THESIS
1994
ix, 70 leaves : ill. ; 30 cm
Abstract
Tissue-type plasminogen activator (t-PA) is currently used as an effective thrombolytic agent to treat cardiovascular diseases and it activates plasminogen which is a key protein in the processes of fibrinolysis. However, its plasma half-life is only 4-10 minutes in man. In this study, the protein was coupled to dextran molecule with the aim of prolonging its circulating lifetime. Gel filtration on HPLC Protein-Pak SW300 was capable of separating dextran-t-PA (Dx-t-PA) and residual t-PA, thereby monitoring the coupling process. Although Dx-t-PA conjugates could be successfully synthesized from both N-bromoacetyl-aminoethylamino-dextran (DxBr) and dialdehyde-dextran (Dx(CHO)
2) with close to complete yield, the specific plasminogen-activating activity was vastly reduced from 4.6x10
-3 min...[
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Tissue-type plasminogen activator (t-PA) is currently used as an effective thrombolytic agent to treat cardiovascular diseases and it activates plasminogen which is a key protein in the processes of fibrinolysis. However, its plasma half-life is only 4-10 minutes in man. In this study, the protein was coupled to dextran molecule with the aim of prolonging its circulating lifetime. Gel filtration on HPLC Protein-Pak SW300 was capable of separating dextran-t-PA (Dx-t-PA) and residual t-PA, thereby monitoring the coupling process. Although Dx-t-PA conjugates could be successfully synthesized from both N-bromoacetyl-aminoethylamino-dextran (DxBr) and dialdehyde-dextran (Dx(CHO)
2) with close to complete yield, the specific plasminogen-activating activity was vastly reduced from 4.6x10
-3 min
-2μg
-1 to 8.5x10[superscritpt -5] min
-2μg
-1 in the case of Dx(CHO)
2, and 3.2x10
-5 min
-2μg
-1 in the case of DxBr. Addition of Tween 80 which removes interactions among t-PA molecules could not restore the enzyme activity. Therefore, no pharmaceutically useful Dx-t-PA conjugates were synthesized through the application of DxBr or Dx(CHO)
2.
Dextran-hemoglobin (Dx-Hb) conjugates, in contrast, are readily synthesized without loss of oxygen-biding capacity, and have been investigated as a potential blood substitute. Since their rheological properties are important to their behavior in the blood stream, their flow properties have been examined in this study. Whole blood, stroma-free hemoglobin (SFH) as well as Dx-Hb samples displayed a shearthinning behavior starting from around l00 sec
-l. Dx-Hb conjugates obtained from different synthetic conditions differed greatly in viscosity, ranging from 2 cps to 12 cps or higher. A set of synthetic conditions has been found that permit the preparation of Dx-Hb with similar or even lower viscosities than whole blood. The reduction of blood viscosity especially at low flow rates by in vitro blood substitution with such optimized Dx-Hb conjugates were largely proportional to the extent of substitution.
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