Cannabidiol Mitigates Valproic Acid-Induced Developmental Toxicity and Locomotor Behavioral Impairment in Zebrafish

Background: Valproic acid (VPA), an anticonvulsant used in epilepsy, has deleterious effects on embryonic development and is considered an environmental risk factor for autism spectrum disorders. There is a growing need for easy and rapid ways to study its effects on embryonic development. The zebrafish model is a cost-and time-effective tool able to facilitate mechanistic studies and high-throughput drug screening. Epileptic patients are increasingly looking to natural compounds to avoid the strong side effects of synthetic drugs, and cannabinoids appear promising. We evaluated the potential of cannabidiol to mitigate the negative effects of VPA on developing zebrafish embryos.Methods: Wild-type AB embryos, untreated or exposed to VPA (5, 10 or 20 mu M) and/or cannabidiol (1, 2 or 3 mu M), were evaluated at up to 120 hours post-fertilization. Developmental endpoints: survival, hatching, heart rate, morphology, and locomotor behavior (tail coiling and visual motor response test). Three replicates were evaluated per group, for a total of 120 larvae per treatment.Results: Although VPA-treated groups showed significantly reduced survival rates compared to control group fish (p <= 0.01), zebrafish simultaneously treated with VPA (5 and 10 mu M) and cannabidiol (3 mu M) displayed survival rates similar to those of untreated controls. Hatching rate, body length and eye area were not influenced by any treatment, but the highest VPA dose and all cannabidiol doses caused a significant increase in burst activity (p <= 0.0001). Compared with controls, the pericardial area was larger only in larvae treated with VPA at the highest concentration (p <= 0.01). Each VPA treatment caused tachycardia (p <= 0.0001), while cannabidiol 3 mu M induced bradycardia (p <= 0.01). Finally, simultaneous treatment with VPA 5 mu M and cannabidiol 3 mu M avoided almost all the adverse effects of the two compounds administered individually, stabilizing heart rate and locomotor behavior at control levels.Conclusions: This study adds further information on the embryotoxic effect of VPA in the zebrafish model and offers new insights into the use of cannabidiol as an alternative natural drug able to mitigate the deleterious effects of VPA. Multi-laboratory large-scale validation and new genomic and molecular analyses are required to clarify the mechanism of action of VPA on developing embryos and the role of cannabidiol as a potential natural protective agent against its toxic effects.