In reply

Abstract

In reply: We read with interest the article by Feys and colleagues1 comparing nitrite/nitrate (NO2−/NO3−) levels during storage and preparation of platelet concentrate (PC) from pooled buffy coats. Although they did not measure nitrite separately, their results suggest no substantial production of nitric oxide (NO) in stored PCs since NO produced in large quantities would likely affect the nitrite/nitrate levels. It is also consistent with our report2 that apheresis PCs did not produce NO by endogenous nitric oxide synthase (NOS) during storage. However, based on our electron paramagnetic resonance results, NO level in PCs was higher than that in plasma. Furthermore, we also showed that there was a slight decrease in nitrite levels during storage. We believe that our results suggest a possibility of a nitrite reduction system in PCs or nitrite reaction with residual hemoglobin, cell free or in red blood cells (RBCs), possibly indicative of some NO metabolic processes. Interestingly, Feys and colleagues observed an increase in nitrite/nitrate levels immediately after the procedures of PC preparation from buffy coats in which centrifugations and dilution with additive solution are used. As they suggested, it is possible that RBCs and white blood cells in buffy coats contribute to this increase in nitrite/nitrate levels as a native mechanism to prevent overt platelet (PLT) activation during preparation. Some authors have suggested the presence of active NOS in RBCs, although the definitive proof of functional NOS in RBCs is still under debate.3 In addition, it is still not clear if PLTs themselves express NOS.4 Considering the fact that buffy coat PCs show the lowest level of PLT activation by in vitro assays compared with apheresis PCs or PLT-rich plasma (PRP)-derived PCs,5 it would be interesting to see if the procedures of apheresis or PRP PC preparations also increase nitrite and nitrate levels. As Feys and colleagues note, production of NO in these preparations may be important for the maintenance of PLT function during in vitro storage, allowing clinical utility of PLT transfusions. ANS is a co-inventor of a patent issued to NIH for the use of sodium nitrite in the treatment of cardiovascular diseases. The authors declare that they have no conflicts of interest relevant to the manuscript submitted to TRANSFUSION.