Camphor Attenuates Hyperalgesia in Neuropathic Pain Models in Mice

Abstract

Background

The treatment of neuropathic pain is still a major troublesome clinical problem. The existing therapeutic drugs have limited analgesic effect and obvious adverse reactions, which presents opportunities and challenges for the development of new analgesic drugs. Camphor, a kind of monoterpene, has been shown anti-inflammatory and analgesic effects in traditional Chinese medicine. But we know little about its effect in neuropathic pain. In this article, We have verified the reliable analgesic effect of camphor in the neuropathic pain model caused by different predispositions.

Methods

The nociceptive response of mice was induced by transient receptor potential A1 (TRPA1) agonist to verify the effect of camphor on the nociceptive response. Multiple paclitaxel (PTX) injection models, Single oxaliplatin (OXA) injection models, Chronic constriction injury (CCI) models and Streptozotocin-induced (STZ) diabetic neuropathic pain models were used in this study. We verified the analgesic effect of camphor in mice by acetone test and conditioned place aversion test. At the same time, comparing the adverse reaction of nervous system between camphor and pregabalin at equivalent dose in locomotor activity test and rotarod test. Using patch clamp to verify the effect of camphor on dorsal root ganglion (DRG) excitability.

Results

In behavioral test, compared with vehicle group, camphor significantly reduced the spontaneous nociception caused by TRPA1 agonist-formalina and allyl isothiocyanate (AITC). Compared with vehicle group, camphor significantly reduced the flinching and licking time in neuropathic pain model mice, including PTX, OXA, STZ and CCI induced peripheral neuralgia models. Compared with vehicle group, pregabalin significantly increased the resting time and reduced the average speed without resting and distance in locomotor activity test, reduced the time stayed on rotarod in rotarod test. In patch clamp test, compared with vehicle group, camphor significantly reduced the action potential (AP) firing frequency of DRG.

Conclusion

Camphor can alleviate the symptoms of hyperalgesia in various neuropathic pain models, and has no obvious adverse reactions compared with pregabalin. This effect is related to the down-regulation of DRG neuron excitability.

Keywords:

• camphor
• neuropathic pain
• TRPA1
• hyperalgesia

Acknowledgments

We are grateful for financial support from the National Natural Science Foundation of China (Nos. 82273784), the 1.3.5 Project for Disciplines of Excellence, West China Hospital, Sichuan University (Nos. ZYYC21002 and Nos. ZYGD20005), the Clinical Research Innovation Project, West China Hospital, Sichuan University (Nos. 2019HXCX06), Post-Doctor Research Project, West China Hospital, Sichuan University (Nos. 2021HXBH078), the natural Science Foundation of Sichuan Province (Nos. 2023NSFSC1568) and the Sichuan University postdoctoral interdisciplinary Innovation Fund.

Disclosure

The authors report no conflicts of interest in this work.