Sources of Urokinase

Urokinase utilized for medical purposes was principally obtained from human urine in the past. The initial manufacturing steps typically involved concentrating and partially purifying the enzyme by precipitation using sodium benzoate, ammonium sulfate, or ethanol. Chromatography steps employed in further purification of the enzyme include anion-exchange, affinity, and gel-filtration chromatography [18-20]. Current therapeutic urokinase preparations are principally obtained by cell culture methods. One-chain high-molecular-mass urokinase has been produced by recombinant technology in a number of systems, including Escherichia coli, mammalian cells, and yeast cells [21]. However, it has been highlighted that urokinase derived from different expression systems do not possess identical fibrinolytic properties. It has been reported that recombinant nonglycosylated one-chain urokinase from E. coli had a higher catalytic efficiency against plasminogen than native one-chain urokinase. Similarly, nonglycosylated recombinant one-chain urokinase from mammalian cells had a greater catalytic and fibrinolytic activity than glycosylated recombinant one-chain urokinase from the same cell line [21]. In addition, other studies have found that the carbohydrate component of one-chain urokinase is not important for its fibrinolytic activity in plasma, but provides fibrin specificity [21,22]. Fibrin specificity is an important characteristic of selecting the best form of urokinase (i.e., one-chain, two-chain, or low molecular mass) for utilization as a therapeutic agent to reduce the risk of systemic bleeding. This characteristic also plays a role in identifying the best source of the enzyme for therapeutic applications. One-chain high-molecular-mass urokinase possesses fibrin-specific clot lysis due to its activation to the catalytically active two-chain form primarily at the fibrin clot surface. Neither the high-molecular-mass two-chain form nor the low-molecular-mass form possess this specificity and will therefore activate plasmino-gen throughout the circulation, whether clot-bound or free [21,23].

Abbokinase (tradename) is one of the principal urokinase-based products on the market and is produced by Abbott Laboratories. Abbokinase is derived from human neonatal kidney cells grown in tissue culture. The urokinase incorporated in this product is the low-molecular-mass form and consists of an A chain of 2 kDa linked by a sulfhydryl bond to a B chain of 30.4 kDa. Abbokinase is supplied as a sterile, lyophilized, white powder containing 250,000 IU urokinase as well as mannitol, albumin, and sodium chloride per vial. The powder is reconstituted in water for injection prior to intravenous infusion [24]. Other urokinase-based products include Actosolv produced by Behringwerke (Marburg, Germany); Ukidan, a two-chain urokinase derived from human male urine, Ukidan produced by Serono Pharma International (Aubonne, Switzerland); and Uronase produced by Mochida (Tokyo, Japan) [19]. Some of these products (particularly those derived from human urine) have been discontinued. New recombinant products include Saruplase (res-cupase) produced by Gruenenthal GmbH (Aachen, Germany). This preparation consists of the one-chain urokinase expressed in E. coli. Saruplase failed to obtained approval in 1998 due to the increased risk of hemorrhage associated with the preparation [25].

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