Venoms of Iranian Scorpions (Arachnida, Scorpiones) and Their Potential for Drug Discovery

Scorpions, a characteristic group of arthropods, are among the earliest diverging arachnids, dating back almost 440 million years. One of the many interesting aspects of scorpions is that they have venom arsenals for capturing prey and defending against predators, which may play a critical role in their evolutionary success. Unfortunately, however, scorpion envenomation represents a serious health problem in several countries, including Iran. Iran is acknowledged as an area with a high richness of scorpion species and families. The diversity of the scorpion fauna in Iran is the subject of this review, in which we report a total of 78 species and subspecies in 19 genera and four families. We also list some of the toxins or genes studied from five species, including Androctonus crassicauda, Hottentotta zagrosensis, Mesobuthus phillipsi, Odontobuthus doriae, and Hemiscorpius lepturus, in the Buthidae and Hemiscorpiidae families. Lastly, we review the diverse functions of typical toxins from the Iranian scorpion species, including their medical applications.

Arizona bark scorpion venom resistance in the pallid bat, Antrozous pallidus

The pallid bat (Antrozous pallidus), a gleaning bat found in the western United States and Mexico, hunts a wide variety of ground-dwelling prey, including scorpions. Anecdotal evidence suggests that the pallid bat is resistant to scorpion venom, but no systematic study has been performed. Here we show with behavioral measures and direct injection of venom that the pallid bat is resistant to venom of the Arizona bark scorpion, Centruroides sculpturatus. Our results show that the pallid bat is stung multiple times during a hunt without any noticeable effect on behavior. In addition, direct injection of venom at mouse LD₅₀ concentrations (1.5 mg/kg) has no effect on bat behavior. At the highest concentration tested (10 mg/kg), three out of four bats showed no effects. One of the four bats showed a transient effect suggesting that additional studies are required to identify potential regional variation in venom tolerance. Scorpion venom is a cocktail of toxins, some of which activate voltage-gated sodium ion channels, causing intense pain. Dorsal root ganglia (DRG) contain nociceptive neurons and are principal targets of scorpion venom toxins. To understand if mutations in specific ion channels contribute to venom resistance, a pallid bat DRG transcriptome was generated. As sodium channels are a major target of scorpion venom, we identified amino acid substitutions present in the pallid bat that may lead to venom resistance. Some of these substitutions are similar to corresponding amino acids in sodium channel isoforms responsible for reduced venom binding activity. The substitution found previously in the grasshopper mouse providing venom resistance to the bark scorpion is not present in the pallid bat, indicating a potentially novel mechanism for venom resistance in the bat that remains to be identified. Taken together, these results indicate that the pallid bat is resistant to venom of the bark scorpion and altered sodium ion channel function may partly underlie such resistance.

Proteomic analysis of the venom and characterization of toxins specific for Na+- and K+-channels from the Colombian scorpion Tityus pachyurus

The Colombian scorpion Tityus pachyurus is toxic to humans and is capable of producing fatal accidents, but nothing is known about its venom components. This communication reports the separation of at least 57 fractions from the venom by high performance liquid chromatography. From these, at least 104 distinct molecular weight compounds were identified by mass spectrometry analysis. The complete amino acid sequences of three peptides were determined and the partial sequences of three others were also identified. Electrophysiological experiments conducted with ion-channels expressed heterologously on Sf9 cells showed the presence of a potent Shaker B K(+)-channel blocker. This peptide (trivial name Tpa1) contains 23 amino acid residues closely packed by three disulfide bridges with a molecular mass of 2,457 atomic mass units. It is the third member of the sub-family 13, for which the systematic name is proposed to be alpha-KTx13.3. The mice assay showed clearly the presence of toxic peptides to mammals. One of them named Tpa2, containing 65 amino acid residues with molecular mass of 7,522.5 atomic mass units, is stabilized by four disulfide bridges. It was shown to modify the Na(+)-currents of F-11 and TE671 cells in culture, similar to the beta scorpion toxins. These results demonstrate the presence of toxic peptides in the venom of T. pachyurus and confirm that accidents with this species of scorpion should be considered an important human hazard in Colombia.

Predicting scorpion sting incidence in an endemic region using climatological variables

Scorpionism is a public health problem in several regions of the world. The highest mortality, with over 1000 deaths per year, has been reported in Mexico. We analysed the significance of climatological variables to predict the incidence of scorpion stings in humans in the state of Colima (Mexico) for the years 2000-2001. The pluvial precipitation (mm), the evaporation (mm), and the mean, maximum, and minimum temperatures (degrees C) were obtained from local meteorological offices. There are approximately 3 stings/year per 1000 people in municipalities of Colima and Villa de Alvarez and about 18-30 stings/year per 1000 people in the rest of the municipalities. There is very little rain and there are few stings in the winter when the minimum temperature is below about 16 degrees C. The number of scorpion stings is independent of the actual rainfall when this is above 30 mm/month. Using multiple linear regression, we used a backward model selection procedure to estimate that the minimum temperature is correlated with scorpion sting incidence with a statistically significance of 95%. We briefly discuss the application of predictive models of scorpion sting incidence in the appropriate allocation of antivenom serum in hospital clinics.

First chemical synthesis of a scorpion α-toxin affecting sodium channels: The Aah I toxin ofAndroctonus australis hector

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.

Evaluation of scorpion stings: the poison center perspective

Scorpion venom causes excessive adrenergic discharge and cardiotoxicity. Publications on scorpion stings using mainly admission data, has led to the belief that most scorpion stings are severe and mandate an observation period of at least 12 h regardless of symptomatology. We to assessed the characteristics of scorpion sting victims with emphasis on severity and time to presentation by retrospective poison center chart review of 225 calls over 12-mo. Thirteen percent of patients were asymptomatic and 72% and 15% were mild or moderately to severely ill, respectively. The most frequent manifestations were pain (97.3%), cardiovascular signs (23.1%) and ECG changes (13.7%). Ninety-four percent of the patients presented within 6 h; 86% within 3 h. Ninety-two percent of moderate to severe patients, including those with moderate to severe cardiotoxicity, presented within 3 h; 100% within 6 h. Clinical severity of the stings was greater in females than in males. No association was found between degree of severity and time to presentation and age. Most scorpion stings in Israel (at least those occurring in the north and central regions) are mild. The majority of envenomated patients present for medical assistance within 3 h including all patients with moderate to severe cardiotoxicity. Because of severity of potential complications, that scorpion sting victims should be observed in the emergency department for 6 h from the time of sting and should be admitted if symptoms other than local pain develop. Reduction of unnecessary in-hospital observation time is expected to save public health money.

Scorpion envenomation and serotherapy in Morocco

A clinical and biologic study was conducted in Morocco to assess the efficiency of antivenom therapy for treating victims of scorpion stings. Epidemiologic and clinical data were collected from 275 patients envenomed by Androctonus mauretanicus mauretanicus and Buthus occitanus scorpions. Patients received antivenom or other drugs. Blood samples were collected at the time of hospital admission and 1 hr and 3 hr after treatment. Serum venom levels were quantified by using an ELISA. An association was found between clinical signs of envenoming and the level of venom in serum. Patients classified as grade II (moderate envenoming) had higher serum levels of venom level than patients classified as grade I (mild envenoming). At admission to the hospital, the mean venom concentration was not significantly different between the group not treated with antivenom, the group who received 2-5 ml of antivenom, and the group who received 10 ml of antivenom. A significant decrease in serum venom levels and an improvement in the clinical conditions were observed in patients administered 10 ml of antivenom. The lower decrease in serum venom levels in patients who received 2-5 ml of antivenom was due to lower doses of antivenom. No difference in the venom concentration was observed in patients who were not treated with antivenom. The absence of administration of antivenom increased the risk of developing clinical signs at the end of the hospitalization period. However, this risk was much higher when more than 1 hr elapsed between the time of the scorpion sting and the time of hospital admission. The results demonstrate that antivenom is effective in decreasing circulating venom and morbidity. Serotherapy is more efficient when given as soon as possible after envenomation and with adequate quantities of antivenom.

Mapping of an epitope recognized by a neutralizing monoclonal antibody specific to toxin Cn2 from the scorpion Centruroides noxius, using discontinuous synthetic peptides

The Na+-channel-affecting toxin Cn2 represents the major and one of the most toxic components of the venom of the Mexican scorpion Centruroides noxius Hoffmann. A monoclonal antibody BCF2 raised against Cn2 has been shown previously to be able to neutralize the toxic effect of Cn2 and of the whole venom of C. noxius. In the present study the epitope was mapped to a surface region comprising the N- and C-terminal segments of Cn2, using continuous and discontinuous synthetic peptides, designed on the basis of the sequence and a three-dimensional model of Cn2. The study of peptides of varying length resulted in the identification of segments 5-14 and 56-65 containing residues essential for recognition by BCF2. The peptide (abbreviated SP7) with the highest affinity to BCF2 (IC50 = 5.1 microM) was a synthetic heterodimer comprising the amino acid sequence from position 3-15 (amidated) of Cn2, bridged by disulfide to peptide from position 54-66, acetylated and amidated. Similar affinity was found with peptide SP1 [heterodimer comprising residues 1-14 (amidated) of Cn2, bridged with synthetic peptide 52-66 (acetylated)]. SP1 and SP7 were used to induce anti-peptide antibodies in mouse and rabbit. Both peptides were highly immunogenic. The sera obtained were able to recognize Cn2 and to neutralize Cn2 in vitro. The most efficient protection (8.3 microgram Cn2 neutralized per mL of serum) was induced by rabbit anti-SP1 serum.