Protein Kinase C Mediates UVB Light Induced Changes In Human Platelets that Lead to Inflammation In a Two-Event Animal Model of Transfusion Mediated Acute Lung Injury

Abstract 3358

Pathophysiology of acute lung injury (ALI) includes an inflammatory component with recruitment and activation of neutrophils to the lungs. One proposed mechanism of transfusion related acute lung injury (TRALI) involves two events; the first is a generalized inflammatory response, as would occur in sepsis, which leads to activation of endothelial cells and sequestration of neutrophils to the lungs. The second is an infusion of a transfusion product that contains HLA or HNA antibodies or biologic modifiers such as lipids from stored cells. The second event activates the neutrophils sequestered in the lungs which lead to neutrophil degranulation, superoxide release and localized tissue damage. Growing evidence suggests that platelets exert proinflammatory actions which include supporting tissue infiltration of neutrophils in septic lung injury. In a separate 2010 ASH abstract we show that ultraviolet B light (UVB, 2.4 J/cm²) exposed human platelets (HPs) mediate lung injury in a two-event animal model of ALI. UVB exposure has been reported to activate platelet protein kinase C (PKC). We compared the effects of UVB exposure to PKC activation by a PKC agonist, PMA (30 nM), in aggregation, activation and potential to cause lung injury in the two-event animal model. HPs were collected by apheresis and stored overnight with experiments performed on day 1 post collection. Platelet aggregation induced by increasing concentrations of ADP (5-20 mM) was potentiated by pretreatment with UVB or PMA. TRAP (20 mM) induced aggregation was inhibited by UVB, but unchanged by PMA pretreatment. Both UVB and PMA increased platelet PAC-1 binding and p-selectin expression. Pretreating HPs with a PKC inhibitor prevented all of PMA induced PAC-1 binding and inhibited UVB induced PAC-1 binding by 40%. Furthermore, the PKC inhibitor partially reduced p-selectin expression on PMA and UVB treated HPs, whereas p-selectin expression on control HPs remained unchanged. The UVB HPs or PMA HPs were evaluated in the two-event animal model of ALI. Immunodeficient (SCID) mice were used to minimize the species difference (Piper et al., Transfusion 47:1540-9, 2007). MIP-2 elevation in plasma is a marker of acute inflammation and was increased following LPS administration. Infusion of control HPs as the second event moderately increased MIP-2. When UVB HPs or PMA HPs were infused MIP-2 was significantly elevated compared to control HPs. Pretreatment of UVB HPs with the PKC inhibitor (RO31-8425) reduced MIP-2 elevation to the level of control platelets. In summary, UVB HPs can cause ALI in animals pretreated with LPS (separate 2010 ASH abstract as mentioned above). Changes to the platelets induced by UVB appear to be mediated by PKC since a PKC agonist (PMA) has similar effects on platelets in aggregation and activation as does UVB and PKC inhibitor partially inhibits UVB induced platelet activation. In vivo, both UVB and PMA treated HPs elevated MIP-2 plasma levels when injected after LPS and this response was prevented by treatment of platelets with a PKC inhibitor prior to UVB exposure. The UVB induced activation leads to a conformational change in GpIIb/IIIa which potentiates weak agonist induced aggregation and mediates an acute in vivo inflammatory response that may be responsible for the acute lung injury in the animal model. Understanding the underlying mechanisms of UVB exposure induced changes in platelets would be beneficial in designing methods to reduce the UVB associated ALI in an animal model and potentially in patients susceptible to TRALI by a primary sensitizing event and infused with high dose UVB exposed platelets. The findings and conclusions in this abstract have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy.