Effect of acute and chronic ethanol administration on rat liver alpha 2,6-sialyltransferase activity responsible for sialylation of serum transferrin

B cells suppress medullary granulopoiesis by an extracellular glycosylation-dependent mechanism

The immune response relies on the integration of cell-intrinsic processes with cell-extrinsic cues. During infection, B cells vacate the marrow during emergency granulopoiesis but return upon restoration of homeostasis. Here we report a novel glycosylation-mediated crosstalk between marrow B cells and hematopoietic progenitors. Human B cells secrete active ST6GAL1 sialyltransferase that remodels progenitor cell surface glycans to suppress granulopoiesis. In mouse models, ST6GAL1 from B cells alters the sialylation profile of bone marrow populations, and mature IgD+ B cells were enriched in sialylated bone marrow niches. In clinical multiple myeloma, ST6GAL1 abundance in the multiple myeloma cells negatively correlated with neutrophil abundance. These observations highlight not only the ability of medullary B cells to influence blood cell production, but also the disruption to normal granulopoiesis by excessive ST6GAL1 in malignancy.

Asialo-transferrin: Biochemical aspects and association with alcohol abuse investigation

Asialo-human transferrin (asialo-hTf) is a glycoform of the human serum protein transferrin characterized by the lack of the sialic acid (SA) terminal unit. It is known that glycosylation micro-heterogeneity and the presence of SA are strongly involved in protein functioning and pathophysiological activities. Some hTf glycoforms are valuable biomarkers for the detection of both genetic defects of glycosylation and/or sialoform distribution changes. The detection of the carbohydrate deficient transferrin (CDT) glycoforms is currently a widely employed method for the diagnosis of chronic alcohol abuse. The physiological significance of asialo-hTf is still unclear, despite its important biological implications. The current knowledge suggests that asialo-hTf may be involved in regulation of iron transport and release at the hepatic level, which, consequently, could strongly be affected by alcohol consumption. For these reasons, a deeper understanding of asialo-hTf structure and its physiological role is required, and an improved method of its analysis would favor the detection of both chronic abuse and other habits of alcohol intake and/or misuse. Thus, suitable analytical methods possessing higher sensitivity and specificity in comparison with the currently available techniques are certainly recommended. The present review summarizes the studies on asialo-hTf structure, roles, and detection techniques mainly in relation to its possible use as a potentially additional useful biomarker of alcohol abuse, and underlines its prospective value as a forensic and diagnostic tool.

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.

Chronic alcohol consumption augments loss of sialic acid residues and alters erythrocyte membrane charge in type II diabetic patients

In this study, the effects of alcohol consumption on erythrocyte membrane properties in type 2 diabetic patients were investigated. Therefore, we measured total and lipid-bound sialic acid (LSA) levels, sialidase activities, and erythrocyte membrane negative charge. Three groups, including control group (n = 20), alcohol-consuming diabetic patients group (n = 14), and diabetic patients without alcohol consumption group (n = 42), were created. Plasma total sialic acid (TSA) levels of the alcohol-consuming diabetic group were elevated as compared to the healthy control and diabetic group (p < 0.001 and p < 0.01, respectively). TSA levels of the diabetic group were significantly elevated as compared to the healthy control group (p > 0.001). Plasma LSA levels of the alcohol-consuming diabetic group were higher than that in the healthy control and diabetic group (p < 0.05 and p < 0.05, respectively). LSA levels of the diabetic group were found to be high as compared to the healthy control group (p < 0.05). Plasma sialidase activities of the alcohol-consuming diabetic group and diabetic group were significantly elevated as compared to the healthy control group (p < 0.05 and p < 0.05, respectively). Sialidase activities of the alcohol-consuming diabetic group were elevated as compared to the diabetic group, but this was not statistically significant (p > 0.05). Erythrocyte membrane negativity levels of the alcohol-consuming diabetic group and diabetic group were significantly decreased (p < 0.001 and p < 0.001, respectively) as compared to the healthy control group. Erythrocyte membrane negativity levels of the alcohol-consuming diabetic group were decreased as compared to the diabetic group, but this was not statistically significant (p > 0.05). In conclusion, our results indicate that chronic alcohol consumption may augment membrane alterations in type 2 diabetic patients.

Online single-step analysis of blood proteins: the transferrin story

The serum iron transport protein human transferrin (hTf) is a glycoprotein (MW approximately 79.6 kDa) containing two Asn-linked sites of glycosylation. The presence of specific glycoforms of hTf has been used as an indicator of carbohydrate-deficient glycoprotein syndrome (CDGS) or an indicator of alcohol abuse. The exact nature of the glycoforms described in the literature is controversial. In this work we demonstrate that the altered hTf glycoforms have lost one or both complete glycan side chains. Furthermore, we demonstrate using a combination of online immunoaffinity-postconcentration-mass spectrometry in conjunction with a blood spot cartridge that we can determine the relative quantities of the hTf glycoforms using <5 microL blood in under 30 min. This is in contrast to previous methods that used 1 mL and took 4 days. We show that this method can be useful to analyze hTf from CDGS and alcoholic patients.

The sialyl-alpha2,6-lactosaminyl-structure: biosynthesis and functional role

Sialylation represents one of the most frequently occurring terminations of the oligosaccharide chains of glycoproteins and glycolipids. Sialic acid is commonly found alpha2,3- or alpha2,6-linked to galactose (Gal), alpha2,6-linked to N-acetylgalactosamine (GalNAc) or alpha2,8-linked to another sialic acid. The biosynthesis of the various linkages is mediated by the different members of the sialyltransferase family. The addition of sialic acid in alpha2,6-linkage to the galactose residue of lactosamine (type 2 chains) is catalyzed by beta-galactoside alpha2,6-sialyltransferase (ST6Gal.I). Although expressed by a single gene, this enzyme shows a complex pattern of regulation which allows its tissue- and stage-specific modulation. The cognate oligosaccharide structure, NeuAcalpha2,6Galbeta1,4GlcNAc, is widely distributed among tissues and is involved in biological processes such as the regulation of the immune response and the progression of colon cancer. This review summarizes the current knowledge on the biochemistry of ST6Gal.I and on the functional role of the sialyl-alpha2,6-lactosaminyl structure.

Sialic acid: new potential marker of alcohol abuse

BACKGROUND

A number of laboratory markers are suggested for the detection and monitoring of alcohol abuse. However, there is still a need to find better indicators of alcohol abuse. Sialic acid (SA) is the name for a series of acyl-derivatives of neuraminic acids that occur as nonreducing terminal residues of glycoproteins or glycolipids in biological fluids and cell membranes. In this study, we investigated the diagnostic value of SA as a marker of alcohol abuse.

METHODS

Sera from social drinkers (n = 38) and alcoholics (n = 77) were analyzed for sialic acid by a colorimetric assay and for carbohydrate-deficient transferrin (CDT) by a radioimmunoassay method. Mean corpuscular volume (MCV), gamma-glutamyltransferase (GGT), aspartate aminotransferase (ASAT), and alanine aminotransferase (ALAT) were determined by using routine methods.

RESULTS

The sialic acid levels of both female and male subjects were significantly (p < 0.001) increased among alcoholic subjects when compared with social drinkers. SA levels were decreased after 3 weeks of treatment. The sensitivity and specificity for SA, respectively, were 57.7 and 95.5 for women and 47.8 and 81.3 for men. The respective values for CDT were 57.7 and 95.5 for women and 78.3 and 100.0 for men; for GGT, 60.0 and 95.5 for women and 60.9 and 87.5 for men; for MCV, 52.4 and 95.5 for women and 47.8 and 100.0 for men; for ASAT, 53.8 and 95.5 for women and 43.5 and 100.0 for men; and for ALAT, 38.5 and 90.9 for women and 39.1 and 87.5 for men. Among women, SA and GGT, and among men CDT, showed the largest area under receiver operation curve.

CONCLUSION

This study indicated that sialic acid levels were elevated by high alcohol consumption and reduced during abstinence, especially among women. Thus, sialic acid seems to be an interesting marker that needs further evaluation as a diagnostic tool for alcohol abuse.

Serum and saliva levels of sialic acid are elevated in alcoholics

BACKGROUND AND METHODS

Recently, sialic acid has been suggested as a potential marker for alcohol abuse. In this study, social drinkers and alcoholics were analyzed with a modified version of Warren's method for sialic acid and traditional markers of alcohol abuse in serum (n = 38; n = 87), saliva (n = 36; n = 29), and urine (n = 37; n = 83), respectively. The alcoholics were participating in an alcohol dependency treatment program and were followed in this study for 5 weeks.

RESULTS

The sialic acid concentrations in female and male alcoholics were significantly higher in serum (p < 0.001;p < 0.001 respectively) and saliva (p < 0.05; p < 0.05) but not in urine, compared with social drinkers. The diagnostic efficiency of serum sialic acid was higher than that for traditional markers: 77% for female subjects and 64% for male subjects. The corresponding results for saliva were 72% and 53%. The sialic acid concentrations were significantly decreased during the alcohol dependency treatment program (after 5 weeks of treatment) in both females and males.

CONCLUSIONS

This study confirms that serum sialic acid is a valuable marker for detecting and monitoring alcohol abuse. This work also indicates that sialic acid in saliva could be used possibly as a noninvasive marker for alcohol abuse.

Structural studies on sugar chains of carbohydrate-deficient transferrin from patients with alcoholic liver disease using lectin affinity electrophoresis

It is well-known that microheterogeneity of human serum transferrin observed in alcoholics manifests as sialic acid-deficient transferrin isoforms, otherwise known as carbohydrate-deficient transferrin (CDT). A recent study demonstrated that serum CDT lacked one or both of the entire carbohydrate chains but the investigation required several troublesome procedures. The aim of the present study was to confirm the sugar chain structures of serum transferrin, and of serum CDT in particular, from patients with alcoholic liver disease (ALD) using conventional lectin affinity electrophoresis which might be useful in the clinical setting. The serum CDT obtained from ALD-patients was partially purified using an anion exchanger. Serum transferrin and the partially purified serum CDT were investigated by concanavalin A (Con A)- and Datura stramonium agglutinin (DSA)-affinity electrophoresis followed by antibody-affinity blotting and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with Western blotting. By Con A-affinity electrophoresis, serum CDT was separated into weakly reactive and nonreactive transferrins which showed slower electrophoretic mobilities than those from the healthy controls. Moreover, nearly all of the serum CDT was nonreactive with DSA. On SDS-PAGE, the molecular masses of serum CDT were estimated to be approximately 75 and 72 kDa, which corresponded to those of partially and completely deglycosylated transferrin obtained from the healthy controls (78 kDa), respectively. In conclusion, these results indicated that the sugar chain structures of serum CDT from patients with ALD show not merely a loss of terminal sialic acids, but also the absence of asparagine-N-linked oligosaccharides.

Serum carbohydrate-deficient transferrin: mechanism of increase after chronic alcohol intake

Carbohydrate-deficient transferrin (CDT) is now considered to be the most sensitive and specific biological marker of alcohol abuse. However, the mechanism by which chronic alcohol consumption causes an elevation of CDT levels in serum is still not understood. Therefore, we fed eight pairs of male rats a nutritionally adequate liquid diet containing either alcohol (36% of energy) or isocaloric dextrose (control) for 4 weeks, after which blood and liver samples were obtained. Serum CDT content in alcohol-treated rats increased by 45% (P < .05) in ethanol-fed animals compared with their corresponding controls. In contrast, in rats fed ethanol, the activities of sialyltransferase (ST), galactosyltransferase (GT), and N-acetylglucosamine transferase (N-AGT), which are glycosyltransferases involved in transferrin carbohydrate side chain synthesis, were diminished by 24% and 40% (P < .05), 23% and 51% (P < .05, .001), and 20% and 26% (P < .05) in total liver homogenates and Golgi fraction (GF) 1, respectively, when expressed as units/100 g body weight. These enzymes were also significantly less active in hepatic GFs 2 and 3. The depression of the transferase activities in ethanol-fed rats appeared to be due, at least in part, to enzyme inactivation by acetaldehyde, whereas ethanol itself was without effect. Similar results were obtained in humans: five alcohol abusers were found to exhibit a 23% decrease in hepatic sialyltransferase and a 41% increase in sialidase activities, respectively, when compared with three nondrinking subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ethanol on human colon carcinoma CaCo-2 and HT-29 cell lines during the maturation process

The aim of the study was to ascertain whether the exposure to ethanol of human colon carcinoma CaCo-2 and HT-29 cell lines affects the differentiation process. As an index of enterocytic differentiation, the expression of sucrase, alkaline phosphatase, alpha 2,6-sialyltransferase toward the N-acetyllactosaminic sequence, and beta 1,4-N-acetylgalactosaminyltransferase (beta 1,4GalNAc-transferase) was examined. The latter enzyme is responsible for the biosynthesis of Sda carbohydrate histo-blood antigen, which mainly occurs in human colonic cells; its expression in CaCo-2 cells depends strictly on the enterocytic differentiation. The addition of ethanol in the culture medium resulted in a significant increment of sucrase and alpha 2,6-sialyltransferase activities in both cell lines, as well as the beta 1,4GalNAc-transferase activity in CaCo-2 cells and alkaline phosphatase activity in HT-29 cells. The increment was dose-dependent in the range between 50 and 200 mM ethanol and evident after 2 days of exposure in both cell systems. These results support the notion that, as occurs for cell lines of different origin, the ethanol in vitro positively affects the differentiation of intestinal cells, namely along the enterocytic lineage. The putative mechanism by which ethanol interferes with the maturation process of colonic cells is discussed.

Laboratory markers of ethanol intake and abuse: a critical appraisal

Laboratory markers for ethanol intake and abuse and chronic alcoholism currently in use have been critically reviewed. The merits and pitfalls of each test have been evaluated. The clinical use of the new test of carbohydrate-deficient transferrin has been particularly emphasized. Carbohydrate-deficient transferrin currently provides the highest specificity and sensitivity of all commonly used markers of alcoholism.

Carbohydrate-deficient transferrin in the ethanol-consuming rat model

Regular ethanol consumption leads to the appearance of carbohydrate-deficient transferrin in the plasma of human subjects. The mechanism for this finding remains uncertain. We have exposed female Wistar rats to ethanol from 3 weeks of age to 22 weeks and have studied transferrin in these animals. Isoelectric focusing (IEF) of serum identified two additional transferrin forms in the ethanol-exposed rats. Routine staining and immunofixation demonstrated transferrin focused at pH 5.45 and 5.65. Neuraminidase-treated normal rat serum focused in 2 bands at pH 5.85 and 6.15 corresponding to the additional bands in ethanol-treated rats. Human transferrin exposed to neuraminidase focused at pH 5.7 as described by others. The results suggest that the rat may be used as an animal model to study the complex effects of ethanol on transferrin and iron metabolism.

Ethanol effects on total sialic acid of various brain regions and visceral organs

These experiments were designed to extend our earlier observations on acute ethanol effects on brain sialic acid (SA), an acidic sugar component of membrane gangliosides and many glycoproteins. Here, we tested for differential effects of ethanol on total sialic acid in various brain regions and for effects on other organs, such as liver, kidney, heart, and skeletal muscle. Subjects were young adult, male rats. The first experiment compared two commonly accepted analytical methods for brain SA on peripheral tissues. Consistently higher levels were evident with the resorcinol method in all tissues, especially in liver, compared with the thiobarbiturate method. Resorcinol-measured levels in the liver and kidney were on the order of 350 micrograms/g, wet weight. In the brain of controls, the resorcinol method revealed total SA levels to be on the order of 550-650 micrograms/g in the basal ganglia, cerebral cortex, cerebellum, and hippocampus. Brainstem levels were significantly lower. Ethanol, given IP at 2 g/kg, seemed to decrease total SA in all brain regions at four hours after injection, with statistically significant decreases in the hippocampus and brainstem. With 3 g/kg, only the cerebellum showed a significant decrease at four hours, compared to saline-injected controls, but the decrease was large (25%). Analysis of the other organs showed that, compared to saline-injected controls, ethanol decreased SA in the liver. There was a small, but significant, decrease in heart SA at four hours after 3 g/kg. In skeletal muscle, ethanol significantly increased total SA at 2 g/kg, but not at 3 g/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

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.