TSII toxin isolated from Tityus serrulatus scorpion venom: behavioral, electroencephalographic, and histopathologic studies

Effects of Brazilian scorpion venoms on the central nervous system

In Brazil, the scorpion species responsible for most severe incidents belong to the Tityus genus and, among this group, T. serrulatus, T. bahiensis, T. stigmurus and T. obscurus are the most dangerous ones. Other species such as T. metuendus, T. silvestres, T. brazilae, T. confluens, T. costatus, T. fasciolatus and T. neglectus are also found in the country, but the incidence and severity of accidents caused by them are lower. The main effects caused by scorpion venoms - such as myocardial damage, cardiac arrhythmias, pulmonary edema and shock - are mainly due to the release of mediators from the autonomic nervous system. On the other hand, some evidence show the participation of the central nervous system and inflammatory response in the process. The participation of the central nervous system in envenoming has always been questioned. Some authors claim that the central effects would be a consequence of peripheral stimulation and would be the result, not the cause, of the envenoming process. Because, they say, at least in adult individuals, the venom would be unable to cross the blood-brain barrier. In contrast, there is some evidence showing the direct participation of the central nervous system in the envenoming process. This review summarizes the major findings on the effects of Brazilian scorpion venoms on the central nervous system, both clinically and experimentally. Most of the studies have been performed with T. serrulatus and T. bahiensis. Little information is available regarding the other Brazilian Tityus species.

Tityus serrulatus venom--A lethal cocktail

Tityus serrulatus (Ts) is the main scorpion species of medical importance in Brazil. Ts venom is composed of several compounds such as mucus, inorganic salts, lipids, amines, nucleotides, enzymes, kallikrein inhibitor, natriuretic peptide, proteins with high molecular mass, peptides, free amino acids and neurotoxins. Neurotoxins are considered the most responsible for the envenoming syndrome due to their pharmacological action on ion channels such as voltage-gated sodium (Nav) and potassium (Kv) channels. The major goal of this review is to present important advances in Ts envenoming research, correlating both the crude Ts venom and isolated toxins with alterations observed in all human systems. The most remarkable event lies in the Ts induced massive releasing of neurotransmitters influencing, directly or indirectly, the entire body. Ts venom proved to extremely affect nervous and muscular systems, to modulate the immune system, to induce cardiac disorders, to cause pulmonary edema, to decrease urinary flow and to alter endocrine, exocrine, reproductive, integumentary, skeletal and digestive functions. Therefore, Ts venom possesses toxins affecting all anatomic systems, making it a lethal cocktail. However, its low lethality may be due to the low venom mass injected, to the different venom compositions, the body characteristics and health conditions of the victim and the local of Ts sting. Furthermore, we also described the different treatments employed during envenoming cases. In particular, throughout the review, an effort will be made to provide information from an extensive documented studies concerning Ts venom in vitro, in animals and in humans (a total of 151 references).

Molecular targets for antiepileptic drug development

This review considers how recent advances in the physiology of ion channels and other potential molecular targets, in conjunction with new information on the genetics of idiopathic epilepsies, can be applied to the search for improved antiepileptic drugs (AEDs). Marketed AEDs predominantly target voltage-gated cation channels (the alpha subunits of voltage-gated Na+ channels and also T-type voltage-gated Ca2+ channels) or influence GABA-mediated inhibition. Recently, alpha2-delta voltage-gated Ca2+ channel subunits and the SV2A synaptic vesicle protein have been recognized as likely targets. Genetic studies of familial idiopathic epilepsies have identified numerous genes associated with diverse epilepsy syndromes, including genes encoding Na+ channels and GABA(A) receptors, which are known AED targets. A strategy based on genes associated with epilepsy in animal models and humans suggests other potential AED targets, including various voltage-gated Ca2+ channel subunits and auxiliary proteins, A- or M-type voltage-gated K+ channels, and ionotropic glutamate receptors. Recent progress in ion channel research brought about by molecular cloning of the channel subunit proteins and studies in epilepsy models suggest additional targets, including G-protein-coupled receptors, such as GABA(B) and metabotropic glutamate receptors; hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel subunits, responsible for hyperpolarization-activated current Ih; connexins, which make up gap junctions; and neurotransmitter transporters, particularly plasma membrane and vesicular transporters for GABA and glutamate. New information from the structural characterization of ion channels, along with better understanding of ion channel function, may allow for more selective targeting. For example, Na+ channels underlying persistent Na+ currents or GABA(A) receptor isoforms responsible for tonic (extrasynaptic) currents represent attractive targets. The growing understanding of the pathophysiology of epilepsy and the structural and functional characterization of the molecular targets provide many opportunities to create improved epilepsy therapies.

The epileptic seizures induced by BmK I, a modulator of sodium channels

In the present study, the susceptibility to rat epileptic seizures induced by the intrahippocampal administration of BmK I, a modulator of sodium channels purified from the venom of Chinese scorpion, has been investigated. The results showed that the strong epileptic behaviors and discharges in the hippocampus were evoked by BmK I dose-dependently. The hippocampal c-Fos expression displayed two peak waves in a specific spatio-temporal pattern elicited by BmK I. The whole cell patch clamp recordings showed that the inactivation of sodium currents in rat cultured hippocampal neurons was prolonged significantly by BmK I, and restored partially after washing. These results indicated that the rat hippocampus is a susceptible target for the proconvulsant effects of BmK I, and the induction of epileptic seizures may be ascribed to the modulation of BmK I on the inactivation of voltage-gated sodium channels distributing in the rat hippocampal neurons.

Primary structure, behavioral and electroencephalographic effects of an epileptogenic peptide from the sea anemone Bunodosoma cangicum

The primary structure of cangitoxin (CGX), a 4958 Da peptide from the sea anemone Bunodosoma cangicum, was determined: GVACRCDSDGPTVRGNSLSGTLWLTGGCPSGWHNCRGSGPFIGYCCKK. CGX contains all the 11 residues that are conserved and the 5 that are conservatively substituted within or between the type 1 and type 2 sequences of sea anemone peptides with specific action on voltage-sensitive sodium channels. Furthermore, it also has 6 identities (Asp9, Arg14, Asn16, Leu18, Trp33 and Lys48) and 1 homology (Arg36) in the 8 residues of the pharmacophore of the sea anemone ApB which are essential for interaction with mammalian sodium channels. The intrahippocampal injection of CGX induces several sequential behavioral alterations--episodes of akinesia alternating with facial automatisms and head tremor, salivation, rearing, jumping, barrel-rolling, wet dog shakes and forelimb clonic movements--and the electroencephalography analysis shows that they were followed by important seizure periods that gradually evolved to status epilepticus that lasted 8-12 h, similar to that observed in the acute phase of the pilocarpine model of epilepsy. These results suggest that CGX may be an important tool to develop a new experimental model of status epilepticus which may contribute to understanding the etiology of epilepsy and to test the effects of new antiepileptic drugs.