Both PCTs significantly reduce thrombus formation rate but by different biochemical mechanisms.

BACKGROUND Ultraviolet (UV) light illumination in the presence of exogenously added photosensitizers has been used to inactivate pathogens in platelet (PLT) concentrates for some time. The THERAFLEX UV‐C system, however, illuminates PLT concentrates with UV‐C light without additional photoactive compounds. In this study residual PLT function is measured in a comprehensive paired analysis of UV‐C–treated, gamma‐irradiated, and untreated control PLT concentrates. STUDY DESIGN AND METHODS: A pool‐and‐split design was used with buffy coat–derived PLT concentrates in 65% SSP+ additive solution. Thrombus formation kinetics in microfluidic flow chambers onto immobilized collagen was investigated with real‐time video microscopy. PLT aggregation, membrane markers, and cellular metabolism were determined concurrently. RESULTS Compared to gamma‐treated and untreated controls, UV‐C treatment significantly affected thrombus formation rates on Days 5 and 7, not Day 2. PLT degranulation (P‐selectin) and PLT apoptosis (annexin V binding) was slightly but significantly increased from Day 2 on. UV‐C treatment moreover induced integrin αIIbβ3 conformational changes reminiscent of activation. However, subsequent integrin activation by either PAR1‐activating hexapeptide (PAR1AP) or convulxin was unaffected. This was confirmed by PLT aggregation studies induced with collagen, PAR1AP, and ristocetin at two different agonist concentrations. Finally, UV‐C slightly increased lactic acid production rates, resulting in significantly decreased pH on Days 5 and 7, but never dropped below 7.2. CONCLUSION UV‐C pathogen inactivation treatment slightly but significantly increases PLT activation markers but does not profoundly influence activatability nor aggregation. The treatment does, however, attenuate thrombus formation kinetics in vitro in microfluidic flow chambers, especially after storage.

BACKGROUND: Pathogen inactivation and cold or cryopreservation of platelets (PLTs) both significantly affect PLT function. It is not known how PLTs function when both are combined. STUDY DESIGN AND METHODS: Standard PLTconcentrates (PCs) were compared to pathogeninactivated PCs treated with amotosalen photochemical treatment (AS-PCT) when stored at room (RT, 22 C), cold (4 C, n = 6), or cryopreservation (−80 C, n = 8) temperatures. The impact of alternative storage methods on both arms was studied in flow cytometry, light transmittance aggregometry, and hemostasis in collagen-coated microfluidic flow chambers. RESULTS: Platelet aggregation of cold-stored AS-PCTPLTs was 44% AE 11% compared to 57% AE 14% for coldstored standard PLTs and 58% AE 21% for RT-stored AS-PCT PLTs. Integrin activation of cold-stored AS-PCT PLTs was 53% AE 9% compared to 77% AE 6% for cold-stored standard PLTs and 69% AE 13% for RT-stored AS-PCT PLTs. Coagulation of cold-stored AS-PCT PLTs started faster under flow (836 AE 140 sec) compared to cold-stored standard PLTs (960 AE 192 sec) and RT-stored AS-PCT PLTs (1134 AE 220 sec). Fibrin formation rate under flow was also highest for cold-stored AS-PCT PLTs. This was in line with thrombin generation in static conditions because cold-stored AS-PCT PLTs generated 297 AE 47 nmol/L thrombin compared to 159 AE 33 nmol/L for cold-stored standard PLTs and 83 AE 25 nmol/L for RTstored AS-PCT PLTs. So despite decreased PLT activation and aggregation, cold storage of AS-PCT PLTs promoted coagulation. PLT aggregation of cryopreserved AS-PCT PLTs (23% AE 10%) was not significantly different from cryopreserved standard PLTs (25% AE 8%). CONCLUSION:This study shows that cold storage of AS-PCT PLTs further affects PLT activation and aggregation but promotes (pro)coagulation. Increased procoagulation was not observed after cryopreservation. ABBREVIATIONS: AS-PCT = amotosalen photochemical treatment; ETP = endogenous thrombin potential; MP = microparticle; PC(s) = platelet concentrate(s); PS = phosphatidylserine; RT = room temperature; TF = tissue factor. From the

RF-PRT of single plasma units generates reactive oxygen species that adversely affect biomolecular integrity of relevant plasma constituents, a side-effect, which can be bypassed by applying hypoxic conditions during the pathogen inactivation process.

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