Extended Storage of Platelets in a Novel Organ Preservation Solution, Somah

Background:

Extended storage of platelet in lesion free state is of critical importance and is tenuous at best in currently available additive solutions thus requiring innovations in storage modalities. We have recently demonstrated that donor hearts obtained for transplant can be stored at ambient temperature in Somah solution of our design. Unlike other clinically used solutions, rationally designed Somah maintains cellular homeostasis and high-energy state of the heart during extended storage, circumventing hypothermic injury and thus facilitating optimal functional recovery of heart upon reperfusion. This study was designed to evaluate the ability of Somah to preserve platelets in lesion free state during extended storage by modulation of analogous biochemical pathways as in the heart.

Study Design and Methods:

Blood was collected in ACD and the platelets (PRP) were isolated using standard protocol (n=3). Platelets were stored in Somah, PAS III and PAS III-M solutions at concentration of 65% at ambient temperature (22 ^oC) for 12 days under asepsis. The storage solutions were periodically assessed for pO₂, pCO₂, HCO^-₃, pH, Glucose and lactic acid using Abaxis iStat. Platelet morphology was evaluated with confocal microscopy; platelet activation and apoptosis was measure by quantitating and localizing phosphtidylserine (PS) exposure using Alexa 488-lactoadherin binding, flow cytometry, and confocal microscopy over the storage period.

Results:

Platelets demonstrated active metabolism in Somah. Glucose concentration decreased in Somah from 225 mg/dL to 110 mg/dL while the lactate concentration increased from 1.45 mMol/L to 9.0 mMol/L during the 12 day storage. Strong buffering capacity of Somah maintained the pH near neutrality. pO₂ and pCO₂remained at 165 mmHg and 30 mmHg respectively. In contrast, glucose decreased from 134 mg/dL to 102 mg/dL and lactate increased from 0.97 mMol/L to 15.6 mMol/L in the PAS group. PS exposure increased from 0.2% to 12.8 % at 12 days in platelets stored in Somah, in contrast, PS exposure increased from 0.2% to 30.7% during the same period in platelets stored in PAS solutions, respectively. Morphology of platelets was well maintained in Somah but not in the PAS solutions. There was no significance difference in measured values between PAS III and PAS III-M.

Conclusion:

Unique composition of Somah facilitates modulation of anaerobic and aerobic metabolism by diverting lactate into oxidative phosphorylation pathways, thus maintaining the energy state and cellular homeostasis. Intact morphology, active metabolism and minimal exposure of PS indicate that platelets were well preserved in Somah during extended storage. Work is under way to extend the storage further, evaluate high-energy stores, CD 62p, vWF expression and functional in vitro activation of platelets stored in Somah. These preliminary studies indicate Somah can be a viable alternative for storage of platelets in lesion free state during extended storage.