The simplified technique of high resolution two-dimensional polyacrylamide gel electrophoresis: biomedical applications in health and disease

Electron transfer studies of a conventional redox probe in human sweat and saliva bio-mimicking conditions

Modern day hospital treatments aim at developing electrochemical biosensors for early diagnosis of diseases using unconventional human bio-fluids like sweat and saliva by monitoring the electron transfer reactions of target analytes. Such kinds of health care diagnostics primarily avoid the usage of human blood and urine samples. In this context, here we have investigated the electron transfer reaction of a well-known and commonly used redox probe namely, potassium ferro/ferri cyanide by employing artificially simulated bio-mimics of human sweat and saliva as unconventional electrolytes. Typically, electron transfer characteristics of the redox couple, [Fe(CN)₆]^3−/4− are investigated using electrochemical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. Many different kinetic parameters are determined and compared with the conventional system. In addition, such electron transfer reactions have also been studied using a lyotropic liquid crystalline phase comprising of Triton X-100 and water in which the aqueous phase is replaced with either human sweat or saliva bio-mimics. From these studies, we find out the electron transfer reaction of [Fe(CN)₆]^3−/4− redox couple is completely diffusion controlled on both Au and Pt disc shaped electrodes in presence of sweat and saliva bio-mimic solutions. Moreover, the reaction is partially blocked by the presence of lyotropic liquid crystalline phase consisting of sweat and saliva bio-mimics indicating the predominant charge transfer controlled process for the redox probe. However, the rate constant values associated with the electron transfer reaction are drastically reduced in presence of liquid crystalline phase. These studies are essentially carried out to assess the effect of sweat and saliva on the electrochemistry of Fe^2+/3+ redox couple.

Proteomics of brain extracellular fluid (ECF) and cerebrospinal fluid (CSF)

Mass spectrometry has become the gold standard for the identification of proteins in proteomics. In this review, I will discuss the available literature on proteomic experiments that analyze human cerebrospinal fluid (CSF) and brain extracellular fluid (ECF), mostly obtained by cerebral microdialysis. Both materials are of high diagnostic value in clinical neurology, for example, in cerebrovascular disorders like stroke, neurodegenerative diseases like Alzheimer's Disease, Parkinson's Disease, amyotrophic lateral sclerosis (ALS), traumatic brain injury and cerebral infectious and inflammatory disease, such as multiple sclerosis. Moreover, there are standard procedures for sampling. In a number of studies in recent years, biomarkers have been proposed in CSF and ECF for improved diagnosis or to control therapy, based on proteomics and mass spectrometry. I will also discuss the needs for a transition of research-based experimental screening with mass spectrometry to fast and reliable diagnostic instrumentation for clinical use.

The proteome of human brain microdialysate

Background

Cerebral microdialysis has been established as a monitoring tool in neurocritically ill patients suffering from severe stroke. The technique allows to sample small molecules in the brain tissue for subsequent biochemical analysis. In this study, we investigated the proteomic profile of human cerebral microdialysate and if the identified proteins might be useful predictors for disease characteristics in stroke for tissue at risk in the contralateral hemisphere. We analysed cerebral protein expression in microdialysate from three stroke patients sampled from the hemisphere contralateral to the lesion. Using a proteomic approach based on two-dimensional gel electrophoresis and subsequent mass spectrometry, we created a protein map for the global protein expression pattern of human microdialyste.

Results

We found an average of 158 ± 24 (N = 18) protein spots in the human cerebral microdialysate and could identify 95 spots, representing 27 individual proteins. Most of these have been detected in human cerebrospinal fluid before, but 10 additional proteins mainly of cerebral intracellular origin were identified exclusively in the microdialysate.

Conclusions

The 10 proteins found exclusively in human cerebral microdialysate, but not in cerebrospinal fluid, indicate the possibility to monitor the progression of the disease towards deterioration. The correlation of protein composition in the human cerebral microdialysate with the patients' clinical condition and results of cerebral imaging may be a useful approach to future applications for neurological stroke diagnosis, prognosis, and treatment.

Identification of protein components in human acquired enamel pellicle and whole saliva using novel proteomics approaches

Precursor proteins of the acquired enamel pellicle derive from glandular and non-glandular secretions, which are components of whole saliva. The purpose of this investigation was to gain further insights into the characteristics of proteins in whole saliva and in vivo formed pellicle components. To maximize separation and resolution using only micro-amounts of protein, a two-dimensional gel electrophoresis system was employed. Protein samples from parotid secretion, submandibular/sublingual secretion, whole saliva, and pellicle were subjected to isoelectric focusing followed by SDS-PAGE. Selected protein spots were excised, subjected to "in-gel" trypsin digestion, and examined by mass spectrometry (MS). The data generated, including peptide maps and tandem MS spectra, were analyzed using protein data base searches. Components identified in whole saliva include cystatins (SA-III, SA, and SN), statherin, albumin, amylase, and calgranulin A. Components identified in pellicle included histatins, lysozyme, statherin, cytokeratins, and calgranulin B. The results showed that whole saliva and pellicle have more complex protein patterns than those of glandular secretions. There are some similarities and also distinct differences between the patterns of proteins present in whole saliva and pellicle. MS approaches allowed identification of not only well characterized salivary proteins but also novel proteins not previously identified in pellicle.

Peptide mapping of proteins in human body fluids using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Human body fluids have been rediscovered in the post-genomic era as great sources of biological markers and perhaps particularly as sources of potential protein biomarkers of disease. Analytical tools that allow rapid screening, low sample consumption, and accurate protein identification are of great importance in studies of complex biological samples and clinical diagnosis. Mass spectrometry is today one of the most important analytical tools with applications in a wide variety of fields. One of the fastest growing applications is in proteomics, or the study of protein expression in an organism. Mass spectrometry has been used to find post-translational modifications and to identify key functions of proteins in the human body. In this study, we review the use of human body fluids as sources for clinical markers and present new data that show the ability of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) to identify and characterize proteins in four human body fluids: plasma, cerebrospinal fluid (CSF), saliva, and urine. The body fluids were tryptically digested without any prior separation, purification, or selection, and the digest was introduced into a 9.4 T FTICR mass spectrometer by direct-infusion electrospray ionization (ESI). Even though these samples represent complex biological mixtures, the described method provides information that is comparable with traditional 2D-PAGE data. The sample consumption is extremely low, a few microliters, and the analysis time is only a few minutes. It is, however, evident that the separation of proteins and/or peptides must be included in the methodology, in order to detect low-abundance proteins and other proteins of biological relevance.

Proposal of sampling process for collecting human sweat and determination of caffeine concentration in it by using GC/MS

Caffeine concentration in human sweat was estimated by measuring separately the amounts of water and caffeine. After washing a finger with tap water for 15 s and waiting 2 min for drying, 70 microL aqueous ethanol solution in a small vial (0.6 mL) was used to sample for several minutes. Then 3 microL of the aliquot was used for GC/MS analysis of caffeine. As a first-order relationship between the sweat amount secreted on the left and right hands was obtained (correlation factor 0.848), the amount of sweat secretion during sampling on one hand was estimated by the value obtained on the other hand. This new indirect evaluation was used for the estimation of the amount of sweat secreted during sampling. Typical variations of caffeine concentration in sweat were demonstrated. Thirty minutes after the intake of caffeine, it was secreted in sweat, and the secretion had continued for more than 4 h.

The protein composition of ferret parotid saliva as revealed by high-resolution electrophoretic methods

Ferret parotid saliva has been analysed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE) to determine, for the first time, its protein composition. SDS-PAGE, in combination with Coomassie Brilliant Blue (CBB) staining, revealed up to 20 bands and the patterns were characterised by major protein constituents of Mr 105000, 51000, 47000, 33000, 22000 and 16 400 common to all samples from all animals. Sequential samples collected from the same animal during prolonged stimulation of the parasympathetic nerve (40 min at 40 Hz) showed subtle but reproducible protein changes. Saliva collected from different animals varied widely in the amount of a protein Mr 66000. 2-DE, in combination with silver staining, revealed up to 300 spots and the patterns were characterised by major protein constituents of Mr 105000 (pI 6.3-7.2), Mr 66000 (pI 4.7-5.3), Mr 51000 (pI 5.0-5.7), Mr 47000 (pI 6.0-7.5), and Mr 33000 (pI 4.7-6.0). Many of the polypeptide spot clusters consisted of one or more horizontal strings of spots suggesting extensive microheterogeneity. Both SDS-PAGE and 2-DE indicated that the protein patterns of ferret parotid saliva evoked by electrical stimulation of the parasympathetic nerve in the absence or presence of atropine are similar, i.e., the protein composition of the atropine-resistant nonadrenergic, noncholinergic (NANC) secretion is similar to that of saliva evoked in the absence of muscarinic receptor blockade.

High-resolution electrophoretic analysis of rat parotid salivary proteins

Silver staining and high-resolution electrophoretic methods have been used to compare the protein composition of rat parotid saliva evoked in response to (i) parasympathetic stimulation (including the nonadrenergic, noncholinergic, atropine-associated secretion), (ii) sympathetic stimulation, or (iii) the infusion of neuropeptides with secretagogue activity (substance P, calcitonin gene-related peptide, neuropeptide Y, or vasoactive intestinal peptide). The different stimuli influenced the protein concentration and flow rate of the evoked secretion but had little effect upon the protein composition of the saliva. In contrast to earlier studies using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie blue staining, the combination of silver staining and two-dimensional electrophoresis (2-DE) revealed many newly detected proteins. The results indicate that the protein composition of rat parotid saliva is more complex than previously reported but is unaffected by the mode of stimulation.

Using native gel in two-dimensional PAGE for the detection of protein interactions in protein extract

A two-dimensional (2-D) gel electrophoresis system in which native and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) are performed subsequently to analyze protein mixtures is described. Reasonably good resolution and excellent reproducibility was obtained when the proteins in the soluble protein extract from E. coli cells were separated using this procedure. Perhaps more importantly, the relevance of this native/SDS-2-D PAGE for the detection of protein interactions in a complicated protein mixture was examined using the interaction between interleukin-2 (IL-2) and its receptor alpha chain (IL-2Ralpha) in the E. coli protein extract as a model system. Native gel was used to preserve the interactions between the two molecules and SDS gel was used to maximize the separation of the denatured proteins. Mobility changes of these two proteins on 2-D maps resulted from the formation of IL-2/IL-2-2Ralpha complex were clearly observed despite of the presence of a large number of other protein spots. Thus, this approach is a useful complement to the standard 2-D gel electrophoresis system for analyzing complicated protein mixture, especially for the study of protein interactions.

Clinical analysis of human urinary proteins using high resolution electrophoretic methods

The application of isoelectric focusing (IEF), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) for high resolution electrophoretic analysis of human urinary proteins is reviewed. In each case, the information is tabulated chronologically with details of sample preparation, electrophoretic system, detection method and clinical application. The text includes an historical perspective of the use of each method for urinalysis and a detailed review of the application of the methods to the investigation of renal disease, renal transplantation, Bence Jones proteinuria (BJP), diabetes mellitus, cadmium toxicity, nephrolithiasis and cancers of the urogenital tract.

Analysis of Bence Jones proteinuria by high resolution two-dimensional electrophoresis

Analysis of Bence Jones proteinuria by high resolution two-dimensional electrophoresis (2-DE) and immunoblotting reveals a complex pattern of light chain (LC) isoforms corresponding to the free monoclonal Bence Jones protein and its fragments. Replica blotting gives duplicate blots for LC typing (lambda, chi) and, under the conditions employed, leaves sufficient protein for Coomassie Blue staining of the urinary protein profile and pIIMr determination of the LC isoforms. Carrier ampholytes (CAs, in our "simplified" 2-DE system) and immobilised pH gradients (IPGs, in the Multiphor 2-DE system) give similar LC isoform patterns. Artifacts, including cone-like distortions and trailing "piggyback" spots, are visualised with both 2-DE systems. IPGs are advantageous as they allow reproducible detection of strongly basic LC isoforms by isoelectric focusing (under equilibrium conditions) without recourse to CA nonequilibrium pH gradient electrophoresis.

Development of mini-gel technology in two-dimensional electrophoresis for mass-screening of samples: application to tears

Despite the extensive literature available on tear proteins and lipids, very little has been reported on the tear fluid as a whole and it's changes in contact lens wear or ocular diseased patients. Initially a human reflex tear two-dimensional map was created by Molloy et al. (Electrophoresis 1997, 18, 2811-2815), using this information a process for mass-screening was established. The large format two-dimensional technique was evaluated, using a basal tear reference map, and modified to describe a fast, efficient and cost effective method of protein separation. The use of one pH 3-10 18 cm nonlinear immobilised pH gradient (IPG) strip and two mini-gels for the second-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) results in an effective separation of tear proteins which will be applied in diagnostic studies of tear samples.

A two-dimensional protein map of human amniotic fluid at 17 weeks' gestation

Using updated technical procedures (immobilized pH gradients for isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis: IPG/SDS-PAGE) we provide a two-dimensional (2-D) map of amniotic fluid (AF) proteins. This map comprises over 800 silver-stained spots. Over 150 spots have been identified by matching on the net with human plasma and cerebrospinal fluid maps available from SWISS 2DPAGE database; several additional spots were assigned by immunoblotting and/or microanalytical techniques. This report details our investigation on AF proteins focusing on the 17th week of gestation, when AF is most commonly used for clinical evaluation of fetal disorders. As a whole, the map displays a number of potential markers for fetal development and for gestation abnormalities. The 2-D electrophoretic technique allows the monitoring of all these proteins at the same time along with additional spots that may prove of diagnostic significance.

Two-dimensional electrophoresis of human urinary proteins following concentration by dye precipitation

The use of dye precipitation for concentration of proteins prior to 2-DE has been demonstrated by application to human urine. The precipitation methods (T. Marshall and K. M. Williams, Clin. Chem. 1993, 39, 2314-2318; T. Marshall et al., Electrophoresis 1995, 16, 28-31) have been adapted for two-dimensional electrophoresis (2-DE) by modifying the reagent composition and adding sodium dodecyl sulphate (SDS) to the assay mixture. These modifications extend the precipitation range of the methods and overcome the problem of soluble glycoprotein-dye complexes. The protein-dye complex is recovered by centrifugation and dissolved in a small volume of sample denaturing buffer. The dye separates from the protein on 2-DE (forming a sharp band at the anodal end of the isoelectric focusing gel) so that the positional coordinates of the polypeptides are unaffected by the treatment. Dye precipitation provides a simple, rapid and highly economic method for concentrating urines of low to intermediate protein content (0.02-0.50 g/L) prior to 2-DE analysis.

Two-dimensional electrophoretic patterns of acute-phase human serum proteins in the course of bacterial and viral diseases

Acute-phase serum proteins were analyzed by two-dimensional electrophoresis with isoelectric focusing in 3-10 immobilized pH gradients. Most spots were identified by reference to the plasma map in the SWISS-2DPAGE database. Serum amyloid A protein spots were identified by immunoblotting with specific antiserum and by matching determined with predicted values of electrophoretic parameters. Changes in the concentrations of alpha 1-antitrypsin, leucine-rich glycoprotein, haptoglobin, serum retinol-binding protein and transthyretin were quantitated by densitometry of silver-stained gels. Electrophoretic patterns from 18 patients with bacterial diseases and 16 patients with viral diseases were compared. The incidence of serum amyloid A protein spots was 18/18 in bacterial diseases and 6/16 in viral diseases. As the the other reactants studied, variations were simultaneous in bacterial disease and tended to be staggered in viral diseases.

Two-dimensional protein electrophoresis and multiple hypothesis testing to detect potential serum protein biomarkers in children with fetal alcohol syndrome

Fetal alcohol syndrome (FAS) surveillance and intervention efforts are hampered by the lack of a specific biochemical test for diagnosis of the syndrome. Based on the hypothesis that abnormalities in growth and development (key features of FAS) involve altered protein metabolism, we analyzed serum proteins by two-dimensional gel electrophoresis and image analysis to search for potential protein biomarkers of FAS. Serum samples from 12 participants in whom FAS had been diagnosed and 8 sex- and age-matched participants whose mothers did not consume alcohol were analyzed in duplicate to determine whether the integrated intensities of matched proteins are significantly altered in children with FAS. Multiple hypothesis testing on 34 of the gels consisting of more than 1700 spots per gel revealed 21 proteins that we classified as potential protein biomarkers of FAS on the basis of significant t-test differences at p < 0.02. We classified 8 of the proteins as candidate biomarkers on the basis of significant concentration differences between case and control subjects at p < 0.01. One of the proteins is clearly an isoform of retinol binding protein; two appear in the area of the gel where alcohol dehydrogenase is expected to appear; one appears to be an isoform of alpha-1-antitrypsin; three appear to be isoforms of the beta-chain of haptoglobin; three may be forms of immunoglobulin light chains; and several others have not been associated with known proteins. No single protein differentiated all case subjects from control subjects, but stepwise canonical discriminant analyses revealed four groups of spots that distinguished between FAS case and control subjects with no misclassifications.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical applications of two-dimensional electrophoresis

Two-dimensional electrophoresis is increasingly being used as an important tool for biological research although it continues to have few direct clinical applications. In the absence of simple systems to identify and quantify individual proteins or groups of proteins it is unlikely that clinical applications will increase. Measurement of some individual proteins, for example a single acute phase reactant, often yields as much clinically useful information as could be currently expected from quantitation of several proteins with the same physiological role. Cost-containment pressures within the clinical laboratory will prevent the technique from becoming widely used in the clinical laboratory until it can clearly demonstrate that it can produce clinically important and necessary information that can not be obtained by other means. We continue to believe that the technique's greatest potential lies in identifying a protein or proteins whose concentration can be correlated with a disease and whose concentration varies with the progress of the disease. Antibodies to such proteins can then be produced and used to quantify the disease-associated proteins by a simple procedure, such as nephelometry. In spite of our belief of the likely clinical application of the technique there appears to be no systematic use of two-dimensional electrophoresis for this purpose. With clinical specimens a few investigators still run gels of serum or urine from patients with apparently unusual disorders and compare them visually with gels from healthy individuals. Nevertheless, the technique continues to have considerable unmet promise for clinical applications.

Protein study of T and B acute lymphoblastic leukemia cell lines

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was used to identify cellular proteins in T and B acute lymphoblastic leukemia (ALL) cell lines. Five lines, REH and BALL-1 of B-cell lineage, CCRF-CEM and HPB-ALL of T-cell lineage, and a normal Epstein-Barr virus (EBV)-transformed line of B-origin (SKLN1) were studied. The lines were immunophenotyped using flow cytometry and lineage associated monoclonal antibodies. Whole cell lysates of the cell lines were subjected to 2-D PAGE analyses. 2-D gels were analyzed with an image scanning computer and the qualitative as well as quantitative differences of the protein patterns were studied. Despite the great similarities in the patterns of the B- and T-gels, three proteins were unique to B-cell lines, while eight were unique to T-cell lines. Using cell lines is the first step toward identifying potential markers in ALL and can provide important information regarding the human ALL databases. Whether these proteins are definite markers for B- or T-ALL or are unique to the cell lines studied needs further exploration.

Electrophoretic analysis of stimulated cat parotid saliva

The proteins of parasympathetically stimulated cat parotid saliva were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and high resolution two-dimensional electrophoresis (2-DE). SDS-PAGE revealed up to 30 polypeptide bands in microliter volumes of unconcentrated saliva. The patterns were highly reproducible and characterized by prominent bands of M(r) 57,000, M(r) 30,000 and M(r) 15,000. The major protein (M(r) 30,000) appeared as a dimer (M(r) 60,000) when electrophoresed under non-reducing conditions but dissociated into its monomeric form when the SDS concentration of the denatured samples was increased from 1 to 5%. This indicates a noncovalent association. The protein patterns of saliva from different cats differed slightly but sequential samples from the same cat (collected during 90 min of stimulation) showed little change in protein pattern apart from a fall in total protein content. Following 2-DE, the major protein (M(r) 30,000) appeared as a complex array of at least eight spots in two tiers (pI 5.2-6.2; M(r) 28,000 and 32,000). The characteristics of this protein are discussed with reference to allergy to cats.

Two-dimensional electrophoresis analysis of human serum proteins during the acute-phase response

The serum of patients with meningitis, due to infection by Haemophilus influenzae type b, was analyzed. Several known acute-phase proteins were separated by two-dimensional electrophoresis and estimated quantitatively. In addition, hitherto undescribed reactants were recognized. Gels were calibrated and relevant spots related to master spot numbers in the human serum protein database.