Effects of Tityus serrulatus scorpion venom and one of its purified toxins (toxin gamma) on the isolated guinea-pig heart

Effect of Tityus serrulatus scorpion venom on isolated jejunum: A very useful tool to study the interaction between neurons in the enteric nervous system

Scorpion envenomation is a public health problem in tropical and subtropical areas. In Brazil, Tityus serrulatus is the biggest cause of accidents with venomous animals. Tityus serrulatus venom causes symptoms related to a great activation of the autonomic system attributed to a massive release of sympathetic and parasympathetic mediators. This effect is attributed to the presence of toxins acting in Na⁺ and K⁺ ion channels, leading to an increase in cell excitability. Although gastrointestinal symptoms, like diarrhoea and sialorrhea, is observed in moderate to severe cases, little attention is given in clinical reports. Gastrointestinal motility is controlled by the enteric nervous system which is composed of a wide variety of interconnected neurons that are influenced by the sympathetic and parasympathetic nervous systems. Thus, this work aimed to characterize the effects of Tityus serrulatus venom on sympathetic and parasympathetic neurotransmission of rat jejunum, as well as to investigate possibles effects on other neurons of the enteric nervous system. To this, we verify the effects of Tityus serrulatus venom on the contractility of isolated rat jejunum through organ-bath experiments. We observed that venom can induce both contraction and relaxation. The contraction was partially inhibited by atropine (1 μM) and by suramin (0.1 mM) through tetrodotoxin-resistant and sensitive mechanisms. The relaxation was completely inhibited by 3 μM propranolol and partially inhibited by 1 μM phentolamine. Suramin induced a slowing of relaxation curve. Tetrodotoxin completely inhibits the relaxation induced by Tityus serrulatus venom, but the contraction curves were only partially reduced in their initial portion. The final part of the curve was largely enhanced by Tetrodotoxin. Atropine blocks almost completely the contraction curve in the presence of Tetrodotoxin. These results indicate that Tityus serrulatus venom induces the release of both excitatory (predominantly acetylcholine) and inhibitory (mainly noradrenaline) neurotransmitters. The effects of Tityus serrulatus venom on organ contractility was quite complex and seem to derive from a diffuse and nonspecific release of mediators from autonomic and enteric nervous systems. Further investigation of venom action and its isolated toxins can reveal important aspects to deepen our knowledge about the enteric nervous system transmission and the interaction between excitatory and inhibitory mediators as well as the physiological role of Na⁺ and K⁺ ion channels in gut motility.

CPP-Ts: a new intracellular calcium channel modulator and a promising tool for drug delivery in cancer cells

Scorpion sting envenoming impacts millions of people worldwide, with cardiac effects being one of the main causes of death on victims. Here we describe the first Ca²⁺ channel toxin present in Tityus serrulatus (Ts) venom, a cell penetrating peptide (CPP) named CPP-Ts. We show that CPP-Ts increases intracellular Ca²⁺ release through the activation of nuclear InsP3R of cardiomyocytes, thereby causing an increase in the contraction frequency of these cells. Besides proposing a novel subfamily of Ca²⁺ active toxins, we investigated its potential use as a drug delivery system targeting cancer cell nucleus using CPP-Ts’s nuclear-targeting property. To this end, we prepared a synthetic CPP-Ts sub peptide^14–39 lacking pharmacological activity which was directed to the nucleus of specific cancer cell lines. This research identifies a novel subfamily of Ca²⁺ active toxins and provides new insights into biotechnological applications of animal venoms.

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).

Effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide in rat atria: an in vitro study

Scorpion envenomation is considered public health problem in Northern African countries. The mechanisms of cardiac dysfunction following scorpion envenomation are not fully understood. This study examined the effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide (ANP) release from rat atrium using in vitro organ perifusion. Male Sprague Dawley rats were used in this study. Three experiments were conducted. In experiment 1, atrial tissues were exposed either to Krebs-bicarbonate buffer medium (control) or to scorpion toxin (10(-8) M to 10(-6) M). In experiment 2, animals were chemically sympathectomized with a single intraperitoneal injection of 6-hydroxydopamine (6-OHDOPA) at a dose of 40 microg/g 24 h before sacrifice. Vehicle-treated rats served as control. Atrial tissues were collected and perifused in the presence of 10(-6) M scorpion toxin. In experiment 3, atrial tissues were exposed to 10(-6) M scorpion toxin either in the absence or presence of 10(-6) M propranolol (a beta-adrenoceptor blocker), or 10(-6) M tetrodotoxin (a sodium channel blocker). ANP levels released in the perifusion medium were determined by radioimmunoassay. The scorpion toxin at 10(-6) M induced a significant (p<0.01) increase (106%) in ANP levels. This effect was decreased (20%) by 6-OHDOPA. Propranolol and tetrodotoxin significantly (p<0.01) inhibited 55% and 60%, respectively, the toxin-induced ANP release. The data show that the North African scorpion toxin from Androctonus australis garzonii increases the ANP release in rat atrium through stimulation of sympathetic cardiac nerves and sodium channels activation.

Scorpion venom increases mRNA expression of lung cytokines

Previous studies have demonstrated that scorpion toxins increase the serum levels of IL-1, IL-6, INF-gamma, and GM-CSF in patients with severe shock and pulmonary edema. Moreover, it has been shown that experimental models of scorpion envenomation presented an increase in serum levels of IL-1, IL-6, IFN-gamma and nitric oxide. Thus, it is possible that the cytokine release may contribute to the onset and maintenance of the pulmonary edema induced by scorpion venom. This study was designed to investigate whether inflammatory and non-inflammatory cytokines, contribute to the pulmonary injury induced by infusion of Tityus serrulatus scorpion toxin in rats. We show that scorpion venom not only increases the expression of mRNA pulmonary inflammatory cytokines but also non-inflammatory cytokines as well. Moreover, the expression of IL-1alpha, IL-1beta and IL-6 mRNA was shown to be higher among the remaining detectable cytokines. The findings of this study provide additional insight towards the understanding of the pathophysiology of the pulmonary edema induced by scorpion venom. The increased level of pulmonary cytokines observed during the pulmonary edema may be responsible for the exacerbation and maintenance of the inflammatory response to scorpion venom in the lungs.

Selective release of ATP from sympathetic nerves of rat vas deferens by the toxin TsTX-I from Brazilian scorpion Tityus serrulatus

1. The effects of the main component of the Tityus serrulatus scorpion venom, toxin TsTX-I, were studied on the contractility and release of neurotransmitters in the rat vas deferens. Since TsTX-I is known to act on sodium channels, we used veratridine, another sodium channel agent, for comparison. 2. Toxin TsTX-I induced concentration-dependent contractions with an EC(50) value of 47.8+/-0.1 nM and a maximum effect of 84.4+/-10.4% of that for BaCl(2). 3. Contractions by TsTX-I were abolished by denervation or tetrodotoxin (0.1 microM), showing that the toxin effects depend on the integrity of sympathetic nerve terminals. 4. To check for the presence of a noradrenergic component, experiments were conducted after removal of adrenergic stores in nerve terminals by reserpinization (10 mg kg(-1), 24 h prior to experiments) or blockade of alpha(1) adrenoceptors by prazosin (30 microM), showing that these procedures did not modify the response to TsTX-I, and therefore that adrenoceptors were not involved in contractions. 5. To check for the presence of a purinergic component, experiments were carried out after blockade of P(2X) receptors by suramin (0.1 mM) or desensitization by alpha,beta-methylene-ATP (30 microM). These agents greatly abolished the contractile response to TsTX-I (about 83% by desensitization and 96% by suramin), showing the involvement of purinergic receptors. 6. The release of noradrenaline and purinergic agents (ATP, ADP, AMP and adenosine) was detected by HPLC. Together, the total release of purines in the presence of TsTX-I was about 42 times higher than in the control group. In contrast, TsTX-I did not modify the overflow of noradrenaline, showing that the release was selective for purines. 7. The release of purinergic agents was reduced by the N-type calcium channel blocker omega-conotoxin GVIA (1 microM) and by the P/Q-type blocker omega-conotoxin MVIIC (1 microM), showing that the effects of TsTX-I are calcium-dependent. 8. The results show that TsTX-I produced a selective release of purines from postganglionic sympathetic nerves in the rat vas deferens.

[Cardiovascular dysfunction following severe scorpion envenomation. Mechanisms and physiopathology]

The seriousness of scorpion envenomation results essentially from left cardiac function with pulmonary oedema and/or a state of shock. Adrenergic myocarditis, toxic myocarditis and myocardial ischemia are the 3 mechanisms that explain the cardiac dysfunction. Myocardial ischemia is not only due to the release of catecolamines but also the effect of the cytokines and/or neuropeptide Y on the coronary vessels. The cardiac damage can be due or enhanced by the depressive effect of the cytokines on the myocardial cells. The frequently observed hyperglycaemia only enhances the state of the already damaged myocardium.

Direct vs. mediated effects of scorpion venom: an experimental study of the effects of a second challenge with scorpion venom

OBJECTIVE

To assess the respective roles of venom and of catecholamines following scorpion envenomation and to verify whether a second challenge with scorpion venom induces the same consequences than a first one.

DESIGN AND SETTING

Controlled animal study in a university research laboratory.

SUBJECTS

Anesthetized and ventilated dogs.

INTERVENTIONS

Fifteen dogs received intravenously a sublethal dose of scorpion venom (0.05 mg/kg). In the reenvenomated group (n=5) a second venom challenge with one-half sublethal venom dose was performed 30 min after the first one. The control group (n=10) received saline. Five additional animals served as sham.

MEASUREMENTS AND RESULTS

Plasma toxin and catecholamine levels and a set of usual hemodynamic measurements were repeatedly measured in the first hour following envenomation. In the reenvenomated group another set of measurements was performed 5 min after the second challenge. Changes in toxin, catecholamines, and the main hemodynamic parameters were compared between the study groups. Initial peak toxin levels were similar in the two groups. They induced a striking increase in circulating catecholamines, a fall in heart rate, and an increase in mean arterial and pulmonary artery occluded pressures and in systemic vascular resistance. In the reenvenomated group the second challenge with scorpion venom achieved a toxin blood level similar to the first peak. However, it was not associated with a significant effect either on catecholamines release or on hemodynamics. Subsequent trends in hemodynamic changes were similar to those observed in the control group.

CONCLUSIONS

These data emphasize the limited role of direct effects of scorpion venom on the cardiovascular system and the key role of catecholamines.

Scorpion venom stimulates biliary/duodenal motility and pancreatic exocrine secretion

Scorpion envenomation causes severe upper abdominal pain associated with nausea and vomiting. Although scorpion venom (SV) stimulates pancreatic and gastric secretion in animal models, its effects on duodenal and biliary motility have not been reported. The aim of this study was to determine the effects of SV on sphincter of Oddi (SO), duodenal and gall bladder motility and pancreatic amylase output. Anaesthetized Australian possums (n = 21) were infused with SV via intravenous or closed intra-arterial routes. Blood pressure, SO, duodenal and gall bladder motility were continuously monitored for 4 h. Trans-sphincteric flow (TSF), an indicator of bile duct resistance, was measured concurrently. The amylase output in pancreatic juice was also measured. SV infusion resulted in profound transient increase in blood pressure, SO motility and a significant decrease in TSF. No significant differences were noted in SO basal pressure changes. A transient increase in gall bladder tone, duodenal contraction amplitude and frequency, and amylase output were noted. Following the peak in blood pressure, amylase output, SO, gall bladder and duodenal motility were depressed. SV induces a rapid but transient increase in biliary and duodenal motility that is associated with stimulation of pancreatic amylase output. These changes may contribute to gastrointestinal symptoms associated with early phases of envenomation.

Evidence of myocardial ischaemia in severe scorpion envenomation. Myocardial perfusion scintigraphy study

OBJECTIVE

To explore the myocardial perfusion by thallium-201 scintigraphy for patients with evidence of myocardial damage after scorpion envenomation.

DESIGN

Prospective study over 1-year period.

SETTING

Medical intensive care unit of a university hospital (Sfax, Tunisia).

PATIENTS

We have prospectively included six patients admitted for scorpion envenomation over a period of 1 year in the 22-bed intensive care unit (ICU) of our university hospital. The evidence of myocardial damage was confirmed by electrocardiography and echocardiography in all patients. Myocardial perfusion scintigraphy ((201)Tl scintigraphy) coupled with radionuclide ventriculography ((99m)Tc) was performed for all patients, occurring 32 h on average (range 12-72 h) after the sting.

RESULTS

Radionuclide ventriculography was abnormal in all cases; the abnormalities observed were similar to those observed by echocardiography. Moreover (201)Tl scintigraphy showed evidence of myocardial hypoperfusion in all cases. The myocardial hypoperfusion grade and localisation were more marked in the abnormal localisation shown by echocardiography and electrocardiography, compared to the normal wall. Repeated studies, obtained only in two patients within 6 and 15 days, respectively, showed considerable, but not complete, improvement of wall motion and myocardial perfusion. Segments with improved perfusion showed greatly improved regional wall motion.

CONCLUSION

This study confirms the evidence of myocardial hypoperfusion after severe scorpion envenomation.

Effects of the venom of a Mygalomorph spider (Lasiodora sp.) on the isolated rat heart

We studied the effect of the venom of the Brazilian spider, Lasiodora sp. (Mygalomorphae, Theraphosidae), on force generation and electrical activity in the isolated rat heart. Previous work showed that this venom is excitotoxic to excitable cells due to Na(+) channel gating modifier activity [Toxicon 39 (2001) 991]. In the isolated heart, the venom (10-100 microg bolus administration) caused a dose-dependent bradycardia, with transient cardiac arrest and rhythm disturbances. The electrocardiogram showed that the reduction of heart rate was due to sinus bradycardia, sinus arrest and partial or complete A-V block. All of the effects were reversible upon washout of the venom. The effect of the venom was potentiated by the anticholinesterase neostigmine (3.3 microM), suppressed by the muscarinic acetylcholine receptor antagonist atropine (1.4 microM), and inhibited by the vesicular acetylcholine transporter inhibitor (-)-vesamicol (10 microM). Tetrodotoxin (200 nM) did not inhibit the effect of the venom. Together, these data suggest that this Lasiodora venom evokes vesicular release of acetylcholine from parasympathetic nerve terminals by activating tetrodotoxin-resistant Na(+) channels.

Clinical description of Parabuthus transvaalicus scorpionism in Zimbabwe

An epidemiological and clinical study of Parabuthus transvaalicus scorpionism was conducted in Zimbabwe. Ten per cent of stings resulted in severe scorpionism. The clinical features of 17 patients with severe envenomation were primarily neuromuscular, with significant parasympathetic nervous system and cardiac involvement. The clinical course was prolonged compared to other scorpion syndromes, and significant therapeutic benefit was demonstrated in terms of hospital stay in response to species specific antivenom. The case fatality rate was 0.3%, with deaths in children below 10 years and adults above 50 years. The mortality rate in the district was 2.8 per 100,000 per year. This syndrome from a buthid scorpion resembles in many respects buthid scorpionism described elsewhere in the world, but shows important differences, notably cardiac involvement in the absence of clinical evidence of circulating catecholamines. The relevance of these findings to buthid scorpionism generally are presented as a hypothesis, in which it is postulated that the cardiac effects of the toxins are direct and primary, and autonomic effects secondary but synergistic, determining the ultimate clinical picture.

Hemodynamic effects following injection of venom from the scorpion Leiurus quinquestriatus

PURPOSE

The present study tested the hypothesis that scorpion sting induces left ventricular (LV) hypokinesia and myocardial ischemia shortly after injection due to reduction of coronary blood flow (CBF) and increased oxygen demand.

METHODS

In 5 mechanically ventilated, open-chest dogs, we measured LV function following i.v. injection of venom (0.05 mg/kg) obtained from the scorpion Leiurus quinquestriatus. Hemodynamic responses to the venom were followed up for 90 minutes.

RESULTS

The venom induced significant combined respiratory and metabolic acidosis (arterial pH progressed from 7.35 +/- 0.03 at baseline to 7.10 +/- 0.06 at 90 minutes). There were large increases in blood pressure, LV end systolic pressure, stroke work, and velocity of contraction. Twenty minutes following venom injection, cardiac output (CO) increased by 37% but then declined to 36% below baseline by 90 minutes (P < .05). CBF increased significantly in proportion to increased perfusion pressure; hence, there was no change in coronary vascular resistance. There was no evidence of myocardial ischemia or LV dysfunction because there was no change in myocardial pH, percentage fiber shortening, or LV end-diastolic pressure. Despite the fact that some variables returned to baseline at 90 minutes, they did not reach steady state; thus, the preparation would have continued to deteriorate.

CONCLUSIONS

Myocardial ischemia does not occur in this dog model immediately following administration of scorpion venom. There are significant peripheral circulatory effects of the venom, which account for many of the hemodynamic changes.