Sanne de Bruin

133 Metabolic changes in erythrocytes in vivo, during storage and after transfusion A decreasing GSH/GSSG ratio despite higher PPP activity suggests that the oxidative stress exceeds the antioxidant capacity of RCCs. Several techniques have been tested to counteract this issue by broadly using two different kind of approaches; reducing the oxidative stress by reducing the ROS formation or increasing anti-oxidant capacity by adding more antioxidants to the additive solution 49,58 . It is hypothesized that by depleting oxygen from RCCs, less ROS will be formed which results in less oxidative stress. While accumulation of oxidative stress markers, such as prostaglandins and thromboxane were still observed during anaerobic storage 49 , it is also shown that storage under hypoxic conditions resulted in a better preservation of glutathione homeostasis 52 and higher fluxes through the PPP 52 . In another study vitamin C (ascorbate) and N-acetylcysteine were added during storage, both known as anti-oxidants, which resulted in higher GSH levels and less accumulation of GSSH 58 . In addition, lower oxidative stress markers including malondialdehyde, were observed resulting in decreased haemolysis compared to controls 58 . Thus adding anti-oxidants could be a solution for reducing the damage caused by oxidative stress. However, this is at the cost of a reduced glucose uptake by RCCs because glucose and ascorbate both compete for the same transporter into the cell, leading to reduced flux through the glycolysis and PPP 58 . Donor erythrocyte metabolism after transfusion In contrast to the large number of studies performed on metabolic changes during in vivo aging and during storage, little is known about the metabolic recovery from stor- age in RCCs after transfusion. It is known that certain aspects of the storage lesion are reversible 62–64 . This is underscored by different in vitro rejuvenation techniques 65 . Sev- eral studies have shown that by adding different substrates e.g. pyruvate, phosphate, adenine and inosine, several metabolite levels increase 65 . However, these rejuvenation techniques are labour intensive and therefore not well applicable in blood bank practice. There are a limited number of studies that address the recovery of donor erythrocytes after transfusion, which are presented below. Glycolysis Data on the recovery of glycolysis intermediates levels after transfusion are still lacking. However, limited data on the recovery of ATP levels, the main product of glycolysis are available 62,63 . A restoration of ATP levels can be used as a measure of glycolysis activity. It has been observed that ATP levels can restore from ATP depletion after transfusion 5