Mumper R J, Hoffman A S
Center for Pharmaceutical Science & Technology, College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536-0082, USA.
AAPS PharmSciTech. 2000 Mar 3;1(1):E3. doi: 10.1208/pt010103.
Hirudin is a 65-amino acid peptide and the most potent and specific known inhibitor of thrombin (K(i) = 0.2 pM). The short elimination half-life of hirudin from the body (1 hour) necessitates the use of a sustained and controlled delivery system. A proliposome method was used to entrap hirudin in liposomes coated with palmitoyl dextran-coated liposomes and lipid-assemblies. In vitro release studies of hirudin were performed using the lipid systems enclosed in dialysis membranes or deposited in the pores of a vascular graft. The activity of hirudin and released hirudin was measured using a thrombin chromogenic substrate assay. Entrapment efficiencies of hirudin in lipid-assemblies approached 100%, however, the release of hirudin from these systems was rapid with 90% released in 17 hours. Entrapment efficiencies of hirudin in coated-liposomes ranged from 5% to 55% and were dependent on several variables. Palmitoyl dextran- coated-liposomes showed a burst of 30% hirudin released in 5 hours with an additional 10% to 35% released over the next 600 hours. In all samples, 30-40% of the hirudin remained associated with the lipid-systems even after 600 hours. The released hirudin retained only 33% of its ability to inhibit thrombin when released from uncoated liposomes. However, hirudin retained 95% of its thrombin inhibitory activity when released from palmitoyl dextran-coated liposomes. Coated liposomes were found to stabilize hirudin and result in greater retention of hirudin's ability to inhibit thrombin's enzymatic activity, although the mechanism is not yet understood.
水蛭素是一种由65个氨基酸组成的肽，是已知的对凝血酶最有效且最具特异性的抑制剂（抑制常数K(i)=0.2皮摩尔）。水蛭素在体内的消除半衰期较短（1小时），因此需要使用持续且可控的给药系统。采用前体脂质体方法将水蛭素包裹于涂有棕榈酰葡聚糖的脂质体和脂质组装体中。使用包裹在透析膜中的脂质系统或沉积在血管移植物孔隙中的脂质系统进行水蛭素的体外释放研究。使用凝血酶显色底物分析法测量水蛭素及其释放出来的水蛭素的活性。水蛭素在脂质组装体中的包封率接近100%，然而，水蛭素从这些系统中的释放速度很快，17小时内释放了90%。水蛭素在包衣脂质体中的包封率在5%至55%之间，且取决于几个变量。棕榈酰葡聚糖包衣脂质体显示，5小时内有30%的水蛭素突发释放，在接下来的600小时内又有10%至35%的释放。在所有样品中，即使在600小时后，仍有30%-40%的水蛭素与脂质系统相关联。当从未包衣的脂质体中释放时，释放出来的水蛭素仅保留其抑制凝血酶能力的33%。然而，当从棕榈酰葡聚糖包衣脂质体中释放时，水蛭素保留了其95%的凝血酶抑制活性。尽管其机制尚不清楚，但发现包衣脂质体可使水蛭素稳定，并使其抑制凝血酶酶活性的能力得到更大程度的保留。
