Heparin activities

Sample Collection and Enzyme Stability. Serum samples are collected with chemically clean, sterile glassware. Blood is allowed to clot at room temperature, the clot is gently separated from the test tube with an applicator stick, and the blood is centrifuged for 10 minutes at 1,000 g. If the red cells are known to contain the enzymes whose activity is being measured, as in the case of LD, even slightly hemolyzed serums must be discarded. When acid phosphatase is to be measured, the serum should be placed immediately in ice and processed as soon as possible, or it should be acidified by the addition of a small amount of sodium citrate. Anticoagulants such as EDTA, fluoride and oxalate inhibit some serum enzymes. However, heparin activates serum lipoprotein lipase. 

It is of interest to note that the crystalline barium heparinate, which is an acid salt, tends to lose its anticoagulant powers very readily and that the authors consider that sulfur content gives no indication of heparin activity.93 Some polysaccharide sulfuric esters from marine algae possess anticoagulant activity. 

K5. Kom, E. D., Clearing factor, a heparin-activated lipoprotein lipase. II. Substrate specificity and activation of coconut oil. J. Biol. Chem. 215, 15-26 (1955). 

Converting to oral anticoagulant therapy Perform baseline coagulation tests to determine prothrombin activity when heparin activity is too low to affect PT or INR. When the results of the initial prothrombin determinations are known, initiate the oral anticoagulant in the usual amount. Thereafter, perform coagulation tests and prothrombin activity at appropriate intervals. When the prothrombin activity reaches the desired therapeutic range, discontinue heparin and continue oral anticoagulants. 

Table 11 demonstrates, as in the previous case, the increased amount of immobilized heparin when the spacer was used the anticoagulant activity of immobilized heparin being around 10% of the initial heparin activity. The reason for the observed loss of initial activity is probably the inaccessibility of the immobilized heparin for high-molecular proteins (thrombin with a molecular mass of 34000 and antithrombin III with a molecular mass of 65 000) as the permeability of the grafted gels, whose water content was only 55 %, [Pg.113]

Bleeding complications were doubled with GPIIb/llla blockade in early studies (8,10). However, the use of weight-adjusted low dose of heparin [activated clotting time (ACT) target of 200-250 seconds] and optimal management of vascular access site (rapid sheath removal within four to... 

In conclusion, satisfactory methods are now available for the extraction and purification of heparin these have been developed in the light of modern knowledge of heparin activity. The homogeneity of heparin preparations may also be ascertained before structural studies are begun. 

The preceding data suggest that the activity of heparin is not simply a function of the degree of sulfation, since heparin preparations of high activity contain fewer sulfate groups than the more weakly acting, synthetic products. Karrer and associates" also point out that the relatively rapid disappearance of heparin activity in vivo, compared to the slow disappearance of activity of synthetic, sulfated polysaccharides, may be due to a different mode of action. 

R25. Rosenman, R. H., and P riedman, M., In vivo studies of the role of albumin in endogenous and heparin-activated lipemia-clearing in nephrotic rats. J. Clin. Invest. 36, 700-705 (1957). 

When used in full therapeutic doses, UFH must be monitored to determine the appropriate dose to administer. The choice of assay is based on chnician preference and institutional availabihty. The aPTT remains the most commonly used test to monitor UFH therapy in North America. In some European countries, anti-factor Xa heparin activity is used commonly. The aPTT should be measured prior to the initiation of therapy to determine the patient s baseline. When administered by intravenous infusion, the response to therapy... 

Heparin inhibits blood coagulation both in vivo and in vitro. In combination with a co-factor, antithrombin III, heparin interferes with several steps in the coagulation process. Furthermore, heparin activates lipoprotein-lipase, which splits triglycerides into free fatty acids and glycerol. 

Figure 6. APTT heparin activity assay curve. Key 9, control heparinized plasma (units mL plasma) calibration APTT and O, derivatized heparin (at known weight concentrations, mg/mL plasma) APTT.

After determining the control heparin-APTT response curve, derivatized heparin was added to unheparinized bovine plasma (the same plasma used for preparing the control response curve) at known weight concentrations, and APTT was determined. Based on the interpolated heparin activity (units/mL plasma) of the derivatized heparin at known weight concentration (mg/mL plasma), the anticoagulant activity (units/mg) of the N-acetylated and hydroxyl- and carboxylic-derivatized heparins was determined. 

Olson ST, Chuang YJ. Heparin activates antithrombin anticoagulant function by generating new interaction sites (exosites) for blood clotting proteinases. Trends Cardiovasc Med 2002 12 331-338. 

Desai UR, Petitou M, Bjork I, Olson ST. Mechanism of heparin activation of antithrombin. Role of individual residues of the pentasaccharide activating sequence in the recognition of native and activated states of antithrombin. J Biol Chem 1998 273 7478-7487. 

Reynaud, D., Hinek, A., and Pace-Asciak, C.R. (2002) The Hepoxilin Analog PBT-3 Inhibits Heparin-Activated Platelet Aggregation Evoked by ADP, FEBS Lett. 515,58-60. 

Heparin resistance is defined as the requirement of more than 35,000 units in a 24-h period to maintain a therapeutic activated partial thromboplastin time. In some cases, elevated factor VIII levels can factitiously lower the aPPT without influencing heparin activity measured by anti-Xa assays, leading to a misdiagnosis of heparin resistance. A case of apparent heparin resistance due to increased factor VIII levels in an elderly male with infective endocarditis was reported [18 ]. 

PolettL L and Lay, L (2003) Chemical contributions to imderstanding heparin activity synthesis of related sulfated oligosaccharides. Eur. J. Org, Chem., 2999-3024. 

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