Neutralization of the edema-forming and myotoxic activities of the venom of Potamotrygon motoro Müller and Henle, 1841 (Chondrichthyes - Potamotrygoninae) by antivenoms and circulating immunoglobulins.

Freshwater stingrays are cartilaginous fish with stingers at the base of their tail. The stinger is covered with an epithelium containing mucous and venom glands. Human envenomation usually occurs when a person steps on a stingray hiding in the sand and the fish sinks its stinger into the victim, causing an extremely painful wound which generally leads to tissue necrosis. Medical treatment is based on the use of painkillers, anti-inflammatory drugs and antibiotics, as there is to date no specific antidote for envenomation by freshwater stingrays. The aim of this study was therefore to investigate whether sera containing anti-P. motoro antibodies can neutralize the edema-forming and myotoxic activities of Potamotrygon motoro venom. To this end, two protocols were used: seroneutralization and vaccination of mice. The seroneutralization protocol involved intramuscular injection of the P. motoro venom in the mice gastrocnemius followed by administration of hyperimmune mouse serum anti P. motoro dorsal extract and stinger extract via the ophthalmic venous plexus. The vaccination protocol involved immunizing the mice with dorsal or stinger extract adsorbed to aluminum hydroxide followed by intramuscular challenge with the P. motoro venom. The gastrocnemii of all the animals were removed for histopathological and stereological analyses, and blood was collected via the ophthalmic venous plexus to measure IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ, TNF, C-reactive protein and total creatine kinase. Protocols did not neutralize the edema-forming or local myotoxic induced by P. motoro venom under the experimental conditions tested. But systemic rhabdomyolysis was only completely neutralized in animals vaccinated with the stinger extract. Cytokine analysis revealed that under the experimental conditions used here, seroneutralization induced release of Th1, Th2, Th17 and Treg cytokines whereas vaccination induced a Th1 response.

Systemic rhabdomyolysis induced by venom of freshwater stingrays Plesiotrygon iwamae and Potamotrygon motoro (Chondrichthyes-Potamotrygonidae) from the Amazon Basin.

Injuries caused by freshwater stingrays are characterized by intense pain and pathological changes at the lesion site, including oedema, erythema and, in most cases, necrosis. In this study, the systemic myotoxic activity induced by mucus extracts from the dorsal region and stinger of the stingrays Plesiotrygon iwamae and Potamotrygon motoro was described, analysed and quantified. Twenty-four hours after injection of 400 µg of the extracts into the gastrocnemius muscle of mice, the following effects were observed: coagulative necrosis of the muscle tissue, muscle fibre regeneration and the presence of inflammatory infiltrates, including neutrophils, macrophages, and a reduced number of eosinophils and lymphocytes. These changes were also observed, although to a lesser extent, in the gastrocnemius muscles of the contralateral limbs, demonstrating that the extracts from the two species could induce systemic rhabdomyolysis. Based on morphometric analysis, it was observed that the stinger extract of P. motoro was more potent in inducing local and systemic myotoxic activity, followed by the dorsal extract from P. motoro and stinger and dorsal extracts from P. iwamae, which induced similar effects.