Effects of ethanol and acetaldehyde on the maturation of hepatic secretory glycoproteins

Transferrin Isoforms, Old but New Biomarkers in Hereditary Fructose Intolerance

Hereditary Fructose Intolerance (HFI) is an autosomal recessive inborn error of metabolism characterised by the deficiency of the hepatic enzyme aldolase B. Its treatment consists in adopting a fructose-, sucrose-, and sorbitol (FSS)-restrictive diet for life. Untreated HFI patients present an abnormal transferrin (Tf) glycosylation pattern due to the inhibition of mannose-6-phosphate isomerase by fructose-1-phosphate. Hence, elevated serum carbohydrate-deficient Tf (CDT) may allow the prompt detection of HFI. The CDT values improve when an FSS-restrictive diet is followed; however, previous data on CDT and fructose intake correlation are inconsistent. Therefore, we examined the complete serum sialoTf profile and correlated it with FSS dietary intake and with hepatic parameters in a cohort of paediatric and adult fructosemic patients. To do so, the profiles of serum sialoTf from genetically diagnosed HFI patients on an FSS-restricted diet (n = 37) and their age-, sex- and body mass index-paired controls (n = 32) were analysed by capillary zone electrophoresis. We found that in HFI patients, asialoTf correlated with dietary intake of sucrose (R = 0.575, p < 0.001) and FSS (R = 0.475, p = 0.008), and that pentasialoTf+hexasialoTf negatively correlated with dietary intake of fructose (R = -0.386, p = 0.024) and FSS (R = -0.400, p = 0.019). In addition, the tetrasialoTf/disialoTf ratio truthfully differentiated treated HFI patients from healthy controls, with an area under the ROC curve (AUROC) of 0.97, 92% sensitivity, 94% specificity and 93% accuracy.

Relationship between serum sialic acid and sialylated glycoproteins in alcoholics

AIMS

Total sialic acid (TSA) has been suggested as a marker for chronic alcohol abuse. It seems that the elevation of TSA during excessive alcohol consumption reflects the changes in sialylated glycoproteins in the sera. On the other hand, chronic ethanol consumption increases the desialylation rate of many serum glycoproteins. The aim of this study was to evaluate the relationship between the total and free form of sialic acid levels (FSA), and the concentration of sialylated glycoproteins in alcoholics.

METHODS

We determined the serum concentration of many glycoproteins (alpha1-antitrypsin, alpha1-acid glycoprotein, haptoglobin, ceruloplasmin, transferrin, complement C3 protein, fibrinogen and immunoglobulin G) in a sample of 100 alcoholics and 30 healthy controls. Total sialic acid was determined by the enzymatic method and its free form by using a modification of the thiobarbituric acid method.

RESULTS

Among alcoholics, we found increased concentrations of alpha1-antitrypsin and alpha1-acid glycoprotein but decreased levels of transferrin. The concentrations of TSA and FSA were significantly higher in alcoholics than in healthy controls. The tested glycoproteins, except for transferrin and immunoglobulin G, positively correlated with TSA and FSA. The correlations with TSA were higher than that with FSA.

CONCLUSIONS

Chronic alcohol abuse alters the concentrations of some sialylated glycoproteins in the sera. The alpha1-antitrypsin, alpha1-acid glycoprotein, and transferrin are the only affected glycoproteins. The serum level of total and free form of sialic acid in the sera of alcoholics depends on the concentration of the most sialylated glycoproteins.

Use of serum carbohydrate-deficient transferrin values to exclude alcoholic hepatitis from non-alcoholic steatohepatitis: a pilot study

BACKGROUND

Since no clinical or biochemical parameters allow an accurate diagnosis of non-alcoholic steatohepatitis (NASH), the diagnosis by exclusion of alcoholic hepatitis is necessary. However, it is difficult to get the accurate amount of alcohol consumed from the patients, especially from females. To differentiate between NASH and alcoholic hepatitis, we investigated whether serum biochemical markers of chronic alcohol abuse are useful or not.

METHODS

Sera were obtained from 13 patients with NASH and 26 patients with alcoholic hepatitis. Diagnoses in these patients were confirmed histologically by needle biopsy of the liver. All patients with alcoholic hepatitis consumed more than 80 g of ethanol/day for more than 10 years. As markers of chronic alcohol abuse, serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), hyaluronate, mean corpuscular volume of red blood cells (MCV) and carbohydrate-deficient transferrin (CDT) were measured.

RESULTS

Among alcohol markers, serum values of AST, AST/ALT ratio, GGT, CDT and MCV in patients with alcoholic hepatitis were significantly higher than those in patients with NASH, respectively. However, serum values of these markers, except for CDT, were overlapped in many cases of NASH and alcoholic hepatitis. Serum CDT values of all patients with NASH were lower than the cutoff value, 2.66%, and those of all patients with alcoholic hepatitis were higher than the cutoff value.

CONCLUSION

The results of the present study suggest that serum CDT level could be used to differentiate between NASH and alcoholic hepatitis.

Monitoring glycosylation pattern changes of glycoproteins using multi-lectin affinity chromatography

Previously, we reported that the distribution of glycoproteins into the lectin displacement fractions of a multi-lectin affinity column was determined by the glycosylation patterns of the proteins. This distribution was observed by the sequential use of displacers specific to the lectins in the column. In this study we have evaluated the multi-lectin column (containing Concanavalin A, Wheat germ agglutinin and Jacalin lectin) to screen glycoproteins with known glycosylation pattern changes. The presence of a glycoprotein in a given displacer fraction was determined by LC-MS/MS analysis of a tryptic digest. We have used the enzyme neuraminidase to modify the oligosaccharide chains present in human transferrin, and used the enzymes, neuraminidase and fucosidase, to modify glycoproteins present in human serum. Then, by comparison with the untreated samples, we demonstrated a distribution shift of the enzyme-treated serum glycoproteins in the displacement fractions isolated from the multi-lectin column. The fractions were analyzed by a protein assay, Sequest rank comparison and peak area measurement from the extracted ion chromatogram. The results indicated that the multi-lectin affinity column (M-LAC) is sensitive to changes in the content of sialic acid and fucosyl residues present in serum glycoproteins, and has the potential to be used to screen serum proteins for glycosylation changes due to disease. In addition, the use of a glycosidase to induce specific structural changes in glycoproteins can support the development of multi-lectin column formats specific for detecting changes in the glycoproteome of certain diagnostic fluids and types of disease.

The Potential Beneficial Effect of Glycine on the Carbohydrate Moieties of Glycoproteins in an Experimental Model of Alcohol-Induced Hepatotoxicity

Glycine is known to have a protective role against alcohol-induced liver damage. The aim of our study was to evaluate the effect of glycine on liver and brain glycoproteins in alcohol-fed rats. Administering ethanol (7.9 g/kg of body of weight) every day to Wistar rats for 60 days resulted in significantly elevated levels of liver and brain hexosamine, fucose, and sialic acid and significantly reduced levels of total hexoses as compared with those of the control rats. Simultaneous glycine supplementation (0.6 g/kg of body weight) during the last 30 days of the experiment to rats given alcohol normalized the levels of hexosamine, fucose, and sialic acid and elevated the levels of total hexoses in the liver and brain significantly as compared with unsupplemented alcohol-treated rats. Microscopic examination of alcohol-fed rat liver showed inflammatory cell infiltrates and fatty changes, which were reversed on treatment with glycine. Similarly, alcohol-treated rat brain demonstrated edema, which was markedly reduced on treatment with glycine. Thus glycine administration plays a significant role in reducing the toxicity of ethanol.

Prenatal alcohol exposure affects galactosyltransferase activity and glycoconjugates in the Golgi apparatus of fetal rat hepatocytes

Prenatal exposure to alcohol affects the morphological, structural, and functional features of the Golgi apparatus (GA), thus altering the glycosylation process in fetal hepatocytes. To elucidate the cellular mechanisms underlying these alterations, we have studied the effect of alcohol exposure in utero on the activity of liver galactosyltransferase, an enzyme involved in the glycosylation process, and on the hepatic glycoprotein sugar composition. For this, livers from 21-day-old fetuses obtained from control and ethanol-fed rats were used. Galactosyltransferase (GT) activity was determined in isolated GA cis and trans fractions. Colloidal gold-labeled lectin cytochemistry was used to analyze sugar residues in hepatocytes at the subcellular level. Finally, the integrity of the GA after alcohol treatment was assessed by electron microscopy and by evaluating the distribution of the Golgi beta-COP, a protein involved in vesicular trafficking. Prenatal alcohol exposure induces a significant increase in both liver weight and total protein content in the trans Golgi. Moreover, this treatment decreases the activity of galactosyltransferase, increases alpha-L-Fuc residues, and reduces the number of alpha-Man, GlcNAc(beta1,4,GlcNAc)1,2, GalNAc alpha1,3GalNAc, alpha-GalNAc, and a-Gal residues. Alcohol exposure also causes the Golgi cisternae to disappear in about 30% of the hepatocytes, and reduces 75% the number of anti-Golgi beta-COP protein binding sites. Our results suggest that the decrease in galactosyltransferase activity, the alterations in the oligosaccharide chain composition, and the reduction in the amount of Golgi beta-COP protein could be involved in the alterations in the glycosylation process, as well as in the accumulation of hepatic proteins observed after prenatal alcohol exposure. These alterations could contribute, therefore, to the alcohol-induced injury in the developing liver.

Chronic ethanol feeding alters the structure and function of the epidermal growth factor receptor in rat stomach

We investigated the effect of chronic ethanol feeding on the EGF receptor in rat stomach. Adult male rats were fed either an isocaloric control or ethanol (EtOH)-containing liquid diet (36% total calories as EtOH) for 4 weeks EtOH significantly reduced the specific binding of 125I-EGF to the gastric mucosal membrane (control vs. EtOH, 2.07 +/- 0.2 vs. 0.94 +/- 0.16 fmol/mg protein; p < 0.01). Scatchard analysis suggested that the lower binding might be due to the reduction of EGF receptor number, and/or the affinity of the high-affinity binding site. Western blot analysis, using anti-EGF receptor antibody, revealed four immunoreactive protein bands (180, 150, 60, and 50 kDa) in the lectin-purified gastric membrane prepared from both groups. However, the intensities of these protein bands in the EtOH-fed animals were 90% lower compared to the controls. In the EGF-responsive protein kinase assay, 32P-ATP was incubated with lectin-purified samples in the absence or presence of 1 microM EGF. EGF stimulated autophosphorylation of the EGF receptor (180 kDa) in stomach from the control groups, but not the EtOH-fed animals. This EtOH-related alteration of the gastric EGF receptor may be one of the mechanisms underlying the gastric pathology associated with alcohol abuse.