Effect of gamma irradiation on the behavioral properties of crotoxin

New insights into the structural characteristics of irradiated crotamine

Background

Since ionizing radiation has the potential to alter the molecular structure and affect the biological properties of biomolecules, it has been successfully employed to attenuate animal toxins. The present study aimed to characterize the structural modifications on irradiated crotamine, a toxin from Crotalus durissus terrificus venom, using circular dichroism (CD), fluorescence, Fourier transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM) and differential scanning calorimetry (DSC).

Methods

A combination of size exclusion and ion-exchange chromatography was used to purify the peptide using crude venom. The pure toxin was then submitted to 2 kGy gamma irradiation doses from a cobalt-60 source. Native and irradiated crotamine were analyzed using a fluorescence spectrophotometer. Wavelength was fixed at 295 nm and fluorescence emission scans were collected from 300 to 400 nm. CD and FTIR techniques were used to identify the secondary structure of both samples. DSC analyses were performed at a starting temperature of 20 °C up to a final temperature of 90 °C. AFM provided a 3D profile of the surfaces of both crotamine forms adsorbed on mica.

Results

Fluorescence spectroscopy showed that the quantum yield of the irradiated form decreased. CD spectra of native and irradiated crotamine solutions showed differences between the samples in wavelength, indicating that irradiation induced a transition of a small portion of the random coil regions towards an α-helical conformation. FTIR and CD showed that the native and irradiated crotamine spectra were different with regard to secondary structure. The thermodynamic analysis showed that irradiation caused changes in the calorimetric profile and CD showed that temperature-induced changes also occur in the secondary structure. Finally, AFM showed the possible formation of insoluble aggregates.

Conclusions

Our results indicate that irradiation leads to progressive changes in the structure of the toxin, which could explain a decrease in myotoxic activity.

Evaluation of the effect of gamma rays on the venom of Vipera lebetina by biochemical study

Snake bites represent a serious public health problem in many areas of the world. In Algeria, two widespread snakes are Vipera lebetina and Cerastes cerastes. Vipera lebetina venom causes local hemorrhage and necrosis, and it may lead to permanent limb loss. The principal causes of mortality after snakebites are acute renal failure and hemorrhage, which occur not only locally, at the site of the bite, but also systemically, contributing to the cardiovascular shock characteristic of severe envenomation. Gamma radiation has been shown to be effective for attenuating venom toxicity. Vipera lebetina venom was irradiated with two doses of gamma rays (1 and 2 kGy) from a 60Co source, and the venom's toxic, enzymatic, and structural properties were analyzed. Intraperitoneal injection of the irradiated venoms (100–500 µg/20 g mouse body mass) revealed a significant decrease of the toxicity. Irradiated venoms with 1 and 2 kGy doses were four and nine times less toxic, respectively, than the native venom. A biochemical characterization of in vitro enzymatic activities was performed. Vipera lebetina displayed in vitro caseinolytic, amidolytic, esterasic, coagulant, and phospholipase A2 activities. Caseinolytic, amidolytic, esterasic, and coagulative activities were reduced for the irradiated venoms; only phospholipase A2 activity was abolished in the irradiated venom with a dose of 2 kGy. The native and irradiated venoms were separated by gel filtration and electrophoresis. Chromatographic and electrophoretic profiles were drastically changed as compared with the native venom. Vipera lebetina venom detoxified by gamma rays was used for active immunization, and the presence of antibody in the immune sera was detected by ELISA. The immunogenic properties were preserved and the antisera obtained with the irradiated venoms could cross-react. Antisera were able to neutralize the toxic effect of V. lebetina native venom. These results indicate that irradiation of V. lebetina venom with a dose of 2 kGy can promote a significant detoxification, keeping the immunological properties intact.Key words: Vipera lebetina venom, gamma radiation, enzymes, detoxification, immune sera, immunoreactivity.

A review of 25 years of the social interaction test

The social interaction test of anxiety was developed 25 years ago to provide an ethologically based test that was sensitive to both anxiolytic and anxiogenic effects. It is sensitive to a number of environmental and physiological factors that can affect anxiety. It has detected anxiogenic effects of peptides such as corticotropin-releasing factor (CRF) and adrenocorticotropic hormone (ACTH), and anxiolytic effects of neuropeptide Y and substance P receptor antagonists. It has successfully identified neuropharmacological sites of action of anxiogenic compounds and drug withdrawal. Effects of compounds acting on the gamma-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT) systems have been extensively investigated after both systemic administration and microinjection into specific brain regions. The use of this test has, thus, played a crucial role in unravelling the neural basis of anxiety. It is hoped that in the next 25 years, the test will play a crucial role in determining the genetic basis of anxiety disorders.

Reduction of crotoxin-induced neuromuscular blockade by gamma radiation

A comparative study between crotoxin and gamma irradiated crotoxin was performed on the indirectly evoked twitches and tetani of sciatic nerve-extensor digitorum longus muscle of rats. Crotoxin (3 to 14 microg/ml) decreased the amplitude of twitches and induced a slight tetanic fade, and irradiated crotoxin did not significantly affect either twitch amplitude or tetanic tension. Since gamma radiation reduced the neurotoxicity of crotoxin it may be useful for the production of anticrotalic serum.