Abstract
SUMMARYWe used the MAGL inhibitor JZL184 to prolong the action of 2-AG and combined with the COX-2 inhibitor parecoxib or with the opioid morphine to achieve the synergistic antinociceptive effects on acute and chronic pain in mice. We took mechanical stimuli to evaluate analgesic effect by using electric von Frey instrument. Our results showed that co-administration the subthreshold dosage of JZL184 (4 mg/kg, i.p.) and parecoxib (5 mg/kg, i.p.) did not reduce acute pain in the Brennan’s paw incision (BPI) model, but worked synergistically to relieve the chronic inflammatory pain induced by complete Freund’s adjuvant (CFA). On the other hand, Co-administration of JZL184 (4 mg/kg, i.p.) and morphine (2.5 mg/kg, i.p.) synergistically alleviate the BPI-induced acute pain and CFA-induced chronic pain. Most importantly, comparing with morphine alone, co-administration of JZL184 and morphine displayed excellent pain relief in acute morphine tolerance mice which received 100 mg/kg morphine. Finally, by using Western blotting, we observed that the combined administration of JZL184 and morphine decreased the MAGL and μ-opioid receptor protein levels in the dorsal horn of spinal cord and dorsal root ganglia (DRG). Taken together, our results indicate that the synergistic antinociceptive effect of JZL184 and morphine is better than that of JZL184 and parecoxib, especially in the acute morphine tolerance mice. JZL184 and morphine may work synergistically via the interaction between the endocannabinoid system and opioid system to alleviate inflammatory pain in these mice.
INTRODUCTION
Both cannabis and endocannabinoids alleviate pain via activating cannabinoid receptors, however, the action of endocannabinoids is transient due to their degradation enzymes. The endocannabinoid 2-arachidonoyglyceral (2-AG) can be catalyzed by monoacylglycerol lipase (MAGL) and cyclooxygenase-2 (COX-2), respectively, into arachidonic acid, glycerol, and prostaglandin glycerol esters (PG-Gs). PGE2-G, one of the COX-2 metabolite of 2-AG, exerts a pro-nociceptive action in contrast to the antinociceptive property of 2-AG (Hu et al., 2008; Naidu et al., 2009; Alhouayek and Muccioli, 2014). Therefore, the MAGL inhibitor JZL184 can extend the actions of 2-AG including analgesia. Synergistic effect of analgesics produces greater effects than the sum of individual effects so that we combined low dosages of two analgesic to diminish side effects of high dosage drugs, such as tolerance. In the other hand, endocannabinoids and morphine also work synergistically to produce analgesic effect (Pacher et al., 2006; Scavone et al., 2013). In this study, we combine JZL184 and COX-2 inhibitor parecoxib or the opioid morphine to achieve the synergistic antinociceptive effects on acute and chronic pain in mice, and examining which combination exhibits more powerful potential.
MATERIALS AND METHODS
At least 9-weeks-old male ICR mice from NCKU laboratory animal center (Taiwan) and BioLASCO Taiwan co., ltd (Taiwan) served as subjects. We use electric von Frey instrument to assess mechanical pain threshold of mice’ left hind paw before and after injections of analgesics. There are acute Brennan’s paw incision (BPI)-induced incision and chronic complete Freund’s adjuvant (CFA)-induced inflammatory pain models in this study. Tests take place immediately after BPI surgery and 3 days after CFA injection. The grouping of JZL184 and parecoxib experiment sets are vehicle, JZL184 alone, parecoxib alone, and JZL184 + parecoxib groups; the grouping of JZL184 and morphine experiment sets are vehicle, JZL184 alone, morphine alone, and JZL184 + morphine groups. In acute morphine tolerance model, mice were tested 24 hours after 100 mg/kg morphine injection (i.p.) at day 3 of CFA injection. Finally, we analysis CB1 receptor, MAGL, and opioid μ receptor protein level of PAG, dorsal horn, dorsal root ganglia, and paw by Western blotting.
RESULTS AND DISCUSSION
Our results first showed that co-administration the subthreshold dosage of JZL184 (4 mg/kg, i.p.) and parecoxib (5 mg/kg, i.p.) did not reduce acute pain in the Brennan’s paw incision (BPI) model. However, JZL184 and parecoxib synergistically relieved the chronic inflammatory pain induced by complete Freund’s adjuvant (CFA). On the other hand, Co-administration of JZL184 (4 mg/kg, i.p.) and morphine (2.5 mg/kg, i.p.) synergistically alleviate the BPI-induced acute pain and CFA-induced chronic pain. Most importantly, comparing with morphine alone, co-administration of JZL184 and morphine displayed excellent pain relief in acute morphine tolerance mice which received 100 mg/kg morphine. Finally, by using Western blotting, we observed that the combined administration of JZL184 and morphine decreased the MAGL and μ-opioid receptor protein levels in the dorsal horn of spinal cord and dorsal root ganglia (DRG) of those acute morphine tolerance mice. The decrease of μ-opioid receptor protein levels might represent the exist of interactions of the endocannabinoid system and the endogenous opioid system.
CONCLUSION
This study attempts to examine the potency of JLZ184 as analgesic, and we found that the synergistic antinociceptive effect of JZL184 and morphine is better than that of JZL184 and parecoxib, especially in the acute morphine tolerance mice. JZL184 and morphine may work synergistically via the interaction between the endocannabinoid system and opioid system to alleviate inflammatory pain in these mice. Our findings hence suggest that JZL184 has therapeutic potential to treat chronic pain in morphine tolerance patients in the clinical setting.
| Date of Award | 2018 Aug |
|---|---|
| Original language | Chinese |
| Supervisor | Shu-Jung Hu (Supervisor) |