Effects of sodium nitroprusside on hemodialysis-induced platelet activation

Acetylsalicylic acid decreases clotting in combination with enoxaparin during haemodialysis in vitro

BACKGROUND

Anticoagulation is a cornerstone in haemodialysis (HD) therapy to avoid clotting of blood when it comes into contact with the dialysis membrane. Although heparins are usually administered as anticoagulants, they are not always sufficient to maintain adequate HD. We investigated the additional effect of acetylsalicylic acid compared with standard anticoagulation on maintaining adequate flow properties during HD in vitro.

METHODS

We collected blood from 42 healthy volunteers, between 18 and 60 years of age, into bags filled with 1, 1.5 or 2 mg enoxaparin, with (treatment group) or without (control group) 100 mg of aspirin. Blood was evaluated before, during and at the end of each experiment to determine coagulation parameters, whole blood aggregation and thromboelastogram measurements. Transmembrane pressure was recorded as indirect estimate of dialysis patency. The primary endpoint was time to filter clotting.

RESULTS

Addition of acetylsalicylic acid significantly prolonged the time to circuit clotting from 120 (105-150) min to >180 min (120-180) min (P = 0.047) and allowed lowering the enoxaparin concentration from 2 mg per circuit to 1 mg without an increase in clotting. Furthermore, it reduced the transmembrane pressure from 46 to 4 mmHg (P < 0.001) after 4 h of dialysis. Acetylsalicylic acid better preserved the platelet count (128 versus 116 × 10E9/L, P = 0.01) and improved platelet aggregation at the end of the dialysis procedure.

CONCLUSION

Adding acetylsalicylic acid to HD circuits lowered the transmembrane pressure, better preserved platelet function and prolonged the time to circuit clotting, which in sum increases haemodialyser performance and may facilitate a more effective HD.

Reparixin, a Specific Interleukin-8 Inhibitor, Has No Effects on Inflammation during Endotoxemia

Reparixin antagonizes interleukin-8 (IL-8) on the level of signal transduction in vitro. We hypothesized that IL-8 mediates some of the reactions occurring during acute inflammation and specifically that IL-8 may be a mediator of endotoxin induced neutrophilia. We therefore tested the effects of reparixin on humoral and cellular parameters in LPS-induced acute systemic inflammation. The study is a randomized (3:2 active:placebo), double-blind, placebo-controlled parallel group trial. Twenty healthy male volunteers randomly received either reparixin (12) or placebo (8) intravenously. One hour after the start of reparixin/placebo infusion a bolus of 2 ng/kg endotoxin was infused over 1–2 min. Blood samples were obtained over 24 h. Reparixin, being metabolized to ibuprofen, suppressed serum thromboxane B2 levels by 78% compared to baseline and control at 8 h. LPS-induced neutrophilia was not significantly affected by reparixin in human volunteers. Consistently, reparixin did not alter the lymphocyte or monocyte counts and had no effect on LPS-induced systemic inflammation as measured by tumor necrosis factor alpha (TNF-α) or interleukin-6 (IL-6) release. Regulation of IL-8 receptors CXCR1 and 2 and the degranulation marker CD11b showed the expected kinetics. Reparixin had no effect on thrombin formation as measured by prothrombin fragment (F1+2). In conclusion, our study showed that reparixin was safe but had no impact on endotoxin induced inflammation. In contrast to previous studies with its metabolite ibuprofen, reparixin does not enhance inflammation in this model.

Effects of plasma nitric oxide levels on platelet activation in single donor apheresis and random donor concentrates

P-selectin is an useful marker to determine platelet activation and nitric oxide inhibits platelet activation, secretion, adhesion and aggregation. The aim of this study was to investigate the relationship between nitric oxide and P-selectin values in both single donor apheresis and random donor platelet concentrates. According to the results of this study, we found that the best platelet concentrate is freshly prepared single donor apheresis concentrate and it is important to prevent activation at the beginning of the donation. Nitric oxide, which is synthesized from platelets during the storage period, is not sufficient to prevent platelet activation.

Inhaled nitric oxide inhibits platelet-leukocyte interactions in patients with acute respiratory distress syndrome

INTRODUCTION

In addition to its effects on platelet function, recent studies suggest that inhaled nitric oxide (NO) also influences the function of circulating leukocytes. Therefore, the aim of this work was to investigate the formation of platelet-leukocyte aggregates (PLAs) and platelet and leukocyte cell surface receptor expression during NO therapy in patients with acute respiratory distress syndrome.

METHODS

In 16 patients responding to NO therapy with an improvement in oxygenation (NO group) and in four nonresponders (control), platelet P-selectin expression, platelet fibrinogen binding, the expression CD11a on leukocytes, and the formation of PLAs were investigated at 0, 60, 120, and 180 mins of therapy or at corresponding time points by means of flow cytometry. In addition, PLA was investigated in 30 healthy volunteers during NO inhalation, in five mechanically ventilated patients without acute respiratory distress syndrome and without NO inhalation, and during NO incubation in platelet-rich plasma of ten healthy volunteers in vitro.

RESULTS

NO therapy inhibited PLA formation at 60 (13% +/- 4% in the NO group vs. 19% +/- 7% in the control group, p <.01) and 120 mins (14% +/- 4% vs. 18% +/- 7%, p <.05) and slightly decreased CD11a expression at 60 mins (152 +/- 22 arbitrary units vs. 187 +/- 36 arbitrary units, p <.05). Furthermore, besides inhibiting platelet fibrinogen binding, NO also led to a significant inhibition of P-selectin expression at 120 (38% +/- 4% vs. 43% +/- 5%, p <.05) and 180 mins (34% +/- 5% vs. 43% +/- 6%, p <.01), demonstrating a significant correlation between changes in P-selectin expression and PLA formation. In contrast, PLA formation was not influenced by mechanical ventilation in patients without acute respiratory distress syndrome. These results were further supported by additional studies showing inhibition of PLA formation in healthy volunteers as well.

CONCLUSIONS

NO-dependent inhibition of PLA formation in patients with acute respiratory distress syndrome can be explained by the inhibition in platelet P-selectin expression. Thus, this study provides rational evidence of systemic antileukocytic and antiplatelet properties of NO therapy in the clinical setting.

S-nitrosoglutathione preserves platelet function during in vitro ventricular assist device circulation

Complications (severe bleeding/thromboembolism) may occur during ventricular assist device (VAD) circulation, caused mainly by platelet dysfunction from platelet activation. We hypothesized that S-nitrosoglutathione (GSNO), having platelet activity preservation properties like nitric oxide (NO), may be a titratable agent to diminish platelet activation and thus preserve platelet function. Dose-response measurement of platelet aggregation by GSNO was performed using an aggregometer. GSNO (1,000 microM) caused inhibition of collagen and ristocetin induced aggregation by approximately 50%. Next, in vitro ventricular assist device (VAD) circulation was performed (over 48 hours using human whole blood), both without (control) and with GSNO (1,000 microM), and the aggregability of perfusate was measured at 0, 0.5, 1, 3, 6, 12, 24, and 48 hours. In control VAD circuits, collagen induced platelet aggregability gradually decreased and became significantly lower after 3 hours of circulation. With GSNO, platelet function did not significantly decrease until after 12 hours. Similar results were seen for ristocetin induced aggregation; control aggregation dropped significantly after 6 hours, but not until after 24 hours with GSNO. Liquid phase measurement of total nitrogen oxides (NO(T)) confirmed added GSNO maintained high perfusate NO(T) compared with control. GSNO is effective in preserving platelet aggregation during the first 12 to 24 hours in vitro and may be effective in preserving platelet function by inhibiting platelet activation during in vivo VAD circulation.

Activation of calcium-dependent calmodulin by calcium(II)3(3,5-diisopropylsalicylate)6(H2O)6 decreases thrombin receptor activating peptide-induced P-selectin expression

We examined the influence of 3,5-diisopropylsalicylic acid (3,5-DIPS) and calcium(II)3 (3,5-diisopropylsalicylate)6 (H2 O)6 [Ca(II)3 (3,5-DIPS)6 ], a new activator of calcium-dependent calmodulin-triggered nitric oxide synthase, on thrombin-induced platelet P-selectin expression. Citrated whole blood samples were incubated with either ethanol vehicle, 3,5-DIPS, or Ca(II)3 (3,5-DIPS)6. These whole blood samples were also co-incubated with thrombin receptor activating peptide (TRAP) or adenosine diphosphate (ADP), to up-regulate P-selectin (CD62P) on platelets. Both TRAP and ADP up-regulated P-selectin on platelets compared with platelets in whole blood samples that were not incubated with either platelet activator. Co-incubation of whole blood samples with TRAP, ADP together with 3,5-DIPS, or Ca(II)3 (3,5-DIPS)6 revealed that Ca(II)3 (3,5-DIPS)6 caused a decrease in platelet P-selectin expression for TRAP, ADP, and no-activator co-incubated samples of whole blood. Incubation of platelets with 3,5-DIPS also caused a decrease in ADP-induced up-regulation of P-selectin but failed to affect TRAP or no-activator-treated platelets. Incubation of whole blood with Ca(II)3 (3,5-DIPS)6 induced some hemolysis. We found that hemolysis increases basal P-selectin expression on platelets. We therefore conclude that Ca(II)3 (3,5-DIPS)6 decreased not only basal, but also hemolysis-induced P-selectin expression on platelets. In contrast, incubation of haemolysed whole blood with SIN-1 (standard nitric oxide-releasing drug) had no effect on P-selectin expression. In summary, Ca(II)3 (3,5-DIPS)6, a new calmodulin-dependent nitric oxide synthase activator, decreases P-selectin expression of human platelets in response to thrombin receptor activation. Improved calcium-dependent calmodulin activators may become useful drugs for the treatment of disorders associated with platelet activation, and P-selectin may decrease expression due to hemolysis.

Effects of nitric oxide on platelet activation during plateletpheresis and in vivo tracking of biotinylated platelets in humans

BACKGROUND

The use of platelet transfusions has risen considerably over the last few years, which leads to the collection and transfusion of a greater number of donor plateletpheresis units. Plateletpheresis activates platelets in platelet concentrates, which determines the degree of the storage lesion subsequently observed.

STUDY DESIGN AND METHODS

As nitric oxide (NO) is a potent inhibitor of platelet aggregation and activation, a placebo-controlled crossover trial was performed in healthy young male volunteers to determine whether the NO-donating compound, sodium nitroprusside (SNP), decreases platelet activation during apheresis and whether activated (p-selectin+) platelets circulate in vivo after transfusion. The study also investigated whether nonradioactive biotin labeling of apheresis platelets is feasible for the study of platelet recovery after transfusion in humans.

RESULTS

Platelet activation increased after plateletpheresis in the platelet components, but SNP did not inhibit platelet activation during apheresis, as measured by the percentage of p-selectin expression and the secretion of soluble p-selectin and RANTES. Only a minor increase in p-selectin+ platelets was seen in peripheral blood at 60 minutes after transfusion of the platelets, a rise that was considerably less than that calculated in p-selectin+ platelets if they all were recovered as activated platelets after transfusion. Biotin-labeled platelets averaged 1.5 percent at 10 minutes after transfusion and increased slowly to 2.6 and 3.4 percent after 60 minutes and 24 hours, respectively (p<0.05).

CONCLUSION

SNP does not decrease platelet activation during apheresis and subsequent storage, and only a minor proportion of activated (p-selectin+) platelets circulate after transfusion in men. Moreover, biotin labeling of PCs can safely be used in humans for the study of platelet recovery after transfusion, and measuring recovery at 1 hour may lead to an underestimation of the true recovery when activated platelets are transfused.