We have investigated the antihyperalgesic effects of limonene in mice that received intrathecal injection of gp120.Main methods:
Male Swiss mice received gp120, IL-1β or TNF-α intrathecally or sterile saline as a control. A mechanical sensitivity test was performed at 2 and 3 h after the injection. Spinal cord and blood samples were isolated for protein quantification.Key findings:
Intrathecal administration of gp120 increased mechanical sensitivity measured with an electronic Von Frey apparatus, at 2 and 3 h after the injections. Limonene administered orally prior to gp120 administration significantly decreased this mechanical sensitivity at 3 h after the gp120 injection. In addition, intrathecal injection of gp120 increased IL-1β and IL-10 in serum, and limonene prevented the ability of gp120 to increase these cytokines. Limonene also inhibited TNF-α and IL-1β-induced mechanical hyperalgesia. Western blot assay demonstrated limonene was capable of increasing SOD expression in the cytoplasm of cells from spinal cord at 4 h after intrathecal IL-1β injection.Significance:
These results demonstrate that gp120 causes mechanical hyperalgesia and a peripheral increase in IL-1β and IL-10, and that prior administration of limonene inhibits these changes. Also limonene modulates the activation of SOD expression in the spinal cord after spinal IL-1β application. The ability of limonene to inhibit the mechanical hyperalgesia induced by gp120, TNF-α and IL-1β emphasizes the anti-inflammatory action of limonene, specifically its ability to inhibit cytokine production and its consequences.