Capillary electrophoresis in the analysis of therapeutic peptides-A review

Therapeutic peptides are a growing class of innovative drugs with high efficiency and a low risk of adverse effects. These biomolecules fall within the molecular mass range between that of small molecules and proteins. However, their inherent instability and potential for degradation underscore the importance of reliable and effective analytical methods for pharmaceutical quality control, therapeutic drug monitoring, and compliance testing. Liquid chromatography-mass spectrometry (LC-MS) has long time been the "gold standard" conventional method for peptide analysis, but capillary electrophoresis (CE) is increasingly being recognized as a complementary and, in some cases, superior, highly efficient, green, and cost-effective alternative technique. CE can separate peptides composed of different amino acids owing to differences in their net charge and size, determining their migration behavior in an electric field. This review provides a comprehensive overview of therapeutic peptides that have been used in the clinical environment for the last 25 years. It describes the properties, classification, current trends in development, and clinical use of therapeutic peptides. From the analytical point of view, it discusses the challenges associated with the analysis of therapeutic peptides in pharmaceutical and biological matrices, as well as the evaluation of CE as a whole and the comparison with LC methods. The article also highlights the use of microchip electrophoresis, nonaqueous CE, and nonconventional hydrodynamically closed CE systems and their applications. Overall, the article emphasizes the importance of developing new CE-based analytical methods to ensure the high quality, safety, and efficacy of therapeutic peptides in clinical practice.

Determination of short-chain fatty acids as putative biomarkers of cancer diseases by modern analytical strategies and tools: a review

Short-chain fatty acids (SCFAs) are the main metabolites produced by bacterial fermentation of non-digestible carbohydrates in the gastrointestinal tract. They can be seen as the major flow of carbon from the diet, through the microbiome to the host. SCFAs have been reported as important molecules responsible for the regulation of intestinal homeostasis. Moreover, these molecules have a significant impact on the immune system and are able to affect inflammation, cardiovascular diseases, diabetes type II, or oncological diseases. For this purpose, SCFAs could be used as putative biomarkers of various diseases, including cancer. A potential diagnostic value may be offered by analyzing SCFAs with the use of advanced analytical approaches such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) coupled with mass spectrometry (MS). The presented review summarizes the importance of analyzing SCFAs from clinical and analytical perspective. Current advances in the analysis of SCFAs focused on sample pretreatment, separation strategy, and detection methods are highlighted. Additionally, it also shows potential areas for the development of future diagnostic tools in oncology and other varieties of diseases based on targeted metabolite profiling.

Comparison of polypharmacy and pharmacotherapy among seniors in social institutions in 2001 and 2019

INTRODUCTION

Polypharmacy (polypharmacotherapy) is a serious problem among seniors. The aim of the work was to compare pharmacotherapy and polypharmacy among seniors in social facilities in 2001 and 2019.

METHODOLOGY

As of December 31, 2001, we collected data on the pharmacotherapy of 151 residents of two retirement homes (average age 75.1 years, 68.9% women). We compared the results with the pharmacotherapy of residents of two facilities for seniors as of October 31, 2019 (237 seniors, average age 80.5 years, 73.4% women). According to the medical records, we determined and compared the regularly used medicines of all residents, the use of medicines by age and sex, the use of 0-4 medicines, 5-9 medicines, 5 or more medicines, 10 or more medicines and the groups of medicines according to the ATC classification. For statistical processing, we used the t-test and chi-square test.

RESULTS

In 2001, residents regularly used a total of 891 medicines, 18 years later, they used a total of 2099 medicines. We observed a significant increase in the average number of regularly used medications per resident by more than a half (from 5.90 medications to 8.86 medications), in women from 6.11 drugs to 9.24 drugs and in men from 5.45 drugs to 7.81 drugs. The number of residents with polypharmacy (regular use of ≥ 5 drugs) increased by almost a quarter (from 70.2% to 87.3%), and the number of seniors with excessive polypharmacy (regular use of ≥ 10 drugs) increased 4.6 times (from 9, 3% to 43.5%).

CONCLUSION

Our work confirmed that over the course of 18 years, the number of medications used by seniors in social-type institutions has increased. It also points to the trend of increasing polypharmacy and excessive polypharmacy among seniors, especially at the age of 75+ and among women.

Amino acids in inflammatory bowel diseases: Modern diagnostic tools and methodologies

Amino acids are crucial building blocks of living organisms. Together with their derivatives, they participate in many intracellular processes to act as hormones, neuromodulators, and neurotransmitters. For several decades amino acids have been studied for their potential as markers of various diseases, including inflammatory bowel diseases. Subsequent improvements in sample pretreatment, separation, and detection methods have enabled the specific and very sensitive determination of these molecules in multicomponent matrices-biological fluids and tissues. The information obtained from targeted amino acid analysis (biomarker-based analytical strategy) can be further used for early diagnostics, to monitor the course of the disease or compliance of the patients. This review will provide an insight into current knowledge about inflammatory bowel diseases, the role of proteinogenic amino acids in intestinal inflammation and modern analytical techniques used in its diagnosis and disease activity monitoring. Current advances in the analysis of amino acids focused on sample pretreatment, separation strategy, or detection methods are highlighted, and their potential in clinical laboratories is discussed. In addition, the latest clinical data obtained from the metabolomic profiling of patients suffering from inflammatory bowel diseases are summarized with a focus on proteinogenic amino acids.

Comparison of 1D a 2D ITP-MS performance parameters and application possibilities: Ultratrace determination of B vitamins in human urine

The possibility to investigate analytes at ultra-low concentration levels still remains a hot topic in bioanalysis. In this area, various preconcentration techniques are an integral part of analytical procedures. When applying electromigration separation techniques, an isotachophoresis has been advantageously employed many times for this purpose. To solve current biomedical tasks effectively, an advanced two-dimensional isotachophoretic instrument (in a hydrodynamically closed separation system with an enhanced sample load capacity) hyphenated with mass spectrometry (ITP-ITP-MS) has been proposed by Foret and coworkers. As a continuation, this work represents the first study dealing with a full validation of an ITP-ITP-MS method. In order to see the benefits of an online ITP sample pretreatment (preconcentration and clean-up) on the performance parameters, the developed 2D ITP-MS method was compared with a corresponding 1D ITP-MS method. Application potentialities of the compared methods were demonstrated via a determination of two B vitamins, namely thiamine and pyridoxine, in human urine samples. The developed 2D ITP-MS method showed its enhanced effectivity and usefulness for a routine biomedical use (here, a reliable screening of trace B vitamins in human urine without an offline sample preparation).

Determination of Branched-Chain Amino Acids in Food Supplements and Human Plasma by a CE-MS/MS Method with Enhanced Resolution

In the presented study, a capillary electrophoresis-mass spectrometry method combining high separation efficiency and sensitive detection has been developed and validated, for the first time, to quantify branched chain amino acids (valine, isoleucine, leucine) in commercial food and sport supplement samples and human plasma samples. The separations were performed in a bare fused silica capillary. The background electrolyte was composed of 500 mM formic acid with pH 2.0. The plasma sample pretreatment was realized by simple protein precipitation with acetonitrile. Injection of a short zone of highly basic electrolyte before the sample injection and application of the negative pressure on the separation were accompanied by enhanced resolution of the isobaric amino acids—isoleucine and leucine. The developed method was characterized by favorable validation parameters, such as linearity (r² > 0.99), accuracy and precision, the limit of detection, lower limit of quantification, or robustness. These parameters were more than sufficient for the quantification of branched chain amino acids in various samples. The determined concentrations of branched chain amino acids in food and sports supplements were in very good agreement with the content declared by the manufacturer. The investigated concentrations of branched chain amino acids were in the range 294.68–359.24 µM for valine, 91.76–95.67 µM for isoleucine, and 196.78–251.24 µM for leucine. These concentrations fall within the physiological limits. The developed CE-MS/MS method represents a suitable alternative to traditional approaches used in branched chain amino acid quality control and bioanalysis.

Ultrasensitive determination of serotonin in human urine by a two dimensional capillary isotachophoresis-capillary zone electrophoresis hyphenated with tandem mass spectrometry

A two-dimensional capillary isotachophoresis-capillary zone electrophoresis method hyphenated with tandem mass spectrometry was developed and validated for ultrasensitive quantification of serotonin in real human urine samples. Under optimal conditions, the separation was achieved within 12 min (including on-line sample preparation) with the limit of detection of 34 pg mL^-1 (due to a large volume sample injection, here 10 µL, and isotachophoretic preconcentration). This concentration limit represents the lowest value for serotonin in comparison to other previously published separation methods employing mass spectrometry detection and applied to urine matrices. Thanks to high orthogonality, on-line concentration and clean-up effects of this approach, other excellent validation parameters such as linearity (coefficient of determination > 0.99), inter-day and intra-day precision (relative standard deviations 3.5-12.2%), accuracy (relative errors within 99-109.4%), and recovery (96-102%) could be easily obtained too. To demonstrate applicability of the method, we monitored serotonin levels in various real samples (from a healthy volunteer and clinical ones). The determined levels, normalized on the creatinine concentrations, were in the range of 6.81-12.86 ng mmol^-1 creatinine This advanced method is suggested for an effective, reliable, high sample throughput, and low cost routine clinical screening or targeted metabolomic studies of serotonin in urine samples.

Porous graphitic carbon based chromatography hyphenated with mass spectrometry: A new strategy for profiling thiopurine nucleotides in patients with inflammatory bowel diseases

Thiopurine (TP) treatment is discontinued in up to 30% of patients suffering from inflammatory bowel diseases (IBD) due to various adverse effects. Therapeutic drug monitoring of biologically active TP metabolites, i.e. thiopurine nucleotides (TPN), can help to optimize the efficacy and safety of the TP treatment. In our work, a novel strategy for TPN profiling, based on a porous graphitic carbon (PGC) chromatography, was developed. The validated PGC-MS method was compared with ion-exchange LC-MS, a currently leading analytical approach established for the determination of TPN. The innovative approach enabled an enhancement of several key performance parameters demanded in a clinical routine use, namely (i) selectivity (time- and mass-recognition of all 12 TPN in one run), (ii) sensitivity (2-5-fold increase in intensities of the analytical signals), (iii) sample throughput (25% shorter analysis time). Application of the novel TPN profiling strategy to a pilot clinical study (12 patients) revealed significantly higher levels of 6-methylthioguanine 5'-diphosphate (MeTGDP) in non-responsive IDB patients treated with azathioprine. Some other TPN are very close to the critical level (p = 0.05) and they will need larger groups of IBD patients to confirm definitively their relevance. In conclusion, the developed PGC-MS method represents a significant improvement to currently available methods for detailed profiling of TPN and its use in bigger clinical studies should lead to a better understanding of the relationship between TPN profiles and therapeutic outcome.

A simple and rapid LC-MS/MS and CE-MS/MS analytical strategy for the determination of therapeutic peptides in modern immunotherapeutics and biopharmaceutics

Modern therapy of metabolic, neurodegenerative, inflammation, or cancer diseases is recently based on an immunotherapeutic approach. The peptide conjugates represent innovative and effective therapeutics that are better tolerated and are much more specific than small molecule-based medicines. The nature and manufacturing process of these therapeutics make their analysis very challenging. Here, two robust analytical methods based on an on-line combination of ultra-high-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) and capillary electrophoresis with tandem mass spectrometry (CE-MS/MS) were developed for fast determination of immunogenic synthetic peptide (peptide sequence CADNLHKVVGQST) in a conjugate with bovine serum albumin (BSA) as a carrier protein and is a peptide, conjugate formulated with a vaccine adjuvant - Alhydrogel® 2 %. An effective non-enzymatic release step of the peptide from the final peptide conjugate based on acid hydrolysis with the use of 2% formic acid was successfully tested and implemented. The proposed methods were validated according to the ICH guideline and parameters such as linearity, precision, and accuracy, the limit of detection (LOD) or limit of quantification (LOQ) were assessed. Calibration curves were linear within the range of 1-30 μg.mL^-1 and the correlation coefficients were higher than 0.99. The intraday and interday precisions were 3.2-8.1 % (UHPLC-MS/MS), 1.6-9.3 % (CE-MS/MS) and 3.6-10.3 % (UHPLC-MS/MS), 4.1-10.2 % (CE-MS/MS), respectively. The recovery ranged in the interval of 98.4-107.4 % for UHPLC-MS/MS method and 100.3-103.2 % for CE-MS/MS method. The presented approaches represent an effective tool for simple, rapid and robust quantification of immunogens in modern immunotherapeutics and other biopharmaceuticals with appropriate peptide sequences.

Positive pharmacokinetic effect of azathioprine co-medication on infliximab trough levels is dose-dependent

BACKGROUND

Thiopurines seem to have positive effect on the pharmacokinetics of anti-tumor necrosis factor biologics. It has been suggested that a reduced dose of thiopurines is sufficient to achieve this synergism.

AIMS

To assess the differences of infliximab (IFX) trough levels according to the dose of concomitantly used azathioprine (AZA).

PATIENTS & METHODS

All IBD patients treated with IFX (Remicade^®) in two IBD centres between November 2015 and April 2017 were eligible. Infliximab trough levels were assessed by ELISA (Ridascreen^®, R-Biopharm). The differences in IFX trough levels according to AZA dose were analyzed statistically.

RESULTS

In total, 125 patients were included, 42 pts (33.6%) on infliximab monotherapy, 83 pts (66.4%) using combined immune suppression. The respective median IFX levels according to AZA dose were as follows: group 1 (no concomitant AZA) 2.83 μg/ml (range 0-12); group 2 (AZA dose less than 1 mg/kg) 4.91 μg/ml (range 0.09-15.36); group 3 (AZA dose 1 < 2 mg/kg) 5.67 (range 0.16-16.97); group 4 (AZA dose above 2 mg/kg) 7.53 μg/ml (range 1.15-8.73). The differences in IFX trough levels between the respective groups according to AZA dose were statistically significant (p = 0.0159).

CONCLUSION

The positive effect of azathioprine on infliximab levels seems to be dependent on the dose of concomitantly used azathioprine.

Structural aspects of heterotrinuclear Pt2M, PtM2, and PtMM′ complexes – distortion isomers

In this review, the structural parameters of 18 heterotrinuclear Pt2M (M=Hg, Zn, Cd, Au, Mn, Ag, Pd), PtM2 (M=Al, Ga, Sb, In, Mo, Fe), PtFeMn, PtHgMn, and PtFeOs types are summarized and analyzed. The Pt atoms are four-, five-, and even six-coordinated, among which the four-coordinated ones are the most common. The M atoms are found to be two- (Hg), three- (Hg), four- (Hg, Sb, In, Ag, Au), and six- (Ga, In, Al, Mo, Mn, Fe, Pd) coordinated and even sandwiched (FeC10). There is a wide variety of donor atoms (ligands) (O+NL, N+CL, NL, CO, CN, CL, Cl, SL, PL, I), which build up the respective inner coordination spheres about the metal atoms. The 17 complexes contain two crystallographically independent molecules within the same crystal, and 1 complex contains four such molecules. In each complex, the respective molecules are differing mostly by the degree of distortion in metal-metal and metal-ligand bond distances and ligand-metal-ligand bond angles, and are examples of distortion isomerism.

Stereochemistry of heterobinuclear Pt-M complexes

In this review, the structural parameters of almost 30 isomers of heterobinuclear Pt-M (M=Sn, Tl, Cu, Ag, Ti, W, Cr, Fe, Co, Ni, Mn, Pd, or Rh) complexes are summarized and analyzed. There are three types of isomers: distortion (by far the prevailing type), polymerization, and mixed isomers. On the basis of Pt-M distance, there are two groups of complexes: one in which the Pt-M bond distances are <3.0 Å (M=Sn, Tl, W, Cr, Mn, Ni, or Pd) and the other one in which the Pt-M separations are >3.0 Å (M=Cu, Ag, Ti, W, Fe, Co, or Rh). Platinum atoms exist in two oxidation states: +2 and +4. The former by far prevails with a square-planar arrangement with varying degrees of distortion. The Pt(IV) atoms are six-coordinated. The inner coordination spheres about M atoms range from two-coordinated (AgNCl) to sandwiched (FeC10). There is wide variety of donor atoms (ligands) (H, OL, NL, CL, BL, Cl, SL, PL, Br, or I) that build up the respective inner coordination spheres about central metal atoms.

Germicide wound pad with active, in situ, electrolytically produced hypochlorous acid

We describe a new wound dressing technology that can actively generate an inorganic germicide agent, in situ, within the wound pad. The technology provides real time control over the quantitative, spatial and temporal delivery of the germicide. The identity of the germicide is hypochlorous acid (HClO). The HClO is produced in a flexible wound pad, made of a composite of thin (micrometer scale) layers of various materials, with different electrochemical properties that enhance HClO production. Active control over the production of HClO is achieved by control of the pH and of the electric potential across the layers. The effectiveness of the Active HClO Pad (AHClOP) concept is demonstrated in a study on sterilization of E. coli in a deep wound contamination simulating gel. The performance of the AHClOP is compared with that of four commercial wound dressings. Results show that the AHClOP can sterilize throughout the gel, while the commercial dressings cannot.

Simultaneous analysis of vitamins B in pharmaceuticals and dietary supplements by capillary electrophoresis hyphenated with triple quadrupole mass spectrometry

The advanced hyphenated method based on capillary electrophoresis (CE) on-line combined with electrospray ionization (ESI) and tandem mass spectrometry (MS/MS, here triple quadrupole, QqQ) was developed and applied in pharmaceutical analysis in this work. Under the optimized CE separation (background electrolyte: 50 mmol/L formic acid with pH 2.05), ESI ionization (sheath liquid: 0.1% v/v formic acid in 50% v/v aq methanol) and QqQ detection (100-160V fragmentor voltage, 15-25eV collision energy, depending on the type of analyte) conditions, highly efficient, reproducible, accurate, sensitive (sub microg/mL LODs) and selective (each analyte was unequivocally specified by two characteristic MS signals, i.e. qualifier, quantifier) determination of vitamins B was achieved. All vitamins B, namely thiamine, riboflavin, nicotinamide, nicotinic acid, pantothenic acid, pyridoxine, biotin, folic acid and cyanocobalamine, were simultaneously determined in various dosage forms (injection solution, tablets, and effervescent tablets) within ca. 16 min. The main benefits of the proposed CE-ESI-QqQ method in comparison with the CE-UV ones are considerably enhanced sensitivity and selectivity. Other benefits are low cost, simplicity, flexibility and environmental aspects when comparing CE-ESI-QqQ with HPLC-MS. Successful validation and application of the proposed CE-ESI-QqQ method suggest its routine use in highly effective and reliable multi-drug quality control.

Determination of selenium in clinical plasma samples related to atopic dermatitis study by chronopotentiometric stripping method

Galvanostatic stripping chronopotentiometry (GSC) was developed and applied for the determination of selenium in human plasma. In this work GSC based on composite carbon electrode coated by a gold layer was optimized concerning various electrochemical parameters (coating procedure, electrolysis potential, electrolysis time, dissolution current). Along with this, the sample preparation was optimized with respect to mineralization conditions (type and concentration of decomposition agent, temperature, time). The human plasma samples mineralized in an autoclave under the optimized conditions (160 degrees C, 100 min, 22 mol/l HNO3) were appropriately diluted by background electrolyte solution (0.100 mol/l H2SO4 + 0.001 mol/l HCl) and directly analyzed by the optimized GSC method. The proposed method was characterized by excellent performance parameters, the limit of detection was 0.2 ng/ml, accuracy <5%, reproducibility <4%. The proposed method was applied for the investigation of the relationship between atopic dermatitis and selenium concentration in human plasma. Here, patients suffering from atopic dermatitis were monitored during their treatment with a pharmaceutical preparation containing inorganic selenium (Zinkosel). After six months therapy increased levels of selenium in plasma were detected in 76% of the patients with an improvement of the clinical state in 65% of the patients.

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

An analysis of recent trends indicates that CE can show real advantages over chromatographic methods in ultratrace enantioselective determination of biologically active compounds in complex biological matrices. It is due to high separation efficiency and many applicable in-capillary electromigration effects in CE (countercurrent migration, stacking effects) enhancing significantly (enantio)separability and enabling effective sample preparation (preconcentration, purification, analyte derivatization). Other possible on-line combinations of CE, such as column coupled CE-CE techniques and implementation of nonelectrophoretic techniques (extraction, membrane filtration, flow injection) into CE, offer additional approaches for highly effective sample preparation and separation. CE matured to a highly flexible and compatible technique enabling its hyphenation with powerful detection systems allowing extremely sensitive detection (e.g. LIF) and/or structural characterization of analytes (e.g. MS). Within the last decade, more as well as less conventional analytical on-line approaches have been effectively utilized in this field and their practical potentialities are demonstrated on many new application examples in this article. Here, three basic areas of (enantioselective) drug bioanalysis are highlighted and supported by a brief theoretical description of each individual approach in a compact review structure (to create integrated view on the topic), including (i) progressive enantioseparation approaches and new enantioselective agents, (ii) in-capillary sample preparation (preconcentration, purification, derivatization), and (iii) detection possibilities related to enhanced sensitivity and structural characterization.

Enantiomeric purity control of levocetirizine in pharmaceuticals using anionic cyclodextrin mediated capillary electrophoresis separation and fiber-based diode array detection

The present work illustrates potential of anionic cyclodextrin (CD) mediated capillary electrophoresis (CE) separation technique coupled with on-capillary diode array detector (DAD) for highly reliable enantioselective determination of dextrocetirizine (DCET) besides its major active compound (levocetirizine, LCET) in pharmaceuticals (commercial tablets). DAD detection was utilized for the characterization of composition of each separated zone via match of corresponding tested (analyte in dosage form) and reference (standard analyte in water) UV-VIS spectrum (scanned in interval 200-800 nm) being expressed mathematically through Pearson's correlation coefficient (PCC). It was demonstrated, comparing the reference and real spectra of CET enantiomers, that the applied separation method was selective enough to produce pure (spectrally homogeneous) zones of interest without any interfering comigrating compound (PCCs values were equal or higher than 0.99). Successful validation of the proposed CE-DAD method suggests its routine use for the control of enantiomeric purity of pharmaceuticals.

Determination of amlodipine enantiomers in pharmaceuticals using capillary electrophoresis separation and diode array detection

The present work describes a capillary zone electrophoresis (CZE) separation technique coupled with on-capillary diode array detector (DAD) for highly reliable enantioselective determination of amlodipine (AML) in commercial tablets. For the separation of AML enantiomers, (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CD) was an appropriate chiral selector providing complete enantioresolution. Optimized separation conditions consisted of 50 mmol/l glycine-acetate buffer, pH 3.2, 50 mg/ml HP-beta-CD. Hydroxyethylcellulose (HEC, 0.2% w/v) served as an electroosmotic flow (EOF) suppressor in this buffer. DAD detection was used for the characterization of the composition of separated zones according to differences in corresponding UV-VIS spectra (scanned in interval 200-800 nm). It was demonstrated, comparing reference and real spectra of the analytes, that the proposed separation method was selective enough to produce pure (non-mixed, i.e. spectrally homogeneous) analyte zones without any interfering compound. Successful validation and application of the proposed CZE-DAD method suggest its routine use in enantioselective control of AML in pharmaceuticals.

Determination of Fexofenadine in Tablets by Capillary Electrophoresis in Free Solution and in Solution with Cyclodextrins as Analyte Carriers

Capillary electrophoresis (CE) methods for the determination of fexofenadine (FEX) in commercial pharmaceuticals were developed. It was demonstrated that FEX could be effectively analyzed in free solution cationic CE at low pH. Another analytical approach studied was based on cyclodextrin (CD) modified CE where highly charged CD derivatives served as analyte carriers. In this way, the separation range was spread to physiological pH region and a CE analysis of FEX, present actually in its zwitterionic form, could be accomplished. Several parameters affecting the separations were studied, including the type and concentration of carrier ion, counterion, analyte carrier, and pH of the buffer. The methods based on the free solution CE and CD-modified CE were compared each other, validated, and applied for the determination of FEX in tablets.

Potentialities of ITP-CZE method with diode array detection for enantiomeric purity control of dexbrompheniramine in pharmaceuticals

The present work illustrates potentialities of on-line combined isotachophoresis-capillary zone electrophoresis (ITP-CZE) separation techniques coupled with on-capillary diode array detector (DAD) for enantiomeric purity testing of drugs in pharmaceuticals. The general advantages of the proposed method are its (i) high selectivity, (ii) low concentration limit of detection (LOD) obtainable, (iii) enhanced sample loadability, and (iv) enhanced reliability. For separation of brompheniramine (BP) enantiomers, serving as model analytes, carboxyethyl-beta-cyclodextrin (CE-beta-CD) was appropriate chiral selector providing complete enantioresolution. Given by a high sample load capacity (30 microl sample injection volume) and preconcentration of the analytes in ITP stage, concentration LOD of levobrompheniramine (LBP), serving as model impurity, was 2.5 ng/ml (8 x 10(-9)mol/l). Such separation and detection conditions enabled to easily determine LBP in samples containing a 10(3) excess of dexbrompheniramine (DBP). DAD detection in comparison with single wavelength detection can enhance value of analytical information when analytes and interferents have different spectra (distinguishing impurities in analyte zone, confirmation of migration positions of migrants). In this context purity of BP zones was confirmed with higher reliability in pharmaceutical sample. Moreover, distinguishing the trace analyte signal superposed on the baseline noise was provided with sufficient reliability (for this purpose the background correction and smoothing procedure had to be applied to the raw DAD spectra). Successful validation and application of the proposed ITP-CZE-DAD method suggest its routine use for the enantiomeric purity testing of pharmaceuticals.

Possibilities of column coupling electrophoresis provided with a fiber-based diode array detection in enantioselective analysis of drugs in pharmaceutical and clinical samples

The present work illustrated possibilities of column coupling electrophoresis combined with ionizable chiral selector and diode array detection (DAD) for the enantioselective analysis of trace drugs (pheniramine and its analogs) in pharmaceutical and clinical samples. Isotachophoresis (ITP), on-line coupled with capillary zone electrophoresis (CZE), served as an ideal injection technique (high sample load capacity, narrow and sharp drugs zones) of on-line pretreated samples (preseparation, purification and preconcentration of drugs) for the CZE stage. Enhanced (enantio)separation selectivity of CZE with ionizable chiral selector (carboxyethyl-beta-cyclodextrin recognized between drugs enantiomers on one hand as well as between drugs and sample matrix constituents on the other hand) enabled to obtain pure zones of the drugs enantiomers, suitable for their detection and quantitation. DAD in comparison with single wavelength UV detection enhanced value of analytical information verifying purity of drugs enantiomers zones (indicating interferents with different spectra to those of drugs). Obtained results indicated pure zones of interest confirming effective ITP-CZE (enantio)separation process. Distinguishing the trace analytes signals superposed on the baseline noise was provided with sufficient reliability (for this purpose the background correction and smoothing procedure had to be applied to the raw DAD spectra). The proposed ITP-CZE-DAD methods were characterized by favorable performance parameters (sensitivity, linearity, precision, recovery, accuracy, robustness, selectivity) and successfully applied for (i) enantiomeric purity testing of dexbrompheniramine in commercial pharmaceutical tablets and (ii) enantioselective metabolic study of pheniramine in human urine.

Enantioselective analysis of pheniramine in urine by charged CD-mediated CZE provided with a fiber-based DAD and an on-line sample pretreatment by capillary ITP

Application potentialities of CZE on-line coupled with capillary ITP and DAD to the identification and determination of trace concentration levels (microg/L) of pheniramine (PHM) enantiomers and their metabolites present in complex ionic matrices of biological origin (urine) are shown. An enhanced (enantio)selectivity of the CZE separation system obtained by the addition of carboxyethyl-beta-CD (CE-beta-CD) to the carrier electrolyte provided CZE conditions for a reliable identification of similar/identical DAD spectra of structurally related compounds (PHM enantiomers and their metabolites) in clinical urine samples differing in qualitative and quantitative composition of sample matrix constituents. A high sample loadability (a 30 microL sample injection volume), partial sample clean-up (removing macroconstituents from the sample), and preconcentration of the analytes in ITP stage resulted in the decrease of concentration LOD for PHM enantiomers in urine to 5.2 and 6.8 microg/L (2.2 x 10(-8) and 2.8 x 10(-8) mol/L), without using any sample pretreatment technique. The background correction and smoothing procedure applied to the raw DAD spectra provided analytically relevant DAD spectra of PHM enantiomers and their metabolites also when they were present in urine sample (30 microL injection volumes of ten-times diluted urine sample) at a 9 x 10(-) (8) mol/L concentration. DAD spectra of PHM enantiomers present in urine samples matched their reference spectra with reasonable certainties. DAD spectra of PHM metabolites were compared with the reference spectra of PHM enantiomers and a good match was found which indicates the similarities in the structures of enantiomers and their metabolites detected in the urine samples. This fact allows performing the quantitative analyses of PHM metabolites in the urine samples by applying the calibration parameters of PHM enantiomers also for PHM metabolites and the results show the possibilities of using the ITP-CZE-DAD combination for the direct analysis of PHM enantiomers and/or their metabolites in urine without any sample pretreatment. ITP-CZE-DAD method with oppositely charged selector is suggested to use in clinical research as it provides favorable performance parameters including sensitivity, linearity, precision, recovery, and robustness with minimal demands on sample preparation.

Determination of dimethindene enantiomers in pharmaceuticals by capillary electrophoresis with carboxyethyl-beta-cyclodextrin

Cyclodextrin-mediated capillary zone electrophoresis in a hydrodynamically closed separation system with suppressed electroosmotic flow and UV absorbance photometric detection was developed for a high effective separation and quantitation of dimethindene enantiomers in various pharmaceutical formulations (solution, gel, capsules). The running buffer consisted of epsilon-aminocaproic acid (20 mmol/l) adjusted to pH 4.5 with acetic acid, negatively charged carboxyethyl-beta-cyclodextrin (2.5 mg/ml), serving as chiral selector, and 0.1% (w/v) methylhydroxyethylcellulose, serving as an electroosmotic flow suppressor. The proposed method was successfully validated appraising parameters of sensitivity, linearity, precision, accuracy/recovery and robustness and it is useful for routine use.

COPing with hypoxia

To understand how cells respond to altered oxygenation, a frequent experimental paradigm is to isolate known components of bona fide oxygen responsive proteins. Recent studies have shown that a protein known as CSN5 or JAB1 interacts with both the HIF-1alpha oxygen-responsive transcription factor and its oxygen-dependent regulator, the Von Hippel-Lindau (pVHL) tumor suppressor. CSN5 is a component of the COP9 Signalosome (CSN) which is a multi-subunit protein that has high homology to the lid of the 19S lid of 26S proteasome. The exact function of the CSN5 interaction with pVHL and HIF-1alpha remains to be fully elucidated, but it is clear that the interaction is both oxygen dependent and that CSN5 may play different roles under oxic and hypoxic responses. Further, evidence has also been published indicating that pVHL can be potentially post-translationally modified by CSN5 (de-neddylation) and that CSN5 transcription is regulated by hypoxia as are many of the key pVHL/HIF-1alpha regulatory genes such as the PHDs and OS-9. This review will give a broad overview of known CSN5 and COP9 Signalosome functions and how these functions impact the pVHL/HIF-1alpha signaling complex and potentially other oxygen-sensitive response networks.

Simultaneous Determination of Essential Basic Amino Acids in Pharmaceuticals by Capillary Isotachophoresis

Capillary isotachophoresis (ITP) in cationic regime of the separation with conductometric detection has been used for the separation and determination of basic amino acids (arginine, histidine, and lysine) in pharmaceutical preparations. Several electrolyte systems of different compositions and pH were examined. The optimized ITP electrolyte system consisted of 10 mmol/L potassium acetate adjusted to pH 4.0 with acetic acid as the leading electrolyte with the electroosmotic-flow (EOF) suppressing additive, 0.2% (w/v) methylhydroxyethylcellulose (m-HEC), and 10 mmol/L beta-alanine as the terminating electrolyte. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid and highly reproducible assay of these amino acids. Good quantitation was obtained in short analysis times (a single analysis took about 10 min). The minimal sample pretreatment and low running costs make the proposed ITP method a good alternative to commonly used analytical methods. The obtained results suggest that the proposed method is suitable for routine assay of basic amino acids in pharmaceuticals.

Comparison of capillary zone electrophoresis and isotachophoresis determination of dimethindene enantiomers in pharmaceuticals using charged carboxyethyl-beta-cyclodextrin as a chiral selector

Charged cyclodextrin-mediated capillary electrophoretic methods (capillary zone electrophoresis [CZE] and isotachophoresis [ITP]) in a hydrodynamically closed separation system with suppressed electroosmotic flow and UV absorbance photometric detection (for CZE) or conductivity detection (for ITP) were developed for a highly effective separation and quantitation of dimethindene enantiomers in various pharmaceutical formulations (solution, gel, capsules). Optimized electrolyte systems were based on low-mobility buffer constituents (epsilon-aminocaproic acid, beta-alanine, potassium acetate, acetic acid), negatively charged (at pH > 4.5) carboxyethyl-beta-cyclodextrin (CE-beta-CD), serving as chiral selector, and methylhydroxyethylcellulose, serving as an electroosmotic flow suppressor. Complete enantioseparations of dimethindene in the presence of low concentrations of CE-beta-CD (2.5 mg/ml in CZE, 6.0 mg/ml in ITP) clearly indicated a role of charge of this chiral selector in enantioresolution. It also outlined the potential of charged CD-derivatives as chiral selectors for various CE techniques. The proposed methods were successfully validated, appraising parameters of sensitivity, linearity, precision, accuracy/recovery, and robustness, and then, they were applied to pharmaceutical samples. Consistent results obtained by both CE methods indicate their usefulness for routine use.

[Separation of dimetinden enantiomers in drugs by means of capillary isotachophoresis]

Capillary isotachophoresis was employed to separate and determine dimethinden enantiomers in various dosage forms. Several types of chiral selectors were tested in various electrolyte systems of different composition and different pH. The optimal leading electrolyte was composed of 10 mmol/l potassium acetate and acetic acid to achieve pH 4.8 with an addition of 4 mmol/l carboxyethyl-beta-cyclodextrin as the chiral selector and 0.2% of methylhydroxyethylcellulose (m-HEC) to suppress the electroosmotic flow. The terminating electrolyte was betaalanine of a concentration of 5 mmol/l. The evaluation included the precision, correctness, linearity, robustness, and selectivity of the elaborated ITP method. The pretreatment of the sample prior to analysis consisted in the dissolution and dilution of the appropriate dimethinden-containing dosage form with demineralized water to achieve the required concentration. Such a pretreated sample was directly dosed into the apparatus.

[Isotachophoretic determination of desloratadine in tablets and syrup]

Desloratadine was determined in two dosage forms (tablets and syrup) with the use of the method of capillary isotachophoresis. Several electrolyte systems of varying composition and varying pH were tested. Two electrolyte systems were selected for the validation of the method and determination of desloratadine in real samples. In both electrolyte systems, the precision, correctness, linearity, robustness, and selectivity of the ITP method were evaluated. The pre-treatment of the sample prior to analysis consisted in dissolving and diluting the pertinent desloratadine-containing dosage form with demineralized water to the required concentration. This pre-treated sample was fed directly to the apparatus.

Determination of Salbutamol in Pharmaceuticals by Capillary Electrophoresis

A capillary electrophoresis (CE) method for the separation and determination of salbutamol (SAL) in commercial pharmaceuticals was developed. Several parameters affecting the separations were studied including type and concentration of the carrier ion, counter ion, and the pH of the buffer. A hydrodynamically closed CE separation mode employing a 300 mum I.D. capillary, dynamically coated by polymeric buffer additive, provided good performance parameters (precision, accuracy, sensitivity). The obtained results suggest that the proposed method is suitable for routine assay of SAL in pharmaceutical preparations and can be used as an alternative to the conventional open CE mode for this application.

[Dimethindene determination in various dosage forms by means of capillary isotachophoresis]

Capillary isotachophoresis was employed to determine dimethindene in various dosage forms. Several electrolyte systems of varying compositions and varying pH were tested. For validation of the method and the determination of dimethindene in real samples (gel, drops, capsules), two electrolyte systems were selected. Precision, correctness, linearity, robustness, and selectivity of the ITP method were evaluated for both electrolyte systems. The pre-treatment of the sample prior to analysis consisted in dissolving and diluting the pertinent dosage form containing dimethindene with demineralized water to the required concentration. The sample adjusted in this way was directly dosed into the apparatus.

Enantioselective analysis of cetirizine in pharmaceuticals by cyclodextrin-mediated capillary electrophoresis

The present paper demonstrates the potential of cyclodextrin (CD)-mediated CE for the chiral analysis of a drug of zwitterionic nature, viz. cetirizine (CET). Various separation mechanisms were applied and several parameters affecting the separation were studied, including the type and concentration of chiral selector, coselector, and carrier ion, and pH of buffer. The optimal separation conditions were based on a medium buffer pH (approximately 5.2) (migration velocity of CET molecule was near to zero) and a highly substituted CD derivative, sulfated-beta-CD, serving as an analyte carrier in the anionic regime of the separation with suppressed electroosmotic flow. In this way, a baseline enantioseparation, reasonable separation efficiency, and short analysis time could be easily achieved. Acceptable validation criteria for sensitivity, linearity, precision, accuracy, and robustness were obtained using a hydrodynamically closed CE separation system. The proposed method was successfully applied to the enantioselective assay of CET in pharmaceutical formulations using fexofenadine (FEX) as an internal standard.

Enantioselective determination of pheniramine in pharmaceuticals by capillary electrophoresis with charged cyclodextrin

Cyclodextrin (CD)-mediated capillary zone electrophoresis (CZE) in hydrodynamically closed separation system was developed for the separation and quantitation of pheniramine (PHM) enantiomers. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, carrier cation and counterion, and the pH of the buffer. A high effectivity of oppositely migrating carboxyethyl-beta-cyclodextrin (CE-beta-CD) to separate the PHM enantiomers was demonstrated in detail. The optimized chiral analysis of the antihistamine drug was performed in a buffer consisted of 20 mmol/l epsilon-aminocaproic acid adjusted to pH 4.5 with acetic acid, containing negatively charged CE-beta-CD (2.5 mg/ml) as chiral selector and 0.2% (w/v) methylhydroxyethylcellulose (m-HEC) as an electro-osmotic flow (EOF) suppressor. Acceptable validation criteria for sensitivity, linearity, precision, accuracy/recovery were included. The proposed CZE method was successfully applied to the assay of PHM in pharmaceutical formulations using dioxopromethazine as an internal standard.

[Use of capillary isotachophoresis for the determination of pheniramine in granulated powders]

The method of capillary isotachophoresis was used to assay pheniramine in granulated powders. Several electrolyte systems of different composition and different pH were tested. Two electrolyte systems were selected for the validation of the method and pheniramine determination in real samples. Precision, accuracy, linearity, robustness, and selectivity of the ITP method for both electrolyte systems were evaluated. The pre-treatment of samples prior to analysis consisted in dissolving pheniramine-containing granulated powder in demineralized water and subsequent diluting with demineralized water to required concentration.

Determination of promethazine hydrochloride in pharmaceuticals by capillary isotachophoresis

Capillary isotachophoresis (ITP) in cationic regime of the separation with conductometric detection has been used for the separation and determination of promethazine hydrochloride (PRO) in commercial mass-produced pharmaceutical preparations. Several electrolyte systems of different compositions and pH were examined and the optimized ITP electrolyte system consisted of 10 mmol/l of potassium acetate adjusted to pH 4.8 with acetic acid as the leading electrolyte with electroosmotic flow (EOF) suppressing additive, 0.2% (w/v) methylhydroxyethylcellulose (m-HEC), and 5 mmol/l of beta-alanine as the terminating electrolyte. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid, and highly reproducible assay of promethazine. The calibration graph relating the ITP zone length to concentration of the analyte was rectilinear in the range of 40-200 mg/l of the drug standard, with a coefficient of determination r(2)=0.9992. The relative standard deviation (RSD) was 1.12% (n=6) when determining 100 mg/l of PRO in standard sample. Good quantitation was obtained in short analysis time (a single analysis took 6 min). The recoveries of drug from samples were found to be 97.22% (tablets), 99.72% (injections), and 99.14% (syrup). The minimal sample pretreatment and low running cost make the proposed ITP method a good alternative to commonly used analytical methods.

Analytical characterization of heparin by capillary zone electrophoresis with conductivity detection and polymeric buffer additives

A capillary zone electrophoresis (CZE) method for the analytical characterization of intact (high-molecular-weight) heparin was developed. For the first time, a hydrodynamically closed CZE separation system with conductivity detector was used for the separation, detection and quantitation of this highly sulfated, linear polysaccharide. Glycine (25mM) adjusted to pH 9.0 by bis-Tris-propane served as the running electrolyte system. Polymeric additives, polyvinylpyrrolidone (PVP), dextran (DEX), were used to improve the separation selectivity as they strongly retarded the heparin macromolecule while they did not practically influence comigrating inorganic anions. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid and reproducible assay of heparin in raw materials and isotonic saline. Here, the use of the conductivity detector was advantageous as it allowed heparin to be analyzed without a sample pretreatment. The CZE method should be an alternative to the pharmacopoeial conventional gel electrophoresis having used in the quality control of heparin so far. In addition, it should be convenient to quantitative estimation of heparin present in a preparation used, e.g., as the chiral selector in CE separations.

Capillary zone electrophoresis determination of loratadine in tablets

A capillary electrophoretic method was developed for the determination of loratadine in pharmaceutical formulations. Capillary zone electrophoresis (CZE) separation and UV absorbance photometric detection were carried out in a 160 mm capillary tube with a 300 microm internal diameter, hydrodynamically (membrane) closed. The influences of pH, carrier cation and counter ion on the migration parameters of loratadine were studied and the following conditions were selected: 24 mmol/l glycine as a carrier cation, 1.6 mmol/l citric acid and 84 mmol/l acetic acid as counter ions at pH 3.2, 100 microA and 25 degrees C. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid and highly reproducible assay of loratadine. The determination of loratadine in tablet forms was demonstrated as an application of the method. CZE analysis was completed within 6 min. The detection limit of loratadine was 1.96 micro/mol/l at a 240 nm detection wavelength and the relative standard deviation for its determination was 0.6% for migration time and 1.1% for peak area. CZE in a hydrodynamically closed separation system, used for the first time for the analysis of loratadine, should also be convenient for complex biological sample applications, as it is easily combinable online with the purification CE modes (e.g. ITP).

Chiral separation of dioxopromethazine in eye drops by CZE with charged cyclodextrin

Capillary zone electrophoresis (CZE) with carboxyethyl-beta-cyclodextrin (CE-beta-CD) dissolved in the operating buffer was used for the separation and determination of enantiomers of phenothiazine antihistaminic, dioxopromethazine, in commercial pharmaceutical preparation, eye drops. This chiral selector, negatively charged under given separating conditions (20 mmol/l epsilon -aminocaproic acid, acetic acid, pH 4.5), was effective in enantioresolution of the antihistamine even at its low concentrations (3-6 mg/ml) in the buffer solution. CZE identification and quantitation of the relevant constituents present in the preparation (dioxopromethazine enantiomers, phenylephrine) were based on the response of photometric absorbency detector, operating at a 275 nm detection wavelength. Changes in pH, type and concentration of chiral selector were studied in relation to chiral resolution. Acceptable validation criteria for sensitivity, precision, linearity and repeatability are included.

Capillary isotachophoresis of cystine in urine with on-line isotachophoresis sample pretreatment

Capillary isotachophoresis (ITP) with on-line isotachophoresis sample pretreatment and conductivity detection has been proposed as a method for the separation, detection and determination of cystine present in urine. Sample pretreatment was achieved using a 90 mm FEP capillary tube with a 800 microm internal diameter. ITP separations and conductivity detection were carried out in a 160 mm capillary tube with a 300 microm internal diameter, filled with a hydrochloric acid leading electrolyte and glycine terminating electrolyte, at 50 microA and 25 degrees C. The results show that the proposed method is suitable for resolution of cystine from matrix interferents present in the urine samples and is able to detect it at 10(-4) mol/l concentrations by a universal detection technique after removal of a significant part of the anionic constituents of the sample migrating in the on-line coupled capillary isotachophoresis stack. This simple ITP procedure for monitoring cystine in urine samples requires no sample preparation. This makes it an alternative to the currently used procedures.

Separation of multicomponent mixtures of 2,4-dinitrophenyl labelled amino acids and their enantiomers by capillary zone electrophoresis

The use of capillary zone electrophoresis (CZE) for the separation of a group of 33 2,4-dinitrophenyl labeled amino acids (DNP-AA), including DNP-AA racemates, DNP-L-AA enantiomers and achiral DNP-AAs, was investigated. Alpha-, beta- and gamma-cyclodextrins (CDs) and their derivatives (hydroxypropyl derivatives of alpha-, beta- and gamma-CDs, polymeric beta-CD and 6A-methylamino-beta-cyclodextrin (MA-beta-CD)) served as complexing agents and chiral selectors in this investigation. Although native alpha- and gamma-CDs and their derivatives influenced the effective mobilities of the studied DNP-AAs in different ways, they generally failed to resolve enantiomers of the individual DNP-AAs. On the other hand, beta-CD and all of its derivatives were found to be effective in this respect. Of these, the best results were achieved with a positively charged MA-beta-CD and this chiral selector resolved enantiomers of ten DNP-AA racemates available for this study. However, a complete resolution of these enantiomers in one CZE run required that the effect of the chiral selector be complemented by complexing effects of polyvinyl pyrrolidone (PVP) or gamma-CD. Complexing and chiral recognition capabilities of MA-beta-CD combined with complexing effects of gamma-CD and PVP provided separating conditions suitable for the CZE separations of multicomponent mixtures of DNP-AAs with preserved resolutions of the enantiomers. For example, a mixture consisting of 43 DNP-AA constituents was resolved using an MA-beta-CD/gamma-CD combination with three peak overlaps.

[Occurrence of abnormal late ventricular potentials in myocardial ischemia and the determination of risk of sudden cardiac death in patients after myocardial infarct]

BACKGROUND

The crucial step in prevention of sudden cardiac death (SCD) is a method of a precise and most accessible identification of those patients with ischaemic cardiac disease (ICD), especially after MI, who are highly presumptive candidates of malign ventricular arrhythmias. The selection of individuals exposed to risk, and individual judgment of the threat to patients after MI is a complex problem. Patients after MI are endangered by reinfarction, cardiac failure, heart wall rupture and primary ventricular tachyarrhythmia. Stratification of patients exposed to a presumably higher risk of probable new coronary event and malign ventricular arrhythmia with an early decision to intervene, gains practical clinical significance. Similarly, it is important to identify also the patients after MI exposed to lower risk, who need no interventional therapeutical procedure. The cardiologic practice utilizes several examinatory procedures and tests, prevailingly of non-invasive character.

AIMS AND OBJECTIVES

The study reviews the latest information on pathophysiology and current level of clinical interpretation of non-invasive ecg procedure from the field of high-resolution electrocardiography including the late ventricular potentials (LVP). The study is aimed at: a) presentation of a review of available information from the field of electrophysiology and clinical electrocardiography and the mechanism of impact of myocardial ischaemia on the existence of high-frequency, but at the same time extremely low-amplitude potentials abnormalities in the course of QRS complex and S-T segment (LVP), b) presentation of a review on the informative value and clinical significance produced by non-invasively detected electrophysiological heterogeneity of myocardium during ischaemia, aiding the short-term and long-term prognosis judgments in patients with ICD, especially after undergoing its most serious form--myocardial infarction. Beside the group analysis the study is also aimed at individual non-invasive judgment of risk of the development of malign ventricular arrhythmias in patients with acute coronary syndromes. (Fig. 3, Ref. 41.)

Intracellular polymerization of the serpin plasminogen activator inhibitor type 2

Plasminogen activator inhibitor type 2 (PAI-2) is synthesized in two molecular forms: an intracellular, nonglycosylated form and an extracellular, glycosylated form. The bitopological distribution of PAI-2 is caused by an inefficient internal secretion signal. In addition, the secretion efficiency of PAI-2 seems to differ, depending on the cell type, differentiation state, and culture conditions. In recombinant cell clones designed for the synthesis of the secreted form of PAI-2, the fraction of secreted PAI-2 decreased with increasing expression levels. Subcellular fractionation of cell clones with higher expression levels revealed that PAI-2 accumulating in the cell was mainly associated with the organelles of the secretory pathway. Electrophoresis under nondenaturating conditions revealed that the PAI-2 retained at higher expression levels was mainly polymerized. Polymers of PAI-2 were also detected in cytosolic extracts prepared from human placenta and phorbol ester-stimulated U 937 cells, indicating that intracellular polymerization of PAI-2 may occur in the cytosols of cells that normally express PAI-2 under physiological conditions. When purified PAI-2 or cellular extracts were incubated at 37 degrees C for 24 h most of the PAI-2 protein was found to polymerize. Polymer formation was prevented by the addition of synthetic peptides with sequences corresponding to residues P2 to P14 in the reactive center loop of PAI-2 and antithrombin. These synthetic peptides also caused dissociation of prepolymerized purified PAI-2 and PAI-2 polymers in cellular extracts. Incubation with unrelated peptides of the same size had no effect on polymer formation or dissociation of preformed polymers, indicating that polymerization of PAI-2 occurs by the loop-sheet mechanism. Taken together, our data suggest that the wild-type form of PAI-2, like some natural pathological genetic variants of alpha1-antitrypsin, antithrombin, and C1 inhibitor readily polymerizes intracellularly and that polymerization may lead to a reduced secretion efficiency.

Plasminogen-activator inhibitor type 2 (PAI-2) is a spontaneously polymerising SERPIN. Biochemical characterisation of the recombinant intracellular and extracellular forms

Plasminogen-activator inhibitor type 2 (PAI-2) is a specific inhibitor of plasminogen activators (PA) that exists in an intracellular, low-molecular-mass form and a secreted, high-molecular-mass form that varies with respect to glycosylation. Here we have developed expression systems for both forms of PAI-2 and biochemically characterised the purified proteins. In order to obtain efficient secretion, we constructed an artificial signal sequence and fused it to the coding region of PAI-2. With this construct, more than 90% of PAI-2 was secreted as a glycosylated, 60-kDa molecular-mass form, but the level of expression was low and unstable. To obtain higher expression of secreted PAI-2, a novel expression vector based on the Semliki-forest-virus replicon was used. Secreted PAI-2 was purified to homogeneity and N-terminal sequence analysis showed that the artificial signal peptide was correctly removed. The intracellular, non-glycosylated form of PAI-2 was expressed in Escherichia coli and purified to homogeneity. Both the secreted and the intracellular forms of PAI-2 were found to inhibit plasminogen activators by forming SDS-resistant complexes and the second-order rate constants were similar for both forms, ranging over 2.4-2.7 x 10(6) M-1s-1 for urokinase-type PA, 2.5-2.7 x 10(5) M-1s-1 for two-chain tissue-type PA and 0.8-1.2 x 10(4) M-1s-1 for single-chain tissue-type PA. None of the purified PAI-2 forms bound to vitronectin. Circular-dichroism spectral analysis revealed that PAI-2 has a CD spectrum that resembles ovalbumin more than PA-inhibitor type 1, confirming the greater similarity between these two members of the serine-protease inhibitor family. Similar to what has been described for the Z-form of alpha 1-antitrypsin, purified PAI-2 was found to spontaneously form polymers during incubation at room temperature. Attempts to convert PAI-2 to a stable locked conformation resembling the conformation of latent PAI-1 by treatment with diluted guanidinium chloride were unsuccessful. Instead, this treatment enhanced the formation of PAI-2 polymers, possibly by the loop-sheet polymerisation mechanism described for alpha 1-antitrypsin.