Scorpion venom increases acetylcholine release by prolonging the duration of somatic nerve action potentials

Effect of animal venom toxins on the main links of the homeostasis of mammals (Review)

The human body is affected by environmental factors. The dynamic balance between the organism and its environment results from the influence of natural, anthropogenic and social aspects. The factors of exogenous origin determine development of adaptive changes. The present article summarises the mechanisms of animal venom toxins and homeostasis disruption in the body of mammals. The mechanisms underlying pathological changes are associated with shifts in biochemical reactions. Components of the immune, nervous and endocrine systems are key in the host defense and adaptation processes in response to venom by triggering signalling pathways (PI3kinase pathway, arachidonic acid cascade). Animal venom toxins initiate the development of inflammatory processes, the synthesis of pro-inflammatory mediators (cytokines), ROS, proteolytic enzymes, activate the migration of leukocytes and macrophages. Keratinocytes and endothelial cells act as protective barriers under the action of animal venom toxins on the body of mammals. In addition, the formation of pores in cell membranes, structural changes in cell ion channels are characteristic of the action of animal venom toxins.

Novel Neurotoxic Activity in Calliophis intestinalis Venom

In this work, we investigated the in vitro neurotoxicity of Calliophis intestinalis venom using chick biventer cervicis neuromuscular preparations and electrophysiological analysis of voltage-gated sodium (Na_V) channels expressed in HEK293 cells. We found that the indirect twitches of the neuromuscular preparations decreased over time when exposed to venom. However, the responses of these preparations to the agonists acetylcholine, carbachol, and potassium chloride were not changed after incubation with the venom. Our electrophysiological experiments show that C. intestinalis venom acts as a Na_V channel antagonist-the first known from a vertebrate venom-by decreasing the peak current of Na_V1.4 channels without changing the kinetics of activation or inactivation. Our proteomic results accord with earlier analyses and find that the venom contains three-finger toxins, cysteine-rich secretory proteins, kunitz peptides, phospholipase A₂s, snake venom metalloproteases, and vespryns. Some of the three-finger toxins are similar to the δ-elapitoxins from the venom of the closely related Calliophis bivirgatus. However, δ-elapitoxins act as Na_V channel agonists in C. bivirgatus whereas C. intestinalis venom contains Na_V channel antagonists. The toxins and mechanisms responsible for the neuromuscular symptoms remain unclear as does the identity of the Na_V channel antagonists. These aspects of this unusual venom require further study.

The effects of Tityus bahiensis scorpion venom on the contractility of jejunum, vas deferens, and the aorta is differentially affected by tetrodotoxin

The pharmacological effects of the crude venom of the scorpion Tityus serrulatus or its isolated toxins have been widely studied. However, few studies are available on Tityus bahiensis venom. We recently discovered that T. serrulaus venom leads to the release of tetrodotoxin-resistant acetylcholine. Thus, our objective was to verify whether T. bahiensis venom could have a similar action in the jejunum. Furthermore, we evaluated the possibility that this action occur in other tissues innervated by the autonomic nervous system. Thus, organ bath studies were conducted to evaluate the contractile and relaxant effects of venom on the jejunum, vas deferens and aorta of rats in the presence or absence of tetrodotoxin. We observed that jejunum, vas deferens and aorta contracted when the T. bahiensis venom was applied. In the jejunum, the venom reveals a contractile component resistant to tetrodotoxin. It also was able to relax pre-contracted preparations of jejunum and aorta but not vas deferens. Only in the aorta, the relaxation was resistant to tetrodotoxin. The effects of scorpion venoms are attributed to its action on ionic channels leading to neuronal depolarization and neurotransmitter release. Our results indicated that a similar mechanism is present in the observed effects of the venom. However, another mechanism must be present in the venom-induced contraction in the jejunum and relaxation in the aorta. Possible involvement of tetrodotoxin-resistant sodium channels or non-neuronal release of neurotransmitters is discussed. We emphasize that the study of the Tityus scorpion's venom, especially T. bahiensis, is of great importance because it can unveil unknown pharmacological and physiological mechanisms of excitable cells.

Interleukin-1 receptor-induced PGE2 production controls acetylcholine-mediated cardiac dysfunction and mortality during scorpion envenomation

Scorpion envenomation is a leading cause of morbidity and mortality among accidents caused by venomous animals. Major clinical manifestations that precede death after scorpion envenomation include heart failure and pulmonary edema. Here, we demonstrate that cardiac dysfunction and fatal outcomes caused by lethal scorpion envenomation in mice are mediated by a neuro-immune interaction linking IL-1 receptor signaling, prostaglandin E_2, and acetylcholine release. IL-1R deficiency, the treatment with a high dose of dexamethasone or blockage of parasympathetic signaling using atropine or vagotomy, abolished heart failure and mortality of envenomed mice. Therefore, we propose the use of dexamethasone administration very early after envenomation, even before antiserum, to inhibit the production of inflammatory mediators and acetylcholine release, and to reduce the risk of death.

Cardiac dysfunction is a major complication that precedes death after scorpion envenomation. Here, authors show that heart failure and mortality are caused by excessive acetylcholine release, which requires IL-1R-dependent PGE2 production. Dexamethasone treatment effectively inhibits cardiac dysfunction and mortality.

Neurotoxicity of Tityus bahiensis (brown scorpion) venom in sympathetic vas deferens preparations and neuronal cells

Systemic scorpion envenomation is characterized by massive neurotransmitter release from peripheral nerves mediated primarily by scorpion venoms neurotoxins. Tityus bahiensis is one of the medically most important species in Brazil, but its venom pharmacology, especially regarding to peripheral nervous system, is poorly understood. Here, we evaluated the T. bahiensis venom activity on autonomic (sympathetic) neurotransmission by using a variety of approaches, including vas deferens twitch-tension recordings, electrophysiological measurements (resting membrane potentials, spontaneous excitatory junctional potentials and whole-cell patch-clamp), calcium imaging and histomorphological analysis. Low concentrations of venom (≤ 3 μg/mL) facilitated the electrically stimulated vas deferens contractions without affecting postsynaptic receptors or damaging the smooth muscle cells. Transient TTX-sensitive sustained contractions and resting membrane depolarization were mediated mainly by massive spontaneous ATP release. High venom concentrations (≥ 10 μg/mL) blocked the muscle contractions and induced membrane depolarization. In neuronal cells (ND7-23wt), the venom increased the peak sodium current, modified the current-voltage relationship by left-shifting the Nav-channel activation curve, thereby facilitating the opening of these channels. The venom also caused a time-dependent increase in neuronal calcium influx. These results indicate that the sympathetic hyperstimulation observed in systemic envenomation is presynaptically driven, probably through the interaction of α- and β-toxins with neuronal sodium channels.