Paeoniflorin attenuates postoperative pain by suppressing Matrix Metalloproteinase-9/2 in mice

Recent studies have implicated that matrix metalloproteinase (MMP)-9 and MMP-2 play key roles in neuropathic pain due to their facilitation of inflammatory cytokine maturation and induction of neuroinflammation. However, the role of MMP-9/2 in postoperative pain is still unclear. We previously suggested that the natural compound paeoniflorin inhibited microglia activation induced by morphine treatment. In the present study, we demonstrated that paeoniflorin could alleviate postoperative pain via specific inhibition of matrix metalloproteinases (MMPs).

Mice received a plantar incision surgery and their mechanical allodynia was assessed with von Frey filaments. The activity of MMP-9/2 was determined by gelatin zymography. Cell signalling was assayed by western blot and immunohistochemistry.

The expression of MMP-9/2 was significantly increased in mice spinal cords with plantar incision surgery. Paeoniflorin remarkably suppressed the activity of MMP-9/2 and relieved plantar incision-induced mechanical allodynia. Interestingly, the administration of paeoniflorin blocked the maturation of interleukin-1β, which is a critical substrate of MMPs. Thereafter, paeoniflorin markedly suppressed microglia activation, inhibited the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and the expression of neuronal c-Fos.

These results indicated that MMP-9/2 activation in spinal microglia plays a key role in incision-induced mechanical allodynia in mice. Moreover, utilizing paeniflorin blockage of the microglia MMP-9/2 activity might represent a valuable alternative for treating postoperative pain.

Our results provided direct evidence for the first time that paeoniflorin can inhibit plantar incision-induced microglia TLR4/MMP-9/2/IL-1β signalling pathway and suppress postoperative pain. Thus, regulation of microglia MMP-9/2 may provide a new strategy for ameliorating postoperative pain.