N-acetyl-cysteine attenuates neuropathic pain by suppressing matrix metalloproteinases

The treatment of neuropathic pain remains a clinical challenge because of its unclear mechanisms and broad clinical morbidity. Matrix metalloproteinase (MMP)-9 and MMP-2 have previously been described as key components in neuropathic pain because of their facilitation of inflammatory cytokine maturation and induction of neural inflammation. Therefore, the inhibition of MMPs may represent a novel therapeutic approach to the treatment of neuropathic pain. In this study, we report that N-acetyl-cysteine (NAC), which is a broadly used respiratory drug, significantly attenuates neuropathic pain through a unique mechanism of MMP inhibition. Both the in vitro (0.1 mM) and in vivo application of NAC significantly suppressed the activity of MMP-9/2. Orally administered NAC (50, 100, and 200 mg/kg) not only postponed the occurrence but also inhibited the maintenance of chronic constrictive injury (CCI)induced neuropathic pain in rats. The administration of NAC blocked the maturation of interleukin-1 beta, which is a critical substrate of MMPs, and markedly suppressed the neuronal activation induced by CCI, including inhibiting the phosphorylation of protein kinase C gamma, NMDAR1, and mitogen-activated protein kinases. Finally, NAC significantly inhibited CCI-induced microglia activation but elicited no notable effects on astrocytes. These results demonstrate an effective and safe approach that has been used clinically to alleviate neuropathic pain through the powerful inhibition of the activation of MMPs.