Possible mechanisms of action of cobra snake venom cardiotoxins and bee venom melittin

Effect of ammodytin L from Vipera ammodytes on L-6 cells from rat skeletal muscle

Ammodytin L (AMDL) is a myotoxic phospholipase-like protein from the venom of Vipera ammodytes with a serine in position 49 instead of an aspartate, therefore this toxin is devoid of phospholipase activity, and the membrane-damaging effect does not involve any step of phospholipase activity. The aim of the present study was to analyze the effect of AMDL on L-6 cells from rat skeletal muscle to investigate its mechanism of action and the role of calcium ions in its muscle-damaging activity. Our data indicate that the effect of ammodytin L is strongly dependent on the degree of cell differentiation. Low doses of myotoxin gave rise to a marked release of creatine kinase in myotubes differentiated from L-6 myoblasts and the presence of calcium ions plays a role in the cytotoxic effect. The presence of EGTA in the incubation buffer reduced by 50% the release of creatine kinase. No membrane damage was observed in myoblasts, but there was a significant increase of intracellular calcium concentration measured with Fura-2. A non-specific membrane effect of AMDL was ruled out using platelets as reference cells: no platelet aggregation pattern and no increase in intracellular calcium were observed.

Melittin increases AMPA receptor affinity in rat brain synaptoneurosomes

Recent experimental evidence suggests that phospholipase-induced changes in binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtype of glutamate receptors account for the increase in synaptic response observed in long-term potentiation (LTP). In the present study, we report that treatment of rat telencephalic synaptoneurosomes with the bee venom peptide melittin, a potent activator of endogenous phospholipases, increased [3H]AMPA binding to the AMPA receptor. The action of melittin was concentration-dependent (EC50 value = 10 micrograms/ml) and did not require the presence of extracellular calcium. Saturation kinetic experiments revealed that the increase in [3H]AMPA binding produced by melittin was due to an enhancement in the affinity of the AMPA receptor, an effect markedly reduced by the phospholipase A2 (PLA2) inhibitor bromophenacyl bromide (BPB). In contrast to BPB, inhibitors of cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism did not interfere with the melittin-induced increase in [3H]AMPA binding. In neonatal synaptoneurosomes, the effect of melittin on [3H]AMPA binding was significantly reduced when compared to adult synaptoneurosomes, an effect which is consistent with the observation that LTP is not present in very young animals. The results indicate that activation of endogenous phospholipases may be an important mechanism in the regulation of AMPA receptor properties in LTP.

Phospholipase-like myotoxins induce rapid membrane leakage of non-hydrolyzable ether-lipid liposomes

Two phospholipase-like myotoxins--ammodytin L from Vipera ammodytes and myotoxin II from Bothrops asper--are shown to be able to induce leakage of liposomes made from non-hydrolyzable ether-linked phospholipids. This demonstrates that the cytolytic activity of these toxins is completely independent of any remaining enzyme activity or contamination with active phospholipases.

Myocarditis following envenoming with Vipera palaestinae in two horses

Cardiac disease developed several days to weeks after resolution of local inflammation caused by envenoming by Vipera palaestinae in two horses. In one horse (case A), referred to the hospital for recurrent abdominal pain 8 days after envenoming, a tachyarrhythmia was detected; ventricular premature depolarizations were diagnosed by ECG. A second horse (case B) was found dead without premonitory signs 60 days after envenoming. In both horses, there was extensive necrosis of cardiac ventricular tissues.