Isolation and pharmacological characterization of a phospholipase A 2 myotoxin from the venom of the Irian Jayan death adder (Acanthophis rugosus)

Abstract

1 It has long been thought that death adder venoms are devoid of myotoxic activity based on studies done on Acanthophis antarcticus (Common death adder) venom. However, a recent clinical study reported rhabdomyolysis in patients following death adder envenomations, in Papua New Guinea, by a species thought to be different to A. antarcticus. Consequently, the present study examined A. rugosus (Irian Jayan death adder) venom for myotoxicity, and isolated the first myotoxin (acanmyotoxin-1) from a death adder venom. 2 A. rugosus (10-50 μg ml -1) and acanmyotoxin-1 (MW 13811; 0.1-1 μM) were screened for myotoxicity using the chick directly (0.1 Hz, 2 ms, supramaximal V) stimulated biventer cervicis nerve-muscle (CBCNM) preparation. A significant contracture of skeletal muscle and/or inhibition of direct twitches were considered signs of myotoxicity. This was confirmed by histological examination. 3 High phospholipase A 2 (PLA 2) activity was detected in both A. rugosus venom (140.2±10.4 μmol min -1 mg -1; n=6) and acanmyotoxin-1 (153.4±11 μmol min -1 mg -1; n=6). Both A. rugosus venom (10-50 μg ml -1) and acanmyotoxin-1 (0.1-1 μM) caused dose-dependent inhibition of direct twitches and increase in baseline tension (n=4-6). In addition, dose-dependent morphological changes in skeletal muscle were observed. 4 Prior incubation (10 min) of CSL death adder antivenom (5 units ml -1; n=4) or inactivation of PLA 2 activity with 4-bromophenacyl bromide (1.8 mM; n=4) prevented the myotoxicity caused by acanmyotoxin-1 (1 μM). 5 Acanmyotoxin-1 (0.1 μM; n=4) displayed no significant neurotoxicity when it was examined using the indirectly (0.1 Hz, 0.2 ms, supramaximal V) stimulated CBCNM preparation. 6 In conclusion, clinicians may need to be mindful of possible myotoxicity following death adder envenomation in Irian Jaya.