Developing recombinant phospholipase D1 (rPLD1) toxoid from Iranian Hemiscorpius lepturus scorpion and its protective effects in BALB/c mice

Genome-wide identification, structural homology analysis, and evolutionary diversification of the phospholipase D gene family in the venom gland of three scorpion species

BACKGROUND

Venom phospholipase D (PLDs), dermonecrotic toxins like, are the major molecules in the crude venom of scorpions, which are mainly responsible for lethality and dermonecrotic lesions during scorpion envenoming. The purpose of this study was fivefold: First, to identify transcripts coding for venom PLDs by transcriptomic analysis of the venom glands from Androctonus crassicauda, Hottentotta saulcyi, and Hemiscorpius lepturus; second, to classify them by sequence similarity to known PLDs and motif extraction method; third, to characterize scorpion PLDs; fourth to structural homology analysis with known dermonecrotic toxins; and fifth to investigate phylogenetic relationships of the PLD proteins.

RESULTS

We found that the venom gland of scorpions encodes two PLD isoforms: PLD1 ScoTox-beta and PLD2 ScoTox-alpha I. Two highly conserved regions shared by all PLD1s beta are GAN and HPCDC (HX2PCDC), and the most important conserved regions shared by all PLD2s alpha are two copies of the HKDG (HxKx4Dx6G) motif. We found that PLD1 beta is a 31-43 kDa acidic protein containing signal sequences, and PLD2 alpha is a 128 kDa basic protein without known signal sequences. The gene structures of PLD1 beta and PLD2 alpha contain 6 and 21 exons, respectively. Significant structural homology and similarities were found between the modeled PLD1 ScoTox-beta and the crystal structure of dermonecrotic toxins from Loxosceles intermedia.

CONCLUSIONS

This is the first report on identifying PLDs from A. crassicauda and H. saulcyi venom glands. Our work provides valuable insights into the diversity of scorpion PLD genes and could be helpful in future studies on recombinant antivenoms production.

Complete neutralization of the lethality of Hemiscorpius lepturus crude venom by a novel anti-recombinant phospholipase D1 IgGs

Treatment of scorpion envenomation is a challenging issue since serotherapy is implemented by administration of polyvalent equine antisera. In our previous study we discovered that recombinant phospholipase D1 (Hl-RecPLD1) is responsible for the lethality of Hemiscorpius lepturus (H. lepturus) venom in mice. Accordingly, this study was aimed to investigate the protectivity of purified anti-Hl-RecPLD1 IgG against the lethality or major complications of H. lepturus venom. The neutralization efficiency of purified anti-Hl-RecPLD1 IgGs against sphingomyelinase activities of the crude venom and Hl-RecPLD1 was also assessed. Anti-Hl-RecPLD1 IgGs at optimum amount of 3.7 mg completely neutralized one Lethal Dose 100 (LD₁₀₀) of crude venom in mice. The anti-Hl-RecPLD1 IgGs remarkably reduced the necrosis area from 6.5 to 1 cm² in rabbit derma, induced by the crude venom. The anti-Hl-RecPLD1 IgGs remarkably reduced the sphingomyelinase and hemolytic activities of crude venom as well. In conclusion, a novel rabbit monovalent IgG against Hl-RecPLD1 was able to completely protect the mice against the lethality of H. lepturus crude venom and reduced its toxicity as well. Such monovalent anti-Hl-RecPLD1 IgGs may have potential applications in serotherapy of H. lepturus envenomation.

Sajedi R, Pooshang Bagheri K, Sabatier JM, Shahbazzadeh D. Novel Mutant Phospholipase D from Hemiscorpius lepturus Acts as A Highly Immunogen in BALB/c Mice Against the Lethality of Scorpion Venom

Hemiscorpius lepturus (H. lepturus) which belongs to the Scorpionidae family, is the deadliest scorpion in Iran. It causes pathological manifestations like dermonecrosis, hemolysis, renal failure, necrotic ulcers, and in some cases, even death. The venom of this scorpion is well-known for its cytotoxic effects in comparison with the other venomous scorpions which show significant neurotoxic effects. Due to the painless nature of the sting of this scorpion, the clinical symptoms occur in victims 24 to 72 h post-sting. In our previous studies during the last decade, we demonstrated that the medical complications are attributable to the presence of phospholipase D (PLD) as a major toxin in the venom. With the purpose of designing and constructing a vaccine against H. lepturus for humans, animal model experiments were performed. To achieve this goal, non-toxic PLD was developed by mutation of two critical catalytic residues-His12 and His48-into alanines and the product was then denominated mut-rPLD1. The in-vivo tests showed that the mice immunized with interval doses of 10 µg of mut-rPLD1, were completely protected against 10× the LD100 of the venom. In conclusion, this mutant may be an effective vaccine candidate against scorpion envenomation by H. lepturus in future clinical studies.

Innovative Immunization Strategies for Antivenom Development

Snakes, scorpions, and spiders are venomous animals that pose a threat to human health, and severe envenomings from the bites or stings of these animals must be treated with antivenom. Current antivenoms are based on plasma-derived immunoglobulins or immunoglobulin fragments from hyper-immunized animals. Although these medicines have been life-saving for more than 120 years, opportunities to improve envenoming therapy exist. In the later decades, new biotechnological tools have been applied with the aim of improving the efficacy, safety, and affordability of antivenoms. Within the avenues explored, novel immunization strategies using synthetic peptide epitopes, recombinant toxins (or toxoids), or DNA strings as immunogens have demonstrated potential for generating antivenoms with high therapeutic antibody titers and broad neutralizing capacity. Furthermore, these approaches circumvent the need for venom in the production process of antivenoms, thereby limiting some of the complications associated with animal captivity and venom collection. Finally, an important benefit of innovative immunization approaches is that they are often compatible with existing antivenom manufacturing setups. In this review, we compile all reported studies examining venom-independent innovative immunization strategies for antivenom development. In addition, a brief description of toxin families of medical relevance found in snake, scorpion, and spider venoms is presented, as well as how biochemical, bioinformatic, and omics tools could aid the development of next-generation antivenoms.