Constitutive synthesis of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAT-1): Conditions and therapeutic targets

Review: Diabetes as a procoagulant condition

Major known effects of the metabolic derangements of diabetes in haemostasis are induction of platelet-vascular activation by hyperglycaemia, the increase in fibrinogen, modification of fibrin substrate by glucose and hypofibrinolysis related to insulin resistance. The platelet effects are specifically expressed during high shear stress and may be relevant in particular for developing of micro-angiopathy. Hypofibrinolysis, increased fibrinogen and modifications of fibrin may aggravate microthrombosis and organ damage and contribute to precipitation of coronary and cerebral infarction. In addition to specific anti-diabetic medication to reduce the haemostatic effects, specific antiplatelet and profibrinolytic treatments may be relevant for reducing further the morbidity and mortality in diabetics for both micro- and macro-angiopathy.

Low level of tissue plasminogen activator activity in non-diabetic patients with a first myocardial infarction

OBJECTIVE

To explore the role of tissue plasminogen activator (tPA) activity and plasminogen activator inhibitor type 1 (PAI-1) in survivors of a first myocardial infarction (MI). Insulin and proinsulin were analysed as potential risk factors.

DESIGN

Case-control study in northern Sweden.

SUBJECTS

A total of 115 patients under 65 years of age with a first MI were enrolled and recalled for further examination 3 months later. Twenty-seven patients were excluded, 17 with known diabetes and 10 who did not come to the follow-up, giving a final number of 88 patients, 73 men and 15 women. Patients were age- and sex-matched with control subjects drawn from the local cohort in the MONICA population survey 1994.

MAIN OUTCOME MEASURES

We compared MI patients and controls using univariate and multiple regression analyses including odds ratios (OR).

RESULTS

PAI-1 activity, fibrinogen, postload insulin and -proinsulin were significantly higher and tPA activity significantly lower in MI patients in the univariate analysis. In a multiple regression analysis, including also age, sex and cardiovascular risk factors, these parameters were divided in quartiles. The lowest quartile of tPA activity was significantly associated with MI (OR = 19.1; CI 3.0-123) together with the highest quartiles of fibrinogen (OR = 25; CI 5.2-120) but other variables were not.

CONCLUSION

Low tPA activity, i.e. low fibrinolytic activity, characterized nondiabetic subjects after a first MI which is not explained by concomitant disturbances in metabolic and anthropometric variables.

Work stress and metabolic and hemostatic risk factors

OBJECTIVE

A high level of work stress has been associated with cardiovascular disease. However, the pathophysiological mechanisms underlying this association remain unclear. This study examined the effect of work stress on a cluster of metabolic and hemostatic risk factors.

METHODS

Blood was collected three times, on the first, third, and fifth day of a work week, from 124 middle-aged, white-collar workers. Metabolic measures were insulin, glucose, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and total cholesterol. Hemostatic measures were fibrinogen, tissue-type plasminogen activator activity, tissue-type plasminogen activator antigen, and type 1 plasminogen activator inhibitor antigen. Chronic work stress was defined according to Siegrist's model as 1) a combination of high effort and low reward at work (effort-reward imbalance) or 2) high overcommitment (an exhaustive work-related coping style).

RESULTS

Overcommitment, but not imbalance or the imbalance-overcommitment interaction, was associated with an impaired fibrinolytic system, as reflected in decreased tissue-type plasminogen activator activity levels and increased type 1 plasminogen activator inhibitor antigen levels on all three measurement occasions. After controlling for body mass index, total cholesterol, triglycerides, high-density lipoprotein/low-density lipoprotein cholesterol ratio, glucose, and insulin, the relation between overcom-mitment and the fibrinolytic factors was attenuated but remained significant.

CONCLUSIONS

The results suggest that individuals with an exhaustive coping style at work have an impaired fibrinolytic capacity that is possibly due to the effects of chronic stress on insulin resistance.

Gene polymorphism of t-PA is associated with forearm vascular release rate of t-PA

We have observed marked interindividual differences in release rates of tissue-type plasminogen activator (t-PA) among healthy subjects. The objective of the current study was to test the hypothesis that there is an association between a genetic variation at the t-PA locus and the in vivo release rate of t-PA. Fifty-one healthy males were studied at rest in the morning and 27 of these were also subjected to a mental stress test. Net release rates of total t-PA across the forearm vascular bed were calculated as the product of the venoarterial concentration gradient and forearm plasma flow. Zygosity for an Alu-repeat polymorphism in intron 8 of the t-PA gene was determined by a polymerase chain reaction. Basal t-PA release rates differed markedly by genotype (ANOVA, P<0.05); subjects homozygous for the insertion had a significantly higher release rate (mean 10.9 ng. min-1. L-1, n=19) than both heterozygotes (4.5 ng. min-1. L-1, n=26) and subjects homozygous for the deletion (0.9 ng. min-1. L-1, n=6). After 2 minutes of mental stress release rates had increased approximately 2-fold in all groups. Arterial and venous plasma levels of t-PA were unrelated to genotype. In conclusion, the current results provide the first evidence of an association between a common genetic variation at the t-PA locus and interindividual differences in net release rates of t-PA in vivo. The relationship is not reflected by circulating steady-state plasma levels and can thus not be disclosed by conventional venous plasma sampling.

Tissue plasminogen activator and risk of myocardial infarction. The Rotterdam Study

BACKGROUND

Impaired fibrinolytic capacity, as assessed by euglobulin clot lysis time or plasma concentration of fibrinolytic parameters, has been associated with an increased risk of myocardial infarction (MI). We studied the association of a polymorphism in the gene for TPA and of plasma concentrations of TPA (antigen and activity) with the prevalence of MI.

METHODS AND RESULTS

A case-control study was performed. Subjects with a history of MI (n = 121) and controls (n = 250) were drawn from the Rotterdam Study, a population-based cohort study of 7983 subjects > or = 55 years old. We determined TPA antigen and activity in plasma and genotyped all subjects for the Alu repeat insertion/deletion polymorphism in intron h in the TPA gene. Homozygosity for the insertion was associated with twice as many cases of MI as was homozygosity for the deletion (odds ratio, 2.24; 95% CI, 1.11-4.50). TPA antigen was positively associated with the risk of MI; compared with that in the lowest quartile, the relative risks (odds ratio) in the second, third, and upper quartiles were 1.7 (CI, 0.9-3.3), 2.3 (1.2-4.4), and 2.0 (1.0-3.8), respectively. When adjusted for body mass index, HDL and total cholesterol, systolic and diastolic blood pressures, and current smoking, the risk associated with TPA antigen concentration was attenuated. Increased concentrations of TPA activity tended to be associated with an increased risk of MI.

CONCLUSIONS

This study provides evidence for an independent association of the insertion allele of the insertion/deletion polymorphism in the TPA gene with nonfatal MI. Increased TPA antigen is associated with an increased risk of MI; however, this association was not independent of cardiovascular disease risk factors.

Increased levels of tissue plasminogen activator antigen in essential hypertension. A population-based study in Sweden

OBJECTIVE

To investigate components of the haemostatic and fibrinolytic system in borderline hypertensives and hypertensives, drug-treated or not, from a defined population.

DESIGN AND METHODS

A randomly selected sample of the population of northern Sweden, 1558 subjects aged 25-64 years, was studied. Eight per cent of them were being treated with antihypertensive drugs (trHT). Remaining subjects were classified according to their mean diastolic blood pressure (DBP). Normotension, DBP < 85 mmHg, was found in 63%, borderline hypertension (bHT), DBP 85-94 mmHg, in 21% and untreated hypertension (uHT), DBP > or = 95 mmHg, in 8% of the subjects.

RESULTS

Mean age increased from the normotensive group through the bHT and uHT groups to the trHT group, members of which were the oldest. Age-adjusted values for the body mass index, waist: hip ratio, serum triglyceride and Phadeseph plasma insulin levels increased with each level of hypertension. Plasma fibrinogen levels and plasminogen activator inhibitor type 1 activity (in men) increased stepwise from normotensives through bHT and uHT to the highest values found in the trHT group. The tissue plasminogen activator (tPA) activity in men declined strongly across the groups, trHT having the lowest fibrinolytic activity (P < 0.001). tPA antigen levels increased strongly from normotensives through bHT to uHT, but then were lower in the trHT group. Even after adjustment for possible confounders, men in the uHT group had 21% higher (P = 0.027) tPA antigen levels than did the normotensives. In bHT men, the tPA antigen and plasminogen activator inhibitor type 1 activities were 14 and 24% respectively, higher (P < 0.01) than those in the normotensives.

CONCLUSION

Hypertension is associated with multiple metabolic and fibrinolytic disturbances that are accentuated in drug-treated hypertensives and already discernible in subjects with borderline hypertension. Decreased fibrinolysis is associated with, and possibly secondary to, metabolic disturbances linked to the insulin-resistance syndrome. The independent increase in tPA antigen in hypertensive men might indicate an endothelial dysfunction.

Inherited defects of the protein C anticoagulant system in childhood thrombo-embolism

Childhood thrombo-embolism is mostly the result of inherited thrombophilia or vascular insults combined with risk factors such as peripartal asphyxia, fetopathia diabetica, exsiccosis, septicaemia, central lines, congenital heart disease, cancer, trauma, surgery or elevated antiphospholipid antibodies. Inherited thrombophilia includes mainly defects of the protein C pathway, resistance to activated protein C, protein C or protein S deficiency. Resistance to activated protein C, in the majority of cases caused by the point mutation Arg 506 Gln of the factor V gene, has emerged as the most important hereditary cause of thrombo-embolism in adults and children. However, since an acquired risk of thrombo-embolic complications frequently masks the inherited deficiency in affected children, children with thrombo-embolism should have adequate laboratory evaluation for inherited coagulation disorders, especially the protein C pathway. Until more data on childhood thrombo-embolism are available, treatment recommendations will continue to be extrapolated from guidelines for adults.

Tissue plasminogen activator and plasminogen activator inhibitor-1 in stroke patients

BACKGROUND AND PURPOSE

Abnormal endogenous fibrinolytic activity may be a risk factor for stroke. Since the possible variation of tissue-type plasminogen activator (TPA) antigen and plasminogen activator inhibitor-1 (PAI-1) antigen concentrations over time after stroke has been rarely studied, it was examined in plasma from stroke patients in the acute and convalescent phases of the disease and in a control group.

METHODS

Plasma concentrations of TPA and PAI-1 were determined in 135 stroke patients and in 77 control subjects. All but 4 patients were examined within 7 days after stroke onset, and 32 patients and 18 control subjects were reexamined 2 to 4 years later.

RESULTS

In the acute phase, stroke patients had significantly higher TPA (median, 10 micrograms/L) and PAI-1 (median, 14 micrograms/L) antigen concentrations, compared with control subjects (median values, 6 micrograms/L [P = .0001] and 8 micrograms/L [P < .01], respectively); TPA levels were higher in both the cerebral infarction (n = 122) and cerebral hemorrhage (n = 12) subgroups, whereas PAI-1 levels were higher in the cerebral infarction subgroup only. Stepwise logistic regression analysis (with correction for age, sex, history of hypertension, diabetes mellitus, and heart disease) showed TPA antigen level to be an independent discriminator between the cerebral infarction subgroup and control subjects (P = .0001), whereas the corresponding difference for PAI-1 antigen levels just failed to reach significance (P = .05). TPA antigen levels were correlated with concentrations of serum cholesterol (Spearman's rho = 0.15; P < .05), serum triglyceride (rho = 0.33; P = .0001), and plasma homocysteine (rho = 0.19; P < .01). PAI-1 antigen levels were correlated with serum triglyceride levels only (rho = 0.41; P = .0001). At reexamination after 2 to 4 years, neither TPA nor PAI-1 levels had changed significantly from the baseline values.

CONCLUSIONS

In stroke patients, high TPA antigen concentrations may indicate an activation of the fibrinolytic system or may be due to a delayed clearance of TPA complexed with inhibitors. High PAI-1 antigen concentrations in patients with cerebral infarction represent increased fibrinolytic inhibition. The findings in this longitudinal study suggest that TPA and PAI-1 antigen concentrations both differ little between the acute and convalescent phases after stroke.

Beneficial effect of a moderately energy-restricted diet on fibrinolytic factors in non-obese men

Impaired fibrinolytic activity has been reported in the elderly and is thought to play a role in the etiology of cardiovascular disease, one of the leading causes of death in most Western countries. Since restriction of energy intake has been demonstrated to act beneficially on the aging process in a variety of species, we studied the effect of a 10-week moderately energy-restricted (ER) regimen (80% of habitual) on plasminogen activator inhibitor (PAI) activity, PAI-1 antigen, tissue plasminogen activator (tPA) activity, and tPA antigen in non-obese, middle-aged men. Moreover, the relationship between these fibrinolytic markers and glucose tolerance was investigated. Weight loss in the ER group (n = 16) was considerable (-7.4 +/- 1.7 kg, P < .001). Subjects in the control group (n = 8) also lost some weight (-2.1 +/- 1.5 kg, P < .01). Fasting glucose levels decreased in the ER group (-0.31 +/- 0.48 mmol/L, P < .05), which was correlated with the extent of weight loss (P < .01). Baseline insulin levels at 2 hours after an oral glucose load correlated with baseline PAI activity (P < .001) and PAI-1 antigen levels (P < .001). PAI activity decreased in the ER group (-2.94 +/- 2.90 IU/mL, P < .001), particularly in subjects with a high baseline PAI activity (> 9 IU/mL). Furthermore, energy restriction led to decreased PAI-1 antigen concentration (P < .05), a nonsignificant increase in tPA activity, and a decrease in tPA antigen concentration (P < .001). All these changes were more clear in subjects with a high baseline PAI activity. These results suggest that 10 weeks of moderate energy- restriction has a profibrinolytic effect in non-obese, middle-aged men, at least in subjects with higher baseline PAI activity (> 9 IU/mL). Moreover, in line with the suggestion that high PAI activity goes together with insulin resistance, a relationship between insulin concentration after a glucose load and PAI activity was found.

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.