Isoelectric focusing (IEF) and immunofixation for determination of disialotransferrin

Different patterns of human serum procollagen C-proteinase enhancer1 (PCPE1)

BACKGROUND

Procollagen C-proteinase (PCP) enhancer 1 (PCPE1) specifically stimulates the PCP activity of bone morphogenic protein 1 (BMP1), a multisubstrate enzyme essential to the formation of extracellular matrix, via direct interaction with its substrate procollagen. Thus, in this study we sought to determine if serum PCPE1 (sPCPE1), a regulator of collagen formation, can be used as a diagnostic marker of collagen metabolism/remodeling.

METHODS

We developed a method to track sPCPE1, and the findings were applied to evaluate the association of sPCPE1 glycopatterns with growth and presence of bone complication.

RESULTS

Isoelectric focusing revealed that sPCPE1 has a multi-band appearance and that sPCPE1 glycopatterns are due to an N-linked oligosaccharide decorated with sialic acid. Evaluation of PCPE1 glycopatterns in different groups of subjects revealed a significant difference among preterm babies, term babies, and adults. Furthermore, in adults with breast cancer, the glycopattern intensity correlated with the presence of bone metastasis.

CONCLUSIONS

The sPCPE1 glycopattern appears to be associated with the physiological and pathological states of bone. This study shows for the first time sPCPE1 glycopattern and suggest that changes in glycosylation of the protein may be in correlation with collagen metabolism. Studies are currently underway to determine its appearance in the serum of normal population on one hand and its appearance during growth and metabolic bone diseases on the other hand.

Screening and diagnosis of congenital disorders of glycosylation

The aim of this paper is to review the diagnostics of congenital disorders of glycosylation (CDG), an ever expanding group of diseases. Development delay, neurological, and other clinical abnormalities as well as various non-specific laboratory changes can lead to the first suspicion of the disease. Still common screening test for most CDG types, including CDG Ia, is isoelectric focusing/polyacrylamide gel electrophoresis (IEF). IEF demonstrates the hypoglycosylation of various glycoproteins, usually serum transferrin. Other methods, such as agarose electrophoresis, capillary electrophoresis, high-performance liquid chromatography, micro-column separation combined with turbidimetry, enzyme-(EIA) and radioimmunoassay (RIA) have also been used for screening. However, these methods do not recognize all CDG defects, so other approaches including analysis of membrane-linked markers and urine oligosaccharides should be taken. Confirmation of diagnosis and detailed CDG subtyping starts with thorough structure analysis of the affected lipid-linked oligosaccharide or protein-(peptide)-linked-glycan using metabolic labeling and various (possibly mass-spectrometry combined) techniques. Decreased enzyme activity in peripheral leukocytes/cultured fibroblasts or analysis of affected transporters and other functional proteins combined with identification of specific gene mutations confirm the diagnosis. Prenatal diagnosis, based on enzyme assay or mutation analysis, is also available. Peri-/post-mortem investigations of fatal cases are important for genetic counseling. Evaluation of various analytical approaches and proposed algorithms for investigation complete the review.

Pitfalls and drawbacks in screening of congenital disorders of glycosylation

Congenital disorders of glycosylation include a group of diseases, each of them caused by different protein (mostly enzyme) impairment due to a specific gene defect. The many subtypes are classified according to clinical features, enzymology and molecular genetic analyses. Problems in diagnostics arise from the great diversity in clinical presentation, usually age-related, and different severities of individual types of these, by far underdiagnosed, diseases. Also the biochemical findings tend to vary, even within a single type. No one screening test, common for all types, is available so far. Several methods of choice may be used in the first approach; other procedures must follow for detailed typing of the defect. Possible drawbacks and pitfalls in the diagnostics from the viewpoint of our 3-year studies and practical screening experience are presented.

Chromatographic methods for the determination of markers of chronic and acute alcohol consumption

The development in chromatographic methods for the determination of markers of alcohol consumption is summarized in this review. The markers included in this article are ethanol in body fluids, ethanol congeners, fatty acid ethyl esters (FAEEs), ethyl glucuronide (EtG), cocaethylene (CE), carbohydrate-deficient transferrin (CDT), phosphatidylethanol (PEth), 5-hydroxytryptophol (5-HTOL), dolichol, ketone bodies, acetaldehyde-protein adducts, and salsolinol (SAL). Some of these markers for alcohol consumption do not only indicate previous ethanol ingestion, but also approximate the amount of intake and the time when ethanol ingestion last occurred. Basic information about the procedures, work-up, and chromatographic conditions are summarized in tables. Also the main metabolic pathways and reaction schemes are demonstrated in figures. Some examples of typical applications are presented. The author points out that in many of the reviewed papers validation data of the procedures as well as specificities and sensitivities were not clearly presented and consequently were not comparable.

Determination of biological markers for alcohol abuse

Alcoholism is one of the most frequent addictions and an important subject in forensic medicine and clinical toxicology. Several laboratory abnormalities are associated with excessive alcohol consumption. They are useful in the diagnosis of alcoholism especially during the follow-up of various treatment programs. The biological markers mostly used for diagnosis of alcoholism are presented. Especially, methods for the determination of the following diagnostic tools are reviewed: congener alcohols, gamma-glutamyltransferase, aspartate and alanine aminotransferase, beta-hexosaminidase, erythrocyte aldehyde dehydrogenase, alpha-amino-n-butyric acid to leucine ratio, macrocytosis, carbohydrate-deficient transferrin, (apo)lipoproteins, fatty acid ethyl esters, blood acetate, acetaldehyde adducts, 5-hydroxytryptophol, dolichol and condensation products. No laboratory test exists that is reliable enough for the exact diagnosis of alcoholism. The combination of physician interview, questionnaire and laboratory markers is necessary for the diagnosis of alcoholism.

A simple method for carbohydrate-deficient transferrin measurements in patients with alcohol abuse and hepato-gastrointestinal diseases

Carbohydrate-deficient transferrin (CDT) is known to be increased in alcohol abuse. Several methods were developed for its measurement (e.g. isoelectric focusing with Western blotting or immunofixation, anion-exchange chromatography followed by immunoassays). We describe a greatly simplified isoelectric focusing technique which does not require immunofixation. CDT results obtained with this method were compared to other biological markers of alcohol abuse, i.e. mean corpuscular volume (MCV), aspartate aminotransferase (ASAT) and gamma-glutamyl-transferase (GGT), in 55 patients distributed in three groups (i.e. healthy control subjects, control patients suffering from various hepato-gastrointestinal diseases and alcohol abusing patients). Sensitivity and specificity were 33-89%, 61-57%, 89-49% and 83-100% for MCV, ASAT, GGT and CDT, respectively. We conclude that our method is highly suitable for routine clinical use.

Validation by isoelectric focusing of the anion-exchange isotransferrin fractionation step involved in determination of carbohydrate-deficient transferrin by the CDTect assay

Serum concentration of carbohydrate-deficient transferrin (CDT) is used for laboratory diagnosis of chronic alcohol abuse. Using isoelectric focusing for validation of the initial isotransferrin fractionation step involved in the determination of CDT by the CDTect assay, we found a complete in vitro iron saturation of transferrin and sufficient stability of the transferrin iron load during column passage; effective separation of non-CDT-isotransferrins and CDT-isotransferrins at the microcolumns; partial coelution of trisialo-Fe2-transferrin, which did not significantly affect CDT measurement; partial retention of CDT-isotransferrins, especially disialo-Fe2-transferrin, which may cause falsely negative results for CDT at the upper reference limits; good precision of the isotransferrin fractionation step; and no significant effects of low concentrations of serum protein and transferrin. We strongly urge standardization of CDT analysis and suggest isoelectric focusing for validation of CDT analysis methods and verification of odd results.