The effects of gaseous nitric oxide on platelets and leukocytes in membrane oxygenators

Nitric oxide (NO), known as a potent endogenous platelet anti-adhesive, anti-aggregating, and disaggregating radical, was shown to reduce platelet trapping in microporous membrane oxygenators [1]. In an additional study we investigated the effects of gaseous NO on platelet and leukocyte activation markers during extracorporeal circulation. Two parallel separated extracorporeal circuits (n = 6) were filled with heparinized (1 IE/ml) fresh drawn blood from one healthy volunteer. The gas inlets of both oxygenators (M8 Jostra/Germany) received dry gas (21% oxygen, 5% carbon dioxide, 84% nitrogen); gaseous NO (20 ppm) was added to the gas inlet of one of the oxygenators, whereas the other one was used for control. Blood samples obtained from a venous reservoir and from the blood donor were investigated by flow cytometry for the following markers: leukocytes-CD11a, CD11b, HLA-DR, CD62L (L-selectin), and CD14. Platelets-P-selectin (CD62P), CD42b (GPlb), CD41a (GPIIbIIIa), and activated conformationally changed GP-IIbIIIa. Additional, platelets were stimulated with ADP (10 µM), epinephrine (10 µM), or both (each 5 µM) to investigate platelet reactivity. Further analysis included: coagulation parameters (fibrinogen, ATIII, heparin-time, prothrombin-time, fibrin monomers); platelet counts (in quadruplet); blood gas analysis; and leukocyte differential count. The main results are: (i) NO significantly attenuated platelet trapping within the membrane oxygenator (Fig 1); (ii) In both oxygenators only small amounts (1-2%) of circulating activated (P-selectin or activated GPIIbIIIa) platelets were detectable over time; (iii) platelet reactivity to stimulating agents decreased during circulation, indicating platelet damage; (iv) NO seemed to preserve platelet reactivity to some degree which was pronounced with duration of circulation (Fig 2); (v) there was no significant difference in loss of leukocytes, ie trapping of PMN and monocytes (lymphocytes remained stable) between the two oxygenators; (vi) leukocyte adhesion molecule expression was significantly altered during circulation, however, no differences were found between NO and control: HLA-DR and CD14 increased on monocytes, CDlla increased on lymphocytes, CDllb increased on monocytes and PMN, and L-selectin was reduced on monocytes and PMN, whereas L-selectin expression on lymphocytes increased over time; (vii) no significant differences were found lor coagulation parameters or blood gas analysis.

Conclusion

Gaseous NO attenuated platelet trapping within the used membrane oxygenators. NO had no effects on leukocyte trapping or altered adhesion molecule expression on circulating leukocytes. NO preserved platelet reagibility to stimulating agents under these special conditions which stands in contrast to its known inhibitory effects on platelet activation marker expression [2]. Further studies should demostrate whether application of gaseous NO to membrance oxygenators might be advantageous during extracorporeal lung assist.

Figure 1

Platelet (squares) and hemoglobin (circles) values in percent from baseline (start). ^*P < 0.05, ^**P < 0.01, paired t-test.

Figure 2

Activated GPIIb-IIIa on platelets stimulated with 10 µM ADP (A), 10 µM epinephrine (EPI) (B), or 5 µM ADP + 5 µM EPI (C) at different timepoints. Note the time-dependent loss of reactivity to stimulating agents in both membrane systems, however, gaseous NO preserved reagibility, demonstrating the protective effect of NO on platelets (^*P < 0.05, paired t-test).