BIO-TRANSFORMATION AND PHARMACOKINETICS OF SINGLE CHAIN UROKINASE-TYPE PLASMINOGEN ACTIVATOR IN RABBITS AND RHESUS MONKEYS

AIM: The concentration profiles of recombinant human single chain urokinase-type plasminogen activator (rh-sc-uPA) and bio-transformation to two-chain metabolite (tc-uPA) were studied after iv bolus injection of ¹²⁵I-rh-sc-uPA in rabbits. Fibrinolytic components-time curves in plasma were determined after iv bolus injection at different doses of rh-sc-uPA in rhesus monkeys and were compared with natural urokinase (n-tc-uPA). METHODS: Aprotinin was added into plasma immediately after sampling for preventing the conversion of single-chain to two-chain. Plasma ¹²⁵I-sc-uPA concentrations was determined by RP-HPLC of dithiothreitol (DTT) treated plasma, while concentrations of ¹²⁵I-sc-uPA+¹²⁵I-tc-uPA was obtained by analysis of untreated DTT plasma. Concentration of fibrinolytic components was assayed by fibrin plate method in vitro. RESULTS: The ¹²⁵I-sc-uPA and ¹²⁵I-tc-uPA were both detected after iv bolus injection of in rabbits. The ¹²⁵I-sc-uPA concentrations were best fit by a two-compartment model with T_1/2α and T_1/2β equaled to 7 and 43 min, respectively. ¹²⁵I-tc-uPA concentrations were best fit by a one-compartment model with elimination T_1/2　of 9 min. Nearly 38% of ¹²⁵I-sc-uPA transformed to ¹²⁵I-tc-uPA. Concentration of fibrinolytic components decreased rapidly after iv bolus injection of 7.5×10⁴, 1.5×10⁵, and 3.0×10⁵ U.kg^-1 rh-sc-uPA in rhesus Monkeys. Elimination T_1/2　were 6.3±1.8, 11.5±2.1 and 12.3±2.9 min, respectively (P<0.05～P<0.01). Systemic clearance were 0.051±0.030, 0.022±0.006 and 0.016±0.003 L.min^-1.kg^-1, respectively (P<0.05). Concentration of fibrinolytic components after 1.5×105 U.kg^-1 of rh-sc-uPA was significantly lower than that after n-tc-uPA. CONCLUSION: ¹²⁵I-rh-sc-uPA and its active metabolite-¹²⁵I-rh-tc-uPA were detected after iv of ¹²⁵I-rh-sc-uPA in rabbits, their pharmacokinetic behaviors were different. Deposition profiles of fibrinolytic components after iv of various doses of rh-sc-uPA in monkeys follows non-linear pharmcokinetics.