic ethanol misuse exerts a more complex effect on the glycans of transferrin than previously realized.

Abnormal fluidity and surface carbohydrate content of the erythrocyte membrane in alcoholic patients

Erythrocyte membranes from 11 healthy individuals and 11 alcoholic patients, examined within 24 hr of withdrawal, were studied for membrane fluidity as assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene and for the concentrations of sialic acid and galactose in the membrane surface. Basal fluorescence polarization was significantly higher in the alcoholics and the membranes were clearly more resistant to the fluidizing effect of ethanol added in vitro. The concentrations of sialic acid as well as galactose were significantly reduced in the patients. The increased resistance to the fluidizing effect of ethanol added in vitro appeared to be functionally related to reduced concentrations of terminal sialic acid and terminal and sialic acid-bound beta-galactose in the membrane surface. The increased basal rigidity is probably due to concomitant changes in the lipid bilayer of the membrane. The results also showed, for the first time, that similar perturbations of membrane fluidity occur in human alcoholics as have been found previously in chronically ethanol-treated animals.

Functional properties of isolated hepatocytes from ethanol-treated rat liver

Gluconeogenesis and palmitate incorporation into triacylglycerols and phosphatidylcholine were measured in isolated hepatocytes from control and ethanol-treated rats. Basal gluconeogenesis and its hormonal response decreased in hepatocytes from ethanol-treated animals; palmitate incorporation into triacylglycerols increased. In ethanol-treated rat liver, 45Ca2+ uptake and methylating capacity were reduced, and the hormonal response exhibited differences in binding parameters of insulin.

Changes in (Na+ + K+) ATPase activity and the composition of surface carbohydrates in erythrocyte membranes in alcoholics

(Na+ + K+)ATPase activity and sensitivity to the inhibitory effect of ethanol and noradrenaline in vitro as well as the concentrations of sialic acid, galactose, and hexosamine were determined in erythrocyte membranes in 20 healthy controls and in 20 alcoholic patients within 24 hr of withdrawal. Basal (Na+ + K+)ATPase activity, the sensitivity of the enzyme to inhibition by ethanol and noradrenaline added in vitro, and the concentrations of sialic acid and galactose were significantly reduced in the patients (p less than 0.0005). All of these abnormalities were significantly correlated to each other as well as to the estimated daily quantity of ethanol consumed. After enzymatic removal of terminal sialic acid and terminal and sialic acid-bound beta-galactose, the (Na+ + K+)ATPase differences between the patients and the controls were eliminated. The results showed that the previously reported reduced inhibition of (Na+ + K+)ATPase by ethanol in the presence of noradrenaline in brain membranes in chronically ethanol-fed animals is also found in erythrocyte membranes in alcoholic humans. Abnormal carbohydrate composition of glycolipids and/or glycoproteins of the membrane surface appeared to be related to the (Na+ + K+)ATPase changes, possibly due to interference either with K+ transport or surface electrostatics or, directly or indirectly, with the conformation of (Na+ + K+)ATPase.

Detection of erythrocyte membrane proteins, sialoglycoproteins, and lipids in the same polyacrylamide gel using a double-staining technique

A silver/Coomassie brilliant blue R-250 staining technique that permits a color-coded differentiation of erythrocyte membrane proteins, sialoglycoproteins, and lipids in a single one-dimensional NaDodSO4/polyacrylamide gel has been described. Gels stained first with silver stain and then with Coomassie blue (CB) showed the characteristic blue staining of all conventional CB-sensitive membrane polypeptides, whereas periodic acid-Schiff reagent-sensitive sialoglycoproteins and lipids stained yellow. Several yellow Ag-stained bands corresponding to major and minor sialoglycoproteins were detected at Mr X 10(-3) of 88, 72, 65, 41, 35, 31, 28, 24, and 20. Neuraminidase treatment of intact erythrocytes caused shifts in the electrophoretic mobilities of several yellow-stained bands without affecting the CB-stained polypeptide pattern. These observations afforded evidence that the yellow-staining bands were sialoglycoproteins and lipids. The double-staining technique was used in a topological analysis of the membrane surface of the erythrocyte using protease digestion and selective solubilization. Trypsin cleaved the yellow bands at Mr 88,000 and 41,000. Membrane-associated cleavage products were noted at Mr 58,000 and 38,000. Pronase treatment of intact cells gave membrane-associated cleavage products at Mr 38,000 (yellow) and two CB-stained bands at Mr 58,000 and 60,000. These results suggested that the double-staining technique may be applicable in compositional and topological analyses of other biological membranes.

Carbohydrate composition of erythrocyte membranes and glycosidase activities in serum in patients with myotonic dystrophy, limb-girdle dystrophy and congenital myotonia

A number of abnormalities in cell membrane function, including cells other than muscle cells, have been described in patients with inherited muscular diseases such as myotonic dystrophy and congenital myotonia. The basic molecular defects are, however, still unknown. The complex carbohydrates of membrane-bound glycoconjugates are of vital importance for the normal performance of the cell membrane. In this study the concentrations of the three major carbohydrates (sialic acid, galactose and hexosamines) of the erythrocyte membrane were therefore determined in patients with myotonic dystrophy, limb-girdle dystrophy and congenital myotonia. The activities of relevant glycosidases in serum were also assayed. In each of the three diseases pertinent changes of the carbohydrate pattern were found. In patients with myotonic dystrophy the sialic acid and in patients with limb-girdle dystrophy the hexosamine concentration was significantly reduced (P less than 0.0005). The sialic acid, galactose and hexosamine concentrations were all significantly increased in patients with congenital myotonia. No increase of the neuraminidase (sialidase) activity was found in sera from patients with myotonic dystrophy. In patients with limb-girdle dystrophy, the activities of serum hexosaminidases were normal. These results support the contention that certain inherited muscular diseases may represent generalized membrane disorders, and suggests that disturbances of membrane-bound glycoproteins and/or glycolipids might be of importance in the pathogenesis of some of these disorders.

The sialic acid and galactose concentrations in erythrocyte membranes in patients with myotonic dystrophy, limb-girdle and facioscapulohumeral dystrophy

Sialic acid is an important constituent of membrane-bound glycoproteins and glycolipids. It occurs linked to galactose at the surface of the membrane and is involved in, e.g., cation exchange, receptor function, maintenance of membrane polarity and intercellular interactions. In myotonic dystrophy there is evidence of an as yet basically undefined plasma-membrane abnormality. Considering the importance of sialic acid in membrane function, sialic acid as well as galactose concentrations were measured in erythrocyte membranes from 17 patients with myotonic dystrophy and compared to 17 matched healthy controls. There was a highly significant (P less than 0.0005) reduction of the sialic acid concentration in the patients, while no significant difference in galactose concentration was found. In 16 patients with limb-girdle and facioscapulohumeral dystrophy, sialic acid and galactose concentrations did not differ from matched controls. The possible importance of a reduced concentration of membrane-bound sialic acid in myotonic dystrophy is discussed in relation to previously reported biochemical membrane abnormalities in this disease.

Effect of ethanol on synaptosomal sialic acid metabolism in the developing rat brain

The total, glycoprotein-bound and glycolipid-bound sialic acid concentration, ad the activities of ecto-sialyltransferase and neuraminidase were determined in synaptosomes from preweanling ethanol-treated and control rats. The period of treatment corresponded to that of maximal synaptogenesis and peak synthesis of sialoglycocompounds (days 27-37 postconception). The average of the peak blood ethanol concentration was 271 mg/100 ml. In the ethanol-treated animals the sialic acid concentration was significantly reduced (approximately 20%) with an equally distributed decrease of glycoprotein- and glycolipid-bound sialic acid. The activity of ecto-sialyltransferase with asialofetuin as exogeneous acceptor was significantly diminished (about 30%) in the ethanol-treated pups. Neuraminidase showed an unchanged activity after correction for the reduction of endogeneous sialic acid substrate concentration. The total protein and lipid concentrations of the synaptosomal preparations did not differ between the groups. These results suggest that ethanol treatment during on of the vulnerable periods of brain development causes an inhibition of the incorporation of sialic acid into synaptosomal membrane-bound sialoglycocompounds. Such an effect of ethanol exposure might disturb intercellular interactions and the functional performance of the membrane during development, and could be of importance in the pathogenesis of the central nervous system manifestations of the fetal alcohol syndrome.