Detection of Biomarkers for Alcoholism by Two-Dimensional Differential Gel Electrophoresis

Proteomic profiling of human sera for discovery of potential biomarkers to monitor abstinence from alcohol abuse

Although numerous biomarkers or biomarker candidates have been discovered to detect levels of drinking and intervals of time after last drinking episode, only a few biomarkers have been applied to monitor abstinence in a longer interval (≥6 wks) from alcohol abuse. Considering sample sources, sensitivity, and specificity, new biomarkers from blood with better accuracy are needed. To address this, serum proteomic profiles were compared between pre- and post- treatment samples from subjects seeking treatment for alcohol abuse and dependence in an intensive 6 wk daily outpatient program using high-abundance plasma protein immunodepletion and LC-MS/MS techniques. Protein identification, quantification, candidate biomarker selection, and prioritization analyses were carried out. Among the 246 quantified serum proteins, abundance of 13 and 45 proteins in female and male subjects were significantly changed (p ≤ 0.05), respectively. Of these biomarker candidate proteins, 2 (female) and 8 (male) proteins were listed in category 1, with high area under the receiver operating characteristic curve, sensitivity, specificity, and fold change. In summary, several new biomarker candidates have been identified to monitor abstinence from alcohol abuse.

Increased serum levels of pigment epithelium-derived factor by excessive alcohol consumption-detection and identification by a three-step serum proteome analysis

BACKGROUND

The search for biological markers of alcohol abuse is of continual interest in experimental and clinical alcohol research. We previously used gel-free proteome analysis methods such as the ProteinChip(®) system and the ClinProt™ system to search for new serum markers for alcoholism and found several novel marker candidates. As serum contains thousands of proteins and peptides that are present in a large dynamic concentration, depletion of the abundant proteins and further fractionation of the remainder is necessary to get into the deep proteome. We recently described a simple and highly reproducible three-step method for identifying potential disease-marker candidates among the low-abundance serum proteins.

METHODS

Two serum samples-one on admission and one after 8 weeks of abstinence-were obtained from 8 patients with alcohol dependency. The samples were subjected to a three-step serum proteome analysis. The steps were the following: first, immunodepletion of the 6 most abundant proteins; second, fractionation using reverse-phase high-performance liquid chromatography; and third, separation using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Differences revealed by protein staining were further confirmed by Western blotting and by enzyme-linked immunosorbent assays (ELISA).

RESULTS

Three-step serum proteome analysis revealed that the serum levels of 5 proteins, alpha2-HS glycoprotein, apolipoprotein A-I, glutathione peroxidase 3, heparin cofactor II, and pigment epithelial-derived factor (PEDF), were significantly greater on admission than after 8 weeks of abstinence. We focused on PEDF because alterations in its levels in alcoholic subjects are not well known. Western blotting and ELISA confirmed the upregulation of PEDF. Serum PEDF levels were significantly greater in moderate to heavy habitual drinkers (14.2 ± 7.7 μg/ml) than in healthy subjects without a drinking history (5.5 ± 3.0 μg/ml) (p < 0.001). The serum PEDF levels in subjects with nonalcoholic chronic liver diseases were comparable to the PEDF levels in healthy subjects.

CONCLUSION

  Three-step serum proteome analysis reveals that excessive alcohol drinking increases the PEDF level.

2-D DIGE to expedite downstream process development for human monoclonal antibody purification

Two-dimensional fluorescence difference gel electrophoresis (2-D DIGE) is an established method for assessing protein expression strategies, understanding pathogenesis mechanisms, characterizing biomarkers, and controlling therapeutic processes. We applied 2-D DIGE to facilitate the development of a purification process for a recombinant IgG1 antibody against Rhesus D antigen expressed by Chinese hamster ovary cells. The variability of two expression clones as well as the influence of cell viability on the host-cell protein pattern was assessed quantitatively. Up to 800 different spots were identified. 2-D DIGE showed that differences in cell viability had more influence on the protein expression pattern than did the expression clone itself. After purification of the IgG from different culture supernatants, the protein patterns on 2-D DIGE were identical, indicating the validity of purification scheme.

A proteomic workflow for discovery of serum carrier protein-bound biomarker candidates of alcohol abuse using LC-MS/MS

The diagnosis and care of patients with alcohol abuse and dependence is hampered by a lack of sensitive and specific screening and monitoring tests. Proteomics is a good approach to search for biomarkers of alcohol abuse. Serum carrier protein-bound proteins have attracted significant interest because they remain a relatively un-mined region of the proteome. In the present study, a proteomic workflow including LC-MS/MS with enrichment of serum carrier protein-bound biomarkers technique was applied to profile the changes in quality and quantity of serum carrier protein-bound proteins for the discovery of novel biomarker candidates of alcohol abuse. In total, 311 proteins identified with high confidence were discovered to be bound to serum carrier proteins. Complement isoforms, Ig fragments, and apolipoprotein family proteins are the main serum carrier-bound proteins. Protein quantification analysis with and without concern as to gender revealed that gender is a critical consideration for biomarker development in alcohol abuse. Identified proteins not previously associated with alcohol abuse include gelsolin, selenoprotein P, serotransferrin, tetranectin, hemopexin, histidine-rich glycoprotein, plasma kallikrein, and vitronectin. Altered abundance of these proteins suggests that they may be potential novel biomarkers for alcohol abuse.

Application of proteomic technologies to discover and identify biomarkers for excessive alcohol consumption: A review

Since currently available markers of alcohol abuse are not satisfactory, searches for novel markers are warranted. Proteomic analyses are promising tools to discover and identify novel biomarkers. Using two different proteomic technologies, surface enhanced laser desorption/ionization time-of-flight mass spectrometry and agarose fluorescent two-dimensional difference gel electrophoresis, we could detect and identify a total of 11 potential biomarkers of excessive alcohol consumption. It was noteworthy that the down regulation of the 5.9 kDa protein fragment was consistently seen in habitual drinkers and the diagnostic efficiency was greater than those of conventional markers such as gamma glutamyl transferase and carbohydrate deficient transferrin.