Effects of hemodialysis on platelets

Effect of Different Dialysis Membranes on Platelet Function. A Tool for Biocompatibility Evaluation

Intradialytic coagulative and platelet activation, one of the main consequences of blood-membrane contact, was studied in a group of 5 RDT patients with a comparative evaluation of 3 different dialytic membranes: Cuprophan (CU), Polysulfone (PS) and Cellulose Triacetate (CT). Each patient underwent 5 consecutive dialysis sessions with the above mentioned membranes. Intradialytic platelet activation was studied through a morpho-functional evaluation between the mean platelet volume (MPV) and Serotonin (S), ß-Thromboglobulin (ß-TG) and Platelet Factor 4 (PF4) serum levels. These determinations were made before HD (time 0) and after 30', 120’ and 240'. We also checked the intradialytic status of thrombogenesis and fibrinolysis determining aPTT, thrombin time, fibrinogen, antithrombin III (AT III), α-2 antiplasmin and plasminogen, at the same time intervals. All membranes tested (CU, PS, CT) caused appreciable intradialytic platelet activation, above all after 15’ and at the end of dialysis sessions, more marked for CU than PS or CT. In particular MPV showed a decrease throughout the session (-5% at 30’ and -9% at 240') while S, ßTG and PF4 peripheral blood levels showed a significant increase at the same intervals with CU membrane. Lastly coagulative and fibrinolytic parameters showed no significant differences among any of the membranes tested.

ABO-incompatible kidney transplant recipients have a higher bleeding risk after antigen-specific immunoadsorption

Pretransplant removal of antiblood group ABO antibodies is the cornerstone of all current ABO-incompatible (ABOi) transplantation programmes. In our protocol, plasmapheresis (PP) is performed with a plasmafilter followed by immunoadsorption (IA) of anti-ABO antibodies. The bleeding complications of this technique are not known. We analysed the data of all 65 consecutive ABOi kidney transplantations between March 2006 and October 2013 and compared these with matched 130 ABO-compatible (ABOc) kidney transplantations. Cases differed from controls in the pre-operative regimen, which included IA-PP and rituximab, tacrolimus, mycophenolate mofetil, prednisone and immunoglobulines. Data on platelet count, blood loss and red blood cell (EC) transfusions during 48 h postoperatively were collected. ABOi patients received EC transfusions more frequently than controls (29% vs. 12%, P = 0.005). Intra-operative blood loss was higher (544 vs. 355 ml, P < 0.005) and they experienced more major bleeding (≥3 EC within 24 h, 15% vs. 2%, P < 0.0005). Platelet count decreased by 28% after the pre-operative IA. In a multivariate model, only the number of pre-operative IAs was associated with the number of ECs given (OR per IA 1.9, P < 0.05). ABOi kidney transplant recipients have a high postoperative bleeding risk, correlating with the number of pre-operative IA sessions performed.

Evaluation of three different methods to prevent dialyzer clotting without causing systemic anticoagulation effect

Thrombogenicity is one of the most important biocompatibility markers of artificial material. Anticoagulation is commonly used to reduce thrombogenicity of the extracorporeal circuit (ECC) during intermittent hemodialysis (IHD). In some situations, systemic anticoagulants are contraindicated. The aim of our study was to compare thrombogenicity parameters during IHD with three different methods without a systemic anticoagulation effect. In a prospective, randomized, and crossover study, we examined 10 stable patients during IHD with (i) regular saline flushes of ECC; (ii) regional citrate anticoagulation (RCA); and (iii) AN69 ST membrane after ECC priming according to the manufacturer's recommendations. Before IHD and after 10, 60, 120, and 240 min, we measured the platelet count and the plasma concentrations of platelet factor 4 (PF4) and thrombin/antithrombin complexes (TAT). All 10 procedures with RCA were successfully completed after 4 h, whereas 6/10 procedures with saline flushes and 5/10 procedures with AN69 ST were finished prematurely because of clotting (P < 0.05). The TAT production was significantly increased during saline flushes and AN69 ST compared with RCA (P < 0.05). Platelet activation demonstrated by rising PF4 was present during all three methods. Markers of coagulation cascade activation were progressively increasing during IHD with RCA, saline flushes, and AN69 ST. The activation was significantly lower during RCA, and according to thrombogenicity, RCA is the most effective among compared anticoagulation methods.

Intradialytic and postdialytic platelet activation, increased platelet phosphatidylserine exposure and ultrastructural changes in platelets in children with chronic uremia

The present research evaluated the intradialytic and postdialytic changes in platelet factor-4 and beta-thromboglobulin plasma levels by enzyme-linked immunoadsorbent assay method and platelet aggregation by ADP as well as flow cytometric percentage of annexin-V-positive platelets as a measure of phosphatidylserine externalization and ultrastructural examination of platelets in 37 uremic patients on regular hemodialysis and 25 age-matched and sex-matched controls. Platelet factor-4 plasma levels increased, remain consistently high during hemodialysis session (20.24 +/- 3.05 IU/ml after 30 min, P < 0.001 and 23.67 +/- 3.68 IU/ml after 240 min, P < 0.001) and returned to control values (6.10 +/- 1.54 IU/ml) only after 24 h following the end of the session. beta-Thromboglobulin showed a trend similar to that of platelet factor-4. Platelet aggregation by ADP showed reduced function in comparison with controls (69.32 +/- 12.37 versus 91.95 +/- 1.59%, P < 0.001). Flow cytometric percentage of annexin-V-positive platelet was significantly elevated (P < 0.001) in uremic patients when compared with normal controls. Ultrastructural studies of platelets 30 min after starting of dialysis showed degranulation of its granules and at 240 min showed complete degranulation, whereas in the postdialytic phase (12 h after the end of dialysis) refilled alpha-granules started to appear. Positive correlations were found between platelet concentration and platelet factor-4 and beta-thromboglobulin plasma levels during and after dialysis (P < 0.001) and with annexin-V-positive platelets percentage (P < 0.001). In conclusion, activated platelets were found in chronic hemodialysis patients, a finding that may explain why uremic patients often suffer from thrombotic accidents. The platelet activation is associated with exposure of phosphatidylserine on the platelet exterior. Platelet factor-4 and beta-thromboglobulin are released from platelets as a result of a defect in their granules membrane as shown by the electron microscopy, mainly as a consequence of the blood-membrane contact during dialysis, and they return only slowly to control values.

Hemocompatibility and anaphylatoxin formation of protein-immobilizing polyacrylonitrile hemodialysis membrane

Plasma proteins were covalently immobilized onto polyacrylonitrile (PAN) membrane to evaluate the hemocompatibility and anaphylatoxin formation. This is used as a model to study the effect of protein-adsorption on the blood-contacting response of hemodializing membranes. The proteins used were either platelet-adhesion-promoting collagen (COL) or platelet-adhesion-inhibiting human serum albumin (HSA). The microstructure and characterization of the protein-immobilizing PAN membranes were evaluated by Coomassie dye assay, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle measurement. PAN-HSA membrane improved not only hemocompatibility including less platelet adhesion, longer blood coagulation times, and higher thrombin inactivity level, but also induced lower complement activation. On the other hand, PAN-COL membrane exhibited blood incompatibility, although induced less increase of C3, C4 antigens of serum. Overall results of this study demonstrated that the immobilization of HSA onto the surface of PAN membrane would be beneficial to improve the hemocompatibility and to reduce the anaphylatoxin formation during hemodialysis.

Platelet activation and PDGF-AB release during dialysis

During hemodialysis the blood-membrane contact causes a release of platelet granule content, which contains Platelet Derived Growth Factor (PDGF-AB). In view of its possible role in accelerated atherosclerotic processes, we evaluated the intra- and post-dialytic changes in PDGF-AB serum levels during hemodialysis sessions performed with Hemophan and Polysulfone membranes. PDGF-AB, PF4, betaTG and MPV levels were determined in the peripheral blood in 30 patients each of whom underwent 6 dialysis sessions: 3 with Hemophan (HE) membrane and 3 with Polysulfone (PS) membrane, interpolated by a wash out session with PS membrane. Blood samples were taken at times 0', 30', 120', 180', 240' during dialysis sessions and at 1, 4 and 20 hours after the end of the session. Statistical analysis was done using the ANOVA one way test and Student's t test PDGF-AB serum levels initially increased and, except for a sharp fall at 120', remained constantly high during HD with both membranes tested, not returning to basal values until 20 hours after the end of the session. PF4, betaTG and MPV all showed a similar trend to PDGF. No statistically significant difference was found between the two membranes tested. PDGF-AB, a powerful growth factor in cells of mesenchymal origin, is released during dialysis mainly as a result of the blood-membrane contact. This we found regardless of the type of dialyzer we tested, and, above all, proved to return very slowly to basal values. We speculate that the release of PDGF-AB could play a part like other atherosclerosis risk-factors in the appearance and worsening of atherosclerotic lesions in hemodialysis patients.

Intra- and post-dialytic platelet activation and PDGF-AB release: cellulose diacetate vs polysulfone membranes

BACKGROUND

During haemodialysis the blood-membrane contact causes a release of platelet granule content, which contains platelet-derived growth factor AB (PDGF-AB). In view of the potential role of this in altering biocompatibility during haemodialysis, we evaluated the intra- and post-dialytic changes in PDGF-AB serum levels during haemodialysis sessions performed with cellulose diacetate (CDA) and polysulfone (PS) membranes respectively.

METHODS

PDGF-AB, platelet factor 4 (PF4), beta thromboglobulin (betaTG), and mean platelet volume (MPV) levels were determined in 30 patients, each of whom underwent six dialysis sessions: three with a CDA and three with a PS membrane. Blood samples were taken at times 0, 15, 30, 120, 180, and 240 min during dialysis and at 1, 4, and 20 h after the end of the session. Statistical analysis was performed using a one-way ANOVA and Student's t test.

RESULTS

PDGF-AB at 15 min was increased to +41+/-9% with CDA vs +20+/-5% with PS (P<0.001) from the T0 values, and at 120 min it was +19+/-8% with CDA vs -25+/-9% with PS (P<0.001) from T0 levels. At 240 min it was +95+/-14% with CDA vs +49+/-15% with PS (P<0.001) from the T0 values, returning to basal only 20 h after the end of the session. betaTG at 15 min was +60+/-8% for CDA vs +24+/-7.5% for PS (P<0.001) from the T0 values. PF4 showed a similar trend to betaTG. MPV at 30 min from the start of dialysis was 7.4+/-0.3 fl with CDA and 8+/-0.3 fl with PS (P<0.001), and at 240 min MPV was 7.9+/-0.3 fl with CDA and 8.4+/-0.3 fl with PS (P<0.001).

CONCLUSIONS

Platelet activation and platelet release reactions are lower with PS than with CDA membranes. PDGF-AB, released during and after dialysis, represents a clear biocompatibility marker. Its slow return to basal values and its action on vascular cells make it a potential risk factor for atherosclerosis in uraemic patients.

PDGF-AB release during and after haemodialysis procedure

BACKGROUND

During haemodialysis blood membrane contact causes the release of the content of platelet alpha-granules, which contain platelet-derived growth factor (PDGF). In view of its possible role in accelerated atherosclerotic processes, we evaluated the intra- and post-dialytic changes in PDGF-AB serum levels during haemodialysis sessions performed using a cellulosic membrane.

METHODS

Using the ELISA method, PDGF-AB, platelet factor-4 (PF4) and beta-thromboglobulin (beta-TG) levels were determined in peripheral blood, as well as in arterial and venous haemodialyser lines, in 10 patients each of whom underwent five consecutive dialysis sessions with a CU membrane. Blood samples were taken at 0, 15, 30, 60, 120, 180 and 240 min during dialysis and at 1, 4 and 20 h after the end of the session. In the same group of patients the levels of the same molecules were also determined after a heparin bolus injection of 4500 IU, blood samples were taken at 0, 15 and 30 min after injection of the bolus.

RESULTS

PDGF-AB serum levels increased, remained consistently high during the haemodialysis session (in particular +134+/-20% after 30 min, P<0.001, and +140+/-5% after 240 min, P<0.001) and returned to basal values only after 20 h following the end of the session. PF4 and beta-TG showed a similar trend to PDGF. The heparin bolus injection caused only a small increase (+15+/-5% at 30 min) in PDGF-AB serum levels.

CONCLUSIONS

PDGF-AB is released during dialysis mainly as consequence of the blood-membrane contact and it returns only slowly to basal values.

Platelet-activating factor production during hemodialysis: effect of BN 52021

Platelet activating factor (PAF) production and platelet-lipoxygenase activity were studied during hemodialysis (HD) with cuprophane membranes. Six patients were treated with first-use dialyzers (FU), and 6 patients with reused dialyzers (RU). In a random and double-blind design, 2 HD were performed for each patient, with or without BN 52021 pretreatment, a selective PAF antagonist. Platelet and leukocyte counts were performed before pretreatment and 30 min before HD starting (T-30), at the beginning of HD (T0) and after 15 and 30 min of HD (T15, T30). PAF production was analyzed by direct phase HPLC. To determine platelet-lipoxygenase activity, 12-HETE was detected by reverse phase high performance liquid chromatography (HPLC) after blood stimulation by the ionophore A23187. In the FU group, PAF and 12-HETE were produced during the first 30 min of HD. After BN 52021 pretreatment, PAF production was suppressed and platelet-lipoxygenase activity reduced. In the RU group, neither PAF nor 12-HETE production occurred, and BN 52021 had no effect. We conclude that PAF, which was involved in both platelet and leukocyte activation that occurred during hemodialysis, can be considered as a bio-incompatibility marker.