Hyaluronidase activity of Indian ornamental tarantula (Poecilotheria regalis) venom is significantly reduced by commercial Latrodectus mactans and American scorpion antivenoms.

A recent clinical case involving a Poecilotheria regalis bite was treated with Mexican L. mactans antivenom (Aracmyn Plus, Silanes, Mexico), resulting in the improvement of some of the symptoms. This could be attributed to cross-reactivity caused by structural similarities between certain components of L. mactans and P. regalis venoms. The aim of the present study was to evaluate the cross-reactivity of P. regalis venom with commercial antivenoms that target the venom of the Latrodectus mactans spider and American scorpions. Hyaluronidase activity was evaluated via a turbidimetric method, while edema was evaluated in rat paw via a histopathological analysis. Cross-reactivity was determined using SDS-PAGE and western blotting. The results obtained showed that both antivenoms significantly reduced the hyaluronidase activity of P. regalis venom and that induced by other tarantula venoms. Aracmyn Plus did not reduce inflammation caused by P. regalis venom. Furthermore, it was previously observed that this antivenom failed to reduce the characteristic muscle cramps induced by this venom. Finally, western blotting revealed that both antivenoms showed cross-reactivity with P. regalis venom. The above findings suggest that hyaluronidases and other high-molecular-weight components exhibit structural similarities across the venoms from different arachnid species.