Bleeding associated with heparin contaminants

Interactions of oversulfated chondroitin sulfate (OSCS) from different sources with unfractionated heparin

In 2008, oversulfated chondroitin sulfate (OSCS) was identified as the main contaminant in recalled heparin. Oversulfated chondroitin sulfate can be prepared from bovine (B), porcine (P), shark (Sh), or skate (S) origin and may produce changes in the antithrombotic, bleeding, and hemodynamic profile of heparins. This study examines the interactions of various OSCSs on heparin in animal models of thrombosis and bleeding, as well as on the anticoagulant and antiprotease effects in in vitro assays. Mixtures of 70% unfractionated heparin (UFH) with 30% OSCS from different sources were tested. In the in vitro activated partial thromboplastin time (aPTT) assay, all contaminant mixtures showed a decrease in clotting times. In addition, a significant increase in bleeding time compared to the control (UFH/saline) was observed. In the thrombosis model, no significant differences were observed. The OSCSs significantly increased anti-Xa activity in ex vivo blood samples. These results indicate that various sources of OSCS affect the hemostatic properties of heparin.

A robust method to quantify low molecular weight contaminants in heparin: detection of tris(2-n-butoxyethyl) phosphate

Recently, oversulfated chondroitin sulfate (OSCS) was identified in contaminated heparin preparations, which were linked to several adverse clinical events and deaths. Orthogonal analytical techniques, namely nuclear magnetic resonance (NMR) and capillary electrophoresis (CE), have since been applied by several authors for the evaluation of heparin purity and safety. NMR identification and quantification of residual solvents and non-volatile low molecular contaminants with USP acceptance levels of toxicity was achieved 40-fold faster than the traditional GC-headspace technique, which takes ~120 min against ~3 min to obtain a (1)H NMR spectrum with a signal/noise ratio of at least 1000/1. The procedure allowed detection of Class 1 residual solvents at 2 ppm and quantification was possible above 10 ppm. 2D NMR techniques (edited-HSQC (1)H/(13)C) permitted visualization of otherwise masked EDTA signals at 3.68/59.7 ppm and 3.34/53.5 ppm, which may be overlapping mononuclear heparin signals, or those of ethanol and methanol. Detailed NMR and ESI-MS/MS studies revealed a hitherto unknown contaminant, tris(2-n-butoxyethyl) phosphate (TBEP), which has potential health risks.

A new approach for heparin standardization: combination of scanning UV spectroscopy, nuclear magnetic resonance and principal component analysis

The year 2007 was marked by widespread adverse clinical responses to heparin use, leading to a global recall of potentially affected heparin batches in 2008. Several analytical methods have since been developed to detect impurities in heparin preparations; however, many are costly and dependent on instrumentation with only limited accessibility. A method based on a simple UV-scanning assay, combined with principal component analysis (PCA), was developed to detect impurities, such as glycosaminoglycans, other complex polysaccharides and aromatic compounds, in heparin preparations. Results were confirmed by NMR spectroscopy. This approach provides an additional, sensitive tool to determine heparin purity and safety, even when NMR spectroscopy failed, requiring only standard laboratory equipment and computing facilities.

"Linkage region" sequences of heparins and heparan sulfates: detection and quantification by nuclear magnetic resonance spectroscopy

The (13)C NMR spectra of most heparin and heparan sulfate preparations display minor signals not attributable to the glycosaminoglycan chains of these polysaccharides. These signals have been "concentrated" in oligosaccharides isolated from an acid hydrolyzate of heparin and shown to arise from the sequence GlcA-Gal-Gal-Xyl of the "linkage region" (LR) connecting the carbohydrate chains to the peptide chains in the original proteoglycans. Mono- and two-dimensional (1)H and (13)C NMR analysis of the major oligosaccharide (LR-OLIGO) indicated the prevalent structure GlcA-GlcNAc-GlcA-Gal-Gal-Xyl, where GlcNAc is partially 6-O-sulfated. (13)C NMR signals at 84.6 and 85.0 ppm, arising from C-3 of the two Gal residues, lend themselves to easy detection and quantification of the linkage region in heparins and heparan sulfates and can be used to assess the importance of the LR in the modulation of various biological activities of these glycosaminoglycans.

Chemical composition, particle size range, and biological activity of some low molecular weight heparin derivatives

Several low molecular weight (LMW) heparin sodium derivatives from different sources, as well as some related regular heparin sodium preparations, were examined for chemical composition by high field (300 MHz) 1H NMR spectroscopy, for particle size range by quasi-elastic light scattering (QELS) methods, and for anti-coagulation potency and anti-factor Xa activity by the standard U.S. Pharmacopeial assays described for regular heparin. The NMR spectra provided insight into possible modes of depolymerization used to generate the LMW heparins, as well as into the presence of dermatan sulfate or other chemical contaminants. The QELS analysis permitted the heparin preparations to be characterized and compared by virtue of their distinctive particle size distributions.

In vitro studies of the interaction of heparin, low molecular weight heparin and heparinoids with platelets

Heparin, low molecular weight heparins, and heparinoids were studied for their ability to inhibit the aggregation of platelets by various agonists and for their ability to adhere to collagen. Heparin was a very effective inhibitor of aggregation with collagen and with ristocetin as it was with adhesion to collagen. The heparinoids showed little effect on aggregation or adhesion. Heparan sulfate and pentosan polysulfate did show slight inhibitory activity against collagen aggregation and adhesion and both interacted with the antibody induced by heparin therapy. It is of interest that dermatan sulfate and the pentasaccharide were almost inert in these experiments, and are unlikely to induce bleeding by inhibition of platelet function. It is highly probable that interference with the interaction of von Willebrand factor with platelets and collagen is a major mechanism for bleeding in the heparinized patient.

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.

Impairment of primary haemostasis by low molecular weight heparins in rats

Different low molecular weight (LMW) heparins were tested on primary haemostasis in rats. Four preparations were studied; one was devoid of any effect on the bleeding time, while the other three prolonged the bleeding time to varying extents. As a consequence we studied the effect of these heparins on platelet aggregation. The fractions which prolonged the bleeding time, also inhibited the ex vivo and in vitro platelet aggregation, whereas the one devoid of any effect on the bleeding time did not affect platelet aggregation. Similar results were obtained using both platelet-rich plasma (PRP) and gel-filtered platelets. The in vitro response of platelets to aggregating agents may offer a parameter to detect the presence of 'bleeding factor(s)' in some LMW heparin preparations.