ATTENUATION OF SNAKE VENOMS BY IONIZING RADIATION: A RETROSPECTIVE

NANCI DO NASCIMENTO

IPEN/CNEN-SP

Snake envenomation is a serious public health problem in Brazil, with around 20.000 cases reported every year. Serum therapy is the only known treatment, the antiserum  being produced by immunizing horses with crude venom. Obviously, this treatment induces deleterious effects, impairing the animals lifespan. Ionizing radiation has been known as an effective tool to attenuate venoms and toxins since the early 70´s. Our group, as well as others around the world, has been working on the effects of ionizing radiation as a tool to improve antisera production by attenuating venom toxicity without affecting its immunogenic properties. The first experiments were performed using crude bothropic and crotalic venom. The results were rather promising, with a toxicity decrease of around five folds and with these toxoids inducing protective antibodies with no detectable deleterious effects on serum-producing animals. The next step was to further characterize the effects of radiation on the venom components, aiming to identify the mechanism of toxicity attenuation. Purified toxins were used as probes to analyze the functional and structural modifications induced by radiation. All the experiments indicate that the toxins, following irradiation, undergo structural modifications, such as oxidation and unfolding, associated with a dose-dependent loss of enzymatic activity. These alterations lead to a toxicity decrease, while enhancing phagocytosis by antigen presenting cells trough receptors specialized in the removal of oxidized proteins. Also, unfolding promotes exposure of neoepitopes, increasing the repertoire of  cell surface receptors able to recognize these modified biomolecules. Pilot experiments performed on goats indicate that irradiated venoms induced high titers of neutralizing antibodies, without any detectable toxic manifestations.