Low molecular weight heparins: an emerging new class of glycosaminoglycan antithrombotics

Buccal delivery of low molecular weight heparin by cationic polymethacrylate nanoparticles

Buccal delivery seems to be a very promising administration route for macromolecular drugs. Here, we explored the potential of cationic polymethacrylate nanoparticles (NPs) as a carrier system for the buccal delivery of low molecular weight heparin (LMWH). LMWH-loaded NPs were prepared by emulsification solvent diffusion method and the NPs were analyzed for their physiochemical properties, rheological evaluations and ex vivo transport studies across buccal mucosa. The prepared LMWH-loaded NPs showed a mean diameter between 400 and 500nm with unimodal size distribution with negative surface charge. Viscosity measurements revealed a positive rheological synergism between the prepared NPs and mucin when mixed under physiological conditions. After 4h, about 6.3±0.9% of LMWH was released in case of using Eudragit^® RS (ERS); while Eudragit^® RL (ERL) NPs released only 3.0±0.3 % of its LMWH content and this incomplete release was slightly ameliorated in the presence of mucin reaching to 7.2±0.3 % and 4.8±0.3 % for ERS and ERL, respectively. The ex-vivo permeability of heparin through the buccal mucosa was significantly increased after using polymetharylate NPs while no heparin permeation was detected from free heparin solution. Confocal laser scanning microscopy (CLSM) imaging indicated the mucoadhesive properties of the polymetharylate NPs where the drug-free NPs were detected in the superficial layers of buccal mucosa. LMWH-loaded NPs had less mucoadhesive properties showing significant deeper penetration of the mucosa. The results indicated that mucoadhesive cationic polymethacrylate NPs offer a possible approach for the buccal delivery of heparin.

The low molecular weight heparin, tinzaparin, in thrombosis and beyond

Standard unfractionated heparin (UFH) has been in clinical use for over 50 years. The commercial use of low molecular weight heparins (LMWHs) began in the mid 1980s for hemodialysis and the prophylaxis of deep vein thrombosis (DVT). Initially, the clinical development of LMWHs was concentrated on the European continent. Subsequently, LMWHs were introduced in North America as well. In the initial stages of development of these drugs only nadroparin, dalteparin and enoxaparin were used. Subsequently, several other LMWHs such as ardeparin, tinzaparin, reviparin and parnaparin were introduced. LMWHs constitute a group of important medications with total sales reaching nearly 2.5 billion dollars with expanded indications reaching far beyond the initial indications for the prophylaxis of post-surgical DVT. This review highlights the pharmacology of tinzaparin. Unlike other LMWHs, tinzaparin is prepared by enzymatic hydrolysis with heparinase, while various chemical depolymerization methods are used for the synthesis of other LMWHs. As compared with the standard heparin, LMWHs have different pharmacodynamic, and pharmacokinetic properties; they also differ in clinical benefits.

Low molecular weight heparin-induced liver toxicity

The authors report two cases of hepatotoxicity induced by low molecular weight heparin. A 26-year-old woman and a 33-year-old man were treated with low molecular weight heparin for pulmonary embolism and cerebral infarction, respectively. They both developed derangement in liver function tests a few days after commencement of the low molecular weight heparin. The derangement in liver function tests was associated with a decreased serum complement 3 activity. Their liver functions recovered over a period of 2 to 3 months after low molecular weight heparin was stopped. Liver biopsy in the woman demonstrated balloon degeneration with scattered foci of hepatocytic necrosis, suggesting a complement-mediated hepatocellular damage.

Venous thrombosis: diagnosis and treatment; new methods and strategies for management

Venous thrombosis most often attacks patients who have had alterations of venous stasis, endothelial damage, and/or hypercoagulability. Diagnosis generally depends on venography or duplex doppler ultrasonography; treatment is usually started with heparin and may proceed to warfarin alone.

Differential interactions of heparin and heparan sulfate glycosaminoglycans with the selectins. Implications for the use of unfractionated and low molecular weight heparins as therapeutic agents

The selectins are calcium-dependent C-type lectins that bind certain sialylated, fucosylated, sulfated glycoprotein ligands. L-selectin also recognizes endothelial proteoglycans in a calcium-dependent manner, via heparan sulfate (HS) glycosaminoglycan chains enriched in unsubstituted glucosamine units. We now show that these HS chains can also bind P-selectin, but not E-selectin. However, while L-selectin binding requires micromolar levels of free calcium, P-selectin recognition is largely divalent cation-independent. Despite this, HS chains bound to P-selectin are eluted by ethylenediamine tetraacetic acid (EDTA), but only at high concentrations. Porcine intestinal mucosal (mast cell-derived) heparin (PIM-heparin) shows similar properties, with no binding to E-selectin, calcium-dependent binding of a subfraction to L-selectin and to P-selectin, and calcium-independent binding of a larger fraction to P-selectin, the latter being disrupted by high EDTA concentrations. Analysis of defined heparin fragment pools shows a size dependence for interaction, with tetradecasaccharides showing easily detectable binding to L- and P-selectin affinity columns. L-selectin binding fragments include more heavily sulfated and epimerized regions and, as with the endothelial HS chains, they are enriched in free amino groups. The P-selectin binding component includes this fraction as well as some less highly modified regions. Thus, endothelium-derived HS chains and mast cell-derived heparins could play a role in modulating the biology of selectins in vivo. Notably, P- and L-selectin binding to sialyl-Lewisx and to HL-60 cells (which are known to carry the native ligand PSGL-1) is inhibited by unfractionated pharmaceutical heparin preparations at concentrations 12-50-fold lower than those recommended for effective anticoagulation in vivo. In contrast, two low molecular weight heparins currently considered as clinical replacements for unfractionated heparin are much poorer inhibitors. Thus, patients undergoing heparin therapy for other reasons may be experiencing clinically significant inhibition of L- and P-selectin function, and the current switchover to low-molecular weight heparins may come at some loss of this effect. Low-dose unfractionated heparin should be investigated as a treatment option for acute and chronic diseases in which P- and L-selectin play pathological roles.

Thrombosis and the pharmacology of antithrombotic agents

OBJECTIVE

To provide an overview of the current state of knowledge regarding the physiology of hemostasis, the pathophysiology of thrombosis, and the pharmacology of antithrombotic agents.

DATA SOURCES

A MEDLINE search was conducted to identify pertinent literature published since 1984. Recently published textbooks devoted to the subjects of hematology, hemostasis, and thrombosis also were reviewed, particularly their bibliographies. The bibliographies of selected review articles also were reviewed.

STUDY SELECTION

As the amount of literature was vast, only the most significant and noteworthy published studies were reviewed. Review articles and book chapters authored by researchers of international reputation also were reviewed.

DATA EXTRACTION

Identified studies from the primary literature and selected reviews were analyzed carefully. Information regarding hemostasis, thrombosis, and antithrombotic drugs was extracted. Particular attention was given to data regarding drugs currently available or soon to be available on the US market.

DATA SYNTHESIS

Knowledge regarding the regulation of blood coagulation has expanded substantially in recent years. Hemostasis involves the dynamic interplay of numerous intravascular constituents, including the vessel wall, circulating procoagulants and anticoagulants, platelets, and fibrinolytic proteins. Thrombosis is the abnormal formation of a clot within the vascular system. When sufficiently large, thrombi can prevent the flow of blood and nutrients to vital tissues. Thrombosis is associated with many common diseases and is among the leading causes of death in developed countries. Many drugs are now available to prevent the formation and propagation of thrombi. These agents work by different pharmacologic mechanisms and are useful in different clinical situations.

CONCLUSIONS

Thrombosis research has increased our understanding of the pharmacology of antithrombotic drugs and promoted the discovery of new agents targeted more specifically toward the critical steps in pathologic clot formation. New agents have the potential for greater efficacy and fewer adverse effects. An increased understanding of hemostasis, thrombosis, and the pharmacology of antithrombotic drugs should enable the clinician to use these agents appropriately.

Pharmacodynamics, clinical indications, and adverse effects of heparin

Heparins are a heterogenous group of naturally occurring glycosaminoglycans characterized by anticoagulant activity and a wide range of molecular weights (low molecular weight or fractionated heparins evolving within the past two decades). Cofactors for endogenous inhibitors of coagulation (antithrombin III and heparin cofactor II), heparin administration results in a hypocoagulable state. Various platelet activities, including inhibition of activity induced by platelet-derived growth factors on vascular smooth muscle, also have been noted. Divorced of anticoagulant nature, novel applications may include a role in atherosclerosis prevention, acceleration of collateral coronary as well as peripheral circulation (i.e., angiogenesis), and continued (chronic) post-myocardial infarction therapy. Established indications include treatment of various thrombotic diseases, unstable angina, and thrombosis chemoprophylaxis in medical/surgical patients. The antithrombotic potential of the heparins is used also in thrombosis management related to extracorporeal circulatory assistance or dialysis devices. Heparin's therapeutic potential in the postphlebitic syndrome as well as in acute treatment of myocardial infarction (primarily and adjunctively with various thrombolytic agents) continues to undergo evaluation; however, early data review shows favorable trends for its inclusion in situations that favor thrombus generation (e.g., anterior myocardial infarction). Although associated with thrombocytopenia or hypertransaminasemia, the heparins are relatively well tolerated. In a small subset of patients, a severe thrombocytopenia may ensue, which generally resolves on medication withdrawal. As this class of glycosaminoglycans becomes better characterized, new indications may emerge for both native and the newer fractionated heparins.