A proton magnetic resonance spectral study of heparin

Approaches to Assure Similarity between Pharmaceutical Heparins from Two Different Manufacturers

Pharmaceutical heparins from different manufacturers may present heterogeneities due to particular extraction and purification procedures or even variations in the raw material manipulation. Heparins obtained from different tissues also differ in their structure and activity. Nevertheless, there is an increased demand for more accurate assessments to ensure the similarities of pharmaceutical heparins. We propose an approach to accurately assess the similarity of these pharmaceutical preparations based on well-defined criteria, which are verified with a variety of refined analytical methods. We evaluate six commercial batches from two different manufacturers which were formulated with Brazilian or Chinese active pharmaceutical ingredients. Biochemical and spectroscopic methods and analysis based on digestion with heparinases were employed to evaluate the purity and structure of the heparins. Specific assays were employed to evaluate the biological activity. We observed minor but significant differences between the constitutive units of the heparins from these two manufacturers, such as the content of N-acetylated α-glucosamine. They also have minor differences in their molecular masses. These physicochemical differences have no impact on the anticoagulant activity but can indicate particularities on their manufacturing processes. The protocol we propose here for analyzing the similarity of unfractionated heparins is analogous to those successfully employed to compare low-molecular-weight heparins.

Purification of the human fibroblast growth factor 2 using novel animal-component free materials

This paper analyzes the use of animal-component free chromatographic materials for the efficient purification of the human fibroblast growth factor 2 (hFGF-2). hFGF-2 is produced in Escherichia coli and purified via three different chromatography steps, which include a strong cation exchange chromatography as a capture step, followed by heparin affinity chromatography and an anion exchange chromatography as a polishing step. The affinity chromatography step is based on the animal-derived material heparin. Chemically produced ligands provide a viable alternative to animal-derived components in production processes, since they are characterized by a defined structure which leads to reproducible results and a broad range of applications. The alternative ligands can be assigned to adsorber of the mixed-mode chromatography (MMC) and pseudo-affinity chromatography. Eight different animal-component free materials used as adsorbers in MMC or pseudo-affinity chromatography were tested as a substitute for heparin. The MMCs were cation exchangers characterized with further functional residues. The ligands of the pseudo-affinity chromatography were heparin-like ligands which are based on heparin's molecular structure. The alternative methods were tested as a capture step and in combination with another chromatographic step in the purification procedure of hFGF-2. In each downstream step purity, recovery and yield were analysed and compared to the conventional downstream process. Two types of MMC - the column Foresight^TM Nuvia^TM cPrime^TM from Bio-Rad Laboratories and the column HiTrap^TM Capto^TM MMC from GE Healthcare Life Sciences - can be regarded as effective animal-component free alternatives to the heparin - based adsorber.

Heparin: role in protein purification and substitution with animal-component free material

Heparin is a highly sulfated polysaccharide which belongs to the family of glycosaminoglycans. It is involved in various important biological activities. The major biological purpose is the inhibition of the coagulation cascade to maintain the blood flow in the vasculature. These properties are employed in several therapeutic drugs. Heparin’s activities are associated with its interaction to various proteins. To date, the structural heparin-protein interactions are not completely understood. This review gives a general overview of specific patterns and functional groups which are involved in the heparin-protein binding. An understanding of the heparin-protein interactions at the molecular level is not only advantageous in the therapeutic application but also in biotechnological application of heparin for downstreaming. This review focuses on the heparin affinity chromatography. Diverse recombinant proteins can be successfully purified by this method. While effective, it is disadvantageous that heparin is an animal-derived material. Animal-based components carry the risk of contamination. Therefore, they are liable to strict quality controls and the validation of effective good manufacturing practice (GMP) implementation. Hence, adequate alternatives to animal-derived components are needed. This review examines strategies to avoid these disadvantages. Thereby, alternatives for the provision of heparin such as chemical synthesized heparin, chemoenzymatic heparin, and bioengineered heparin are discussed. Moreover, the usage of other chromatographic systems mimetic the heparin effect is reviewed.

Re-visiting the structure of heparin

The sulfated polysaccharide heparin has been used as a life-saving anticoagulant in clinics well before its detailed structure was known. This mini-review is a survey of the evolution in the discovery of the primary and secondary structure of heparin. Highlights in this history include elucidation and synthesis of the specific sequence that binds to antithrombin, the development of low-molecular-weight heparins currently used as antithrombotic drugs, and the most promising start of chemo-enzymatic synthesis. Special emphasis is given to peculiar conformational properties contributing to interaction with proteins that modulate different biological properties.

Low-molecular-weight heparins: differential characterization/physical characterization

Low-molecular-weight heparins (LMWHs), derived from unfractionated heparin (UFH) through different depolymerization processes, have advantages with respect to the parent heparin in terms of pharmacokinetics, convenience of administration, and reduced side effects. Each LMWH can be considered as an independent drug with its own activity profile, placing significance on their biophysical characterization, which will also enable a better understanding of their structure-function relationship. Several chemical and physical methods, some involving sample modification, are now available and are reviewed.

Heparin-protein interactions

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

Physiochemical characterization of low molecular weight heparin

Nuclear magnetic resonance spectroscopy (NMR), Raman spectroscopy, dynamic light scattering (DLS), and high performance exclusion chromatography (HPEC) were used to characterize two different commercial preparations of low molecular weight (LMW) heparin, produced either by peroxide cleavage or deaminative cleavage using nitrous acid. Proton NMR showed < 2% contamination by dermatan sulfate in the material produced by deaminative cleavage using nitrous acid and < 4% for the material produced by peroxide cleavage. The Raman spectra of the nitrous acid produced material showed an equivalent amount of O-sulfation to that in the material produced by peroxide, but about a 10% reduction in the content of N-sulfated glucosamine, as expected from the deamination reaction. DLS and HPEC indicated the presence of < 0.2% of very high molecular weight/aggregate material for the peroxide preparation compared to 1% for the nitrous acid-prepared material. The weight average molecular weight (Mw) determined from HPEC was 5900 Da for the nitrous acid-prepared material and 6850 Da for the peroxide-produced material. The number average molecular weight (Mn) calculated from this data was 5200 Da for the nitrous acid preparation and 5300 Da for the peroxide-produced material. In addition, the nitrous acid-prepared material exhibited a much narrower size distribution of oligomeric species, as evidenced by the polydispersity (Mw/Mn) of 1.1 for the nitrous acid-prepared material, as compared with a value of 1.3 for the peroxide-prepared material. These studies demonstrate that significant differences between preparations of LMW heparin can be resolved using these techniques. This is of critical importance in the design of quality assurance methods.

Regioselectivity in the sulfation of some chemically-modified heparins, and observations on their cation-binding characteristics

Two modified forms of heparin, polymers A and B, have been prepared, one containing residues of nonsulfated alpha-L-idopyranosyluronic acid (3) and the other residues of alpha-L-galactopyranosyluronic acid (7), in place of the normal alpha-L-idopyranosyluronic acid 2-sulfate (1). In addition, both A and B contained 2-acetamido-2-deoxy-alpha-D-glucopyranosyl 6-sulfate residues (6) in place of the corresponding N-sulfated residues (2) of the original heparin. These polymers were subjected to sulfation under various conditions. Examination of the products by NMR spectroscopy showed that polymer A was sulfated initially at position-3 of residue 3, and that slower substitution occurred at position-3 of 6. By contrast, polymer B exhibited low regioselectivity, as sulfation occurred with about equal facility at positions-2 and -3 of 7, and -3 of 6. The sulfation products had no significant anti Xa activity. Based on the paramagnetic effects of Cu2+ and chemical shift displacements induced by Ca2+, NMR spectroscopy was used to compare cation-binding properties of A and B with those of heparin. In contrast to heparin, which forms a complex with Cu2+ detectable at a level of < 10(-3) mol per dimeric unit of the polymer, neither A nor B exhibited an interaction with the cation. However, polymer A was found to bind Ca2+, in this respect being distinct from the related modification, 1-->6, which contains a 2-sulfate group in 1, as well as from polymer B.

Regioselectivity in the sulfation of dermatan sulfate and methyl 4,6-O-benzylidene-alpha-D-idopyranoside

The sulfation of dermatan sulfate by SO3-trimethylamine in N,N-dimethylformamide led to substitution initially at HO-6 of residues of 2-acetamido-2-deoxy-beta-D-galactopyranosyl 4-sulfate (1), to produce the 4,6-disulfate (6). When this step reached a level of greater than 50%, sulfation occurred with equal facility at HO-2 and HO-3 of residues of alpha-L-idopyranosyluronic acid (2), giving rise to a mixture of 2-,3-, and 2,3-disulfates. An analogous substitution pattern was observed for HO-2 and -3 of a simpler idopyranose unit, in the sulfation of methyl 4,6-O-benzylidene-alpha-D-idopyranoside (12). This lack of regioselectivity in the reaction of 2 (and 12) contrasts markedly with the high affinity of the reagent for HO-3 of residues of alpha-L-idopyranosyluronic acid present in a modified form of heparin. It is attributed to a difference between the two polymers in the relative orientation of their neighboring amino sugar residues, whereby there is an unobstructed access of the reagent in one instance, and hindrance of HO-2 selectively in the other. Enzymolysis by chondroitinase ABC was found to yield unsaturated disaccharide containing residues of 4,6-disulfate, as well as larger fragments containing unsaturated glycosyl groups derived from L-idopyranosyluronic acid 2-sulfate, evidence of a relatively broad enzyme specificity. The presence of extra sulfate groups in dermatan sulfate did not enhance its weak antithrombotic activity, as measured by anti Xa assay, in disagreement with earlier reports.

Physicochemical characterization of the First World Health Organization International Standard for low molecular weight heparin derivatives

High-field (300 MHz) 1H NMR spectral analysis and particle size distribution analysis employing the quasielastic light scattering (QELS) technique were performed on samples of the 1st International Standard for low molecular weight (LMW) heparin derivatives recently selected by the World Health Organization (WHO). We propose that the results of these analyses, which showed that the material is highly homogeneous in particle size and retains spectral features characteristic of its porcine mucosal origin, form an appropriate basis for physicochemical comparison between the "Standard" and other LMW heparin preparations.

Heparin in molluscs: chemical, enzymatic degradation and 13C and 1H n.m.r. spectroscopical evidence for the maintenance of the structure through evolution

The structural features and anticoagulant activity of heparins isolated from three species of molluscs (Anomalocardia brasiliana, Donnax striatus and Tivela mactroides) are reported. It is shown by chemical analyse, type of products formed by action of heparinase and heparitinase II, anticoagulant activity, 13C and 1H n.m.r. spectroscopy, that the mollusc heparins are virtually indistinguishable from heparins present in mammalian tissues. These data, taken as a whole, suggest that heparin has maintained its main structural features through evolution. The implications of these findings are discussed.

Nuclear magnetic resonance spectra of heparin in admixture with dermatan sulfate and other glycosaminoglycans. 2-D spectra of the chondroitin sulfates

Characteristics of the 1H-n.m.r. spectra of heparin admixed with other glycosaminoglycans are described with respect to the identification of the latter as possible contaminants of pharmaceutical heparins. Chemical shift differences are sufficiently large, particularly with the aid of resolution enhancement, to allow for the detection of dermatan sulfate, chondroitin 4- or 6-sulfate, hyaluronic acid, or heparan sulfate as a minor constituent in the presence of heparin. The acetamidomethyl resonance region (delta 1.95-2.15) is especially useful in this context, both for identification and quantitative estimation. Whereas dermatan sulfate is a common contaminant of pharmaceutical heparin preparations, in some instances comprising 10-15 percent of the polymer mixture, the other glycosaminoglycans, by contrast, were not detected in such preparations. Two-dimensional heterocorrelation and homo-correlation n.m.r. experiments have provided 1H- and 13C-chemical shift data that complete or verify (or both) previous information available for heparin, dermatan sulfate, and chondroitin 4- and 6-sulfates (chondroitins A and C).

Monitoring the purity of pharmaceutical heparin preparations by high-field 1H-nuclear magnetic resonance spectroscopy

High-field (300 MHz) 1H NMR spectral analyses are reported for various sodium or calcium heparin products available on the Canadian market. Dermatan sulfate (chondroitin sulfate B) was detected as a contaminant in virtually all of these products. Its content varied among the suppliers from less than 1 to 15%, and also over nearly the same range within the groups of heparin preparations of particular suppliers. No correlation was found between in vitro biological activities (potency and anti-factor Xa by the USP tests) and the levels of dermatan sulfate found. Other components, or unlisted constituents, detected in some preparations were paramagnetic metal ions, polyols, and lidocaine.

N.m.r. spectroscopic observations related to the function of sulfate groups in heparin. Calcium binding vs. biological activity

Chemically-modified heparins containing different combinations of N- and O-sulfate groups were prepared. Characterized by high field 1H- and 13C-n.m.r. spectroscopy, the polymers exhibited chemical shift variations in general accord with shielding differences expected on removal of sulfate substituents, and additional variations that probably arose from conformational changes in the polymers. Whereas the anticoagulant activity of heparins, as measured by USP, anti-Xa, and thrombin-time assays, was invariably reduced by the chemical transformations effected, the ability of heparin to bind calcium ions was found to be dependent on retention of the 2-sulfamino group, whether or not O-sulfate groups were present. The results suggest that the 2-sulfamino group is essential for maintaining a molecular conformation consistent with the ability for the L-iduronic acid residues to complex with calcium ions. Also, they show that although the anticoagulant and calcium-binding properties of heparin may be interdependent, they are not determined by the same structural entities in the polymer.

Heparan sulphates from porcine intestinal mucosa. Preparation and physicochemical properties

A series of fractions of heparan sulphate has been prepared from the glycosaminoglycuronans of porcine intestinal mucosa, in order to relate their physicochemical properties with their biochemical and biological activities. They fall into three classes which may be distinguished by differences in molecular weight distribution and in extent of sulphation. For heterogeneous polymers such as heparan sulphates purification and fractionation must be regarded as interchangeable terms, and some preparative procedures appear to have rather specific effects on the properties of samples isolated by their use. Such considerations apply particularly in the undemarcated boundary region between heparan sulphates and heparin, a region which includes certain 'high activity' heparin fractions of current biological and clinical interest.

Glycosaminoglycans: structure and interaction

In the last few years, there has been considerable progress in the studies on glycosaminoglycans, a group of acidic polysaccharides present in the intercellular matrix of connective tissue. X-ray diffraction studies have indicated that these polymers can exist in the condensed phase in some helical form. Chiroptical and hydrodynamic measurements have provided significant information regarding the molecular conformation in solution and other physicochemical properties of the polymers. Studies related to the interaction properties of glycosaminoglycans with polypeptides, metal ions, and other molecules are numerous. This review covers mainly the results and their interpretations of both published and as yet unpublished material of the 1970s, but certain previous data are also included. A present-day concept regarding the structure and interaction properties of these molecules on the basis of various physicochemical measurements is presented. The biosynthesis and metabolism of glycosaminoglycans, and the structure of proteoglycans and glycoproteins, are not discussed.