Urokinase

Description

Urokinase is an enzyme that is extracted from human urine or kidney cells, which directly cleaves specific peptide bonds, in particular the Arg-560–Val-561 bond in the plasminogen molecule, thus transforming it into plasmin.

Chemical Properties

White or almost white, amorphous powder.

Originator

Abbofinase,Abbott,UK,1962

Uses

It is used for the same indications as streptokinase.

Uses

Plasminogen activator; fibrinolytic; enzyme.

Uses

The effect of systemic administration of urokinase is unclear. One study reported the effectiveness of superselective ophthalmic artery fibrinolytic therapy of urokinase for CRVO. Urokinase was infused through a microcatheter into the ostium of the ophthalmic artery via the femoral artery. Six eyes of 26 patients had a significant improvement in VA 24 hours after the fibrinolysis; eyes with combined central retinal artery occlusion and CRVO with recent visual impairment appeared to be the most responsive.

Manufacturing Process

In 20 liters of human urine is dissolved 1,200 grams of sodium benzoate (6% weight by volume). The solution is acidified with aqueous hydrochloric acid (assay about 7.5% HCl) to a pH of 4.5 resulting in a heavy precipitation. This requires 10% of the original urine volume, or about 2 liters of aqueous hydrochloric acid. The suspension is stirred 20 minutes and is then allowed to stand for about 30 minutes. The mixture so obtained is filtered on a Buchner funnel that has been prepared with a precoat of benzoic acid crystals over filter paper. The filter cake is washed with a saturated benzoic acid solution, then sucked dry. The benzoic acid cake with the adsorbed urokinase weighs 2,060 grams.
The filter cake is stirred with 3.1 liters of acetone. The volume of acetone used is about 1.5 times the weight of the cake resulting in about a 65% acetone concentration. The benzoic acid dissolves in the acetone and the urokinase flocculates out. Sodium benzoate, about 1% of the weight of the cake, or 21 grams, is added to speed up the formation of the precipitate. The suspension of crude urokinase in acetone is filtered on a Buchner funnel using filter paper precoated with a diatomaceous silica product (Celite 505). The precipitate is washed with acetone until the filtrate is water clear. The precipitate is then washed with ether and air dried. The yield of powder so obtained is 2.3 grams.
Four batches of urokinase, obtained in this manner from 202 liters of urine, is pooled, amounting to 23.5 grams. The combined urokinase is suspended in 750 ml of 0.1 M phosphate-saline buffer at pH 6.2, stirred to dissolve the urokinase and centrifuged to remove the Celite. The residue is extracted two more times with 500 ml portions of 0.1 M phosphate-saline buffer. The combined extracts are filtered and labelled Extract 1.The residue is extracted three more times with 600 ml portions of buffer, the combined extracts are filtered and labelled Extract 2.
The clarified solution of the first phosphate-saline buffer extract, 1,320 ml, is passed through 110 cm of Amberlite XE-64 ion exchange resin contained in a column 10 cm in diameter. The resin exchange column has a hold-up volume of about 2.8 liters. The second extract (Extract 2) of the Celite residue, 1,720 ml, is then passed through the same exchange column. The column is washed with 11.4 liters of the phosphate-saline buffer. Then the adsorbate is eluted with 9 liters of 0.5 M sodium chloride. The eluate is dialyzed through a viscose regenerated cellulose membrane against distilled water. The active fractions within the dialysis sacs, totaling 4,940 ml, are pooled and lyophilized. The yield is 2.5 grams having an activity of 415,000 units or 166 units per milligram.

brand name

Abbokinase (Imarx).

Therapeutic Function

Anticoagulant

General Description

Urokinase (Abbokinase) is a glycosylatedserine protease consisting of 411 amino acid residues,which exists as two polypeptide chains connected by a singledisulfide bond. It is isolated from human urine or tissueculture of human kidneys. The only known substrate ofurokinase is plasminogen, which is activated to plasmin, afibrinolytic enzyme. Unlike streptokinase, urokinase is adirect activator of plasminogen. Urokinase is nonantigenicbecause it is an endogenous enzyme and, therefore, may beused when streptokinase use is impossible because of antibodyformation. It is administered intravenously or by theintracoronary route. Its indications are similar to those ofstreptokinase.

Biochem/physiol Actions

Urokinase expression and invasiveness suppression by urinary trypsin inhibitor acts through MEK/ERK/c-Jun-dependent signaling pathways.

Mechanism of action

Urokinase is an enzyme with the ability to directly degrade fibrin and fibrinogen. It is now isolated from cultures of human fetal kidney cells and is composed of two polypeptide chains with molecular weights of 32 and 54 kDa.

Pharmacokinetics

This method of isolation is much more efficient than the original isolation of urokinase from human urine. Because of its source, the human body does not see urokinase as a foreign protein. Therefore, it lacks the antigenicity associated with streptokinase and frequently is used for patients with a known hypersensitivity to streptokinase. Plasmin cannot be used directly because of the presence of naturally occurring plasmin antagonists in plasma. No such inhibitors of urokinase exist in the plasma, however, allowing this enzyme to have clinical utility. Even so, urokinase is much more expensive (threefold the price of streptokinase) and has an even shorter half-life (15 minutes). Urokinase also has other fibrin-nonspecific actions similar to streptokinase.

Clinical Use

Fibrinolytic agent:
Thrombosed arteriovenous shunts and intravenous cannulas
Treatment of thromboembolic occlusive vascular disease, e.g. DVT, PE, peripheral vascular occlusion

Safety Profile

An experimental teratogen. Experimental reproductive effects. Used in the treatment of diseases caused by blood clots.

Metabolism

Urokinase is eliminated rapidly from the circulation by the liver.
The inactive degradation products are excreted mainly via the kidneys and also the bile.

Purification Methods

Crystallisation of this enzyme is induced at pH 5.0 to 5.3 (4o) by careful addition of NaCl with gentle stirring until the solution becomes turbid (silky sheen). The NaCl concentration is increased gradually (over several days) until 98% of saturation is achieved whereby urokinase crystallises out as colourless thin brittle plates. It can be similarly recrystallised to maximum specific activity [104K CTA units/mg of protein (Sherry et al. J Lab Clin Med 64 145 1964)]. [Lesuk et al. Science 147 880 1965, NMR: Bogusky et al. Biochemistry 28 6728 1989.] Itisa plasminogen activator [Gold et al. Biochem J 262 1989, de Bock & Wang Med Res Rev 24(1) 13 2004].