Reply to: Comments on “Glucose ameliorates the metabolic profile and mitochondrial function of platelet concentrates during storage in autologous plasma”

Dear Sirs,

We thank you for the opportunity to reply to the letter entitled “Comments on Glucose ameliorates the metabolic profile and mitochondrial function of platelet concentrates during storage in autologous plasma”¹ in which Dr. Badlou (the Author of the letter) critically commented the results reported in our study on the beneficial effect of glucose addition to improve storage of platelet concentrates².

The first and last criticisms raised by Dr. Badlou refer to the possibility of bacterial growth caused by glucose addition. We clearly stated in our report that at the end of the storage period each bag of platelet concentrate was checked for sterility by plating an aliquot of the concentrate in Columbia CAN/Mac Conkey/MSA2/Sabouraud growth media (Microbiol s.n.c., Cagliari, Italy) and no type of contamination was found in any of the platelet concentrate analysed².

The second criticism raised by Dr. Badlou concerns the possibility of an inflammatory state caused by a circulating glucose higher than 25 mM. In this regard, we would like to point out that Dr. Badlou did not consider at all what might be the approximate concentration of circulating glucose after an infusion of a bag supplemented with the highest glucose dosage tested in our study. Briefly, the amount of glucose in the control platelet concentrates was about 29 mM to which a maximal concentration of 55 mM was added, giving a final glucose content in the platelet concentrates of 84 mM. In our clinical protocols of platelet concentrate transfusions, the maximal volume of concentrate infused into a patient is 200 mL. This means that, hypothesising the use of platelet concentrates enriched with glucose at the highest concentration, the patient would receive 84 mM/200 mL ≈ 17 mmol of glucose. Assuming a plasma volume of about 3 L, the glucose concentration due to an enriched platelet concentrate would be 5.6 mM/L plasma. In the case of a normal value of circulating glucose (about 5 mM/L plasma), a transient increase to a final value of 10–11 mM/L plasma is expected when using platelet concentrates enriched with the highest glucose dosage tested in our study. This value (10–11 mM/L plasma) is well below the threshold of 25 mM glucose cited by Dr. Badlou and, therefore, no risks of inflammation would occur when transfusing glucose-enriched platelet concentrates.

In his third observation, Dr. Badlou affirms that “Due to amyloids and cross beta-sheets forming of various functional receptor proteins of platelets, which were not measured in almost any of the published studies, including that by Amorini et al., platelets become hyperactive, and their functions change dramatically and unpredictably”. That is, Dr. Badlou criticised our results not because of a wrong incubation protocol, sample preparation, or analytical method used, but merely because we did not consider the parameters he considered in his study³. We could easily argue that since Dr. Badlou did not consider any parameter related to platelet energy metabolism (no measurement of any of the biochemically relevant phosphorylated compounds such as ATP, GTP, ADP, AMP, etc.) in his studies^1,3 the platelet concentrates stored under the conditions suggested by Dr. Badlou would survive for a very short time upon transfusion because of profound energy imbalance during storage caused by decreased substrate availability. Although we did not measure functional receptor proteins, we certainly demonstrated that platelet concentrates stored with increasing glucose have a much better profile of metabolites representative of energy metabolism, including ATP, and this was accompanied by a much lower release of lactate dehydrogenase in the suspending medium, i.e. a higher number of viable platelets was present in platelet concentrates stored with glucose addition.

In conclusion, our study approached the problem of platelet storage using the same “philosophy” used in other cases of storage (red blood cells, organs) in which substrates are added in relevant amounts to ensure cellular energy metabolism⁴. In addition, in evaluating effectiveness of the various additive concentrations, we looked at parameters related to energy metabolism (high energy phosphates, mitochondrial membrane potential, etc.) since it is not possible to hypothesise prolonged survival of platelets on re-transfusion if their energy metabolism is impaired (i.e., higher ATP = longer time of survival upon re-transfusion).

Last but not least, we believe that the validity of a study can be confuted only by repeating the study in identical conditions and obtaining opposite results, or when citing abundant data in literature reporting opposite results not considered by the study. This was not the case of the letter of Dr. Badlou which is, on the contrary, based on personal opinions, most of which are probably caused by a rather hasty reading of our paper, overlooking the fact that we had no cases of bacterial contamination and not calculating the increase in glycaemia upon transfusion of platelet concentrates enriched with 55 mM glucose.