Clot lysis: role of plasminogen activator inhibitors in haemostasis and therapy.

An unimpeded circulation of blood depends on the concerted activation of coagulation and fibrinolytic factors. The latter entails the controlled, localised conversion of plasma zymogen plasminogen to the active enzyme plasmin mediated by tissue-type plasminogen activator (tPA). Bulk of tPA activity is in the proximity of the endogenous plasminogen activator inhibitor (PAI) as an active complex. The advent of molecular biology techniques has enabled isolation of cDNA for the inhibitors PAI-1, PAI-2 and PAI-3 and data indicate that these belong to the serine protease inhibitor (Serpine) family with arginine as its active site but immunologically distinct from each other. Enhanced tPA or PAI-1 forms one of the risk factors related to cardiac diseases and thrombotic disorders. A line of therapy entails lowering of PAIs with concomitant increase in tPA levels leading to net enhancement in fibrinolytic activity. In as much as plasminogen activators exert their action extracellularly, they are accessible to inhibitors and therefore PAIs could have a therapeutic potential and serve as prognostic indicators in cancer. Documented findings related to the biochemical characteristics and therapeutic potential of PAIs are presented and discussed in the review.

Enhanced expression of urokinase-type plasminogen activator in the rat endometrium following induction of decidualisation.

Urokinase-type plasminogen activator(uPA) assayed in uteri of cycling and deciduoma bearing rats shows detectable levels of this enzyme in endometrium. Zymographic analysis confirms uPA of decidual tissue and, following artificial induction of decidualisation, uPA activity constantly increases in the decidualising endometrium reaching a peak on day 9 of pseudopregnancy. Endometrial uPA of nonpregnant rats does not show any significant change during estrous cycle. Results are discussed in relation to expression of this activator in endometrium of rats during morphogenesis of decidual cells.

Plasminogen activator: Isolation and purification from lymphosarcoma of ascites bearing mice.

Plasminogen activator secreted by lymphosarcoma (ascites) of mice was purified up to 163-fold by ammonium sulphate fractionation at 35% saturation and chromatography on p-aminobenzamidine-Sepharose 4B. The purified activator contained specific activity of 9980 IU/mg. The plasminogen activator displayed homogeneity by polyacrylamide slab gel electrophoresis and high performance liquid chromatography. The activator consisted of a single polypeptide chain with an apparent molecular weight of 66,000 daltons as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing conditions as well as gel filtration on Sephadex G-100. Distinct differences between this activator and urokinase were discernible in respect of specific activities, fibrin affinity and immunochemical properties. The lymphosarcoma activator appears to be of tissue-type origin since it showed gross similarity to standard tissue plasminogen activator in terms of modes of binding to fibrin and immunological attributes.

Isolation and purification of plasminogen activator from Yoshida ascites Sarcoma of rats.

The plasminogen activator was purified to the extent of 150-fold from 20,000 x g supernatant of Yoshida ascites Sarcoma by ammonium sulphate precipitation at 33% saturation followed by affinity chromatography on p-aminobenzamidine-Sepharose 4B. The specific activity of the purified activator was 10,260 IU/mg expressed in terms of International units of urokinase, the known activator of plasminogen. The activator was homogeneous by polyacrylamide slab gel electrophoresis with an apparent molecular weight 75 kDa by gel filtration on Sephadex G-100. Analysis by SDS-polyacrylamide gel electrophoresis under reducing conditions, revealed the presence of two subunits of about 48 and 29 kDa. The activator displayed binding preference to fibrin and was immunologically distinguishable from urokinase, indicating that it could be of non-urokinase origin. The preparation further revealed similarity to standard tissue plasminogen activator with respect to fibrin binding and immunological cross reactivity.