The effect of dialysis on the thrombgenicity of platelets and the role of the polymorphisms of the most frequent platelet antigenes

The association between renal dysfunction and bleeding has been recognized since more than 200 years ago. Although uremic deaths have declined, morbidity and mortality from bleeding remain a significant clinical problem. There are good data, however, supporting the view that impaired platelet function is one of the main determinants of uremic bleeding. This impairment is multifactorial and includes defects intrinsic to the platelet as well as abnormal platelet-endothelial interaction. Uremic toxins and anaemia also play a role. The bleeding time (BT) is a measure of the interaction of platelets with the blood vessel wall. A prolonged bleeding time may occur in thrombocytopenia (platelet count usually below 50,000/microL), qualitative platelet abnormalities (eg, uremia), von Willebrand disease (VWD), some cases of vascular purpura, and severe fibrinogen deficiency, in which it is probably the result of platelet dysfunction. Human platelets carry membrane glycoproteins (GPs) that play a critical role in platelet aggregation. Recently, platelet dysfunction was addressed specifically by analyses of these platelet surface glycoproteins . The main platelet glycoproteins are glycoprotein Ib/IX/V and glycoprotein IIb/IIIa while Ia/IIa glycoprotein plays a smaller role. We investigated the distribution of polymorphisms of human platelet antigens that encode platelet glycoproteins (GPs) in Greek patients on haemodialysis (HD). The polymorphic systems we have studied were HPA-1 and HPA-3 on the fibrinogen receptor (GlycoproteinIIb/IIIa), HPA-2 on the von Willebrand factor receptor (GPIb/IX), and HPA-5 on one of the platelet collagen receptors (GPIa/IIa). The aim of this study was firstly to genotype the patients on haemodialysis of a Greek renal unit according to their polymorphisms of Human platelet antigens (HPA 1, -2, -3, and -5), secondly to measure the changes at the bleeding time met at the patients of this renal unit during a session of dialysis under the diverse characteristics of the procedure and finally to examine the association of the biallelic polymorphisms of the four most common genes (HPA 1, 2, 3 and 5) that encode the platelet glycoproteins with the primary cause of End-Stage Renal Disease in hemodialysis (HD) patients from Greece. Fifty-five (55) stable on chronic maintenance haemodialysis (HD) patients were chosen (22 female, 33 male), aged from 23 to 87 years old, (mean 66), being on dialysis for 53±34 months. They had no haematological disease. The haemoglobin, platelet count and fibrinogen serum levels were in normal ranges. Primary diseases for the HD patients in the study were as follows: Hypertension, Diabetes Mellitus, Glumerulonephritis, Polycystic disease, Obstructive nephropathy, Autoimmune disease, Unknown/Other. Parametric and nonparametric tests were used for the statistical analysis of our data. DNA was isolated from peripheral blood collected from these patients and by using specific primers the alleles (a)and (b) for each gene HPA-1, -2, -3, and -5 were determinated giving results similar to the findings of other studies internationally. Ivy technique was used for bleeding time measurement. Bleeding time as a mean average value was statistically different pre- and post- dialysis (P<0.05) finding the explanation to the improvement of uremic toxins and secondly to hematocrit level changes . Finally, the presence of all eight alleles HPA -1a, HPA-1b, HPA-2a, HPA-2b, HPA-3a, HPA-3b, HPA 5a, and HPA-5b was studied in association of the pathophysiology which led the patients to the end-stage of renal disease (primary disease) There was a statistically significant association between the presence of the HPA-1b allele and Hypertension as the primary cause of End Stage Renal Disease. (65% of patients with Hypertension vs 23% of patients with all other causes carried the HPA-1b allele, p = 0.02, Fisher’s exact test). A number of clinical studies have suggested that carriage of the low frequency allele (b) of the human platelet antigen 1(HPA-1b) system is a risk factor for coronary thrombosis. Platelet thrombogenicity depends on the function of platelet surface glycoproteins, which are the protagonists in a series of events including vessel wall adhesion, activation and thrombus formation. A number of genetic and structural polymorphisms have been associated with alterations in the function and/or antigenic behaviour of the glucoprotein molecules. In analogy with the polymorphisms of certain plasma coagulation proteins, which result in thrombophilia, it has been speculated that some platelet glycoprotein polymorphisms might represent risk factors for arterial occlusive and stiffness disease. Research in this field has focused mainly on glycoprotein IIb-IIIa, and specifically on the human platelet antigen 1b(HPA-1b) polymorphism. If the association between a glycoprotein polymorphism and platelet-dependent arterial behaviour was a causal one, it is appealing to hypothesize that the HPA-1b polymorphism entails a factor for glycoprotein IIb-IIIa complex activation and the beginning of a cascade leading to hypertension. Although our study is limited by the sample size, our results provide powerful clues that the relation of polymorphism HPA-1b and arterial hypertension can be causal or at least the presence of the HPA-1b allele may be a contributing factor to the development of End Stage Renal Disease due to hypertension in HD patients in Greece.Μία in vivo μελέτη της φαινοτυπικής έκφρασης των αιμοπεταλίων με την εξωνεφρική κάθαρση ως συνάρτηση του γονοτύπου τους που ακολούθησε τα βήματα: 1. Γονοτύπηση αιμοπεταλίων των ασθενών για τα αλλοαντιγόνα HPA-1, -2, -3 και -5. 2.Διαστρωμάτωση του προς μελέτη πληθυσμού με κριτήρια (ανεξάρτητες μεταβλητές): (α) τον αιμοπεταλιακό γονότυπο, (β) τις θεμελειώδεις παραμέτρους της αιμοκάθαρσης και (γ) βασικά στοιχεία του ιστορικού του κάθε ασθενούς. 3.Προσδιορισμός του χρόνου ροής για κάθε ασθενή προ και αμέσως μετά την εξωνεφρική κάθαρση Τα αποτελέσματα συνηγορούν επί της περαιτέρω επίδρασης του σακχαρώδη διαβήτη στον χρόνο ροής των ασθενών με νεφρική ανεπάρκεια που παρουσιάζουν από τα αρχικά στάδια της νόσου διαταραχές στη συμπεριφορά των αιμοπεταλίων. Η εξωνεφρική κάθαρση δεν επηρεάζει δυσμενώς την ήδη επηρεασμένη λειτουργικότητα των αιμοπεταλίων αντιθέτως παρατηρήθηκε βελτίωση του χρόνου ροής στο τέλος μιας τυπικής συνεδρίας αιμοκάθαρσης χωρίς επιπλοκές. Οι πολυμορφισμός ΗΡΑ 1b φαίνεται να είναι ανεξάρτητος παράγοντας κινδύνου για την αρτηριακή υπέρταση στους ασθενείς με νεφρική ανεπάρκεια τελικού σταδίου, ενώ περαιτέρω διερεύνηση χρήζει η πιθανή προστατευτική δράση των πολυμορφισμών HPA-1a για την αρτηριακή υπέρταση και HPA-2b για τον σακχαρώδη διαβήτη