ProET-1 plasma concentrations in subjects with end-stage CKD and renal failure were investigated for a possible association between reduced endothelial integrity and aberrations in the morphology of PLT granules or markers indicating activation of coagulation.
The in vivo inactive biomarker proET-1 reflects the level of the bioactive peptide ET-1. ProET-1 is the precursor of ET-1, which reveals stability ex vivo. Results of the study demonstrate that ProET-1 plasma concentrations are obviously increased in the subjects’ group with end-stage CKD and renal failure if compared with a group of apparently healthy subjects. Results are in accordance with the findings of other authors, who demonstrated increasing endothelin plasma concentrations with progression of renal failure [17, 18]. Altered expression of microcirculation parameters with age is a commonly occurring phenomenon. In the age of 25 till 65 years concentrations of proET-1 increase by 20% . However, on the basis of age related shifts, the increase in proET-1 concentrations in the groups with end-stage CKD and renal failure are obviously higher than expected. ProET-1 plasma concentrations in the subjects’ group with end-stage CKD demonstrate a statistically significant increase if compared with the subjects’ group with renal insufficiency. Endothelial injury is considered to initiate increased secretion of ET-1 and to effectuate vasoconstriction, increased intraglomerular pressure, and decreased glomerular filtration . ET-1 concentrations are demonstrated to correlate with blood pressure, suggesting that ET-1 may contribute to hypertension . Reduced endothelial integrity is considered to be associated with increased incidence of cardiovascular disease . Together with inflammation, hyperhomocysteinaemia and anaemia, cardiovascular disease yields an additional risk factor in subjects with end-stage CKD .
Moreover, results of our study demonstrate that the amount of depleted PLT granules is obviously increased in the subjects’ group with end-stage CKD if compared with the group with renal failure. Subjects with end-stage CKD are on regular HD-treatment. Pathophysiological mechanisms inducing activation of coagulation are based on Virchow’s triad including modifications in vessel wall, blood flow and composition of blood components [20–22]. During HD treatment, blood constituents interact with the foreign surfaces within the extracorporeal circuit (ECC), including the wall of blood lines, the artificial dialyzer membrane and mechanical forces of the roller pump. Within the ECC endothelium is lacking and activation of PLTs and biomarkers inducing activation of coagulation are released by mechanical triggers . In order to prevent clotting in the ECC during HD, a bolus of low molecular weight heparin or unfractionated heparin is supplied at the start of each HD session. Despite appropriate anticoagulation treatment, the rather unphysiological conditions within the ECC, amplified by pre-dialysis increased uraemia related factors, induce PLT activation. Increase of PLT activation and procoagulant activity is demonstrated in HD patients [24, 25]. PLTs are activated within the ECC, as detected by increase in the expression of CD62p and release of β-tromboglobulin (β-TG) within the ECC . PLT activation is associated with exposure of phosphatidylserine on the PLT exterior. Platelet factor-4 and β-TG are released from PLTs as a result of a defect in their granules membrane mainly as a consequence of the blood-membrane contact during HD and return only slowly postdialytic to control values .
In this study mean concentrations of TAT and fibrinogen reveal results within the reference range. However, in the group with end-stage CKD increased TAT or fibrinogen concentrations are established in respectively 15% and 40% of the subjects, indicating activation of the coagulation pathway or an acute phase response already before the beginning of a new HD session. The inner negatively charged wall of the ECC induces activation of FXII and subsequently the intrinsic coagulation pathway. Increased concentrations of TAT as well as prothrombin fragment 1 + 2 treatment during HD indicate that thrombin is generated [12–14]. Additionally, it has been demonstrated that thrombin is involved in the activation process of PLTs, neutrophils, and monocytes, and acts on endothelium in order to release a variety of vasoactive and inflammatory mediators .
With respect to different biomarkers of activation of PLTs and the coagulation pathway dissimilar results could be obtained. Although activation of PLTs and the coagulation pathway is present, concentrations of activation and release products staying within the reference values could also be detected as a result of different release times, presence of neutralizing agents and removal by the dialyzer membrane [11, 14].
Results of our study demonstrate that uraemia is associated with endothelial damage and aberrations in the staining density of PLT granules in subjects with CKD. Uraemic toxins, especially protein-bound toxins, are likely pathogenic agents inducing endothelial damage in CKD . In case of renal failure, endothelial damage and cardiovascular complications like hypertension are closely linked [28, 29]. Concerning interpretation of our experimental data, we hypothesize that increased proET-1 concentrations reflect ongoing stress on the endothelium amongst others due to uraemia. Biomarkers like proET-1 and aberrations in the staining density of PLT granules contribute in the early detection of procoagulant activity of the endothelium. Therefore, the level of proET-1 concentration and the amount of depleted PLT granules will add an important link to the degree of endothelial integrity and the severity of CKD.