PV2: a novel toxin isolated from the eggs of P. canaliculata.

FRASSA,V.; DREON MS,; HERAS, H.

S.M. Tucumán

Workshop; IV International workshop on the biology of Ampullariidae; 2010

INIBIOLP

It is well known that some animals may become toxic by the acquisition of toxic compounds from their food, thus providing protection from predators. Usually females sequester these toxins to endow eggs with chemical defenses. In contrast with this strategy, here we show the identification and characterization of a neurotoxin of proteinaceous nature which is synthesized by females of P. canaliculata to protect their eggs. Egg extracts from the freshwater apple snail Pomacea canaliculata displayed a neurotoxic effect in mice upon intraperitoneal injection (i.p.) (LD50, 96 h 2.3 mg/kg). After assaying egg extracts, total lipids and several protein fractions, we found that the toxicity was associated with only one of the proteins. The biochemical, biophysical and immunological characterization of this toxic protein indicated that it was indistinguishable from PV2, one of the major glyco-lipoprotein of the egg perivitellin fluid. In comparison with other toxins, PV2 can be classified as extremely toxic, considering that the LD50, 96 h, with a single dose, was around 0.25 mg/kg. The neurotoxin was heat sensitive and there was evidence of circulating antibody response to sublethal i.p. doses on mice. In addition we also showed oral immunization of rats specific to the larger subunit of PV2. Clinical signs, histopathological and immunocytochemical studies revealed damage mostly in mice spinal cord. Experiments showed chromatolysis and a decreased response to calbindin D-28K associated with a significant increase of TUNEL-positive cells in the dorsal horn neurons. These results suggest that calcium buffering and apoptosis may play a role in the neurological disorders induced by the toxin in mammalian central nervous system. The fact that PV2 is a large oligomeric protein excludes any direct action on the spinal cord due to low permeability of the blood–nerve barrier. However, their subunits, probably the 67 kDa, are small enough to penetrate the barrier by endocytosis.