Toxicity and behavioural effects of ocfentanil and 2-furanylfentanyl in zebrafish larvae and mice

The introduction of the so-called New Psychoactive Substances represents a problem of global concern due to several factors, including multiplicity of structures, poorly known activity, short half-life in the market, lack of pure standards etc. Among these problems, of the highest relevance is also the lack of information about metabolism and adverse effects, which must be faced using simple and low-cost animal models. On these grounds, the present work has been carried out on 5 days post fertilization zebrafish (Danio rerio) larvae in comparison with adult mice (Mus musculus). Ocfentanil and 2-furanylfentanyl were administered at different concentrations to zebrafish larvae (1, 10 µM) and mice (0.1, 1, 6, 15 mg/kg). The behavioural assay showed a decrease in basal locomotor activity in zebrafish, whereas in mice this effect was evident only after the mechanical stimulus. Larva extracts and mice urine were analysed by using liquid chromatography coupled to high resolution mass spectrometry to identify the metabolic pathways of the fentanyl analogs. For 2-furanylfentanyl, the most common biotransformations observed were hydroxylation, hydration and oxidation in zebrafish larvae, whereas mice produced mainly the dihydrodiol metabolite. Hydroxylation was the major route of metabolism for ocfentanil in zebrafish larvae, while in mice the O-demethylated derivative was the main metabolite. In addition, a study was conducted to evaluate morphological effects of the two drugs on zebrafish larvae. Malformations were noticeable only at the highest concentration of 2-furanylfentanyl, whereas no significant damage was observed with ocfentanil. In conclusion, the two animal models show similarities in behavioral response and in metabolism, considering the different biological investigated.

Zebrafish larvae: A new model to study behavioural effects and metabolism of fentanyl, in comparison to a traditional mice model

In an effort to find alternatives to study in vivo the so-called New Psychoactive Substances (NPS), the present work was undertaken to investigate the use of zebrafish larvae as animal model in pharmaco-toxicology, providing behavioural and metabolism information. For this purpose, fentanyl, the progenitor of an extremely dangerous group of NPS, was administered at different doses to zebrafish larvae (1, 10, 50, 100 µM) in comparison to mice (0.1, 1, 6, 15 mg/kg), as a well-established animal model. A behavioural assay was performed at the time of the peak effect of fentanyl, showing that the results in larvae are consistent with those observed in mice. On the other hand, several morphological abnormalities (namely yolk sac edema, abnormal pericardial edema, jaw defect and spinal curvature) were found in larvae mostly at high fentanyl doses (50, 100 µM). Larva extract and mice urine were analyzed by using liquid chromatography coupled to high resolution mass spectrometry to identify the metabolic pathways of fentanyl. The main metabolites detected were norfentanyl and hydroxyfentanyl in both the tested models. In conclusion, the present study provides evidence that fentanyl effects on zebrafish larvae and metabolism are similar to rodents and consequently support the hypothesis of using zebrafish larvae as a suitable rapid screening tool to investigate new drugs, and particularly NPS.

In vitro and in vivo pharmacological characterization of the synthetic opioid MT-45

MT-45 is a synthetic opioid that was developed in the 1970s as an analgesic compound. However, in recent years MT-45 has been associated with multiple deaths in Europe and has been included in the class of novel psychoactive substances known as novel synthetic opioids (NSOs). Little is known about the pharmaco-toxicological effects of MT-45. Therefore, we used a dynamic mass redistribution (DMR) assay to investigate the pharmacodynamic profile of this NSO in vitro compared with morphine. We then used in vivo studies to investigate the effect of the acute systemic administration of MT-45 (0.01-15 mg/kg i.p.) on motor and sensorimotor (visual, acoustic and tactile) responses, mechanical and thermal analgesia, muscle strength and body temperature in CD-1 male mice. Higher doses of MT-45 (6-30 mg/kg i.p.) were used to investigate cardiorespiratory changes (heart rate, respiratory rate, SpO₂ saturation and pulse distention). All effects of MT-45 were compared with those of morphine. In vitro DMR assay results demonstrated that at human recombinant opioid receptors MT-45 behaves as a potent selective mu agonist with a slightly higher efficacy than morphine. In vivo results showed that MT-45 progressively induces tail elevation at the lowest dose tested (0.01 mg/kg), increased mechanical and thermal antinociception (starting from 1 to 6 mg/kg), decreased visual sensorimotor responses (starting from 3 to 6 mg/kg) and reduced tactile responses, modulated motor performance and induced muscle rigidity at higher doses (15 mg/kg). In addition, at higher doses (15-30 mg/kg) MT-45 impaired the cardiorespiratory functions. All effects were prevented by the administration of the opioid receptor antagonist naloxone. These findings reveal the risks associated with the ingestion of opioids and the importance of studying these drugs and undertaking more clinical studies of the current molecules to better understand possible therapeutic interventions in the case of toxicity.