Toxicity and mAChRs binding activity of Cassiopea xamachana venom from Puerto Rican coasts

A separation of toxic components from the upside down jellyfish Cassiopea xamachana (Cx) was carried out to study their cytotoxic effects and examine whether these effects are combined with a binding activity to cell membrane receptors. Nematocysts containing toxins were isolated from the autolysed tentacles, ruptured by sonication, and the crude venom (CxTX) was separated from the pellets by ultracentrifugation. For identifying its bioactive components, CxTX was fractionated by gel filtration chromatography into six fractions (named fraction I-VI). The toxicity of CxTX and fractions was tested on mice; however, the hemolytic activity was tested on saline washed human erythrocytes. The LD50 of CxTX was 0.75 μg/g of mouse body and for fraction III, IV and VI were 0.28, 0.25 and 0.12 μg/g, respectively. Fractions I, II and V were not lethal at doses equivalent to LD50 1 μg/g. The hemolytic and phospholipase A2 (PLA2) activities of most fractions were well correlated with their mice toxicity. However, fraction VI, which contains the low molecular mass protein components (≤10 kDa), has shown no PLA2 activity but highest toxicity to mice, highest hemolytic activity, and bound significantly to the acetylcholine muscarinic receptors (mAChRs) isolated from rat brain. The results suggested that fraction VI contains proteinaceous components contributing to most of cytolysis as well as membrane binding events. Meanwhile, fraction IV has shown high PLA2 that may contribute to the venom lethality and paralytic effects.