Feasibility study: Varespladib protects CD-1 mice from lethal doses of whole bee (Apis mellifera) venom

Swarming Hymenoptera attacks can deliver high cumulative doses of venom resulting in death and life-threatening or chronically disabling injuries. Varespladib, a potent inhibitor of snake venom secretory PLA2 (sPLA2), is a relatively weak inhibitor of whole bee venom sPLA2 in vitro (pico-to low nanomolar for snake venom compared to $$ M for Apis millera). Animal studies of varespladib against wasp (Vespa mandarinia) venom have shown promise against both nephropathy and coagulopathy, major markers of severe systemic toxicity distinct from hypersensitivity such as anaphylactoid and anaphylaxis reactions. We conducted a simple pilot study to evaluate if varespladib could feasibly decrease mortality against lethal doses of honeybee (Apis mellifera) venom in a murine model. When pre-mixed with a single dose of 10 mg/kg varespladib and administered intravenously (IV), varespladib prevented all mortality (0 of 10) in comparison to a cohort of mice administered lethal doses of whole bee venom alone (6 of 10) during a 24-h study period (N = 10 each group; log rank χ² = 8.29; p < 0.005), and it eliminated signs of toxicity within 2 h while control animals either died or continued to show signs of toxicity. Survival in these animals despite poor in vitro sPLA2 inhibition suggests that suppression of the host sPLA2 response itself might play a role in the treatment of venom toxicity using an enzyme inhibitor rather than antivenom antibodies. Varespladib could be a useful tool for dissecting fundamental interactions between exogenous toxins and their corresponding endogenous counterparts.