The majority of the effects observed upon envenomation by scorpaenoid fish species can be reproduced by the cytolysins present in their venoms. Fish cytolysins are multifunctional proteins that elicit lethal, cytolytic, cardiovascular, inflammatory, nociceptive, and neuromuscular activities, representing a novel class of protein toxins. These large proteins (MW 150–320 kDa) are composed by two different subunits, termed α and β, with about 700 amino acid residues each, being usually active in oligomeric form. There is a high degree of similarity between the primary sequences of cytolysins from different fish species. This suggests these molecules share similar mechanisms of action, which, at least regarding the cytolytic activity, has been proved to involve pore formation. Although the remaining components of fish venoms have interesting biological activities, fish cytolysins stand out because of their multifunctional nature and their ability to reproduce the main events of envenomation on their own. Considerable knowledge about fish cytolysins has been accumulated over the years, although there remains much to be unveiled. In this review, we compiled and compared the current information on the biochemical aspects and pharmacological activities of fish cytolysins, going over their structures, activities, mechanisms of action, and perspectives for the future.

The genus Conus includes over 900 species of marine invertebrates known as cone snails, whose venoms are among the most powerful described so far. This potency is mainly due to the concerted action of hundreds of small bioactive peptides named conopeptides, which target different ion channels and membrane receptors and thus interfere with crucial physiological processes. By swiftly harpooning and injecting their prey and predators with such deadly cocktails, the slow-moving cone snails guarantee their survival in the harsh, competitive marine environment. Each cone snail species produces a unique venom, as the mature sequences of conopeptides from the venoms of different species share very little identity. This biochemical diversity, added to the numerous species and conopeptides contained in their venoms, results in an immense biotechnological and therapeutic potential, still largely unexplored. That is especially true regarding the bioprospection of the venoms of cone snail species found off the Brazilian coast - a region widely known for its biodiversity. Of the 31 species described in this region so far, only four - Conus cancellatus , Conus regius , Conus villepinii , and Conus ermineus - have had their venoms partially characterized, and, although many bioactive molecules have been identified, only a few have been actually isolated and studied. In addition to providing an overview on all the cone snail species found off the Brazilian coast to date, this review compiles the information on the structural and pharmacological features of conopeptides and other molecules identified in the venoms of the four aforementioned species, paving the way for future studies.

The scorpionfi sh Scorpaena plumieri is one of the most venomous fi sh species in the Brazilian coast. Amongst many biological activities, the S. plumieri fi sh venom (SpV) promotes hemagglutination. Although this activity appears to be associated to the presence of C-type lectins in the venom, it has not yet been chemically or functionally characterized. In the present work we sought to advance the characterization of the hemagglutinating activity associated to this venom. By fractionating SpV through saline precipitation followed by size exclusion chromatography we obtained two purifi ed fractions -HF1 and HF3 -with Ca 2+ -dependent agglutinating activity against rabbit erythrocytes, which remained stable upon storage at 4 and -80 o C. HF1 and HF3 were bacteriostatic against Gram-positive bacteria (Staphylococcus aureus), displaying minimum inhibitory concentration (MIC) of 50 and 200 μg/mL, respectively. In addition, a resazurin-based viability assay revealed that both fractions, at doses up to 370 μg/ mL, were cytotoxic against tumor and non-tumor cell lines. Finally, a tendency towards edema formation could be detected when the fractions -particularly HF1 -were injected into mice footpads. We believe our data contribute to a better understanding of the biological properties of the so often neglected fi sh venoms.