Toxicity of scorpion venom in chick embryo and mealworm assay depending on the use of the soluble fraction versus the whole venom Tom van der Valk a , Arie van der Meijden b, * a Department of Integrative Zoology, IBL, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands b CIBIO Research Centre in Biodiversity and Genetic Resources, InBIO, Universidade do Porto, Campus Agr ario de Vair~ ao, Rua Padre Armando Quintas 7, 4485-661 Vair~ ao, Vila do Conde, Portugal article info Article history: Received 20 April 2014 Received in revised form 5 June 2014 Accepted 11 June 2014 Available online 19 June 2014 Keywords: Venom Scorpion LD 50 Chicken embryo Mealworms Toxicity abstract The LD 50 is an important metric for venom studies and antivenom development. It has been shown that several variables in the protocol influence the LD 50 value obtained, such as venom source, extraction and treatment and administration route. These in- consistencies reduce the utility of the results of these test for comparative studies. In scorpion venom LD 50 assays, often only the soluble fraction of the venom is used, whereas other studies use the whole venom. We here tested the toxicity of the soluble fraction in isolation, and of the whole venom in two different systems: chick embryos and meal- worms Tenebrio molitor . Ten microliters of venom solutions from Hadrurus arizonensis, Leiurus quinquestriatus, Androctonus australis, Grosphus grandidieri and Heterometrus lao- ticus were applied to five day old chicken embryos at stage 25e27. Our results showed no significant differences between the LD 50 based on the whole venom versus that of only the soluble fraction and in the chicken embryo assay in four of the five scorpion species tested. H. laoticus however, showed a significantly lower LD 50 value for the whole venom than the soluble fraction. In assays on mealworms however, this pattern was not seen. Nonetheless, caution may be warranted when using LD 50 values obtained from only the soluble fraction. The LD 50 values of the five species in this study, based on the chicken embryo assay, showed good correlation with values from the literature based on mouse studies. This suggests that the chick embryo assay may be an economic alternative to rodent assays for scorpion LD 50 studies. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Many animal venoms are a complex mixture of different compound classes including large proteins, peptides, small molecules and salts. Venom peptides are often exaptations of normal metabolic peptides (Vonk et al., 2013), which were duplicated and subsequently adapted to their role in disrupting the target organism's physiology (Cao et al., 2013; Fry et al., 2009). The high level of biological activity in venoms has been suggested to evolve in an arms-race of the source organism in defense against, or for incapacita- tion of, a specific class of organisms (Barlow et al., 2009). In addition to toxins directed against their arthropod prey (e.g. Arnon et al., 2005; D’Suze et al., 2004; De Dianous et al., 1987; García et al., 1997; Pimenta et al., 2001; Selisko et al., 1996), venoms from scorpions may addi- tionally contain toxins against vertebrate predators (Ghane et al., 2008; Lazarovici and Zlotkin, 1982; Luo et al., 1997; Possani et al., 1999). It also has antibacterial properties (Remijsen et al., 2010). As in snake venom (Daltry et al., * Corresponding author. Tel.: þ351 916712100. E-mail address: mail@arievandermeijden.nl (A. van der Meijden). Contents lists available at ScienceDirect Toxicon journal homepage: www.elsevier.com/locate/toxicon http://dx.doi.org/10.1016/j.toxicon.2014.06.007 0041-0101/© 2014 Elsevier Ltd. All rights reserved. Toxicon 88 (2014) 38e43