Sex differences in complex regional pain syndrome type I (CRPS-I) in mice

Abstract

Background

Sex differences have been increasingly highlighted in complex regional pain syndrome (CRPS) in clinical practice. In CRPS type I (CRPS-I), although inflammation and oxidative stress have been implicated in its pathogenesis, whether pain behavior and the underlying mechanism are sex-specific is unclear. In the present study, we sought to explore whether sex differences have an impact on inflammation, oxidative stress, and pain sensitivity in CRPS-I.

Methods

Chronic post-ischemia pain (CPIP) was established in both male and female mice as an animal model of CRPS-I. Edema and mechanical allodynia of bilateral hind paws were assessed after reperfusion. Blood samples were analyzed for serum levels of oxidative stress markers and inflammatory cytokines.

Results

Both male and female mice developed edema. Male mice developed CPIP at day 3 after reperfusion; female mice developed CPIP at day 2 after reperfusion. Female mice displayed significantly earlier and higher mechanical allodynia in the ischemic hind paw, which was associated with higher serum levels of IL-2, TNF-α, isoprostanes, 8 OhdG, and malondialdehyde at day 2 after reperfusion. Moreover, female mice showed significantly lower SOD and IL-4 compared to male mice at day 2 after reperfusion.

Conclusion

Our results indicate that sex differences in inflammatory and oxidative stress states may play a central role in the sex-specific nociceptive hypersensitivity in CRPS-I, and offer a new insight into pharmacology treatments to improve pain management with CRPS.

Keywords:

• sex differences
• complex regional pain syndrome
• chronic post-ischemia pain
• inflammatory response
• oxidative stress

Acknowledgments

The authors are grateful for the enthusiastic support of Mr Kai Zhang in creating the figures. This study was supported by the National Natural Science Foundation of China (grant no 81671891).

Disclosure

The authors report no conflicts of interest in this work.