Peptide mapping of β-casein by capillary zone electrophoresis

A method to the study of -casein proteolysis by aspartic proteinases is developed. The 3% trichloroacetic acid-soluble peptides of -casein digested with cardosin A were separated by capillary zone electrophoresis under different experimental conditions in an uncoated fused silica capillary. The best separation was at pH 3.01, 30 kV and 30 °C.     

Determination of genomic 5-hydroxymethyl-2’-deoxycytidine in human DNA by capillary electrophoresis with laser induced fluorescence

Recent studies reported the presence of 5-hydroxymethylcytosine (5 hmC) as an additional modification in mammalian genomic DNA. To date, 5 hmC has been detected only in mouse DNA isolated from embryonic stem cells, some adult tissues and in DNA from human bone marrow. Understanding its biological function will require the development of sensitive analytical methods that allow the detection and quantification of 5-hydroxymethylcytosine along with 5-methylcytosine and cytosine.

Here we report the validation of a fast and sensitive method for the quantification of global 5-hydroxymethyl-2'-deoxycytidine (5 hmdC) in DNA. The method is based on a procedure consisting of fluorescence labeling of deoxyribonucleotides and analysis by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). A double stranded DNA fragment containing a defined number of 5 hmdC residues was used for peak assignment, to establish separation conditions and to determine the limit of detection (LOD). The method yielded a LOD for 5 hmdC of 0.45 amol, which is equivalent to approximately to one 5 hmdC per 4,000 normal nucleotides (0.025%) using 1 μg of DNA as the matrix.

By applying the calibrated assay to the analysis of various DNAs we show that 5 hmdC is present in human tissue and human cancer cell lines. We demonstrate that by using CE-LIF DNA can be analyzed in one run for both methylation and hydroxymethylation of cytosine with high sensitivity and accuracy.     

Sensitive analysis of α-synuclein by nonlinear laser wave mixing coupled with capillary electrophoresis

Multi-photon nonlinear laser wave-mixing spectroscopy is a novel absorption-based technique that offers excellent detection sensitivity for biomedical applications, including early diagnosis and investigation of neurodegenerative diseases. α-Synuclein is linked to Parkinson's disease (PD), and characterization of its oligomers and quantification of the protein may contribute to understanding PD. The laser wave-mixing signal has a quadratic dependence on analyte concentration, and hence the technique is effective in monitoring small changes in concentration within biofluids. A wide variety of labels can be employed for laser wave-mixing detection due to its ability to detect both chromophores and fluorophores. In this investigation, two fluorophores and a chromophore are studied and used as labels for the detection of α-synuclein. Wave-mixing detection limits of PD-related protein conjugated with fluorescein isothiocyanate, QSY 35 acetic acid, succinimidyl ester, and Chromeo P503 were determined to be 1.4 × 10⁻¹³ M, 1.4 × 10⁻¹⁰ M, and 1.9 × 10⁻¹³ M, respectively. Based on the laser probe volume used, the corresponding mass detection limits were determined to be 1.1 × 10⁻²³ mol, 1.1 × 10⁻²⁰ mol, and 1.5 × 10⁻²³ mol. This study also presents molecular-based separation and quantification of α-synuclein by laser wave mixing coupled with capillary electrophoresis.     

Sensitive detection of C-reactive protein in serum by immunoprecipitation–microchip capillary gel electrophoresis

Sepsis represents a significant cause of mortality in intensive care units. Early diagnosis of sepsis is essential to increase the survival rate of patients. Among others, C-reactive protein (CRP) is commonly used as a sepsis marker. In this work we introduce immune precipitation combined with microchip capillary gel electrophoresis (IP–MCGE) for the detection and quantification of CRP in serum samples. First high-abundance proteins (HSA, IgG) are removed from serum samples using affinity spin cartridges, and then the remaining proteins are labeled with a fluorescence dye and incubated with an anti-CRP antibody, and the antigen/antibody complex is precipitated with protein G-coated magnetic beads. After precipitation the complex is eluted from the beads and loaded onto the MCGE system. CRP could be reliably detected and quantified, with a detection limit of 25 ng/μl in serum samples and 126 pg/μl in matrix-free samples. The overall sensitivity (LOQ = 75 ng/μl, R² = 0.9668) of the method is lower than that of some specially developed methods (e.g., immune radiometric assay) but is comparable to those of clinically accepted ELISA methods. The straightforward sample preparation (not prone to mistakes), reduced sample and reagent volumes (including the antibodies), and high throughput (10 samples/3 h) are advantages and therefore IP–MCGE bears potential for point-of-care diagnosis.     

Separation and detection of individual Aβ aggregates by capillary electrophoresis with laser-induced fluorescence detection

The separation and detection of individual amyloid beta (Aβ) aggregates by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was demonstrated. Samples were prepared with either Aβ (1-40) or Aβ (1-42) peptides and were characterized by CE with ultraviolet (UV) absorbance detection and transmission electron microscopy (TEM). Using thioflavin T (ThT) in the electrophoresis buffer, electrophoresis of aggregate-containing samples (5.0-s injection) produced up to several hundred narrow (< 20 ms FWHM [full width at half maximum]) fluorescence peaks. Injection of Aβ (1-40) monomer samples resulted in no additional peaks compared with controls. The CE-LIF results were validated by bulk ThT fluorescence measurements for the same samples. The potential of laser-induced fluorescence anisotropy (LIFA) with CE to characterize individual Aβ aggregates also was investigated.     

Measurement of DNA damage in peripheral blood by the γ-H2AX assay as predictor of colorectal cancer risk

The detection of γ-H2AX focus is one of the most sensitive ways to monitor DNA double-strand breaks (DSBs). Although changes in γ-H2AX activity have been studied in tumor cells in colorectal cancer (CRC), changes in peripheral blood lymphocytes (PBLs) have not been examined previously. We hypothesize that higher levels of irradiation-induced γ-H2AX in PBLs may be associated with an elevated risk of colorectal cancer (CRC). In a case-control study, the baseline and ionizing radiation (IR)-induced γ-H2AX levels in PBLs from frequency-matched 320 untreated CRC patients and 320 controls were detected by a laser scanning cytometer-based immunocytochemical method. We used unconditional multivariable logistic regression to evaluate CRC risk by using the ratio of IR-induced γ-H2AX to the baseline levels with adjustment of age, sex and smoking status. We found CRC cases had significantly higher γ-H2AX ratio (1.5 vs. 1.41, P < 0.0001) compared with controls. When using the median γ-H2AX ratio of controls as a cutoff point, we found higher γ-H2AX ratio was significantly associated with an increased risk of CRC (OR = 6.72, 95% CI = 4.54–9.94). Quartile analyses also showed significant dose–response relationship between higher γ-H2AX ratio and increased risk of CRC (P for trend < 0.0001). Age, sex, BMI and smoking status also influenced the association of γ-H2AX ratio with CRC risk; however, no interactions with γ-H2AX ratio were observed. These results support the premise that DSBs in peripheral blood as measured by γ-H2AX level might represent an intermediate phenotype to assess the risk of CRC. Future prospective studies are necessary to confirm our findings in independent populations.     

Determination of the chiral status of different novel psychoactive substance classes by capillary electrophoresis and β-cyclodextrin derivatives

Besides the abuse of well-known illicit drugs, consumers discovered new synthetic compounds with similar effects but minor alterations in their chemical structure. Originally, these so-called novel psychoactive substances (NPS) have been created to circumvent law of prosecution because of illicit drug abuse. During the past decade, such compounds came up in generations, the most popular compound was a synthetic cathinone derivative named mephedrone. Cathinones are structurally related to amphetamines; to date, more than 120 completely new derivatives have been synthesized and are traded via the Internet. Cathinones possess a chiral center; however, only little is known about the pharmacology of their enantiomers. However, NPS comprise further chiral compound classes such as amphetamine derivatives, ketamines, 2-(aminopropyl)benzofurans, and phenidines. In continuation of our project, a cheap and easy-to-perform chiral capillary zone electrophoresis method for enantioseparation of cathinones presented previously was extended to the aforementioned compound classes. Enantioresolution was achieved by simply adding native β-cyclodextrin, acetyl-β-cyclodextrin, 2-hydroxypropyl-β-cyclodextrin, or carboxymethyl-β-cyclodextrin as chiral selector additives to the background electrolyte. Fifty-one chiral NPS served as analytes mainly purchased from online vendors via the Internet. Using 10 mM of the aforementioned β-cyclodextrins in a 10 mM sodium phosphate buffer (pH 2.5), overall, 50 of 51 NPS were resolved. However, chiral separation ability of the selectors differed depending on the analyte. Additionally, simultaneous enantioseparations, the determination of enantiomeric migration orders of selected analytes, and a repeatability study were performed successfully. It was proven that all separated NPS were traded as racemic mixtures.     

Identification of the modifying sites of mono-PEGylated salmon calcitonins by capillary electrophoresis and MALDI–TOF mass spectrometry

A capillary electrophoretic method (CE) was developed for the determination of the PEG-modification sites of three positional isomers of mono-PEG modified salmon calcitonins (mono-PEG-sCTs). Resistance to proteolytic degradation on the PEG modification sites resulted in different patterns of CE electropherograms for the tryptic digested mono-PEG-sCTs isomers, and the PEG modification sites were assigned accordingly. The PEG-modification sites were also confirmed directly by determining the molecular masses of the tryptic digested PEG-modified fragments of respective mono-PEG-sCT by the matrix-assisted laser desorption ionization time-of-flight (MALDI–TOF) mass spectrometry.     

Analysis of the substrate specificity of α-L-arabinofuranosidases by DNA sequencer-aided fluorophore-assisted carbohydrate electrophoresis

Applied Microbiology and Biotechnology - Carbohydrate-active enzyme discovery is often not accompanied by experimental validation, demonstrating the need for techniques to analyze substrate...     

Separation and analysis of β-lactamantibiotics by high-performance capillary electrophoresis: Enzymatic synthesis, a case study

High-performance capillary electrophoresis (CE) and HPLC were compared for the analysis of some enzymatically synthesised lactam antibiotics. The main advantage for CE, besides its lower operational costs, is the short analysis time. It was further found that CE could be used for a variety of antibiotics and their building blocks by small adjustments, affecting the mobility of the solutes, in the analysis method. The compounds studied have a typical detection limit of 10 mM for both CE and HPLC.     

Study of polar metabolites in tobacco from different geographical origins by using capillary electrophoresis–mass spectrometry

Many metabolites in plant are highly polar and ionic. Their analysis using gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry can be problematic. Therefore a capillary electrophoresis–mass spectrometry (CE–MS) method with charge-driven separation characteristic was developed to investigate polar metabolites in tobacco. To obtain as many features as possible, extraction of polar metabolites was optimized by the design of experiments and evaluated by univariate statistics. Method validation was carried out to evaluate the analytical characteristics including calibration curve, precision, sample stability and extraction reproducibility. The developed method was successfully applied in studying 30 tobacco leaves obtained from Yunnan and Guizhou provinces in China. A total of 154 polar metabolites were identified based on available database. Multivariate pattern recognition clearly revealed the metabolic differences between the two geographic areas and 43 significantly different metabolites were defined by the non-parametric hypothesis test (Mann–Whitney U test) and false discovery rate. Some key metabolites involved in photosynthesis such as ribulose 1,5-disphosphate, fructose 1,6-diphosphate, glycine, betaine, GABA and serine were found to be susceptible to environmental conditions. This study shows that the metabolic profiling based on CE–MS can clearly discriminate tobacco leaves of different geographical origins and understand the relationship between plant metabolites and their geographical origins.     

Purification of protein–DNA complexes by native gel electrophoresis for electron microscopy study

Electrophoretic separation under native conditions may be used for purification of protein molecules and their complexes with DNA and other ligands. Here, we employed this approach to separate protein-DNA complexes with a molecular weight of approximately 200 kDa: mono- and dinucleosomes. The purified mononucleosomes were subjected to single particle electron microscopy study using negative stain contrasting, and the two-dimensional projections of the nucleosomes at 25 Å resolution were obtained. A comparison of the nucleosome projections before and after separation in the native PAGE revealed different orientation of particles on the carbon film.     

Is the repair of oxidative DNA base modifications inducible by a preceding DNA damage induction?

In mammalian cells, 7,8-dihydro-8-oxoguanine (8-oxoG) and some other oxidative guanine modifications are removed from the DNA by base excision repair, which is initiated by OGG1 protein. We have tested whether this repair is inducible in mouse embryonic fibroblasts (MEFs), MCF-7 breast cancer cells and primary human fibroblasts by a pretreatment with the photosensitizer Ro19-8022 plus light, which generates predominantly 8-oxoG, or with methyl methanesulfonate (MMS), which generates alkylated bases and abasic sites (AP sites). The results indicate that the repair rate of the oxidative guanine modifications induced by the photosensitizer was not increased if a priming dose of the oxidative or alkylating agent was applied 6 or 18h prior to a challenging dose, although pretreatments with both agents resulted in two-fold elevated glutathione levels as an indication for an adaptive response. Similarly, the activity of total protein extracts of the cells to incise at a single 8-oxoG residue in an oligonucleotide was unchanged. It has to be concluded that the repair of 8-oxoG is not inducible by oxidative or alkylation damage.     

Mechanisms of DNA damage induced by morin,an inhibitor of amyloid β-peptide aggregation

Morin is a potential inhibitor of amyloid β-peptide aggregation. This aggregation is involved in the pathogenesis of Alzheimer’s disease. Meanwhile, morin has been found to be mutagenic and exhibits peroxidation of membrane lipids concurrent with DNA strand breaks in the presence of metal ions. To clarify a molecular mechanism of morin-induced DNA damage, we examined the DNA damage and its site specificity on ³²P-5′-end-labeled human DNA fragments treated with morin plus Cu(II). The formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, was also determined in calf thymus DNA treated with morin plus Cu(II). Morin-induced DNA strand breaks and base modification in the presence of Cu(II) were dose dependent. Morin plus Cu(II) caused piperidine-labile lesions preferentially at thymine and guanine residues. The DNA damage was inhibited by methional, catalase and Cu(I)-chelator bathocuproine. The typical ?OH scavengers ethanol, mannitol and sodium formate showed no inhibitory effect on DNA damage induced by morin plus Cu(II). When superoxide dismutase was added to the solution, DNA damage was not inhibited. In addition, morin plus Cu(II) increased 8-oxodG formation in calf thymus DNA fragments. We conclude that morin undergoes autoxidation in the presence of Cu(II) via a Cu(I)/Cu(II) redox cycle and H₂O₂ generation to produce Cu(I)-hydroperoxide, which causes oxidative DNA damage.     

Development of a urinary free cortisol assay using solid-phase extraction–capillary electrophoresis

In clinical practice, the measurement of urinary free cortisol (UFC) provides the most sensitive and specific diagnostic information for excess adrenal production of cortisol. The existing methodologies (RIA and HPLC) are time consuming, costly, involve tedious extractions, derivatizations and problems with non-specific interactions with cortisol metabolites in urine. In the present study, we describe the development of an SPE–CE method for the rapid analysis of UFC. UFC was concentrated using SPE C₁₈ cartridges (3M Empore) under a vacuum and eluted with acetonitrile–SDS. The use of 10% acetone to wash cartridges before final elution with acetonitrile–SDS showed significant improvements in the free cortisol recovery. The complete extraction was accomplished in 10–15 min with a recovery of 89–94%. CE analysis was done on a Beckman P/ACE 5010 with detection at 254 nm using a neutral capillary. Detection limits of free cortisol in urine was improved to 10 μg/l with SPE compared to 500 μg/l without SPE. No interferences either from BSA or other urinary cortisol metabolites affected the free cortisol determinations. The results showed the feasibility of a rapid UFC detection with improved sample handling capacity.     

Separation of 1–23-kb complementary DNA strands by urea–agarose gel electrophoresis

Double-stranded (ds), as well as denatured, single-stranded (ss) DNA samples can be analyzed on urea–agarose gels. Here we report that after denaturation by heat in the presence of 8 M urea, the two strands of the same ds DNA fragment of ∼1–20-kb size migrate differently in 1 M urea containing agarose gels. The two strands are readily distinguished on Southern blots by ss-specific probes. The different migration of the two strands could be attributed to their different, base composition-dependent conformation impinging on the electrophoretic mobility of the ss molecules. This phenomenon can be exploited for the efficient preparation of strand-specific probes and for the separation of the complementary DNA strands for subsequent analysis, offering a new tool for various cell biological research areas.     

Combined use of [TBA][L-ASP] and hydroxypropyl-β-cyclodextrin as selectors for separation of Cinchona alkaloids by capillary electrophoresis

In this paper, a new capillary electrophoresis (CE) separation and detection method was developed for the chiral separation of the four major Cinchona alkaloids (quinine/quinidine and cinchonine/cinchonidine) using hydroxypropyl-β-cyclodextrin (HP-β-CD) and chiral ionic liquid ([TBA][L-ASP]) as selectors. Separation parameters such as buffer concentrations, pH, HP-β-CD and chiral ionic liquid concentrations, capillary temperature, and separation voltage were investigated. After optimization of separation conditions, baseline separation of the three analytes (cinchonidine, quinine, cinchonine) was achieved in fewer than 7 min in ammonium acetate background electrolyte (pH 5.0) with the addition of HP-β-CD in a concentration of 40 mM and [TBA][L-ASP] of 14 mM, while the baseline separation of cinchonine and quinidine was not obtained. Therefore, the first-order derivative electropherogram was applied for resolving overlapping peaks. Regression equations revealed a good linear relationship between peak areas in first-order derivative electropherograms and concentrations of the two diastereomer pairs. The results not only indicated that the first-order derivative electropherogram was effective in determination of a low content component and of those not fully separated from adjacent ones, but also showed that the ionic liquid appeared to be a very promising chiral selector in CE.     

Determination of β-blockers in pharmaceutical and human urine by capillary electrophoresis with electrochemiluminescence detection and studies on the pharmacokinetics

A novel method for simultaneous determination of atenolol, metoprolol and esmolol was proposed by capillary electrophoresis (CE) separation and electrochemiluminescence (ECL) detection. Poly-β-cyclodextrin (Poly-β-CD) was used as an additive in the running buffer to improve the separation of three analytes. The conditions for CE separation, ECL detection and effect of Poly-β-CD were investigated in detail. The three β-blockers with very similar structures were well separated and detected under the optimum conditions. The linear ranges of the standard solution for atenolol and esmolol were 2.5-125 μmol/L with a detection limit (S/N=3) of 0.5 μmol/L, and for metoprolol was 0.5-25 μmol/L with a detection limit of 0.1 μmol/L. For three β-blockers from spiked aqueous and urine samples, the accuracy and precision including intraday and interday experiments were performed by calculating the recovery, the relative standard deviations of the ECL intensity and the migration time, respectively. The developed method was applied to the determination of metoprolol content in commercial pharmaceutical, and the analytical results are in good agreement with the nominal value with recoveries in the range of 98.7-105%. The proposed method was also applied to the monitoring of pharmacokinetics for metoprolol in human body.     

Estimation of allele frequency in pooled DNA by using PCR–RFLP combined with microchip electrophoresis

Biallelic marker, most commonly single nucleotide polymorphism (SNP), is widely utilized in genetic association analysis, which can be speeded up by estimating allele frequency in pooled DNA instead of individual genotyping. Several methods have shown high accuracy and precision for allele frequency estimation in pools. Here, we explored PCR restriction fragment length polymorphism (PCR–RFLP) combined with microchip electrophoresis as a possible strategy for allele frequency estimation in DNA pools. We have used the commercial available Agilent 2100 microchip electrophoresis analysis system for quantifying the enzymatically digested DNA fragments and the fluorescence intensities to estimate the allele frequencies in the DNA pools. In this study, we have estimated the allele frequencies of five SNPs in a DNA pool composed of 141 previously genotyped health controls and a DNA pool composed of 96 previously genotyped gastric cancer patients with a frequency representation of 10–90% for the variant allele. Our studies show that accurate, quantitative data on allele frequencies, suitable for investigating the association of SNPs with complex disorders, can be estimated from pooled DNA samples by using this assay. This approach, being independent of the number of samples, promises to drastically reduce the labor and cost of genotyping in the initial association analysis.     

The separation of the α-chains of collagen by free-flow electrophoresis

1. The separation of the alpha-components of codfish-skin and calf-skin collagen from the higher-molecular-weight components was accomplished by gel filtration with Bio-Gel P-300 resin in 5m-lithium chloride and at pH7.4. 2. From this fraction three distinct alpha-components, corresponding to the alpha1-, alpha2- and alpha3- chains of collagen, were isolated by free-flow electrophoresis in 6m-urea at 4 degrees . At the temperatures and pH values used there was no detectable degradation of the alpha-chains.