Our long term aim is to develop a galactosylated and sialylated platelet product that can be stored in the cold in order to prolong shelf life and minimize risk of bacterial growth. Currently, platelets can only be stored at room temperature as platelets stored in the cold disappear rapidly from the circulation after transfusion. Storage at room temperature (RT) is favorable for the growth of bacteria and conducive to detrimental changes in platelet structure and function. Therefore platelets are currently licensed for room temperature storage for only 5-7 days. It has been established that exposed glycans are important for clearance of 4 hour chilled mouse platelets, we now have evidence suggesting a more profound role of galactose in the control of clearance of platelets stored in the cold for over 24 hours. Cold storage induces clustering of glycans on the platelet surface, leading to galactose recognition by the asialo-glycoprotein receptor located on liver macrophages and hepatocytes, and consequently to platelet ingestion by these cells. This masking of exposed galactose and GlcNAc on the surface of platelets is hypothesized to restore circulation of cold stored platelets. Preliminary results demonstrate that human platelets, besides containing a galactosyltransferase which transfers galactose from the donor substrate UDP-galactose to GlcNAc, contain an endogenous sialyltransferase, which catalyzes the transfer of sialic acid from the donor substrate CMP- sialic acid to exposed galactose. Therefore the enzymatic modification of platelet surface proteins can be achieved without the addition of exogenous glycosyltransferases by the simple addition of the donor substrates UDP-galactose and CMP-sialic acid. The novel approach of taking advantage of platelets own enzymatic machinery to modify glycans that would otherwise be recognized by liver macrophages after the chilling of platelets, offers a highly innovative, new and simple solution to the old problem of the clearance of transfused cold stored platelets.
Specific aims for SBIR Phase I: To carry out preclinical work required to support an IND for the use of UDP-galactose CMP-sialic acid in humans and the conductance of a human feasibility trial.
Specific Aim 1 : Determine the role of the ASGP receptor in the clearance of long-term cold-stored platelets.
Specific aim 2 : Test the effect of masking exposed galactose and GlcNAc on clearance of long-term chilled mouse platelets.
Specific Aim 3 : Test the effect of UDP-galactose and CMP-sialic acid treatment on in vitro phagocytosis of long-term chilled human platelets. Milestone: Demonstration of increased survival of long- term cold-stored galactosylated and sialylated platelets (66% as compared with RT stored platelet control). Future progression for SBIR Phase II Human safety and feasibility trial with combined galactosylated and sialylated platelets. This will be performed as an autologous trial with dual radioactive labeling of glycosylated and non-glycosylated splits, comparing glycosylated chilled platelets with either RT or 4?C stored control. The need to keep platelets at room temperature prior to transfusion heightens the risk of bacterial infection. And leads to functional and structural degradation of platelets stored. The short shelf life (5-7 days) of procured platelets coupled to fluctuating demands for platelet transfusions mean that many units of procured platelets cannot be used because of outdating and leads to a high wastage rate that and may cost the American health care system over a billion dollars annually. If glycan modification safely prolongs the circulation of refrigerated platelets in humans, it could contribute to better control of platelet inventories, diminution of bacterial contamination, and increased ability to provide platelets of improved functional quality to patients needing platelet transfusion. ? ? ? ? ? ?
