Sanne de Bruin

131 Metabolic changes in erythrocytes in vivo, during storage and after transfusion lation, which results in decreased PFK activity 43 . To counteract this phenomenon and thereby improve energy metabolism and oxygenation capacity in stored RCCs, alkaline additive solutions are developed 44–46 . The rationale behind this is that increasing the pH would lead to less inhibition of PFK activity resulting in more substrate for 2,3-DPG and ATP production. It is shown that RCCs stored in AS-7, an alkaline additive solution, uti- lize more glucose compared to AS-3, a non-alkaline additive solution 47 . Moreover, most glycolytic intermediate levels are higher in AS-7 compared to AS-3. Only pyruvate and lactate levels were similar in AS-3 and AS-7 47 . RCCs stored in PAGGGM consume more glucose and producemore lactate, resulting in higher ATP and 2,3-DPG levels compared to RCCs stored in SAGM 45,48 . In PAGGGM 2,3-DPG levels initially increase during the first two to three weeks. After this period the 2,3-DPG level gradually decreases to base- line level. This level is significantly higher than in non-alkaline additive solutions. ATP and 2,3-DPG molecules also inhibit PFK activity, however this negative feedback loop is inhibited under anaerobic conditions. In line with this, RCCs stored under anaerobic conditions in non-alkaline additive solutions showed higher ATP and 2,3-DPG levels despite a CO 2 dependent decline of pH 49–52 . The pentose phosphate pathway and glutathione metabolism The oxidative and non-oxidative phase of the PPP are both influenced by cold stor- age. In general the oxidative part of the PPP remains active where the non-oxidative PPP part is inhibited. It is observed that the non-oxidative PPP activity gradually de- clines over time 40,42,53 . It is reported that in SAGM RCCs at the end of storage no glyc- eraldehyde-3-phosphate is produced through the PPP, thus suggesting a blockade in the non-oxidative PPP 40 . This part of the PPP consists of multiple reversible reactions. The direction in which the flux through the non-oxidative PPP occurs is dependent on storage time 42 . During the first ten days the non-oxidative PPP provides mainly glycol- ysis intermediates. From day ten until day seventeen the flux reverses and provides relatively more intermediates for adenine monophosphate production 42 . During the last phase of storage (day 18-42) the non-oxidative PPP provides ribose-5-phosphate as substrate for the glycolysis again 42 . Oxidative PPP activity is influenced by the additive solution used. In RCCs stored in AS-1 the PPP activity remains stable during storage 36 . In RCCs stored in AS-3, initially oxidative PPP intermediate levels increase during the first week of storage but from day 7 the activity declines gradually 53 . AS-7 stored RCCs showed higher PPP activation than AS-3 47 which can be explained by the fact that the optimal pH for G6PD activity is 8 54 . Therefore, an alkaline additive storage solution is beneficial for PPP activity. Contradictory results 5