Immunohistochemical localization of plasminogen activators in human saphenous veins

Oxidative stress and release of tissue plasminogen activator in isolated rat hearts

To evaluate the potential of tissue plasminogen activator (t-PA) as a marker of endothelial activation or injury, the dose-response relationship between reactive oxygen intermediates and t-PA release was investigated in isolated rat hearts. After stabilization the hearts were perfused for 10 minutes with different concentrations of hydrogen peroxide (H2O2) (0 (control perfusion), 20, 40, 80, 120, 160, or 200 microM) (n = 8 hearts/group), followed by 30 minutes recovery. Higher concentrations than 80 microM induced cardiac dysfunction and a dose-dependent release of lactate dehydrogenase, indicating myocyte injury. H2O2-concentrations of 80 microM and more caused a significant, but temporary t-PA release. Peak t-PA release occurred more rapidly with higher concentrations, but otherwise there was no difference dependent on the H2O2-dose. The effects of H2O2 (120 or 200 microM) on t-PA release were also compared to the effects of bradykinin. Both were given for 10 minutes as above, and the procedure was repeated after 10 minutes recovery. Bradykinin (50 or 500 nM) released t-PA with the same magnitude, but with peak values occurring earlier than t-PA release induced by H2O2. Bradykinin, but not H2O2, induced t-PA release during the second exposure, suggesting different mechanisms of release.

IN CONCLUSION

Perfusion with H2O2 leads to a dose-dependent myocardial injury in isolated rat hearts. H2O2 also causes an acute t-PA release without dose-dependency, suggesting an all or nothing response of the endothelium. t-PA may be used as an indicator of, but cannot quantify endothelial activation or injury.

Release of tissue plasminogen activator during reperfusion after different times of ischaemia in isolated, perfused rat hearts

Tissue plasminogen activator (t-PA) is a potential marker of endothelial cell activation or injury. The relationship between duration of ischaemia and release of t-PA during reperfusion was investigated in isolated rat hearts exposed to either 5, 10, 20, 30, 40, or 60 min of global, normothermic ischaemia followed by 30 min of reperfusion (n = 8 in each group). t-PA activity was measured (chromogenic peptide substrate assay) in the effluent before ischaemia, and after 2.5, 5, 7.5, 10, 20, and 30 min of reperfusion. Release of lactate dehydrogenase (LD), a marker of myocyte injury, was measured before ischaemia and after 5 min reperfusion. Left ventricular pressures were measured by a balloon in the left ventricle. Ischaemia for 20 min or less had only minor effects on cardiac function. Thirty min or more of ischaemia induced ventricular fibrillation during reperfusion in most hearts. After ischaemia t-PA outflow increased, but without any significant difference between groups. Peak release occurred after either 2.5 or 5 min of reperfusion. After 10 min reperfusion the release was not different from the basal value. In contrast, postischaemic release of LD correlated to the length of ischaemia. To conclude, t-PA release from the ischaemic-reperfused rat heart is independent of the length of ischaemia. Thus the potential of t-PA to quantify endothelial injury appears to be limited.

Reactive oxygen intermediates and ischemia-reperfusion injury release tissue plasminogen activator from isolated rat hearts

Tissue plasminogen activator (t-PA) is a marker of endothelial cell injury or activation. The release of t-PA from isolated rat hearts (Langendorff model) subjected to ischemia-reperfusion or reactive oxygen intermediates (ROI) generated by H2O2 was investigated. H2O2 (200 microM) increased t-PA activity in the coronary effluent to 305 +/- 84% of initial value (mean +/- SEM, p < 0.04 vs controls) at the end of a 10 min intervention. The hydroxyl radical scavenger thiourea (10 mM) only partially inhibited the increase (175 +/- 27%, p < 0.01 compared to controls). 20 min normothermic ischemia increased t-PA activity to 416 +/- 108% (p < 0.005 compared to controls) at the start of reperfusion. In conclusion, cardiac injury by ischemia-reperfusion or ROI increases release of t-PA.

High-level expression of recombinant human tPA in cultivated canine endothelial cells under varying conditions of retroviral gene transfer

Successful genetic transduction of endothelial cells (EC) provides a theoretic means of increasing luminal secretion of tissue-type plasminogen activator (tPA) and lessening arterial and venous thrombotic processes. To identify the duration and number of retroviral exposures for an optimal tPA expression, enzymatically derived adult canine jugular venous EC were subjected to different exposure regimens using an amphotropic murine retroviral vector, MFG, containing the human tPA gene. Human tPA antigen secretion and its functional activity were determined at 2 days (subconfluent cells) and 14 days (confluent cells) after retroviral exposure. High-level secretion of human tPA was detected among transduced EC in all experimental groups. No secretion of human tPA occurred in control EC exposed to media alone. At 2 days after transduction, no significant differences in tPA secretion rates occurred among the different exposure regimens. At 14 days, the 12-hour X two-exposure group exhibited higher tPA secretion rates than all other exposure regimens (analysis of variance, p < 0.05). All exposure groups at 14 days exhibited significantly higher tPA secretion compared with those at 2 days (analysis of variance, p < 0.05). The presence of retroviral sequences in the genome of transduced EC was confirmed by Southern blot analysis. At 14 days, increased EC numbers were observed in vector-exposed wells compared with controls. Human tPA functional activity paralleled tPA antigen secretion. Genetically modified canine EC are capable of high levels of constitutive expression of human tPA after relatively short exposures to a retroviral vector containing the reporter gene. Increased cell number of tPA-transduced EC in culture suggests that tPA also may have other biologically important effects. These results support the efficacy of MFG-tPA gene transfer as a means of genetically modifying EC fibrinolytic activity and establishes the potential of this technology in vivo.

Inhibition of fibrinolysis by cellular glutathione depletion in the rabbit

The effect of cellular glutathione depletion on fibrinolytic activity in the arterial wall and on the levels of components of the plasma fibrinolytic system was studied in rabbits. Intraperitoneal administration of buthionine sulphoximine (4.5 mmol/kg body wt), an inhibitor of gamma-glutamyl cysteine synthetase, induced a significant reduction in liver glutathione concentrations with a peak decrease of 51% at 7 hours and a progressive return to normal values. The glutathione concentration in aortic tissue was also significantly reduced 7 h after administration of the depleting agent. Fibrinolytic activity in the arterial wall was inhibited following buthionine sulphoximine administration and only reappeared at 24 hours postinjection. Diethyl maleate administration (3.2 mmol/kg body wt i.p.) also depleted liver and aortic glutathione and inhibited fibrinolysis in the arterial wall. Treatment with both glutathione-depleting agents induced a significant reduction in the functional activity of tissue plasminogen activator (t-PA) (-61% and -27% respectively for buthionine sulphoximine or diethyl maleate) and a significant increase in that of plasminogen activator-inhibitor (PAI) (+61% and +27% respectively), while alpha-2-antiplasmin activity was not modified. Our data suggest a modulatory role of glutathione in the release and/or clearance of the components of the fibrinolytic system in the rabbit.

Release of both urokinase and tissue plasminogen activator from veins in vitro

Specimens of human veins were incubated in culture media, in which the concentrations of urokinase (UK) and tissue plasminogen activator (t-PA) were determined by radioimmunoassay and immunoradiometric assay. Both UK and t-PA were released to the media, in which the concentration of plasminogen activators was correlated to the weight of the specimens. The release of t-PA was maximal on the first day, after which it rapidly decreased, and t-PA was not demonstrable after the third day of incubation. By contrast, UK was continuously liberated to the media during the study period of 5 days. The present results indicate that both UK and t-PA are present in the vein wall and probably released by different cells.