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Abstract

The storage of platelets under routine blood bank storage conditions leads to a loss of viability and responsiveness known as platelet storage lesion. Potential causes, which may produce the storage lesion, include increased metabolism of activated platelets, activation of blood enzyme pathways by contact with the polymer surfaces of blood collection packs, and aging of platelets. Complement activation occurs in platelet concentrates (PCs) during collection, processing and storage, which may contribute to the platelet storage lesion; however, no direct evidence supports this hypothesis. If complement contributes to the storage lesion then the inclusion of specific complement inhibitors in PCs should reduce the extent of the platelet storage lesion. The project was designed to determine whether the addition of a complement inhibitor prevents complement activation in PCs, whether that complement inhibition is related to an improvement or deterioration in the quality of stored platelets and thirdly, whether the inhibitor remains active throughout the 5-day storage period of PCs. Concentrates were split into mini-units and treated with the specific complement inhibitors N-acetyl-aspartyl-glutamic acid (NAAGA) or NAAGA-Na, EDTA or buffer. Samples were collected on day 0, 1, 3 and 5 or alternatively, daily during storage. Complement activation was monitored by measuring C3a and SC5b-9 levels. Platelet quality was assessed by morphology, hypotonic shock response (HSR), and platelet activation marker expression. Stability of the inhibitor was determined by monitoring its residual complement inhibitory activity in the bag over the storage period using a modified hemolytic assay. NAAGA treatment in the first study demonstrated a decreased C3a generation and delayed generation of membrane attack complex, C5b-9 (MAC) (p<0.05). By morphology and HSR, complement inhibition by NAAGA improved the platelet quality (p<0.05). NAAGA slowed the rate of platelet activation, but did not prevent it. NAAGA-Na treatment in the second study also decreased C3a levels and delayed MAC generation (p<0.05). However, by morphology scores and HSR, there was no difference in the two treatments. NAAGA-Na was stable throughout the storage period as determined by the modified hemolytic assay (p<0.05). The first study provides direct evidence that complement activation contributes to the platelet storage lesion; however, complement activation is clearly not the sole cause of the storage lesion. Although in the second study complement inhibition was not related to an improvement of platelet quality, we cannot exclude the possibility that complement is one of the likely candidates that may have an impact on the extended storage of PCs.