Identification and designing an analgesic opioid cyclic peptide from Defensin 4 of Mesobuthus martensii Karsch scorpion venom with more effectiveness than morphine

Considering the limitations of use and side effects of existing analgesics, the discovery of new analgesics is necessary. Venoms of organisms are an important source of analgesic peptides. In this study, using computational biology methods such as molecular docking simulation, molecular dynamics, and predictions of physicochemical and biological properties based on various machine learning algorithms, a non-toxic 9-amino acid peptide from Defensin 4 of Mesobuthus martensii Karsch scorpion venom was discovered for the first time and named Buthicyclin. The peptide was synthesized cyclically by creating a disulfide bond, and its secondary structure was determined by Circular Dichroism (CD). Next, peptide toxicity was evaluated using MTT, hemolysis, and lethal dose (LD₅₀) methods. Subsequently, in animal tests using Tail-flick, Hot plate, and Formalin-induced paw-licking methods, the analgesic effects of Buthicyclin in acute and inflammatory pain were evaluated, and its possible analgesic mechanism was determined. Buthicyclin has a coil-like structure and can be considered a cyclic coil with a disulfide bond. This peptide is non-toxic so its LD₅₀ of this peptide was higher than 20 mg/kg. All analgesic tests showed that Buthicyclin peptide, at 1 mg/kg and 2 mg/kg (significantly greater), was more potent and stable than 2 mg/kg morphine in all time intervals. The results also indicated that Buthicyclin could exert its analgesic effects through binding to opioid receptors. Given the potent and long-lasting analgesic effects of Buthicyclin and its non-toxicity, Buthicyclin can be considered a promising candidate for new analgesic drugs. However, this claim requires more preclinical and clinical trials.