The anticoagulant effect of Apis mellifera phospholipase A2 is inhibited by CORM-2 via a carbon monoxide-independent mechanism.

Bee venom phospholipase A2 (PLA2) has potential for significant morbidity. Ruthenium (Ru)-based carbon monoxide releasing molecules (CORM) inhibit snake venoms that are anticoagulant and contain PLA2. In addition to modulating heme-bearing proteins with carbon monoxide, these CORM generate reactive Ru species that form adducts with histamine residues resulting in changes in protein function. This study sought to identify anticoagulant properties of bee venom PLA2 via catalysis of plasma phospholipids required for thrombin generation. Another goal was to determine if Ru-based CORM inhibit bee venom PLA2 via carbon monoxide release or via potential binding of reactive Ru species to a key histidine residue in the catalytic site of the enzyme. Anticoagulant activity of bee venom PLA2 was assessed via thrombelastography with normal plasma. Bee venom PLA2 was then exposed to different CORM and a metheme forming agent and anticoagulant activity was reassessed. Using Ru, boron and manganese-based CORM and a metheme forming agent, it was demonstrated that it was unlikely that carbon monoxide interaction with a heme group attached to PLA2 was responsible for inhibition of anticoagulant activity by Ru-based CORM. Exposure of PLA2 to a Ru-based CORM in the presence of histidine-rich human albumin resulted in loss of inhibition of PLA2. Ru-based CORM likely inhibit bee venom PLA2 anticoagulant activity via formation of reactive Ru species that bind to histidine residues of the enzyme.