Heparinoids complexes

The ideal surface for contact with human blood is the surface of blood vessels, and the immediate surface contains heparinoid complexes. Heparin, a negatively charged polysaccharide, has been bonded to silicon rubber and other polymers. In one procedure, a quaternary ammonium compound is first adsorbed on die polymer substrate and heparin is 111 turn adsorbed on the positively charged surface. Chemical bonding of heparin has also been achieved. Such surfaces do not cause clotting of contacted blood. 

Heparins and heparinoids are grouped in Table 3.2. Some are naturally occurring compounds, whilst others are derivatives prepared from heparins or from mucopolysaccharides. Semi-synthetic compounds have been prepared by degradation of natural polysaccharides followed by sulphation with chlorsulphonic acid or methyl sulphate . The common activities shown by the heparins and heparinoids—complexing with organic bases and proteins, antilipaemic activity and anticoagulant activity—are also shown by various sulphonic acid dyes and by polyphosphates. The table is completed with a list of those preparations that have been issued to provide depot preparations of heparins and heparinoids. 

Sodium salt has a special connotation in describing these substances. The almost universal practice in analyses of heparin preparations is to bum a sample moistened with sulphuric acid in oxygen, weigh the ash, and calculate from the sulphated ash the equivalent sodium. This is evidently a questionable practice. The metal cations bound must be identified. As heparin and heparinoids complex with ions, there is interference with various colour and precipitation reactions for ions unless the heparin sample is first subjected to combustion. Flame analyses of Boots and Evans heparin for... 

Figure 6 Effective molar ratio of AT-III and SCM-DAC-70 to inhibit thrombin activity applying gel filtration chromatography on Sephadex G-lOO (o), relative inhibition of thrombin activity by the AT-III-heparinoid complex.

Heparinoid polysaccharides such as heparan sul te and heparin are able to interact with numerous proteins and influence vital biological processes. Heparinoid mimetics were prepared to reduce the structural complexity of heparinoids and to obtain selectivities. This artide summarizes the development of heparinoid mimetics of different classes including representative syntheses and biological activities. Largely simplified compounds with regard to structure and synthetic access are described which maintain or exceed the activity of heparinoid polysaccharides. One of the recipes to increase binding or modify pharmacokinetic parameters was the introduction of hydrophobic groups. 

Low molecular weight heparins, heparin fractions, or other sulfated polysaccharides still have the same or a similar complexity as heparin and are, therefore, not regarded as heparinoid mimetics only compounds with one defined carbohydrate backbone serving as a template for sulfates will be discussed in this context. 

Interactions of heparinoids with the most diverse proteins such as enzymes and enzyme inhibitors, cytokines, and adhesion molecules have been described. To date, many more than a hundred heparin binding proteins are known. A number of heparin binding proteins are members of the serpin family of serine protease inhibitors. The best described example is antithrombin [4]. Antithrombin III (AT III) is able to inhibit various serine proteases involved in the blood coagulation process by formation of stable, equimolar complexes. Binding of heparin to AT III accelerates the kinetics of this complex formation by several orders of magnitude. This has been the basis for the successful clinical use of heparin as an anticoagulant for nearly sixty years. 

Another serine protease inhibitor of the al-antitrypsin family (serpin) is heparin cofactor II (HCII), which also forms a 1 1 complex with thrombin, but does not react with factor Xa [4,10]. The rate of inhibition of thrombin is not only increased by heparinoids but also by the related glycosaminoglycan dermatan sulfate. The identification of an inhibitor variant and site-directed mutagenesis studies on HC II cDNA led to the understanding that the binding sites for heparin and dermatan sulfate may be overlapping but not identical. Further proteinase inhibitors interacting with heparinoids are tissue factor pathway inhibitor and protease nexin-1. 

Benzidine, cetylpyridinium chloride (C.P.C.), cetyltrimethyl ammonium bromide (cetavlon) and other long chain amines form insoluble complexes with heparinoids and are universally used as precipitating agents for heparinoids. The solubility characteristics in salt solutions have been established by Scott . Brucine and choline also give crystalline complexes with heparin in the presence of aqueous alcohol and acetone. The choline complex shows no loss of cholinergic activity, indicating complete dissociation in solution. 

Heparinoids and mucopolysaccharides react with, and modify, many of the plasma proteins. Heparin combines with fibrinogen, globulins and albumin. As judged by electrophoresis and various types of analysis and staining, the particular plasma protein components with which heparin combines are dependent upon the concentration of protein, concentration of heparin, pH value, and salts present. This explains the somewhat contradictory statements in literature about combinations of heparin with plasma proteins. The combination may result in change of solubility of the protein and reverse protein tests . Heparin can modify the murexide reaction for calcium in serum by affecting the calcium-protein-heparin complex. Many heparinoids... 

Heparinoids and Mucopolysaccharides as Complexes, Clathrates, Ion-Exchange Compounds... 

Having considered the complexes which heparin (and heparinoids and mucopolysaccharides) form, we can ask the question whether such complexes are present in the materials as prepared. It is self-evident that such complexes must be present and this immediately explains why heparin usually occurs as a multi-component system. 

Heparinoids are sulfated polysaccharides, prepared semisynthetically by sulfura-tion of partially degraded polysaccharides, or occurring naturally in plant or animal tissue possessing the properties described above for heparin - high sulfate content, solubility in water, insoluble in alcohol, etc., complexing with proteins, and metachro-matically with dyes. 

Heparins and heparinoids form complexes with proteins and bases, and as shown by the ability to produce metachromasia with submicro quantities are very effective complexing agents in trace amounts. Hence, these substances in trace amounts affect many biological agents such as enzymes, etc. When heparin or a heparinoid is injected in animal or man, an enzyme appears in the blood plasma, lipoprotein lipase. When an oil emulsion is incubated with varying amounts of blood plasma obtained after injection of heparin, the oil is cleared. The heparin has caused the release of this enzyme from tissues to the blood. Heparin and heparinoids have a pronounced action on many enzymes - proteolytic enzymes, carbohydrases, etc. and may inhibit, activate. 

A model [22] of how heparin acts specifically in many biological systems in modifying activities of complex ions may be provided by the metachromatic effect on dyes referred to earlier. The dye. Azure A, shows maximum light absorption at 610 nm. This is decreased when heparin is added, and a new absorption band at 505 mu develops. Heparins and heparinoids are able to produce this color change at very low concentrations and under conditions unfavorable to other metachromatic inducing substances. However, little attention has been paid to the numerous experimental observations reported on metachromasia with heparin and heparinoids, of practical importance to those using this color reaction in studies on heparin and mast cells. In... 

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