Effect of calcineurin inhibitors on myotoxic activity of crotoxin and Bothrops asper phospholipase A2 myotoxins in vivo and in vitro

Abstract

Previous studies have shown that calcineurin activity plays a critical role in the myotoxic activity induced by crotoxin (CTX), a group II phospholipase A 2 (PLA 2 ) with neurotoxic and myotoxic actions. In order to address whether calcineurin is also important for the activity of nonneurotoxic group II PLA 2 myotoxins we have compared the effects of calcineurin inhibition on the myotoxic capacity of CTX and the nonneurotoxic PLA 2 s, myotoxin II (Mt II) and myotoxin III (Mt III) from Bothrops asper venom. Rats were treated with cyclosporin A (CsA) or FK506, calcineurin inhibitors, and received an intramuscular injection of either CTX, Mt II or Mt III into the tibialis anterior. Animals were killed 24 h after injection of toxins. Tibialis anterior was removed and stored in liquid nitrogen. Myofibers in culture were also treated with CsA or FK506 and exposed to CTX, Mt II and Mt III. It was observed that, in contrast to CTX, CsA and FK506 do not attenuate myotoxic effects induced by both Mt II and Mt III in vivo and in vitro. The results of the present study suggest that calcineurin is not essential for the myotoxic activity of Mt II and Mt III, indicating that distinct intracellular pathways might be involved in myonecrosis induced by neurotoxic CTX and non-neurotoxic Bothrops sp. PLA 2 myotoxins. Alternatively, calcineurin dependent fast fiber type shift might render the muscle resistant to the action of CTX, without affecting its susceptibility to Bothrops sp. myotoxins.

Calcium imaging of muscle cells treated with snake myotoxins reveals toxin synergism and presence of acceptors

“…Receptors for myotoxins isolated from the venom of Oxyuranus scutellatus have been identified [15,16] and it has been suggested that the receptor of the Lys49 myotoxin is the VEGF (vascular endothelial growth factor) receptor itself [17,18]. The presence of specific plasma membrane receptors is also supported by the selectivity of some myotoxins for type I muscle fibers [19,20]. The finding that various snake myotoxins are more toxic to differentiated myotubes than to undifferentiated myoblasts [21,22] may indeed suggest the presence of specific toxin receptors in the differentiated, but not in the undifferentiated, cells.…”

Envenomations by Bothrops and Crotalus Snakes Induce the Release of Mitochondrial Alarmins

“…Moreover, BaV myotoxins are able to affect types I, IIA and IIB muscle fibers, whereas crotoxin is more selective towards oxidative types I and IIA fibers [36]; since tibialis anterior muscle is predominantly constituted by type II fibers [59] such difference might have implications in the mtDNA release. Differences in the mechanism of action of crotoxin and BaV myotoxins were shown by their different myotoxic response to the pretreatment of animals with calcineurin [60], an observation that might be related to the variable specificity towards different muscle fiber types.…”

Cellular pathology induced by snake venom phospholipase A2 myotoxins and neurotoxins: common aspects of their mechanisms of action

“…c) An important consequence in muscles is that the damaged mitochondria release cell death mediators through the opening of the permeability transition pore [114]. This is suggested by the ability of cyclosporin A to abrogate myotoxicity induced by crotoxin [38] because cyclosporin A inhibits the opening of the permeability transition pore. If Ca 2+ -induced mitochondrial alterations and loss of function are relatively simple to detect in vivo, this may not be the case for other less-prominent intracellular organelles.…”

“…The binding of notexin to muscle cell plasma membrane has been documented by immunoelectron microscopy [37]. Furthermore, the ability of cyclosporin A, an inhibitor of calcineurin, to suppress the myotoxic action of crotoxin can be interpreted on the basis of the calcineurininduced shift of muscle fiber type to crotoxinsusceptible type I, slow oxidative fibers [38]. However, the identity of receptors remains elusive.…”