Improvements in a competition assay to detect scrapie prion protein by capillary electrophoresis

Direct SARS-CoV-2 Detection System Utilizing Simple-to-Use Capillary Gel Electrophoresis Sample-to-Result

AIM

We present a Direct SARS-CoV-2 Detection System that achieves sample-to-results in less than two hours in three simple steps.

METHODS

The Detection System includes Direct one-step Reverse Transcription PCR (RT-PCR) reagents (Qexp-MDx kit), a portable thermal cycler (Qampmini) with a preprogrammed chip and a simple-to-use Capillary Gel Electrophoresis system (Qsep Series Bio-Fragment Analyzer) with high fluorescence detection sensitivity to solve the problems associated with traditional real-time PCR (qPCR) systems which produces high false positive results.

RESULTS

The proposed simple-to-use detection platform can provide high detection sensitivity (identify less than 20 copies) and fast results (less than 120 minutes), which would be suitable for field testing applications.

CONCLUSION

Our high detection sensitivity platform provides fast and accurate results in 120 minutes without doing DNA/RNA extraction.

Detection and control of prion diseases in food animals

Transmissible spongiform encephalopathies (TSEs), or prion diseases, represent a unique form of infectious disease based on misfolding of a self-protein (PrP^C) into a pathological, infectious conformation (PrP^Sc). Prion diseases of food animals gained notoriety during the bovine spongiform encephalopathy (BSE) outbreak of the 1980s. In particular, disease transmission to humans, to the generation of a fatal, untreatable disease, elevated the perspective on livestock prion diseases from food production to food safety. While the immediate threat posed by BSE has been successfully addressed through surveillance and improved management practices, another prion disease is rapidly spreading. Chronic wasting disease (CWD), a prion disease of cervids, has been confirmed in wild and captive populations with devastating impact on the farmed cervid industries. Furthermore, the unabated spread of this disease through wild populations threatens a natural resource that is a source of considerable economic benefit and national pride. In a worst-case scenario, CWD may represent a zoonotic threat either through direct transmission via consumption of infected cervids or through a secondary food animal, such as cattle. This has energized efforts to understand prion diseases as well as to develop tools for disease detection, prevention, and management. Progress in each of these areas is discussed.

Capillary electrophoresis for the analysis of contaminants in emerging food safety issues and food traceability

This review presents an overview of the applicability of CE in the analysis of chemical and biological contaminants involved in emerging food safety issues. Additionally, CE-based genetic analyzers' usefulness as a unique tool in food traceability verification systems was presented. First, analytical approaches for the determination of melamine and specific food allergens in different foods were discussed. Second, natural toxin analysis by CE was updated from the last review reported in 2008. Finally, the analysis of prion proteins associated with the "mad cow" crises and the application of CE-based genetic analyzers for meat traceability were summarized.

Capillary electrophoresis for the characterization of quantum dots after non-selective or selective bioconjugation with antibodies for immunoassay

Capillary electrophoresis coupled with laser-induced fluorescence was used for the characterization of quantum dots and their conjugates to biological molecules. The CE-LIF was laboratory-built and capable of injection (hydrodynamic and electrokinetic) from sample volumes as low as 4 μL via the use of a modified micro-fluidic chip platform. Commercially available quantum dots were bioconjugated to proteins and immunoglobulins through the use of established techniques (non-selective and selective). Non-selective techniques involved the use of EDCHCl/sulfo-NHS for the conjugation of BSA and myoglobin to carboxylic acid-functionalized quantum dots. Selective techniques involved 1) the use of heterobifunctional crosslinker, sulfo-SMCC, for the conjugation of partially reduced IgG to amine-functionalized quantum dots, and 2) the conjugation of periodate-oxidized IgGs to hydrazide-functionalized quantum dots. The migration times of these conjugates were determined in comparison to their non-conjugated QD relatives based upon their charge-to-size ratio values. The performance of capillary electrophoresis in characterizing immunoconjugates of quantum dot-labeled IgGs was also evaluated. Together, both QDs and CE-LIF can be applied as a sensitive technique for the detection of biological molecules. This work will contribute to the advancements in applying nanotechnology for molecular diagnosis in medical field.

Progress and limits of TSE diagnostic tools

Following the two "mad cow" crises of 1996 and 2000, there was an urgent need for rapid and sensitive diagnostic methods to identify animals infected with the bovine spongiform encephalopathy (BSE) agent. This stimulated research in the field of prion diagnosis and led to the establishment of numerous so-called "rapid tests" which have been in use in Europe since 2001 for monitoring at-risk populations (rendering plants) and animals slaughtered for human consumption (slaughterhouse). These rapid tests have played a critical role in the management of the mad cow crisis by allowing the removal of prion infected carcasses from the human food chain, and by allowing a precise epidemiological monitoring of the BSE epizootic. They are all based on the detection of the abnormal form of the prion protein (PrP(Sc) or PrP(res)) in brain tissues and consequently are only suitable for post-mortem diagnosis. Since it is now very clear that variant Creutzfeldt-Jakob disease (vCJD) can be transmitted by blood transfusion, the development of a blood test for the diagnosis of vCJD is a top priority. Although significant progress has been made in this direction, including the development of the protein misfolding cyclic amplification (PMCA) technology, at the time this paper was written, this objective had not yet been achieved. This is the most important challenge for the years to come in this field of prion research.

Characterization of quantum dots using capillary zone electrophoresis

Commercially available quantum dots (QDs) were characterized using CE. The CE instruments were laboratory-built, each being capable of both electrokinetic and hydrodynamic injection. Modes of detection include UV absorption and LIF. The CE-LIF system was further modified to handle microliter sample volumes during injection. Sodium phosphate (5-25 mM, pH 7.5-11) was found to be a good buffer electrolyte. Sodium mercaptoproprionate CdTe/CdS (ADS620) QDs and carboxylic acid CdSe/ZnS (T2-Evitag) QDs yielded high separation efficiencies of N = 1.5x10(6) plates at t(M) = 10 min and N = 1.0x10(5) plates at t(M) = 3.8 min, respectively. Apparently the EDC/sulfo-NHS bioconjugation chemistry worked well with the neutral T2-Evitag QDs, but not so well with the negatively charged ADS620 QDs. This preliminary knowledge will serve as a basis for new CE immunoassay studies of QD-biomolecule conjugates and their immunocomplexes with target analytes.

Capillary Electrophoresis-Based Noncompetitive Immunoassay for the Prion Protein Using Fluorescein-Labeled Protein A as a Fluorescent Probe

A novel CE-based noncompetitive immunoassay for prion protein (PrP) was established. Fluorescein isothiocyanate (FITC)-labeled protein A (FITC-PrA) was used as a fluorescent probe to tag monoclonal antibody through noncovalent binding of FITC-PrA to the Fc region of the antibody. The FITC-PrA-Ab was incubated with the analyte, prion protein, under optimized condition, forming the immunocomplex FITC-PrA-Ab-PrP. The complex was separated and analyzed by capillary zone electrophoresis. The addition of carboxymethyl-beta-cyclodextrin in the running buffer as dynamical coating reagent improved the reproducibility and the resolution. The complex was isolated in less than 1 min with theoretical plates of 3.8 x 10(4). Relative standard deviations of peak height and migration time for the complex were 3.46 and 1.48%, respectively. A linear relationship was established for the bovine recombinant prion protein (rPrP) concentration in the range from 0.2 to 2.0 mug/mL and the peak height. The correlation factor was r2 = 0.9969. The estimated detection limit for rPrP was approximately 6 ng/mL, which is 3 times the signal-to-noise ratio. The method was successfully applied for testing blood samples from scrapie-infected sheep.

Detection of prion protein using a capillary electrophoresis-based competitive immunoassay with laser-induced fluorescence detection and cyclodextrin-aided separation

The development of capillary electrophoresis (CE)-based competitive immunoassay for prion protein (PrP) using carboxymethyl beta-cyclodextrin (CM-beta-CD) as a buffer additive is described here. The assay was based on the competitive binding of PrP and a fluorescein-labeled peptide from the prion protein with a limiting amount of specific antibody. The amount of both free and fluorescein-labeled peptide bound to antibody (immunocomplex) were determined by CE with laser-induced fluorescence detection. In the presence of PrP, the peak height ratio of the immunocomplex and the free peptide was altered compared to the control. These changes were directly proportional to the amount of PrP present. The fluorescently labeled peptide spanning amino acid positions 140-158 of the PrP and its corresponding monoclonal antibody is reported here. The reaction times of the antibody with either the peptide or the recombinant PrP was less than 1 min and is a large improvement over the 16-18 h required to achieve equilibrium for polyclonal antibodies. CM-beta-CD was explored as a buffer additive to suppress analyte adsorption and enhance separation selectivity in the CE analysis. A fast (1.1 min), selective (resolution 4.7), and reproducible (relative standard deviations of migration time for free and bound fluorescein isothiocyanate (FITC)-peptide 0.56% and 0.64%, respectively) separation was obtained with 0.6% CM-beta-CD in 25 mM N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS) at pH 8.8. The concentration detection limit of the assay for recombinant PrP was determined to be 80 ng/mL (or mass detection limit 1 pg). When blood samples from scrapie-infected sheep and from normal sheep were tested, the results of the blood assay were consistent with scrapie status of the sheep as determined post mortem by Western blot analysis. Development of this assay will lead to a potentially robust, rapid, and specific preclinical diagnosis for transmissible spongiform encephalopathies (TSEs) in animals and humans.

Capillary isoelectric focusing of the scrapie prion protein

Prion diseases or transmissible spongiform encephalopathies belong to a group of neurodegenerative diseases that infect both animals and humans. These diseases are associated with an accumulation of fibrils in the brains of infected individuals. These fibrils are composed of an abnormal isoform of a host-encoded glycoprotein that is characterized by its insolubility and partial resistance to proteases. Another characteristic of the scrapie prion protein (PrPsc) is the wide range of isoelectric points (pI values) that have been observed on conventional isoelectrofocusing gels. In this study, we explored the use of capillary isoelectric focusing (cIEF) to characterize the pI values for PrPsc isolated from sheep and hamster brain. We used a Beckman 5500 P/ACE using UV detection at 280 nm. A cIEF 3-10 Kit from Beckman Instruments was used to perform the analysis. The PrPsc was solubilized in 0.01 M Tris-HCl, pH 8.00 containing 2 mM EDTA. 5% SDS and 10% hexafluoroisopropanol at 100 degrees C for 10 min. The solubilized PrPsc was placed over a high-performance hydrophilic interaction column. After elution, the peaks were concentrated and assayed for immunoreactivity with specific antisera. The peaks that contained immunoreactivity were then placed on the cIEF capillary. The samples containing PrPsc were solubilized in 1% n-octylglucoside before isoelectric focusing. The scrapie infected sheep sample had peaks with pI values ranging from 5.2 to 3.00 with a major peak at 3.09. The normal sheep brain had pI values that were higher. The hamster adapted scrapie strain had peaks with pI values ranging from 6.47 to 3.8. These pI values were slightly higher than those obtained for the sheep samples. The use of cIEF to determine the pI values of PrPsc led to the identification of a major species of PrPsc from sheep with a very acidic pI.

A diagnostic test for scrapie-infected sheep using a capillary electrophoresis immunoassay with fluorescent-labeled peptides

Scrapie in sheep and goats is the prototype of transmissible spongiform encephalopathies found in humans and animals. A feature of these diseases is the accumulation of rod-shaped fibrils in the brain that form from an aggregated protein. This protein (PrPSC) is a protease-resistant form of a normal host cell protein. When the aggregated protein is denatured in sodium dodecyl sulfate (SDS) and beta-mercaptoethanol, a monomer form of approximately 27 kDa molecular mass is observed. A competition immunoassay to detect PrPSC from scrapie-infected sheep was developed using free zone capillary electrophoresis with laser-induced fluorescence (LIF) for detection and flourescein-labeled synthetic peptides from PrPSC. Antibodies were made to each respective peptide and used in the competition assay. The fluorescent-labeled peptides bound to the antibody were separated from the unbound peptides using 200 mM Tricine, pH 8.0, containing 0.1% n-octylglucoside and 0.1% bovine serum albumin (BSA). The amount of antibody that would bind approximately 50% of the fluorescent-labeled peptide was determined for each peptide. When unlabeled peptide was added to the assay, approximately 2 fmoles of the peptide could be measured. When PrPSC extracted from infected sheep brain was added to the assay, approximately 135 pg of PrPSC could be detected. When preparations from normal sheep were assayed, there was little or no competition for the bound peptides. Assays using two of the peptides, peptides spanning amino acid positions 142-154 and 155-178, clearly differentiated scrapie-positive sheep from normal animals. This assay is a new method that can be used to diagnose scrapie and, possibly, other transmissible spongiform encephalopathies in animals and in humans.

Affinity capillary electrophoresis

The application of affinity capillary electrophoresis (ACE) to the study of molecular interactions is reviewed. ACE appears to be a sensitive, versatile and convenient tool to obtain reliable data on binding constants and stoichiometries of interacting systems using the Hummel-Dreyer method and variants thereof. A powerful feature is the possibility to analyze simultaneously the affinity of a large number of compounds for the same ligand, making it a promising tool for the screening of large combinatorial libraries.

Capillary zone electrophoresis of proteins

This review article with 237 references is focused on capillary zone electrophoresis (CZE) of proteins. It includes discussion of modeling electrophoretic migration of proteins, sample pretreatment before the analysis, methods reducing the sorptions of proteins on the capillary wall, and techniques for increasing selectivity by using electrolyte additives including the sieving matrices. Significant progress in detection techniques, namely in laser-induced fluorescence and mass spectrometry, is emphasized. Modifications of CZE using specific interactions, such as affinity capillary electrophoresis or capillary immunoelectrophoresis, are debated as well as combination of CZE with other separation methods such as high performance liquid chromatography (HPLC). A number of practical applications of CZE of proteins are described.

Use of capillary sodium dodecyl sulfate gel electrophoresis to detect the prion protein extracted from scrapie-infected sheep

Scrapie in sheep and in goats is the prototype of a group of transmissible spongiform encephalopathies (TSE). A feature of these diseases is the accumulation in the brain of rod shaped fibrils that form from an aggregated protein that is a protease-resistant form of a modified normal host cell protein. In this study, we compared SDS gel capillary electrophoresis to conventional SDS-PAGE and Western blot to detect the monomer of this aggregated protein. This prion protein was extracted from the sheep brain by homogenizing the brain stem (10%, w/v) in 0.32 M sucrose and by using a series of ultracentrifugation steps and treatment with sodium lauroyl sarcosine and proteinase K. After the final centrifugation step, the pellet was resuspended in 0.01 M Tris pH 7.4 in a volume equivalent to 0.1 ml/g of brain used. This resuspended pellet was treated with 1% SDS and 5% 2-mercaptoethanol and boiled for 10 min. The analysis was done in a Beckman P/ACE 5500 using a SDS gel capillary (eCap SDS14-200 Beckman capillary). In infected sheep brain samples, but not normal sheep, a major peak at a molecular mass of 16.1 kDa and a minor peak with a leading shoulder were observed. Since the molecular mass determined for this protein was lower than that estimated on Western blot (22.4 kDa), a Ferguson plot was made to determine if there were abberations in the molecular mass determination. After correction, the major peak was estimated to be 19.2 kDa. This has a better correlation with that determined by SDS-PAGE and Western blot. The equivalent amount of brain sample in the capillary was approximately 50 micrograms. For Western blot, the amount of brain sample was approximately 20 mg. For this assay, this is approximately 100 times less than that needed for Western blot for sheep samples.