This is the first study to demonstrate that there are no differences in fibrin clot structure, thrombin generation process or fibrinolytic activity in two forms of endocrine hypertension (PA and PPGL) as compared to matched patients with EHT. During follow-up fibrin clot parameters and activation of blood clotting and fibrinolysis remained unchanged after causative treatment, both in patients with PA and in PPGL patients. It is of note that all studied, hypertensive groups were characterized by more compact fibrin clot structure, faster clot formation and enhanced thrombin generation in comparison to healthy controls. The prothrombic state of hypertensive patients have been reported previously.[11,18,32]
The harmful effects of aldosterone on the cardiovascular system were observed in several studies and multiple pathomechanisms have been postulated.[12,18] In different animal models, experimental evidence has linked aldosterone excess with vascular and perivascular inflammation, oxidative stress and fibrosis, whereas fibrin clot structure or fibrinolysis have not been comprehensively investigated in PA patients.
The available evidence, both on animal models and in humans, suggests that the renin–angiotensin–aldosterone system (RAAS) may participate in the regulation of fibrinolytic activity.[19–23] PAI-1 is the most important physiological inhibitor of t-PA in plasma and thus plays an important role in the regulation of the plasminogen activator/plasmin system. Elevated levels of PAI-1 have been implicated in the pathogenesis of thromboembolic disease.[19,23] In a large study of Sechi et al. the positive association with increasing plasma renin activity in 247 patients with EHT was demonstrated for plasma fibrinogen, D-dimer and PAI-1 levels, what proved that there is an independent association between renin, aldosterone and markers of prothrombic state in EHT. In one small study in humans (four normotensives and six patients with EHT), in vivo data suggest that infusion of angiotensin II results in a rapid increase in circulating levels of PAI-1 and therefore in suppression of fibrinolysis. In another study the effect of activation of the endogenous RAAS on the plasma fibrinolytic balance in nine healthy human subjects was examined. The data suggested that activation of the RAAS results in increased PAI-1 antigen during the morning hours, and that interruption of the RAAS with the angiotensin-converting-enzyme inhibitor (quinapril) significantly lowers PAI-1 antigen and activity without lowering t-PA antigen.
In PA patients PAI-1 levels and t-PA levels were investigated in two independent studies by Sang et al. and Petrak et al. Sang et al. compared 36 PA patients and 31 EHT patients and found no differences in PAI-1 levels, nor other investigated biomarkers of endothelial dysfunction, what stays in line with the results of our study (no differences in PAI-1 level between PA and EHT groups). Petrak et al. assessed the levels of biochemical markers, including t-PA in different hypertensive groups (EHT, PA, pheochromocytoma and controls). They found no differences in t-PA levels in PA and EHT, what also confirms our results. In our study, unlike in Petrak et al. study, we found a higher level of t-PA antigen in PA patients as compared to healthy controls. No statistical differences in PAI-1 level between the groups were noted. In general, however, when we sum up all assessed fibrinolytic parameters, we may conclude that both PA and EHT are characterized by rather impaired fibrinolysis as compared to healthy controls.
In our study, we did not, therefore, prove that an excess of aldosterone caused by autonomous overproduction influences fibrinolytic activity in a different way than observed in the conditions of exogenous and endogenous RAAS stimulation. It is of note, that despite normalisation of the aldosterone level in 3 months follow-up, there were no differences in PAI-1 and t-PA levels at baseline and after causative treatment. Our observation suggests that the effect of the RAAS on fibrinolytic activity is not mediated by aldosterone, but, as was proven in previous studies, through angiotensin II.[19–21]
To sum up, our study showed there is no evidence that patients with PA are characterized by more prothrombotic fibrin clot phenotype, clotting or fibrinolytic alterations as compared to patients with EHT. Therefore we did not prove that in those patients an impaired fibrin clot structure, or an fibrinolytic system alteration mediates increased cardiovascular risk in PA patients in comparison to EHT.
It has been shown that patients with PPGL may present diverse cardiovascular complications and are at high risk of cardiovascular events. Some effects of PPGL on the coagulation system and fibrinolytic activity have also been described. Over the past few years the investigators observed that in the experimental models parenteral administration of adrenaline enhanced blood coagulation in animal models and in human subjects.[27–29] It was also shown that infusion of adrenaline may lead to the activation of both the coagulation and fibrinolytic system, as reflected by the increase in factor V activity, factor VIII activity, von Willebrand factor antigen, t-PA antigen and PAP. In the study by Petrak et al. t-PA levels were compared in patients with pheochromocytoma, EHT, PA and healthy controls. Patients with pheochromocytoma were characterized by higher t-PA levels than controls and PA, but not statistically higher than patients with EHT. This finding was not confirmed in our study, however, both studies have different methodologies. We designed the study to compare groups (PA vs. EHT vs. healthy controls and PPGL vs. EHT vs. healthy controls) that were carefully matched in regard to age, sex, BP levels (clinical and 24-h), lipid, glucose levels and BMI. We believed that such study design allows as precisely as possible to estimate the potential effect of aldosterone or catecholamines excess on the parameters of fibrinolysis, ignoring the effect of other factors such as BP levels or glucose and/or lipid disorders. In line with these assumptions in our study, we did not compare directly PA and PPGL groups. Both studies share the same limitation related to the small sample sizes, but finally lead to the similar conclusions—prolonged activation of catecholamines and mineralocorticoids in the circulation of patients with endocrine hypertension did not appear to lead to any marked signs of potent biochemical markers of endothelial dysfunction nor clot structure, clotting and fibrinolytic activity (our study).
Nevertheless, it should be noted that some markers of activation of fibrinolysis (t-PA) have been observed both in experimental models and in one clinical study on pheochromocytoma patients. However not confirmed in our study, this hypothesis is worth to be further investigated.[25–30]
In PPGL patients there were no differences in key haemostatic variables, that is, markers of fibrin clot structure and function, however, we noticed that patients with EHT as compared to PPGL were characterized by the tendency to have an enhanced thrombin generation (higher ETP and thrombin peak; p = .052). Those differences might have reached statistical significance in larger studied groups, however, even now it might be speculated that patients with EHT tend to generate larger thrombin amounts what was also discussed previously.
Our study is the first study assessing comprehensively fibrin clot structure and haemostasis in patients with secondary forms of hypertension characterized by particularly high cardiovascular risk—patients with PA and patients with PPGL. The strength of our study is the diagnostic and therapeutic approach to the patients included. In all patients, secondary forms of hypertension were diagnosed and finally treated according to the best current knowledge. Another important aspect is the evaluation of fibrin clot properties using well-established plasma-based assays, along with blood clotting and fibrinolysis in two-time points, which was performed in the leading centre for coagulation disorders. On the other hand, the main limitation of the study are a relatively small sample size, which might have affected the power of statistical analysis and hampered the data interpretation.
We showed that despite a well-documented increased risk of cardiovascular events in PA and PPGL patients, there are no differences in clot structure, clotting and fibrinolytic activity in hypertensive PA and PPGL patients as compared to matched patients with EHT. All hypertensive groups are characterized by more compact fibrin clot structure, faster clot formation and enhanced thrombin generation as compared to healthy controls.
The results of the present prospective study show that patients with PA and PPGL are at a prothrombic state comparable to patients with EHT. Therefore, it may be postulated that the high risk of cardiovascular events in PA and in PPGL patients observed in comparison to EHT is not mediated through fibrin clot structure alterations, nor through other investigated prothrombic mechanisms associated with thrombin generation and fibrinolytic activity.
National Centre of Science, Cracow, Poland, Grant/Award Number: 2013/11/N/NZ5/03740
This study was supported by a research grant of the National Centre of Science, Cracow, Poland (Grant No. 2013/11/N/NZ5/03740). The authors would like to thank Dr. Joanna Natorska, Dr. Jakub Siudut and Dr. Michal Zabczyk for technical assistance.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Clin Endocrinol. 2022;96(2):114-122. © 2022 Blackwell Publishing