Melittin and phospholipase A2 from bee (Apis mellifera) venom cause necrosis of murine skeletal muscle in vivo

Abstract

Melittin and phospholipase A2 (PLA2) from bee (Apis mellifera) venom were tested for their ability to induce necrosis of skeletal muscle cells after intramuscular injection into mice. Light and electron microscopic examination of tissue indicated that both melittin (4 μg/g) and bee venom PLA2 (4 μg/g) caused necrosis of skeletal muscle cells within 30 min after i.m. injection. Early changes in the cells consisted of delta lesions, indicating a ruptured plasma membrane, and hypercontraction of myofibrils. By 24 hr the affected cells appeared as an amorphous mass of disorganized and disrupted myofibrils contained in an intact basal lamina. To ensure that the myotoxic activity of the melittin preparation was not due to contaminating PLA2 activity, the preparation was treated with p-bromophenacyl bromide (p-BPB), a known inhibitor of PLA2 activity. The p-BPB-treated melittin was determined to have no detectable PLA2 activity using a sensitive muscle cell culture assay, and it still induced myonecrosis, although to a lesser extent and of a slower onset. Additionally, p-BPB treatment of purified bee venom PLA2 completely inhibited its myotoxic activity. These results indicate that both melittin and bee venom PLA2 are capable of inducing necrosis of skeletal muscle cells upon i.m. injection, and that the catalytic and myotoxic activities of bee venom PLA2 are inhibited by p-BPB. Also, melittin and contaminating PLA2 in the melittin fraction may be acting synergistically to induce a stronger and more rapid myotoxic effect than occurs with either alone.