Implication of system xc− in complete Freund's adjuvant-induced peripheral inflammation and associated nociceptive sensitization

Abstract

Background

Persistent inflammation leading to neuronal sensitization in pain pathways, are key features of chronic inflammatory pain. Alike macrophages in the periphery, glial cells exacerbate hypersensitivity by releasing proalgesic mediators in the central nervous system. Expressed by peripheral and central immune cells, the cystine-glutamate antiporter system x_c⁻ plays a significant role in inflammatory responses, but its involvement in chronic inflammatory pain remains underexplored. We herein investigated the contribution of this exchanger in nociceptive hypersensitivity triggered by a peripheral inflammatory insult.

Methods

Complete Freund's adjuvant (CFA) was injected into the left hind paw of wild-type C57Bl/6 female mice, of xCT-deficient mice (specific subunit of system x_c⁻) and of mice receiving the system x_c⁻ inhibitor sulfasalazine. Paw edema was measured over three weeks and pain-associated behaviors were evaluated. Additionally, pro-inflammatory cytokine levels were assessed in blood samples.

Results

CFA injection led to a persistent increase in paw edema and hypersensitivity to mechanical and thermal stimuli, which were less pronounced in xCT-deficient mice. This reduced sensitivity was accompanied by lower systemic pro-inflammatory cytokine levels in xCT-deficient mice. Accordingly, pharmacological inhibition of system x_c⁻ with sulfasalazine, either before or after pain induction, efficiently reduced the algesic and inflammatory responses to CFA in wild-type mice.

Conclusion

Our findings reveal a critical role for system x_c⁻ in the pathophysiology of inflammatory pain. xCT deficiency reduces pain behaviors and peripheral inflammation, positioning system x_c⁻ as a promising therapeutic target for alleviating chronic inflammatory pain.