Physical Exercise Induces Enhancement of Urokinase-Type Plasminogen Activator (u-PA) Levels in Plasma

Increased level of circulating cell-free mitochondrial DNA due to a single bout of strenuous physical exercise

Purpose

Physical exercise is reported to affect the immune response in various ways. Thus, the levels of pro-inflammatory cytokines as well as the abundance of circulating leukocytes are changed. In this study, the occurence of circulating cell-free mitochondrial DNA (cfmtDNA) and nuclear DNA (nDNA) was investigated in connection with a single bout of strenuous physical exercise.

Methods

Healthy volunteers performed a controlled ergo-spirometry cycle test and venous blood samples were taken at different time-points to analyze the concentration of blood components before, during and after the test. The number of circulating leukocytes was measured, as well as secretion of the soluble urokinase activator receptor (suPAR).

Results

Cf-mtDNA significantly increased during exercise, compared to baseline values and after 30 and 90 min of rest. Circulating leukocytes increased during exercise, but returned to baseline levels afterwards. Surface expression of the urokinase plasminogen activating receptor (uPAR) on neutrophils decreased significantly during exercise. The concentration of suPAR tended to increase during exercise but only significantly after 90 min of rest.

Conclusion

Increased concentration of cf-mtDNA indicates that cell damage takes place during high intensity training. Hypoxia and tissue damage are likely causes of cf-mtDNA from muscle cells. The levels of cf-mtDNA remain high during the initial rest, due to the decreasing numbers of leukocytes normally clearing the plasma from cf-mtDNA. The increased levels of suPAR further emphasize that strenuous physical exercise causes a reaction similar to inflammation. Further studies are needed to detect the source of increased cf-mtDNA and the corresponding increase of suPAR liberation.

Comparison of t-PA and u-PA levels in maximal treadmill and deep-water running

BACKGROUND

The differences of urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA) between maximal treadmill and deep-water running have not been reported. The purpose of this investigation was to compare u-PA and t-PA levels during maximal treadmill and deep-water running.

METHODS

Six male subjects carried out two maximal exercises, one on a treadmill and the other running in deep water using a vest. The u-PA, t-PA, total plasminogen activator inhibitor (PAI-1), epinephrine, and norepinephrine in plasma and lactate and ammonia in blood concentrations were measured after maximal exercise.

RESULTS

The blood lactate and ammonia concentrations were significantly higher in treadmill running than in deep-water running during recovery following exercise (P < 0.05). At 1 min after exercise, the plasma epinephrine, norepinephrine levels, and the u-PA and t-PA levels were higher in treadmill running compared with that in deep-water running (P < 0.05). No significant difference between the two runs was found in PAI-1 level.

CONCLUSION

The maximal treadmill running induced a greater increase in u-PA and t-PA levels than maximal deep-water running.

Exercise and Training Effects on Blood Haemostasis in Health and Disease

In recent years, the dysfunction of the haemostatic system in relation to the clinical complications from arterioscleroses and cardiovascular diseases has become more recognised. Blood coagulation and fibrinolysis comprise two important physiological systems, which are regulated by a balance between activators and inhibitors. Activation of blood coagulation is associated with accelerated clot formation, whereas activation of blood fibrinolysis enhances the breakdown of the blood clot. Available evidence suggests that strenuous exercise induces activation of blood coagulation with simultaneous enhancement of blood fibrinolysis. Although the responses of blood coagulation and fibrinolysis appear to be related to the exercise intensity and its duration, recent reports suggest that moderate exercise intensity is followed by activation of blood fibrinolysis without concomitant hyper-coagulability, while very intense exercise is associated with concurrent activation of blood coagulation and fibrinolysis. Similar to blood coagulation and fibrinolysis, systemic platelet-related thrombogenic factors have been shown to be involved in the initiation and progression of atherogenesis and plaque growth. Although exercise effects on platelet aggregation and function in healthy individuals have been examined, the results reported have been conflicting. However, for patients with coronary heart disease, the balance of evidence available would strongly suggest that platelet aggregation and functions are increased with exercise. Few studies are available concerning the influence of training on blood coagulation and fibrinolysis and the exact effects of exercise training on the equilibrium between blood coagulation and fibrinolysis is not as yet known. Although the effects of physical training on platelets have been briefly investigated, available meagre evidence suggests that exercise training is associated with favourable effects on platelet aggregation and activation in both men and women.

Urokinase-type plasminogen activator up-regulates its own expression by endothelial cells and monocytes via the u-PAR pathway

Signal transduction by urokinase-type plasminogen activator (u-PA) bound to its cell receptor has been well established. In the present study, we found, for the first time to our knowledge, that u-PA promotes its own synthesis by endothelial cells and monocytes. This phenomenon was characterized and shown to involve the u-PA receptor (u-PAR) pathway. The finding may be of general importance, since most cells that express u-PAR also produce u-PA. Human umbilical vein endothelial cells (HUVECs), U937 monocytes, and human peripheral blood monocytes (PFMCs) were incubated with diisopropylfluorophosphate (DFP)-pretreated u-PA, the amino-terminal fragment (ATF) of u-PA, or the kringle domain. A threefold up-regulation of u-PA secretion and synthesis by u-PA or ATF was found. The predominant effect was expressed in HUVECs, in which u-PA mRNA was also up-regulated. The u-PA kringle domain had no effect on u-PA synthesis, leading to the conclusion that the EGF domain was responsible. This was also consistent with the additional finding that the u-PAR, to which the EGF domain binds, was necessary for the up-regulation. The results indicate that u-PA up-regulates itself via its EGF domain and u-PAR. The possibilities that the results were related to displacement of receptor-bound u-PA or the blocking of u-PA incorporation into the cells were excluded. A modest up-regulation of u-PAR was also associated with this phenomenon.

Effect of endurance training and seasonal fluctuation on coagulation and fibrinolysis in young sedentary men

The effect of 12 wk of submaximal training on hemostatic variables was studied in 20 young sedentary men (Tr) and 19 nontraining matched controls (Con). After training, a more pronounced increase in factor VIII coagulant activity (P < 0.01), reflected in a decrease in activated partial thromboplastin time (P < 0.01) during maximal exercise, was seen. Both basal plasminogen activator inhibitor 1 antigen (PAI-1 Ag) and activity (PAI-1 Act; P < 0.05), as well as basal and exercise-induced tissue-type plasminogen activator antigen (t-PA Ag; P < 0.05), were decreased after training. The overall effect on fibrinolysis was reflected in an increase in the t-PA Act/t-PA Ag ratio in the Tr group. In contrast, during the same period (February-June), the Con group demonstrated an increase in basal PAI-1 Ag and PAI-1 Act (P < 0.05), together with an increase in basal and exercise-induced t-PA Ag (P < 0.05). Both basal and exercise-induced t-PA Act were unchanged, but t-PA Act/t-PA Ag was decreased (P < 0.05) in the Con group. We conclude that physical training promotes both coagulation and fibrinolytic potential during exercise and may reverse unfavorable seasonal effects on fibrinolysis.

The circulatory regulation of TPA and UPA secretion, clearance, and inhibition during exercise and during the infusion of isoproterenol and phenylephrine

BACKGROUND

Exercise to exhaustion and infusions of isoproterenol and phenylephrine were used to study interactions between plasminogen activator regulation and the control of regional blood flow in 10 healthy males.

METHODS AND RESULTS

Experimental measurements of cardiac output, heart rate, tissue plasminogen activator (TPA), urokinase plasminogen activator (UPA), plasminogen activator inhibitor (PAI-1), C1-inhibitor, and TPA/C1-inhibitor complex during the infusions and exercise were used to develop a comprehensive fluid-phase model of the circulatory regulation of fibrinolysis. alpha- and beta-adrenergic agonists increased TPA and UPA in plasma by different mechanisms: Phenylephrine decreased hepatic blood flow and thus clearance while isoproterenol stimulated increased secretion of TPA and UPA. Exercise to exhaustion increased TPA and UPA through a combination of increased secretion and decreased clearance. The time course of UPA and TPA release were similar, but the magnitude of their secretion responses differed. In vivo, C1-inhibitor bound to TPA at a rate of 553 mol-1.s-1. C1-inhibitor contributed equally with PAI-1 to TPA inhibition when active PAI-1 levels were low (20 to 50 pmol/L) but was less important when active PAI-1 levels were high.

CONCLUSIONS

We conclude that secretion, inhibition, clearance, and regional blood flow effects must all be taken into account when evaluating changes in plasminogen activator levels.

Hypofibrinolysis in patients with hypercoagulability: the roles of urokinase and of plasminogen activator inhibitor

The prevalence of abnormalities of fibrinolysis in patients with venous thromboembolism is as yet unknown. Defined abnormalities include congenital dysfunction and deficiency of plasminogen, and probably impaired plasminogen activation secondary to elevated levels of plasminogen activator inhibitor type 1 (PAI-1) or to impaired release of tissue plasminogen activator (tPA). In this preliminary study, we analyzed plasma samples from 21 patients for whom an investigation for possible thrombophilia was requested. Twenty of the patients had venous thromboembolism, and one had arterial thrombosis at an early age. Two patients had deficiency of protein C or protein S, but no other recognized biochemical disturbances related to thrombophilia were identified. Patient samples and plasma from 25 normal controls were assayed for tPA activity, PAI-1 activity, and urokinase (uPA) activity and antigen. tPA activity and antigen were not significantly different in patients than in controls. PAI-1 activity was significantly greater in patients (P < 0.0001). uPA activity was not different in the two groups. However, uPA antigen was significantly reduced in patients compared to controls (P = 0.001). These data suggest that hypofibrinolysis leading to a risk of thrombosis may be caused not only by elevated PAI-1 activity but also by reduced total uPA concentration.

Effect of endurance training on angiogenic activity in skeletal muscles

The effect of endurance training on angiogenic activity in skeletal muscle was investigated using cell culture. The exercised rats were trained on a rodent treadmill, 5 days a week for 9 weeks. After the training program, a significant increase (7.8%) in mass was found in soleus muscle (MS), although we noted no apparent increase in gastrocnemius muscle and extensor digitorum longus muscle. The extracts from all the muscles (especially from the MS) of trained rats considerably increased the capillary growth in an in vitro angiogenesis model, in which microvascular fragments and myofibroblastic (Mf) cells isolated from lipid tissues were grown in co-culture. In addition, the extract from the MS of trained rats increased the DNA synthesis and growth of bovine capillary endothelial (BCE) cells, although the extract did not stimulate the growth of Mf cells. Moreover, the extract from the MS of trained rats notably enhanced the activity of plasminogen activator in the conditioned medium of BCE cells compared with that of sedentary rats. On the other hand, extracts from the MS of both sedentary and trained rats increased the synthesis of collagen by Mf cells and metalloproteinase activity in the conditioned medium of BCE cells to the same degree. These results suggest that endurance training increases the angiogenic activity in skeletal muscles.

Changes in the fibrinolytic system associated with physical conditioning

The effects of physical conditioning on plasma fibrinolytic activity were studied in two groups of subjects. Volunteers not engaged in any sport were compared with individuals having been subjected to aerobic conditioning (middle-distance runners, defined as men running more than 80 km per week). Plasma concentrations of the different components of the fibrinolytic system were evaluated before and immediately after a maximal effort treadmill protocol. Comparison of the resting parameters revealed that under basal conditions for plasma concentrations of plasminogen, fibrinogen, alpha 2-antiplasmin, protein C and protein S there were no differences between the two groups. Concentrations of the fibrin degradation products (FbDP) and fibrinogen degradation products (FgDP) were significantly higher in the runners than in the control group, indicating an increased fibrinolytic potential that seemed to be a consequence of the reduced formation of tissue plasminogen activator-plasminogen activator inhibitor (t-PA-PAI) complexes. Acute maximal exercise resulted in pronounced fibrinolysis, evidenced by the elevation of FbDP and FgDP concentrations, in both groups of subjects. The acceleration of the fibrinolytic activity was larger in conditioned individuals, which could be accounted for by a higher t-PA release and reduced formation of t-PA-PAI complexes when compared to the untrained subjects.

Urokinase-type plasminogen activator release after DDAVP in von Willebrand disease: different behaviour of plasminogen activators according to the synthesis of von Willebrand factor

Nine healthy volunteers and 23 patients with various types of von Willebrand disease were studied before and after DDAVP infusion. We investigated the behaviour of factor VIII/von Willebrand factor measurements, and of tissue plasminogen activator and urokinase-type plasminogen activator. In mild von Willebrand disease the increase of both plasminogen activators was similar to that seen in normal controls. A different fibrinolytic behaviour was found in the type I platelet low and in the type III von Willebrand disease patients. An impaired and absent fibrinolytic response to DDAVP was seen in the former and in the latter von Willebrand disease, respectively. A close relation between either u-PA and t-PA or von Willebrand factor was observed. The possibility of a linkage among these three proteins was discussed.