Studies on the Specific Fibrinolytic Effect of Human Extrinsic (Tissue-Type) Plasminogen Activator in Human Blood and in Various Animal Species in Vitro

Abstract

SummaryHuman extrinsic (tissue-type) plasminogen activator (EPA) was highly purified from the culture fluid of a human melanoma cell line, both as a one-chain or as a two-chain molecule. Its specific fibrinolytic effect on human whole blood clots or plasma clots with different degrees of fibrin crosslinking was evaluated in an in vitro system, composed of a 125I-fibrin labeled clot, hanging in circulating human plasma. After infusion of EPA (30 IU per ml over 3 hrs), non-crosslinked clots lysed more extensively (75-100 percent in 5 hrs) than totally-crosslinked clots (50-65 percent), and no difference was found between one-chain or two-chain EPA. The extent of lysis of totally-crosslinked human or animal plasma clots hanging in autologous plasma induced by EPA varied markedly from one species to the other. When 90 IU of EPA were infused over 3 hrs, crosslinked human plasma clots dissolved for over 95 percent within 5 hrs. Under comparable conditions, the degree of lysis was 80 percent in primate plasma (cynomolgus fascicularis), 60 percent in cat and rabbit plasma, 30 percent in dog plasma and only 10 percent in rat plasma. Systemic activation of the fibrinolytic system in the circulating plasmas was minor and dose-dependent in all species, but complete fibrinogen breakdown was not observed in any species following infusion of up to 90 IU EPA per ml plasma.It is concluded that the human system is more susceptible to EPA induced fibrinolysis than the other animal systems which were investigated, and that even totally-crosslinked clots can be lysed after infusion of EPA.

Human Recombinant Tissue-Plasminogen Activator (Alteplase): Why Not Use the ‘Human’ Dose for Stroke Studies in Rats?

“…These data, together with the fact that the cumulated reperfusion flow induced by 0.9 mg/kg rtPA was only one-half instead of one-tenth that induced by 10 mg/kg rtPA-as it might be expected from the in vitro studies of Korninger and Collen (1981)-indicate that the dose of 0.9 mg/kg rtPA could be as appropriate as that of 10 mg/ kg rtPA for performing preclinical stroke studies in rodents. Particularly, using 0.9 mg/kg rtPA could be of major importance for pharmacological considerations.…”

Thrombolytic properties of an inactive proenzyme form of human urokinase secreted from human kidney cells.

“…Our studies provide evidence that single-chain pro-urokinase is a more specific and effective thrombolytic agent than urokinase and that its thrombolytic properties are similar to those of t-PA (9,19,20). Single-chain pro-urokinase with its inactive proenzyme form and its high affinity for fibrin might be better than urokinase for use in thrombolytic therapy.…”

“…Thrombolysis by urokinase is associated with systemic plasminogen activation, the degradation of fibrinogen and the coagulation proteins in circulating blood (5,25). In contrast, the t-PA produced by a human melanoma cell line has been shown to be a more specific and effective thrombolytic agent than urokinase because of its high affinity for fibrin and its thrombus-localized stimulation of plasminogen activator activity without the activation of systemic plasminogen or the degradation of plasma proteins (9,16,20).…”

Effect of Delayed Thrombolysis with rt-PA in a Rat Embolic Stroke Model

“…Another problem is the poor affinity of human-derived rt-PA to rat plasminogen [�1O% compared with human plasminogen (Korninger and Collen, 1981)]. This problem was overcome by us ing 20 mg rt-PA/kg body weight (Overgaard et aI., 1992c) which is comparable to a dosage of � 1 mg/kg used in most human trials.…”