Varespladib (LY315920) inhibits neuromuscular blockade induced by Oxyuranus scutellatus venom in a nerve-muscle preparation

The phospholipase A(2) (PLA(2)) inhibitors varespladib (LY315920) and its orally available derivative methyl-varespladib (LY333013) have been proposed as potential therapies for the treatment of snakebite envenomings in which toxicity depends on the action of PLA(2)s. In this study, the ability of LY315920 to abrogate the effect of the potent neumtoxic venom of Oxyuranus scutellatus (taipan) was assessed using the mouse phrenic nervediaphragm preparation. LY315920 inhibited the venom when (a) incubated with venom before addition to the medium; (b) added to the medium before addition of venom, and; (c) added to the medium within 30 min after addition of venom, and even after the onset of decline in twitch response. This contrasts with previous results with antivenom using the same experimental model, in which the window of time when antibodies are effective is shorter than 10 min. It is proposed that such differences may depend either on the higher affinity of the inhibitor for PLA(2)s or on the possibility that LY315920 reaches the cytosol of the nerve terminals, inhibiting neumtoxins that have been internalized. Our findings bear implications on the therapeutic potential of varespladib in neurotoxic snakebite envenomings mediated by presynaptically-acting PLA(2)s. (AU)