The pharmacology of heparin and heparinoids

Oral absorption and clearance of partially depolymerized fucosyl chondroitin sulfate from sea cucumber

Partially depolymerized holothurian glycosaminoglycan (DHG), a fucosyl chondroitin sulfate chains isolated from sea cucumber, was administered by the intravenous and oral routes to experimental animal. After intravenous injection, clearance of DHG, as measured by the postcolumn HPLC, displayed complex kinetics that were not dose dependent. DHG was excreted unchanged in the urine. No degradation products of DHG were detected by either gel filtration or anion exchange HPLC at any time in plasma, indicating that administered DHG is not catabolyzed by mammalian. Anion exchange chromatographic behavior of DHG excreted into urine after oral administration showed that partial desulfation might occur through intestinal absorption. After oral administration of DHG (50 mg/kg), 0.1% of the dose was found in urine collected for 24 hours. More than 5% of intravenously administered DHG (1 mg/kg) was excreted into urine in 24 hours. These results are suggesting that orally administered macromolecules such as DHG are absorbed in the gastrointestinal tract.

High-performance liquid chromatographic-mass spectrometric analysis of oligosaccharides from enzymatic digestion of glycosaminoglycans. Application to human samples

Glycosaminoglycan contents were evaluated in plasma and urine samples from volunteers treated intravenously with a mixture of dermatan sulphate and heparin, combining a novel liquid chromatographic-mass spectrometric technique for the determination of oligosaccharides from glycosaminoglycans with a classical technique for the extraction of glycosaminoglycans from biological samples (precipitation with cetylpyridinium chloride). In plasma samples dermatan sulphate and heparin can be measured for 2 h after treatment; urine excretion was detectable for 24 h. These results suggest that this novel approach is promising for future studies on the pharmacokinetics of glycosaminoglycans, although some technical aspects need further improvement, mainly regarding the procedures for sample clean-up; cetylpiridinium precipitation is a complex procedure and the recovery is limited.

Protective role of heparin on in vitro functional aortic response in Watanabe heritable hyperlipidemic rabbits

The effects of prolonged in vivo heparin treatment upon vasomotor responses and content of cholesterol and energy related compounds were studied in isolated thoracic and abdominal aortas from Watanabe heritable hyperlipidemic (WHHL) rabbits. Unfractionated heparin was administered subcutaneously (2 mg/kg twice a day) to 3-month-old WHHL rabbits for a period of 6 months. A group of WHHL rabbits was treated with saline solution and considered as control. Aortic cholesterol infiltration and serum cholesterol were not significantly decreased by the prolonged heparin treatment. In heparin-treated WHHL rabbits, the in vitro aortic endothelium-dependent relaxation produced by acetylcholine or calcimycin (A 23187) was greater than in saline-treated WHHL group. ATP-induced aorta relaxation (endothelium-dependent and endothelium-independent) did not vary significantly in the two groups of WHHL rabbits, even after mechanical removal of endothelium. Also the noradrenaline-induced aorta contraction did not vary between the two groups of WHHL rabbits. No significant variation in energy-related compounds (except for ADP) was found in the aortic arch. These results suggest that heparin produces a protective effect on aortic tissue by acting mainly at endothelial level.

Predicting the pharmacodynamics of heparin: a clinical evaluation of the Hepcon System 4

The magnitude of the anticoagulation response to heparin (heparin responsiveness) varies substantially from patient to patient. Identifying extremes of sensitivity and resistance prior to intravenous administration of heparin would facilitate anticoagulation for cardiopulmonary bypass (CPB). The performance of the Hepcon System 4 (HemoTec, Inc, Englewood, CO), an instrument designed for that purpose, was tested. Using nonheparinized blood samples from 157 patients scheduled for surgery requiring CPB, this device performed activated coagulation times (ACT) with three different concentrations of in vitro heparin. After determining each patient's in vitro heparin response, the heparin dose predicted to produce ACT values of 480 seconds (group 1, N = 77) or 600 seconds (group 2, N = 80) was administered. Five minutes later each patient's ACT was determined with the Hemochron method (International Technidyne, Inc, Edison, NJ). Simultaneously, several other variables that might predict heparin responsiveness were investigated. When compared with the observed ACT, the Hepcon System 4 inadequately predicted the response. There was considerable scatter in this comparison, but most frequently the in vitro method substantially underestimated the in vivo heparin dose requirement. Heparin responsiveness decreased significantly with high platelet counts and advanced age, but was unaffected by the initial hematocrit, ACT, partial thromboplastin time, or preoperative heparin therapy. Previous investigations have not identified a relationship between advanced age and reduced heparin responsiveness. Combining the Hepcon heparin dose-response in vitro method with the other parameters evaluated, stepwise regression could only account for 39% of the observed variability in heparin responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-density-lipoprotein binding by mast-cell granules. Demonstration of binding of apolipoprotein B to heparin proteoglycan of exocytosed granules

To study the interaction between low-density lipoprotein (LDL) and granules from rat serosal mast cells in vitro, mast cells were stimulated with the degranulating agent 48/80 to induce exocytosis of the secretory granules. Subsequent incubation of the exocytosed granules with 125I-LDL resulted in binding of the labelled LDL to the granules. When increasing amounts of agent 48/80 were added to mast-cell suspensions, a dose-dependent release of granules was observed and a parallel increase in the amount of 125I-LDL bound to granules resulted. 125I-LDL bound to a single class of high-affinity binding sites on the granules. At saturation, 105 ng of LDL were bound per microgram of granule protein. The lipoprotein binding to mast-cell granules was apolipoprotein(apo)-B + E-specific. Thus 125I-LDL binding to the granules was effectively compared for by LDL (apo-B) or by dimyristoyl phosphatidylcholine vesicles containing apo-E, but not by high-density lipoprotein (HDL3) containing apo-AI as their major protein component. Neutralization by acetylation of the positively charged amino groups of apo-B of LDL or presence of a high ionic strength in the incubation medium prevented LDL from binding to the granules, indicating the presence of ionic interactions between the positively charged amino acids of LDL and negatively charged groups of the granules. It could be demonstrated that LDL bound to the negatively charged heparin proteoglycan of the granules. Thus treatment of granules with heparinase resulted in loss of their ability to bind LDL, and substances known to bind to heparin, such as Toluidine Blue, avidin, lipoprotein lipase, fibronectin and protamine, all effectively competed with LDL for binding to the granules. The results show that LDL is efficiently bound to the heparin proteoglycan component of mast-cell granules once the mast cells are stimulated to release their granules into the extracellular space.

An inverse relationship between heparin content and antibody response in genetically selected mice. Sex effect and evidence of a polygenic control for skin heparin concentration

The heparin content of genetically selected mice with high and low antibody response to bacterial antigens is reported. An inverse relationship between antibody titres and concentration of heparin was observed for both male and female mice. The lower-antibody-responder line contains twice as much heparin as the higher-responder ones. Furthermore, the female mice also contained twice as much heparin as the male mice. Genetic analysis of the parental and interline hybrids has shown a partial dominance for the character 'heparin content' in favour of the high-heparin phenotype and this character appears to be subjected to polygenic control. The possible biological role of heparin and/or mast cells in the surveillance of the organism against some pathogens is discussed in the light of these and other findings.

Selective appearance of heparin in mammalian tissues during development

The distribution of heparin in tissues of bovine and porcine fetuses of different ages as well as in the adult animals is reported. Heparin is present almost exclusively in the hematopoietic and lymphoid tissues of fetuses (spleen, liver, thymus and lymph nodes), whereas ileum, skin and lung besides lymph nodes and bovine thymus are the heparin-rich tissues in adult animals. The small amount of heparin in fetal tissues, its decrease in porcine liver and spleen, its appearance in skin, ileum and lung, tissues directly exposed to the environment after birth, its preferential localization at the maternal side of the placenta together with other data led to the suggestion that heparin may be involved with defense mechanisms.

Heparin and atherosclerosis. A review of old and recent findings

This article reviews the experimental and clinical evidence regarding heparin therapy in the prophylaxis of coronary heart disease. The actions of heparin take place at the vascular endothelium where injected heparin concentrates, and within the bloodstream. At the endothelium heparin acts to prevent endothelial injury, prevent thrombin generation, prevent platelet adhesion to endothelium, and to decrease uptake of serum lipoproteins. Within the bloodstream heparin increases lipoprotein lipase activity and reduces the concentration of atherogenic very low-density lipoproteins. The reduction in lipemia enhances oxygen transfer from blood to the tissues, and decreases thrombin or ADP-induced platelet aggregation. Heparin increases the concentration of high-density lipoproteins. It decreases hypercoagulability and inhibits overactivation of serum complement. Heparin reduced atherosclerosis in most studies in cholesterol-fed animals. In human subjects who had a myocardial infarct at least one year before the onset of treatment, long-term intermittent heparin therapy significantly decreased cardiovascular deaths as compared to control groups.

Selective distribution of the heparin in mammals: conspicuous presence of heparin in lymphoid tissues

The systematic study on the distribution of heparin in 12 tissues of eight mammalian species is reported. It is shown that heparin varies from 1 microgram/g of dry tissue in cat liver up to 1000 micrograms/g of dry tissue in bovine ileum. Heparin was present in relatively high amounts in lung, ileum and skin, of most of the species analysed. It was also observed that heparin was conspicuously present in high amounts in thymus and lymph nodes of all the species except for rabbits. Conversely, heparin was not detected in brains of all the species and also in none of the rabbit tissues. Based on this characteristic distribution the possible physiological role of heparin is discussed.

Heparin: an old drug with a new paradigm

Recent studies have shown that heparin is a biochemical representative of a distinct class of compounds known as linear anionic polyelectrolytes. Members of this class are mixtures of individual highly negatively charged chains that show a wide spectrum of specific reactions with biologically active proteins. Upon administration, heparin chains enter a cellular pool and effectively prevent thrombosis by increasing the electronegative potential of the vessel wall. Anticoagulant activity is an unusual feature of a few heparin chains and appears to play a minor role in many clinical uses and in physiological and pathological responses.

Prophylaxis and therapy of venous thromboembolism

Heparin is an anticoagulant drug which is used for the prophylaxis and treatment of venous thromboembolism and for the treatment of some cases of arterial thromboembolism. Venous thromboembolism is the commonest preventable cause of death in hospitalized patients, and the best approach to reduce its morbidity and mortality is the use of safe, effective, prophylaxis in patients at high risk. The use of low doses of heparin given s.c. (5000 units, 8 hourly)) has been shown in prospective clinical trials to be effective prophylaxis against venous thrombosis and nonfatal and fatal pulmonary embolism in patients undergoing general abdominothoracic surgery, without producing dangerous bleeding. Low-dose heparin, however, is not totally effective in patients undergoing hip surgery and suprapubic prostatectomy. The lack of benefit in these patients may be related to the intensity of the provocation to thrombosis. The use of heparin in large doses to treat thrombosis is associated with hemorrhagic complications in up to 30% of patients. There is evidence that continuous i.v. heparin is associated with fewer hemorrhagic complications than intermittent i.v. heparin, but the frequency is not related to the dose or to the use of laboratory monitoring. Hemorrhagic complications occur more frequently in elderly patients and in females and is more common following surgical operations. The frequency of recurrent venous thromboembolism is low in patients on therapeutic doses of heparin, and there is no difference in the frequency of recurrence in patients receiving heparin by continuous i.v. or intermittent i.v. administration.

Antithrombotic drugs: part I

There are three categories of antithrombotic agents: drugs which prevent fibrin fromation (the anticoagulants and defibrinating enzymes), drugs which prevent platelet adhesion or aggregation (the antiplatelet drugs), and thrombolytic drugs which induce fibrin degradation. Clinical studies have now led to a better understanding of the relative value of these drugs in different thrombotic disorders. In addition, knowledge of the mechanism of action of some of these drugs has recently been much advanced. The anticoagulant drugs in clinical use are heparin and the oral anticoagulants. Heparin is a potent inhibitor of several steps on the intrinsic coagulation pathway through its effect on a plasma cofactor, antithrombin III. its action is immediate, but heparin must be given parenterally. Oral anticoagulants act more slowly, by reducing the hepatic synthesis of biologically active factors II, VII, IX and X, but can be given by mouth. Heparin is therefore most suitable for starting anticoagulant treatment, while oral anticoagulants are generally used for prolonged therapy. The value of the anticoagulants as antithrombotic agents has been best assessed by studying their effectiveness in preventing and treating venous thromboembolic disease. Oral anticoagulants have been repeatedly shown to prevent venous thrombosis and pulmonary embolism in patients at high risk of developing these complications. However, the increased risk of postoperative bleeding has prevented their widespread use for this purpose in surgical patients. Recently, the use of low doses of heparin, given subcutaneously before and after surgery, has been shown to markedly reduce the incidence of venous thrombosis and pulmonary embolism (including fatal pulmonary embolism) after major elective abdominal surgery, and to produce only a slight increase of postoperative bleeding. This represents a major advance in anticoagulant prophylaxis of venous thromboembolism insurgical patients. However, low dose heparin prophylasix is relatively ineffective in patients having hip surgery, and has not been evaluated in patients having other types of orthopaidic surgery. There is direct evidence that antocoagulant therapy prevents death and recurrent embolism in patients who have developed pulmonary embolism, and considerable indirect evidence that it prevents pulmonary embolism, and considerable indirect evidence that it prevents pulmonary embolism (and death from pulmonary embolism) in patients who have venous thrombosis. The incidence of further venous thromboembolism or bleeding during treatment appears to be minimised when heparin is given by continuous intravenous infusion in a dose sufficient to produce a moderate, but no excessive, prolongation of a heparin-sensitive, in vitro coagulation test. The tests most commonly used to monitor heparin therapy was based on either the whole blood clotting time or the activated partial thromboplastin time...