Separation of different forms of transferrin by isoelectric focusing to detect effects on the liver caused by xenobiotics

Transferrin D protein variants in the diagnosis of congenital disorders of glycosylation (CDG)

Congenital disorders of glycosylation are a rapidly growing group of inherited (neuro)metabolic disorders characterized by defects in glycosylation of proteins and lipids. This study discusses an analytical problem in the differentiation between hypoglycosylation and transferrin (Tf) protein variants. Analysis of serum Tf by isoelectric focusing is used as a common method suitable for screening 19 out of a total of 22 types of glycosylation defects identified so far. In three members of a family, several indicators showed evidence of a Tf protein variant, however, routine neuraminidase-based demonstration failed to confirm this result. On the assumption that we should be able to exclude Tf protein variants at the screening-level of the diagnostic algorithm, our concern is a possible cause of our failure to confirm some of the Tf D variants (in contrast to the other C, B and D allelic combinations that are commonly well identified). Several explanations are discussed.

Genetic variants of transferrin in the diagnosis of protein hypoglycosylation

Human transferrin (Tf) shows genetic polymorphisms, which may interfere in the screening of congenital disorders of glycosylation (CDG). Isoelectric focusing followed by direct immunofixation was used for Tf analysis in controls and several groups of patients. Equivocal results in one case have been recognized as a rare Tf CD variant. A higher incidence of some genetic variants has been reported in connection with certain diseases; of the seven Tf phenotypes detected in our set of samples, an apparently higher frequency of Tf C1C2 variant found in some groups of patients was not significant.

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.

Glycosylation of transferrin in Alzheimer's disease and alcohol-induced dementia

Transferrin is a glycosylated metal-binding serum protein. Carbohydrate-deficient transferrin (CDT) is a marker of recent and heavy alcohol intake. A genetic variant of transferrin, TfC2, occurs with increased frequency in patients with Alzheimer's disease (AD). Hence the question arose whether, in addition to an altered amino acid sequence, there could also be a difference in the glycosylation state of transferrin in patients with dementia. Serum samples of 37 AD and 13 Alcohol-induced dementia patients as well as 10 healthy controls were analyzed for abnormal Tf variants, using isoelectric focusing followed by blotting with anti-Tf antibodies. This allowed the direct visualization of glycosylation variants of transferrin, and assessment of any increase in underglycosylated forms (di-, mono- and asialo transferrin).

Carbohydrate deficient transferrin in alcoholic liver disease: mechanisms and clinical implications

Carbohydrate-deficient transferrin (CDT) is now considered to be the most sensitive and specific biological marker of alcohol abuse. The mechanism by which chronic alcohol consumption causes an elevation of CDT levels in serum is discussed. The sensitivity and specificity of various test procedures are compared, with special emphasis on the impact of liver disease. Clinical applications are reviewed, including the utility of CDT as a marker of relapse in alcoholic patients, and the use of CDT for the systematic screening of drinking in vulnerable populations as part of a public health approach to alcoholism.

Specific, sensitive and accurate quantification of albumin, retinol binding protein and transferrin in human urine and serum by zone immunoelectrophoresis assay (ZIA)

For zone immunoelectrophoresis assay (ZIA) glass tubes, ID 2 mm and 90 mm high, are filled to 2/3 with buffer containing agarose and antibodies against the protein to be quantified, each sample being pipetted on top of separate agarose gel rods. On electrophoresis at 35-150 V for several hours, the sample proteins enter the gel with resultant immunoprecipitates, visualized by staining. The extension of each immunoprecipitation zone from the upper gel surface (measured with a ruler) is directly proportional to the amount of protein in each sample and can easily be quantitated by comparison with a linear calibration curve. ZIA can be used for quantification of several proteins in blood serum and plasma as well as in urine, as is illustrated for albumin, retinol-binding protein (RBP) and transferrin. The recovery of the pure proteins added to urine is often close to 100%. ZIA has many advantages: (i) simple apparatus and procedure (no gel punching nor cooling), (ii) minimal antiserum consumption (1 mL may allow > 1000 assays), (iii) electrophoresis can be performed within a few hours or overnight, (iv) low coefficient of variation (often < 4%), (v) linear calibration curves, (vi) low detection limit (< 20 ng/mL), (vii) wide concentration ranges, (viii) no kits nor unique antisera preparation are required, and (ix) good agreement with the results from other methods.

The analysis of human serum transferrins with the PhastSystem: quantitation of microheterogeneity

The PhastSystem was used for three different analyses of human serum transferrins (Tf) by isoelectric focusing: (i) The distribution of iron over the two iron binding sites by separation of the four forms: apoTf, TfFeC, FeNTf and Fe2Tf by using less than 1 microL serum or plasma. The focused bands were visualized by immunoprecipitation and quantified by densitometry. (ii) The relative proportions of the diferic sialo-transferrin fractions in human sera or plasma were determined in a similar way. (iii) The presumed genetic variants can be determined. The methods are easy and reproducible and require much less sample (0.3 microL), time (1 h per run) and antibody (10 microL/sample) than crossed immunoelectrofocusing.

Isoelectric focusing/western blotting: a novel and practical method for quantitation of carbohydrate-deficient transferrin in alcoholics

Carbohydrate-deficient transferrin (CDT) has been described as the single, most accurate marker of chronic alcohol consumption. Rapid, sensitive, and specific measurement of serum CDT levels can thus provide important clinical information concerning patient diagnosis and treatment. To date, however, methods used for assessing CDT concentrations [e.g., analytical isoelectric focusing combined with immunofixation and micro anion-exchange chromatography followed by radioimmunoassay (RIA)] have not been practical enough for widespread laboratory application. In the present study, we examined the use of a different technique, namely isoelectric focusing (IEF) combined with Western blotting (IEF/WB). Serum proteins (20-40 micrograms) were first focused according to isoelectric points (pI) on high-resolution agarose IEF gels (ampholyte pH range of 5-8) containing nonionic detergent. The focused proteins were transferred electrophoretically to nitrocellulose filters, and then stained immunochemically with antihuman transferrin IgG. IEF/WB completely resolved CDT (focusing at pI 5.7 and 5.9) from other serum transferring isoforms, as assessed with neuraminidase-generated CDT standards. Computerized densitometric scanning of the immunoblots allowed CDT levels to be quantitated directly rather than as a quotient. Serum CDT content determined by IEF/WB was highly correlated (r2 = 0.962; n = 17) with values determined previously by RIA. In a larger subject group, CDT levels (mg/liter) measured by IEF/WB were 139 +/- 54 in recently-drinking alcoholics (n = 58), 81 +/- 8 in abstaining alcoholics (n = 7), and 68 +/- 16 in healthy control subjects (n = 16).(ABSTRACT TRUNCATED AT 250 WORDS)