Comparison of established and novel purity tests for the quality control of heparin by means of a set of 177 heparin samples

Chemical and biological differences between original and mimetic pentosan polysulfates

Pentosan polysulfate sodium (PPS) is a semi-synthetic, heparin-like polysaccharide with manifold therapeutic actions. It is approved for treatment of bladder pain syndrome / interstitial cystitis in humans and treatment of musculoskeletal diseases in animals. PPS is produced by a complex procedure using beech wood as starting material. It consists of a mixture of sulfated glucuronoxylans, whose structural composition cannot be fully characterized by physicochemical analysis. The question arises whether PPS follow-on products are identical with the original and thus meet the requirement for generic drug application. The aim of this study was to investigate whether commercially available PPS products differ in physicochemical characteristics and biological effects from the original. Ten PPS preparations from different manufactures were analyzed using orthogonal analytical techniques including, inter alia, size exclusion chromatography with triple detection, nuclear magnetic resonance spectroscopy, and high-resolution mid-infrared spectroscopy in aqueous solution with chemometric evaluation. For functional analysis, we measured the plasma kallikrein generation in human plasma and FXII activation. The study revealed significant structural and biological differences between PPS from different sources. Therefore, follow-on products cannot be considered identical but at best similar to original PPS. However, their similar efficacy and safety have still to be proven by comprehensive studies.

Is infrared spectroscopy combined with multivariate analysis a promising tool for heparin authentication?

The investigation of the possibility to determine various characteristics of powder heparin (n = 115) was carried out with infrared spectroscopy. The evaluation of heparin samples included several parameters such as purity grade, distributing company, animal source as well as heparin species (i.e. Na-heparin, Ca-heparin, and heparinoids). Multivariate analysis using principal component analysis (PCA), soft independent modelling of class analogy (SIMCA), and partial least squares - discriminant analysis (PLS-DA) were applied for the modelling of spectral data. Different pre-processing methods were applied to IR spectral data; multiplicative scatter correction (MSC) was chosen as the most relevant. Obtained results were confirmed by nuclear magnetic resonance (NMR) spectroscopy. Good predictive ability of this approach demonstrates the potential of IR spectroscopy and chemometrics for screening of heparin quality. This approach, however, is designed as a screening tool and is not considered as a replacement for either of the methods required by USP and FDA.

Tools for the Quality Control of Pharmaceutical Heparin

Heparin is a vital pharmaceutical anticoagulant drug and remains one of the few naturally sourced pharmaceutical agents used clinically. Heparin possesses a structural order with up to four levels of complexity. These levels are subject to change based on the animal or even tissue sources that they are extracted from, while higher levels are believed to be entirely dynamic and a product of their surrounding environments, including bound proteins and associated cations. In 2008, heparin sources were subject to a major contamination with a deadly compound-an over-sulphated chondroitin sulphate polysaccharide-that resulted in excess of 100 deaths within North America alone. In consideration of this, an arsenal of methods to screen for heparin contamination have been applied, based primarily on the detection of over-sulphated chondroitin sulphate. The targeted nature of these screening methods, for this specific contaminant, may leave contamination by other entities poorly protected against, but novel approaches, including library-based chemometric analysis in concert with a variety of spectroscopic methods, could be of great importance in combating future, potential threats.

Simple and rapid quality control of sulfated glycans by a fluorescence sensor assay--exemplarily developed for the sulfated polysaccharides from red algae Delesseria sanguinea

Sulfated polysaccharides (SP) from algae are of great interest due to their manifold biological activities. Obstacles to commercial (especially medical) application include considerable variability and complex chemical composition making the analysis and the quality control challenging. The aim of this study was to evaluate a simple microplate assay for screening the quality of SP. It is based on the fluorescence intensity (FI) increase of the sensor molecule Polymer-H by SP and was originally developed for direct quantification of SP. Exemplarily, 65 SP batches isolated from the red alga Delesseria sanguinea (D.s.-SP) and several other algae polysaccharides were investigated. Their FI increase in the Polymer-H assay was compared with other analytical parameters. By testing just one concentration of a D.s.-SP sample, quality deviations from the reference D.s.-SP and thus both batch-to-batch variability and stability can be detected. Further, structurally distinct SP showed to differ in their concentration-dependent FI profiles. By using corresponding reference compounds, the Polymer-H assay is therefore applicable as identification assay with high negative predictability. In conclusion, the Polymer-H assay showed to represent not only a simple method for quantification, but also for characterization identification and differentiation of SP of marine origin.

High-throughput differentiation of heparin from other glycosaminoglycans by pyrolysis mass spectrometry

Sensors with high chemical specificity and enhanced sample throughput are vital to screening food products and medical devices for chemical or biochemical contaminants that may pose a threat to public health. For example, the rapid detection of oversulfated chondroitin sulfate (OSCS) in heparin could prevent reoccurrence of heparin adulteration that caused hundreds of severe adverse events including deaths worldwide in 2007-2008. Here, rapid pyrolysis is integrated with direct analysis in real time (DART) mass spectrometry to rapidly screen major glycosaminoglycans, including heparin, chondroitin sulfate A, dermatan sulfate, and OSCS. The results demonstrate that, compared to traditional liquid chromatography-based analyses, pyrolysis mass spectrometry achieved at least 250-fold higher sample throughput and was compatible with samples volume-limited to about 300 nL. Pyrolysis yielded an abundance of fragment ions (e.g., 150 different m/z species), many of which were specific to the parent compound. Using multivariate and statistical data analysis models, these data enabled facile differentiation of the glycosaminoglycans with high throughput. After method development was completed, authentically contaminated samples obtained during the heparin crisis by the FDA were analyzed in a blinded manner for OSCS contamination. The lower limit of differentiation and detection were 0.1% (w/w) OSCS in heparin and 100 ng/μL (20 ng) OSCS in water, respectively. For quantitative purposes the linear dynamic range spanned approximately 3 orders of magnitude. Moreover, this chemical readout was successfully employed to find clues in the manufacturing history of the heparin samples that can be used for surveillance purposes. The presented technology and data analysis protocols are anticipated to be readily adaptable to other chemical and biochemical agents and volume-limited samples.

Glycosaminoglycan-mediated selective changes in the aggregation states, zeta potentials, and intrinsic stability of liposomes

Though the aggregation of glycosaminoglycans (GAGs) in the presence of liposomes and divalent cations has been previously reported, the effects of different GAG species and minor changes in GAG composition on the aggregates that are formed are yet unknown. If minor changes in GAG composition produce observable changes in the liposome aggregate diameter or zeta potential, such a phenomenon may be used to detect potentially dangerous oversulfated contaminants in heparin. We studied the mechanism of the interactions between heparin and its oversulfated glycosaminoglycan contaminants with liposomes. Herein, we demonstrate that Mg(2+) acts to shield the incoming glycosaminoglycans from the negatively charged phosphate groups of the phospholipids and that changes in the aggregate diameter and zeta potential are a function of the glycosaminoglycan species and concentration as well as the liposome bilayer composition. These observations are supported by TEM studies. We have shown that the organizational states of the liposome bilayers are influenced by the presence of GAG and excess Mg(2+), resulting in a stabilizing effect that increases the T(m) value of DSPC liposomes; the magnitude of this effect is also dependent on the GAG species and concentration present. There is an inverse relationship between the percent change in aggregate diameter and the percent change in aggregate zeta potential as a function of GAG concentration in solution. Finally, we demonstrate that the diameter and zeta potential changes in POPC liposome aggregates in the presence of different oversulfated heparin contaminants at low concentrations allow for an accurate detection of oversulfated chondroitin sulfate at concentrations of as low as 1 mol %.

Electrophoresis for the analysis of heparin purity and quality

The adulteration of raw heparin with oversulfated chondroitin sulfate (OSCS) in 2007-2008 produced a global crisis resulting in extensive revisions to the pharmacopeia monographs and prompting the FDA to recommend the development of additional methods for the analysis of heparin purity. As a consequence, a wide variety of innovative analytical approaches have been developed for the quality assurance and purity of unfractionated and low-molecular-weight heparins. This review discusses recent developments in electrophoresis techniques available for the sensitive separation, detection, and partial structural characterization of heparin contaminants. In particular, this review summarizes recent publications on heparin quality and related impurity analysis using electrophoretic separations such as capillary electrophoresis (CE) of intact polysaccharides and hexosamines derived from their acidic hydrolysis, and polyacrylamide gel electrophoresis (PAGE) for the separation of heparin samples without and in the presence of its relatively specific depolymerization process with nitrous acid treatment.

In vivo and in vitro hemostatic activity of Chromolaena odorata leaf extract

CONTEXT

Chromolaena odorata (L.) R.M.King & H.Rob. (Asteraceae) or Siam weed has long been used to stop bleeding in Thailand and many countries. Only the aqueous leaf extract was investigated in in vivo and there have been conflicting results of in vitro hemostatic mechanisms of this plant.

OBJECTIVE

The most appropriate C. odorata leaf extract that promoted the highest hemostatic activity and the hemostatic mechanisms of these plant extracts will be investigated.

MATERIALS AND METHODS

The lyophilized aqueous leaf extract and alcoholic (50, 70, and 95% ethanol) extracts from the fresh and dried leaves were investigated both in vivo and in vitro. The bleeding time in male Wistar rats was measured to investigate the hemostatic effect. The hemostatic mechanisms were tested using in vitro platelet aggregation and blood coagulation tests in sheep plasma.

RESULTS

All extracts displayed significantly reducing bleeding time (<2.5 min) in rats but did not induce platelet aggregation or blood clotting in the in vitro study. The in vitro blood clotting times of all extracts were >0.6 min. Ethanol extract (70%) from the dried leaves proved to be the extract producing the highest hemostatic activity in vivo with the bleeding time of 1.85 min.

DISCUSSION AND CONCLUSION

The in vivo study with rats confirmed the significant ability of this plant extract to stop bleeding. However, the sufficient amount of calcium and active compounds which are aggregating and clotting agents to enhance blood coagulation and platelet aggregation in in vitro tests should be further studied.

The use of glycoinformatics in glycochemistry

Glycoinformatics is a small but growing branch of bioinformatics and chemoinformatics. Various resources are now available that can be of use to glycobiologists, but also to chemists who work on the synthesis or analysis of carbohydrates. This article gives an overview of existing glyco-specific databases and tools, with a focus on their application to glycochemistry: Databases can provide information on candidate glycan structures for synthesis, or on glyco-enzymes that can be used to synthesize carbohydrates. Statistical analyses of glycan databases help to plan glycan synthesis experiments. 3D-Structural data of protein-carbohydrate complexes are used in targeted drug design, and tools to support glycan structure analysis aid with quality control. Specific problems of glycoinformatics compared to bioinformatics for genomics or proteomics, especially concerning integration and long-term maintenance of the existing glycan databases, are also discussed.

Liquid chromatography-nuclear magnetic resonance coupling as alternative to liquid chromatography-mass spectrometry hyphenations: curious option or powerful and complementary routine tool?

Combining the most powerful separation techniques, i.e. liquid chromatography (LC) or capillary electrophoresis (CE) with a information rich detection system - the mass spectrometer or the nuclear magnetic resonance (NMR) spectrometer - has been pursued for more than three decades. This compilation shall provide an overview of the advantages and limitations of the LC-NMR hyphenation in the light of its most valued application-the unequivocal analyte identification. Especially the post LC trapping of analytes with an in-line solid phase extraction (SPE) device prior to transferring the analyte of interest to the NMR spectrometer (LC-SPE-NMR) proved to be a robust installation allowing a significant cut-down of the amount of analyte needed for the generation of high quality heteronuclear NMR shift correlation data. Different available technical realizations will be discussed and typical application examples from natural product research and from industrial settings will be given.

Heparin sodium compliance to USP monograph: structural elucidation of an atypical 2.18 ppm NMR signal

The ¹H nuclear magnetic resonance (NMR) acceptance criteria in the new heparin US Pharmacopeia (USP) monograph do not take into account potential structural modifications responsible for any extra signals observed in ¹H NMR spectra, some purified heparins may be non-compliant under the proposed new USP guidelines and incorrectly classified as unsuitable for pharmaceutical use. Heparins from the "ES" source, containing an extra signal at 2.18 ppm, were depolymerized under controlled conditions using heparinases I, II, and III. The oligosaccharides responsible for the 2.18 ppm signal were enriched using orthogonal chromatographic techniques. After multiple purification steps, we obtained an oligosaccharide mixture containing a highly enriched octasaccharide bearing the structural modification responsible for the extra signal. Following heparinase I depolymerization, a pure tetrasaccharide containing the fingerprint structural modification was isolated for full structural determination. Using 1D and 2D ¹H NMR spectroscopy, the structural moiety responsible for the extra signal at 2.18 ppm was identified as an acetyl group on the heparin backbone, most likely resulting from a very minor manufacturing process side reaction that esterifies the uronic acid at position 3. Such analytical peculiarity has always been present in this heparin source and it was used safety over the years.

Competitive inhibition of heparinase by persulfonated glycosaminoglycans: a tool to detect heparin contamination

Heparin and the low molecular weight heparins are extensively used as medicinal products to prevent and treat the formation of venous and arterial thrombi. In early 2008, administration of some heparin lots was associated with the advent of severe adverse effects, indicative of an anaphylactoid-like response. Application of orthogonal analytical tools enabled detection and identification of the contaminant as oversulfated chondroitin sulfate (OSCS) was reported in our earlier report. Herein, we investigate whether enzymatic depolymerization using the bacterially derived heparinases, given the structural understanding of their substrate specificity, can be used to identify the presence of OSCS in heparin. We also extend this analysis to examine the effect of other persulfonated glycosaminoglycans (GAGs) on the action of the heparinases. We find that all persulfonated GAGs examined were effective inhibitors of heparinase I, with IC(50) values ranging from approximately 0.5-2 μg/mL. Finally, using this biochemical understanding, we develop a rapid, simple assay to assess the purity of heparin using heparinase digestion followed by size-exclusion HPLC analysis to identify and quantify digestion products. In the context of the assay, we demonstrate that less than 0.1% (w/w) of OSCS (and other persulfonated polysaccharides) can routinely be detected in heparin.

High-sensitivity visualisation of contaminants in heparin samples by spectral filtering of 1H NMR spectra

A novel application of two-dimensional correlation analysis has been employed to filter (1)H NMR heparin spectra distinguishing acceptable natural variation and the presence of foreign species. Analysis of contaminated heparin samples, compared to a dataset of accepted heparin samples using two-dimensional correlation spectroscopic analysis of their 1-dimensional (1)H NMR spectra, allowed the spectral features of contaminants to be recovered with high sensitivity, without having to resort to more complicated NMR experiments. Contaminants, which exhibited features distinct from those of heparin and those with features normally hidden within the spectral mass of heparin could be distinguished readily. A heparin sample which had been pre-mixed with a known contaminant, oversulfated chondroitin sulfate (OSCS), was tested against the heparin reference library. It was possible to recover the (1)H NMR spectrum of the OSCS component through difference 2D-COS power spectrum analysis of as little as 0.25% (w/w) with ease, and of 2% (w/w) for more challenging contaminants, whose NMR signals fell under those of heparin. The approach shows great promise for the quality control of heparin and provides the basis for greatly improved regulatory control for the analysis of heparin, as well as other intrinsically heterogeneous and varied products.