Anti-hyperalgesic effect of Lippia grata leaf essential oil complexed with β-cyclodextrin in a chronic musculoskeletal pain animal model: Complemented with a molecular docking and antioxidant screening.

Background: Due to its unclear pathophysiology, the pharmacological treatment of fibromyalgia is a challenge for researchers. Studies using medicinal plants, such as those from the genus Lippia, complexed with cyclodextrins (CDs) have shown innovative results.

Objective: The present research intended to evaluate the effect of an inclusion complex containing β-cyclodextrin (βCD) inclusion complex with Lippia grata (LG) essential oil in a chronic musculoskeletal pain model, its central activity and its possible interaction with neurotransmitters involved in pain.

Methods: After acid saline-induced chronic muscle pain, male mice were evaluated for primary and secondary hyperalgesia and muscle strength. Moreover, an antagonist assay was performed to assess the possible involvement of the opioidergic, serotonergic and noradrenergic pathways. In addition, Fos protein in the spinal cord was assessed, and a docking study and antioxidant assays were performed.

Results: The treatment with LG-βCD, especially in the dose of 24mg/kg, was able to significantly decrease (p<0.05) the paw withdrawal and muscle threshold. Furthermore, LG-βCD was shown to affect the opioidergic and serotonergic pathways. There were no significant changes in muscle strength. Fos protein immunofluorescence showed a significant decrease in expression in the dorsal horn of the spinal cord. The main compounds of LG showed through the docking study interaction energies with the alpha-adrenergic and μOpioid receptors. In all antioxidant assays, LG exhibited stronger antioxidant activities than LG-βCD.

Conclusion: This study suggested that LG-βCD could be considered as a valuable source for designing new drugs in the treatment of chronic pain, especially musculoskeletal pain.